Symposium.,,sppns:ored by · Air Line Pilots Association 

Air Transport Association of America 

Federal Aviation Adminis~ tion 

Nation;:tl Oceanic and Atmospheric Administration 

U.S. Geologic l:St.!~ vey ~ 
Cover. Ash billows from the vent of Mount St. Helens volcano, Washington, during 

the catastrophic eruption that began at 8:32 a.m. Pacific Daylight Time on May 18, 

1980. View is to the northeast. USGS photograph taken at about noon by Robert M. 

Krimmel. 
Volcanic Ash and Aviation Safety: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

Edited by Thomas J. Casadevall 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

Proceedings of the First International Symposium on Volcanic Ash 

and Aviation Safety held in Seattle, Washington, in July 1991 

Symposium sponsored by 

Air Line Pilots Association 

Air Transport Association of America 

Federal Aviation Administration 

National Oceanic and Atmospheric Administration 

U.S. Geological Survey 

Symposium co-sponsored by 

Aerospace Industries Association of America 

American Institute of Aeronautics and Astronautics 

Flight Safety Foundation 

International Association of Volcanology and Chemistry of the Earth's Interior 

National Transportation Safety Board 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1994 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director 

For sale by U.S. Geological Survey, Map Distribution 

Box 25286, MS 306, Federal Center 

Denver, CO 80225 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government 

Library of Congress Cataloging-in-Publication Data 

International Symposium on Volcanic Ash and Aviation Safety (1st : 1991 Seattle, 

Wash.) 

Volcanic ash and aviation safety : proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety I edited by Thomas J. Casadevall ; symposium 

sponsored by Air Line Pilots Association ... [et al.], co-sponsored by Aerospace Industries Association of America ... [et al.]. 

p. cm.-(U.S. Geological Survey bulletin; 2047) 

"Proceedings of the First International Symposium on Volcanic Ash. and Aviation 

Safety held in Seattle, Washington, in July 1991." 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:2047 

1. Volcanic ash, tuff, etc.-Congresses. 2. Aeronautics-Safety measuresCongresses. I. Casadevall, Thomas J. II. Air Line Pilots Association. III. Title. 

IV. Series. 

QE75.B9 no. 2047 

[QE461] 

557.3 s-dc20 

[629.13'0289] 94-17789 
FOREWORD 

A Boeing 747 jumbo jet approaching the Anchorage International Airport, Alaska, on 

December 15, 1989, lost power to all four engines and nearly crashed as a result of flying 

through volcanic ash erupted from Redoubt Volcano. In separate incidents in 1982, two 

commercial jumbo jets en route to Australia across Indonesia suffered loss of engine thrust 

from ingesting volcanic ash from the erupting Galunggung Volcano, Java, and descended 

more than 20,000 ft before the engines could be restarted. These are not the only incidents 

of this kind. During the past 15 years, about 80 commercial jet aircraft have suffered damage from inadvertently flying into ash clouds that had drifted tens to hundreds of miles 

from erupting volcanoes. 

The U.S. Geological Survey (USGS) has been involved in research on geologic hazards, such as volcanic eruptions and earthquakes, since its earliest days. With the Disaster 

Relief Act of 1974, the USGS was given formal responsibility "to provide technical assistance to State and local governments to ensure that timely and effective disaster warning is 

provided" for all geologic hazards. Addressing the threat of volcanic ash to aircraft safety, 

however, requires far more than the monitoring of volcanoes and warning of erupting ash 

clouds by the Survey. The ash must be traced and its likely trajectory must be forecast; aircraft must be alerted, and proper evasive actions must be taken by pilots. Agencies such as 

the National Weather Service and National Environmental Satellite Data and Information 

Service (both part of the National Oceanic and Atmospheric Administration), the National 

Aeronautics and Space Administration, and the Federal Aviation Administration are partners critical to the success of this mission. The International Civil Aviation Organization, 

various pilots' associations, air carriers, aircraft manufacturers, and many others are 

important as well. 

The Redoubt encounter spurred government and university scientists, pilots, and representatives of the aviation industry to work together to reduce the hazards caused internationally by volcanic ash. As a result of the concern generated by the Redoubt eruptions 

and associated aircraft encounters, the First International Symposium on Volcanic Ash and 

Aviation Safety was held in Seattle, Washington, July 8-12, 1991. This volume contains 

the proceedings from that meeting. 

Volcanologists and the subject of volcanic ash clouds are relatively new to discussions 

of aviation hazards. As a result, the various parties concerned with the hazard have had to 

set up new communication channels and to bridge substantial differences in organizational 

culture and professional language. The Seattle symposium in 1991 alerted and educated 

many about ash hazards to aviation. More importantly, it started a serious dialogue that 

resulted in a series of follow-up workshops, improvements in the detection and tracking of 

ash clouds, and revised warning and response procedures. These are the actions that will 

be needed if the hazard of ash in airways is truly to be mitigated. 

~'/.~ Dallas L. Peck 

U.S. Geological Survey 

Director, 19 81-1993 

III 

CONTENTS 

Foreword 

By Dallas L. Peck.................................................................................................. III 

Introduction 

By Thomas J. Casadevall ...................................................................................... . 

Issues and Needs 

Developments Since the Symposium 

International Efforts 

Efforts in the United States 

Future Directions 

Acknowledgments 

References Cited 

Introductory Remarks for the First International Symposium on Volcanic Ash and 

Aviation Safety, Seattle, Washington, July 1991 

By Donald D. Engen.............................................................................................. 7 

Technical Reports 

Volcanoes and Ash Clouds 

Volcanoes and Aviation Safety in Costa Rica 

By Jorge Barquero ............................................................... .......... .............. 9 

A Method for Characterizing Volcanic Ash from the December 15, 1989, 

Eruption of Redoubt Volcano, Alaska 

By Gregory K. Bayhurst, Kenneth H. Wohletz, and Allen S. Mason.......... 13 

The Concentration of Ash in Volcanic Plumes, Inferred from Dispersal Data 

By Marcus I. Bursik, R.S.J. Sparks, Steven N. Carey, and 

JennieS. Gilbert................................................................................. 19 

Electrical Phenomena in Volcanic Plumes 

By JennieS. Gilbert and Stephen J. Lane.................................................... 31 

Volcanic Ash: What It Is and How It Forms 

By Grant Heiken ... . . .......... ......... ..... . . ............. .... . . ................. ... . . ... . . . ............ 39 

Volcanism in the Canadian Cordillera: Canada's Hazard Response 

Preparedness 

By Catherine J. Hickson............................................................................... 4 7 

Volcanic Ash in Kamchatka as a Source of Potential Hazard to 

Air Traffic 

By Vladimir Yu. Kirianov.. ........ ..... . . .. ........... .... . . ... ..... . . . .. . . .. ... . . . .. . . . ............ 57 

Ash Clouds: Characteristics of Eruption Columns 

By Stephen Self and George P.L. Walker ........ ...... .. ............ .............. .... ...... 65 

Volcanoes: Their Occurrence and Geography 

By Tom Simkin............................................................................................ 75 

v 
VI CONTENTS 

Technical Reports-Continued 

Volcanoes and Ash Clouds-Continued 

The Controls of Emption-Column Dynamics on the Injection and 

Mass Loading of Ash into the Atmosphere 

By R.S.J. Sparks, Marcus I. Bursik, Steven N. Carey, 

Andrew W. Woods, and JennieS. Gilbert.......................................... 81 

Melting Properties of Volcanic Ash 

By Samuel E. Swanson and James E. Beget................................................ 87 

Ash-Fall Deposits from Large-Scale Phreatomagmatic Volcanism: 

Limitations of Available Eruption-Column Models 

By Colin J.N. Wilson................................................................................... 93 

The Injection of Volcanic Ash into the Atmosphere 

By Andrew W. Woods and Juergen Kienle.................................................. 101 

Damage and Impacts 

Influence of Volcanic Ash Clouds on Gas Turbine Engines 

By Michael G. Dunn and Douglas P. Wade................................................. 107 

Volcanic Ash-Aircraft Incidents in Alaska Prior to the Redoubt Eruption 

on 15 December 1989' 

By Juergen Kienle .. .. .. .. .. .... . . . .......... .... . . . .... ... . . . .... .. .. . . . ................. .... .. .. . .. .... . 119 

Mitigation of Volcanic Ash Effects on Aircraft Operating and 

Support Systems 

By J.R. Labadie............................................................................................ 125 

Impact of Volcanic Ash from 15 December 1989 Redoubt Volcano 

Eruption on GE CF6-80C2 Turbofan Engines 

By Zygmunt J. Przedpelski and Thomas J. Casadevall............................... 129 

Economic Disruptions by Redoubt Volcano: Assessment Methodology 

and Anecdotal Empirical Evidence 

By Bradford H. Tuck and Lee Huskey........................................................ 137 

Effects of Volcanic Ash on Aircraft Powerplants and Airframes 

By Lester M. Zinser .. .... .... . . . .. .. .... .. .... .. . . .... ... . . . .... .. .... . . .. .... .. .. . . .. .. .... .... . . .. .. . . 141 

Communications and Procedures 

AlA Recommendations Aimed at Increased Safety and Reduced Disruption 

of Aircraft Operations in Regions with Volcanic Activity 

By AlA Propulsion Committee 334-1, 

Zygmunt J. Przedpelski, Chairman.................................................... 147 

Recommended Flight-Crew Procedures if Volcanic Ash is Encountered 

By Ernest E. Campbell................................................................................. 151 

Development of a Real-Time ATC Volcanic Ash Advisory System Based on 

the Future Aviation Weather System 

By James E. Evans....................................................................................... 157 

Warning Systems and Pilot Actions 

By Peter M. Foreman................................................................................... 163 
CONTENTS 

Technical Reports-Continued 

Communications and Procedures-Continued ... Volcanic Ash-The International Regulatory Aspects 

By Tom Fox................................................................................................. 169 

Seattle Air Route Traffic Control Center Response to Eruptions of 

Mount St. Helens 

By Robert F. Hamley and Donald H. Parkinson .. .. . ........ ............ .. . . .. . . . . . . .. . . 17 5 

An Automated Volcanic Ash Warning System 

By David M. Harris . . . ......... .. . . . . ...... ........... .. . . . . . . ......... .. . . . .. . . . . .. . . . . . . .............. 183 

Aviation Safety and Volcanic Ash Clouds in the Indonesia-Australia 

Region 

By R. Wally Johnson and Thomas J. Casadevall ... . . . ...... .. . . .. ...................... 191 

The Smithsonian's Global Volcanism Network: Facilitating 

Communication of Volcanic-Eruption Information 

By Lindsay McClelland............................................................................... 199 

Volcanic Ash and Aircraft Operations 

By Edward Miller........................................................................................ 203 

Volcanic Event Notification at Mount St. Helens 

By Bobbie Myers and George J. Theisen.................................................... 207 

Aviation Safety Measures for Ash Clouds in Japan and the System of Japan 

Air Lines for Monitoring Eruptions at Sakurajima Volcano 

By Saburo Onodera and Kosuke Kama ...... ........ ........................................ 213 

Volcanic Ash Warnings in the Australian Region 

By Rodney J. Potts and Frank Whitby........................................................ 221 

Ash Cloud Aviation Advisories 

By Thomas J. Sullivan and James S. Ellis.................................................. 229 

Meteorology and Ash-Cloud Monitoring 

Alaska Volcano-Debris-Monitoring System: New Technologies to Support 

Forecasting Volcanic-Plume Movement 

By Gary L. Hufford..................................................................................... 239 

A Statistical Approach to the Assessment of Volcanic Hazard for 

Air Traffic: Application to Vesuvius, Italy 

By Giovanni Macedonia, P. Papale, M. Teresa Pareschi, Mauro Rosi, 

and Roberto Santacroce..................................................................... 245 

Using a Personal Computer to Obtain Predicted Plume Trajectories During 

the 1989-90 Eruption of Redoubt Volcano, Alaska 

By Thomas L. Murray, Craig I. Bauer, and John F. Paskievitch ........ ... . ..... 253 

Volcanic Eruptions and Atmospheric Temperature 

By Reginald E. Newell and Zhong Xiang Wu . . ......... ......... .. ........... ........... 257 

A Mesoscale Data Assimilation System Adapted for Trajectory Calculations 

Over Alaska 

By Thomas W. Schlatter and Stanley G. Benjamin..................................... 269 

VII 
VIII CONTENTS 

Technical Reports-Continued 

Meteorology and Ash-Cloud Monitoring-Continued 

Modeling Volcanic Ash Transport and Dispersion 

By Barbara J.B. Stunder and Jerome L. Heffler.......................................... 277 

Development of a Prediction Scheme for Volcanic Ash Fall from 

Redoubt Volcano, Alaska 

By Hiroshi L. Tanaka . ............... ....... ........... ...... ........... ............ ................ .... 283 

The Aeronautical Volcanic Ash Problem 

By Jerald Uecker.......................................................................................... 293 

Defining a Keep-Out Region for Aircraft After a Volcanic Eruption 

By Peter L. Versteegen, Douglas D. D' Autrechy, Michael C. Monteith, 

and Charles R. Gallaway ... ................... ................................ ... . ......... 297 

Detection and Tracking 

Detection and Discrimination of Volcanic Ash Clouds by 

Infrared Radiometry-I: Theory 

By Alfred J. Prata and Ian J. Barton .......... ....................... ......... .. . ............... 305 

Detection and Discrimination of Volcanic Ash Clouds by 

Infrared Radiometry-II: Experimental 

By Ian J. Barton and Alfred J. Prata ............................................................ 313 

Satellite Monitoring of Volcanoes Using Argos 

By J.P. Cauzac, Christian Ortega, and Laurel Muehlhausen . . . .. . . . . . . . . . . . . . . .. . . 319 

Current and Future Capabilities in Forecasting the Trajectories, Transport, 

and Dispersion of Volcanic Ash Clouds at the 

Canadian Meteorological Centre 

By Real D' Amours....................................................................................... 325 

An Aircraft Encounter with a Redoubt Ash Cloud (A Satellite View) 

By Kenneson G. Dean, Lawrence Whiting, andHaitao Jiao....................... 333 

GEO-TOMS: Total-Ozone Mapping Spectrometer for Ozone and 

Sulfur-Dioxide Monitoring from a Geostationary Satellite 

By Ulli G. Hartmann, Robert H. Hertel, Herbert A. Roeder, 

and J. Owen Maloy............................................................................ 341 

Passive, Two-Channel, Thermal-Infrared Imaging Systems for 

Discrimination of Volcanic Ash Clouds 

By Frank R. Honey...................................................................................... 347 

Seismic Identification of Gas-and-Ash Explosions at Mount St. HelensCapabilities, Limitations, and Regional Application 

By Chris Jonientz-Trisler, Bobbie Myers, and John A. Power.................... 351 

Infrasonic and Seismic Detection of Explosive Eruptions at Sakurajima 

Volcano, Japan, and the PEGASAS-VE Early-Warning System 

By Kosuke Kamo, Kazuhiro Ishihara, and Makoto Tahira.......................... 357 

Volcanic Hazard Detection with the Total Ozone 

Mapping Spectrometer (TOMS) 

By Arlin J. Krueger, Scott R. Doiron, Gregg S.J. Bluth, Louis S. Walter, 

and Charles C. Schnetzler .................................................................. 367 
CONTENTS 

Technical Reports-Continued 

Detection and Tracking-Continued 

Monitoring Volcanic Eruptions Using NOAA Satellites 

By Michael Matson, James S. Lynch, and George Stephens...................... 373 

Volcanic Tremor Amplitude Correlated with Eruption Explosivity and its 

Potential Use in Determining Ash Hazards to Aviation 

By Steven R. McNutt................................................................................... 3 77 

Airborne Radar Detection of Volcanic Ash 

By Mark E. Musolf...................................................................................... 387 

Radar Remote Sensing of Volcanic Clouds 

By William I. Rose and Alexander B. Kostinski......................................... 391 

Tracking of Regional Volcanic Ash Clouds by Geostationary 

Meteorological Satellite (GMS) 

By Yosihiro Sawada.................................................................................... 397 

Observations ofthe 1989-90 Redoubt Volcano Eruption Clouds Using 

AVHRR Satellite Imagery 

By David J. Schneider and William I. Rose................................................ 405 

Application of Contemporary Ground-Based and Airborne Radar for the 

Oservation of Volcanic Ash 

By Melvin L. Stone . ......... ............... ................................ ............................ 419 

The Potential for Using GPS for Volcano Monitoring 

By Frank H. Webb and Marcus I. Bursik.. .......... ...................... ............ ...... 429 

Selected Glossary of Volcanology and Meteorology.......................................................... 437 

List of Selected Acronyms.................................................................................................. 439 

Authors' Address List . . . . .. . . . . .. . . . ... . .. ........... ... . . . . . . . ... . . . . .. . . . . .. . . . .. . . . . ........... ... ..... . . .. ................ 443 

IX 

INTRODUCTION 

By Thomas J. Casadevall 

Volcanic ash from the 1989-90 eruptions of Redoubt 

Volcano disrupted aviation operations in south-central 

Alaska and damaged five jet passenger aircraft, including a 

new Boeing 747-400, which cost in excess of$80 million to 

repair (Steenblik, 1990). The Redoubt eruptions served to 

increase interest by the aviation community in volcanic hazards and made it clear that mitigating the hazards of volcanic 

ash to aviation safety would require the cooperation and 

efforts of volcanologists, meteorologists, air traffic managers, engine and airframe manufacturers, and pilots. 

Soon after the December 1989 eruptions of Redoubt, 

Senator Ted Stevens of Alaska requested that Federal agencies form an interdepartmental task force to develop and 

coordinate both an immediate and a long-term response to 

the Redoubt eruptions. In March 1990, in response to this 

request, the U.S. Geological Survey, the Federal Aviation 

Administration (FAA), and the National Oceanic and Atmospheric Administration (NOAA) formed an interagency task 

group and began planning for an international technical symposium to review the available information about volcanic 

ash clouds and to assess what was being done to address the 

ash hazard, both domestically and internationally. This interagency group received strong support from the aviation community, and the Federal agencies were soon joined by the Air 

Line Pilots Association (ALP A), the Aerospace Industries 

Association (AlA), the Air Transport Association (A TA), 

the Flight Safety Foundation (FSF), and the American Institute of Aeronautics and Astronautics (AIAA). An important 

early result from this cooperation was the "First International 

Symposium on Volcanic Ash and Aviation Safety," to 

address the effects of volcanic activity on aviation safety in 

a multidisciplinary way and at a global scale. The aims of the 

symposium were: to bring together individuals who were 

interested in the volcanic ash problem but who may have 

been unaware of other scientists, engineers, pilots, and aviation authorities with similar interests; to encourage and 

define needed improvements in the detection, tracking, and 

warning of volcanic ash hazard so that aircraft may avoid ash 

clouds; and to review the effects of volcanic ash on aircraft 

so that pilots who encounter ash can respond appropriately. 

The symposium was held in Seattle, Wash., from July 8-12, 

1991. 

The symposium was attended by more than 200 participants from 28 countries, representing the major air carriers, 

airplane and engine manufacturers, pilots and aviation safety 

organizations, air traffic managers, meteorologists, and volcanologists. More than 100 technical presentations were 

made during the symposium, including a special session on 

the effects on aviation operations of the June 15, 1991, eruption of Mt. Pinatubo in the Philippines (Casadevall, 1991). 

Field trips to the Federal Aviation Administration air traffic 

control facility in Auburn, Wash., to the Boeing 737 assembly plant in Renton, Wash., and to the Mount St. Helens 

National Volcanic Monument gave participants the opportunity to view the volcanic hazard-aviation problem from several perspectives. Such broad participation demonstrated a 

clear need and wide support for a meeting of this type. 

In the past 15 years, more than 80 jet airplanes have 

been damaged owing to unplanned encounters with drifting 

clouds of volcanic ash in air routes and at airports. Seven of 

these encounters caused in-flight loss of jet engine power, 

which nearly resulted in the crash of the airplane. The repair 

and replacement costs associated with airphine-ash cloud 

encounters are high and, to date (May 1994), have exceeded 

$200 million. In addition to the high economic costs of these 

encounters, more than 1,500 passengers aboard the seven 

airliners that temporarily lost engine power were put at 

severe risk. 

The hazard is compounded by the fact that volcanic ash 

clouds are not detectable by the present generation of radar 

instrumentation carried aboard aircraft and are not likely to 

be detectable in the foreseeable future. Complete avoidance 

of volcanic ash clouds is the only procedure that guarantees 

flight safety, and this avoidance requires communication 

between the pilot and observers outside the aircraft. 

Since the Seattle meeting, eruptions at Pinatubo, 

Sakurajima Volcano (Japan), Pacaya Volcano (Guatemala), 

Galeras Volcano (Colombia), Hudson and Lascar Volcanoes 

(Chile), Mt. Spurr (Alaska), Nyamuragira Volcano (Zaire), 

Sheveluch Volcano (Russia), and Manam Volcano (Papua 

New Guinea) have further disrupted air traffic, damaged aircraft in flight, and delayed flights and curtailed operations at 

a number of airports. The issue of volcanic hazards and aviation safety continues to be timely and in need of more effort 
2 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

if we are to improve the margin of flight safety in the presence of volcanic ash. 

ISSUES AND NEEDS 

During the symposium, discussions focused on the following technical areas: the 1989-90 Redoubt eruptions and 

their impacts on aviation operations, the nature of volcanoes 

and their ash clouds, the effects of volcanic ash on aircraft, 

methods and procedures of communicating the ash-cloud 

hazard to pilots, the role of meteorology and the use of atmospheric models to forecast cloud movement, and detection 

and tracking of ash clouds. This volume contains reports for 

60 of the 108 technical presentations made during the symposium. The papers presented about the Redoubt eruptions 

have been published elsewhere (Miller and Chouet, 1994). 

In addition to the technical presentations, symposium 

discussions identified a number of key issues and needs that 

participants felt must be addressed in order to mitigate the 

volcanic threat to aviation safety. These included: 

1. Improved communications among volcano observers, 

meteorologists, air traffic controllers, flight dispatchers, and pilots about drifting ash clouds, including 

immediate notification of volcanic eruptions to pilots. 

2. Improved education of pilots, flight managers, and 

manufacturers about the ash-cloud hazard, including 

specific recommendations for avoiding ash clouds. 

3. Improved detection and tracking of ash-cloud movement using remote-sensing techniques and atmospheric-transport models. 

4. Improved monitoring of the Earth's active volcanoes, 

especially in the remote Aleutian-Kamchatka-Kurile 

volcanic region. 

5. New methods for eruption identification and ashcloud detection. 

6. Development of instruments that will enable pilots to 

detect ash clouds while in flight, especially useful 

when flying over remote, unmonitored regions of the 

Earth. 

7. Development of better methods to remove and clean 

ash from airplanes and airports. 

8. Determination of minimum levels of ash concentration that are capable of damaging aircraft and engines. 

9. Development of a worldwide notification system and 

clearinghouse for information about active volcanoes, 

including planning charts to show the location of volcanoes relative to air routes. 

DEVELOPMENTS SINCE THE 

SYMPOSIUM 

A number of ad hoc working groups were formed following the symposium to examine these topics and have produced significant progress on many of these technical issues. 

Accomplishments include: 

1. A training video for pilots entitled "Volcanic Ash 

Avoidance," produced by the Boeing Company in 

cooperation with the Air Line Pilots Association and 

the U.S. Geological Survey (Boeing Company, 1992). 

2. An international workshop on communications 

among volcanologists, meteorologists, air traffic managers, and pilots was held in Washington, D.C., in 

September 1992. 

3. An FAA review on aviation safety as affected by volcanic ash (FAA, 1993a). 

4. A workshop on the dynamics and characteristics of 

the ash clouds from the 1992 eruptions of Mt. Spurr 

was held in Washington, D.C., in April 1993 (FAA, 

1993b). 

5. An international workshop on volcanic ash and airports was held in Seattle, Wash. (Casadevall, 1993). 

6. New communications links with Russians for warnings and information about Kamchatkan volcanoes, 

which underlie the increasingly busy air routes of the 

north Pacific region, were established in 1993 (Miller 

and Kirianov, 1993). 

7. An interagency plan for volcanic ash episodes in 

Alaska was put into effect by the FAA, NWS, USGS, 

Department of Defense, and the State of Alaska in 

1993 (Alaska Interagency Operating Plan, 1993). 

8. A global planning chart showing the position of active 

volcanoes relative to air routes and air navigation aids 

was published (Casadevall and Thompson, 1994). 

INTERNATIONAL EFFORTS 

Since 1982, the International Civil Aviation Organization (ICAO) has worked to address the volcanic threat to aviation safety worldwide (Fox, 1988, this volume). This threat 

came to wide public attention in 1982 when two 747 passenger jets encountered ash at night from separate eruptions of 

Galunggung Volcano in Indonesia. In these incidents, volcanic ash extensively damaged exterior surfaces, instruments, 

and engines, resulting in the loss of thrust and powerless 

descents of nearly 25,000 feet before the pilots of both aircraft restarted their engines and landed safely at Jakarta 

(Smith, 1983). The Galunggung encounters occurred for-two 

main reasons. First, the pilots were unable to see the ash or 

to otherwise detect it using on-board instruments, and sec-
INTRODUCTION 3 

ond, no warnings about the activity of the volcano were contained in the aeronautical information generally available to 

pilots, such as notices of significant meteorological 

r.vents-SIGMET's-or in notices to airmen-NOTAM's. 

These incidents led in 1982 to the formation of a volcanic ash 

warning group under leadership of the ICAO. 

Eruptions and aircraft encounters with ash clouds during the past 15 years have prompted several other important 

international efforts to mitigate the volcanic hazard to aviation safety. Because volcanic ash clouds are carried by 

upper-level winds and often cross national boundaries as 

well as boundaries separating flight-information regions, 

efficient and prompt communications between regions are 

essential to avoiding encounters. The May 1985 encounter 

between a jumbo jet and an ash cloud from an eruption of 

Soputan Volcano in Indonesia prompted the Indonesian and 

Australian governments to form a bilateral volcanological/ 

airspace liaison committee to improve communications 

about volcanic eruptions in the Indonesian region (Johnson 

and Casadevall, this volume). In North America, drifting ash 

clouds from the 1989-90 eruptions of Redoubt Volcano, and 

the 1992 eruptions of Mt. Spurr, sent ash clouds over Canada 

and disrupted operations in Canadian airspace. These incidents prompted establishment of closer bilateral communications between Canadian and U.S. agencies including 

volcanologists, meteorologists, and air traffic controllers 

(Hickson, this volume). 

In 1988, ICAO member states adopted regulations to 

provide alerts to pilots about eruptive activity worldwide. 

These efforts included a special volcanic activity report form 

(V AR), which requires that pilots make a number of critical 

observations about the location, timing, and nature of an ash 

cloud. This information is communicated directly to the 

nearest area control center and is introduced into the communication network so that other aircraft may avoid airspace 

contaminated by volcanic ash (Fox, 1988, this volume). 

Also in 1988, the World Organization of Volcano 

Observatories (WOVO), in cooperation with ICAO and with 

the International Association of Volcanology and Chemistry 

of the Earth's Interior (IAVCEI), requested WOVO member 

institutions to establish contacts with civil aviation authorities to improve communications between ground-based 

observatories and air traffic in order to minimize the volcanic hazards to aircraft. Currently, WOVO is examining ways 

to improve the exchange of information between observatories and agencies concerned with aviation operations, including the use of electronic mail (Riehle and Fink, 1993). 

Following the 1991 Seattle symposium, ICAO 

addressed the volcanic threat to aviation safety at regional 

meetings in Bangkok (September 1992) and Mexico City 

(October 1992). In November 1992, changes to the international standards and recommended practices for meteorological services (ICAO, 1992) went into effect. The changes 

relate to the types of information about volcanic clouds that 

are entered into aeronautical communications networks 

using the SIGMET mechanism. The new regulations require 

that a volcanic advisory forecast be issued every 4 hours 

regarding the status of a volcanic cloud, with a 12-hour forecast of ash-cloud behavior. 

Information for these advisories could come from many 

sources, but would most likely come from analysis of satellite images and from analysis of ash-cloud movement using 

atmospheric-transport models (Stunder and Heffter, this volume; Tanaka, this volume). For example, an important 

source of information for these volcanic advisories for the 

Southwest Asia region is the Darwin Regional/Specialized 

Meteorological Centre, established in 1993 by the Australian 

Bureau of Meteorology. The Darwin center utilizes satellite 

imagery to provide outlook advisory information about the 

occurrence and movement of ash clouds from eruptions in 

the Indonesian region. The center also serves as a venue for 

training meteorologists from the Asian region about detection and tracking of volcanic ash clouds so other countries in 

the region might carry out similar analysis at the local level. 

To further assist ICAO member states in meeting the 

requirements for more detailed advisories, ICAO established 

a special implementation project to member states with 

active volcanoes as well as to those states responsible for 

flight information in regions adjacent to areas with active 

volcanoes. Through this project, an ICAO team consisting of 

a- volcanologist and an aeronautical meteorologist visited 

countries in the Asia-Pacific region in 1992-93 (Casadevall 

and Oliveira, 1993) and the South American region in 

1993-94 to advise on methods for meeting the new ICAO 

regulations. The new regulations should result in more rapid 

and clearer communications about volcanic ash clouds to the 

aviation community. 

In addition to these bilateral efforts to improve the 

speed and quality of information, several countries have 

addressed specific volcanic threats to aviation operations by 

applying existing technology and by seeking to develop new 

methods and equipment for ash detection. For example, in 

1991, scientists and aviation authorities in Japan installed 

specialized seismic and infrasonic detectors at Sakurajima 

Volcano to detect ash-producing eruptions. Results from 

these sensors are continuously transmitted to nearby 

Kagoshima Airport to provide real-time notification of 

explosive eruptions that threaten airport operations (Kamo 

and others, this volume; Onodera and Kamo, this volume). In 

another example, scientists in Australia are seeking ways to 

supplement information that is available to the pilot by 

developing an ash-detection sensor that can be carried 

onboard the aircraft to detect the presence of ash in the flight 

path (Barton and Prata, this volume; Prata and Barton, this 

volume). Such a sensor would be especially valuable for 

international flights over regions where volcanoes are poorly 
4 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

monitored and where ground-based communications are 

poorly established. 

EFFORTS IN THE UNITED STATES 

The United States has approximately 56 volcanoes with 

historical eruptive activity; 44 are located in Alaska. The 

U.S. Geological Survey (USGS) is the principal Federal 

agency with responsibility for assessing volcanic hazards 

and monitoring active volcanoes in the United States 

(Wright and Pierson, 1992). This work is carried out primarily from volcano observatories in Hawaii, Alaska, California, and Washington. For example, the Alaska Volcano 

Observatory monitors the activity of volcanoes in the Cook 

Inlet area, including Redoubt and Spurr. Continuous seismic 

and other monitoring of these volcanoes, day and night, in all 

seasons and weather conditions, enables volcanologists to 

detect eruption precursors as well as eruptions themselves. 

Early detection of eruptions and prompt communication of 

this information to the FAA and to the National Weather Service offices in Anchorage are an essential part of the role 

played by USGS scientists in mitigating the ash hazard to 

aircraft. 

The National Oceanic and Atmospheric Administration 

(NOAA) and the Federal Aviation Administration (FAA) 

also have responsibilities for dealing with the hazard of volcanic ash clouds that affect aviation operations in the United 

States. Cooperation between these two agencies was formalized shortly before the December 1989 eruption of Redoubt, 

when a memorandum of understanding between the agencies 

created a volcanic hazard alert team and established procedures to respond to volcanic eruptions affecting air operations in the United States. Since 1989, these procedures have 

been activated for eight volcanoes in the United States (J. 

Lynch, NOAA-SAB, written commun., March 1993). In 

1993, a letter of agreement between the USGS and NOAA 

attempted to speed the exchange of information that notifies 

the aviation community of ash-cloud hazards and formalized 

the de facto collaboration between these agencies that has 

existed since the Redoubt eruptions. 

The principal tools used by NOAA for assessing volcanic activity are analysis of data from satellites (Krueger and 

others, this volume; Matson and others, this volume) and 

wind-field data, which enables the forecast of drifting ash 

clouds (Murray and others, this volume; Stunder and Heffter, 

this volume). Since 1990, the National Weather Service 

office in Anchorage has implemented several new techniques for detecting and tracking volcanic ash clouds from 

volcanoes in the Cook Inlet and Aleutian regions (Hufford, 

this volume). These efforts are integrated with the monitoring efforts of the Alaska Volcano Observatory and with the 

air-traffic-control efforts of the FAA. The FAA, through its 

area control centers, has the primary responsibility for communicating with pilots and for providing NOT AM's. 

Following the 1989-90 eruptions of Redoubt, the 1992 

eruptions of Mt. Spurr also had an important impact on aviation, affecting operations in Alaska, Canada, and the conterminous United States (Alaska Volcano Observatory, 

1993). Ashfall from the August 18, 1992, eruption of Mt. 

Spurr deposited from 1 to 3 mm of ash in Anchorage and 

caused Anchorage airports to curtail operations for several 

days (Casadevall, 1993). The cost of airport cleanup alone in 

Anchorage from the August 18 ashfall was more than 

$650,000. The ash cloud from the September 17 eruption 

disrupted air traffic routing around the volcano-2 days later 

it disrupted air routes over western Canada and in the congested air corridors of the northeastern United States. Fortunately, there were no encounters between aircraft and the 

drifting Spurr ash clouds. The lack of damaging encounters 

following the Spurr eruptions reflects increased awareness 

about the hazards of ash clouds and improvements made 

since 1990 in the warning, detection, and tracking of volcanic clouds. These improvements are largely a direct result of 

the previously mentioned initiatives by Federal and international agencies to reduce the hazards from volcanic ash. 

From an operational perspective, experience in the Australia-Indonesia region and in Alaska has indicated that the 

threat of volcanic ash can be effectively addressed at the 

regional or local level. For example, the 1989-90 Redoubt 

eruptions and the 1992 Spurr eruptions prompted Federal 

and State agencies in Alaska to establish a regional plan for 

aviation-related volcanic hazards (Alaska Interagency Operating Plan, 1993). The plan outlines the responsibilities of 

the agencies involved in eruption responses to meet the public's need for information to protect against volcanic ash 

hazards. The Redoubt and Spurr eruptions also prompted 

U.S. and Canadian agencies to refine bilateral operational 

plans for communicating about volcanic hazards (Hickson, 

this volume). 

In addition to the efforts by international and Federal 

agencies, the major airplane and jet engine manufacturers 

have also studied the damage to aircraft from ash encounters 

in efforts to develop mitigation strategies, including practical 

steps for pilots to minimize damage should an ash cloud be 

entered accidentally. The manufacturer's principal trade 

association, the Aerospace Industries Association (AlA), 

formed a volcanic ash study committee in 1991 to evaluate 

the volcanic threat to aviation safety (AlA Propulsion Committee, this volume). The findings of this committee are 

reflected in a number of the reports presented in Seattle 

(Campbell, this volume; Dunn and Wade, this volume; 

Przedpelski and Casadevall, this volume). 

The Air Line Pilots Association (ALP A), the Air Transport Association (ATA), and the Flight Safety Foundation 

(FSF), as well as the American Institute of Aeronautics and 
INTRODUCTION 5 

Astronautics (AIAA) and the Aerospace Industries Association (AlA) have all taken active roles to communicate about 

the ash problem with their members and constituents, both 

nationally and internationally. ALP A and ATA were sponsors ofthe Seattle Symposium, along with the FAA, NOAA, 

and the USGS. AlA, AIAA, FSF, lA VCEI, and the National 

Transportation Safety Board were co-sponsors of the 

symposium. 

FUTURE DIRECTIONS 

As we gain understanding about the nature of ash 

clouds and the hazard of volcanic ash to aviation operations, 

we constantly improve our abilities to deal with the threat 

(Casadevall, 1992). Multidisciplinary cooperation and communications were major factors in the success of the Seattle 

meeting. This cooperation created an excitement among the 

participants that has been kept alive at later workshops and 

in cooperative efforts such as the production of the Boeing 

training video (Boeing Company, 1992). Even though the 

ash-aviation safety problem is global in scope, the solutions 

that have worked best have often been on a local or regional 

scale. The optimal solutions require understanding the location and character of the nearby active volcanoes, the structure of the air routes that cross or pass by these volcanoes, 

and an understanding and use of all available resources to 

detect, track, and forecast the movement of ash clouds. At 

the same time, as new pilots are introduced to new routes, 

efforts to educate pilots must continue. 

The Seattle symposium and the efforts following the 

symposium indicate that we have much to do to satisfactorily 

address concerns about the threat of volcanic ash to aviation 

safety. This requires application of existing technologies, 

such as methods that enable scientists to detect eruptions 

from remote, unmonitored volcanoes; early detection of ash 

clouds; tracking of ash clouds in real time; and development 

of better and faster ways to get information into the cockpit. 

Also, despite the recent advances in testing jet engines for 

their tolerances to volcanic ash (Dunn and Wade, this volume) and advances in using remote-sensing technologies to 

detect and track ash clouds (Schneider and Rose, this volume; Wen and Rose, 1994), it is essential that ash clouds be 

sampled directly as they drift from their source volcanoes 

(Riehle and others, 1994). Only direct sampling will allow us 

to obtain information with which to corroborate and validate 

laboratory tests and computational models. The results of the 

Seattle symposium should be viewed as a start of efforts to 

address the threat that ash clouds present to aviation safety. 

Volcanoes will certainly continue to erupt, and air traffic and 

aircraft sophistication will continue to grow. To successfully 

coexist with the threat of volcanic ash, we must continue to 

address the volcanic hazard in a responsible fashion. Open 

communications about these efforts are essential to successfully dealing with the volcanic hazard to aviation safety. 

ACKNOWLEDGMENTS 

The success of the Seattle symposium required the 

energy and efforts of a large number of colleagues. The symposium was organized under the leadership of Chris Newhall 

of the USGS and came about through the efforts of an interagency task group that was first suggested by Senator Ted 

Stevens of Alaska. Principal representatives on this task 

group included Robert Machol of the FAA, Mike Matson of 

NOAA, Doug Wade of the Department of Defense, Ed 

Miller of the Air Line Pilots Association, and Don Trombley 

of the Air Transport Association. Their assistance and support in the production of this report is gratefully acknowledged. The editor of this report served on this task group as 

program coordinator for the symposium. 

Several colleagues provided long-term encouragement 

for this project, including Grant Heiken (Los Alamos 

National Laboratory), Tom Fox (ICAO), Mike Dunn (CALSPAN), Tom Simkin (Smithsonian Institution), and Bill 

Rose (Michigan Technological University). A special thanks 

goes to Robert Wesson of the USGS, who had the earliest 

and clearest vision of what the Seattle symposium should be. 

The cooperation of those who acted as reviewers is 

especially appreciated. They include: Robert Anders, Steve 

Brantley, Marcus Bursik, Dan Dzurisin, David Harris, Grant 

Heiken, Wally Johnson, Steve Lane, Steve McNutt, C. Dan 

Miller, Tom Murray, Tina Neal, Chris Newhall, John Power, 

Jim Riehle, Bill Rose, Dave Schneider, Steve Self, George 

Stephens, Barbara Stunder, and Bob Tilling. 

Deloris Klausner of the Branch of Volcanic and Geothermal Processes (USGS, Denver) was responsible for collating all the manuscripts. Rick Scott, geologist and technical 

publications editor (USGS, Denver), provided editorial guidance and supervised preparation of illustrations and the final 

layout of the volume. 

REFERENCES CITED 

Alaska Interagency Operating Plan, 1993, Alaska Interagency Operating Plan for Volcanic Ash Episodes: Anchorage, Alaska, 

Alaska Division of Emergency Services, Alaska Volcano Observatory, Department of Defense, Federal Aviation Administration, and National Weather Service, June 16, 1993, 18 p. 

Alaska Volcano Observatory, 1993, Mt. Spurr's 1992 eruptions: 

Eos, Transactions, American Geophysical Union, v. 74, p. 217 

and 221-222. 
6 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Boeing Company, 1992, Volcanic ash awareness: Seattle, Wash., 

Boeing Customer Training and Flight Operations Support, video 911202, 33 minutes. 

Casadevall, T.J., ed., 1991, The First International Symposium on 

Volcanic Ash and Aviation Safety, Program and Abstracts: 

U.S. Geological Survey Circular 1065, 58 p. 

Casadevall, T.J., 1992, Volcanic hazards and aviation safety-Lessons of the past decade: FAA Aviation Safety Journal, v. 2, no. 

3, p. 9-17. 

--1993, Volcanic ash and airports: U.S. Geological Survey 

Open-File Report 93-518, 53 p. 

Casadevall, T.J., and Oliveira, F.A.L., 1993, Special project in the 

Asia/Pacific region boosts awareness of danger posed by volcanic ash: ICAO Journal, v. 48, no. 8, p. 16-18. 

Casadevall, T.J., and Thompson, T.B., 1994, Volcanoes and air 

navigation aides-A global planning chart: U.S. Geological 

Survey Geophysical Investigations Map GP-1011. 

Federal Aviation Administration, 1993a, Assuring aviation safety after volcanic eruptions: Washington, D.C., Office of the 

Associate Administrator for Aviation Safety, Special Review, 35 p. 

--1993b, FAA Workshop on old volcanic ash clouds: April 

22-23, 1993: Washington D.C., Office of the Chief Scientist, 

abstract volume, 37 p. 

Fox, T., 1988, Global airways volcano watch is steadily expanding: 

ICAO Bulletin, April, p. 21-23. 

International Civil Aviation Organization [ICAO], 1992, Meteorological service for international air navigation-International 

standards and recommended practices: Montreal, International 

Civil Aviation Organization, Annex III to the Convention for 

International Civil Aviation, 11th edition, 82 p. 

Miller, T.P., and Chouet, B.A., eds., 1994, The 1989-1990 eruption 

of Redoubt Volcano, Alaska: Journal of Volcanology and Geothennal Research, v. 62. 

Miller, T.P., and Kirianov,V.Y., 1993, Notification procedures for 

Kamchatkan volcanic eruptions: A case history of Sheveluch 

Volcano, April, 1993: U.S. Geological Survey Open-File Report 93-569, 9 p. 

Riehle, J.R., and Fink, J.H., 1993, Some advantages of global electronic communications among volcanologists [abs.]: World 

Organization of Volcano Observatories workshop (Volcano 

observatories, surveillance of volcanoes, and prediction of 

eruptions), Guadeloupe, 13-17 December, 2 p. 

Riehle, J.R., Rose, W.l., Schneider, D.J., Casadevall, T.J., and 

Langsford, J.S., 1994, Unmanned aerial sampling of a volcanic 

ash cloud: Eos, Transactions, American Geophysical Union, v. 

75, p. 137-138. 

Smith, W.S., 1983, High-altitude conk out: Natural History, v: 92, 

no. 11, p. 26-34. 

Steenblik, J.W., 1990, Volcanic ash: A rain of terra: Air Line Pilot, 

June/July 1990, p. 9-15, 56. 

Wen, Shiming, and Rose, W.l., 1994, Retrieval of sizes and total 

masses of particles in volcanic clouds using A VHRR bands 4 

and 5: Journal of Geophysical Research, v. 99, p. 5421-5431. 

Wright, T.L., and Pierson, T.C., 1992, Living with volcanoes: U.S. 

Geological Survey Circular 1073, 57 p. 
INTRODUCTORY REMARKS FOR THE 

FIRST INTERNATIONAL SYMPOSIUM ON 

VOLCANIC ASH AND AVIATION SAFETY, 

SEATTLE, WASHINGTON, ruLY 1991 

By Donald D. Engen, Former Administrator, Federal Aviation Admnistration 

PERSPECTIVES ON THE HAZARDS OF 

VOLCANIC ASH 

I feel as if I have lived close to volcanoes. I was Commanding Officer of the U.S.S. Mt. Katmai-a U.S. Navy 

ammunitions ship-and lived on top of 28,000 tons of high 

explosives. The U.S. Navy has historically named ammo 

ships after volcanoes for some perverse reason. I was determined not to be the first Captain to go up with his ship! 

Twenty years ago, and even 10 years ago, no one that I knew 

would have even thought about organizing a symposium on 

volcanic ash as an air-safety issue. To those of us in aviation, 

volcanoes were those spectacular peaks that were reassuring 

landmarks en route to wherever we were going. To volcanologists, airplanes were a way to get a good view of volcanoes 

and a step toward getting information to provide warning to 

the communities near active volcanoes. I am not sure what 

meteorologists thought-perhaps that volcanic eruptions 

made for some pretty interesting clouds from time to time. 

Volcanic ash was not high on aviation's list of concerns, and 

airplanes were far from volcanologists' thoughts. To be sure, 

there were a few visionaries, but very few. 

Then we started flying civil aircraft higher and in areas 

of the world where we had not flown so regularly before. 

Many international pilots encountered local situations in 

which they had little experience. Meteorologically, we found 

Meltemes, Mistrals, Siroccos, WilliWaws, and jet streams. 

Volcanoes attracted sightseers, and pilots flying near eruptions found volcanic ash to be injurious to the long life of aircraft engines and airframes. Then we found that volcanic ash 

clouds extended far from their source. At night or in instrument flight conditions (IF C), the ash cloud could not be seen, 

and we had damage incidents. 

The International Civil Aviation Organization (ICAO) 

saw the need to address this hazard, and international networks such as the World Organization of Volcano Observatories (WOVO) were used as resources. Aviation shorthand 

messages to pilots, such as notices of significant meteorological events (SIGMET's) and notices to airmen (NOT AM's), 

were used to give wide dissemination to pilot reports 

(PIREP's) concerning ash clouds. The World Meteorological Organization (WMO) began using satellites for tracking 

ash clouds and for forecasting. The International Airways 

Volcano Watch was established. 

We have had a number of volcanic ash encounters in the 

past 10 years, and we have almost lost some civil air carrier 

airplanes. More recently, we have had tWo major American 

military airfields shut down in the Philippines. Some say that 

there is a growing need for an on-the-scene knowledgeable 

pilot or dispatcher to provide operational information when 

airports are near or within a fallout area. 

Today, everyone who has come to this meeting understands that we need to think about ash as an air-safety issue. 

To be sure, ash clouds are not an everyday issue, and they do 

not provide frequent hazard. But, if encountered, volcanic 

ash can spoil your entire day. Since Mount St. Helens awakened us in 1980, we have had 20 known encounters and three 

near accidents of wide-bodied jet airplanes worldwide. I will 

bet that Captain Moody will tell us at lunch today that his 

thoughts about Indonesian volcanoes changed dramatically 

one night in 1982. We will hear about other volcanoes as 

well-in Indonesia, Mexico, Japan, the former USSR, and 

elsewhere. These volcanoes have briefly but dangerously 

filled our airways with ash. 

With great credit to ICAO and others, as I have said, 

important steps have been taken. Pilot operating handbooks 

have new pages, and volcanologists talk with aviation 

7 
8 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

meteorologists and air traffic control centers (ATC). But, as 

we saw last month near Pinatubo, the risk is not decreasing. 

In fact, the risk seems to be growing with the increasing 

numbers of long-distance night flights over remote volcanic 

areas. Encounters invariably cause damage and can easily be 

catastrophic. 

Some important information is already known, but this 

information is not widely disseminated. Over the course of 

the next 3 days, we are going to hear from the world's 

experts about what is known about this problem. We will 

hear from the people who take the pulse of volcanoes, from 

those who have developed new methods for tracking ash 

from space, from those who have flown into and around ash 

clouds, and from those who have dealt with the damage. We 

will learn about the state-of-the-art warnings of impending 

or actual eruptions from monitored volcanoes (a relatively 

small subset of all volcanoes), about satellite detection of ash 

plumes, about subsequent movement of the resulting clouds 

of ash, about the most common effects of ash on airframes, 

instruments, and engines of airplanes, and about what pilots 

should do in case of an accidental encounter. 

There are also many unknowns and gaps in worldwide 

coverage. These shortcomings will also be covered over the 

next 3 days. As a pilot, let me raise some questions. Suppose 

the volcanologists tell us that Redoubt or Pinatubo have just 

erupted an ash cloud. Can they tell us how high the cloud will 

rise? Can they tell us if it has a lot of ash or just a lot of 

steam? The meteorologists can tell us about winds at different altitudes. But can they tell us what altitudes actually have 

ash and in which direction the ash is moving? And can they 

revise their notices frequently as wind patterns change, as 

new images or data are received, and as ash progressively 

falls from the cloud? How will we know where the cloud is 

at night or if we are in instrument flight conditions? The 

A TC might be able to warn us that there is a hazard ahead, 

but can they tell us how serious it is, or how long it will 

remain a hazard? And can they be sure that alternative routes 

do not also have ash? Once ash is encountered, should we 

climb, descend, or reverse course? Will the ash cloud show 

on my radar with greater definition than moisture? 

If you came to hear well-tested solutions, you are 5 

years too early. If you came to be part of the solutions, you 

are in the right place at the right time. We are all pioneers on 

this subject. This is the first time that all of the world's 

experts have come to put their heads together, and it is the 

first time that so many of you who need this information 

have come to hear it. But, unlike some subjects, where the 

world really is divided into experts, beginning students, and 

advanced students, we need to teach each other. And to do 

that, we need plenty of lively discussion. Your questions are 

important, because nobody in this room has thought about 

the problem from every angle. 

We have structured the meeting to encourage discussion and to make sure that we do not just talk with our own 

colleagues. No question will go unanswered-if we cannot 

handle it at the time, we will come back to it. No idea will go 

unrecorded-we are providing you with deposit slips for an 

idea bank where you can reinforce the ideas you offer in discussion. We will have poster sessions for person-to-person 

discussions. And, as some of you have already found, symposiums are a great place to meet the people that we will 

need to be talking with in the years to come. 

Volcanologists seem always to talk to volcanologists, 

pilots to pilots, and meteorologists to meteorologists. To 

have communication, you must have listeners as well as talkers. There is a great need for practical communications 

across the disciplines represented here. There is a driving 

need to prevent a major aviation accident, which has not yet 

happened. There is a driving need for better understanding of 

volcanoes on the part of all of us. That is why we are here. 

We are delighted to see such a diverse group. To participants from outside the United States, "Welcome!" Your 

participation adds meaning and knowledge to this symposium. I hope, through your participation, that other nations 

will join the search for knowledge. To participants from disciplines that barely knew of each other's existence, say hello 

to each other because the solution to your problem concerning volcanic ash may lie in your new friend's area of 

expertise. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANOES AND AVIATION SAFETY IN COSTA RICA 

By Jorge Barquero 

ABSTRACT 

The active volcanoes in Costa Rica are located in Guanacaste Volcanic and Central Volcanic Ranges. Poas and 

Irazu Volcanoes have had several strombolian eruptions in 

historical times that produced large quantities of ash. Fine 

ash moved to the west and southwest of the volcanoes, reaching different distances and altitudes due to predominant 

trade-wind directions. Therefore, precautions should be 

taken for air traffic during future eruptions. 

Costa Rica's Juan Santamaria International Airport in 

San Jose is located 23 km south ofPoas Volcano and 42 km 

west of Irazu Volcano. Commercial airline routes are over or 

very close to the volcanoes. For example, Poas Volcano 

(8,884 ft high) is in the route of commercial airlines to 

Miami, which fly at a minimum altitude of 12,000 ft. Irazu 

Volcano (11,457 ft high) is in the airline route to Panama, 

with a minimum flying altitude of 14,000 ft. 

The cooperation between pilot, air traffic controller, 

and volcanologists is very important. From the air, it is possible to see anomalous activity in volcanoes. For example, in 

1962 a pilot called a newspaper to report the first columns of 

vapor issued by Irazu Volcano during the 1963-65 active 

period. In 1989, Poas Volcano had very strong gas emissions. At times, private and commercial airline pilots 

reported to air traffic controllers strong odors and the height 

of gas columns. 

It is imperative to take into account possible ash and gas 

eruptions when planning air traffic and future airport sites. 

INTRODUCTION 

The active volcanoes in Costa Rica are located in the 

Guanacaste and Central Volcanic Ranges. In recent times, 

Rincon de Ia Vieja, Arenal, Poas, Barba, Irazu, and Turrialba 

Volcanoes have had explosive ash-producing eruptions. Ash 

clouds have been carried to the west and southwest ofthe volcanoes because these are the directions of the prevailing 

winds. 

The Juan Santamaria International Airport, located 20 

km from the capital of San Jose and served by both national 

and international commercial airlines, is located in the central part of Costa Rica, to the south and west of the active 

volcanoes Poas and Irazu (fig. 1). As a result of the location 

of the airport, the air traffic routes pass over or near volcanoes that have very high eruption potential. This circumstance makes it mandatory to take precautions with air traffic 

during eruptions. 

DATA AND RESULTS 

Poas Volcano, located 23 km, (14.4 mi) to the north of 

Juan Santamaria International Airport, rises to 2, 708 m 

(8,884 ft). It has been active since 1828, and its last major 

active period took place between 1953 and 1955 (table 1). 

Ash clouds produced during this eruption were carried 

mainly to the west, to the southwest, and sporadically to the 

south. 

Since 1987, Poas has ejected a gas column that sometimes reaches 2,000 m above the crater level, and its strong 

sulfurous odor has been reported by pilots. The minimum 

altitude for the airway over this volcano is 3,158 m (12,000 

ft). This is the primary commercial airway to Miami, and it 

is used daily by planes that carry hundreds of passengers. 

Irazu Volcano is located 42 km to the east of the Juan 

Santamaria International Airport and has an altitude of3,443 

m (11,457 ft). The commercial airway connecting Santamaria, Limon, and Panama (at a minimum altitude of 4,320 m 

or 14,000 ft) passes directly over Irazu Volcano; thus, there 

is a great deal of air traffic over this volcano daily. 

In historical time, Irazu has been very active, with 

recorded eruptions since 1723. The last period of activity 

took place between the years of 1963 and 1965. Constant ash 

eruptions reaching heights of approximately 6,200 m 

(20,000 ft) were reported, and ashes were carried to the west 

and southwest by the prevailing winds. Deposition of this 

pyroclastic debris affected all of the Central Valley, in which 

the international airport is located. Official information concerning emergencies suffered by airplanes during this time 

does not exist, but there are accounts of problems during that 

period. The most outstanding report tells about a Pan Am 

DC-6 plane that flew through an ash cloud from Irazu and 

was forced to land in Panama in 1963. This plane had problems with its windows and engines. Ash was an effective 

abrasive. One precaution taken by domestic airlines and private airplane owners was to make check-ups of airplanes 

9 
10 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

more often than required. Overhauls were done more often 

than during normal conditions, and, in some cases, engines 

were replaced. 

Arenal Volcano, located 73 km ( 45 mi) to the northwest 

of Juan Santamaria Airport, has an altitude of1,630 m (5,380 

ft). Planes flying to Managua, Nicaragua, follow an air route 

close to this volcano at a minimum altitude of 3,400 m 

(11,000 ft). Several airplanes carrying passengers fly this 

route each day. Arenal is an active volcano, and, since 1968 

(23 years of activity at present), ash columns over altitudes 

NICARAGUA 

10°-

85° 

PACIFIC OCEAN 

EXPLANATION 

NUMBER ON MAP AIRWAY ROUTE MINIMUM FLIGHT 

NUMBER ALTITUDE 

CD A-502 11,000 ft 

® B-767 12,000 ft 

® A-1200 12,000 ft 

@) B-650 14,000 ft 

Figure 1. Airway routes over active volcanoes in Costa Rica. 

of3,048 m (10,000 ft) have been reported. Wind carries the 

pyroclastic debris toward the west and southwest, reaching 

different points according to the wind velocity. 

Pilots have knowledge of Arenal activity and the dangers it represents, so they take precautions and report information to the airport regarding the height and direction ofthe 

ash cloud. This has helped to prevent airplane accidents on 

this route. 

Some of the volcano-monitoring methodologies that 

are currently in use in Costa Rica are shown in table 2. 

-1F 

CARIBBEAN SEA 

84° 

·~ <( 

-~ :::2: 

""" <( _go ~ 

, z ,./ <( S" a.. \: I 

'\ 

. 
VOLCANOES AND AVIATION SAFETY IN COSTA RICA 11 

Table 1. Year(s) of eruption and eruption type for some major 

volcanoes in Costa Rica. 

Year( s) of eruption Eruption type 

Rincon de Ia Vieja Volcano 

1860 ................... Normal explosions. 

1863 ................... Normal explosions. 

1966 ................... Phreatic explosions. 

1969 ................... Phreatic explosions. 

1970 ................... Phreatic explosions. 

1983 ................... Phreatic explosions. 

1987 ................... Phreatic explosions. 

1991 ................... Phreatic explosions. 

Arenal Volcano 

1525 ................... Normal explosions. 

1968-present ...... Nuees ardentes, pyroclastic flows, 

phreatic explosions, lava flows. 

Poas Volcano 

1834 ................... Normal explosions. 

1838 ................... Normal explosions. 

1880 ................... Phreatic explosions. 

1907 ................... Phreatic explosions. 

1910 ................... Phreatic explosions. 

1914 ................... Phreatic explosions. 

1946 ................... Phreatic explosions. 

1952 ................... Phreatic explosions. 

1953-55 ............. Magmatic eruptions. 

1961 ................... Phreatic explosions. 

1963 ................... Phreatic explosions. 

1964 ................... Phreatic explosions. 

1972 ................... Phreatic explosions. 

1974 ................... Phreatic explosions. 

1976 ................... Phreatic explosions. 

1977 ................... Phreatic explosions. 

1978 ................... Phreatic explosions. 

1979 ................... Phreatic explosions. 

1987 ................... Gas eruptions. 

1988 ................... Gas eruptions. 

1989 ................... Gas eruptions. 

1990 ................... Gas eruptions. 

1991 ................... Gas eruptions. 

1992 ................... Gas eruptions. 

CONCLUSIONS 

Several airways cross over or near Costa Rica's active 

volcanoes, and, therefore, air traffic is vulnerable in the event 

of ash eruptions. The prevailing wind direction in central 

Costa Rica and the location of Juan Santamaria International 

Airport with respect to the active volcanoes makes this airport vulnerable to ash deposition during volcanic eruptions. 

Table 1. Year(s) of eruption and eruption type for some major 

volcanoes in Costa Rica-Continued. 

Year( s) of eruption Eruption type 

Irazu Volcano 

1723 ................... Normal explosions. 

1726 ................... Normal explosions. 

1821 ................... Normal explosions. 

1822 ................... Normal explosions. 

1826 ................... Normal explosions. 

1842 ................... Normal explosions. 

1844 ................... Normal explosions. 

184 7 ................... Normal explosions. 

1870 ................... Normal explosions. 

1882 ................... Normal explosions. 

1917-1921 ......... Phreatic explosions. 

1924 ................... Normal explosions. 

1928 ................... Normal explosions. 

1930 ................... Normal explosions. 

1933 ................... Normal explosions. 

1939 ................... Normal explosions. 

1963-1965 ......... Phreatic explosions. 

Turrialba Volcano 

1750 ................... Normal explosions. 

1864 ................... Normal explosions. 

1866 ................... Normal explosions. 

Table 2. Volcano-monitoring methodologies in use in Costa 

Rica. 

Rincon de Ia Vieja Volcano 

Thermometry of crater lake; dry inclinometry; seismology. 

Arenal Volcano 

Radon emanometry; river and thermal-spring water analysis; 

gas traps; acid rain; ash collectors; dry inclinometry; horizontal 

distances network; vertical leveling lines; seismology. 

Poas Volcano 

Thermometry of fumaroles and hot-water lakes; analysis of gas 

condensates; river and thermal-spring water analysis; gas traps; 

acid rain; radon emanometry; dry inclinometry; horizontal 

distances network; vertical leveling lines; seismology. 

Irazu Volcano 

Thermometry of hot-water lakes; analysis of gas condensates; 

analysis of water samples from crater lake, rivers, and thermal 

springs; radon emanometry; dry inclinometry; geodetic network; 

vertical leveling lines; seismology. 

Turrialba Volcano 

Thermometry of fumaroles; analysis of gas condensates; gas 

traps; radon emanometry; dry inclinometry; seismology. 
12 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

RECOMMENDATIONS 

1. Plan, in advance, contingency or alternate airways to 

prevent planes from crossing over or near volcanoes 

that may be erupting. 

2. Complete the construction of Tomas Guardia Airport 

as an alternate international landing site in case Juan 

Santamaria airport is closed. 

3. Personnel ofObservatorio Vulcanologico y Sismologico de Costa Rica (OVSICORI) should always be in 

close contact with the Office of Civil Aeronautics and 

should provide information on the state of activity of 

the volcanoes, especially when anomalous activity is 

present. Pilots, through the air traffic controllers, 

should inform OVSICORI of unusual volcanic activity as seen from the air. 

4. An ad hoc group should be integrated with staff 

from the Office of Civil Aeronautics, pilots, and 

OVSICORI to draft a plan of action in case of volcanic eruptions. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

A METHOD FOR CHARACTERIZING VOLCANIC ASH 

FROM THE DECEMBER 15, 1989, ERUPTION OF 

REDOUBT VOLCANO, ALASKA 

By Gregory K. Bayhurst, Kenneth H. Wohletz, and Allen S. Mason 

ABSTRACT 

The development of an automated program for characterization of particles using a scanning electron microscope 

(SEM) with an energy dispersive X-ray detector (EDS) has 

greatly reduced the time required for analysis of particulate 

samples. The SEM system provides a digital representation 

of all particles scanned such that further measurement of the 

size, shape, and area are a product of image processing. The 

EDS and associated software provides information as to the 

particles' chemical composition. Data obtained from the 

SEM by this method are reduced by computer to obtain distribution graphs for size, density, shape, and mineralogy. 

These SEM results have been tested by comparisons with 

results obtained by traditional optical microscopy-the 

results obtained by optical microscopy support the SEM 

results and provide details concerning crystallinity and glass 

content. 

This method was applied to the ash that damaged the 

engines from the Boeing 7 4 7-400 flight of December 15, 

1989 (Brantley, 1990), which flew into the ash cloud from 

Redoubt Volcano. The sample was collected from the pitotstatic system and had not been exposed to any engine parts 

that might have changed its characteristics. The sample analysis presented here demonstrates the capabilities and information obtainable from our automated SEM technique. 

INTRODUCTION 

Studies of volcanic ash particles can be used to understand problems associated with volcanic ash clouds such as 

aircraft engine damage, visibility, atmospheric dispersion, 

and deposition of ash (Heiken, this volume). By using several analytical techniques, particles can be characterized in 

terms of size, shape, mass, mineralogy, and chemical composition. These characteristics provide detailed information 

necessary to understand the nature of volcanic ash clouds. 

METHODS OF STUDY 

SAMPLE PREPARATION 

Loose samples, such as the ash collected from the pitotstatic system, can easily be prepared by traditional thin-section techniques. This involves mixing the ash with epoxy on 

a microscope slide and then polishing flat to a desired thickness. Both the SEM technique and optical microscopy techniques can use the same slide. 

If the sample has been collected on filters, it is necessary to remove the particles from the filter medium. For ash 

collected on cotton or paper filters, the filters can be ashed in 

a low-temperature radio-frequency oven. The ashing 

destroys the filter material and leaves the particles unaltered. 

The particles then can be mixed with epoxy and made into a 

thin section. 

SEM PARTICLE-ANALYSIS PROGRAM 

The SEM uses a software program originally developed 

by L.J. Lee Group, Inc. for identification of airborne asbestos particles. It was modified to analyze volcanic ash particles. For each particle, the size, diameter, area, elemental 

composition and density are recorded. The location of each 

particle is also noted for easy return to a particular particle if 

detailed examination is needed. 

TREATMENT OF DATA 

The data is first transferred from the SEM into a spreadsheet from which various operations are performed. These 

operations characterize the particles as to their mineralogy, 

morphology, densities, and abundances. The spreadsheet 

and operations are done with BBN Software Products Corporation's RS-1 software program (G. Luedemann and G. 

Bayhurst, unpub. data, 1989). 

13 
14 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Mineral definitions used in this report. 

[Numbers in definitions column indicate weight percent] 

Mineral Definitions 

Quartz ............................. Si;::: 90 

Calcite ............................. Ca;::: 90 

Magnetite ........................ Fe+ Ti :::: 90 

Gypsurnlanhydrite ............ Ca + S;::: 90; Ca > 41; S > 29 

Mica/clay ......................... Ca + K + Al + Si;::: 80; Fe> 4; 

K>4;23 <Si<80 

Feldspar .......................... Ca + Na + K + A1 + Si ;::: 80; 

Fe~ 4; A1 + Si >59; 30 < Si < 80 

Amphibole ....................... Fe + Mg + K + Ca + A1 + Si ~ 80; 

Fe > 5; K ;::: 3; 28 > Si > 80 

Using the chemical analysis for each particle, the mineralogy is determined based on seven minerals or mineral 

classes. If the particle does not meet the criteria of the mineral definitions (table 1), it is labeled as "other." Because the 

SEM gives only chemical composition and not crystal structure, the glass content of the ash is not available by this 

method. The particles are then plotted according to the frequency of their mineral content. 

The mean diameter, which is based on 16 measurements, is used to establish size frequencies. These size frequencies are calculated for both mineral type and overall 

bulk particles. The longest diameter measurement and the 

shortest measurement are ratioed without regard to mineralogy to provide an aspect ratio that gives an indication of 

shape. Digital image representation also allows computation 

of a shape factor given as the particle perimeter squared 

divided by the product of its area and 4 pi. 

By using the results from the chemical analysis, we can 

determine the mass of each particle by combining densities 

and diameters. The densities are based on values for oxides 

for each element in the particle such as Si02, Na20, and 

CaO. The masses are used in several ways. The mass for 

each particle can be plotted on a log cumulative mass versus 

log diameter to give mass accumulation curves. The mass 

distribution can also be expressed as a percent total versus 

phi (phi = -logz x (diameter in mm)) and analyzed using the 

sequential fragmentation/transport (SFT) model of W ohletz 

and others (1989). 

The final function of the software is to determine various statistical values for each sample. Our statistics summary contains the mean, standard deviation, minimum, and 

maximum for several parameters and automatically prints 

out a summary sheet. 

To verify our programs, we prepared chemical-composition standards by grinding well-characterized mineral standards to a fine powder. The powders were then prepared in 

the exact same manner as the ash particles. To verify our 

sizing-routine software, we used National Institute of Standards and Technology (NIST) standards for particle size. 

The software program that identifies minerals from chemical 

analysis was also tested by using these composition standards, achieving 95 percent or better correct identification. 

PETROGRAPHIC METHODS 

Several hundred particles were examined and counted 

by standard petrographic methods on an optical microscope. 

This method allows us to determine not only the mineralogy 

of the particle but also if the particle is noncrystalline or 

glass. The importance of this is that the glass component of 

the volcanic cloud has a big influence on melting temperatures (Swanson and Beget, this volume). 

RESULTS AND DISCUSSION 

The mineralogy of the ash particles determined by 

chemical composition was about 70 percent feldspar. The 

other components were quartz, magnetite, mica or clay, calcite, and amphiboles (fig. 1). An occasional particle of gypsum or anhydrite was also observed. By using fairly large 

ranges for defining the minerals or mineral groups, only 

about 10 percent of the ash was unidentified. The majority of 

unidentified particles appear to be mixtures of mineral 

phases that were probably welded on glass fragments. This 

result suggests that about 10 percent of the sample is composed of lithic fragments. 

The optical analysis gives another perspective of the 

mineralogy in that the glass component can be readily identified. The results from the optical analysis showed that the 

particles are mostly plagioclase feldspar (46.7 percent), with 

many ofthem being fractured. The glass component was second most abundant at 28.6 percent. The following were 

80 

I- 70 EXPLANATION z 

UJ 

u 60 ~Quartz 

UJ 

a: B1l Magnetite 

a.. 50 IIIIIJ] Mica and clay z 

>=' 40 .. Gypsum 

u E3 Feldspar z 30 

UJ Ill Amphibole . :::> 20 CJ Other 0 

UJ 

0::: 

LL 10 

0 

Figure 1. Mineralogy of ash particles from the December 15, 

1989, eruption of Redoubt Volcano as determined by scanning 

electron microscopy. 
CHARACTERIZING VOLCANIC ASH, DECEMBER 15, 1989, ERUPTION, REDOUBT VOLCANO, ALASKA 15 

Table 2. Bulk chemistry of glass from Redoubt volcanic ash 

from December 15, 1989, eruption. 

Species Weight percent 

Si02................................... 69.9 

Al203································· 10.4 

FeO.................................... 5.0 

MgO.................................. 0.5 

CaO................................... 8.4 

Na20.................................. 4.3 

K20 ................................... 0.1 

minor components: pyroxene 2.8 percent, homblendes 4.2 

percent, opaque minerals 5.6 percent, altered rock 7.0 percent, and magnetite 5.2 percent. The petrographic name of 

this sample is a hornblende, two-pyroxene andesite. 

If we assume that the glass component has nearly the 

same chemical composition as the crystalline minerals, then 

the results of the two methods are in good agreement. For 

example, if approximately 30 percent of the chemically 

defined feldspar particles are noncrystalline, then the percentage of crystalline feldspar would be approximately 49 

percent. 

With our method, we are able to obtain bulk-chemistry 

compositions by simply averaging each chemical component. For example, the average Si02 composition from our 

Redoubt sample was 69.9 percent. Because of the high glass 

content, the overall bulk chemistry (table 2) showed a higher 

Si02 concentration than the magma erupted during this time 

(Nye and others, 1990). This result is, however, consistent 

with other studies of Redoubt volcanic ash (Swanson and 

Beget, 1991 ). 

Our sizing routine showed that, for this sample, the 

majority of the particles were 20 f..lm or less (fig. 2). The 

different mineral types can show slight differences in size 

distribution from the overall distribution, but they still show 

800 EXPLANATION 

(f) 

700 PARTICLE SIZE, IN MICRONS w 

_J 

.. >1 s 10 0 

f= 600 llll!.lil > 1 0 s 2 0 0:: 

<( 500 bd >20 S30 0.. 

I t!!!!i!i:tt:l >30 S 40 

(f) 

<( 400 ~ >40S50 

u.. 300 IIIIIIIl >50 s 60 0 

a: ~ >60S70 .w 

co 200 c::J >70 ~ 

::::> 100 z 

0 

Figure 2. Size distribution of all minerals contained in ash from 

the December 15, 1989, eruption of Redoubt Volcano. 

that most of the particles are smaller than 20 f..tm (fig. 3 ). The 

information obtained from size distributions can provide 

insight as to the factors controlling the type of damage done 

to aircraft engines. For example, if the ash encountered had 

a large percentage of coarse particles, then increased damage 

from abrasion might be observed. If the ash is fine, it will 

melt more rapidly and contribute to the material adhering to 

turbine surfaces. 

Aspect ratios can be used for several purposes. The 

morphology of the particle can be described in this way. 

Aspect ratios that are close to 1 indicate that the particle is 

approximately equant in shape. For example, the aspect ratio 

of the feldspar particles (and glass) showed that about in onethird of them were equant (fig. 4). Also, the average shape 

factor for the sample is 1.16, which characterizes nearly 

equidimensional, polygonal cross sections. 

The mass distribution curve gives other important 

information about the nature of the volcanic ash. In our 

Redoubt sample, even though the small particles were the 

most numerous, they contributed only a small amount of the 

mass (fig. 5). Another way of looking at mass distribution is 

the phi plot (fig. 6). This plot shows that over 60 weight percent of the sample occurs between 62 f..tm (4.0 phi) and 125 

f..lm (3.0 phi). The overall mean diameter is 78 f..tm. 

SFT analysis shows that the size distribution is polymodal, which is likely a consequence of the various densities 

and shapes in crystals, glass, and lithics that determine the 

mass-to-size ratio. Furthermore, SFT analysis (fig. 7) shows 

a mean diameter of3.68 phi (0.078 mm) and a standard deviation of0.79 phi (+0.57 mm, -0.033 mm) and predicts this 

distribution by three subpopulations: (1) crystals (mode = 

0.210 mm), (2) lithic fragments (mode= 0.099 mm), and (3) 

en 60 EXPLANATION 

w PARTICLE SIZE, IN MICRONS .....J 

() ~s10 1- 50 a: - ~ 10 and< 20 <( 

a.. ITIIID ~ 20 and < 30 

a: 40 lrt=::t::::] ~ 30 and< 40 <( 

a.. § ~40 and< 50 en 

.....J 

Q 30 o~so w 

LL 

LL 20 0 

a: 

w 

co 10 

:E 

::J 

z 0 

Figure 3. Size distribution of feldspar minerals from the December 15, 1989, eruption of Redoubt Volcano. 
16 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

(/) 40 

w 

_J 

0 35 EXPLANATION 

Ia: 

<( 30 

a... 

ASPECT RATIO 

- ~ 1 and< 2 

a: 

<( 25 

a... 

(/) 

0 20 

- ~2 and< 3 

§ ~3and<4 

WdjJ ~ 4 and < 5 

_J 

w 

LL 15 

LL 

rnrrn ~ 5 and < 6 

~~6 0 10 a: 

w 

co 5 ~ 

:::,) 

z 0 

Figure 4. Aspect ratios of feldspar particles from the December 

15, 1989, eruption of Redoubt Volcano. Aspect ratio is determined 

by dividing the longest diameter by the shortest diameter. 

10-2 

(/) 

:~ 

<( 1 o-3 

a: 

(.!) 

~ 10-4 

en 

~ 10-5 

~ 

10 100 1poo 

DIAMETER, IN MICRONS 

Figure 5. Mass distribution curve of ash particles found in ash 

from the December 15, 1989, eruption of Redoubt Volcano. 

50 

w LJ.......J 40 oa.. ~ .-<( 

as(/) 

UI 30 

0::(/) 

~<( 4.0 

.- ~. 20 IZ 

(.!)<( 

-u 

w.....J 

so 10 > 

0 

Figure 6. Phi size distribution plot of ash particles from the December 15, 1989, eruption of Redoubt Volcano. Phi= -log2 x (diameter in mm). Individual bars along x-axis are labeled with size in 

phi units. 

glass (mode = 0.041 mm). The dispersion values of these 

subpopulations are analogous to standard deviations for lognormal distributions. In addition, the dispersion values have 

physical significance: with increasing dispersion, subpopulation distributions are generally more peaked, which results 

from more evolved particle fragmentation and size sorting. 

The crystal subpopulation (1) has a dispersion value of 0.50, 

which reflects the tight distribution in size determined by 

growth kinetics. Positive dispersion values generally come 

about from particle aggregation or nucleation, whereas negative values arise from fragmentation and attrition. In contrast, the glass subpopulation (3) has a dispersion value of 

-0.51, which is a function of its fragmentation and transport 

history (dispersion values of -0.6 or greater are typical of 

fragmentation by water-magma interaction). The lithic subpopulation (2) has a dispersion value (0.15) that indicates 

some aggregation after its fragmentation. 

The statistical summary (table 3) gives overall averages 

for many important parameters of the volcanic ash sample. 

This summary can be used to study the differences between 

different ashes or samples of the same ash. 
CHARACTERIZING VOLCANIC ASH, DECEMBER 15, 1989, ERUPTION, REDOUBT VOLCANO, ALASKA 17 

Subpopulation size characteristics analyzed by the 

sequential fragmentation/transport (SFI) model of 

Wohletz and others (1989). 

[See Wohletz and others (1989) for additional explanation] 

Subpopulation Mode Dispersion Fraction 

phi nun 

Crystals 2.25 (0.210) 0.50 0.08 

Lithic fragments 3.34 (0.099) 0.15 0.07 

Glass 

50 

II 

(9 

w 

~ 

I- 25 z 

w 

0 

a: 

w 

a.. 

4.60 (0.041) -0.51 0.21 

~ 

I \ 

I \ EXPLANATION 

I ' -Crystals I 

I 

I ' ' --- Lithic fragments 

I ' • • • • • • Glass ' I ' I ' I ' I 

I 

I ' 

0 1 2 3 4 5 6 7 

SIZE, IN PHI UNITS 

Figure 7. Subpopulation size characteristics of ash from the 

December 15, 1989, eruption of Redoubt Volcano. 

CONCLUSIONS 

To understand the nature of volcanic ash clouds, we 

must understand the nature of the particles that make up the 

cloud. By combining SEM and optical petrographic techniques with powerful software analysis and theories on particle transport, we obtain detailed information on the 

Table 3. Statistical summary for Redoubt volcanic ash from 

December 15, 1989, eruption. 

Average Standard Maximum 

deviation 

Diameter (~m) 13.3 12.9 141.0 

Aspect ratio 3.5 3.1 

Area(~m ) 284.0 889.8 11,989.0 

Density (g/cm3) 2.42 0.79 6.6 

characteristics of the particles in volcanic ash clouds. The 

characteristics of the ash cloud will determine where it goes, 

how long it will stay in the atmosphere, how much damage 

it will cause to an aircraft, and its effects on the environment. 

The volcanic ash ingested by the Boeing 747-400 that 

encountered the Redoubt ash cloud on December 15, 1989, 

has characteristics of material derived from eruption of 

andesitic magma by rapid release of high-pressure gases, 

perhaps by a hydrovolcanic mechanism. Optical microscope 

inspection revealed glass, blocky shards of minerals, and 

hydrothermally altered andesitic rock fragments. The chemical analysis derived from SEM analysis confirms the 

andesitic nature of the ash. Size analysis shows fragmentation characteristic of an evolved fragmentation process, such 

as is expected for a water-magma interaction. The shape 

analysis revealed dominantly low shape factors, characteristic ofhydrovolcanic ash. Knowing the chemical composition 

and finding that a large fraction of particles have a glass 

structure, the melting-temperature range can be estimated. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14, 1989-August31, 1990: U.S. Geological Survey Circular 1061, 33 p. 

Nye, C.J., Swanson, S.E., and Miller, T.P., 1990, The 1989-1990 

eruption of Mt. Redoubt-Magma chemistry [abs.]: Eos, 

Transactions, American Geophysical Union, v. 43, p. 1705. 

Wohletz, K.H., Sheridan, M., and Brown, W., 1989, Particle size 

distributions and the sequential fragmentation/transport theory 

applied to volcanic ash: Journal of Geophysical Research, v. 

94,p. 15703-15721. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

THE CONCENTRATION OF ASH IN 

VOLCANIC PLUMES, INFERRED FROM DISPERSAL DATA 

By Marcus I. Bursik, R.S.J. Sparks, Steven N. Carey, and JennieS. Gilbert 

ABSTRACT 

The mass concentration of pyroclasts of a particular 

grain size decreases as an exponential function of time in 

the body of the umbrella cloud that forms at the top of 

explosive volcanic-eruption plumes. Data on deposit-thickness variations and grain-size distributions of ash deposits 

can be used to infer particle concentrations in volcanic 

clouds using a simple physical model for sedimentation 

from umbrella clouds. The concentrations of ash in plumes 

that penetrate the operating heights of commercial aviation 

greatly exceed the concentrations that cause engine damage 

and failure (> 2,000 mg/m3) and dangerous concentrations 

(> 50 mg/m3) can persist for hundreds of kilometers downwind of the vent. However, aggregation of volcanic ash in 

the atmosphere can lead to much more rapid decreases in 

concentration. 

INTRODUCTION 

Volcanic plumes spreading rapidly within the atmosphere pose a serious risk to aviation. The umbrella cloud 

formed at the top of a volcanic eruption column is an example of an intrusive gravity current containing suspended particles spreading within a density-stratified, less turbulent 

fluid (Allen, 1985; Sparks, 1986; Simpson, 1987; Self and 

Walker, this volume; Sparks and others, this volume). Volcanic particles remain suspended in such currents as far as 

hundreds of kilometers from the vent. We have developed a 

theory describing sedimentation from such currents and have 

successfully used it to evaluate the dispersal of particles 

from currents of contrasting scales, geometries, and source 

fluids (Sparks and others, 1991; Bursik and others, 1992a). 

We review the theory and introduce a way to reconstruct ash 

concentrations within a volcanic cloud from sedimentological data on tephra-fall deposits. These results can be used to 

infer ash concentrations that might be expected at various 

distances during hypothetical modem eruptions. We consider the sedimentation of individual particles from clouds 

with radial symmetry and infer pyroclast concentrations 

within the clouds. We also investigate the concentration of 

suspended particles within currents in which the flow has 

been distorted into an elongated shape by wind. Finally, we 

consider a generalization of the model and estimate concentrations of particles within umbrella clouds for given plume 

heights and initial grain-size populations. 

Our approach is a valid representation of sedimentation 

from plumes for times and distances from the volcanic vent 

before the coherent gravity current thins significantly by 

gravity flow and sedimentation and is subsequently broken 

up by ambient atmospheric turbulence (Allen, 1985; Simpson, 1987). Thus, the model is certainly valid for the area 

near the vent and is probably valid for great distances from 

the vent because umbrella clouds can begin as flows several 

kilometers thick. Bursik and others (1992b) have shown that 

the dispersal of the Mount St. Helens plume is consistent 

with gravity-current behavior up to a distance of 600 km 

from the vent. After current break-up, diffusion-type models 

(Suzuki, 1983; Armienti and others, 1989) can be used to 

infer particle concentration, transport, and deposition by 

atmospheric advection and turbulence. 

SEDIMENTATION THEORY 

For particles uniformly distributed within a fluid by turbulence, Hazen (1904) showed that the incremental number 

of particles deposited is proportional to the number per unit 

thickness of fluid times the thickness of the layer from which 

particles could be expected to fall. Einstein and Krone 

(1962) and Martin and Nokes (1988) obtained similar relationships for deposition of suspended particles in flumes and 

small laboratory tanks where no particles are resuspended. 

Applying these results to a turbulent gravity current flowing 

within a stratified fluid as an interflow or intrusion (Manins, 

1976), we suggest that the total mass of particles, m, of a 

given size fraction being transported within a control volume 

moving with the fluid decreases as: 

19 
20 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

dm = -Ax (O) v (O) dt (1) 

where 

A is the area of the lower interface of the fluid parcel, 

X(O) is the mass concentration of particles of a given size 

fraction at the base of the volume, 

hence, AX(O) is the mass of particles per unit height in the 

volume at its base, 

v(O) is the terminal fall velocity of the particles at the 

base, 

tis time, 

hence, v(O) dt is the thickness of the fluid layer from 

which particles settle out. 

If (X) is the mean concentration of particles averaged over 

the current thickness, h, then A(X) = m/h, and the differential equation expressing the loss of particles from the current can be written: 

am m 

-+uVm = ---v(O) dt kh (t) (2) 

where 

u is current velocity, and 

k = (x)/x(O), which is a constant if similarity is 

maintained. 

It can be shown that, by making the proper substitutions in 

equation 1, equation 2 holds for concentration, x, as well as 

mass, m. Although gravity currents are inherently transient, 

conditions within the body of such a flow are approximately 

steady at a large distance from the advancing front. For 

steady flow, equation 2 holds not only for m and X but also 

for the mass of particles carried by the current through time, 

M = m1t, where 1t is any finite time. If 1t = T, eruption duration, then M is the mass of material deposited beyond any 

given distance. Furthermore, for any downcurrent distance, 

~' equation 2 can be directly integrated, resulting in: 

(3) 

and 

{ r v (o) } 

(X) = <xo) exp - Jo kh (~) u (~) dS (4) 

where 

Mo and Xo are boundary values. 

There are two cases of volcanological interest to consider when evaluating the integral on the right hand side of 

equations 3 and 4. In the first case, the umbrella cloud is axisymmetric, resulting from radial spreading in a still atmosphere (fig. 1A). The second case arises when the cloud is 

modified by wind to assume an elongated shape (fig. 1B). 

We examine these two situations below, then we extend the 

results to a generalized geometry. 

A 

B 

I 

Plume 

axis 

DISTA!a FRCM PLUME AXIS 

Translation of comer to surface 

aiXi sedimentation maxim.un, x 0 

Figure 1. A, Diagram showing a physical model of the sedimentation of tephra of a particular grain size around an eruption column with no wind. The graph shows the variation of particle 

concentration for one grain-size fraction within the umbrella 

cloud. Sediment mass per unit area on the ground (unit sedimentation), S = -dM/dr (l/27tr), varies in the same manner. B, Schematic 

diagram of the lateral transport of ash by wind from the comer of 

the column to illustrate downwind displacement of the accumulation maximum, xo. 

RADIAL GEOMETRY 

We first consider the case of axisymmetric (radial) flow 

developed at the top of a volcanic eruption plume with no 

wind. In the volcanic column that feeds the umbrella cloud, 

vertical velocities are typically 50 to over 200 m/s (Woods, 

1988). Although coarse tephra falls out at the plume margins, the high velocities result in most tephra being transported to the plume top where it is swept into the umbrella 

current. At the height of neutral buoyancy, where the column 

density equals the density of the surrounding atmosphere, 
CONCENTRATION OF ASH IN VOLCANIC PLUMES, INFERRED FROM DISPERSAL DATA 21 

the plume diverts laterally and there is a rapid decrease in 

vertical velocity at a well-defined corner (fig. 1A). With no 

crosswind, the flow is completely driven by gravity and 

assumes a near-radial symmetry. Tephra is supported by turbulence within the current as it falls out at the base into the 

underlying quiescent atmosphere. 

Integration of the right hand side in equation 3, assuming conservation of volumetric flux, Q, between the ascending column and the current (thus Q = 2rcrhu and dQ/dr = 0) 

leads to the result: 

(5) 

where 

ro is the radial distance of the plume comer from the vent 

(fig. 1A), and 

Mo is the mass injected into the current during the 

eruption. 

The mass of particles deposited in concentric rings of unit 

width on the ground is thus given by -dM/dr: 

-dM 2rcvrM0 -1tv (/ -r~)IQ 

dr Q e (6) 

Sparks and others (1991) have presented laboratory 

experiments on sedimentation of particles from radially 

expanding gravity currents generated by turbulent, particleladen plumes that show good agreement with the theory in a 

form analogous to equation 6. 

Bursik and others (1992a) have compared the sedimentation theory to grain-size-distribution data of the Fogo A 

Plinian deposit on Sao Miguel in the Azores (Walker and 

Croasdale, 1971). Values of Mo andrcv/Q were determined 

from field data for each grain-size class by iterative curve fitting to integrated accumulation data. The slightly elliptical 

geometry of the thickness contours in the Fogo deposit, 

caused by low winds(:: 2 m/s) was accommodated by substituting a constant of 1.83 forrc. Detailed descriptions of the 

deposits and analysis of the field data are presented in Bursik 

and others (1992a). Beyond 7 km, the field data give excellent fits to the Gaussian functions (fig. 2A and 2B) with the 

slopes dependent on grain size as predicted by equation 5. 

Tephra in the size range 500 to 2,000 Jlm settles through the 

atmosphere with a speed determined by the relationship for 

fall at high Reynolds number (Woods and Bursik, 1991). We 

therefore expect the coefficient 1.83v/ Q to be proportional to 

the square root of the grain diameter. Figure 2C shows that 

the Fogo data fit this prediction well. From the data in figure 

2C, the value of Q, hence the total plume height and magma 

discharge rate, can be estimated for the eruption. The estimated total plume height of 21 km and magma discharge rate 

of 1.1x104 m3/s, assuming an eruption temperature of 

800°C, are in reasonable agreement with an independent 

assessment of the plume height (27 km) and magma discharge rate (5.3x104 m3/s) based on the maximum dispersal 

of lithic clasts. 

The above results can be used to infer particle concentrations within the Fogo A umbrella cloud. Given known 

masses of particles, M, deposited beyond a radial distance, r, 

the average concentration is given by: 

<x> 

where 

M 

QT 

(7) 

T is equal to about 12 hours (Carey and Sigurdsson, 

1989). 

Equation 7 can be applied to each of six grain-size fractions 

and the results summed to obtain the total concentration of 

lithics plus crystal fragments that are > 500 Jlm: 

6 

6 LMi 

L<x>i = i = 1 (8) 

QT i= 1 

Because lithics and crystals constitute about 14 percent of 

the deposit mass at each locality (Walker and Croasdale, 

1971 ), we can then estimate the average concentration of all 

clasts that are > 500 Jlm within the spreading umbrella 

cloud along the main (eastward) dispersal axis (fig. 2D). 

The results suggest that the cloud contained a rather concentrated suspension of these particles, with the smallest fraction becoming enriched relative to larger size fractions with 

distance from vent. For the Fogo A eruption, concentration 

dropped by an order of magnitude as the cloud spread 

downwind about 10 km. Note also that the concentration of 

pyroclasts that are > 500 Jlm was probably > 50 mg/m3 up 

to 20 km from the vent. Even so, most of the ash within the 

cloud was probably considerably smaller than 500 Jlm in 

diameter and remained in the atmosphere for great distances 

from the volcano. 

VOLCANIC UMBRELLA CLOUD 

MODIFIED BY A CROSSFLOW 

For cases in which the volcanic umbrella current has 

been distorted by prevailing winds, it is useful to rewrite 

equation 3 in the form: 

(9) 

where 

x is downwind distance, and 

w is the maximum crosswind width to which the current 

has expanded due to gravity. 

Equation 9 is easily integrated if v, Q, and u (wind speed) 
22 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

2,000-4,000 J,tm • 

• 

~ 2.5x1 o·• 

• • 

• 

• ~ g 1.5x1 o- 8 

~ • ai 

• ~ 0 ~------~------~------~--_.~ 

0 10 20 

s x 1 o· 9 L--__ ..._ __ __._ __ ---~.. __ L...-_....L..-_...~-_-...~ 

2x1 o· 2 6x10" 2 1x10" 1 1x10" 1 

A DISTANCE FROM VOLCANO, IN KILOME1ERS SQUARE ROOT OF GRAIN SIZE, 

c IN SQUARE ROOT MEIERS 

I I T I I I 

• • • • 1- • • - c ,.., 

·-

EXPLANATION 

0 c - • 0 0 c 

0 c 

-o- 500-1,000 J,tm 

-+--1 ,000-2,000 J,tm 

----2,000-4,000 J,tm 

1- EXPLANATION 0 c 

o':'c -

• P+L+C >500 J.lm 00 c 

c L+C >500 J.lm 0 

1 0 

---<>-- 4,000-8,000 J,tm 0 L+C, 500-1,000 J.lm 

0.001 1 I I 

0 100 200 300 8 12 16 20 

B ~-r , IN SQUARE KILOMETERS D DISTANCE FROM VOLCANO, IN KILOME1ERS 

Figure 2. A, The sediment accumulation, S, of lithic clasts in the size interval2,000--4,000 Jlm in the Fogo A Plinian deposit as a function 

of distance from vent. B, The natural logarithm of the ratio M!M0, where M is the total sedimentation beyond a given distance and Mo is 

the boundary value, is plotted against the difference of the distance squared from the position of maximum sedimentation, Yl- r0

2. Data 

are shown for four different grain-size intervals, 8,000--4,000,4,000-2,000, 2,000-1,000, and 1,000-500 Jlm. C, The Gaussian coefficient, 

B = 1.83v/Q, is plotted against the square root of grain size, showing that the data agree with the equation for settling velocity. D, Inferred 

concentration of pyroclasts in the Fogo A umbrella cloud as a function of distance from the vent along the dispersal axis. Concentrations 

in other directions would be somewhat lower. In this figure, k (equation 2) is assumed to equal unity. P, pumice; L, lithic (rock) fragments; 

C, crystals. 

are asswned constant, and if dwldt = u dw/dx = (g'h)ll2, 

where g' is the reduced gravity and h is current thickness, 

assumed constant for any x. Because the atmosphere is continuously stratified and the plume thins downwind, (g'h)l/2 

becomes ANh, where /.., is a constant of order unity that 

depends on flow geometry and ambient stratification (Simpson, 1987; Woods and Kienle, this volume) and N is the 

buoyancy frequency of the atmosphere with a value of 

approximately 0.035 s-1. Under these assumptions, w is 

given by: 

1/2 w = (2/..,NQx) /u (10) 

The solution to equation 9 is therefore: 

where 

x0 is the distance to the maximum in mass accumulation 

on the ground for a particular size fraction. 

The sedimentation within a unit area (unit sedimentation), 

S = (-dM/dx)(llw), can furthermore be shown to be equal 

to: 

{ 2v ( 312 312)} S = S0 exp -

3

u ../2/..,N/Q x -x0 (12) 
CONCENTRATION OF ASH IN VOLCANIC PLUMES, INFERRED FROM DISPERSAL DATA 23 

Satellite observations of the current generated by the 

initial blast/surge cloud of Mount St. Helens on May 18, 

1980, and the subsequent Plinian tephra fall fit this model 

well. The blast (phase I) cloud as well as the later phase III 

cloud migrated downwind at a velocity of 28 m/s (SarnaWojcicki and others, 1981; Criswell, 1987) to distances of at 

least 600 km ( 15: 15 PDT in fig. 3A), and the observed lateral 

expansion with distance agrees with equation 10, once the 

current attained the assumed geometry at about 10:45 PDT 

(fig. 3B). Using equation 10 and the above values for Nand 

u, we infer that 'A.Q = 3.9x109 m3/s. 

A 

350 

~ ~ 300 

~ z 

- 250 

200 

150 

B 

0 ~----~----L-~--~--~~--~ 

0 1 x 1 0

4 2x 1 04 

TIME AFfER 8:42 PDT, IN SECONDS 

14 16 18 20 22 24 26 

SQUARE ROOT OF DISTANCE FROM VOLCANO, 

mSQUAREROOT~OME~ 

Figure 3. Data on the geometry and speed of the distal current generated by Mount St. Helens on May 18, 1980 (taken from SarnaWojcicki and others, 1981). A, The speed, u, of the eastward drift of 

the current front, 28 m/s, agrees well with wind speeds measured 

within the region of approximately 30 m/s (Sarna-Wojcicki and others, 1981; Carey and Sigurdsson, 1982; Sparks and others, 1986; 

Criswell, 1987). B, The development of plume width, w, with distance follows equation 10 (see text). Width was measured as the 

greatest north-south extent of the current at the times and maximum 

distances shown in A. 

Crystal accumulation data for the 2.5-, 3-, 3.5-, and 4-<1> 

(177-, 125-, 88-, and 63-Jlm) size fractions ofthe May 18 ash 

fall deposit show maxima that increase in distance from the 

volcano with decreasing grain size (fig. 4). Virtually all of 

the ash at these distances was deposited from the Plinian 

plume (Carey and others, 1990). These peaks probably represent the downwind translation of each sedimentation curve 

from the comer region between the column margin and laterally moving gravity current (fig. 5A). Thus, significant 

downwind transport occurred after the crystals fell from the 

base of the umbrella region. This is in contrast to the proximal data for the Fogo A ash fall deposit, where the accumulation peaks for coarser particles are displaced only 

negligibly one from another. Accumulation data on the 

downwind side of the maxima fit equation 12 well (fig. 5B), 

with a decrease in sedimentation with distance that is a function of particle settling velocity, v. We note that this Plinian 

deposit was not formed from the giant cloud generated in the 

initial blast but from the eruptive activity that followed it. 

We are therefore assuming in our analysis that the lateral 

spreading of the Plinian plume was similar to that of the initial mushroom cloud. 

For particles in the size range 63 to 177 Jlm, the 

fall velocity, v, is a complex function of grain size (Bursik and others, 1992b; Armienti and others, 1989). The 

exponential constant in equation 12 should be proportional to the fall speeds given by Armienti and others 

(1989). Thus, the exponential constant in equation 12, 

which is proportional to v, should be proportional to the 

square root of the grain diameter. The data agree with 

this prediction (fig. 5C). The slope, 2(2AN/Q)112!3u, has 

a value of 8.35x1o-s. Using wind values from Carey and 

others (1990), we infer that IJQ = 1.8x1o-to s/m3. Combining the values for 'A.Q and IJQ leads to the conclusion 

that 'A, = 0.83, Q = 4.7x109 m3/s, and plume height 

above vent, H, = 20 km, which agrees reasonably well 

with observed plume heights of 11-17 km observed during the Plinian phase (Harris and others, 1981) and 

heights of 13-16 km calculated from the dispersal of the 

largest clasts (Carey and others, 1990). We can examine 

the translation of particles below the umbrella region 

(fig. 5A) by calculating the transport using the wind 

intensities recorded in the area of Mount St. Helens on 

the morning of May 18 (Carey and Sigurdsson, 1982). 

The trend of the observed data crosses the predicted 

trends, with agreement occurring for the 177- and 125-

Jlm fractions. Significant deviations are found to occur 

for grain sizes of less than 63 Jlm, with the predicted 

transport distances being much larger than the observed. 

This divergence is likely due to the process of particle 

aggregation, which resulted in the premature deposition 

of fine ash and the production of a secondary thickness 

maximum in the area of Ritzville, Wash. (Carey and Sigurdsson, 1982). 
24 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

-

-

0 

A 

-

-

0 

0 

B 

I f I I I 

)( )( 177-250 Jliil 

)( 

)( 

)( 

I I ouou I ou I 

200 400 

I I I 

125-177 Jliil 

oo 0 

0 0 

0 

I 

200 400 

DISTANCE FROM VOLCANO, 

IN KILOMETERS 

-

-

-

c 

-

-

-

D 

2 

1 -

[J 

0 

0 

2 

-

1 

0 

0 

0 

I I 

[J 

[J 

...,c eel 

200 

I I 

0 

0 

0 

hn n1 

0 

I I 

[J 

I 

I 

I 

88-125 Jliil 

400 

I 

63-88 Jliil 

00 

I 

200 400 

DISTANCE FROM VOLCANO, 

IN KILOME1ERS 

-

-

-

-

-

-

Figure 4. Downwind variation of felsic crystal unit sedimentation, S, in kglm2, with distance from the vent for the A, 177-250-Jlm size . 

class; B, 125-177-Jlm size class; C, 88-125-Jlm size class; and D, 63-88-Jlm size class for the Mount St. Helens May 18, 1980, Plinian deposit. Accumulation maxima (peaks) from the fit of 7th-order polynomials to the data are indicated with arrows. 

Concentrations within the umbrella cloud of the crystal 

size fractions can be calculated from: 

2 <x> = Sv/Tu (13) 

The May 18 eruption had a duration, T: 8 hours, hence 

all variables in equation 13 can be constrained with available 

data. Figure 5D is a plot of the estimated decrease of concentration of the felsic crystal fractions from 63 to 177 J.Lm along 

the dispersal axis, to the east of the volcano. The concentration of these crystal fractions is rather dilute, being below the 

critical value of 50 mg/m3. However, the crystals constitute 

less than about 50 percent of the total mass in each of these 

grain-size fractions, and most of the deposit is finer than 63 

J.Lm (Carey and Sigurdsson, 1982). As with the Fogo A cloud, 

the larger grain-size fractions become depleted relative to the 

smaller fractions with increasing distance because of their 

higher fall velocities. A strong wind decreases the sedimentation of pyroclasts at a given distance (equation 12). The 20 

m/s wind at the base of the May 18 cloud allowed the concentration of these crystal fractions to drop by an order of 

magnitude only after the cloud spread downwind about 100 

km, and concentration of the 63- to 177-J..Lm crystal fractions 

alone was still > 1 mg/m3 at 100 km from vent. 

THEORETICAL PARTICLECONCENTRATION VARIATIONS 

Reasonable agreement exists between sedimentological 

observations and the theoretical model of flow and sedimentation in volcanic umbrella clouds. We have shown that the 

sedimentological data can be used ("inverted") to infer 
CONCENTRATION OF ASH IN VOLCANIC PLUMES, INFERRED FROM DISPERSAL DATA 25 

particle concentrations within volcanic plumes (equations 7, 

8, and 13). The model can also be used in a "forward" sense 

to predict concentrations of particles in hypothetical plumes 

with distance from a volcano as a function of plume height 

and wind conditions. Even though a fully comprehensive 

model of plume dispersal by the wind has not been developed, 

some useful guidelines on likely concentrations can be given. 

We have calculated ash concentrations as functions of 

distance from the vent for specific, end-member cases of 

plume geometry. For this purpose, we have chosen a model 

grain-size distribution, given in table 1, which is typical of 

the grain-size distributions estimated for Plinian eruptions 

(Woods and Bursik, 1991 ). We have assumed that 70 percent 

by weight of the ejecta are finer than 2,000 !liD and have calculated the changes in concentration of each grain size with 

0 

A 

6 

• 

• 0 

• 0 

lJ EXPLANATION 

2.5 $= 177-250 ()liD) 

Clo 3$=125-177 

3.5 Ill= 88-125 • Observed o• 4 4> = 63-88 

4.5$=44-63 o Model 

2 

0 200 400 600 800 1 000 1200 

DISTANCE OF SEDIMENTATION MAXIMUM FROM VOLCANO, 

IN KILOME1ERS 

EXPLANATION 

10° ~--~--~~~~~~x~~1--7=7~-2~s~o-~-; 

---<>-125-177 j.llTl 

-a- 88-125 J.Lm 

-o-63-88 J,Lm 

~ 10-2 

104 

0 2,000 4,000 6,000 

B x312 - Xo312, IN METERS312 

c 

distance. The initial concentration is related to plume height 

as calculated by Sparks and others (this volume). Our calculations assume one particular grain-size distribution of the 

ejecta, but the changes in concentration are very sensitive to 

the initial size distribution in the plume. This point is illustrated by calculation of the residence time of particles of different diameter in a 5-km-thick layer in the atmosphere 

centered at 12.9 km (39,000 ft) altitude. The estimated settling velocities of different particle sizes with a density of 

2,000 kg/m3 at these altitudes are listed in table 1. From this 

information, equation 2 can be used to estimate the time 

taken for the concentration of each size to decrease by 1/e of 

the initial concentration. This time is also that for each grain 

size to fall a distance of 5 km under static conditions. The 

orders-of-magnitude changes in residence time among the 

2x1 0-7 

OL----~----L---.L--J...--~---~ 

ffi 1 00 

E-< 50 

0 1 2 3 

FALL SPEED AT BASE OF UMBRELLA CLOUD, 

IN METERS PER SECOND 

EXPLANATION 

X 177-250 J.Lm 

I I <> 125-177 J,Lm 

Cl 

10 

88-125 J,Lm 

1- '•• 

z~ 0 63-88 J.Lm 

Ou 

~~ E-<u Zffi 

a~ ZIZl 

8~ 0.1 

~d 

~~ 0.01 

~ 

~ 0.001 

D 

1--

1-

-

0 

• 63-250 J.Lm total 

xox• "• • (crystals only) 

0 D 0 () • •• 

0 • X • • 8<> 

D 

X X 

X 

I I I I 

so 100 150 200 

DISTANCE FROM VOLCANO, 

IN KILOMETERS 

-

• ~ 

0 

( 

250 

Figure S. A, The observed positions of crystal accumulation peaks (from fig. 4) for the May 18, 1980, Mount St. Helens ash fall deposit 

compared to their calculated (model) positions based on their translation in the eastern Washington wind field after falling from the base of 

the umbrella cloud (assumed for the calculations to be at an altitude of 12 km). B, The decrease in normalized sediment accumulation, S/So, 

with distance for the Mount St. Helens fallout is consistent with a distance to the three-halves, x312, dependence for the 177-250- to 63-88-

~m crystal size fractions. C, The value of the exponent in equation 12 (see text), 2v/3u(2AN/Q)lf2, is consistent with the terminal velocity 

for these grain-size fractions. D, Average crystal concentrations inferred for the Plinian umbrella cloud from data in Band C. 
26 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Model grain-size distribution in weight percent for calculations ofthe changes of ash concentration in volcanic plumes with 

distance from the vent. 

[The grain-size distribution assumes that 30 weight percent of the ejecta have a grain 

size greater than 2 mm. The estimated terminal fall velocity of each particle size with 

a density of 2,000 kg/m3 at 12.9 km (39,000 ft) altitude is based on high-Reynoldsnumber settling of particles> 355 Jlm and on low-Reynolds-number settling of particles< 355 Jlm (Wilson and Huang, 1979)] 

Grain Weight Fall Residence 

size ().1m) percent speed (m/s) time 

1,400 9.0 9.0 9.3 min 

710 10.8 6.4 13.0 min 

355 12.4 3.2 26.0 min 

171 10.8 1.9 43.0 min 

90 9.0 0.64 2.2h 

44 7.2 0.15 9.3 h 

22 5.4 0.05 l.ld 

11 3.6 0.012 4.8 d 

5.5 1.8 0.0025 23.1 d 

particles typically present in plumes indicates that size distribution must have a major influence on the change of concentration with distance and time in a volcanic plume. 

For dispersal in the absence of wind (equation 5), 

plumes that reach the stratosphere can form umbrella clouds 

that maintain high concentrations for substantial distances 

from the volcano (fig. 6A). For example, a 22.8-km-high 

plume still has a concentration of 2,000 mg/m3 at 100 km, 

and a 9.8-km-high plume has a concentration of 50 mgfm3 at 

200 km distance. The sensitivity of concentration variations 

to total grain-size distributions is illustrated by the variations 

of the relative concentrations of each grain size with distance 

for a 22.8-km-high (75,000 ft) plume (fig. 6B). Large grain 

sizes decrease their concentration much more rapidly. 

Dispersal by a constant wind blowing much faster than 

the gravitational spreading speed can be approximated with 

a cloud layer of constant thickness and width. Our calculations suggest that wind speed plays an important role in 

determining the concentrations of ash likely to be encountered by aircraft in dispersing plumes (fig. 7A). These calculations, however, do not take into consideration particle 

aggregation, which is likely to decrease concentrations from 

those predicted because of premature fallout. A number of 

studies (Sorem, 1981; Brazier and others, 1982; Carey and 

Sigurdsson, 1982; Gilbert and others, 1991) have shown that 

fine ash particles aggregate in the plumes and consequently 

fall out much more rapidly than predicted by consideration 

of the fall velocities of individual particles. Observations 

indicate that particles less than 63 J.Lm are strongly susceptible to aggregation processes. For example, much of the sub63-J..Lm ash in the May 18th plume of Mount St. Helens fell 

out at 300 to 450 km to produce secondary thickening of the 

ash deposit (Carey and Sigurdsson, 1982). To illustrate the 

effect of aggregation on our results we have assumed that all 

the particles less than 63 J.Lm in the size distribution of table 

1 fall as aggregates with sizes from 90 to 1,400 J.Lm. We 

assume that these aggregates are evenly distributed in each 

of the size intervals above 63 J.Lm and have calculated the 

variation of concentration with distance in a 10 m/s wind. 

Figure 7 B compares these calculations with the case of individual particle fallout and shows that ash concentration 

decreases much more rapidly with aggregation. These calculations indicate that much more needs to be known about 

aggregation processes in order to predict concentrations of 

ash in volcanic clouds. 

The model can be generalized by calculating concentration as a function of area to which the cloud has spread. 

Equation 4 can be written in the form: 

<x> (X0)exp {-f.; dS} (14) 

100 

22.8 

10 17.3 

12.9 

1 

1 10 100 1,000 10,000 

DISTANCE FROM VOLCANO, 

A IN KILOMETERS 

~ 

~ 10 

z~ Grain ~> sizes 

~~ .1 ZE 

~as 

~~ .01 

0~ U> 

~~ .001 

<....:~ ~ .0001 ~ 1 10 100 1,000 10,000 

DISTANCE FROM VOLCANO, 

B IN KILOMETERS 

Figure 6. A, Ash concentration in an umbrella cloud (in mglm3) 

is plotted against distance for six different column heights and for 

dispersal in the absence of wind. B, Relative concentration of ash is 

plotted against distance for each grain size class for a 22.8-k:m-high 

column in the absence of wind. 
CONCENTRATION OF ASH IN VOLCANIC PLUMES, INFERRED FROM DISPERSAL DATA 27 

10 

A 

~ 

~~ z~ 10,000 O::a 

~~ 

~~ 1,000 ~u 

u~ 

zu:~ op.. 100 

<o 

~~ 10 ~::3 u:~d 

:E:E 

~ 

B 

100 

DISTANCE FROM VOLCANO, 

IN KILOMETERS 

10 100 

DISTANCE FROM VOLCANO, 

IN KILOMETERS 

1,000 

1,000 

Figure 7. A, Concentration of ash (in mg!m3) is plotted against distance for a 22.8-km-high column erupted in no wind and for downwind transport of a layer 5 km thick with its base at 15.9 km altitude 

for wind velocities of 10, 20, and 30 m/s, and for the case of no wind. 

B, Comparison of the downwind change in ash concentration between the case of individual fallout of all sizes and the case where 

particles less than 63 J..Lm aggregate. Calculations are for a wind 

speed of 10 rnls and a 5-km-thick layer with base at 15.9 km. Details 

of the calculations with particle aggregation are given in text. 

where 

p = Q/uh is the outer perimeter of a control volume 

defined by an isochronous surface to which material 

had spread by a certain time within the umbrella 

cloud. 

Integration of (14) thus yields: 

<x> = {Xt)e -vAIQ (15) 

where 

X is measured at the perimeter of A, the area to which particles of a given grain size have traveled, and 

XI = xoeAoviQ, the "virtual" sedimentation at A = 0. 

If plume height, H, and the total grain-size distribution of 

material entering the umbrella cloud can be estimated, then 

equation 13 can be applied to predict the total concentration 

of particles within the cloud, {Xr). {Xr) is the sum of the 

concentration of particles within each of N individual particle-size classes: 

10 100 500 

RADIAL DISTANCE, IN KILOME1ERS 

1 0

2 1 0

4 

A AREA, IN SQUARE KILOMETERS 

~ 1 0

5 

zs O::;s 

h 1 0

3 

UJU 50 

~~ 101 

oP.. ufJ'} 

~~ 10" 1 

i~ 25 1 o· 3 

1 0 100 

RADIAL DISTANCE, IN KILOMETERS 

1 02 1 0

4 

B AREA, IN SQUARE KILOMETERS 

Figure 8. A, Ash concentration as a function of the area encompassed by an isochronous surface within the umbrella cloud for column heights from 10 to 40 km. The grain-size distribution is that 

from table 1. B, Concentration variation for different total grain-size 

distributions with means shown next to curves. The standard deviation, in <j> units, for each curve was assumed to be 2.5. Distributions 

are for phreato-Plinian/coignimbrite (mean = 82 J..Lm), Vulcanian 

(330 J.Lm), Plinian (1,500 J.Lm), and Strombolian (26 mm) eruptions 

(Woods and Bursik, 1991 ). 
28 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

where 

N 

L <xn>e-v~.AIQ 

i = l 

Xil is the sedimentation at A = 0, and 

(16) 

v; is the terminal velocity of the ith particle-size class, and 

Q = 713IP·3 (Bursik and others, 1992a). 

We have estimated concentrations with area for a range 

of particle-size distributions and eruption-plume heights. We 

have used four different particle-size distributions covering 

the range typical of various types of eruptions (Woods and 

Bursik, 1991). Figure 8A shows calculations for plume 

heights from 10 to 40 km. Even relatively small Plinian 

plumes, approximately 10 km high, will have dangerously 

high concentrations of pyroclasts over large areas (::: 106 

km2). Figure 8B compares calculations for a 17.3-km plume 

with different grain-size models. As expected, plumes that 

contain fmer grained material, such as those generated by 

coignimbrite or phreato-Plinian eruptions (Wilson, this volume), will retain dangerous concentrations as they spread to 

encompass large areas(::: 106 km2). It is much more difficult 

for plumes containing large particles, such as those generated by Strombolian eruptions, to persist over similar vast 

regions. In addition, Strombolian eruptions rarely attain the 

high mass eruption rates, hence column heights, of the other 

eruption types. Equation 16 thus gives the quantitative basis 

for estimation of concentration variations within volcanic 

umbrella clouds, including those in which wind plays an 

important role in tephra dispersal. 

CONCLUSIONS 

The sedimentation of large, nonaggregating pyroclasts 

from volcanic umbrella clouds has been successfully 

modeled using a simple treatment. The agreement of the 

model with grain-size data from ash fall deposits suggests 

that estimates of ash concentrations within the cloud are 

reasonable. Using both direct estimates from sedimentological data and the predictions of a plume model, we have 

shown that concentrations of ash in volcanic clouds that 

penetrate altitudes where commercial airplanes fly can 

exceed (by several orders of magnitude) the concentrations 

known to cause severe engine damage or failure. Dangerous concentrations can potentially persist for hundreds of 

kilometers from the vent. However, the model is clearly 

sensitive to the overall size distribution of ejecta and needs 

to include the processes of ash aggregation due to electrostatics (Gilbert and others, 1991) and moisture within the 

umbrella cloud. 

ACKNOWLEDGMENTS 

Research was supported by grants from the Venture 

Research International Unit, by NSF grant EAR 9104 770, by 

a NERC Fellowship to J.S.G., by a NATO fellowship to 

M.I.B. (awarded in 1988) and by NATO collaborative 

research grant (CRG 910096). M.I.B. acknowledges an 

NRC-JPL (Caltech) research associateship, under contract 

to NASA. 

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Allen, J.R.L., 1985, Principles of Physical Sedimentology: London, 

George Allen and Unwin, 272 p. 

Armienti, P., Macedonio, G., and Pareschi, M.T., 1989, A numerical model for simulation of tephra transport and deposition: 

Applications to May 18, 1980, Mount St. Helens eruption: 

Journal of Geophysical Research., v. 93, p. 6463-6476. 

Brazier, S.A., Davis, A.N., Sigurdsson, H., and Sparks, R.S.J., 

1982, Fall-out and deposition of volcanic ash during the 1979 

explosive eruption of the Soufriere of St. Vincent: Journal of 

Volcanology Geothermal Research, v. 14, p. 335-359. 

Bursik, M.l., Sparks, R.S.J., Carey, S.N., and Gilbert, J.S., 1992a, 

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Volcanology, v. 51, p. 28-40. 

Criswell, W., 1987, Chronology and pyroclastic stratigraphy ofthe 

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Einstein, H.A., and Krone, R.B., 1962, Experiments to determine 

modes of cohesive sediment transport in salt water: Journal of 

Geophysical Research, v. 67, p. 1451-1461. 

Gilbert, J.S., Lane, S.J., Sparks, R.S.J., and Koyaguchi, T., 1991, 

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Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. 

Helens, Washington: U.S. Geological Survey Professional Paper1250,p.323-334. 
CONCENTRATION OF ASH IN VOLCANIC PLUMES, INFERRED FROM DISPERSAL DATA 29 

Hazen, A., 1904, On sedimentation: Transactions, American Society of Civil Engineering, v. 53, p. 45-88. 

Manins, P.C., 1976, Intrusion into a stratified fluid: Journal of Fluid 

Mechanics, v. 74, p. 547-560. 

Martin, D., and Nokes, R., 1988, Crystal settling in a vigorously 

convecting magma chamber: Nature, v. 332, p. 534-536. 

Sarna-Wojcicki, A.M., Shipley, S., Waitt, R.B., Jr., Dzurisin, D., 

and Wood, S.H., 1981, Areal distribution, thickness, mass, volume, and grain size of airfall ash from the six major eruptions 

of 1980, in Lipman, P.W., and Mullineaux, D.R., eds., The 

1980 Eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 577-600. 

Simpson, J.E., 1987, Gravity Currents in the Environment and 

the Laboratory: Chichester, England, Ellis Horwood Limited, 

244p. 

Sorem, R.K., 1981, Volcanic ash clusters: Tephra rafts and scavengers: Journal of Volcanology Geothermal Research, v. 23, p. 

63-71. 

Sparks, R.S.J., 1986, The dimensions and dynamics of volcanic 

eruption columns: Bulletin of Volcanology, v. 48, p. 3-15. 

Sparks, R.S.J., Carey, S.N., and Sigurdsson, H., 1991, Sedimentation from gravity currents generated by turbulent plumes: Sedimentology, v. 38, p. 839-856. 

Sparks, R.S.J. Moore, J.G., and Rice, C., 1986, The giant umbrella 

cloud from the May 18, 1980, eruption of Mount St. Helens: 

Journal Volcanology Geothermal Research, v. 28, p. 257-274. 

Suzuki, T., 1983, A theoretical model for the dispersion of tephra, 

in Shimozuru, D., and Yokoyama, 1., eds., Arc Volcanism: 

Physics and Tectonics: Tokyo, Terrapub, p. 95-113. 

Walker, G.P.L., and Croasdale, R., 1971, Two Plinian type eruptions in the Azores: Journal of the Geological Society of London,v. 127,p. 17-55. 

Wilson, L., and Huang, T.C., 1979, The influence of shape on the 

atmospheric settling velocity of volcanic ash particles: Earth 

and Planetary Science Letters, v. 44, p. 311-324. 

Woods, A.W., 1988, The fluid dynamics and thermodynamics of 

Plinian eruption columns: Bulletin of Volcanology, v. 50, p. 

169-193. 

Woods, A.W., and Bursik, M.I., 1991, Particle fallout, thermal disequilibrium and volcanic plumes: Bulletin of Volcanology, v. 

53, p. 559-570. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

ELECTRICAL PHENOMENA IN VOLCANIC PLUMES 

By JennieS. Gilbert and Stephen J. Lane 

ABSTRACT 

Observations of lightning and St. Elmo's fire within 

volcanic eruption plumes suggest high degrees of charge. 

Measurements of electrical charge on ash particles falling 

from the eruption plumes of Sakurajima Volcano in Japan 

indicate that the particles are nearly saturated with charge. 

Charge-to-mass (Q/m) ratios range from +3xJ0-4 to 

+6xJ0-4 C kg-1 and from -2xJ0-4 to -5xJ0-4 C kg-1. 

Sequential positive and negative deviations of electric potential gradient from background of several orders of magnitude 

were measured during explosions that generated particles. 

No deflections from background were found during explosions that released only gases. During fallout of particles, 

negative electric potential gradients occurred, whereas positive gradients were observed during fallout of acid rain. The 

fluctuations of potential gradient during the generation of 

particle-laden plumes and the observation that falling particles carried an average negative charge, while acid raindrops 

carried an average positive charge, suggest a dipole arrangement of charge within plumes such that positive charges 

dominate at the top of the plume and negative charges dominate at the base. The charge polarity may be reversed for 

other volcanoes. The presence of charged liquid drops of 

condensed volcanic gases suggests that charge is generated 

mainly by fracto-emission processes during magma fragmentation within the vent, rather than by collision effects 

within the plume. 

INTRODUCTION 

Spectacular displays of lightning are common in particle-laden volcanic plumes, indicating that locally the air ionization limit has been exceeded (Blythe and Reddish, 1979). 

Amongst many other examples, lightning has been observed 

at Vesuvius in 1872 (Palmieri, 1873), Krakatoa in 1883 

(Simkin and Fiske, 1983), Vesuvius in 1906 (Perret, 1924), 

Stromboli in 1907 (Perret, 1924), Anak Krakatau in 1933 

(Simkin and Fiske, 1983), Surtsey in 1964 (Anderson and 

others, 1965), Heimaey in 1973 (Brook and others, 1974), 

Usu in 1977 (Kikuchi and Endoh, 1982), Mount St. Helens 

in 1980 (Rosenbaum and Waitt, 1981), Redoubt in 1990 

(Hoblitt and Murray, 1990), Hudson in 1991 (Jose Naranjo, 

University of Chile, Santiago, Chile, oral commun., 1992), 

and Sakurajima (present authors). Therefore, high degrees of 

electrical charge are present in volcanic plumes, and this 

electrical charge, as well as producing magnificent visual 

displays, may also encourage particle aggregation and thus 

increase the sedimentation rate of particles (Sorem, 1982; 

Gilbert and others, 1991 ). Aircraft in flight accumulate fairly 

large potentials (Newman and Robb, 1977) from contact 

with atmospheric particles, which may or may not be 

charged. These potentials "bleed off' in the form of a corona 

or point discharge, also known as St. Elmo's fire. Severe St. 

Elmo's fire around aircraft has been reported by pilots unfortunate enough to encounter volcanic plumes while in flight 

(E.H.J. Moody, British Airways, oral commun., 1991). 

Our aim is to assess the magnitude of charging in volcanic plumes and to understand the origin of the charged particles. In order to do this, we present results of two series of 

field experiments carried out at Sakurajima Volcano in May 

1990 and March-May 1991. In the first experiments, we 

measured the amounts of charge present on particles falling 

from Sakurajima's plumes, and in the second, we measured 

perturbations of the atmospheric electric potential gradient 

from the background fair-weather field during eruptions. 

Sakurajima is an andesitic stratovolcano, I, 118m high 

in southern Kyushu, which has had repeated flank and summit eruptions during historic times. Because Vulcanian-type 

summit eruptions have occurred on a daily basis since 1955, 

Sakurajima is the ideal "working laboratory" for volcanicplume experiments. During May 1990, the eruptions were of 

a continuous style and lasted for a few days. In contrast, in 

March-May 1991, the eruptions were of an explosive style, 

accompanied by explosion earthquakes and atmospheric 

shock waves, and were sustained for only a few hours. During both periods, plumes reached a maximum height of 3 km 

above the summit and were frequently distorted by the wind 

so that particles were deposited asymmetrically around the 

vent on the surrounding countryside, including several villages, Kagoshima City, and Kagoshima International Airport. These different styles of activity complemented the 

type of experiment carried out each year. 

31 
32 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

EXPERIMENTS 

I. MEASUREMENTS OF ELECTRICAL 

CHARGE ON FALLING PARTICLES 

PREVIOUS WORK 

Hatakeyama (1958) used a collecting device in contact 

with an electrometer in order to measure the average charge 

carried by particles falling from the eruption plume of 

Asama, Japan, on 2 August 1941. The experiment was carried out 50 km from the vent and the average charge was 

found to be -1.2 esu per gram (approximately --4x1o-7 C 

kg-1). 

APPARATUS 

Our experiments differed from those of Hatakeyama 

(1958) in that we separated positively from negatively 

charged particles and measured the amount of charge carried 

by each. Particles(> 500 f..Lm wide) falling directly from the 

eruption plume were allowed to pass between two parallel 

copper plates mounted in a grounded case. One plate was 

connected to Earth, the other to a high-voltage supply (±3 

kV), to yield an electric field of 1.2x105 V m-1 between the 

plates that separated the positively and negatively charged 

particles. The charge on particles contacting the grounded 

plate was measured by a Keithley 614 electrometer. Leakage 

currents across the plastic insulators that supported the 

plates, or resulting from any corona discharge within the 

apparatus (although surfaces were rounded to minimize this 

effect), were only just detectable at < 0.1 pA when humidity 

was low. Under conditions of high humidity, leakage currents became appreciable(> 10 pA). The plates were covered 

with a layer of oiled aluminum foil to which particles would 

adhere. After each experiment, the particles were removed 

from the foil by reflux degreasing in isopropyl alcohol and 

weighed to determine the charge-to-mass (Q/m) ratio of the 

sample. The size distribution of the samples was determined 

from silicon X-ray images of particles resting on a carbon 

substrate using the Link Analytical Featurescan facility. 

RESULTS 

Results of two experiments (figs. 1 and 2) from two 

different eruptions indicate substantial changes in the gradient (nC min-1) between the shielded state of the apparatus 

(when no particles were collected) and the exposed state. 

Figure 1 shows data for an experiment carried out during 

fallout of dry aggregated particles. A -3-kV supply was 

used in order to accelerate negatively charged particles 

toward the grounded plate where the amount of charge carried was measured. After a stabilization period of 64 minutes, during which time the apparatus was shielded, a light 

ashfall was allowed to pass between the parallel plates. This 

resulted in an increase in gradient (nC min-1 ), indicating the 

accumulation of negatively charged particles on the 

grounded plate. During the period 70 to 76 minutes into the 

experiment, the fall almost ceased and the nC min-I rate 

returned approximately to the background state. Between 76 

and 84 minutes, light fall occurred and a steeper nC min-I 

gradient was reestablished. After 84 minutes,c fall ceased 

and again the readings returned to the background level. 

The Q/m ratio for the sample collected in this experiment 

was -2.7x10-4 C kg-I. Grain size (on a number-frequency 

basis) was in the range 0.9-152 f..Lm, the mean diameter 20.7 

f..Lm, the 95th percentile 54 f..Lm, and maximum-frequency 

diameter 54.5 f..Lm. The grounded plate carried 1.5 mg and 

the kV plate 0.5 mg of particles. In this experiment, 93 

weight percent of the sample passed between the plates and 

therefore carried insufficient Q/m ratio to contact the plates. 

No aggregated particles were observed adhering to the oiled 

plates. This implies either that the aggregates had insufficient Q/m ratio to be attracted to the plates or that they were 

fragmented by the electric field and the resulting particles 

were attracted to both plates. 

In a different experiment (fig. 2), a +3-kV supply was 

used (i.e., positively charged particles were accelerated 

toward the grounded plate for measurement). After a stabilization period of 21 minutes, a light ashfall was allowed to 

pass between the plates. This resulted in an increased nC 

min-1 gradient. After 68 minutes, the apparatus was shielded 

so that no particles could accumulate and the leakage current 

C/) 

OJ 

~ 

0 

....J 

:::> 

0 

u 

0 

z 

<( 

z 

~ 

ui 

(.!) 

a: 

<( 

I 

u 

0.2,.---------------------, 

•••••••••o 0.1 

0.0 

·0.1 

-0.2 

·0.3 

0 

Fall almost 

o ceased 

0 

0 

0 

0 

0 Oooooe••••••• ••• 1f 

Fall stopped 

·0.4 .__.____.1....-_..___.l....-_..___..____..___..____.._. 

6 5 75 8 5 95 

TIME, IN MINUTES 

Figure 1. Charge (nC) versus time (minutes) for parallel plates experiment using -3-kV supply. The charge-to-mass ratio was found 

to be -2.7xl0-4 C kg-1. The period when the plates were shielded 

from ashfall is indicated by solid symbols; open symbols indicate 

the period when the plates were exposed to ashfall. Temperatures 

and relative humidities at the start and finish of the experiment were 

25°C, 44 percent; and 23 °C, 48 percent, respectively. 
ELECTRICAL PHENOMENA IN VOLCANIC PLUMES 33 

CfJ 

CXl 6.0 

~ 

0 

....J 

::::> 

0 

u 

0 

z 4.0 

<( 

z 

~ 

ui 

(!) 

0::: 

<( 2.0 I 

u 

TIME, IN MINUTES 

Figure 2. Charge (nC) versus time (minutes) for parallel plates 

experiment using +3-kV supply. The charge-to-mass ratio was 

found to be +4.9xi0-4 C kg-1. The period when the plates were 

shielded from ashfall is indicated by solid symbols; open symbols 

indicate the period when the plates were exposed to ashfall. Best fit 

straight lines for the solid symbols are shown. Temperatures and 

relative humidities at the start and finish of the experiment were 

20°C, 66 percent; and l9°C, 74 percent, respectively. 

returned approximately to the pre-collection state. The Q/m 

ratio for this experiment was +4.9x10-4 C kg-1. Grain size 

(on a number-frequency basis) was in the range 1-253 f.lm, 

the mean diameter 28 f.lm, the 95th percentile 71 f.lm, and 

maximum-frequency diameter 49.1 f.lm. The grounded plate 

carried 2.6 mg and the kV plate 3.7 mg of particles. In this 

experiment, 77 weight percent of the sample passed between 

the plates. Again, no aggregates were observed on the plates. 

DISCUSSION 

The Q/m ratios measured in this work are an average 

over a wide range of particle sizes (1-250 f.lm). Smaller particles will have a higher Q/m ratio than larger particles due 

to their larger surface area to volume ratios (charge resides 

on the surface of particles) and due to the Paschen law 

(Blythe and Reddish, 1979). The Q/m values used as data for 

figures 1 and 2 yield surface-charge densities (assuming 

spherical particles and maximum-frequency diameters) of 

-7x1o-5 and +9xlo-5 C m-2, respectively. The theoretical 

maximum surface-charge density on a flat surface in the 

atmosphere is ±2.6x1o-5 C m-2, above which air breakdown 

occurs. As particle size decreases below about 1 mm, the 

divergence of the electric field away from the particle surface reduces the effective spark gap of the system, allowing 

higher surface-charge densities to be stable in air (Blythe and 

Reddish, 1979). Blythe and Reddish (1979) calculated from 

the Paschen law that particles 50 f.lm in diameter may sustain 

surface-charge densities of approximately 1.5x10-4 C m-2 

but that these levels are difficult to observe experimentally. 

They state that, for practical purposes, the maximum charge 

per unit mass carried by a stream of insulating particles may 

be calculated assuming a surface-charge density of±1x1o-5 

C m-2. The particles produced during Sakurajima' s eruptions thus appear to be charged almost to the air ionization 

limit; that is, they are nearly saturated with charge. 

II. MEASUREMENTS OF ELECTRIC 

POTENTIAL GRADIENT CHANGES 

DURING ERUPTIONS 

PREVIOUS WORK 

The effect of eruption plumes, fallout of particles, and 

acid rain on the atmospheric electric potential gradient is not 

well understood. However, abundant measurements of electric-potential-gradient changes beneath and within thunderclouds suggest that most have a concentration of positive 

charges in their upper regions, with a lower region of negative charge and a further concentration of positive charge in 

a limited zone at the base of the cloud (Chalmers, 1967). This 

arrangement is thought to result from charge-separation processes operating at different levels within the cloud (Chalmers, 1967). Charge distributions have also been described in 

dust devils (Freier, 1960; Crozier, 1964), and in non-raining 

clouds (Whitlock and Chalmers, 1956). Electric-potentialgradient measurements made during fair weather, beneath 

clouds, and during rainfall and snowfall are available 

(Chalmers, 1967). Hatakeyama (1949) recorded a negative 

potential gradient during the overhead passage of the particle-laden cloud from Yake-yama Volcano in Japan. During 

eruptions of Aso Volcano in Japan, Hatakeyama and 

Uchikawa (1952) observed an eruption plume dominated by 

positive charge in its lower region and by negative charge in 

its upper region. At Surtsey, electric-potential-gradient data 

were collected by towing an electrometer and radioactive 

probe mounted on a ship beneath the particle-laden plume 

(Anderson and others, 1965), but the potential-gradient 

changes resulting from the presence of the plume were difficult to decouple from the effects of breaking sea waves on 

lava flows. Kikuchi and Endoh (1982), situated 5 km NE. of 

the vent of Usu Volcano, Japan, measured a negative field 

associated with the generation of a particle-laden plume on 

12 August 1977. On this occasion, the plume did not pass 

overhead but moved to the NW. On 13-14 August, these 

authors measured alternating positive and negative potential 

gradients during particle fallout. High-speed monitoring of 

the atmospheric electric potential gradient during explosive 

eruptions at Sakurajima (Matsumoto and others, 1988) found 
34 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

gradient changes of the order of 1 V m-1 approximately one 

second after an explosion. These changes in gradient were 

correlated with shock waves. None of the above volcanic 

studies investigated the effect of acid rainfall on the potential 

gradient. 

APPARATUS 

Here we report electric potential gradient measurements made: (1) as particle-laden plumes passed overhead, 

as well as at distance from the field meter, (2) as plumes of 

condensing gases passed overhead, and (3) during periods of 

particle fallout and acid rainfall. Measurements were made 

between 2 and 5 km from the vent using a stationary, tripodmounted, grounded John Chubb electrostatic field meter 

(JCI 111 ). The height from the base of the tripod to the measuring aperture of the field meter was 1.5 5 m. The advantage 

of using the tripod was to produce a noise free amplification 

of the signal (measured to be a factor of 20) in order to overcome increased meter noise levels due to aperture and Earthconnection contamination. Data presented here have been 

corrected to ground-level potential gradients. 

RESULTS 

Figure 3A shows data collected during an explosion at a 

locality 2.75 km SSE. and downwind (on axis) of the active 

vent. During the experiment, the weather was fine with no 

cloud cover and a light breeze. For the first 206 minutes of 

the experiment, Sakurajima erupted mainly white plumes of 

condensing gases, which rose approximately 300 m above 

the vent. Occasional particle-laden plumes of similar size 

were generated that produced very light ashfall. Vent noise 

was absent or restricted to low rumblings. At 206 minutes, a 

loud detonation was heard and was followed by bombs a few 

meters wide being thrown out of the vent, after which a dark 

particle-laden plume rose to a height of approximately 3 km 

above the vent. At this height, the plume formed a laterally 

spreading gravity current. At 207.5 minutes, the potential 

gradient had dropped to -0.4 kV m-1 after which it started to 

rise rapidly. At 209 minutes, the cloud was observed to be 

directly overhead, and at 212 minutes, fallout of particles< 1 

em in diameter commenced. At 213 minutes, the maximum 

positive potential gradient of2.5 kV m-1 was obtained, after 

which the potential gradient decreased. At 219 minutes, the 

maximum negative potential gradient of -2.7 kV m-1 was 

obtained, by which time the rate of particle fallout had 

slowed. By 235 minutes, the potential gradient had returned 

to approximately the pre-explosion background value and 

there was a very light fallout; the bulk of the plume had dispersed with only small emissions coming from the vent. 

Data for another explosion are seen in figure 3B. This 

experiment was run at a locality 2 km SW. of the vent. At the 

time of the explosion, the wind direction was NNW., and 

therefore, the experiment was run off the dispersal axis. 

During the experiment, prior to the explosion, the cloud 

cover was 0-20 percent and there was a slight breeze. During 

the first 82 minutes, Sakurajima was erupting white plumes 

of condensing gases that rose to a maximum height of200 m. 

At 82 minutes, a loud detonation was heard, at which time a 

dark particle-laden plume ascended to a height of 1.5 km 

above the vent before spreading laterally. After 84 minutes, 

the potential gradient had dropped from background to -1.0 

kV m-1, after which it began to rise. At 87 minutes, the 

potential gradient was 1.5 kV m-1. By 88 minutes, the plume 

had started to disperse, leaving only a small, particle-laden 

plume emanating from the vent. During dispersal of the 

a: 

L.U 

1-

L.U 

~ 

0:: 

UJ 

Fallout ~/c 

commences o 0

0 0 0 

0 0 

Eruption cloud g o 

overhead -----+- g 

0 

0 

0 0 00 0 0 0 000 0 0 0 0 0 oO 0010oJ 

Ash-rich 

explosion 

/c;PO 0 0 OgoO 0 

: &.l 0 0~ ~g 

~ ~ 

~ ·3L---------~--------~--~o----~------~ 

~ A 

0 

> 

0 

....J 

Q 

z 

1-' 

z 

L.U 

0 

<( 

0:: 

(.9 

....J 

<( 

i= 

z 

L.U 

to 

1 9 0 21 0 230 

Plume 

Ash-rich ~...--dispersing explosion : o ! ; 0

0 \!go 0 ooooooooooooooooao Oooooooooooo 

gO 

0 

Cb 

~ ·2L----------L----------~--------~----~ 

B 7 0 9 0 11 0 

Ash-poor explosion 

+ o o o o 0 o o 0 o 0 o 0 0 o o o o o o o<>ooo o o oo o o 0 o 

0 

Plume ~ di'spersing 

-1 L--------------1..-------------'-----------~ 

c 140 160 

TIME, IN MINUTES 

Figure 3. Potential gradient (kV m-1) versus time (minutes). A, 

Explosion at 13:39local time (local time= Greenwich mean time+ 

9 hours) on 3 May 1991. Temperatures and relative humidities at 

the start and finish of the experiment were 18°C, 45 percent; and 

21 °C, 39 percent, respectively. B, Explosion at 10: 16local time on 

30 April 1991. Temperatures and relative humidities at the start and 

finish of the experiment were l6°C, 66 percent; and l9°C, 58 percent, respectively. C, Explosion at 15:44 local time on 30 April 

1991. The temperature and relative humidity one-halfhour into the 

experiment were 22°C and 54 percent, respectively. 
ELECTRICAL PHENOMENA IN VOLCANIC PLUMES 35 

caD> 

0.0 

Cl90 0 0 

0 6> 00 0 6D r:91f c:::: 

L.U 

oooo ~ ~ Ash tall 1 oO 0 

f- 0 L.U 0 0 starts ~ 0 

c:::: !/ q, 

L.U \oj c... Windy en 

~ 

0 0 

> 0 

0 0 ....J 

:;;2 0 

0 

~ Strong gusts Small shockwave; c9 1-' of wind z gentle eruption 0 w 

0 

<( 0 0::: 

<!) 

....J 

<( 0 

i= 

z 

L.U 

f0 

c... 

Cb 

0 0 

0 G) 

oo 0 

0 0 

·1.5 

0 1 0 0 200 

TIME, IN MINUTES 

Figure 4. Potential gradient (kV m-1) versus time (minutes) during ashfall on 25 March 1991. Temperatures and relative humidities at the 

start and 90 minutes into the experiment were 24°C, 69 percent; and 24°C, 73 percent, respectively. 

plume, the electric potential gradient decayed approximately 

exponentially to the pre-explosion background level. No 

ashfall occurred at the measurement locality. 

Figure 3C shows the effect on the potential gradient of 

an explosion that generated only gases. The experiment was 

run at a locality 2.75 km SSE. and downwind of the vent. 

Prior to the explosion, there was a gentle breeze and no cloud 

cover. During this time Sakurajima was erupting small white 

plumes up to 150m high of condensing gases and low rumblings were coming from the vent. After 159 minutes, a loud 

detonation was heard after which a white plume rose approximately 1.5 km from the vent before spreading laterally. The 

generation of this plume had no observable effect on the 

potential gradient. By 174 minutes, the plume had dissipated. No particles fell from the plume. 

Figure 4 shows the effect of ashfall on the electric 

potential gradient. The data were collected at a locality 3.5 

km E. and downwind of the vent, at which time there was 

approximately 20 percent cloud cover and a breeze. During 

the first 180 minutes of the experiment, white plumes of condensing gases< 300m high were erupted intermittently, at 

which time the volcano was either silent or rumbling. At 135, 

141, and 158 minutes, strong gusts of wind gave rise to 

potential gradients of -0.25 kV m-1, -0.45 kV m-1, and 

-0.21 kV m-1 respectively. After 180 minutes, a detonation 

was heard and a particle-laden plume ascended approximately 500 m above the vent. The plume then moved overhead. Light ashfall commenced at 219 minutes and 

continued until the end of the experiment. During this time, 

the potential gradient decreased to nearly -1.5 kV m-1• 

The effect of plume-induced acid rain on the electric 

potential gradient was investigated in an experiment (fig. 5) 

carried out a locality 2.25 km NW. and downwind of the 

vent. At this time, the weather was overcast with 100 percent 

cloud cover. Sakurajima was erupting a plume (> 300 m 

high), and rumblings were coming from the vent. A light fall 

of particles (> 2 mm in diameter) occurred for the first 30 

minutes of the experiment. Between the periods 15-22 and 

32-41 minutes, gentle, particle-free liquid drops fell, irritating the skin. The drops were tested with pH indicator paper 

and found to have a pH of< 1. The drops were generated by 

condensation of volcanic gases. 
36 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

O.Sr-------------------------------------------------------------------~ 

0:: 

L.U 

1--

L.U 

~ 

0:: 

L.U 

a.. 

(j) 

~ 

0 

> 0 

_J 

~ 

z 

t-' 

z 

L.U 

0 

<( 

0:: 

(.9 

_J 

<( 

i= 

z 

L.U 

to 

a.. 

0 

0 

0 

0 

• #tb 

• 0 

0 

• 0 

0 

co 

•• 

eo 

0 

0 •• 

0 , • 0 

• OJ 

0 

Light ashtall 

commences 

oo 

0 

0 

0 

0 

Light ashtall 

ceases 

-0.6 L...---------------------''-----------------------I.__ ____________________ .._____J 

0 1 0 0 

TIME, IN MINUTES 

Figure 5. Potential gradient (kV m-1) versus time (minutes) during plume-induced acid rainfall on 27 Aprill991. At the start and finish 

of the experiment, temperatures and relative humidities were l6°C, 90 percent; and l9°C, 74 percent, respectively. Solid symbols indicate 

periods of rainfall. 

DISCUSSION 

The potential gradient data are consistent with particles 

falling from the plume with a net average negative charge 

(fig. 4) and acid rainfall with an average positive charge (fig. 

5). Explosions that generated no particles produced no measurable fluctuations in the potential gradient (fig. 3). Explosions that generated particles were characterized by large 

changes in potential gradient (figs. 3A and 3B). This implies 

that lava-dome rupture during explosive steam eruptions 

does not necessarily generate large amounts of particles or 

result in significant charge separation. Processes that generate considerable quantities of particles, such as degassing of 

magma, do result in the generation of charged particles and 

volcanic gases (ions). 

Explosive eruptions resulting in particle generation 

exhibit sequences of potential gradient reversals (figs. 3A 

and 3B). These reversals may be explained in this case by 

assigning an average negative charge to particles and positive charge to the erupted gases, which condense to yield 

positively charged liquid drops. Figure 6 shows one series of 

possible explanations for the potential gradient reversals. 

In the early stages of the eruption (fig. 6A), positively 

charged gases separate from the particles at the top of the 

column due to settling of ash particles. Particle aggregation 

would enhance this process by increasing the rate of fallout 

from the top of the cloud. Separation causes the initial negative-potential-gradient pulse seen in both on-axis (fig. 3A) 

and off-axis (fig. 3B) situations. This is due to the negatively 

charged (on average) base of the column being closer to the 

field meter than the positively charged (on average) top of 

the column. A laterally spreading gravity current develops 

(fig. 6B) and higher wind speeds accelerate the gases ahead 

of the particles at high altitudes and give rise to the positive 

potential gradient in the on-axis data (fig. 3A). Gases escaping from the side of the plume generate a positive potential 

gradient in the off-axis data (fig. 3B). 

In the final stages of the eruption (fig. 6C), the plume 

recedes from the off-axis field meter generating the nearexponential decay in potential gradient (fig. 3C). As the 

plume moves over the on-axis field meter, negatively 

charged particle-laden regions of the plume dominate the 

potential gradient and the near-exponential decay as the 

plume retreats is punctuated by periods of ashfall (fig. 3A). 

Hatakeyama and Uchikawa (1952) proposed a dipole 

model to explain their observations but assigned charge of 

one sign to large particles and charge of the other sign to 

small particles. We see no physical justification for particle 

size to control charge polarity of insulating particles because 
ELECTRICAL PHENOMENA IN VOLCANIC PLUMES 37 

charge transfer on contact is driven by differences in surface 

work function. This function depends on surface composition of particles, which may be different from their bulk 

composition. Previous workers (Hatakeyama and Uchikawa, 

1952; Hatakeyama, 1958) have suggested that charging of 

particles occurs within the plume due to grain-grain collisions. This mechanism does not adequately explain the generation of charged gaseous species that condense to form 

charged liquid drops. We propose that charge is generated by 

fracto-emission (Donaldson and others, 1988) processes during vesiculation and fragmentation of magma within the 

vent, where particle generation is taking place. These processes yield both ionized volcanic gas and charged particles. 

The generation rates of charged material within a convecting 

low-density plume must be significantly lower than within 

the fragmentation zone. The polarity of the charges generated may depend on the volcano or eruption studied and may 

be a function of magma chemistry (Hatakeyama and 

Uchikawa, 1952; Anderson and others, 1965). 

We calculate to a first approximation that, in order to 

generate a potential gradient of 2.5 kV m-1 (fig. 3A), a minimum excess charge concentration in the gas cloud of 

c 

Off-axis 

Gas cloud 

Ash cloud 

Off-axis field meter 

D Orraxis field meter 

______.Prevailing wind 

On-axis 

Figure 6. Schematic representation of the growth and dissipation 

of an eruption plume to explain changes in potential gradient measured at ground level. See text for explanation. 

approximately 1010 elementary charges per cubic meter (e 

m-3) is required if a gas/particle separation distance of 10 m 

is assumed. Similarly, Anderson and others (1965) calculated an excess charge of2x1010 e m-3 for the eruption cloud 

of Surtsey. Assuming the same excess charge concentration 

for the particle-laden cloud, a value of surface-charge density of to-5 C m-2 (Gilbert and others, 1991) and 25-Jlmdiameter particles, calculations give an excess charged-particle concentration of 105 m-3. This yields an excess mass 

loading of 1 o-6 kg m-3 of charged particles. Hatakeyama 

(1958) found an overall (positive plus negative) charge-tomass (Q/m) ratio for falling particles of -4x1o-7 C kg-1, and 

Gilbert and others (1991) found an absolute (positive or negative) Q/m ratio for falling particles of -2xto-4 to -5x10-4 

C kg-1. This implies that the excess charge is carried by 

approximately 0.1 percent of the particles. Therefore, the 

total mass loading of the Sakurajima plumes may be of the 

order of to-3 kg m-3. Assuming that the erupted material 

contains 2 weight percent gas and the horizontal cross-sectional-area ratio of the top of the column to the vent is 104, a 

mass loading of 5x1o-3 kg m-3 is calculated. The Mount St. 

Helens initial eruption cloud of 18 May 1980 was calculated 

to support a total of8.5xto-3 kg m-3 of fine particles (Harris 

and others, 1981). This indicates that only a small difference 

in the generation rates of positively and negatively charged 

particles and gaseous ions is required to produce the 

observed electric potential gradient fluctuations. 

RECOMMENDATIONS FOR 

AIRCRAFT SAFETY 

We have shown that particles falling from volcanic 

plumes may be highly charged and that the presence of a particle-laden plume (in contrast to a plume of condensing 

gases) may significantly alter the fair-weather potential gradient. In order to detect the presence of erupted material, we 

suggest that aircraft in flight should monitor: (1) potential 

gradient changes (certain patterns may be distinctive to particle-laden plumes), (2) particulate and ion concentrations by 

means of current flowing from corona-discharge bars (high 

currents may indicate the presence of either charged or 

uncharged particles), and (3) atmospheric S02/HCl concentrations (high concentrations ·may indicate the presence of a 

plume). 

The effects of volcanic particles on jet engines are well 

known (Campbell, 1991 ). However, particles may also effect 

other aircraft systems. The development of "fly-by-wire" 

aircraft may mean that safety becomes dependent on the 

functions of static-sensitive semiconductor devices. Because 

charged particles may be ingested into the cooling systems 

of aircraft electronics, therefore, the development of closed 

cooling systems would be desirable. 
38 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

ACKNOWLEDGMENTS 

We thank Professor K. Kamo and staff of the Sakurajima Volcanological Observatory for assistance during field 

work and R.S.J. Sparks for comments. J.S.G. acknowledges 

support by the NERC and BP Venture Research for research 

funds and the Royal Society for expenses to attend the First 

International Symposium on Volcanic Ash and Aviation 

Safety. J.S.G. and S.J.L. thank the Royal Society for field 

and apparatus expenses. S.J.L. thanks the U.S. Geological 

Survey for providing support to attend the First International 

Symposium on Volcanic Ash and Aviation Safety. Link 

Analytical Ltd. made available the Featurescan package. 

REFERENCES CITED 

Anderson, R., Bjornsson, S., Blanchard, D.C., Gathman, S., Hughes, J., Jonasson, S., Moore, C. B., Survilas, H.J., and Vonnegut, 

B., 1965, Electricity in volcanic clouds: Science, v. 148, p. 

1179-1189. 

Blythe, A.R., and Reddish, W., 1979, Charges on powders and 

bulking effects: Institute of Physics Conferences Series, v. 48, 

p. 107-124. 

Brook, M., Moore, C.B., and Sigurgeirsson, T., 1974, Lightning in 

volcanic clouds: Journal of Geophysical Research, v. 79, p. 

472-475. 

Campbell, E.E., 1991, 7 4 7-400 airplane damage survey following a 

volcanic ash encounter [abs.], in Casadevall, T.J., ed., First International Symposium on Volcanic Ash and Aviation Safety: 

U. S. Geological Survey Circular 1065, p.l4. 

Chalmers, J.A., 1967, Atmospheric Electricity: London, Pergamon 

Press, 515 p. 

Crozier, W.D., 1964, The electric field of a New Mexico dust devil: 

Journal of Geophysical Research, v. 69, p. 5427-5429. 

Donaldson, E.E., Dickinson, J.T., and Bhattacharya, S.K., 1988, 

Production and properties of ejecta released by fracture of materials: Journal of Adhesion, v. 25, p. 281-302. 

Freier, G.D., 1960, The electric field of a large dust devil [abs.]: 

Journal of Geophysical Research, v. 65, p. 3504. 

Gilbert, J.S., Lane, S.J., Sparks, R.S.J., and Koyaguchi, T., 1991, 

Charge measurements on particle fallout from a volcanic 

plume: Nature, v. 349, p. 598-600. 

Harris, D.M., Rose, W.I., Roe, R., and Thompson, M.R., 1981, Radar observations of ash eruptions, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. Helens, 

Washington: U.S. Geological Survey Professional Paper 1250, 

p. 323-333. 

Hatakeyama, H., 1949, On the disturbance of the atmospheric potential gradient caused by the smoke cloud of the volcano 

Yake-yama: Journal of Meteorological Society of Japan, v. 27, 

p. 372-376. 

---1958, On the disturbance of the atmospheric electric field 

caused by the smoke cloud of the volcano Asama-yama: Meteorological Geophysics v. 8, p. 302-316. 

Hatakeyama, H., and Uchikawa, K., 1952, On the disturbance of the 

atmospheric potential gradient caused by the eruption smoke of 

the volcano Aso: Meteorological Geophysics, v. 2, p. 85-89. 

Hoblitt, R.P., and Murray, T.L., 1990, Lightning detection and location as a remote eruption monitor at Redoubt volcano, Alaska [abs.]: Eos, Transactions, American Geophysical Union, v. 

71, p. 1701. 

Kikuchi, K., and Endoh, T., 1982, Atmospheric electrical properties 

of volcanic ash particles in the eruption of Mt. Usu volcano, 

1977: Journal ofthe Meteorological Society of Japan, v. 60, p. 

548-561. 

Newman, M.M., and Robb, J.D., 1977, Protection for aircraft, in 

Golde, R.H., ed., Lightning: New York, Academic Press, p. 

659-696. 

Matsumoto, S., Ueki, S., and Nishi, K., 1988, A study of the processes of explosive eruptions of Sakurajima by means of observations of electric field in the atmosphere, Earth's current, and 

ground motion: Sakurajima Volcano Observatory Report [in 

Japanese],p. 117-126. 

Palmieri, L., 1873, The Eruption of Vesuvius in 1872: London, 

Asher & Co., 148 p. 

Perret, F.A., 1924, The Vesuvius eruption of 1906: Carnegie Institution ofWashington Publication 339, 151 p. 

Rosenbaum, J.G., and Waitt, R.B., Jr., 1981, Summary of eyewitness accounts of the May 18 eruption, in Lipman, P.W., and 

Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. 

Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 53-67. 

Simkin, T., and Fiske, R.S., 1983, Krakatau 1883, The Volcanic 

Eruption and its Effects: Washington, D.C., Smithsonian Institution Press, 464 p. 

Sorem, R.K., 1982, Volcanic ash clusters: Tephra rafts and scavengers: Journal of Volcanology and Geothermal Research, v. 13, 

p. 63-71. 

Whitlock, W.S., and Chalmers, J.A., 1956, Short period variations 

in the atmospheric electric potential gradient: Quarterly Journal of the Royal Meteorological Society, v. 82, p. 325-326. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC ASH: WHAT IT IS AND HOW IT FORMS 

By Grant Heiken 

ABSTRACT 

There are three basic eruption processes that produce 

volcanic ash: (1) decompression of rising magma, gas-bubble growth, and fragmentation of the foamy magma in the 

volcanic vent (magmatic), (2) explosive mixing of magma 

with ground or surface water (hydrovolcanic), and (3) fragmentation of country rock during rapid expansion of steam 

and (or) hot water (phreatic). Variations in eruption style 

and the characteristics of volcanic ashes produced during 

explosive eruptions depend on many factors, including 

magmatic temperature, gas content, viscosity and crystal 

content of the magma before eruption, the ratio of magma 

to ground or surface water, and physical properties of the 

rock enclosing the vent. 

Volcanic ash is composed of rock and mineral fragments and glass shards; in many eruptions, there are also acid 

droplets coating ash-grain surfaces. The shard shapes and 

sizes depend upon the shape and size of gas bubbles present 

within the magma immediately before eruption and fragmentation of the magma. Particle sizes range from meters for 

large blocks expelled near the volcanic vent to nanometers 

for fine ash and aerosol droplets within well-dispersed 

eruption plumes. 

INTRODUCTION 

What is volcanic ash? The question has been asked 

repeatedly since the time of Aristotle. Early scientists were 

able to do some remarkable studies of volcanic ashes and the 

eruptions that produced them, but they were limited by scale. 

It has only been during the last few decades that we have had 

the laboratory equipment to characterize the broad spectrum 

of volcanic ash types, down to a scale of tenths of micrometers. Only in the last 20 years have we had the ability to go 

beyond sampling ash deposits on the ground to sampling 

with aircraft and balloons to collect in situ samples from 

eruption plumes at elevations up to 20 km. This paper will 

review the major volcanic ash types and the broad spectrum 

of explosive eruption types that have produced them. 

ASH FROM A RECENT ERUPTION 

THAT AFFECTED 

AIR TRAFFIC-AUGUSTINE 

VOLCANO, ALASKA 

The 1986 eruption of Augustine Volcano in Alaska sent 

eruption plumes to the east and south from the volcano and 

had considerable impact on airline traffic in the Anchorage 

area. Ash samples were collected at Anchorage International 

Airport, located 280 km NE. of the volcano. The airport was 

showered with light dustings of ash for 9 days after the eruption began (Rose and others, 1988). Median grain size of the 

ash at Anchorage was around 30 f..Lm (fig. 1) and consisted of 

glass shards broken from the foaming, rising magma; glassy 

lava fragments from the older lava dome; and mineral fragments (fig. 2). As is the case for most moderate-size eruptions like this one, the glass shards were coated with acid 

condensates and very fine dust, which consists of even finer 

grained ash (fig. 3); this bonding may occur because of static 

charge (Carey and Sigurdsson, 1982; Sorem, 1982; Gilbert 

and others, 1991 ). These ashes are typical of the hundreds of 

active or dormant stratovolcanoes along the Pacific Rim. 

However, volcanic ashes are very diverse in their origins and 

compositions, and this introduction provides only a general 

view of explosive eruption processes and their products, 

which we have grouped under the category "volcanic ash." 

The physical properties of volcanic ashes depend 

mostly on their relative proportions of glass, mineral fragments, and rock fragments. Also important to the physical 

properties are chemical compositions of these components 

and their grain size. Fine-grained glassy volcanic ash is used 

commercially as an abrasive, but there are few quantitative 

data available on the abrasive qualities of ash. The hardness 

of components of a volcanic ash (based on the Moh's scale 

used by mineralogists: talc has a hardness of 1; diamond has 

a hardness of 1 0) can be approximated with silica-rich glass 

(hardness= 5.5) and minerals ranging in hardness from 2 for 

some clays to 7 for quartz. Melting temperatures for volcanic 

glass and the rheology of the molten material are covered in 

this volume in a paper by Swanson and Beget. 

39 
40 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

EXPLOSIVE FRAGMENTATION OF 

SILICIC MAGMAS 

Observations of fragmentation processes within explosive eruptions are limited. We can get reasonably close to 

only the smallest, and generally the most silica-poor and 

least explosive, eruptions of magma (molten rock). These 

eruption types are, however, of minimal interest for aviation 

safety because they are small. Numerical models of magma 

fragmentation and the formation of volcanic ash are, at best, 

first approximations-at least until we find a way to place 

instruments within the throat of a volcano that will survive 

full eruption. 

MAGMATIC ERUPTIONS 

Eruption explosivity is related mostly to overpressures 

within magma caused by gases coming out of solution as the 

magma nears the Earth's surface and encounters atmospheric pressure (fig. 4). Verhoogen (1951), in an analysis of 

gas-bubble nucleation, growth, and rise within magmas, concluded that volcanic ash formed when expanding bubbles 

within rising magma coalesced. That is most likely correct 

for lava fountains of low-viscosity magmas but not for the 

formation of pumice and volcanic ash from magmas with 

~ 

~ 

cy ~ ~ 

s ~ 

'' / 6 / 

~ 

~ 

/ 

0 ' ill~ ' 

5 10 15 ID 2> 45 

PARTICLE SIZE, IN MICROMETERS 

Figure 1. Grain size of volcanic ash from the April2, 1986, eruption of Augustine Volcano (Alaska). This ashfall sample was collected at the Anchorage International Airport, 280 km NE. of the 

volcano. Eruption plumes from this eruption commonly reached 

altitudes of 3 to 4 km, with occasional ash columns reaching 12 km 

(Rose and others, 1988). Grain sizes were measured with a Horiba 

particle-size analyzer. 

more silica-rich compositions such as those of Redoubt and 

Pinatubo Volcanoes. Pumice, which is a silicate foam composed of glass, gas bubbles, and minerals, would not exist if 

all bubbles in the magma had coalesced and disintegrated as 

Verhoogen had proposed. Alfred Rittmann (1936), a pioneer 

Clay fragments 

Amphibole 

Pyroxene 

Plagioclase 

Rock fragments 

Glass from rock fragments 

Glass shards 

A 

VOLUME PERCENT OF 

VOLCANIC ASH SAMPLE 

Figure 2. Particle types within the ashfall collected at Anchorage 

Airport, March 28, 1986, from the eruption of Augustine Volcano. 

A, Grain count, showing percentage of particle types within this ash. 

The most common particle type from this eruption was glass shards, 

explosively broken from a foaming magma rising in the volcano. 

Other particles include individual minerals from the magma, bits of 

a lava that occupied the volcano's throat before eruption, and fragments from the claystone underlying the volcano. B, Scanning electron photomicrograph that shows mostly equant, curved glass shards 

that were broken from a quickly chilled magma foam. The curved 

surfaces are remnants of bubble walls. 
VOLCANIC ASH: WHAT IT IS AND HOW IT FORMS 41 

0.1 0.3 0.9 

, ,,,,,, 

',',',., ', ',',', ',',,',',', ',.',. 

1111111111-I; 

'- ; ; ; ~; ; ; ; '""" 

>2 

GRAIN SIZE, IN MICROMETERS 

Figure 3. Grain size of volcanic ash from the eruption plume from 

the 1986 eruption of Augustine Volcano that was sampled I 0 km 

downwind from the volcano by aircraft between major eruption 

phases. Even within plumes emanating from the volcano during relatively "quiet" phases, there are numerous particles, albeit small 

ones, as compared with ash produced during the larger eruptions 

(e.g., compare with fig. 1). The sample was collected with a quartz 

crystal microcascade sampler by Ray Chuan (Brunswick 

Corporation). 

in volcanology, proposed that gases in the magma come out 

of solution as magma rises through conduits to shallow 

depths. After the magma reaches the Earth's surface and an 

eruption begins, the highly viscous foam is disrupted by 

decompression before bubble coalescence can occur. This 

theory has been supported by shock-tube analogies (Bennett, 

197 4), and computer experiments by several research groups 

in the United States and England (e.g., Wohletz and others, 

1984). 

The distinctive shapes and physical properties of pumice are controlled by the history of gas-bubble growth, the 

presence or absence of phenocrysts as nucleation points 

(phenocrysts are those mineral grains that crystallized within 

the magma before eruption), and the type of fragmentation of 

the magma foam during eruption. There may be as many size 

and shape distributions of gas bubbles within pumice as 

there are volcanic eruptions, but most are interpreted as 

having grown either continuously during shallow magma 

rise and eruption (i.e., one generation) or discontinuously-before and during eruption (i.e., two generations). A 

hypothetical example (fig. 4; adapted from Heiken and 

W ohletz, 1991) of how pumice and ash form during an 

explosive eruption of silica-rich magma, based on the characteristics of gas bubbles within pumice and volcanic ash 

particles, follows: 

The example is a silica-rich magma (70 weight percent 

Si02), which contains 2 to 3 weight percent H20. Bubble 

growth may begin at depths of 1 to 3 km below the Earth's 

surface, where gas pressure exceeds litho static pressure (i.e., 

the pressure produced by the mass of rock overlying the 

magma body). If C02 gas is present, it may exsolve and form 

gas bubbles at even greater depths (Holloway, 1976). If the 

magma contains abundant crystals (i.e., phenocrysts), nucleation and bubble growth on mineral surfaces may produce 

pumice fragments containing bubble clusters. Gas bubbles 

clustered around phenocrysts or other inclusions may coalesce and form large cavities within the magma foam. 

As rising magma approaches the Earth's surface and 

lithostatic pressure due to the weight of the overlying rock 

decreases, uniform bubble growth may create a foam consisting of evenly spaced bubbles (with the exception of 

larger bubble clusters around phenocrysts). Expansion of 

these bubbles and surface tension of thinning bubble walls 

may increase the bulk viscosity of the magma considerably 

and give it a fmite yield strength, making it more brittle. 

The higher viscosity prevents any significant buoyant 

bubble rise. 

If bubble growth occurs at shallow depths, near the 

vent, the pumice pyroclasts may contain nearly spherical 

vesicles. In this situation, there is no time before fragmentation for vesicles to be elongated by flow into tube-like 

shapes. The glassy ash particles produced in this type of 

eruption consist of arcuate, blocky shards. 

After a vent or conduit is opened to the surface, the 

magma flow rate increases greatly. If this flow rate exceeds 

that of the rising bubbles, the gas bubbles are sheared by 

flow into long tubes or pita-bread-like shapes. 

The more-or-less brittle mass of magma foam is disrupted by a large pressure differential at the magma/atmosphere interface. A shock wave moves ahead of the pumice 

and ash out of the vent, while an expansion wave propaga-ces 

down into the inflated magma and allows its rapid decompression (Wohletz and others, 1984). The nearly solid foam 

is broken into particles at a fragmentation surface in the conduit, and the particles are accelerated out of the vent. The 

explosive eruption process for silica-rich magmas is likely 

driven by this pressure differential and only partly by bubbles coalescing and breaking. 

Large magnitude explosive eruptions, with eruption 

columns reaching heights of as much as 50 km, are called 

Plinian eruptions, after the A.D. 79 eruption ofMt. Vesuvius 

in Italy described by the Roman, Pliny the Younger. These 

eruptions eject large pumice particles, which can be up to 

decimeters long and fall out within tens of kilometers of the 

vent. However, smaller ash particles produced by these 

extremely energetic eruptions, or those carried along with 

pyroclastic flows, can be found far from their source. Some 
42 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

... ·:. · · :_ :-: · · ·." · · · : · .. -= Subso{lic .-: • . ·. . . · .... · ...... ·. . .. 

. .'· ·.: · · ·:. · .. bispersio~·ot · · ·: 

· ·. · . : : : ·: . Pumice, ash, and 

-::· ·::.: . : :-g~s : ··-:.: ._.·.: . 

• • .. ." : Jj .. · : • • •• : '-.~·-: • • : : 

: ... . : ·Fr~9hien~ati~n su·rf~~e ::..:.:_ . . . ... . .. ·. . .. . . . 

· ~· ·:~ ·.<.'G~sb~bbi~s;h :>··.:·.':~·.: . .'· · .: magma foam are.'··.: · · ·: 

. ·. · . :Stretched by flowing . : : : 

. · .· . .magma in the conduit. : · .·· .. · ........... : :. ·.·· .. ·· .. . . ". . .. .... " . . : :· \iol~tiie's .e.xs~fving: · · o 1 o o 

· · · ·from magma with ·. o 11 o 0 

. , a ·: decreasing pressure : 11 o o 0 

: · at shallow . ·. · .· : · o o 0 

· · : depths. · · .. o o • • • • : : : • 0 0 
VOLCANIC ASH: WHAT IT IS AND HOW IT FORMS 43 

Figure 4 (facing page). Schematic diagram of processes leading to the formation of volcanic ash within explosive volcanic eruptions. This 

diagram is based nearly entirely on inference and some experimental studies ofthe processes of gas exsolution and explosive decompression 

of a rising magma with a composition similar to that found in the eruptions of Augustine Volcano. Scanning electron photomicrographs 

shown in the circles are about 300 J.Lm in diameter. As magma rises to a depth where the pressure of gas in solution exceeds that of the overlying rock, some of that gas comes out of solution as small bubbles. As the pressure is lowered, those bubbles continue to grow. After the 

eruption begins, movement of the magma foam in the conduit may stretch the bubbles into elongate, tapered tubes. A fragmentation surface 

between the pressurized magma foam and the ambient atmosphere tears the brittle foam apart and accelerates the pieces out of the conduit 

in the eruption column. The particles are carried into eruption clouds and eventually fall to the ground, their final position depending on the 

height of the eruption column, the strength of winds, and particle size and density. (The samples used here to demonstrate the appearance of 

volcanic ashes within the eruption column are from coarse ash fallout deposits-in situ samples from eruption columns have never been 

collected.) 

fine-grained ash deposits are made up mostly of the lighter 

glass shards, separated from denser mineral and rock grains 

by either gravitational segregation within the eruption plume 

or by the buoyant rise of gases from the eruption clouds. 

Glass shards are pieces of bubble walls broken from the 

magma foam rising in the volcanic vent. The shard shapes 

depend on bubble shapes and sizes within the magma foam 

and the eruption processes responsible for the fragmentation. 

Shards exhibit a wide range of appearances, ranging from 

slightly curved, thin glass plates broken from large, thinwalled spherical gas bubbles, to hollow needles broken from 

pumiceous melts containing vesicles stretched by flow 

(Heiken and Wohletz, 1985). The example shown in figure 5 

is a glass shard collected over central Wyoming at an altitude 

of 18 km, 72 hours after the May 18, 1980, eruption of 

Mount St. Helens. 

Figure 5. Ash from the May 18, 1980, eruption of Mount St. 

Helens, Washington. The 7-J.Lm-long glass shard shown here is from 

a sample collected by high-altitude aircraft at an altitude of 18.3 km 

(60,000 ft) over south-central Wyoming on May 21, 1980. This 

shard is from a sample with a median particle size of 1.5 J.Lm. 

HYDROVOLCANIC ERUPTIONS 

Hydrovolcanic eruptions occur when molten rock 

comes into contact with ground water or the surface water in 

lakes, marshes, and littoral areas. Formation and collapse of 

steam films at the water/molten rock interface causes deformation and fragmentation of the melt and explosive expansion of high-pressure steam. The rapid superheating of water 

results in eruptions that are more efficient at fragmenting and 

dispersing volcanic ash than those eruptions that are driven 

only by bubble growth and decompression. Eruptions can be 

driven by gas-bubble growth and magmatic overpressures, 

as well as by magma/water interactions. Hydrovolcanic 

eruptions produce very fine grained volcanic ash, made up 

mostly of bits broken from glass bubble walls. Hydrovolcanic ashes may have median grain sizes as low as 40 J..Lm, and 

we now recognize that the very fine grained components 

(<10 J..Lm) of such eruptions stay in stratospheric suspensions 

long enough to be carried thousands of kilometers (Self and 

Sparks, 1978; Wilson, this volume). 

SMALL-VOLUME EXPLOSIVE 

ERUPTIONS 

The examples given so far are from the most explosive 

types of volcanic eruptions, which erupt silica- and gas-rich 

magmas (table 1). However, the majority of the Earth's subaerial volcanoes erupt mostly basaltic lava flows and relatively small volumes of volcanic ash and coarser ejecta 

(Basalt is a silica-poor-< 52 weight percent Si02-and 

iron-rich magma type that comprises most ofthe Earth's volcanic rocks). Eruptions of basalt typically have only a very 

small explosive component. 

LAVA FOUNTAINS (HAWAIIAN ERUPTIONS) 

Low-viscosity (< 103 poise) basaltic magmas erupt as 

lava fountains and as lava flows. These eruptions are seen 

safely every year by thousands of tourists in Hawaii. The 

lava fountains range from a few meters to over I km in 
44 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Explosive eruption types and their products. 

[Approx., approximate; ang., angular; frags., fragments; med., medium] 

Height of Approx. area Ash comQosition (Qercent) Types of Potential 

eruption column affected by Glass shards Mineral Rock glass particles hazard to Examples 

(km) ash fallout (km2) and pumice grains fragments in ash avaiation 

Plinian eruptions 

10-40 Hundreds to ::60-100 ::0-35 0-30 em- to J.lm-size High; over 

tens of thousands ang. shards and large regions 

umice 

Plinian-hydrovolcanic eruptions 

20-50 Tens of thousands ::60-100 ::0-35 ::0-40 mm- to J.lm-size High; over 2 

to hundreds of thousands ang. shards and large regions 

rare umice 

Vulcanian eruptions 

0.3-3.03 Tens to hundreds ::10-30 ::10-30 ::70-90 mm-size ang. frags. High locally; 4 

and rare droplets med. regionally 

Strombolian eruptions 

0.1-2.05 0.5-5.0 ::60-80 ::1-5 ::20-40 em- to mm-size Low 6 

ang., blocky frags. 

Hawaiian eruptions 

< 0.1-0.5 < 0.05-0.05 ::60-80 ::1-5 ::20-40 em- to mm-size Low 7 

droplets and bombs 

Surtseyan (hydrovolcanic) eruptions 

0.3-2 1.0-200 ::70-100 ::0-10 ::5-30 mm- to J.lffi-size Med. locally 8 

ang., blocky frags. 

1 Krakatau, Indonesia, 1883; Pinatubo, Philippines, 1991; Mount St. Helens, USA, 1980. 

2 Taupo, New Zealand, approx. 150 A.D. 

3 Rarely to more than 10 km. 

4 Fuego, Guatemala, 1966; Ngauruhoe, New Zealand, 1974. 

5 Rarely to more than 3 or 4 km. 

6 Stromboli, Italy, (to the present day); Cerro Negro, Nicaragua, 1968. 

7 Kilauea volcano, Hawaii, (most of the time). 

8 Surtsey, Iceland, 1963; Taal, Philippines, 1977. 

height and deposit welded spatter (bombs and ash) as a circular or oval apron around a central vent or as ridges parallel 

to a fissure vent. Sprays of low-viscosity basaltic liquid that 

form the fountains are driven by expansion of magmatic 

gases. Particles from lava fountains range in size from 

bombs 1 m or more across to spheres a few micrometers in 

diameter. Coarser ejecta are deposited within a few hundred 

meters of the vent and finer ash, including filamentous 

Pele's hair, is swept downwind and deposited as ashfall. 

Nearly all fountaining is accompanied by lava flows. 

STROMBOLIAN ERUPTIONS AND 

CINDER CONES 

Explosive bursts of solidified and partly solidified 

bombs, blocks, and ash moving in ballistic trajectories are 

known as Strombolian activity, named after Stromboli, a 

volcano in the Aeolian Islands, Italy. Strombolian eruptions 

consist of weak to violent ejection of partly fluid blobs. 

Nearly all of the ejecta falls ballistically around the vent, 

building a "cinder" or "scoria" cone (McGetchin and others, 

1974). Activity at cinder cones can switch rapidly between 

lava fountaining, Strombolian bursts, and Vulcanian eruptions. Volcanic ashes from Strombolian deposits range from 

irregular, smooth-skinned, bubbly droplets of glass to 

blocky, crystalline rock fragments with few gas bubbles. 

This spectrum of textural types is represented in all size categories, from large bombs several meters in diameter to scoria and fine ash. 

VULCANIAN ERUPTIONS 

Among the smaller eruption types, Vulcanian eruptions 

are those characterized by intermittent explosions that 

deposit ash composed of mostly older solidified lava 
VOLCANIC ASH: WHAT IT IS AND HOW IT FORMS 45 

particles (MacDonald 1972; Self and others, 1979). These 

eruptions are most likely caused by overpressures developed 

within blocked vents. The eruption mechanism is not clear 

but most likely consists of alternating magmatic and hydrovolcanic processes. Sometimes the eruption will shift 

between Vulcanian and Strombolian, controlled by either a 

blocked or open vent. Vulcanian eruptions are associated 

with some cinder cones, craters in stratovolcanoes, and lava 

domes. Vulcanian eruptions can produce eruption clouds 

that generally rise several kilometers, and occasionally to 

tens of kilometers, above the vent. These eruptions can also 

erupt small pyroclastic flows (table 1 ). Because the original 

material is rich in water vapor, steam may condense between 

ash grains and pyroclastic flows are turned into mudflows 

along the lower flanks of a volcano. At Ngauruhoe Volcano 

in New Zealand, the cannon-like explosions and subsequent 

ash falls and pyroclastic flows are believed to have been 

caused by pulverization of a lava plug in the conduit by a 

combination of magma degassing and vaporization of 

ground water (Nairn and Self, 1978). 

PHREATIC ERUPTIONS 

Perturbations of a geothermal system by injection of 

new magma at depth, changes in ground-water level, or tectonic activity may cause explosive steam eruptions without 

the eruption of any magma. This type of activity, known as a 

phreatic eruption, is possible at many types of volcanoes and 

even in geothermal areas with no volcanic activity. Steam 

eruptions may occur with no subsequent activity, as was the 

case for Soufriere de Guadeloupe in 1976-77 (Heiken and 

Wohletz, 1985), or they may precede significant magmatic 

eruptions, such as those that occurred at Mount St. Helens, 

1980, and Pinatubo, 1991. The eruptions consist of intermittent or continuous explosive steam bursts and can form large 

craters. Ejecta from steam eruptions are made up of hydrothermally altered or weathered rock fragments and mud. 

CONCLUSIONS 

There are three basic mechanisms of fragmentation in 

volcanic eruptions: ( 1) the decompression of rising magma, 

gas-bubble growth, and subsequent fragmentation as it leaves 

the conduit, (2) the explosive mixing of magma with ground 

or surface water, and (3) fragmentation of country rock by 

rapid expansion of steam and superheated hot water. The 

variations of eruption style and the characteristics of volcanic 

ash produced in explosive eruptions depend on factors such 

as the temperature, volatile content, viscosity and phenocryst 

content of magmas, the ratio of magma to ground or surface 

water, and physical properties of rock enclosing the vent. 

The variations of physical and chemical properties of these 

ashes are as complex as the volcanoes that produced them. 

ACKNOWLEDGMENTS 

This review was supported by the Los Alamos National 

Laboratory's Institutional Supporting Research Program and 

under the auspices of the U.S. Department of Energy. A long 

collaboration with Kenneth W ohletz has made this work 

possible. 

REFERENCES CITED 

Bennett, F.D., 1974, On volcanic ash formation: American Journal 

of Science, v. 274, p. 648-661. 

Carey, S.N., and Sigurdsson, H., 1982, Influence of particle aggregation on deposition of distal tephra from the May 18, 1980, 

eruption of Mount St. Helens volcano: Journal of Geophysical 

Research, v. 87, p. 7061-7072. 

Gilbert, J.S., Lane, S.J., Sparks, R.S.J., and Koyaguchi, T., 1991, 

Charge measurements on particle fallout from a volcanic 

plume: Nature, v. 349, p. 598-600. 

Heiken, G., and Wohletz, K., 1985, Volcanic Ash: Berkeley, University of California Press, 246 p. 

---1991, Fragmentation processes in explosive volcanic eruptions, in Fisher, R.V., and Smith, G., eds., Sedimentation in 

Volcanic Setting: Society of Economic Mineralogists and Paleontologists Special Publication 45, p. 19-26. 

Holloway, J.R., 1976, Fluids in the evolution of granitic magmas: 

Consequences of finite C02 solubility: Geological Society of 

America Bulletin, v. 87, p. 1513-1518. 

MacDonald, G.A., 1972, Volcanoes: Englewood Cliffs, New Jersey, Prentice-Hall, 510 p. 

McGetchin, T.R., Settle, M., and Chouet, B.A., 1974, Cinder cone 

growth modeled after Northeast Crater, Mount Etna, Sicily: 

Journal of Geophysical Research, v. 79, p. 3257-3272. 

Nairn, I.A., and Self, S., 1978, Explosive eruptions and pyroclastic 

avalanches from N gauruhoe in February, 197 5: Journal of Volcanology and Geothermal Research, v. 3, p. 39-60. 

Rittmann, A., 1936, Vulkane und ihre Tatigkeit: Stuttgart, Ferdinand Enke Verlag, 188 p. 

Rose, W. I., Heiken, G., Wohletz, K., Eppler, D., Barr, S., Miller, 

T., Chuan, R., and Symonds, R., 1988, Direct rate measurements of eruption plumes at Augustine Volcano: A problem of 

scaling and uncontrolled variables: Journal of Geophysical Research, v. 93, p. 4485-4499. 

Self, S., and Sparks, R.S.J., 1978, Characteristics of widespread pyroclastic deposits formed by the interaction of silicic magma 

and water: Bulletin Volcanologique, v. 41, p. 196-212. 

Self, S., Wilson, L., and Nairn, I.A., 1979, Vulcanian eruption 

mechanisms: Nature, v. 277, p. 440-443. 

Sorem, R.K., 1982, Volcanic ash clusters: Tephra rafts and scavengers: Journal of Volcanology and Geothermal Research, v. 13, 

p. 63-71. 

Verhoogen, J., 1951, Mechanisms of ash formation: American 

Journal of Science, v. 249, p. 729-739. 

Wohletz, K.H., McGetchin, T.R., Sandford, M.T., III, and Jones, 

E.M., 1984, Hydrodynamic aspects of caldera-forming eruptions: Numerical models: Journal of Geophysical Research, v. 

89, p. 8269-8286. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANISM IN THE CANADIAN CORDILLERA: 

CANADA'S HAZARD RESPONSE PREPAREDNESS 

By Catherine J. Hickson 

ABSTRACT 

British Columbia and the Yukon are geologically 

dynamic regions, encompassing subduction zones, rifting, 

and thermal anomalies (hot spots). Approximately 100 volcanic vents are arranged in five broad belts and in other more 

widely scattered regions. Holocene eruptions have occurred 

in four of the belts. The most recent documented event, a 

small basaltic eruption, occurred about 200 years ago in 

northwestern British Columbia. The most recent large explosive eruption occurred about 1.2 thousand years ago when a 

vent near the Alaska-Yukon border expelled about 30 km3 of 

pyroclastic material, covering 300,000 km2 of the Yukon 

under a blanket of ash. In southwestern British Columbia, a 

Plinian eruption from Mount Meager stratovolcano, 

occurred about 2.4 thousand years ago. This eruption spread 

ash across southern British Columbia into Alberta. 

In Canada, an integrated response plan to deal with volcanic hazards is now in place and involves all levels of government. Four key agencies operate jointly to ensure timely 

and appropriate response to a volcanic eruption, including 

the safe passage of air traffic. Response procedures are 

being coordinated between the United States and Canada to 

ensure safety and minimize disruption among residents and 

aviators. 

INTRODUCTION 

Canada is not generally thought of as a "volcanic" 

country, but there have been several large Holocene eruptions (about 10,000 years ago) in British Columbia and the 

Yukon that, if repeated today, would cause severe disruption 

of people, resource extraction, and transportation (Hickson, 

1992a, 1992b ). This paper summarizes what is known of 

Holocene volcanism in Canada, reviews concepts of volcanic hazards and risk, and comments on Canada's preparedness to deal with volcanic hazards. 

Western Canada is part of the "Pacific Ring ofFire"-a 

continuous line of subduction zones and transform faults that 

encircle the Pacific Ocean. This dynamic environment has 

produced five broad belts of volcanoes plus other isolated 

and tectonically less well defined volcanic regions (fig. 1). 

The Garibaldi and Wrangell volcanic belts owe their origin 

to subduction; the Stikine volcanic belt to crustal extension, 

and the Anahim volcanic belt to a mantle plume or "hot 

spot." Deep faults and crustal dynamics in other regions 

formed volcanic fields such as Wells Gray-Clearwater and 

other isolated cones, or cone fields, in British Columbia and 

the Yukon. 

HOLOCENE ERUPTION HISTORY OF 

WESTERN CANADA 

WRANGELL VOLCANIC BELT 

The volcanoes in the Wrangell belt extend from southwestern Yukon into Alaska (fig. 1 and 2). Built over a span 

of 25 m.y., these volcanoes are related to subduction of the 

Pacific plate beneath North America off the coast of Alaska 

(Skulski and Francis, 1986; Skulski and others, 1988; 

Stephens and others, 1984) and comprise the eastern end of 

the historically active Aleutian arc (fig. 1). The Wrangell 

belt is oldest in the eastern (Yukon) portion of the Aleutian 

arc and becomes progressively younger westward into 

Alaska (Richter and others, 1990). Magma compositions 

span basalt to rhyolite, but andesitic lavas dominate. The 

most voluminous eruptive activity appears to have ended 

200,000 years ago as the tectonic regime at the margin progressively changed from dominantly subduction to strikeslip movement (Richter and others, 1990). The most 

significant Holocene eruptions produced the "White River" 

ash from Mount Churchill (McGimsey and others, 1990), 

located in Alaska just west of the Canadian border (fig. 3). 

Based on radiocarbon dating, two eruptions occurred at 

1,800 and 1,200 years B.P. These eruptions ejected an estimated 30 km3 of material and covered 300,000 km2 of the 

Yukon with a blanket of ash (fig. 3) (Lerbekmo and Campbell, 1969). 

47 
48 VOLCANIC ASH AND AVIATION SAFETy: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

/~ 

r--- ._.-/"\,) 

w:oc:A~ 'S. 

GULF 

ry: .11 LlC:KA 

PACIFIC 

PLATE 

.L..U.J...J. Subduction zone 

0 200 

km 

Scale: Approximate 

I 

/ / 

/ 

/ 

/ 

/ 

Figure 1. Major tectonic elements of western North America. Double lines mark the Explorer, Juan de 

Fuca, and Gorda ridges (R), which are active spreading centers. Subduction (zones marked by hatchured 

lines) occurs northward from the Mendocino fracture zone (FZ) to the northern tip of the Explorer plate and 

along the northern segment of the Fairweather fault (F) and Aleutian trench. Some of the more prominent 

Holocene volcanic vents are shown as triangles. Small arrows mark the sense of motion along major transform faults. 
VOLCANISM IN THE CANADIAN CORDILLERA: CANADA'S HAZARD RESPONSE PREPAREDNESS 49 

VCDLCANIC BELTS AND FIELDS 

bf THE CANADIAN CORDILLERA 

"'\ 

ngell Volcanic Be~ 

1 

) 

( 

'-\ 

\ 

l) 

(Late Miocene- Holocene) 

Legend 

• Late Miocene - Pliocene volcanic complexes 

• Large Quaternary volcanic complexes 

• 

• 

Quaternary Cinder cones/small shield volcano 

Quaternary Chilcotin basalt 

Neogene Chilcotin basalt 

-.+r High-altitude air routes over western Canada 

\A 

f''" t::: 

0 

z 

ells Gray-Clearwater 

\L \..Volcanic Field 

\.\ 

Figure 2. Quaternary volcanic elements that make up the Canadian Cordillera are shown overlain by major national and international 

air routes. 
50 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

[1\\'i"\1 St. Helens Wn 

~ (508 years BPl 

White River 

(younger layer) 

(-1200 years BPl 

~ White River 

~ (older layer) 

(-1800 years BPl 

nTI Bridge River 

L_j (2400 years BP) 

~St. Helens Yn 

~ (3400 years BPl 

• Erupt ive Center 

200 

Figure 3. Presently known distribution of major Holocene tephras 

in the Canadian Cordillera, with the exception of historic eruptions. 

Dates are approximate radiocarbon years before present, and only 

selected eruptive centers are shown. 

STIKINE VOLCANIC BELT 

The Stikine volcanic belt, consisting of over 50 Quaternary volcanic centers, extends northward from the Skeena 

River to the British Columbia-Yukon border (figs. 1 and 2). 

This belt lies east of the transition from transform faulting to 

subduction along the North American-Pacific plate margin 

(fig. 1) and is related to crustal extension (Souther, 1992). 

Eruption of alkaline basalt to rhyolite magmas has produced 

stratovolcanoes, shield volcanoes, and small cinder cones. 

Detailed mapping exists of the two largest volcanic complexes in the belt, Mount Edziza (Souther, 1990, 1992) and 

Level Mountain (Hamilton, 1981 ). Holocene eruptions in the 

belt are confined to small basaltic cone-building events. The 

Tseax River Cone (fig. 2), at the southern end of the belt, 

erupted about 200 years ago (Sutherland-Brown, 1969) and 

is Canada's youngest known volcanic eruption. Northward 

migration of the junction between the three tectonic plates 

(the Pacific, North American, and Explorer plates) during 

the last 25 m.y. diminished extensional stresses in the region, 

likely reducing the possibility of future felsic (peralkaline 

rhyolite and dacite) eruptions. Small basaltic cone-building 

events are still a possibility, and the impact of such an eruption on downstream habitation or installations must not be 

overlooked (Souther, 1981 ). 

ANAHIM VOLCANIC BELT 

The Anahim volcanic belt extends across central British 

Columbia from the coast to the Fraser River (figs. 1 and 2). 

Volcanism becomes progressively younger from west (more 

than 12 Ma) to east (less than 7,000 years old), supporting 

the hypothesis that these volcanoes owe their origin to a 

mantle hot spot (Hickson, 1986; Souther, 1986). The belt 

consists of large alkalic shield volcanoes and small basaltic 

cinder cones. Volcanism appears to have ceased in the westem parts of the belts, but if the hypothesis is correct, future 

volcanism can be expected in the vicinity ofNazko Cone and 

east of it. Radiocarbon dating of Nazko Cone suggests that 

the last eruptive period was 7,200 years ago (Souther and 

others, 1987). Future volcanism is most likely in the form of 

basaltic cinder cones, but eruptions of less mafic magma, 

typical of the eastern portions of the belt, cannot be ruled out. 

ALERT BAY VOLCANIC BELT 

The Alert Bay volcanic belt is a poorly studied group of 

volcanic rocks at the northern end of Vancouver Island (fig. 

2), which appear to have been active in Pliocene and Pleistocene time. No Holocene eruptions are known (Armstrong 

and others, 1985), and volcanic activity in this belt has most 

likely ceased. 

GARIBALDI VOLCANIC BELT 

The Garibaldi volcanic belt is the northernmost segment of the Cascade arc, a chain of major andesitic to dacitic 

stratovolcanoes extending northward from northern California to British Columbia (fig. 1). The arc appears to be segmented (Guffanti and Weaver, 1988; Sherrod and Smith, 

1990); the central portion of the arc is the most active (Scott, 

1990) and the northern end least active (Sherrod and Smith, 

1990). Long repose periods, up to several thousand years, 

between major explosive events at the major volcanoes 

(Mounts Meager, Cayley, and Garibaldi), appears to typify 

the Canadian portion of the Cascade arc. A number of studies 
VOLCANISM IN THE CANADIAN CORDILLERA: CANADA'S HAZARD RESPONSE PREPAREDNESS 51 

address volcanism in the Garibaldi volcanic belt (Mathews, 

1952, 1958; Green, 1981, 1990; Green and others, 1988; 

Souther, 1980; Read, 1990; Stasiuk and Russell, 1989, 

1990). These studies have identified eruptive periods that are 

shown diagrammatically in figure 4. 

Volcanoes of the Garibaldi belt have been sporadically 

active over a time span of several millions of years (fig. 4). 

The most recently documented eruption was about 2,400 

years ago at Mount Meager (fig. 5). This eruption may have 

been close in size to that of the May 18, 1980, eruption of 

Mount St. Helens. Ash from this eruption can be traced 

eastward to western Alberta (fig. 3). Hot springs in the 

A 

1.0 

u n•o "'"'""" 30 "'"' '""" 

Age (Ma) 

*- radiometric dates 

B 

0.4 

Age (Ma) 

* radiometric dates 

A - andesite 

D- dacite 

0.4 Age (Ma) o.s 0.8 

* A 

flows 

ash 

dome 

breccia 

63 total event s 

D -dacite A - andesite B - basalt 

1.0 

vicinity of Mounts Cayley and Meager suggest that magmatic heat is still present. The long history of volcanism in 

this region, coupled with continued subduction off the 

coast, suggests that volcanism has not yet ended in the 

Garibaldi volcanic belt. 

OTHER REGIONS 

Throughout British Columbia and the Yukon, isolated 

monogenetic cinder cones and cone fields can be found (fig. 

2). The most significant concentration of these is probably 

- _ flows 5<588 dome 

ash ~;~;s;;3 brec cia 

3.2 3.6 

Age (Ma) 

*-radiometric dates A -andesite o - dacite B -basalt 

c 

D 

~: ** :?: . ~* u . D 

<t 

2.0 

A 

A? 

Age (Ma) 

*- radiometric dates 

D 

Age (Ma) 

2.8 

D -dacite 

flows 

· ash 

:888 dome 

~!~fl~ breccia 

A - andesite 

* D 

54 

total events 

24.5 

events/Ma 

B -basalt 

Figure 4. Diagrammatic representation of eruptive activity within the Garibaldi volcanic belt. Height of each histogram gives a very crude 

indication of the size of the eruption. A, Mount Garibaldi volcanic field. B, Garibaldi Lake volcanic field. C, Mount Cayley volcanic field. 

D, Mount Meager and Elaho Valley volcanic complexes. Data from Mathews (1952, 1958), Green (1981, 1990), Souther (1980), Read 

(1990), Stasiuk and Russell (1989, 1990). 
52 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 5. Vent area of Mount Meager, which erupted about 2,400 

years ago. Crater is open to the east (foreground) and is 1.5 km 

wide at the rim. The crater is outlined by steep ridges surrounding 

the small dome and short lava flow, which are visible in the center 

of the picture. 

the Wells Gray-Clearwater region of British Columbia 

(Hickson, 1986). Volcanism over several million years has 

produced numerous small-volume flows and cinder cones. 

The youngest of these, Kostal Cone (fig. 6), may be only a 

few hundred years old. 

The scattered, isolated cones and cone fields throughout 

British Columbia and the Yukon, are unlikely to erupt again, 

but they do identify weaknesses in the crust that may preferentially channel magma to produce more small-volume 

basaltic eruptions in the future. An exception to this is Volcano Mountain in the Yukon, a small basaltic shield volcano 

and associated vents that have erupted several times in their 

1- to 2-million-year history (Jackson and Stevens, 1992). 

VOLCANIC HAZARDS AND 

VOLCANIC RISK 

Erupting volcanoes may pose a number of specific hazards such as lava flows, pyroclastic flows and surges, fallout 

of ash, debris flows (lahars), avalanches, seismic activity, 

ground deformation, tsunami, acid rain, and poisonous gases 

(Blong, 1984; Tilling, 1989). What hazard will occur at 

which volcano depends to large degree on the composition 

of the erupting magma (table 1). Basaltic eruptions pose a 

minimal hazard in comparison with explosive andesitic, dacitic, or rhyolitic eruptions. 

Basaltic eruptions, though generally considered least 

hazardous, may have a significant impact if the eruption 

occurs during winter months in regions of heavy snow-pack. 

The eruption may trigger debris flows (lahars) or floods from 

rapidly melting snow. Some basaltic eruptions in Canada 

have been near glaciers, and subglacial volcanism has 

Figure 6. Kostal Cone, a basaltic cinder cone in Wells Gray Provincial Park, British Columbia. 

occurred in British Columbia in the past (Mathews, 1947; 

Hickson, 1986). This form of volcanism can produce potentially destructive water outburst floods known as 

jokulhlaups, and water-magma interactions can potentially 

produce very large phreatic or phreato-magmatic eruptions-even if the magma is basaltic. 

Erupting volcanoes pose a hazard when something of 

value (such as human lives, property, or resources) is 

impacted to its detriment. Risk is usually assessed on the 

basis of the number of human lives that may be lost as a 

result of a hazardous event. Yokoyama and others (1984) 

devised a method for assessing risk at a volcano that takes 

into account past activity at the volcano, present seismicity 

and ground deformation, and population at risk. Using this 

scheme and considering our present understanding of the 

volcanic record in Canada, no Canadian volcano falls into 

the high-risk category. Canada is still relatively underpopulated, thus a volcanic eruption within Canada, with few 

exceptions, will probably result in few if any direct casualties, baring aviation emergencies. The legacy of any large 

explosive eruption in Canada will be regional disruption of 

aviation, loss of resources such as forests and spawning 

streams, and displacement of people. 

In the short term, perhaps the greatest impact on Canada may be from eruptions elsewhere in western North 

America. Prehistoric eruptions of Mount St. Helens left thin 

ash layers in southern British Columbia, and the eruption of 

Mount Mazama deposited a blanket of ash several centimeters in thickness over southern British Columbia and much 

of Alberta (fig. 3). Most recently, within 24 hours of the 

May 18, 1980, eruption of Mount St. Helens, light ashfall 

in southern British Columbia, Alberta, and Saskatchewan 

caused concern among residents and the aviation 

community. 
VOLCANISM IN THE CANADIAN CORDILLERA: CANADA'S HAZARD RESPONSE PREPAREDNESS 53 

Table 1. General relationships between volcano types, predominant lava, eruption styles, and common eruptive characteristics. 

[from Tilling, 1989, table 1.1, p. 2] 

Volcano 

type 

Predominant lava 

Composition Viscosity 

Eruption 

style 

Common eruptive 

characteristics 

Basaltic 

(mafic) 

Fluidal Generally non-explosive 

to weakly explosive 

Lava fountains, lava flows 

(long), lava lakes and pools. 

Andesitic Less fluidal Generally explosive, but 

sometimes non-explosive 

Lava flows (medium), 

explosive ejecta, tephra falls. 

Composite2 Dacitic to rhyolitic Viscous to Typically highly explosive, Explosive ejecta, tephra falls, 

(felsic, silicic) very viscous, but but can be non-explosive, pyroclastic flows and surges, 

can be non-explosive especially after a large eruption lava domes. 

1 Generally located in the interior of tectonic plates ("intraplate") and presumed to overlie "hot spots,'• but also may occur in other 

tectonic settings (e.g., Hawaii, Galapagos, Iceland, Kamchatka). 

2 Generally located along or near the boundaries of convergent tectonic plates (subduction zones); also called stratovolcanoes 

(e.g., Cascade-Garibaldi volcanic belt, Wrangell volcanic belt). 

In Alaska, during the 1989-90 eruptions of Redoubt 

Volcano, tephra drifted into Canada at least twice, and in 

1992, Mount Spurr erupted three times, sending ash plumes 

into Canadian airspace, including some parts of west-central 

Yukon. An eruption of Mount Baker in northern Washington 

State, close to one of Canada's busiest terminal areas (fig. 2), 

could have serious repercussions. Response procedures are 

being coordinated between the United States and Canada to 

ensure safety and minimize disruption among residents and 

aviators. 

VOLCANO MONITORING 

In Canada at present, there is no specific program to 

monitor volcanoes. However, certain seismic stations in the 

regional seismic network, put in place to study tectonic 

earthquakes, are located to optimize coverage of nearby 

Holocene volcanoes. At present, only seismic stations in the 

southwestern portion of the network, covering the Garibaldi 

volcanic belt, are telemetered directly to the Geological Survey of Canada's (GSC) western seismic base at the Pacific 

Geoscience Centre (PGC) on Vancouver Island. In this part 

of the network, it is possible to detect and locate earthquakes 

of magnitude 1.0 and above. This is sufficient sensitivity to 

detect precursor seismic activity in the Garibaldi volcanic 

belt. 

A program is in place to upgrade the network and to 

telemeter stations to PGC from other parts of western Canada. When completed, the network will allow real-time 

detection and location of earthquakes magnitude 3 and 

greater throughout western Canada. With the exception of a 

very large impending eruption, this will be insufficient for 

detection of precursor activity associated with smaller Vulcanian or Strombolian eruptions, such as those of the 1992 

eruptions of Mount Spurr. It should, however, be sufficient 

to permit officials to confirm or deny a reported large volcanic eruption. 

PREPARING FOR AN ERUPTION 

Despite infrequent natural disasters, Canadians have 

not ignored the fact that they live in a geologically active 

region in which future earthquakes and volcanic eruptions 

are a certainty. However, Peterson and Tilling (in press) find 

that countries faced with infrequent volcanic eruptions, even 

when that country is scientifically advanced, have extreme 

difficulty dealing with volcanic events. "Unrest at long-quiescent volcanoes is particularly difficult to diagnose: such 

unrest does not necessarily culminate in an eruption, but if an 

eruption does occur, it may be particularly violent. Either 

outcome poses difficult challenges to scientists, not only in 

their study of the volcano, but in their public relations." 

(Peterson and Tilling, in press). 

Monitoring unrest at a volcano is a complex exercise 

that does not necessarily result in easy or straightforward 

answers. Figure 7 shows the communication network 

between the GSC and other agencies that would become 

involved in any volcanic emergency in Canada. Communication between the groups and emergency planning are the 

key to effective response to a natural disaster. 

Emergency planning in British Columbia is carried out 

by the Provincial Emergency Program (PEP) and Emergency Preparedness Canada (EPC) (Anderson and others, 

1990; Dalley, 1992; Pollard, 1992). At present, the level of 

preparedness for a volcanic eruption consists of a notification network set up between the government agencies 

involved (fig. 7) and formalized in the Interagency Volcanic 

Event Notification Plan (IVENP, available from the author). 
54 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

GEOLOGICAL 

IUIIVIY 

OF 

CANADA 

TIIANIPOIIT 

CANADA 

Alii TIIAFFIC 

IIIIVICII 

Figure 7. Communication pathways for notification, coordination, and response of government agencies in Canada and data-input sources, such as seismographs, satellites, and wind models. 

Also shown are agencies outside the formal notification network, 

such as local governments, which may provide an eruption alert or 

require information on an eruption. Also listed are agencies in 

neighboring American States, which may, in a similar manner, 

provide eruption alerts or require notification of an eruption in 

Canada. Abbreviations used in this figure: U.S.G.S., U.S. Geological Survey; RCMP, Royal Canadian Mounted Police; 

F.E.M.A., Federal Emergency Management Agency; NOAA, National Oceanic and Atmospheric Administration; F.A.A., Federal 

Aviation Administration. 

Terms of reference for the working group include participation of the agencies in planning and simulation exercises and 

yearly updates to the plan. 

Each agency in the plan has specific responsibility to 

pass information on to other involved agencies and to 

respond according to its individual mandate. Reports of a 

volcanic eruption within Canada are transmitted around the 

network for response and confirmation. For example, Transport Canada Aviation is responsible for transmitting, in a 

timely manner, information regarding an eruption to ensure 

the safe passage of aircraft around the affected area. The 

PEP will be responsible for notification of the municipality 

and people living in the region affected. The GSC assumes 

responsibility for seismic confirmation of an event (within 

the limitations of the current seismic network), hazard warning, monitoring and passing information on to the other 

involved agencies as outlined in its "statement of responsibility" in the IVENP. Presently, the "statement of responsibility" gives an optimum situation that will require resources 

beyond those currently available from the GSC. However, 

work is underway to identify sources of expertise and equipment that could be called upon to help in the case of a volcanic emergency. It will be the responsibility of the GSC Staff 

Volcanologist to make sure that people and equipment are 

identified. The IVENP, internal response plans, and interagency contacts are kept current. 

CONCLUSIONS 

Western Canada has been spared volcanism on a human 

time frame-but has not on a geological one. Volcanic 

activity has occurred in the past, and we must try to look 

beyond the short human memory when we are dealing with 

geologic hazards that have recurrence intervals of longer 

than 50 years. Hazard zonation and planning must be an 

integral part of our future if we are to save lives and property. 

In the area of emergency planning for volcanic eruptions, we 

can help by increasing public awareness and putting into 

place well-thought-out emergency plans. Detailed geological work has begun at specific volcanoes to help quantify the 

risk from future eruptions, but more work is necessary. This 

work should be carried out before rezoning or major shifts in 

population occur. 

ACKNOWLEDGMENTS 

M. Stasiuk compiled the data for figure 4; his help is 

sincerely appreciated. D. McDonald, I. Alarie, and B. Vanlier helped with preparation of the manuscript. T. Neal, T. 

Spurgeon, and L. Jackson provided thoughtful reviews of the 

manuscript. 

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of the Meager Mountain volcanic complex, southwestern British Columbia: Geological Survey of Canada Paper 89-1 E, p. 

189-196. 

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102 p. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC ASH IN KAMCHATKA AS A SOURCE OF 

POTENTIAL HAZARD TO AIR TRAFFIC 

By Vladimir Yu. Kirianov 

ABSTRACT 

The degree of hazard to air traffic from volcanic ash 

clouds over Kamchatka and the North Kuriles (Russian 

Federation) is assessed from analyses of the eruptive activity of Sheveluch, Bezymianny, Kliuchevskoi, Karymsky, 

Avachinsky, Gorely, Alaid, and Ebeko Volcanoes and 

records of wind speed and direction from the Earth's surface to 15 km. The most hazardous volcanoes are Kliuchevskoi and Alaid because they may eject tephra to altitudes of 

10-15 km and their eruptions may last for several months. 

Ash clouds from most of the volcanoes generally move in 

an easterly and southeasterly direction in response to prevailing winds. 

INTRODUCTION 

Since 1982, when two jumbo-jet aircraft lost engine 

power owing to encounters with ash clouds from eruptions 

ofGalunggung Volcano in Indonesia, there has been a growing interest in the threat that volcanoes pose for aviation 

operations. In addition to the potential human costs, aircraft 

damaged through encounters with volcanic ash have cost in 

excess of $100 million to repair (Steenblik, 1990). As air 

transportation increases, this problem will become more 

acute, especially in volcanically active areas such as in Kamchatka, Eastern Russia, where 29 active and potentially 

active volcanoes exist and where several eruptions occur 

each year (fig. 1). 

This study discusses explosive activity of the Kamchatkan volcanoes during the last decade in order to determine altitudes and directions of future eruption plumes and 

their hazards to aviation. Considered in this study are specific features of atmospheric circulation over Kamchatka; 

the type, frequency, and duration of eruptions; the distribution of volcanic ejecta in the atmosphere; and the altitudes 

and directions of eruption plumes over Kamchatka and 

adjoining areas. 

VOLCANIC ASH AND ATMOSPHERIC 

CIRCULATION 

The atmospheric circulation in Kamchatka has been 

analyzed on the basis of data from 1961-81 and 1988 supplied by 12 meteorological and two aerological stations and 

from synoptic bulletins of the Kamchatkan Hydrometeorological Survey. These data indicate that the circulation 

regime changes drastically over Kamchatka because of the 

effects of both large-scale atmospheric processes and 

regional features. Most of the region is characterized by seasonal wind variation, particularly near the eastern coast. In 

the central regions, this seasonal wind variation is distorted 

by mountain-valley circulation. 

On average, approximately 70 cyclones 1 pass through 

Kamchatka each year, chiefly in autumn and winter. 

Cyclones migrate from Japan along the Kamchatkan east 

coast to the Aleutian Islands or into the Bering Sea and produce strong winds. Analysis of vertical distribution of meteorological parameters (wind, temperature, moisture) 

demonstrates that the most pronounced variations take place 

in the upper troposphere near the tropopause, which in Kamchatka ranges from 8 to 11 km annually. 

The distribution of volcanic ash over large distances is 

dependent on the character of circulation in the stratosphere. 

Over the northern part of the Pacific Ocean, volcanic ash is 

transported by wind currents from west to east, i.e., from the 

Kamchatka Peninsula toward the Aleutian Islands. 

During an eruption, the large amounts of material 

ejected into the stratosphere form ash clouds in which the 

maximum ash concentration is at altitudes several kilometers 

above the tropopause. The highest altitudes of volcanic-particle concentration have been determined to be between 18 

I Cyclone as used in this paper refers to a center or area oflow pressure 

usually a few hundred kilometers in diameter and does not refer to the very 

intense, twisting storms of less than l km in diameter, i.e., tornadoes, as 

commonly used in the United States. 

57 
58 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

and 21 km. Lidar data and modeling results show that during 

the Fuego (Guatemala) eruption of 1974, approximately onehalf of the erupted material lingered within a 15- to 22-kmwide belt at 15- to 17-km altitude. Because present-day airliners fly at altitudes not exceeding 15 km (9 km over Kamchatka), we shall consider the characteristic features of 

volcanic material transport up to altitudes of 15 km. 

The general pattern of volcanic ash distribution shows 

that its transport during ejection and within the troposphere 

is dependent on wind speed and direction, which may vary 

with altitude. During the Mount St. Helens eruption on May 

18, 1980, the direction of ash transport varied from northeast 

at 2,300 m altitude, to the east at 11,300 m altitude, and to the 

100 KILOMETERS I 

.~· 

NIKOLSKO ~LAN# : . 

Figure 1. Location of volcanoes and meteorological and aerological stations in Kamchatka. Volcanoes are shown by starburst symbol; airports are shown by solid triangles; meteorological stations 

are shown by open circles containing roman numerals. 

southeast at 26,000 m altitude (Sarna-Wojcicki and others, 

1981). During the Sheveluch eruption on November 12, 

1964, however, a constant wind blew from the west and 

northwest at all altitudes between 3,000 m and 15,000 m. 

Similarly, during the Avachinsky eruption on January 13, 

1991, the wind blew from the northeast at all altitudes up to 

11 km so that the width of the ashfall area at a distance of 

25-30 km from the crater did not exceed 4 km (fig. 2). 

Angles of wind shear direction at all altitudes in both cases 

did not exceed 50°. 

11,000 

(/) 9000 c:: 

LU 

1-

LU 8000 

:2: 7000 ~ 

LJ 6000 Cl 

:::> 

1- 5000 

~ <( 4000 

3000 

20000 I 

180° 270" 360. 

A WIND DIRECTION 

11,000 

10,000 TROPOPAUSE 

(/) 9000 c:: 

LU 

1- sooo LU 

:2: 7000 ~ 

LJ 6000 Cl 

:::> 5000 1-

~ 4000 <( 

3000 

2.000 

5 10 15 2.0 '2.5 30 

B 

WIND SPEED, 

IN METERS PER SECOND 

Figure l. The Avachinsky Volcano eruption on January 13, 

1991: A, wind-direction profile; B, wind-speed profile. 
VOLCANIC ASH IN KAMCHATKA AS A SOURCE OF POTENTIAL HAZARD TO AIR TRAFFIC 59 

Table 1. Volcanoes in Kamchatka and the Kurile Islands that have erupted during the last 10 years and the possible character of their 

future eruptions. 

[A, andesite; AB, andesitic basalt; B, basalt; comp., composition; freq., frequency. Altitude refers to the maximum altitude of the eruption cloud. Direction refers to the most likely 

directions that the eruption cloud may drift] 

Name of Coordinates Height Date of most 

volcano (lat, long) (m) recent eruption 

Sheveluch 55.97°N., 161.58°E. 3,395 Jan. 1991 

Bezymianny 55.97°N., 160.59°E. 2,800 Mar. 1990 

K.liuchevskoi 55.06°N., 160.64°E. 4,850 Mar. 1990 

Avachinsky 53.22°N., 159.00°E. 2,751 Jan. 1991 

Gorely 52.45°N., 158.12°E. 1,829 1986 

Karymsky 54.07°N., 159.60°E. 1,486 1982 

Alaid 50.80°N., 155.50°E. 2,339 Apr.-June 1981 

Ebeko 50.67°N., 155.93°E. 1,138 1987, 1988-90 

1 A few tens of seconds to minutes. 

2 Hours to days. 

3 Days to months. 

Analysis of prevalent wind directions and speeds at 

various altitudes over Kamchatka indicate the following: 

1. Wind directions change with the seasons, which 

points out the monsoon character of circulation in 

Kamchatka. 

2. The prevailing surface-wind directions at four key 

measurement stations in the regions of active volcanoes are: to the southeast and east at Lopatka Cape; to 

the northwest, southeast, and east at PetropavlovskKamchatsky; to the southeast, south, and southwest at 

Semyachik; and to the west, east, and southeast at 

Klyuchi. At all these points, the winds blew to the 

southeast at a speed of 4.5-11.2 m/s for more than 20 

percent of the year. 

3. Air masses in the troposphere over PetropavlovskKamchatsky between 3- to 9-km altitude flow to the 

east, southeast, and northeast, and the average maximum speed of the wind increases from 10.3 m/s at 3-

km altitude to 23 m/s at 9-km altitude. 

In the city of Klyuchi (fig. 1), the wind at an altitude 

of between 3 and 9 km blows predominantly to the 

east, southeast, and south and the wind speed 

increases with increasing altitude. It is noteworthy 

that, during some large historic eruptions (Bezymianny in 1956 and Ksudach in 1907) and during several eruptions in the Holocene (Avachinsky, 

Sheveluch, and Ksudach), the ash plume drifted to the 

north. This is atypical because air masses here move 

in a northerly direction at all altitudes, on average, 

only about 15 days per year. Therefore, forecasting 

the direction of possible ashfalls in future eruptions of 

Kamchatkan volcanoes should be made carefully. 

4. The wind direction in the stratosphere is constant, and 

air masses move east and southeast at speeds from 20 

to 36 m/s. 

Rock Eruption :freq. Possible features of future erumions 

comp. per year Altitude (km) Duration Direction 

A 10 4-8 1 E.,SE. 

A 1-2 5-8 2 NE.,E.,S. 

B 1 6-10 3 E., SE., S. 

AB,A 1 4-10 2 NE.,SE. 

A 1 3-8 3 E.,SE. 

A 1 2--6 2 E.,SE.,S. 

B 1 815 3 NE.,E., SE. 

A 100 1-2 NE.,E., SE. 

ACTIVE VOLCANOES IN 

KAMCHATKA 

At present, the Kamchatka volcanoes most dangerous 

to air traffic are Sheveluch, Kliuchevskoi, Bezymianny, 

Avachinsky, Gorely, and Karymsky (fig. 1). The Kurile volcanoes, Alaid on Atlasov Island (the ashes of which fell on 

Petropavlovsk-Kamchatsky during the 1981 eruption) and 

the very active Ebeko on Paramushir Island, must also be 

considered. The characteristics of Kamchatka and Kurile 

eruptive activity during the last decade are discussed below 

and are summarized in table 1. 

SHEVELUCH 

(LAT 56.78°N., LONG 161.58°E., ELEVATION 3,395 M) 

The northernmost active volcano in Kamchatka, Sheveluch, is noted for formation of extrusive domes that are subsequently destroyed during great explosive eruptions with 

directed blasts (fig. 3). The most recent such eruption 

occurred on November 12, 1964 (Gorshkov and Doubik, 

1965), and sent an eruption cloud to 12-km altitude as determined from a TU-104 jet airplane, which was making a 

scheduled flight near Sheveluch at that time. 

In 1980, an andesitic extrusive dome started to grow 

within the crater, and gas-and-ash explosions began in 1984. 

These explosions are similar in style: they occurred suddenly, lasted for only a few tens of seconds, and resulted in 

a cauliflower-like eruption column (Zharinov and others, 

1990) that reached 4- to 6-km altitude. 

Recently, the frequency of eruptions increased from 

4-5 per year (1984-85) up to approximately 3,340 per year 

beginning in 1987. The latest activity was on August 4, 1990, 

when the ash cloud rose to 6-km height and then drifted 
60 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

280km 

I I 

d 

AGATTU ISLAND 

Figure 3. Distribution of ash for the eruptions of Bezymianny 

Volcano in 1955-56 and Sheveluch Volcano in 1964 (from Melekestsev, 1989). 

eastward; on January 13, 1991, when the ash material was 

transported southward in the direction of Klyuchi; and on 

April6, 1991, when the ash was transported westward. 

BEZYMIANNY 

(LAT 55.97°N., LONG 160.59°E., ELEVATION 2,800 M) 

Bezymianny is one of the most active volcanoes in 

Kamchatka. On March 30, 1956, a tremendous explosion 

destroyed the top of the volcano in an eruption similar to 

Mount St. Helens in 1980. Since then, the volcano has been 

in a stage of intermittent dome extrusion and eruption (Gorshkov and Bogoyavlenskaya, 1965). During the period 

1981 to 1984, five eruptions of Bezymianny were recorded, 

the largest on October 13-14, 1984, when 0.011 km3 of 

rock was ejected. The eruption column rose to 9-km altitude, and an ash plume drifted 40 km to the southeast 

(Malyshev, 1987). On June 30 and July 1, 1985, the climactic stage of one of the largest eruptions of the dome 

occurred at Bezymianny with the volume of material 

erupted placed at 0.05 km3 (Alidibirov and others, 1988). 

From mid-December 1985 to mid-April 1986, the volcano 

was in a state of repose. In the remainder of 1986 and in 

1987, the activity of the volcano was again high (Ivanov 

and others, 1984), continuing to the present. Ash ejections 

seldom exceed 5- to 6-km altitude, and explosive activity 

lasts commonly for a few hours to a few days. 

KLIUCHEVSKOI 

(LAT 56.06°N., LONG 160.64°E., ELEVATION 4,850 M) 

Kliuchevskoi is also one of the most active volcanoes 

in Eurasia, with numerous eruptions during the last decade. 

In April 1984, a summit eruption of the Vulcanian-Strombolian type began. During the paroxysmal activity at the 

summit crater, the altitude of the eruption cloud was 12 km 

(Fedotov and others, 1987). Because the lower boundary 

of the tropopause during the eruption was at 8-km altitude, 

this ash entered the stratosphere. The eruption ended on 

January 28, 1985, and the total volume of pyroclastics 

ejected was 0.1 km3. 

On December 2, 1985, a series of vigorous phreatic 

explosions sent a gas-and-ash column to 9.6-km altitude 

(Belousov, 1989). The direction of ash dispersal and the 

area (45x1,115 km) of the gas-ash cloud were determined 

by using the lidar of the Kamchatkan Hydrometeorological 

Survey. On December 2, 1985, the tropopause was at 

7.8-km altitude, and, therefore, part of the material went 

into the stratosphere and the cloud started to spread horizontally. At an altitude of 9 km, a southeasterly wind with 

a speed of 5 m/s stretched the cloud into a plume more 

than 50 km long (Belousov, 1989). 

Frequent explosive-effusive eruptions of the Strombolian type continued from the Kliuchevskoi summit crater 

during 1986-90. The maximum altitude reached by the eruption column during various stages of the eruption was 

1,500--2,000 m above the crater rim. A large eruption from 

the summit crater lasted from January 29 to November 10, 

1990. As a result, the ash fell on the Commander Islands, 

Sredinny Ridge, and to the north of Sheveluch Volcano. The 

ash cloud rose to a height of 8 km above the crater. 

Other active volcanoes whose eruptions may be hazardous to aviation near Petropavlovsk-Kamchatsky are those of 

the A vachinsky and Zhupanovsky volcanic groups and Mutnovsky, Karymsky, Gorely, Opala, Ksudach, Alaid, and 

Ebeko. During the last 1,800 years, at least 17 ashfalls were 

related to eruptions of these volcanoes. In historic time, ashfalls were observed during the eruptions of Avachinsky Volcano in 173 7, 1779, 1945 and 1991; Go rely in 1828 and 

1832; Karymsky in 1963; and Alaid in 1981. 
VOLCANIC ASH IN KAMCHATKA AS A SOURCE OF POTENTIAL HAZARD TO AIR TRAFFIC 61 

KARYMSKY 

(LAT 54.07°N., LONG 159.60°E., ELEVATION 1,486 M) 

Karymsky is a small but very active andesitic stratovolcano located approximately 125 km northeast of Petropavlovsk-Kamchatsky (fig. 1). The explosive-effusive 

eruption that commenced in 1978 ceased in 1982. Eruptions were mainly of the Vulcanian and Vulcanian-Strombolian types. The characteristic feature of the Karymsky 

eruptions is the formation of a lava dome in the central part 

of the crater, the destruction of which is linked to large 

explosive eruptions of Vulcanian type that change the morphology of the crater. A series of strong Vulcanian explosions that began in August-September 1982 had ceased by 

October (Ivanov and others, 1984)-although a small 

amount of fumarolic activity occurs in the crater and nearcrater part of the volcano. 

The mass of pyroclastics ejected during 1980-82 was 

about 40 million tons. During the eruption on May 11, 1963, 

the ash cloud drifted over Petropavlovsk-Kamchatsky. 

Meteorological data obtained on May 11 in PetropavlovskKamchatsky indicate that the transport of ash could take 

place in the troposphere at altitudes of 3 to 11 km, where a 

constant northerly and northeasterly wind blew at a speed of 

12-18 rnls. At 12- to 15-km altitude in the stratosphere, air 

masses drifted in northwest and west directions. 

AVACHINSKY 

(LAT 53.22°N., LONG 159.00°E., ELEVATION 2,751 M) 

A vachinsky Volcano is located 27 km north of Petropavlovsk-Kamchatsky (fig. 1). On January 13, 1991, an 

eruption started with two explosions producing a gas-andash column that rose to 8- to 9-km altitude and moved southeast toward Petropavlovsk-Kamchatsky at a speed of 100 

km/hr. Ash began falling at the town in less than 1 hour after 

the start of the eruption. The width of the ashfall was approximately 3-4 km, and the area of ashfall was 400-500 km2 (1. 

Melekestsev, oral commun., 1991). 

The eruption continued until January 24, 1991, with 

intense ashfalls on January 16 and 17. On January 16, the 

eruption cloud drifted southeast, and satellite photographs 

indicated it was 200 km long and 1.5-2 km wide. On January 

17, the ash cloud from A vachinsky Volcano, according to 

satellite images, drifted northeastward. After January 13, the 

height of gas-ash ejections generally did not exceed 200-300 

m and seldom reached 2,000 m altitude above the crater. 

GORELY 

(LAT 52.45°N., LONG 158.12°E., ELEVATION 1,829 M) 

Gorely Volcano, approximately 65 km south of Petropavlovsk-Kamchatsky (fig. 1), erupted in 1980-81 and 

1984-85. The eruption of June 1980 to July 1981 produced 

eruption columns of the Vulcanian type that rose to 5 km 

above the crater and ejected 48 million tons of ash (Ivanov 

and others, 1982). The December 1984 eruption resembled 

the previous one: eruption clouds rose 2 km above the crater, 

and approximately 1 million tons of ash were ejected 

(Ivanov and others, 1985). During 1985, the volcano was in 

a stage of phreatomagmatic eruptions of different intensity, 

and the height of the eruption column ranged from 100 to 

3,500 m above the crater. The area of ashfall was small and 

confmed to the volcano edifice. The eruption varied from 

separate outbursts to a continuous emission of steam in thin 

jets or columns from which a cumulus cloud generally 

formed. The dynamics of the steam-gas jet were dependent 

on weather conditions (wind speed and direction and air 

humidity)-in clear, windless weather, the steam-gas column reached maximum altitudes. Frequently, the eruption 

cloud formed one or occasionally two thick steam-gas 

plumes 200 m high and extending 20-150 km downwind 

from the volcano (Ivanov and others, 1985). 

During recent years, Gorely Volcano has been in a stage 

of minor eruption. On April 25, 1986, near the top of the 

8£11/Nt; 

SEA 

ATTUISLAND 

~ 

0 

AGATTU ISLAND ~ 

' ·~I> .JI ADAK ISLAND 

Figure 4. Distribution of ash for the eruptions of Alaid Volcano 

on April 27, 1982, and of the northern breakthrough of Tolbachik 

Volcano in 1975 (from Melekestsev, 1989). 
62 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

active crater, a steam-gas emission oflight brown color (due 

to entrained ash particles) was observed. Ash covered an 

area surrounding the crater of 300 km2, and the weight of 

ejected ash was estimated to be 3, 780 tons. Ash-and-steam 

clouds slowly stretched in the form of a thin plume for distances up to 100 km. 

OTHER VOLCANOES 

Eruption of Alaid Volcano (lat 50.80°N., long 

155.50°E.), presents substantial hazard to airliners making 

flights over Kamchatka. Alaid, on one of the northernmost of 

the Kurile Islands (fig. 1), is an almost perfect cone rising to 

2,339 m high above sea level. The most recent explosive 

eruption from the summit crater took place between April 27 

and June 5, 1981 (fig. 4), when 650 million tons of material 

were ejected. Satellite data indicates that ejections during the 

initial stage of the eruption reached 15-km altitude and an 

ash plume extended for more than 1,500 km (Sawada, 1983). 

The volume of ash that fell in Severokurilsk, within 45 km of 

the volcano, was 15-20 kg/m2. In the western Aleutian 

Islands, the ash layer was 3 mm thick (Fedotov and others, 

1981, 1982, 1986). On May 5 and 6, 1981, ash was detected 

Figure 5. Eruption ofKarymsky Volcano in December 1977. Photograph by N.P. Smelov. 
VOLCANIC ASH IN KAMCHATKA AS A SOURCE OF POTENTIAL HAZARD TO AIR TRAFFIC 63 

in the atmosphere above San Francisco, Calif., at an altitude 

of 12-13 km. 

The airport in Severokurilsk (fig. 1) can also sustain 

damage from nearby Ebeko Volcano (lat 50.67°N., long 

155.93°E., elevation 1,138 m), whose most recent eruption 

began in late 1988 and continued to the summer of 1990. 

The frequency of gas-ash outbursts from the crater was several hundred per month, and, in some cases, the interval 

between eruptions was less than several minutes. Eruption 

material was ejected to altitudes ranging from a few hundred 

meters up to 1-2 km for periods up to several tens of 

seconds. 

CONCLUSIONS 

At the time this report is being prepared (1992), international airways pass approximately 400--500 km east of 

Kamchatka in the region of Attu Island. (This may change 

shortly as new airways are planned that will directly overfly 

the Kamchatka Peninsula.) Volcanic hazards for airplanes 

arise chiefly from explosive Plinian eruptions with volcanic 

ash transport to the east. Eruption columns rise to 10-km altitude, and ash may be transported for hundreds of kilometers 

downwind from the volcano. Due to the long duration of 

eruptions, ash fallout near the volcano from the eruption column is possible in all directions. The most likely direction 

for ash transport from Kamchatkan eruptions is to the east, 

southeast, and south at altitudes of 6 to 1 0 km. Ash clouds 

drifting for hundreds of kilometers from the eruption center 

present real dangers to airplanes as well as to airports ofKlyuchi, Ust-Kamchatsk, and Kozyrevsk. 

Bezymianny Volcano probably causes danger to air 

traffic only a few days per year during periods of actual eruption. The radius of the maximum hazard reaches a few tens 

of kilometers from the volcano. Ash transport is likely to 

occur at 5- to 8-km altitude to the northeast and south. Certain dangers may arise to airliners operating to and from the 

airports of Klyuchi and Kozyrevsk. In its present style of 

activity, Bezymianny Volcano presents little danger to air 

traffic carried out at 9-km altitude and higher. 

At Sheveluch Volcano, hazards can arise from shortterm, frequent explosions at the extrusive dome with the 

eruption cloud reaching 8-km altitude. The comparatively 

small ash concentrations in the Sheveluch ash clouds suggests that the airspace at 4- to 8-km altitude within 50 km of 

the eruption center during a one-half-hour period beginning 

at the onset of the eruption is the most dangerous to airliners. 

Explosions usually last a few tens of seconds, and prevailing 

ash transport is to the east and southeast. Such eruptions of 

Sheveluch are of concern to local air flights operating at Klyuchi and Ust-Kamchatsk airports. 

Karymsky Volcano (fig. 5) is hazardous to aviation 

within 100 km of the eruption center. Individual large eruptions under certain weather conditions can result in ashfall in 

the airports of Petropavlovsk, Elizovo, and Milkovo. Prevailing ash transport can be at 2- to 6-km altitude to the east, 

southeast, and south. 

Future eruptions at A vachinsky Volcano can produce 

ash that would drift at 4- to 1 0-km altitude to the northeast 

and southeast. Eruptions may last from a few hours to a few 

weeks. Movement of the ash may cause certain danger to 

national airlines and to domestic flights, including the 

regions of the Petropavlovsk and Elizovo airports. At the 

Gorely and Mutnovsky Volcanoes, eruptions may last from 

a few days to several months. The probable ash transfer may 

take place at 3- to 8-km altitude to the east. The eruption 

cloud can be transported for distances from a few tens to a 

few hundreds of kilometers. Under certain weather conditions, the ash can cause danger to aircraft operating at the 

Elizovo airport. 

Eruptions from Alaid Volcano are potentially hazardous to international flights along North-Pacific air routes 

(e.g. Anchorage-Seoul, Anchorage-Khabarovsk, etc.) as 

well as to domestic flights. Ash produced by Alaid may be 

transported many hundreds of kilometers from the volcano. 

The ash is likely to be transported at 8- to 15-km altitude to 

the northeast, east, and southeast. Large ashfalls are 

expected in the airports of Ozernovsky and Severokurilsk. 

The eruptions at the Ebeko Volcano (Paramushir 

Island) can produce ash that will drift at 1- to 2-km altitude 

to the northeast and southeast. The greatest danger may arise 

to local air routes and to the airport of Severokurilsk. 

ACKNOWLEDGMENTS 

I thank Drs. Thomas P. Miller (U.S. Geological Survey), I.V. Melekestsev, and 0. A. Braitseva for helpful discussions of this work. I am also indebted to Loubon F. 

Serkova for translation of the manuscript into English. 

REFERENCES CITED 

Alidibirov, M.A., Bogoyavlenskaya, G.E., Kirsanov, LT., Firstov, 

P.P., Girina, O.A., Belousov, A.B., Zhdanova, E. Yu., and 

Malyshev, A.l., I988, Eruption of Bezymianny Volcano in 

I985: Volcanology and Seismology, no. 6, p. 3-I8 [in Russian]. 

Belousov, A.B., 1989, Phreatic explosion from the Kliuchevskoi 

Volcano on December 2, I985: Voprosy Geografii Kamchatki, 

no. I 0, p. I 08-II 0 [in Russian]. 
64 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Fedotov, S.A., Khrenov, A.P., and Sharinov, N.A., 1987, The Kliuchevskoi Volcano, its activity during 1932-1986 and possible 

development: Volcanology and Seismology, v. 4, p. 3-17 [in 

Russian]. 

Fedotov, S.A., Ivanov, B.V., Avdeiko, G.P., Flerov, G.B., Andreev, 

V.N., Dvigalo, V.N., Doubik, Yu. M., and Chirkov, A.M., 

1981, Eruption of Alaid Volcano in 1981: Volcanology and 

Seismology, v. 5, p. 82-87 [in Russian]. 

Fedotov, S.A., Ivanov, B.V., Flerov, G.B., Avdeiko, G.P., Andreev, 

V.N., Budnikov, V.A., Gordeev, E.I., Dvigalo, V.N., and Shirokov, V.A., 1982, Study of Alaid eruption (Kurile Islands) in 

1981: Volcanology and Seismology, no. 6, p. 9-27 [in Russian]. 

Fedotov, S.A., Ivanov, B.V., Gushchenko, I.I., Dvigalo, V.N., 

Sharinov, N.A., Khrenov, A.P., and Chirkov, A.M., 1986, Volcanic activity in the Kurile-Kamchatka zone in 1980-1984: 

Volcanology and Seismology, no. 2, p. 3-20 [in Russian]. 

Gorshkov, G.S., and Bogoyavlenskaya, G.E., 1965, Bezymianny 

Volcano and the characteristic features of its most recent eruption in 1955-1963: Moscow, Nauka, p. 172 [in Russian]. 

Gorshkov, G.S., and Doubik, Yu. M., 1965, The directed blast at 

Sheve1uch Volcano, in Volcanoes and Eruptions: Moscow, 

Nauka, p. 3-37 [in Russian]. 

Ivanov, B.V., Andrea, V.N., Bogoyavlenskaya, G.E., Doubik, Yu. 

M., Kirsanov, LT., Rulenko, O.P., Firstov, P.P., and Chirkov, 

A.M., 1982, Activity of volcanoes in Kamchatka and Kurile Islands in 1981: Volcanology and Seismology, no. 4, p. 103-108 

[in Russian]. 

Ivanov, B.V., Chirkov, A.M., Doubik, Yu. M., Khrenov, A.P., Dvigalo, V.N., Razina, A.A., Stepanov, V.V., and Chubarova, 

O.S., 1984, The state of activity of active volcanoes in 

Kamchatka and Kurile Islands in 1982: Volcanology and Seismology, no. 4, p. 104--110 [in Russian]. 

Ivanov, B.V., Droznin, V.A., and Vakin, E.A., 1985, The eruption 

of Gorely Volcano in 1985: Volcanology and Seismology, no. 

4, p. 93-99 [in Russian]. 

Malyshev, A.I., 1987, The eruption of Bezymianny Volcano in 

1981-1984: Volcanology and Seismology, no. 2, p. 89-93 [in 

Russian]. 

Me1ekestsev, LV., 1989, Great volcanic ash falls in the region of 

Petropav1ovsk-Kamchatsky: Voprosy Geografii Kamchatki, 

no. 10, p. 101-108 [in Russian]. 

Sarna-Wojcicki, A.M., Shipley, S., Waitt, R.B., Dzurisin, D. and 

Wood, S.H., 1981, Areal distribution ofthickness, mass, volume, and grain size of air-fall ash from the six major eruptions 

of 1980, in Lipman, P.W., and Mullineaux, D.R., eds., The 

1980 Eruptions of Mount St. Helens, Washington: U. S. Geological Survey Professional Paper 1250, p. 577-600. 

Sawada, Y., 1983, Analysis of eruption clouds by the 1981 eruptions of Alaid and Pagan Volcanoes with GMS images: Papers 

in Meteorology and Geophysics, v. 34, no. 4, p. 307-324. 

Steenblik, J.W., 1990, Volcanic ash-A rain ofterra: Air Line Pilot, June/July, p. 9-15, 56. 

Zharinov, N.A., Zhdanova, E. Yu., Belousov, A.B., Gorelchik, V.I., 

Belousova, M.G., Garbuzova, V.T., and Demenchuk, Yu. B., 

1990, Eruptions and seismic regime of the Northern volcanic 

group in 1986-1987: Volcanology and Seismology, no. 3, p. 

3-20 [in Russian]. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

ASH CLOUDS: CHARACTERISTICS OF 

ERUPTION COLUMNS 

By Stephen Self and George P.L. Walker 

ABSTRACT 

An eruption column is the vertical or subvertical part of 

the ash emissions issuing from an explosive volcanic vent or 

from the top of a pyroclastic (ash) flow. Eruption columns 

range in height from low, small-scale bursts to huge convective systems that rapidly transport ash, volcanic gases, and 

entrained air into the stratosphere. Some eruption columns 

are the product of instantaneous releases of ash and gas, and 

their rise constitutes an isolated thermal, while others are 

more steady convecting systems that are fed by a nearly constant rate of release of material from the vent (maintained). 

Eruption columns have a lower gas-thrust region (the jet of 

material leaving the vent-this commonly represents less 

than 10 percent of the total eruption-column height) and a 

buoyant convective-thrust region that constitutes most of the 

column in large Plinian and Vulcanian eruptions but may be 

small in Hawaiian and Strombolian types. Above this is the 

umbrella region, a zone of momentum-driven rise and considerable lateral spreading from which ash fall begins as 

material is fed into the downwind plume. Characteristics of 

eruption columns vary according to the style of explosive 

eruption, and this paper summarizes most of the important 

types. Although almost all types of explosive eruption are 

capable of generating ash columns and plumes that are hazardous to aircraft, Vulcanian eruption columns are probably 

the most dangerous on a worldwide basis owing to their frequency, unpredictability, high fine-ash content, and ability to 

easily reach altitudes well in excess of common flight paths. 

INTRODUCTION 

Volcanic ash clouds pose a considerable danger to aviation. These laterally spreading, wind-driven clouds are 

parts of an atmospheric dispersal system that transports 

pyroclastic material (ash) and gas upward from the volcanic 

vent and spreads them in the atmosphere. The vertical to 

inclined part of the dispersal system, termed the eruption column, is the major control on the heights of ash clouds. The 

downwind, drifting part of the system we refer to as the 

plume (fig. 1). We review the current understanding of 

eruption-column processes, discuss the range in column 

characteristics for different types of volcanic eruptions, and 

give an assessment of which eruption types may be the most 

hazardous to flying aircraft. Previously, Rose (1986) has 

reviewed volcanic clouds from the perspective of hazards to 

aviation. The same basic components exist in all types of 

explosive volcanic eruption columns, and these will be discussed first. 

COMPONENTS OF THE ERUPTION 

COLUMN 

Our understanding of volcanic phenomena such as 

eruption columns comes both from observations and measurements on erupting volcanoes and from fluid-dynamic 

modeling of the behavior of buoyantly convecting systems, 

verified in some cases by analog experiments using (most 

often) aqueous fluids. An eruption column consists of a lowermost gas-thrust region, a convective-thrust region, and an 

uppermost umbrella region (Wilson, 1976; Sparks, 1986; 

Woods, 1988). This three-fold division applies to all columns, from those that are steady systems supplied by a maintained release of material from the vent to those that are 

produced by an instantaneous explosion and rise as an 

isolated thermal. 

GAS-THRUST REGION 

At the base of the eruption column, the fragmenting 

eruptive mixture that has been produced in the volcanic conduit by decompression-induced expansion of volatiles in the 

magma (and perhaps by other mechanisms) undergoes a 

drop in pressure as it enters the atmosphere. The accompanying expansion of the system produces a jet at the vent mouth 

(the magma- or rock-air interface). The vent mouth may be 

deep within a crater, and not readily visible to the observer, 

or at the surface. The jet, which is initially denser than the 

ambient air, forms the gas-thrust part of the column. Air is 

engulfed in great quantities into this vertical or subvertical 

65 
66 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Umbrella 

region 

ERUPTION 

COLUMN 

Convective 

thrust 

Figure 1. Three parts or regions of an eruption column: gas 

thrust, convective thrust, and umbrella. 

turbulent jet (Wilson, 1976), and the structure is subjected to 

enormous atmospheric drag. Even in violent, high-intensity 

eruptions in which exit velocities approach the maximum 

possible for volcanic venting on Earth (about 650--700 m/s; 

McGetchin and Ulrich, 1973; Wilson, 1976), the gas-thrust 

region will not exceed about 3 km in height due to drag 

forces. The resulting rapid deceleration can slow the jet to 

speeds of a few tens of meters per second; thus, at the top of 

the gas-thrust region, velocities in the column may be at a 

minimum. In some eruption columns, the upward velocity 

falls below this minimum only at the top of the umbrella 

region, where the thermal and kinetic energy of the column 

is exhausted. 

In many eruptions, loss of coarse material known as 

ballistic ejecta occurs from the gas-thrust region (fig. 2). 

Also, if the eruptive mixture does not entrain sufficient air to 

attain a bulk density less than that of the ambient atmosphere, gravitational collapse of part or all of the column will 

occur, forming either fire fountains or pyroclastic (ash) 

flows, depending on the type of eruption. This aspect will be 

dealt with in detail later. Although important in column 

dynamics, the gas-thrust zone rarely contributes more than 

10 percent to the column's total height and is therefore oflittle concern to flying aircraft. 

CONVECTIVE-THRUST REGION 

If sufficient air is entrained into the jet, the eruption column overshoots its first neutral buoyancy level and passes 

into the convective-thrust region where turbulent convective 

rise of the erupted mixture due to its heat content and lower 

than ambient density becomes the dominant driving force. 

Convective thrust exerts the greatest influence on eruptioncolumn height, accounting for between 50--90 percent of the 

Figure 2. Instantaneous Vulcanian explosion from Anak Krakatau in September 1979. Note the large ballistic blocks separating 

from the gas-thrust region. Photograph courtesy of Michael R. Rampino. 

altitude reached, and ultimately controls the nature of the 

whole eruption cloud. In this region ofbuoyancy, the greater 

the heat input at the base, either as an instantaneous release 

or a maintained flux, the higher the column will rise (Morton 

and others, 1956). In basic terms, H, the column height, is a 

function of the thermal flux into the system (Q), such that 

(17) 

where 

n = 3 or 4, depending upon whether the shape of the 

source vent is circular or linear, respectively (Wilson 

and others, 1978; Woods, 1988; Stothers and others, 

1986), 

K is a constant that varies mostly according to the density 

stratification of the ambient atmosphere and whether 

the thermal energy input is maintained or instantaneous, and 

Q (for a steady column from an approximately circular 

vent) is the heat flux given, for example, as J/s; for a 

linear vent or fissure, Q is the heat flux per unit length 

of the fissure (J/s/m). 

For the rise of an isolated thermal, Q is the total energy in 

the instantaneous release (J). For steady discharge from a 

circular vent, Q is largely determined by the amount of 

magma being erupted and its general properties; therefore, 

column height is proportional to magma flux rate, which we 

term intensity. Although we will not go into details here, 

the major constraints on column behavior are thus the mass 
ASH CLOUDS: CHARACTERISTICS OF ERUPTION COLUMNS 67 

eruption rate and initial velocity of the fragmenting magma, 

the size of the vent, and the amount of volcanic gas escaping 

from the magma (see Sparks and others, this volume, for a 

more detailed treatment). 

Not all convecting ash columns come directly from 

vents and the gas-thrust region, however. Some rise from the 

tops of eruptive phenomena known as pyroclastic (ash) 

flows, and there is a direct relationship between the magma 

flux at the vent feeding the pyroclastic flows, the size of the 

pyroclastic flows, and the height reached by ash columns rising off the flows (Woods and Wohletz, 1991). Co-ignimbrite 

ash columns differ from most other columns in having no 

gas-thrust region: rise takes place entirely by convective 

thrust. They also form above pyroclastic flows derived from 

the collapse of unstable parts of steep-sided lava domes, in 

which case there is no preliminary venting of material. Some 

of the ash columns in early 1990 from the Alaskan volcano, 

Redoubt, were of this type (Scott and McGimsey, in press). 

Many different types of explosive eruptions occur 

worldwide, giving a considerable range of eruption-column 

characteristics such as height, width, vertical rise rates, and 

ash and gas contents. In the least energetic types, most of the 

erupted material collapses as a fire fountain at the top of the 

gas-thrust region, and only a small proportion of finest material, the released volcanic gases, and the engulfed and heated 

air rise in the convective region. Much of the magma in such 

eruptions is only poorly fragmented and the predominant 

large bombs fall out without cooling significantly, a situation 

of poor thermal efficiency between hot material and 

(I} . 

. 

h 

..JL 

v 0 

entrained air (Woods and Bursik, 1991 ). This behavior characterizes Hawaiian and Strombolian eruptions, which have 

the lowest columns. In the more intense eruptions, Vulcanian 

to Plinian, where most of the magma is highly fragmented 

into small pieces, almost all the erupted material passes into 

the convective region. The high degree of heat transfer 

between hot clasts and gas and the entrained air (high thermal efficiency) and the increase in column velocities above 

the gas-thrust region gives a strongly buoyant system. In 

order to maintain rise, the bulk density of the column (ash 

plus gas plus entrained air) must always be less than the 

ambient density. As the column rises, there is a complex 

interplay between cooling resulting from altitude in the troposphere and the cooling of the column owing to entrainment of air that is colder and denser. 

Bursik and Woods (1991) recently showed that columns that undergo marked acceleration with height over 

some height range in the convective region are the result of 

particular combinations of mass eruption rate and initial 

velocity. They termed such columns superbuoyant as 

opposed to those that rise at rates similar to or only slightly 

above the velocity minimum. Needless to say, many eruption 

columns are superbuoyant and most will overshoot their 

upper or second neutral buoyancy level in the atmosphere, 

which is generally somewhere in the middle to upper troposphere. Above this point, they rise owing to momentum 

rather than convective lift. 

There is thus a range of convective column behaviors 

(see also Sparks and others, this volume), from weakly rising 

h 

Figure 3. Three possible modes of behavior of eruption columns-intensity of eruption increases from left to right. Wind is 

from the left in each case. At side of each diagram are shown normalized velocity (v) profiles versus height (h) for these columns. Left, weak isolated thermals, which are influenced by the wind. Center, a higher intensity buoyant column, influenced 

by the wind only at the top. Right, a high intensity, superbuoyant column with a pronounced umbrella region. 
68 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 4 (above and facing column). Examples of different types 

of eruption column. A, Instantaneously generated buoyant thermal 

from a Vulcanian explosion of Ngauruhoe Volcano, North Island, 

New Zealand, in 1975, being blown over by a wind of about the 

same velocity as the average column rise rate. Final elevation 

reached by plume top was about 12,000 ft. (Photograph courtesy of 

New Zealand Geological Survey.) B, A maintained Plinian column 

from Mount Pinatubo on June 12, 1991. (U.S. Geological Survey 

photograph courtesy of David Harlowe.) C, Mount St. Helens eruption column with umbrella cloud rising off blast flow at about 09:52 

Pacific Daylight Time, 18 May 1980. Maximum height reached by 

this co-ignimbrite thermal was 85,000 ft (26 km). Photograph produced by James F. Kolberg (from Sparks and others, 1986). 

ones that are easily pushed over by the wind, to those that 

rise to the tropopause and then stop due to the inversion in 

atmospheric temperature, to those that punch through the 

tropopause and rise considerable distances into the stratosphere (figs. 3 and 4). All convecting columns eventually 

slow down and stop primarily because of the density stratification of the atmosphere and the resulting fact that, at some 

height, they consist of material that is denser than the surrounding air. 

UMBRELLA REGION 

In the upper part of the convectively rising region, 

velocities decrease and the slowing top of the column acts as 

a cap on the still rapidly rising material below. As a result, 

gravity forces the column to expand laterally and form the 

characteristic umbrella-, mushroom-, or anvil-shaped top to 

the convecting region (fig. 4C), analogous to a large cumulonimbus cloud. In the most energetic, high-intensity eruption 

columns, the expansion is strongly radial, and spreading may 

occur to distances of tens of kilometers upwind. Umbrella 

clouds can form in the troposphere as well as the stratosphere 

and may thus present a considerable hazard to aviation: flying upwind of a rising eruption column may not keep an aircraft out of the ash if a spreading umbrella cloud begins to 

develop. 
ASH CLOUDS: CHARACTERISTICS OF ERUPTION COLUMNS 69 

As the material rising in an eruption column slows in 

the upper part of the convective-thrust or umbrella region, 

the largest and densest particles can be no longer supported 

by the upward velocity of the column and particle fall out 

begins (Carey and Sparks, 1986; Wilson and Walker, 1987). 

Spreading of the ash also takes place into the downwind 

plume from the umbrella region, often after the umbrella 

cloud has subsided from its maximum height (Bursik and 

others, this volume). A recent discovery, based on temperatures of the tops of eruption columns measured from the data 

provided by thermal infrared sensors on weather satellites, 

has shown that the umbrella cloud may be in marked thermal 

disequilibrium with the ambient and may be undercooled by 

up to several tens of degrees Celsius (Woods and Self, 1992). 

The undercooling is due in part to the extreme adiabatic 

expansion that occurs in the umbrella region, and the denser 

umbrella region therefore tends to subside until it reaches a 

level of neutral buoyancy, from which downwind dispersal 

of ash takes place. 

As discussed above, eruption columns can also be subdivided into those that grow above maintained ( quasi-continuous) explosive venting and those that develop above 

essentially instantaneous or short-lived explosions (Wilson 

and Self, 1980). Because the all-important heat source is not 

maintained in the latter, the physics governing columns from 

instantaneous explosions is slightly different (Morton and 

others, 1956). The rise height of the isolated thermal type is 

controlled by the total mass erupted rather than the mass flux 

as is the case for the maintained eruption columns (Wilson 

and others, 1978; Woods, 1988). A simple way of distinguishing these two modes of behavior is that, in the instantaneous type, the heat source (usually explosive magma 

output) cuts off before the top ofthe column reaches its maximum height, and the column acts as a simple thermal rising 

through the atmosphere. Conversely, for the maintained 

case, the heat source lasts longer than the time taken for the 

column to reach its maximum height, but it need not be 

steady; even a series of discrete explosions spaced seconds 

to minutes apart can generate a maintained column because 

rise times to maximum elevations are generally of the order 

of minutes to tens of minutes. 

In an attempt to express some of these theoretical considerations as information of use to aviation, we next place 

the various characteristics and scales of eruption columns 

into a global context according to explosive eruption type 

and frequency of occurrence. 

FREQUENCY AND TYPES OF 

EXPLOSIVE ERUPTIONS 

Of most importance to aviation are, (1) the height that 

columns can reach and then disperse their load of ash into the 

prevailing winds, (2) the column rise rates, (3) the content of 

fine ash that may be suspended or falling in the atmosphere 

for considerable distances or periods, and (4) the duration of 

the ash clouds. This information has been combined into 

table 1, which gives a simple breakdown into the more common eruption types, Hawaiian, Strombolian and small Vulcanian, with an average frequency of 5-10 eruptions per yr; 

the less frequent ones, such as sub-Plinian to small Plinian, 

larger Vulcanian, and phreatomagmatic eruptions, with 1-2 

eruptions per yr; and the rarer types, including major Plinian 

and large co-ignimbrite ash-cloud-forming eruptions with, 

on average, less than 1-2 eruptions per decade. Although 

quite common, phreatomagmatic eruptions, in which magma 

mixes explosively with surface or subsurface water, have not 

been mentioned before because their eruption columns are 

broadly similar but less well understood than dryer, dominantly magmatic ones (Wilson, this volume). Table 1 is 

based on years of volcanological observation and study of 

erupting volcanoes and their deposits and is necessarily a 

summary. 

Almost all types of eruption columns can inject ash to 

sufficient heights to be hazardous to aircraft, so even modest 

eruptions pose a potential danger (Simkins, this volume). 

The largest eruptions, with the biggest columns, although 

potentially the most dangerous, are also the rarest. The most 

common eruptions, the Hawaiian and Strombolian type, produce little fine ash and usually present no danger to aviation 

in general. However, their ash-producing capabilities should 

not be underestimated for aircraft venturing close to the 

eruption. For instance, the 1973 Strombolian eruption at 

Heimaey, Iceland, produced fine ash-laden clouds that rose 

to 30,000 ft during 1- to 2-day periods several times during 

its 3-month-long eruption. 

A schematic view of the distribution of hazards to aircraft from explosive eruptions of three selected frequencies 

is given in figure 5. These intervals also broadly correspond 

to certain magnitudes (equivalent to bulk volume of magma 

released) and types of eruptions, as shown on table 2. 

SPECIFIC ERUPTION TYPES 

GROUPED BY COLUMN HEIGHT 

COLUMNS EXCEEDING 39,000 FEET (12 KM) 

Such columns issue from Vulcanian and violent 

Strombolian (Walker, 1973) eruptions and from 

phreatomagmatic eruption columns that may rise above 

vents in shallow seas or lake water or on glacier-clad volcanoes. Many but not all result from instantaneous to intermittent explosions and, thus, behave as isolated thermals. 

The columns generally display normal buoyancy characteristics but can be superbuoyant; these columns seldom 

extend far above the tropopause. Often they are affected by 

the wind due to the relatively slow velocities of convection 

and become inclined (fig. 4A). Umbrella regions can 

develop at the tops of these columns, and during the recent 

1989-90 eruption of Redoubt, several examples were 
70 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Summary of characteristics of volcanic eruption columns. 

[Rise velocities given are for convective-thrust region. Ash content refers to amount of material< 2 mm in diameter. See table 1 in Heiken (this 

volume) for further characteristics of explosive eruptions] 

Eruption type: Hawaiian/Strombolian 

Global frequency per year: 5-10. 

Maximum height I width (in thousands of feet): 26-33 I 7-13. 

Average rise rate (in feet per second): 15-35. 

Duration (in hours); continuity: 10-1,000's; intermittent to semicontinuous. 

Ash content: Low to moderate. 

Other features: "Dry," volatile-bearing column; few fine particles; may be difficult to detect visually. 

Recent examples: Kilauea, 1983-86; Pacaya, 1990; Oshima, 1986; Stromboli, continuous. 

Potential hazard to aviation: Low. 

Eruption type: Surtseyan (phreatomagmatic) 

Global frequency per year: 1-2. 

Maximum height I width (in thousands of feet): 26-39 I 13-20. 

Average rise rate (in feet per second): 15-35. 

Duration (in hours); continuity: 10-1,000's; intermittent to semicontinuous. 

Ash content: High. 

Other features: Wet, steam-laden columns; ash rich; much aggregation of particles. 

Recent examples: White Island, 1976-82; Ukinrek, 1977; Surtsey, 1963-65. 

Potential hazard to aviation: Medium locally. 

Eruption type: Vulcanian 

Global frequency per year: > 10. 

Maximum height I width (in thousands of feet): 32-62 I 20-32. 

Average rise rate (in feet per second): 50-260. 

Duration (in hours); continuity: 5-lOO's; extremely spasmodic to semicontinuous. 

Ash content: Moderate to high. 

Other features: Very common; widely variable style of activity; associated with small ash flows. 

Recent examples: Redoubt, 1989-90; Sakurajima, continuous; Fuego, 1974-79. 

Potential hazard to aviation: High locally, moderate regionally. 

Eruption type: Sub-Plinian to Plinian (including phreatomagmatic) 

Global frequency per year: 0.1-1. 

Maximum height I width (in thousands of feet): 39 to> 150 I 32-260. 

Average rise rate (in feet per second): 65-233. 

Duration (in hours); continuity: < 1 to 200; semicontinuous to continuous. 

Ash content: Moderate to high. 

Other features: Coarse and fine particles in high column; often short-lived but maintained. 

Recent examples: Hekla, 1991; Mount St. Helens, 1980. 

Potential hazard to aviation: High over large regions. 

Eruption type: Ash flow, co-ignimbrite ash cloud 

Global frequency per year: < 0.1 . 

Maximum height I width (in thousands of feet): 39 to> 130 I 262-490. 

Average rise rate (in feet per second): 260-650. 

Duration (in hours); continuity: a few(?) to 100(?); semicontinuous to continuous. 

Ash content: High. 

Other features: Very high rise rates; large magnitude; infrequent. 

Recent examples: Small: Mount St. Helens, 1980; Pinatubo, 1991. Large: Katmai, 1912. 

Potential hazard to aviation: High over large regions. 
Side View 

Top View 

ASH CLOUDS: CHARACTERISTICS OF ERUPTION COLUMNS 71 

Major Plinian/ashflow 

eruption with recurrence 

interval of 20 years 

Vu lean ian/sub-PI in ian 

eruption with recurrence 

interval of one year 

Vu lean ian/Su rtseyan/ 

Strombolian eruption 

>10 per year 

0 10 KILOMETERS 

Ash content and 

local turbulence 

Extension, with time, 

in wind direction 

Vertical 

velocity 

/ ' t, ) High 

- Extreme (_:1 Very high 

• Extreme 

Figure 5. Schematic diagram showing the distribution of hazards to aircraft around explosive eruption columns of three selected frequencies. Upper diagram is sectional view; lower diagram is plan view. Vertical and horizontal scales are equal. 
72 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 2. Approximate recurrence intervals and bulk volumes of 

magma released for various eruption types. 

Approximate Eruption Amount of 

interval type magma (km3

) 

1 per 20 years .. .. .... Major Plinian/ignimbrite ............ > 2-4 

1 per year ...... .. ...... Large Vulcanian or 

small sub-Plinian .. ..................... 0.5-2 

10 per year .. .... ... ... Small Vulcanian, Strombolian, phreatomagmatic .............. 0. 5 

carefully monitored and observed (Woods and Kienle, in 

press). As mentioned above, some of these were co-ignimbrite ash clouds that rose off small pyroclastic flows and 

reached only 40,000 ft. 

Eruptions producing these columns can be short-lived, 

but many last for weeks to months, during which time material is vented sporadically. They may have a single or several 

climactic phases when maintained columns are generated for 

periods of up to a few hours, as in the Redoubt case. The 

mechanisms of magma fragmentation, including generation 

of fine ash by explosive mixing with water in the 

phreatomagmatic examples, usually lead to a very high content of fine ash (Heiken, this volume). Because some of these 

eruptions last for months to years and due to their intermittent nature and the unpredictable generation of rapidly rising 

columns, they loom large in the list of those that have caused 

aircraft-ash cloud encounters, for example, Galunggung 

(1982-83) and Redoubt (1989-90). 

COLUMNS EXCEEDING 50,000 FEET (15 KM) 

These large columns include those of maintained Vulcanian and Plinian eruptions (fig. 4B) and co-ignimbrite ash 

clouds that rise off pyroclastic flows. The columns are generally maintained, except for some co-ignimbrite ash clouds, 

which rise rapidly to great heights and then disperse ash into 

the ambient wind field. An example of the latter occurred in 

early stages of the May 18, 1980, Mount St. Helens eruption 

(fig. 4C), when a giant umbrella cloud rose off the whole 

area covered by the blast flow (a kind of pyroclastic flow) 

and formed a co-ignimbrite thermal that rose from a few 

thousand feet to 88,000 ft in about 4 minutes (Sparks and 

others, 1986; Woods and Self, 1992; Bursik and others, this 

volume). Within another 3 minutes, the umbrella cloud 

spread laterally to occupy an area of over 3,000 mi2, including pushing some 15 mi upwind at the 60,000-70,000-ft 

level. The spectacular rise rate demonstrated by the Mount 

St. Helens example is not unusual for large Vulcanian, Plinian, and co-ignimbrite columns. Indeed, rise rates in excess 

of 650 ft/s (200 m/s) are estimated by models for the highest 

intensity columns (Woods and Wohletz, 1991). 

Umbrella regions of eruption columns can cover 

immense areas; we have recently experienced the giant cloud 

from the large Plinian eruption of Mount Pinatubo on Luzon 

in the Philippines, which on June 15-16, 1991, attained a 

diameter in excess of 800 mi and an area of about 520,000 

mi2 (Global Volcanism Network, 1991a; S. Self, University 

of Hawaii, unpub. data). This cloud was the result of a combination of a Plinian eruption column reinforced by co-ignimbrite ash clouds. 

In eruptions that produce very high columns, fine ash is 

generated in great abundance and fallout occurs from both 

the umbrella region and downwind plume for hundreds to 

thousands of miles over a period of many hours to a few 

days. The record of historic volcanism suggests that such 

high-intensity eruption columns are short-lived, usually lasting for less than a couple of days, and ash avoidance is simply a matter of waiting this period out. However, as the 

Pinatubo eruption has shown, pre- and post-climactic explosions, either from vents or from secondary explosive activity 

in freshly deposited pyroclastic flows, may produce periodic 

ash columns of the isolated-thermal type that attain heights 

of 30,000-50,000 ft. In many cases, post-climactic activity 

lasts for several weeks to months. 

A WORD ABOUT EXTREMES 

There are several interesting and potentially dangerous 

aspects of eruption columns that we have not discussed. 

Some of these are briefly mentioned here while discussing 

the extremes of the spectrum of explosive eruptive phenomena. Thankfully, most of these features are rare. 

Maximum column heights probably reach about 

160,000 ft (50 km) above the Earth because of the combined 

effects of drag on the huge ash-cloud system and the steadily 

warming stratosphere, which limits buoyant rise. In recent 

historic events, the Plinian and co-ignimbrite ash columns 

from the Tambora 1815 eruption probably reached about 

130,000 ft (40 km) altitude, as perhaps did the same types of 

clouds from Krakatau in 1883 (Rampino and Self, 1982; 

Carey and Sigurdsson, 1989). The 1956 Bezymianny eruption in Kamchatka produced a short-lived column, similar in 

type to the Mount St. Helens umbrella cloud described 

above, that is purported to have reached 148,000 ft (45 km) 

(Gorshkov, 1959), and the Pinatubo giant cloud reached at 

least 98,000 ft (30 km), although its maximum elevation is 

yet to be determined. 

Despite the fact that the great altitudes attained by some 

eruption columns are well above the limits of aircraft, an 

important corollary of the great heights is that the fallout of 
ASH CLOUDS: CHARACTERISTICS OF ERUPTION COLUMNS 73 

ash from such clouds will cover enormous areas. Large Plinian and co-ignimbrite umbrella ash clouds may cover more 

than 1 million mi2; we alluded above to the half-million-mi2 

coverage of the Pinatubo cloud. Fallout downwind from 

such clouds could occur over continent- or ocean-sized 

areas. If clouds of these dimensions were to occur in an area 

of concentrated air traffic, such as over Europe from a large 

eruption in southern Italy or, less likely, over the continental 

United States from a large eruption in the Cascades, then 

there would be total disruption of air traffic until the cloud 

dispersed or was carried away from the region and fallout 

ceased. Moreover, because a few inches of ash can collect on 

the ground over the entire area encompassed by giant ash 

clouds, the impact on regions with many airports may be 

crippling. 

Large Vulcanian explosions can generate strong shock 

waves around the eruption column (Nairn, 1976) because the 

initial exit velocities are supersonic (> 340 m/s at sea level). 

In recent eruptions, shock waves have not been propagated 

large distances. However, in past eruptions, most notably 

Krakatau 1883, shock waves, manifested as great explosions, dissipated over distances of hundreds to perhaps thousands of miles (Francis and Self, 1983). Quite how these 

shock waves were generated is not known, and it is also not 

known what damage they might cause to an aircraft because 

the characteristics of the shock front are unexplored. 

SUMMARY 

Volcanic ash reaches altitudes where it is dangerous to 

aircraft by rising in eruption columns. The dominant process 

in the columns is thermal convection, driven by the release 

of heat from the erupting magma, and the most significant 

part of a column in terms of controlling its height is the convective-thrust region. There is a size spectrum of eruption 

columns, ranging from low ones above Hawaiian-type fire 

fountains to huge Plinian and co-ignimbrite ones that can 

reach well over 100,000 ft in altitude. At the upper end of 

many columns, ash is spread over a wide area in the umbrella 

region, which gradually subsides and becomes extended 

downwind to form the ash plume. Most eruption columns, 

even those from small eruptions, can reach altitudes where 

the ash dispersed from them will constitute a hazard to commercial and military air traffic. 

This review does not consider the deleterious effects of 

ash encountered by flying aircraft, which is a main theme of 

this volume. However, one aspect that should not be overlooked is the fate of the volcanic gases that rise in the column 

and are dispersed with the ash plume. Some of these species, 

especially sulfur dioxide, form acid aerosols that have longer 

residence times in the atmosphere than the much denser silicate ash particles-these aerosols are essentially invisible. 

Aircraft that have inadvertently flown through aerosol 

clouds in the troposphere and lower stratosphere have sustained serious damage, particularly window crazing. Several 

incidents occurred in the months after the March-April 1982 

El Chichon eruption in Mexico (Williams, 1989). 

RECOMMENDATIONS 

It is difficult to identify the most significant type of 

eruption in terms of hazard to aircraft; commercial and military aviation should be concerned about ash clouds from all 

types of explosive eruptions. However, for several reasons, 

Vulcanian eruptions probably pose the most significant 

threat. They are common (> 10 per yr), and the eruption columns are loaded with fine ash; the eruption columns can 

reach up to 65,000 ft, well above flight corridors. During an 

eruptive episode, explosions can occur without warning and 

produce rapidly rising columns. Vulcanian eruptive episodes 

may last for weeks, months, or even years, e.g., Sakurajima 

in Japan. Since 1955, this volcano has been continually 

active in a mode of intermittent explosions, each explosion 

generating a simple thermal. In August 1991, an explosion at 

Sakurajima caused an ash-encounter incident with an aircraft 

(Global Volcanism Network, 1991b; Onodera and Kamo, 

this volume). Several examples of this type of eruption, 

be~ides Sakurajima, are already notorious in the aviation 

community, namely Galunggung, Redoubt, and Unzen. 

ACKNOWLEDGMENTS 

We thank Andrew W. Woods and Peter W. Francis for 

useful discussions, Marcus I. Bursik and Thomas J. Casadevall for encouraging us to contribute to the First International 

Conference on Volcanic Ash and Aviation Safely and to 

write this article. This is School of Earth Science and Technology (SO EST) contribution number 2944. 

REFERENCES CITED 

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collapsing eruption columns: Journal ofVolcanology and Geothermal Research, v. 45, p. 347-350. 

Carey, S.N., and Sigurdsson, H., 1989, The intensity of Plinian 

eruption columns: Bulletin of Volcanology, v. 51, p. 28-40. 

Carey, S.N., and Sparks, R.S.J., 1986, Quantitative models of the 

fall out and dispersal of tephra from volcanic eruption columns: Bulletin of Volcanology, v. 48, p. 109-125. 

Francis, P.W., and Self, S., 1983, The eruption ofKrakatau: Scientist America, v. 249, p. 172-187. 
74 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Gorshkov, G.S., 1959, Gigantic eruption of the volcano 

Bezymianny: Bulletin of Volcanology, v. 20, p. 77-109. 

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---1991 b, Bulletin of the Global Volcanism Network, Smithsonian Institution, v. 16, no. 7, p. 10. 

McGetchin, T.R., and Ulrich, G.W., 1973, Xenoliths in maars and 

diatremes with inferences for Moon, Mars, and Venus: Journal 

of Geophysical Research, v. 78, p. 1832-1853. 

Morton, B., Taylor, G.I., and Turner, J.S., 1956, Turbulent gravitational convection from maintained and instantaneous sources: 

Proceeding of the Royal Society, v. 225, p. 1-23. 

Nairn, LA., 1976, Atmospheric shock waves and condensation 

clouds from Ngauruhoe explosive eruptions: Nature, v. 259, p. 

190-192. 

Rampino, M.R., and Self, S., 1982, Historical eruptions ofT am bora 

(1815), Krakatau ( 1883) and Agung (1963), their stratospheric 

aerosols, and climatic impact: Quaternary Research, v. 18, p. 

127-143. 

Rose, W.I., 1986, Interaction of aircraft and explosive eruption 

clouds: A volcanologist's perspective. American Institute of 

Aeronautics and Astronautics Journal, v. 25, p. 52-58. 

Scott, W.E., and R.G. McGimsey, in press, Character, mass, distribution, and origin of tephra-fall deposits of the 1989-1990 

eruption of Redoubt Volcano: Journal of Volcanology and 

Geothermal Research. 

Sparks, R.S.J., 1986, The dimensions and dynamics of volcanic 

eruption columns: Bulletin of Volcanology, v. 48, p. 3-15. 

Sparks, R.S.J., Moore, J.G., and Rice, C.J., 1986, The initial giant 

umbrella cloud of Mount St. Helens: Journal of Volcanology 

and Geothermal Research, v. 28, p. 257-274. 

Stothers, R.S., Wolff, J.A., Self, S., and Rampino, M.R., 1986, Basaltic fissure eruptions, plume heights, and atmospheric aerosols: Geophysical Research Letters, v. 13, p. 725-728. 

Walker, G.P.L., 1973, Explosive volcanic eruptions-A new classification scheme: Geologische Rundschau, v. 62, p. 431-446. 

Williams, R., 1989, The crazy windows: American Heritage oflnvention and Technology [General Motors], Winter 1989, p. 64. 

Wilson, L., 1976, Explosive volcanic eruptions III-Plinian eruption columns: Geophysical Journal of the Royal Astronomical 

Society, v. 45, p. 543-556. 

Wilson, L., and Self, S., 1980, Volcanic eruption clouds: Density, 

temperature, and particle content estimates from cloud motion: 

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Wilson, L., Sparks, R.S.J., Huang, T.C., and Watkins, N.D., 1978, 

The control of eruption column heights by eruption energetics 

and dynamics: Journal of Geophysical Research, v. 83, p. 

1829-1836. 

Wilson, L., and Walker, G.P.L., 1987, Explosive volcanic eruptions 

IV-Ejecta dispersal in Plinian eruptions, the control of eruption conditions and atmospheric properties: Geophysical Journal of the Royal Astronomical Society, v. 89, p. 651-679. 

Woods, A.W., 1988, The fluid dynamics and thermodynamics of 

Plinian eruption columns: Bulletin of Volcanology, v. 50, p. 

169-193. 

Woods, A.W., and Bursik, M.I., 1991, Particle fallout, thermal disequilibrium and volcanic plumes: Bulletin of Volcanology, v. 

53, p. 559-570. 

Woods, A.W., and Kienle, J., in press, The dynamics and thermodynamics of volcanic clouds: Theory and observations from 

the April 15 and 21 eruptions of Redoubt Volcano, Alaska: 

Journal of Volcanology and Geothermal Research. 

Woods, A. W., and Self, S., 1992, Thermal disequilibrium at the top 

of volcanic clouds and its effect on the estimation of cloud 

heights: Nature, v. 355, p. 628-630. 

Woods, A.W., and Wohletz, K., 1991, Dimensions and dynamics of 

coignimbrite eruption columns: Nature, v. 350, p. 225-227. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANOES: THEIR OCCURRENCE 

AND GEOGRAPHY 

By Tom Simkin 

ABSTRACT 

The explosive volcanoes that threaten air safety 

tend to be arranged in long, linear belts near boundaries 

where crustal plates are converging. These belts cover less 

than 0.6 percent of the Earth's surface. At least 1,300 volcanoes have erupted in the last 10,000 years and, because the 

lifetimes of most volcanoes are very long, they are likely to 

erupt again in the future. Among these 1,300 volcanoes, 

however, only about 60 are active in a typical year, and that 

activity may range from the mild pyrotechnics of Italy's 

Stromboli to prehistoric catastrophes that dwarf recent eruptions such as Mount St. Helens, 1980; Krakatau, 1883; or 

Pinatubo, 1991. Like earthquakes, the bigger eruptions happen less often than the smaller, with St.-Helens-sized events 

occurring perhaps once per decade and events such as Ruiz, 

1985, and Redoubt, 1989, several times a year. During the 

years 1975-85, more than 63 eruptions penetrated the altitude range of air traffic and at least nine passed into the 

stratosphere where volcanic products are easily dispersed 

around the world. 

Eruption durations are often not recorded historically, but they are known to range from minutes to thousands 

of years. The median duration is 7 weeks, and few eruptions 

last longer than 3 years. Pulses of activity mark all but the 

shortest eruptions, and the paroxysmal event may come at 

any time from the first day (as occurs in 45 percent of all 

eruptions) to months or even years after the start of eruption. 

Of particular importance for volcano hazards is the fact that 

unusually violent eruptions commonly occur after unusually 

long periods of repose. The historic record in many parts of 

the world is far shorter than the hundreds or thousands of 

quiet years that precede violent eruptions, meaning that 

some of our most dangerous volcanoes may be those not currently recognized as "active." Of the 16 largest explosive 

eruptions in the 19th and 20th centuries, all but four were the 

first historic eruption known from the volcano. These factors 

emphasize the importance of communicating reports of new 

eruptions. We at the Smithsonian hope for more news from 

"eyes in the sky" and will do our best to disseminate volcano 

reports as we have been doing for nearly a quarter century. 

INTRODUCTION 

Anyone interested in keeping aircraft separated 

from erupting volcanoes needs to know where volcanoes are, 

what they do, and how often they do it. This paper will 

attempt to answer these questions, while admitting at the outset that the more fundamental questions-what is the schedule of forthcoming eruptions?-simply cannot be answered. 

For nearly a quarter of a century, however, our group at the 

Smithsonian has been gathering data on both current volcanism (McClelland and others, 1989) and earlier activity of 

the last 10,000 years (Simkin and others, 1981 ). These two 

allied programs offer useful background for anticipating the 

volcanic activity that is likely in the years ahead. 

VOLCANO GEOGRAPHY AND 

FORMATION 

The distribution of known volcanoes is shown in 

figure 1. These volcanoes are on land or in sufficiently shallow water that their geologically recent eruptive activity has 

been recognized by humans. They are the volcanoes that 

pose potential threats to aviation, but the reader who is also 

interested in the way the Earth works should keep in mind 

that they make up only a small proportion of the world's true 

volcano population. Calculated total amounts oflava reaching the Earth's surface each year (Crisp, 1984) suggest that 

nearly four-fifths of this lava is erupted on the deep ocean 

floor, at or near the oceanic rifts where the Earth's plates are 

moving away from each other. Very little is known about 

this style of volcanism, nearly all of which passes unnoticed 

by humans, but it is largely non-explosive and insulated from 

even the lowest flying aircraft by more than 1,000 m of sea 

water. 

About 1,300 volcanoes are shown in figure. 1: 

roughly one-half have had historically documented eruptions 

(a common definition of the word "active"), and all are 

believed to have erupted within the last 10,000 years. Some 

are geographically scattered, but most are strongly concentrated in linear belts. These cover less than 1 percent of 

75 
76 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Earth's surface but account for 94 percent of all historic 

eruptions. Readers familiar with the concept of plate tectonics will recognize that these volcanic belts mark the boundaries between major crustal plates. Most of the belts shown 

in figure 1 lie near deep oceanic trenches, where a thinner 

oceanic plate descends under an overriding plate. The volcanoes are roughly 100-200 km above an inclined earthquake zone that traces the downward path of the oceanic 

plate. This tectonic setting is important to understanding 

volcanoes because fluids that rise from this down-going slab 

induce melting in the overlying plate, thereby forming molten rock, or magma. On its path upward toward the Earth's 

surface, magma often stops along the way, where some of it 

may cool and crystallize or cause melting of surrounding 

rocks. This slow, complex, and varied route to the surface 

yields diverse, ever-changing magma compositions at different places and times. It should come as no surprise, then, that 

the resulting types and sizes of eruptions are complex and 

varied: they are therefore notoriously difficult to predict, 

even when warning signs are recognized. 

Before reaching the surface, magma commonly 

forms large, irregularly shaped chambers or reservoirs only 

6-8 km below the surface. Here it may reside for tens to perhaps even millions of years in apparent quiescence. During 

this time, however, cooling and crystallization relentlessly 

change the magmas to ever more explosive compositions. 

The remaining liquid becomes richer in volatile components 

such as water, carbon dioxide, and sulfur dioxide, increasing 

pressures within the chamber. A variety of triggers may 

eventually drive the magma upward toward the surface. 

Nearly all magmas formed in this converging-plate-margin 

setting are sufficiently gas rich and viscous that, within a few 

kilometers of the surface, the final depressurization drives 

the gas/liquid mixture violently upward, as a carbonated 

beverage leaving a quickly uncorked container. The liquid 

is exploded into countless fragments. These fragments, 

called volcanic ash, are then carried high into the atmosphere 

by expanding volcanic gases. This generalized description 

may explain why volcano repose periods can be very long, 

particularly on a scale of human lifetimes, and why the 

longer periods of apparent quiescence are often broken by 

unusually violent eruptions. In many parts of the world, the 

historic record is very short, relative to the lengths of 

volcanic repose periods. Thus the distinction drawn in 

Figure 1. Global volcano distribution. Open triangles represent volcanoes believed to have erupted within the last 10,000 years, and 

filled triangles indicate those that have erupted within the 20th century. Volcanoes with uncertain status are not shown. Readers interested 

in more detail (plus the relationship to the world's earthquakes and physiography) are referred to the 1xl.5-m wall map, "This Dynamic 

Planet," available from the U.S. Geological Survey (Simkin and others, 1989), or the more detailed information in the forthcoming second 

edition of the Smithsonian publication, "Volcanoes of the World" (first edition is McClelland and others, 1989). 
VOLCANOES: THEIR OCCURRENCE AND GEOGRAPHY 77 

figure 1-between volcanoes that have erupted this century 

and those with lesser evidence for eruptions in the last 

10,000 years-should not be misleading: all volcanoes must 

be considered potentially dangerous. 

The above attempt to describe how volcanoes work 

has focused on those near converging plate boundaries. Volcanoes occur in other tectonic settings, and their processes 

differ accordingly, but these differences will not be 

described here because it is the converging-plate-boundary 

setting that poses by far the greatest volcanic threat to air 

safety. As mentioned above, volcanoes at diverging plate 

boundaries are largely on the sea floor, emerging above the 

oceans in only a few places like Iceland. Volcanoes in the 

interior of tectonic plates-the so-called "hot-spots"-make 

up only a small proportion of the worlds' volcano population. Those in continental interiors tend to have exceedingly 

long repose periods but are capable of enormous damage (an 

eruption of Yellowstone caldera 2 million years ago, for 

example, produced more than 2,500 km3 of tephra, dwarfing 

the largest eruptions of history). Volcanoes in the interior of 

oceanic plates, like Hawaii, tend to erupt low-viscosity lava 

flows rather than explosive ash; therefore, they present a relatively low threat to aircraft. 

ERUPTION FREQUENCY AND 

MAGNITUDE 

Eruption reporting has historically depended both 

on human observers and on documentation in the scientific 

literature. We believe that the apparent increase in volcanism during the last 200 years (fig. 2) represents increased 

reporting-more observers, in wider geographic distribution, with better communication, and broader publication-rather than any significant change in the planet's rate 

of volcanism (Simkin and others, 1981). In particular, note: 

(1) that the number of active volcanoes has leveled off 

between 60 and 70 per year in the last several decades, (2) 

that the largest apparent drops in volcanism correspond precisely to the two world wars (when observers and publishers 

were otherwise preoccupied), and (3) that the apparent 

increase has been almost wholly in smaller eruptions, 

whereas the frequency of large events (product volumes 

~ 0.1 km3, and less likely to be missed at a distance) has 

changed little in the last 120 years. 

The lower plot on figure 2 raises the important point 

that eruption size varies, as most aspects of volcanism, over 

a very large range. A 1977 eruption in Iceland produced a 

carefully measured 26 m3 of lava (a significant fraction of 

which has been used for scientific study), whereas the largest 

historic eruption, that of Indonesia's Tam bora in 1815, produced over 150 billion m3 (or 150 km3) (Sigurdsson and 

Carey, 1989). Volcanology does not have an instrumentally 

determined magnitude scale to measure bigness, as the Richter scale that is used for earthquakes. Although global satelc:r: 

<( 

LU 80 >-

c:: 

LU 

c.. 

LU 

> 60 i= 

u 

<( 

(/) 

LU 

0 40 

z 

<( 

u 

_J 

0 

> 20 u.. 3 0 

c:r: 2 

LU 

aJ 

~ 

:::> 1850 1900 1950 

z 

YEAR 

Figure 2. Volcanic activity since 1790. The dark line superimposed on the annual counts of active volcanoes is a 1 0-year running 

average, to show general trends. The lower plot, with expanded 

scale on the right, shows only larger eruptions with tephra volumes 

of~ 0.1 km3 (VEl~ 4). 

lite monitoring allows measurement of total S02 for specific 

eruptions (Krueger and others, this volume), this capability 

has existed only since late 1978. To allow quantification 

through use of the historic and geologic record, the volcanic 

explosivity index (VEl) was developed by Newhall and Self 

(1982). The VEl is based primarily on volume of explosive 

products (called tephra, estimated or measured after the 

event) but also utilizes eruptive-cloud height (available for 

many witnessed eruptions) and more qualitative indicators 

as necessary. In a manner similar to the Richter scale, the 

VEl advances by single integers, each indicating a volume 

increase of roughly 1 0 times over the previous number. We 

have incorporated the VEl wherever possible with the 7,656 

dated eruptions in our volcano database and find that, again 

like earthquakes, there are many more small ones than large 

(Simkin and others, 1981; McClelland and others, 1989). 

We estimate that, on the average, eruptions with VEl ~ 2 (at 

least 106m3 of tephra) take place somewhere on Earth every 

few weeks. Those producing 107 m3 of tephra (VEl~ 3, 

such as Colombia's Ruiz eruption, which generated such 

fatal mudflows in 1985) take place several times per year. 

Eruptions with VEl ~ 5, such as Mount St. Helens, 1980 

(eruptions with~ 109 m3, or 1 km3, of tephra), occur perhaps 

once per decade, and those such as Krakatau, 1883 (VEl 6, 

or~ 10 km3 of tephra), occur on the order of once per century. Eruptions of special significance to this symposium-Redoubt, 1989; Galunggung, 1982; and Pinatubo, 

1991-are currently rated at VEl 3, 4, and 6, respectively. 

Only one known historic event, Tambora, 1815, warrants a 

VEl 7 (~ 100 km3 of tephra), and millennia may pass, on the 

average, between eruptions of this magnitude. 
78 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

The Tambora eruption led to 92,000 deaths, and its 

globally dispersed aerosol cloud acted as a filter to reduce 

incoming solar radiation at the Earth's surface. Cooling of 

the global climate resulted, and the following summer 

brought June snowfalls in New England and widespread 

crop failures around the world. However, far larger eruptions 

are known from the prehistoric record and will cause enormous devastation when they occur again. 

Of more immediately concern for air safety considerations is the high frequency with which ash clouds reach 

altitudes used by commercial aircraft. As a part of regular 

Smithsonian reporting of global volcanic activity, we have 

tried to keep track of reported cloud heights, and in compiling the first 1 0 years of these reports (McClelland and others, 

1989) we tabulated the data shown in figure 3. During the 

years 1975-85, more than 63 ash clouds are known to have 

penetrated the 8-13-km (27,000-43,000-ft) air-traffic range. 

At least nine ash clouds passed through the tropopause into 

the stratosphere, where volcanic products are readily dispersed around the world. The fine particles that reach the 

upper atmosphere fall very slowly, assuring their presence as 

an air-traffic hazard for days after their initial eruption. Our 

1975-85 average of at least six ash clouds per year to airtraffic heights, plus the volcano distribution shown in figure 

1, gives some indication of the odds for encounters with 

commercial aircraft. 

ERUPTION DURATION 

The durations of individual eruptions, as most 

other measures of volcanic activity discussed in this review, 

cover a very broad range. Some, such as the 26 m3 of lava 

erupted from an Icelandic geothermal borehole in 1977, last 

only a few minutes, whereas others, such as Stromboli's 

long-running show north of Sicily, continue for thousands 

of years. However, the median duration of historical eruptions in the Smithsonian database is 7 weeks, and few eruptions last longer than 3 years. Pulses of activity mark all but 

the shortest eruptions, and the paroxysmal event may come 

at any time from the first day (as occurs in 45 percent of all 

27~------------------------------~= 

C/) 

c:: 

w 

1--

w 

::2: 

0 

.....J 

:;;2 20 

z 

w' 

0 

~ 

~ <t 

0 

6 ~ 10-······ 

z 

<t 

u 

.....J 

0 

> 10 100 

NUMBER OF CLOUDS: 1975-85 

1-

w 

w 

LJ... 

LJ... 

80 ° C/) 

0 

z 

<t 

C/) 

:J 

60 ~ 1-

z 

w' 

0 

40 ~ 

~ <t 

0 

:::::> 

20 g 

u 

6 

z 

<t 

0 ~ 0 

> 

Figure 3. Volcano-cloud altitudes, 1975-85. Cwnulative frequency of maximwn cloud height for each eruption during the 10-

year period. Frequency is on a logarithmic scale, with one cloud 

reaching 26 km, two clouds reaching at least 20 km, three clouds 

reaching at least 19 km, etc. Cloud heights include satellite and radar measurements, pilots' sightings, and estimates by ground observers. Some purely vapor clouds may be included in the data set, 

although our intent was to count only ash clouds. Multiple pulses of 

activity in long-running eruptions (see discussion in text under 

"Eruption Duration") are not counted because so many of these 

pulses pass unobserved-their inclusion would greatly increase the 

total nwnbers. Figure from McClelland and others (1989). 
VOLCANOES: THEIR OCCURRENCE AND GEOGRAPHY 79 

eruptions) to months or even years after the start of eruption. The dramatic event that first captured the attention of 

the airline community in 1982, Eric Moody's 13-minute 

glide over Indonesia in a powerless jumbo jet, came a full 

80 days after eruptive activity began at Galunggung 

(although less than 2 hours after local residents saw the start 

of that particular eruptive pulse). The same volcano nearly 

brought down another aircraft 19 days later and did not end 

its full eruption until 9 months after it began. This eruption 

sequence attracted virtually no international media attention 

until the aircraft incidents, even though it was of a size (VEl 

4) that occurs only about once a year. It had earlier caused 

the evacuation of 75,000 people and the deaths of 27 by 

mudflows. Clearly, attention must be paid by the airline 

community to any eruption approaching this size, and interest must continue long after its start. 

VOLCANO INFORMATION AND 

COMMUNICATION 

The airline community can stay abreast of current 

volcanic activity through the Smithsonian's Global Volcanism Network (see McClelland, this volume) and may contribute information to it as well. The larger program, of 

which this network is a part, will also continue historical 

work on past eruptions and continue to provide the data necessary to place unobtrusive volcano symbols on pilots' 

maps. Good maps will allow volcanic belts to be recognized 

and individual volcanoes identified if active. All of us who 

set foot in airplanes are interested in improving air safety, 

and we will do what we can to help. In order to improve 

understanding of volcanoes-the fundamental element in 

volcano prediction-the scientific community needs more 

information. We hope for more volcano news from "eyes in 

the sky" and will do our best to disseminate volcano reports 

as we have been doing for nearly a quarter century. Pilots can 

get information to us through the reporting form designed for 

the purpose (Fox, this volume). This information may be 

sent by telephone (202-357-1511) or fax (202-357-2476). 

ACKNOWLEDGMENTS 

It is a pleasure to acknowledge Lee Siebert's huge 

contribution to the volcano data file from which most of 

these data have been drawn and Roland Pool, who has both 

maintained the data file and constructed figures 1 and 2. The 

manuscript has benefited from reviews by Jim Luhr, Lindsay 

McClelland, Lee Siebert, Steve Brantley, and Tom 

Casadevall. 

REFERENCES CITED 

Crisp, J.A., 1984, Rates of magma emplacement and volcanic output: Journal of Volcanology and Geophysical Research, v. 20, 

p. 177-211. 

McClelland, L., Simkin, T., Summers, M., Nielsen, E., and Stein, 

T.C., 1989, Global Volcanism 1975-1985: Englewood Cliffs, 

N.J., Prentice Hall, and Washington, D.C., American Geophysical Union, 657 p. 

Newhall, C.G., and Self, S., 1982, The volcanic explosivity index 

(VEl): An estimate of explosive magnitude for historical volcanism: JournalofGeophysicalResearch, v. 87,p. 1231-1238. 

Sigurdsson, H., and Carey, S., 1989, Plinian and co-ignimbrite tephra fall from the 1815 eruption ofTambora Volcano: Bulletin 

of Volcanology, v. 51, p. 243-270. 

Sunkin, T., Siebert, L., McClelland, L., Bridge, D., Newhall, C.G., 

and Latter, J.H., 1981, Volcanoes of the World: A Regional Directory, Gazetteer, and Chronology of Volcanism During the 

Last 10,000 Years: Stroudsburg, Pa., Hutchinson Ross, 240 p. 

Simkin, T., Tilling, R.I., Taggart, J.N., Jones, W.J., and Spall, 

Henry, 1989, This dynamic planet: Volcanoes, earthquakes, 

and plate tectonics: U.S. Geological Survey and Smithsonian Institution [available from the U.S. Geological Survey 

or the Museum of Natural History, Smithsonian Institution, 

Washington, D.C.]. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

THE CONTROLS OF ERUPTION-COLUMN DYNAMICS 

ON THE INJECTION AND MASS LOADING OF 

ASH INTO THE ATMOSPHERE 

By R.S.J. Sparks, Marcus I. Bursik, Steven N. Carey, 

Andrew W. Woods, and JennieS. Gilbert 

ABSTRACT 

Eruption columns inject large masses of volcanic ash 

rapidly to levels in the atmosphere where commercial aircraft fly. An eruption column consists of three dynamic 

regions: a basal gas-thrust region, a central buoyant convective region, and an upper umbrella-cloud region where the 

column spreads out at its level of neutral buoyancy. The 

height of an eruption column is a strong function of the volumetric discharge rate of magma, which determines the flux 

of thermal energy into the atmosphere. Eruption columns 

can either be generated at a point source or can be generated 

from a large region due to buoyant ascent of ash from pyroclastic flows. Ascent velocities of volcanic columns are typically 50 to 200 m/s, resulting in rapid injection (on the order 

of a few minutes) of large concentrations of ash at heights 

where aircraft fly. The mass loadings of ash in the umbrella 

region can vary from 2,500 mg m-3 for a 7-km-high column 

(23,000 ft) to over 20,000 mg m-3 for a 40-km-high (130,000 

ft) column, with a linear variation in between. These concentrations are much higher than those known to cause serious 

problems to aircraft and engine failure. 

INTRODUCTION 

Explosive volcanic eruptions can form large plumes of 

tephra or ash and aerosols that penetrate to altitudes 

exceeding 7 km (23,000 ft), where the plumes pose hazards 

to aviation. The concentrations and grain-size distributions 

of ash particles are of particular significance to aviation 

safety because high ash concentrations (> 50 mg/m3) have 

caused engine failure (Dunn and Wade, this volume). This 

paper provides an analysis of the factors that control the 

injection rate of ash into the atmosphere and the mass loading of ash that results. The paper is a companion to one by 

Bursik and others (this volume), which considers the dispersal and sedimentation of ash from volcanic plumes and 

how concentration can be inferred from sedimentological 

data. The general physical principles that govern the structure and dynamic behavior of eruption columns are 

reviewed. We will also use available models to predict the 

mass concentrations and mass loading rates of the atmosphere for eruptions of different intensities. 

In this paper, tephra is used as a collective term for all 

kinds of volcanic ejecta, including common terms such as 

ash, pumice, scoria, lithics, crystals, rock fragments, volcanic bombs, etc. From the perspective of aviation safety, it is 

fine-grained tephra (volcanic ash) that is of interest. 

ERUPTION-COLUMN STRUCTURE 

AND DYNAMICS 

GENERAL FEATURES 

A volcanic eruption column may be conveniently 

divided into three dynamic regimes (Self and Walker, this 

volume) (fig. 1). At the base of the column, mixtures of 

tephra and gas are discharged into the atmosphere at high 

velocity. Energy for the discharge is derived from decompression, liberation of gaseous phases from the magma, and 

vaporization of meteoric water. Velocities are typically in 

the range of 100 to more than 500 m/s (Wilson, 197 6; Wilson 

and others, 1980). Explosive activity can vary from discrete 

explosions to continuous discharges. The lower part of the 

column is characterized by rapid decelerations as surrounding still air is entrained into the turbulent flow. This can be 

modeled as a momentum jet and has been termed the gasthrust region (Sparks and Wilson, 1976; Sparks, 1986). In 

many cases, the discharge pressure at the vent is above atmospheric, and the flow rapidly expands as it adjusts to atmospheric pressure (Kieffer and Sturtevant, 1984; Woods, 

1988). The flow in this region is complex, often supersonic, 

and remains poorly understood. However, the gas-thrust 

81 
82 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

region is only a small fraction of the total column height, and 

the details of the dynamic behavior in this region have little 

influence on ash dispersal, with the important exception of 

collapsing columns, which will be discussed further below. 

For many eruptions, turbulent entrainment and heating 

of surrounding air causes the column to become buoyant. 

Typically, a few hundred meters to a few kilometers above 

the vent, buoyancy forces become dominant and the column 

can be regarded as a plume (Sparks, 1986; Woods, 1988). 

The main part of the column is thus termed the convective 

region (fig. 1 ), and the energy for ascent is a result of hot 

tephra heating entrained air. Two significant features of volcanic eruption columns need emphasis. First, high eruption 

columns derive their energy from the thermal energy of the 

tephra, which is at least an order of magnitude larger than the 

kinetic energy of the explosions. Second, the bulk density of 

tephra and gas emerging from the vent is always greater than 

the surrounding atmosphere at one bar pressure so that buoyancy is entirely a consequence of turbulent entrainment and 

heating of air. 

Volcanic plumes eventually reach a level in the densitystratified atmosphere where they become neutrally buoyant. 

The momentum of the plume however causes them to ascend 

considerably farther-to a height, Ht. The cloud then subsides and spreads out as a lateral gravity flow at the height of 

neutral buoyancy to form the umbrella cloud (fig. 1). 

L.U 

> -z t:io 

L.U-

>(.!) 

zw 

oc::: 

u 

1-

C/) 

::::>z 

C:::Q 

II-(!) 

•LU 

~c::: 

(.!) 

Ht -----

THEORETICAL MODELS 

Understanding of volcanic-plume dynamics is now reasonably good and is based on the seminal work of Morton 

and others (1956) on plume fluid dynamics. Wilson and others (1978) and Settle (1978) showed that the theoretical analysis of plume ascent in a stratified environment could be 

adapted to volcanic plumes, despite their enormous scale. 

They proposed that the column height, H1 (in meters), was 

directly proportional to the volumetric discharge rate of 

magma, Q (in m3/s). 

(18) 

where 

p is the magma density, 

s the heat capacity of the magma, and 

!1T is the temperature difference between the magma and 

the atmosphere at vent level. 

The constant of 8.2 in equation 1 is derived by taking Morton and others' (1956) theoretical results for a standard 

atmosphere with a temperature gradient of 6.5°C/km. 

Observations (fig. 2) show remarkably good agreement with 

equation 1 (Wilson and others, 1978; Sparks, 1986) despite 

the many complexities that might be expected in a volcanic 

plume in comparison to the simple plume analysis of 

VELOCITY 

1-

:::c 

Q 

L.U 

:::c 

DENSITY 

Figure 1. Schematic diagram of an eruption column showing three dynamic regions (after Sparks, 1986). Note the substantial overshoot 

of the column to height Ht and spread of the umbrella cloud as a gravity current at the height of neutral buoyancy, HB. 
MASS LOADING OF ASH INTO THE ATMOSPHERE 83 

Morton and others (1956). Only eruptions with discharge 

rates of 500 m3fs or greater can generate plumes with 

heights exceeding 1.5 km (25,000 ft)-these plumes reach 

altitudes sufficient to pose a hazard to intercontinental 

flights. However, smaller plumes may pose local hazards 

around airports during landing and takeoff. Typically, 

between six and 12 eruptions a year will form columns of 7 

km or more in altitude (Simkin, this volume). Most significantly, equation 1 allows a good rule of thumb for estimating the rate of mass loading of the atmosphere with volcanic 

ash from column-height observations. 

More detailed numerical models of volcanic-plume 

ascent have now been published (Wilson, 1976; Sparks and 

Wilson, 1982; Sparks, 1986; Woods, 1988; Woods and Bursik, 1991). Woods and Bursik (1991) have presented the 

most comprehensive and internally consistent model of 

plume ascent, and the following discussion is largely based 

on their results. These more detailed models show that column height is dependent on many variables. Atmospheric 

temperature structure, grain-size distribution of the ejecta, 

vent dimensions, gas compositions, discharge velocity, 

magma temperature, exit pressure, and atmospheric moisture 

content can be shown to influence column height at a fixed 

discharge rate. However, these dependencies are rather 

weak, and the numerical results are sufficiently close to 

equation 1 for heights up to 45 km (150,000 ft) so that equation 1 forms a very useful formula for interpreting columnheight observations. Indeed, the observations of heights and 

discharge rates from historic eruptions are simply not sufficiently accurate to be able to recognize many of the subtle 

effects that are apparent in the numerical results. 

50 Cf) 

a: 

w, 

1-

w 40 ~ 

0 

.....1 

S2 

~ 301-

r.: 

J: 

(!) 

:~ 20 

z 

~ 

:::> 10 .....1 

'0 

I (.) 

I 

I 

• I 

I 

I 

I 

e; 

el 

7 

~ 

., • ........ . / / 

..... / 

.--· --

I 

10 102 103 104 105 

VOLUME ERUPTION RATE, 

_!_N CU~IC METERS PER SECOND 

106 

150,000 

1-

w 

w 

u. 

z 

100,000 ~ 

(!) 

w 

J: 

z 

~ 

50,000 3 

0 

(.) 

Figure 2. Relationship of column height to volume eruption rate 

for several historic eruptions (after Wilson and others, 1978; 

Sparks, 1986). The dashed curve represents equation 1 (see text). 

Eruption columns increase in width with height due to 

turbulent entrainment of air. The numerical results of 

Woods (1988) indicate typical spreading rates (db/dz) of0.2 

to 0.25, where b is the column radius and z is the height 

above the vent. The spreading rate is approximately constant 

over most of the column height. The rather few published 

observations (e.g., Sparks and Wilson, 1976; Woods, 1988) 

show reasonable agreement with these results. Column 

velocities are high and are typically in the range of 50 to 

more than 200 m/s. Thus, eruption columns ascend to 

heights of 7 km or more in only a few minutes, giving little 

opportunity to warn aircraft at the beginning of an eruption. 

Broadly, ascent velocities increase with column height, 

reflecting the increase in intensity (i.e., discharge rate). 

From the point of view of tephra dispersal, the velocities in 

the convective region are far larger than the terminal velocities of all but the largest fragments so that almost all the 

tephra is transported efficiently to the top of the column. 

Entrainment of surrounding air creates a significant inward 

flow toward the column. At the plume edge, the radial 

inward velocities are approximately one-tenth of the ascent 

velocities (Turner, 1979; Sparks, 1986) so that inflow 

speeds of 5 to 20 m/s are typical. Only clasts exceeding several centimeters in diameter can escape from the plume margins (see Bursik and others, 1992, for a more detailed 

analysis). 

Theoretical models (Woods, 1988) assume a steady 

flow and seem to provide a good description of eruptions 

even if they are of short duration and manifestly unsteady. 

Explosive eruptions of the Soufriere de St. Vincent in 1979 

(Sparks and Wilson, 1982), Mount St. Helens in October 

1980 and Lascar Volcano, Chile, in February 1990, consisted of several discrete explosions that merged into 

plumes. In the case of Lascar, three explosions occurred in 

less than 4 minutes. Studies of photographs and movies of 

these eruptions (Sparks and Wilson, 1982, and unpublished 

student dissertations at Bristol University) show that the 

motions and structure are well described by simple plume 

theory and the model of Woods (1988). 

The umbrella cloud has an initial depth that is determined principally by the excess momentum of the plume . 

Theoretical analyses and experimental studies (Morton and 

others, 1956; Turner, 1979) suggest that the height of neutral buoyancy, HB, is related to column height, Ht, by HB = 

0.7 Ht (fig. 1). There are little published data, but observations of plumes indicate that this is a useful approximation. 

Due to momentum, the cloud rises and cools and is therefore significantly denser than its surroundings, due both to 

lower temperature and particle content. Consequently, the 

umbrella cloud spreads radially as a gravity current at a 

level centered around the height of neutral buoyancy 

(Sparks and others, 1986). 
84 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

CO-IGNIMBRITE CLOUDS 

An important category of eruption column is generated 

by a rather different mechanism. Commonly, explosive 

eruptions generate pyroclastic flows or nuees ardentes 

(glowing clouds). A pyroclastic flow is a form of gravity current that flows down the slopes of a volcano and is essentially an avalanche of tephra and gas. They can be formed by 

a mechanism known as column collapse (Sparks and Wilson, 

1976). The explosively erupted mixture does not entrain 

enough air to become buoyant and forms a collapsing fountain of tephra and gas a few hundred meters to a few kilometers high, which feeds the pyroclastic flows. Flows can also 

be generated by lateral blast, as at Mount St. Helens on May 

18, 1980 (Hoblitt and others, 1981 ). The deposits from pyroclastic flows are commonly termed ignimbrites by geologists, and the associated columns are term co-ignimbrite 

clouds. 

Pyroclastic flows can generate high columns by a process known as lift-off (Sparks and others, 1986). As the flow 

moves away from the volcano, mixing occurs with surrounding air, and particles are deposited. The hot, dilute cloud that 

is generated eventually becomes buoyant and lifts off the 

flow. In the case of the 1980 blast flow of Mount St. Helens, 

a giant cloud 25 to 30 km (80,000 to 160,000 ft) high was 

generated over an area of 600 km2 by lift-off (Sparks and 

others, 1986). The phenomena has been reproduced in laboratory experiments (Carey and others, 1988). Theoretical 

models of the process treat the co-ignimbrite cloud as a 

steady plume (Woods and Wohletz, 1991). Enormous 

amounts of fine-grained ash can be injected into the stratosphere in a very short period (a few minutes) (Sparks and 

Walker, 1982). The huge plume generated by Pinatubo in the 

Philippines on June 15, 1991, also has the features of a coignimbrite cloud. 

THE EFFECT OF WIND ON VOLCANIC 

PLUMES 

There is a great deal of engineering literature on the distortion and dispersal of industrial plumes and fire plumes by 

wind (e.g., Briggs 1969). This literature, however, is of 

rather limited use with regard to the study of powerful volcanic plumes with heights sufficiently great to emplace tephra 

either into the stratosphere or to heights that are of concern 

to aviation. Relations of plume shape, height, and wind 

velocity are empirical and have been developed for relatively 

weak plumes where ascent velocities are comparable to or 

less than wind velocities. Even a 10-km-high column is 

orders of magnitude more powerful than most industrial 

plumes and has ascent velocities that exceed typical jetstream velocities(> 30 m/s). 

Carey and Sparks (1986) classified eruption columns 

into three types. First, weak plumes (typically much less than 

10 km in height) are distorted by the wind, and the empirical 

results of industrial studies on plume shape are appropriate. 

Second, intermediate plumes ascend with little distortion by 

the wind and then mushroom into the umbrella region and 

spread somewhat upwind before the wind influences the dispersal of the cloud. The 1980 Mount St. Helens Plinian 

plume (16 to 18 km high, or approximately 55,000 ft) is a 

good example. Finally, very powerful plumes spread out 

radially in all directions as a giant gravity current in the 

umbrella region; the wind has very little influence in the initial stages of these eruptions. The 1980 cloud of Mount St. 

Helens spread to 10 km upwind (Sparks and others, 1986) 

and expanded to about 100-km diameter before downwind 

dispersal became substantial. It took only 20 minutes to 

expand to 1 00-km diameter, emphasizing the threat that a 

high-intensity eruption in its initial stages poses to aircraft. 

The 1991 Mount Pinatubo cloud is reported to have moved a 

remarkable 300 km upwind. Both of these examples of 

highly energetic plumes were co-ignimbrite clouds. 

MASS LOADING MODELS 

The December 15, 1989, incident near Redoubt Volcano, Alaska, involving a Boeing 747-400, indicated that ash 

concentrations of 2,000 mg m-3 were encountered (Dunn 

and Wade, this volume). The U.S. Military regard particle 

loadings of 50 mg/m-3 or more as potentially hazardous. We 

have, therefore, used the dynamic models described earlier 

to estimate typical concentrations of ash generated in the 

umbrella-cloud region. In the companion paper (Bursik and 

others, this volume), we consider how these concentrations 

change as the ash is dispersed away from the volcano. 

The first concern is the particle-size distribution of the 

ejecta. Reconstructions of the total grain-size distributions in 

explosive eruptions (Sparks and others, 1981; Woods and 

Bursik, 1991) indicate that typically 70 percent of the ejecta 

is less than 2 mm. Therefore, we restrict our discussion to 

considering the concentrations of the less-than-2-mm ash. 

However, such reconstructions are limited by the poor 

knowledge of the proportions of very fine ash particles(< 10 

!J.m) generated in such eruptions. Because almost all tephra 

is transported into the umbrella cloud, the concentrations 

calculated here are not sensitive to size distributions. However, the size distribution will have a strong influence on 

subsequent dispersal. 

We have first calculated mass loadings for columns 

from 9.8 to 40.5 km (32,000 to 133,000 ft) and have approximated the results of Woods (1988) together with equation 1 

to calculate the height of neutral buoyancy (HB) and the 

upward flow rate at the top of the convective region (fig. 1) 

for an eruption temperature of 1,000°C. Figure 3 shows the 

calculated mass loadings as a function of column height. All 

columns greater than 7 km high (23,000 ft) generate mass 

loadings that are at least two orders of magnitude higher than 

the U.S. Military threshold of 50 mg m-3, and all exceed the 
MASS LOADING OF ASH INTO THE ATMOSPHERE 85 

(/) 

a: 

w 

1-

w 

~ 

0 

.....J 

S2 

~ 

1-" 

I 

C!J 

w 

:r: 

z 

~ 

::::> 

.....J 

0 

() 

50 

150,000 

40 

30 100,000 

20 

50,000 

10 

0+-------~------.-----~------~ 

0 10,000 

MASS LOADING, IN MILLIGRAMS 

PER CUBIC METER 

20,000 

Iw 

w 

u. 

~ 

1-" 

I 

C!J 

w 

:r: 

z 

~ 

::::> 

.....J 

0 

() 

Figure 3. The calculated mass loadings of tephra in the umbrella 

region of eruption columns are plotted as a function of column 

height using equation 1 (see text) as an approximation. 

2,000 mg m-3 value associated with the December 15, 1989, 

Redoubt incident. Mass loading increases with column 

height because the increase in mass discharge rate has a 

greater influence than the decrease of atmospheric density in 

higher columns. 

We have further examined the variation of mass loadings with temperature and eruptive style using the numerical 

computer code developed by Woods (1988). Calculations 

have been made for a steady, maintained eruption column 

and for release of a volcanic thermal (an instantaneous 

release of buoyant fluid), as might happen when a co-ignimbrite cloud lifts off at temperatures of 1 ,200°K, 1 ,000°K, and 

800°K. These more detailed numerical calculations yield 

concentrations in general agreement with the simpler 

approach, but some interesting details are revealed. As eruption temperature decreases, the mass loading increases for a 

given column height (fig. 4A), showing that a wide range of 

loadings can occur-any ash-dispersal model should use the 

maximum mass loading condition to predict a worst case 

scenario (Harris, this volume). One other interesting feature 

of figure 4A is that the mass loading increases rapidly as column height increases for plumes that penetrate the tropopause, located at about 11 km in the present model 

calculations. This is because the overshoot distance above 

the neutral buoyancy height is reduced by the much stronger 

stratification above the tropopause,- and, hence, the material 

is not as dilute when the column comes to rest. 

Figure 4B presents similar calculations for a discrete 

volcanic thermal using the model of Woods and Kienle (in 

press). The mass loadings in volcanic thermals are similar to 

those in maintained plumes and vary with height in the same 

manner. The loadings are a little larger for a given column 

height and temperature because large thermals do not entrain 

air as efficiently as steady plumes. 

(/), 

a: 

w 

~· ~ 

0 

.....J 

S2 

~ 

z 

~ 

::::> 

.....J 

0 

() 

u. 

0 

I-

:r: 

C!J 

w 

:r: 

(/) 

a: 

20 

15 

10 

5 

0 

1,000 

A 

:1-

w 

w 

u. 

50,000 ~ 

z 

~ 

::::> 

.....J 

0 

25,000 ~ 

0 

1-

:r: 

C!J 

w 

I 

2,000 3,000 4,000 5,000 6,000 7,000 8,000 

MASS LOADING, IN MILLIGRAMS 

PER CUBtC METER 

~ 20+------~--~--~-----~----~~ 1-

w 

w 

u. 

w 

::iE 

0 

.....J 15 

S2 

~ 

o" 10 ::::> 

0 

.....J 

() 

u. 5 

0 

1-

:r: 

C!J 

w 

:r: 

B 

600"1< 

3,000 6,000 9,000 

MASS LOADING, IN MILLIGRAMS 

PER CUBIC METER 

50,000 ~ 

o" 

::::> 

0 

.....J 

() 

25,000 ~ 

12,000 

1-

:r: 

C!J 

w 

:r: 

Figure 4. Mass loadings of tephra as a function of column height 

for three different eruption temperatures using the numerical model 

of Woods (1988) for an atmosphere with the tropopause at an altitude of 11 km. A, maintained eruption columns. B, volcanic 

thennals. 

CONCLUSIONS 

Explosive volcanic eruptions are sufficiently powerful 

to inject large amounts of ash into the stratosphere. The 

injection height is determined by magma discharge rate and 

can be approximately estimated from equation 1. Explosive 

eruptions typically generate a large proportion of particles 

less than 2 mm in diameter, which are efficiently transported 

to the top part of the column known as the umbrella cloud. 

Typical mass loadings vary from 3,000 to over 20,000 mg 

m-3 for columns in the height range of> 7 to 40 km (23,000 

to 130,000 ft). 

From the perspective of aviation safety the following 

points emerge: 

1. The mass loadings greatly exceed the safety thresholds and values of concentration that cause engine 

failure. It is therefore necessary to establish how the 

mass concentrations change as the plume is 
86 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

dispersed-this problem is addressed in the companion paper (Bursik and others, this volume). 

2. Many eruptions involve fairly steady discharges of 

tephra over many hours or even days from point 

sources. Such eruptions can be monitored, and aircraft can be organized so as to avoid the plumes. 

However, shorter lived explosions and high-intensity 

eruptions can inject large masses of ash into the 

stratosphere in several minutes--once in the stratosphere, they can be dispersed rapidly by jet-stream 

winds. 

3. Co-ignimbrite clouds pose a particularly difficult 

threat because they are generated from large areas 

rather than point sources and are formed very rapidly. 

ACKNOWLEDGMENTS 

Research has been supported by the following organizations: Venture Research International (R.S.J.S. and 

J.S.G.), N.S.F. grant number EAR-8804117 (S.N.C), a 

NERC Fellowship (J.S.G.), and NATO collaborative grant 

(CRG 910096). 

REFERENCES CITED 

Briggs, G.A., 1969, Plume Rise: U.S. Atomic Energy Commission, 

SOp. 

Bursik, M.l., Sparks, R.S.J., Gilbert, J.S., and Carey, S.N., 1992, 

Sedimentation of tephra by volcanic plumes: I. Theory and its 

comparison with a study of the Fogo A Plinian deposit, Sao 

Miguel (Azores): Bulletin of Volcanology, v. 54, p. 329-344. 

Carey, S.N., Sigurdsson, H., and Sparks, R.S.J., 1988, Experimental studies of particle-laden plumes: Journal of Geophysical 

Research, v. 93, p. 15314-15328. 

Carey, S.N., and Sparks, R.S.J., 1986, Quantitative models of the 

fallout and dispersal of tephra from volcanic eruption columns: 

Bulletin of Volcanology, v. 48, p. 109-125. 

Hoblitt, R.P., Miller, C.D., and Vallance, J.W., 1981, Origin and 

stratigraphy of the deposit produced by the May 18 directed 

blast, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 

Eruptions of Mount St. Helens, Washington: U.S. Geological 

Survey Professional Paper 1250, p. 401-420. 

Kieffer, S.W., and Sturtevant, B., 1984, Laboratory studies ofvolcanic jets: Journal Geophysical Research, v. 98, p. 8253-8268. 

Morton, B.R., Taylor, G.l., and Turner, J.S., 1956, Turbulent gravitational convection from maintained and instantaneous 

sources: Transaction of the Royal Society London, ser. A, v. 

234, p.1-23. 

Settle, M., 1978, Volcanic eruption clouds and thermal power output of explosive eruptions: Journal of Volcanology and Geothermal Research, v. 3, p. 309-324. 

Sparks, R.S.J., 1986, The dimensions and dynamics of volcanic 

eruption columns: Bulletin of Volcanology, v. 48, p. 3-15. 

Sparks, R.S.J., and Walker, G.P.L., 1982, The significance ofvitric 

enriched air-fall ashes associated with crystal-enriched ignimbrites: Journal of Volcanology and Geothermal Research, v. 

28, p. 257-274. 

Sparks, R.S.J., and Wilson, L., 1976, A model for the formation of 

ignimbrite by gravitational column collapse: Journal of the 

Geological Society of London, v. 132, p. 441-451. 

---1982. Explosive volcanic eruptions, V. Observations of 

plume rise at Soufriere St. Vincent: Geophysical Journal of the 

Royal Astronomical Society, v. 69, p. 551-570. 

Sparks, R.S.J., Moore, J.G., and Rice, C.J., 1986, The initial giant 

umbrella cloud of Mount St. Helens: Journal of Volcanology 

and Geothermal Research, v. 28, p. 257-274. 

Sparks, R.S.J., Wilson, L., and Sigurdsson, H., 1981, The pyroclastic deposits of the 1875 eruption of Askja: Royal Society of 

London Philosophical Transactions, ser. A, v. 299, p. 241-273. 

Turner, J.S., 1979, Buoyancy Effects in Fluids: Cambridge, England, Cambridge University Press, 368 p. 

Wilson, L., 1976, Explosive volcanic eruptions: III-Plinian eruption columns: Geophysical Journal of the Royal Astronautical 

Society, v. 45, p. 543-556. 

Wilson, L., Sparks, R.S.J., and Walker, G.P.L., 1980, Explosive 

volcanic eruptions: IV-The control of magma properties and 

conduit geometry on eruption column behavior: Geophysical 

Journal of the Royal Astronautical Society, v. 83, p. 

1829-1836. 

Wilson, L., Sparks, R.S.J., Huang, T.C., and Watkins, N.D., 1978, 

The control of eruption column heights by eruption energetics 

and dynamics: Journal of Geophysical Research, v. 83, p. 

1829-1836. 

Woods, A.W., 1988, The thermodynamics and fluid dynamics of 

eruption columns: Bulletin ofVolcanology, v. 50, p. 169-191. 

Woods, A.W. and Bursik, M.I., 1991, Particle fallout, thermal disequilibrium and volcanic plumes: Bulletin of Volcanology, v. 

53, p. 559-572. 

Woods, A.W., and Kienle, J., in press, The dynamics and thermodynamics of volcanic clouds: Theory and observations from 

the April 15 and 21 eruptions of Redoubt Volcano, Alaska: 

Journal of Volcanology and Geothermal Research. 

Woods,A.W., and Wohletz, K., 1991, Dimensions and dynamics of 

co-ignimbrite eruption columns: Nature, v. 350, p. 225-227. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

MELTING PROPERTIES OF VOLCANIC ASH 

By Samuel E. Swanson and James E. Beget 

ABSTRACT 

Volcanic ash from eastern Aleutian volcanoes (typical 

of circum-Pacific volcanoes) is composed of rhyolitic (silica-rich) glass, minerals (feldspars, pyroxene, hornblende 

and Fe-Ti oxides), and rock fragments. Melting temperatures of the glasses, estimated from liquidus phase relations 

in the system SiOz-KAlSi308-NaAlSi30s, ranged from 

1,000°C to 1,300°C, whereas minerals begin melting at 

about 1, 1 00°C. 

Volcanic ash that is ingested into operating turbofan 

engines will partially melt (i.e., all of the glass and some of 

the minerals). The molten ash is then deposited on hightemperature parts of the turbine-this can result in engine 

shutdown. 

Reduction of engine operating conditions to idle settings lowers the engine temperatures below the melting point 

of volcanic glass (below 1,000°C), thus preventing the melting of ingested volcanic ash. However, at idle conditions, 

engines still operate at temperatures in excess of the glass 

transition temperature (700°-860°C), and annealing of glass 

particles to hot parts of the turbine may still be a problem. 

INTRODUCTION 

Volcanic ash is a widespread product of eruptions of 

volcanoes that are located around rim of the Pacific Ocean. 

Ash is formed by explosive fragmentation and quenching of 

magma (crystals + melt + gas) during an eruption. Melt in the 

magma is quenched to a glass when the temperature is rapidly lowered upon exposure to atmospheric conditions. The 

explosive character of these volcanoes is caused by the silica-rich melt, which often contains dissolved volatile components, such as HzO or S02. Crystallization of mineral 

phases (e.g., plagioclase, pyroxene, hornblende, Fe-Ti 

oxides, etc.) gradually enriches non-crystallizing components in the melt. In the case of components like silica or 

sodium, their concentrations in the crystallizing phases are 

low relative to their concentration in the melt, resulting in 

their overall enrichment. Bulk lava compositions from these 

volcanoes range from basalt to dacite (lavas generally 

contain from 48 to 70 weight percent SiOz), and the melt 

fraction between mineral grains is andesitic to rhyolitic 

(53-78 weight percent Si02). The glassy fragments in 

volcanic ash are the non-crystalline part of the magma and, 

hence, have the lowest crystallization temperature. Conversely, the glass also has the lowest melting temperature. 

When volcanic ash is ingested into operating jet aircraft 

engines, it is the glass particles that will melt first. As aircraft 

engine operating temperatures are lowered in an effort to 

reduce the ash fusion within the engine (Campbell, this volume; Casadevall and others, 1991; Przedpelski and Casadevall, this volume), it is the melting temperature of glass 

particles that will determine the operating temperatures 

below which the ash will not melt in the engine. The purpose 

of this paper is to review the compositions of glasses found 

in volcanic ashes from typical circum-Pacific volcanoes and 

to estimate their melting temperatures by comparison to published phase diagrams available in the geological and engineering literature. We report here on the melting properties 

of the more common silica-rich glasses. Mafic (andesitic) 

glass, similar to that erupted in the 1992 eruption of Mt. 

Spurr (Alaska), is currently under study and will be the subject of a future report. Alaskan volcanoes in the eastern Aleutian arc were selected for study because of their recent 

activity and potential hazard to aircraft safety (Steenblik, 

1990; Przedpelski and Casadevall, this volume; Kienle, this 

volume). Several Alaskan volcanoes in the eastern Aleutian 

arc (fig. 1) have produced widespread volcanic-ash deposits 

that have covered south-central Alaska. Ash may be produced in short-lived, large eruptions (Novarupta in 1912, 

Spurr in 1953 and 1992) or in a series of intermittent, small 

eruptions (Redoubt Volcano, 1989-90). Jet aircraft encounters with ash have been recorded from eruptions of Augustine in 1976 and Redoubt in 1989 (Steenblik, 1990; 

Casadevall, 1991; Kienle, this volume). 

METHODS OF STUDY 

All of the glass samples used in this study were 

obtained from volcanic ash deposits from south-central 

Alaska. The White River ash and the ash from Hayes 

Volcano are voluminous prehistoric ashes that covered 

south-central Alaska (Riehle, 1985; Westgate, 1990; Beget 

and others, 1991). Novarupta, which erupted in 1912, is the 

largest historic Alaskan eruption and spread ash throughout 

southern Alaska (Griggs, 1922; Hildreth, 1987). Ash from 

Augustine Volcano, the most active volcano in the eastern 

87 
88 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

156° 154° 152° 150° 

62° 

MT. HAYES 

<1<ClOO ... 0 50; MILES 

I I I I I I I I I I I 

0 50 KILOMETERS 

REDOUBT 

VOLCANO ... 

~ 

~ 

~ 

s~ GULF OF 

ALASKA 

Figure 1. Volcanoes (solid triangles) in the eastern Aleutian 

volcanic arc, Alaska. 

Aleutian arc, was collected from prehistoric deposits on 

Augustine Island that span approximately 2, 700 years of 

eruptive history (Swanson and Kienle, 1986; Beget and 

Kienle, 1992). Ash from Redoubt Volcano is represented by 

samples from the 1989-90 eruption. Together, this suite of 

samples provides a representative collection of the ashes that 

is to be expected from eruptions of these Alaskan volcanoes. 

ANALYTICAL TECHNIQUES 

Glass from these ash samples was analyzed with a 

Cameca MBX electron microprobe at Washington State 

University using a 15-kV electron beam and a sample current of 13.5 nA. A beam spot diameter of 8 !lm was used, 

and the counting time was 10 seconds. The glass analyses 

are reported as oxides and are normalized to 100 percent. 

Actual totals ranged from 98 to 100 percent, depending on 

the degree of hydration (water in the glass.) Well-characterized natural glasses were used as standards (KCl was used 

for Cl measurements). 

RESULTS 

When compared with lavas, glass particles (shards of 

quenched melt) in the volcanic ash from Alaskan volcanoes 

are much richer in silica as a consequence of crystallization 

50 

... Lavas ... .--Glass---. 

particles 

~30 

l.l.J 

(_) 

c: 

~20 

10 

0 

50 60 70 80 

A 

Si02

. IN WEIGHT PERCENT 

50 ... Lavas ... 

50 60 ~ 70 80 

Si02

• IN WEIGHT PERCENT 

B 

Figure 2. Silica contents of lavas (bulk samples) and glass particles (shards) in volcanic ashes from A, Redoubt and B, Augustine 

Volcanoes. The numbers of analyses of lavas and glasses from each 

volcano are in excess of 50 and have been normalized to I 00 percent 

for comparison. Volcanic glass i's consistently higher in silica than 

the whole-rock lavas. Glass analyses are from unpublished data in 

the authors' files (representative analyses given in table 1). Lava 

compositions for Augustine Volcano are from Kienle and others 

(1983) and Daley (1986); compositions for Redoubt Volcano are 

from Nye and others (in press) and Swanson and others (in press). 

to form phenocryst minerals before eruption. For example, 

lavas from Redoubt Volcano have basaltic and andesitic bulk 

compositions (50-64 weight percent Si02, fig. 2), whereas 

the glass in the volcanic ash from the 1989-90 eruption of 

Redoubt ranges from 69 to 78 weight percent Si02 (fig. 2). 

Similar relations are shown for Augustine Volcano (fig. 2), 

but the Augustine glasses show a more restricted range of 

compositions (75-78 weight percent Si02). 

Representative glass compositions are shown in table 1 

both as weight percent oxide and as normative minerals. The 

normative composition is the rock analysis recalculated to a 

set of standard anhydrous normative minerals. For silica-rich 

volcanic rocks or glasses, the abundant normative minerals 

are quartz (Q), albite (Ab ), and orthoclase (Or), with lesser 

amounts of anorthite (An), corundum (C), hypersthene (Hy), 
Table 1. Representative electron microprobe analyses of volcanic glass from ash from Alaskan volcanoes. 

[Analyses are presented as weight percent of oxides and as nonnative minerals (see text for explanation of nonnative minerals). Numbers in parentheses represent units of standard deviation] 

Quantity Redoubt Volcano (12/15/89) AugMstine Volcano Hayes Volcano White River ash 

anal ed 

Analyses expressed as weight percent of oxides 

Si02 69.35 (0.45) 71.91 (0.31) 75.94 (0.36) 77.81 (0.35) 75.38 (0.36) 76.36 (0.31) 73.65 (0.36) 73.77 (0.43) 

Ti02 0.51 (0.11) 0.45 (0.03) 0.31 (0.07) 0.22 (0.01) 0.39 (0.04) 0.37 (0.06) 0.23 (0.03) 0.21 (0.02) 

Alz03 15.59 (0.54) 14.75 (0.16) 13.32 (0.21) 12.40 (0.18) 12.98 (0.10) 12.58 (0.17) 14.50 (0.14) 14.54 (0.26) 

Fe20 3tota1 3.26 (0.31) 2.58 (0.14) 1.46 (0.22) 1.22 (0.09) 2.30 (0.15) 2.06 (0.12) 1.94 (0.21) 1.71 (0.14) 

MgO 0.87 (0.17) 0.67 (0.02) 0.30 (0.11) 0.23 (0.03) 0.49 (0.05) 0.43 (0.05) 0.54 (0.03) 0.36 (0.03) 

CaO 3.25 (0.29) 2.48 (0.10) 1.57 (0.25) 1.16 (0.10) 2.28 (0.27) 2.04 (0.16) 2.23 (0.10) 1.85 (0.11) 

Na20 4.37 (0.18) 4.21 (0.08) 3.92 (0.21) 3.71 (0.12) 3.95 (0.13) 3.89 (0.09) 3.93 (0.08) 4.16 (0.13) 

K20 2.54 (0.12) 2.79 (0.11) 3.04 (0.14) 3.14 (0.17) 2.00 (0.27) 1.98 (0.08) 2.62 (0.11) 3.07 (0.10) 

Cl 0.17 (0.08) 0.16 (0.02 0.15 (0.04) 0.13 (0.06) 0.24 (0.11) 0.29 (0.07) 0.36 (0.03) 0.33 (0.03) 

nl 11 7 5 7 18 16 15 15 

Analyses recast as nonnative minerals 

Q 26.04 30.43 37.69 41.38 39.13 41.14 35.18 33.32 

Or 15.01 16.49 17.97 18.56 11.82 11.70 15.48 18.14 

Ab 36.98 35.62 33.17 31.39 33.42 32.92 33.25 35.20 

An 15.70 12.30 7.7 5.75 11.31 10.12 11.06 9.18 

c 0.00 0.30 0.73 0.79 0.17 0.33 1.14 1.01 

Hy 2.17 1.67 0.75 0.57 1.22 1.07 1.34 0.90 

Hm 3.26 2.58 1.46 1.22 2.30 2.06 1.94 1.71 

Tn 0.30 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Ru 0.39 0.45 0.31 0.22 0.39 0.37 0.23 0.21 

1 Number of points per analysis, n. 

Novaruota 

78.20 (0.37) 76.94 (0.17) 

0.18 (0.06) 0.35 (0.07) 

12.00 (0.15) 12.29 (0.12) 

1.34 (0.15) 1.87 (0.13) 

0.14 (0.05) 0.26 (0.04) 

0.85 (0.19) 1.27 (0.09) 

4.07 (0.13) 3.98 (0.13) 

3.03 (0.10) 2.85 (0.08) 

0.19 (0.03) 0.19 (0.03) 

18 10 

40.90 39.77 

17.91 16.84 

34.44 33.68 

4.22 6.30 

0.48 0.35 

0.35 0.65 

1.34 1.87 

0.00 0.00 

0.18 0.35 

~ tr.l 

t"" 

~ 

z 

0 

""d 

~ 

0 

""d 

tr.l 

...... 

~ 

tr.l 

(/) 

0 

"Tj 

< 0 

t"" 

(1 

~ n 

> (/) 

::r:: 

00 

\0 
90 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Q 

EXPLANATION 

t::,. Redoubt 

• Augustine 

o Hayes 

x Novarupta 

+ White River 

AbL-----------------~----------------~or 

Figure 3. Nonnative compositions (in terms of albite, Ab; orthoclase, Or; and quartz, Q-see text for explanation) of glasses from 

the White River ash, the 1912 eruption ofNovarupta, and eruptions 

ofMt. Hayes and Augustine and Redoubt Volcanoes. The Redoubt 

data are for glasses from the 1989-90 eruption. White River, Augustine, and Hayes data are from prehistoric ashes. Mt. Hayes data are 

from Beget and others (1991); other data are from the authors' 

unpublished files. 

hematite (Hm), sphene (Tn), and rutile (Ru). The recalculation of the oxide components into normative minerals 

facilitates comparison of glass compositions to experimental 

laboratory results on melting temperatures of rocks. 

Glass compositions displayed on triangular variation 

diagrams, with normative components as the variables, cluster into fields for each suite of glasses (fig. 3). Glasses from 

single, short-lived eruptions (e.g., White River ash and 

Novarupta) cluster in small fields, whereas glasses from 

multiple eruptions (Augustine and Hayes) defme slightly 

larger fields. The 1989-90 Redoubt glasses form a range of 

compositions related to the mixing of two different magmas 

(with different compositions of melt quenched to glass) in 

the early (December 1989) stages of the eruption (Swanson 

and others, in press). 

MELTING RELATIONS OF GLASSES 

Liquidus phase relations (temperatures required to 

completely melt a solid) at a pressure of 1 bar in the system 

Si02 (quartz, Q}-KAlSi30s (orthoclase, Or}-NaAlSi30s 

(albite, Ab) are shown in figure 4. This system is well 

known to geologists as the "granite system" because of its 

use in describing the melting and crystallization behavior of 

granitic rocks. The triangular composition diagram is 

divided into primary phase fields by boundary curves. Isotherms (lighter solid lines that represent constant 

temperature) describe the melting temperatures for any 

solid that contains the normative minerals quartz, orthoclase, and albite (fig. 4). The boundary curve between the 

primary phase fields of the Si02 polymorphs cristobalite 

(Cr) and tridymite (Tr), and alkali feldspar (Af) has a temperature minimum (m, fig. 4) at 960°C. For any combination of these three normative minerals (quartz-orthoclasealbite), melting at 1 bar will initially start at 960°C, and the 

composition of the first melt will correspond to m (fig. 4). 

The incongruent melting ofK-feldspar (Or) at low pressure 

is represented by the boundary curve between alkali feldspar (At) and leucite (Lc) phase fields (fig. 4). The small 

(10-20 bar) pressure increase within operating turbofan 

engines does ·little to change the 1 bar melting relations of 

figure 4. 

In addition to the albite (Ab ), orthoclase (Or), and 

quartz (Q) components, the volcanic glasses contain appreciable normative anorthite (An) (table 1 ). Addition of the 

anorthite component raises the melting temperatures relative 

to the anorthite-free albite-orthoclase-quartz compositions; 

however, the magnitude of this effect is difficult to predict, 

especially for this system without water. Experiments done 

on ingestion of dust containing appreciable anorthite component along with albite, orthoclase, and quartz into operating 

jet engines find that ash begins to melt at temperatures of 

about 1,000°C (Kim and others, 1992). These results are in 

good agreement with the predictions from figure 4, where 

Figure 4. Liquidus phase diagram for the system Ab-Or-Q at one 

bar pressure, modified from Schairer (1950). Heavy lines are 

boundary curves with arrows indicating the direction to lower temperature. Primary phase fields are shown for cristobalite (Cr), 

tridymite (Tr), alkali feldspar (At), and 1eucite (Lc). Symbol, m, indicates temperature minimum on boundary curve between cristobalite/tridymite and alkali feldspar. See text for further explanation. 
MELTING PROPERTIES OF VOLCANIC ASH 91 

the beginning of melting for anorthite-free compositions 

occurs at 960°C. Thus, the effect of anorthite on melting 

relations seems small and is probably on the order of less 

than 50°C. Melting of any volcanic glass that contains normative quartz, orthoclase, and albite can be modeled in the 

system albite-orthoclase-quartz, as illustrated for the glasses 

in this study on figure 5. Augustine glasses plot between the 

1,200°C and 1,300°C isotherms; the glasses from the Hayes 

Volcano and Novarupta plot between the 1,100°C and 

1,200°C isotherms; and White River glasses plot near the 

1,100°C isotherm (fig. 5). 

The large field of Redoubt glass compositions (fig. 5) is 

caused by variation in composition of glass shards erupted 

during December 1989 (table 1) and gives a melting range of 

1,000°-1,200°C. These glasses (with the higher silica contents-77 to 78 weight percent Si02) were erupted from 

December 1989 to April 1990; they melt at temperatures of 

1,100°C to 1,200°C. Lower silica glasses (68 to 73 weight 

percent Si02) were only erupted during December 1989 and 

melt at lower temperatures: 1 ,000°C to 1,1 00°C. 

Maximum-cruise operating temperatures ofhigh performance turbofan engines currently used on long-range commercial aircraft (747-400, DC-10, etc.) are on the order of 

1,400°C (E.E. Campbell, Boeing Co., oral commun., 1991; 

Kim and others, 1992). Most of the compositions in the system albite-orthoclase-quartz are above liquidus temperatures 

at 1,400°C (fig. 4)-this includes all the volcanic glasses 

modeled in this study (fig. 5). Indeed, some of the minerals 

found in the volcanic ash (e.g., sadie plagioclase) will also 

melt at 1 ,400°C. Ingestion of volcanic ash by turbofan 

engines effectively grinds the ash to fine particles (:: 7 J..Lm; 

Figure 5. Composition fields of volcanic glasses (fig. 3) on liquidus Ab-Or-Q phase diagram at 1 bar pressure showing isotherms that 

define melting temperatures for various glasses. A, Augustine; N, 

Novarupta; H, Hayes; WR, White River; R, Redoubt. 

C/) 

=:) 

~1,400 L..J..J 

u 

C/) 

~1.200 ~ 

L..J..J 

0 

~.1.000 L..J..J 

a: 

=:) 

~ a: 800 L..J..J 

Di 

Operating temperature 

---~-~-~a~l~~~~~~~~-

Ab~ 

~ Operating temperature 

~ 600 ------------------~-----~0~~------

40 50 60 70 80 

Si02

• IN WEIGHT PERCENT 

Figure 6. Melting relations of plagioclase (An-Ab), pyroxene 

(Di-En), and volcanic glasses (from fig. 5) at 1 bar pressure. Dashed 

lines represent the approximate operating temperatures of typical 

high-performance turbofan engines at idle and maximum-cruise 

conditions. 

Casadevall and others, 1991) and, in the process, erodes the 

tips of the compressor airfoils (Przedpelski and Casadevall, 

this volume). This combination of small ash particle size and 

the high operating temperatures of the engine ensures that 

much of the volcanic ash will melt upon ingestion into an 

operating engine and be deposited on the turbine (specifically 

on the high-pressure nozzle guide vanes). 

A reduction of engine thrust to idle has been recommended if a jet aircraft encounters volcanic ash in the air 

(Campbell, this volume; Przedpelski and Casadevall, this 

volume). Turbofan engines operating at idle run at about 

600°C, considerably below the melting temperatures of all 

volcanic glass (fig. 6). Cooling of turbofan engines from 

normal operating temperatures (1,400°C) to idle temperatures is almost instantaneous. Volcanic ash will not melt 

when ingested into the engines at idle conditions (600°C). In 

addition, the rapid cooling from operating conditions to idle 

thrust setting induces a thermal shock related to the differential thermal expansion of the molten glass and the enginemetal substrate that can remove much of the previously 

melted glass that was deposited in the engine. 

CONCLUSIONS 

Ingestion of volcanic ash by high performance turbofan 

engines at operating conditions melts glass shards and some 

of the minerals that make up the ash (fig. 6). Volcanic glass 

compositions can show wide variations and still be melted 

upon ingestion into the engine because of high engine operating temperatures. Operating temperatures must be lowered 

below the lowest melting temperature(:: 1,000°C for glass, 

fig. 6) to prevent melting of ingested volcanic ash. Reduction of engine operating conditions to idle settings(:: 600°C) 

will prevent melting of ingested volcanic ash. 
92 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

RECOMMENDATIONS 

Industry recommendations involving aircraft encounters with airborne volcanic ash (Lloyd, 1990; Campbell, this 

volume; Przedpelski and Casadevall, tlus volume; AlA, 

1991) emphasize the need to exit the ash as quickly as possible and to reduce engine thrust to idle. Reduction of engine 

operating temperatures will prevent the melting of volcanic 

ash (including glass) ingested into the engines. Dynamic 

experiments done on ingestion of dust into operating engines 

(e.g., Kim and others, 1992; Dunn and Wade, this volume) 

should be done with volcanic ash (including an abundance of 

glass) at engine-idle temperatures. The question to be 

answered is whether glass particles can anneal and flow as a 

supercooled liquid above the glass transformation temperature (Tg), the temperature between lower temperature glass 

and higher temperature supercooled liquid (Carmichael and 

others, 1974). For most silicate glasses, Tg is about 0.66 of 

the melting temperature (Carmichael and others, 1974). 

Volcanic glasses in this study thus have glass transformation 

temperatures of about 700°-860°C. Will these volcanic 

glasses anneal at engine-idle conditions and adhere to the 

hotter parts of the engine? Probably not. The glass transformation temperatures are close to the idle operating temperatures (:: 600°C), and the transit time of the ash through the 

engine is short. M.G. Dunn does not believe that glass 

annealing will occur (CALSPAN, oral commun., 1991) and 

does not find an adhesion of ash below 1 ,000°C in his experiments (Kim and others, 1992; Dunn and Wade, this volume). However, such ash-ingestion experiments should be 

tried at engine-idle conditions with a volcanic ash rich in 

volcanic glass. 

ACKNOWLEDGMENTS 

Funding for this study was provided by the Alaska 

Volcano Observatory. Samples of Redoubt Volcano tephra 

were supplied by Robert G. McGimsey of the U.S. Geological Survey. Tephra glass analyses were done at Washington State University with the able assistance of Scott 

Cornelius and Diane Johnson. Discussions with Michael 

G. Dunn of CALSPAN and preprints of his papers on 

dynamic experiments with dust and jet engines provided a 

much needed "reality check" on some of the conclusions 

presented in this paper. Several industry people, including 

Ernie Campbell of Boeing Commercial Airplanes, Zygmunt Przedpelski of General Electric Aircraft Engines, and 

Peter Kingston of Rolls Royce Inc., provided useful copies 

of graphic materials. 

REFERENCES CITED 

AlA, 1991, AlA recommendations aimed at increased safety and 

reduced disruption of aircraft operations in regions with volcanic activity: Washington, D.C., Aerospace Industries Association of America, 7 p. 

Beget, J.E., and Kienle, J., 1992, Cyclic formation of debris avalanches at Mount St. Augustine Volcano: Nature, v. 356, p. 

701-704. 

Beget, J.E., Reger, R.D., Pinney, D., Gillispie, T., and Campbell, 

K., 1991, Correlation of the Holocene Jarvis Creek, Tangle 

Lakes, Cantwell, and Hayes tephras in southcentral Alaska: 

Quaternacy Research, v. 35, p. 74-189. 

Carmichael, I.S.E., Turner, F.J., and Verhoogen, J., 1974, Igneous 

Petrology: New York, McGraw-Hill, 739 p. 

Casadevall, T.J., ed., 1991, First International Symposium on Volcanic Ash and Aviation Safety: U.S. Geological Survey Circular 1065,58 p. 

Casadevall, T.J., Meeker, G.P., and Przedpelski, Z.J., 1991, Volcanic ash ingested by jet engines [abs.], in Casadevall, T.J., ed., 

First International Symposium on Volcanic Ash and Aviation 

Safety: U.S. Geological Survey Circular 1065, p. 15. 

Daley, E.E., 1986, Petrology, geochemistry, and the evolution of 

magmas from Augustine Volcano, Alaska: Fairbanks, Alaska, 

University of Alaska Fairbanks, unpub. M.S. thesis, 106 p. 

Griggs, R.F., 1922, The Valley ofTen Thousand Smokes: Washington, D.C., National Geographic Society, 340 p. 

Hildreth, W., 1987, New perspectives on the eruption of 1912 in the 

Valley ofTen Thousand Smokes, Katmai National Park, Alaska: Bulletin of Volcanology, v. 47, p. 680-697. 

Kienle, J., Swanson, S.E., and Pulpan, H., 1983, Magmatism and 

subduction in the eastern Aleutian arc, in Shimozuru, D., and 

Yokoyama, I., eds., Arc Volcanism: Physics and Tectonics: 

Boston, D. Reidel, p. 191-224. 

Kim, J., Dunn, M.G., Baran, A.J., Wade, D.P., and Tremba, E. L., 

1992, Deposition of volcanic materials in the hot sections of 

two gas turbine engines, in 1992 ASME International Gas Turbine Conference, Cologne, Germany, 1-4 June 1992, 31 p. 

Lloyd, A.T., 1990, Vulcan's blast: Boeing Airliner, April-June 

1990, p. 15-21. 

Nye, C.J., Swanson, S.E., and Miller, T.P., in press, Geochemistry 

of the 1989-1990 eruption of Redoubt Volcano: Part I. Evidence from major and trace element chemistry: Journal of Volcanology and Geothermal Research. 

Riehle, J.R., 1985, A reconnaissance of the major tephra deposits in 

the upper Cook Inlet region, Alaska: Journal of Volcanology 

and Geothermal Research, v. 26, p 37-74. 

Schairer, J.F., 1950, The alkali feldspar join in the system 

NaAlSi04-KAlSi04-Si02: Journal of Geology, v. 58, p. 

512-517. 

Steenblik, J.W., 1990, Volcanic ash, a rain of terra: Air Line Pilot, 

June/July p. 9-15, 56. 

Swanson, S.E., and Kienle, J., 1986, The 1986 eruption ofMt. St. 

Augustine, field test of a hazard model: Journal of Geophysical 

Research, v. 93, p. 4500-4520. 

Swanson, S.E., Nye, C.J., Miller, T.P., and Avecy, V.F., in press, 

Geochemistry of the 1989-1990 eruption of Redoubt Volcano: 

Part II. Evidence from mineral and glass chemistry: Journal of 

Volcanology and Geothermal Research. 

Westgate, J.A., 1990, White River ash, in Wood C.A., and Kienle, 

J., eds., Volcanoes of North America: New York, Cambridge 

University Press, p. 92. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

ASH-FALL DEPOSITS FROM LARGE-SCALE 

PHREATOMAGMATIC VOLCANISM: LIMITATIONS OF 

AVAILABLE ERUPTION-COLUMN MODELS 

By Colin J.N. Wilson 

ABSTRACT 

Existing models for volcanic eruption plumes are successful in predicting sizes and growth rates, and the dispersal 

characteristics of the resulting fall deposits given an estimate 

of the magma-output rate. These models work well for "dry" 

eruptions, where the gases involved were originally dissolved in magma. The models predict that, in "wet" activity 

where abundant external water mixes with the magma during 

eruption and flashes to steam, the eruption plume should be 

lower and the resulting fall deposits less widely dispersed for 

a given magma-output rate. However, parts of the fall deposits from the very large, wet, 22,500-year-old Oruanui eruption (New Zealand) show the opposite behavior and 

represent the most powerfully dispersed fall deposits yet 

documented. These data imply that available eruption-column models, developed for dry eruptions, break down at 

some stage in wet eruptions, but the relative proportions of 

magma to water and the magma volumes and output rates at 

which this breakdown occurs are unknown. Thus, predictions of the sizes and growth rates of large, wet eruption 

plumes and evaluation of the threats they pose to aviation are 

not possible at present. 

INTRODUCTION 

Several theoretical models are now available for understanding the dynamics of volcanic eruption columns. They 

are valuable tools for quantifying the sizes, growth rates of, 

and particle concentrations in observed and prehistoric ash 

plumes, given simple field data or estimates of starting conditions. As such, these models have great potential for realtime monitoring of eruption plumes and evaluating the risks 

posed to aircraft (Macedonia and others, this volume). 

To date, these models have been developed from and 

mostly applied to observed and prehistoric volcanic eruptions that were essentially dry; that is, the only gases 

involved were those originally dissolved in the magma (typically ~ 6 weight percent). However, many cases are known 

where mixing of the hot magma with an abundant supply of 

external water (e.g., lakes, rivers, glacier ice, seawater, 

ground water) occurred during the eruption (e.g., Fisher and 

Schmincke, 1984; Heiken, this volume). In such 

phreatomagmatic or wet activity, the magma is chilled and 

fragmented while the water flashes to steam with accompanying explosions. No large-scale examples of this activity 

have been quantitatively observed, but deposits from such 

eruptions are common in the geological records of many 

volcanoes. 

Large, wet eruptions present severe problems for the 

aviation industry. The eruptions may produce prodigious 

amounts of fmely divided material, and the dynamics of and 

settling of ash from the resulting eruption plumes are poorly 

understood. This paper uses data from one of the largest 

known, prehistoric, wet eruptions, the 22,500-year-old (14C 

years) Oruanui eruption in New Zealand, to show that, at this 

extreme of scale, (1) such eruptions can cause extremely 

wide dispersal of ash, (2) available eruption-column models 

cannot be applied to this style of activity, and (3) other factors need to be taken into account before a model for large, 

wet eruption plumes can be developed and a quantitative 

assessment made of hazards to aviation. 

MODELS FOR ERUPTION COLUMNS 

Available models (e.g., Wilson, 1976; Wilson and others, 1978; Sparks, 1986; Woods, 1988) assume that the 

erupted mixture ofpyroclasts (magma fragments) and gas is 

ejected from the vent as a dense, highly turbulent jet containing a range of particle sizes from sub-micron dust to meterscale blocks. This jet mixes with the atmosphere; heat is 

transferred from the hot ash particles to cold air; large, dense 

blocks detach from the jet; and the jet decelerates rapidly 

through work against gravity and friction with the atmosphere. The jet always starts out denser than the atmosphere, 

but, thereafter, two modes of behavior are possible and can 

sometimes occur simultaneously. If the jet can mix with and 

heat enough cold air, it can expand to become a buoyant thermal plume and form a high eruption column (e.g., Self and 

Walker, this volume; Sparks and others, this volume). The 

column will rise to the level in the atmosphere where it is 

93 
94 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

neutrally buoyant and then spread laterally to form an 

"umbrella cloud" (Sparks, 1986). Particles released from the 

column or umbrella cloud fall back to the land surface to produce pyroclastic fall deposits. On the other hand, if the eruption rate of material is too large, or the jet does not mix 

effectively with enough air to reduce its density, then once its 

upward momentum has been lost, the jet will not be buoyant 

and will collapse back on itself to generate a ground-hugging 

current of pyroclastic debris. As this current moves, it will 

deposit material to form pyroclastic flow (dense current) or 

surge (dilute current) deposits. 

For buoyant thermal plumes, the final heights reached 

are considered to be proportional to the thermal flux; that is, 

the height reached by the eruption column is, in essence, proportional to the magma-eruption rate because it is the thermal energy in the pyroclasts (magma fragments) that drives 

the column. Models are available (e.g., Carey and Sparks, 

1986; Wilson and Walker, 1987; Pyle, 1989; Bursik and others, 1992) that relate the grain-size characteristics of fall 

deposits to the height of their parental eruption column and 

the inferred thermal (i.e., magma) discharge rate. Such models are extremely valuable because they allow us to invert 

field data from the geological record to reconstruct the 

dynamics of prehistoric eruptions. These models are also 

potentially valuable tools for atmospheric modelers and the 

aviation industry to give plausible estimates of how rapidly 

and high an eruption column will rise, how rapidly it will 

expand laterally, and what the ash concentration in a plume 

will be given some simple information or estimates of starting conditions. 

However, these models make the key assumption that 

all the thermal energy is present as sensible heat, the transfer 

of which causes the temperature of the material to change. 

In many volcanic eruptions, both observed (such as Surtsey-Thorarinsson and others, 1964-and Taal-Moore 

and others, 1966) and prehistoric, this assumption is clearly 

questionable because there is evidence for the interaction 

between magma and an abundant external supply of water 

around and below the vent area. In such wet eruptions, part 

of the sensible heat from the magma is used to heat and boil 

water, reducing the temperature of the erupted jet and storing energy as latent heat that is taken up or released during a 

phase change at constant temperature. In existing eruptioncolumn models, a reduction in temperature is predicted to 

reduce the height of any buoyant thermal plume, and the 

resulting fall deposits should thus be less widely dispersed 

than those of a dry plume with the same magma-output rate. 

The extreme limit of wet plume behavior is a conventional 

water-vapor cloud system. Although the total thermal budget of conventional cloud systems may be enormous, they 

are unable to penetrate the tropopause, except by minor 

overshooting. In contrast, dry volcanic eruption plumes may 

penetrate the tropopause and reach heights of 30-50 km. 

New studies (Glaze and others, 1991) have suggested that 

latent heat release from condensing water in the air ingested 

into and carried up with the plume may boost the heights 

reached by small tropospheric plumes. However, the 

amount of latent heat thus made available is limited by the 

amount of water available in the atmosphere, and, in eruptions such as that considered here, this amount of latent heat 

will be dwarfed by the thermal effects of large-scale interaction between the plume and surface water. In this paper, I 

use data from parts of the fall deposit generated during the 

very large, wet Oruanui eruption, New Zealand (Self and 

Sparks, 1978; Self, 1983; Wilson, 1991) to show that models developed for dry eruption plumes break down when 

applied to large, wet eruptions. 

THE ORUANUI ERUPTION 

The Oruanui eruption occurred 22,500 years ago (1 4C 

years) at Taupo Volcano in the central North Island of New 

Zealand. It produced (fig. 1) a widespread and voluminous 

(~ 500-km3 bulk volume) fall deposit from a buoyant thermal plume before, during, and after pyroclastic flow activity that generated a 300-km3 (bulk volume) pumiceous flow 

deposit (ignimbrite) (Wilson, 1991; C.J.N. Wilson, unpub. 

data). The ignimbrite is nowhere welded (a process in 

which particles in the deposit are hot enough (~ 570°C) to 

stick together-comparable to sintering processes in powder metallurgy), even where the ignimbrite is > 200 m 

thick. This evidence, together with estimates of emplacement temperatures from paleomagnetic techniques (E.A. 

McClelland, Cambridge University, and C.J.N. Wilson, 

unpub. data) and my observations of the limited amount of 

charring of vegetation overrun by the pyroclastic flows, 

imply that none of the flows were emplaced at temperatures 

of more than 300°--400°C. The cooling from the magma 

temperature of about 800°C (Dunbar and others, 1989) is 

inferred to have been caused by mixing of the eruption 

plume with water from a proto-Lake Taupo (Self and 

Sparks, 1978; Self, 1983). If equilibrium between the water 

and fragmented magma is assumed, and the whole of the 

eruption jet shared the maximum 300°--400°C temperature 

range, then at least 100-150 km3 of water was evaporated 

during the eruption. The Oruanui fall deposit is generally 

fine grained and contains evidence that much of it was 

flushed out of the atmosphere by water as mud, rain, or 

hail. Both the fall deposits and ignimbrite indicate that the 

wet Oruanui eruption column was distinctly cooler 

(because of magma-water interaction) than the typical dry 

eruption columns that have been modeled and, hence, 

should have been lower and, by implication, weaker. 

ORUANUI FALL DEPOSIT: BEDS A AND B 

The Oruanui fall deposit contains several layers or beds 

that are distinctive and can be correlated for distances of tens 

to hundreds of kilometers. Two of them, informally labeled 

beds A and B (fig. 2), are particularly widespread and are 
ASH-FALL DEPOSITS FROM LARGE-SCALE PHREATOMAGMATIC VOLCANISM 95 

1-

z 

~ CD 

Q) 

E ---::-------~ 

~ t-----'----------as far as 90 kilometers-------,-----~--

A 

0 

New Caledonia 

New Zealand 

70 ern 

B 0 

Tonga '\:>, 

PACIFIC OCEAN 

1000 KILOMETERS 

EXPlANATION 

Thickness of Oruanui ignimbrite 

More than 200 meters 

100-200 meters 

50-,-l 00 meters 

0-50 meters 

Figure 1. A, Schematic diagram showing the stratigraphic relationships of the fall deposit and ignimbrite generated during the Oruanui 

eruption. B, Map ofisopachs (contours ofthickness) ofthe Oruanui fall deposit. The thickness values represent those inferred to have been 

present immediately after the eruption; most of the deposit has since been removed by erosion. The source vent is now concealed beneath 

Lake Taupo, which infills the collapse caldera left behind after this eruption. C, Map showing the area covered by and thicknesses of the 

Oruanui ignimbrite. 

considered here. Although most of the Oruanui fall deposits 

were clearly emplaced as wet, poorly sorted material flushed 

out of the plume by rain and (or) hail and are thus typical of 

the wet eruptive style, parts of beds A and Bare moderately 

to well sorted, lack evidence for wet deposition, and more 

resemble typical dry-eruption fall deposits. However, observations on, and inferred emplacement temperatures for, 

ignimbrite coeval with beds A and B show that the plume was 

cool and water rich during emplacement of these beds. Maps 

(fig. 3) show the contours of thickness (isopachs) for the two 

beds and the variations in length of the five largest pumice 

fragments found in each bed (isopleths). Integration of the 

thickness data using the method of Pyle ( 1989) yields bulkvolume estimates of 8 km3 for bed A and 14 km3 for bed B. 
96 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

ERUPTION-COLUMN MODELS AND 

ORUANUI BEDS A AND B 

Eruption-column models use the changes in thickness 

and grain size of fall deposits away from the vent as a measure of the power of the eruption and wind regime. Two 

models are used here, both of which use the eruption-column 

model of Sparks (1986) to produce theoretical relationships 

between dispersal patterns of pyroclasts and eruption-column height. The model of Pyle (1989) uses the overall dispersal characteristics of the deposit to infer the eruptioncolumn height and classify the deposit. This model neglects 

the effects of wind but leads to reasonable estimates of column height for observed and prehistoric eruptions, even 

when strong winds were present. The model of Carey and 

Sparks (1986) uses the dispersal patterns of coarse pumice or 

dense, rock clasts to estimate eruption-column heights and 

wind speeds. In addition, the Oruanui beds are compared 

with the widely used eruption classification for fall deposits 

originally developed by Walker (1973). 

In the Pyle (1989) model (fig. 4), both beds A and B 

plot well beyond the inferred extreme for normal, dry, fall 

deposits, and column-height estimates cannot be made. The 

rates of thinning of beds A and B are extremely low but so 

also are the rates at which they become finer, and their 

overall bclbt ratios (see fig. 4 for definition of parameters) 

are thus similar to typical dry-eruption fall deposits. Using 

the Carey and Sparks (1986) model (fig. 5), the Oruanui 

beds give high but superficially plausible values for column 

height and wind strength, although the column heights are 

significantly different from those implied by Pyle's (1989) 

model. However, despite the broad resemblance of beds A 

and B to many dry fall deposits, these figures are not reliable because of the known low temperature of the eruption 

plume; Carey and Sparks (1986) specifically warn against 

using their model for wet eruption deposits. In Walker's 

(1973) classification (fig. 6), both Oruanui beds show evidence for extremely powerful eruption plumes, with A and 

B having dispersal indices at least an order of magnitude 

larger than those documented for most dry-eruption fall 

deposits, which have been inferred by other models to have 

been emplaced from plumes 30--50 km high. 

DISCUSSION AND CONCLUSIONS 

It is clear that there are contradictions involved in trying 

to model the eruption plumes ofOruanui beds A and B. Existing theory suggests that the loss of sensible heat in the plume 

through magma-water interaction would have reduced the 

eruption-column height and, hence, the power with which the 

clasts were dispersed. On the other hand, beds A and B plot 

well beyond any documented dry-eruption fall deposits in the 

Pyle (1989) and Walker(1973) classifications, which use dispersive power as an ordinate (figs. 4, 6). Thus, estimates of 

___ column height and wind speed made with the Carey and 

bed 8 

bed A 

foss il soi l 

Figure 2. Photograph of basal parts of the Oruanui fall deposit, 

showing beds A and B. The darker coloration near the base of bed B 

is due to a higher content of fine ash material. Locality is near 

Taihape township (grid reference U211710782), 90 km south of 

vent. Scale in inches and millimeters. 

Sparks (1986) model (fig. 5) are almost certainly invalid, 

despite the often similar appearance of beds A and B to conventional, dry, fall deposits. 

The theories behind models for dry eruption columns are 

soundly based. The resulting models are successful when 

applied to observed events (e.g., Mount St. Helens) and give 

plausible and realistic estimates of column parameters 

(height, discharge rate) for prehistoric, dry eruptions, based 

on measurements from fall deposits. These models have also 

been used to predict the thicknesses and areas covered by fall 

deposits from hypothetical future eruptions (e.g., Macedonio 

and others, 1990). However, the presence of significant 

magma-water interaction in an eruption makes application of 

these models suspect (and completely invalid at the extremes 

of eruptive size and violence shown by the Oruanui event). 

The powerful dispersal of the Oruanui fall beds implies 

that if wet eruption plumes are lower in height (because of 

latent-heat effects), then either plume expansion rates are correspondingly more rapid or there is some as yet undiscovered 

mechanism (e.g., organized cellular convection) in the eruption plume that causes pyroclasts to be carried farther from 

the vent before deposition occurs. In either case, no model 

exists to predict the growth rates and nature of such an eruption cloud. 

No information is yet available to show at what scale of 

magma-output rate and (or) amount of magma-water interaction the breakdown occurs of dry eruption-column models. In 

the 1,800-year-oldTaupoeruption(WilsonandWalker, 1985), 

twowetfalldepositsweregeneratedbetweenepisodesofmore 

voluminous dry fall activity (Walker, 1981). The two wet 

deposits are found in significant amounts farther upwind than 

the dry deposits, implying that wet eruption plumes of even 

moderate size (bulk volumes of the two deposits are 1.9 and 

1.1 km3) may start to behave in a significantly different way 

from dry plumes. The formulation of a model for wet eruption 

plumes and relating it to existing ideas about the behavior of 
ASH-FALL DEPOSITS FROM LARGE-SCALE PHREATOMAGMATIC VOLCANISM 97 

',, 

'5cm 10cm 

thickness, em thickness, em 

PACIFIC OCEAN PACIFIC OCEAN 

100 KILOMETERS 100 KILOMETERS 

ORUANUI FALL DEPOSIT BED A ORUANUI FALL DEPOSIT BED B 

PACIFIC OCEAN PACIFIC OCEAN 

maximum pumice size, mm maximum pumice size, mm 

A B 

Figure 3. Isopach and isopleth (contours of equal grain size) maps of A, Oruanui fall deposit bed A and B, Oruanui fall deposit bed B. 

Maps show variations in thickness (top) and maximum pumice sizes (bottom). Maximum pumice sizes represent the average length of 

the five largest pumice clasts found at each locality. 

dry plumes is thus an important goal, both for understanding 

plume dynamics as well as for predicting the nature of the hazards they pose and the rapidity with which they develop. 

Four features of wet eruption plumes are particularly relevant to aviation safety: ( 1) Wet eruptions generate higher proportions of fine ash particles than dry eruptions, and smaller 

particles may thus stay aloft for longer times and persist to 

greater distances from the volcano than predicted by available 

models; (2) in large, wet eruptions such as the Oruanui, the 

radial expansion rate of the plume (as indicated by the 

extremely widespread dispersal of pyroclasts) may be significantly more rapid than predictable from dry-plume models, 

or the plume may incorporate organized cellular convection, 

which would present additional hazards to aircraft; (3) there 

is abundant evidence from rain- and hail-flushed beds in the 

Oruanui fall deposits for significant amounts of ash transport 

in the troposphere, and, thus, any aircraft encountering a 

large, wet plume may not be able to escape into ash-free air 

merely by diving; ( 4) the amounts of water inferred to be 

present in a large, wet plume may cause additional problems 

to aircraft, such as adhesion of moist to wet ash on the aircraft 

skin. Any schemes to identify eruption plumes and minimize 

the risks to aviation traffic therefore need to take account of 

our current lack of understanding of wet eruption plumes. 
98 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Finer 

grained 

Coarser 

grained 

0 

i= 

<( 

a: 2 

..0 

-(.) 

..0 

3 

4 

0.1 

Weakly 

dispersed 

0 

0 

1 km 8 km 15 km}bc values 

I 0 

10 100 

bt, IN KILOMETERS 

< > Powerfully 

dispersed 

Figure 4. Oruanui fall beds A and B (solid triangles) plotted on 

the classification diagram of Pyle ( 1989). Parameters bt and be are 

the average distances over which the deposit thickness and maximum clast sizes decrease by a factor of one-half, respectively-this is analogous to the half-life in radioactive decay. Pyle 

suggested that the value of be = 15 km (corresponding to an eruption-plume height of about 55 km) represented a likely maximum 

for dry-eruption fall deposits. Open circles are data points from a 

selection of dry fall deposits. 

Finer 

grained 

x 

w 

Cl 

z zlo~ -u 1-a:: 

<(w 

1-a.. z 

wz 

~­

(!) 

<( 

a:: 

u. 

Coarser 

grained 

Surtseyan 

75 

100 

40 L.U 

(.9(/) 

Zc::: 

~ ~ 30 

ow 

z~ 

-o 

$::::! 20 (/)~ 

~~ a: 

u 10 

WIND VELOCITY B 

.... ~--~---+~--+-43km 

30 40 50 60 70 

MAXIMUM DOWNWIND RANGE, 

IN KILOMETERS 

Figure 5. Plot of downwind range versus crosswind range of 

pumice clasts (approximately 40 mm in diameter) in Oruanui beds 

A and B (solid triangles) superimposed on the relevant model of 

Carey and Sparks (1986, fig. 16a). In their model, the difference between the two ranges yields a unique value of column height and 

average wind velocity for dry-eruption fall deposits. 

Phreatoplinian 

bt, IN KILOMETERS 

Weakly 

dispersed 

Powerfully 

dispersed 

Figure 6. Oruanui fall beds A and B (solid triangles) plotted on the "F-D diagram" introduced by Walker (1973) and subsequently modified. This version is from Fisher and Schmincke (1984). The fragmentation index is the weight percent of the deposit finer than 1 mm along 

the dispersal axis where it is crossed by the 0.1 T max isopach (T max is the maximum thickness, obtained by extrapolation). The dispersal 

index is the area covered by 0.01 Tmax or more of material. Fields for various eruptive styles are shown. The deposits of most powerful, dry 

eruptions plot in the Plinian field. 
ASH-FALL DEPOSITS FROM LARGE-SCALE PHREATOMAGMATIC VOLCANISM 99 

ACKNOWLEDGMENTS 

This work is supported by the Royal Society of London. 

I thank R.S.J. Sparks for services rendered and B.F. Houghton, D.M. Pyle, and S. Self for reviews. 

REFERENCES CITED 

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comparison with a study of the Fogo A Plinian deposit, Sao 

Miguel (Azores): Bulletin of Volcanology, v. 54, p. 329-344. 

Carey, S.N., and Sparks, R.S.J., 1986, Quantitative models of the 

fallout and dispersal of tephra from volcanic eruption columns: 

Bulletin of Volcanology, v. 48, p. 109-125. 

Dunbar, N.W., Kyle, P.R., and Wilson, C.J.N., 1989, Evidence for 

limited zonation in silicic magma systems, Taupo Volcanic 

Zone, New Zealand: Geology, v. 17, p. 234-236. 

Fisher, R.V., and Schmincke, H.-U., 1984, Pyroclastic Rocks: Berlin, Springer Verlag, 472 p. 

Glaze, L.S., Wilson, L., and Baloga, S.M., 1991, Theoretical eruption column heights: The effects oflatent heat and particle fallout [ abs.]: Transactions, American Geophysical Union (Eos ), 

Supplement, 1991 Fall Meeting Abstracts, p. 568. 

Macedonia, G., Pareschi, M.T., and Santacroce, R., 1990, Renewal 

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v. 40, p. 327-342. 

Moore, J.G., Nakamura, K., and Alcaraz, A., 1966, The 1965 eruption ofTaal Volcano: Science, v. 155, p. 955-960. 

Pyle, D.M., 1989, The thickness, volume and grain size of tephra 

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Self, S., 1983, Large-scale phreatomagmatic silicic volcanism, a 

case study from New Zealand: Journal of Volcanology and 

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Self, S., and Sparks, R.S.J., 1978, Characteristics of widespread pyroclastic deposits formed by the interaction of silicic magma 

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Sparks, R.S.J., 1986, The dimensions and dynamics of volcanic 

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G., 1964, The submarine eruption off the Vestman Islands, 

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---1981, Characteristics of two phreatoplinian ashes and their 

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Wilson, C.J.N., 1991, Ignimbrite morphology and the effects of 

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VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

THE INJECTION OF VOLCANIC ASH 

INTO THE ATMOSPHERE 

By Andrew W. Woods and Juergen Kienle 

ABSTRACT 

In this paper, we present some physical models that can 

describe the ascent of volcanic ash into the atmosphere during a volcanic eruption. We consider both sustained volcanic 

eruption columns and discrete volcanic thermal clouds. To 

test the modeling approach, we compare our predictions of 

the ascent rate of a model cloud with some observations of 

the ascent of the ash cloud during the April 15, 1990, eruption of Redoubt Volcano, Alaska. We also consider the 

radial spreading of ash as a gravity current following 

emplacement by the column and compare our theory with 

the observations from the April 21, 1990, eruption of 

Redoubt, Alaska. Both styles of eruption behavior are hazardous for aircraft. 

INTRODUCTION 

There is a range of styles of explosive volcanic eruption 

that can produce large convecting ash clouds and thereby 

inject ash high into the atmosphere. Ash can rise high into 

the atmosphere if the hot, erupted material can mix with and 

heat up a sufficient mass of air so that the bulk density of the 

mixture decreases below the ambient (Self and Walker, this 

volume). The typical ascent time of this ash to its maximum 

height is on the order of a few minutes; if this time is longer 

than the time over which the material is erupted and becomes 

buoyant, then the cloud will rise as a discrete volcanic thermal cloud (Wilson and others, 1978; Woods and Kienle, in 

press). Such volcanic thermal clouds formed, for example, 

during the April 15 and 21, 1990, eruptions of the Redoubt 

Volcano, Alaska. Figure 1 is a photograph of the April 21 

eruption cloud, which ascended about 12 km into the atmosphere. The main eruption cloud has reached its maximum 

height and has begun to spread laterally into the atmosphere. 

A relatively small, vertical column may be seen below this 

main cloud. This column contains material rising from the 

ground after the ascent of the main cloud-this material is 

less energetic than that in the main thermal cloud. In the photograph, a small secondary lateral intrusion has begun to 

develop from this column. 

In a more sustained eruption, lasting several hours, 

material is continually erupted from the vent. In this case, a 

maintained eruption column, injecting ash high into the 

atmosphere, will form if the hot ash can entrain and heat a 

sufficient quantity of air so that the bulk density of the mixture falls below that of the ambient. Two different mechanisms of buoyancy generation are possible, and, during the 

course of an eruption, the style of eruption may change from 

one to the other: (1) If the erupted material is ejected upward 

from the vent very rapidly, the dense jet may entrain sufficient air to become buoyant before its upward momentum is 

exhausted; in this case, the material continues rising upward, 

driven by its own buoyancy thereby forming a classical Plinian eruption column (Sparks, 1986; Woods, 1988) such as 

the A.D. 79 eruption ofMt. Vesuvius, Italy. (2) If the erupted 

material is ejected from the vent with smaller momentum, 

that material will collapse back and spread out along the 

ground as an ash flow in a similar manner to the motion of 

water in a fountain. However, the material in the spreading 

ash flow may become buoyant through entrainment and mixing with air and sedimentation of large particles as it propagates along the ground. It will then rise off the ground to 

form a maintained eruption column, in this case called a coignimbrite eruption column (Sparks and Walker, 1977; 

Woods and Wohletz, 1991). Historical examples of eruptions, which include phases in which co-ignimbrite eruption 

columns developed, include the massive 1815 eruption of 

Tambora, Indonesia, and the 1912 eruption of Katmai, 

Alaska. Co-ignimbrite eruption columns tend to form during 

massive eruptions (Woods and Wohletz, 1991 ). 

Both discrete and maintained eruption clouds can inject 

vast quantities of ash into the atmosphere-they thereby 

pose a serious safety problem for aircraft. However, sustained eruption columns are perhaps more hazardous for aircraft because they may persist for hours and can therefore 

inject very large quantities of ash, which spreads over a very 

wide area in the atmosphere. In order to evaluate the dangers 

of an eruption for aircraft, it is important to know the extent 

of the region in which the mass loading of ash in the air is at 

hazardous concentrations. When ash has been carried 

upward to its maximum height by the eruption column, it 

101 
102 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 1. Photograph of the volcanic eruption cloud fonned during the April 21, 1990, eruption of Redoubt Volcano, Alaska, seen 

from the Kenai Peninsula, east of the volcano. The main cloud ascended about 12 km, and the secondary intrusion ascended to analtitude of about 6 km. Photograph by Mark and Audrey Hodges. 

spreads out laterally under gravity above its neutral buoyancy height and is carried by the wind to form a large, laterally spreading ash plume (fig. 2). The maximum ash 

concentration in this ash plume occurs at the top of the eruption column (before it is diluted through mixing with the 

ambient as it travels downwind). 

In the following section, we describe the Plinian eruption-column model ofWoods (1988) and the model of a volcanic thermal cloud of Woods and Kienle (in press). In order 

to test the modeling approach, we compare the predicted rate 

of ascent of a volcanic thermal, using the model of Woods 

and Kienle (in press), with the observed ascent of the thermal 

cloud during the April 15, 1990, eruption of the Redoubt 

Volcano, Alaska. We also investigate the radial spreading of 

the ash as a gravity current after it is emplaced into the atmosphere by the eruption; we compare a simple model with 

observations of the spreading umbrella cloud following the 

April21, 1990, eruption ofRedoubt Volcano. Details of the 

mass loading in eruption columns and the downwind dispersal of ash are given in other articles in this volume 

(Sparks and others, this volume; Bursik and others, this volume; Self and Walker, this volume). 

MODELING THE DYNAMICS OF 

ERUPTION CLOUDS 

Although the initial momentum of the material erupted 

from the vent accounts for the first few kilometers of the 

ascent, it is the generation of buoyancy that enables the material to ascend tens of kilometers (Woods, 1988). This buoyancy is generated through the entrainment of vast quantities 

of ambient air, which is heated and expands, ultimately lowering the density of the column below that of the surrounding 

air. Once buoyant, the material rises through the atmosphere 

until reaching the height at which its density equals the ambient again, called the neutral buoyancy height. At this point, 

the inertia of the material causes the material to continue rising some distance until the material comes to rest. It then 

collapses downward toward the neutral buoyancy height and 

spreads out laterally. In this overshoot region, the density of 

the cloud exceeds that of the surroundings, and the cloud 

may actually become tens of degrees colder than the environment (Woods and Self, 1992). This undercooling of the 

eruption cloud causes difficulties in the interpretation of 

thermal satellite images of the top of eruption columns; in 

particular, it is very difficult to estimate the height of the 

cloud top using the observed cloud-top temperature and 

radiosonde measurements of the environmental temperature 

as a function of altitude (Woods and Self, 1992). 

In the past 10-15 years, a number of models have 

been developed to describe the motion of maintained volcanic eruption columns. These are summarized and reviewed 

in the paper by Woods (1988), in which a dynamically consistent model is presented. This steady-state model is based 

upon the conservation of mass, momentum, and enthalpy, 

assuming that the column entrains ambient air at a rate proportional to the vertical velocity of the column at any 

height, following Morton and others (1956). The model 

incorporates a number of simplifications, which are good 

approximations in many explosive volcanic eruptions. 

These include the assumptions that (1) the material in the 

eruption column behaves as a single-phase, perfect gas, (2) 

there is little interphase mass or momentum transfer, (3) the 

system is in thermodynamic equilibrium, and ( 4) all of the 

solid material is fine-grained ash and therefore ascends to 

the top of the column. 

Eruption 

column 

Top of column 

- Ash plume 

Neutral , spreading 

buoyancy , \ \ downwind 

height \ \ , . 

\ \ \ \ 

/\\ 

Ash fallout \ '\ \\ \ 

\ \ \ \ \ 

Volcano 

Figure 2. Schematic diagram of eruption column, spreading umbrella cloud, and downwind ash plume. Figure shows location of 

neutral buoyancy height. 
THE INJECTION OF VOLCANIC ASH INTO THE ATMOSPHERE 103 

In figure 3, we present a graph, calculated using this 

model, showing how the total height of rise of the column and 

the neutral buoyancy height ofthe column vary with the mass 

eruption rate for three different initial temperatures. In this 

graph, it may be seen that the rate of increase of column 

height decreases once it passes through the tropopause. This 

is because the temperature begins to increase with height in 

the stratosphere, causing the atmosphere to become much 

more stratified. It may also be seen that, because hotter columns generate more buoyancy, they tend to rise higher. Further details of the model are described in Woods (1988). 

Woods and Bursik ( 1991) have extended this model to 

include the effects of fallout of the larger solid clasts below 

the top of the column. They showed that, if many of the 

clasts do fall out (as occurs in eruptions of larger mean 

grain size), then the eruption column becomes progressively smaller. This is because more of the thermal energy 

is removed by these solids, and, ultimately, the material in 

the column has insufficient thermal energy to become 

buoyant and a collapsed fountain forms. Woods and 

Wohletz (1991) have shown that the ascent of a co-ignimbrite eruption column rising off a hot ash flow (Sparks and 

Walker, 1977) may also be described using this model. In 

this case, the material being supplied to the column originates from a large area; initially it has little upward 

momentum and is only just buoyant relative to the surrounding ambient atmosphere. However, after entraining 

more air, the material rapidly expands and becomes buoyant and, as a consequence, accelerates upward. Woods and 

Wohletz ( 1991) calculated that the ascent height of these 

co-ignimbrite columns was much less than that of Plinian 

columns because, typically, only about one-third of the 

25 

z~ 

~(/) 20 :::>a: 

....JL.U 

Qluw 

1.1.~ 15 

oo 

I-::! 

:c~ 

<.9Z 

w- 10 

:c 

5 

6 

1,000°K 

1,200°K / 

o 1-:;;:;::.r' 

800 -~:;:.:--"-1 ,OOOo K 

:-:: :':""'"" "'' ""\ ~:~: ~-

6.5 7 7.5 8 8.5 

LOGARITHM OF (MASS ERUPTION RATE, 

IN KILOGRAMS PER SECOND) 

Figure 3. Calculations of neutral buoyancy height (dashed lines) 

and total column height (solid lines) as a function of erupted mass 

flux. Curves are given for three eruption temperatures (800°K, 

1,000°K, 1,200°K). Calculations are based on the model of Woods 

( 1988) using the standard atmosphere model described therein for 

which the tropopause is located at 11 km. 

8.5 9 9.5 

LOGARITHM OF (MASS OF ASH IN 

CLOUD, IN KILOGRAMS) 

10 

Figure 4. Calculations of neutral buoyancy height (dashed 

lines) and total cloud height (solid lines) as a function of erupted 

mass. Curves are given for three eruption temperatures (600°K, 

800°K, 1 ,000°K). Calculations are based on the model of Woods 

and Kienle (in press) using the standard atmosphere as described 

in figure 3. 

erupted ash and solid material is elutriated from the ash 

flow into the rising cloud. This reduces the source of thermal energy, which results in ascent of the cloud. 

Using a similar approach, Woods and Kienle (in press) 

have presented a model of the ascent of discrete volcanic 

clouds. In this model, the discrete cloud is assumed to ascend 

as a sphere that entrains ambient air and therefore increases 

in radius as it ascends. The model calculates the altitude and 

radius of the cloud as well as the average density, temperature, and velocity in the cloud as functions of time. An 

important difference between the motion of a maintained, 

steady eruption column and a discrete volcanic thermal 

cloud is that, as a volcanic thermal rises, there is an additional drag exerted upon the cloud as a result of the air that 

must be displaced by the rising cloud. This is usually referred 

to as the virtual mass (Batchelor, 1967) and is incorporated 

in the model of Woods and Kienle (in press). 

In figure 4, we present calculations using this model of 

the ascent height and neutral buoyancy height of a volcanic 

thermal cloud, such as that developed following the eruption Redoubt Volcano (fig. 1). We present calculations for 

three different initial temperatures as a function of the initial mass of the thermal cloud. The results are qualitatively 

similar to those in figure 3, which describe maintained 

eruption columns. 

TESTING ERUPTION-CLOUD 

MODELS 

Relatively few detailed observations of volcanic eruptions, recording the ascent height of the cloud as a function 

of time or the velocity in a maintained eruption column as a 
104 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

TIME, IN SECONDS 

Figure 5. Comparison of observed ascent of the April 15, 1990, 

Redoubt eruption cloud with the model predictions of the total cloud 

height (solid lines) and the height of the center of the cloud (dashed 

lines). Calculations are shown for two initial, model cloud temperatures (600°K and 700°K), which represent bounds on the initial temperature of the cloud (Woods and Kienle, in press). The data were 

collected by analysis of video recordings of the cloud ascent. Horizontallines through data points represent error bars. 

function of height, have been published; such observations 

are necessary to test the accuracy of the modeling approach. 

Sparks and Wilson (1982) tracked several plume fronts rising from the crater of Soufriere St. Vincent and compared 

this with a model of a starting plume, and Sparks (1986) 

reported some satellite observations of the ascent of the lateral blast cloud of Mount St. Helens, May 18, 1980, and 

compared these with the theory of Morton and others (1956). 

More recently, Woods and Kienle (in press) have reported on 

some slow-scan video-camera recordings of the rise of the 

April 15, 1990, eruption cloud of Redoubt Volcano and compared this with a new model of a volcanic thermal. 

During the April 15, 1990, eruption of Redoubt 

Volcano, a hot ash flow was produced from the explosion of 

a volcanic dome. This ash flow traveled along the ground for 

3-4 km, following a natural ice canyon carved in a glacier. 

As the flow entrained and heated ambient air, the upper part 

of the flow became buoyant and rose into the atmosphere, 

forming a large, convecting volcanic thermal cloud. In figure 

5, we present a graph showing the observed height of the 

cloud as a function of time as deduced from the slow-scan 

video recording. Post-eruption studies of the far-field air-fall 

(Scott and McGimsey, in press) and near-field flow deposits 

(C.A. Neal, oral commun., 1991) give estimates for the total 

mass of material erupted from the volcano during this eruption as approximately 2.5x109 kg. Using this data and the 

conservation of enthalpy in the flow (Sparks, 1986), we estimate that the temperature of the elutriated cloud was 

600°K-700°K, assuming that it was just buoyant on ascent. 

This data provides the initial conditions for our model of the 

ascent of the thermal cloud and, in figure 5, we also present 

model ascent curves for clouds rising off the flow with temperatures of 600°K and 700°K. In these calculations, we 

have used meteorological radiosonde data from three stations near Redoubt Volcano taken at about the time of the 

eruption. It may be seen that the model is able to reproduce 

most of the features of the buoyant ascent very satisfactorily, 

especially the time scale of the ascent and the height of rise 

of the cloud. This gives us confidence in the accuracy, at 

least in terms of the order of magnitude, of the predictions of 

these models. Further details of this comparison and the field 

data are given in Woods and Kienle (in press). 

In addition to field observations, some recent controlled laboratory experiments have been able to test 

aspects of these models (Woods and Caulfield, 1992). 

There are mixtures of methanol and ethylene glycol (MEG) 

with density less than that of water that, upon mixing with 

water, become more dense than water. Therefore, with sufficient initial momentum, a downward-propagating, but 

light, jet of MEG can entrain and mix with ambient water 

to become dense and thereby continue propagating downward (in an analogous fashion to a Plinian eruption column) (Woods and Caulfield, 1992). However, a relatively 

light jet of MEG, with sufficient initial downward momentum, comes to rest before it can mix with sufficient water to 

become dense; in this case, a collapsed fountain forms and 

the MEG mixture rises back up around the source. Woods 

and Caulfield ( 1992) developed a simple theoretical model 

of their laboratory experiments based on the same conservation laws as used in the eruption-column model of 

Woods (1988). The conditions under which experimental 

column collapse occurs were successfully compared with 

the model predictions; this further confirms the validity of 

the underlying physics in the models. 

SPREADING UMBRELLA CLOUDS 

We now describe the initial spreading of the umbrella 

cloud once it is emplaced into the atmosphere by the eruption column-the subsequent dispersal and fallout of ash 

has been described by Bursik and others (1992; this volume). Following injection into the atmosphere by the eruption column, the first stage of ash dispersal consists of the 

radial gravitational spreading of the cloud toward its neutral 

buoyancy height. This is the dominant mechanism causing 

lateral spreading of the ash cloud during the first few minutes after the ash is injected into the atmosphere. However, 

when the rate of spreading decreases below typical velocities associated with the ambient wind field and ambient turbulence, this gravitational spreading may become of 

secondary importance in comparison to the wind as an ashdispersal mechanism. During the May 18, 1980, eruption of 

Mount St. Helens, the ash plume spread out under gravity 

from a radius of about 20 km to nearly 50 km in about 10 

minutes (Sparks, 1986, fig. 5), whereas the April 21, 1990, 
THE INJECTION OF VOLCANIC ASH INTO THE ATMOSPHERE 105 

eruption cloud at Redoubt Volcano spread out from a radius s,ooo 

of about 6 km to over 15 km in about 10 minutes under 

gravity before being carried downwind. Woods and Kienle 

(in press) have described a simple model of the gravitational 

spreading of an ash cloud following Simpson (1987). In the 

model, the radial inertia of the cloud balances the gravitational force, which results from the vertical displacement of 

the air by the cloud. Woods and Kienle (in press) predict 

that an instantaneously emplaced cloud spreads radially at a 

rate proportional to (time)113, and an umbrella cloud continually supplied from below spreads at a rate proportional to 

(time )21

3 until the dispersal becomes dominated by wind. 

As can be seen in figure 6, this model compares favorably 

with direct observations from the spreading of the April21, 

1990, eruption cloud of Redoubt Volcano, which was 

emplaced nearly instantaneously. 

CONCLUSIONS 

We have described models of both instantaneous and 

maintained eruption columns. These models are based upon 

the conservation of mass, momentum, and enthalpy. We 

have compared our model of a thermal cloud with the observations of the Redoubt Volcano eruption of April 1990. We 

have also discussed simple models of the radial spreading of 

the umbrella cloud and have shown that the simple model 

compares favorably with observations from the April 21, 

1990, eruption of Redoubt Volcano. The models have shown 

that even relatively small eruption clouds can ascend up to 

tens of kilometers into the atmosphere, causing a serious 

hazard for aircraft, which typically fly in the troposphere 

below about 11 km. Once the ash cloud has reached its neutral buoyancy height, the ash may then spread several hundred or even thousands of kilometers before settling from the 

atmosphere. A particularly important result of the modeling 

is that the upper surface of an eruption column may actually 

become tens of degrees colder than the surrounding environment, owing to the inertial overshoot of the erupted mixture 

above the neutral buoyancy height. This can lead to difficulties in interpreting the height of eruption clouds from thermal satellite images (Woods and Self, 1992). In a companion 

paper in this volume (Sparks and others, this volume), the 

models described herein have been used to calculate the ash 

loading at the top of eruption columns. 

REFERENCES CITED 

Armienti, P., Macedonio, G., and Pareschi, M.T., 1988, A numerical model for simulation of tephra transport and deposition: 

Applications to May 18, 1980 Mount St. Helens eruption: Journal of Geophysical Research, v. 93, p. 6463-6476. 

Batchelor, G.K., 1967, An Introduction to Fluid Dynamics: Cambridge, Cambridge University Press, 615 p. 

~0 

Clw 

LUCJ 

CJ:::J au 

en en ::::>0:: 

- LU Cl~ 

<(W 

c::~ 

oo 

::::>::::! 

0~ ....lz U4,000 

3,000 

2,000 

1,000 

EXPLANATION 

o Main cloud 

• Lower intrusion 

I 

OL---~--~--~--~----L---~---L--~ 

0 200 400 600 800 

TIME, IN SECONDS 

Figure 6. Comparison of observed spread of umbrella cloud that 

fonned following the April21, 1990, eruption of Redoubt Volcano 

and a simple model of a radially spreading gravity current, after 

Woods and Kienle (in press). The graph shows the rate of spread of 

the main cloud as well as the lower secondary intrusion, which can 

be seen in figure 1. The data were obtained from analysis of photographs by Mark and Audrey Hodges. Vertical lines through data 

points indicate error bars. 

Bursik, M.I., Sparks, R.S.J., Gilbert, J., and Carey, S., 1992, Dispersal of tephra by volcanic plumes: A study of the Fogo A 

eruption, Sao Miguel (Azores): Bulletin of Volcanology, v. 54, 

p. 329-344. 

Morton, B., Taylor, G. 1., and Turner, J. S., 1956, Turbulent gravitational convection from maintained and instantaneous source: 

Proceedings of the Royal Society, Series A, v. 234, p. 1-23. 

Scott, W.E., and McGimsey, R.G., in press, Character, mass, distribution, and origin of tephra-fall deposits of the 1989-1990 

eruption of Redoubt Volcano, Alaska: Journal of Volcanology 

and Geothennal Research. 

Simpson, J., 1987, Gravity Currents in the Environment and the 

Laboratory: Chichester, Ellis Horwood, 244 p. 

Sparks, R.S.J., 1986, The dimensions and dynamics of volcanic 

eruption columns: Bulletin of Volcanology, v. 48, p. 1-16. 

Sparks, R.S.J., and Walker, G.P.L., 1977, The significance ofvitric-rich airfall deposits: Journal of Volcanology and Geothermal Research, v. 2, p. 329-341. 

Sparks, R.S.J., and Wilson, L., 1982, Explosive volcanic eruptions,V-Observations of plume dynamics during the 1979 

Soufriere eruption, St. Vincent: Geophysical Journal of the 

Royal Astronomical Society, v. 69, p. 551-570. 

Wilson, L., Sparks, R.S.J., Huang, T.C., and Watkins, N.D., 1978, 

The control of eruption column heights by eruption energetics 

and dynamics: Journal of Geophysical Research, v. 83, p. 

1829-1836. 
106 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Woods, A.W., 1988, The fluid dynamics and thermodynamics of 

eruption columns: Bulletin of Volcanology, v. 50, p. 169-191. 

Woods, A.W., and Bursik, M.I., 1991, Particle fallout, thermal 

disequilibrium and volcanic plumes: Bulletin of Volcanology, 

v. 53, p. 559-570. 

Woods, A.W., and Caulfield, C.P., 1992, An experimental investigation of explosive volcanic eruptions: Journal of Geophysical Research, v. 97, p. 6699-6712. 

Woods, A.W., and Kienle, J., in press, The dynamics and thermodynamics of volcanic clouds: Theory and observations from 

the April 15 and April 21, 1990 eruptions of Redoubt Volcano, Alaska: Journal of Volcanology and Geothermal Research. 

Woods, A.W., and Self, S., 1992, Thermal disequilibrium at the top 

of volcanic clouds and its effect on estimates of the column 

height: Nature, v. 355, p. 628-630. 

Woods, A.W., and Wohletz, K., 1991, The dimensions and dynamics of coignimbrite eruption columns:· Nature, v. 350, p. 

225-227. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

INFLUENCE OF VOLCANIC ASH CLOUDS 

ON GAS TURBINE ENGINES 

By Michael G. Dunn and Douglas P. Wade 

ABSTRACT 

Results are reported for a technology program 

designed to determine the behavior of gas turbine engines 

when operating in volcanic ash clouds. The response of 

several different engines, among them the Pratt and 

Whitney JT3D turbofan and the Pratt and Whitney J57 turbojet, has been determined. 

The damage that an engine will experience depends 

upon the particular engine, the thrust setting at which the 

engine is operating when it encounters the dust cloud, the 

constituents of the cloud, and the respective melting temperatures of the various constituents. In addition, the rate at 

which events will occur depends upon the particle density 

(or concentration) of the ash cloud. 

An important part of the research effort at Calspan 

Advanced Technology Center has been to identify which 

engine parameters available to the flight crew can provide an 

early warning of impending engine problems. Having determined that one is operating in a potentially dangerous environment, it is then important to determine how to safely 

operate a damaged engine. 

INTRODUCTION 

The reality of the danger ofthe volcanic eruption clouds 

to commercial aircraft operation has been dramatically illustrated since 1980. During the past several years, the airframe 

and engine companies have become involved in trying to 

understand the nature of the problems associated with aircraft interactions with volcanic ash clouds. Campbell (1991) 

described four 747 aircraft encounters with volcanic ash 

clouds, beginning with the June 1982 encounter of a British 

Airways 747-200 aircraft over West Java, Indonesia, and 

concluding with the December 1989 encounter between a 

747-400 aircraft with the Redoubt Volcano ash cloud near 

Anchorage, Alaska. The Boeing 7 4 7 is not the only aircraft 

that has experienced difficulty when operating in volcanic 

ash clouds (Campbell, 1991). The adverse influence of volcanic ash has been observed to occur in most modem power 

plants, such as the Rolls Royce RB211, the Pratt and 

Whitney JT9D, and the General Electric CF6. Measurement 

programs designed to ascertain the response of gas turbine 

engines when operated in dust-laden environments are 

needed to recommend operational procedures under those 

conditions. The dust of interest here is volcanic ash composed of rock and mineral particles that become airborne as 

a result of an explosive volcanic eruption. 

Gas turbine engines are routinely tested for the effect of 

ingestion of solid particles according to the procedures of 

Military Specification MIL-E-5007D, commonly known as 

the "Arizona road-dust test." During the last several years 

the material used in this test was changed from a mixed silicate mineralogy to crushed quartz. Encounters with volcanic 

ash clouds are much different than those experienced with 

MIL-E-5007D. Specifically, these differences involve the 

chemical and mineralogical composition, particle-size distribution, and particle concentration in the cloud. 

A research program in the area of gas turbine propulsion, ongoing at Calspan Advanced Technology Center in 

Buffalo, N.Y., utilizes a unique facility and experimental 

technique that exposes operating gas turbine engines to an 

adverse environment similar to that associated with a volcanic ash cloud without endangering either an airplane or a 

flight crew. The response of several different engines, 

including the Pratt and Whitney JT3D turbofan and the Pratt 

and Whitney J57 turbojet, to typical volcanic ash clouds has 

been investigated. 

The behavior of individual components that make up a 

volcanic ash cloud are studied separately using an Allison T56 

combustor canister, a row ofT56 high-pressure-turbine inlet 

nozzle guide vanes (NOV's), a dust-injection system, and an 

external air compression source. Data obtained using this 

device provide guidance to the researcher prior to full-scale 

engine measurements. A reasonable estimate of the behavior 

of a particular ash and the threshold temperature at which 

some components of the material in this ash might melt and 

deposit on the NOV's can be determined with this test system. 

The damage modes that an engine will experience 

depend upon the particular engine, the thrust setting at which 

the engine is operating when the dust cloud is encountered, 

the constituents of the cloud, and the respective melting 

107 
108 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 1. Large-engine research cell includes the engine test 

stand, operating equipment, and instrumentation. Major features of 

the experimental apparatus are a noise-suppression system and a 

dust-injection system. The noise-suppression system used for these 

measurements is an air-cooled unit consisting of a primary intake silencer, a secondary intake silencer, an engine test stand enclosure, 

and a silencer system made up of an augmenter tube, an exhaust plenum, and an exhaust silencer. 

temperature of the cloud constituents. In addition, the rate at 

which events will occur depends upon the particle density (or 

concentration) of the cloud. 

Several different mechanisms may be responsible for 

altering engine performance during or after exposure to a 

volcanic ash cloud, and the potential of each mechanism 

should be recognized. The volcanic-ash-cloud encounter 

may be manifested in one or more of the following ways: 

(a) deposition of material on hot-section components, (b) 

erosion of compressor blades and rotor-path components, 

(c) partial or complete blocking of fuel nozzles, (d) partial 

or total blockage of cooling passages, (e) oil system or 

bleed air supply contamination, (f) fogging of the windscreen and landing lights, (g) contamination of the electronics because of dust ingested through the environmental 

control system (ECS), (h) erosion of antenna surfaces, and 

(i) plugging of the pitot-static system. Most of these phenomena have been experienced in the ash cloud encounters 

reported by Smith (1983) and Chambers (1985). Compressor erosion causes a loss of surge margin even if deposition 

does not occur (Tabakoff and Hussein, 1971 a, 1971 b; Hussein and Tabakoff, 1973; Grant and Tabakoff, 1975; and 

Tabakoff and Bahan, 1981 ). 

The work described in this paper shows how the ash 

cloud could be recognized if natural light or cloud conditions 

preclude direct visual observation, the type of engine damage expected from ash-cloud encounters, which of the 

engine diagnostics provide an indication of engine degradation, and how one manipulates the controls to generate significant thrust after engines have been severely damaged. 

Early results of this research were reported by Dunn and others (1987a, 1987b) and Batcho and others (1987). 

EXPERIMENTAL APPARATUS 

This type of research requires a unique facility that 

allows detailed measurements of propulsion-system tolerance for a full-scale engine under controlled laboratory conditions. The large-engine research facility at Calspan is 

located within a large building, thus permitting tests unhampered by weather. The test setup includes the engine test 

stand, operating equipment, and instrumentation (fig. 1). 

Two major features of the experimental apparatus are a 

noise-suppression system and a dust-injection system. The 

noise-suppression system used for these measurements is an 

air-cooled unit consisting of a primary intake silencer, a secondary intake silencer, an engine test stand enclosure, and an 

exhaust-silencer system made up of an augmenter tube, an 

exhaust plenum, and an exhaust silencer (fig. 1). 

The dust-injection system (DIS) is an important part of 

the test apparatus and was designed to accurately regulate 

the dust environment. The dust-injection system must provide a controlled range of particle sizes and concentrations, 

all evenly dispersed in the incoming air. The DIS, shown 

schematically in figure 2, consists of a dust tube, dust-injection nozzles, weigh-belt feeder and dust reservoir, and a bellmouth. The weigh-belt feeder includes process-monitoring 

instrumentation to allow precise control of dust being fed to 

the test engine. The dust is delivered to the injection nozzles 

by compressed air. A more detailed description of the experimental apparatus is given in Dunn and others (1987b). 

Figure 2. Schematic diagram of dust-injection system (DIS). The 

DIS is designed to accurately regulate the dust environment and 

must provide a controlled range of particle sizes and concentrations, 

all evenly dispersed in the incoming air. The DIS consists of a dust 

tube, dust-injection nozzles, weigh-belt feeder and dust reservoir, 

and a bellmouth. The weigh-belt feeder includes process-monitoring instrumentation to allow precise control of dust being fed to the 

test engine. The dust is delivered to the injection nozzles by compressed air. From Dunn and others (1987b ). 
INFLUENCE OF VOLCANIC ASH CLOUDS ON GAS TURBINE ENGINES 109 

CLOUD PREPARATION AND 

ANALYSIS 

The engines discussed here were all operated in air 

laden with particulate material from a mixture of two types 

of soils (sand and clay), two types of volcanic ash, and 

small amounts of a clay additive. The sandy soil is composed of decomposed granite obtained from the northwestem Santa Monica Mountains (Hollywood Hills area). The 

• ICH lEU 33St• INT 

"JS• IlK KEUEM -RAY HI • 2 IEU.I'CH 

Il 

I 

m 

I I . 11) 

., 

.! 

B ;~ I ! ~ 

II' ; IIi I 

12 14 16 Qe 1.1 

Figure 3. A, Scanning electron photomicrograph of black scoria 

sample. B, Composition spectrum of black scoria sample. 

clayey soil is weathered material from Corona, Calif. Two 

different volcanic ashes have been used: 1980 Mount St. 

Helens ash from near Portland, Oreg., and Twin Mountain 

basaltic scoria from Twin Mountain quarry near Des 

Moines,~. Mex. 

An analysis of the scoria (Dunn and others, 1987a) 

shows it to be approximately 85 percent basaltic glass, with 

the remaining 15 percent of the material being plagioclase 

and pyroxene. Figure 3A is a scanning electron photomicrograph of the scoria, and fig. 3B shows the elemental composition spectrum of the black scoria. Figures 4A and B are a 

photomicrograph and an elemental composition spectrum, 

respectively, for Mount St. Helens ash. 

TEST PROCEDURES AND 

TEARDOWN OBSERVATIONS 

TEST PROCEDURES 

During the course of the engine-testing program, many 

different engines have been utilized. The detailed test procedure differs depending upon the engine. Prior to exposing 

the engine to a dusty environment, a set of baseline measurements is obtained at many different power lever angle (PLA) 

settings. All of the available engine parameters are recorded, 

including the exhaust-gas temperature (EGT), fuel flow rate, 

inlet total pressure (PT2), fan-exit total pressure (PT2.s), 

engine pressure ratio (EPR), interstage pressure, high-compressor static-discharge pressure (Ps3), engine thrust, burner 

static pressure (PB), core speed ~2), and fan speed ~ t)· 

During this baseline measurement series, the engine also 

undergoes several 6-second periods of accelerations and 

decelerations. 

OBSERVATIONS DURING TESTING 

Common to all engines tested, we find that, immediately upon introduction of the dust, a striking glow is 

observed at the fan face. The glow is the well-known phenomenon St. Elmo's glow (or fire) that results from a discharge of electrostatic charge that has built up because of 

dust particles striking the moving metallic surfaces. St. 

Elmo's glow was observed by the British Airways crew during their encounter with the Galunggung volcanic ash cloud 

(Smith, 1983). 

Figure 5 shows the dust tube, the dust-injection nozzles, and the fan face glow. Figure 6 is a photograph of 

the fan face. The first-fan-stage rotor fence and the firststage inlet guide vane are not obscured by the glow 

because the momentum exchange between these surfaces 

and the dust particles is too low to cause charge accumulation. The second-stage inlet guide vane appears as a 

shadow in the illumination field of the first and second 

rotors. Three silhouettes appearing on figure 6 are the 
110 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 4. A, Scanning electron photomicrograph of Mount St. 

Helens ash. B, Composition spectrum of Mount St. Helens ash 

sample. 

result of the dust-injection nozzles. The location of these 

nozzles can be more clearly seen on figure 5. A very 

bright ring of light appears at the first and second rotor tip/ 

shroud regions. The illumination in this region may be 

brighter for several reasons; these include: (a) higher dustparticle concentrations caused by centrifuging, (b) greater 

optical depth and unobstructed view of the illumination, 

and (c) scintillation at the rotor tip. Also visible in this 

photograph is the bullet nose and a total-pressure probe. 

It has also been observed that a few of the enginereadout parameters respond very quickly to the presence of 

a dust cloud. For example, the burner static pressure (PB) 

and the high compressor static discharge pressure (Ps3) 

respond in almost identical fashion (fig. 7). The pressure 

increase can be very rapid. Also included on figure 7 are 

the fuel-flow rate and the fan total-pressure ratio, both of 

which are influenced by the dust cloud. The rate of pressure increase is a strong function of the power lever angle 

(PLA) setting and the dust cloud concentration. Figure 8 

illustrates that the turbine inlet temperature (FTIT) also 

responds rapidly when a dust cloud is encountered, but 

again this response is a strong function of the PLA setting 

and the dust cloud concentration. The engine pressure ratio 

(EPR) and core speed (N2) are also shown on figure 8. 

Changes in the core speed (N2) and the fan speed (N t) are 

indirect indicators of the material deposition or erosion as 

detected through the response of the control system. 

ENGINE TEARDOWN RESULTS 

All of the engines tested in this program were disassembled for inspection when they could no longer be operated 

safely. Both in-flight experience and laboratory experience 

have demonstrated that if one continues to operate at high 

thrust levels in a volcanic ash cloud, then it is likely that the 

engine will surge and flame out (Przedpelski and Casadevall, 

this volume). As noted earlier, the three dominant factors of 

immediate concern to pilots are material deposition occurring on the high-pressure-turbine nozzle guide vanes 

(NGV's), erosion of the fan and compressor blades, and deposition of carbon-like material on the fuel nozzles. Fogging 

of the windscreen and landing lights, contamination of the 

environmental control system (ECS), and contamination of 

the oil supply may also become a problem. 

The build-up of material on the nozzle guide vanes 

causes the very rapid increase in burner static pressure and in 

compressor discharge static pressure shown in figure 7. At 

high altitude, this pressure increase can lead to surge and 

engine flame-out. Figure 9 shows a portion of the nozzle 

guide vane row taken from an engine that was subjected to a 

dust mixture containing black scoria. This figure illustrates 

the heavy deposits on the leading edge and on the pressure 

surface. Figure 10 shows these deposits and illustrates that 

the cooling holes near the tip endwall are blocked, whereas 

those near the hub endwall are still open. 

It has been observed that the remelted deposits are relatively brittle. The thermal properties of the deposited material are very different from those of the metal airfoils. One 

of the reasons that it has been possible to restart engines that 

have shut down at altitude after encountering a volcanic ash 

cloud is probably that some of the deposited material can be 

blown off the surface by ram air after the engine cools down. 

Evidence of partial material removal from the vanes can be 

seen on figure 9. 
INFLUENCE OF VOLCANIC ASH CLOUDS ON GAS TURBINE ENGINES 111 

Figure 5. Photograph of St. Elmo's glow at fan face. Figure shows the dust tube, the dust-injection nozzles, and the fan-face glow. The 

first-fan-stage rotor fence and the first-stage inlet guide vane are not obscured by the glow (see text). The second-stage inlet guide vane 

appears as a shadow in the illumination field of the first and second rotors. 

Figure 11 shows several of the fuel nozzles from the 

same engine mentioned above. The material on these nozzles 

is basically carbon (T. Casadevall, written commun., 1991). 

The center hole of the nozzle, from which the fuel is sprayed, 

was open and was found to be capable of passing fuel at the 

design flow rate. However, the swirl vanes were plugged, 

thus inhibiting atomization of the fuel. Because of this plugging, it is extremely difficult (if not impossible) to restart an 

engine that has been damaged in this way since this material 

cannot be blown off by ram air. 

In addition to the difficulties caused in the hot section 

of the engine as a result of exposure to the volcanic ash 

cloud, the compressor can also sustain severe damage. Tip 

erosion is illustrated in figure 12. Throughout the compressor, tip-region erosion occurred on almost every stage. Figure 13 shows an example of the ninth-stage compressor 

blade row taken from the engine discussed in connection 

with figures 9-12. The trailing edge of the airfoil in the tip 

region became so thin that the material folded away from the 

pressure surface. Compressor wear is an irreversible process, and once the engine has operated in a volcanic ash 

cloud for any significant time period, the blades must be 

replaced. 

As illustrated by the 747 aircraft experiences described 

in Smith (1983) and Campbell (1991), the volcanic ash cloud 

material makes its way through the environmental control 

system (ECS) and into the cabin. Laboratory experiments 

(Dunn and others, 1987b) were performed to ascertain the 

relative amount of dust material that is passed by the ECS. 

Dust particles may erode the duct-wall material (fig. 14). 

The absolute level of contamination of the bleed air at any 

inlet dust concentration is defined as the fraction of the input 
112 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 6. Photograph of St. Elmo's glow at fan face. Three silhouettes are the dust-injection nozzles. The location of these nozzles can 

be more clearly seen on figure 5. A bright ring of light appears at the first and second rotor tip/shroud regions. 

dust that appears in the bleed. In the three cases sampled, 

this fraction was approximately constant, with an average 

value of 2.2 parts per thousand. The efficiency of the particle-collection process at the bleed can be obtained from this 

contamination level and the estimated air-mass flow in the 

bleed manifold. In our case, the latter is 0.5 percent of the 

total mass flow into the engine. This results in a 45 percent 

particle-collection efficiency in the ECS bleed. 

The collection efficiency depends primarily on the 

geometry of the engine near the ECS bleed and the local air 

velocity. The engine geometry is fixed, and the contribution 

of changes in the local air velocity to the collection efficiency with moderate changes in thrust setting is expected to 

be small. Thus, the collection efficiency is relatively independent of thrust setting, and its measured level can be used 

to estimate the absolute level of contamination for the bleed 

air at power settings other than cruise. For example, at a 

high-thrust condition, an increase in ECS airflow of about 50 

percent would produce an absolute level of contamination 

for the bleed air equal to 3.4 parts per thousand. 

CONCLUSIONS 

As a result of information obtained during the course of 

tests utilizing many different gas turbine engines, the following conclusions can be drawn: 

1. The presence of St. Elmo's glow at the engine face is 

indicative of dust in the environment. 

2. The manner in which the engine will behave in a dust 

environment is dependent upon the dust concentration, 

the dust constituents, the operating turbine-inlet temperature of the engine, and the engine control system. 

3. The turbine inlet temperature required to cause material deposition on the hot-section components is 
INFLUENCE OF VOLCANIC ASH CLOUDS ON GAS TURBINE ENGINES 113 

EXPLANATION 

------ ~ Fuel flow 

Burner pressure ratio 

- - - - - ~ High-compressor pressure ratio 

0 

~ 

c 

~ co 

9 

-----<:; Fan total-pressure ratio 

~ 0.2 s 

0 

DUST ON DUST OFF 

I 

_Q_ __ I a: 

:::> 

(/) 

(/) 

UJ 

.....J 

l..L1 

.....J 

UJ 

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l..L 

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a: 

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0 

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UJ(/) 

<..?(/) 

z~ ~a.. 

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~ a: 

UJ 

a: 

:::> 

(/) 

(/) 

UJ 

a: 

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a: 

UJ 

z 

a: 

:::> 

a:J 

z 

UJ 

<..? ~~---L--~--L_~ __ _L __ ~--~18 z - 2 - 1 0 1 2 3 4 ~ 

TIME, IN MINUTES Q 

Figure 7. Time history of engine parameters during dust experiments. Pn, inlet total pressure; Pn.s. fan-exit total pressure; 

Ps3, high-compressor static-discharge pressure; P8 , burner static 

pressure. 

approximately 2,000°F (1,094°C). Many older 

engines, which operate at lower temperature, will not 

experience deposition but will experience compression system erosion. The newer engines will experience both deposition and erosion unless the thrust 

level is reduced in order to lower the turbine inlet 

temperature. 

4. It must be emphasized that engine operation time in a 

dust-laden environment is limited. If entrance into 

the cloud is unavoidable, then the air crew is advised 

to reduce thrust, exit the cloud, and carefully monitor 

engine diagnostics (especially the EPR, EGT, fuel 

flow, core speed, and fan speed). This combination of 

parameters will help determine the degree of engine 

damage and how the control system is handling the 

problem. The reader is referred to the report of the 

Aerospace Industries Association (AlA) committee 

on volcanic ash for recommendations on how to 

~~ Cll 

~--~ 30 

i= 

l..L 

z 20 

UJ 

~ 10 

~ 

I 

u 

D 

EXPLANATION 

-- -- -- ~ (Fnnavs /~ 

PT6/PT2 

-----0 High-compressor speed 

DUST ON DUST OFF 

0" 

/ 

0/ 

7 

/ 

;/ _p~ r 

-o o-1/ 

-()-~-{)--- --[I--{}---[]----()--- j 

- 2 - 1 4 

TIME, IN MINUTES 

UJ 

a: 

:::> 

(/) 

(/) 

UJ 

0:-""N 

a..~ 0.1 UJz I£ 

(3~ 

~Q 

~~ wO: 

<..? 

z 

~ 

I 

u 

a: 

0 

(/) 

(/) 

UJ 

a: 

a.. 

~'E 

500 8 e-

±-: 

S2~ IUJ 

~g, 

UJ 

<..? 

z 

~ 

I 

u 

Figure 8. Time history of engine parameters during dust experiments. FTIT avg• average turbine inlet temperature; e, ratio of total 

temperature to National Aeronautic and Space Administration 

(NASA) standard sea-level temperature of 58. 7°F; T n, turbine temperature; Pn, inlet total pressure; Py6, total pressure. 

operate a commercial aircraft if the air crew should 

unexpectedly find itself in a volcanic ash cloud (AlA 

Propulsion Committee 334-1, this volume; Campbell, 

this volume). 

5. Prolonged operation in the dust-laden environment 

may result in permanent engine damage. If the aircraft is operating at high altitude, the surging associated with this type of damage may cause engine 

flame-out. If the fuel nozzles have not become covered with carbon, then it should be possible to restart 

the engine at lower altitude. Some of the deposited 

material will have blown off during the period of time 

that the engine was inoperable. 

6. A significant amount of material will make its way 

through the environmental control system and into the 

electronics cabinets and the cabin itself. The particle 

size of this material is on the order of 6 J..Lm. 
114 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 9. Photograph of nozzle guide vane for first-stage high-pressure turbine. Figure shows a portion of the nozzle guide vane row taken 

from an engine that was subjected to a dust mixture containing black scoria. This figure illustrates the heavy deposits on the leading edge 

and on the pressure surface. 
INFLUENCE OF VOLCANIC ASH CLOUDS ON GAS TURBINE ENGINES 115 

Figure 10. Photograph of nozzle guide vane for first-stage high-pressure turbine. Note remelted ash deposits and that the cooling holes 

near the tip endwall are blocked, whereas those near the hub endwall are still open. The remelted deposits are relatively brittle and some of 

the deposited material can be blown off the surface by ram air after the engine cools down. Evidence of partial material removal from the 

vanes can be seen on figure 9. 
116 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 11. Photograph of fuel nozzles from the engine shown in 

figures 9 and 10. The material on these nozzles is carbon (T. Casadevall, written commun., 1991 ). The center hole of the nozzle, from 

which the fuel is sprayed, was open and capable of passing fuel at 

the design flow rate; however, the swirl vanes were plugged, thus 

inhibiting atomization of the fuel. 

Figure 12. Photograph of second-stage fan showing blade tip erosion. Throughout the compressor, tip-region erosion occurred on 

almost every stage. 

Figure 13. Photograph of high-pressure compressor ninth-stage 

rotor. Figure shows an example of the ninth-stage compressor blade 

row taken from the engine shown in figures 9-12. The trailing edge 

ofthe airfoil in the tip region became so thin that the material folded 

away from the pressure surface. 

Figure 14. Photograph of environmental control system plumbing showing erosion of duct walls. Scale is in inches. 
INFLUENCE OF VOLCANIC ASH CLOUDS ON GAS TURBINE ENGINES 117 

REFERENCES CITED 

Batcho, P.F., Moller, J.C., Padova, C., and Dunn, M.G., 1987, Interpretation of gas turbme response due to dust ingestion: 

ASME Journal of Engineering for Gas Turbines and Power, v. 

109, p. 344-352. 

Campbell, E.E., 1991, 747-400 Airplane damage survey following 

a volcanic ash encounter [abs.], in Casadevall, T.J., ed., First 

International Symposium on Volcanic Ash and Aviation Safety: U.S. Geological Survey Circular 1065, p. 14. 

Chambers, J.C., 1985, The 1982 encounter of British Airways 747 

with the Mt. Galunggung eruption cloud: Reno, Nev., AIAA 

23rd Aerospace Sciences Meeting, AIAA Paper No. 85-0097, 

5p. 

Dunn, M.G., Padova, C., and Adams, R.M., 1987a, Operation of 

gas turbine engines in dust-laden environments: Paris, France, 

AGARD-Advanced Technology of Aero Engine Components, 

May 4-8, 1987, 14 p. 

Dunn, M.G., Padova, C., Moller, J.E., and Adams, R.E., 1987b, 

Performance deterioration of a turbofan and a turbojet engine 

upon exposure to a dust environment: ASME Journal of Engineering for Gas Turbines and Power, v. 109, p. 336-343. 

Grant, G., and Tabakoff, W., 1975, Erosion prediction in turbomachinery resulting from environmental solid particles: Journal of 

Aircraft, v. 12, p. 471-478. 

Hussein, M.F., and Tabakoff, W., 1973, Dynamic behavior of solid 

particles suspended by polluted flow in a turbine stage: Journal 

of Aircraft, v. 10, p. 434-440. 

Smith, W. S., 1983, High-altitude conk-out: Natural History, v. 92, 

no. 11, p. 26-34. 

Tabakoff, W., and Bahan, C., 1981, Effects of solid particles suspended in fluid flow through an axial flow compressor stage 

[abs.]: Bangladore, India, Fifth International Symposium on 

Airbreathing Engines. 

Tabakoff, W., and Hussein, M.F., 1971 a, Effects of suspended solid 

particles on the properties in cascade flow: AIAA Journal, v.9, 

p. 1514-1519. 

Tabakoff, W., and Hussein, M.F., 1971b, Pressure distribution on 

blades in cascade nozzle for particulate flow: Journal of Aircraft, v. 8, p. 736-738. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC ASH-AIRCRAFT INCIDENTS IN ALASKA 

PRIOR TO THE REDOUBT ERUPTION ON 

15 DECEMBER 1989 

By Juergen Kienle 

ABSTRACT 

Commercial and military propeller-driven and jet aircraft have encountered airborne volcanic ash in the Cook 

Inlet region three times prior to the near crash of a Boeing 

747-400 jet downwind from Redoubt Volcano on 15 

December 1989. Aircraft flew into ash plumes in 1953 

when Mt. Spurr erupted and in 1976 and 1986 when 

Augustine Volcano erupted. Damage to aircraft in all incidents was restricted to severe sandblasting, and no engine 

failures occurred. 

INTRODUCTION 

The volcanoes of the Cook Inlet region, Alaska, make 

up the eastern end of the Aleutian volcanic arc. Air routes 

connecting Europe and North America with the Far East follow great-circle routes, which parallel much of the volcanic 

chain. Three volcanoes in Cook Inlet, Mt. Spurr, Redoubt 

Volcano, and Augustine Volcano (fig. 1 ), have erupted several times this century for a total of 10 eruptions between 

1900 and 1992, or about once every 10 years on average. In 

recent decades, the eruption rate has almost doubled. Since 

1950, Augustine erupted three times, Redoubt twice, and 

Spurr twice, totaling seven eruptions in the past 43 years or 

once every 6 years on average. Each eruptive cycle of the 

three volcanoes produced multiple explosions and associated 

ash plumes. Iliamna Volcano, located between Redoubt and 

Augustine Volcanoes (fig. 1 ), has not had an ash eruption in 

historic times, although large steam plumes have been 

reported frequently to the Alaska Volcano Observatory 

(AVO). 

The Alaska Volcano Observatory gives special attention to the four Cook Inlet volcanoes, which are west and 

southwest of Anchorage (fig. 1 ). AVO operates remote, 

continuously recording, radio-telemetered seismic stations 

on all four Cook Inlet volcanoes and slow-scan television 

cameras, which are focused on Spurr and Redoubt. For the 

recent eruptions of Spurr (1992), Redoubt (1989-90), and 

Augustine (1986), this has allowed scientists to forecast 

eruptive activity and to give adequate warnings to the 

commercial aircraft industry and to the U.S. military, either 

before or at the onset of explosive, ash-producing eruptions. Because ash is mainly advected by tropospheric 

winds, plume-path predictions issued in recent years by 

AVO have been used by carriers to avoid aircraft-ash 

encounters (Casadevall, in press). 

This paper gives a brief description of aircraft-ash incidents over Cook Inlet between 1953 and 1986, before the 

near-fatal encounter of a Boeing 747-400 jet with a Redoubt 

ash plume on 15 December 1989. 

AIRCRAFT-ASH ENCOUNTERS 

OVER COOK INLET, 1953-86 

MT. SPURR, 1953 

On 9 July 1953, at about 17:00 local time, the Crater 

Peak vent on the southern flank of Mt. Spurr erupted suddenly, without much warning, sending a dark, ash-rich column to a height of 21 km (70,000 ft). Juhle and Coulter 

(1955) report that the ash cloud, carried by gentle westerly 

winds, drifted over Anchorage by noon. Heavy ash fall 

lasted for about 3 hours and darkened the skies so much that 

the city lights had to be turned on from noon until 15:00. 

Eventually 3 to 6 mm (114 inch) of fine dust settled over the 

city, including Anchorage Airport and Elmendorf Air Force 

Base, disrupting air traffic for 2 days. 

By chance, the eruption was witnessed at close range by 

pilots of two U.S. Air Force planes on a reconnaissance mission near the volcano (Juhle and Coulter, 1955; Wilcox, 

1959). The following pilots' account is quoted from an Air 

Force press release of 10 July 1953 (taken from Wilcox, 

1959): 

At 05h 05m Lieutenant Metzner noticed a column of smoke 60 miles ahead 

that was about 15,000 ft high and one-eighth mile wide. As he approached 

the smoke it was apparent that the eruption causing it was becoming 

increasingly severe with the smoke growing rapidly in height. At about 25 

miles distance, the volcano was recognized as the 11,070-foot high Mt. 

Spurr. Both planes approached the mountain at about 15,000 ft and circled 

the volcano at about 05h 25m. They noticed the continuing increase in the 

intensity and size of the column of smoke with lightning flashes through its 

core every 30 seconds. Smoke issued from the volcano in violent billows at 

119 
120 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

the 7,000-foot level of the mountain caused by huge subterranean explosions. Tremors on the mountainsides were visible from the aircraft and 

were followed by snow slides on the mountain. The smoke had by now 

reached the 30,000-foot level, rolling upward and assuming the shape of 

the atomic bomb mushroom. Clouds of smoke were every shade of gray 

from black at the crater to pure white at the top. By this time the width had 

increased to about a mile at the base and 30 miles at its widest part. 

About 05h 40m Lieutenant Metzner climbed in order to estimate the 

height of the mushroom. The top of the stalk, or the bottom of the mushroom, was 30,000 ft and the top of the mushroom had climbed to 70,000 

ft. Lightning was now flashing from top to bottom of the mushroom at 

three-second intervals. 

At about 6h OOm volcanic ash began falling from the mushroom on all 

sides and finally made the entire area hazy. A clear definition of the volcano and the mushroom rapidly faded and the patrol returned to its base. 

Another pilot report confirmed that ash was still being 

erupted vigorously 4 hours later, at 09:00. The activity 

declined toward noon but resumed at 15:30; other eruptions 

took place later that day (Wilcox, 1959). Wilcox further 

states that, on the next day, 10 July, the vent was only steaming, except for a strong ash-laden surge at 15:30, which rose 

to 6 km (20,000 ft). Juhle and Coulter were in the field at the 

volcano from 11 to 14 July and again on 16 July, during 

which time they observed steam clouds to heights of 6 km, 

with occasional puffs of black dust (Wilcox, 1959). 

One of the two F-94 jet aircraft that were flying near 

Mt. Spurr on the morning of 9 July flew through the cloud 

and had its Plexiglas cockpit canopy frosted by the "sandblasting" action of the ash (Juhle and Coulter, 1955). The 

following information is summarized from a U.S. Air Force 

report on the Mt. Spurr eruption (U.S. Air Force, 1955): 

During the peak of eruptive activity, three jet aircraft of the 66th FighterInterceptor Squadron were dispatched through the ash plume to bring back 

first-hand, eyewitness accounts of the eruption. [There is a conflict with the 

report of Juhle and Coulter (1955), which says that only one jet flew 

through the eruption cloud.] Upon return to Elmendorf AFB, all three jets 

had sandblasted wing leading edges, windshields, side panels, and front 

portions of the canopies, greatly reducing pilot visibility. Some panels later 

had to be replaced. 

As a precaution, all aircraft of the U.S. Air Force's 5039th Air Transport 

Squadron in flyable condition (26 planes) were evacuated to Laird and 

Eielson Air Force Bases near Fairbanks. However, only four F-94 interceptors were able to engage in the evacuation; loss of power in the dusty air on 

take-off grounded the other interceptors. These were hangared in time, 

except for several large C-124 transport aircraft (Globe Trotters). Floatequipped L-28's of the 5th Liaison Squadron were moved from Anchorage 

to Lake Louise. Wheel-equipped Beavers were placed inside hangars. Two 

radar stations in the Anchorage area, one on Fire Island, were taken off the 

air to prevent damage to the antenna drive and generators. 

Most seriously affected by the ash fall were the propeller-driven C-124 

transport aircraft stored outside, which required 10 days of cleanup to 

remove the fine volcanic ash from the aircraft. From 9 to 13 July, tactical 

aircraft were unable to take to the air over Elmendorf because of dusty conditions and remobilized ash on runways and taxiways. The lOth Air Division of the Alaska Air Command lost its ability to meet its air defense 

mission and it passed the responsibility for fighter interception and radar 

control to the 11th Air Division at Laird AFB. It was only on 17 July, eight 

days after the eruption, that the three Elmendorf fighter-interceptor squadrons returned to normal operations. For all practical purposes, Elmendorf 

AFB was closed to air traffic from 9 to 17 July. The east-west runway was 

GULF OF 

ALASKA 

Figure 1. Location of volcanoes in the area of Cook Inlet (solid 

triangles) and places mentioned in the text. Elmendorf Air Force 

Base is located near Anchorage. 

cleared for emergency flying only. Aircraft landed, but had to immediately 

cut off engines while on the runway before being towed to the hangar. The 

reverse procedure was used for emergency takeoffs to reduce exposure of 

the airplanes to the pervasive dust. 

The cleanup operation produced many engineering headaches. The soft, 

clinging ash first had to be cleared from all aircraft surfaces, taxiways, runways and parking ramp~. All moving parts, air intakes, accessory cases, 

filters and screens required thorough cleaning to prevent corrosion and 

contamination. 

A truck-mounted jet engine, originally designed to remove ice from railroad tracks, proved to be the most useful tool in clearing ash from large 

swaths of ground; for example, within 40 hours this jet-blower cleared 

some 440,000 m2 of pavement at the Anchorage International Airport. 

There are no known records of commercial aircraft 

being affected by the 9 July eruption of Mt. Spurr. As 

became clear after encounters between volcanic ash and aircraft at Galunggung, Indonesia, in 1982, and more recently 

at Redoubt, propeller-driven airplanes that operate at low 

engine temperatures fare much better than jets in severe, 

dusty conditions. 

AUGUSTINE VOLCANO, 1976 

Augustine Volcano, located in lower Cook Inlet (fig. 1 ), 

erupted in January 1976 after 12 years of dormancy (fig. 2). 

Sub-Plinian eruptions occurred from 22 to 26 January and 

spread ash generally northward and eastward over the Kenai 

Peninsula, with fine ash falling as far away as Sitka, 1, 100 

km (684 mi) downwind (Kienle and Shaw, 1979). 
VOLCANIC ASH-AIRCRAFT INCIDENTS IN ALASKA PRIOR TO THE REDOUBT ERUPTION 

Figure 2. Augustine Volcano in eruption on 6 February 1976. Photograph from the west coast of Augustine 

Island, courtesy of Gacy Gunkel. 

121 
122 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

One of the 22 January Augustine eruptions occurred in 

the midst of a U.S. Air Force defense exercise. Reports of 

greatly reduced visibility were received from pilots in two 

F-4E Phantom jets flying in formation through an eruption 

cloud. These observations were used by Kienle and Shaw 

(1979) to estimate the minimum mass concentration of particulate material contained in that eruption cloud. No 

mechanical problems or serious power loss were reported by 

the pilots. The following is an excerpt of a report by the two 

F-4E Phantom jet pilots who had taken off from Galena, 

Alaska, on 22 January 1976, heading south for King Salmon 

(from Kienle and Shaw, 1979; U.S. Air Force, 1976): 

The two jets were flying in clouds, cruising at 9 km (3I,OOO ft). We were 

still in the weather when suddenly at I4:30 AST the ordinary gray clouds 

slightly darkened for a moment or two, then there was instant complete 

darkness. There was no turbulence associated with this darkness. The two 

jets were flying in close formation about I 0 meters apart. Had the lead 

plane not immediately turned on its lights, the following pilot would have 

lost contact; he could barely see the lead plane I 0 meters away with its 

lights on. Upon landing in King Salmon, the canopy of the aircraft was 

seen to be scoured, and the paint at the wing tips was sandblasted off. Very 

fine, jewelers-rouge-colored material was ingested into the cockpit through 

the engine air intakes. The material was sticky and was found in every 

nook and cranny of the planes. 

A second incident concerns three Japan Airline jet airplanes en route to Tokyo on the afternoon of 25 January 

1976. As recounted by Mr. K. Noguchi of Japan Airlines 

(Kienle and Shaw, 1979): 

After cargo flight JL 672 took off from Anchorage at I6:00 AST, the DC-8 

was about to reach its cruising altitude of IO km (33,000 ft), 25 minutes 

after takeoff, traveling along air route J-50I when it suddenly encountered 

an ash cloud near Whitefish Lake (25 km southeast of Sparrevohn). Upon 

landing in Tokyo the scoured center windshield had to be replaced. Much 

ash had adhered to the plane and slight abrasion damage was found on 

external radio parts, landing gears and the air-conditioning system, but 

none of these parts needed to be replaced. 

Two other passenger planes, a Boeing 747 and a DC-8, 

also bound for Tokyo and departing within 1 hour after 

flight JL 672, reported ash suddenly adhering to the planes 

at cruising altitude (about 10 km) near Sparrevohn, which 

also caused minor damage but not as extensive as that to the 

DC-8 flight JL 672. 

Kienle and Swanson (1985), in a report on volcanic 

hazards for Augustine Volcano, discussed the hazard of volcanic ash to aircraft and delineated very high risk, high-risk, 

moderate, and low-risk hazard zones in the vicinity of 

Augustine Island. 

AUGUSTINE VOLCANO, 1986 

Augustine erupted again in 1986, with strong eruptive 

activity concentrated in the period between 27 and 31 March. 

The sequence of events was similar to the 1976 eruption, 

with an initial, highly explosive vent-opening phase lasting 

4 days, followed later in the year by less explosive activity 

associated with the extrusion of a new lava dome (Swanson 

and Kienle, 1988). The eruptive cycle ended in September 

1986, but from April on, the eruption did not present a substantial hazard to aircraft. 

During the March 1986 eruption of Augustine Volcano, airborne ash again presented a hazard to aircraft operations throughout the Cook Inlet basin and to airports in 

Anchorage because of predominantly southerly winds 

(Yount and others, 1987). The eruption was anticipated by 

Alaskan volcanologists (Kienle and others, 1986; Kienle, 

1986), and T. Miller and M. E. Yount of the U.S. Geological Survey office in Anchorage held briefings with the Federal Aviation Administration (FAA) and the U.S. Air Force 

on 18 March 1986, 9 days prior to the eruption, to warn 

about the possibility of an eruption and the consequences to 

aircraft operations. 

Early on the morning of 27 March 1986, just after the 

eruption had begun, the U.S. Air Force evacuated planes 

from Anchorage and kept them away until 30 March. Even 

though the Anchorage International Airport was never officially closed during the most explosive phase of the eruption, 

most commercial carriers either canceled or diverted their 

Anchorage flights between 27 and 29 March. 

The following is a summary taken from Aviation Week 

and Space Technology (1986): 

From March 27 to 29, air carrier service to Anchorage was nearly at a 

standstill. Subsequently, the wind shifted to a northerly direction carrying 

the ash away from the Cook Inlet bowl, now affecting the airline traffic 

between Anchorage and airports at Kodiak and King Salmon. Volcanic ash 

generally stayed below I5,000 ft ( 4.5 km) but a stronger eruption on March 

3I sent an ash plume up to 30,000 ft (9 km). 

Alaska Airlines had its worst day on 28 March, when it canceled 40 out of 

68 Anchorage arrivals and departures. Twenty-seven to 29 March, the 

Anchorage stop of the airline's Seattle-Anchorage-Fairbanks flights, coming and going, were deleted. Western Airlines canceled all of its flights to 

and from Alaska 27-28 March and flew some flights on 29 March. United 

Airlines, Northwest Airlines and other international carriers that fly from 

Europe and Far East Asia over the North Pole canceled service during the 

worst ash conditions. United canceled 35 flights between 27 and 29 March. 

Local commuter airplane traffic between Anchorage and the Kenai Peninsula also was largely shut down and the Federal Aviation Agency [sic] 

(FAA) temporarily shut down its air-route surveillance radar at Kenai for 

two days. With shifting winds on 31 March 1986, ash was cleared from the 

air over most of the Cook Inlet basin, and normal air operations resumed. 

CONCLUSIONS 

A comparison of the eruptions of these volcanoes demonstrates that, as we learn to live with the high activity level 

of Cook Inlet volcanoes, we improve our ability to cope with 

the problem of volcanic ash and aviation safety. Air traffic 

has increased dramatically in Alaska since the eruption of 

Mt. Spurr in 1953. High-bypass, turbine-powered jet aircraft 

have replaced larger, propeller-driven passenger planes; 

both factors increase the risk of danger from encountering 

airborne volcanic ash. On the other hand, the volcanological 

community in Alaska has come together since 1953. The 

1953 Mt. Spurr eruption caught everyone off-guard, but we 
VOLCANIC ASH-AIRCRAFT INCIDENTS IN ALASKA PRIOR TO THE REDOUBT ERUPTION 123 

were better prepared in 1976 and 1986 for the Augustine 

eruptions, having instrumented that volcano with radio-telemetered seismographs starting in 1970. In 1986, briefings 

with the aviation community were held by U.S. Geological 

Survey volcanologists 9 days prior to the onset of the eruption that paralyzed air traffic in Cook Inlet for 4 days. Significantly, there were no encounters of aircraft, either private or 

military, with volcanic ash during the most vigorous phase of 

the 1986 Augustine eruption. 

The close cooperation among volcanologists ofthe U.S. 

Geological Survey, the Alaska Geological Survey, and the 

University of Alaska, Fairbanks, that had developed during 

the 1986 Augustine eruption was formalized in March 1986 

with the founding of the Alaska Volcano Observatory. Since 

then, AVO has instrumented all four Cook Inlet volcanoes 

with at least four seismometers at each volcano. In addition, 

remotely controlled slow-scan television cameras have been 

installed to continuously observe Mt. Spurr and Redoubt 

Volcano, and we have plans to do the same for Augustine 

Volcano. Satellite surveillance of the volcanoes and eruptive 

plumes has become routine at the AVO laboratory in Fairbanks (Dean and others, this volume), and an array of lightning detectors can track electrified plumes in Cook Inlet. 

Radars and television cameras have been used to track rising 

eruption columns and their dispersal by wind. 

During the two recent eruptions in Cook Inlet at 

Redoubt Volcano (1989-90) and at Mt. Spurr (1992), AVO 

went on 24-hour watches for several months. Communication with the carriers and Federal agencies involved with air 

traffic (Federal Aviation Administration, National Weather 

Service) were increased and resulted in the production of 

daily updates on the status of the active volcano and the forecasting of potential plume trajectories every 6 hours (or more 

often during active phases of ongoing eruptions) (Murray 

and others, this volume). 

In spite of the better level of preparedness in recent 

years, there was a near fatal encounter of a Boeing 7 4 7-400 

with an ash plume of Redoubt Volcano on 15 December 

1989 (Casadevall, in press). The aviation and volcanology 

communities in Alaska must jointly strive to avoid any other 

encounters of this type. 

ACKNOWLEDGMENTS 

I thank Tina Neal and one anonymous reviewer for their 

constructive editing of the original draft. This work was supported by the Alaskan Volcano Observatory through U.S. 

Geological Survey Grant 14-08-0001-0574. 

REFERENCES CITED 

Aviation Week and Space Technology, 1986, Alaska air traffic disrupted by ash from volcano: v. 124, no. 14, p. 36. 

Casadevall, T.J., in press, The 1989-1990 Eruption of Redoubt 

Volcano, Alaska: Impacts on aircraft operations: Journal of 

Volcanology and Geothermal Research. 

Juhle, W., and Coulter, H.W., 1955, The Mt. Spurr eruption, July 9, 

1953: Transactions of the American Geophysical Union, v. 36, 

p. 188-202. 

Kienle, J., 1986, Augustine Volcano: Awake again?: Eos, Transactions of the American Geophysical Union, v. 67, p. 172-173. 

Kienle, J., Davies, J.N., Miller, T.P., and Yount, M.E., 1986, The 

1986 eruption of Augustine Volcano: Public safety response by 

Alaskan volcanologists: Eos, Transactions of the American 

Geophysical Union, v. 67, p. 580--582. 

Kienle, J., and Shaw, G.E., 1979, Plume dynamics, thermal energy, 

and long distance transport of Vulcanian eruption clouds from 

Augustine Volcano, Alaska: Journal of Volcanology and Geothermal Resources, v. 6, p. 139-164. 

Kienle, J., and Swanson, S.E., 1985, Volcanic hazards from future 

eruptions of Augustine Volcano, Alaska: University of Alaska 

Geophysical Institute, Report UAG R-275, 122 p. 

Swanson, S.E., and Kienle, J., 1988, The 1986 eruption ofMt. St. 

Augustine: Field test of a hazard evaluation: Journal of Geophysical Research, v. 93, p. 4500--4520. 

U.S. Air Force, 1955, History of the Alaskan Air Command, Part 2, 

natural phenomenon, Mt. Spurr eruption: Anchorage, Alaska 

Air Command, Elmendorf Air Force Base, p. 73-80. 

---1976, History of the 21st composite wing: Anchorage, 

Alaska Air Command, Elmendorf Air Force Base, v. 1, 121 p. 

Wilcox, R.E., 1959, Some effects of recent volcanic ash falls with 

especial reference to Alaska: U.S. Geological Survey Bulletin 

1028-N,p.409-476. 

Yount, M.E., Miller, T.M., and Gamble, B.M., 1987, The 1986 

eruption of Augustine Volcano, Alaska: Hazards and effects: 

U.S. Geological Survey Circular 998, p. 4-13. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

MITIGATION OF VOLCANIC ASH EFFECTS ON AIRCRAFT 

OPERATING AND SUPPORT SYSTEMS 

By J.R. Labadie 

ABSTRACT 

On 18 May 1980, Mount St. Helens erupted, covering 

50 percent of Washington State with approximately 1 km3 

of ash. Government agencies, airports, utilities, and private 

corporations within the impacted areas were all forced to 

cope with ash deposits ranging in depth from 3 mm to 7 5 

mm while maintaining essential services and carrying on 

normal activities. Volcanic ash is abrasive, mildly corrosive, conductive (especially when wet), and may carry a 

high static charge for up to 2 days. The ash is fmely 

divided, easily entrained in the air by wind or vehicle 

movement, and may remain suspended for many minutes. 

Due to the combination of these qualities, volcanic ash is 

pervasive. Techniques for reducing the effects of volcanic 

ash are basically "low tech" and can be grouped into three 

broad categories: keeping the ash out, controlling what gets 

in, and disposing of the ash. Mitigation actions will be 

required on a continuous basis as long as ash is present. 

Effective mitigation depends on prior planning and preparation, mobilization of resources, and persistence. 

INTRODUCTION 

This report addresses techniques for mitigating the 

effects of volcanic ash on selected categories of critical 

equipment. It is based on information developed and experience gained with volcanic ash fallout produced during the 

eruption of Mount St. Helens in the State of Washington. 

On 18 May 1980, Mount St. Helens erupted, covering 

50 percent of Washington with approximately 1 km3 of ash. 

Although 19 of39 counties in the State received some volcanic ash, five eastern counties were severely impacted. Government agencies, airports, utilities, and private corporations 

were all forced to cope with ash deposits ranging in depth 

from 3 to 75 mm while maintaining essential services and 

continuing normal activities. A review of the available literature (damage survey reports, newspaper and magazine articles, and Federal and State agency advisories) formed the 

basic groundwork for this report. In-depth interviews with 

equipment users, service companies, airport operators, 

utilities, and others impacted by the ash elicited detailed 

information on ash-related damage and on methods of dealing with the ash. Research for this article was originally conducted under the sponsorship of the Air Force Office of 

Scientific Research and the Defense Advanced Research 

Projects Agency (Labadie, 1983). 

EFFECTS OF VOLCANIC ASH 

Volcanic ash is abrasive, mildly corrosive, and conductive (especially when wet) and may also carry a high static 

charge for up to 2 days after being ejected from a volcano 

(Heiken, this volume). The ash is easily resuspended by 

wind or vehicle movement and may remain suspended for 

many minutes. Due to the combination of these qualities, 

volcanic ash is pervasive. It can penetrate all but the most 

tightly sealed enclosures, and it can be very difficult to 

remove from electronic components. 

Ash deposited on electronic components can cause arcing, short circuits, and intermittent failures because it is conductive. High-voltage circuits and components are especially 

vulnerable. Ash dampened by rain can cause arcing, flashovers, and pole fires on electrical-distribution systems. 

Resulting outages may hamper mitigation efforts that require 

electrical power. 

The ash easily absorbs water and can weigh up to 

1,400 kg/m3; water-laden ash may collapse or damage flat 

roofs. Wet ash is very slippery and can cause traction problems. Dry ash, when blown into the air, reduces visibility 

and piles up on roads, runways, and taxiways. Ash must be 

physically removed and controlled after removal to prevent 

reentrainment. 

Moving parts are subject to abrasion damage from volcanic ash. The ash is attracted to and entrained in any 

exposed lubricant; thus, abrasion effects will continue even 

after the bulk of the ash has been removed. Bearings, brakes, 

and transmissions will wear out very quickly. Computer 

disks, disk drives, and heads are very sensitive to abrasion 

and are easily damaged by ash. In addition, ash adhering to 

125 
126 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

painted or polished surfaces will scratch and scour the surface unless it is removed carefully. 

Filters on air handling and computer systems may 

become clogged with ash to the point that airflow is completely stopped, leading to equipment overheating. Clogged 

filters may collapse and severely contaminate the internal 

environment. Additional filtration can reduce ash penetration, but only at the cost of reduced airflow to critical equipment. Filtration systems that incorporate centrifugal 

separators can handle ash much more easily. 

VOLCANIC ASH MITIGATION 

Techniques for reducing the effects of volcanic ash can 

be grouped into three broad categories: (1) keeping the ash 

out, (2) controlling what gets in, and (3) disposing of the ash. 

These categories are more illustrative than discrete, and 

some mitigation techniques will apply in all three cases. Mitigation actions will be required on a continuous basis as long 

as ash is present. Settled ash is easily reentrained, and a 2-

mm layer can be as troublesome as a 50-mm layer. 

The most effective technique for reducing ash-related 

damage or upset to equipment is to avoid using the equipment: shut down, close up, keep inside, or seal the area until 

the ash can be removed. This tactic is acceptable only for 

short periods of time because operations must be resumed at 

some point. In any case, disposal techniques will not eliminate all of the ash. A residue will remain on the ground and 

will be blown into the air by wind, passing vehicles, and aircraft takeoffs. Thus, an accelerated and intensive program of 

inspection, maintenance, cleaning, and monitoring will be 

necessary during and after the main part of ash deposition. 

Cleaning the ambient air-and keeping it clean-is the 

key to reducing operation and maintenance problems. Blowing ash off of a circuit board is useless if the ash is fine 

enough to remain suspended for several minutes. The difficulty of attempting to perform maintenance tasks in an 

already ash-contaminated atmosphere is obvious. "Cleanroom" procedures can be used to isolate an area and keep it 

free of ash, but only under ideal circumstances. Some equipment-aircraft engines, for example-are too large for such 

treatment. Tents or tarps can be used to reduce gross contamination. However, fine particles can penetrate very small 

openings and seams; it is this property that makes fine particles so damaging to critical equipment. 

Some mitigation procedures may cause additional problems or may actually be counterproductive, depending on the 

circumstances. For example, adding filtration to a computer 

system will reduce the amount of ash contamination, but it 

will also decrease the air flow. The resulting rise in temperature may change the operating characteristics of sensitive 

components or even cause damage. Adding a larger fan 

would increase the air flow, but not all computers, especially 

smaller units, can be easily modified. Another example is 

the use of moisture to control ash. Wetting carpets will 

increase relative humidity and help to keep the ash down; 

however, wet or even damp volcanic ash is conductive. 

No single technique will be absolutely effective; a combination of techniques has been found to provide the best 

results for managing volcanic ash. Constant monitoring and 

reassessment of ash effects and the mitigation process will 

be required to achieve the most effective balance between 

operational requirements and the desired level of damage 

limitation. The following sections summarize ash mitigation 

techniques for selected aircraft and support systems. 

AIRCRAFT SYSTEMS 

The basic mitigation tactic to protect aircraft systems 

is avoidance of exposure to ash. The airports and airfields 

surveyed after the Mount St. Helens eruption simply shut 

down for the duration of the ash problem or until the ash 

had been removed. Airlines rerouted traffic away from ashimpacted airports. 

Sealing aircraft seams, ports, vents, and other openings with duct tape will keep out the bulk of the ash, especially if the aircraft is under cover. Maintaining positive 

pressure within aircraft components would help to keep ash 

out, but it is difficult, if not impossible, to pressurize an aircraft on the ground without damaging ground equipment. 

Techniques include: 

• Blow or vacuum ash before washing; otherwise, ash 

tends to flow into ports, vents, or control surfaces. 

• Flush or wash residue. Do not scrub or sweep. 

• Wash gear, underside, air-conditioning intakes, and 

engines. 

• Check pH of aircraft/engine surfaces for acidity. 

• Neutralize acidic residue by adding petroleum-based 

solvent to wash water. 

All of the above techniques require large amounts of 

time, manpower, and equipment. All have significant effects 

on the level and scope of continued operations. These techniques were tried under conditions of greatly reduced operating levels; however, there is some question as to their 

effectiveness during normal (or near-normal) operations. 

For example: 

• Sealing an aircraft would take 4-5 hours, and removing all seals and tape would take 1-2 hours. It is very 

hard to seal an aircraft completely because of numerous ports, vents, seams, and joints. 

• Ash buildup in or around hatch seals could cause pressurization problems. 

• Fuel tank vents must be open during loading, unloading, and transfer of fuel. If vents are plugged with 

ash, or if sealed, the tank could collapse. A 4-5 psi 

vacuum is sufficient to cause collapse. 
MITIGATION OF VOLCANIC ASH EFFECTS ON AIRCRAFT OPERATING AND SUPPORT SYSTEMS 127 

RUNWAYS 

If aircraft operations are not suspended, runways must 

be continually cleaned as ash is resuspended by wind, aircraft takeoff, and ground vehicle movement. There is some 

disagreement on the proper use of water in cleaning runways. Some sources felt that water turns the ash to sludge 

(or causes it to harden), whereas others found it impossible 

to control the ash without wetting it first. Open-graded (popcom surface) runways are to some extent self-cleaning 

because the engine blast on takeoff will blow ash out of crevIces. Basic techniques include: 

• Wet ash with water trucks, 

• Blade into windrows, 

• Pick up with belt or front-end loaders, 

• Haul to dump areas, and 

• Sweep and flush residue. 

• Sweep/vacuum ash first, then flush with water (best 

for ramps, etc.). 

• Push ash to runway edge and plow under or cover 

with binder such as Coherex or liquid lignin. 

• Install sprinklers along edges of runway to control 

resuspension of ash from aircraft engine blast or 

wing-tip vortices. 

• Keep residue wet on taxiways and ramps. 

LANDING AIDS AND 

AIR TRAFFIC CONTROL 

Protection of landing aids and air traffic control systems will require periodic cleaning, maintenance, and monitoring. Also, turning off unnecessary equipment will 

reduce exposure. Exposed light and indicator systems, 

radar antennas, and any equipment that requires cooling air 

are especially vulnerable to ash contamination and damage. 

Interruption of commercial power supplies will require 

backup generators, which are also vulnerable to ash damage. Techniques include: 

• Replace antennas that have Teflon insulators. Because 

ash is hard to remove and will cause shorting, ceramic 

insulators should be used, 

• Seal relay boxes and remove indicator units and light 

systems to prevent ash entry, 

• Increase cleaning and maintenance of systems that 

cannot be sealed or that require cooling air, 

• Vacuum or blow ash out and clean relays with contact 

cleaner, 

• Use high-pressure water wash on exposed antenna 

rotor bearings and then relubricate, 

• Cover exposed joints, seams, and bearings, 

• Seal buildings, control access, vacuum shoes and 

clothes, and 

• Reduce operating levels: shut down unused equipment, reduce broadband displays to a minimum, and 

reduce cooling and power consumption. 

GROUND SUPPORT EQUIPMENT 

The consensus of those interviewed is that ground support equipment is the key to flight operations. If ground 

support equipment is unserviceable because of ash, aircraft 

cannot be launched. Unfortunately, there are more problems than solutions in the ash contamination of ground 

equipment. 

Gas turbines, air compressors, and air conditioners 

operate by ingesting large volumes of air. This equipment 

has only coarse filtration (or none at all), and extra filtration 

cannot be added without impacting operation. Using air conditioners to pressurize aircraft compartments would only 

blow ash into the aircraft and ruin the air conditioners in the 

process. Techniques include: 

• Constant cleaning and maintenance, 

• Do not wash equipment, because water turns ash to 

sludge and washes it into the equipment, 

• Vacuum equipment, 

• Change oil and filters more often, and 

• Change design to include better filtration. 

COMPUTER SYSTEMS 

The most widely advised damage-prevention tactic is to 

shut down all computer and electronic systems until the ash 

has been completely removed from the area and from the 

equipment. Computer heads and disks, and any high-voltage 

circuits, are especially vulnerable to ash upset and damage. 

Ash on digital circuits will not cause much of a problem 

because of the low voltages involved. High-voltage or highimpedance circuits are very vulnerable to leakage caused by 

semiconductive ash. Ash that is acidic is conductive as well 

as corrosive. Continual cleaning and aggressive protection of 

computer systems should allow for continued operation in all 

but the heaviest ash fallout. Techniques include: 

• Clean and condition surrounding air to keep ash out of 

equipment. 

• Cotton mat filters used in clean rooms were found to 

be best for filtering particles, but they reduce air flow. 

A solution is to use larger fans to maintain required 

air flow. Rack-mounted equipment can be modified 

to add a larger fan, but smaller instruments or components with a built-in fan would require a design 

change to increase fan capacity. 

• Use fluted filters as a compromise; this increases 

surface area, but reduces air flow by only about 20 

percent. 

• Humidifying ambient air (e.g., wetting carpets) will 

help to control ash reentrainment. 

• Ash on equipment can be blown out with compressed 

air. If the air is too dry, static discharge could damage 

sensitive components (e.g., integrated circuits). If the 

air is too damp, the ash will stick. Relative humidity 

of25-30 percent is best for compressed air. 
128 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

• Cleaning with a pressurized mixture of water and 

detergent and using a hot-water rinse is quite effective; however, this process requires at least partial disassembly. 

• Ash may have a high static charge and be hard to dislodge, thus requiring brushing to dislodge particles. 

• Accelerate filter change; use prefilters. 

• Change to absolute filters; these will keep out particles down to 1 J..Lm and smaller. 

• Keep computer power on for filtration, but do not 

operate, especially disk drives. · 

• Maintain room-within-a-room configuration, restrict 

access, recirculate air, and accelerate cleaning of the 

critical area. 

RADAR AND OPTICAL SYSTEMS 

Most radar equipment in the heaviest ash-fall areas was 

shut down for the duration of severe ash contamination. 

Thus, few problems were recorded aside from cleanup and 

control of residual ash. The simplest mitigation tactic is to 

cease operations. Techniques include: 

• Repair and clean high-voltage circuits. 

• Wash antenna rotor bearings, relubricate, and cover 

exposed bearings. 

• Ash on optical components should be blown away or 

washed with copious amounts of water. Do not wipe, 

brush, or rub, as this will abrade the optics. 

• Take care not to wash ash into optical-instrument 

mounts on aircraft (e.g., sextant). 

• Tum off nonessential radar equipment to reduce cooling load and power requirements. 

• Transfer radar coverage to other facilities; combine 

sectors. 

• Remove and replace camera bearings and clean gear 

drives. 

• Protect video tape from ash because it will cause 

"drop-outs" and scratches. 

PLANNING FOR ASH MITIGATION 

Techniques for reducing the impacts of volcanic ash are 

basically "low tech" and depend more on procedural 

approaches tha:r: on technical fixes. Also, they are quite 

labor and resource intensive. Normal stock of daily-use 

items such as filters, lubricants, spare parts, cleaning supplies, etc., may be expended much faster than they can be 

replaced through the normal reordering process. Prior planning is necessary to reduce the severity of ash effects. Planning actions include: 

• Conduct a vulnerability analysis of equipment and 

facilities to determine which would be most impacted 

by ash, which are adequately protected, and which 

need long-term or expedient modification. 

• Develop a priority list of facilities that must be kept in 

operation versus those that can be closed or shut 

down for the duration of ash fall. 

• Ensure hazard-alert and information channels are 

properly maintained with the U.S. Geological Survey 

(USGS), Federal Emergency Management Agency 

(FEMA), the National Weather Service (NWS), local 

news media, and State and local governments. 

• Establish plans and procedures for alerting and notification, reduced operations, accelerated maintenance, protection of critical facilities, and cleanup 

and disposal. 

• Alert air traffic controllers and airport operations personnel to notify aircraft as soon as volcano "watch" 

and "warning" notices are received. Normal air traffic and weather radars cannot detect lower, but potentially hazardous, ash-density levels; therefore, 

relatively large "keep-out zones" should be established at night or during bad weather once the warning notice is issued. Personnel should also be alerted 

to the existence of fallout beneath the clouds and 

severe lightning conditions, etc. 

• Stockpile spare parts for critical equipment, filters, 

and cleaning and disposal equipment. 

• Plan for extended cleanup and maintenance activities 

including 24-hour operations, augmentation of the 

work force, and training of cleanup crews. 

• Ensure that sufficient water and backup power is 

available to support cleanup operations, should normal supply sources fail. 

Ash cleanup operations may continue for weeks or 

months if multiple eruptions occur. Effective mitigation of 

volcanic ash effects depends on prior planning and preparation, mobilization of resources, and persistence. 

REFERENCE CITED 

[In addition to the cited reference, this report was based on 

many interviews with equipment users, service companies, 

airport operators, and utilities. Information pertaining to 

these interviews may be available from the author-see 

Authors' Address List section at the end of this volume.] 

Labadie, J.R., 1983, Teal Granite: Mitigation of volcanic dust effects: IRT Corporation, [final report prepared for U.S. Air 

Force Office of Scientific Research and the Defense Advanced 

Research Projects Agency], 29 p. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

IMPACT OF VOLCANIC ASH FROM 15 DECEMBER 1989 

REDOUBT VOLCANO ERUPTION ON 

GE CF6-80C2 TURBOFAN ENGINES 

By Zygmunt J. Przedpelski and Thomas J. Casadevall 

ABSTRACT 

The 1989-90 eruptions of Redoubt Volcano, Alaska, 

and the near tragedy on 15 December 1989 of KLM flight 

867, a Boeing 747-400 aircraft powered by General Electric 

(GE) CF6-80C2 engines, underscore the threat to aircraft 

safety from volcanic ash clouds. 

An eruption of Redoubt at 10: 15 a.m. Alaska Standard 

Time (AST) produced an ash-rich eruption column that 

climbed to approximately 40,000 ft altitude. Wind speeds at 

high altitudes at the time were 100 knots from south-southwest. At 11:46 a.m., KLM flight 867 entered the volcanic ash 

cloud at approximately 25,000 ft altitude, 150 nautical miles 

northeast of Redoubt. Immediately the aircrew increased 

power and attempted to climb out of the ash cloud. Within 1 

minute, the four engines decelerated below idle. The aircraft 

descended approximately 13,000 ft before the crew restarted 

the four engines and resumed flight to Anchorage. Even 

though there were no injuries to passengers, the damage to 

engines, avionics, and aircraft structure from this encounter 

was significant. Similar engine thrust loss and engine and 

aircraft damage was experienced by two Boeing 747 aircraft 

during 1982 volcanic eruptions of Galunggung Volcano in 

Indonesia. 

The primary cause of engine thrust loss in these events 

was the accumulation of melted and resolidified ash on the 

stage-1-turbine nozzle guide vanes. These deposits reduced 

the effective flow of air through the engine causing compressor stall. Reduction of thrust level while in an ash cloud 

significantly reduces the rate of engine-performance 

degradation. 

STATEMENT OF PROBLEM 

The loss of thrust on all engines during an approximately 1-minute exposure to the Redoubt volcanic ash 

cloud could have resulted in a major tragedy. Fortunately 

the alert flight crew was able to restart all engines and 

make a safe landing at Anchorage. The events preceding 

and subsequent to the cloud encounter and the engines' 

response and physical conditions were analyzed to identify 

procedures that would reduce the probability of future 

occurrences of similar events, which threaten flight safety. 

Additional discussion of the Redoubt activity and its effects 

on aircraft operations and airplane damage my be found in 

reports by Brantley (1990), Campbell (1991), Casadevall 

(in press), and Steenblik (1990). 

METHODS OF STUDY 

The following data sources were used to reconstruct the 

event, to establish the specific cause(s) of thrust loss and to 

recommend appropriate preventive/corrective actions: 

• Interviews with and statements from the flight crew of 

KLM flight 867. 

• Tape recordings and transcripts of radio communications between air traffic controllers and KLM flight 

867 and other flights in the Anchorage area prior to 

and during the event. 

• Forecasted and recorded wind aloft data. 

• Digital flight-data recorder (DFDR), aircraft condition monitoring systems (ACMS), and the non-volatile memory (NVM) of the engine full-authority 

digital electronic controls (FADEC). 

• Event descriptions and findings from other aircraft-volcanic cloud encounters. 

• CF6-80C2 engine steady-state and transient operating 

characteristics with normal and degraded component 

efficiencies. 

• On-site (Anchorage) external inspection of the aircraft 

and all engines and borescope inspection of engines 1 

and2. 

• Complete analytical disassembly and inspection of 

engine 1 at the KLM maintenance facility at Schiphol 

Airport, Amsterdam. 

• General Electric experience with engines exposed to 

sand/dust environment in the field and during controlled factory tests. 

• Analysis of samples of volcanic ash recovered from 

the four engines. 

129 
130 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

63' 

62' 

61' 

153' 152' 151' 150' 

///' 

Limit of ashfall // 

'y/ 

// 

//1!. 

/ Mount 

/ McKinley 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I ,.""' I,,/ 

*Redoubt Volcano 

149' 

5 

Figure 1. Map showing flight path ofKLM 867 (heavy solid line) 

and limits of detectable ash fall (heavy dashed lines) from 15 December 1989 eruption of Redoubt Volcano. Numbers on map, explained below, are keyed to principal events for KLM flight 867. 

AST, Alaska Standard Time. 1, 11 :40 AST, airplane begins descent 

from 35,000 ft; alters course to avoid ash cloud. 2, 11:46 AST, airplane encounters ash cloud at 25,000 ft. 3, 11:47 AST, airplane loses power on all four engines after climbing to 27,900 ft. 4, 11:52 

AST, airplane engines 1 and 2 restart at 17,200 ft. 5, 11:55 AST, airplane engines 3 and 4 restart at 13,300 ft; flight is resumed to Anchorage. 6, 12:25 AST, airplane lands at Anchorage International 

Airport. Map modified from Casadevall (in press). Flight-route data 

provided by National Transportation Safety Board ( 1991) and FAA 

Flight Standard Division, Anchorage. Ash-fall data modified from 

Scott and McGimsey (in press). 

Figure 2 (facing column). Encounter ofKLM flight 867 with ash 

from Redoubt Volcano, 15 December 1989: engine and aircraft parameters (engine fuel flow, exhaust-gas temperature (EGT), core 

speed (N2), fan speed (N1), pitch angle, airspeed, and altitude) from 

cloud entry to shutdown. AST, Alaska Standard Time. 

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TIME (AST) 

EXPLANATION 

• Engine 1 

o Engine 2 

• Engine 3 

0 Engine 4 
IMP ACT OF VOLCANIC ASH FROM REDOUBT VOLCANO ERUPTION ON TURBOFAN ENGINES 131 

Figure 3. Dark, glassy deposits of remelted volcanic ash on leading edge of stage-1 high-pressure-turbine (HPT) nozzle guide vane 

(NGV). 

Figure 4. Leading-edge deposits dislodged during disassembly of 

stage-1 high-pressure-turbine (HPT) nozzle guide vanes (NGV's). 

RESULTS AND OBSERVATIONS 

A major eruption of Redoubt Volcano occurred at 

10:15 a.m. ASTon 15 December 1989 and lasted for about 

1 hour. This was the third large eruption from the volcano 

on this day (Brantley, 1990). At 11:46 a.m. AST, while leveling off at an altitude of 25,000 ft, KLM 867 entered a 

heavy volcanic cloud. Maximum power climb was selected 

and approximately 1 minute later, after climbing to approximately 27,900 ft, all engines decelerated. Engines 1 and 3 

decelerated to sub-idle core rotor speed (N2), while engines 

2 and 4 settled down at 80 percent N2 for approximately 20 

seconds before decelerating to sub-idle N2. The time 

sequence of events is shown on the annotated aircraft flight 

path in figure 1. Aircraft and engine response during this 

critical period is shown in figure 2. 

TRAILING·EDGE SlOTS 

Figure 5. Sketch of deposits on stage-1 HPT nozzle guide vanes, 

based on borescope inspection of engine 1. 

The location of the ash cloud ( 154 nautical miles from 

Redoubt on 217° true heading) was consistent with the forecasted and pilot-reported winds aloft and with the ash release 

at the beginning of the eruption cycle. Prior to the encounter, 

the exact location of this cloud was not known by the crew 

of KLM 867. Pilot reports (Pireps) and radar data available 

to Anchorage air traffic controllers indicated either the presence of more than one ash cloud and (or) a large dispersion 

of the main cloud resulting from the high velocity gradient of 

winds aloft as a function of altitude. 

The fire warning bell and the displayed message 

"CARGO FIRE FWD" occurred shortly after engine deceleration and was interpreted by the Captain to be a false message. This was confirmed by inspection, which showed no 

evidence of compartment fire. 

The engines' operation during the high-power climb 

was consistent with rapid reduction of the stage-I nozzle 

guide vane (NGV) flow area and associated reduction in 

high-pressure-turbine (HPT) efficiency. Approximately onehalf of the maximum deterioration was still present following the successful restarts. Visual inspection ofthe number 1 

engine revealed thick deposits of melted and resolidified ash 

material on some ofthe stage-I NGV's (fig. 3). These deposits were brittle at room temperature, and many pieces fell off 

during engine transportation and disassembly (fig. 4). The 

remaining deposits could be easily removed by hand. It was 

inferred that these deposits built up to maximum just prior to 

engine deceleration and gradually became dislodged during 

the start attempts and during subsequent engine operation. 

Based on borescope inspections conducted at Anchorage, 

approximately 40 percent of the NGV's were still covered by 

thick deposits after landing (fig. 5). 

Engine fuel levers were moved to the "OFF" position 

and engine restarts were initiated immediately after the loss 
132 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 6. Accumulation of unmelted volcanic ash in the highpressure-turbine rotor. 

of power. Engines 1 and 2 were successfully started at an 

altitude of 17,200 ft (after five or six attempts). Engines 3 

and 4 were successfully started at an altitude of 13,300 ft 

(after eight or nine attempts). "Autostart" mode was used 

and at least one start appeared to have been correctly terminated by the F ADEC start/stall logic just before being terminated by the crew. The windmilling N2 was in excess of 30 

percent, and the entire start sequence varied from approximately 30 seconds to 60 seconds during each attempt. 

The engines did not overheat during deceleration or 

during subsequent aborted starts. The highest exhaust-gas 

temperature (EGT) of930°C was recorded on engine 1 dur--

ing the initial deceleration. There was no unusual thermal 

distress observed during disassembly of this engine. 

The general condition of all hardware in engine 1 was 

consistent with the performance level recorded prior to landing. In addition to the remains of the heavy, stage-1 nozzle 

deposits, the following performance-related observations 

were made: 

• No measurable erosion or other damage to the lowpressure system (fan, booster, and low-pressure turbine (LPT)). 

• Minor compressor erosion, most pronounced in the 

mid and aft rotating stages. 

• Stage-1 high-pressure-turbine (HPT) blade tips were 

"ground off' (approximately 0.060 inches of tip material was missing). 

• Buildup of hard material on stage-1 HPT shrouds. 

• Thin but hard deposits on stage-1 HPT blade pressure 

surfaces. 

• Engine 1 inspection indicated that there was no significant plugging of any of the HPT cooling circuits; 

however, there was a heavy, fine, powdery ash 

buildup within the HPT rotor cavities (fig. 6). 

The general physical conditions (distress and presence 

of ash deposit) of all four engines were very similar. The compressor-discharge-pressure (Ps3) sensing line on engine 1 

was unobstructed. The Ps3 readings obtained from the ACMS 

system during and after the deceleration indicated that Ps3 

signals to the engine electronic controls were unrestricted. 

The DFDR was not recording for 2 minutes 5 seconds after 

the initial engine deceleration when all four electrical generators dropped offline. The engine F ADEC remained powered 

and was controlling the engines during that time and provided 

valuable information stored in the NVM. 

CONCLUSIONS 

SPECIFIC 

Engine deceleration from high power to below idle was 

initiated by high-pressure-compressor (HPC) stall. The stall 

margin loss was caused by stage-1 HPT nozzle effectiveflow-area restriction and associated HPT efficiency loss. The 

stage-1 HPT bucket-clearance increase was caused by local 

buildup of hard, resolidified ash material on the shroud surface (fig. 7), which ground off the bucket-tip material. 

The stage-1 nozzle effective-flow-area restriction was 

caused by resolidification and buildup of melted ash particles on the leading edges and pressure surfaces of the individual NGV's. This effective-flow-area restriction was 

estimated to be 8 percent. This buildup also resulted in an 

increase in pressure loss across the nozzle and a reduction in 

HPT efficiency. Total HPT efficiency loss, including the 

stage-1 HPT blade-clearance increase was estimated to be 7 

percent. High-pressure-compressor (HPC) erosion (fig. 8), 

caused by ingestion of ash particles, resulted in minor stallmargin decrease and compressor-efficiency loss estimated to 

be 1 percent. 

The lowering of the temperature following manual fuel 

supply cut-off increased the viscosity and brittleness of the 

built-up material. The thermal and pressure/velocity transients associated with the fuel off/on/off cycle dislodged 

some of the nozzle deposits. The density of these deposits 

was low, and, consequently, there was no downstream airfoil 

Figure 7. Deposits of solidified, remelted ash on stage-I highpressure-turbine shrouds. 
IMPACT OF VOLCANIC ASH FROM REDOUBT VOLCANO ERUPTION ON TURBOFAN ENGINES 133 

Figure 8. High-pressure-compressor (HPC) blades, showing 

erosion of leading edges and blade tips. 

damage. Successful starts were achieved after a portion of 

these deposits were dislodged. 

During the starts, "auto.start" mode was used and at 

least one start appeared to have been correctly terminated by 

the FADEC start/stall logic. Most of the starts, however, 

were terminated by the crew overriding the autostart 

sequence and thus negating the adaptive automatic restart 

features of the control system while, in some of these cases, 

the engine or engines appeared to be on the way to a successful start (fig. 9). Continued engine operation, following successful restarts, dislodged additional stage-1 deposits. 

Permanent engine performance degradation was the result of 

compressor erosion and the stage-1 HPT blade-clearance 

mcrease. 

The absence of any thermal damage to the engines was 

the result of the combination of decisive and skillful actions 

of the crew and the responsiveness and built-in protection in 

the FADEC system. 

The presence of ash particles set off the fire warning 

bell in the cargo compartment and displayed the "CARGO 

FIRE FWD" message (the cargo-compartment fire detector 

is a smoke/particle detector-unlike the engine-compartment detector, which is activated by temperature). 

The ash concentration at 25,000 ft altitude was estimated at 2 g/m3, based on the rate of nozzle-deposit buildup 

compared to the rates measured during engine tests conducted by Calspan (Dunn and Wade, this volume). 

Ash particles exiting the fan air stream ranged in size 

from 10 to 100 microns and most closely represent the size 

of particles encountered by KLM 867 in flight. The particles 

found within HPT passages, which were believed to be representative of the size distribution entering the combustor, 

were typically 6-10 microns in size. The ash contained some 

volcanic-glass material with a melting point of 1 ,200°C. This 

material is considered to be responsible for rapid buildup of 

deposits on the stage-1 NGV's; however, components ofthe 

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TIME (AST) 

EXPLANATION 

• Engine 1 

o Engine 2 

o Engine 3 

0 Engine 4 

I 

-

-

-

Figure 9. Encounter of KLM flight 867 with ash from Redoubt 

Volcano, 15 December 1989: engine parameters (exhaust-gas temperature (EGT), core speed (N2), and fan speed (Nl)) during first 

recorded restart attempt. AST, Alaska Standard Time; FADEC, 

full- authority digital electronic controls. 

ash with higher and lower melting points were also present 

in the NGV deposits. The unmelted particles adhered to the 

semi-molten layer of glassy material on stage-1 NGV's 

(Casadevall and others, 1991 ). 

GENERAL 

Relatively "new" (within hours of eruption) volcanic 

clouds contain concentrations of ash that can cause complete loss of engine power in approximately 1 minute when 

the engine is operating at combustor-discharge temperatures in excess of the melting temperature of the ash. The 

primary mechanism of engine power loss during these 

high-engine-power and high-ash-concentration exposures is 

the buildup of melted and resolidified ash material on the 

stage-I N GV' s, resulting in flow -area reduction, turbineefficiency loss, and compressor stall. Permanent damage to 

the engine under these conditions is limited if the engine is 
134 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

not exposed to overtemperature during the stall or subsequent restart attempt(s). 

Time, altitude, and airspeed permitting, the engine can 

be restarted by the fuel off/on/off cycles, breaking up the 

deposit material, which is brittle at low temperatures. 

FADEC with built-in start/stall/overtemperature logic in the 

autostart mode simplifies and speeds up the restart sequence 

and prevents further engine damage. 

Reduction of engine power to flight idle upon inadvertent entry into a volcanic cloud will eliminate the stage1 NGV buildup because the combustor-discharge temperature at idle is below the melting point of volcanic-ash constituents. 

Operation in an ash cloud will result in compressor airfoil and flowpath erosion and eventual compressor stall. 

Compressor stall is an airflow discontinuity resulting in loss 

of thrust and internal temperature increase. The time 

required to reach this condition is at least an order of magnitude longer than the time to produce significant ash accumulation on the NGV's at the high-power level (assuming the 

same ash concentration). Compressor erosion is permanent, 

and engine operability and available thrust will be adversely 

affected. The compressor-erosion rate can be significantly 

reduced by decreasing the core engine rotational speed (N2). 

Damage mechanisms in the longer term include the 

restriction of HPT cooling circuits, which may result in hotsection distress, and the contamination of the lubrication system, which may result in premature bearing distress. Another 

possible damage mechanism is the restriction of air-flow 

passages around the fuel nozzles-this leads to poor fuel 

atomization and the inability to start the engine. 

SAFETY RECOMMENDATIONS 

CREW ACTIONS 

Entering into a volcanic ash cloud can be recognized by 

St. Elmo's Fire/corona discharge (night or day), dust and 

smell in the cockpit/cabin, and outside darkness (day time 

only) (Campbell, this volume). If a volcanic ash cloud is 

inadvertently entered, disconnect the autothrottle, reduce 

power to flight idle, increase compressor air bleed to maximum possible, and exit the cloud as quickly as possible. 

Bleed air is air extracted from the compressor for use in various aircraft systems. Increased extraction increases stall 

margin. There is no universal "best" procedure for exiting 

the cloud; however, generally a 180° tum will result in the 

fastest cloud exit. Avoid rapid throttle movements (up or 

down) to prevent a possible compressor stall (Campbell, this 

volume; Miller, this volume). 

If power reduction to flight idle is not possible, reduce 

power to the lowest level consistent with other requirements 

and exit the cloud as quickly as possible. Monitor exhaustgas temperature as the primary engine instrument indicating 

ash accumulation at the stage-1 high-pressure-turbine nozzle 

guide vanes. IfEGT exceeds the red line or increases rapidly, 

the throttle should be closed and fuel levers moved to "OFF" 

to minimize engine thermal damage and increase the probability of successful restart. 

Restarts should be initiated immediately. More than one 

attempt may be required to obtain a successful start. 

Autostart should be used (if available) because it simplifies 

the starting procedure and provides engine overtemperature 

protection. Compressor bleed should be turned on during 

restarts and during subsequent engine operation to maximize 

stall margin. Following restart, the engine performance/stall 

margin/EGT may improve with time, but it will not reach the 

pre-ash-encounter level. Rapid throttle movement and maximum-power operation should be avoided, if possible, 

because stall margin is decreased and some cooling-circuit 

plugging may be present. 

REGULATORY AGENCIES 

The greatest threat to aircraft and engines is presented 

by "new" clouds (within hours of eruption) that contain large 

concentrations of ash particles. The communication network 

between volcanic-activity-monitoring agencies and air-traffic-control agencies should be improved so that volcanic 

activity of the type that can result in substantial release of ash 

into the atmosphere can be communicated immediately to 

the affected air crews. In early phases following the eruption, 

the cloud position should be continuously tracked at all altitudes utilizing winds aloft, pilot reports, and other available 

means. Appropriate air-traffic-control measures should be 

taken to provide aircraft-cloud separation. 

The ash-particle size distribution and concentration in 

volcanic eruption clouds should be documented. In addition, 

engine and (or) combustor tests should be sponsored by the 

Federal Aviation Administration (FAA) to establish threshold values for "safe" levels of ash concentration and the 

"safe" range of combustor temperature. This information, 

combined with updated dispersion and theoretical fallout 

models (and with improved cloud tracking) can establish 

when an ash cloud ceases to be a flight hazard. These efforts 

will enhance aviation safety and reduce air traffic delays 

resulting from volcanic activity. 

ACKNOWLEDGMENTS 

During this investigation, many GE engineers contributed to the hardware reviews and engineering analysis. The 

following individuals, outside the GE organization, provided background data and constructive suggestions that 

made this report possible: Captain K.F. van der Elst, Commander of KLM flight 867; Mr. Roy C. Daw, NTSB 

(National Transportation Safety Board), Anchorage 

Regional Office, Alaska; and Dr. Michael G. Dunn, Arvin/ 

Calspan, Buffalo, New York. In addition, special thanks go 
IMPACT OF VOLCANIC ASH FROM REDOUBT VOLCANO ERUPTION ON TURBOFAN ENGINES 135 

to the KLM maintenance personnel at Schiphol Airport 

who performed the disassembly and inspections of the 

engines involved in this event. 

REFERENCES CITED 

Brantley, S.R., 1990, The eruption of Redoubt Volcano, Alaska, 

December 14, 1989-August 31, 1990: U.S. Geological Survey 

Circular 1061, 33 p. 

Casadevall, T.J., in press, The 1989-1990 eruptionofRedoubtVolcano, Alaska: Impacts on aircraft operations: Journal ofVolcanology and Geothermal Resources. 

Casadevall, T.J., Meeker, G.P., and Przedpelski, Z.J., 1991, Volcanic ash ingested by jet engines [abs.], in Casadevall, T.J., ed., 

First International Symposium on Volcanic Ash and Aviation 

Safety, Program and Abstracts: U.S. Geological Survey Circular 1065, p. 15. 

Campbell, E.E., 1991,747-400 airplane damage survey following a 

volcanic ash encounter [abs.], in Casadevall, T.J., ed., First International Symposium on Volcanic Ash and Aviation Safety, 

Program and Abstracts: U.S. Geological Survey Circular 1065, 

p. 14. 

National Transportation Safety Board [NTSB], 1991, Aircraft Accident Report ZAN ARTCC #100, KLM 867, H/B74F December 15, 1989 2048 UTC: unpub. report, 726 p. 

Scott, W.E., and McGimsey, R.G., in press, Character, mass, distribution, and origin of tephra-fall deposits of the 1989-1990 

eruption of Redoubt Volcano, south-central Alaska: Journal of 

Volcanology and Geothermal Research. 

Steenblik, J.W., 1990, Volcanic ash: A rain of terra: Air Line Pilot, 

June/July 1990, p. 9-15, 56. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

ECONOMIC DISRUPTIONS BY REDOUBT VOLCANO: 

ASSESSMENT METHODOLOGY AND ANECDOTAL 

EMPIRICAL EVIDENCE 

By Bradford H. Tuck and Lee Huskey 

ABSTRACT 

The eruptions of Redoubt Volcano in 1989-90 imposed 

significant economic costs on Alaska residents, airlines and 

other businesses serving Alaska, government agencies, and 

travelers going to or coming from Alaska. This paper presents a set of principles, or guidelines, for the classification 

and aggregation of costs and benefits associated with the 

eruptions. These costs include both market-measured costs 

and non-market-measured costs, such as waiting time. 

INTRODUCTION 

This paper describes a social accounting framework 

designed to classify real economic costs and benefits, as well 

as related redistributions of economic activity associated 

with the eruptions of Redoubt Volcano between December 

1989 and April 1990. Conceptually, we are trying to compare economic activity that would have occurred if the eruptions had not taken place with activity that actually took 

place. The difference between these two situations represents the net economic cost of the eruptions. 

There are two major reasons for measuring these costs. 

The first is to provide an aggregate measure of the net economic costs associated with the Redoubt Volcano eruptions 

and the distribution of those costs among geographic areas. 

Estimates such as these are often instrumental in obtaining 

Federal or State government assistance (if available in a 

timely fashion). The second use is to provide an indication 

of those costs that could be avoided or lessened with the 

implementation of various mitigation measures. This is 

essential information for the evaluation of investment in mitigation measures. 

DESIGNING THE ACCOUNTS 

There are several issues that have been considered in 

the design of the accounting framework. A review of these 

will help in understanding both what is and what is not being 

measured. Readers interested in substantially more detailed 

discussions of social income accounting may consult 

Yanovsky (1965) or Eisner (1989). 

The present accounting framework is intended to 

reflect three measures of economic activity: real economic 

costs, real economic benefits, and redistributions of costs or 

benefits. 

Costs are incurred as a result of using up factors of production, or inputs, and may be of two types: direct damage 

costs and mitigation costs. Direct damage costs are defined 

as costs resulting directly from the volcanic eruption, such as 

a jet engine repair, ash cleanup and removal, and "waiting 

time" costs of individuals. These are costs that would not 

have occurred except for the eruptions. Mitigation costs 

includes those costs associated with mitigation of the effects 

of present or future volcanic eruptions. These are costs 

intended to reduce future damages. Included in this category 

would be airborne radar to track ash clouds, costs of monitoring volcanic activity, and installation of special dikes to 

protect the Drift River oil-loading facility. 

Some real economic benefits may also have resulted 

from the eruptions (e.g., volcanic ash used in pottery, the 

inevitable T-shirt, or tourist flights around the volcano). 

More difficult to value, but of greater potential long-run significance, might be increased knowledge related to predicting eruptions, appropriate flight procedures when 

encountering volcanic ash clouds, etc. However, we expect 

that most perceived benefits are really redistribution effects. 

The third category of measurement addresses redistributions of economic activity. Distributional effects related to 

volcanoes are discussed in detail in Blong (1984). These 

redistributions occur when economic activity shifts from one 

geographic locale to another as a result of the eruptions. For 

example, a flight scheduled to land in Anchorage is diverted 

to Fairbanks. Fairbanks gains income that is lost in Anchorage. Redistribution also occurs when components of income 

are shifted from one owner to another. For example, when a 

damaged jet engine is replaced, there is a redistribution of 

economic profit from the aircraft owner (or insurer) to the 

firm doing the repair. 

The inclusion of costs, benefits, and redistributions 

arising from transportation delays (and cancellations) 1s 

137 
138 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

another major aspect of accounting for economic costs 

related to the Redoubt eruptions. Consequences of travel 

delays, trip cancellations, and, to a lesser extent, freight and 

postal service delays are not directly measured by the market 

but are likely to be substantial. 

Benefits, costs, and distributional effects depend on 

both the geographic area encompassed and timing. The geographic frame of reference in the present study is global, in 

the sense that costs, benefits, and redistributions associated 

with the eruptions are included regardless of where they 

occurred. Geographic sub-units are established to identify 

localized effects. The timing of costs may also provide useful information, and, where possible, we will measure costs 

relative to specific eruptions. 

THE BASIC RULES 

Before looking at some illustrations of the application 

of our accounting principles, it is helpful to summarize the 

specific rules that we are using to measure volcano-related 

economic impacts. 

1. Any economic action (i.e., the use of factor inputs, 

such as labor, capital, or purchased intermediate 

inputs) that occurs because of an eruption, which otherwise would not have occurred, is treated as a change 

from the "without eruption" state. If the action can be 

expected to increase the consumer's utility, or "economic well-being" compared to the non-eruption 

case, the change is treated as a benefit. If the action is 

to maintain (or attempt to maintain) a consumer's preeruption utility level or restore their utility level, then 

the change is treated as a cost. As indicated above, 

these costs are further divided into two categories: 

direct damage costs and mitigation costs. 

2. Benefits or costs may be measured either by the monetary value of factor inputs used in the production process (the value added measure) or by the market price 

of the good or service produced but, however measured, cannot be counted twice (i.e., double counted). 

3. The estimate of the net economic cost of the eruptions 

is the difference between measured total costs and 

total benefits. 

SOME EXAMPLES 

We can now illustrate the use of the accounting framework with several examples. First considered is the privately 

owned Drift River Oil Terminal, located on the west shore of 

Cook Inlet at the mouth of the principal river draining the 

north flank of Redoubt Volcano. Oil produced from Cook 

Inlet platforms is transported by pipeline to the Drift River 

facility for storage and loading on to tankers. Debris flows 

from the eruptions caused flooding, threatened the physical 

integrity of Drift River Terminal, forced the closing of the 

facility, and lead to cessation of production from the Cook 

Inlet fields. Subsequently, the facility was repaired, levees 

were installed to protect the facility, and operation of the 

facility and production from Cook Inlet fields resumed. 

From a conceptual point, what costs should be charged 

against the eruptions? 

Firstly, the cost of levees should clearly be included 

because the levees were a State-imposed precondition for 

reopening the facility. Secondly, other modifications to the 

facility to prevent the recurrence of adverse flooding effects 

would also be included. These are examples of mitigation 

costs. Costs of shutting down and restarting Cook Inlet production facilities should also be included and should reflect 

direct damage costs. State royalty income at the time of the 

eruptions was about $39,000 per day (Brantley, 1990). The 

economic cost of replacing the revenue flow (e.g., as measured by the cost of borrowing to replace the revenue flow) 

would also be a direct cost. The same principle would apply 

to the delay in producer earnings. 

A second example considers the repair of damage to 

aircraft. A highly reported incident occurred when a Boeing 

747-400 flew through an ash cloud on December 15, 1989, 

and lost power in all four engines. Although the engines were 

restarted and the plane landed safely, the aircraft required 

extensive repair work (Przedpelski and Casadevall, this volume). All four engines were replaced, as were portions of the 

electrical and avionics systems. In addition, the aircraft 

required a thorough cleaning to remove ash. The reported 

repair costs were estimated at approximately $80 million 

(Steenblik, 1990). 

How do the account principles treat these expenditures? 

First, the repair and cleaning costs are a direct result of the 

eruption and reflect the use of resources to repair damage 

caused by the eruptions. Secondly, only a portion of the 

costs of engine and electronics replacement should be 

included. The portion that should be included would be 

equal to the cost of replacing the remaining economic life of 

the damaged equipment. For example, if an engine had 20 

percent of its economic life remaining at the time of the incident, then replacement of that 20 percent should be charged 

against the eruption (i.e., a cost of the eruption), whereas the 

balance would be treated as new investment and not counted 

as a cost of the eruption. 

A third illustration of our account principles relates to 

the treatment of a canceled or rescheduled event. The annual 

Anchorage "Christmas Carol" production scheduled for several performances prior to Christmas had to be postponed. 

The actors, actresses, and stage crew were in Anchorage, but 

the shipment of stage sets (to be transported by air freight) 

was delayed several times. Although the production did 

finally take place after several reschedulings, there was a significant loss in revenue. 

What are the losses associated with this event? Following the principle of "resources used," the loss should be 

equal to the resources used in the "non-production." This 
ECONOMIC DISRUPTIONS BY REDOUBT VOLCANO 139 

would include the opportunity cost of the actors, actresses, 

and stage crew (as measured by their compensation), their 

housing and transportation costs, the earnings that the Performing Arts Center could have obtained if used for an 

alternative event, the cost of promotional activity, etc. 

There is also an economic cost reflected in the time 

invested by volunteer participants. 

A final example addresses the issue of waiting time. 

Disruption of flight schedules and outright cancellation of 

flights resulted in extensive, and often lengthy, delays for air 

travelers. In many cases, the end result was complete trip 

cancellation on the part of the individual traveler. There are 

two dimensions to these waiting-time costs with which we 

try to deal. The first is the temporary non-utilization of factor inputs where the foregone use cannot be recaptured in the 

future. For example, a business traveler stranded in Seattle 

on a trip from San Francisco to Anchorage (and unable to 

conduct business from the airport) spends a certain number 

of hours waiting to complete the trip. This waiting time is a 

cost of production and a use of the factor input, labor. As 

such, it can be valued at its regular rate of compensation. 

The second type of waiting-time cost is associated 

with final consumption of air travel (i.e., consumer travel). 

In this case, the cost of waiting is the value of leisure time 

that the consumer has given up. For example, a student 

returning home to Anchorage for the Christmas holidays 

has to spend two days in the Seattle airport. These two days 

are days that the student does not get to spend with family 

(or friends already back from other schools). Typically, the 

value of leisure time is measured by its opportunity cost, or 

what the individual could have earned if they had chosen to 

work rather than to have taken leisure time. We follow that 

convention in these accounts. Thus, the cost of the student's waiting time would be equal to what the student 

could have been earning had that student chosen to work 

(instead of being a student). Discussion of the measurement 

and use of leisure time is more fully treated in Kendrick 

(1987) and Eisner (1989). 

SUMMARY 

In summary, we have attempted to state a set of"rules" 

to guide the classification and aggregation of economic costs 

and benefits associated with the eruptions of Redoubt Volcano during 1989-90. Compilation of these costs and benefits provides both an indication of the overall costs to society 

of the eruptions and a reference against which future mitigation efforts can be evaluated. 

ADDENDUM 

Since this report was prepared, we have completed the 

study of economic consequences of the 1989-90 Redoubt 

Volcano eruptions (Tuck and others, 1992). Table 1 contains 

a summary of the findings regarding the economic impact of 

the Redoubt Volcano eruptions on the aviation industry. 

Table 1. Estimated economic impacts of the 1989-90 eruption of Redoubt Volcano on the aviation 

industry. 1 

["Big Four," United, Delta, Northwest, and Alaska Airlines;?, no estimate available for economic impact for this category; Na., 

estimated economic impact not allocated to this category; AlA, Anchorage International Airport. All figures in U.S. dollars] 

Category December 1989 January 1990 Total 

Domestic passenger traffic 

''Big Four" (B4) 837,884 349,138 1,187,022 

Domestic total - B4 433,511 35,673 469,184 

International passenger traffic ? ? ? 

Domestic freight Minimal Minimal Minimal 

International freight Na. Na. 15,000,000 

AlA revenues 

Landing fees 177,464 77,696 255,160 

Concessions 508,216 487,339 995,555 

Fuel flowage fees 135,060 205,460 340,520 

Airport support industries 

Fuel distribution Na. Na. 50,000 

Ground crews and service Na. Na. 600,000 

Catering Na. Na. 43,500 

Concessions Na. Na. 285,000 

Passenger waiting time 1,144,800 689,000 1,833,800 

Estimated production losses Na. Na. 21,059,741 

Equipment damage costs Na. Na. 80.070,000 

Total aviation costs 101,129,741 

1 Source of information: Tuck and others (1992). 
140 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

REFERENCES CITED 

Blong, R.J., 1984, Volcanic Hazards: A Sourcebook on the Effects 

of Eruptions: Sydney, Academic Press, 424 p. 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14, 1989-August 31, 1990: U.S. Geological Survey Circular 1061, 33 p. 

Eisner, Robert, 1989, The Total Incomes System of Accounts: Chicago, University of Chicago Press, 416 p. 

Kendrick, J.W., 1987, Happiness is personal productivity growth: 

Challenge, v. 30, p. 37-44. 

Steenblik, J.W., 1990, Volcanic ash-A rain of terra: Airline Pilot, 

June/July, p. 9-15. 

Tuck, B. H., Huskey, L., and Talbot, L., 1992, The economic consequences of the 1989-90 Mt. Redoubt eruptions: University of 

Alaska, Anchorage, Institute of Social and Economic Research, [unpub. report prepared for the U.S. Geological Survey 

Alaska Volcano Observatory], 39 p. 

Yanovsky, M., 1965, Social Accounting Systems: Chicago, Aldine 

Publishing Company, 237 p. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

EFFECTS OF VOLCANIC ASH ON AIRCRAFT 

POWERPLANTS AND AIRFRAMES 

By Lester M. Zinser 

ABSTRACT 

This paper discusses the effects of volcanic ash on an 

aircraft used as a research platform to penetrate and sample 

volcanic eruption clouds directly over and near the vent. Scientific objectives were to acquire as pure and uncontaminated sample of the ash as possible and to determine the 

composition and concentration of volcanic ejecta. Over the 

years, aircraft have accidentally encountered volcanic clouds 

at different altitudes with varying effects on powerplants and 

airframes. However, little was known about how flying 

directly through a dense eruption cloud would affect aircraft 

performance and materials. The paper combines the results 

of scientific expeditions to three volcanoes in Guatemala in 

1978 and 1980 and to Mount St. Helens in 1980. 

INTRODUCTION 

The airplane used for this research was a Beechcraft 

Queen Air Model B-80 powered by two Lycoming IGS0-

540 reciprocating engines. On-board research equipment 

and the responsible organizations were as follows: 

1. Air intake/exhaust-U.S. Geological Survey (USGS), 

2. Air intakes-National Center for Atmospheric 

Research (NCAR), 

3. 

4. 

5. 

Quartz microbalance--California Measurements, Inc., 

Inertial navigation system-NCAR, 

H20 sampler-USGS, 

6. Giannini 35-mm camera-NCAR, 

7. Huebert sampler-Colorado College, 

8. Heidt air-sample bottles-NCAR, 

9. Correlation spectrometer-Dartmouth College. 

Although some equipment required special external 

ports extending beyond the fuselage, the scientific equipment had little to no effect on the aircraft's aerodynamic performance. The main limitation was the bulk and the weight, 

which reduced passenger space and fuel load and thus 

reduced the time spent on station. The time on station turned 

out to be important because volcanoes do not erupt on command. Thus, we often circled a volcano for periods up to 

several hours, awaiting an eruption. Logbook entries show 

26 flights between the three projects with a total of 7 to I 0 

hours in volcanic clouds of varying density. 

METHOD OF STUDY 

The first two studies (1978 and 1980) were carried out 

in Guatemala (Rose and others, 1980). Following the return 

from Guatemala in late February 1980, Mount St. Helens was 

showing signs of activity, and the airplane was scheduled for 

a trip to Portland, Oreg. For the Central America trip, logistics 

and obtaining permission to fly a research aircraft over three 

active volcanoes (Fuego, Pacaya, and Santiaguito) was the 

most difficult part of the program. Once the paperwork was 

accomplished, the procedure was to fly to the volcano of 

interest for the day and circle the crater until it erupted, or 

until fuel supply (3.5-hr maximum) warranted a return to our 

base at La Aurora International Airport, Guatemala City. 

There were many ideas as to what triggers an eruption-high tide, low tide, sun spots, Pele was upset-however, none were correct. The best we could do in planning a 

flight was to pick a day and take our chances. Dr. Richard 

Cadle (NCAR) had some experience sampling fumes from 

the Hawaiian volcano, Kilauea, but none of the scientists 

were aware of any flights directly over a crater through an 

ash or vaporous emission or through low-level pyroclastic 

eruptions. In other words, no one knew what the maximum 

ash concentration in a volcanic cloud was that could be 

flown through without disastrous results. 

OBSERVATIONS AND RESULTS 

On 10 February 1978, Fuego Volcano (3,763 m) 

erupted with a dense black plume (fig. 1), oxygen masks 

were put on and set at 100 percent oxygen; research equipment was readied; and a penetration run began. The plume 

was estimated to be 200-300 m above the crater when first 

sighted. The plume expanded rapidly as the aircraft 

approached and rose to an altitude between 300 and 400 m 

above the vent. 

141 
142 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 1. Small explosion from Fuego Volcano (3,763 m), Guatemala, produces a dark, ash-rich column that rises about 300 m 

above the summit, 10 February 1978. 

The aircraft entered the eruption cloud about 300 m 

above the volcano and was traveling 70 m/s. The plume was 

estimated to be about 300-400 m in diameter, which gives a 

residence time in the plume of from 4 to 6 seconds. On a later 

mission, following an overnight eruption of Fuego, the 

plume had stagnated owing to low wind conditions and was 

held in place by a temperature inversion (fig. 2)-the entire 

3-hour flight was flown in the ash cloud. 

What happens when one penetrates a volcanic plume? 

In the plume shown in figure 1 we found: 

1. Zero to limited visibility, 

2. Heat and slight turbulence, which caused a bump with 

each entry into the cloud, 

3. Copious quantities of ash entering the cabin through 

fresh air vents, 

4. The fuel-air ratio was upset, engines sputtered, and 

manifold pressure fell off rapidly, 

5. Once through the cloud, engine performance 

improved--everyone breathed a sigh of relief, especially the pilot. 

The first flight through the Fuego plume became a standard for me, as well as for the researchers. If the eruptions 

looked larger and darker than the Fuego plume, direct penetration was avoided until some of the heavier material had 

fallen out. The plume from the Santiaguito vent at Santa 

Maria Volcano (3,772 m) (fig. 3) was lighter in color and less 

dense in appearance-! experienced no power loss while in 

the cloud. However, flight crews were exposed to hydrogen 

sulfide, and the use of 100 percent oxygen was mandatory. 

The plume from Pacaya Volcano (2,552 m) (fig. 4) was 

white, and flying through the cloud was similar to flying 

through a cumulus cloud. Water droplets formed on the 

windscreen, and there was no evidence of solid ash particles. 

A total of 32 hours was flown for volcanic research in 

1978-this includes an estimated 5 hours in plumes of different density. Those 5 hours were enough to etch the windshield, bum out the bearings on one generator, dull the paint, 

abrade and destroy the landing-light glass covers and the 

running lights, damage the de-ice boots, pit the leading edge 

of the propellers, and dull the chrome-plated prop domes. 

Upon return from Guatemala in 1978, substantial maintenance (including replacing the windshields) was needed to 

bring the Queen Air up to standard. 

When we returned to Guatemala in February 1980, we 

were more knowledgeable about the hazards and damaging 

effects of volcanic ash. I devised a method to protect the forward-facing windscreen from abrasion by taping a 0.007-

inch film of clear mylar to the windshield. The mylar had to 

be replaced after each ash flight (fig. 5). 

During the 1980 program in Guatemala, we flew a 

total of 36 hours, including an estimated 3 hours in the 

plumes of Santiaguito and Pacaya. Fuego was inactive. A 

daily cleaning and oiling of the air-intake filters was 

needed. A daily inspection of all 24 spark plugs was conducted in addition to the normal pre-flight inspection, 

which usually required replacing the bottom-row 12 plugs 

because black, glassy, obsidian-like deposits completely 

covered the electrodes. I have not been able to determine 

why the top plugs stayed relatively clean. 

The temperature in the cylinder at the point of ignition 

is near 3,000°F (1,648°C)-well above the temperature 

Figure 2. Ash cloud and small eruption column following an 

overnight eruption of Fuego Volcano, February 1978. The plume 

had stagnated owing to low wind conditions and was held in place 

by a temperature inversion. 
EFFECTS OF VOLCANIC ASH ON AIRCRAFT POWERPLANTS AND AIRFRAMES 143 

Figure 3. The plume from the Santiaguito vent at Santa Maria 

Volcano (3,772 m) was lighter in color and less dense in appearance 

than plumes from Fuego Volcano (figs. I and 2). The airplane experienced no power loss while in the cloud; however, hydrogen sulfide 

gas was detectable by odor. 

needed to melt the rhyolite glass particles found in the February 1978 eruption clouds of the Guatemalan volcano, Santiaguito (Rose, 1987). Magma solidifies from 1 ,250°C down 

to 700°C (Decker and Decker, 1981), so it seems reasonable 

to think that both upper and lower sets of spark plugs would 

be exposed to the same high temperature and that both sets 

would keep the magma liquid and expel it along with 

unburned exhaust gases. However, that was not the case. 

Evidently, the bottom plugs cool more in the combustion 

cycle and allow melted ash to congeal on the electrodes. 

The ejecta from the 1980 eruption of Mount St. Helens 

presented similar problems to those of the Central America 

volcanoes and added a new one: wet volcanic ash. On 7 

April 1980, Mount St. Helens erupted a gray to black 

plume to an estimated 300 m above the vent, and, as the 

fallout began, a dark curtain of material fell from the plume 

Figure 4. The white, water-rich plume from Pacaya Volcano 

(2,552 m) formed above a small lava lake. Flying through the cloud 

was similar to flying through a cumulus cloud. Water droplets 

formed on the windscreen, and there was no evidence of solid ash 

particles in this cloud. 

\ 

Figure 5. To protect the forward-facing windscreen from abrasion by volcanic ash, a 0.007-inch film of clear mylar was taped to 

the windshield. The mylar had to be replaced after each ash flight. 

(fig. 6). We circled and penetrated the heavy ash curtain. 

We were surprised. What appeared to be just an ash curtain 

similar to many we had flown through before was really a 

shower of muddy ash. The powerplants nearly stopped; the 

mylar-covered windscreen became opaque; and forward 

visibility was reduced to zero. The muddy ash shower 

reduced in intensity, and we made seven more trips through 

the cloud before returning to Portland. We landed with the 

aid of air-traffic-control radar. 

On 10 April 1990, we returned to Jeff co Airport at 

Broomfield, Colo. During routine maintenance on 14 April 

1990, an oil sample was analyzed with the following results 

(numbers in parentheses represent values before volcanic 

ash sampling; numbers not in parentheses represent values 

after volcanic ash sampling-units are in part per million): 

Fe: (98), 293; Ag: (0), 1; AI: (20), 119; Cr: (9), 29; Cu: (16), 
144 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 6. On 7 April 1980, Mount. St. Helens (2,549 m) erupted 

a gray to black plume to an estimated 300m above the vent, and, as 

the fallout began, a dark curtain of material fell from the plume. The 

1980 Mount St. Helens ejecta was wet, which caused it to adhere to 

the exterior of the airplane. 

36; Mg: (4), 18; Ni: (7), 21; Si: (39), 168; Ti: (0), I; Mo: (0), 

2. The most common elements and metallic compounds in 

the Lycoming IGS0-540 powerplant are: tin, aluminum, 

bronze, steel, and chrome. Magma contains trace amounts of 

the same elements (Decker and Decker, 1981). 

The question is: Where did the increases in these elements come from? Was it from abrasion of the powerplant 

by the ingested material; was it from the volcanic ash itself; 

or was it a combination of factors? No doubt the high silicate count is from ingested ash. The high iron count is 

probably a combination of ash and engine abrasion. The 

origin of the silver is unknown. Some Lycoming engines 

used some silver in the supercharger bearings, but I could 

not determine if the Lycoming engines on our airplane 

were manufactured with silver in these bearings. Because 

alumina is the second most abundant part of volcanic rocks 

and also a very common product in aircraft engines, I 

would assume the high count was due to a combination of 

ash and abrasion. The cylinder walls were chrome plated, 

and silicate grinding contributed to the increase in chromium. Copper was probably ground out of the various 

bronze bushings in the engine. The magnesium increase 

appears to be mostly from ingested ash. There are probably 

some compounds in the engine with nickel in them-there 

was a large increase of nickel over the "normal" sample. 

Titanium probably came from the ash, and molybdenum 

could have been scrubbed from some engine alloy. 

CONCLUSIONS 

Judging from the increase of metallic elements shown 

by the oil analysis, it is obvious that the ingestion of volcanic 

ash is detrimental to aircraft powerplants. Ash will shorten 

the operating life of reciprocating engines and may, under 

sustained, severe volcanic-ash ingestion, cause engine failure. I did not have a complete engine failure. It is my opinion 

that jet turbine engines, because of their higher operating 

temperatures and finer tolerances, are even more susceptible 

to complete failure than reciprocating engines. Not only is 

the ash damaging to the engines, but airframes and engine 

components can be destroyed as well. Windshields are especially vulnerable to abrasion and crazing. 

RECOMMENDATIONS 

First and foremost, avoid volcanic clouds. Admittedly, 

avoiding volcanic clouds is difficult at best. The Air Line 

Pilots Association in 1990 issued a form entitled "Operation 

in the Vicinity ofVolcanic Ash Clouds." Flight organizations 

who operate anywhere near areas containing active volcanoes 

should be in possession of these important guidelines. 

Because pilots are often the first to observe volcanic 

activity, especially at remote volcanoes, they should report 

this activity using the reporting form approved by the International Civil Aviation Organization (Fox, this volume). 

For scientific research of volcanoes which requires 

entry into an ash cloud, use an aircraft with reciprocating 

engines; do not use turbine engines. Protect the windscreen 

if at all possible. Clear mylar of 0.007-inch thickness can 

be taped to the windshield without affecting visibility. 

Check and clean the air-intake filters after every penetration. Run a frequent oil analysis. Inspect the pitot-static 

system for clogging by ash. Inspect spark plugs and replace 
EFFECTS OF VOLCANIC ASH ON AIRCRAFT POWERPLANTS AND AIRFRAMES 145 

as necessary. After each flight through a volcanic plume, 

carry out a thorough inspection of the airplane. 

ACKNOWLEDGMENTS 

Thanks are extended to Mr. Dan Fletcher, A VCO 

Lycoming Textron, Williamsport, Pa.; Colorado Aero Tech, 

Broomfield, Colo.; Mr. John Stone and the maintenance staff 

at National Center for Atmospheric Research; and Weststar 

Aviation, Grand Junction, Colo. Special thanks are due to 

Dr. William Rose, Michigan Technological University; Dr. 

Richard Cadle, National Center for Atmospheric Research, 

Boulder, Colo.; Dr. Richard Stoiber, Dartmouth College; 

and many graduate students for their valuable advice about 

volcanoes. 

REFERENCES CITED 

Decker, R.W., and Decker B., 1981, Volcanoes: San Francisco, 

W.H. Freeman and Co., 110 p. 

Rose, W.I., Jr., Chuan, R.L., Cadle, R.D., and Woods, D.C., 1980, 

Small particles in volcanic eruption clouds: American Journal 

of Science, v. 280, p. 671-696. 

Rose, W.R., 1987, Interaction of aircraft and explosive eruption 

clouds: A volcanologist's perspective: American Institute for 

Aeronautics and Astronautics Journal, v. 25, p. 53-56. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

AlA RECOMMENDATIONS AIMED AT INCREASED SAFETY 

AND REDUCED DISRUPTION OF AIRCRAFT OPERATIONS 

IN REGIONS WITH VOLCANIC ACTIVITY 

By AlA Propulsion Committee 334-1, Zygmunt J. Przedpelski, Chairman 

INTRODUCTION 

The multiple-engine power loss on Royal Dutch Airlines (KLM) Flight 867 following an inadvertent encounter 

with a volcanic ash cloud from Redoubt Volcano, Alaska, on 

15 December 1989 underscored the threat of volcanic eruptions to aviation. The Aerospace Industries Association of 

America (AlA) ad hoc propulsion committee (PC-334-1) 

was formed to evaluate this threat and to make appropriate 

recommendations to the aviation industry and responsible 

government agencies. 

COMMITTEE OBJECTIVES 

The mission of this committee was to assess the volcanic ash threat to commercial aviation and to make recommendations to the industry and government agencies 

involved. The recommendations, when implemented, should 

accomplish the following: 

• Reduce the probability of inadvertent aircraft-volcanic ash encounters of the kind that almost resulted in a 

tragedy in the past (KLM in 1989 and Singapore Airlines and British Airlines in 1982). 

• Reduce the interruptions to normal air traffic flow in 

regions with volcanic activity (e.g., Anchorage, 

December 1989 to April1990). 

MEMBERSHIP 

Major U.S. and foreign aircraft and aircraft engine 

manufacturers were represented on the committee. In addition, experts in the field of volcanic activity and engine performance in dust- and ash-contaminated air were invited to 

join the committee. All of the individuals selected had 

extensive experience in aircraft and engine operations with 

specific expertise in volcanic-ash-environment operations, 

including Mount St. Helens 1980, Galunggung 1982, and 

Redoubt Volcano 1989-90. The committee membership is 

shown in table 1. 

PRESENTATIONS AND DATA 

ANALYSIS 

The AlA committee met February 20-21, 1991, in Denver, Colo., at the Central Region headquarters of the U.S. 

Geological Survey. The meeting included presentations by 

various committee members and discussions on recommendations by the committee. The following presentations were 

made, reviewed, and analyzed by committee members: 

• KLM Flight 867 incident including air traffic center 

(ATC) and crew procedures, the engine/aircraft performance, inspection findings, and conclusions. 

• Mount St. Helens and Galunggung volcanic ash-aircraft encounters, with emphasis on differences and 

similarities to the KLM 867 incident. The specific 

cases analyzed in depth were: 

• Mount St. Helens: L 100 (C-130) Transamerica 

event, 

• Galunggung: B747 British Airways event, and 

• Galunggung: B747 Singapore Airlines event. 

• Results on controlled dust and volcanic-ash-ingestion 

engine tests conducted under contract to the U.S. Air 

Force by Calspan Laboratory. 

• Current and proposed air-crew procedures addressing volcanic ash cloud avoidance, recognition, and 

recommended procedures following an inadvertent 

ash-cloud penetration. The recommended procedures 

of Airbus, Boeing, McDonnell-Douglas, Pratt and 

Whitney, General Electric, and Rolls Royce were 

reviewed. Boeing B747 procedures were used as a 

reference. 

• Worldwide threat of volcanic eruptions with emphasis 

on ash-cloud-producing volcanoes and regions. 

• Ash-cloud detection and tracking methods: infrared, 

ground and airborne radar, satellite, visual, etc. 

• Braking effectiveness on wet and dry runways contaminated with ash. 

147 
148 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

CONCLUSIONS AND LESSONS 

LEARNED 

Modem turbine engines can sustain serious, flightsafety-threatening damage when exposed to volcanic ash for 

even very limited periods of time. The successful completion of military specification MIL-E 5007 (or equivalent) 

sand-ingestion tests by a particular engine model does not 

provide assurance of sustained operability in a volcanic ash 

cloud because concentrations of volcanic ash that are orders 

of magnitude higher may be present and because of the different physical and chemical nature of volcanic ash. Older 

generation turbine engines, which operate at a lower combustor discharge temperature, are not as susceptible to the 

high-pressure-turbine deposit buildup and area blockage (as 

is true for current production engines and future engine 

designs). However, all turbine engines are vulnerable to 

compressor erosion. The committee had no specific data on 

aircraft piston-engine damage caused by volcanic ash, but 

literature search indicates that piston engines are also damaged by exposure to volcanic ash. 

Design changes to improve engine resistance to volcanic ash ingestion would, at best, result in minor improvement 

but at a significant increase in fuel consumption and engine 

weight. 

Damage to aircraft systems from volcanic ash ingestion, while not primary in terms of flight-safety threat, contributes to the crew workload in an already stressful 

situation. The major concerns are loss of airspeed indication, 

reduced visibility due to windshield erosion, loss ofHF (high 

frequency) communications and degradation of the VHF 

(very high frequency) communications, and possible degradation of electronic controls and instrumentation caused by 

ash contamination. 

Volcanic-ash-ingestion events, while infrequent, are 

major flight-safety concerns. All members felt that a onetime spurt of activity generated by the Redoubt-KLM 867 

incident is effective in reducing the probability of a volcanicash-caused aircraft accident in the near term. However, 

many of the committee members remembered similar activities following the 1980 Mount St. Helens and the 1982 

Galunggung eruptions. It was agreed that institutionalized, 

recurring training of air crews and air traffic controllers, who 

may be exposed to volcanic activities, is required to achieve 

lasting air-safety benefits from the previously learned lessons. 

Increased air crew and air traffic center (A TC) awareness of the threat posed by volcanic ash and adherence to the 

current operating instructions, which emphasize avoidance, 

recognition, and procedures to be followed in the event of 

inadvertent ash-cloud encounter, should reduce the probability of ash-caused aircraft accidents. Improved airborne 

detection means (akin to weather radar for detection of 

Table 1. Membership of AlA Propulsion Committee 334-1. 

[AlA, Aerospace Industries Association of America; IAE, International Aero Engines 

(a joint company of Rolls Royce, Pratt and Whitney, and a Japanese consortium); 

CFMI/SNECMA, CFM International/Societe Nationale d'Etude et de Construction de 

Moteurs d'Aviation] 

Name Affiliation 

Michael Dunn ............... Calspan Laboratory 

George P. Sallee ............ *Boeing Commercial Airplane Co. 

Ernest Campbell ........... *Boeing Commercial Airplane Co. 

John Lane ..................... *McDonnell-Douglas 

L.H. Kosowsky .............. *United Technology/Norden Systems 

AI Weaver ..................... *United Technology/Pratt & Whitney 

William Quaile ............. *United Technology/Pratt & Whitney 

Thomas Casadevall ....... U.S. Geological Survey 

Craig Bolt .................... .IAE 

Tony Wassel ................. Rolls Royce 

Michel Tremaud ............ Airbus 

Yves Halin .................... CFMI/SNECMA 

Zygmunt Przedpelski I ... *GE Aircraft Engines 

* fudicates AIA member. 

I Committee chairman. 

heavy precipitation) are needed. Improved ash-cloud tracking, including estimates of ash-particle density utilizing 

satellite and ground tracking means, is also needed to 

enhance safety and reduce disruptions to normal air-traffic 

operations in regions with volcanic activity. 

The issue of braking effectiveness on runways covered 

with volcanic ash (dry and wet) was raised, and no reliable 

data is known to exist at this time. 

In general, the existing air crew operating instructions 

dealing with volcanic ash environment are adequate. However, in order to facilitate transition from one aircraft model 

to another, these instructions should be standardized as much 

as possible. 

An engine in-flight shut down (IFSD) is a rare event. 

Many airline crews never encounter one. The need to restart 

an engine in the air is even rarer. This, combined with the 

different air-start versus ground-start engine characteristics 

has made it unlikely that the crew will follow optimum procedures for air starts. This was demonstrated in the KLM 867 

event and may have been a contributor to late and (or) unsuccessful restart attempts in other cases of engine IFSD's associated with inclement weather. 

The Calspan controlled engine-test data indicates that 

buildup on high-pressure turbine nozzle vanes in ash environment can be avoided if combustor exit temperature can 

be maintained below a specified value. This suggests that, 

in a case where the recommended procedure of reducing 

power to flight idle cannot be followed (i.e., when adequate 

terrain clearance cannot be maintained), a higher power 

level that is capable of maintaining altitude can be used for 

a limited time period. It is estimated that the "useful" 
AlA RECOMMENDATIONS AIMED AT SAFETY IN REGIONS WITH VOLCANIC ACTIVITY 149 

engine life (determined by compressor erosion) is on the 

order of 10 times longer that the "useful" engine life when 

rapid buildup is occurring on high-pressure turbine (HPT) 

nozzle vanes. The performance/stall-margin loss caused by 

compressor erosion is, however, unrecoverable. It is, therefore, the committee's position that flight idle power, which 

eliminates nozzle buildup and greatly reduces compressor 

erosion, should be the recommended procedure when inadvertent ash-cloud entry is made. 

The committee considered the options of shutting down 

some engines during inadvertent ash-cloud entry. It also considered a procedure of engine deceleration/acceleration to 

break loose some of the nozzle deposits, lower the compressor operating line, and regain stall margin. While these procedures may be useful under some conditions, the additional 

complexity these procedures force upon a crew in a very 

stressful situation is considered counterproductive. 

SPECIFIC RECOMMENDATIONS 

All aircraft manufacturers should review the flightmanual procedures pertaining to operations in areas contaminated by volcanic ash. The Boeing 747 operating instructions can be used as a guide to achieve maximum possible 

standardization. Two specific items should be added to the 

Boeing 747 operating instructions: 

1. The preferred method for exiting volcanic cloud conditions is a 180° tum. 

2. APU (auxiliary power unit) start should be added to 

items to be accomplished in case of inadvertent volcanic cloud penetration (subject to comparison of the 

maximum APU combustor-discharge temperature versus the threshold for turbine-nozzle deposit buildup). 

All aircraft manufacturers should provide a section in 

maintenance manuals that would provide the guidance for 

necessary maintenance and (or) inspections to be accomplished following an aircraft encounter with volcanic ash. 

Aircraft manufacturers, with assistance from the 

engine manufacturers, should define maximum engine 

power levels (expressed in engine pressure ratio (EPR), fan 

speed (Nl), and (or) exhaust-gas temperature (EGT) levels) 

that will minimize buildup of melted and resolidified ash 

on HPT nozzle guide vanes. These values should be added 

to flight-manual procedures and should be used only when 

the recommended flight idle power will not assure adequate 

terrain clearance. 

Aircraft manufacturers should ensure that cooling air 

for electronic compartments is filtered to prevent ash contamination of vital electrical/electronic systems. This is 

most important in current and future fly-by-wire aircraft. 

Aircraft manufacturers, with assistance from engine 

manufacturers, should consider addition of a time-delay circuit to allow an air-started engine to reach stabilized idle 

speed before the electrical or generator load is applied. 

This would facilitate engine restarts under less-than-ideal 

conditions. 

FAA and other equivalent government agencies should 

require that air crews practice engine air-restart procedures 

in a simulator on recurring basis. Normal and deteriorated 

engine-start characteristics should be simulated. 

FAA should support technology program efforts leading toward development of a practical airborne volcanic-ashcloud detection device. 

FAA should support efforts to improve satellite and 

ground tracking of volcanic ash clouds. These efforts should 

eventually lead to quantification of ash concentration to 

determine when existing clouds are or are not threatening to 

air traffic. 

FAA and other airspace operating agencies should put 

in place a worldwide communication alert system to provide swift warning of the location and severity of volcanic 

ash clouds. 

FAA should sponsor tests utilizing the B747 windshield 

from KLM 867. Tests should determine if spraying windshield rain repellent fluid and actuating the wipers can be 

used to improve visibility through an eroded windshield (the 

windshield is currently at the Jet Propulsion Laboratory, Pasadena, Calif.). If positive, the results should be incorporated 

into flight-manual procedures dealing with operation in 

areas contaminated with volcanic ash. 

FAA should sponsor a program to quantify the coefficient of friction on runways contaminated with volcanic 

dust (wet and dry). The results in the form-fabricatingeffectiveness advisory should be incorporated into appropriate sections of flight manuals by manufacturers of all 

aircraft affected. 

FAA and other equivalent government agencies 

should require that air crews be trained and tested periodically on knowledge of inclement weather procedures, 

including operations in areas contaminated with volcanic 

ash. Similar training and testing should be conducted for 

ATC personnel assigned to geographic locations near 

known volcanic activity. 

The lessons learned from aircraft-volcanic ash 

encounters should be communicated worldwide, utilizing 

all available forums (International Civil Aviation Organization (ICAO), Flight Safety Foundation, Air Transport Association and its equivalents, Federal Aviation Administration 

and its equivalents, Air Line Pilots Association and its 

equivalents). 

AlA should support the effort of the ICAO volcanic 

warning study group. This effort, when completed, should 

lead to improved reporting and dissemination of worldwide 

volcanic activity. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

RECOMMENDED FLIGHT -CREW PROCEDURES IF 

VOLCANIC ASH IS ENCOUNTERED 

By Ernest E. Campbell 

ABSTRACT 

Recent major volcanic eruptions have impacted air 

operations and have resulted in significant airplane damage. 

The encounter of a 7 4 7-400 airplane with volcanic ash is 

reviewed to demonstrate the extent of damage that can occur 

in just a few minutes. In this event, all four engines flamed 

out in less than 1 minute. Airplane engines, surfaces, windows, electronic equipment, and the pneumatic system were 

severely damaged. Approximately $80 million was required 

to restore the airplane. 

When volcanic eruptions are reported, flight crews 

should use all possible means to avoid the area. However, at 

night or during flight in clouds, the ash may not be observed 

visually, and airplane radar systems are not capable of 

detecting volcanic ash. Recognition of an ash encounter may 

be accomplished by observing one or more of the following: 

heavy static discharges, glow in engine inlets, ash appearing 

in the cockpit and cabin with an acrid odor, multiple engine 

malfunctions or flameouts, and a decrease in airspeed. 

If volcanic debris is inadvertently encountered, immediately reduce thrust to idle and exit the ash as quickly as 

possible. Autothrottles should be turned off in order to maintain idle thrust. Tum on engine and wing anti-ice (increase 

air bleed) to improve engine surge margin. Monitor exhaustgas-temperature (EGT) limits. Restart engines if required. 

Monitor airspeed and pitch attitude to detect a blocked 

pitot system. Airplane and engine damage may or may not 

be apparent; therefore, a landing at the nearest suitable airport is recommended. Report all volcanic ash encounters as 

soon as possible. 

INTRODUCTION 

The recent eruptive sequence of Redoubt Volcano and 

Mt. Spurr in Alaska, Mt. Unzen in Japan, and Mt. 

Pinatubo in the Philippines has again demonstrated the 

potential for a dangerous confrontation between explosive 

volcanic eruptions and air operations. In as much as all 

engines are subjected to the same adverse environment 

during an encounter, there is an appreciable probability of 

an all-engine power loss or flameout. The purpose of this 

paper is to discuss flight-crew procedures following an 

inadvertent volcanic ash encounter. 

AN ENCOUNTER OF A 747 WITH 

VOLCANIC ASH 

Most of the recent volcanic ash encounters have 

occurred on 747- and DC-10-type aircraft because they are 

the long-range airplanes used to fly the Pacific "ring of fire" 

routes. The following review of a 7 4 7 encounter with volcanic ash demonstrates the extent of damage that can occur in 

just a few minutes. All models of modem airplanes equipped 

with high-bypass engines are susceptible to the same type of 

damage, assuming the same amount of volcanic ash is 

encountered. 

Redoubt Volcano, near Anchorage, Alaska, experienced an eruption on December 14, 1989. On the following 

day, a 7 4 7-400 airplane powered by GE CF6-80C2 engines 

entered an ash cloud at 25,000 ft and experienced flameouts 

on all four engines. 

During descent to 25,000 ft, the airplane entered a thin 

layer of altostratus clouds when it suddenly became very 

dark outside. The crew also saw lighted particles (St. 

Elmo's fire) pass over the cockpit windshields. At the same 

time, brownish dust with a sulfurous smell entered the 

cockpit. The Captain commanded the Pilot Flying to start 

climbing to attempt to get out of the volcanic ash. One 

minute into the high-power climb, all four engines flamed 

out. Due to the volcanic ash and dust in the cockpit, the 

crew donned oxygen masks. 

The Pilot Flying noticed the airspeed decaying, initially 

at a normal rate (given the airplane's attitude), but suddenly 

very fast. All airspeed indications were then lost due to volcanic dust contamination in the pitot system. At the same 

time, there was a stall warning and the stick shaker was activated with no signs of buffeting. The Pilot Flying rather 

firmly put the nose of the aircraft down to avoid a stall and 

initiated a tum to the left in a further attempt to get out of the 

volcanic ash. 

151 
152 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

The crew noticed a "Cargo Fire Forward" warning and 

deduced that the fire warning was caused by the volcanic 

ash, so no further action was taken. 

As the engines spooled down, the generators tripped off 

and all instruments were lost except for instruments powered 

by the batteries. 

During the time the engines were inoperative, the cabin 

pressure remained within limits and no passenger oxygen 

masks deployed. The crew elected not to deploy the masks 

because the passenger-oxygen-mask system would have 

been contaminated by volcanic dust in the cabin air. 

An emergency was declared when the airplane passed 

through approximately 17,000 ft. The crew stated that a 

total of seven or eight restart attempts were made before 

engines 1 and 2 finally restarted at approximately 17,200 ft. 

Initially, the crew maintained 13,000 ft with engines 1 and 

2 restarted, and, after several more attempts, engines 3 and 

4 were also restarted. 

Volcanic ash had entered the pi tot-static system; all airdata systems had become unreliable. However, the left-hand 

altimeter indicated correct values. Furthermore, the rudder 

ratio light was on, indicating contamination of this system 

also. Because of the rudder ratio being incorrect, the aircraft 

was difficult to handle, especially during the period that only 

engines 1 and 2 were operating. The inertial guidance 

ground speed was used for speed reference after having 

checked with air traffic control (ATC) that the indicated values were correct. 

After passing abeam and east of Anchorage at 11,000 ft, 

the airplane was given radar vectors for a wide right-hand 

pattern to runway 06 and further descent to 2,000 ft. The 

Captain had the runway continuously in sight during the 

approach; however, vision through the windshields was 

impaired by the "sandblasting" from the volcanic ash in such 

a way that the Captain and First Officer were only able to 

look forward with their heads positioned well to the side. 

During the last part of the approach, an "Equipment Cooling" overheat message occurred, but the Captain elected to 

disregard this message because landing was imminent. 

After landing, the Captain cleared the landing runway 

and taxied the aircraft to the assigned gate. When turning 

toward the gate the Captain transferred control to the Pilot in 

the right-hand seat, because his vision through the left-hand 

windshield was impaired in such a way that he could not see 

the gate during the last part of the docking procedure. 

Inspection of the airplane revealed the following: 

• All four engines suffered extensive damage and had to 

be replaced. Inspection of engine 1 found that, in the 

first stage of the high-pressure turbine, ash had melted 

and resolidified (or "ceramatized") on the leading 

edges of the nozzle vanes. The solid ash deposits 

extended along 75 percent or more of each leading 

edge with an average depth of about 1.5 mm. A preliminary hypothesis suggests that the extent of the 

melted and resolidified volcanic ash deposit on the 

high-pressure turbine nozzle vanes increased the 

operating-line pressure ratio of the compressors, 

resulting in engine surge. The repeated restart 

attempts resulted in partial break up of the deposit 

through "thermal shock." This, in combination with 

improved engine-surge margin at lower altitudes, 

resulted in a successful restart of all four engines. 

• The entire pneumatic system, the air conditioning 

system, and the equipment cooling system were 

heavily contaminated by volcanic ash. A major portion of the pneumatic system was removed, cleaned, 

and reinstalled. 

• Both the Captain's and the Copilot's windshields were 

"sandblasted" and had to be replaced. The leading 

edges of the wings, the winglets, the vertical fin, and 

the horizontal stabilizer were "sandblasted" and had 

to be replaced. Other protruding parts of the aircraft-for example, all antennas, probes, ice detectors, and angle-of-attack vanes-were damaged and 

had to be replaced. 

• The pitot-static system was damaged and heavily contaminated. The pitot and static ports had to be removed 

and replaced and the system purged of all ash. 

• The entire fuselage, except for the area behind the aft 

pressure bulkhead, had to be cleaned very carefully. 

This included all cockpit instrument panels; all circuit-breaker panels; passenger cabin areas; baggage 

compartments; and the areas above the cabin ceiling 

panels, including all systems present in these areas 

and the entire environmental control system. 

• The entire electrical and avionics systems were contaminated and had been exposed to possible overheating due to loss of cooling air. All electrical and 

avionics units had to be replaced. 

• The smoke detection system was contaminated 

throughout. The entire unit, including associated 

plumbing and ejectors, had to be replaced. 

• The fuel system, the hydraulic system, and the potable-water systems had to be cleaned and checked for 

proper operation. 

• The cabin windows, forward of the wing, were eroded 

and pitted and had to be replaced. 

• Approximately $80 million was required to restore the 

airplane. 

ENGINE DAMAGE/THRUST LOSS 

Of primary concern following an inadvertent encounter 

with a dense cloud of volcanic ash is almost immediate 

engine damage followed by engine surge, thrust loss, and 

possible flameout of all engines. During a less severe 

encounter, the flight crew may observe fluctuating engine 

parameters such as a decrease in engine speed and a slow to 

rapid rise in EGT and fuel flow. 
RECOMMENDED FLIGHT -CREW PROCEDURES IF VOLCANIC ASH IS ENCOUNTERED 153 

The nature of volcanic ash particles is such that molten 

deposits accumulate rapidly upon ingestion, reducing highpressure-turbine inlet-guide-vane area and covering turbine 

airfoil cooling holes. Engine power loss occurring shortly 

after entering volcanic ash clouds has been attributed to 

compressor-operating-parameter changes. The nozzleguide-vane-throat area is radically reduced, causing the 

burner pressure (static) and the compressor discharge pressure (static) to increase rapidly. This event causes the engine 

to surge. In addition, considerable erosion occurs on compressor blades together with heavy airfoil damage. 

The factors that influence the degree of erosion and 

that can also affect performance, particularly of the compressor blades, are: particle hardness and concentration, 

particle impact velocity (thrust setting) and angle, and core 

protection. 

Volcanic ash contains materials of different compositions. Of importance to jet engine performance is the melting temperature of these materials. Glasses have a 

characteristic melting point of between 600°C and 800°C. 

Crystalline particles melt in the range of 1,100°C and 

1,200°C. Thrust settings above flight idle will produce temperatures capable of melting volcanic materials. Therefore, 

it is extremely important to immediately retard thrust levers 

to idle (altitude permitting) if volcanic ash is inadvertently 

encountered. Reducing thrust to idle will also reduce compressor erosion damage. 

In addition to engine damage or flameout, volcanic ash 

has a significant effect on the engine's ability to start. In 

severe cases, it may not be possible to restart the engines. 

Starting ability is enhanced by decreasing altitude and by 

allowing the hot section to cool. However, in the event of an 

all-engine flameout, an immediate restart should be 

attempted. Flight crews should be made aware that engine 

acceleration during start at altitude is very slow when compared to ground starts. Also, volcanic ash damage due to 

eroded compressors and deposits on fuel nozzles will further 

increase the engine-acceleration time during in-flight starts. 

Compressor bleed (engine and wing anti-ice plus all air conditioning packs) should be on during restarts and during subsequent operation to maximize engine-surge margin. 

OPERATING INSTRUCTIONS 

AVOIDANCE 

A void flight in areas of known volcanic activity, particularly at night or in instrument meteorological conditions 

(IMC), when volcanic ash and dust may not be visible. 

When planning a flight into an area with a reported or 

known potential for volcanic activity, review all notices and 

directives for current status of that activity. 

Plan the flight to remain well clear of reported activity. 

If possible, stay upwind of volcanic ash and dust. 

Do not rely on airborne weather radar to detect and display volcanic ash and dust. Airborne weather radar systems 

used on commercial airplanes are not designed to detect very 

small ash and dust particles. 

When flying near an erupting volcano, act immediately 

to get as far from the ash and dust cloud as possible. 

When practical, tum to a heading directly away from, 

and upwind from, the ash cloud. 

RECOGNITION 

Volcanic ash and dust may be difficult to detect at night 

or during flight through clouds; however, the following conditions have been observed by flight crews: 

• At night, heavy static discharges (St. Elmo's fire) 

around the windshield, accompanied by a bright white 

glow in the engine inlets. 

• At night, landing lights cast sharp, distinct shadows in 

volcanic clouds (unlike the fuzzy, indistinct shadows 

that are cast against weather clouds). 

• Volcanic ash and dust (haze) appearing in the cockpit 

and cabin. Volcanic dust collecting on top of flat surfaces. 

• An acrid odor similar to electrical smoke or burnt 

dust. The smell of sulfur may also be present. 

• Multiple engine malfunctions, such as surge, increasing exhaust-gas temperature, torching from tailpipe, 

and flameouts. 

• Decrease in indicated airspeed. 

• An increase in cabin altitude or loss of cabin pressure. 

PROCEDURES 

If volcanic debris is inadvertently encountered, accomplish the following: 

• Immediately reduce thrust to idle. This will lower 

EGT, which in tum will reduce the debris buildup on 

the turbine blades and hot-section components. Volcanic dust can cause rapid erosion and damage to the 

internal components of the engines. 

• Autothrottles off (if engaged). The autothrottles 

should be turned off to prevent the system from 

increasing thrust above idle. Due to the reduced surge 

margins, limit the number of thrust adjustments and 

make changes with slow and smooth thrust-lever 

movements. 

• Exit volcanic cloud as quickly as possible. Volcanic 

ash may extend for several hundred miles. The shortest distance/time out of the dust may require an 

immediate, descending 180° tum. Setting climb thrust 

and attempting to climb above the volcanic cloud is 

not recommended due to accelerated engine damage/ 

flameout at high thrust settings. 
154 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

• Engine and wing anti-ice on. All air conditioning 

packs on. Tum on engine and wing anti-ice systems 

and place all air conditioning packs to on to further 

improve engine stall margin by increasing bleed-air 

flow. It may be possible to stabilize one or more 

engines at idle thrust setting where the EGT will 

remain within limits. An attempt should be made to 

keep at least one engine operating at idle and within 

limits to provide electrical power and bleed air for 

cabin pressurization until clear of the volcanic dust. 

• Start the auxiliary power unit (APU), if available. The 

APU can be used to power the electrical system in the 

event of a multiple-engine power loss. The APU may 

also provide a pneumatic air source for improved 

engine starting, depending on the airplane model. 

• Oxygen mask on and 100 percent, if required. If a significant amount of volcanic dust fills the cockpit or if 

there is a strong smell of sulfur, don oxygen mask and 

select 100 percent. Manual deployment of passenger 

oxygen masks is not recommended if cabin pressure 

is normal because the passenger oxygen supply will 

be diluted with volcanic-dust-filled cabin air. If the 

cabin altitude exceeds 14,000 ft, the passenger oxygen masks will deploy automatically. 

• Ignition on. Place ignition switches to "on" as appropriate for the engine model (position normally used 

for in-flight engine start). Cycling of fuel levers 

(switches) is not required. For airplanes equipped 

with autostart systems, the autostart selector should 

be in the "on" position. The autostart system was 

designed and certified with a "hands-off' philosophy 

for emergency air starts in recognition of crew workload during this type of event. 

• Monitor EGT. If necessary, shut down and then 

restart engines to keep from exceeding EGT limits. 

• If not already closed, close the outflow valves. 

• Do not pull the fire switches. 

• Leave fuel boost pump switches "on" and open crossfeed valves. 

• Do not use fuel heat-this would be undesirable if on 

suction fuel feed. 

• Engine restart. If an engine fails to start, try again 

immediately. Successful engine start may not be possible until airspeed and altitude are within the airstart 

envelope. Monitor EGT carefully. If a hung start 

occurs, the EGT will increase rapidly. If engine is 

just slow in accelerating, the EGT will increase 

slowly. Remember, engines are very slow to accelerate to idle at high altitude, especially in volcanic 

dust-this may be interpreted as a failure to start or 

as a failure of the engine to accelerate to idle or as an 

engine malfunction. 

• Monitor airspeed and pitch attitude. If unreliable, or 

if a complete loss of airspeed indication occurs (volcanic ash may block the pitot system), establish the 

appropriate pitch attitude dictated by the operation 

manual for "flight with unreliable airspeed." If airspeed indicators are unreliable, or if loss of airspeed 

occurs simultaneously with an all-engine thrust loss, 

shutdown, or flameout, use the attitude indicator to 

establish a minus one degree pitch attitude. Inertial 

ground speed may be used for reference if indicated 

airspeed is unreliable or lost. Ground speed may also 

be available from approach control during landing. 

• Land at the nearest suitable airport. A precautionary 

landing should be made at the nearest suitable airport 

if airplane damage or abnormal engine operation 

occurs due to volcanic dust penetration. 

Because of the abrasive effects of volcanic dust on 

windshields and landing lights, visibility for approach and 

landing may be markedly reduced. Forward visibility may 

be limited to that which is available through the side windows. Should this condition occur, and if the autopilot system is operating satisfactorily, a diversion to an airport 

where an auto landing can be accomplished should be considered. If forward visibility is restricted, consider having 

the airplane towed to the parking gate. 

GROUND OPERATION AT AIRPORTS 

AFFECTED BY VOLCANIC ASH 

• During landings, limit reverse thrust. The use of maximum reverse thrust may impair visibility and ingest 

dust into the engines. 

• The presence of a light layer of dust that obliterates 

the markings on a runway could have a detrimental 

effect on braking. The effects of a heavy layer are 

unknown. Exercise caution when ash has fallen on 

wet surfaces because surfaces may be slippery and 

braking may be less effective. 

• Brake wear will be accelerated; however, properly 

sealed bearings should not be affected. 

• Avoid static operation of engines above idle power. 

• Do not taxi with any engine shut down. Use all 

engines for taxi. 

• Thrust during taxi should be limited to that which is 

required to sustain a slow taxi speed. 

• Avoid operation in visible dust. Ash and dust should 

be allowed to settle prior to initiating a takeoff roll. 

• Use a rolling takeoff procedure. 

• Restrict ground use of the APU to engine starts. 

• Avoid use of air conditioning packs on the ground if 

recirculation fans will maintain adequate comfort 

level. If air conditioning on the ground is necessary, 

operate at full cold setting if dust is visible and precondition at the terminal using a filtered ground cart if 

available. Use bleeds off for takeoff if operating procedures permit the configuration. For air conditioning pack operation, consult the operations manual. 
RECOMMENDED FLIGHT -CREW PROCEDURES IF VOLCANIC ASH IS ENCOUNTERED 155 

• Do not use windshield wipers for dust removal. Wash 

deposits off with water and wipe residue off with a 

soft cloth. 

SUMMARY 

Flight crews, dispatchers, and air traffic controllers 

must be aware of any potential volcanic activity affecting 

their area of operation. They must check notices and air traffic control directives for the current status of any volcanic 

activity. Should an inadvertent penetration of a volcanic 

dust cloud be made, flight crews must be aware of the 

potential problems and be prepared to deal with the arising 

flight conditions. Also, crews should be aware of the operational conditions at airfields that are contaminated with volcanic ash and dust. If at all possible, avoid penetration of a 

volcanic ash cloud. 

ACKNOWLEDGMENTS 

I wish to acknowledge and thank the engine manufac-

_turers (General Electric, Pratt and Whitney, and Rolls 

Royce) and the United States Air Force for information that 

they provided regarding engine operation in volcanic ash 

and dust. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

DEVELOPMENT OF A REAL-TIME ATC 

VOLCANIC ASH ADVISORY SYSTEM BASED ON THE 

FUTURE AVIATION WEATHER SYSTEM1 

By James E. Evans 

ABSTRACT 

The overall U.S. air traffic control (ATC) decisionmaking and communications system should incorporate volcanic ash as a type of aviation weather hazard into the 

planned aviation weather system, which will be deployed in 

the United States starting in 1996. This weather system is 

based on the concept of a four-dimensional (4-D) (3 spatial 

dimensions and time) gridded database for current and predicted hazard locations with a variety of graphics products 

tailored to the needs of various users. Real-time information 

from ground sensors, air-carrier aircraft, unmanned air vehicles, and satellites would be used to estimate the current and 

predicted locations of hazardous ash. To achieve this system, 

research is needed on defining harmful ash densities, determining an optimal approach for estimating the density and 

extent of ash clouds, and validating models for predictions 

regarding ash clouds. 

INTRODUCTION 

Inadvertent ingestion of volcanic ash by jet engines has 

caused exstensive damage to a number of aircraft recently 

and could have caused fatal accidents in at least three cases. 

The operational system used to cope with the 1989-90 eruptions of Redoubt Volcano in Alaska utilized trajectory analysis to estimate ash locations with current textual aviation 

weather advisories (e.g., significant meteorological advisory 

(SIGMET), notices to airmen (NOT AM), or center weather 

advisory (CWA)) as a principal means of conveying information to pilots and controllers (Mostek, 1991; Heffter and 

others, 1991; Murray and others, this volume; Hufford, this 

volume; D' Amours, this volume). Manually generated 

graphics were distributed by facsimile (Criswell, 1991) to 

planners but not to pilots or controllers. Consequently, visual 

observations of ash clouds by pilots (or the lack thereof) 

were critical to air traffic control decision making (Criswell, 

1991, Haeseker, 1991). This system had failures in assisting 

1 This work was supported by the Federal Aviation Administration. 

pilots to avoid hazardous ash-cloud encounters and has a tendency for "over warning," which negatively impacts air 

operations and damages the credibility of the advisory program. A major problem that may arise with operational planning based on trajectory analysis to delineate the region of 

hazard in a relatively short period (e.g., 24 hours) after an 

eruption has occurred is that the possible area of warning for 

an ash encounter may be enormous. 

From the viewpoint of surveillance and information 

dissemination, the recommended system (fig. 1), treats volcanic ash as a type of spatially extended aviation weather 

hazard similar to in-flight icing. Real-time information from 

ground, aircraft, and satellite sensors would be combined 

with the numerical-model predictions of ash transport to provide real-time, current and predicted locations of various 

levels of ash concentration in the 4-D gridded database generated by the aviation gridded forecast system (AGFS). This 

4-D database would be used to disseminate graphical depictions of the current and predicted ash locations by the aviation weather product generator (A WPG). 

A key element of the recommended system is the determination of spatial location of damaging ash concentrations 

(as opposed to the current estimates of an unspecified ash 

concentration over very large geographical areas). Anumber of options are considered for achieving this capability. 

Particular attention is paid to the ongoing validation of ashlocation and concentration estimates as the ash clouds move 

away from the immediate vicinity of the volcano. This paper 

concludes with some recommendations for the research and 

development program and system-deployment decisions that 

will be needed to achieve an operationally useful system. 

Related proposals for an integrated detection and warning system have been made by Harris (this volume), 

D' Amours (this volume) and Stunder and Heffter (this volume). D' Amours, and Stunder and Heffter, principally treat 

the prediction problem without addressing how the initial 

ash-cloud 3-D spatial distribution will be determined. Harris 

suggests estimating ash-cloud parameters from the amplitude and duration of eruption-related harmonic tremor with 

subsequent ash-location forecasting by trajectory analysis. 

By contrast, we suggest the use of radars and sensors carried 

157 
158 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

PROALERS 

SATELLITE I RADIOSONDES 

UAV I LASER RADAR I 

~ 

Figure 1. Major elements of recommended volcanic-ash-advisory system for aviation. Gridded wind forecasts are combined with 

ash locations measured near and downwind of volcanoes to generate 4-D, predicted locations of ash clouds. Distribution of the 4-D 

ash locations are accomplished by the FAA/NWS (Federal Aviation Administration/National Weather Service) weather-infonnation systems. UAV, unmanned aircraft vehicle; A/C, aircraft; 

A WPGIITWS, aviation weather product generator/integrated terminal weather system; AGFS, aviation gridded forecast system; 

NMC, national meteorological center; ATC, air traffic control. 

by a dedicated, unmanned aircraft vehicle (UAV) to estimate 

the initial concentration; the use of full, 4-D, gridded models 

to estimate future ash locations; and the use of airborne measurements by air-carrier aircraft and dedicated UA V' s to validate the estimated ash concentrations. 

THE PLANNED AVIATION 

WEATHER SYSTEM 

The Federal Aviation Administration (FAA) and 

National Weather Service (NWS) are currently deploying a 

number of sensors useful for ash surveillance and for measuring meteorological quantities (e.g., wind and clouds) that 

relate to ash transport and surveillance. The next-generation 

weather radars (NEXRAD) being procured for en-route airspace are significantly more capable of ash detection than 

current NWS radars-they also provide radial-velocity estimates (Stone, this volume). NEXRAD routinely produces 

graphical products, such as maps of echo tops and layered 

reflectivities, that can be used directly by A TC planners and 

controllers to provide some safety information on ash clouds 

while they are detectable by the radar. Additionally, 

NEXRAD has algorithms to analyze 3-D features of storms 

and extract pertinent aviation variables, such as the presence 

of hail and tornadoes. This computation capability could be 

adapted to automatically estimate the spatial extent of an ash 

cloud as an input to subsequent prediction programs. 

The knowledge of the state of the atmosphere downwind of the volcano will be greatly expanded as a result of 

improved wind sensors and analysis systems. National 

Oceanic and Atmospheric Administration's (NOAA) forecast systems laboratory has been developing the aviation 

gridded forecast system, which is a high-resolution, state-ofthe-atmosphere estimation system that plays a key role in the 

recommended system. The AGFS, which will be tested in 

1994 and implemented nationally in 1996, uses the current 

balloon atmospheric soundings (Holland and others, 1992), 

the aircraft communications addressing and reporting system 

(A CARS), and pro filer data (Hassel and Hudson, 1991 ), as 

well as numerical-forecast-model results to create a highresolution (30-km horizontal resolution, 25 vertical levels, 

hourly estimates based on a 6-hour analysis cycle), gridded 

database of meteorological variables (e.g., winds, temperature) and aviation weather impact products (e.g., cloud locations) using the mesoscale analysis and prediction system 

(MAPS) (Schlatter and Benjamin, this volume). Owing to 

computer-load constraints, the initial coverage for the AFGS 

will be for the continental United States. However, the computational algorithms used have been adapted for Alaska and 

could be implemented locally. Extension of AGFS/ A WPG 

coverage to western Canada may also be warranted. It should 

be noted that the AGFS/ A WPG will provide many economic 

benefits to aviation in that area, including better wind estimates for air routes from the United States to Japan. 

Reliable real-time dissemination of ash-location information to pilots and controllers is essential. Fortunately, the 

distributed nature of the volcanic-ash hazard is quite analogous to many weather phenomena. A key element in the 

weather-information-dissemination system will be the 

regional and national A WPG (fig. 2), which utilizes the 

information from NEXRAD and gridded state-of-the-atmosphere information, such as that provided by the AGFS, to 

create real-time aviation terminal weather products for a 

variety of users and systems (Sankey and Hansen, 1993). 

The regional A WPG (RA WPG), associated with the various 

FAA enrollee centers, is a very attractive vehicle for display 

of the real-time and predicted ash locations to en-route controllers and various traffic management units because it also 

will communicate alphanumeric and graphical weather 

information to pilots via the data-link processor. The A WPG 

should be operationally available in the 1997-98 time frame. 

Real-time ash-location estimates would be provided both 

graphically and in text, to en-route air traffic controllers, 

flight service station specialists, and pilots to assist in tactical 

decision making. Since the initial A WPG graphical products 

would be created and distributed by commercial vendors 

such as Atmospheric Research Systems, Inc. (ARSI on fig. 

2), airline dispatch, airport operators, and others would have 

ready access to the same information as FAA users. 

It is also important that high resolution information be 

available in the terminal area of major airports that may be 

affected by ash clouds. Studies of aircraft routes in the vicinity of storms have shown that pilots will fly much closer to 

hazardous regions in conducting landing and takeoff 

operations than they would while en route, where they would 
DEVELOPMENT OF A REAL-TIME ATC VOLCANIC ASH ADVISORY SYSTEM 159 

deviate to avoid a hazardous region. In addition, pilots are 

particularly concerned about the operations disruption from 

overly conservative hazard warnings in the terminal area. 

The integrated terminal weather system (ITWS) provides 

very high resolution, gridded analyses (2-km horizontal grid, 

5-minute update), as well as dissemination of weather information for the terminal area based on information from the 

A WPG, Weather Forecast Office (WFO), and the FAA/ 

National Weather Service terminal-area sensors (Evans, 

1991 b; Albers, 1992). The ITWS has access to a wide variety 

of weather sensors in and around the terminal area, such as 

the terminal Doppler weather radar (TDWR), and could easily be augmented to include ash-location information from 

other sensors, such as laser radars. The ITWS will include 

color displays for terminal-area traffic managers as well as 

graphical information for terminal radar approach control 

facility (TRACON) controllers. ITWS prototypes will commence long-term operationally oriented demonstrations in 

1994-the ITWS will be operationally deployed in 1999 

(Sankey and Hansen, 1993). 

OPERATIONAL REQUIREMENTS FOR 

AN ASH ADVISORY SYSTEM 

No operational requirements have yet been formally 

stated by the FAA for a volcanic-ash-advisory system. The 

growing experience with providing operational hazardousweather products is germane to assessing the requirements 

for volcanic ash surveillance. In particular, warnings of wind 

shear due to micro bursts and gust fronts have been provided 

operationally to terminal controllers and supervisors at three 

different major airports since 1988 (Evans, 1991a). The 

operational analyses (Stevenson, 1991) carried out in conjunction with these and other tests and demonstrations suggest the following guidelines: 

1. Air-traffic-control personnel and aircraft pilots should 

not be expected to interpret meteorological and ashlocation data from sensors to assess the degree of 

hazard. 

2. A sound technical basis for the hazard levels (e.g., tolerable time exposure to various ash concentrations) 

yielding ash alerts is essential for design of an effective advisory system. 

3. Operational requirements for minimum acceptable 

levels for hazard detection and false-alarm probabilities must be closely related to the expected operational 

disruption. For example, false-alarm probabilities that 

were operationally acceptable in low-wind-shear environments were found to be operationally disruptive in 

high-traffic environments with frequent wind-shear 

events (Stevenson, 1991). 

4. Informal systems users groups (e.g. representatives 

from airlines, pilot groups, airport authorities, 

Figure 2. Planned aviation weather product generator system 

when deployed in 1996. Graphical weather products derived from 

3-D, gridded database are distributed to FAA en-route and terminal 

facilities by the meteorological weather processor (MWP) and via 

aircraft situation displays (ASD) used for traffic management. 

Flight service stations (AFSS) and airline users will receive similar 

graphical products from commercial vendors. AM Weather, 

NOAA aviation weather program broadcast on the Public Broadcasting System; ARSI, Atmospheric Research Systems, Inc.; 

ARTCC, air route traffic control center; ATCSCC, air traffic control system command center; CWSU, Center Weather Service 

Unit; DUAT, direct-user access terminal; Eta, estimated time of arrival; ETMS, enhanced traffic management system; HARS, highaltitude routing system; MAPS, mesoscale analysis and prediction 

system; NA WAU, national weather advisory unit; NEXRAD, 

next-generation weather radar; NMC, National Meteorological 

Center; TMUS, traffic management units; TSC, transportation system center; WSU, weather service unit. 

aviation administrations, safety boards, researchers, 

and information providers) that periodically review 

the scientific knowledge, operational needs, system 

performance, and operational use of the products can 

be very useful for reaching rapid operational acceptance and utility for a new system capability such as 

the recommended volcanic-ash-advisory system. 

A major problem in developing an effective ash-advisory system is the poor understanding of tolerable levels of 

ash ingestion for the engine type of concern to air carriers. 

Although several very useful studies have been carried out 

(Dunn and Wade, this volume; Przedpelski and Casadevall, 

this volume), there appears to be no published experimental 

or simulation data on damage to high-bypass engines as a 

function of ash concentration and exposure duration. Obtaining improved information on tolerable ash concentrations/ 

exposure durations is essential for the development of an 

improved ash-advisory system. 
160 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

ASH-CLOUD-CHARACTERIZATION 

OPTIONS 

Another essential element of the proposed system is 

improved initial estimates of the spatial distribution of operationally significant ash concentrations including ash type, 

particle size, and density in both clear air and in the presence 

of weather clouds. It is very important that the system have 

some capability to automatically accomplish this objective 

in the presence of clouds because many of the potentially 

active areas may be cloud covered during significant portions of the year. 

Weather radars can provide 3-D ash-cloud characterization through rain clouds. However, three problems arise: 

determination that an eruption is underway, discrimination 

between rain and ash clouds, and estimating the pertinent 

parameters of an ash cloud. The initial determination of an 

eruption and discrimination between rain and ash clouds can 

be based on a variety of clues, including seismic tremors 

(Harris, this volume), lightning (Hoblitt, 1991 ), and satellite 

observations (Matson and others, this volume; Schneider and 

Rose, this volume). Initially, the determination that an eruption has occurred and delineation of ash-cloud regions (e.g., 

by entering bounding polygons) would be accomplished 

manually by Central Weather Service Unit (CWSU) meteorologists using information from sensors as well as from volcanologists. Estimation of ash-cloud parameters would then 

be accomplished automatically using volume-scanned radar 

data within the bounding polygon regions. 

Estimating the distribution of ash-particle sizes and 

types cannot be directly accomplished with the microwave 

weather radars of greatest interest (Harris and Rose, 1983; 

Stone, this volume) or from current satellites in a time frame 

compatible with a real-time advisory system. Harris and 

Rose (1983) have discussed estimating ash-cloud parameters 

from radar data by using ash-fall data. It may be possible to 

utilize their technique for real-time estimation in situations 

where ash-fall measurements have been made on similar previous eruptions. 

The use of a dedicated, multi-wavelength laser may 

also be useful in estimating particle sizes when the cloud 

cover permits. However, the high rate of attenuation in 

either ash clouds or rain clouds makes lasers an unattractive 

choice as a sole means of ash surveillance, particularly from 

ground-based locations. For example, the University of 

Washington measurements of Redoubt Volcano plumes 

showed cases where the ash in an upper layer cloud was not 

detected due to attenuation of the laser beam by a lower altitude, dense cloud (Hobbs and others, 1991). Similar measurements using lasers and in-situ sampling are needed for 

ash prediction model verification. However, suitable 

manned aircraft are expensive to operate and may not be 

available on short notice. 

A UA V with instruments (payload of approximately 

150-200 lb) is an attractive option for directly measuring ash 

concentrations and transporting lasers for ash-cloud mapping. Advances in UA V designs, autonomous guidance and 

worldwide availability of navigation aids and communications have made UA V' s cost effective for atmospheric 

soundings. It appears (P. Jarvinen, Lincoln Laboratory, written commun., 1992) that the engine of a UAV can be protected from ash-particle ingestion, and impact erosion by ash 

particles can be kept to manageable levels. The piston-powered Amber UA Vis particularly attractive at this time due to 

its technical characteristics (38 hours endurance at 17,000 ft 

altitude; operation up to altitudes of 28,000 ft-up to 40,000 

ft with a turbocharger-a 70-100-lb internal payload; a 100-

lb external payload) and because several U.S. Government 

owned Amber systems may be available. The proposed 

mode of operation would be to map ash-cloud extents in a 

vertical plane normal to the axis of the plume at some 

selected distance downwind of the volcano (far enough to 

avoid the large fragments that rapidly precipitate out of the 

cloud). The downwind spatial distribution of the ash cloud 

would be updated on a schedule dictated by the winds and 

the demonstrated capability of the ash-prediction models. It 

should be noted that there are a number of small-scale turbulence and mesoscale weather features that are not captured in 

the improved forecast models that will utilize the MAPS 

grid. Consequently, it appears necessary for the foreseeable 

future to have the ability to validate ash-cloud predictions 

downwind on an ongoing basis until ash density is no longer 

at hazardous levels. 

It may be cost effective to instrument some air-carrier 

aircraft that operate in areas with many volcanoes, such as 

the North Pacific and Alaska regions. Data from in situ volcanic-ash-detection sensors could be reported over the 

ACARS link. The information from such aircraft would be 

used principally to provide additional confirmation of the 

accuracy of ash predictions and to provide a "heads up" 

warning to pilots of situations in which the ash densities 

were approaching levels that could damage the aircraft. For 

example, if the aircraft were to encounter much higher ash or 

volcanic gas concentration levels than were predicted, the 

ACARS could be used to identify cases where the prediction-model estimates were significantly in error. The advantage of using ACARS in this context is that the ashprediction systems will already be accessing the ACARS 

data on a continuing basis in real time. Consequently, corrections to the predicted ash-cloud-concentration estimates 

could be generated quickly and transmitted to the aviation 

community. 

CONCLUSIONS AND 

RECOMMENDATIONS 

The aviation weather system currently under development by the FAA and NWS should play a critical role in the 

development of a more effective, real-time, volcanic-ashadvisory system based on the generation and dissemination 
DEVELOPMENT OF A REAL-TIME ATC VOLCANIC ASH ADVISORY SYSTEM 161 

of a graphical, 4-D, volcanic-ash product. A number of 

research and programmatic challenges exist including: 

1. Quantitative assessment of ash concentrations that 

may be of concern for flameout of modem, highbypass jet engines; 

2. Development of an effective system for unambiguous 

3-D ash-concentration measurements near and downwind of erupting volcanoes; 

3. Validation of the accuracy of models that predict the 

spatial distribution of ash; and 

4. Refinement of the human/machine interface for the 

system (e.g., by rapid prototype testing). 

A product-users group should be established to provide 

feedback and suggestions as the ash-advisory system 

evolves. Extending the coverage of the AGFS/ A WPG system to Alaska and the western portion of Canada is essential. 

ACKNOWLEDGMENTS 

An unpublished review of literature on volcanic ash 

generation and physical properties by D.C. Johnson was of 

considerable assistance in developing this paper, and studies 

by P. Jarvinen on ash-cloud-mapping approaches formed 

much of the basis for the UA V recommendations. B. Carmichael of the National Center for Atmospheric Research 

provided figure 2. 

REFERENCES CITED 

Albers, S.C., 1992, The LAPS wind analysis: Fourth workshop on 

operational meteorology, Whistler, B.C., Canada: American 

Meteorological Society, p. 186-195. 

Criswell, C.F., 1991, Volcano eruption notification and aircraft 

avoidance [abs.], in Casadevall, T.J., ed., First International 

Symposium on Volcanic Ash and Aviation Safety: U.S. Geological Survey Circular 1065, p. 16. 

Evans, J.E., 199la, The terminal Doppler weather radar (TDWR) 

system at one year before deployment, in Third International 

Conference on Aviation Weather Systems, Paris, France, 1991: 

American Meteorological Society, p. Jl-J6. 

---1991b, The integrated terminal weather system (ITWS), in 

Third International Conference on Aviation Weather Systems, 

Paris, France, 1991: American Meteorological Society, p. 

118-123. 

Haeseker, E., 1991, Alaska Airlines operating procedures during 

the 1989-1990 Redoubt eruptions [abs.], in Casadevall, T.J., 

ed., First International Symposium on Volcanic Ash and Aviation Safety: U.S. Geological Survey Circular 1065, p. 20. 

Harris, D.M., and Rose, W.I., 1983, Estimating particle sizes, concentrations, and total mass of ash in volcanic clouds using 

weather radar: Journal of Geophysical Research, v. 88, p. 

10969-10983. 

Hassel, N., and Hudson, E., 1991, Description of the wind profiles 

installed in Homer, Alaska [abs.], in Casadevall, T.J., ed., First 

International Symposium on Volcanic Ash and Aviation Safety: U.S. Geological Survey Circular 1065, p. 22. 

Heffter, J.L., Stunder, B.J., and Rolph, G.D., 1990, Long-range 

forecast trajectories of volcanic ash from Redoubt Volcano 

eruptions: Bulletin of American Meteorological Society, v. 71, 

p. 1731-1738. 

Hobbs, P.V., Radke, L.F., Lyons, J.H., Ferek, R.J., Coffman, D.J., 

and Casadevall, T.J., 1991, Airborne measurements of particle 

and gas emissions from the 1990 volcanic eruptions of Mount 

Redoubt: Journal of Geophysical Research, v. 96, p. 

18735-18752. 

Hoblitt, R.P., 1991, Lightning detection and location as a remote 

ash-cloud monitor at Redoubt Volcano, Alaska [abs.], in Casadevall, T.J., ed., First International Symposium on Volcanic 

Ash and Aviation Safety: U.S. Geological Survey Circular 

1065, p. 24. 

Holland, G.J., McGeer, T., and Youngren, H., 1992, Autonomous 

aerosondes for economic atmospheric soundings anywhere on 

the globe: Bulletin of American Meteorological Society, v. 73, 

p. 1987-1998. 

Mostek, A., 1991, NOAA's response to the Mount Redoubt eruptions of December 1989 [abs.], in Casadevall, T.J., ed., First International Symposium on Volcanic Ash and Aviation Safety: 

U.S. Geological Survey Circular 1065, p. 33. 

Sankey, D., and Hansen, A., 1993, FAA's work in improving aviation weather, in Ninth International Conference on Interactive 

Information and Processing Systems for Meteorology, Oceanography and Hydrology, Anaheim, CA, 1993: American Meteorological Society, p. 200-209. 

Stevenson, L., 1991, Summary of findings from the PIREP-based 

analyses conducted during the 1988 to 1990 evaluations of 

TDWR-based and TDWR-LLWAS based alert services provided to landing/departing pilots: Cambridge, Mass., Volpe 

National Transportation Systems Center Report DOT/FAA 

DOT-VNTSC-F AA-91 d-15, 46 p. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

WARNING SYSTEMS AND PILOT ACTIONS 

By Peter M. Foreman 

ABSTRACT 

Encounters with volcanic ash are a major threat to flight 

safety. Aircraft must follow flight paths that avoid ash 

clouds-these flight paths must be based on a knowledge of 

the location and probable motion of the ash clouds. There is 

no reliable means of detecting volcanic ash from an aircraft. 

Therefore, aircraft require a warning from outside. 

A warning system will depend upon the cooperation 

of geological agencies, meteorologists, and the air traffic 

services. Because volcanic ash clouds are difficult to 

locate, eruptions should trigger activation of the aviation 

warning system. 

Pilots require concise, self-evident messages in aeronautical language to cause them to change their flight path in 

a timely manner. Pilots can assist the warning system by 

reporting their observations. Pilots should be informed of 

the dangers of volcanic ash encounters, and they should be 

given training on recognition and mitigation. 

INTRODUCTION AND NATURE OF 

THE PROBLEM 

The first notable encounter was the British Airways 74 7 

near Galunggung, Indonesia, in 1982. It showed that, in such 

encounters, we might expect a loss of engine power, problems with airspeed indications, and extensive abrasion damage, including a loss of windshield transparency. The 

encounter placed the flight in great danger, and it required 

heroic and persistent efforts by the crew to restart the engines 

and bring the flight to a safe conclusion (Tootell, 1985). 

During the eruption of Redoubt Volcano in Alaska on 

15 December 1989, a new B747-400 on a flight from 

Amsterdam to Anchorage flew into the plume and lost power 

from all four engines. The crew were able to restart the 

engines and land the flight safely. The initial estimate of 

damage to the aircraft was $80 million, including the 

replacement of all four engines (Brantley, 1990). 

In spite of the severity of these encounters, the persons involved were lucky. We cannot rely on luck in the 

future. We must implement measures to keep aircraft out 

of volcanic ash. 

The adverse results from encounters with volcanic ash 

fall into six categories: 

1. Impact.-Severe damage within several miles from 

the volcano. 

2. Abrasion.-Leading edges, mechanical, and hydraulic systems. 

3. Accretion.-Ash melts, followed by accretion on turbine nozzles: flameout. 

4. Corrosion.-Volcanic gases combine with water 

vapor to form acids. 

5. Adhesion.-Ash adheres to surfaces and clogs passages for cooling and sensing. 

6. Physiological.--Gases and particles are noxious to 

aircraft occupants. 

HOW MUCH VOLCANIC ASH 

IS A DANGER? 

It is estimated that the B747-400 encountered an ash 

cloud with a density of approximately 2 g/m3 of air. The 

larger particles in that cloud were in the range of 100--400 

microns. Whereas some U.S. military engines are designed 

to tolerate dust or sand, there is no design tolerance for dust 

or ash built into civil aircraft. The military specification calls 

for engines to be able to tolerate 0.05 g of fine sand per cubic 

meter of air, one-fortieth of the density encountered by the 

B747-400 at Redoubt. A qualified military engine in a 

ground-level test ran into severe difficulties and stalling at a 

density of 0.5 g/m3 of air, or one-quarter the density encountered by the B747-400 (Dunn and Wade, this volume). 

Ground tests have also revealed a previously unsuspected problem of the turbine engine: fuel-nozzle coking 

that occurs after prolonged exposure to ash at densities lower 

than those that cause accretion in the turbine. The coking 

problem can also lead to engine failure, and, when it does, 

there is no possibility of restarting the engine. 

EXTERNAL WARNING SYSTEMS 

It has been asked, why do pilots not keep a sharp 

lookout and steer away from volcanic ash clouds? The 

crew of the B747-400 reported that they descended into a 

163 
164 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

smooth layer of cloud with a white top surface, which 

looked like a weather cloud. At night, or when flying 

within a prevailing meteorological cloud structure, there 

may be no opportunity for a pilot to detect an ash cloud 

before flying into it. Therefore, the safety of air transport 

requires an ash warning system. 

Detecting and locating airborne volcanic ash is a challenge. Sometimes, visual observations are the first and best 

reports of a remote volcanic eruption. However, visual 

reports have also been responsible for large numbers of false 

alarms. Airborne weather radar is not useful for locating volcanic ash, and there are no airborne systems that provide reliable detection and location from a distance. Therefore, 

aviation needs an external warning system. If an airborne 

system were to become available in the future, there would 

be an economic debate on whether to install such equipment 

on board all aircraft, or whether to rely on external systems 

in strategic locations. 

The reliability of detection of volcanic eruptions is 

dependent on the degree of monitoring of activity at the volcano. Real-time seismic monitoring is the fundamental 

method for detecting eruptions, but the seismic signals may 

leave ambiguities that have to be resolved before announcing 

an eruption. Other monitoring systems at the volcano complement the seismic information and can reduce the interval 

of uncertainty. These techniques include television, lightning detectors, weather radar, and infrasound. V olcanologists have a limited ability to forecast some eruptions. Short 

time intervals are relevant to aviation safety, and minutes of 

undetected eruption constitute a distinct hazard. If a few 

minutes of advance warning of an eruption could be provided, safety would be greatly enhanced. 

KILOMETERS 

30 WEST 

25 

20 

15 

10 

WARNING-SYSTEM 

CHARACTERISTICS 

To ensure aviation safety, it is necessary that reports of 

eruptions are processed without delay into warnings to pilots 

and amendments to air traffic clearances. The first 

announcement of the start of an eruption should go to air traffic control. Initially, there is no need to try to predict where 

the ash is, or where it is going. It will be in an expanding, 

rising column over the volcano. 

There are large differences between volcanic eruptions, 

so it is not easy to generalize. However, it is instructive to 

study the May 18, 1980, eruption of Mount St. Helens. Figure I shows the elevation and distribution of the ash in a 

west-to-east vertical profile of the Mount St. Helens eruption 

cloud. This eruption was larger than the 15 December 1989 

eruption at Redoubt Volcano, Alaska, but was smaller than 

the 15 June 1991 eruption at Pinatubo in the Philippines. 

Volcanoes are a threat to air safety from the moment 

that they erupt. Volcanic ash is driven into the sky by a combination of gas thrust and convection. The Mount St. Helens 

ash took approximately 5 minutes to reach aircraft-cruising 

altitudes (Rosenbaum and Waitt, 1981) at a rate of climb of 

approximately 5,000 ft per minute. A warning system should 

be capable of a 5-minute response time once an eruption has 

been detected. It is important that the processes of the warning system do not contribute unnecessary additional delays. 

Winds play the dominant role in the distribution of 

volcanic ash. The agency for subsequent ash-location advisories should be the meteorological office. All reports of 

ash-ejecting eruptions should be sent to that office so that 

the computerized model of winds over the eruption site can 

be used, in conjunction with dispersion models, to predict 

FEET 

EAST 100,000 

90,000 

80,000 

70,000 

60,000 

50,000 

40,000 

30,000 

20,000 

10,000 

-1 ~==~==~==~==~~==~===:~~~~==~~~==~==~~==~==~==~==~--~ 0 MEAN SEA 

40 35 30 25 20 15 1 0 5 0 5 1 0 15 20 25 

DISTANCE FROM VOLCANO, IN KILOMETERS 

30 35 40 45 50 55 LEVEL 

Figure 1. Diagrammatic east-west profile of May 18, 1980, Mount St. Helens eruption showing vertical growth and lateral expansion of 

plume. Times shown are Pacific Daylight Time (e.g., 0838). From Sarna-Wojcicki and others (1981, fig. 331). 
WARNING SYSTEMS AND PILOT ACTIONS 165 

ash trajectories. Figure 2 shows a synoptic plot of the May 

18, 1980, eruption at Mount St. Helens. 

With a knowledge of the start time of an eruption and 

wind velocities at different levels, an expanding envelope of 

"probably contaminated" airspace may be declared and 

updated from time to time. This information should be sent, 

without delay, to the appropriate air traffic control centers 

(A TC) to ensure that aircraft in the hazard areas are directed 

to safer skies. The ash-plume advisory should also be sent to 

airline-operations dispatch offices so that future flights are 

planned to avoid the ash plume. 

The use of digital communications systems will permit 

rapid warning-response times after eruption detection. The 

first step to set up a fast response warning system would be 

establishing arrangements for intraagency exchange of digital data. 

Once air traffic is safely rerouted, then other, more suitable, aircraft can probe the area to discover the nature and 

extent of the ash plume without necessarily having to enter 

the ash cloud. Satellite images and visual observations can 

be expected to further define the ash. Once a region has been 

surveyed and found to be safe for airliners, it can be 

reopened. 

Figure 3 is a schematic diagram of a generic warning 

system. The prime sensor inputs are shown in rounded 

boxes, and the primary agencies are shown in shaded, square 

boxes. Primary communications links are shown by heavy 

lines. On the ground, these links should include digital data 

streams backed up by voice telephone, fax, and teletype. The 

ground-air link would be radio telephone and, where available, datalink. The supporting ground agencies are shown in 

unshaded, square boxes. These agencies protect the system 

by providing redundant channels for communication, shown 

by thin lines. The system should accept the input of visualobservation reports at any point. 

Because ash on the move does not respect jurisdictional 

boundaries, it is vital to exchange information between 

countries. Links between similar agencies such as the U.S. 

Federal Aviation Administration and the Canadian transportation agency, Transport Canada, already exist. It is a matter 

of expediting the flow of information about eruptions and 

plume trajectories. All communication links should function 

in both directions. 

~-·-··-··-··-··BRITISH COLUMBIA CANADA ··-··-··-··-··-·· ,) -----·-··-··T··-ruNiiffi.s:rAiis \ I I 

. I I 

__,.• 

WASHINGTON 

0 0LYMPIA 

~ /"'- _... .. ___,.·· a--.. ..,., " 

Portland 

OREGON 

100 200 300 KILOMETERS 

50 100 150 MILES 

I 

r· 

I 

L, I 

J 

I 

I 

I 

I 

I 

( 

I 

0 BOISE 

MONTANA 

IDAHO 

Pocatello 0 

Figure 2. Isochron map showing maximum downwind extent of ash from airborne ash plume erupted from Mount St. Helens on May 18, 

1980, and carried by the fastest moving wind layer (as observed on satellite photographs). Times shown are Pacific Daylight Time (e.g., 

0845). From Sarna-Wojcicki and others (1981, fig. 332). 
166 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

WEATHER RADAR 

LIGHTNING DETECTORS 

INFRA-SOUND DETECTO 

TELEVISION 

NEIGHBORING GEOLOGICAL ._ ____ _J 

AGENCY 

NEIGHBORING WEATHER 

SERVICE 

Figure 3. Generic warning system schematic diagram. Prime sensor inputs are shown in rounded boxes. Primary agencies are shown 

in shaded, square boxes. Primary communications links are shown 

by heavy lines. Supporting ground agencies are shown in unshaded, 

square boxes (these agencies provide redundant channels for communication, shown by thin lines). The system should accept the input of visual-observation reports at any point. 

Ideally, volcanologists and their expert monitoring 

systems should be the ones to notify of an eruption. This 

will eliminate many false alarms. Realistically, many geological agencies do not have continuous, fast-reaction capability. When there is no expert system, the eruption report 

may come from aviation or civil authorities. There is great 

merit in the system currently operated by the Alaska Volcano Observatory, which varies the degree of alertness 

based on objective criteria concerning the activity at or 

beneath a volcano. 

There may be difficulty in operating such a system in 

some parts of the world, but there should be little difficulty 

in doing so in North America, Europe, and Japan. Eruption 

monitoring is only required in areas of potential, explosive, 

volcanic eruption. However, meteorological agencies and 

air-traffic services should be prepared to deal with ash that 

has traveled downwind for considerable distances. 

THE AIR-TRAFFIC-CONTROL 

FUNCTION 

Air traffic controllers should become more active in 

assisting pilots to avoid ash. It is important to appreciate 

the difference between avoiding thunderstorms, where the 

prime detection equipment is carried on board the aircraft, 

and volcanic ash, where primary detection and prediction is 

ground based. 

There will be three distinct air-traffic-control scenarios. 

In the first, aircraft will be flying in controlled airspace and 

under controller surveillance. Once the air traffic controller 

knows where the ash plume lies, he will be in a position to 

issue escape advisories to all aircraft under his control and in 

danger of flying into the ash. Other aircraft should receive a 

general volcanic ash warning, giving plume location and trajectory relative to aeronautical features. 

In the second scenario, the aircraft will be flying in controlled airspace under procedural control without controller 

surveillance. In this scenario, the controller may not be 

aware of precise aircraft location and will probably not be 

able to issue an escape advisory. However, the controller 

could issue a volcanic ash warning, giving plume location 

and trajectory relative to aeronautical features. 

In the third scenario, the aircraft will be flying outside 

controlled airspace. There is then no air-traffic-control 

function, but the air traffic services for the flight-information region should issue a volcanic ash warning message, 

giving plume location and trajectory relative to aeronautical 

features. 

THE VOLCANIC-ASH-ADVISORY 

ESCAPE VECTOR 

When aircraft are under surveillance and control by a 

controller who has an ash-plume location and trajectory forecast-perhaps in the form of an image on his air-traffic-display system-the controller should be able to divert 

conflicting air traffic away from the ash. This would be 

achieved by directing a message to the aircraft to cause it to 

turn. It would also be technically possible to use datalink to 

upload a plume image to an aircraft's electronic flight instrument system (EFIS). 

There is a probability that more than one aircraft might 

need to take immediate action to avoid the plume. To ensure 

minimum delay, the controller should issue an escape message using phraseology similar to the following: 

Pan, Pan. Pan, Pan. Pan, Pan. All stations. All stations. All stations. This is 

Vancouver Center. Volcanic eruption at 2143 Zulu; Vancouver VOR radial 

087 DME 55. Advisory escape vectors; Air Canada 149 050; time air 1165 

060; speedbird 682 300. Repeat. Advisory escape vectors; Air Canada 149 

050; time air 1165 060; speedbird 682 300. Over. 

There will remain a degree of uncertainty about the 

location and extent of an ash cloud. For this reason the 

escape message from A TC should be phrased as an advisory 

vector. It cannot override the ultimate authority of the crew 

to deal with any situation that threatens the safety of the aircraft. There is the possibility that, once the crew are alerted 

to the ash, they may be in a better position to plan their own 

escape route. By giving the escape vector advisory status, 

the crew has the option to disregard it if they see that it is not 

safe. However, in the absence of any other observation, they 

would be well advised to follow the advisory. 

The advisory escape vector avoids giving a long message about the origin, location, nature, and trajectory of the 

ash cloud. It is in a form that pilots are used to hearing and 

translating quickly into a modification of the aircraft flight 

path. There is a minimum of cockpit data processing 

required to implement a vector. 
WARNING SYSTEMS AND PILOT ACTIONS 167 

THE VOLCANIC ASH WARNING 

Those aircraft not in immediate conflict with the ash 

cloud, or not under surveillance and (or) control, should be 

issued a volcanic ash warning (VA W). In a control and surveillance environment, this would follow the volcanic ash 

advisory escape vector transmission. The VA W should be 

revised from time to time as the plume develops and travels 

downwind. The VA W message should use aeronautical terminology and units of measurement to describe the present 

situation and the forecast of plume movement. It might contain phraseology similar to the following: 

All stations. All stations. All stations. This is Vancouver Center. Volcanic 

ash warning: volcanic eruption at Mount Baker. Vancouver VOR radial 087 

DME 55. Started at 2143 Zulu. Severe volcanic hazards from surface to 

flight level four zero zero within four zero miles. Plume spreading from 

flight level two zero zero to flight level four zero zero within arc zero four 

zero to one two zero degrees magnetic to distance one one zero miles at 

2220 Zulu. Plume speed eight zero knots. Out. 

After the eruption ceases, the plume will detach from 

the vent but will continue to remain aloft and travel downwind. The shape may be distorted by vertical wind shear 

and may develop two or more distinct arms; it may split into 

separate entities. We do not know how long it remains a hazard to aircraft, but, if we can detect it, we should avoid it. 

One of the aircraft damaged in the recent Mt. Pinatubo 

series of eruptions met the ash 600 nautical miles west of the 

volcano. This ash must have been airborne for a long time. 

Thus, it is necessary to keep redefining the plume and passing the latest information to pilots. Simply saying that an 

eruption occurred several hours earlier is not much help. 

That information needs additional data before it can be of 

any use. Subsequent VA W messages should continue to 

describe the extent of the plume and its trajectory, in plain 

aeronautical language, with updates at intervals not to 

exceed 2 hours. 

THE ROLE OF PILOTS 

Pilots are the last link in the chain of safety actions to 

avoid or mitigate encounters with volcanic ash. In order for 

pilots to be effective, it is necessary that the rest of the system meets the needs of the pilots. Pilots view the sky in 

terms of routes, fixes, and (or) coordinates. To cause pilots 

to respond rapidly to a message, it must be given to them in 

terms that do not require translation. 

Approximately 600 of the 1,500 potentially active volcanoes are classified as active. Volcanoes are not generally 

marked on aeronautical route charts, and most pilots would 

be hard pressed to come up with the names of more than five 

volcanoes. Giving pilots references to volcanoes by name 

will not produce a rapid response. Another problem is that 

many of the names are unfamiliar and in foreign languages 

that are hard to pronounce. Even if a pilot has a chart with 

volcanoes on it, the spoken name may not be quickly related 

to the written name on the chart. There may well be ambiguity between a pilot's understanding of a spoken name and 

charted names. Therefore, a statement of where an emption 

is occurring expressed in aeronautical terminology will be 

more helpful to a pilot than the name of a volcano. A bearing 

and distance from a navigational fix, or a latitude and longitude, will give a pilot the location. 

Statements of distance should be expressed in nautical 

miles, rate of movement in knots, and plume heights should 

be given to pilots in flight levels (pressure altitude measured 

in hundreds of feet). References to time should always be in 

Coordinated Universal Time. 

PLUME A VOIDANCE 

Before operating in a region of known potential volcanic activity pilots should check SIGMET's (significant 

meteorological information reports), NOT AM's (notices to 

airmen), ATC directives, and PIREP' s (pilot reports) for that 

region. To aid in identifying regions that are potentially 

active at a particular time, a system based on the Alaska Volcano Observatory color codes could be useful for aviation 

and would draw closer attention to the situation when 

required. The exact defmitions of the conditions indicated by 

the colors would need international aviation recognition and 

agreement before the system could be fully implemented. 

The conditions green and yeilow might normally be supplied 

only to air traffic centers and air-carrier dispatch offices and, 

on request, to other users. Condition orange or red should 

give rise to a special NOT AM. 

There is a need for a message priority flag on volcanic 

information. KLM Royal Dutch Airlines has suggested 

VARTAM (volcanic ash report to airmen) as a special category of volcanic NOTAM. There is a precedent for 

NOT AM's of this kind in the usage: SNOTAM is used in 

some countries for snow information. If the V ART AM idea 

is accepted, the International Federation of Air Line Pilots' 

Associations (IF ALP A) would like to propose the variation 

SIGV AR for a significant volcanic ash report or volcanic 

SIGMET. 

All information products mentioned above are text 

messages. With the aeronautical information communication systems in use today, there is a need for text messages to 

serve some parts of the world. However, many users and 

agencies have graphical capabilities. For pilots, graphic 

products are much easier to use and are more compelling in 

terms of amending flight plans for the purpose of avoidance. 

The standard graphic product is the significant weather 

chart, SIGWX. There is a new internationally recognized 

symbol to represent a volcanic eruption in progress on the 

SIGWX chart. However, volcanic ash affecting an airspace 

might come from a volcano off the charted area. Ash itself 

is not an agreed item for display on the SIGWX chart. Other 

graphic products that can be used to display information 
168 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

about the ash-cloud envelope are trajectory and dispersion 

forecasts, created manually or by computer. 

Armed with this information, pilots should plan to 

avoid known volcanic ash. In the absence of a clear understanding of the quantitative long-term effects of flight 

through low ash concentrations, there is no basis to justify 

planned flight through ash. It is best to avoid volcanic ash 

clouds by flying around or over them. Ash plumes contain 

numerous particles that settle from the cloud. Therefore, 

beneath the cloud there will be a rain of particles. Pilots 

should respond quickly and decisively to any warnings or 

directives received in flight. 

MITIGATION FOLLOWING AN 

ENCOUNTER 

Emphasis must be placed on the avoidance of ash. But, 

if ash penetration occurs, crews should know what to do. 

Criteria for recognizing that one's airplane is in a volcanic 

ash plume, and suggested procedures for escaping from a 

plume, are covered in the paper by Campbell (this volume). 

There are procedures that are specific to certain types of aircraft, and information from the aircraft manufacturer is the 

best guide to the operation of individual aircraft. There are 

some other principles that are generic. 

Several carriers have developed useful flight-simulator 

exercises. As with any non-normal flight condition, there is 

great benefit to be derived from simulated flight training. 

When the undesired event occurs with little warning, the 

simulator experience is a great help to the crew. 

The type-specific procedures must take precedence, but 

generics are useful to know. The following recommendations are taken from a list compiled by the Aerospace Industries Association (Campbell, this volume). 

SPECIAL AIR REPORT OF 

VOLCANIC ACTIVITY 

Pilot observations of volcanic activity are of use to 

others. IF ALP A is a member of the ICAO (International 

Civil Aviation Organization) volcanic ash working group, 

which has produced a special air report of volcanic activity 

form (V AR). Pilots should make sure that V AR forms are 

carried on board their aircraft if they operate near any area 

of potential volcanic activity. The form is a guide to the 

reporting technique. If all the prompts on the form are 

answered, a detailed and useful report will result. The form 

should be handed in to the local meteorological office on 

arrival, but this may not take place for several hours. In the 

meantime, pilots should seek the cooperation of some air 

traffic controller or radio operator and report the first eight 

sections (Fox, 1988). 

CONCLUSIONS AND 

RECOMMENDATIONS 

Pilots need information to alert them to the dangers of 

volcanic ash encounters and the procedures for avoidance. 

Training in procedures is vital to prepare pilots to act in a 

timely manner. 

It would be useful to develop a full understanding of 

how long hazardous particles might remain aloft. Knowing 

when to downgrade a warning can be almost as important as 

issuing one. 

It is recognized that upgrading our abilities to respond 

to the problems of volcanic ash will require additional 

expenditures. However, continuing to operate as we have is 

not only dangerous, it is also very expensive. Over the past 

12 years, the air transport industry and its insurers have 

incurred costs running into the hundreds of millions of dollars due to encounters with ash. An effective warning system 

is possible with existing technologies. A system that can 

reduce the number of such encounters should be considered 

worthy of financial support. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14, 1989-August 31, 1990: U.S. Geological Survey Circular 1061, 33 p. 

Fox, T., 1988, Global airways volcano watch is steadily expanding: 

International Civil Aviation Organization (ICAO) Bulletin, 

April, p. 21-23. 

Rosenbaum, J.G., and Waitt, R.B., Jr., 1981, Summary of eyewitness accounts of the May 18 eruption, in Lipman, P.W. and 

Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. 

Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 53-67. 

Sarna-Wojcicki, A.M., Shipley, S., Waitt, R.B., Jr., Dzurisin, D., 

and Wood, S.H., 1981, Areal distribution, thickness, mass, volume, and grain size of air-fall ash from the six major eruptions 

of 1980, in Lipman, P.W. and Mullineaux, D.R., eds., The 

1980 Eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 577-600. 

Tootell, E., 1985, All 4 engines have failed; The true and triumphant story of flight BA 009 and the Jakarta incident: Auckland, Hutchinson Group Ltd., 178 p. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC ASH-THE INTERNATIONAL 

REGULATORY ASPECTS 

By Tom Fox 

ABSTRACT 

The incidents in Indonesian airspace in 1982 in which 

two jumbo-jet transport aircraft suffered engine flameout 

due to ingestion of volcanic ash from the Mt. Galunggung 

eruption prompted the International Civil Aviation Organization (ICAO) to move quickly to amend its international 

regulatory documents to include requirements to provide 

volcanic ash warnings to aircraft. In order to implement such 

an international warning system, it was also necessary to 

organize an International Airways Volcano Watch based on 

observations from a number of international observing 

networks administered by other United Nations agencies. 

INTRODUCTION 

When I look back almost a decade ago and try to imagine if I would have believed it possible that, within a decade, 

an international symposium would be devoted entirely to the 

aviation hazard posed by volcanic ash, my imagination fails 

me. As everyone here is aware, in June 1982, the aviation 

community, and indeed just about everyone else, heard 

details of the drama involving a British Airways B747, 

which encountered a volcanic ash cloud from Galunggung 

Volcano and lost power on all four engines when flying at 

37,000 ft on a flight from Kuala Lumpur, Malaysia, to Perth, 

Australia. 

Initially, there was considerable skepticism that volcanic ash could have been the cause of the incident, and, even 

when this was later confirmed on examination of the affected 

engines and by the occurrence of a repeat performance a few 

weeks later when a Singapore airlines aircraft had a similar 

encounter, there were still those who classified the incident 

as a rare event. 

Rare event or not, the International Civil Aviation 

Organization, the International Air Transport Association 

(lATA), and the International Federation of Air Line Pilots' 

Associations (IFALPA) took the warning seriously and 

immediately recognized the extreme hazard that a volcanic 

ash cloud posed for any aircraft unfortunate enough to 

encounter it. 

DEVELOPMENT OF INTERNATIONAL 

REGULATORY MATERIAL 

The ICAO Air Navigation Commission moved swiftly 

and provided member states (i.e., countries) with interim 

measures to be taken when volcanic eruptions occur in 

flight-information regions (FIR's) for which they are responsible, pending the development of the necessary formal 

amendments to international regulatory documents. 

The formal amendments were subsequently developed 

with the assistance of the volcanic ash warnings (VA W' s) 

study group and became applicable in 1987 (Fox, 1988). The 

VA W study group had been created by the Air Navigation 

Commission to assist the Secretariat in developing amendments to international regulatory documents that provide for 

volcanic ash warnings. The group comprises experts in operations, aeronautical meteorology, and volcanology from 

three member states and five international organizations. 

Presently, international regulatory provisions require 

that information on volcanic activity, including pre-eruption 

activity, and information about a volcanic eruption and the 

resulting ash cloud should be transmitted to aircraft operating on air routes that could be affected and, if necessary, 

arrangements made to activate alternative routes around the 

affected area. This information is required to be transmitted 

in the form of notices to airmen (NOTAM's) issued on the 

initiative of area control centers (ACC's). Information of enroute weather phenomena that may affect the safety of 

aircraft operations (significant meteorological advisory 

(SIGMET) messages) is issued by meteorological watch 

offices (MWO's). The provision of this information forms 

part of the duties of the ACC and MWO responsible, in their 

respective fields, for a particular flight-information region 

(FIR). 

The fundamental question is how and from where the 

ACC and MWO are expected to obtain the initial 

information that a volcanic eruption has occurred or that a 

169 
170 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

volcanic ash cloud exists at critical flight levels near an air 

route. 

In the final analysis, the specific means employed by a 

member state in discharging its responsibilities for an ACC 

or MWO is a matter for the member state concerned. 

However, it has been clear from the beginning that the 

volcanic ash problem is of international concern and usually 

of regional operational impact. Under these circumstances, 

ICAO, with the assistance of other international organizations, established an International Airways Volcano Watch 

(IA VW) in 1987 to ensure that any information available in 

a member state concerning volcanic activity is injected as 

soon as possible into the aviation system via the ACC and 

(or) MWO of the FIR concerned (Heiken, 1988). To achieve 

this, we have sought and obtained full cooperation from a 

number of international organizations. 

INTERNATIONAL AIRWAYS 

VOLCANO WATCH (IAVW) 

The idea behind the IA VW was that it should be based 

on an observing triad comprising: 

1. Observations from existing ground-based stations 

drawn from all known organized international observing networks, regardless of their particular specialized 

function, 

2. Special aircraft reports, and 

3. Observations from satellites (meteorological and nonmeteorological, as appropriate). 

GROUND-BASED OBSERVING 

STATIONS 

In the case of the ground-based networks, ICAO only 

has a direct influence on aeronautical meteorological stations, which are not normally located near active volcanoes. 

Nevertheless, we began with these stations by introducing 

provisions in the relevant international regulatory documents 

(i.e., ICAO Annex 3/W orld Meteorological Organization 

(WMO) technical regulations) requiring the issuance of 

volcanic activity reports by these stations and providing a 

standard format. These provisions were then used as a model 

when we requested the cooperation/operation of other international organizations in providing for similar reports from 

their observing networks. 

In this regard, WMO has introduced provisions into its 

international regulatory documents covering the globalobserving-system component of the World Weather Watch 

(WWW) to ensure that reports of volcanic activity are made 

and transmitted to the relevant ACC or MWO by synoptic, 

agricultural, hydrological, and climatological observing 

stations and by merchant ships providing routine weather 

reports. The World Organization of Volcano Observatories 

(WOVO),a commission of the International Association of 

Volcanology and Chemistry of the Earth's Interior 

(IA VCEI), has made arrangements for volcanic activity 

reports to be sent to the relevant ACC's and MWO's by 

volcano observatories strategically sited to monitor active 

volcanoes; the necessary telephone/telex/fax contact 

numbers of the ACC' s/MWO' s have been provided to 

WOVO for this purpose. Member states have also been 

requested to make necessary arrangements to ensure that any 

information on volcanic activity that may become available 

from other national sources, such as forestry posts, border 

customs/immigration/police/army posts, etc. (many of 

which are located in remote regions within sight of volcanoes), should also be sent to the ACC/MWO of the FIR in the 

member state where the event is located. It is expected that 

such arrangements could be made separately for each government department or, better still, as part of the member 

state's national disaster plan. The intended thrust of these 

arrangements is that all member states should be aware that 

if there is a volcanic eruption anywhere in their territory, 

aviation needs to know about it as soon as possible. The 

ACC concerned will then decide whether or not it is likely to 

be of concern to aviation and how to proceed. 

AIRBORNE OBSERVATIONS 

The second leg of the observing triad is based on reports 

of observations of volcanic activity by pilots. This source of 

information is critically important because "unfortunately" a 

pilot is often the first to observe the eruption (or at least the 

resulting ash cloud). I say "unfortunately" because observation, especially at night, is generally only possible when 

"encountering" the ash cloud, and it is aircraft encounters 

with ash clouds that we wish to avoid. In order to assist the 

pilot in sending such reports, an ICAO special air report of 

volcanic activity report (V AR) form (fig. 1) was developed 

by the VA W study group, based upon two earlier reporting 

forms tested by the Air Transport Association of America 

and Qantas Airlines (Johnson and Casadevall, this volume). 

IA TA and IF ALP A are making continuous efforts to 

ensure that airlines and pilots are aware of the special air 

report of volcanic activity by including such information in 

training documentation and in operating manuals. It will be 

noted that the first eight items listed in the form concern 

information that is needed immediately and, therefore, is to 

be transmitted to the air traffic service (ATS) unit by radio. 

An additional seven items concern information that is to be 

completed in written form and handed in at the next point of 

landing. On receipt by the ATS unit, the information is to be 

relayed immediately to other aircraft concerned, passed to 

the ACC for decision regarding the issuance of a NOTAM, 

and forwarded to the associated MWO for issuance of a SIGMET. Subsequent NOTAM's would include additional 

information, as necessary, concerning rerouting, etc., 
VOLCANIC ASH-THE INTERNATIONAL REGULATORY ASPECTS 171 

MODELVAR 

Aircraft identification 

(as per Item 7 Pilot-in- Dep. from . . . . . . . Date Time ........ UTC 

Operator of flight plan) . . . . . command Arr. at . . . . . . . . . . Date Time •....... UTC 

Addressee 

AIREP SPECIAL 

1 Aircraft identification 

2 Position 

3 Time 

s 

E 4 Flight level or altitude 

c 5 Volcanic activity observed at (position or bearing and distance from aircraft) T 

I 6 Air temperature 

0 

N 7 Spot wind 

1 8 Supplementary information 

(Brief description of activity 

including vertical and lateral extent 

of ash cloud, horizontal movement, 

rate of growth, etc. as available) 

The following information is not for transmission by RTF 

TICK[{.) THE APPROPRIATE BOX 

9 Density of ash cloud (a) wispy 0 (b) moderate dense 0 (c) very dense 0 

10 Colour of ash cloud (a) white 0 (b) light grey 0 (c) dark grey 0 

s (d) black 0 

E 

c 11 Eruption (a) continuous 0 (b) intermittent 0 (c) not visible 0 

T 

I 12 Positior of activity (a) summit 0 (b) side 0 (c) single 0 

0 (d) multiple (e) not observed 0 

N 

13 Other observed features of eruption (a) lightning 0 (b) glow 0 (c) large rocks 0 

2 (d) ash fall out (e) mushrooming cloud 0 (f) nil 0 

14 Effect on aircraft (a) communications 0 (b) nav. systems 0 (c) engines 0 

(b) pitot static 0 (e) windscreen 0 (t) windows 0 

(g) nil 0 

15 Other effects (a) turbulence 0 (b) St. Elmos Fire 0 (c) fumes 0 

(d) ash deposits 0 

16 Other information Add any information considered useful 

Figure 1. Volcanic ash reporting form (VAR) approved by the International Civil Aviation Organization for use by pilots. This form is 

carried by each pilot in their flight handbook. Items 1-8 (section 1) are to be reported immediately by the pilot to the responsible air-trafficcontrol center. Items 9-16 (section 2) are to be completed and filed after landing. 

whereas subsequent SIGMET' s would include trajectory 

forecasts, etc. Member states have also been requested to 

arrange matters so that general aviation pilots are made aware 

that any information they may have concerning volcanic 

activity is to be passed immediately to the A TS unit with 

which they are in contact. 
172 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

MONITORING BY SATELLITE 

The third leg of the observing triad is based on monitoring volcanic eruptions and volcanic ash clouds by satellites. 

In this regard, ICAO has requested WMO to advise on the 

regional meteorological centers that could assist in monitoring volcanic ash clouds and providing trajectory forecasts. In 

addition, WMO is coordinating the further development of 

forecasting techniques needed to provide trajectory forecasts. National and regional arrangements have been made in 

the two regions that have been most affected by the volcanic 

ash problem, in Southeast Asia and in North and Central 

America. However, as illustrated by a number of papers in 

this symposium, there are a number of difficulties in the 

interpretation of satellite data to detect and track volcanic 

ash clouds. Effective satellite monitoring of all potential 

problem areas 24 hours per day, preferably automated, is the 

ideal, but it does not seem that this will be realized in the near 

future. Currently, work is proceeding through WMO to have 

the necessary WMO regulatory documents amended to 

information 

real-time No t~ 

\. 

introduce volcanic ash monitoring and trajectory forecasting 

as part of responsibility of certain regional meteorological 

centers that have the necessary capability. Similarly, the 

ICAO communications/meteorology/operations (COM/ 

MET/OPS) divisional meeting (held in Montreal in 1990 

jointly with the ninth session of the WMO Commission for 

Aeronautical Meteorology) recommended that volcanic ash 

clouds should be included on the significant weather forecasts (SIGWX) issued by regional-area forecast centers as 

part of the world-area forecast system (WAFS). In this 

regard, WMO has developed the necessary symbols for the 

depiction of volcanic ash clouds on WAFS SIGWX forecast 

charts. The lA VW is shown diagrammatically in figure 2. 

NON-REAL-TIME INFORMATION ON 

VOLCANIC ACTIVITY 

In addition to the foregoing real-time information on 

volcanic activity, relevant ICAO regulatory documents also 

Succeeding 

aircraft 

% Direct exchange 

of information ~ MET watch 

office (MWO) 

Weather satellite monitoring 

of volcanic activity 

Figure 2. Organization of the voluntary International Airways Volcano Watch (lA VW). HF, high frequency; VHF, very high frequency; 

see text for other acronyms. 
VOLCANIC ASH-THE INTERNATIONAL REGULATORY ASPECTS 173 

require that member states should include, as necessary, in 

their aeronautical information publications (AlP's) details 

concerning any volcanoes located in the flight-information 

region for which they are responsible. Moreover, the Smithsonian Institution has kindly agreed to routinely provide 

copies of their Bulletin of the Global Volcanism Network 

every month to ACC's/MWO's that require it (McClelland, 

this volume). This publication keeps ACC's!MWO's 

informed on the current status of active volcanoes and 

thereby provides important background information. 

CURRENTANDFUTURE 

WORKINICAO 

The foregoing describes the international regulatory 

aspects of the problem as they stand today. Although there 

will certainly be amendments to regulatory documents to 

improve or add to existing procedures in the future, most 

effort needs to be brought to bear on the effective implementation of existing procedures. Some of the problems (such as 

the initial observation of an eruption by satellite or otherwise, the development of techniques to assess the content 

and density of the spreading volcanic ash cloud, and the 

associated safety margin for jet engines needed to permit the 

reopening of affected routes) are of a technical nature and 

will not be solved overnight. Other problems, however, are 

of a more procedural nature and should be amenable to 

improvement. Indeed, it is earnestly hoped that the results of 

the exchange of information and ideas at this symposium 

will help to achieve this goal. 

From the international perspective, the single most 

important procedural problem is that of communications. 

The flow of information from initial observation, from whatever source, to the ACC and MWO is fraught with problems. 

To start, non-aviation sources generally have little or no 

experience in working with the aviation system, and clear 

channels of communication have to be developed. Necessary 

procedures have to be kept current because years may go by 

without them ever having to be activated. Such problems are 

to be expected, given the disparate parties involved. What is 

not usually expected is that a similar problem could exist in 

the communication of such information between the A TS 

unit and the pilot. In fact, however, often there is such a 

problem, which not only affects the provision of warnings of 

volcanic ash but also other hazardous phenomena, such as 

wind shear, clear-air turbulence, etc. The communication 

pressures on A TS units these days are such that it is 

extremely difficult for them to act as virtually the only communication interface between meteorological departments 

and the pilot. As air traffic continues to grow, it seems likely 

that major improvements will be difficult to achieve until the 

advent of datalink communications later in this decade. In 

the meantime, efforts will continue to be made to mitigate 

the problem and, in this regard, the need to provide information quickly in a concise, operationally relevant format will 

be paramount. 

One example of an effort to improve communications is 

the color-code system developed in Alaska to indicate the 

status of a volcano (Brantley, 1990). A color code, based on 

the Alaskan code was proposed at the second meeting of the 

ICAO Asia/Pacific Volcanological/ Airspace meeting in 

Bangkok in September 1992, and member states in the Asian 

and Pacific regions will be encouraged to use this code when 

reporting volcanic eruptions to ACC' s and MWO' s. Could 

this format be used worldwide, or would specific criteria 

need to be developed for different types of volcanoes, and, if 

so, how many? The views of volcanologists on these 

questions would be very useful because such an agreed-upon 

format would lend itself very well to inclusion in ICAO 

international regulatory documents. 

In order to tackle some of the communications 

problems, the ICAO council, in 1992, approved a special 

implementation project in the Asian and Pacific regions for 

1992-93 in which a two-person team (comprising an aeronautical meteorologist and a volcanologist) will visit a 

number of member states in the regions to advise, as necessary, on local arrangements for the routing of information on 

volcanic eruptions from observing stations through the 

ACC/MWO to the pilot. 

In the immediate future, ICAO, with the assistance of 

the VA W study group, will finalize preparation of a handbook covering all aspects of the volcanic ash problem to 

serve as up-to-date guidance material for member states. 

Completion of the handbook was postponed until after this 

symposium so as to permit the inclusion of the latest experience gained during the recent volcanic eruptions at Redoubt 

Volcano in Alaska and Mount Pinatubo in the Philippines. 

The importance of the Redoubt Volcano eruptions 

cannot be over emphasized because they have finally 

dispelled any lingering doubts about the operational hazard 

posed by volcanic ash; they have provided an opportunity for 

a detailed examination of the operational procedures; and 

perhaps most important, they have been the catalyst that 

prompted the holding of this international symposium. I am 

confident that, given the continued enthusiasm of the people 

involved in all their various fields of endeavor, the volcanic 

ash problem will be resolved in a satisfactory manner. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, 

Alaska, December 14, 1989-August 31, 1990: U.S. Geological 

Survey Circular 1061, 33 p. 

Fox, Tom, 1988, Global airways volcano watch is steadily expanding: ICAO Bulletin, April, p. 21-23. 

Heiken, G., 1988, Volcanic ash warnings for civil aviation: A 

summary report on activities of the volcanic ash warnings 

study group of the International Civil Aviation Organization: 

Bulletin of Volcanology, v. 50, p. 135-136. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

SEATTLE AIR ROUTE TRAFFIC CONTROL CENTER 

RESPONSE TO ERUPTIONS OF MOUNT ST. HELENS 

By Robert F. Hamley and Donald H. Parkinson 

ABSTRACT 

Following notification of an eruption of Mount St. 

Helens, the Seattle air route traffic control center (ARTCC) 

weather service and traffic management units begin a mutual 

effort to determine the horizontal and vertical extent of the 

ash plume. Ash-cloud reports are gathered from ground and 

airborne observers, available imagery is used when possible, 

and ash-plume movement is determined using available 

wind data in conjunction with observations. Ash-plume area 

and movement must be determined as quickly and accurately 

as possible so that air traffic can be kept well away from the 

hazard. 

Data sources, including satellite and radar imagery, are 

of extremely limited value for minor volcanic eruptions. 

Visual ash-cloud reports have been the primary information 

source on the presence of ash but are not available after dark. 

Credibility and completeness of reports is a major problem 

even during daylight hours. Considerable upper-wind data 

and wind forecast guidance is available but must be used 

with caution and considerable cross-checking. Aircraft wind 

reports provide an essential supplement and verification. 

Based on the observed and predicted extent of the ash 

plume, the traffic management unit (TMU) examines the 

impact of the event on air traffic routes, several of which are 

close to Mount St. Helens. Advisories are sent to air traffic 

facilities and to system users that identify affected areas and 

suggest alternate routes. 

INTRODUCTION 

When Mount St. Helens volcano erupts, the ash cloud 

spewed into the atmosphere can quickly create an emergency 

situation to the pilot who unknowingly enters it. Engines, 

both jet and piston, are easily damaged by volcanic ash when 

it is present in sufficient quantities. It is an urgent matter that 

pilots be made aware of the location of a volcanic ash plume. 

Upon notification of an eruption, the Federal Aviation 

Administration (FAA) ARTCC in Seattle takes immediate 

action for the protection of air tr~ffic. Under the direction of 

the ARTCC area manager-in-charge (AMIC), the TMU and 

the Center Weather Service Unit (CWSU), affiliated with the 

National Weather Service, become involved in a joint 

response effort. The problem is to determine the vertical and 

horizontal extent and short-term horizontal movement of the 

ash plume and to provide that information to pilots and the 

air traffic system (A TS) as quickly as possible. 

The focus of this paper is on the minor eruptions of 

Mount St. Helens during the period 1989 through early 1991. 

These involved bursts of steam and unknown concentrations 

of ash that reached altitudes of 12,000 to 25,000 ft. The 

limitations confronting the response effort and the lack of 

knowledge regarding the actual hazard to aircraft are more 

acute for these smaller events than for major eruptions. The 

degree of uncertainty underscores the importance of treating 

them as legitimate hazards to air traffic even if the risks 

might be negligible. 

EVENT NOTIFICATION 

Seattle ARTCC normally receives very early notice of 

an eruption of Mount St. Helens. Initial notification often 

comes from a pilot who is in continuous radio contact with 

an air traffic controller. Pilots flying under visual flight rules 

(VFR), and thus not required to be in radio contact with an 

air traffic controller, also may contact Seattle ARTCC to 

give notice of an observed eruption. When either the U.S. 

Geological Survey Cascade Volcano Observatory or U.S. 

Forest Service personnel in the area become aware of an 

eruption, Seattle ARTCC is designated as the first facility to 

notify (Myers and Theisen, this volume). 

Seattle ARTCC is therefore in a position to provide 

early event notification to other agencies and to react 

promptly in issuing advisories to the air traffic control 

(ATC) system and system users. Facilities that Seattle 

ARTCC contacts for event notification, including those 

involved in advisory and forecast support, in most cases have 

had no prior notice of an event before being contacted by 

Seattle ARTCC. Notification performed by Seattle ARTCC 

is shown in table 1. 

175 
176 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Mount St. Helens eruption notification and forecast 

coordination involving Seattle air traffic control. 

Seattle center receives notification of an eruption of 

Mount St. Helens from: 

• Pilot reports 

• Cascade Volcano Observatory, U.S. Geological Survey 

• U.S. Forest Service, Mount St. Helens office 

Notification given by Seattle center includes the following: 

• Washington and Oregon Departments of Emergency 

Management 

• Cascade Volcano Observatory, U.S. Geological Survey 

• U.S. Forest Service, Mount St. Helens and Mount Hood 

offices 

• FAA regional office, northwest mountain region 

• Air traffic control facilities (regional) 

• National Air Traffic Control System Command Center 

Notification given by the center weather service meteorologist 

for forecast and warning coordination: 

• Forecast office, National Weather Service, Seattle, Wash. 

• Synoptic analysis branch, National Meteorological Center, 

Camp Springs, Md. 

• National aviation weather advisory unit, Kansas City, Mo. 

LOCATING THE ASH PLUME 

Before air traffic can be properly directed to stay clear 

of volcanic ash, the ash plume must be located and its height 

estimated as accurately as possible. Satellite and radar imagery available in the Central Weather Service Unit can be 

used for this purpose, and pilot reports can be solicited 

through center controllers. 

Satellite imagery now available in the CWSU has been 

recently (October, 1991) upgraded. Data from the geostationary orbiting environmental satellite (GOES) is available 

via satellite link to a new meteorological workstation, known 

as the meteorologist weather processor (Hamley and 

Schultz, 1992). 

Visible and infrared images are received each half-hour 

and can be viewed on a high-resolution monitor with 

animation capability, an unlimited degree of zoom, and the 

capability of infrared color enhancement. Previously, one 

hard-copy satellite image was received each half-hour via 

Harris laserfax. Radar data is derived from five air traffic 

control radars (FAA and military), located in Washington 

and Oregon, and two National Weather Service (NWS) 

radars. 

Table 2 provides a subjective assessment of radar and 

satellite performance that could be expected during a major 

eruption. Images are viewed on the meteorologist weather 

processor, either individually or within a mosaic, and may 

also be animated. Mosaic-display capability and animation, 

previously unavailable, are both incorporated into the new 

system. Imagery now available to the CWSU is superior in 

many respects to that which successfully detected the ash 

Table 2. Imagery available in the Center Weather Service Unit 

through meteorologist weather processor. 

[MWP, meteorologist weather processor; GOES, geostationary orbiting environmental 

satellite; ATC, air traffic control; NWS, National Weather Service] 

Satellite imagery 

GOES infrared and visible images available via satellite link 

and viewed on high-resolution monitor. Infrared colorenhancement and animation capability. 

Radar imagery 

Viewed on MWP monitors. Individual radar images or mosaic 

display of all; includes animation capability. Data is available 

from the following ATC and NWS radars: 

Site Radar type 

Portland, Oreg. 

Salem, Oreg. 

Spokane, Wash. 

Seattle, Wash. 

Condon, Oreg. 

Klamath Falls, Oreg. 

Missoula, Mont. 

SR74C (NWS) 

RSRI (ATC) 

PS67 (ATC) 

RSRl (ATC) 

RSR3 (ATC) 

PS67 (ATC) 

WSR57(NWS) 

Estimated ash-plume detection capabilities and limitations 

of available imagery during a major eruption 

Imagery Characteristics 

type Day Night 

Radar 

Satellite 

images 

(visible 

light) 

Satellite 

images 

(infrared) 

Positive detection. Poor Same as day time. 

definition of horizontal 

ash distribution; no vertical discrimination. Detection limited by ground 

clutter and obscured by 

precipitation. 

Detection limited by con- No data. 

trast with cloud cover; 

otherwise good during 

bright daylight. 

Excellent detection of ash Same as day time. 

plume extending above surrounding cloud cover. Estimation of plume height is 

accurate within approx. 

5,000 ft. 

plume following the May 18, 1980, eruption of Mount St. 

Helens. We therefore assume that it would yield considerable 

information in the event of a major eruption and large ash 

plume. In contrast, radar and satellite imagery provided us 

with little or no data during the minor eruptions of the 1989 

to 1991 period, due to the small size of these events. Small 

plume size, low plume height, low ash content, and surrounding cloud cover all contributed to our inability to identify an 

ash plume in radar or satellite images. We doubt that new 

image-viewing and processing methods available with the 

meteorologist weather processor will make up for these deficiencies because the problem is insufficient image data. 
SEA TILE TRAFFIC CONTROL CENTER RESPONSE TO ERUPTIONS OF MOUNT ST. HELENS 177 

Lack of available ash-plume data does not lessen the 

need to respond to a possible airborne hazard. Other 

resources must be used to the fullest degree, including pilot 

reports and observations from ground observers. These 

sources have provided most of the data on volcanic emissions that has been used in making decisions at Seattle 

ARTCC. 

The meteorologist and the TMU supervisor coordinate 

on the need for information that can be supplied by pilots. 

The TMU solicits these reports through center controllers 

and disseminates them to both the air traffic system and the 

aviation community. Other visual reports may come from 

the Cascade Volcano Observatory, the U.S. Forest Service, 

Table 3. Information from visual observations about ash plumes 

from Mount St. Helens. 

[TMU, traffic management unit] 

Information sources 

Pilot reports 

Pilot reports go directly to air traffic controllers and are passed 

on to the TMU. TMU and center weather service solicit 

additional reports through controllers. TMU transmits reports 

for distribution within the air traffic system and externally. 

Surface observations 

Calls are made to, or received from, Cascade Volcano 

Observatory (U.S.Geological Survey) and Mount St. Helens 

office (U.S. Forest Service). Routine, non-automated, hourly 

surface observations are available from: Portland, Oreg.; 

Toledo, Wash.; Hillsboro, Oreg.; Yakima, Wash.; Troutdale, 

Oreg.; The Dalles, Oreg. 

Information supplied 

Pilot reports 

Area description of plume and plume movement. Physical 

description of plume, including apparent ash content. Increase 

or decrease in plume activity and whether plume is continuing 

to rise. Accurate plume-top report if aircraft is near altitude of 

plume top. 

Surface observations 

Same overall as for pilot reports except more limited, as 

indicated below. 

Limitations 

Pilot reports 

Darkness, surrounding cloud cover, and flight visibility. 

Difficulty in describing plume area and assessing ash content. 

Also limited by number of aircraft in volcano area. No aircraft 

above about 40,000 ft; therefore, no accurate estimate of plume 

top is possible at altitudes significantly above 40,000 ft. 

Surface observations 

Darkness, surrounding cloud cover and visibility. Perspective 

and distance from volcano limit accurate description of real 

extent, movement, and physical appearance. Plume-top 

estimates not reliable. 

or from manned weather-observing stations in the general 

area, depending upon the degree of day light and the amount 

of cloud cover. 

Sightings made by ground and airborne observers can 

establish the direction of movement of the plume and provide a very general description of its size, ash content, and 

ash fallout. Pilot reports are the best source to determine the 

plume altitude within narrow limits. However, none of these 

data, even collectively, can give us a comprehensive picture 

of plume area. Table 3 summarizes information provided by 

visual observations. 

Credibility of ash reports must be questioned because 

they are quite often misleading. Pilots sometimes seem predisposed to observe ash around Mount St. Helens or in any 

area where it has been previously reported. Still, pilot reports 

have been our most valued, and sometimes exclusive, source 

of data pertaining to an ash plume. 

FORECASTING SHORT-TERM 

PLUME MOVEMENT 

Once the general area that may be subject to airborne 

ash has been determined, then plume drift must be considered. Because we attempt to anticipate movement in the very 

short term, the current drift tendency (as dictated by upper 

winds and seen by observers) will weigh heavily in advisory 

products. Ash movement through a range of altitudes must 

be considered because wind direction and plume travel may 

vary greatly through the vertical range of the plume. 

Upper-air observations, including wind measurements 

from the surface to more than 50,000 ft, are taken twice daily 

(at 00 UTC and 12 UTC) by stations in the upper-air-observation network. The site at Salem, Oreg., located 85 miles 

southwest of Mount St. Helens, is the site closest to the volcano and it is often the most representative of wind flow over 

the mountain. However, this may not be the case if there is 

significant shear or curvature in the wind field between 

Salem and Mount St. Helens or in the event that wind velocity has changed since the previous observation was taken. 

We therefore must consider wind data observed from other 

sites in the region and interpolate as necessary. 

Automated upper-wind forecasts (Aviation Weather 

Services, 1985, p. 4-18) from the National Meteorological 

Center in Washington, D.C., are also available to the meteorologist. These apply to numerous points in Washington and 

Oregon and to nine different altitude levels from 3,000 

through 39,000 ft. In assessing upper winds, currency of 

observed data and verifying time of forecast winds must both 

be taken into account. A comparison of satellite photos and 

upper-level forecast charts can sometimes reveal a problem 

with the model run and its wind forecasts. 

Pilot reports are another important source of upper-wind 

information. In the case of a minor eruption with satellite 

imagery unable to define an ash plume, pilot-reported upper 

winds are perhaps the deciding input in the determination of 
178 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

126° 125° 124° 123° 122° 121° 120° 119° 118° 11]0 116° 115° 114° 

49° 

48° 

47° 

46° 

45° 

EUG 

44° 0 

43° 

42° 

I 

I 

I 

10 LWS 

\ 

_,---~--~ 

PDT 1 

OREGON 

I I IDAHO 

l" 

( 0801 

I 

I 

-----.&... I ____ _ 

Figure 1. Example of plume-trajectory forecast for Mount St. 

Helens (MSH). Shaded triangular region shows area projected to be 

impacted by a hypothetical ash cloud that would be expected to 

move to the east of a line from Mount St. Helens to Wenatchee, 

Wash., and east from a line from the volcano to the area of Redmond, Oreg. (RDM). SEA, Seattle, Wash.; PDX, Portland, Oreg.; 

LKV, Lakeview, Oreg.; PDT, Pendleton, Oreg.; YKM, Yakima, 

Wash.; BOI, Boise, Idaho; EUG, Eugene, Oreg.; LWS, Lewiston, 

Idaho. 

plume movement. These can be solicited by the 1MU from 

any aircraft, but a variety of aircraft with areal navigation 

systems are equipped with a digital display of wind velocity 

that can be communicated to the ARTCC upon request. 

A plume-trajectory forecast (fig. 1), coordinated 

between the CWSU and the National Weather Service forecast office in Seattle, Wash., furnishes short-term input to air 

traffic advisories following an eruption of Mount St. Helens. 

This forecast depicts a triangular area intended to indicate 

the maximum amount of airspace into which the plume is 

spreading. Wind velocity and direction of plume movement 

are indicated for a number of levels extending from 6,000 ft 

to the top of the plume, if known, but not exceeding a maximum altitude of between 50,000 and 55,000 ft. 

ASSESSING POTENTIAL AIR 

TRAFFIC IMPACT 

Although the occurrence of a volcanic event can potentially impact air traffic operations at all airports in the Pacific 

Northwest, the greatest impact is likely to be experienced by 

flights traveling to and from Seattle-Tacoma (SEA) and 

Portland (PDX) International Airports. Prevailing winds 

across the northwestern United States vary from southwesterly to northwesterly most of the time. Thus, all arrival and 

WASHINGTON 

OREGON 

N e8KE 

l To LKV To 801 

50 1 DO NAUTICAL MILES 

Figure 2. Proximity of Mount St. Helens (MSH) to major air 

traffic routes. SEA, Seattle, Wash.; PDX, Portland, Oreg.; BKE, 

Baker, Oreg.; LKV, Lakeview, Oreg.; PDT, Pendleton, Oreg.; 

YKM, Yakima, Wash.; BOI, Boise, Idaho. 

departure routes southeast of SEA and east of PDX are prime 

candidates to be affected by a volcanic eruption. These 

routes are shown in figure 2 and include: 

1. The departure route that proceeds southeasterly from 

SEA. This route splits 50 nautical miles south-southeast of SEA, with one stream proceeding east-southeast to Baker, Oreg. (BKE), passing 27 nautical miles 

east of Mount St. Helens at its closest point. The second stream continues south-southeasterly to Lakeview, Oreg. (LKV), and passes 15 nautical miles east 

of the volcano. More than 140 flights are scheduled 

daily along these routes. 

2. The arrival route that approaches SEA from the southeast, via Pendleton, Oreg. (PDT), and Yakima, Wash. 

(YKM). More than 80 scheduled flights daily use this 

route, which passes within 60 miles of the volcano at 

its closest point. 

3. The arrival routes that approach PDX from the east, 

via Pendleton, Oreg. (PDT), or Boise, Idaho (BOI). 

This route passes just north of Mount Hood in Oregon, less than 45 miles from Mount St. Helens. Seventy to 75 flights are scheduled daily along this route. 

4. The departure route from PDX to the east, which proceeds directly to PDT en route to eastern destinations. 

This route is flown daily by 25 to 30 scheduled flights 

and passes 27 miles south of the volcano. 

5. The heavily traveled route for SEA departures to 

PDX. More than 75 scheduled flights daily use this 
SEATTLE TRAFFIC CONTROL CENTER RESPONSE TO ERUPTIONS OF MOUNT ST. HELENS 179 

route, with an additional 30-50 unscheduled flights 

commonly using the route on a daily basis. This route 

passes within 6 nautical miles of the volcano and is 

named for the mountain (HELNS arrival). 

These five routes, all of which pass within 60 nautical 

miles of Mount St. Helens, are utilized by more than 400 

flights daily proceeding to and from SEA and PDX. Naturally, the impact of a volcanic event upon air traffic will vary 

according to the magnitude of the event itself, but even a 

fairly minor eruption, such as the one on November 5, 1990, 

affects these corridors, causing a major disruption of the air 

traffic system during the time that flight operations are 

restricted in the area. An event approaching the scale of the 

cataclysmic eruption of May 18, 1980, which produced an 

enormous amount of airborne volcanic ash, would impact 

not only the routes described above but would have a farreaching effect on air traffic over the entire region. 

NOTIFICATION OF SYSTEM USERS 

Once the scope of the volcanic ash hazard has been 

determined, Seattle AR TCC personnel execute a series of 

procedures designed to warn air traffic system users of the 

potential hazard and to safely and efficiently route traffic 

around the hazard area. Warnings and advisories are transmitted by the traffic management unit, the area manager-incharge, and the Center Weather Service Unit (CWSU). 

The CWSU meteorologist is required to issue a center 

weather advisory (CWA) designating the affected area and 

describing plume height and movement. The CW A is a 

meteorological advisory written in a coded format and is 

valid up to a maximum of 2 hours. The area affected by the 

plume is described in the heading of the advisory, whereas 

plume movement and altitude is mentioned in the text. A 

CW A is broadcast by all operational sectors at Seattle 

ARTCC. The FAA manual supplement, "Aviation Weather 

Services" (1985), describes the format and use of CWA's. 

The following is an example of a CW A: 

ZSEl CWA 01 011400-011600. From 40SE OLM to YKM to RDM to 

20N PDX to 40SE OLM. Ash plume from Mount St. Helens moving 

southeast above FL200 and moving east-northeast below FL200. 

Unknown amounts of ash to FL300.1 

In addition to transmitting a CW A, the meteorologist 

will also coordinate with the National Aviation Weather 

Advisory Unit in Kansas City, Mo., for the possible issuance 

of a longer term national advisory product known as a significant meteorological advisory, or SIGMET, which can be 

valid up to 4 hours (Aviation Weather Services, 1985). 

The AMIC is primarily responsible for ensuring that all 

appropriate air traffic control facilities and system users are 

made aware of the event. Alert messages are transmitted, 

1 In air traffic control, altitudes above 18,000 ft are described in hundreds of feet. FL200 therefore represents 20,000 ft. 

either verbally or via teletype, to all ARTCC control-room 

personnel, the FAA northwest mountain region duty officer, 

the Seattle ARTCC air traffic manager and assistant manager, and all other air traffic control facilities contained 

within Seattle ARTCC airspace. The AMIC is also responsible for relaying a notice to airmen (NOT AM) to the appropriate FAA flight service station for immediate 

dissemination to pilots. For example: 

Airborne hazard: Drifting volcanic ash from Mount St. Helens to a 

point 50 miles south of Mount St. Helens from the surface to FL300, 

drifting southwestward. Avoidance advised. 

Such a NOTAM is transmitted by FAA flight service 

stations via the transcribed weather broadcast network and 

by A TC towers via the automatic terminal information system. The TMU supplements these broadcasts by advising the 

Air Traffic Control System Command Center (ATCSCC) in 

Washington, D.C., which, in turn, transmits advisories to all 

20 ARTCC's in the contiguous United States and to all commercial air-carrier companies. 

TMU is also responsible for determining alternate 

routes around the hazard area and for coordinating these 

routes with A TCSCC for transmission to air carriers and 

other air traffic control facilities. These advisories are 

updated as appropriate, depending on the scope of the event. 

When conditions are severe enough to warrant restricting air traffic from a hazardous area, Seattle AR TCC has the 

authority to transmit a NOTAM that temporarily suspends 

flight operations in the affected area. This NOT AM is transmitted nationally and is regulatory in nature. An example of 

such a NOT AM is as follows: 

Flight restrictions at Mount St. Helens effective immediately until further 

notice. Pursuant to FAR 91.137b, temporary flight restrictions are in effect 

for a 50-mile radius of Mount St. Helens and on a line from Mount St. 

Helens to Pendleton, Oreg., 50 miles either side, at or below 30,000 ft to 

provide a safe environment for aircraft operations. Seattle ARTCC is the 

agency in charge. 

IMPROVEMENTS IN THE RESPONSE 

PROCESS 

MODIFYING RESPONSE STRATEGIES 

We believe that the future ability of Seattle A TC center 

to respond to a volcanic event can be improved by changes 

in response methods. One change would involve our early 

notification of the National Weather Service Synoptic Analysis Branch (SAB). Their use of the MciDAS III system 

(Soumi and others, 1983) for viewing satellite imagery has 

produced some plume data even during minor eruptions of 

Mount St. Helens. Immediate contact of the SAB may produce valuable, near real-time input to short-term air traffic 

advisories. 

We also advocate increased awareness by ground and 

airborne observers of the need for accuracy and completeness of visual observations. This is especially true for pilots 

because we rely so heavily on their reports. Information of 
180 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

value to the response process includes an estimate of plume 

dimensions and, in the case of pilot reports, the altitude of the 

plume, whether it is continuing to rise, and direction of 

plume drift. Comments on the physical appearance of the 

plume, including its density and apparent ash content, would 

also be of value. The International Civil Aviation Organization (ICAO) format for reporting volcanic ash (Fox, this 

volume) would be sufficient to meet the informational needs 

that we have identified, and we recommend that it be used. 

Recent eruptions of Mt. Spurr have demonstrated that 

the problems associated with forecasting ash-plume movement and routing air traffic clear of the hazard are 

continuing. During the most recent event (August 1992), the 

lack of accurate information regarding plume scope and 

movement resulted in aircraft being routed into areas in 

which airborne volcanic ash was present. These events also 

pointed out the need for improved communications and 

coordination regarding volcanic events between Canadian 

and U.S. agencies involved in air traffic control and aviation 

weather services. 

NEW TECHNOLOGY 

Other improvements in the response process are 

inevitably linked to coming technology. The deployment of 

the NEXRAD (Next Generation Radar WSR-88D) national 

Doppler radar network will include two sites within radar 

range of Mount St. Helens (Seattle and Portland) and two 

other sites at somewhat longer range (Spokane, Wash., and 

Pendleton, Oreg.) but located in the direction that prevailing 

winds would tend to carry an ash plume (Klazura and Imy, 

1992). Commissioning of these radars is scheduled during 

the period 1994 to 1996. 

The velocity azimuth display (V AD) available with 

NEXRAD radars will provide the radar operator with data 

that can be used to interpret winds aloft, which is currently 

not possible with conventional radars. Winds can be interpreted using radar-return data from widespread precipitation 

as well as from clear air. It should be noted, however, that 

radar return in clear-air situations is very limited both vertically and horizontally. 

We are not aware of any data on NEXRAD performance in the detection of volcanic ash. It seems plausible 

that NEXRAD radars would be superior to conventional 

radars in detecting returns from volcanic ash, given their 

much greater power and sensitivity. If so, they would yield 

considerable data on plume distribution and ash concentration in addition to data on winds that are carrying the plume. 

Automated methods of tracking and characterizing an 

ash plume would merit consideration for the short-term 

period following an eruption (about 2 hours), during which 

Seattle center must act to protect the safety of air traffic. An 

example is the "atmospheric diffusion particle-in-cell" 

technique described by Ellis and Sullivan (1991), which was 

used experimentally following a minor volcanic event 

("puff') of Mount St. Helens. 

SUMMARY 

The efforts of the Seattle A TC center to respond to the 

minor eruptions of Mount St. Helens since 1989 have consistently encountered a lack of information regarding the extent 

and concentration of volcanic ash, or even whether a legitimate hazard exists. The response has been driven by the 

absolute necessity to err on the side of safety, due to the 

proximity of major air routes to Mount St. Helens and the 

known destructive effects of volcanic ash on aircraft 

engines. 

For eruptions of small magnitude, existing satellite and 

radar imagery often provide little or no usable data pertinent 

to an ash plume. Ash-plume observations from pilots and 

ground observers are often limited, questionable, or unavailable due to darkness. Thus, observed and forecast upper 

winds often provide most of the guidance in assessing shortterm plume extent and movement. 

Deployment of Doppler radars is expected to bring 

improved ash detection as well as the capability of assessing 

upper winds through interpretation of radar return, but to a 

degree that is yet unknown. 

In attempting to improve our response effort to a volcanic eruption in the region, we have proposed the following: 

1. Immediate consultation with the Synoptic Analysis 

Branch, Washington, D.C., for plume-trajectory guidance. 

2. Improvement in our coordination with Canadian air 

traffic and weather officials. 

3. Use of the ICAO VAR (volcanic activity report) volcanic pilot report format by pilots in reporting volcanic 

activity (Fox, this volume). 

4. Future use of short-term computer models for characterizing and forecasting ash plumes. 

REFERENCES CITED 

Aviation Weather Services, 1985, A supplement to Aviation 

Weather AC-00-6A: Washington, D.C., U.S. Department of 

Transportation and U.S. Department of Commerce, 148 p. 

Brown, R.A., and Wood, V.T., 1987, A guide for interpreting 

Doppler velocity patterns: Norman, Okla., NOAA National 

Severe Storms Laboratory, p. 7-21. 

Ellis, J.S., and Sullivan, T.J., 1991, AD PIC calculated volcanic ash 

cloud transport and fallout from the 20 December 1990 Mount 

Saint Helens puff, in Casadevall, T.J., ed., First International 

Symposium on Volcanic Ash and Aviation Safety, U.S. 

Geological Survey Circular 1065, p. 18. 
SEA TILE TRAFFIC CONTROL CENTER RESPONSE TO ERUPTIONS OF MOUNT ST. HELENS 181 

Hamley, R.F., and Schultz, R.F., 1992, A brief introduction to the 

meteorologist weather processor: Salt Lake City, National 

Weather Service, Western Region Technical Attachment No. 

92-28,9 p. 

Klazura, G.E., and lmy, D.A., 1992, Description of initial set of 

analysis products available on the WSR-880 radar system: 

Norman, Okla., National Weather Service, Operational 

Support Facility, 10 p. 

Soumi, V.E., Fox, R., Limaye, S.S., Smith, W.L., 1983, MciDAS 

III-A modem interactive data access and analysis system: 

Journal of Climatology and Applied Meteorology, v. 22, 

p. 765-778. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

AN AUTOMATED VOLCANIC ASH 

WARNING SYSTEM 

By David M. Harris 

ABSTRACT 

The requirements for an automated volcanic ash warning system are outlined, along with a possible system architecture and description of operation. The system would 

detect volcanic clouds by coexistence of anomalous electric 

fields and thermal infrared sources in the lower atmosphere 

above volcanoes. These can be measured by using groundbased electric-field mills and infrared radiometers, respectively. Antecedent, strong volcanic tremor would be used as 

additional evidence permitting instrumental observations to 

be interpreted as an eruption producing volcanic ash. Equations for estimating the cumulative mass erupted and the 

mass eruption rate from volcanic-tremor data, in terms of 

reduced displacements, are given in this paper. The 

equations are based on the linear relation between eruptive 

masses of air-fall ash and pyroclastic deposits and the 

integral of volcanic-tremor amplitude for six eruptions of 

Mount St. Helens. Mass eruption rates and eruptive masses 

determined from volcanic-tremor data would be used with a 

plume-rise model to estimate the input source parameters to 

an ash-transport model and forecast model. The integrated 

system would perform volcano monitoring, data analysis, 

ash-cloud forecasting, hazards evaluation, notification, and 

data communications. The volcano-monitoring strategy is 

based on coverage of volcanoes that pose the greatest risk to 

aviation and other interests. 

INTRODUCTION 

Volcanic ash clouds pose a significant hazard to 

in-flight aircraft (Rose, 1987). An effective volcanic ash 

warning system is needed (Reddan, 1985; Foreman, this 

volume). This paper describes a system that might meet this 

need. The ideas in this paper were originally expressed in the 

abstract of Harris and Mitchell (1986), who proposed a 

system concept based on using volcanic-tremor amplitudes 

to determine mass eruption rates and electric-field sensors to 

detect ash clouds. 

The purpose of this paper is to describe an automated 

system for detecting volcanic ash clouds, forecasting their 

hazards to aviation, and notifying users. This paper includes 

suggested functional and performance requirements for a 

volcanic ash warning system and outlines a possible system 

design. The focus of this paper is on system architecture and 

on methods for obtaining from volcanological observations 

the interpretive data required for ash-cloud detection and the 

quantitative data required for transport and forecast calculations. 

SYSTEM REQUIREMENTS 

The design and implementation of a volcanic ash warning system must be based on detailed consideration of user 

requirements, eruptive phenomena, and sound engineering 

practices. An ad hoc approach to warning-system design and 

implementation is not likely to yield the best technical 

approach or optimum system performance. Some suggested 

requirements for a volcanic ash warning system are listed in 

table 1 (performance requirements) and table 2 (functional 

requirements). 

SYSTEM ARCHITECTURE 

The volcanic ash warning system architecture is shown 

in figure 1. There are six subsystems (volcano monitoring, 

volcano data collection, communications, ash transport and 

forecasting, hazards evaluation, and notifications). Each 

subsystem includes a hardware layer and a software layer. 

Only the software layer is shown in figure 1. The system 

hardware (computer and communications interfaces) could 

be located at an existing volcano observatory or regional air 

route traffic control center (ARTCC). A single site could 

provide volcanic ash hazard warnings for volcanoes in the 

operations area for one or more ARTCC's. The system 

receives periodic status reports and data streams from datacollection subsystems at monitored volcanoes. 

The monitoring strategy involves installation and maintenance of volcano data collection modules at volcanoes 

selected by eruption probability and risk to. aviation. New 

sites would be added after onset of premonitory activity. 

183 
184 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Suggested performance requirements for volcanic ash 

warning system. 

[nm, nautical miles; kft, 1,000 feet] 

Performance criteria 

Detection-range limits (minimum) 

Mass-eruption rate 

Total mass erupted 

Response time 

Initial advisory 

Official warning 

Forecast 

Reliability 

Suggested requirement 

1 x 106 to 5 x 109 kg s-1 

108 to 1013 kg 

3 minutes after event 

6 minutes after event 

6 minutes after event 

System availability > 99 percent 

Hazard-detection probability > 95 percent 

Error rate for warnings (total) 

Inappropriate warnings 

False warnings 

No warning 

Error rate for notifications 

Forecast Accuracy 

Ash-cloud front 

Horizontal edge 

Altitude (top) 

Ash concentrations 

< 10 percent 

< 5 percent 

< 5 percent 

< 5 percent 

< 3 percent 

20 to 50 nm at 1 to 4 hr 

15 to 30 nm at 1 to 4 hr 

10 kft (about 3 km) 

±50% of reported value 

Rapid deployment would be facilitated by a modular system 

architecture and use of standard data-communications hardware. Although the system coverage would not be complete, 

available resources would be focused on volcanoes deemed 

likely to erupt and (or) that are deemed to represent a high 

risk to aviation. 

VOLCANO DATA COLLECTION 

SUBSYSTEM 

The purposes of the volcano data collection subsystem 

are to provide answers to the following questions in near real 

time: 

1. Is an explosive eruption occurring? 

2. Is an ash cloud present? 

3. If an eruption occurred, how long did it last and what 

was the mass eruption rate as a function of time? 

This is the minimum volcanological data needed by a 

volcanic ash hazard warning system. The monitoring methods and frequency of observation must be adequate to ensure 

prompt detection of an explosive volcanic eruption larger 

than either of two specified thresholds defined by mass 

eruption rate and mass erupted. Table 1 includes suggested 

ranges for these system-design parameters, subject to 

evaluation of system costs and benefits. 

Table 2. Suggested functional requirements for volcanic ash 

warning system. 

[ATC, air traffic controller; haz., hazard] 

Volcano data-collection subsystem 

•Monitor volcanic tremor amplitude and frequency spectra 

•Monitor atmosphere for evidence of pyroclastic eruption 

•Monitor atmospheric electric-potential gradient 

Volcano monitoring subsystem 

•Process messages from volcano data-collection subsystem 

•Determine whether an eruption is occurring 

•Detect explosive volcanic activity 

•Determine whether an ash cloud is present 

•Determine mass eruption rate 

•Log time, eruption rate, status, and source location 

Ash transport and forecasting subsystem 

•Retrieve wind forecasts from database 

•Initialize plume algorithm 

•Initialize ash-transport and settling algorithm 

•Perform ash-transport and dispersion simulations 

•Generate volcanic-ash-cloud forecasts and ash-fall maps 

•Maintain atmospheric wind database 

•Generate and update plume forecast and aviation haz. maps 

•Track and report ash cloud locations 

Hazards evaluation subsystem 

•Evaluate the ash cloud forecasts 

•Determine the type, location, and magnitude of hazards 

•Identify jet routes and aviation facilities at risk 

•Select warning messages 

•Prepare aviation hazards forecasts for release 

•Generate prioritized notification list 

•Recommend air-space closures and restrictions 

Notifications subsystem 

•Notify users of hazards via messages and files 

•Issue warnings, route messages, and verify receipt 

•Maintain messages and distribution lists 

•Interface to ATC's and other communications systems 

Communications subsjstem 

•Communications resource management 

•Route messages 

•Acquire meteorological data from remote systems 

•Retrieve data from observatories in near real time 

•Perform notification tasks 

•Log communications activity 

Database management subsystem 

•Maintain system and operational data 

System status monitoring requirements 

•Perform system-level status monitoring and reporting 

•Perform subsystem status monitoring and reporting 

•Perform system calibration and testing 

The volcano data collection subsystem would include a 

digital seismograph, an electric-field mill, a thermal 

radiometer, a system controller, and a radio communications 

interface. The digital seismograph and data-collection 
AN AUTOMATED VOLCANIC ASH WARNING SYSTEM 185 

~"' 

l

Meteorologicalf/ :::\~ data ~ r., ·$' ~ ... ~ ~ 

~~ 0 

Wind forecasts, Notifications and maps 

soundings Acknowledgments 

Volcano status 

Air routes, waypoints, 

airports, and cities 

I Messages I 

Figure 1. System architecture and data-flow diagram for the volcanic ash warning system (YAWS). Data flows and directions are indicated by lines. Shaded boxes represent VA WS subsystems and external systems (National Meteorological Center and air route traffic control 

centers); unshaded boxes represent data files. The volcano-data-collection subsystem is linked to the communications subsystem by satellite 

communications or some other data communications system (not shown). 

system must provide the capability to record and perform 

spectral analysis (Nishi, 1987) of discrete seismic events and 

volcanic tremors in near real time (Hurst, 1985; Endo and 

Murray, 1991). The amplitude of volcanic tremor may be 

used to characterize eruption styles (McNutt, this volume; 

Endo and Murray, 1991) and to estimate mass eruption rates 

(this paper). The functional roles of the above volcanomonitoring techniques in the context of an automated 

volcanic ash warning system are described below. 

DETECTION OF ASH CLOUDS AND 

EXPLOSIVE ERUPTIONS 

The capability to detect volcanic ash clouds by instrumental methods is not yet available at most volcano 

observatories (Brantley, 1990; WOVO, 1991). Weather 

radar systems can provide ash-cloud detection and tracking 

capabilities in areas with radar coverage, assuming the target 

can be correctly identified (Harris and others, 1981; Harris 

and Rose, 1983). Weather radar may not be practical or 

affordable in remote areas. Lightning-positioning and tracking systems (Lyons and others, 1985) have been used to 

detect cloud-to-ground lightning in ash clouds (Boblitt and 

Murray, 1990; Brantley, 1990). Microbarograph arrays 

(Onodera and Kamo, this volume) measure acoustic waves 

from volcanic explosions and locate their source from 

atmospheric propagation times. The microbarograph array 

can detect onset of explosive activity under certain 

conditions, but its capability to detect continued eruption of 

ash clouds may require more evaluation. 

Harris and Mitchell (1986) suggested using electricpotential-gradient sensors to detect ash clouds. Electric 

fields in the vicinity of ash clouds change greatly during and 

after ash eruptions, both near the source and in residual ash 

clouds (Hatakeyama, 1943, 1958; Hatakeyama and 

Uchikawa, 1952; Kikuchi and Endoh, 1982; Hobbs and 

Lyons, 1983; Gilbert and others, 1991; Gilbert and Lane, this 

volume). Hatakeyama' s work shows that ash clouds 

produced by explosive eruptions can be detected by using 

electric-field mills to measure atmospheric electric fields 

and disturbances caused by electrified ash clouds. The 

system design described here is based on electric-field 

measurements, following the pioneering work of 

Hatakeyama and coworkers, but the particular detection 

technology is not important. The important matter is that the 

technology employed must represent the best combination of 

reliability, detection threshold, detection delay time, false 
186 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

detection rate, and practicality, which must be determined by 

parallel-field evaluations of these methods. 

The feasibility of using ground-based electric-field measurements to detect ash clouds has been demonstrated by 

Hatakeyama and coworkers (Hatakeyama, 1943, 1958; 

Hatakeyama and Kubo, 1943a, 1943b; Hatakeyama and 

Ishikawa, 1946). Ash clouds from Asama Volcano in Japan 

were detected about 50 km downwind from the volcano. Electric-field measurements obtained at distances of 1 to 9 km 

from their source indicate that the vertical potential gradients 

from ash clouds are initially positive (downward-directed 

fields), but the sign of the field typically changes with time 

or distance downwind from the vent (Harris, unpub. data), 

based on data from small eruptions of Aso (Hatakeyama and 

Uchikawa, 1952) and Asama (Hatakeyama, 1958). Field 

measurements of electric charge on falling ash (Hatakeyama, 

1958; Kikuchi and Endoh, 1982; Gilbert and others, 1991) 

show that ash particles are electrically charged. Finally, electric fields can persist in mature ash clouds for at least several 

hours, as shown by Hatakeyama (1949), owing to the existence of residual charge on far-flung fine ash. 

Volcanic eruption columns rise to great heights in the 

atmosphere only if the eruption column is hot and entrains 

sufficient air to develop a buoyancy force that counters the 

gravitational force (Morton and others, 1956; Wilson, 1976; 

Sparks and Wilson, 1982). Although volcanic plumes are 

optically thick, they provide a thermal source that should be 

detectable by a ground-based infrared radiometer or imaging 

infrared sensor such as a digital infrared camera. This provides the capability to detect an anomalous, extended infrared source generally associated only with high-temperature 

explosive eruptions. Thermal radiometric monitoring of the 

airspace immediately above volcanic vents should provide 

positive identification of thermal plumes and information 

not available from other monitoring instruments. 

The volcano-monitoring system would include quantitative criteria for a logical determination of whether an ash 

cloud is present or absent. The criteria would be based on 

thermal infrared observations, atmospheric electric-field 

measurements, and the amplitude of antecedent volcanic 

tremor. The system would consider an ash cloud to be 

probable whenever there is evidence of thermal plumes and 

electrified ash clouds, based on data from thermal 

radiometers and electric-field mills. These sensors should 

provide ancillary data with the least ambiguity for 

identifying conditions consistent with pyroclastic eruptions 

whenever strong volcanic tremor is present. When such 

conditions are met, the mass eruption rate would be 

determined instrumentally from volcanic-tremor amplitude. 

DETERMINATION OF MASS ERUPTION RATE 

An instrumental method for determining the mass eruption rate in near real time is an essential component of a 

volcanic ash warning system. Such information is needed to 

initialize volcanic-ash-transport and distribution models. I 

will show that the mass eruption rate can be determined in 

near real time from volcanic-tremor amplitudes. 

Consider the hypothesis that volcanic-tremor amplitude 

is linearly proportional to the 'mass eruption rate during 

explosive eruptions. If this hypothesis is true, then the 

integrals of the volcanic-tremor amplitude with time must 

also be proportional to the integral of the eruption rate with 

time. The integral form of this hypothesis is satisfied for six 

eruptions of Mount St. Helens. 

Table 3. Volcanic-tremor amplitude, reduced displacement integral, and mass of eruption products 

at Mount St. Helens, 1980. 

[Tg, teragrams (1012 g); rei., relative; disp., displacement] 

Volume of Mass of Mass of Total mass Integral of Reduced disp. 

Date pyroclastics 1 flows2 air-fall deposits3 of deposits4 volcanic tremor integral6 

(1980) (km3) (Tg) (Tg) (Tg) amplitude5 (rei.) (cm2/s) 

May 18 0.12 170 490 660 2,880 1.9x 106 

May25 0.001 1.5 42 44 590 3.8x105 

June 12 0.01 15 45 60 463 3.0x105 

July 22 0.006 8.7 4.0 13 115 7.5x104 

Aug. 7 0.004 5.8 1.0 6.8 124 8.lxl04 

Oct.16-18 0.001 1.5 0.7 2.2 25 1.6x104 

1 Rowley and others (1981 ). 2 Calculated from volume using an in situ pyroclastic flow density of 1,450 kg/m3 reported by 

Wilson and Head ( 1981 ). 

3 Sarna-Wojcicki and others (1981). 4 Sum of columns 2 and 3. 

5 Calculated graphically using tremor amplitude versus time plots shown in Scandone and 

Malone (1985, fig. 2). 6 This paper. 
AN AUTOMATED VOLCANIC ASH WARNING SYSTEM 187 

1015 

en 

~ May 18 I 

<( 

c:::: 

(!) 

z 

en' 

I- 1014 u 

::> 

0 

0 May25 c:::: 

a.. 

z 

0 

~ July 22 

a.. 1013 

::> 

c:::: 

UJ 

L1. 

0 

en 

en 

<( 

~ 

1012 

101 102 103 

INTEGRAL OF TREMOR AMPLITUDE, 

IN RELATIVE UNITS 

Figure 2. Masses of eruption products versus integral of volcanictremor amplitude for six eruptions of Mount St. Helens during 1980. 

The ordinate shows the total mass of pyroclastic flow plus air-fall 

ash deposit for each eruption, based on the works of Rowley and 

others (1981) and Sarna-Wojcicki and others (1981). The abscissa 

shows the integrated volcanic-tremor amplitude during each eruption, calculated from the graphs in figure 2 of Scandone and Malone 

(1985). The symbol sizes reflect estimated errors of ±30 percent for 

erupted mass and ±10 percent for the integral of tremor amplitude. 

The line with slope 1 shows a relation between the integral of tremor 

amplitude and total mass erupted. 

Table 3 shows data for six explosive eruptions of 

Mount St. Helens. The integral of the mass eruption rate is 

equal to total mass erupted during the time interval. It 

includes the sum of air-fall ash deposits (Sarna-Wojcicki and 

others, 1981) and pyroclastic flow deposits (Rowley and 

others, 1981). The time interval is the whole eruption. The 

volcanic-tremor-amplitude integrals were calculated using 

seismic data of Scandone and Malone (1985), based on data 

from station SMW, located 162 km from Mount St. Helens. 

Figure 2 shows that the mass of eruption products and the 

integrated tremor amplitude are directly proportional to one 

another. The errors are estimated to be on the order of 30 

percent or larger for eruptive masses and about 10 percent or 

less for the tremor amplitude. These eruptions varied in 

duration, peak tremor amplitudes, total amounts erupted, and 

in the relative masses of pyroclastic flow and air-fall ash 

deposits. Despite these differences, the integrals of volcanictremor amplitudes and eruption rates are approximately 

proportional to one another for these eruptions of Mount St. 

Helens. 

If the linear relationship between tremor amplitude and 

mass eruption rate applies to explosive eruptions elsewhere, 

determination of mass eruption rates in near real time would 

be possible. For generality, a relationship should be based on 

the reduced displacement of volcanic tremor, rather than 

tremor amplitude. Reduced displacements of volcanic 

tremor (McNutt, 1992) can be calculated only indirectly 

from data in Scandone and Malone (1985) because they did 

not report absolute tremor amplitudes or seismograph magnification. The reduced displacement integrals in table 3 

were calculated by scaling the peak tremor amplitudes for 

the Mount St. Helens eruption on the afternoon of the May 

18, 1980, to peak values of reduced displacement (260 cm2) 

reported by others (Fehler, 1983; McNutt, 1992). Using this 

approach, the cumulative mass erupted (M) at time t may be 

determined from the integral of the reduced displacement 

(R(t)) using the relation: 

t 

M (t) (kg) = J~~ dt = 

0 

t 

5 -2 J 1.5 x 10 kg (em s) R (t) dt (1) 

0 

Similarly, the mass eruption rate is given approximately 

by: 

dM -1 5 2 dt (kg s ) = 1.5 x 10 R (em ) (2) 

The coefficient has an uncertainty of about 50 percent. 

Table 3 lists the integral of the reduced displacements calculated by this method for the six eruptions. 

The method described here might be used to determine 

mass eruption rates and eruptive masses to an accuracy of a 

factor of 2 for Plinian-type eruptions from a central vent, as 

at Mount St. Helens in 1980. The equations and predictive 

method described here can be tested by analyzing volcanictremor data and measured pyroclastic flow and air-fall ash 

deposits for other well-documented explosive eruptions 

(Wilson and Head, 1981). Much of the effort in volcano 

monitoring for eruption-prediction purposes involves 

recording and analyzing seismic data, often in near real time. 

During eruptions, routine seismic data analysis could include 

automated measurement of volcanic-tremor amplitude and 

reduced displacements to provide estimation of eruption 

rates and eruptive masses. The practicality of making 

tremor-amplitude measurements, including spectral analysis, in near real time has been demonstrated by Hurst (1985), 

Nishi (1987), and Endo and Murray (1991). 
188 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

DESCRIPTION OF OPERATION 

The methods described above can be used to determine 

whether an ash cloud is present and the mass eruption rate in 

near real time. The mass eruption rate estimated from 

seismic data can be used along with plume-rise models 

(Wilson and others, 1978) and upper-atmosphere soundings 

to initialize ash-cloud properties (height, base, radius, 

particle concentration) required by an ash-transport and forecast model (Carey and Sigurdsson, 1982; Sparks and others, 

this volume). Some assumptions about particle-size distribution, settling speeds, and particle aggregation (Sorem, 1982) 

must be made. Essentially, the volcanological observations 

can be transformed in near real time to quantitative inputs 

required by ash-transport models, which may be used to 

generate short-range and long-range ash-cloud forecasts. 

The accuracy of such forecasts depends sensitively on ashcloud initialization, atmospheric turbulence, accuracy of 

wind forecasts, and modeling errors. It is essential to update 

the wind forecast used by the transport model via incorporation of ash-cloud-tracking observations. 

The volcanic ash warning system illustrated in figure 1 

is based on the capability to generate meaningful ash-cloud 

forecasts within 1 minute after receiving volcanological data. 

This would be a challenging software development task, but 

it appears feasible. The hazards-evaluation subsystem 

reviews the ash-transport-model forecasts against a database 

of air routes, aviation facilities, and other user interests to 

determine notification requirements. The notifications subsystem forwards the summary information (maps, text 

messages, synthesized voice mail) to end users via the 

communications subsystem. The system should be designed 

to operate as an automated expert system, with provision for 

mandatory review of all meteorological and volcanological 

data, warning messages, and forecasts. The highest reliability 

and minimum response time for a volcanic ash warning 

system can be achieved only by full system integration that 

includes automatic transfer of operational data from volcano 

observatories to forecast centers and end users. The system 

must, however, provide the capability for a consensus review 

of all warnings and forecasts by a qualified volcanologist, 

forecast meteorologist, and air-space-operations manager. 

SUMMARY AND CONCLUSIONS 

The system requirements for a possible volcanic ash 

warning system have been outlined. The recommended 

system architecture and data flows are based on use of modular subsystems, each of which performs a group of related 

functions. The subsystems include volcano data collection, 

volcano monitoring, ash transport and forecasting, hazards 

evaluation, notification, database management, and communications. The minimum information required from volcano 

observatories for source-based ash-transport and forecast 

models includes accurate determination of (1) whether an 

eruption is occurring, (2) whether ash cloud(s) were generated, and (3) the mass eruption rate as a function of time. 

Thermal infrared measurements and atmospheric electricfield measurements should be used to detect conditions 

resulting from thermal plumes and electrified ash clouds, 

respectively, that result from pyroclastic and explosive eruptions. Dual-sensor measurements should provide ancillary 

data with the least ambiguity for identifying conditions 

permissive of pyroclastic eruption when strong volcanic 

tremor is present. When such conditions are met, the mass 

eruption rate can be determined instrumentally from 

volcanic-tremor amplitude. The integral of the volcanictremor amplitude was proportional to the total mass of pyroclastic and air-fall ash deposits for six eruptions of Mount St. 

Helens in 1980. This finding is the basis for a seismic 

method to measure eruption rates in near real time. It is also 

the basis for estimating the rate and total amount of volcanic 

ash erupted into the atmosphere with an accuracy of a factor 

of 2. Representative values of cloud dimensions, heights, 

and particle concentrations can be estimated from plume-rise 

models by using the mass eruption rate. Additional data 

required include an assumed particle-size distribution, 

atmospheric sounding data, and wind data. The volcanic ash 

warning system described here should accept manual and 

automated inputs from existing volcano-monitoring systems 

and provide forecasts in various formats. The system should 

include a mandatory consensus review of all input data, forecasts, and warnings by a qualified volcanologist, forecast 

meteorologist, and air-space-operations manager. The system described would automate many of the operations and 

functions that are now performed manually. Such a system 

would enhance aviation safety. 

ACKNOWLEDGMENTS 

I am grateful to my wife, Lorna Harris, for research 

support and to Advanced Control Technology of Albany, 

Oreg. (Mr. Jon Walker, President), for travel support. I also 

thank Herb J. Mitchell for early discussions of the ideas in 

this paper. I also extend my thanks to W.l. Rose and T.J. 

Casadevall for their helpful comments. 

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measurement (RSAM): A volcano monitoring and prediction 

tool: Bulletin of Volcanology, v. 53, p. 533-545. 
AN AUTOMATED VOLCANIC ASH WARNING SYSTEM 189 

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Hatakeyama H., and Ishikawa, T., 1946, On the variation of the 

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31433,24 p. 

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VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

AVIATION SAFETY AND VOLCANIC ASH CLOUDS 

IN THE INDONESIA-AUSTRALIA REGION 

By R. Wally Johnson and Thomas J. Casadevall 

ABSTRACT 

Six encounters between aircraft and volcanic ash clouds 

from Indonesian volcanoes took place between 1982 and 

1985. These incidents reflect the high frequency of explosive 

eruptions during the early 1980's and an increase in the number of long-haul, international flights by jet-powered, widebody aircraft. The ingestion of volcanic ash by jet engines, in 

some cases, has caused multiple engine failures. In addition, 

aircraft exteriors and engines are damaged by the abrasive 

effects of ash. The encounters raised the level of concern 

about the impact of volcanic eruptions on aviation in the 

Indonesia-Australia region and prompted joint AustralianIndonesian efforts to eliminate future encounters. The threat 

to aviation in the region can be mitigated through enhanced 

monitoring of Indonesian volcanoes, better communication 

between observers of eruptive activity and in-flight air 

crews, and more effective use of near real time satellite 

imagery, particularly systems that discriminate volcanic ash 

clouds from weather clouds. Early-warning arrangements at 

present are not satisfactory. Development of on-board ash 

detectors would represent a significant advance in an earlywarning capability for aviation. 

INTRODUCTION 

Indonesian volcanoes were the focus of interest and 

concern to the international aviation community between 

1982 and 1985, when six passenger airliners, mainly widebody Boeing 747's, encountered volcanic ash clouds 

produced by three volcanoes in different parts of Indonesia. 

There had been earlier encounters between aircraft in flight 

and volcanic ash in other parts of the world: Sakurajima 

Volcano (Japan, 1975-86), Mt. Spurr (Alaska, United States, 

1953), Augustine Volcano (Alaska, 1976), and Mount St. 

Helens (Washington, United States, 1980). However, the 

June-July 1982 encounters of two 747 aircraft with ash from 

Galunggung Volcano in western Java, Indonesia, were 

especially notable because they caused multiple engine failures (Smith, 1983; Tootell, 1985). This necessitated the 

powerless glide of the stricken aircraft down to altitudes 

where the engines could be restarted in a more oxygen-rich 

atmosphere. The incidents generated widespread belief that 

two major aviation disasters had been narrowly avoided. 

Similar events involving multiple engine failures have taken 

place subsequently when aircraft encountered ash from 

Redoubt Volcano (Alaska, 1989) and Mt. Pinatubo (Philippines, 1991) volcanoes, and these incidents have reinforced 

the concern about the threat that volcanoes pose to aircraft. 

Five of the six aircraft affected in Indonesia in 1982-85 

were flying at night, en route to Australia. The pilots had 

received no early warning that they were about to fly into a 

volcanically hazardous area, and ash clouds were not detectable on flight-deck radar screens. Australian authorities 

showed particular concern about these ash encounters, especially after May 1985, when a Boeing 747 aircraft of Australia's national carrier, Qantas Airways, Ltd., flew into an ash 

cloud from Soputan Volcano. The purpose of this paper is to 

focus on the particular nature of the aircraft-ash-cloud 

problem in the Indonesia-Australia region, to summarize 

how authorities have responded to the need for improved 

early-warning capabilities for aviation, and to discuss methods for mitigating the threat in the future. 

AIR TRAFFIC IN INDONESIA 

The frequency of air traffic in the Indonesia-Australia 

region has increased dramatically since the World War II. 

There are currently between 780 and 800 international 

flights into and out of Australia each week (C.G. Barnes, 

Australian Civil Aviation Authority, oral commun., 1991). 

The majority of these international flights utilize the principal air corridors of the Indonesia-Australia region, which 

cross volcanically active areas in a complex pattern (fig. 1). 

International air traffic over Indonesia typically ends or 

originates in Australia or New Zealand, and many aircraft 

use the major international airports of Jakarta (SoekarnoHatta International Airport) and Denpasar, Bali. Most international aircraft must cross the volcanically active part of 

Indonesia at night because of Australian city curfews that 

were established in the 1960's to minimize the noise of jet 

191 
192 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

INDIAN OCEAN 

1000 km 

Volcanoes whose eruptions 

• have been observed end 

reported since 1600 AD 

Other volcanoes thought to 

o have been active during 

lest 10,000 years 

Figure 1. Air routes and volcanoes in Indonesia. Adapted from a chart in the Qantas route intelligence manual: "Volcanic Information, 

Indonesia" (ICAO, 1993). Volcano data are from Simkin and others (1981). Solid circles represent recently active volcanoes. Open circles 

represent other potentially active volcanoes. Solid squares represent major cities: KL, Kuala Lumpur; S, Singapore; J, Jakarta. 

traffic landing and taking off at night. Aircraft are required 

to arrive or depart most Australian cities between 0600 and 

2300 hours. Furthermore, modern jet airliners fly at high altitudes and cover long distances between refueling stops. This 

is in contrast to pre-jet days, before the early 1960's, when 

most air traffic operated during daylight hours, had frequent 

stops, and flew at lower altitudes. Pilots, therefore, had more 

opportunities to learn about and see volcanoes and to take 

appropriate evasive action should an eruption take place. 

The 1982-85 period was exceptional in the Indonesian 

region for the high number of passenger jet aircraft that 

encountered volcanic eruption clouds and for the multiple 

engine failures caused by these encounters. An important 

point to note is that multiple engine failures appear to affect 

only modern, finely tuned, jet engines and that there are no 

reported aircraft-ash-cloud encounters in the Indonesian 

region involving the failure of turboprop engines in pre-jet 

days. The 1982-85 period of incidents, therefore, appears to 

coincide with the more common usage of jet engines in 

modern times and with the large number of eruptions in the 

Indonesian region during 1982-85 that produced large ash 

clouds that reached aircraft cruising altitudes of 10-12 km. 

AIRCRAFT-ASH-CLOUD INCIDENTS 

There are six known incidents in the 1982-85 period: 

1. A domestic Indonesian Douglas DC-9 of Garuda Airlines, on the Jakarta-Yogjakarta route, flew through 

ash from Galunggung on 5 April 1982 (Qantas Airways, Ltd., unpub. data, 1982). The aircraft required 

maintenance, but no abnormal engine operations were 

reported. Indonesian authorities issued a notice to 

airmen (NOTAM) on April 6, instructing that airspace 

within 17 km of the volcano should be avoided. However, the restricted area did not embrace the established international air routes, so the NOTAM was 

limited to internal Indonesian distribution. 

2. A British Airways Boeing 747 (flight BA 009) 

cruising at 37,000 ft flew into Galunggung ash on 24 

June 1982 at about 2040 hours (Jakarta time) and 

about 330 km south of Jakarta while en route from 

Kuala Lumpur to Perth, Western Australia (Smith, 

1983; Tootell, 1985). St. Elmo's fire (static electricity) danced along the windscreen, and "smoke" and 

an acrid smell were noticed on the flight deck and in 

the main cabin. One engine failed within minutes, and 

the three others stalled shortly thereafter. The aircraft 

descended steeply for 13-14 minutes before the 

engines were restarted progressively at 13,000 ft. One 

engine subsequently surged and was shut down. A 

safe landing was made eventually at Jakarta's Halim 

International Airport. Aircraft damage, especially 

abrasion effects to leading edges and contamination 

of oil and air systems, was extensive, and three 

engines and front windshields were replaced in 

Jakarta before the airplane was ferried back to 

England. An international NOTAM was issued after 

the incident, and aircraft reroutings took place, but 

normal routing was resumed on 2 July after the 

NOTAM was canceled. 

3. The crew of a Singapore Airlines Boeing 747 (flight 

SQ 24A) on the same flight path as BA 009, but 40 

minutes later, on 24 June 1982, reported "smoke contamination" in the main cabin. The aircraft reached 

Perth without further incident where an inspection 
AVIATION SAFETY AND VOLCANIC ASH CLOUDS IN THE INDONESIA-AUSTRALIA REGION 193 

was carried out. Small fragments of rock were found 

in all engine tailpipes, but no damage was noted to 

leading edges, and oil filters were clear. 

4. A Singapore Airlines Boeing 747 (flight SQ 21A) en 

route between Singapore and Melbourne, ran into 

Galunggung ash at about 2130 hours (Jakarta time) on 

13 July 1982 and suffered similarly to the BA 009 

flight three weeks earlier. There were multiple engine 

failures and damage to airframe and powerplant 

systems (Singapore Airlines, 1982). A two-engine 

emergency landing was made at Jakarta, where all 

four engines had to be replaced. Aircraft rerouting 

recommenced. 

5. A British Airways Boeing 747 flying at 10.6 km 

altitude between Singapore and Perth on 23 July 1983 

had been rerouted north of Galunggung, but it 

encountered an eruption cloud from Colo Volcano 

(Una Una Island, Sulawesi) at 1955 hours (Jakarta 

time). Pilots noted a "volcanic smell, lack of visibility, and St. Elmo's Fire around the windshield" 

(SEAN Bulletin, 1983). The aircraft returned to Singapore for inspection, but did not sustain significant 

damage. 

6. A Qantas Airways Boeing 747 (flight QF 28) 

encountered ash from Soputan Volcano, Sulawesi, at 

about 2400 hours (Jakarta time) on 19 May 1985 

while flying from Hong Kong to Melbourne (Qantas, 

1985; Bailey, 1985). The cabin filled with dust, there 

was St. Elmo's fire around the windshield, and the 

aircraft vibrated badly for several minutes, but the 

engines did not stall. The aircraft landed safely in 

Melbourne where the aircraft was withdrawn from 

service for five days while the engines were removed 

and cleaned. 

VOLCANOES IN INDONESIA 

Indonesia is only one of several countries in the southeast Asia and southwest Pacific region that have active 

volcanoes. Papua New Guinea, the Philippines, Solomon 

Islands, Vanuatu, Tonga, and New Zealand are all volcanically active, but Indonesia has more volcanoes than any of 

them and, indeed, more than any country in the world 

(Simkin and others, 1981 ). The Indonesian archipelago 

extends more than 6,000 km from the northwestern tip of 

Sumatra in the west to Irian Jay a in the east. It contains about 

130 active volcanoes, including nearly 80 that have erupted 

in the past 400 years or so (fig. 1). About 50 volcanoes are 

monitored regularly through a network of observatories 

operated by the Volcanological Survey of Indonesia (VSI) 

(Pardyanto and others, 1986). The volcanoes are in linear 

belts and groups scattered along the archipelago, and their 

eruption clouds represent a formidable threat to aviation. 

Figure 2. A volcanic ash column rises from Galunggung 

Volcano, West Java, on 16 August 1982. The city of Taskimalaya 

is shown in the foreground. Galunggung eruptions such as this produced ash clouds that were involved in four encounters with jet 

passenger aircraft during 1982. Photograph by J.P. Lockwood. 

There were 35 eruptions from Indonesian volcanoes 

from January 1980 through September 1985-a notably high 

level of activity when compared to previous decades 

(Pardyanto and others, 1986). Twenty-seven of these 

eruptions required no evacuation of people and presented 

little threat to property, including aircraft. Major eruptions 

during this period that threatened life and property (and 

resulted in evacuations) included those of Gamalama (1980, 

1983), Galunggung (1982-83), Soputan (1982, 1984-85), 

Colo (1983), Merapi, central Java (1984), Karengetang 

(1984), and Sangeang Api (1985). The largest eruptions 

were from Galunggung Volcano in western Java (fig. 2), 

which produced more than 30 large explosive eruptions 

between April1982 and January 1983, including clouds that 

rose more than 10 km above sea level-that is, up to, or 

above, the cruising level of international airliners (Katili and 

Sudradjat, 1984a). 
194 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

VOLCANO MONITORING AND 

FORECASTING IN INDONESIA 

Precise forecasting of volcanic eruptions is a difficult 

problem, but progress has been made over the last 20 years 

(Decker, 1986; Souther and others, 1984; Sudradjat and 

Tilling, 1984; Swanson and others, 1985; Banks and others, 

1989). This progress has relied heavily on interpreting 

results from a wide range of monitoring methods, including 

visual observations, seismological recordings, deformation 

studies, temperature records, geochemical collections of 

gases and condensates, and geophysical methods such as 

magnetic and gravity recordings. However, not all of these 

diverse and specialized methods are necessary for the basic 

monitoring and forecasting of eruptions. Changes in the state 

of a volcano normally can be detected if the volcano is under 

visual and seismological observation and if the observers 

have an understanding of its previous eruptive activity. 

Studies of volcanic earthquakes are relied on in Indonesia, as elsewhere in the world, to provide early warning of 

impending activity. Seismometers are the standard equipment in VSI observation posts, and visual observations and 

changes in seismicity are the primary methods of monitoring. Other supplementary methods include: (1) studies of 

ground deformation (spirit-level measurement and precise 

distance measurement), (2) geochemical studies of gases and 

condensates from fumaroles and water from crater lakes and 

hot springs, emission rates of sulfur-dioxide gas, and chemical analysis of eruption products (ash and lavas), (3) geophysical methods employing measurement of self-potential 

and geomagnetic variations (Sudradjat, 1991). In addition, 

satellite imagery has been used to monitor the movement of 

volcanic plumes (Malingreau and Kaswanda, 1986; Sudradjat, 1989). 

VSI successes in its volcano-monitoring program 

include the 1983 Colo eruption where precursory signs of 

restlessness on Una Una island were detected and interpreted 

to indicate the likelihood of an imminent eruption (Katili and 

Sudradjat, 1984b). The Una Una population of 7,000 was 

evacuated (McClelland and others, 1989) before major eruptive activity devastated the island. However, difficulties 

arise where unmonitored volcanoes such as Galunggung 

reawaken after long periods of repose (Sudradjat and Tilling, 

1984). Nevertheless, regular observations and seismological 

monitoring were begun following the initial activity at 

Galunggung in April 1982 and were used to forecast more 

than 20 of the eruptions that took place during the remainder 

of the year (Katili and Sudradjat, 1984a). 

Effective eruption forecasting in Indonesia relies not 

only on monitoring precursory activity, but also on expedient communication of monitoring results to specialists able 

to interpret the data and able to evaluate probable future 

behavior. Indonesian volcano observatory posts are staffed 

typically by observers with secondary-school training. Many 

posts are equipped with radios for direct communication 

with volcanologists at VSI headquarters in Bandung, West 

Java. However, some observatories without radios are 

unable to provide timely notification of events. Old reports 

of activity are of limited value-delays of minutes or hours 

can be significant. Information at VSI headquarters then 

must be evaluated and interpreted before it is passed on to 

other agencies. VSI amended their communication system in 

1986 to expedite communications with the aviation community. Observer reports of volcanic activity are still provided 

directly to Bandung, but observers have been authorized to 

contact local airports directly should they observe highrising (higher than 1 km) eruption plumes. 

Transmission of monitoring data automatically from a 

remote volcano directly to Bandung or other major centers 

may seem desirable. However, this requires development of 

equipment capable of operating reliably under fairly severe 

conditions, such as the acid and humid environments found 

on tropical Indonesian volcanoes. Drawbacks are that the 

equipment is expensive, requires specially trained personnel 

for maintenance, is liable to breakdown, and is susceptible to 

vandalism. Such expensive, "high-technology" methods, 

therefore, have not been a practical solution for monitoring 

volcanoes where government budgets are restrictive but 

where there is no shortage of trainable local observers. 

Budget restrictions also prevent monitoring being undertaken on many potentially active Indonesian volcanoes. 

VULCAN-ADS AND OTHER 

RESPONSES 

Aviation, meteorological, and volcanological authorities in Indonesia and Australia began collaborating on ways 

to mitigate aircraft-ash-cloud incidents shortly after the 

Galunggung encounters in 1982. Collaboration was formalized in 1985 when the Volcanological/ Airspace Liaison 

Committee-Australia/Indonesia (VULCAN) was formed. 

The committee consists of two working groll:ps: the 

VULCAN-ADS working group is Australia based; the 

VULCAN-IND is Indonesia based. Each, working group 

consists of counterpart members representing different agencies. VULCAN-ADS consists of representatives from the\ 

Australian Civil Aviation Authority (CAA), the Bureau of 

Meteorology (BOM), Australian Geological Survey Organization (AGSO), Qantas Airways, Ltd., and the Commonwealth Scientific and Industrial Research Organization 

(CSIRO). VULCAN-IND consists of representatives of the 

Indonesian Directorate General of Air Communications, the 

Bureau of Meteorology and Geophysics, and the Volcanological Survey of Indonesia, as well as representatives from 

the three principal Indonesian domestic carriers, Garuda, 

Merpati, and Bouraq. 

VULCAN-ADS is an advisory and liaison group that 

supports the Airways Volcano Watch, part of the Australian 

CAA operational services section, which acts as a clearing 
AVIATION SAFETY AND VOLCANIC ASH CLOUDS IN THE INDONESIA-AUSTRALIA REGION 195 

house for information on volcanic activity affecting Australian civil aviation. VULCAN-AUS provided major input at a 

special meeting organized by the International Civil A viation Organization (ICAO) regional office in Bangkok, held 

in 1986, and assisted in the production of the ICAO regional 

handbook "Volcanic Ash and Aircraft Operation" (ICAO, 

1993). Extensive discussions at the 1986 meeting led to 

proposed changes to the ICAO regulatory documents to take 

into account volcanic-ash-cloud encounters. ICAO (Montreal) in 1982 had established its Volcanic Ash Warnings 

(VA W) study group, of which the chairman of VULCANADS is a member. The VA W study group also produced recommendations that subsequently were adopted by ICAO 

member states and promulgated by the ICAO Air Navigation 

Bureau (Fox, this volume). 

VULCAN-AUS was responsible also for recommending the establishment of the volcanic ash detection and 

aviation safety (VADAS) study group. VADAS was set up 

by CSIRO in 1987 specifically to explore technological 

solutions (satellite and on-board detection equipment) to the 

aircraft-ash-cloud problem (Prata, 1990). 

SATELLITE MONITORING 

The Australian Bureau of Meteorology, since 1982, has 

used images from the Japanese geostationary meteorological 

satellite (OMS), located at 35,700 km above the equator at 

long 140°E., in detecting volcanic eruption plumes ~n the 

western Pacific. Images from the infrared and visible channels of OMS were used by BOM meteorologists B.N. 

Hanstrum and A.S. Watson (Hanstrum and Watson, 1983) to 

determine the height of 1982 Oalunggung eruption clouds 

and to track the clouds in conjunction with upper-wind 

trajectories. Sawada (1989) also reported on OMS images of 

Indonesian eruption plumes for the 1982-85 period. 

BOM issues "volcanic ash advisories" to aviation 

authorities through the aeronautical fixed telecommunications network (AF1N) in Australia (fig. 3). BOM normally 

searches for eruption clouds on OMS images after receiving 

notification of a volcanic eruption from the relevant neighboring country (such as Indonesia) or from pilot reports. 

Eruption clouds are difficult to distinguish on OMS images 

when, as commonly happens in the Indonesian region, there 

are weather clouds on the same image. This is because both 

types of cloud have similar reflective properties in the visible 

and infrared parts of the electromagnetic spectrum. However, Australian scientists F.R. Honey and W. Carroll 

(Honey, this volume) proposed a concept whereby volcanic 

clouds could be discriminated using data from the advanced 

very high resolution radiometer (A VHRR) on board the 

polar-orbiting NOAA-7 satellite. This initial proposal was 

tested and developed rigorously in CSIRO by A.J. Prata 

(Prata, 1989a, 1989b; Prata and others, 1985). Discrimination of ash clouds from water-ice clouds is possible because 

Figure 3. Infonnation flow for the Australian volcanic ash warning network starts with sightings of eruption clouds in neighboring 

countries (for example, Indonesia) made by ground-based observers and (or) from in-flight pilot reports (AIREP's). The notifications 

move through the international air traffic services (A TS) center (for 

example, in Jakarta) and then to (1) the regional meteorological 

authority (for example, Jakarta), (2) an adjacent Australian ATS 

center (Perth, Darwin, or Sydney), (3) Australian weather services 

offices (WSO), and (4) the National Meteorological Centre (NMC), 

Melbourne, to the NOT AM (notices to ainnen) office (Sydney), 

which is responsible for the distribution of NOT AM's. These reach 

pilots through preflight briefing offices and by advisories from the 

Australian ATS center. NMC issues SIGMET's (significant meteorological phenomena) and volcanic ash cloud advisories, which are 

distributed to the Australian A TS centers, briefing offices, and the 

NOTAM office. The Airways Volcano Watch receives both 

NOT AM's and SIGMET's and serves as a link to both VULCANADS (see text) and the International Civil Aviation Organization 

(ICAO). AFTN, aeronautical fixed telecommunications network; 

MET, meteorology. 

of the reverse absorption effect in A VHRR channels 4 and 5 

(Prata and Barton, this volume). 

A VHRR receiving stations are operated by BOM in 

Perth and Melbourne, and a third station opened in 1992 in 

Darwin. The Australian AVHRR receiving stations cover 

much of Indonesia and the Philippines, all of Papua New 
196 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Guinea, and most of the rest of the southwest Pacific (Potts 

and Whitby, this volume). This network of AVHRR stations 

is expected to enhance ash-cloud early-warning capability 

for aviation. 

AUSTRALIAN ASH-CLOUD 

WARNING SYSTEM 

Warnings of the threat to aircraft from volcanic ash 

clouds in the Australian region are provided by means of an 

integrated communications network that includes volcanological, meteorological, and aviation authorities (fig. 3). 

There are three main features of interest in the Australian 

network: 

1. The system relies on the provision of information on 

volcanic eruptions from volcanological authorities in 

foreign countries or from pilots flying in foreign airspace. Australia has no active volcanoes of its own 

(excluding Big Ben Volcano on Heard Island in the 

Indian Ocean) and, therefore-unlike other technologically advanced and volcanically active countries 

such as Japan and the United States-does not have a 

volcanological authority as part of its own domestic 

communications network. 

2. Pilots receiving in-flight information about eruption 

clouds must hope for rapid and effective communication links between observers and ground-based 

authorities, but they may have to wait unacceptably 

long times before being notified that an eruption has 

taken place or is in progress. Communications may be 

slow or break down at some of the many links shown 

in figure 3. 

3. Analysis of satellite images is part of the system 

(undertaken at the BOM National Meteorological 

Centre, Melbourne-MET NMC in fig. 3). Twentyfour-hour analysis of AVHRR images has been 

carried out since early 1993 by operational meteorologists at the Darwin receiving station. 

Improvements in the communication network, therefore, are of fundamental importance to the mitigation of 

aircraft encounters with volcanic ash clouds in the 

Indonesia-Australia region. Aircraft will remain vulnerable 

to the effects of eruption clouds until such improvements are 

made. 

ON-BOARD ASH DETECTORS 

The alternative to, or supplement for, an enhanced communication network is the provision of aircraft-mounted 

equipment that can detect ash clouds remotely ahead on the 

aircraft flight path. Such an instrument could employ any 

one of several remote-sensing techniques (Prata, 1990). The 

advantage of such a system is that the pilot is afforded 

independence from the potentially weak volcano-to-pilot 

communication system referred to in the previous section. 

The Australian prototype of a simple, passive instrument has been constructed and tested on ash-bearing clouds 

emitted from Sakurajima Volcano in Japan (Prata and others, 

1991; Barton and Prata, this volume; Prata and Barton, this 

volume). The prototype is a multi-channel radiometer that 

uses similar wavelengths to those of the AVHRR (see 

above). A unique signature for volcanic ash clouds was 

determined from the Sakurajima measurements: more radiation was received at 10.9 microns than at 11.8 microns, 

whereas the opposite effect was measured when viewing 

water clouds and clear skies. The instrument is expected to 

be capable of detecting ash clouds 100 km ahead of the aircraft, thereby providing sufficient time for pilots to take 

appropriate action. Further development will include a simplification of the prototype for practical use on flight decks 

and possible incorporation of the concept into a multifunctional sensor capable also of detecting wind shear and 

clear-air turbulence. 

ACKNOWLEDGMENTS 

The authors gratefully acknowledge the contribution by 

the Australian Civil Aviation Authority, Canberra, in the 

production of figure 3. They also thank Subroto Motjo, 

Director of the Indonesian Volcanological Survey, Bandung, 

for reviewing an early version of the paper, and I. Barton, R. 

Lunt, S.D. Needham, A.J. Prata, R.I. Tilling, and R.J. Tingey 

for reviews of a later version of the paper. Johnson publishes 

with the permission of the Director, Australian Geological 

Survey Organization. 

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VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

THE SMITHSONIAN'S GLOBAL VOLCANISM 

NETWORK: FACILITATING COMMUNICATION OF 

VOLCANIC-ERUPTION INFORMATION 

By Lindsay McClelland 

ABSTRACT 

The Smithsonian Institution's Global Volcanism Network (GVN, formerly SEAN, the Scientific Event Alert 

Network) has gathered and disseminated information about 

the world's volcanic activity since 1975. In its 17 years of 

monitoring, GVN has reported activity at nearly 300 volcanoes, including eruptions that produced the globe-circling 

stratospheric cloud from Mexico's El Chich6n Volcano in 

1982 and two of this century's largest eruptions: at Pinatubo 

(Philippines) and Hudson (Chile) in 1991. 

Information is provided to GVN by a worldwide network of about 1,500 correspondents, scientists, government 

officials, airplane pilots, and others with knowledge of 

volcanic activity. The bulletin is sent monthly to the correspondents and is also available by subscription through the 

American Geophysical Union (AGU) and on electronic mail. 

GVN quickly notifies scientists and officials of eruptions 

that provide significant opportunities for research and (or) 

threaten life and property. News of an eruption that may 

affect aviation is immediately forwarded to NOAA's 

(National Oceanic and Atmospheric Administration) Synoptic Analysis Branch and to the Federal Aviation Administration (FAA) in Washington, D.C. Only by exchanging 

information among many sources-volcanologists, atmospheric scientists, satellite observers, pilots, and air traffic 

facilities-will fully informed decisions about the appropriate response to an eruption be possible. 

INTRODUCTION 

To operate safely in the vicinity of an erupting volcano, 

aviation authorities and pilots must have timely, accurate 

information about the locations of ash clouds. Programs to 

provide warning to aviation personnel of eruption clouds are 

in place in some regions, including the United States, Japan, 

and Indonesia. In the United States, satellite monitoring of 

volcanic clouds in U.S. flight-information regions (FIR's) 

has been in place since 1989 via an agreement between 

NOAA and the FAA (Lynch, 1991). Updates of this agreement now link the observatories of the U.S. Geological Survey (USGS) with regional offices of the FAA and the 

National Weather Service (NWS) (Hamley and Parkinson, 

this volume). 

Japan's Sakurajima Volcano has plagued operations at 

nearby Kagoshima Airport since 1955 (Katow, 1988; 

Onodera and Kamo, this volume), but careful planning and 

prompt communication from volcano-observatory personnel 

to aviation authorities have allowed continued air service 

without major mishap. 

Many international flights to and from Australia pass 

over Indonesia, which includes more than 15 percent of the 

world's potentially active volcanoes (Simkin, this volume). 

The volcanic threat to aircraft flying in this area has been 

reduced through the dedicated efforts of officials from both 

Australia and Indonesia (Johnson and Casadevall, this volume). 

Using a combination of direct visual observation and 

instruments, new eruptive pulses at a carefully monitored 

volcano should be evident within minutes (Alaska Volcano 

Observatory Staff, 1990; Onodera and Kamo, this volume), 

and news of eruptive activity can be forwarded immediately 

to appropriate authorities. However, only a small percentage 

of the world's potentially active volcanoes are rigorously 

monitored, and, at many of those, communications links 

with aviation authorities have not been established. 

Volcanic cloud avoidance would be greatly aided by the 

development of a cockpit instrument that could reliably 

detect dangerous ash concentrations while they are still far 

from the aircraft (Honey, this volume). Work in Australia to 

develop an on-board sensor is encouraging (Prata and others, 

1991; Barton and Prata, this volume) and may lead to a commercially available instrument. Nevertheless, before such an 

instrument becomes available, only a rapid, effectively targeted communications system will keep aircraft and their 

occupants safe in volcanically active areas. 

199 
200 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

THE GLOBAL VOLCANISM 

NETWORK 

The Smithsonian Institution has been communicating 

information about the world's volcanic activity for nearly a 

quarter century. Reports on current eruptions began from 

Cambridge, Mass., in 1968 when the Center for Short-Lived 

Phenomena (CSLP), with a broad-based charter to serve as a 

clearing house for transient natural events, sent out its first 

notifications by postcard. The Scientific Event Alert Network (SEAN), with its monthly bulletin, was established in 

1975 with CSLP personnel brought to Washington to build 

closer ties with Smithsonian scientists. In recognition of 

SEAN's increasing focus on volcanic activity, its name was 

changed to the Global Volcanism Network (GVN) in 1990. 

GVN is part of the larger global volcanism program that 

also includes an extensive database of Holocene volcanism 

(the last 10,000 years) and archives of volcano maps, photographs, satellite images, and other documentation. This program, in turn, is part of the Department of Mineral Sciences, 

which includes not only laboratory and library facilities, but 

also research volcanologists and major collections of volcanic products. All are housed in the Smithsonian Institution's 

National Museum of Natural History, on the Mall in Washington, D.C., and all constitute valuable resources for GVN 

personnel in tracking volcanic activity around the world. 

Since 1975, activity has been reported from almost 300 

volcanoes. Globe-circling stratospheric clouds were produced in 1982 by El Chich on (Mexico) and in 1991 by two 

of the century's largest eruptions, at Pinatubo (Philippines) 

and Hudson (Chile), but numerous, less dramatic eruptions 

with potential for regional effects on aviation occurred during the same period. Nearly 100 post-1975 eruptions had 

volcanic explosivity indices (VEl) of 3 or greater, indicating 

that they produced eruption columns that rose to at least 3 km 

above sea level and (or) had tephra volumes in excess of 10 

million m3 (Newhall and Self, 1982). Changes that might 

precede an eruption are also reported and can provide valuable time for short- to medium-term contingency planning. 

At the heart of the global volcanism network are its 

1,500 correspondents around the world, who report eruption 

information and, in turn, receive the monthly bulletin. Many 

are volcanologists who monitor a single volcano or volcanic 

region and can thus provide detailed information from the 

ground when an eruption begins. Others are atmospheric 

scientists, remote-sensing satellite specialists, government 

officials responsible for volcanic hazards, or members of the 

aviation community. Communication across these disciplinary and agency lines has proven valuable, yielding important 

new information and suggesting new and fruitful lines of 

inquiry. The bulletin is available by subscription through the 

American Geophysical Union (2000 Florida Ave. N.W., 

Washington, DC 20009), on electronic mail systems 

(OMNET, 70 Tonawanda St., Boston, MA 02124; KOSMOS/Pinet, AGU/American Institute of Physics; and Bitnet, 

VOLCANO Listserv, information at AUHF@ ASUCAD), 

and (in summary or extract form) in Bulletin of Volcanology, Eos, and Geotimes. The first 10 years of the bulletin's 

volcano reports were published as Global Volcanism 

1975-1985 (McClelland and others, 1989), and its sequel is 

in preparation. 

GVN quickly forwards news of any eruption that might 

affect aviation to NOAA's Synoptic Analysis Branch and to 

FAA headquarters in Washington, D.C. GVN supports their 

efforts by consulting local volcanologists for information 

about the eruption and searching Smithsonian resources for 

data about the volcano's geography and eruption history. In 

turn, GVN forwards observations from satellites and aircraft 

to volcanologists studying the eruption and to officials 

responsible for the safety of people living nearby. However, 

GVN has neither funding nor staff for 24-hour, 7-day 

operation, so responsibility for immediate monitoring and 

communication of volcanic hazards to aircraft must remain 

with other organizations. 

COMMUNICATIONS BETWEEN 

VOLCANO OBSERVERS AND 

AVIATION OFFICIALS 

An eruption's effects on aviation are rarely confined to 

a single country. Large volcanic clouds pay no attention to 

national boundaries, and aircraft from dozens of nations may 

fly through airspace rendered hazardous by ash. Although 

single-nation efforts are valuable, a more effective international communications system is needed to ensure aviation 

safety during explosive eruptions. Unfortunately, it remains 

difficult for volcanologists to communicate with the aviation 

community. The many (16 reported) aircraft encounters with 

Pinatubo's recent eruption cloud suggest that news of even 

this dramatic, well-publicized eruption did not always reach 

airlines and air traffic control facilities in a timely manner. 

No international system yet exists through which volcanologists can directly receive the aviation system's official warnings of volcanic hazards to aircraft, such as NOT AM's 

(notices to airmen) and SIGMET's (significant meteorological advisories). Knowledge of these messages would help 

volcanologists and remote-sensing specialists evaluate the 

effectiveness of their communications with the aviation 

community during an eruption, and it would help catch 

errors and omissions promptly before they could lead to a 

disastrous aircraft-ash encounter. 

When accessible, pilot reports of eruptive activity have 

proven very valuable in assessing the characteristics and 

vigor of an eruption, and a volcanic activity report form has 

been developed for the International Civil Aviation Organization by the International Federation of Air Line Pilots 

Associations and others (Fox, this volume; Miller, this volume). Eruption-cloud observations are to be immediately 

communicated by radio to the regional air traffic control 
SMITHSONIAN'S VOLCANISM NETWORK: FACILITATING VOLCANIC-ERUPTION INFORMATION 201 

center, so that other pilots in the area can be promptly 

informed. The completed form is to be given to company 

officials after landing. However, communication channels 

are needed to forward pilot observations of eruptions to local 

volcanologists and, internationally, to GVN, remote-sensing 

specialists, other airlines, and air traffic authorities. 

COMMUNICATING SATELLITE 

OBSERVATIONS OF ERUPTION 

CLOUDS 

Large explosive eruptions can often be detected by 

satellite and the resulting plumes tracked for long distances. 

Images from NOAA's polar-orbiting weather satellites were 

used by Matson and Robock (1984) to document the 1982 El 

Chich6n plume for several weeks as it circled the globe. 

Geostationary weather satellites provide more frequent coverage, returning data as often as once every 30 minutes, 

although resolution is lower than for polar-orbiting satellites, 

spectral information is limited, and viewing angle is poor in 

some areas (such as at high latitudes). Analysis by Sawada 

(1987) of227 eruptions within the field of view from Japan's 

geostationary meteorological satellite showed that only 

about 14 percent could be detected, but almost all eruptions 

were evident when their clouds rose to more than 10 km 

altitude. No plumes smaller than about 20 km in horizontal 

extent or 4 km altitude were observed. 

Eruption clouds remain difficult to distinguish from 

weather clouds, but use of multispectral data (presently 

available only from polar-orbiting satellites) offers promise 

as a technique for detecting the silicate particles that are 

present in virtually all fresh volcanic plumes (Schneider and 

Rose, this volume). Other characteristic components of volcanic clouds, notably so2, may also aid in their remote 

detection. The total ozone mapping spectrometer (TOMS), 

now on polar-orbiting satellites, is sensitive to so2, whose 

presence in a cloud is a clear indication of volcanic origin 

(Krueger and others, this volume). Despite infrequent realtime monitoring, TOMS data have on several occasions 

provided the first news of eruption clouds originating from 

volcanoes in remote areas. TOMS tracked the main Pinatubo 

cloud until it extended beyond the west coast of Africa and 

documented the Hudson plume during its 1-week circling of 

the globe. By coordinating TOMS data with observations 

from other weather satellites, more plumes could be tracked 

and the number of "false alarms" significantly reduced. 

Rapid communication between volcanologists and satellite observers should be established and, where it already 

exists, strengthened, to solicit ground confirmation of suspected plumes and to trigger satellite searches for plumes 

from new eruptions. Although monitoring of the entire globe 

could theoretically be accomplished from a single site, 

communication remains difficult across great distances (and 

many time zones )-therefore, monitoring from existing 

national and regional satellite-observation centers would be 

more effective. Most of these centers are focused on meteorology, operate on a 24-hour schedule, and are already 

oriented toward rapid communication of hazardous conditions. Each should establish close ties with local volcanologists, air traffic officials, and airlines in order to determine 

procedures to be followed in the event of a large eruption. 

The valuable work by NOAA's satellite specialists during 

recent eruptions demonstrates that existing meteorological 

personnel are able to search effectively for and track 

volcanic clouds with modest additional training. 

ANTICIPATING ERUPTIONS 

The locations and recent eruptive histories of many of 

the world's potentially active volcanoes have been documented (Simkin and others, 1981 ), and others, which have 

not been identified, are likely to be within known volcanic 

belts (Simkin, this volume). The most violent eruptions 

typically occur from volcanoes that have been quiet for 

hundreds to thousands of years and can often be the first historic eruption at a site not recognized as potentially active 

(Simkin and Siebert, 1984), as dramatically illustrated by 

eruptions of El Chich6n and Pinatubo. Planning for future 

eruptions should thus focus on entire volcanic regions, as 

well as on the most frequently active volcanoes within those 

regions. 

Maps that show the relationship between volcano 

locations and air routes are not yet available, but they would 

be valuable to plan effectively for future eruptions on both a 

global and regional scale. Air routes downwind from active 

volcanic regions should be identified, and the necessary 

communications links between volcanologists, satellite 

specialists, aviation authorities, and airlines should be 

established. Such maps would also become powerful operational tools if current satellite data could be electronically 

superimposed upon them-the resulting image showing 

source volcano, eruption-cloud position, forecast cloud 

trajectories, and air routes could be transmitted to distant 

computer screens, both on the ground as well as in the 

cockpit. 

Volcanic eruptions rarely occur without warning. 

Increased earthquake activity, swelling of the volcano, and 

(or) changes in gas emission generally precede an eruption 

by days to years. Given even minimal monitoring, one or 

more of these premonitory signs is usually recognized before 

an eruption, or they may be noticed and reported by people 

living near an unmonitored volcano. Although such episodes 

of unrest often do not culminate in an eruption (Newhall and 

Dzurisin, 1988), they can provide valuable time in which to 

prepare contingency plans, thereby reducing the risk of an 

ash encounter if an eruption occurs. 

Detailed pre-eruption planning is essential if communications links are to work smoothly when an eruption begins, 
202 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

and aviation officials should establish good working relationships with their region's volcanologists before the next 

large eruption. A valuable directory published by the World 

Organization of Volcano Observatories (Sigvaldason, 1991) 

describes personnel, equipment, and monitoring work at 

more than 40 facilities worldwide, many of which are 

responsible for more than one volcano. 

News of possible pre-eruption activity needs wider and 

more rapid distribution, but money is also needed to 

establish at least minimal monitoring, perhaps as little as a 

single seismometer, at each of the world's potentially active 

volcanoes. The International Decade for Natural Disaster 

Reduction provides a logical framework for increased 

volcano monitoring, and the aviation community should add 

its considerable influence to proposals by volcanologists for 

improvements in monitoring capabilities. 

Improved communication remains the key to avoiding 

disastrous aircraft encounters with eruption clouds. Effective communication must cut across international boundaries, organizational barriers, and scientific disciplines. 

GVN can help by catalyzing crucial communications links, 

providing information about monitoring efforts at individual 

volcanoes and volcanic regions, and continuing its primary 

role of supplying prompt information about current volcanic 

activity. 

ACKNOWLEDGMENTS 

Tom Simkin deserves special thanks for editing that 

improved this report. This paper has also benefited from 

thoughtful reviews by Steve Brantley and Tom Casadevall. 

Captain Ed Miller of the Air Line Pilots Association has 

spent untold hours patiently and graciously educating me 

about aviation. Most importantly, the Global Volcanism 

Network could not function without the enthusiasm and 

dedication of its correspondents, who have consistently 

shared detailed preliminary information with their colleagues, often under the pressure of an ongoing eruption. 

REFERENCES CITED 

Alaska Volcano Observatory Staff, 1990, The 1989-1990 eruption 

of Redoubt Volcano: Eos, Transactions, American Geophysical Union, v. 71, no. 7, p. 265,272-275. 

Katow, K., 1988, Flight operation procedure for avoiding volcanic 

eruption clouds, in Proceedings, Kagoshima International Conference on Volcanoes, p. 666-669. 

Lynch, J ., 1991, Mount Redoubt: Tracing volcanic ash plumes from 

space [abs.], in Casadevall, T.J., ed., First International Symposium on Volcanic Ash and Aviation Safety: U.S. Geological 

Survey Circular 1065, p. 30. 

Matson, M., and Robock, A., 1984, Satellite detection of the 1982 

El Chich6n eruptions and stratospheric dust cloud: Geoffsica 

Internacional, v. 23, p. 117-127. 

McClelland, L., Simkin, T., Summers, M., Nielsen, E., and Stein, 

T.C., 1989, Global Volcanism 1975-1985: Englewood Cliffs, 

N.J., Prentice Hall, and Washington, D.C., American Geophysical Union, 657 p. 

Newhall, C.G., and Dzurisin, D., 1988, Historical unrest at large 

calderas of the world: U.S. Geological Survey Bulletin 1855, 

1108 p. 

Newhall, C.G., and Self, S., 1982, The volcanic explosivity index 

(VEl): An estimate of explosive magnitude for historical volcanism: Journal of Geophysical Research (Oceans and Atmospheres), v. 87, p. 1231-1238. 

Prata, A.J., Barton, I.J., Johnson, R.W., Kamo, K., and Kingwell, J., 

1991, Hazard from volcanic ash: Nature, v. 354, p. 25. 

Sawada, Y oshiro, 1987, Study on analysis of volcanic eruption 

cloud image data obtained by the geostationary meteorological 

satellite (GMS): Technical reports of the Meteorological Research Institute [Japan], no. 22, 335 p. 

Sigvaldason, G., ed., 1991, Directory of volcano observatories, 

1990-1991: Reykjavik, WOVOIUNESCO, 99 p. 

Simkin, T., and Siebert, L., 1984, Explosive eruptions in space and 

time: Durations, intervals, and a comparison of the world's active belts, in Boyd, F.R., ed., Explosive Volcanism: Inception, 

Evolution, and Hazards: Washington, D.C., National Academy 

of Sciences Press, p. 110-121. 

Simkin, T., Siebert, L., McClelland, L., Bridge, D., Newhall, C.G., 

and Latter, J.H., 1981, Volcanoes of the World: Stroudsburg, 

Pa., Hutchinson Ross, 233 p. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC ASH AND AIRCRAFf OPERATIONS 

By Edward Miller 

ABSTRACT 

The aviation community has been subjected to volcanic 

eruption hazards on several occasions over the past decade, 

usually in rather dramatic fashion. Volcanic ash, injected 

into the stratosphere by explosive eruptions, is abrasive and 

will cause serious damage to aircraft engines, control 

surfaces, windshield and windows, and landing lights. Ash 

clouds are difficult and sometimes even impossible to 

distinguish from weather clouds. 

This paper explores the ground detection, reporting, 

and dissemination of information critical to crew members 

operating in the vicinity of known volcanoes and discusses 

the operational needs of flight-crew members. Pilots need to 

be educated about the hazards of volcanic ash. Pilots need 

two tools for reporting and coping with volcanic ash: a copy 

of the ICAO volcanic activity report form (V AR) and a chart 

portraying air routes and locations of known volcanoes. 

INTRODUCTION 

The aviation community has been dramatically introduced to volcanic eruption hazards over the past half 

century. Volcanic ash, a by-product of many explosive volcanic eruptions, is often injected into the upper troposphere 

and stratosphere and spreads laterally in the upper-level 

wind flow. The ash is abrasive and capable of causing serious damage to aircraft engines, control surfaces, windshields 

and windows, and landing lights. The dust can clog the pitotstatic systems, which determine airspeed and altitude, and 

can damage sensors that deliver electronic data to automated 

systems used to fly modern aircraft. Mixed with weatherassociated clouds, ash is difficult and sometimes impossible 

to identify. 

INTERNATIONAL EFFORTS 

Since 1944, when a squadron of B-25's on the ground 

in Italy were destroyed by volcanic ash from Mt. Vesuvius, 

aircraft have been sustaining damage in varying degrees 

from volcanic ash. In 1982, two B747's, one British Airways 

the other Singapore Airlines, came very close to disaster in 

Indonesian airspace because of volcanic ash (Smith, 1983; 

Tootell, 1985). Shortly after these incidents, the air navigation commission of the International Civil Aviation Organization (ICAO) formed the volcanic ash warning (VA W) 

study group to deal with the threat of volcanic ash (Fox, this 

volume). 

The study group developed procedures and guidance 

for dealing with volcanic activity and reporting the activity 

to aircraft and control centers in a timely manner. Working 

within the frame work of ICAO, implementation of these 

procedures required formal amendments to the ICAO regulatory documents. The VA W study group recommended 

amendments to annexes 3, 11, and 15 to document 4444 

(Procedures for Air and Air Traffic Services) and document 

8400 (ICAO Abbreviations and Codes )-the study group 

also recommended changes to the provisions for the use of 

notices of significant meteorological events (SIGMET's), 

notices to airmen (NOTAM's), and special air reports of 

volcanic activity (VAR's). All formal amendments require 

consultation with member states of ICAO, a time-consuming 

but necessary step. During these discussions, the air navigation commission provided interim measures for member 

states to use and organized an International Airways Volcano Watch, which maximizes the value of existing 

observing networks from several diverse fields. These networks include: 

1. World Organization of Volcano Observatories 

(WOVO). WOVO, under the aegis of the International Association of Volcanology and Chemistry of 

the Earth's Interior (IAVCEI), includes volcanological 

observatories located in different countries and under 

different authorities. The member observatories form 

a global network that has the potential to provide volcanic activity reports in real time to air traffic control 

centers and world meteorological centers. 

2. World Meteorological Organization (WMO). The 

WMO includes meteorological watch offices that 

receive information from meteorological, hydrological, agricultural, and climatological observing stations; merchant ships, which routinely provide 

meteorological reports; and meteorological satellites. 

Approximately 7,000 merchant ships are capable of 

reporting regular meteorological observations to 

203 
204 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

coastal stations. Allowing for port visits when the 

ship crews are not observing, the WMO estimates 

that about 4,000 ships actively report from all global 

shipping lanes. A small number of ships also make 

upper-air measurements. These reports are received at 

the World Meteorological Centre at Bracknell, 

England, every 24 hours. 

Satellite monitoring of volcanic eruptions and volcanic 

ash clouds is not without problems. Geostationary weather 

satellites cannot track volcanic ash clouds once they mingle 

with weather clouds. The NASA (U.S. National Aeronautics 

and Space Administration) Nimbus 7 satellite, and a recently 

launched Soviet satellite, each have the total ozone mapping 

spectrometer (TOMS) on board, which is capable of detecting sulfur dioxide in the volcanic ash cloud (Krueger and 

others, this volume). NOAA (U.S. National Oceanic and 

Atmospheric Administration) satellites with the advanced 

very high resolution radiometer (A VHRR) are also capable 

of detecting a volcanic ash cloud (Schneider and Rose, this 

volume). Both TOMS and AVHRR methods are time 

consuming, and only a limited number of centers have the 

satellite-data receiving and processing equipment. 

RECENT EVENTS 

Events of recent years have reminded us with alarming 

regularity that aircraft and volcanic ash do not mix well. 

Windshields have been rendered opaque, engines have 

failed, and severe damages have left air carriers with aircraft 

useless to them without costly repair. On December 15, 

1989, a Boeing 747-400 airliner en route from Amsterdam to 

Anchorage encountered volcanic ash from the Redoubt 

Volcano in Alaska and suffered a simultaneous four-engine 

flameout (Przedpelski and Casadevall, this volume) and, 

despite state-of-the-art technology, the aircraft was rendered 

an expensive glider for several minutes. The crew was aware 

of a volcanic eruption in the vicinity of Anchorage prior to 

their departure from Amsterdam. At 11:27 a.m. Alaska Standard Time (AST), the flight was in the Fairbanks area and 

was informed of a second Redoubt eruption. The pilot 

requested and received a radar vector around the reported ash 

cloud. At 11:46 a.m., during a descent from 35,000 ft, the aircraft entered a benign-looking stratus cloud at 26,000 ft. 

Dust and smoke in the cockpit came to the crew's attention 

first. The cloud was unnaturally dark, and St. Elmo's glow 

shone at the windows. The crew applied full power to climb 

out of the ash cloud, and after about 1 minute of high power, 

all engines spooled down to below idle, followed by a loss of 

airspeed and activation of the stick shaker. The stick shaker, 

a stall warning device, alerted the pilot that the aircraft was 

approaching stall. The next alarm was a false fire warning 

bell and crew-alerting system message, "cargo fire forward." 

The crew initiated appropriate emergency procedures, 

declared an emergency to the Anchorage air traffic control 

center, and initiated restart procedures for the engines. The 

aircraft departed the cloud at 20,000 ft, and, after five or six 

attempts, the crew successfully restarted engines 1 and 2 at 

an altitude of 17,200 ft, producing enough power to maintain 

level flight. After three additional attempts, engines 3 and 4 

were also restarted. The remainder of the flight occurred 

without further incident, and the airplane landed safely in 

Anchorage. 

The aircraft sustained heavy damage during its encounter with the ash cloud (Campbell, 1991). All four engines 

suffered damage to their compressors, combustion chambers, and turbine sections. The intake turbine blades showed 

excessive wear, and the combustion section had areas 

blocked. The ash was redeposited as a glass-like material on 

hot parts of the engines (Przedpelski and Casadevall, this 

volume). The pitot-static system was contaminated, resulting 

in a loss of airspeed indications. Contamination of the ventilation system caused the avionics compartment to overheat, 

rendering all components to be suspect of failure. The fuel 

system and hydraulic systems were contaminated with 

volcanic ash and required purging. 

Even though there is no "degree" of hazard scale, pilots 

should know that, after loss of one or more engines due to 

volcanic ash and subsequent relights, they will deal with 

permanently damaged engines and aircraft. Further flight 

should be planned with that fact in mind. 

PILOT DETECTION OF VOLCANIC 

ASH CLOUDS 

Pilots are often the first to detect a volcanic eruption, 

even when the volcano in question is extensively monitored. 

Moreover, considering the number of volcanoes not yet 

monitored and the potential threat to aviation, pilot reports 

take on new importance. Pilots must report any atmospheric 

hazard to flight that they observe, and volcanic ash definitely 

qualifies as an atmospheric hazard. 

Pilots are obliged to report known atmospheric hazards 

along routes of flight. The ICAO-approved special air report 

of volcanic activity (or volcanic activity report form, V AR) 

was deemed necessary because of the hazardous nature of 

volcanic ash clouds and their unpredictability. The form was 

designed for the needs of pilots and volcanologists (Fox, this 

volume). Items numbered 1 through 8 of the V AR are to be 

transmitted over the air traffic control frequency to the air 

traffic control center. Aircraft on and monitoring the control 

center radio frequency will receive the information at the 

same time the control center does. The reported information 

received by the listening aircraft will aid them in discerning 

their degree of hazard and what response is necessary. The 

remainder of the form is to be filled out when duties permit 

and is turned in at the first point of landing. 

Existing aircraft hardware is incapable of detecting volcanic ash; pilots are the only on-board system capable of 
VOLCANIC ASH AND AIRCRAFf OPERATIONS 205 

detection! Recently, the Australian Office of Space Science 

and Application (COS SA) has developed a prototype instrument for in-flight detection of volcanic ash-this instrument 

is currently being tested (Barton and Prata, this volume; 

Prata and Barton, this volume). 

INFORMATION AND RESPONSE 

Airborne flight crews will receive radio reports of volcanic-ash-cloud information either from another flight crew 

or from the controlling air traffic center. Future communications linkages include printed messages received in the 

cockpit via datalink. The pilot's first task after receiving this 

information is to determine the location of the event and 

assess the threat to the present route of flight. A pilot 

observing a suspected ash cloud should report it following 

the format of the volcanic activity report form (V AR) (Fox, 

this volume, fig. 1). Section I, items 1 through 8, are all that 

are required to be given at or shortly after the encounter and 

gives other crews in the area enough information to plan a 

prudent course of action. 

By applying the air report information to a chart that 

depicts volcanoes and air routes, the pilot could quickly have 

a graphic picture of the affected area and determine the position of the aircraft relative to the ash cloud. The pilot could 

plan avoidance of the ash by comparing cloud tops, aircraft 

performance, and other options available. Course correction, if appropriate, may be determined after looking at the 

information now depicted on the chart. Some questions to be 

asked are: Is a course correction necessary? If so, how far? 

What altitude is available on the other route? What will the 

correction cost in fuel bum? Is a new route necessary just 

long enough to avoid the cloud and then return to the original 

route, or will a whole new route be required? Is fuel sufficient to reach the planned destination after this reroute, or 

must an alternate destination be arranged? If the flight is 

short of the established point of equal time, is it necessary to 

return to the departure station? 

The following weaknesses in accurate pilot reporting of 

volcanic activity are possible: 

1. The initial encounter may require immediate emergency action. Filing a report by radio, and completing the report form, may initially have low priority. 

2. Weather and time of day may preclude the possibility 

of a pilot report. A volcano may only release steam 

clouds whose size and color may vary due to atmospheric conditions and time of day. The steam clouds 

will trigger reports of an eruption that must be treated 

as an ash-cloud eruption. Verification of pilot reports 

is not always possible, and there is always a time 

delay, even when verification facilities are in place. 

This situation could be improved with pilot training 

that covers the hazards of volcanic ash to aircraft and 

aircraft systems. Understanding how and what to 

report when sighting volcanic activity fills that 

requirement. 

3. Powerful eruptions that penetrate the stratosphere will 

form a mushroom cloud similar to an atomic explosion (Johnson and Casadevall, this volume; Self and 

Walker, this volume). Pilots may view the ascending 

column of volcanic ash and must be aware than an ash 

umbrella could be damaging to the aircraft. 

4. Ash clouds are difficult to identify in darkness. 

Nighttime reporting has only been possible after 

entering ash clouds. Without airborne detection 

devices, early warning is not always possible. The 

following characteristics of ash encounters have been 

reported by flight crews: 

a. Smoke or dust in the cockpit. 

b. An acid odor similar to that of electrical smoke. 

c. Multiple engine malfunctions, such as compressor stalls, increasing operating temperatures, 

torching from tailpipe, and engine flameouts. 

d. St. Elmo's glow and static discharges around 

the windshield, accompanied by a bright orange 

glow in the engine inlets. Volcanic ash clouds 

may contain sufficient electrical charge to generate lightning (Gilbert and Lane, this volume), 

a recognition advantage for the pilot, particularly at night. Most pilots will avoid lightning 

but may not necessarily be aware that a volcanic 

ash cloud is in their path. 

SIGMET (SIGNIFICANT 

METEOROLOGICAL INFORMATION) 

AND PIREP (PILOT REPORT) 

ICAO defines the SIGMET as "information issued by a 

meteorological watch office concerning the occurrence or 

expected occurrence of specified en-route weather phenomena that may affect the safety of aircraft operations." 

SIGMET's, by design, block off large areas of airspace, and 

volcanic ash clouds may occupy only a relatively small area 

of the SIGMET-noted area. With updated pilot reports, areas 

free of volcanic ash can be determined with more 

confidence. 

Pilots have reported that relaying information about 

where the ash cloud is not, can be more important than information about where the cloud is because open areas permit 

aircraft to operate (Haeseker, 1991). However, such an 

operation requires very close monitoring, with updates as 

frequent as 15 minutes or less from aircraft in the operation 

area. Usually, this will only be possible during daylight 

hours-another unfortunate restriction. Considering an 

alternative of no operation at all, the above has valid 

application. Departure and arrival airports must be open and 

remain open, and alternate airports must be available. Aircraft must be flown in visual conditions under visual flight 
206 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

rules (VFR) away from clouds, even though the pilot may be 

flying under instrument flight rules (IFR). Constant communication must be maintained between the aircraft and the 

traffic control center. The center may be receiving updates 

directly from a volcano-observation facility and will correlate that information with pilot reports. Base operations and 

airline dispatchers must also be in the information loop. 

Flight regulations require that aircraft captains have the 

final word on whether this type of operation is safe and 

prudent. This plan, with the best information, may be limited 

by the controlling center's ability to reroute traffic. The case 

of limited ability may not hinge on center staff, but on 

terrain, volume of traffic, and limited corridors open to 

traffic even under normal conditions. 

CONCLUSIONS 

• Although much has been done to mitigate the dangers 

of volcanic ash to aircraft, more is needed. There are 

1,500 known volcanoes worldwide, and about 600 of 

these volcanoes are considered active (Simkin, this 

volume). An average of 55-60 volcanoes erupt each 

year, and about eight to ten of these eruptions produce 

ash clouds that reach flight altitudes. 

• Considering the limited number of monitored volcanoes and the limits on satellite detection of volcanic 

ash clouds, we conclude that pilots must be especially 

attentive to the hazards of volcanic ash intruding into 

airspace. 

• Pilots already look out for one another by reporting 

in-flight weather conditions such as mountain waves, 

clear-air turbulence, and thunderstorms that are all 

hazardous to flight. 

• Pilots are knowledgeable about atmospheric hazards. 

This knowledge is acquired from actual experience 

and from required weather training courses for licensing purposes. Volcanic ash is a relatively new hazard, 

and although not many crews have experienced flight 

into a volcanic ash cloud, it is regrettable that the 

number of crews with this experience is growing. 

RECOMMENDATIONS 

• Pilot training is the first priority. Pilots must understand that volcanic ash is not like sand or dust, and 

they must know how to recognize inadvertent entry 

into an ash cloud. 

• Pilots must understand the recommended procedures 

for exiting the cloud in order to minimize damage to 

their aircraft (Campbell, this volume). 

• A volcanic ash training video has been developed by 

the Boeing Company in cooperation with the Air Line 

Pilots' Association and the U.S. Geological Survey. 

This video has been distributed widely, and ICAO 

will provide translations into French, Russian, and 

Spanish. 

• Presently, neither the new video nor previous volcanic 

ash information developed by airframe and engine 

manufacturers is mandated for inclusion in pilot training syllabi. Minimum requirements should be that 

every licensed pilot view the training video. More 

effective training would require the inclusion of volcanic ash hazards into ground school courses required 

for a pilot's license. An ideal training program would 

include the required ground school, the video, and a 

volcanic ash drill during the simulator portion of the 

pilot training course. 

• Proper tools must be provided that will assist pilots. 

They must have the ICAO volcanic activity report 

(VAR) form. The VAR form is already in use by some 

airlines. In addition, commercial chart makers such as 

Jeppesen-Sanderson, Inc., have been encouraged to 

prepare charts showing vokanoes and air routes. 

• Finally, airline management must be convinced that 

the charts, the video, and the training programs are 

necessary, and regulations must be rewritten to implement the change. 

REFERENCES CITED 

Campbell, E.E., 1991, 7 4 7-400 airplane damage survey following a 

volcanic ash encounter [abs.], in Casadevall, T.J., ed., First International Symposium on Volcanic Ash and Aviation Safety: 

U.S. Geological Survey Circular 1065, p. 14. 

Haeseker, E., 1991, Alaska Airlines operating procedures during 

the 1989-1990 Redoubt eruptions [abs.], in Casadevall, T.J., 

ed., First International Symposium on Volcanic Ash and A viation Safety: U.S. Geological Survey Circular 1065, p. 20-21. 

Smith, W.C., 1983, High-altitude conk out: Natural History, v. 92, 

no. 11, p. 26-34. 

Tootell, B., 1985, All4 Engines Have Failed; The True and Triumphant Story of Flight BA 009 and the Jakarta Incident: Auckland, Hutchinson Group, Ltd., 178 p. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC EVENT NOTIFICATION AT 

MOUNT ST. HELENS 

By Bobbie Myers and George J. Theisen 

ABSTRACT 

During the 1980--86 eruptions of Mount St. Helens, 

hazards information was quickly disseminated through a 

U.S. Geological Survey Cascades Volcano Observatory-U.S. Forest Service notification system. Written and 

verbal statements issued jointly by the Cascades Volcano 

Observatory (CVO) and University of Washington were 

released to the Forest Service for telephone call-down to 

governmental agencies and private interests. Once the calldown was underway, public and media information tapes 

were updated and press releases were issued. Because most 

of these eruptions had recognizable precursors, a series of 

information statements and eruption forecasts was issued 

during the weeks to hours before an eruption, thus providing 

advance warning of volcanic activity and associated hazards. 

Hundreds of small gas and ash emissions also occurred 

during 1980--86, most without recognizable precursors. The 

lack of precursors made advance warning of these events 

impossible; instead, information statements were issued 

after the larger, more visible events. The occurrence of occasional small, unpredictable, ash-producing explosions at 

Mount St. Helens during 1989-91, coupled with increased 

concern about the hazards of volcanic ash to aviation, 

prompted CVO to develop a seismic-alarm system that triggers on small volcanic events. This alarm system activates 

CVO' s 24-hour telephone beeper. In addition, the Federal 

Aviation Administration (FAA) can also activate the CVO 

beeper to report possible volcanic activity. These two modifications improve CVO' s response time for non-predictable, 

sudden-onset events and help the FAA quickly verify pilot 

reports of possible volcanic plumes. 

INTRODUCTION 

When Mount St. Helens awoke in March 1980, there 

was an immediate need for the rapid dissemination of information about volcanic events and hazards. An emergency 

coordination center (ECC) was established at the U.S. Forest 

Service (USFS) facility in Vancouver, Wash. The facility 

was staffed 24 hours a day by USFS personnel experienced 

with emergency response. During critical times, the ECC 

was also staffed by representatives of the U.S. Geological 

Survey Cascades Volcano Observatory, emergency management agencies, and private companies. A communications 

network (fig. 1) and telephone call-down procedures were 

developed to facilitate rapid dissemination of information 

about the activity of the volcano. Information was also 

disseminated through public meetings, press conferences, 

U. S. GEOLOGICAL SURVEY 

CASCADES VOLCANO OBSERVATORY 

AND 

UNIVERSITY OF WASHINGTON GEOPHYSICS PROGRAM 

I 

I 

I 

I 

I 

I 

I 

I 

I U. S. FOREST SERVICE I 

I EMERGENCY COORDINATION CENTER I 

I 

I 

I 

I 

I 

I 

I EMERGENCY I FEDERAL AVIATION f--- 1--- MANAGEMENT 

' ADMINISTRATION I AGENCIES I 

I 

I 

I 

I 

I NATIONAL OCEANIC - OTHER FEDERAL, I .., ___ AND ATMOSPHERIC t--- STATE AND LOCAL 

ADMINISTRATION AGENCIES 

(-I PRIVATE 

NEWS MEDIA BUSINESSES 

Figure 1. Communication and notification network for rapid dissemination of volcanic hazards information at Mount St. Helens. 

Statements issued jointly by the Cascades Volcano Observatory 

and the University of Washington are disseminated by the U.S. 

Forest Service emergency coordination center. Although all participants have the opportunity to communicate with each other, the 

main channels for distribution of formal statements and notifications are shown by heavy lines. Dashed lines represent secondary 

links during the early 1980's, which have become primary links in 

recent years. 

207 
208 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Example of statements by CVO and UW released by 

ECC during the March-April 1982 eruptive period of Mount St. 

Helens. 

[CVO, Cascades Volcano Observatory; UW, University of Washington; ECC, emergency coordination center; PST, Pacific Standard Time. For most eruptions of Mount 

St. Helens, a series of statements predicting an eruption and providing information on 

eruptive activity after it began was written by CVO and UW and released by the ECC 

through a formal call-down procedure. These statements were based primarily on recognition of a repeated pattern of precursors. When the patterns changed, statements 

were necessarily less detailed. The following example represents one of the most detailed series] 

March 5, 1982 

0900 PST; EXTENDED OliTLOOK ADVISORY: 

Seismicity at Mount St. Helens increased around February 21 

and has remained at a level somewhat above background since 

that time. Approximately 100 earthquakes that occurred during 

this period have been located. These earthquakes fall into two 

groups: (1) a "deep" group of very small earthquakes with 

centers at 6- to 11-km depths, and (2) a shallow group of 

somewhat larger (magnitude 1 or less) earthquakes located at 

3-4 km up to the surface. There is a pronounced lack of 

seismicity at a depth of 4-6 km. 

Although poor weather during the past week has hampered 

observations and monitoring on the mountain itself, 

measurements made last week show only slow ground 

deformation in the immediate vicinity of the dome and no 

significant increase in gas emissions. 

March 12, 1982 

0800 PST; EXTENDED OliTLOOK ADVISORY: 

Seismicity beneath Mount St. Helens continues at elevated 

levels, but individual earthquakes are of low magnitude. 

Earthquakes have been occurring in 1-2-day-long episodes 

separated by 1-2-day intervals of decreased activity. The 

earthquakes are occurring between the surface and a depth of 

about 6 miles. Rates of ground deformation in the crater area 

have increased during the last two weeks, and they are similar 

to patterns observed before previous dome-building eruptions. 

Based on rates of deformation, an eruption is likely within the 

next 3 weeks. Deformation is confined to the crater areas, 

suggesting that renewed dome growth will occur. The current 

seismic patterns differ from any observed before 1980-81 

eruptions, however, and raise the possibility of more hazardous 

variations in eruptive behavior. If there were to be any 

pyroclastic flows, from either an explosive eruption or collapse 

of the steep north face of the dome, the possibility of rapid 

snowmelt would be a concern. 

March 15, 1982 

1900 PST; ADVISORY: 

Accelerating rates of ground deformation in the crater of Mount 

St. Helens suggest that an eruption, most likely of the domebuilding type, will probably begin within 1 to 5 days. Deep 

earthquakes have almost ceased, and shallow earthquakes 

continue at a moderate rate. A further increase in shallow 

seismicity is likely before the eruption starts. 

Table 1. Example of statements by CVO and UW released by 

ECC during the March-April 1982 eruptive period of Mount St. 

Helens-Continued. 

March 19, 1982 

0900 PST; ERUPTION ALERT: 

Seismicity at Mount St. Helens has increased significantly 

during the past day. This indicates that an eruption will begin 

soon, probably within the next 24 hours. The character of both 

the seismicity and deformation in the crater area indicated that 

the most likely type of activity is dome growth. 

1933 PST; ERUPTION ALERT: 

Verbal statement that eruption had begun at 1927. (Significant 

increase in seismicity and pilot and radar reports of an ash 

plume indicated start of eruption.) 

2025 PST; ERUPTION UPDATE: 

The eruption has subsided for the time being, and an ash plume 

is blowing to the SSE. and S. with a lesser amount to the SSW. 

The size of the eruption and the amount of the ash appear to be 

like those of the summer 1980. 

March 21,1982 

0900 PST; ERUPTION UPDATE: 

There is a new lobe being added to the SE. side of the lava 

dome in the crater of Mount St. Helens. The new extrusion 

began during the night. Seismicity and tilt are now following 

patterns observed during other recent periods of dome growth. 

March 24, 1982 

1730 PST; ERUPTION UPDATE: 

Growth of the new dome lobe has slowed significantly over the 

past 2 days, but rates of deformation on the north side of the 

dome have increased over the same period. Until additional 

measurements are made, it would be premature to declare this 

eruption over. Seismometers are recording decreasing numbers 

of avalanches as growth of the new lobe slows. 

AprilS, 1982 

0100 PST; ERUPTION UPDATE: 

Seismicity still continues at moderate to high levels. 

Fluctuations in seismicity correspond to pulses of gas and ash, 

the largest of which began at 1237 a.m. and rose to a maximum 

of about 32,000 ft. There does not appear to be much ash in the 

plume, but minor ashfall was reported earlier tonight at 

Packwood. No increases have been reported in river levels. 

1800 PST; ERUPTION UPDATE: 

Seismicity is continuing at a moderate to high level. The status 

of the volcano remains unchanged since the previous advisory 

(1 a.m., 4/5/82). Some additional dome growth and (or) smallscale explosive activity is likely; larger explosive activity is less 

likely but cannot be ruled out. 
VOLCANIC EVENT NOTIFICATION AT MOUNT ST. HELENS 209 

Table 1. Example of statements by CVO and UW released by 

ECC during the March-April 1982 eruptive period of Mount St. 

Helens-Continued. 

April6, 1982 

0915 PST; ERUPTION UPDATE: 

Another new lobe is being added to the dome. This reduces the 

immediate likelihood of larger explosive activity, but small, 

intermittent gas and ash pulses may continue to occur. 

April12, 1982 

1515 PST; ERUPTION UPDATE: 

Seismicity, deformation and gas emissions at Mount St. Helens 

have returned to low levels, indicating that the eruption that 

began on 3/19/82 is over. 

and briefings with governmental agencies and private 

businesses (Miller and others, 1981). Written "volcanic and 

seismic activity reports" were issued daily. These "daily 

updates" provided information on the status of the volcano 

and any significant changes or observations during the previous 24 hours. 

Since 1980, this notification system has been modified 

in response to changes in volcanic activity, funding, and the 

concerns of government, business, and the public. Key 

changes include the capability of issuing written predictions 

weeks in advance of most eruptions; eliminating the need for 

24-hour duty for both USFS/ECC and CVO staff except 

when eruptions are imminent; entering all predictions and 

updates into a computer "news" system for easy review by 

those on the call-down list; updating volcanic activity reports 

and information tapes weekly or monthly (rather than daily) 

when the volcano is quiet; and, most recently, developing a 

seismic alarm to alert scientists to small events that occur 

without precursors. 

NOTIFICATION BEFORE AND DURING 

EVENTS WITH PRECURSORS 

Since May 18, 1980, 21 magmatic eruptions have 

occurred at Mount St. Helens; 5 were predominantly explosive, and 16 were predominantly non-explosive, domebuilding eruptions. Several eruptions involved both explosive and dome-building activity. The last magmatic eruption 

was a dome-building eruption in October 1986. Scientists at 

CVO in Vancouver, Wash., and at the University of Washington (UW) Geophysics Program in Seattle were able to 

predict most of these eruptions based on evaluation and 

interpretation of data from an extensive monitoring network 

(Swanson and others, 1985). Initially, these predictions were 

issued as verbal statements, but, after December 1980, they 

were issued as written statements. Both types of statements 

were distributed by the USFS through the ECC. 

Table 2. Examples of "daily updates" about Mount St. Helens 

issued by CVO and UW after the March 15, 1982, advisory and 

before the March 19, 1982, alert. 

[CVO, Cascades Volcano Observatory; UW, University of Washington; PST, Pacific 

Standard Time] 

March 16, 1982 

0800 PST: 

Geologists and hydrologists from the Geological Survey 

performed on-site monitoring in and around Mount St. Helens 

on March 15, 1982. Measurements showed accelerated rates of 

ground deformation on thrusts and cracks in the crater. 

University of Washington-USGS reports seismicity remains at 

a slight increase over the weekend's activity. Shallow 

earthquakes continue at a moderate rate (see Mount St. Helens 

Advisory, 7:00p.m., March 15, 1982). 

March 17,1982 

0800 PST: 

Good weather permitted on-site monitoring in and around 

Mount St. Helens by geologists and hydrologists of the U.S. 

Geological Survey. Measurements showed continued 

acceleration of ground deformation localized around the lava 

dome. Overflights of the volcano the last two days have shown 

an increase in the number of incandescent areas on the dome. 

University of Washington-USGS reports seismicity remains at 

a moderate rate. 

March 18, 1982 

0800 PST: 

Continued good weather enabled monitoring to be carried out 

in the crater of Mount St. Helens for the third day in a row. 

Measurements performed by geologists from the U.S. 

Geological Survey continued to document accelerating ground 

deformation rates. Airborne gas monitoring around the volcano 

during the past several days has shown that a moderate increase 

in the rate of S02 emissions has occurred. The University of 

Washington-USGS seismic lab reports a slight increase in the 

level of seismicity over that of yesterday, but it still can be 

described as a moderate level. 

For most eruptions, a series of statements was issued 

(table 1), usually beginning with an "extended outlook 

advisory" predicting an eruption within several weeks. As 

the levels of precursory activity increased, the predicted 

eruption window was fine-tuned to days or hours, and 

"eruption advisories" and "eruption alerts" were issued. 

After an eruption began, factual statements were issued 

regarding the character and effects of the eruption, and, 

finally, a statement was issued declaring the eruption to be 

over. The "daily updates" and information tapes for the 

public and media provided additional information on a daily 

basis (table 2). 

If the ECC and CVO, in Vancouver, and the UW 

seismic laboratory, in Seattle, were not already staffed on a 

24-hour basis when an "eruption advisory" was issued, 
210 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

24-hour duty was initiated. USFS, CVO, and UW personnel 

were ready to respond to rapid changes in the level of 

volcanic activity and to answer questions and discuss specific concerns. Because it was not always possible to determine whether there would be explosive activity during an 

eruption, there were regular discussions among the Federal 

Aviation Administration (FAA), National Oceanographic 

and Atmospheric Administration (NOAA), National 

Weather Service (NWS), USFS/ECC, and CVO personnel 

regarding the possibility of ash plumes and their probable 

trajectories. CVO and the USFS reported suspected ashproducing events to the FAA as quickly as possible, and the 

FAA called the ECC or CVO to confirm all pilot reports. 

Initially the FAA was contacted at the local Portland, Oreg., 

area office; however, by the mid-1980's most contact with 

the FAA was made directly with the regional FAA office in 

Auburn, Wash. (Hamley and Parkinson, this volume). 

NOTIFICATION DURING AND AFTER 

EVENTS WITHOUT PRECURSORS 

Between 1980 and 1986, hundreds of small ash emissions also occurred. These small events were known as gas 

and ash emissions or explosions, and they originated from 

cracks and small vents on the dome and sent plumes of steam 

and ash 500 ft (152 m) to 22,000 ft (6,706 m) above the 

volcano. The more vigorous events also erupted showers of 

hot rock fragments from the dome, and some events generated small debris flows. 

Most of these events took place without recognized 

precursors, which made advanced warning of these events 

impossible. Verbal or written statements were issued to all 

concerned agencies after the larger or more visible events 

(table 3). If an event occurred during normal working hours, 

the ECC and CVO updated media and public information 

telephone tapes and contacted the FAA, emergency management officials, and others on the call-down list shortly after 

the event. Because the seismic amplitude of these events was 

too small to trigger alarms on the UW State-wide network, 

scientists were often unaware (until normal working hours) 

of events that occurred during non-working hours. In most 

cases, this was not a problem because these small events 

were frequent enough that government officials and the public became familiar with them. However, the FAA and emergency management personnel occasionally needed to contact 

CVO for more information after the larger events that may 

Table 3. Examples of statements issued by the CVO and UW after eruptive events at Mount St. Helens that occurred without precursors. 

[CVO, Cascades Volcano Observatory; UW, University of Washington; PDT, Pacific Daylight Time; ECC, emergency coordination center] 

June 18,1982 

0930 PDT~ DAILY UPDATES: 

[Distributed by eva computer "news" system] 

University of Washington-USGS reports continued low-level 

seismic activity. Small gas-emission events continue to occur 

daily. The most recent event was at 0621 this morning, June 

18. The plume rose to 12,000 ft. 

April18, 1986 

1200 PDT~ DAILY UPDATES: 

[Distributed by eva computer "news" system] 

Since yesterday's report at 1300, there have been three more 

gas and ash emission events. The first occurred at 1428 on the 

17th and produced a plume to 14,000 ft (according to a local 

pilot). The second event occurred at about 1 a.m. today. Minor 

ashfall from this event was reported SE. of the mountain. Both 

of these events appeared to be slightly smaller (seismically) 

than the 1716 event on the 16th. The third event occurred at 

1116 today and was observed by geologists working in the 

crater and flying in an airplane around the mountain. The 

event appeared to be about the same size (seismically) at 

Yellow Rock as the 1716 event on the 16th. Geologists 

reported that rock fragments were thrown on and around the 

dome. The ash plume rose to 14,000 ft and later drifted higher 

and to the southeast. The event lasted about 5 minutes 

seismically, witl. the vigorous emission lasting just under 2 

minutes. 

April18, 1986-Continued 

When crew first reached the crater this morning they reported a 

light dusting of tephra on the east and southeast flanks of the 

mountain, some tephra on the crater floor, lots of ejected 

material (rock fragments) on top of the dome, and lots of new 

snow in the crater. A pit dug in the snow revealed four, thin 

(dispersed) ash layers from previous events. 

A new update will be issued on Monday unless there is 

significant activity over the weekend. 

May6, 1986 

1300 PDT~ INFORMATION STATEMENT 

[Distributed by Eee formal call-down and eva computer "news" system] 

More than 50 steam and ash explosions have occurred on the 

dome at Mount St. Helens during the last 3 weeks. Seismicity 

has increased from slightly elevated levels at the end of April to 

moderate levels today. Most monitoring equipment on the 

dome has been damaged by the explosion and no longer 

operates. One remaining tiltmeter on the dome shows 

gradually accelerating tilt. Other deformation measurements 

have been hampered by inclement weather, inaccessibility of 

the dome because of the explosions, and loss of many targets. 

Hazards from explosions are most likely to be restricted to the 

crater and flanks of Mount St. Helens. However, small 

mudflows caused by explosions in the crater may flow into the 

North Fork Toutle River, and areas downwind from the volcano 

may occasionally be dusted by small amounts of ash such as has 

occurred recently. 
VOLCANIC EVENT NOTIFICATION AT MOUNT ST. HELENS 211 

have been visible to pilots or the public. This contact was 

made by calling the USFS/Eee telephone beeper number; 

the USPS, in turn, contacted the eva duty scientist by 

telephone or through the beeper, if necessary. 

During 1989-91, at least six, small, ash-producing 

explosions occurred at Mount St. Helens, ending a 3-year 

period during which no eruptive activity took place. Because 

none of the 1989-91 explosions had recognizable precursors, they were not predicted, and no advance warnings were 

issued. The first of these ash-producing explosions (December 7, 1989) occurred during normal working hours; however, the second explosion (January 6, 1990) occurred on a 

rainy Saturday morning, and scientists were unaware of the 

event until several hours later when residents of central 

Washington began reporting light dustings of ash on their 

cars. In fact, eva was not immediately notified when ash 

began falling. Instead, calls from the public prompted the 

media to contact the Alaska Volcano Observatory (AVO) to 

see if the ash was from ongoing activity at Redoubt Volcano, 

near Anchorage. AVO verified that the ash was not from 

Redoubt and contacted eva geologists. 

RECENT MODIFICATIONS TO 

IMPROVE CVO'S RESPONSE TIME 

The delay in eVO's learning about the January 6, 1990, 

event, coupled with increased concerns about the hazards of 

volcanic ash triggered by the Boeing 747 incident in Alaska 

on December 15, 1989 (Brantley, 1990), prompted eva to 

develop a seismic-alarm system that is activated by small, as 

well as large, volcanic events. eva also made a few 

adjustments in the notification and call-down procedures to 

improve communication of hazards information during nonworking hours. 

SEISMIC ALARM SYSTEM 

Because seismicity is one of the main tools used to 

monitor volcanoes, eva and uw maintain a network of 18 

seismic stations within 16 km of Mount St. Helens, including 

three stations in the crater. These stations provide a detailed 

record of seismic activity at Mount St. Helens, including 

earthquakes, tremor, rockfalls, explosions, and mudflows 

(Jonientz-Trisler and others, this volume). Most of these 

seismic events, including many of the small ash-producing 

explosions, are too small to record on the State-wide network 

at UW. However, the events cause significant local ground 

motions that are detected on the Mount St. Helens network 

by the eva real-time seismic-amplitude monitoring system 

(RSAM) as peaks in the time-averaged seismic amplitude 

(Endo and Murray, 1991). 

An RSAM-based seismic-alarm system was developed 

and installed for testing 2 days after the January 6, 1990, 

event and was fully functional by the end of February 1990. 

Table 4. RSAM alarms that have been triggered at Mount St. 

Helens between March 1, 1990, and September 20, 1991. 

[RSAM, real-time seismic-amplitude monitoring system] 

Type of event Number of alarms 

Explosion-like seismic events1 .......................... 16 

Rockfalls (some with dust plumes) ................... 22 

Mount St. Helens earthquakes ............................ 1 

Regional earthquakes ........................................ 12 

Telemetry problems ............................................ 6 

1 Four of these events had confirmed ash plumes. 

With the RSAM system, a computer program compares the 

amplitude of a station's average seismic signal during a 

1-minute interval with empirically determined threshold 

values. If thresholds are exceeded during the same 1-minute 

interval at several (usually three) of the stations in the crater 

and on the volcano flanks, an RSAM alert is generated. The 

computer is set to automatically dial the duty scientist's 

24-hour beeper and transmit a number code indicating an 

RSAM alert. The computer redials the beeper every time a 

new 1-minute RSAM alert is generated. 

Many types of events, including explosions, rockfalls, 

earthquakes, and telemetry problems, can generate alerts 

(table 4). Because an alert does not indicate the nature of the 

event, the duty scientist must examine the seismic signature 

of the event recorded on the seismographs at eva to determine the basis for the alert. Explosion signals can usually be 

identified by careful evaluation of the signal character 

(Jonientz-Trisler and others, this volume). Once an alert is 

received, the speed with which notification is issued will 

depend on the time it takes for the duty scientist to reach 

eva and the scientist's skill at recognizing explosion signals (table 5). 

To date, all known ash-producing explosions since 

March 1, 1990, have generated alerts. However, failure of 

any component (key seismic stations, computer, computer 

programs, phone system, beeper, or beeper-pager system) 

would prevent an alert from getting through. As a precaution, a daily test alert is sent through the system to the 

beeper. 

BETTER TWO-WAY COMMUNICATION 

When ash-producing explosions occur during nonworking hours, the FAA needs a means of quickly contacting eva without the cumbersome and time-consuming process of first calling the USPS beeper. Pilots often are the first 

to observe volcanic plumes; however, sometimes slashburns, storm clouds, or other atmospheric phenomena are 

mistaken for volcanic plumes. When a pilot's report of volcanic activity is received (Fox, this volume), the FAA must 

quickly verify the nature of the event and identify the area 

affected in order to evaluate the impact on air traffic and to 
212 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 5. Example of initial CVO response to a seismic event that 

occurred without precursors during nighttime, November 5, 1990. 

[CVO, Cascades Volcano Observatory; PST, Pacific Standard Time; RSAM, real-time 

seismic-amplitude monitoring system; UW, University of Washington. Note: this was 

the first plume-producing event in 10 months] 

Time 

of event 

(PST) 

Response 

0207 ................ •Seismic event began. 

0208 ................ •RSAM alert transmitted to beeper. 

0209-0217 ........... •Nine more RSAM alerts are transmitted to 

beeper. Scientist on duty awake, 

dressed, and en route to CVO by fourth 

alert. 

0220-0229 ........... •Duty scientist arrives at CVO. 

•Seismic signal evaluated. 

•Scientist-in-charge notified at homeassistance requested. 

•UW seismic analyst notified at home. 

• FAA area manager, Seattle Center, calls 

with two pilot reports of plume to 

30,000 ft. He gives wind direction and 

speed at altitude and states that plume 

will drift SE. Note: CVO duty scientist 

was dialing the FAA on one phone line 

when she received the FAA's call on 

second phone line. 

0230-0239 ........... •Forest Service duty officer notified at 

home-assistance requested. 

•UW updated on situation-assistance 

requested. 

0240 ................ •Continued evaluation and response. 

suggest alternate routes if necessary (Hamley and Parkinson, 

this volume). By dialing the eva beeper number, the FAA 

can now make direct contact, day or night, with the eva 

duty scientist. This change provides rapid verification of 

pilot reports and backup notification for eva in case the 

RSAM alarm system fails. 

Dissemination of information through normal USFS 

channels may also be delayed if eva should need to contact 

the USFS by beeper. To assure that the FAA and NOAA are 

immediately notified of any ash-producing event, they are 

contacted directly by eva as soon as the signal is identified. 

If the USFS is delayed in responding to their beeper, eva 

will initiate further call-down by notifying the Washington 

Department of Emergency Management and others as 

needed. 

CONCLUSIONS 

The development of notification and call-down procedures utilized by eva and USFS at Mount St. Helens provides a means for rapid response to both predicted and nonpredicted events. Although the procedures have worked in 

the past, they have been regularly reviewed and updated to 

reflect changes in the style and frequency of eruptions and to 

meet the changing needs and concerns of emergencyresponse agencies, businesses, and the public. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, 

Alaska, December 14, 1989-August31, 1990: U.S. Geological 

Survey Circular 1061, 33 p. 

Endo, E.T., and Murray, T.L., 1991, Real-time seismic amplitude 

measurement (RSAM): A volcano monitoring and prediction 

tool: Bulletin of Volcanology, v. 53, p. 533-545. 

Miller, C.D., Mullineaux, D.R., and Crandell, D.R., 1981, Hazards 

assessment at Mount St. Helens, in Lipman, P.W., and 

Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. 

Helens, Washington: U.S. Geological Survey Professional 

Paper1250,p. 789-802. 

Swanson, D.A., Casadevall, T.J., Dzurisin, D., Holcomb, R.T., 

Newhall, C.G., Malone, S.D., and Weaver, C.S., 1985, Forecasts and predictions of eruptive activity at Mount St. Helens, 

U.S.A.: 1975-1984: Journal of Geodynamics, v. 3, p. 397-423. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

AVIATION SAFETY MEASURES FOR ASH CLOUDS 

IN JAPAN AND THE SYSTEM OF JAPAN AIR LINES 

FOR MONITORING ERUPTIONS AT 

SAKURAJIMA VOLCANO 

By Saburo Onodera and Kosuke Kamo 

ABSTRACT 

In Japan, 21 cases of volcanic ash encounters by aircraft 

were reported between 1973 and 1991. More than half of 

these encounters were with ash clouds produced by eruptions 

of Sakurajima Volcano, South Kyushu. Japan Air Lines 

(JAL) and Sakurajima Volcanological Observatory, Kyoto 

University (SVO) developed the volcano watching system 

(VWS) to mitigate the volcanic ash hazards to aircraft in the 

vicinity of Sakurajima Volcano. The system functions in all 

weather conditions and alerts flight dispatchers at 

Kagoshima International Airport without delay. It has been 

deployed at the JAL office at Kagoshima Airport since 

March 1991. 

Between April 1 and May 31, 1991, 159 explosive 

eruptions took place at Sakurajima Volcano. The VWS 

system was operating at the time of eruption in 56 cases-it 

judged 49 cases as "explosive eruptions" and 7 cases as 

"eruptions." The agreement ratio of the system with the 

observations for this term is 88 percent. 

COUNTERMEASURES TO 

VOLCANIC ASH HAZARDS TO 

AVIATION IN JAPAN 

There are 83 active volcanoes and approximately 80 

airports for civil aviation in Japan (fig. 1). On an average, 

six volcanoes erupt each year. Twenty-one cases of volcanic 

ash encounters by aircraft were reported between 1973 and 

1991 (table 1). The records show that most of the damage 

was to the exterior of aircraft, including windshields-to 

date, no damage to engines has been reported. 

The Japan Meteorological Agency (JMA) constantly 

watches 19 volcanoes by monitoring volcanic smoke, seismic events and tilt changes, and by field observation. JMA 

issues significant meteorological advisory information 

"" 

~ 

32° ~ . 

~ . 

~· . 

. ~ "P 

28. 

(j, 

~ ~· 

8 .. 

Figure 1. Locations of active volcanoes and airports for civil 

aviation in Japan. Solid triangles and open circles represent active 

volcanoes and civil airports, respectively. S, Sakurajima Volcano; 

K, Kagoshima International Airport. 

(SIGMET's) concerning en-route weather phenomena that 

may affect the safety of aircraft operation. In the case of volcanic activity, when volcanic ash reaches an altitude of 

25,000 ft above sea level, JMA issues a SIGMET and a 

"volcanic observation" report, which includes the name of 

the volcano and the time of eruption, as well as any additional information available about the activity. The eruption 

213 
214 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Effects on aircraft caused by volcanic eruptions in Japan. 

Date Volcano Airport Aircraft 

2/3/73 As am a Haneda DC8 

4/8/75 Sakurajima Kagoshima L1011 

8/7/77 Usu Chitose DC8 

8/7/77 Usu Chitose DC8 

8/7/77 Usu Chitose Ll011 

8/7/77 Sakurajima Kagoshima Ll011 

11/19/77 Sakurajima Kagoshima DC8 

12/25/77 Sakurajima Kagoshima Ll011 

12/4/78 Sakurajima Kagoshima Ll011 

11/18/79 Sakurajima Kagoshima Ll011 

11/18/79 Sakurajima Kagoshima LlOll 

12/24/79 Sakurajima Kagoshima YSll 

11/23/82 Sakurajima Kagoshima B727 

6/24/86 Sakurajima Kagoshima DC9 

11/21/86 lzu-Oshima Narita B747 

11/21/86 Izu-Oshima Narita DC8 

11/21/86 Izu-Oshima Narita DClO 

11/21/86 Izu-Oshima Narita B747 

6/3/91 Sakurajima Miyazaki MD80 

6/3/91 Unzen Kumamoto A300 

8/5/91 Sakurajima Kagoshima B737 

1 Yoshitama (1984). 2 T.J. Casadevall (written commun., 1991). 

information is passed on immediately by JMA to the responsible air traffic control center (A TC) and to airline companies (fig. 2). 

Airlines restrict their flights in ash-contaminated areas. 

Flight dispatchers prepare prediction charts of possible airspace contaminated by volcanic ash, and, on this chart, they 

plot the latest upper-level wind data over the volcano to predict beforehand the hazardous area for the day. The chart is 

referred to by pilots and dispatchers in pre-flight briefings 

and by dispatchers for flight advisories to pilots. 

A TC provides every possible service to pilots when 

avoidance of ash is required. For example, A TC at 

Kagoshima approves any heading or altitude requests by 

pilots when circumstances permit and when they request 

them with the term "due to volcanic ash." Special contingency avoidance routes are established in the vicinity of 

active volcanoes (Yoshitama, 1984). 

SAKURAJIMA VOLCANO AND 

KAGOSHIMA AIRPORT 

More than half of the incidents involving volcanic ash 

and aircraft in Japan were reported in the vicinity of Sakurajima Volcano, South Kyushu (table 1). The present eruptive 

activity at Sakurajima Volcano is from the summit crater and 

commenced in 1955. Explosive eruptions from the volcano 

are of the Vulcan ian type (Self and Walker, this volume) and 

Effect on aircraft 

Damage on windshield. 

Damage on windshield. 1 

Damage on windshield. 

Damage on windshield. 

Damage on windshield. 

Damage on windshield. 

Damage on windshield. 

Damage on windshield. 1 

Damage on windshield. 1 

Damage on windshield. 1 

Damage on windshield. 1 

Damage on windshield. 1 

Damage on windshield. 1 

Damage on windshield. 

Spark was found on windshield. 

Volcanic ash debris found on windshield. 

Abrasion on leading edge flap and stabilizer. 

Damage on windshield. 

Some damage on fuselage. 2 

Encountered during climb, no damage. 2 

Damage on windshield. 

are accompanied by explosion earthquakes and remarkable 

eruptive phenomena, such as strong air-shocks, lightning, 

and the ejection of volcanic bombs and large amounts of ash 

(fig. 3). The number of the explosive eruptions between 

1955 and 1991 was 6,360. On average, more than 100 explosions occurred each year, and volumes of ejected ash were 

estimated be 5-30 million metric tons annually (fig. 4 ). 

Kagoshima International Airport is one of the eight 

busiest airports in Japan, with more than 130 takeoffs and 

landings per day. Operations are mostly during day time. 

The airport is located 25 km north of Sakurajima Volcano 

(fig. 5). The volcanic ash clouds ejected by the explosive 

eruptions have frequently reached 3,000 m above the summit 

crater (1,118 m). The normal operating altitude of arriving 

aircraft in this area is between approximately 500 m above 

and 800 m below the summit. Thus, around the airport, several avoidance routes have been established to prevent aircraft from encountering ash clouds (fig. 6). The route 

selection is mainly made by dispatchers. 

The Kagoshima Local Meteorological Observatory 

(KLMO) of JMA, located in Kagoshima City approximately 

10 km west of the crater (fig. 5), uses special procedures in 

reporting explosions at Sakurajima Volcano to ATC and airlines with a view to minimizing the delay in reporting. These 

include the use of a video camera at KLMO that produces a 

real-time image of the volcano that is transmitted to ATC at 

Kagoshima International Airport. However, because of the 

proximity of the airport to the volcano, even less delay in 
AVIATION SAFETY MEASURES FOR ASH CLOUDS IN JAPAN AND SYSTEM FOR MONITORING ERUPTIONS 215 

AI REP 

Aircraft Air Traffic I SIGMET Control Center 

SIGMET AI REP 

SIGMET AI REP SEXX71 SIGMET 

AI REP 

ATC 

I 

Airline 

I unit (Agreement) 

SIGMET AI REP Japan Meteorological 

Agency 

(Headquarters) 

SIGMET Seismological AI REP and 

Volcanological Generai-ADESS 

Department 

Aviation AI REP vo Aviation Weather 

Weather SEXX71 sv Service Center SEXX72 VR Service Center SIGMET Section for Cooperation with 

Air Traffic Control Center 

SIGMET 

SEXX72 VO AI REP 

District SV SEXX71 

Meteorological VR SEXX72 

Observatory 

Locai-ADESS 

vo VO SIGMET 

sv SV SEXX71 

Local 

~ VR SEXX72 New Tokyo 

Meteorological Aviation Weather 

Observatory Service Center 

Figure 2. Flow of information concerning volcanic activity. 

ATC, air traffic control; VO, volcano observation; SV, seismic 

report; VR, volcano report, ADESS, automated data editing and 

switching system; SIGMET, information concerning en-route 

weather phenomena that may affect the safety of aircraft operation; 

AIREP, air report; SEXX71, header for message containing AIREP 

on volcanic activity; SEXX72, header for message containing volcanic ash information. 

notification of explosions was required for promoting safe 

operations in darkness or under reduced visibility. This is the 

reason Japan Airlines and Sakurajima Volcanological 

Observatory have joined together to develop new countermeasures at Kagoshima International Airport for volcanic 

eruptions. 

VOLCANO WATCHING SYSTEM 

The volcano watching system (VWS) developed jointly 

by JAL and SVO was designed to achieve the following 

objectives: 

1. To detect the explosive eruptions at Sakurajima Volcano without fail in all weather conditions during 

both day and night, and 

2. To immediately notify dispatchers at the airport when 

an explosive event is detected. 

Figure 3. Photograph of a typical explosive eruption at Sakurajima Volcano (13:42, May 17, 1976). 

Both of these objectives are essential to keep flight operations safe in the vicinity of active volcanoes. 

The fundamental function of the system is to distinguish those events that are related to explosive, ash-producing eruptions from several types of volcanic earthquakes, 

which are not necessarily related to ash-producing eruptions. 

Volcanic earthquakes and tremors originated at Sakurajima 

Volcano are classified into five categories (Ishihara, 1988). 

These are A-type earthquakes, B-type earthquakes 

(Minakami, 1974), explosion earthquakes, C-type tremors, 

and D'-type tremors. An A-type earthquake is similar to a 

tectonic earthquake and consists predominantly of high-frequency seismic waves (> 8 Hz). B-type earthquakes are 

dominated by lower frequency signals, generally less than 5 

Hz (McNutt, 1986). B-type earthquakes at Sakurajima Volcano are classified into BL and BH types, whose dominant 

frequencies are 1-3 Hz and 5-8 Hz, respectively (Iguchi, 

1989). Explosion earthquakes are accompanied by remarkable eruptive phenomena, such as strong air-shocks, ejection 

of volcanic bombs and large amounts of ash. C-type seismic 

activity is a kind of volcanic tremor composed of harmonic 

wave trains, and D'-type seismic activity is a non-harmonic 

tremor. 

Explosion earthquakes are accompanied by explosive 

eruptions, and the amplitudes of explosion earthquakes and 

their associated infrasonic waves are greater than those of 

other types of volcanic earthquakes. The maximum amplitudes of explosion earthquakes and air-shocks range from 

3x1o-3 to 3x1o-2 cm/s and from 0.1 to 5 mb, respectively 

(Iguchi and Ishihara, 1990). The reduced displacements 
216 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

600,---------------------------------------------------------------------------------~ 

(/) 

z 

0 

U5 

0>-

....J....J 

c......J 

X<( 

LU:::> 

u..z 

Oz 

ffi<C 

CII 

~ 

:::> 

z 

400 

200 

0 

1955 

1. 

2. 

1960 1965 1970 

EXPLANATION 

DEFINITION OF EXPLOSION BY SVO 

Maximum amplitude of explosion-quake~ 10 !l 

Amplitude of air-shock~ 0.1 mbars at the 

Harutayama Branch (2.7 kilometers 

northwest of the summit crater) 

-

1975 1980 1985 1990 

YEAR 

30 

u -(f) (f) 2 zz <Coo 

~::if- 20 

O::::!u 

>~a: 

u..zf- O_LU 10 (f) I'~ (/)(f)u.. 

<(<(0 

~ 0 

1980 1985 1990 

YEAR 

Figure 4. A, Annual numbers of explosive eruptions at Sakurajima Volcano between 1955 and 1991 (1991 represents data current as of 

June 1, 1991). B, The estimated amount of volcanic ash emitted from the summit crater of Sakurajima between 1978 and 1991 (1991 

represents data current as of May 1, 1991). Arrows indicate explosions accompanied by pyroclastic flows. SVO, Sakurajima Volcanological 

Observatory. 

KLM0 0 

Kagoshima 

International 

Airport 

Figure 5. Location map of Sakurajima Volcano and Kagoshima 

International Airport. SVO, Sakurajima Volcanological Observatory of Kyoto University; KLMO, Kagoshima Local Meteorological 

Observatory of Japan Meteorological Agency; JAL observation site, 

Japan Air Lines observatory. 

(McNutt, 1992) of explosion earthquakes are estimated to be 

50-500 cm2. BL-type and D'-type tremors are also associated with eruptive phenomena at the crater, and continuous 

emission of volcanic ash and intermittent ejection of volcanic bombs are frequently observed to accompany these 

earthquake types (Ishihara and Iguchi, 1990). The maximum 

amplitudes of earthquakes and air-shocks associated with 

BL-type and D'-type events are< 7x1o-3 crnls (reduced displacement < 60 cm2) and < 0.1 mb, respectively, and are 

smaller than those of explosive eruptions (Iguchi and Ishihara, 1990). On the other hand, A-type and BH-type earthquakes are not accompanied by eruptive activity, and no airshocks associated with them have been detected. 

The visual observation of eruptive phenomena at the 

summit is strongly affected by weather conditions. However, earthquakes and air-shocks are continuously monitored 

by instruments. SVO defines explosive eruptions by the 

maximum amplitudes of explosion earthquakes and airshocks. It is possible to distinguish an explosive eruption 

from the other types of volcanic events by the absolute 

amplitudes of earthquakes and air-shocks and by the spectra 

of the earthquakes. The system proposed in this paper monitors both earthquakes and air-shocks and judges whether or 

not explosive eruptions have occurred. 
AVIATION SAFETY MEASURES FOR ASH CLOUDS IN JAPAN AND SYSTEM FOR MONITORING ERUPTIONS 217 

27 

EXPLANATION 

Normal route 

Ash cloud avoidance route. Distance 

between points, in nautical miles, 

is shown 

from _ __. sue 

Figure 6. Normal and avoidance routes around Kagoshima Airport. A voidance routes have been established to prevent aircraft 

from encountering ash clouds. Open triangles, waypoints; open 

circles, towns; solid triangle, Sakurajima Volcano. 

HARDWARE 

The overall monitoring system is shown in figure 7 and 

comprises an observation site at Sakurajima, 4 km east of the 

summit crater (figs. 5 and 8), with data processing at the JAL 

office at Kagoshima International Airport. At the observation site, a three-component seismometer and an infrasonic 

microphone are installed. The seismometer comprises updown, north-south and east-west components and has a frequency range of 1-30Hz and a sensitivity of 2 V/cm/s. The 

microphone detects infrasonic waves in the range from 0.02 

to 100 Hz. Volcanic earthquakes and air-shocks generated 

by volcanic eruptions are observed by the seismometer and 

the infrasonic microphone, respectively. These signals are 

constantly transmitted to the airport by commercial telephone line. At the airport, these signals are transferred from 

the receiver of the telemetering system to a personal computer. The computer process the signals and issues alarms 

according to the seismic and eruptive activity. The total cost 

to install this system was approximately $400,000. Annual 

operating costs are $20,000. 

Company radio 

explosion 

earthquake 

Dispatcher 

Figure 7. Block diagram of the overall observation system 

developed by JAL (Japan Air Lines) and SVO (Sakurajima Volcanological Observatory). 

Figure 8. Photograph of Japan Air Lines observation site at 

Sakurajima Volcano. 

DATA PROCESSING 

The data processing flow chart is shown in figure 9. The 

computer monitors amplitudes of seismic and infrasonic 

waves by digitizing 40 samples per second. When the 
218 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Telemeter output -- -

Simulation of 

diffusion of 

ash cloud 

ERUPTION 

Displayed on CRT 

with sound 

High frequency 

(>5Hz) 

Figure 9. Data processing flow chart to detect volcanic explosions at Sakurajima Volcano. CRT, cathode ray tube. 

amplitude of the seismic wave exceeds the preestablished 

threshold level (0.1x1o-3 cm/s ), the computer judges that a 

seismic event has occurred. According to the levels of the 

infrasonic waves associated with the event and the spectra of 

the seismic wave, the computer categorizes the events into 

"explosive eruptions," "eruptions," and "non-eruptions." 

"Eruptions" correspond to the generation of BL-type 

earthquakes or D' -type tremors and are accompanied with 

weak infrasonic waves and slow, sometimes continuous, 

low-level ejection of volcanic ash. "Non-eruptions" mean 

no remarkable change of eruptive activity above the crater, 

and they correspond to generation of A-type or BH-type 

earthquakes at the volcano or to tectonic earthquakes outside 

the area of Sakurajima Volcano. 

After detection of events, the computer analyzes the 

spectra of the waveforms. When the dominant frequency is 

lower than 2 Hz and the level of infrasonic wave is beyond 

the level (0.13 mb ), the computer judges that the seismic 

event was associated with an "explosive eruption" and issues 

a "warning", which appears on the computer monitor with 

blinking red color and alarm sounds. If the dominant frequency is between 2 Hz and 5 Hz, the computer judges that 

an "eruption" has occurred and issues an alarm "caution" 

with blinking yellow color. When the dominant frequency 

exceeds 5Hz, the computer interprets that A-type or BH-type 

earthquakes or tectonic earthquakes have occurred-these 

are accompanied by no remarkable eruptive phenomena. 

DISPATCHER'S ACTION 

The dispatcher at the JAL office at Kagoshima Airport 

passes the eruption information to pilots as soon as the system issues a "warning" or a "caution." Based on both the 

upper-level wind and visibility, which have a critical affect 

on the dispatcher's recommendations, the dispatcher recommends one of the following advisories to aircraft in bound to 

Kagoshima Airport: 

1. Divert to alternate airport, 

2. Hold over suitable holding position and wait for further information, 

3. Select contingency or alternate arrival route and continue approach, or 

4. Select normal arrival route and continue approach. 

RESULTS OF OPERATION 

The system has been deployed at the JAL office at 

Kagoshima Airport since March 1991. A set of records of an 

explosion earthquake and an air-shock observed by the system is shown in figure 10. Note that the explosion earthquake 

has an emergent onset. The record of the infrasonic microphone shows that the air-shock arrived 10.4 s after the onset 

of the explosion earthquake. Ground motions excited by the 

air-shock were recorded in the seismograms, especially in 

the east-west component. 

Here, we evaluate the correspondence of the judgment 

by the VWS system to actual explosive eruptions using the 

classification criteria by KLMO. As mentioned earlier, the 

Sakurajima Volcanological Observatory has different criteria from JMA-KLMO for recognizing explosive eruptions. 

SVO criteria are based on the volcanic earthquakes and 

infrasonic waves that can be continuously measured and 

does not include visual observation. The criteria of 

JMA-KLMO includes visual observation, as well as use of 

seismic recordings to distinguish explosive eruptions. For 

.. N'-> 

E- W ~ 

., 2;; 

NQ 

~ 

2;; 

E 

0 N-S 

~ ·;;; 

en 

" NQ 

U-D ~ X 

"' ;:! 

0 5 10 

DATE 1992/6/26 TIME13: 10: 54 

Figure 10. Recording of an explosion earthquake and an airshock obtained by the system. Upper three traces represent eastwest, north-south, and up-down components of seismograms, 

respectively. The bottom trace shows the air-shock obtained by the 

infrasonic microphone. 
AVIATION SAFETY MEASURES FOR ASH CLOUDS IN JAPAN AND SYSTEM FOR MONITORING ERUPTIONS 219 

the purpose of detecting an ash-producing explosive eruption, the JMA-KLMO criteria are used here. There is generally excellent correspondence(± 10 percent) in the numbers 

of explosion earthquakes determined by SVO and KLMO 

criteria. 

From April 1 to May 31, 1991, 59 explosive eruptions 

occurred. The system was operating at the time of the eruptions in 56 cases but not for the other 3, due to unscheduled 

outage of the system for maintenance. Of the 56 cases, the 

JAL system judged 49 cases as "explosive eruptions" and 7 

as "eruptions." The agreement ratio of the system with 

observations by JMA for this period is 88 percent. 

The seven cases, which were categorized as different 

types of activity by the respective definitions of the JMA and 

JAL systems, were recorded with a small air-shock, at or less 

than 0.13 mb, on both JMA and JAL equipment. On the 

other hand, the JAL system recorded 15 more cases of 

"explosive eruptions" than JMA. This is again due to the 

rather small explosive eruptions that are just above the 

threshold level that is considered to be acceptable for these 

types of warning systems. 

The small problems we are aware of on this system are 

as follows: 

1. During scheduled maintenance (twice a year) of this 

system, we do not obtain data for a couple of hours, 

2. Gusty winds associated with typhoons cause nuisance 

warnings or false alarms, and 

3. Non-explosive eruptions with small magnitudes are 

not always detected. 

CONCLUSIONS 

The results of field testing of this system in 1991 demonstrate that this system has the capability of (1) detecting 

explosive eruptions of Sakurajima Volcano in all weather 

conditions 24 hours a day, and (2) alerting the airline dispatcher, without time delay. 

The operation of the volcano watching system suggests 

that this is an effective countermeasure to help to reduce 

risks from volcanic ash in areas near airports close to active 

volcanoes. In the future, JAL hopes to include a program to 

calculate diffusion of volcanic ash based on meteorological 

data. The program for the simulation will be designed to 

automatically start when explosive eruptions are detected 

and followed by "caution" or "warning" signals. 

ACKNOWLEDGMENTS 

The authors would like to thank Masato Iguchi and the 

other staff of Sakurajima Volcanological Observatory, 

Kyoto University, who contributed a great deal in developing the system and in preparing this paper. Thomas Casadevall and Stephen McNutt provided helpful reviews. Edward 

Nojiri helped us to prepare the manuscript. 

REFERENCES CITED 

Iguchi, M., 1989, Distribution of the initial motions of volcanic 

microearthquakes (B-type) at Sakurajima Volcano [in Japanese]: Kyoto University, Annual Report, Disaster Prevention 

Research Institute, v. 32, p. 13-22. 

Iguchi, M., and Ishihara, K., 1990, Comparison of earthquakes and 

air-shocks accompanied with explosive eruptions at Sakurajima and Suwanosejima Volcano [in Japanese]: Kyoto University, Annual Report, Disaster Prevention Research Institute, v. 

33B-1, p. 1-12. 

Ishihara, K., 1988, Geophysics, in A Guide Book for Sakurajima 

Volcano: Kagoshima International Conference on Volcanoes, 

p. 29-42. 

Ishihara, K., and Iguchi, M., 1990, The relationship between 

microearthquake swarms and volcanic activity at Sakurajima 

[in Japanese]: Kyoto University, Annuals, Disaster Prevention 

Research Institute, v. 32B-1, p. 1-11. 

McNutt, S.R., 1986, Observations and analysis of B-type earthquakes, explosions, and volcanic tremor at Pavlof Volcano, 

Alaska: Bulletin of the Seismological Society of America, v. 

76, p. 153-175. 

--1992, Volcanic tremor, in Nierenberg, W.A., ed., Encyclopedia of Earth System Science, Academic Press, v. 4, 

p. 417-425. 

Minakami, T., 1974, Seismology and volcanoes in Japan, in 

Civetta, L., Gasparini, P., Luongo, G., and Rapolla, A., eds., 

Developments in Solid Earth Geophysics, Physical 

Volcanology: New York, Elsevier, p. 1-27. 

Y oshitama, T., 1984, Improvement of the ash avoidance procedures 

at Sakurajima Volcano [in Japanese]: Japan Meteorological 

Agency, Aviation Weather Note, v. 29, p. 46-53. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC ASH WARNINGS IN THE 

AUSTRALIAN REGION 

By Rodney J. Potts and Frank Whitby 

ABSTRACT 

As part of its routine operations, the Australian Bureau 

of Meteorology provides warnings to the aviation industry 

for volcanic ash clouds over the Australian region and the 

region to the near north. This service is provided in accordance with international procedures that have been established in recent years. The warnings define the area of the 

ash cloud, the cloud top, and the forecast movement of the 

cloud-these warnings are based on notification of a 

volcanic eruption, satellite imagery, and upper-level wind 

analyses. The high frequency of thunderstorms in the equatorial regions north of Australia often makes identification of 

volcanic ash clouds difficult. Multispectral infrared data in 

the atmospheric window region, available from National 

Oceanic and Atmospheric Administration polar-orbiting 

satellites, have been beneficial for discriminating ash clouds 

from water/ice clouds. The Bureau of Meteorology is 

currently installing an advanced very high resolution radiometer antenna in Darwin, which will give coverage over the 

volcanically active Indonesian region; the operational utility 

of A VHRR data for volcanic ash detection will be evaluated. 

INTRODUCTION 

As part of its routine operations, the Australian Bureau 

of Meteorology (BOM) provides warnings to the aviation 

industry for volcanic ash clouds over the Australian region 

and the region to the near north. This service has been an 

important component of Bureau operations since its introduction in 1982 when two Boeing 747 aircraft encountered 

volcanic ash from Galunggung Volcano in Indonesia (Hanstrum and Watson, 1983). Both aircraft suffered engine 

failure and severe damage to wings and fuselage and were 

forced to make emergency landings at Jakarta. 

Although there are no active volcanoes within Australia, there are many throughout the surrounding islands to the 

north (fig. 1). Most aircraft flights into and out of Australia 

overfly these areas, often at nighttime, and the likelihood of 

an encounter with a volcanic ash cloud presents a serious, 

albeit relatively infrequent, hazard for aircraft operations 

(Johnson and Casadevall, this volume). The greatest threat to 

aircraft arises from Plinian eruptions, which eject large 

amounts of finely divided rock particles (known as volcanic 

ash) and gases high into the atmosphere (Heiken, this 

volume; Self and Walker, this volume). The evolution of the 

ash cloud following a Plinian eruption can be divided into 

two stages: the eruption or nascent cloud stage immediately 

following the eruption and the dispersed cloud stage (Prata, 

1989a; Sparks and others, this volume). During the latter 

stage, the ash cloud will be dispersed by prevailing winds 

and rock particles will settle gradually to the ground. If the 

ash cloud extends over a significant depth, the cloud at 

different levels may be spread in different directions. 

Although the ash may disperse and settle, a hazard for aircraft may exist for some time from sulfurous clouds, which 

can be carried great distances by the prevailing wind. Eventually, the ash and gases will be dispersed and diluted until 

there is no longer a significant hazard to aircraft. 

Plinian eruptions can be observed on visible and infrared satellite imagery, and it is possible to define the 

horizontal and vertical extent of the resultant ash cloud 

(Sawada, this volume; Schneider and Rose, this volume). 

With consideration of the upper winds, it is further possible 

to determine the direction in which the cloud will be 

dispersed. Hanstrum and Watson (1983), Matson (1984), 

Prata and others (1985), and Malingreau and Kaswanda 

(1986) all describe cases where satellite imagery and upperlevel wind data have been used for estimating the location 

and movement of volcanic ash clouds. The techniques 

described in these reports are used in the operational warning 

service currently provided by BOM. This paper describes 

this warning service and discusses the operational problems 

associated with the service, together with proposals for the 

future. 

221 
222 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 1. Active volcanoes in the Indonesia-Papua New Guinea region to the north of Australia. Solid triangles represent volcanoes with 

historical eruptive activity. 

THE VOLCANIC ASH CLOUD 

WARNING SYSTEM 

Meteorological services for aviation are provided under 

guidelines established in joint consultations between the 

World Meteorological Organization (WMO) and the International Civil Aviation Organization (ICAO) (Fox, this 

volume). In accordance with international agreement, meteorological forecast and warning services are provided by the 

meteorological authority within the sovereign state responsible for the flight-information region (FIR). From time to 

time, standards and recommended practices for the provision 

of meteorological services for aviation are reviewed both at 

regional and international levels. 

Warnings for hazardous weather or significant meteorological phenomena are generally provided in the form of a 

significant meteorological advisory (SIGMET) issued by the 

meteorological authority responsible for the FIR. The SIGMET is valid for a period of 4 or 6 hours and includes information on the nature of the hazardous weather, the location 

or area affected, and the forecast trend. Such warnings are 

passed rapidly to air traffic control authorities, aircraft, and 

meteorological offices in adjacent areas. Weather phenomena for which a SIGMET will be issued include active thunderstorms, tropical cyclones, severe turbulence, severe icing, 

severe mountain waves, and volcanic ash clouds. Following 

the aircraft incidents over Indonesia in 1982, volcanic ash 

clouds were included as a phenomena for which a SIGMET 

is to be issued. 

Within the Australian, region the responsible Bureau of 

Meteorology (BOM) Regional Forecasting Center (RFC) 

will issue a SIGMET if a volcanic ash cloud enters Australian airspace. In addition to the SIGMET warning service, 

the Bureau of Meteorology provides a volcanic ash cloud 

advisory service for the Australian region and areas to the 

near north. This service was introduced in 1982 in cooperation with Australia's Civil Aviation Authority and representatives from the aviation industry (Johnson and Casadevall, 

this volume). Because the Bureau has no capability to forecast and identify volcanic eruptions, the objective of the 

advisory service is to confirm the presence of an ash cloud 

and to monitor its movement after a report of an eruption. 

Such reports of an eruption or the presence of an ash cloud 

come from nearby ground-based observers, aircraft reports, 

and local aviation authorities. Satellite imagery and upperlevel wind analyses and forecasts are examined, and the 

advisory message is issued by the National Meteorological 

Centre (NMC). 

In an effort to improve the volcanic ash cloud warning 

service in the Australian-Indonesian region, the Volcanological/ Airspace Liaison Committee-Australia/Indonesia Australian working group (VULCAN-AUS) was established in 

1985 (Johnson and Casadevall, this volume). On the Australian side, the committee comprises representatives from the 

Bureau of Meteorology, Civil Aviation Authority, Commonwealth Scientific and Industrial Research Organization 

(CSIRO), Australian Geological Survey Organization 

(AGSO) (formerly the Bureau of Mineral Resources), and 

the airlines. The objectives of this group are to develop and 
VOLCANIC ASH WARNINGS IN THE AUSTRALIAN REGION 223 

improve procedures for the avoidance of volcanic ash 

clouds, to liaise with scientific groups, to promote research 

on relevant issues, and to liaise with local and international 

organizations and with regional governments in order to 

increase awareness of the dangers to aircraft from volcanic 

eruptions. The group has been instrumental in the 

development of better techniques for identifying volcanic 

ash clouds, improved warning procedures, and improved 

intragovernmental relations between Australia and Indonesia on the problem. 

OPERATIONAL PROCEDURES 

A SIGMET for volcanic ash, or a volcanic ash cloud 

advisory that is issued by the Bureau will describe, if possible, the location, height, and forecast movement of the ash 

cloud and will be based on the eruption notification, hourly 

Japanese geostationary meteorological satellite (GMS) 

images and upper-wind analyses. In the Bureau of Meteorology, the amount of data and the speed with which these data 

can be analyzed and warnings subsequently issued have been 

greatly enhanced with the introduction of the Australian 

region man-computer interactive data access system 

(MciDAS) in forecast offices (LeMarshall and others, 1987). 

This system enables the rapid display and analysis of satellite imagery, numerical-model products, and observational 

data. 

The potential for providing an efficient and effective 

service for the aviation industry can be illustrated by briefly 

examining events following the recent eruption of Mt. 

Pinatubo, Philippines, which occurred at 00:51 UTC 

Figure 2. Geostationary meteorological satellite images for 12 

June 1991 showing Mt. Pinatubo eruption cloud. Latitude and 

longitude grid at 5° intervals. Location of the ash cloud indicated 

by arrows. A, 01:30 UTC; B, 04:30 UTC; C, 07:30 UTC. 

(Coordinated Universal Time), 12 June 1991 (Potts, 1993). 

On subsequent days, there were further eruptions leading up 

to the climactic events of 15 June; however, these are not 

discussed here. The Bureau of Meteorology received notification of the 00:51 UTC eruption from an airline company, 

and immediately began issuing volcanic ash cloud advisory 

messages at regular intervals for the ash cloud. In the ensuing 

days, notification of further eruptions were received 

promptly from aviation authorities in the Philippines, and ash 

cloud advisory messages were issued that defined, where 

possible, the area of the ash cloud and its movement. The 

advisories were well received by the aviation industry. 

The sky was clear over Luzon on 12 June 1991, and the 

00:51 UTC eruption plume was clearly evident on GMS 

satellite images. Figure 2 shows a series of GMS images of 

the eruption from 01:30 UTC to 07:30 UTC. There were no 

further major ash emissions immediately following the 00:51 

UTC eruption, and the ash cloud drifted to the southwest and 
224 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

gradually dispersed, becoming elongated in a northeastsouthwest direction as it moved. After 07:30 UTC, the ash 

cloud continued to move to the southwest, over the South 

China Sea and Indochina, and was visible on imagery until 

early the following day. 

The brightness temperature of the cloud tops can be 

determined from infrared satellite images. Assuming the ash 

cloud radiates as a black body and that the temperature of 

the cloud quickly reaches equilibrium with the environment, 

the cloud height can be estimated. From the satellite-derived 

brightness temperature and the 00:01 UTC vertical-temperature sounding from Clark Air Base, 20 km to the east, the 

cloud top in figure 2 is between 130--100 hPa (15-16 km). 

Upper-wind analysis enable the likely trajectory of the cloud 

to be determined. For the period shown, the highest levels of 

the ash cloud moved to the southwest at approximately 15 

m/s, consistent with the 00:01 UTC upper-wind analysis for 

100 hPa (16 km) (fig. 3A). Figure 2C shows that the ash 

cloud has become elongated in a northeast-southwest direction. The ash cloud in the northeast has a top around 500 hPa 

(approximately 5.6 km) and moved west at approximately 6 

m/s, consistent with the 00:01 UTC upper-wind analysis for 

500 hPa (fig. 3B). 

Although this example demonstrates that an effective 

warning service can be provided for volcanic ash clouds, 

there are significant technical difficulties that must be 

addressed if the service is to become more effective. The 

BOM cannot provide warnings on the likelihood of a volcano erupting. It can only detect and monitor ash clouds 

after emission. It is therefore essential that there is early 

notification of any initial or subsequent volcanic eruption by 

responsible authorities within the country where the eruption 

has occurred; it is also essential that reports from aircraft 

concerning the presence of volcanic ash clouds be passed to 

aviation authorities. Such warnings or reports must be distributed quickly on the international aviation and meteorological communications system. 

Over the tropical regions north of Australia, there is a 

high frequency of thunderstorms, which can develop very 

rapidly to great heights and produce extensive areas of cloud. 

On present GMS satellite imagery, it is often not possible to 

discriminate volcanic ash clouds from water/ice clouds 

(Sawada, this volume). In the 6-year period, 1985-90, a total 

of 81 volcanic ash cloud advisories were issued by the NMC, 

and for 80 percent of these, it was not possible to identify a 

volcanic ash cloud with any confidence due to the presence 

of water/ice clouds. Finally, the duration for which an ash 

cloud remains a hazard to aircraft is not known, and further 

research is required on this subject. 

THE UTILIZATION OF NOAA A VHRR 

SATELLITE DATA 

National Oceanic and Atmospheric Administration 

(NOAA) advanced very high resolution radiometer 

(A VHRR) satellite data offer some promise for the discrimination of volcanic ash clouds from water/ice clouds based 

on differences in the brightness temperature for a cloud measured at 10.8 Jlm (channel4) and at 11.9 Jlm (channelS). The 

difference results from variations in the wavelength dependence of emissivity for water/ice and the pyroclastic material 

found in volcanic ash clouds (Prata, 1989a, 1989b; Barton 

and Prata, this volume; Honey, this volume; Prata and Barton, this volume). 

From Prata (1989b), the infrared radiance, R;, measured 

in a narrow band centered on wavelength 'A;, for a uniform 

cloud layer overlying a non-reflecting surface, assuming no 

scattering and no angular dependence, is approximated by: 

(1) 

where 

1-£; and £; are the transmissivity and emissivity for the 

cloud at wavelength 'A;, 

B; Cn is the Planck function, 

Tc is the cloud-top temperature, and 

1's is the temperature of the surface. 

The brightness temperature of the cloud is then calculated 

from the radiance assuming black body radiation, (i.e., £; = 

1.0). The emissivity, £;, of a cloud is dependent on the microphysical and chemical properties of the cloud, its optical 

depth, and the wavelength at which £; is measured. If the 

cloud is optically thick (E; = 1.0), the brightness temperature 

provides a good estimate of the cloud-top temperature, 

whereas, for an optically thin cloud (E; < 1) overlying a 

relatively warm surface, the brightness temperature will be 

warmer than the true cloud-top temperature. Also, for a cloud 

of given optical depth, if£ ( 10.8 Jlm) < £ ( 11.9 Jlm), it follows 

from equation 1 that brightness temperature T(10.8 Jlm) > 

T(11.9 Jlm). Conversely, if£ (10.8 Jlm) > £ (11.9 Jlm), then 

T(10.8 Jlm) < T(11.9 Jlm). 

In the atmospheric window region, the emissivity for 

water/ice clouds increases with wavelength, and, consequently, the difference, !J.T, in the brightness temperature 

between channel 4 (10.8 Jlm) and channel 5 (11.9 Jlm), 

where AT= T4-T5, is almost always positive. The temperature difference, !l.T, for ash clouds is dependent on the cloud 

constituents, the particle-size distribution of those constituents, and the cloud temperature. Silicates and sulfur dioxide 

are significant constituents of an ash cloud, and, for these, 

emissivity decreases with wavelength. Hence, in many 
~ ~ 

~ 

~ z 8 0 II') - "' ~ "' + 0 " "' ~ 

~ 

z ~ ::5 8 ..:I ....... 

~ ~ f--4 ,....; (/l "" "" 0'1 ~ ~ 0 0'1 u ....... < ~ Q) 4) 

llJ :Z: E z :> 

::r:: 0 = 0 § ~ f--4 

~ J , I= E ~ z <t: ·~ - cJ 

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~~ 8 

~ (5tG ~\' \ "" ..- "' 8 

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u 

r ~. ~ ..:I t r t !' 0 ~ > 11 11 ')\ "' 41 ... ~ 

l!. 

4) 

0. 

0. 

~ 

tit 1\"t t t t t t r ~ 1 ~ \ '\ " f ~ .. rx rx ~ ~ .. ... l ... c:Q i 

ri; 
226 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

circumstances relevant to the volcanic ash cloud detection 

problem, the difference T4-T5 will be negative, enabling the 

discrimination of ash clouds from water/ice clouds (Hanstrum and Watson, 1983; Prata, 1989a, 1989b). Based on the 

same principles, Holasek and Rose ( 1991) used a ratio of raw 

A VHRR counts for channel 4 and channel 5, rather than a 

difference, to discriminate volcanic ash clouds from water/ 

ice clouds for the 1986 eruption of Augustine Volcano, 

Alaska. 

The BOM has recently installed a satellite receiving 

antenna at Darwin, in northern Australia, which enables the 

collection of real-time AVHRR data over the Indonesian 

region. The area of coverage provided by the Darwin 

antenna is illustrated in figure 4. In the equatorial regions, 

the ground track of the NOAA polar-orbiting satellites and 

the scan width of the A VHRR sensor is such that, with two 

satellites, there are only four scans per day at intervals of 

approximately 6 hours for any given location. Although 

there are obvious limitations because of the time between 

scans, it is anticipated the A VHRR data will be a valuable 

complement for hourly GMS imagery. The operational utility of these data for identifying ash clouds will be evaluated 

in the future. 

CONCLUSIONS 

International standards and procedures for the provision 

of warnings for volcanic ash clouds have been established 

12 JUN 91163 NOAA-11 NOAA-10 

Figure 4. Coverage provided by Darwin NOAA satellite-datareceiving antenna. Slanted straight lines indicate satellite flight 

path. Satellite position indicated by time (UTC) for 12 June 1991. 
VOLCANIC ASH WARNINGS IN THE AUSTRALIAN REGION 227 

(Fox, this volume), and, in accordance with these procedures, 

the Bureau of Meteorology provides a significant meteorological advisory (SIGMET) service for ash clouds that enter 

Australian airspace. In addition, the BOM provides a volcanic ash cloud advisory service for areas to the near north of 

Australia. These warnings describe the area of the ash cloud, 

the height, and the forecast movement and are based on eruption advice, hourly GMS images, and upper-level wind analyses. The possibility of providing an effective service for 

aviation is illustrated with a brief study of the eruption of Mt. 

Pinatubo at 00:51 UTC, 12 June 1991. 

There are significant technical difficulties associated 

with the provision of warnings for volcanic ash clouds. The 

BOM can only detect and monitor ash clouds after eruption 

and confirmation of a volcanic eruption. It is therefore 

essential that there is early notification of any initial or subsequent volcanic eruption. Such warnings must be distributed quickly to the international aviation and 

meteorological communications system. Using present 

GMS satellite imagery, it is frequently not possible to discriminate volcanic ash clouds from water/ice clouds. 

A VHRR multispectral infrared satellite data does offer considerable promise in this area. The BOM has recently 

installed, in Darwin, a satellite receiving antenna that 

enables receipt of A VHRR data. These data are now available to operational meteorologists responsible for preparing 

advisories for volcanic ash clouds, and the benefits of the 

data will be evaluated in the future. 

REFERENCES CITED 

Hanstrum, B.N., and Watson, A.S., 1983, A case study of two 

eruptions of Mt. Galunggung and an investigation of volcanic 

eruption cloud characteristics using remote sensing techniques: 

Australian Meteorological Magazine, v. 31, p. 171-177. 

Holasek, R.E., and Rose, W.I., 1991, Anatomy of 1986 Augustine 

Volcano eruptions as recorded by multispectral image 

processing of digital AVHRR weather satellite data: Bulletin 

of Volcanology, v. 53, p. 420-435. 

LeMarshall, J.F., Stirling, L.J., Davidson, R.F., and Hasset, M.J., 

1987, The Australian region MciDAS: Australian Meteorological Magazine, v. 35, p. 55--64. 

Malingreau, J.P., and Kaswanda, 0., 1986, Monitoring volcanic 

eruptions in Indonesia using weather satellite data: The Colo 

eruption of July 28, 1983: Journal of Volcanology and Geothermal Research, v. 27, p. 179-194. 

Matson, M., 1984, The 1982 El Chich6n Volcano eruptions-A 

satellite perspective: Journal of Volcanology and Geothermal 

Research, v. 23, p. 1-10. 

Potts, R.J., 1993, Satellite observations ofMt. Pinatubo ash clouds: 

Australian Meteorological Magazine, v. 42, p. 59--68. 

Prata, A.J., 1989a, Observations of volcanic ash clouds in the 

10-12-J.tm window using AVHRR/2 data: International Journal of Remote Sensing, v. 10, p. 751-761. 

---1989b, Infrared radiative transfer calculations for volcanic 

ash clouds: Geophysical Research Letters, v. 16, p. 1293-1296. 

Prata, A.J., Wells, J.B., and Ivanac, M.W., 1985, A "satellite's eyeview" of volcanoes on the Lesser Sunda Islands: Weather, 

v. 40, p. 245-250. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

ASH CLOUD AVIATION ADVISORIES 

By Thomas J. Sullivan and James S. Ellis 

ABSTRACT 

During the recent eruptions (12-22 June 1991) of the 

Mt. Pinatubo, Philippines, the U.S. Air Force Global 

Weather Central (AFGWC) requested assistance of the U.S. 

Department of Energy's atmospheric release advisory capability (ARAC) in creating volcanic-ash-cloud aviation advisories for the region of the Philippine Islands. Through 

application of its three-dimensional material transport and 

diffusion models using AFGWC meteorological analysis 

and forecast wind fields, ARAC developed extensive daily 

analysis and forecast advisories of ash-cloud position 

extending 48 hours into the future (in 12-hour increments) 

for a period of 5 days. The advisories consisted of "relative" 

ash-cloud concentrations in ten layers (surface to 5,000 ft, 

5,000 to 10,000 ft, and every 10,000 ft up to 90,000 ft). The 

ash was represented as a log-normal size distribution of 

10-200-Jlm-diameter solid particles. Size-dependent "ashfall" was simulated over time as the eruption clouds dispersed. These products were distributed to the AFGWC 

(Offut Air Force Base, Nebraska) and Headquarters First 

Weather Wing (Hickam Air Force Base, Hawaii) for further 

distribution to U.S. Air Force weather units throughout the 

Pacific region, who were supporting the evacuation of U.S. 

personnel from the Philippines. 

For the cataclysmic Pinatubo eruption of 15-16 June 

1991, the complex three-dimensional atmospheric structure 

of the region produced dramatically divergent ash-cloud 

patterns. The large eruptions (> 23,000-33,000 ft high) produced ash-plume clouds with strong westward transport over 

the South China Sea, Southeast Asia, India, and beyond. The 

low-level eruptions ( < 23,000-33,000 ft) and quasi-steadystate venting produced a plume that generally dispersed to 

the north and east throughout the support period. 

INTRODUCTION 

The atmospheric release advisory capability (ARAC) is 

a real-time emergency response and preparedness service 

developed and operating at the Lawrence Livermore 

National Laboratory (LLNL) in Livermore, Calif., for the 

past 17 years. ARAC is a national resource with a suite of 

dispersion models to simulate the consequences of accidental releases of material into the atmosphere on local to global 

scales. Funded by the Departments of Energy (DOE) and 

Defense (DOD), the primary role of ARAC has been to provide calculations for radiological releases. Any U.S. Federal 

agency can request the services of ARAC through DOE as 

delineated in the Federal radiological emergency response 

plan. 

This paper describes how ARAC has responded to other 

than radioactive material releases, summarizes its modeling 

system, and focuses on its response to the June 1991 eruption 

of Mt. Pinatubo, Luzon, the Philippines, as requested by the 

U.S. Air Force. 

BACKGROUND 

Since the beginning of operation in 1974, ARAC has 

been involved in over 600 responses, primarily exercises 

with its supported agencies. In accordance with its charter, 

ARAC has been used for major domestic radiological events 

and some international events where the U.S. Government 

had interests. In addition, as table 1 indicates, ARAC has 

also been used for non-radiological releases within the 

United States. In fact, requests for assistance involving nonradiological releases have equaled those involving radioactive releases. 

The current ARAC system has evolved according to the 

requirements and expectations of its supported agencies as 

well as its experience with responses (Sullivan, 1988). For 

example, a 1976 North Carolina train accident revealed that 

real-time meteorological data automatically formatted for 

use in dispersion models was essential to a rapid response. In 

1978, the unique request by DOE to estimate the atmospheric consequences of the reentry bum-up of the Russian 

nuclear-powered COSMOS 954 satellite prompted th 

ARAC team to develop a high-altitude particle-fall model 

As a result, ARAC was prepared for the subsequen 

COSMOS 1402 reentry in 1981. ARAC's largely manu 

response to the 1979 Three Mile Island accident and th 

1980 Titan II missile accident showed the need for on-lin 

U.S. topography and geography databases. The 1986 Cher 

nobyl accident in the former Soviet Union propelled ARA 

229 
230 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Notable ARAC responses. 

[ARAC, atmospheric release advisory capability] 

Year Location Source Release 

1976 North Carolina Train accident Uranimn hexafluoride1 

1978 Northern Canada COSMOS 954 reentry Fission products 

1979 Three Mile Island Nuclear power plant Mixed fission products 

Harrisburg, Pa. 

1980 Damascus, Ark. Titan ll missile Missile fuel 1 

1981 Indian Ocean COSMOS 1402 reentry Fission products 

1982 South Carolina Savannah River Plant Hydrogen sulfide leak1 

1986 Gore, Okla. Sequoyah Fuels Plant Uranimn hexafluoride1 

1986 Chernobyl, USSR Nuclear power plant Mixed fission products 

1988 Miamisburg, Ohio Mount Plant Tritimn gas release 

1989 Amarillo, Tex. Pantex Plant Tritimn gas release 

1991 Persian Gulf Nuclear facilities Mixed fission products 

Kuwait oil fires Srnoke1 

1991 Philippines Mt. Pinatubo Volcanic ash 1 

1991 Northern California Railroad car spill Toxic gas products1 

1992 Sosnovy Bor, Russia Nuclear power plant Radioactive gas 

1 Release involved toxic chemicals. 

to implement continental-to-hemispheric scale models supported by worldwide meteorological, terrain, and mapping 

data. 

Each response has resulted in expanded capabilities. 

Consequently, for example, ARAC, with some adaptation to 

a new AFGWC wind-model data source, was ready with the 

necessary models and databases to simulate the daily 

regional-scale smoke and soot concentrations from the 

Kuwaiti oil fires in the Persian Gulf region from May to 

October 1991 (Ellis and others, 1992). 

ARACSYSTEM 

The original ARAC concept, prototype development, 

and initial operations from 1974 to 1982 were supported by 

DOE. From 1983 to 1986, the system was redesigned, and a 

high level of automation was implemented to support up to 

100 facilities within the DOE-DOD nuclear community. 

Figure 1 depicts the automated flow of information during an 

ARAC emergency response with the current system. This 

simplified diagram represents only the top-level system 

functions of the ARAC emergency response operating system (AEROS). AEROS automatically assembles necessary 

information for the model-run stream once the minimum 

accident data have been entered using the "problem questionnaire." The questionnaire may either be completed on a 

computer system at one of the remote support facilities or 

manually entered at the ARAC center, based on information 

gathered. 

A meteorological data interpolation code (MEDIC) initializes winds in the three-dimensional volume to be modeled. Relevant topography is applied at the lower boundary, 

then the calculus-of-variation code known as MATHEW 

(Sherman, 1978) imposes mass consistency in order to provide non-divergent flow fields for the dispersion model. The 

atmospheric diffusion particle-in-cell (ADPIC) model of 

Lange (1978) is a Lagrangian particle code that provides the 

dispersion physics for a wide range of substances, e.g., 

gases, solid particles, radioactive material, and non-radioactive material (Foster and Dickerson, 1990). 

Typical model results include plots of deposition of 

material on the ground and instantaneous and time-integrated doses or air concentrations of particles at selected levels above the ground. Species or sources may be combined 

as required and contoured according to specified isopleth 

values. A legend is shown on each plot that describes the 

release, species involved, source type, units, and valid time 

for the contours. 

After a quality assurance review by an assessment 

meteorologist, the plots may be transmitted to a supported 

site computer by modem or faxed to the emergency response 

manager. The time to create and deliver plots to a supported 

site computer can be as little as 15 to 30 minutes after receipt 

of incident information. For non-radiological incidents, the 

response time depends on the complexity of the source term, 

the availability of meteorological data, and the preparation 

of unique model-input parameters (Sullivan, 1991; Walker, 

1989). 

Typically, ARAC response time is equally split 

between computer or voice communications with the site, 
ASH CLOUD AVIATION ADVISORIES 231 

Meteorological 

towers 

(at remote site) 

Remote 

terminal 

Telecopier 

............ 

=~ Page ARAC personnel 

/ 

Source and 

c~~rp~gfe~:ri~ .... 

00 

Model 

parameter 

database 

Topography 

database 

Dose 

database 

Geography 

database 

Figure 1. Schematic flow diagram indicating the major components of the ARAC (atmospheric release advisory capability) 

emergency response operating system. 

automated or manual model-input preparation, model execution, and human interaction with the system. ARAC currently uses Digital Equipment Corporation (DEC) VAX 

8550 computers to run the models and micro-VAX' s to communicate with DEC PC350/380 support facility site computers at 1,200 baud. In 1992-93, ARAC plans to upgrade the 

VAX' s with faster computers and to begin replacing the 

facility computers with Unix-based workstations communicating with ARAC at 9,600 baud. 

MODEL DATA REQUIREMENTS 

To satisfy the request for the Pinatubo ash-cloud-advisory forecasts, ARAC required physical information about 

the events (source terms to the model), such as location, 

times and durations of eruptions, height, width, and diameter 

of the eruption cloud, and ash size and density properties. 

The U.S. Air Force provided the majority of this eventrelated information. The ash-particle information was 

gleaned from scientific reports about eruptions of El 

Chich6n Volcano, Mexico, in 1982, and Mount St. Helens in 

1980. 

Initially, for the Pinatubo response, ARAC's "hemispheric" models, developed in response to the Chernobyl 

accident, were used because twice daily northern hemisphere 

wind-field analyses from AFGWC are routinely received 

and archived at ARAC. With AFGWC priority assistance, 

ARAC began receiving forecast-wind data for 15 standard 

pressure levels of the atmosphere (fig. 2) extending to 10 

millibars or approximately 100,000 ft in altitude. Data to 

these heights were required because of the reported and estimated eruption heights of 25-30 km (80,000-100,000 ft) on 

14-15 June 1991. 

ERUPTION CHARACTERIZATION 

FOR THE MODEL 

After initial experimentation with representation of 

these large explosion clouds, it was decided to model the 

ash-cloud injections as large cylindrical volumes of several 

kilometers radius and vertical extent to serve as the basic 

geometry for release of model "marker" particles. A log-normal particle-size distribution spanning the 10-200 micron 

diameter range was selected; particle density was chosen as 
232 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

GWC Gridded Winds 

20-JUN-91 OOZ 

WIND ANALYSIS 

_. 

26.6m/sec 

max wind 

20.0m/sec 

scale wind 

Figure 2. Overhead view, polar stereographic projection of the 10,000-ft level, northern hemispheric wind field for 20 June 1991,00:00 

UTC. Individual flow elements extend in the direction of the wind as indicated by arrows. Length of arrow shaft indicates relative wind 

speed. GWC, Global Weather Central (U.S. Air Force). 

1.45 g/cm3, based on a sample of ashfall from Mount St. 

Helens. Because several eruptions were to be modeled concurrently, a scaled (relative) release rate proportional to 

explosive energy estimated from the altitude of the cloud top 

was approximated as shown in table 2 using explosion-scale 

algorithms maintained at ARAC. The relative scale and 

chronology of the eruptions modeled are depicted in figure 3. 

RESULTS 

By the conclusion of the first response day, 18 June 

1991, ARAC had produced the first set of ash-cloud-advisory products (fig. 4) using the hemispheric-scale model. 

Plots of "relative" ambient concentrations of particles were 

generated for consecutive 12-hour intervals extending to 48 
ASH CLOUD AVIATION ADVISORIES 233 

30 

zen 90,000 

wl60,000 Ow 

=>w I-LL 

30,000 i=z ....J_ 

<( 

-a: 

WI- ~w 20 

Ow 

::>~ 

t::a 10 1-....J ....J_ 

<(~ 

0000 1200 0000 1200 0000 1200 0000 1200 0000 1200 0000 1200 0000 1200 0000 1200 0000 1200 

6/12/91 6/13/91 6/14/91 6/15/91 6/16/91 6/17/91 6/18/91 6/19/91 16/20/91 

DATE AND TIME (UTC) 

Figure 3. Time sequence and relative eruption heights of events included in ARAC (atmospheric release advisory capability) ash-cloudmodel calculations for eruptions of Mt. Pinatubo during the period 12-20 June 1991. UTC, Coordinated Universal Time. 

hours for the 10 altitude layers specified by the Air Force. In 

an attempt to delineate potentially hazardous areas, relative 

concentration divisions of "heavy/dense," "moderate," and 

"light/diffuse" ash were chosen by identifying the highest 

two orders of magnitude of relative particle concentrations, 

the next largest two orders of magnitude, and then the 

remaining concentrations, respectively. Internal to the 

model, a "normalized unit source" was selected due to the 

complete lack of actual data concerning the mass of the eruptions. A "normalized unit source" is a convenient mechanism for deriving the relative dispersed-material distribution 

for an assumed release or release rate, e.g., 1 g or 1 g/s. When 

specific measurements or estimates are determined, then the 

calculated distributions can be directly scaled to derive 

actual mass-specific concentrations. Unfortunately, the 

meteorological and dispersion-model domain boundary was 

close to the eruption site, with the consequence that these 

calculations were of limited utility for the areas south and 

southwest of Pinatubo. They did, however, cover the primary aerial evacuation route from Cebu to Guam, which 

remained ash-free (fig. 5). 

Table 2. Scaled "relative" release rate, Mt. Pinatubo, 1991. 

[Particle-size distribution: 10-200-Jlm diameter; equivalent energy released given in 

thousands of tons of TNT] 

Estimated cloud Equivalent energy Proportional 

top (km) released release rate 

30 6,000 1.0 

25 3,000 0.5 

19 500 0.08 

7 7 0.001 

4 4 0.00066 

Shortly after transmission of the first calculations, the 

Air Force requested comparable advisories for a more 

detailed subregion of a few thousand kilometers extent centered on the Philippines. Figures 6A and 6B delineate this 

new model subdomain and also reveal the complex, sheared 

wind-flow regimes at 7,500 and 50,000 ft on 18 June 1991. 

Figure 4. Example of the first "forecast ash cloud advisory" map 

prepared for the U.S. Air Force on a hemispheric scale. This plot 

was for the 20,000-30,000-ft altitude layer valid at 00:00 UTC, 20 

June 1991. The "ash" levels are relative to the initial release as discussed in the text. 
234 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

·:.· 

:- · .. 

....... ::; ..... ··· 

'• I • 

B 

Figure 5. Particle-model representation of dispersing ash clouds for all eruptions of Mt. Pinatubo from 12-20 June 1991. A, overhead 

view; B, side view from right to left of the overhead view, looking down the axis of the plume; C, side view from bottom to top (or across 

the pole) of the overhead view-this reveals the vertical structure of the recent eruption and the dispersed debris from the cataclysmic 

eruption (of 15 June 1991) over India. Top of vertical scale on side views is 115,000 ft. 

To prepare these calculations for the subregion, it was necessary to extract grid-point profiles from the hemispheric 

data grids and merge them with available regional rawinsonde data. At the time of the eruptions, this was a manual 

process; now it is substantially automated. Using the same 

"source" scaling parameters and receding eruptions, figures 

7A, 78, and 7C reveal the model representation of the 19 

June 1991, 14:25 UTC eruption after 9 hours of dispersal 
ASH CLOUD AVIATION ADVISORIES 235 

Figure 6. Wind-field calculations for the Philippine Island region 

showing details of the regional calculations for the 19 June 1991 

Pinatubo eruption (during the period of U.S. military air evacuations). Individual flow elements extend in the direction of the wind 

as indicated by arrows. Length of arrow shaft indicates wind speed, 

which ranges from about 5 rnls to about 20 rnls. A, Lower atmosphere (::: 7,500 ft) winds; B, Upper atmosphere (::: 50,000 ft) 

winds. 

simulation. In figure 7, the dominant plume of ash was transported west-southwest over the South China Sea by strong, 

high-altitude winds. A low-altitude, diffuse, meandering 

plume, probably related to residual venting between major 

eruptions, stretches north around Taiwan and wraps back 

around along the South China coast. Figure 8 gives an indication of this low-level plume structure on 20 June. Vertical 

cross-section views of the 19 June 1991 eruption plume at 

00:00 UTC on 20 June show the simulated "ashfall" from the 

southwestward-transported upper plume (15,000-50,000 ft) 

and low-level plume. The resulting dispersing ash clouds are 

shown in figures 8A-8C, revealing the different structures of 

the northeast (lower level) ash stem and vent clouds and the 

southwest (upper level) main explosion cloud and ashfall 

from the above stratospheric injection. Figure 8D is a verifying AFGWC analysis based on defense meteorological 

satellite program (DMSP) visible and infrared images for 20 

June at 01:34 UTC. Immediately evident is the sloped, upper 

cloud and particle fallout structure being driven to the southwest by the higher altitude winds, while the lower "stem" 

and continuous, lower level, post-eruption "venting" ash 

cloud is being swept northeast then northward. 

For the cataclysmic eruption of 15-16 June 1991, the 

complex three-dimensional atmospheric structure in the 

region produced dramatically divergent ash-cloud patterns. 

The large eruptions (> 23,000-33,000 ft) produced ashplume clouds, with strong westward transport over the South 

China Sea, Southeast Asia, the Bay of Bengal toward India, 

and beyond. It is the downwind transport, diffusion, and ash 

fallout of these enormous stratospheric intrusions that 

resulted in the numerous aircraft encounters with ash clouds 

(Casadevall and De Los Reyes, 1991). The low-level 

eruptions ( < 23,000 ft) and quasi-steady-state venting 

produced a plume that generally dispersed to the north and 

east throughout the period. 

POTENTIAL IMPROVEMENTS 

These results show the detailed ash-cloud structure 

achievable with the ARAC three-dimensional modeling 

system. Although the initial approach proved viable and 

successful, further refinement is possible. A distinct need 

exists to quantify eruptions consistently such that "relative" 

ash concentrations relate to specific aviation hazards. 

Research and collaboration with the volcanology community 

could possibly produce an "eruption mass" estimation 

methodology correlated to seismic detection or eruption 

height (Harris, this volume; McNutt, this volume). Particle 

sizes, density, and other relevant characteristics should be 

refined. Databases containing locations and characteristics 

of all known potentially active volcanoes should be 

prepared. Links to volcanologists' alerting networks should 

be established. 
236 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

c 

.. . ~ :' 

.. :·.:. : 1.: -... : 

~ ;.;' 

•' :' 

. -: . . , _:, ... ..· .... . . • • • c .. 0 .--:.· · . . ·: .. .. 

. .. 

B A 

Figure 7. Model representation of the 19 June 1991, 14:25 UTC Pinatubo eruption after 9 hours of dispersal simulation. The dominant 

plume of ash was transported west-southwest over the South China Sea by the strong, high-altitude winds. A low-altitude, diffuse, meandering plume, probably related to residual venting between major eruptions, stretches north around Taiwan and wraps back around along 

the South China coast. A, Overhead "particle cloud" view for the Philippine Island region showing the regional grid calculations of the 19 

June 1991 eruption; B, Viewed from east to west; C, Viewed from south to north. 

POTENTIAL VALUE TO AVIATION 

A few immediate advantages of the ARAC hazard modeling system are: (1) advisory products are not limited or 

affected at night, (2) natural clouds do not obscure or affect 

the modeling technique (as, for example, detection using satellite-based techniques), (3) unaffected routes and areas 

unaffected by ash are apparent, ( 4) altitude layers can be differentiated, (5) ash-cloud dispersion is calculated with winds 

comparable to aircraft computerized flight plans, and (6) the 
ASH CLOUD AVIATION ADVISORIES 237 

0 

A 

10°N Ash possibly 

mixed with 

convective 

activity and 

convective 

debris 

c 0 5°N 

Figure 8. Relative ash concentration isopleths for three altitude layers show the simulated "ashfall" from the southwestward-transported 

upper plume (15,000-50,000 ft) and low-level plume in the Philippine Island region on 20 June 1991, following the eruption of 19 June 

1991. The resulting dispersing ash clouds reveal different structures of the northeast (lower level) ash stem and vent clouds and the southwest (upper level) main-explosion cloud and ashfall from the above stratospheric injection. A, 5,000-10,000 ft; B, 10,000-20,000 ft; C, 

20,000-30,000 ft; D, Air Force Global Weather Central (AFGWC) analysis based on defense meteorological satellite program (DMSP) visible and infrared images for 20 June 1991 at 01:34 UTC. Imagery shows the distribution of weather clouds and ash cloud~; for use as a 

verification of the ARAC model for the period of 20 June 1991. MID CLD, middle cloud; abbreviations in upper right portion of D indicate 

"scattered cumulus development within ash cloud." 
238 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

advisories are graphic charts that are easily interpreted. 

Coupling of aviation operations with this type of hazard 

modeling provides a demonstrated, viable method to keep 

aircraft from unanticipated exposure to volcanic ash clouds. 

Assuming there is sufficient interest from the aviation 

community, a protocol could be established for generation of 

pre-eruptive, precautionary calculations, as well as 

generation of advisories during and after eruption until all 

hazardous quantities of ash are removed from the contaminated airspace. A system for dissemination of these results 

would need to be determined in order that the advisories 

reach all potentially impacted aircraft, carriers, air traffic 

control, and airport authorities. With such a capability 

integrated into global aviation, the hazard due to flight 

operations in areas of volcanic eruption threat could be well 

defined and appropriately avoided by rerouting and 

rescheduling. Terminals at risk could also be avoided thus 

minimizing the risk of aircraft damage, as well as the risk of 

losses owing to grounding of airplanes-either of which 

could have substantial economic impacts. 

SUMMARY 

Modeling the sequence of eruptions from the 1991 

eruptions of Mt. Pinatubo presented ARAC with a unique 

challenge. Based on the results achieved, we conclude that 

application of this modeling methodology could provide 

enhanced safety for the aviation community in the event of 

volcanic eruptions. The modeling system improvements outlined here must be developed if ARAC is to be considered 

for future involvement in a volcanic-ash-cloud hazard advisory service. The U.S. Department of Energy, as manager for 

the ARAC program, must approve any extension of this 

emergency response service into this area of natural hazard 

mitigation before such service could be routinely provided. 

Technology transfer to nongovernment organizations is a 

possible alternative, provided a technically competent organization with strong meteorological and aviation interests 

assumes responsibility for generation of the advisories. 

ACKNOWLEDGMENT 

This work was performed under the auspices of the U.S. 

Department of Energy at Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48 and by EG&G 

under contract number DE-AC08-NV10617. 

REFERENCES CITED 

Casadevall, T.J., and De Los Reyes, 1991, Impact of the June 1991 

Pinatubo eruptions on aircraft operations in the western Pacific 

and Southeast Asia [abs.]: Eos, Transactions, American 

Geophysical Union, v. 72, no. 44 [Supplement], p. 95. 

Ellis, J.S., Foster, C.S., Foster, K.T., Greenly, G.G., Sullivan, T.J., 

Baskett, R.L., Nasstrom, J.S., and Schalk, W.W., 1992, Daily 

dispersion model calculations of the Kuwait oil fire smoke 

plume, in Proceedings of the 85th Annual Meeting: Pittsburgh, 

Pa., Air and Waste Management Association, Paper 92-76.05, 

14 p. 

Foster, K.T., and Dickerson, M.H., 1990, An updated summary of 

MATHEW/ADPIC model evaluation studies: Livermore, 

Calif., Lawrence Livermore National Laboratory, Report No. 

UCRL-JC-104134, 28 p. 

Lange, R., 1978, ADPIC-A three dimensional particle-in-cell 

model for the dispersal of atmospheric pollutants and its comparison to regional tracer studies: Journal of Applied Meteorology, v. 17, p. 320-329. 

Sherman, C.A., 1978, A mass-consistent model for wind fields over 

complex terrain: Journal of Applied Meteorology, v. 17, 

p. 312-319. 

Sullivan, T.J., 1988, ARAC, evolution by accident, in Topical 

Meeting on Emergency Response Modeling, September 

26-28, 1988, Charleston, S.C.: Livermore, Calif., Lawrence 

Livermore National Laboratory, Report No. UCRL-98033, 8 p. 

---1991, ARAC, a computer-based emergency-response doseassessment service with global application potential: Livermore, Calif., Lawrence Livermore National Laboratory, Report No. UCRL-JC-10720, 16 p. 

Walker, H., 1989, Use of the 1:2,000,000 digital line graph data in 

emergency response, in Proceedings of the International Symposium on Cartography and Computing: Bethesda, Md., American Society for Photogrammetry and Remote Sensing and 

American Congress on Surveying and Mapping, p. 472--482. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

ALASKA VOLCANO-DEBRIS-MONITORING SYSTE~v.l: 

NEW TECHNOLOGIES TO SUPPORT FORECASTIN<} 

VOLCANIC-PLUME MOVEMENT 

By Gary L. Hufford 

ABSTRACT 

The eruptions of Redoubt Volcano during 1989-90 

revealed a number of deficiencies in National Weather 

Service (NWS) operations that greatly hampered the 

forecaster's ability to accurately forecast and issue timely 

advisories on the movement of airborne volcanic debris. The 

forecaster lacked knowledge of (1) the physical properties of 

airborne volcanic debris, (2) the initial location of debris in 

the atmosphere, both vertically and horizontally, (3) realtime winds near and downstream of the volcano, and ( 4) 

rapid access to volcanic-debris-tracking models. 

To help resolve these deficiencies, an Alaska volcano 

debris monitoring system has been designed, acquired, and 

installed at the NWS offices in Anchorage, Alaska. The system consists of a wind-profiling Doppler radar that provides 

hourly vertical profiles of winds near the volcano, a satellite 

downlink and processing system for tracking volcanic 

plumes using a variety of polar-orbiting satellites, a C-band 

radar to provide vertical and horizontal extent of the plume 

at and near the volcano, a new volcanic-debris-tracking 

model, and an upgrade to the regional computer and communications network for processing, applications, and display 

of the volcano debris monitoring system database. 

INTRODUCTION 

Volcanic ash injected into the atmosphere from the 

1989-90 Redoubt eruptions became the most common and 

widespread hazard (Brantley, 1990) from this series of eruptions. The ash caused significant damage to property, especially aircraft, and severely disrupted normal activities in 

south-central Alaska, where about 60 percent of the State's 

population lives. 

Redoubt Volcano is one of four active volcanoes that lie 

along the west side of Cook Inlet (fig. 1 ). These four volcanoes have erupted for a combined total of seven times in the 

last 80 years. Some of those eruptive episodes have lasted 

over a 2-year period. The four volcanoes are part of an active 

chain that extends from upper Cook Inlet, southwest along 

the Alaska Peninsula, to the western Aleutians. This chain 

includes a total of 35 volcanoes active during the last century 

(Simkin and others, 1981). 

During the last eruptive episode of Redoubt Volcano, 

the NWS found that there were a number of deficiencies in 

information that greatly hampered the forecaster in 

accurately forecasting and issuing timely advisories on the 

movement and concentration of volcanic debris injected into 

the atmosphere. The forecaster had no information on (1) 

ash particle size and concentration, (2) initial height or horizontal extent of the plume into the atmosphere, (3) real-time 

vertical profiles of the winds near and downstream of the 

volcano, and (4) rapid access to volcanic-ash-trajectory 

models. 

The potential for future hazardous eruptions near Cook 

Inlet led Congress to support a volcano monitoring program 

for south-central Alaska to minimize the affects on the population and commerce. A major participant in the monitoring program is the NWS. The purpose of this paper is to 

describe the technologies that have been chosen by NWS for 

the task of ash detection, monitoring, and tracking in Alaska. 

The system, called the Alaska volcano debris monitoring 

system, consists of new remote-sensing instrumentation, 

development of new predictive models, and an upgrade of 

the NWS regional computer and communications network 

for processing, applications, and display of the integrated 

database from the monitoring system. 

REMOTE-SENSING TECHNOLOGIES 

The remote sensing instrumentation in the Alaska volcano debris monitoring system consists of a Doppler wind 

profiler, a non-Doppler weather radar (C-band), and a polar 

satellite downlink, processing, and display system. 

239 
240 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

0 200 400mi 

0 200 

GULF OF ALASKA 

ISLANDS 

PACIFIC OCEAN 

1- Wrangell 

2- Spurr 

8 -Trident 

9 - Mageik 

10- Martin 

11- Ukinrek 

15- Pavlof 22 - Vsevidof 

23- Kagamil 

24 - Car1isle 

25 - Cleveland 

26- Yunaska 

27- Arnukta 

28- Seguam 

29- Korovin 

3- Redoubt 

4- Iliamna 

5- Augustine 

6- Katmai 

7- Novarupta 

12 - Chiginagak 

13 - Aniakchak 

14- Veniaminof 

16- Shishaldin 

17 - Westdahl 

18- Akutan 

19- Makushin 

20 - Bogoslof 21-0kmok 

30 - Great Sitkin 

31- Kanaga 

32- Tanaga 

33- Gareloi 

34 - Little Sitkin 

35- Kiska 

Figure 1. Volcanoes along Cook Inlet, Alaska, that have shown activity in the last century, including Mt. Spurr (2), Redoubt Volcano (3), 

Iliamna Volcano (4), and Augustine Volcano (5). Source: Alaska Volcano Observatory. 

WIND PROFILER 

A wind-profiling Doppler radar observes the weak 

back-scatter from turbulent inhomogeneities in the atmospheric radio refractive index. The ultra high frequency 

(UHF) system ( 405 MHz) is suited for high-resolution, 

clear-air wind observations from 1 km to 16 km producing 

data every 6 minutes that is arranged into hourly, vertically 

averaged wind profiles (Balsley and Gage, 1982). Many 

studies have been made of the precision of profiler wind 

measurements. Thomas and Williams (1990) report that, in a 

comparison of profiler and rawinsonde (balloon) winds, the 

standard deviation was close to 3 m/s, with an inherent accuracy for the profiler of less than 1 m/s. 

To support the Alaska volcano debris monitoring system, the wind profiler was installed in Homer, Alaska, about 

100 km from Redoubt Volcano (fig. 2) in December 1990. 

The Homer site provides hourly vertical profiles of winds 

near the Cook Inlet volcanoes. Figure 3 shows an example of 

the wind measurements from the Homer pro filer. Other profiler sites are proposed for Talkeetna and Middleton Island, 

Alaska (fig. 2). These two sites will give hourly vertical wind 

profiles at locations downwind from the Cook Inlet volcanoes. These sites will also provide winds along two major 

air-traffic corridors over south-central Alaska that have relatively poor upper-air network coverage (fig. 4). 

C-BAND RADAR (5 CENTIMETER) 

Ground-based radar observations and calculations can 

provide significant information on estimating (1) the height 

of the eruptive column above the volcano, (2) the maximum 

vertical and horizontal dimensions of the ash cloud downwind, and (3) the location and horizontal velocity of the ash 

cloud. NWS radar observations of ash clouds from Mount St. 

Helens demonstrated that weather radar (5 em) can yield 

timely information during and following volcanic eruptions 

(Harris and Rose, 1983). However, there are some constraints. 

One- to 1 0-cm radars sometimes cannot discriminate 

between ash clouds and meteorological clouds and rain targets (Stone, this volume). Thus, on cloudy, rainy days, ash 

plumes may go undetected by weather radar if the radar is the 

only source of detection. In addition, once an ash cloud is in 

the dispersed stage, particle sizes may be too small to be 

detectable by radar. Radar must be used in conjunction with 
ALASKA VOLCANO-DEBRIS MONITORING: FORECASTING VOLCANIC-PLUME MOVEMENT 241 

other observational measurements to be an effective data 

source. 

In October 1990, a 5-cm C-band radar was located in 

Kenai, Alaska, approximately 90 km from Redoubt (fig. 2). 

The radar is mounted on a modified recreational motor home 

and is portable. The unit can be moved rapidly to optimize 

observations of the other volcanoes in the Cook Inlet area. 

Data from the radar site is sent, in real time, by telephone to 

the forecaster in Anchorage for display on remote monitors. 

HIGH RESOLUTION PICTURE 

TRANSMISSION PROCESSING SYSTEM 

NOAA!TIROS (National Oceanic and Atmospheric 

Administration-television and infrared observing satellite) 

polar-orbiting satellites have been used in some cases to 

detect and track ash clouds utilizing a number of 1lnstruments 

on the platform. Advanced very high resolution radiometer 

(A VHRR) visible and infrared imagery have been used to 

track volcanic clouds in Alaska (Holasek and Rose, 1991; 

Schneider and Rose, this volume) and southeast Asia (Prata 

and others, 1985) using standard methods to track meteorological clouds. Infrared imagery has been used to discriminate volcanic clouds from ordinary water/ice clouds utilizing 

two signatures in the brightness temperatures (Prata, 1989). 

The first signature is based on the emission chara,cteristics of 

silicates in the ash cloud. Silicates have a lower emissivity 

at 11 Jlm than at 12 Jlm where water/ice show peak emissivity. This effect is seen as a negative temperature difference 

between channels 4 and 5 of the A VHRR instrument. The 

second signature is a lower emissivity for sulfuric acid 

Figure 2. Location of remote-sensing instrumentation of the Alaska volcano debris monitoring system in relation to the four volcanoes 

along Cook Inlet. 
242 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

12 ,- -,,-.-.--,_,,~--,-.-~,--,-~,--,-~~- 200 

22:00 20:00 18:00 16:00 14:00 12:00 10:00 

TIME (UTC) 

Figure 3. Hourly vertical profiles of wind from the Homer, 

Alaska, profiler for April 2, 1991. Orientation of "arrow" shaft 

indicates wind direction and has a precision of ±10°. "Flag" length 

indicates wind speed: a "half-flag" has a value of 5 knots; a "fullflag" has a value of 10 knots. UTC, Coordinated Universal Time. 

Figure 4. Location of the upper-air (rawinsonde balloon release) 

network in Alaska. 

droplets or acid-coated particles (11 j..tm) when compared to 

water/ice particles (12 j..tm). 

The high spatial resolution of the NOANTIROS polarorbiting satellites (1 km), their great spectral range, and 

frequent coverage make these satellites a significant monitoring and tracking tool over Alaska. At low latitudes, the polar 

orbit limits the view of the same point to only four times per 

day for two satellites. Because the orbits of the satellites are 

near polar and sun synchronous, their orbital paths tend to 

converge at the poles, and, in the higher latitudes, coverage 

can be up to 18 passes per day from the same two polar 

satellites. 

There are other operational instruments on-board the 

NOANTIROS polar-orbiting satellites that have potential to 

support the monitoring and tracking of volcanic plumes. The 

TIROS observational vertical sounder (TOVS) on the polarorbiting satellites should be able to provide considerable 

information on volcanic clouds and conditions around them. 

TOVS consists of a high-resolution infrared radiation 

sounder (HIRS) that contains 20 infrared channels and a passive microwave sounding unit (MSU). TOVS also provides 

vertical profiles of temperature, moisture, and geostrophic 

wind down to the surface in areas of no clouds. This data can 

be used to estimate the maximum height and trajectory of ash 

clouds. 

A high-resolution image-processing system (HIPS) was 

installed in Anchorage, Alaska, in June 1991 (fig. 2). The system includes a tracking antenna located at the international 

airport, an ingest/synchronization computer, a main processor, and four workstations at the three Alaska forecast offices 

(Anchorage, Juneau, and Fairbanks) and the Center Weather 

Service Unit in Anchorage. Eighteen polar-orbiting passes 

over Alaska can be processed to produce at least 12 satelliteimage products per pass; these are distributed via the Alaska 

region operational communications network (ARO-NET). 

The HIPS system was also designed to ingest data from other 

polar-orbiting satellites, including those of the defense meteorological satellite program (DMSP), to increase coverage so 

that an image is available over any given point in Alaska 

every 1.5-2 hours. The aerial coverage for HIPS is within a 

1,500-km radius from Anchorage. 

Satellite data are displayed on workstations, and interactive software allows for complete digital manipulation of 

the imagery and sounding data, including animation, graphic 

overlay, cartographic projections, multispectral classification, windowing, and full color enhancement. 

COMPUTER, COMMUNICATIONS, 

DATA INTEGRATION, AND MODELS 

COMPUTER AND COMMUNICATIONS 

NETWORK 

To insure the optimization of the NWS Alaska 

computers and communications to handle the large volume 

of data from the volcano monitoring system and the gridded 

data sets from various prediction models, the nextgeneration Alaska region operational computer and communications network (ARO-NET) was developed and made 

operational in October 1991 (fig. 5). Computer standards 

such as UNIX (OSF/1 compliance), X-Windows (Motif), 

and IEEE 802.3 Ethernet with TCP/IP network protocol 

have been selected to minimize the difficulties inherent in a 

heterogeneous computer environment. This allows a number 

of different kinds of computers to be used as workstations 

and coupled with an advanced wide- and local-area network 
ALASKA VOLCANO-DEBRIS MONITORING: FORECASTING VOLCANIC-PLUME MOVEMENT 243 

PROFILER' 

ANC 

cwsu 

2/56 kb 

/ 

SATELLITE /~ACKUP / 

e 

Figure 5. Schematic of Alaska region operational computer and communications network (ARO-NET). JNU, Juneau; FAl, Fairbanks; 

ANC, Anchorage; NMC, National Meteorological Center; CWSU, Central Weather Service Unit; HIPS, high-resolution image-processing 

system; GRIB, gridded binary format. 

to integrate data from a combination of sources. New RISC 

(reduced instruction set chip) computers are used as application and file servers on the network, and high-speed digital 

communications lines (56 kb) have been incorporated to 

handle the increased volume of data. 

INTEGRATED DATABASE 

The data from the Alaska volcano debris monitoring 

system, integrated with other conventional data sources in 

Alaska, provides the forecaster with a powerful tool to assist 

in producing effective and timely forecasts. Comparing the 

integrated database to digital predictive-model output fields 

and adjusting the model when necessary will provide the 

forecaster with capabilities never available in field offices in 

the past. As an example, during eruptive events, forecasters 

will have available forecaster-selected, multilevel winds 

valid at 3-hour intervals from the time of initial eruption out 

to 12 hours, and thereafter every 6 hours out to 72 hours. 

These constant-height winds will come from gridded, digitalmodel output and can be displayed as streamlines (wind 

paths). The forecaster will place observed winds from the 

profilers, satellites, rawinsonde balloon releases., and other 

observations over the streamlines. This overlay capability 

will assist the forecaster to initialize, verify, or adjust the predicted model winds. 

ASH DISPERSION MODEL 

The air resources laboratory of NOAA is developing a 

four-dimensional dispersion model for airborne volcanic 

debris (Heffter and others, 1990; Stunder and Heffter, this 

volume). This model will utilize wind data from the technologies described above as well as inputs from NOAA's forecast systems laboratory mesoscale analysis and prediction 

system (MAPS) and National Meteorological Center (NMC) 

boundary-layer forecast meteorological fields. Designed to 

serve aviation and local forecasting, MAPS over Alaska will 

define the tropospheric and lower stratospheric wind fields 

every few hours after eruption. Over the longer term, NMC 

forecast winds will be utilized. In addition, satellite imagery 
244 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

will provide information on the location and horizontal 

extent of the ash cloud. The C-band radar will supply initial 

vertical height and direction of the ash plume at the volcano. 

The dispersion model will forecast concentrations and deposition of volcanic debris for forecast periods from eruption to 

up to 48 hours. The model should be ready for operational 

use in late 1992. 

SUMMARY 

The 1989-90 eruptions of Redoubt Volcano have 

resulted in the establishment of a volcano debris monitoring 

system to improve the accuracy and timeliness of NWS forecast warnings and advisories to the public during eruptions 

of Alaskan volcanoes. The long history of frequent eruptions from volcanoes along Cook Inlet clearly indicates that 

future eruptions are inevitable. 

It is anticipated that improved forecast products will 

have their greatest impact on aviation safety in the Cook 

Inlet region. Because ash is not possible to detect during 

flight with present onboard sensors, effective and timely 

warnings will allow aircraft to avoid ash clouds. 

These more accurate forecast products will be in both 

alphanumeric and graphic form. New products will include 

a graphical advisory, four-dimensional trajectories, and 

descriptive statements to the public and emergencymanagement agencies. 

REFERENCES CITED 

Balsley, B. B., and Gage, K. S., 1982, On the use of radars for operational wind profiling: Bulletin of the American Meteorological Society, v. 63, p. 1009-1018. 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, 

Alaska, December 14, 1989-August 31, 1990: U.S. Geological 

Survey Circular, 1061, 31 p. 

Harris, D.M., and Rose, W.l., Jr., 1983, Estimating particle sizes, 

concentrations, and total mass of ash in volcanic clouds using 

weather radar: Journal of Geophysical Research, v. 88, 

p. 969-983. 

Heffter, J.L., Stunder, B.B., and Rolph, G.D., 1990, Long-range 

forecast trajectories of volcanic ash from Redoubt Volcano 

eruptions: Bulletin American Meteorology Society, v. 71, 

p. 1731-1738. 

Holasek, R.E., and Rose, W. 1., Jr., 1991, Anatomy of 1986 Augustine Volcano eruptions as recorded by multispectral image processing of digital A VHRR weather satellite data: Bulletin 

Volcanology, v. 53, p. 420-435. 

Prata, A.J., 1989, Observations of volcanic ash clouds in the 10-12 

J.Lm window using A VHRR/2 data: International Journal of 

Remote Sensing, v. 10, p. 751-761. 

Prata, A.J., Wells, J.B., and lvanac, M.W., 1985, A satellites view 

of volcanoes on the Lesser Sunda Islands: Weather, v. 40, 

p. 245-250. 

Simkin, T., Siebert, L., McClelland, L., Bridge, D., Newhall, C.G., 

and Latter, J.H., 1981, Volcanoes of the World: Stroudsburg, 

Pa., Hutchinson Ross, 242 p. 

Thomas, D.R., and Williams, S.R., 1990, Analysis of comparative 

wind profiler and radiosonde measurements, in Proceedings of 

the 1Oth Annual Geoscience and Remote Sensing Symposium: 

New York, v. 1, p. 537-540. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

A STATISTICAL APPROACH TO THE ASSESSMENT 

OF VOLCANIC HAZARD FOR AIR TRAFFIC: 

APPLICATION TO VESUVIUS, ITALY 

By Giovanni Macedonia, P. Papale, M. Teresa Pareschi, Mauro Rosi, 

and Roberto Santacroce 

ABSTRACT 

This work uses numerical models that simulate ash 

dispersion to quantify the hazard to aircraft flying into a 

volcanic plume. Mt. Vesuvius, Italy, which last erupted in 

1944, was chosen as a test case by virtue of the generally 

good knowledge of its eruption characteristics and because it 

lies in an area with heavy air traffic. The airport of NapoliCapodichino is located about 10 km from the crater. 

The maximum size of an ash-producing eruption at 

Vesuvius was estimated on the basis of a behavior model that 

assumes that eruption size and explosiveness will increase 

with increasing repose time as a consequence of a roughly 

constant rate of supply of mafic magma to a shallow magma 

chamber. A three-dimensional model was used to simulate 

the transport, diffusion, and fallout of ash and to compute ash 

concentration in the space surrounding the volcano. The simplifying assumptions about the erupting column structure, 

the neglect of long-distance effects (e.g., Earth sphericity), 

and previous numerical simulations indicate a range of applicability of the model from 10 km to 400 km from the vent. 

The computed spatial distribution of ash allows an estimation of dispersed mass in a given airway and represents a 

method to evaluate, for an impending eruption and for an 

assigned wind profile, the minimum safe distance from 

Vesuvius. The model was used to build a three-dimensional 

hazard map, which represents a guide for rerouting air traffic 

in the area. 

INTRODUCTION 

Volcanic ash clouds represent a real threat to aviation 

operations (Scarone, 1987). Ash clouds have caused several 

near disasters in the past decade: Examples include the 24 

June 1982 eruption ofGalunggung Volcano in Java, and the 

15 December 1989 eruption of Redoubt Volcano in Alaska. 

In both cases, a Boeing 747 passenger airplane encountered 

a cloud of volcanic ash produced by an eruption that 

occurred several hours earlier. Ash ingestion caused all four 

engines to shut down, and engine restart was not possible 

until the aircraft descended out of the ash cloud. Both aircraft 

suffered extensive damage to their engines and exterior surfaces (Przedpelski and Casadevall, this volume). 

Other volcanoes that have had an impact on flight operations are St. Augustine, Alaska (Kienle, this volume); Etna, 

Italy; Mount St. Helens, Washington; several Japanese volcanoes (Onodera and Kamo, this volume); Pinatubo, Philippines (Casadevall and De Los Reyes, 1991); and several 

volcanoes in Indonesia. In this report, attention is focused on 

Vesuvius Volcano in Italy, but the approach can be used for 

other case studies. 

Vesuvius was chosen as a test case owing to the generally good knowledge of its eruption characteristics and 

because it lies in an area with heavy air traffic. The volcano 

erupted most recently in 1944. The airport of NapoliCapodichino is located about 10 km from the crater ~d the 

radio beacon of the Sorrento Peninsula, an important air 

node, is about 25 km from the volcano (fig. 1). 

ASH DISPERSION 

When a gas-pyroclast mixture erupts from a volcano to 

form a convective eruption column, the distribution of ash 

particles during fallout is controlled by the dynamics of the 

eruptive column itself and by the wind regime (Self and 

Walker, this volume; Sparks and others, this volume). The 

former controls the proximal distribution of particles, while 

the direction and speed of the wind determine distal ash distribution. To simulate the dynamics of falling particles in the 

air in this wind-controlled region, a continuity equation has 

been used for each settling velocity class, i (Armienti and 

others, 1988; Macedonio and others, 1988): 

245 
246 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

(1) 

where 

Ci(x,y,z,t) is the concentration of the particles with settling velocity class i, 

Ux and Uy are horizontal components of wind, 

Vsi is the settling velocity of class i, 

Kx, Ky. and Kz are atmospheric diffusion coefficients, and 

Si is the source term (the particles of settling velocity 

class i that leave the convective column per unit 

time). 

The above continuity equation was solved by a numerical 

scheme that accounts for complex wind data and mass eruption rates. 

EXPLANATION 

- A35- Airway 

0 5 

I " " I 

10 NAUTICAL MILES 

I I 

20 KILOMETERS 

Figure 1. Air routes in the Vesuvius area. Terrain elevation shown 

by solid-line contours in 1,000-m intervals. Solid straight lines indicate airways. VOR DME, a type of airway navigational aid. 

(/) 

a: 

w 

1-

w 

~ 

0 

_J 

S2 

z 

~ 15 

Cl 

::J 

1-

~ <( 

WIND DIRECTION-10-YEAR AVERAGE 

EXPLANATION 

D Summer wind 

* Winter wind 

oL_~~-L~--L-~-L~--L-~-L~~--~~~ 

(/) 30 

a: 

w 

1-

w 

~ 

0 

_J 

Q 

z 

w~ 15 

Cl 

::J 

1- 10 

~ <( 

5 

0 90 180 270 

WIND DIRECTION, IN DEGREES 

WIND SPEED-10-YEAR AVERAGE 

0 0 5 1 0 15 20 25 30 

WIND SPEED, IN METERS PER SECOND 

360 

Figure 2. Ten-year-average mean wind directions and mean wind 

speeds as a function of altitude. Recorded at Brindisi, Italy, during 

summer and autumn-winter-spring (shown in figure as "winter 

wind"). After Cornell and others (1983). 

For the case of Vesuvius, information concerning 

the wind has been derived from a record of observations 

by the Servizio Meteorologico dell' Aeronautica Militare 

Italian a over a period of 10 years at Brindisi, located 300 

km east of the volcano. These data allow the recognition 

of two different seasonal wind profiles: a summer field 

and an autumn-winter-spring field (Cornell and others, 

1983) (fig. 2). 

The horizontal and vertical diffusion coefficients 

depend on the temporal and spatial scale of the phenomena. 

For example, if the ash particles are settling from great 

heights and with low velocities, turbulent eddies of increasing size have to be considered in the model, with a consequent effective increase of the diffusion coefficients. Mean 

values of 2,000-3,000 m2/s for horizontal diffusion coefficients are expected near Vesuvius. These values have been 
ASSESSMENT OF VOLCANIC HAZARD FOR AIR TRAFFIC: VESUVIUS, ITALY 247 

empirically derived by the simulations of the 79 A.D. Vesuvius eruption (Macedonio and others, 1987, 1988). 

For the model eruption treated in this report, the total 

eruptible mass was estimated to be 2x1 ott kg; the mass eruption rate was estimated at 9.3x106 kg/s for an eruption lasting 6 hours (Macedonio and others, 1990). Using the model 

of Wilson and Walker (1987), a column height of 13 km is 

calculated. The grain size of the pyroclastic particles have 

been assumed to be similar to that of the Plinian phase of the 

eruption of Vesuvius in 79 A.D., and the vertical density distribution of ash in the ascending column has been derived by 

the theoretical model of Suzuki (1983). The settling velocity 

has been derived from shape and density information of 

pyroclasts using the experimental data from Wilson and 

Huang (1979). These data have been fitted by a function 

Cv =aiR+ b, which gives the aerodynamic coefficient, Cv, 

as function of the Reynolds number, R (fig. 3). 

The pyroclastic material was grouped into nine classes 

of settling velocity, Vs (1 to 9 m/s). In order to reduce 

computational time, particles with Vs < 1 m/s were grouped 

into class 1 and those with Vs > 9 mls were grouped into 

class 9. This assumption does not involve dramatic approximations: in fact, with regard to fast-falling particles, figure 

4 shows that only about 10 weight percent of the erupted 

mass has a settling velocity greater than 9 m/s. With regard 

to the slow-falling particles, about 16 weight percent of the 

total mass has settling velocity lower than 1 m/s. However, 

due to electrostatic attraction, fine volcanic ash commonly 

tends to aggregate into clusters (Sorem, 1982; Gilbert and 

others, 1991 ), with typical settling velocity in the range 

0.3-1.0 m/s. In addition, surface tension of condensed 

water that envelopes ash particles may also play a role in 

forming relatively large aggregates at the expense of very 

fine grained material. Very slow settling velocities are, 

therefore, scarcely represented (Carey and Sigurdsson, 

1982; Armienti and others, 1988). 

~ 80 ~· 

r:-

z 

G 6o • u::: 

1..1.. 

UJ 8 40 • 

(.!) 

<( 

~ 20 

20 

Co= 33/R + 1.9 

.. 

40 60 80 100 

REYNOLDS NUMBER, R 

Figure 3. Drag coefficient (Cv) versus Reynolds number (R); 

interpolating curve shown. Data from Wilson and Huang (1979). 

1-

z 

~ 10 

a: 

UJ 

a.. 

II 

~ 5 

~ 

0 

0 5 10 15 20 

SETTLING VELOCITY, IN METERS PER SECOND 

Figure 4. Settling velocity, Vs, plotted against the distribution of 

particles (in weight percent) for expected eruption. 

NUMERICAL RESULTS 

From an analysis of the numerical solutions of equation 

1, utilizing the input data described above, it results that, at a 

given point in space, the concentration, Ci, of the particles 

belonging to settling velocity class i rises from zero to a constant value in a "stabilization time," Tsi, which varies from 

point to point. Figure 5 shows the stabilization times for the 

total mass (concentration integrated over the spatial domain) 

dispersed into the atmosphere for three classes of settling 

velocity. The faster the falling velocity of the particles, the 

quicker the stabilization time. Because the duration of the 

model eruption is finite (in this example 6 hours), the mass 

in the space decreases to zero after a certain time. The data 

of figure 5 refers to the summer mean wind profile (Cornell 

and others, 1983). 

APPLICATIONS ON AIRWAY UG8 

Several simulations were performed to investigate the 

volcanic hazard for an aircraft traveling along the portion 

of airway UG8 between Sorrento and Teano. This route 

passes 20 km west of Vesuvius and carries heavy air traffic 

(fig. 1). For both dominant summer and winter winds, this 

route is located upwind with respect to Vesuvius. We have 

taken into consideration an aircraft traveling at an altitude 

of 11 km with a velocity of 250 m/s. At this altitude, the 

differences between the velocities of the mean summer and 

autumn-winter-spring wind profiles are small(< 10 percent, 

fig. 2). To evaluate the mass of ash particles that may enter 

the jet engines, an engine air flux of 300 kg/s/m2) was 

assumed: 

Figure 6A shows the concentration of ash encountered by aircraft flying northward along the UG8 airway, 

leaving Sorrento at different times after the beginning of 
248 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

m 3 0 

..... 

X 2 (/) 

2 

<( 

a: 

CD V5=3 m/sec 

0 

.....J 

S2 00 ~ 2 4 6 8 

ci 

<( 2 

~ 

::c 

(/) 

<( 

u. 

0 

(/) 

(/) 

<( 

2 

00~----~----_L ______ L_ ____ _L~--~--~ 

4 6 8 10 

TIME, IN HOURS 

Figure 5. Stabilization times (horizontal axis) for the total mass 

(concentration integrated over the spatial domain) dispersed into 

the atmosphere for three classes of settling velocity (1 m/s, 3 m/s, 5 

m/s). The faster the falling velocity of the particles, the quicker the 

stabilization time. Because the duration of the model eruption is 6 

hours, the mass in the airspace decreases to zero after a certain time. 

The simulation was carried out using the summer mean wind profile from Cornell and others (1983). 

the eruption. Figures 6B and 6C show the ash mass flux 

and the mass of ash entering a jet engine per unit inflow 

area. Figures 7A-C show concentration, mass flux, and 

collected mass (per unit inflow area of the engine) in the 

same conditions as in figure 6, but with a wind profile 

rotated 180° (here referred to as the downwind case) to 

account for the "maximum hazard" along the UG8 route. 

In the "upwind" case, a low hazard exists for the UG8 airway. In fact, after the plume concentration has reached its 

maximum (T > Ts) the maximum ash concentration along 

the airway is 1.5xlo-6 gtm3, which results in a mass flux 

within the engine of about 0.5xlo-3 g/s/m2; the mass collected by each engine is about 0.01 g/m2. On the other 

hand, a very high hazard exists in the case of westward 

winds (the "downwind" case). For an aircraft leaving Sorrento in steady-state conditions (T > Ts), the mass of ash 

collected per meter squared is more than 30 kg for the 

flight time between Sorrento and Teano. 

HAZARD MAP 

A hazard map for the air traffic in the Vesuvius area has 

been derived by using the expected eruption rate determined 

in previous works (Santacroce, 1983; Macedonio and others, 

1990). The map was constructed by carrying out about 3,000 

different simulations, one for each wind profile recorded 

during a period of 10 years, and then computing the probability that the spatial concentration at a given point is greater 

than a given threshold. To reduce computational time, vertical diffusion was neglected and only the steady-state solution of the continuity equation was considered. 

Figures SA-C are hazard maps for three different ashconcentration-threshold values: lo-s, 10-4, and lo-3 kg/m3. 

These values correspond, for the portion of the UG8 route 

affected by dispersed ash, to masses entering an engine of the 

order of 0.1-1.0 kg/m2 of engine inlet cross-sectional area 

for an aircraft flying at 250 mls. The areas of equal probability, referring to spatial concentration higher than the given 

threshold, widen toward the ground as a consequence of the 

longer time available for dispersion processes. 

CONCLUSIONS 

A diffusive-advective model was used to simulate the 

dispersion of a volcanic plume in the range from 10 km to 

400 km from Mt. Vesuvius. The spatial concentration evaluated by the model permits estimation of the hazard from volcanic ash for aircraft flying in the area. This approach may 

be applied to other volcanoes, assuming that information on 

wind velocities, atmospheric diffusion coefficients, mass 

eruption rate, and particle settling velocity distribution are 

known. Given the size of the eruption (total erupted mass, 

column height, settling velocity distribution of particles, 
ASSESSMENT OF VOLCANIC HAZARD FOR AIR TRAFFIC: VESUVIUS, ITALY 249 

0.4 

1"'-o 

b 

3 (.0 

b 

>< 0) 

Cl b UJ 

a: >< <( 

a: :::> UJ d I- (/) 

T=O UJ a: ::2! 0 UJ 

u 2 IUJ co ::2! :::> 

u 

a: 

UJ 

a.. (/) 

(/) a: ::2! 10 

::2! UJ <( a.. a: <( 

a: (/) (.9 8 

::2! 0 (.9 ...J 0 <( 

...J a: ~ 6 ~ (.9 

0 ~ 

~ ...J UJ- 4 

z' ~ z 0 0 ~ a 2 

~ 2 UJ- z 

UJ 

z 0 a: 

I- a ~ 12 z z ~ 10 UJ UJ u 

z z a: 0 <( UJ 

u (.9 I- 8 z z 

UJ a: (/) 6 UJ 

I- (/) 

z <( 

4 T=Ts UJ ::2! 

>< ...J 

:::> ~ 2 ...J 

u.. 0 

0 (/) I0 100 200 (/) 00 <( 100 200 

::2! TIME, IN SECONDS 

A B c 

Figure 6. A, Ash concentration encountered by an aircraft flying northward along airway UG8 at an altitude of 11 km leaving Sorrento 

at different times, T, after the beginning of the eruption (upwind case). Ts, "stabilization time" for lower settling velocity class. Times shown 

are: T = 0 (onset of eruption), T = 1/5Ts, and T = Ts. B, Mass flux encountered by aircraft described in A (upwind case). C, Total mass of 

ash entering an engine (upwind case). 

etc.) and a wind profile, the cumulative and instantaneous 

mass of volcanic ash can be computed for a given air-traffic 

route. This makes it possible to estimate the minimum safe 

flying distance from a volcano. Given the wind regimes in 

the area of interest, a hazard map can be produced and used 

to construct air-traffic maps in active volcanic areas. 

ACKNOWLEDGMENTS 

The authors wish to thank the Aeronautica Militare for 

support in drawing the map of air routes in the Vesuvius area 

and the National Group of Volcanology (GNV) for fmancial 

support. 
250 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

0 

UJ 3 0: 

<( 

:::::l 0 0 UJ 

'<:!" (/) 0: 

~ <( 2 :::::l 

>< 0 

(/) 

0: 0: UJ UJ I- a.. UJ 

0 ~ z 0: 0 UJ 

u a.. UJ 0 

UJ 

0: (/) ~ 30 0: a.. UJ <( 

(/) a.. 0: 

~ (/) (!) 

0 <( ~ _J 

0: <( 20 Q (!) 0: 0 

_J (!) ~ 0 Q _J u.i 

~ Q z 

(3 10 ~ z UJ- UJ 

z z (3 <( 0 z (!) 

UJ z 40 z c: 

<( UJ 

(!) Iz 30 z 0.8 UJ 

c: (/) 

UJ (/) 

I- <( z 20 UJ ~ 

>< 0.4 _J 

:::::l ~ 10 _J 0 u.. 0.2 I- (/) 

(/) 

<( 

00 100 200 ~ 100 200 100 200 

TIME, IN SECONDS 

A B c 

Figure 7. A, Ash concentration encountered by an aircraft flying northward along airway UG8 at an altitude of 11 km leaving Sorrento at 

different times, T, after the beginning of the eruption (wind field is rotated 180° from that shown in figure 6 to represent the maximum hazard 

(downwind case)). Ts, "stabilization time" for lower settling velocity class. Times shown are: T= 0 (onset of eruption), T= liSTs, and T= 

Ts. B, Mass flux encountered by aircraft described inA (downwind case). C, Total mass of ash entering an engine (downwind case). 
ASSESSMENT OF VOLCANIC HAZARD FOR AIR TRAFFIC: VESUVIUS, ITALY 251 

11 11 11 11 11 11 

10 10 10 10 10 10 

9 9 9 9 9 9 

(f) 

8 8 8 8 c::: 8 8 w 

Iw 

~ 7 7 7 7 7 7 

0 

....J 

Q 6 6 6 6 6 6 

~ 

u.i 5 5 5 Cl 5 5 5 ::J 

I-

~ 4 4 4 4 4 

<( 4 

3 3 3 3 3 3 

2 2 2 2 2 2 

Figure 8. Hazard maps that show a contouring of the probability (between 0 and 100 percent) that the ash concentration at a given point 

be above a fixed threshold value. These maps are constructed by considering about 3,000 different simulations, one for each wind profile 

recorded during a period of 10 years. Results for three different threshold values are shown: A, w-5 kg!m3; B, 10~ kg/m3; C, w-3 kg/m3. 

These values result in cumulative masses of the order of 0.1-1.0 kg!m2 entering an engine of a jet traveling at 250 rnls along airway UG8. 

The outer contour in each horizontal plane represents a probability of 10 percent. Each successive contour refers to an increase of 10 percent 

in the probability value. Scales on horizontal planes in kilometers. 
252 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

REFERENCES CITED 

Armienti, P., Macedonia, G., and Pareschi, M.T., 1988, A numerical model for simulation of tephra transport and deposition: 

Applications to May 18, 1980, Mount St. Helens eruption: 

Journal of Geophysical Research, v. 93, no. B6, p. 6463-6476. 

Carey S.N., and Sigurdsson H., 1982, Influence of particle aggregation on deposition of distal tephra from the May 18, 1980, eruption of Mount St. Helens volcano: Journal of Geophysical 

Research., v. 87, p. 7061-7072. 

Casadevall, T.J., and De Los Reyes, P.J., 1991, Impact ofJune 1991 

Pinatubo eruptions on aircraft operations in the western Pacific 

and Southeast Asia [abs.]: Eos, Transactions, American Geophysical Union, v. 72, no. 44 [Supplement], p. 95. 

Cornell, W., Carey, S.N., and Sigurdsson, H., 1983, Computer simulation of transport and deposition of the Campanian Y -5 ash: 

Journal of Volcanology and Geothermal Research, v. 17, p. 

89-109. 

Gilbert, J.S., Lane, S.J., Sparks, R.S.J., and Koyaguchi T., 1991, 

Charge measurements on particle fallout from a volcanic 

plume: Nature, v. 349, p. 598-600. 

Macedonia, G., Pareschi, M.T., and Santacroce, R., 1987, Valutazione e controllo di alcuni parametri fisici agenti durante la fase 

Pliniana dell'eruzione del Vesuvio del 79 D.C [in Italian]: 

Rome, Bulletin of the National Group of Volcanology, p. 

445-466. 

---1988, A numerical simulation of the Plinian fall phase of 79 

A.D. eruption of Vesuvius: Journal of Geophysical Research., 

v.93,p. 14817-14827. 

---1990, Renewal of explosive activity at Vesuvius: Models 

for the expected tephra fallout: Journal of Volcanology and 

Geothermal Research, v. 40, p. 327-342. 

Santacroce, R., 1983, A general model for the behavior of the Somma-Vesuvius volcanic complex: Journal of Volcanology and 

Geothermal Research, v. 17, p. 237-248. 

Scarone, H., 1987, Volcanic ash clouds-A continuing threat to international aviation: Earthquakes and Volcanoes, v. 19, p. 

65-73. 

Sorem, R.K., 1982, Volcanic ash clusters: Tephra rafts and scavengers: Journal of Volcanology and Geothermal Research, v. 13, 

p. 63-71. 

Suzuki, T., 1983, A theoretical model for dispersion of tephra, in 

Shimozuru, D., and Yokoyama, 1., eds., Arc Volcanism: Physics and Tectonics: Tokyo, Terra Scientific Publishing Co., p. 

93-113. 

Wilson, L., and Huang, T.C., 1979, The influence of shape on the 

atmospheric settling velocity of volcanic ash particles: Earth 

Planetary Science Letters, v. 44, p. 311-324. 

Wilson, L., and Walker, G.P.L., 1987, Explosive volcanic eruptions 

VI: Ejecta dispersal in Plinian eruptions: The control of eruption conditions and atmospheric properties: Geophysical Journal of the Royal Astronomical Society, v. 89, p. 657-679. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

USING A PERSONAL COMPUTER TO OBTAIN 

PREDICTED PLUME TRAJECTORIES DURING 

THE 1989-90 ERUPTION OF 

REDOUBT VOLCANO, ALASKA 

By Thomas L. Murray, Craig I. Bauer, and John F. Paskievitch 

ABSTRACT 

The Alaska Volcano Observatory (AVO) and the 

Anchorage Weather Service Forecast Office (WSFO) obtain 

predicted plume trajectories daily for Redoubt Volcano, 

Alaska. A model developed by the National Oceanic and 

Atmospheric Administration (NOAA) Air Resource Laboratory calculates predicted plume trajectories. The model, 

running on NOAA's NAS/9000 mainframe computer in 

Suitland, Md., uses forecast wind fields obtained from the 

NOAA National Meteorological Center. The model uses 

measured and forecast winds to predict the path of a 

weightless particle released at various pressure-altitudes 

above a specified location. The paths indicate the general 

direction and speed that ash from an eruption at that location 

will travel. 

In response to the 1989-90 Redoubt eruption, we programmed an IBM-XT-style personal computer to automatically dial the NAS/9000 mainframe computer and obtain the 

predicted trajectories. Twice daily, after the predicted wind 

fields are updated, AVO and WSFO can easily collect and 

plot the trajectories predicted for the next 72 hours. Thus, the 

trajectories are immediately available in the event an 

eruption should occur. The predicted trajectories are plotted 

on a map of Alaska, showing the predicted location of the 

ash plume at 3-hour intervals for different altitudes between 

5,000 and 53,000 ft. The plots are easily telefaxed to 

interested parties. The program has been modified to enable 

the user to obtain predicted plume trajectories for other U.S. 

volcanoes. 

INTRODUCTION 

Volcanic ash ejected into the atmosphere can cause 

severe problems to airplanes and to municipal and industrial facilities, as well as to people on the ground downwind 

from the volcano. Knowing where ash will travel is vital to 

mitigating its effects. If notified in time, people in the path 

of the ashfall can take precautionary measures as complex 

as shutting down portions of a power facility or as simple 

as canceling a dinner date. Conversely, in areas unlikely to 

be affected by ashfall, industry can avoid wasting resources 

in preparation for ash that is not traveling in their direction. 

In this report, we describe a method to routinely acquire 

predicted wind speeds and directions (trajectories) at various pressure-altitudes and to plot and display the data in a 

simple, easy-to-distribute format. The predicted plume trajectories currently provide the only method that predicts, 

before an eruption, where ash will be blown (as opposed to 

tracking already-erupted ash). AVO and WSFO took 

advantage of this capability and informed other agencies 

daily as to where ash from Redoubt would go if the volcano 

were to erupt. In the event of an eruption, the predicted 

plume trajectory, having been plotted earlier, is ready for 

immediate use, thereby saving valuable time. 

During the Redoubt eruption, plots were especially 

useful to the aviation industry. They were sent daily to 

Anchorage International Airport authorities, who then 

distributed them to the airlines, many of which required 

their flight crews to use them in flight planning (Casadevall, in press). 

DESCRIPTION OF PREDICTED PLUME 

TRAJECTORIES 

A computer model, developed by NOAA's Air 

Resource Laboratory (ARL), provides predicted plume trajectories based on forecast wind fields. The wind fields are 

calculated twice daily by the National Weather Service 

(NWS) from observations taken at 00:00 and 12:00 Greenwich Mean Time (GMT) (Heffter and others, 1990). Using 

the latitude and longitude of the volcano and the time of the 

hypothetical eruption, the model predicts the locations of 

dimensionless, weightless particles at 3-hour increments 

253 
254 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

after they are released into the atmosphere at various pressure-altitudes above the volcano. The model ignores effects 

from gravity and dispersion. Unlike volcanic ash, the 

model's ideal particles never fall to Earth, but remain at the 

pressure-altitude at which they were released forever. 

The model accepts times for hypothetical eruptions up 

to 48 hours into the future in 3-hour increments. AVO can 

always have the latest predicted trajectories by obtaining the 

predicted trajectories from the NOAA computer twice daily 

after the latest weather observations are processed. Owing 

to the time required to process weather observations and calculate the predicted wind fields, the latest predictions are 

typically available about 3 hours after the actual measurements, at 03:00 and 15:00 GMT (or 18:00 and 06:00 AST). 

OBTAINING PREDICTED PLUME 

TRAJECTORIES 

Predicted plume trajectory plots were first used to predict trajectories of volcanic ash during the 1980 eruptions of 

Mount St. Helens, Washington (Miller and others, 1981; 

Smith, 1980). At that time, the technique to acquire 

trajectories was time consuming, requiring the full attention 

of a person for an hour or more (E. Brown, oral commun., 

1991). As the level of activity at Mount St. Helens declined, 

the U.S. Geological Survey discontinued obtaining plume 

trajectory data. 

In 1988, NOAA signed a memorandum of understanding with the Federal Aviation Administration (FAA) to 

provide the FAA with predicted plume trajectories (Heffter 

and others, 1990). During the 1989-90 eruptions of Redoubt 

Volcano, NOAA provided trajectory information to the FAA 

within 1 hour of NOAA's notification of the eruption and 

typically within 3 hours of the actual eruption (Heffter and 

others, 1990). Because an ash plume can move hundreds of 

kilometers during a 3-hour delay, AVO and the Anchorage 

WSFO felt that they needed trajectory information more 

quickly in order to issue timely warnings. Ideally, the 

trajectory information would be available before an eruption. 

This would allow AVO and WSFO to concentrate on the 

myriad other tasks involved in monitoring an eruption (data 

analysis, notifying interested agencies, answering media 

inquiries, etc.) and would avoid using personnel or phone 

and computer resources during an eruption to obtain the 

information. It would also allow AVO to include the information in daily updates sent to various public agencies and 

other users, including the aviation community, that could be 

affected by ashfall. Finally, it enabled AVO and WSFO to 

have the information ready for immediate distribution 

should an eruption occur. 

In order to acquire the plume trajectories daily, even 

when there was little chance of an eruption, the process had 

to be simplified, or, as was the case with Mount St. Helens, 

if would fall into disuse. We were able to do this by using 

computer hardware and software unavailable in 1980. The 

necessary equipment consists of an IBM XT (or compatible) 

personal computer, a 1,200-baud Hayes-compatible modem, 

a printer, the software package PROCOMM Plus (for 

communication with the NOAA computer), and Geograf 

Utilities (for the screen and printer graphics drivers). Users 

initiate the program with a few keystrokes and are prompted 

to answer a few questions. Then the program dials the 

NOAA NAS/9000 computer in Suitland, Md., runs the 

plume trajectory program for various hypothetical eruption 

times and pressure-altitudes, logs the data on the XT, and 

finally produces plots of the paths of the predicted plume 

trajectories on the user's printer. The entire process takes 

less than 20 minutes. 

PLOTS OF PROJECTED PLUME 

TRAJECTORIES 

Following the format of Smith (1980), trajectories at 

different pressure-altitudes for a single hypothetical eruption 

time are plotted as a map on a single 8Y2-by-ll-inch sheet. 

The map shows the paths traveled by ideal particles released 

above the volcano at different pressure-altitudes at the hypothetical eruption time indicated on the plot (figs. 1 and 2). 

Symbols along the paths indicate positions of the particles at 

3-hour time intervals. Stronger winds will blow the particles 

faster along their paths, and the symbols will be spaced correspondingly farther apart than for light winds. By plotting 

/>LASKA VOLCANO OBSERVATORY 

DATA COURTESY Of NOM PROJECTED 

PLUME PATHS FOR 

HYPOTHETICAL 

ERUPTION AT 

REDOUBT 

BEGINNING AT 

00:00 AST 

28 FEB 90 

SYMBOL INTERVAL IS 3 HOURS 

_ 1'-11LTJ)_Q~~ _ . o = 5,000 FT 

D.= 10,000 FT <> = 18,000 FT t, = 23,000 FT v = 30,000 FT X = 39,000 FT + = 53,000 FT 

PROJECTIONS BASED 

ON DATA COLLECTED 03:00 AST 

27 FEB 90 

Figure 1. Example of predicted plume trajectories plotted over 

the State of Alaska for a hypothetical eruption beginning at 00:00 

Alaska Standard Time (AST), February 28, 1990. Cordova (CDV), 

McGrath (MeG), Fairbanks (FBX), and Anchorage (ANC) are approximately located. Trajectories for ideal particles released at various pressure-altitudes above Redoubt Volcano are plotted. The 

location of the symbols on the trajectory paths indicate the positions 

of the ideal particles at 3-hour intervals after eruption time. 
USING A PERSONAL COMPUTER TO OBTAIN PREDICTED PLUME TRAJECTORIES 255 

all trajectories on a single map, the user can quickly visualize 

where the ash is likely to go without paging back and forth 

between seven plots of trajectories at individual altitudes. 

The data are plotted on maps of two different scales. One 

covers Alaska (fig. 1), and the second covers Cook Inlet and 

surrounding areas (fig. 2). 

USE OF PREDICTED PLUME 

TRAJECTORIES 

Users of the projected plume trajectories must understand that the trajectories give only a general indication of 

where ash will travel. The accuracy of the trajectories is limited by the accuracy of the predicted winds and the model's 

assumption of a weightless, dimensionless particle. For 

instance, the plots always show a travel path extending for 24 

or more hours for an ideal particle. Users need to be 

informed that, although they may lie in the path of the ideal 

particle as indicated by the plot, gravity will likely cause the 

actual, non-ideal ash to settle before it reaches them. 

The model also does not consider the effect of dispersion of the ash as it travels along the trajectory. Users should 

not be fooled into thinking that they will not be affected by 

ash simply because they are not located directly on the line 

predicted by the model. Until current research (Sparks and 

others, this volume; Stunder and Heffter, this volume; 

Tanaka, this volume) is incorporated into the model, we suggest qualitatively defining the area that may be affected by 

ash as an arc of ±30° along the trajectory as it travels away 

.'LASKA VOLCANO OBSERVATORY 

DATA COURTESY CF NOAA PROJECTED 

FBX PLUME PATHS FOR 

HYPOTHETICAL 

ERUPTION AT 

REDOUBT MeG BEGINNING AT 

00:00 AST 

28 FEB 90 

SYMBOL INTERVAL IS 3 HOURS 

ALTITUDES -o~-5]00FT 

D = 10,000 FT 

<> = 18,000 FT !!, = 23,000 FT 

'V = .30,000 FT X = .39,000 FT + = 53,000 FT 

PROJECTIONS BASED 

ON DATA COLLECTED 03:00 AST 

27 FEB 90 

Figure 2. Example of predicted plume trajectories in figure 1 

plotted over a map of Cook Inlet and surrounding areas for a hypothetical eruption beginning at 00:00 Alaska Standard Time (AST), 

February 28, 1990. Cordova (CDV), McGrath (MeG), Fairbanks 

(FBX) and Anchorage (ANC) are approximately located. 

from the volcano. This would also allow for inaccuracies in 

the predicted trajectory. 

For small to moderate size eruptions, such as those at 

Redoubt, the major factor in the path's accuracy is the accuracy of the predicted winds. Rather than focusing attention 

on one plot at a given altitude, users should look through the 

suite of plots for each day to develop an idea of the stability 

of the weather system. Stable systems will generally have all 

trajectories for all altitudes, except perhaps 5,000 ft, traveling in about the same direction. The effects of the 5,000-ft 

trajectory are usually ignored both because the erupting 

vents at most volcanoes are usually above 5,000 ft in altitude 

and because they usually eject ash into higher altitudes 

where the winds are generally stronger. For stable systems, 

where the winds above 10,000 ft blow in the same general 

direction throughout the day, we feel the accuracy of the predicted winds to be quite good. Such was the case for the February 24, 1990, eruption of Redoubt (fig. 3). On days when 

the winds change or even reverse direction, it may be difficult to predict with any certainty where ash will travel (fig. 

4). It is best to err on the side of caution during such times. 

Heffter and others ( 1990) provide a more detailed analysis of 

the accuracies of the trajectories. 

PLASKA VOLCANO OBSERVATORY 

DATA COURTESY OF NOAA 

FBX 

PROJECTED 

PLUME PATHS FOR 

HYPOTHETICAL 

ERUPTION AT 

REDOUBT 

BEGINNING AT 

06:00 AST 

24 FEB 90 

SYMBOL INTERVAL IS 3 HOURS 

ALTITUDES -o~-5]oofT 

o =· 10,000 FT <> = 18,000 FT !!, = 23,000 FT 'V = .30,000 FT X = 39,000 FT 

+ = 53,000 FT 

PROJECTIONS BASED 

ON DATA COLLECTED 03:00 AST 

24 FEB 90 

Figure 3. Predicted plume trajectories for the February 24, 1990, 

eruption of Redoubt Volcano with the actual ground deposition 

(heavy line) outlined (from Scott and McGimsey, in press). Because the eruption plume reached an altitude of only 28,000 ft 

(Brantley, 1990), the winds at 39,000 and 53,000 ft did not affect 

ash deposition. Note that the spacing between symbols for the 

winds at 18,000, 23,000, and 30,000 ft are more than twice that for 

winds at 5,000 and 10,000 ft-this indicates that the wind speed at 

higher altitudes is more than twice that at lower altitudes. For this 

reason, the pattern of ground deposition was influenced predominantly by the winds at 18,000, 23,000, and 30,000 ft. Cordova 

(CDV), McGrath (MeG), Fairbanks (FBX) and Anchorage (ANC) 

are approximately located. 
256 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

MeG 

/>LASKA VOLCANG OBSERVATORY 

DATA COURTESY OF NOAA 

FBX 

PROJECTED 

PLUME PATHS FOR 

HYPOTHETICAL 

ERUPTION AT 

REDOUBT 

BEGINNING AT 

16:00 ADT 

05 JUN 90 

SYMBOL INTERVAL IS 3 HOURS 

ALTITUDES -o~-s:ooofT 

D = 10,000 FT o = 18,000 FT 6 = 23,000 FT 'V = 30,000 FT X = 39,000 FT 

+ = 53,000 FT 

PROJECTIONS BASED 

ON DATA COLLECTED 04:00 ADT 05 JUN 90 

Figure 4. Plot showing the difficulty in determining where ash 

will travel when wind directions are expected to change. The 

23,000- and 30,000-ft altitudes show the ash first going north and 

then curling to the southeast. The winds at 10,000- and 18,000-ft 

altitudes move the ash south as it falls through those altitudes. Note 

also that the spacing between symbols is significantly less than that 

in figure 3, indicating that the winds are much milder than on February 24, 1990. With this pattern of plume trajectories, it is not possible to say much more than the ash is likely stay in the Cook Inlet 

area (because of the low wind speed) and could affect any or all of 

the area. Cordova (CDV), McGrath (MeG), Fairbanks (FBX) and 

Anchorage (ANC) are approximately located. 

Major eruptions (such as the June 15, 1991, eruption of 

Mt. Pinatubo, Philippines, or those with strong horizontal 

wind components, such as the May 18, 1980, blast of Mount 

St. Helens) are special cases. They can disperse large quantities of ash in any or all directions for many kilometers 

before prevailing winds control the path traveled by the ash 

(Self and Walker, this volume). 

CONCLUSIONS 

Projected plume trajectories are an important tool for 

mitigating hazards associated with ashfall resulting from 

volcanic eruptions. This is the only currently used method 

that predicts plume paths before an eruption. By simplifying 

the procedure to obtain plume-trajectory data, we enabled 

AVO and WSFO to obtain trajectory plots on a routine 

basis. AVO included the trajectory information in its daily 

updates that were sent to various governmental agencies 

and businesses (including Anchorage International Airport, 

where authorities distributed them to all 26 carriers located 

there) (Casadevall, in press). In the event of an eruption, 

projected plume paths were ready for immediate distribution. Thus, AVO and WSFO were able to make full use of 

predicted plume trajectories, both before and after eruptions. 

We recommend that the ARL model be improved to 

include the effects of dispersion and gravity on volcanic ash. 

Such improvements would greatly enhance the effectiveness 

of plume trajectories without adding to the operational cost 

of acquiring them. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, 

Alaska, December 14, 1989-August 31, 1990: U.S. Geological 

Survey Circular 1061, 33 p. 

Casadevall, T.J., in press, The 1989-1990 eruption of Redoubt Volcano, Alaska: Impacts on aircraft operations: Journal of Volcanology and Geothermal Research. 

Heffter, J.L., Stunder, B.J.B., and Rolph, G.D., 1990, Long-range 

forecast trajectories of volcanic ash from Redoubt Volcano 

eruptions: Bulletin American Meteorological Society, v. 71, 

no. 12,p. 1731-1738. 

Miller, C.D., Mullineaux, D.R., and Crandell, D.R., 1981, Hazard 

assessments at Mount St. Helens, in Lipman, P.W. and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. Helens, 

Washington: U.S. Geological Survey Professional Paper 1250, 

p. 789-802. 

Scott, W.E., and McGimsey, R.G., in press, Character, mass, distribution, and origin of tephra-fall deposits of the 1989-1990 

eruption of Redoubt Volcano, south-central Alaska: Journal of 

Volcanology and Geothermal Research. 

Smith, W.K., 1980, A plotting program for producing ashfall 

prediction maps from output of the NOAA forecast trajectory 

program: Application to examples from the 1980 Mount St. 

Helens eruptions: U.S. Geological Survey Open-File Report 

80-2005, 36 p. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC ERUPTIONS AND 

ATMOSPHERIC TEMPERATURE 

By Reginald E. Newell and Zhong Xiang Wu 

ABSTRACT 

Temperature changes associated with volcanic aerosol 

have been studied with radiosonde data since 1960 and with 

satellite microwave-sounding data since 1979. Radiosonde 

data show that temperature in the tropical lower stratosphere 

increased by about 5°C following eruptions of Mt. Agung in 

1963 and El Chich6n Volcano in 1982. The microwave data, 

which give a weighted response to temperature of the lower 

stratosphere, give a zonally averaged temperature increase of 

about 1.6°C in the tropics for both El Chich6n and Pinatubo 

(which erupted in 1991). In spite of large differences in the 

amount of material injected into the lower stratosphere by 

these three volcanoes, there is little difference in the positive 

temperature anomalies. The possible reasons for these equilibrium anomalies are discussed. In the troposphere, temperature seems to have decreased by about 0.3°- 0.4°C after 

Agung, but it is difficult to be certain that there was any 

volcanic decrease in 1982-83 because of the concomitant 

occurrence of a large El Nifio, which is always associated 

with tropospheric heating. Atmospheric temperature 

changes produced by volcanic activity are responsible for the 

largest density changes that occur in and above the tropical 

lower stratosphere. 

On the longer time scale, there is some evidence that 

volcanic activity around the tum of the century caused the 

depression of global sea-surface temperature of approximately 0.5°C at that time. 

INTRODUCTION 

Important parameters for aircraft flight are ambient air 

temperature and air density, which depend on the variation 

of temperature with altitude. Volcanic activity causes 

changes in atmospheric temperature patterns and therefore 

influences these important parameters. 

Volcanic eruptions are clearly not the only factors that 

influence atmospheric temperature. Another major factor, 

which is comparable in magnitude in the lower atmosphere, 

is air-sea interaction, particularly as manifested by the 

tropical El Nifio phenomenon (Philander, 1990). During El 

Nifio, sea-surface temperatures in the eastern equatorial 

Pacific rise to values close to those in the west (::: 30°C), and 

the entire tropical lower atmosphere responds by getting 

warmer. The presence of El Nifio often makes it difficult to 

unravel the influence of volcanic activity on temperature, as 

will be seen below. 

The exact mechanisms by which volcanic eruptions or 

El Nifio events bring about temperature changes in the tropical atmosphere are not known. The general mechanisms 

controlling free-air temperature have been presented by 

Newell and others (1974) and fall into four broad categories: 

solar and infrared radiative interactions, latent heat liberation, conduction of sensible heat from the Earth's surface, 

and atmospheric motions. The constituents introduced into 

the atmosphere by volcanic activity certainly influence the 

first category, but the other three may also be involved. Likewise, although El Nifio may involve air-sea interactions in 

which energy is transferred from the sea to the air (mostly as 

latent heat), there are also likely to be contributions from the 

other categories. 

We review here some of the past work relating volcanic 

activity to atmospheric temperature and present some recent 

work that makes use of microwave sounding units on 

satellites for temperature determination that gives, for the 

first time, global coverage of temperature changes. Throughout, we will take cognizance of the variability of air-sea 

interaction. 

CHANGES IN THE 

TROPOSPHERE-PREVIOUS WORK 

The early work on changes in surface-air temperature 

associated with volcanic eruptions has been summarized by 

Lamb (1970), who also introduced a dust veil index (DVI) as 

an aid to measuring the influence of volcanoes on temperature. Before 1900, the data available to evaluate the index are 

rather sparse-this diminishes its value then, as stressed by 

Bradley (1988) in his study of the DVI and other indices of 

volcanic activity. Lamb (1970) recognized the danger of 

257 
258 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

circular reasoning when using DVI data to compare with 

climate fluctuations because some of the earlier DVI 

estimates included temperature change values. Maximum 

temperature decreases of about 1 °C were found after large 

eruptions (for example Tambora in 1815), but, as Lamb 

(1970) stressed, there has been much debate about the reality 

of the reported changes and their geographical extent. Two 

interesting findings by Bradley (1988) were (1) in the 

Northern Hemisphere, the summer and fall months 

experienced the greatest temperature depression, and (2) 

there was evidence for a small secondary peak in the negative 

1.0 

0.5 

0 

-0.5 

-1.0 

CJ) 1850 1860 1870 1880 1890 1900 1910 :::> A Ci5 

.....J 

w 1.0 u I I I I I I I I I I I I I I I I I I I I I I I I I 

CJ) 

w 

w 0.5 a: 

{!) 

w 

0 0 z 

w 

a: -0.5 :::> 

I-

<( 

a: 

w -1.0 

a.. 1880 1890 1900 1910 1920 1930 

~ B w 

I1.0 

0.5 

0 

-0.5 

-1.0 

1880 1890 1900 1910 1920 1930 

c 

anomalies about 1 year after the first peak response. None of 

the early work included factors other than volcanic activity 

as dependent variables. 

By 1976, it was known that the influence of volcanic 

activity could best be brought out of the record of mean air 

temperature for the tropical troposphere (TTT) in the altitude 

region from 3 to 10 km by first removing the air temperature 

variability associated with El Nifio. This was done using a 

time series of sea-surface temperature (SST) from the eastern 

equatorial Pacific (see Newell and Weare, 1976a, 1976b). 

The approximate regression equation reduced to: 

------- TREND (1888-1988) 

----------- TREND (1856-1988) 

1920 1930 1940 1950 1960 1970 1980 1990 

YEAR 

I I I I I I I I I I I I I I I I I I I I I I I I I 

EXPLANATION 

----------- RECONSTRUCTED DATA 

1940 1950 1960 1970 1980 1990 

YEAR 

----------- TREND 

1940 1950 1960 1970 1980 1990 

YEAR 

Figure 1. A, Time series (1856 to 1988) of marine air temperatures (MAT) in the Northern Hemisphere. B, The component of MAT 

(Northern Hemisphere) that is dependent on turbidity (turbidity is the first factor in a linear regression analysis); data from 1888 to 1988 is 

shown. C, MAT residuals and their trend (Northern Hemisphere) after subtraction of the turbidity component; data from 1888 to 1988 is 

shown. Adapted from Wu and others (1990). 
VOLCANIC ERUPTIONS AND ATMOSPHERIC TEMPERATURE 259 

7 

6 

>-

v 

I- 5 (5 

cc 

0::: 4 ::> 

I3 

A 

2 

3 

2 

6 0 (/) 

-1 

-2 

200 

150 

> 100 0 

50 

c 

0 

1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 

YEAR 

Figure 2. A, Time series of turbidity at Sonnblick, Austria (see text and Wu and others, 1990 for further explanation). B, The southern 

oscillation index (SOl), used to monitor El Nifio. Obtained from an update of early work by Wright (1975). C, Lamb's dust veil index (DVI). 

See Lamb (1970). Figure adapted from Wu and others (1990). 

A TIT = 0.5 ASST + 20 A 'tv (1) 

where 

'tv is the atmospheric transmission measured by solar 

photometers at the Mauna Loa Observatory (lat. 

21 °N.). 

For the Mt. Agung eruption of 1963, the transmission 

decreased by about 3 percent and ASST in late 1963 was 

about 1 °C-therefore, the net effect was only about -0.1 °C. 

But by early 1964,, the SST anomaly turned negative, and 

the largest tropical troposphere negative anomaly of about 

0.5°C then occurred. Further details may be found in papers 

by Newell (1984) and Newell and Hsiung (1984). A discussion of the phase lags is given by Newell and Weare (1976a, 

1976b). There was a phase lag of about 6 months between 

the eastern Pacific SST change and the TTI change. Newell 

and Hsiung (1984) also applied this relationship to the El 

Chich6n eruption of 1982, a case for which the largest phenomenon of the century up to that time occurred in each category: El Nifio was associated with a rise in SST of 4°C, 

and the El Chich6n aerosols showed atmospheric transmission to decrease by more than 13 percent. Such phenomena 

give rise to a net cooling of about 0.6°C when equation 1 is 

applied. Angell (1988) has taken the same approach in the 

examination of the joint effects of El Nifio and volcanoes on 

air temperature, including the weighting of 0.5 applied to 
260 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

the SST contribution-he finds that a decrease of TTT of 

about 0.5°C can be assigned to El Chich6n (he has applied 

more time averaging to the data than was used in our case). 

An obvious flaw in this general approach is that the 

regression parameters cannot be applied quantitatively outside the region for which they were developed. 

We have examined ships' reports of night, marine, air 

temperatures for the past century taken from the Global 

Ocean Surface Temperature Atlas (GOSTA), produced by 

Bottomley and others (1990), and we have related the temperature variability to three variables (Wu and others, 1990): 

atmospheric turbidity, solar irradiance, and the southern 

oscillation index (SOl), which is an index of surface pressure 

anomalies in the Pacific related to El Nifio (Philander, 1990). 

F.igures 1 and 2 show the time series of Northern Hemisphere 

au temperature, the time series of two of these variables 

plus, for illustrative purposes, the DVI of Lamb (1970): 

Using multiple linear regression, it was shown that atmospheric turbidity explained the largest fraction of variance 

for Northern Hemisphere air temperatures, whereas the SOl 

explained the largest fraction for the tropics. 

The turbidity used in these calculations was computed 

from sunshine records that have long been collected at many 

meteorological stations (Helmes, 1987). In the method used, 

an image of the sun produced by a glass sphere burns a trace 

on a card throughout the day. The Campbell-Stokes sunshine 

recorder was brought to its present form in 1880 (see Stokes, 

1880). Stokes (1880) points out that the color selected for the 

card (Prussian blue) gave maximum absorption. The instrument as developed then has been used for 110 years and is 

therefore an excellent tool for the study of global-change 

effects. When volcanic eruption clouds are present, the 

image is only powerful enough to bum the card at a laterthan-usual-time after sunrise or an earlier-than-usual time 

before sunset. From the sun's elevation (a) at first or last 

burn, the turbidity may be obtained as follows (Jaenicke and 

Kasten, 1978): 

Turbidity (Tg) is defined as: 

(2) 

where 

bg is the optical thickness of the atmosphere for Rayleigh 

scattering including ozone absorption and integrated 

over the solar spectrum, 

m is the relative optical air mass, which depends on solar 

elevation angle, 

Io is the irradiance of the extraterrestrial solar constant 

(::::1,370 Wfm2), and 

lcs is the threshold value for burning to start (:= 200 

W/m2). 

Jaenicke and Kasten (1978) show that this relation may be 

approximated as: 

where 

cs = 0.154 In (!Jlcs), in deg-1, and 

C6 = 1.05 In (!Jlcs). 

The turbidity, Tg, so computed is a measure of the number 

of dust-free and dry Ray leigh atmospheres that have the 

same transmittance as that observed in the real dust-laden 

and humid atmosphere. The variation of Tg is only available 

from a few stations before 1900. Sonnblick (lat. 47°N., 

long. 13°E., altitude 3,106 m), Austria, is one station that 

has the advantage of being above the boundary layer of the 

industrial plain of Central Europe. High values of Tg appear 

after the turn of the century accompanying the three large 

volcanic eruptions of 1902 (Mt. Pelee, lat. 15°N., long. 

61 °W.; Soufriere, lat. 13°N., long. 61 °W.; and Santa Maria, 

lat. 14°N., long. 92°W.). If the volcanic explosivity index 

computed by Newhall and Self (1982) was used as a criterion of activity, 1902 had the largest cumulative value in 1 

year during the period from 1883 to 1981, but the volcanological record is not complete before about 1950. There are 

associated low values of Northern Hemisphere marine air 

temperature in this high-activity period-this leads to the 

conclusion that volcanism plays a significant role in cooling 

the lower atmosphere and producing this major minimum of 

the past 100 years. When the tropical atmosphere is considered alone (not shown), marine air temperatures show good 

correspondence with the SOl index, with turbidity the second most important variable. The prime physical process 

acting in this case is, therefore, air-sea interaction. 

These relationships between SOl, turbidity, and air 

temperature may be of some interest for the case of the 

Pinatubo eruption. Based on satellite measurements of S02, 

Bluth and others (1992) report that Mt. Pinatubo ejected 

about 20 megatons (Mt) of sulfur dioxide into the stratosphere between June 10 and June 28, 1991, which is about 

three times the amount measured for the El Chich6n eruption. McCormick and Veiga (1992), from satellite measurements of aerosol find between 20 and 30 Mt of new aerosol 

that were produced by the Pinatubo eruptions compared with 

12 Mt from El Chich6n. A substantial fraction of the new 

aerosol is thought to be formed from the oxidation of so2. 

Concomitantly, there has been a warming of the tropical 

Pacific by as much as about 2°C (Climate Analysis Center, 

1992). 

CHANGES IN THE 

STRATOSPHERE-PREVIOUS WORK 

Whereas the troposphere apparently cools after a large 

volcanic eruption, the stratosphere shows warming, probably 

due to the absorption of solar radiation, although infrared 

absorption may also be important. The tropospheric temperature increase after the eruption of Mt. Agung in March 1963 
VOLCANIC ERUPTIONS AND ATMOSPHERIC TEMPERATURE 261 

6 

(f) 

2 4 

(f) 

__J 

w 

u 2 

(f) 

w 

w 0 cc: 

(.!) 

w 

0 -2 

z 

6 

z 

0 

i= 4 

~ 

cc: 

<( 2 

> 

w 

cc: 0 :::> 

I-

<( 

cc: -2 w 

a.. 

~ 

:t w 

I-

-2 

c l 

1961 1962 1963 1964 1965 1966 

YEAR 

Figure 3. Variations in air temperature in the tropical lower stratosphere after the eruption of Mt. Agung in 1963. Arrows indicate date of 

eruption ofMt. Agung (March 1963). Temperature variations are shown for altitudes of: A, 19.5 km; B, 16.5 km; C, 9.5 km. Monthly means 

were calculated for 5 years before the eruption; deviations from the means were computed, and 3-month running averages were plotted. From 

Newell (1971). Reprinted with permission. 

was the largest non-seasonal anomaly then observed by the 

radiosonde network (about 6°C-see fig. 3), and, although 

the anomaly gradually decreased during and after 1964, it 

persisted for several years (Newell, 1970a, 1970b, 1971). 

Similar increases in the temperature of the lower stratosphere occurred after the eruption of El Chich6n in 1982 

(Labitzke and others, 1983; Parker and Brownscombe, 1983; 

Selkirk and Newell, 1984; Quiroz, 1983; Newell, 1984). 

Somewhat surprisingly, the temperature change after El 

Chich6n was almost the same magnitude as that after Mt. 

Agung in spite of the fact that the aerosol injected, or formed 

in situ from gas-to-particle conversion, was several times 

larger for El Chich6n, and the transmission change illustrated in figure 4 was much larger. In fact, the change after 

the eruption of El Chich on was the largest in the record since 

1958. 

Meridional cross sections of temperature change in the 

lower stratosphere (Newell, 1970b) after the eruption of Mt. 

Agung are quite similar to those of tungsten 185 (185W) 

radioactivity after Pacific nuclear tests (Newell, 1963). The 

185w originated from a single point rather like the volcanic 

eruptions; it was measured by high-altitude aircraft sampling. 

The influence of plume stabilization and the meridional 

spreading by atmospheric large-scale eddy diffusion may be 

seen in both patterns, again providing indirect evidence that 

it is aerosol that is controlling the temperature changes. 

MICROWAVE SOUNDING UNIT 

TEMPERATURE-ANOMALY DATA 

The tropospheric free-air and stratospheric temperature 

perturbations discussed above were based on radiosonde 

data that have a limited geographical coverage, especially 

over the tropical oceans. The measurement of temperature 

by the detection of microwave emission from molecular oxygen using a satellite platform was proposed by Meeks and 

Lilley (1963) as a method to acquire global coverage; this 

has been implemented in a series of National Oceanic and 

Atmospheric Administration (NOAA) satellites since 1979 
262 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

100 

tz 95 L.U 

u 

0:: 

L.U 

a.. 

~ 90 

z 

0 

U5 85 ~ 

~ 

(/) 

z 

<( 80 0:: 

t75 

1960 1965 1970 1975 1980 1985 1990 

YEAR 

Figure 4. Atmospheric transmission at Mauna Loa Observatory, Hawaii (data provided by Ellsworth Dutton, NOAAIERL climate 

monitoring and diagnostics laboratory, Boulder, Colo.). Major ticks represent January of indicated year. 

(Spencer and Christy, 1990; Spencer and others, 1990). 

Microwave sounding units (MSU's) use radiometers sensitive to radiation of 50-60 GHz (0.6-0.5 em). Examples of 

the weighting functions are illustrated in the two papers 

quoted. The 57 .95-GHz channel covers the lower stratosphere; its peak response at about 100 hPa, or about 16 km, 

is below the maximum temperature anomalies shown in figure 3 for Mt. Agung. The 53.74-GHz tropospheric channel is 

centered at about 700 hPa but is also influenced by surface 

temperature. Time series of zonal mean values of these two 

channels are shown in figure 5. To provide information on 

the aerosol, atmospheric transmission at Mauna Loa is also 

included in each part of figure 5. Figure 5C represents tropical ocean surface temperature variations taken from 

GOSTA, so that the influence of oceanic changes on the temperature record may also be appreciated. All values are 

monthly mean anomalies calculated from the 1982-90 

period means and are expressed in terms of the monthly standard deviations; 13-month running means obtained with a 

Gaussian filter are also shown. There is an increase in temperature in the stratosphere commencing soon after atmospheric transmittance decreases for both the El Chich6n and 

Pinatubo eruptions. The maximum increase in both cases is 

about 2.4 standard deviations, or 1.6°C. The same general 

time sequence is evident in radiosonde data analyzed by 

Labitzke and McCormick (1992), but they only extended to 

November 1991. The magnitudes are different from the 

microwave results, with a maximum increase of about 4 oc at 

a pressure level of 50 hPa (:= 21 km). It should be emphasized, as noted above, that the maximum of the weighting 

function is not peaked in altitude with respect to the maximum temperature anomaly. It should also be noted from figure 3 that there are substantial changes in the anomalies with 

longitude, and these are smoothed out in the zonal mean 

values of figure 5. It is of interest that, so far, the two temperature anomalies observed by the microwave technique 

are roughly the same size, even though the amount of so2 

gas released was about three times larger for Pinatubo than 

for El Chich6n. The same situation occurred for radiosonde 

anomalies found for Mt. Agung and El Chich6n. These 

stratospheric temperatures show some evidence of a biennial 

oscillation, the sequence being interrupted and perhaps 

changed in phase by the El Chich6n eruption. 

It was suggested many years ago that biennial temperature changes in the region of the lower stratosphere were 

reflections of a modulation of the rising motion in the tropical Hadley-cell circulation (Newell and others, 1969) and 

that the phase slippage, which was evident in 1963 from 

ozone records, was due to the eruption of Mt. Agung (Newell 

and others, 1974). The same explanations could apply to figure 5 and the record of the Pinatubo eruption. Dutton (1992) 

has shown that the Mauna Loa record of atmospheric transmission also shows evidence of a quasi-biennial oscillation, 

which would presumably be related to horizontal wind 

changes accompanying modulations of vertical motions. 

Figure 5 shows that, in the troposphere, there are three 

major positive excursions in tropical SST and tropical freeair temperature: in early 1983, late 1987 and late 1991-all 

three being related to temperature changes associated with El 

Nino events, which show a maximum SST change in the 

eastern equatorial Pacific. 

Maps of temperature anomalies for the lower tropical 

stratosphere are shown in figure 6 for September 1981 and 

September 1982, before and during the transmission change. 

In September 1981, tropical temperatures are slightly below 

average, whereas, in 1982, there are positive anomalies of 

about 1.5°C with slight maxima in the western Pacific and 

Atlantic, corresponding approximately to the maximum in 
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IVOLCANIC ERUPTIONS AND ATMOSPHERIC TEMPERATURE 

EXPLANATION 

3 

} Atmospheric transmission } Temperature 

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1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993°"

76 

YEAR 

Figure 5. A, Time series of atmospheric transmission and tropical (lat. 20°S.-20°N.) lower stratospheric temperature based on microwavesounding-unit data. Left-hand scale is in standardized units for both parameters ("standardized" is term used here when anomalies are expressed in terms of standard deviation of full time series). Right-hand scale represents actual temperature anomalies. Light lines represent 

actual monthly mean values. Heavy lines represent results of applying an 11-month Gaussian filter. Major ticks on horizontal axis correspond to January of indicated year. B, Tropical (lat. 20°S.-20°N.) tropospheric temperature based on microwave-sounding-unit data. Atmospheric transmission curves identical to those in A. C, Tropical (lat. 20°S.-20°N.) sea-surface temperature shown through December 

1991. Atmospheric transmission curves identical to those in A. 
264 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

30°N 

20°N 

10°N 

0 

1oas 

20°S 

30°S 

A 

30°N 

20°N 

10°N 

0 

10°S 

20°S 

30°S 

B 

30°N 

20°N 

1QoN 

0 

1Qo$ 

20°S 

30°S 

40°E 60°E c 

Figure 6. A, Temperature anomalies (with reference to means for 1982-92) for the lower tropical stratosphere based on September 1981 

microwave-sounding-unit data. Data reflects conditions before El Chich6n eruption. Contours of temperature anomalies are labeled in 

degrees Celsius. B, Temperature anomalies for September 1982 (after El Chich6n eruption). C, Temperature anomalies for March 1992 

(after Mt. Pinatubo eruption). 

back scattering from the cloud measured by lidar (McCormick and others, 1984). A map for March 1992 is also 

included in figure 6 and shows similar anomalies to those 

that occurred after the eruption of El Chich6n. Tropospheric 

temperature anomaly maps illustrate an evolution since the 

eruption of Pinatubo that is dominated by the 1991-92 El 

Nifio. In the tropical Pacific, the period December 

1991-April 1992 shows a bipolar structure centered on the 

equator that resembles the January 1983 pattern we reported 

earlier for the 1982-83 El Nifio (Newell and Wu, 1992). 

Although not included in figure 5, the SST in the eastern 

tropical Pacific showed a maximum positive anomaly (of 

2°-3°C) in May 1992, after which the anomalies decreased 

rapidly and became negative in the middle of July 1992. The 

maxima on either side of the equator may be associated with 

large-scale subsidence. This warming illustrates the great 

difficulty of estimating the influence of volcanic effects on 

the troposphere. 

PHYSICAL MECHANISMS FOR 

OBSERVED CHANGES 

Meridional cross sections of atmospheric sulfate concentrations before and after Mount St. Helens and before and 

after El Chich6n have been drawn up by Newell ( 1984) using 

data from Sedlacek and others (1983) and Mroz and others 

(1983). They show a strong source in the tropics for El 

Chich6n with mixing-ratio isolines sloping downward with 

latitude; significant values are confined to the stratosphere. 

Because sulfate has a low absorptivity for solar radiation, it 

may not be the only item responsible for the climatic effect 

of volcanoes. Ogren and others (1981) found evidence for 

the absorption of visible radiation in the Mount St. Helens 

plume, and Clarke and others (1983) find significant absorption at visible wavelengths in aircraft samples from the El 

Chich6n volcanic eruption cloud; samples were collected in 

the altitude range from 18 to 21 km. Woods and Chuan 
VOLCANIC ERUPTIONS AND ATMOSPHERIC TEMPERATURE 265 

(1983) found similar samples to contain carbon. There were 

no measurements of the infrared properties of this particular 

aerosol. 

Normal background radiative heating-rate components 

in this region are shown in figure 7. The tropical lower 

stratosphere is normally heated by infrared absorption by 

ozone; by ultraviolet ozone absorption; and by solar nearinfrared absorption by water vapor, carbon dioxide, and 

molecular oxygen. Cooling occurs mainly by infrared emission from carbon dioxide and water vapor. If the solar and 

infrared absorption by aerosol produce heating, the additional cooling necessary to produce near-equilibrium temperatures at an elevated temperature level, as was observed 

following these three recent eruptions, must come from net 

infrared divergence from the C02 in the layer. All three are 

associated with lower stratospheric temperatures that are 

about 4 °- 6°C higher than pre-eruption values. This value is 

likely to be that temperature rise that is required to bring 

about an increased C02 infrared flux divergence sufficient to 

offset heating by solar and infrared absorption by the aerosol. 

We have selected temperature, specific humidity and 

ozone conditions appropriate to the tropical west Pacific 

(actually for Guam for August 1991) to compute the results 

used in figure 7. Stratospheric temperatures were then 

increased by about 6°C at 50 hPa and elsewhere using a verC/) 

...J 

<( 30 - u 

C/) 

~ 0 

1-

u 

w 

I 

z 

w"' 

40 -

50 -

70 -

~ 100 -

C/) 

C/) 

w 

cr: 150 - a.. 

2QQ~~~~LLLU~~~LLUUUU~~~LLLU~ 

-2.0 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 

HEATING RATE, IN DEGREES CELSIUS PER DAY 

Figure 7. Radiative heating rate components for the lower stratosphere for conditions in the tropical west Pacific before and after 

an eruption. A sounding for Guam, August 1991, was used. The 

procedure followed for these calculations is that outlined in chapter 

6 of Newell and others (1974) and in Hoffman (1981). Curves labeled "A" indicate data collected after eruption; curves labeled "B" 

indicate data collected before eruption (temperature at 50 hPa is 

6°C higher-see text). C02-IR and H20-IR represent infrared 

cooling rates; S-NIR represents near-infrared solar heating by absorption by 02, C02, and H20; 03-UV is solar heating in the ultraviolet region by absorption by 03; 03-IR is infrared heating by 03. 

tical-profile modification based on a previous paper (on Mt. 

Agung-Newell, 1970b). This is justified by the fact that the 

three volcanoes produced about the same maximum temperature change. Modified cooling rates (in °C/day) are also 

shown in figure 7. Both C02 and H20 show larger infrared 

cooling rates, and 0 3 shows a reduced infrared heating rate; 

the largest influence is from C02. Overall, cooling increases 

by approximately 0.34 °C/day at 50 hPa. Hansen and others 

(1978) compared the results of a one-dimensional model of 

the Mt. Agung eruption cloud with the data on tropospheric 

and stratospheric temperature change included in Newell 

and Weare (1976b) and Newell (1970a) and found quite 

good agreement. Their model would presumably produce a 

similar balance in the lower stratosphere. 

In cases where tropospheric cooling is definitely associated with a volcanic eruption, such as the 1963 Agung 

case, it is not yet known how much of the cooling is caused 

by a deficit of visible radiation at the surface, which would 

reduce evaporation and therefore subsequent latent heating 

in the troposphere, and how much is due to a deficit of solar 

near-infrared radiation reaching the troposphere, which normally produces heating through near-infrared absorption by 

02, C02 and H20, as illustrated in the lower part of figure 7. 

As stressed previously (Newell, 1981 ), it would be valuable 

to measure the wavelength dependence of incoming radiation in and below the volcanic cloud as well as the associated 

infrared fluxes. The problem of detecting a tropical troposphere temperature change after a volcanic eruption is 

clearly complicated by the strong influence of eastern equatorial Pacific sea temperature changes. The tropical air temperature changes associated with these SST changes are 

presumably produced through the intermediate mechanism 

of latent heat liberation. When attempting to account for the 

influence of volcanic eruptions on air temperature, oceanic 

storage of energy and transport by currents may also be 

involved. 

Clearly, representation by a simple relationship like 

equation 1 is not adequate, and more studies with good airand ocean-temperature data are necessary. 

Another factor involved in the determination of stratosphere temperature is vertical motion: enhanced rising 

motion produces cooling, and subsidence produces heating. 

It is possible that the vertical motion in the tropical tropopause region may be responsible for the dips in the two maxima of the stratosphere temperature time series. 

INFLUENCE OF ATMOSPHERIC 

TEMPERATURE AND 

DENSITY CHANGES ON FLIGHT 

PERFORMANCE 

As noted in the Introduction to this paper, air density is 

a critical parameter from the aviation point of view. 
266 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Temperature changes of S0

- 6°C in the tropical belt, perhaps 

on occasion extending up to 30 km or more from the tropical 

tropopause, will increase the scale height and density at all 

higher levels. For example, if the S°C-anomaly extends only 

from 20 to 2S km, the density at 2S km increases by about 1.4 

percent, whereas, if the anomaly extends to 30 km (a not 

unreasonable vertical extent for the aerosol cloud based on 

lidar observations by Adriani and others (1983)), there is a 3 

percent increase at 30 km. These density effects increase aircraft drag, but they also increase engine thrust by about the 

same amount-the net effect on flight performance will be 

small. For vehicles flying at hypersonic speeds, aerodynamic 

heating is of major importance; this is proportional to air 

density and to the cube of velocity (Anderson, 1989) so that 

all vehicles flying at altitudes above the aerosol-warmed 

layer would be subject to enhanced heating. 

CONCLUDING REMARKS 

The influence of volcanic eruptions on tropospheric 

temperature is difficult to determine because of the heating 

effect of El Nifio phenomena every few years; in the case of 

the Mt. Agung and El Chich6n eruptions, it was O.S°C or 

less. In the case of Pinatubo, there was no cooling effect on 

the tropical troposphere for the first 6-8 months after the 

June 1991 eruption, due to El Nino, but this has now ended 

while a significant amount of aerosol remains. 

Microwave-sounding-unit data for the lower stratosphere showed increased temperature by several degrees 

Celsius after the eruptions of El Chich6n in 1982 and 

Pinatubo in 1991. It appears that some of the absorption that 

causes increases in temperature may be in the visible or nearinfrared region. The increase in temperature appears to be 

about the same size for the eruptions of Mt. Agung in 1963, 

El Chich6n in 1982, and Pinatubo in 1991. This may be due 

to the self-limiting effect of enhanced infrared flux divergence caused mostly by atmospheric carbon dioxide. 

The temperature changes associated with volcanic aerosol are the largest that occur in the tropical lower stratosphere. For high-speed aircraft flying at and above about 20 

km, these changes have a significant effect on atmospheric 

density and therefore on aerodynamic heating. 

It is recommended that absorption measurements be 

made as a function of wavelength through significant aerosol 

clouds from future volcanic eruptions. 

ACKNOWLEDGMENTS 

We are grateful to Roy W. Spencer and John R. Christy 

for their kindness in giving us access to the microwavesounding-unit data. Support for this work was provided in part 

by MIT Lincoln Laboratory. Calculations based on recent 

data and revised figures have been supported by the National 

Science Foundation under Grant A TM 9106902. Thanks are 

due to Ellsworth Dutton of the NOAA climate monitoring and 

diagnostics laboratory and to the staff of the Mauna Loa 

Observatory for providing atmospheric transmission data. 

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Newhall, G.G., and Self, S., 1982, The volcanic explosivity index 

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1981, Absorption of visible radiation by aerosols in the volcanic plume ofMt. St. Helens: Science, v. 211, p. 836-838. 

Parker, D.E., and Brownscombe, J.L., 1983, Stratospheric warming 

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Philander, S.G., 1990, El Nifio, La Nifia, and the Southern Oscillation: San Diego, Academic Press, 293 p. 

Quiroz, R.S., 1983, The isolation of stratospheric temperature 

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Sedlacek, W.A., Mroz, E.J., Lazrus, A.L., and Gandrud, B.W., 

1983, A decade of stratospheric sulfate measurements compared with observations of volcanic eruptions: Journal of Geophysical Research, v. 88, p. 3741-3776. 

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Ontario, Oct. 17-21, 1983: U.S. Dept. of Commerce, National 

Oceanic and Atmospheric Administration, 401 p. 

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Woods, D.C., and Chuan, R.L., 1983, Size-specific composition of 

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VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

A MESOSCALE DATA ASSIMILATION SYSTEM ADAPTED 

FOR TRAJECTORY CALCULATIONS OVER ALASKA 

By Thomas W. Schlatter and Stanley G. Benjamin 

ABSTRACT 

Soon after a volcanic eruption, it is possible to locate 

the ash plume from satellite imagery, at least if the sky is 

clear. However, as the plume disperses and thins, remote 

detection becomes more difficult. A series of numerical 

analyses of atmospheric observations, which can supply 

wind data to a trajectory model at frequent intervals, is one 

way to accurately track the ash plume. 

National Oceanic and Atmospheric Administration's 

(NOAA) Forecast Systems Laboratory has developed a 

mesoscale analysis and prediction system (MAPS) for 

assimilating surface and tropospheric weather observations 

over the contiguous United States every 3 hours. Designed to 

serve aviation and local nowcasting, MAPS was implemented at the National Meteorological Center in 1992. It 

relies heavily on automated aircraft reports supplied by 

Aeronautical Radio, Inc. (ARINC) through the aircraft communications addressing and reporting system (ACARS). 

These reports use isentropic coordinates (surfaces of constant potential temperature) in the free atmosphere and terrain-following coordinates near the ground. 

MAPS is being adapted for use over Alaska where a 

special high-resolution topography field has been created to 

account for the rough terrain. However, more ACARS 

reports over all of Alaska must be collected in real time so 

that the tropospheric and lower stratospheric wind field can 

be adequately defined every few hours. 

INTRODUCTION 

When a volcano spews ash high into the atmosphere, it 

is not difficult to identify the location of the eruption unless 

dense clouds hide the ash plume from satellites. If the eruption is sufficiently powerful, ash may enter the stratosphere, 

above the clouds. Aircraft in the immediate vicinity of the 

eruption are subject to the life-threatening hazard of engine 

shutdown. Other substantial hazards remain long after the 

eruption, sometimes far from its origin, and aircraft must 

avoid the drifting ash plume. It is important, therefore, to 

know where the plume is and where it is likely to drift. 

Satellites can track the ash plume as long as it can be 

detected. However, after the plume spreads and disperses, 

tracking becomes more difficult, and the levels where ash is 

concentrated are hard to discern. Trajectories calculated 

from a series of wind analyses or from a numerical forecast 

are solutions to the problems of tracking and predicting the 

plume location. 

Trajectories are only as accurate as the analyses and 

forecasts on which they depend. At NOAA's Forecast Systems Laboratory, in Boulder, Colo., a team of meteorologists, a mathematician, and a systems programmer have been 

working for several years to develop a mesoscale analysis 

and prediction system (MAPS), which exploits several 

sources of atmospheric observations that are available 

almost continuously. Even now, analyses of upper-air conditions from the National Meteorological Center (NMC), in 

Washington, D.C., are available only twice a day, at 00:00 

and 12:00 UTC. Over the contiguous 48 United States, sufficient observations are available to support upper-air analyses every 3 hours. MAPS assimilates these surface and 

tropospheric observations every 3 hours to better describe 

atmospheric conditions and make accurate short-term forecasts out to 12 hours. 

A version of MAPS for the lower 48 States is already 

running experimentally at the National Meteorological Center, and another version is being developed for Alaska. The 

analyses and predictions from MAPS can be used as input 

for trajectory calculations whenever Alaskan volcanoes 

erupt. Simkin and others (1981) list 39 volcanoes on the 

Aleutian Islands, 27 on the Alaskan Peninsula, and 18 elsewhere in the State as being active at least once during the 

past 10,000 years. Beget and others (1991) estimate that 

Alaskan eruptions large enough to disrupt air traffic have an 

average recurrence interval of 5-10 years. The eruption of 

Redoubt Volcano on the west side of Cook Inlet during 1989 

and 1990 is a recent example (Brantley, 1990). 

In this paper, we describe how MAPS works, why it is 

useful for trajectory calculations, how it compares to the 

nested grid model (NGM) (the limited-area model currently 

in use at NMC), how MAPS is being adapted for use over 

Alaska, and some changes that must be made before the 

269 
270 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Alaska version performs as well as the version for the lower 

48 States. 

HOW MAPS WORKS 

MAPS provides high-frequency analyses and shortrange forecasts that incorporate "off-time" observations as 

well as synoptic observations (at 00:00 and 12:00 UTC). The 

current resolution of the MAPS grid is 60 km. The main 

users of MAPS are commercial aviation and operational 

forecasters who need short-term guidance for 6-12 hours 

into the future. The main components of MAPS are shown in 

figure 1. 

EXTERNAL DATA SOURCES 

The upper-air assimilation system relies on two external sources of data: (1) a variety of meteorological observations from the surface, troposphere, and lower stratosphere 

(see following section), and (2) time-dependent boundary 

conditions supplied by NMC's nested grid model (NGM). 

Figure 1. The major components of the mesoscale analysis and 

prediction system (MAPS). The upper-air assimilation cycle is selfcontained except for the external inputs noted at the top. Observations of wind, temperature, pressure, and humidity by balloons, aircraft, radars, or observers are included. NGM, nested grid model at 

the National Meteorological Center, which supplies time-dependent lateral boundary conditions for the MAPS forecast model. 

These boundary conditions are needed for the MAPS hybrid 

prediction model. They specify the evolution of the variables 

along the four edges of the forecast area, which pass through 

southern Canada, northern Mexico, and the coastal waters of 

the Atlantic and Pacific Oceans. 

OBSERVATIONS 

The upper-air assimilation cycle begins with the incorporation of observations from four major sources in the contiguous United States and adjacent portions of Canada and 

Mexico: 

• Rawinsondes-About 80 every 12 hours, providing 

observations of winds, altitudes, temperatures, and 

moisture. 

• Wind profiler demonstration network in the Central 

United States-Twenty of the 30 expected pro filers 

were operating by mid-December 1991. Wind profiling radars provide accurate hourly profiles of the 

horizontal wind in the troposphere and lower 

stratosphere. 

• Surface observations-Six hundred to 900 surface 

observations per hour depending on the time of day 

plus about 25 moored buoys. These observations are 

used to analyze low-level altitudes, winds, temperatures, and moisture. 

• A CARS aircraft reports-These are fully automated 

reports of wind and temperature collected from the 

airlines by ARINC (Aeronautical Radio, Inc.) and 

made available through ACARS, the ARINC aircraft 

communications addressing and reporting system. An 

average of 380 to 1,550 reports were available every 3 

hours during December 1991 (fig. 2). For peak travel 

time, the density of reports can be quite remarkable 

(fig. 3). 

(J)Cl 

C::L.U <(> 

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1,800 

1,600 

1,400 

1,200 

1,000 

800 

600 

400 

200 

0 

00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 

TIME (UTC) 

Figure 2. Average number of fully automated A CARS aircraft 

reports received in 3-hour windows during December 1991. There 

are peaks in air traffic at midday and during the late afternoon. 
MESOSCALE DATA ASSIMILATION SYSTEM ADAPTED FOR TRAJECTORY CALCULATIONS OVER ALASKA 271 

Figure 3. ACARS aircraft reports from between 175 and 225mb (from 36,000 to 41,000 ft altitude) received between 16:30 and 19:30 

UTC 19 January 1990. This represents 40 percent of the number received at all levels. The data plot is interpreted as follows: The staff extends into the wind; thus, winds along the East Coast are approximately from the west. Barbs on the staff give wind speed: small barbs represent 5 m/s; full barbs represent 10 m/s; and flags represent 50 m/s. The observations depict a jet stream from Kansas to the mid-Atlantic 

States. 

ACARS observations are the single most important 

asynoptic data source for the MAPS 3-hour assimilation 

cycle (Benjamin, 1991). They are numerous, distributed 

fairly evenly over the lower 48 States, and are mostly from 

between 400 and 150 millibars (mb) (altitudes between 

24,000 and 45,000 ft). Some ascent and descent data are also 

available. These will soon become much more common and 

will be triggered as aircraft pass through specified altitudes. 

Profilers provide excellent wind data in the lower troposphere, an area where A CARS reports are still sparse. 

Satellite radiances (values of upwelling radiation measured in different wavelength intervals) offer the hope of 

estimating layer temperatures and vertically integrated moisture content. So far, we have been unable to demonstrate that 

this data source improves analyses or forecasts when the 

other sources of data are present. However, over Alaska, 

where observations are sparse in comparison to the lower 48 

States, radiances from the polar-orbiting television and infrared observation satellites (TIROS) may prove more valuable. 

Satellite data are not assimilated in the present version of 

MAPS. 

All incoming observations are subjected to several 

stages of quality control. The most rigorous of these is a 

"buddy" check. At each observation location, a value from 

neighboring observations is interpolated. If the interpolated 

value differs significantly from the observed value at that 

point, we run further tests to determine whether the central 

observation or one of its neighbors is at fault. 
272 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

OBJECTIVE ANALYSIS 

For a meteorologist, the words "objective analysis" 

refer to a programmable method for estimating meteorological parameters on a regular set of points, usually a threedimensional grid. The estimates depend upon the available 

observations, which are usually distributed irregularly in 

space and time. Numerical prediction models are often made 

part of the objective analysis for the reasons mentioned in the 

next section. In the case of MAPS, a 3-hour numerical forecast, valid at the analysis time, provides a first guess for the 

analysis. 

The method of objective analysis employed in MAPS is 

known as optimum interpolation and is statistical in nature. 

The method, popularized by Gandin (1963) and still widely 

used, accounts for the errors in different observing systems. 

It also accounts for the geographical distribution of stations 

relative to each other and to the point being analyzed and 

allows observations of one variable to influence the analysis 

of another. For example, observations of the altitude of constant pressure surfaces influence the analysis of wind. 

Finally, the method mixes information from the forecast 

model and observations in a logical way. 

NUMERICAL PREDICTION MODEL 

A numerical prediction model is an essential component of any system that assimilates meteorological data. 

First, the equations in these models summarize our understanding of atmospheric behavior. Second, our best a priori 

estimate of the current state of the atmosphere comes from a 

numerical prediction model, which provides the background 

for subsequent analysis. Moreover, the statistics of model 

performance tell us how to weight the model prediction (i.e., 

the background) relative to the observations. Third, the 

model imposes dynamic consistency on the system and 

retains the effects of all past observations. 

The prediction model in MAPS is an outgrowth of the 

model introduced by Bleck (1984) and is based on the socalled primitive equations. These consist of three prognostic 

equations (for thermodynamic energy and the two components of horizontal momentum) and three diagnostic equations (the ideal gas law, the mass continuity equation, and the 

hydrostatic approximation). Calculations for both the analysis and the prediction are performed on a 60-km grid at each 

of 25 vertical levels. The model allows for stratiform and 

convective precipitation; turbulent transfer of heat, momentum and moisture in the vertical; and a diurnal heating cycle 

(Benjamin, Brewster, and others, 1991; Benjamin, Smith, 

and others, 1991). 

Figure 4 summarizes the assimilation cycle. New observations are introduced every 3 hours, followed by a 3-hour 

forecast, which extrapolates atmospheric conditions forward 

to the next analysis time. Twice daily, at 00:00 and 12:00 

UTC, the forecast runs out to 12 hours, mainly for comparison with NMC's nested grid model. As soon as NGM results 

are available, the time-dependent lateral boundary conditions for the MAPS domain are updated. 

USING MAPS FOR TRAJECTORY 

CALCULATIONS 

MAPS itself does not compute trajectories; rather, it 

supplies a series of analyzed or predicted wind fields to 

NOAA's Air Resources Laboratory, in Washington, D.C., 

which has long experience in generating trajectories. See 

Stunder and Heffter (this volume) for details on trajectory 

calculations. 

Why should wind fields from MAPS be particularly 

good for the generation of trajectories? The immediate 

answer is that frequent assimilation of "off-time" observations permits sharper definition of mesoscale flow features 

that are tens to hundreds of kilometers in size, thus leading 

to a more accurate wind field. 

A less obvious answer is related to the choice of vertical 

coordinate. Analyses and predictions in MAPS are computed 

in hybrid vertical coordinates (Benjamin, Smith, and others, 

1991 ), which are a combination of two kinds of coordinates. 

In the free atmosphere, we use isentropic coordinates (19 

surfaces of constant potential temperature). In adiabatic flow 

when there are no heat sources or sinks, air on a particular 

isentropic surface will remain on that surface. Under this 

assumption, trajectory calculations become two-dimensional. The vertical spacing of isentropic coordinates is tied 

to the stability of the atmosphere; the surfaces are close 

together when the atmosphere is stably stratified and widely 

12-hour forecast 12-hour forecast 

TIME (UTC) 

00 03 06 09 12 15 18 21 00 

t 3-hour t 3-hour t 3-hour t 3-hour t 3-hour t 3-hour t 3-hour t 3-hour t forecast forecast forecast forecast forecast forecast forecast forecast 

DATA DATA DATA DATA DATA DATA DATA DATA DATA 

t t 

NEW NGM BC's NEW NGM BC's 

Figure 4. A 3-hour assimilation cycle. Every 3 hours, newly observed data are used to analyze atmospheric conditions. These analyses supply the initial conditions for a numerical prediction, which 

advances the atmospheric state forward to the next analysis time, 

when another batch of observations is assimilated. Twice a day, at 

00:00 and 12:00 UTC, the forecast goes out to 12 hours. Each time 

the nested grid model (NGM) runs at NMC, a new set of time-dependent lateral boundary conditions (BC) replaces the old set. 
MESOSCALE DATA ASSIMILATION SYSTEM ADAPTED FOR TRAJECTORY CALCULATIONS OVER ALASKA 273 

(/) 

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0 

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100,-------------------------------~ 

200 

300 

400 

500 

600 

700 

800 

900 

1,000 

410 

380 

360 

350 

342 

335 

330 

325 

320 

316 

312 

308 

304 

300 

296 

292 

286 

280 

272 

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w 

u 

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0::: 

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0:: 

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~ 

Figure 5. An illustration of the hybrid vertical coordinates used 

in MAPS. This vertical cross section was taken at 12:00 UTC 1 

February 1990. It runs from the Pacific Ocean, off the Oregon coast 

on the left, to South Dakota, on the right. Terrain is silhouetted in 

black. Six terrain-following surfaces, each higher one smoother 

than the one below, occupy, on average, the first 150 mb above 

ground. In the free atmosphere, up to 19 isentropic surfaces with 

variable spacing (generally from 4 to 10 degrees Kelvin) are used 

for computation. 

spaced when the lapse rate (decrease of temperature with 

altitude) is steep. This property gives enhanced spatial resolution where it is needed, such as in the vicinity of atmospheric fronts and jet streams. 

One drawback of isentropic coordinates is that they 

become too widely spaced in deep, well-mixed boundary 

layers, which develop often on hot summer days and over 

elevated terrain. To overcome this drawback, terrain-following coordinates are used, spaced about 30 mb (or roughly 

300 m) apart, on average, for the lowest six surfaces. This 

gives reasonable precision in the calculation of vertical 

fluxes of momentum, heat, and moisture close to the ground. 

The hybrid coordinate system is illustrated in figure 5. The 

surfaces move up or down depending upon atmospheric conditions; hence, this depiction is for a specific time and date. 

PERFORMANCE:MAPSVERSUSNGM 

In a recent comparison between MAPS and NMC's 

nested grid model, we interpolated wind predictions by 

MAPS and the NGM to rawinsonde sites in the United States 

and southern Canada. We then computed the magnitude of 

the vector difference between predicted and observed winds. 

The root-mean-squares of these differences appear in figure 

6 as a function of pressure level. The most striking result is 

that 3-hour and 6-hour MAPS wind forecasts are consistently better than the 12-hour NGM forecasts that are valid at 

the same time. This is true at all levels, but it is especially 

true at altitudes between 24,000 and 45,000 ft (or, equivalently, between 400 and 150mb on fig. 6) where commercial 

jets provide most of the A CARS data This demonstrates 

clearly the advantage of frequent assimilation of off-time 

data. The choice of isentropic coordinates is also an advantage; these coordinates tend to crowd together and give good 

vertical resolution in the high troposphere and lower stratosphere in the vicinity of the jet stream. 

During 1992, MAPS ran experimentally in real time on 

NMC's Cray Y-MP supercomputer on a domain covering 

the lower 48 States. Output stored on disks at NMC was 

carefully examined for evidence of mistakes in the computer 

code. By late 1992, the system was running reliably and performing well. Preliminary tests of an Alaskan version of 

MAPS are scheduled for 1993 at the Forecast Systems Laboratory in Boulder, Colo. If the available data show that a 3-

hour assimilation cycle over Alaska is viable, more rigorous 

testing could begin at NMC. 

(/) 100 0:: 

<( 

cc 200 ::::i 

-1 

~ 300 

~ 

u.i 400 c: 

:J 

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(/) 500 UJ 

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0.. 600 u 

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0 800 ~ 

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I I 

/ / 

/ / 

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I \ I 

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5 

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l 

/ 

/ 

EXPLANATION 

\ 

... 

3 MAPS 3-hour forecast 

6 MAPS 6-hour forecast 

N NGM 12-hour forecast 

6 7 8 

ROOT-MEAN-SQUARE VECTOR ERROR, (IN METERS 

PER SECOND) IN PREDICTED WIND 

9 

Figure 6. The root-mean-square vector error in wind forecasts 

produced by MAPS and the NGM. The error was estimated by comparing predicted winds with winds measured by rawinsonde in the 

United States and southern Canada from 26 November through 29 

December 1991. All three forecasts shown are valid at the same 

time. 
274 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

ADAPTING MAPS FOR USE OVER 

ALASKA 

Alaska has far greater topographical relief than any of 

the lower 48 States. It also has a longer, more convoluted 

shoreline. The terrain-following surfaces used in MAPS 

conform to the rough topography as closely as the horizontal resolution allows. Our first experiments over Alaska 

will employ "envelope" topography, obtained from a file of 

very high resolution topography in the following way. For 

each grid box of the prediction model, one adds the standard deviation of altitude to the mean altitude. Envelope 

topography accounts for the fact that mountain barriers to 

the wind are higher than the mean altitude. The MAPS 

domain for Alaska and envelope topography for a 60-km 

grid are shown in figure 7. 

Roughly 50 percent of the domain in figure 7 is covered 

by ocean. The observation sources currently contributing to 

Figure 7. The geographical domain for the Alaska version of MAPS. Tick marks around perimeter are at 60-km spacing. Elevation contours 

for envelope topography (see text) are at 100-m intervals. 
MESOSCALE DATA ASSIMILATION SYSTEM ADAPTED FOR TRAJECTORY CALCULATIONS OVER ALASKA 275 

MAPS will supply scant information over the ocean because 

ACARS data are acquired only within a few hundred kilometers of a ground station. To improve analyses in oceanic 

regions, it will be necessary to adapt MAPS for assimilation 

of ship reports and TIROS radiance data. In addition, the 

western boundary of the NGM is so close to Alaska that the 

inflow conditions are likely to be poorly defined, thus 

quickly contaminating the forecast. To correct this problem, 

we also must replace the time-dependent lateral boundary 

conditions from the NMC's nested grid model with those 

from the aviation (global spectral) model. 

CONCLUDING REMARKS 

MAPS is a system for the frequent assimilation of 

diverse surface, tropospheric, and lower stratospheric 

weather data. The system provides frequent updates on 

atmospheric conditions to aviation and local forecasters. A 

wealth of wind reports available from wind profilers and 

commercial jets permits detailed analyses every 3 hours and 

accurate short-term predictions of winds over the lower 48 

States. These 3-hour "snapshots" and corresponding predictions can feed into trajectory calculations for tracking volcanic plumes and predicting their future movement (Stunder 

and Heffler, this volume). 

One major obstacle prevents immediate application of 

MAPS over Alaska: the lack of data. Many aircraft fly over 

Alaska, and the Aleutian chain is a major international route. 

While many of these aircraft are equipped to provide automated reports, as of summer 1991, the only ground station 

for receipt of these reports was at Anchorage. In the same 

way that thousands of A CARS reports per day make MAPS 

a viable system for the lower 48 States, a similar density of 

reports is required for the Alaskan version. 

The Federal Aviation Administration and Aeronautical 

Radio, Inc. are helping to alleviate this problem. As of January 1993, nine more ground receiving stations are operating in Alaska: at Shemya, Adak, Dutch Harbor, Cold Bay, 

St. Paul Island, Bethel, King Salmon, McGrath, and Fairbanks. By late 1993, eight more are expected in southeast 

Alaska and northwest Canada. This will greatly increase 

the number of reports. Efforts should also be made to 

obtain over-water reports relayed by satellite. Until about 

100 reports can be collected every hour, reasonably distributed over the domain of figure 7, we should not expect that 

a rapid-update assimilation cycle will improve upon the 

operational 12-hour forecasts that are already available. 

ACKNOWLEDGMENTS 

We thank our colleagues, Patty Miller, Tracy Smith, 

and Kevin Brundage and long-term visitors Jean-Marie Carriere and Pan Zaitao for their assistance in developing 

MAPS. We acknowledge the help of the Facilities Division 

of the Forecast Systems Laboratory in decoding A CARS 

reports. This project is funded by the National Weather Service. 

REFERENCES CITED 

Beget, J.E., Swanson, S.E., and Stone, D., 1991, Frequency andregional extent of ash eruptions from Alaskan volcanoes [abs.], 

in Casadevall, T.J., ed., First International Symposium on Volcanic Ash and Aviation Safety, U.S. Geological Survey Circular 1065, p. 13. 

Benjamin, S.G., 1991, Short-range forecasts from a 3h isentropicsigma assimilation system using ACARS data: Boston, Mass., 

American Meteorological Society, Proceedings, Fourth International Conference on Aviation Weather Systems, 24-28 

June,Paris,France,p.329-334. 

Benjamin, S.G., Brewster, K.A., Brummer, R., Jewett, B.F., Schlatter, T.W., Smith, T.L., and Stamus, P.A., 1991, An isentropic 

three-hourly data assimilation system using ACARS aircraft 

observations: Monthly Weather Review, v. 119, p. 888-906. 

Benjamin, S.G., Smith, T.L., Miller, P.A., Kim, D., Schlatter, T.W., 

and Bleck, R., 1991, Recent improvements in the MAPS isentropic-sigma data assimilation system: Boston, Mass., American Meteorological Society, Proceedings, Ninth Conference on 

Numerical Weather Prediction, 14-18 October, Denver, Colo., 

p. 118-121. 

Bleck, R., 1984, An isentropic coordinate model suitable for lee cyclogenesis simulation: Estratto dalla Rivista di Meteorologia 

Aeronautica, v. 44, p. 189-194. 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14, 1989-August 31, 1990. U.S. Geological Survey Circular 1061, 33 p. 

Gandin, L.S., 1963, Objective analyses of meteorological fields: 

Leningrad, Giderometeorologicheskae Izdatel' stvo, [original 

in Russian, translated in 1965 by Israel Program for Scientific 

Translators], 242 p. 

Simkin, T., Siebert, L., McClelland, L., Bridge, D., Newhall, C., 

and Latter, J.H., 1981, Volcanoes of the World: Stroudsburg, 

Pa., Hutchinson Ross Publishing Co., Smithsonian Institution, 

240p. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

MODELING VOLCANIC ASH TRANSPORT 

AND DISPERSION 

By Barbara J.B. Stunder and Jerome L. Heffler 

ABSTRACT 

A real-time long-range volcanic ash forecast transport 

and dispersion model is described. Ash emitted into the 

atmosphere as high as 100mb(:: 53,000 ft) is modeled as a 

nearly steady eruption column. Falling ash is modeled as 

advecting downwind with the National Weather Service 

forecast wind fields. Maps of relative ash concentration for 

various layers in the atmosphere are produced. The presence 

of falling ash is clearly seen in the volcanic eruption example 

shown. Some of the ash shown in the lower layer output map 

must have fallen from above because it cannot be explained 

by transport and dispersion in the lower layer alone. 

INTRODUCTION 

Airline pilots are clearly interested in avoiding volcanic 

ash clouds because of possible damage, ranging from 

abraded windscreens to engine failure. At least five commercialjet aircraft were damaged from encounters with airborne 

ash during the first 3 months of the eruption ofRedoubt Volcano, near Anchorage, Alaska, beginning in December 1989 

(Brantley, 1990). 

A memorandum of understanding (MOU) concerning 

volcano hazards alert between the National Oceanic and 

Atmospheric Administration (NOAA) and the Federal Aviation Administration (FAA) was signed in 1988, prompted by 

the 1980 eruptions ofMount St. Helens, Washington, and the 

1982 eruption of Galunggung, in Java, Indonesia. Under the 

terms of the MOU, the role of NOAA Air Resources Laboratory (ARL) is to provide volcanic-ash-trajectory forecasts. 

Upon notification of an eruption, ARL produces a forecast 

that gives the predicted location of volcanic ash at several 

levels in the atmosphere for times up to 48 hours after the 

eruption. Typically, an updated forecast is made 12 hours 

later when the meteorological analysis and new forecast data 

are available. 

As of 1991, the NOAA-ARL volcano hazards alert 

message consisted of three parts: (1) a text message giving 

the regional extent of the ash cloud at several atmospheric 

levels in 6-hour periods after the release, (2) maps of the 

forecast isobaric trajectories for the ash cloud, and (3) latitude/longitude tabular listings of the trajectories. As an 

example, figure 1 shows the text message for a hypothetical 

50,000-ft eruption of Mount St. Helens at 00 GMT (Greenwich Mean Time), September 11, 1991. Because the trajectories show the predicted path of air parcels rather than ash 

particles, a cautionary note regarding falling ash is added to 

the end of the descriptive paragraph in the text message. The 

48-hour duration 200-mb, 300-mb, 500-mb, and 700-mb trajectory maps and tables are shown in figures 2A-2D. (See 

table 1 for an atmospheric pressure level to altitude reference.) The 200-mb and 300-mb trajectories both show the 

ash cloud moving south, across California, then northeastward, reaching Minnesota 48 hours after the eruption. The 

500-mb trajectory is much shorter, with ash moving south 

across California, but reaching only Arizona at 48 hours. At 

700 mb, ash is predicted to move south to the central California coastal region at 48 hours. 

An evaluation of the forecast trajectories from similar 

model runs for a series of Redoubt Volcano eruptions shows 

that average trajectory forecast error at 300 mb is usually less 

than 25 percent of the downwind distance from the volcano 

(Heffter and others, 1990). Trajectory errors of this magnitude are typical (e.g., Rolph and Draxler, 1990). 

Since December 1992, the ARL product is a graphic 

product. The model is now named the volcanic ash forecast 

transport and dispersion model (V AFT AD). V AFT AD was 

developed to provide a better three-dimensional depiction in 

time of the ash cloud than does the trajectory model. The 

ambiguity of the cautionary warning in the forecast trajectory text message (fig. 1) is addressed. The new model is 

designed for operation on a 386-class personal computer. 

National Weather Service (NWS) forecast wind data on nine 

isobaric levels, from 850 mb to 100 mb, are downloaded 

from an NWS mainframe computer as input to the model 

run. User inputs are volcano name, latitude and longitude, 

eruption date, time, and ash cloud height. Since the total 

amount of ash erupted is usually unknown at the time of the 

eruption, a unit mass is assumed. Also, since the eruption 

duration may not be known, a 3-hour eruption is assumed. 

The dynamics of the eruption column itself are not modeled; 

277 
278 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Selected atmospheric pressure levels. 

Pressure 

(millibars) 

100 

150 

200 

250 

300 

400 

500 

700 

850 

Approximate altitude 

(feet above sea level) 

53,000 

44,000 

39,000 

34,000 

30,000 

24,000 

18,000 

10,000 

5,000 

******************************************************** 

VOLCANO HAZARDS ALERT MT.ST HELENS 

NOAA-AIR RESOURCES LABORATORY 

SILVER SPRING, MD 

09/11/91 1313Z 

MT ST HELENS ERUPTED ON 09/11/91 AT OOOOZ WITH VOLCANIC ASH REPORTED AS HIGH AS 50000 FT. LONG~RANGE FORECAST TRAJECTORIES INDICATE THAT ANY ASH 

REMAINING IN THE ATMOSPHERE WILL MOVE OVER THE FOLLOWING 

REGIONS AT THE HEIGHTS ~ DATE/TIMES GIVEN. CAUT~ON: ASH MAY FALL FROM GIVEN REGIONS TO LOWER HEIGHTS. 

7000 TO 15000 FT WEST OREGON 

WEST OREGON 

WEST OREGON 

NORTH CALIFRNIA 

NORTH CALIFRNIA 

NORTH CALIFRNIA 

NORTH CALIFRNIA 

.NORTH CALIFRNIA 

15000 TO 25000 FT 

WEST OREGON 

NORTH CALIFRNIA 

NORTH CALIFRNIA 

OFFSHOR-S CALIF 

OFFSHOR-S CALIF 

SOUTH CALIFRNIA 

SOUTH CALIFRNIA 

SOUTH CALIFRNIA 

25000 TO 35000 FT 

WEST OREGON 

NORTH CALIFRNIA 

OFFSHOR-S CALIF 

SOUTH CALIFRNIA 

ARIZONA 

UTAH 

NORTHCENTRL US 

NORTHCENTRL US 

35000 TO 45000 FT 

WEST OREGON . NORTH CALIFRNIA 

SOUTH CALIFRNIA 

SOUTH CALIFRNIA 

UTAH 

NORTHCENTRL US 

NORTHCENTRL US 

NORTHCENTRL US 

11/00Z TO 

11/06Z TO 

11/12Z TO 

11/18Z TO 

12/00Z TO 

12/06Z TO 

12/12Z TO 

12/18Z TO 

11/06Z 

11/12Z 

11/18Z 

12/00Z 

12/06Z 

12/12Z 

12/18Z 

13/00Z 

11/00Z TO 11/06Z 

11/06Z TO 11/12Z 

11/12Z TO 11/18Z 

11/18Z TO 12/00Z 

12/00Z TO 12/06Z 

12/06Z TO 12/12Z 

12/12Z TO 12/18Z 

12/18Z TO 13/00Z 

11/00Z TO 11/06Z 

11/06Z TO 11/12Z 

11/12Z TO 11/18Z 

11/18Z TO 12/00Z 

12/0QZ TO 12/06Z 

12/06Z TO 12/12Z 

12/12Z TO 12/18Z 

12/lBZ TO 13/00Z 

11/00Z TO 11/06Z 

11/06Z TO 11/12Z 

11/12Z TO 11/18Z 

11/18Z TO 12/00Z 

12/00Z TO 12/06Z 

12/06Z TO 12/12Z 

12/12Z TO 12/18Z 

12/18Z TO 13/00Z 

******************************************************** 

Figure 1. Volcano-hazards-alert text message for a hypothetical 

eruption to 50,000 ft of Mount St. Helens at 00 GMT (Greenwich 

Mean Time), September 11, 1991. "Z" indicates Zulu (equivalent to 

Greenwich Mean Time or Coordinated Universal Time). 

instead, the eruption is assumed to be nearly steady, with ash 

particles of a given size distribution uniformly distributed 

throughout the column. The uniform vertical distribution is 

clearly an approximation; later versions of the model may 

incorporate more detail in the initial ash distribution. The ash 

falls, disperses, and is advected downwind following the 

forecast wind data. Maps of ash concentration relative to the 

unit source are output for three atmospheric layers of interest 

to the aviation community. Removal of ash by precipitation 

is not considered in order to produce a conservative estimate 

of the concentration and ash cloud location. 

ATMOSPHERIC TRANSPORT AND 

DISPERSION 

The forecast wind data used in the transport and dispersion model are from one of the NWS National Meteorological Center's numerical weather prediction models: either the 

nested grid model (NGM) (Hoke and others, 1989) or the 

aviation run (A VN) of the medium range forecast model 

(Petersen and Stackpole, 1989). Both models are run twice 

daily and produce forecast data at 6-hour intervals. Wind 

fields on the following pressure levels are used by the volcano model: 850, 700, 500, 400, 300, 250, 200, 150, and 100 

mb. The NGM is a regional model covering North America; 

the A VN is a global model. The spatial resolution of the 

NMC output for the NGM and A VN on a polar stereographic 

projection at 60° latitude are 190.5 km and 381 km, respectively. The meteorological model specifications are summarized in table 2. Model output should not be interpreted at 

sub-grid scales. 

Table 2. Specifications ofNMC data used in volcano model. 

[NMC, National Meteorological Center; NGM, nested grid model (Hoke and others, 

1989); A VN, aviation run of the medium range forecast model (Petersen and Stackpole, 

1989)] 

NGM model A VN model 

Coverage North America Global 

Spatial resolution1 190.5 km 381 km 

Forecast period 48 h 72 h 

1 At 60° latitude on a polar stereographic projection. 
A 

AVIATION RUNo OBSERVATION I 

TRA.J START<•) 1 

LEIIEL1 

B 

AVIATION RUN1 OBSERI/ATIIJN1 

TRA.J START <•l o LEIIEL1 

MODELING VOLCANIC ASH TRANSPORT AND DISPERSION 

c 

AVIATION RUN1 OBSERI/ATIDNo 

TRAJ START<.) 1 

LEI/EL1 

D 

AVIATION RUI'h OBSERI/ATIONo 

TRAJ START<•) 1 LEVEL• 

279 

Figure 2. Forecast trajectory map and table corresponding to the text message in figure 1 for the following levels: A, 200mb; B, 300mb; 

C, 500mb; andD, 700mb. Mount St. Helens is identified by"#," and the eruption date and time {GMT, or Z) are given. Numbers along the 

trajectory give time; at 00 GMT the date is shown. 
280 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Transport trajectories are computed using a modified 

Euler advection technique to account for acceleration (Carnahan and others, 1969). This technique was also used by 

Heffler (1983). Horizontal dispersion causes puff size to 

grow linearly with time because: 

a= t/2 (1) 

where 

cr is the horizontal standard deviation, in meters, of the 

concentration, and 

tis time after the eruption, in seconds (Heffler, 1965). 

This horizontal dispersion applies to long-range transport. A 

bivariate normal distribution gives the concentration at any 

radial distance from the center of a puff. 

ASH PARTICULATE 

Given that different volcanoes and even multiple eruptions of one volcano may have different ash-particle size distributions, we assumed one typical distribution for our 

model. Measured ash-particle size distributions are obtained 

from either ground-level samples (e.g., Carey and Sigurdsson, 1982) or airborne samples (e.g., Hobbs and others, 

1982). Because individual ground-level samples are not 

likely to be representative of the population of ash in the 

eruption column, Carey and Sigurdsson (1982) computed the 

"total" particle size distribution for the May 18, 1980, Mount 

St. Helens (MSH) eruption using many ground-level samples. The total particle size distribution is an estimate of the 

overall distribution in the eruption column. The resulting 

MSH total distribution (particles of diameter 2 Jlm to 16 mm) 

could be used in our model, but it does not include the 

smaller particles that remain airborne for extensive periods. 

However, individual airborne samples also may not be 

representative, especially because research aircraft cannot 

safely fly through ash clouds near volcanoes. Airborne samples also do not contain larger particles that have already 

fallen out. Because our prime interest is with particles that 

remain airborne from 24 to 48 hours, we use a particle size 

distribution obtained from aircraft samples taken about 130 

km downwind of a volcano (Hobbs and others, 1991), rather 

than a distribution obtained from ground-level samples. Aircraft samples closer to the volcano were not obtained 

because of safety considerations. The particles considered 

range in diameter from 0.1 Jlm to 100 Jlm. 

Ash particles are assumed to fall as spheres according 

to Stokes' law modified by the Cunningham slip correction 

(Slade, 1968): 

v=C[(gtf2p )/(18Jl)] (2) 

where 

v is the fall velocity (in m/s ), 

g is the gravitational constant (in m/s2), 

dis the particle diameter (in m), 

p is the ash particle density (in g/m3), 

Jl is the kinematic viscosity of air (in g/ms ), 

C=1+[/Jd][2.52+0.8(exp(-0.55d/A.))] is the Cunningham 

slip correction (non-dimensional), and 

A. is the mean free path of air (in m). 

The correction is important only for smaller particles 

(approximately less than 5 Jlm) whose fall velocities are 

greater than those according to Stokes' law because ash particles tend to slip past air molecules. Particle shape and rotation, such as addressed by Wilson and Huang (1979), are 

not considered. Our approximation is applicable given the 

spatial and temporal scales used here. 

MODEL OUTPUT 

Output consists of maps of maximum 1-hour ash concentrations during a 24-hour period (0-24 h or 24-48 h). 

Maps for three layers are given. These layers will be referred 

to as layer 1 (15,000 to 25,000 ft), layer 2 (25,000 to 35,000 

ft), and layer 3 (35,000 to 50,000 ft). Ground-level concentrations are not computed, and altitude is described in units 

of feet in deference to the aviation community. Symbols on 

the output maps indicate ranges of concentration (low, intermediate, and high) relative to the unit source. The exact computed concentration is not used for two reasons: (1) the 

amount of ash emitted is usually unknown, and (2) critical 

concentrations that affect the aircraft or its operation are 

unknown. The intermediate and low relative concentrations 

each span two orders of magnitude. These categories are 

somewhat arbitrary because even the low concentrations 

may still be hazardous to aircraft. 

The forecast transport and dispersion model was run for 

the simulated eruption of Mount St. Helens on September 

11, 1991 (as was the trajectory model-figs. 1 and 2A-2D). 

Figures 3A-3C and 4A-4C show the relative ash concentrations in the three layers for the two successive 24-hour periods after the eruption. For the first 24-hour period (figs. 

3A-3C), the ash moved south across Oregon, continued generally along the California coast, then moved to the northeast 

across southern California toward the Nevada-Utah-Arizona 

region. The pattern in all three layers is fairly similar, with 

"high" concentrations generally found near the volcano. Ash 

concentrations lower than what are categorized as "low" are 

not shown on the maps. In the next 24-hour period (figs. 

4A-4C), the ash was transported from the southern California region to the Lake Superior region, again with similar 

patterns at the three layers. In most areas, the concentrations 

are categorized as "intermediate", with no "high" concentrations and only some "low" concentrations. 
MODELING VOLCANIC ASH TRANSPORT AND DISPERSION 281 

Figure 3. Relative concentration for hypothetical eruption given in 

figure 1 for the first 24-hour period after the eruption (00 GMT September 11 to 00 GMT September 12, 1991) for the following layers: 

A, 35,000 to 50,000 ft; B, 25,000 to 35,000 ft; and C, 15,000 to 25,000 

ft. "0" shows volcano location; "* ,""+,"and"-" indicate high, intermediate, and low relative concentrations, respectively (see text for 

explanation of relative concentration). 

Figure 4. Relative concentration for hypothetical eruption given 

in figure 1 for the second 24-hour period after the eruption (00 GMT 

September 12 to 00 GMT September 13, 1991) for the following 

layers: A, 35,000 to 50,000 ft; B, 25,000 to 35,000 ft; and C, 15,000 

to 25,000 ft. "0" shows volcano location;"*,""+," and"-" indicate 

high, intermediate, and low relative concentrations, respectively 

(see text for explanation of relative concentration). 
282 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

A comparison of the transport and dispersion output 

(figs. 3A-3C and 4A-4C) with the trajectories (figs. 2A-2D) 

shows the presence of falling ash and dispersion. The concentration pattern in figure 3A agrees well with the first 24 

hours of the 200-mb trajectory (fig. 2A). The ash off the California coast reflects the 150-mb trajectory (not shown). The 

concentration pattern in figure 3B agrees well with the 300-

mb (fig. 2B) and 250-mb trajectories (not shown). Some ash 

has fallen from layer 3 to 2 during the first 24 hours. The 

"high" relative concentrations in central California in figure 

3B may result from falling ash, but, otherwise, falling ash is 

not clearly evident for layer 2. In layer 1 (fig. 3C), the ash 

along the coast agrees with the 500-mb and 400-mb trajectories (figs. 2C and 2D), but the large region of ash over southem California and into Arizona is not reflected by the 

trajectories. The ash in that region must have fallen from 

layer 2 and possibly from layer 3. 

For the second 24-hour period, again the layer 2 and 

layer 3 patterns correspond to the trajectories. The layer 1 

pattern also corresponds to the trajectories but clearly contains ash falling from layers 2 and 3. The 500-mb and 400-

mb trajectories corresponding to layer 1 terminate in central 

Arizona and northeastern Utah, respectively, but the ash 

across Wyoming, Montana, the Dakotas, and Minnesota 

must have fallen to this layer. For both 24-hour periods, layer 

1 shows falling ash because the transport winds are much 

slower than those at higher altitudes. Falling ash at layer 2 is 

not apparent in the output maps because the transport winds 

are similar to those at layer 3. 

SUMMARY 

A real-time long-range forecast volcanic ash transport 

and dispersion model has been developed for the aviation 

community. The model uses NWS forecast wind fields and 

Stokes' fall velocity with a slip correction for small particles. 

In the model, ash is emitted into the atmosphere to all layers 

by a nearly steady eruption column. The model produces 

maps of relative ash concentration in three layers in the 

atmosphere for times up to 48 hour after an eruption. Comparison of isobaric trajectories and the model output concentration maps show the presence of dispersion and falling ash. 

In an example, the transport and dispersion model 

shows that a given region contains falling ash, but that same 

region may be free of ash according to the trajectory forecast. 

The trajectory model simply predicts an ash particle's position assuming it flows with the wind at a given atmospheric 

level. However, the transport and dispersion model produces 

a more realistic depiction of the three-dimensional ash plume 

because it accounts for falling and horizontally dispersing 

ash. The model generates relative ash concentrations 

because the critical concentrations that affect aircraft operations and the amounts of ash actually erupted are not known. 

ACKNOWLEDGMENT 

This work was supported by the NOAA-National 

Weather Service Alaska volcano project. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14, 1989-August 31, 1990: U.S. Geological Survey Circular 1061, 33 p. 

Carey, S.N., and Sigurdsson, H., 1982, Influence of particle aggregation on deposition of distal tephra from the May 18, 1980, 

eruption of Mount St. Helens volcano: Journal of Geophysical 

Research, v. 87, p. 7061-7072. 

Carnahan, B., Luther, H.A., and Wilkes, J.O., 1969, Applied Numerical Methods: New York, John Wiley and Sons, Inc., 362 p. 

Heffter, J.L., 1965, The variation ofhorizontal diffusion parameters 

with time for travel periods of one hour or longer: Journal of 

Applied Meteorology, v. 4, p. 153-156. 

--1983, Branching atmospheric trajectory (BAT) model: 

NOAA Technical Memorandum ERL ARL-121, Air 

Resources Laboratory, Rockville, Md., 16 p. 

Heffter, J.L., Stunder, B.J.B., and Rolph, G.D., 1990, Long-range 

forecast trajectories of volcanic ash from Redoubt Volcano 

eruptions: American Meteorology Society Bulletin, no. 71, p. 

1731-1738. 

Hobbs, P.V., Radke, L.F., Lyons, J.H., Ferek, R.J., Coffman, D.J., 

and Casadevall, T.J., 1991, Airborne measurements of particles and gas emissions from the 1990 volcanic eruptions of 

Mount Redoubt: Journal of Geophysical Research, v. 96, p. 

18735-18752. 

Hobbs, P.V., Tuell, J.P., Hegg, D.A., Radke, L.F., and Eltgroth, 

M.W., 1982, Particles and gases in the emissions from the 

1980-1981 volcanic eruptions of Mount St. Helens: Journal of 

Geophysical Research, v. 87, p. 11062-11086. 

Hoke, J.E., Phillips, N.A., DiMego, G.J., Tuccillo, J.J., and Sela, 

J.G., 1989, The regional analysis and forecast system of the 

National Meteorological Center: Weather Forecasting, v. 4, p. 

323-334. 

Petersen, R.A., and Stackpole, J.D., 1989, Overview of the NMC 

production suite: Weather Forecasting, v. 4, p. 313-322. 

Rolph, G.D., and Draxler, R.R., 1990, Sensitivity of three-dimensional trajectories to the spatial and temporal densities of the 

wind field: Journal of Applied Meteorology, v. 29, p. 

1043-1054. 

Slade, D., ed., 1968, Meteorology and atomic energy: U.S. Department of Energy, Division of Technical Information, 445 p. 

Wilson, L., and Huang, T.C., 1979, The influence of shape on the 

atmospheric settling velocity of volcanic ash particles: Earth 

and Planetary Sciences Letters, v. 44, p. 311-324. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

DEVELOPMENT OF A PREDICTION SCHEME 

FOR VOLCANIC ASH FALL FROM 

REDOUBT VOLCANO, ALASKA 

By Hiroshi L. Tanaka 

ABSTRACT 

The purpose of this project is to develop a volcanic 

plume prediction model for volcanoes located in the Cook 

Inlet area, Alaska. Knowing where the ash plume is and predicting where it will go are important for public health and 

safety, as well as for flight operations and mitigating economic damage. For near-real-time plume prediction, acquisition of upper-air wind data is the essential part of the 

prediction scheme. 

In this project, near-real-time meteorological data are 

provided by the National Meteorological Center, transmitted 

via Unidata. Reading the real-time and forecast wind data, 

the prediction model computes advection, diffusion, and 

gravitational fallout for the plume particles from the vertical 

column over the volcano. Three-dimensional dispersal of 

plume particles are displayed on the computerized graphic 

display as a function of time following the eruption. The 

model predictions appear on the screen about 15 minutes 

after the eruption report, showing the geographical distributions of plume dispersal for the following several hours. 

Although the model simulation inevitably has forecast errors 

owing largely to errors in the forecast wind input, the prediction product offers a useful guide for public safety, especially for the Cook Inlet area, Alaska. 

INTRODUCTION 

Anchorage, Alaska is one of the focal points of international aviation activities. The city lies close to several active 

and potentially active volcanoes including Hayes, Spurr, 

Redoubt, Iliamna, Augustine, and Douglas along the west 

shore of Cook Inlet, and Wrangell Volcano to the east. In this 

century Spurr, Redoubt, and Augustine together have had 

eight significant eruptions that have spread ash over a broad 

area of south-central Alaska. It is necessary to establish a 

reliable scheme for predicting the distribution of volcanic 

ash fall after an eruption in order to avoid unnecessary disruptions of aircraft operations. For the plume prediction to be 

operational, an immediate eruption report and real-time 

upper-air data must be available. A quick response is one of 

the priorities of the plume-prediction system. 

The Alaska Volcano Observatory (AVO) at the Geophysical Institute, University of Alaska, Fairbanks, has 

direct access to near-real-time satellite imagery and upperair weather data (Dean and others, this volume). By combining this information with the established eruption-monitoring network provided by AVO, we have established a 

volcanic plume prediction model that predicts volcanic ash 

dispersal as a function of time immediately after the eruption. The upper-air wind data are the fundamental input to 

the plume-prediction model. The National Meteorological 

Center (NMC), in Washington, D.C., offers daily weather 

predictions as well as analyzed and initialized meteorological data on three-dimensional (3-D) gridded mesh. Recently, 

a national program in atmospheric sciences, referred to as 

Unidata, enables university researchers to use the real-time 

NMC data through a satellite downlink (Sherretz and Fulker, 

1988; Tanaka, 1991a, 1991b). Therefore, the real-time 

upper-air wind data are available at AVO. 

In response to the eruption of Redoubt Volcano at the 

end of 1989, a volcanic plume prediction model has been 

developed within the AVO (Tanaka, 1990). This project 

incorporates wind data from Unidata for predicting the distribution of volcanic ash plumes on a real-time basis after an 

eruption is reported. Using the real-time and predicted 

upper-air data, the model computes advection, diffusion, and 

gravitational fallout of the ash particles. Three-dimensional 

distributions of the ash plume are displayed on the computerized graphic display, predicting the direction and dispersion of ash clouds for the first several hours after eruption. 

This report describes the algorithm of the present particletracking model in a Lagrangian framework. The results of 

the demonstrations and the procedure of the informationtransfer network are presented. 

UNIDATA 

Unidata (University data) is a national program for providing near-real-time meteorological data to university 

283 
284 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 1. Example of NMc-data received at the Alaska Climate 

Research Center via Unidata showing the global distribution of 

wind vectors at the 500-mb level, February 3-7, 1989. Length of 

staff indicates wind speed; pointer indicates wind direction. The 

horizontal grid interval available for Unidata is 5° for longitude and 

2.5° for latitude. 

users. The Unidata program center is located in Boulder, 

Colo., and it is managed by the University Corporation for 

Atmospheric Research (UCAR). The Unidata program 

established its own data feed from the National Weather Service operational circuit to distribute the near-real-time and 

forecast meteorological data for university users. Among the 

service programs, the NMC provides global analysis data 

and forecast gridded data. The meteorological data are transmitted by satellite downlink under a contract with Zephyr 

Weather Information Service. 

The NMC meteorological variables of zonal and meridional wind speeds, u and v (m/s); temperature, T (K); geopotential height, <1> (m); and relative humidity, R (percent) are 

given at 2.5° latitude and 5.0° longitude grids at 10 mandatory vertical levels of 1 ,000, 850, 700, 500, 400, 300, 250, 

200, 150, and 100mb over the whole global domain (fig. 1). 

Those basic meteorological variables are transmitted twice a 

day, for 00:00 and 12:00 UTC. In every data transmission, 

the global gridded data include not only the initial conditions 

for the weather-prediction model (plus 0-hour NMC initial 

data) but also the data for the forecasting time of 6, 12, 18, 

24, 30, 36, 48, and 60 hours, provided by the NMC numerical weather-prediction model. The initialized global data at 

forecasting time 00:00 may be regarded as observed data. 

Figure 2 illustrates a relation between NMC data transmission and the volcanic plume prediction. The twice daily 

NMC data, including the forecast data, are stored and 

continuously updated in the computerized database. The 

database always consists of past observed data and forecast 

data for 2 to 3 days ahead. Therefore, when an eruption is 

reported, the prediction model can use the present and future 

upper-air data for the computation of plume advection. The 

forecast upper-air wind data for a 1-day prediction are typically as good as the analyzed wind data (Kalnay and others, 

1990), even though the analysis data often contain considerable discrepancy from the real upper-air wind. 

As an example, figure 3 compares the analyzed wind 

field (solid arrows) at the 500-mb level with the corresponding wind field for the 24-hour forecast from 1 day before 

(dashed arrows). The differences appear to be minor for this 

example, suggesting that the forecast wind field is useful for 

real-time plume prediction. However, the accuracy of the 

predicted wind depends on the weather situation. For example, the prediction is generally good when a persistent, 

blocking, high-pressure system stays near Alaska, but the 

prediction is poor when a low-pressure system is passing the 

Cook Inlet. Moreover, the analyzed wind field, interpolated 

from the upper-air observations onto the longitude-latitude 

grids, often contains considerable errors due to the imperfect 

interpolation technique. Yet, knowing the degree of the analysis error, the NMC upper-air data is still useful for plume 

prediction when no alternative exists. 

DESCRIPTION OF THE MODEL 

The volcanic plume prediction model is constructed by 

an application of pollutant dispersion models (e.g., Praham 

and Christensen, 1977; Suck and others, 1978; Kai and othNMC forecasting by Unidata 

Time (hours) 

Eruption 

t 

Plume prediction) 

Figure 2. Schematic diagram showing the relation between the 

twice-daily NMC data transmitted by Unidata and the volcanic 

plume prediction. Arrow for NMC data describes a data span for the 

forecasting time from 0 to 48 hours. In response to an eruption report, the volcanic plume prediction model reads the archived NMC 

database to run the model using real-time wind data. 
A PREDICTION SCHEME FOR VOLCANIC ASH FALL FROM REDOUBT VOLCANO, ALASKA 285 

Figure 3. Comparison of analyzed wind vectors (solid arrows) at 

the 500-mb level and corresponding wind vector of the 24-hour 

forecast from I day before (dashed arrows), the State of Alaska, 

November 11, 1990. This example indicates the usefulness of the 1-

day forecast data, although the wind error can be large depending 

on the weather situation (see text). 

ers, 1988). The model is based on the three-dimensional (3-

D) Lagrangian form of the diffusion equation. We assume a 

vertical column of pollutant source that diffuses along with 

the Gaussian distribution in the 3-D space. A diffusion 

approximation of the pollutant turbulent mixing is used with 

3-D diffusion coefficients to evaluate the dispersion of pollutant concentration. In the Lagrangian framework, diffusion 

of plume particles may be described by a random walk process (Chatfield, 1984). Here, the diffusion is simulated by a 

sufficiently large number of random variables r;(t), (i = 1 = 

M), representing position vectors of M particles from the origin (the volcanic crater). The diffusion is superimposed on 

advection and gravitational fallout. 

With a discrete time increment, 11t, the Lagrangian form 

of the governing equation may be written as: 

r;(t+i1t) = r;(t) +Vi1t+Zi1t+GJ1t, i=1=:M (1) 

where 

r;(t) is a position vector of an ith particle at time t, 

Vis the local wind velocity to advect the particle, 

Z = (zh, zh, zv) is a vector containing three Gaussian random numbers with its standard deviation (ch, ch, cv) 

for horizontal and vertical directions, and 

G is the gravitational fallout speed approximated by 

Stokes' law. 

Note that the diffusion, Z11t, is direction dependent, and the 

gravity settling, Gf1t, depends on particle size. 

For the computation of advection, the wind velocity, V, 

is obtained from NMC via Unidata. The gridded data are first 

interpolated in time onto the model's time step. The cubic 

spline method (Burden and others, 1981) is used up to the 

3-hour interval, then a linear interpolation is applied for the 

5-minute time steps. The wind velocity at an arbitrary spatial 

point is evaluated using the 3-D B-splines (Burden and others, 1981) from the nearby gridded data. 

For the computation of diffusion, we consider the following diffusion equation in Eulerian form: 

()q - Kn2 -- v q at 

where 

q is the plume mass density, 

V2 denotes a Laplacian operator, and 

K denotes the diffusion coefficient. 

(2) 

For simplicity in derivation and for uncertainty in the magnitude of K, we consider a one-dimensional case in space 

along the x-axis. The solution of the diffusion equation for a 

point source at the origin is given by: 

1 ( x

2 

) 

q (x, t) = 2JiCKt exp - 4Kt (3) 

which may be regarded as a Gaussian distribution with its 

standard deviation 

0" = J2Kt (4) 

It is found that the plume dispersal, represented by a, 

expands in proportion to Ji . On the other hand, a random walk process m 

Lagrangian form is defined as: 

{ 

r(O) =0, 

r (t + dt) = r (t) + z (t) dt 

where 

r(t) is the position of a particle along the x-axis, 

t = n11t, (n = 0, 1, 2, ... N), and 

(5) 

z(t) is the zero-mean Gaussian random number with its 

standard deviation, c. 

For this random walk process, the standard deviation of r(t) 

is given by: 

a = cJ(At (6) 

Comparing these standard deviations in Eulerian form and 

in Lagrangian form, we obtain a relation between the diffusion coefficient, K, and the diffusion speed, c, as: 

c = {2k 

~Lfi (7) 
286 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

The diffusion velocity depends on the time increment of the 

discrete time integration. We use lit = 5 minutes in this 

study. We have repeated diffusion tests with various values 

of K, and the resulting dispersals are compared with satellite 

images of actual dispersals from Redoubt Volcano. With 

these diffusion tests, we fmd that the appropriate diffusion 

coefficients are Kh=104 (m2/s) and Kv=lO (m2fs) for the 

horizontal and vertical directions, respectively. Note that 

values may be different for other volcanoes. 

The diffusion speed may be sensitive to the scale in 

consideration. For example, the present value of the diffusion coefficient varies as the horizontal scale, which ranges 

from several hundreds of kilometers to 1,000 km in length. 

Figure 4 illustrates a result of the diffusion test. The steady 

plume at the origin spreads downstream of the source under 

the influence of constant wind. The theoretical standard 

deviation of the plume dispersal is indicated by the parabolic 

solid line in the figure. 

The gravitational settling is based on Stokes' law as a 

function of the particle size, dt. The fallout speed IGI is 

approximated by the terminal velocity below: 

IGI 

where 

p is the density of plume particles, 

11 is the dynamic viscosity coefficient, and 

g is the acceleration due to gravity. 

(8) 

We have assumed a constant for pg/T\ = 1.08x109 m-ls-1 for 

simplicity. The actual eruption contains large fragments, up 

to few centimeters in diameter, as well as fine ash, which 

occupies a continuous particle-size range to less than 1 J.Lm. 

Large particles typically settle out within a short time, and 

the particle-size spectrum in the air shifts toward smaller 

50~----------------------------------~ 

z 

Q (/) 25 (f)ll: 

u.w 

~~ 

0 -~ 0 0 

:;i.::! 

u~ 

~ ~ -25 w 

> 

-50~--,---~--~---r--~--~--~--~~ 0 50 100 150 200 250 300 350 400 

HORIZONTAL DIFFUSION, IN KILOMETERS 

Figure 4. Plan view showing a 12-hour particle diffusion test for 

a steady plume at a constant zonal wind of 10 rnls. The parabolic 

line in the figure indicates a theoretical standard deviation of the 

plume distribution. 

particles. Because we are interested in particles that can 

travel for several hours, we have assumed that the initial 

particle-size distribution is centered at 100 J.Lm. It is 

assumed that the size distribution in logarithmic axis has a 

Gaussian distribution. Thus, about 95 percent of the particles are supposed to have diameters between 1 J..lm and 1 

em. Using Gaussian random numbers, every particle is 

assigned with its own diameter, between 1 J.Lm and 1 em, 

when it appears at the volcanic crater. In practice, particles 

larger than 100 J.Lm drop quickly, within a few steps of time 

integration. Particles that are less than 100 J..lm in diameter 

can travel far from the source, providing important information on plume dispersion. 

The initial particles are modeled to be uniformly distributed in the vertical column, between the top of the erupting volcano and the specified plume top, using a uniform 

random-number generator. The altitude of the plume top is 

assumed to have been reported to AVO by visual observers, 

which may include pilot reports and reports from groundbased observers. In a case of a short-lived explosive eruption, ash particles are generated only for the initial time of 

the time integration. When the eruption continues for a 

period of more than a few minutes, the model generates new 

particles over the same vertical column for every time step 

during the specified eruption period. For a steady eruption, 

the particle number tends to increase in the model atmosphere before the plume particles have dropped out. Therefore, the number of particles released at every time step is 

adjusted to draw optimal statistical information from the 

model products. · 

The total number of particles in the model atmosphere 

is kept at less than 1 ,000. Although it is possible to increase 

the number toward the limit of computer capability, the time 

integration will then be considerably slower, which is a disadvantage for the urgent prediction requirement. Likewise, 

excessive complication and sophistication are not recommended in the present application for urgent operational prediction. For comprehensive numerical predictions, refer to 

Sullivan and Ellis (this volume), Heffter and others (1990), 

Kai and others (1988), and Draxler (1988). 

The plume-prediction model is tested first with a 

sheared flow in the vertical. Advective wind in the atmosphere has vertical shear with larger velocity, in general, at 

higher altitude. Figure 5 illustrates the result of the vertical 

cross sections of a plume-puff simulation for 1 through 6 

hours after the eruption. Concentrated ash particles are 

released uniformly over the vertical column up to an altitude 

of 10 km at the origin. The plume clouds drift downstream 

by sheared flow. They diffuse and become thinner due to 

removal of larger particles. The result simulates reasonably 

well the transport of the ash plume. 

The plume-prediction model is tuned by comparison 

with actual eruption records of Redoubt Volcano (Brantley, 

1990). Model simulations are conducted for about 30 major 

and minor eruptions during December 1989 through April 
A PREDICTION SCHEME FOR VOLCANIC ASH FALL FROM REDOUBT VOLCANO, ALASKA 287 

1990, and the resulting plume-cloud distributions are 

compared with satellite images (K. Dean, University of 

Alaska, oral commun., 1991). Unfortunately, for this period, 

the Cook Inlet area is mostly covered by dense weather 

clouds, and there were not many satellite images that captured the ash plume immediately after the eruption. 

Figure 6 illustrates a steady plume cloud for December 

16, I989, simulated by this model. Because Redoubt was in 

near-continuous ash emission on this date, we started the 

simulation assuming the eruption occurred at I 0:00 UTC. A 

linear cloud extends from Redoubt Volcano toward the 

northern part of the Kenai Peninsula at I2:30 UTC. In the 

figure, open circles represent particles higher than 1,800 ft 

and solid circles represent particles lower than 1,800 ft. The 

(/) 

0:: 

LJ.J 

ILJ.J 

~ 

0 

....J 

:::.::: 

z 

u.i 

0 

::::> 

II-

....J 

<( 

5 

0 

15 

B 

10 .. ---

5 

0 

15 

c 

. . - . . 1 .. . . . ~ ... ••· . , .. i: .... -.. 

~~· ... : 

~ ·t·;"i . : 0 •• : ::-: • : 

0 1 0 ..... '-0 I 

····\~~;~ -· ····· ····· 

r·.~)~ ~ ~,s~;···:~ : 

; ; 

10 ' ' ... ... .. . . . '' ''!' .. ·· ··· ·~ · ~- ···· .. : ..., .... :. ~ 

! • • 4!:.#• : 

·:~=-:i• • I • . : 

5 ... .. . . ... . ..... .. • .. . •. .-·-!"~ ~ ... .. -~ .......... .. ' . .. vs,_- . J: .. z. .-,., : 00' •Tt. 0 0 I 

. ·.': ._...... : 

···~· .... ' i • i • l o~----~------~----~----~~--~~--~~ 

simulation result is compared with satellite images from the 

NOAA-II advanced very high resolution radiometer 

(A VHRR) at I2: 18 UTC (see fig. 7). In figure 7, the black 

area over Cook Inlet describes a relatively dense ash cloud 

and the shaded area over the Kenai Peninsula represents a 

thin ash cloud. The satellite image describes the detailed 

structure of the cloud, which is beyond the model's resolution. Nevertheless, the overall agreement between the simulated and observed plume distributions is encouraging. 

Figure 8 (A-D) illustrates a sequence of graphic products simulated for the eruption on January 8, I990. The eruption started at I9:09 UTC and continued for 30 minutes. At 

20:00, a cellular ash cloud is located near Redoubt Volcano 

(fig. 8A). The cloud crossed over the Cook Inlet and reached 

D 

E 

....... ............ ..... 

F 

.. ..... ... .. , ... .... .. . 

... ~ ... . ~ .... -· .... :~'~ •.\, ... ; Wt.. • 

--~---- ~ .. ;. .. ~~ --- --· . ... .. ... .. ............ . 

. · ... (~1:··· 

.•\'•aiJ iJ 

. .· ·,trl_~·. :- ..... .. ••••• ··; 1 

· ·· ·· •····-·r ········ ... , . .. . 

• : 0, • • 0 0 

: 

0 o"i: 0

:

00 

I •••• 11,10 

~ o I o :=;: : .. ····· ·· ···: ·· ·-~ ... ~ .. - : . : .. .. •-: .. : ~ '.~ .· .. : .. . :"' ,,..-,.,., : • t' .J l... : i i 

I 

I 

.. ......... . ·f .. .... .. ......... ! ............. ·: ... . ~ ..... .. . 

l ! • -: .. :.T. 

: : ... ::·. ~ 

... .. ...... . [ ... . .... .. . ~_ :., ; ~~ )~ .... . ... . : .... :· .,.~:, ... . : 

.... ~ .. i.'· . l 

; · .. r ' i 

0 100 200 300 400 500 600 0 100 200 300 400 500 600 

0 S T A N C E F R 0 M 0 R I G I N, I N K I L 0 M E T E R S 

Figure 5. Vertical cross sections of a puff plume simulated for 1 through 6 hours after an eruption. In this test run, the initial ash particles 

are released unifonnly over the vertical column up to an altitude of 10 km at the origin. A, plume simulation 1 hour after eruption; B, plume 

simulation 2 hours after eruption; C, plume simulation 3 hours after eruption; D, plume simulation 4 hours after eruption; E, plume simulation 

5 hours after eruption; F, plume simulation 6 hours after eruption. 
288 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

65°00'N .--------:----------:-, ---0 -------, 

; Fairbanks 

' ' ' ' -------------------L.------- ----------- _ ... ------- ---------- - - ' ' ' ' 

60°00'N 

57°30'N ._ ___ _.;:__"""""-..;u...____...........L.. __ _._ _____ __. 

160°W 

Figure 6. Simulated geographical distribution of particles from a 

steady plume for eruption of Redoubt Volcano, which started at 

10:00 UTC, December 16, 1989. Illustration shows the model result 

at 12:30 UTC. Open circles, particles higher than I ,800ft; solid circles, particles lower than 1 ,800 ft. 

the Kenai Peninsula at 21:00 (fig. 8B). The cloud traveled 

over the Kenai Peninsula, indicating north-south elongation 

at 22:00 UTC (fig. 8C). A witness report describes that a 

dense volcanic ash cloud passed the western shore of the 

Kenai Peninsula at this time (Brantley, 1990), and, in downtown Soldotna, day time turned into darkness during the passage of the dense ash cloud. At 23:00, the northern edge of 

the elongated cloud reached just the south of Anchorage, and 

the southern edge of the cloud passed the Alaska coastline 

(fig. 8D). The simulation results are compared with a satellite image at 23:13 (fig. 9), which clearly shows a linear 

plume extending from the northern Kenai Peninsula to the 

Pacific coast near Seward. The satellite observation agrees 

well with the model simulation. 

The graphic outputs (fig. 8) are stored in computer 

memory, which is connected with other systems through 

computer networks. The final stage of plume prediction is to 

distribute the graphic product to various users, including the 

Federal Aviation Administration (FAA), the National 

Weather Service (NWS), and the response center of the 

Alaska Volcano Observatory in Anchorage. In principle, any 

system connected with the ethernet electronic mail network 

can receive the graphic product through the network, and 

users in Anchorage can access the graphic product by telephone modem. For users without any computer facility, the 

graphic product is distributed by telephone facsimile. 

This study demonstrates that the prediction model can 

provide useful information when it is applied for a real 

eruption. We have repeated similar demonstrations for each 

of the eruptions of Redoubt Volcano in 1989-90 and for Mt. 

Spurr in 1992. The results are compared with available satellite observations in order to increase the reliability of the 

prediction model. The model output will be especially useful 

when Cook Inlet is covered by dense cloud when neither satellite observations nor pilot's visual reports are available. 

SUMMARY AND REMARKS 

A volcanic plume prediction model has been developed for Cook Inlet volcanoes in Alaska. Reading the realtime upper-air data provided by NMC via Unidata, the prediction model computes advection, diffusion, and gravitational settling for plume particles released from the vertical 

column over the volcano. Three-dimensional distributions 

of the simulated plume particles are displayed on computerized graphic display. Hence, we can have important information on the predicted location of the ash plume in a realtime basis. 

The model predictions, showing the projected geographical location of the plume clouds for several hours after 

the eruption, can appear on the computer screen about 15 

minutes after eruption reports are received. This prediction is 

immediately available for users through existing computer 

networks. The graphical model output is distributed to 

related organizations using ordinary telephone facsimile. 

The present model simulation will have forecast errors 

owing, in part, to the errors in the forecast wind input. 

65°00'N ..--------..,.....-------...,..., -~0--------, 

; Fairbanks 

------- - ----- - - - -- -L---- - - -- -- - - --- - - - - L ------------------- 0 ' 

' ' ' ' ' ' 

57°30'N L........---_.;:__....._..:.....&-__..,_.._ __ __.__ _____ _. 

160°W 

Figure 7. Sketch of satellite image of the steady plume at 12:18 

UTC, December 16, 1989, derived by analysis ofNOAA-11 data. 

Figure has been scaled to permit comparison with figure 6. Black 

area shows dense core of the ash cloud. Stippled area shows diffuse 

margin of the ash cloud (Kienle and others, 1990). 
A PREDICTION SCHEME FOR VOLCANIC ASH FALL FROM REDOUBT VOLCANO, ALASKA 289 

65°00°N r--------:--------o:---~-----, 

: Fairbanks 

62°30°N ------------------... L.---- -- ... -----------... L.---- --------------- 0 0 

60°00°N 

65°00oN r--------:-------~o:--~o:::-------, 

: Fairbanks 

62°30°N ......................... .............................. I ...................................................... -~- ................................................... ... 

0 0 

0 0 

0 0 

60°00°N 

57"30°N .._ ___ .....;;__....1.-'-....:u...____...-........~.. __ __,_ _____ ___, 57°30°N L----......::_-....J..(........:u...____.o....-.~.. __ __,_ _____ __. 

160°W 155°W 150°W 145°W 160°W 155°W 150°W 145°W 

A C 

65°00oN ,...--------:----------=-: --=-0 ------, 

: Fairbanks 

0 0 

62°30°N ...................................................... ... L .............................. .................. ......... L ................................................... ... 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

'/7/Cinrlhrw">no 

60°00oN 

65°00°N r--------;--------o:---o:::------, 

: Fairbanks 

0 0 

...................................................... ... L ............ .......................................... ... L ...................................................... ... 62°30°N • 0 

• 0 

60°00°N 

57"30oN .._ ___ .....;;_-"'"""'-....:u...____.o....-.~.. __ __,_ _____ __. 57"30°N L...----.....::.....-....1."'-...:u...--=-........~..--__,_-------' 

160°W 155°W 150°W 145°W 160°W 155°W 

B D 

150°W 145°W 

Figure 8. Simulated geographical distribution of a puff plume for the eruption of Redoubt Volcano on January 8, 1990, at 19:09 UTC. 

Model results are shown for A, 20:00 UTC; B, 21:00 UTC; C, 22:00 UTC; D, 23:00 UTC. 

According to the latest statistics, upper-air wind has about 8 

m/s root-mean-square (RMS) error on average for the Northem Hemisphere (Kalnay and others, 1990). Nevertheless, the 

prediction product, knowing the possible prediction errors, 

can offer a useful guide for public safety. The use of gridded 

data from a finer mesh weather prediction model would 

improve the advection computation. Because the NMC gridded data used in this project cover the whole globe, this prediction model can be applied for other volcanoes around the 

world. 

ACKNOWLEDGMENTS 

This project was supported by ASTF grant agreement 

90-2-058 with matching funds from National Science Foundation grant A TM-8923064, A YO/USGS, Anchorage International Airport, Municipality of Anchorage, Japan Airlines, 

Nippon Cargo Airlines, China Airway, Scandinavian Airways System, British Airways, Swissair, and Reeve Aleutian 

Airways. The author appreciates various suggestions from 

S-I. Akasofu and Thomas J. Casadevall. 
290 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 9. Satellite false-color image of the Cook Inlet area of Alaska showing ash plume produced by the eruption of Redoubt Volcano 

on January 8, 1990, at 19:09 UTC. The image shows the distribution of the ash plume at 23: 13 UTC on January 8, 1990 (compare with figure 

8D). The ash plume is elongated to the south-southeast and is shown in pink. The pink cloud east of the linear ash plume is a weather cloud 

and does not contain ash. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14, 1989- August31, 1990: U.S. Geological Survey Circular 1 061, 3 3 p. 

Burden, R.L., Faires, J.D., and Reynolds, A.C., 1981, Numerical 

Analysis: London, Prindle, Weber, and Schmidt, 598 p. 

Chatfield, C., 1984, The analysis of time series, an introduction: 

New York, Chapman and Hall, 286 p. 

Draxler, R.R., 1988, Hybrid single-particle Lagrangian integrated 

trajectories (Hy-Split): Model description: National Oceanic 

and Atmospheric Administration Technical Memorandum, 

ERL ARL-166, 23 p. 

Heffter, J.L., Stunder, B.J.B., and Rolph, G.D., 1990, Long-range 

forecast trajectories of volcanic ash from Redoubt Volcano 

eruptions: Bulletin of the American Meteorological Society, v. 

7l,p.l731-1738. 

Kai, K., Okada, Y., Uchino, 0., Tabata, 1., Nakamura, H., Takasugi, 

T., and Nikaidou, Y., 1988, Lidar observation and numerical 

simulation of Kosa (Asian Dust) over Tsukuba, Japan, during 

the spring of 1986: Meteorological Society of Japan, v. 66, p. 

457-472. 

Kalnay, E., Kanamitsu, M., and Baker, W.E., 1990, Global numerical weather prediction at the National Meteorological Center: 

Bulletin of the American Meteorological Society, v. 71, p. 

1410-1428. 

Kienle, J., Dean, K., Rose, W., and Garbeil, H., 1990, The 1989 

eruption of Redoubt Volcano, Alaska [abs.]: Eos, Transactions, 

American Geophysical Union, v., 71, p. 266. 

Praham, L.P., and Christensen, 0., 1977, Long-range transmission 

of pollutants simulated by a two-dimensional pseudospectral 
A PREDICTION SCHEME FOR VOLCANIC ASH FALL FROM REDOUBT VOLCANO, ALASKA 291 

dispersion model: Journal of Applied Meteorology, v. 16, p. 

896-910. 

Sherretz, L.A., and Fulker, D.W., 1988, Unidata: Enabling universities to acquire and analyze scientific data: Bulletin of the 

American Meteorological Society, v. 69, p. 373-376. 

Suck, S.H., Upchurch, E.C., and Brock, J.R., 1978, Dust transport 

in Maricopa county, Arizona: Atmospheric Environment, v. 

12, p. 2265-2271. 

Tanaka, H.L., 1990, Model used to track volcanic plume: Geophysical Institute Quarterly, University of Alaska, Fairbanks, Fall 

1990, p. 7-8. 

---1991a, Unidata at Alaska.: Unidata Newsletter, Summer 

1991, p. 10-11. 

---1991 b, Weather data access improved: Geophysical Institute Quarterly, University of Alaska, Fairbanks, Summer 1991, 

p. 1-3. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

TilE AERONAUTICAL VOLCANIC ASH PROBLEM 

By Jerald Uecker 

ABSTRACT 

The International Civil Aviation Organization (ICAO) 

requires warnings and flight-planning information about one 

of the most pot1~ntially hazardous but non-meteorological 

aeronautical phenomena that exists, volcanic ash. This paper 

discusses the provision of required information based on the 

experiences gained from eruptions of Mount St. Helens and 

Redoubt Volcano in the United States. The frequency and 

duration of these eruptions, as well as the lack of guidelines 

about ash concentrations and their affect on aircraft, have 

made it difficult to meet the requirements for supporting safe 

and efficient aeronautical operations with available information messages. \Vhile progress has been achieved with warnings and flight-planning data, efficient dissemination has not 

been achieved for graphical representations of ash clouds. 

Meeting aeronautical information requirements for this nonmeteorological phenomenon requires cooperation, research, 

and development among people in various disciplines to 

attain safe and efficient operations. 

INTRODUCTION 

The experi1~nce gained in providing meteorological 

information on volcanic ash clouds to those in aeronautical 

operations has resulted in adjusting some procedures to 

accommodate requirements. This paper briefly discusses the 

requirements and challenges and how support will be 

improved, primarily through communications, in the near 

future. 

During the past decade, a number of aircraft have 

encountered volc:anic ash clouds while in flight. Three incidents involved loss of engine power and posed potential 

disaster for passengers and crew; these encounters caused 

extensive damag·e to the aircraft. Fortunately, such incidents 

have been rare, and disaster has been averted because of 

good crews and ~~quipment. These incidents have, however, 

instilled a healthy awareness of and respect for the problem 

of volcanic ash. 

The relativ«! infrequency of large volcanic eruptions 

and the inability to predict the onset of eruptions in an 

aeronautically timely manner increases the potential danger 

faced by crews and operators. In spite of the non-meteorological nature of volcanic eruptions and ash, the responsibility rests with meteorologists for: (1) the issuance of 

alphanumeric significant meteorological (SIGMET) information to warn of the hazard, and (2) the inclusion of ashcloud information in abbreviated, plain-language, area forecasts and on significant weather charts used for flight 

planning. 

Satellite images, radar data, aircraft reports, and cooperation and information coordination with volcanologists are 

all essential for early detection of eruptions and for tracking 

ash clouds. However, there are considerable limitations 

inherent in the system that provides SIGMET information. 

Two limitations are: (1) forecasting the onset of eruption 

with the timeliness required for aeronautical operations-this goal will certainly elude meteorologists, and (2) 

determining the concentration of erupted ash particles and 

(or) gases that may or may not affect aircraft. Hopefully, 

studies that address these limitations will also provide guidance as to when ash concentrations are sufficiently low so 

that the ash no longer threatens aircraft. 

Wind data in the form of particle-trajectory and dispersion-model forecasts for flight planning are essentially the 

only aspect of the volcanic eruption and ash problem that 

adheres to meteorological prediction principles (Murray and 

others, this volume; Stunder and Heffter, this volume). This 

means that meteorologists need help in providing the best 

ash-cloud-warning service for the aeronautical community. 

The experience in the United States for issuing ash 

cloud warnings and SIGMET's began with the eruption of 

Mount St. Helens in 1980. The St. Helens experience differed considerably from the more than 25 eruptions at 

Redoubt Volcano, which is 177 km southwest of Anchorage, 

Alaska, and to which meteorologists responded beginning in 

December 1989. Mount St. Helens eruptions were longer in 

duration and less frequent that those of Redoubt Volcano. 

Initially, each Redoubt eruption lasted several hours, and 

subsequent eruptions, some consisting primarily of steam, 

lasted less than 30 minutes (Brantley, 1990). 

293 
294 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

ALPHANUMERIC INFORMATION 

REQUIREMENTS 

The international requirements for reports, warnings, 

and forecasts about volcanic ash are contained in the ICAO 

publication entitled "Meteorological Service for International Air Navigation, Annex 3," (ICAO, 1992)-this publication is hereinafter referred to as "ICAO Annex 3." 

United States domestic and international procedures and 

policies meeting these requirements are detailed in National 

Oceanic and Atmospheric Administration (NOAA) and 

National Weather Service (NWS) operations manuals. 

Within the United States, additional measures are taken 

both from a warning and flight-planning point of view. For 

warnings, NWS meteorologists assigned to air route traffic 

control centers {AR TCC) provide center weather advisories 

(CWA's) as a quick response to new or quickly changing 

conditions that may not be detailed in SIGMET's prepared 

by meteorological watch offices (MWO's). For flight planning, trajectory information (see Recent Developments section in this paper) is provided to aeronautical and 

meteorological facilities in accordance with existing agreements. Currently, this information is distributed on a limited basis, but extensive distribution of flight-planning 

information through meteorological graphics communications systems within the United States and internationally 

are planned and are nearing fruition. This will result in 

extensive distribution of this information to the aeronautical community and to information providers. 

REPORTS 

Recommended practices concerning observations and 

reports of volcanic activity by meteorological stations are 

described in the ICAO Annex 3 (chap. 4, p. 20): "The 

occurrence of pre-eruption volcanic activity, volcanic eruptions, and volcanic ash clouds should be reported without 

delay to the associated air traffic services unit, aeronautical 

information services unit, and meteorological watch office. 

The report should be made in the form of a volcanic activity report [VAR-see Fox, this volume] comprising the following information in the order indicated: 

a. Message type: volcanic activity report, 

b. Station identifier: location indicator or name of 

station, 

c. Date and time of message, 

d. Location of volcano and name if known, 

e. Concise description of event, including, as appropriate, level of intensity of volcanic activity, occurrence 

of an eruption and its date and time and the existence 

of a volcanic ash cloud in the area together with 

direction of ash cloud movement and height." 

The standard concerning aircraft observations and 

reports that is cited in ICAO Annex 3 (chap. 5, p. 24) is that 

"special observations shall be made by all aircraft 

whenever ... 

c. Volcanic ash is observed or encountered, ... 

e. Pre-eruption volcanic activity or a volcanic eruption is 

observed." 

Note-Pre-eruption volcanic activity, as used in both contexts cited above, means unusual and (or) increasing volcanic activity that could presage a volcanic eruption. 

The ICAO standard for the contents of special air 

reports of pre-eruption volcanic activity, a volcanic eruption, 

or volcanic ash cloud and their order in the volcanic activity 

report (V AR) (Fox, this volume) is: 

• Aircraft identification, 

• Position, 

• Time, 

• Flight level or altitude, 

• Volcanic activity observed, 

• Air temperature, 

• Wind, and 

• Supplementary information. 

SIGMET INFORMATION 

SIGMET's are aeronautical meteorological warnings, 

and they are issued in alphanumeric form. The ICAO Annex 

3 (chap. 7, p. 34-36) standard on the issuance of SIGMET 

information includes the occurrence and (or) expected 

occurrence of volcanic ash cloud at subsonic, transonic, and 

supersonic cruising levels. The recommended issuance of 

"SIGMET messages concerning volcanic ash cloud ... 

expected to affect a flight-information region (FIR) should 

be issued at least 12 hours before the commencement of the 

period of validity and should be updated at least every 6 

hours." 

This requirement combined the short-term requirement 

for hazardous SIGMET information and the longer term 

requirement for flight-planning data. However, at the ICAO 

communications-meteorology-operations divisions and the 

World Meteorological Organization (WMO) commission on 

aeronautical meteorology meeting (September 1990, held in 

Montreal, Canada), several states that have had experience 

with volcanic activity SIGMET's indicated that permitting 

the period of validity of SIGMET's for volcanic ash to be 

extended up to 12 hours, in their opinion, was quite impossible given current volcanic-activity-observing techniques, 

especially concerning ash particle size and density. 

Even though the requirement does state "up to 12 

hours," local user requirements during the Redoubt Volcano 

eruptions led to SIGMET updates as often as every 2 hours. 

This implied a dichotomy of purpose for the SIGMET (i.e., 

updates every 2 hours and the requirement for an outlook for 

up to 12 hours). 
THE AERONAUTICAL VOLCANIC ASH PROBLEM 295 

A few init:[al Redoubt Volcano eruptions in December 

1989 and January 1990 lasted up to several hours; subsequent eruptions lasted usually less than 30 minutes (Brantley, 1990). With the frequency and duration of Redoubt 

Volcano eruptions, the MWO issuing SIGMET's would not 

have been able to comply with the spirit of the long-term 

requirement at the volcano or for flight-information regions 

(FIR's) affectedl downstream by the ash cloud. 

Another significant aspect of SIGMET's being valid 

essentially from 12 to 24 hours is that the area encompassing 

volcanic ash could be very large. Situations did occur at 

Redoubt Volcano whereby ash was spread at high levels far 

to the southeast and at low levels to the north and northwest. 

In this case, the area was already quite large. However, consider the area that would be covered by ash with the wind 

directions indicated above and with a speed of 100 knots at 

high levels and 25 knots at low levels for a period of 12 to 24 

hours. A SIGMET encompassing such as ash cloud would be 

meteorologically supportable but operationally difficult to 

implement. Even the 4-hour-valid-period SIGMET's issued 

for the initial Itedoubt Volcano ash clouds resulted in large 

areas that unnecessarily restricted air traffic-this is a considerable impac;t at or near high-density routes and aerodromes, such as Anchorage International Airport. 

Ash dispersion can quickly become complicated and 

can cover extensive areas with ash that is emanating only 

from the sourcf:. However, rapidly transported ash at high 

levels that falls into lower levels with different wind directions essentially results in multiple, albeit less concentrated, 

sources and an t~xtremely complicated ash-cloud pattern. 

SilGMET DISSEMINATION 

SIGMET's are disseminated over teletypewriter or 

computer networks in alphanumeric, abbreviated, plain language. ICAO Annex 3 (p. 36) recommends that "SIGMET 

messages should be disseminated to meteorological watch 

offices, ... and to other meteorological offices, in accordance 

with regional air navigation agreement." 

GRAI,HICS REQUIREMENTS 

The requirements for graphical information (i.e., charts 

for flight documentation) reside in ICAO Annex 3, chapter 

9, and is entitlt~d "Service for Operators and Flight Crew 

Members." Flight documentation, usually in the form of 

charts, is provided "to operators and flight crew members 

for: 

a. Pre-flight planning by operators, 

b. Use by flight crew members before departure, 

c. Aircraft in flight." 

For pre-flight planning purposes by the operator, the 

ICAO recommendation for significant en-route weather 

information is that the information should normally be supplied as soon as available, but not later than 3 hours before 

departure. 

Prior to the ICAO/WMO meeting in 1990, different 

ways to portray volcanic ash on significant weather charts 

were tried in the United States for the Redoubt Volcano 

eruptions. However, the inclusion of ash clouds on significant weather forecast charts caused concern among aeronautical operators. One of the early Redoubt eruptions occurred 

before the significant weather chart was disseminated, and 

the projected ash cloud area was determined by trajectory 

information. This area was enclosed by a scalloped line and 

identified with a plain-language note. Unfortunately, the 

area enclosed was larger than it might have been under those 

meteorological conditions, and it caused some anguish 

among users. It should be noted, however, that large areas 

can be expected under certain meteorological conditions. 

Experience with these charts showed that: 

1. Inclusion of ash clouds on significant weather forecast 

charts is consistently possible only if the volcano 

erupts shortly before or during the preparation of a 

chart and, of course, if the meteorologist is notified in 

time, 

2. Providing long-term (up to 12 hours and beyond) volcanic ash information by outlining the ash cloud on 

significant weather charts, while possible, may be 

confusing and may be a disservice to the aeronautical 

user when the area delineated is significantly larger 

than it might be or if the chart is prepared for an eruption that turns out to be mostly steam (hence, posing 

little or no hazard), and 

3. The lead time that must exist so that the charts are 

available to the operator, in addition to the time 

required to prepare the chart, makes it an extremely 

difficult task to include the information as precisely as 

desirable. 

The Redoubt Volcano experience led the United States 

to suggest at the September 1990 ICAOIWMO meeting that 

the best way to inform flight planners about volcanic ash was 

to include a statement such as "see potential SIGMET's for 

volcanic ash" near the volcano on the significant weather 

chart-this statement would be included on all significant 

weather charts until the volcano becomes inactive again. 

Discussions pointed out that longer term, precise information on the occurrence and location of volcanic ash cannot be 

adequately depicted on significant weather charts. The reason for this is that these charts should be in the users' hands 

some 9 hours before the valid time-this time corresponds 

approximately to the midpoint of the flight. Also, these 

charts are prepared up to 6 hours before being disseminated. 

The net result is that a volcanic eruption and ash cloud may 

have occurred at any time during a period of 15 hours and 

may not be depicted on the significant weather chart that the 

air crew receives. It was agreed at the meeting that an ash 
296 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

cloud could not be included reliably for short-term eruptions 

because of timing and dissemination requirements. 

The participants at the ICAO/WMO meeting in 1990 

felt that WMO should be requested to develop, in 

consultation with ICAO, appropriate symbology to represent 

the volcanic ash phenomenon on significant weather 

charts-this resulted in the recommendation that WMO, in 

consultation with ICAO, develop appropriate symbology to 

represent the occurrence of volcanic eruptions on world-area 

forecast system significant weather charts. Subsequently, it 

was agreed that symbology would be added to the significant 

weather chart at the location of the volcano and that adequate 

information would be added to the legend of the chart, 

including a statement advising concerned air crews to 

inquire about SIGMET's in an area where a volcanic eruption or ash contamination is suspected. 

RECENT DEVELOPMENTS 

Since the First International Symposium on Volcanic 

Ash and Aviation Safety in 1991, graphic information has 

been developed. The volcanic ash forecast transport and dispersion 01 AFT AD) model, developed by National Oceanic 

and Atmospheric Administration (NOAA) Air Resources 

Laboratory, is a three-dimensional, time-dependent depiction of the volcanic ash cloud (Stunder and Heffler, this volume). Eruption input includes volcano name and location, 

eruption time, and ash-cloud-top height. The model assumes 

a given particle-size distribution throughout the initial ash 

cloud. Ash is advected horizontally and vertically as it falls 

through the atmosphere, using either the Washington World 

Area Forecast Center global wind and temperature computer 

model data or a U.S. regional model. 

This graphic information, produced automatically and 

shortly after notification of an eruption, will be disseminated 

internationally in addition to significant weather charts on 

ICAO world-area forecast system satellite broadcasts. 

Broadcasts operated by the United States are expected to 

begin in late 1993 or early 1994 over the Americas and in 

late 1994 over the Pacific Ocean-eastern Asia area. In the 

United States, the graphic will be disseminated on meteorological computer and graphic-dissemination systems. 

SUMMARY 

Problems faced by meteorologists and operators concerning: (1) when and where an eruption may occur, (2) the 

timely notification of an eruption in the aeronautical sense, 

and (3) what concentrations of volcanic ash threaten life and 

property, contribute to the difficulty in providing useful volcanic ash information. However, improved dissemination of 

information will significantly assist in planning for efficient 

flight and will contribute to safe operations. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14, 1989-August 31, 1990: U.S. Geological Survey Circular 1061, 33 p. 

International Civil Aviation Organization (ICAO), 1992, Meteorological Service for International Air Navigation, Annex 3 (11th 

ed.): International Civil Aviation Organization. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

DEFINING A KEEP-OUT REGION FOR AIRCRAFT 

AFTER A VOLCANIC ERUPTION 

By Peter L. Versteegen, Douglas D. D' Autrechy, Michael C. Monteith, 

and Charles R. Gallaway 

ABSTRACT 

This paper proposes a methodology for predicting the 

airspace that aircraft should avoid when the air contains volcanic ash. The proposed methodology consists of an ashtransport model and an avoidance-region-definition model. 

The ash model estimates the transport of ash particles from 

volcanic clouds by ambient winds. The avoidance-regiondefinition model uses predicted particle locations to determine a volume in airspace of minimal cross-sectional extent. 

The methodology is based on use of a personal computer and 

can estimate such avoidance regions in near real time. Individual elements of the models are operational but need to be 

configured with a user-friendly interface. Modules must be 

added to bring in wind data from all accessible sources and 

to generate a mass-consistent wind field. Furthermore, sensitivity studies need to be conducted to ensure that useful and 

not overly conservative results are generated. A model such 

as this could link a volcano observatory, a weather station, 

and an aircraft operation center. 

The avoidance volume contains all possible ash-cloud 

particles at a user-specified time of interest. The avoidance 

region is defined as a rectangular prism extending from the 

ground to the top of the volcano cloud. The ash-transport 

model includes the following key elements: the specification 

of initial cloud conditions and a three-dimensional wind 

field, the transport and dispersion characteristics of the 

atmosphere, and the particle terminal fall velocities. The initial conditions of the cloud consist of a description of cloud 

geometry, mass distribution, and particle-size distribution. 

This initial cloud is represented by a number of horizontal 

wafers, each containing the mass and effective radius of each 

of the particle sizes of the distribution. The location of representative particles are computed with a modified Euler 

method, using a time-dependent wind field. Dispersion is 

modeled by an empirical correlation. The fall rate of a particle is determined from its local terminal velocity, which is a 

function of size and altitude. 

INTRODUCTION 

The hazard to aircraft systems due to encounters with 

volcanic dust has been amply demonstrated over the past 20 

years (Casadevall, 1992). Several aircraft have had lifethreatening encounters with volcanic dust, and extensive 

damage has required expensive repairs of aircraft. Wind 

shields are crazed, leading edges become eroded, and excessive ingestion of dust by aircraft engines causes compressor 

erosion and deposition of melted ash in the turbine. Upon 

severe glassification, aircraft engines surge and shutdown 

and are difficult to restart. Two Boeing 747-200 aircraft 

encountered dust from Mt. Galunggung in June and July 

1982 (Tootell, 1985) and experienced engine flameout. Fortunately, the crews were able to restart the engines and land 

the aircraft safely at Jakarta. In December 1989, a B-747-

400, bound from Amsterdam to Anchorage, encountered the 

volcanic ash cloud from the Redoubt Volcano and had a 

four-engine flameout. Fortunately, the pilot was able to 

restart the engines. The aircraft suffered approximately $80 

million of damage (Steenblik, 1990). 

There are currently no safe procedures for operating aircraft when encountering ash clouds from erupting volcanoes. 

Pilots can report suspicious clouds through pilot reports 

(Fox, this volume), and they can follow recommended procedures developed by the Aerospace Industries Association 

volcanic ash committee (AlA Propulsion Committee 334-1, 

this volume). However, ash clouds are often difficult, if not 

impossible, to avoid because, even to the trained eye, a dust 

cloud at high altitude may look like an ordinary water/ice 

cloud. One approach to minimizing the chance of a fatal 

accident is to cancel all flights into a region defined by some 

radius around the erupting volcano. Such an estimate of 

affected area could be so large that such an action could 

severely impact local economies and be costly to the airlines 

due to reductions in passenger and freight load. 

There is a need for a consistent procedure that can 

accurately define the airspace that could be a hazard to aircraft. Once such a region is defined, it can be broadcast via 

297 
298 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

the NOTAM (notice to airmen) process to aircraft that are 

approaching the hazardous airspace. This paper proposes a 

simple method, easily implemented, that could provide 

planning and real-time guidance about the location of the 

hazardous airspace. The approach defines a minimum volume of airspace inside of which all hazardous ash particles 

are expected to be present at the time of the forecast. 

Therefore, the region outside this minimum volume would 

be a zone in which aircraft can safely operate. Uncertainties in winds and methodology can be accounted for by 

suitably defining model parameters that enlarge the 

hazardous region. 

REQUIREMENTS 

Any procedure that defines a restricted region as 

described above must be simple and easy to use, fast running, use local meteorology, make use of existing hardware 

and protocols, and be updateable. The underlying concepts 

of the procedure must be easy to understand and must be 

intuitive; the procedure should be operable by virtually 

anyone without comprehensive training or refresher sessions. The infrequent and widely distributed occurrences of 

volcanic events mean that the procedure would be used 

infrequently. 

The procedure should be fast running so that nearinstantaneous forecasts of airborne ash concentrations can be 

made. For this application a beginning-to-end forecast 

should take no longer than 5 minutes. The model should use 

local meteorology, including local measurements, whenever 

possible. Even though forecasts are generally available and 

would probably be used to generate the first estimates, the 

variability due to local or neighboring terrain should be 

accounted for either explicitly or statistically. The use of 

local measurements should be of high priority because they 

could be the only reliable source of accurate, high-resolution 

information. The model should make use of existing hardware and protocols. This facilitates implementations and 

allows a wider distribution of the results. 

The procedure must be easy to update on a regular 

basis to provide a revised forecast of the hazardous region. 

Such revisions should be made frequently, but they are 

obviously dependent on the acquisition of better initial conditions and winds. 

METHODOLOGY 

The proposed methodology is based on defining a keepout or restricted region in airspace. Aircraft would stay outside of this region for a specified time period. The region is 

defined as a volume reaching from the ground up to the top 

of the volcanic cloud. Alternate, user-specified definitions 

could also be used. This geometry was chosen so that its 

specification is readily implemented in the existing NOT AM 

process by which only simple messages can be transmitted. 

More elaborate procedures can be devised. 

The process involves the computation of particle displacements for different aerodynamic sizes from different 

altitudes, much along the lines of Hopkins and Bridgeman 

(1985). As particles settle, their trajectories are primarily 

affected by winds, atmospheric turbulence, and their own 

physical features. Other processes can be important, but they 

generally serve to reduce dust concentrations in the air and 

reduce direct hazards. Such processes include agglomeration 

of smaller particles into larger ones, the scavenging of particles by precipitation, and ash-induced downdrafts in the lowdensity, high-altitude air. 

The mean wind field is typically the driving factor for 

particle transport and dispersion for the relatively short times 

considered here (several hours). Wind information can come 

from many sources, in different resolutions, and different 

accuracies, but current data are not always guaranteed to be 

available for the volcano region. Winds are available from 

forecasts with various meteorological models, from 

next-generation weather radar (NEXRAD) measurements, 

from TIROS operational vertical sounder (TOYS) measurements, and from rawinsonde measurements. When no data or 

information are available, persistence of the most recent 

winds can be used as a forecast, or analogous historical wind 

patterns anchored to the most recent data can be derived from 

a specialized clustering technique (Cockayne and Singer, 

1991 ). All available wind information should be used in an 

objective analysis scheme to produce reasonably good wind 

fields for particle-transport and dispersion calculations. 

Cloud 

segment 

Ground 

surface 

Figure 1. A volcano cloud is modeled by a stack of non-uniform 

wafers, each representing a characteristic particle size and a fraction of the total ash mass. Winds and gravity transport these 

wafers in multiple directions. 
DEFINING A KEEP-OUT REGION FOR AIRCRAFT AFTER A VOLCANIC ERUPTION 299 

Particles can disperse over a large region, very much 

dependent on wind speed and vertical wind shear. This process is shown schematically in figure I. The duration and 

mass eruption rate may also affect the size of the hazardous 

airspace. The columns of dust erupting from the volcano 

travel with the wind. The dust particles will fall out, and the 

speed of the fall depends on particle sizes. A schematic side 

view of the hazardous region for a single burst and a continuous eruption are shown in figure 2. 

The restricted region is defined as the minimum volume 

inside of which all possible particles are located at the time 

specified. Computer hardware requirements for the proposed 

model are modest and depend on the complexity of the 

desired user interface and the number of particles that need 

to be tracked. The latter can be established through an appropriate set of sensitivity studies. 

THE TRAJECTORY MODEL 

To compute particle locations, we use a trajectory 

model. The model used in this study is properly termed an 

isobaric model, based on a specification of winds on constant-pressure surfaces. Other trajectory models could have 

been used, such as isentropic or isosigma models. For isentropic models, trajectories are defined along surfaces of 

constant potential temperature in an attempt to conserve the 

energy of motion. Isosigma models use a terrain-following 

coordinate system that is a function of pressure. Evidence 

that any of the trajectory models can perform better than 

the other is a function of the meteorological situation. Kuo 

and others (1985) concluded that there was little difference 

between these models in terms of their horizontal transport 

t, 

Hazardous airspace for 

a single-burst eruption 

Hazardous airspace for 

a continuous eruption 

~~" 

~'~.~~ ""~~-~-.. ~~ ', """~~ ~\._ "' " ""'' ', . ~ 

' ~ 0: --~~ 

Figure 2. Side view of the restricted airspace. This is an exaggerated schematic perspective that illustrates the nature of the restricted 

region. Time of eruption is indicated by "t0." 

using the results of 14 experiments from a mesoscale (i.e., 

space scales of 2-2,000 km and a time scale of hours) 

model. They concluded that the limiting factor in these 

investigations was the resolution and quality of the available meteorological data. The isobaric model was thereby 

chosen to be consistent with typical methods for reporting 

wind information. 

The trajectories of the particles are determined using 

the Lagrangian advection methodology. A Lagrangian 

description of a fluid flow is one that describes the path of a 

fluid parcel or particles with respect to space and time (i.e., 

the x, y, and z spatial coordinates and time, t). This differs 

from a Eulerian description of the flow, which provides a 

description of the flow velocity at discrete points at an 

instant in time. An Eulerian description can be thought of as 

a snapshot of a flow field, while a Lagrangian description 

can be thought of as a step-by-step sequence of Eulerian 

flows of a parcel or particle. The trajectory model has been 

used with both a modified Euler advection integration 

scheme (Heffler, 1983), a two-step advection methodology 

that corrects for changing wind-field characteristics during 

the time step, and the Runge-Kutta-Merson variable time 

step, fourth-order method (Press and others, 1986). 

GRAVITATIONAL SETTLING 

The capability to accurately simulate the transport of 

airborne particles is made complex due to the fact that particles settle to the ground at various rates as a function of particle size and shape and atmospheric conditions. Small 

particles tend to reside in the atmosphere for longer periods 

of time after injection, which can allow upper-level wind 

patterns to transport them great distances. Large particles 

can settle to the surface much quicker, and transport distances tend not to be as large. Not only are transport distances affected by particle-settling speeds, but so is the 

transport pattern. As particles of different sizes fall through 

the atmosphere at different rates, winds at a particular level 

will affect the transport of the particle as a function of the 

time spent in that layer. 

We have developed a computer program that computes, 

for specified particle sizes, the fall time through the atmosphere. This program computes the time it takes for smooth, 

spherical particles to fall to the surface from various altitudes. Irregular particles are assumed to be represented by 

their equivalent aerodynamic size, meaning the spherical 

diameter that has the same terminal velocity. 

The atmosphere is modeled with temperature, pressure, 

and density varying as a function of geometric altitude. Temperature is modeled as a combination of linear fits to data 

extracted from the U.S. standard atmosphere. Linear fits are 

used for the regions below 11.1 km and above 20 km, and the 

temperature is assumed to be a constant value of 216.65 K 
300 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

between these altitudes. For altitudes below 11.1 km, the 

temperature is modeled as: 

T=288.13-6.440z 

Above 20.0 km, the temperature is computed as: 

T= 196.75+0.995z 

where 

z is the altitude above mean sea level, in kilometers, and 

Tis temperature in degrees Kelvin. 

Air density, Pa, is modeled as a function of altitude by: 

Pa=Po exp(-z/H) 

where 

Po is the air density, in kg/m3, at mean sea level, and 

His the scale height of the atmosphere. 

The value used for Po is 1.225 kg/m3; the value used for H 

is 8.23 km. 

The dynamic viscosity of the atmosphere is modeled as 

a function of the temperature profile and is calculated as: 

IJ.=~T312f(T+S) 

where 

ll is the dynamic viscosity in kg/see-m, 

~is a constant (1.458x 10--{; kg/sec m K11

2), and 

Sis Sutherland's constant (11 0.4 K). 

The fall time, eh for particle type k, is computed by 

summing the fall time through user-specified atmospheric 

layers (Llz'i) as: 

where 

Vki is the terminal velocity of particle type k in altitude 

slice i. 

The terminal velocity is computed from the following equation: 

V=(!l)(Rep)l(pa)(d) 

where 

the particle Reynolds number (Rep) is calculated using 

the method outlined in Norment (1979). 

Davies (1945) defined a dimensionless number, Nn, as: 

Nn=4gpa(Pp-Pa)d3!(3!l2) 

where 

Pp is the density of the falling particle, in kgfm3, and 

dis the particle diameter, in meters. 

If 140:::; Nn:::; 4.5x107, then: 

logto(Rep)=-1.29536+0.986X +(-0.4667)X2 

+ 1.1235x 1o-3x3 

where 

X=log(Nn). 

For 84.175 :::; Nn:::; 140, then: 

Rep=4.16667x 10-2+(-2.3363x 10-4)Nn 

+2.0154x 1o-6(Nn)2-6.9105x 10-9(Nn)3 

For 0.3261 :::; N D :::; 84.175, the correlation is due to Beard 

(1979): 

Rep=exp [ -3.18657 +0.99269 Y -0.153193 X 1 o-2 Y2 

-0.987059x 1 o- 3 r3-o.0578878x 1 o-3 y4 

+0.855176x 1 o-4y5-o.327815 x 1 o-s y6] 

where 

Y=ln(Nn). 

Stokes' law is used for particles for which N D :::; 0.3261: 

Rep=Nn/24 

When the size of the particles approach the mean free path 

of the molecules through which they are falling, particle 

mobility increases, and the terminal velocities must be modified by a slip correction factor known as the Cunningham 

factor (Cc). The correlation by Flanigan and Taylor (1966) 

was used: 

Cc= 1 + A(2l/d)+Q(2l/d) exp(-Bd/2[) 

where 

dis in meters. 

Using a mean free path, /, of 9.322x 10-8 meters, the value 

of the constants in the equation above are A= 1.234, 

Q=0.413, and B=0.904. Using these values, multiplying by 

Po/Pa, and substituting for Po gives: 

Cc= 1 +2.8x 10-7pald 

where 

d and Pa are in meters and kg/m3, respectively. 

The terminal velocity, V, is multiplied by this factor. 

We typically compute terminal velocities for particles 

residing at the midpoint of 500-m-thick layers of the atmosphere. The incremental fall times through each layer are 

determined using these terminal velocities for all particles in 

the layer. Total fall time is then calculated by summing the 

incremental fall times for each 500-m layer. Total fall times 

as a function of altitude for particles of six diameters, ranging from 30 to 300 J..Lm, is shown in figure 3. 

Analysis of material collected by sampling aircraft and 

on the ground indicates that shapes of dust particles from 

volcanic eruptions can be highly irregular (Leifer and others, 

1981; Newell and Deepak, 1982). The terminal velocities of 

these irregularly shaped particles are defined in terms of an 

equivalent spherical radius as discussed earlier. 

DISPERSION 

The volcanic cloud is modeled by a stack of circular 

wafers of non-uniform size, each representing a portion of 

the total cloud mass and also a portion of the particle-size 

spectrum existing in the cloud at the altitude of the wafer 

(fig. 1). The displacement of each wafer by local winds and 

its fall due to gravity represents the trajectory of the 

representative particle in that wafer. Turbulence in the atmo-
DEFINING A KEEP-OUT REGION FOR AIRCRAFT AFTER A VOLCANIC ERUPTION 301 

20 

CJ) 

a: 

w 

1- 15 w 

~ 

0 

-l 

~ 

z 10 

w~ 

0 

=> 

1- 5 -

i= 

-l 

<( 

0 

0 2 4 6 

EXPLANATION 

Particle diameter (l!m) 

... 300 

8 

0 150 

~ 100 

10 

TIME, IN HOURS 

12 

Figure 3. Duration of fall for particles of different size as a function of the altitude at which they are released. 

sphere causes the wafer to grow in size both horizontally and 

vertically. The horizontal dispersion is modeled by one of 

two models: Heffler (1983) or Gifford and others (1988). 

The Heffler model has been used for the present application; 

however, the choice of model for this application is not very 

critical. Because the horizontal extent of the wafer is of most 

importance, vertical dispersion can be neglected. Conservative assumptions about dispersion due to atmospheric turbulence for the purpose of defining a restricted region are easily 

made. The location of the cloud elements is mainly affected 

by transport by wind. 

INITIAL AND BOUNDARY 

CONDITIONS 

The calculation methodology does not need the exact 

evolution of the eruption column from the onset of eruption. 

We are interested in what happens when the wind takes over 

dispersion of the ash cloud. The initial estimate of ash in the 

air after cloud stabilization can be obtained from Wilson 

(this volume) for wet clouds or from Sparks and others (this 

volume) for dry clouds. To determine all potential particle 

locations, we position many particle sizes at regularly spaced 

altitudes up to the highest altitude of the volcano cloud. The 

initial height and shape of the cloud are estimated based on 

ground, satellite, or pilot observations. The diameter of the 

cloud could be taken as its maximum dimension because that 

would be more conservative than defining the actual shape 

of the cloud. For purposes of defining a conservative 

restricted region, an initial circular cylinder shape is adequate. The particles are specified as a uniform distribution 

that is the same throughout the cloud, and the particles are 

tracked through the wind field as they fall due to gravity. 

MINIMUM RESTRICTED AREA 

Having defined the particle transport and settling methodology and the initial conditions, one can compute the locations of all the particles and the wafers that they represent at 

a given time. A vertical rectangular prism, extending from 

the ground to the top of the cloud, is then defined, enclosing 

the locations of all wafers regardless of their altitude. The 

restricted airspace, or air volume, is then defmed as the rectangular prism with the minimum cross-sectional area that 

encloses all wafers. This cross-sectional area is determined 

by an iterative process. 

AN EXAMPLE 

An example of how the procedures described in the previous sections could be implemented in an operational system is shown for a hypothetical eruption of Iliamna Volcano, 

Cook Inlet, Alaska. The winds in that region are shown in 

figure 4 in the form of zero-mass particle trajectories originating from different altitudes. The winds used in this case 

were from an archive of 2.5°X2.5° gridded wind fields 

obtained from the National Center for Atmospheric 

Research. In an operational scenario, actual winds should be 

used. In the example, the strong vertical shear is clearly evident by the fanning of the trajectories. Each trajectory is due 

to winds of a different altitude. The locations of all the 

Figure 4. Map of Cook Inlet area, Alaska, showing the trajectories of particles with zero mass originating at different altitudes being transported over an undefined period. Fan-like patterns are the 

result of vertical wind shear. 
302 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

wafers, represented by particles with mass, are calculated at 

different times, and a minimum volume is fitted around their 

locations. The results of the enclosed area computation as a 

function of angle are shown in figure 5. The inset in this figure defines the baseline angle. For the example, the minimum cross-sectional areas, and, hence, air volumes, are 

shown in figure 6 for two different forecast times. 

As conceptualized, the software that would perform this 

calculation can be started at any time. When an eruption is 

about to take place, a user would provide some initial 

estimate of the eruption. The user selects the volcano of 

interest (fig. 7) and initiates the calculation process. 

Next, screen 2, (fig. 8), is displayed instantaneously. A 

first estimate of the basic cloud parameters can be made here 

by entering appropriate values in the data blocks shown. The 

user is prompted throughout this process by the software, 

and help functions would be available to provide guidance. 

Pressing the "Go" button begins execution and results in a 

display of the restricted region shown in figure 9. If this 

region is found acceptable, the "Description" button is 

selected (fig. 10). Acceptability is subjective and is a function of the data that is available. The result is subsequently 

translated into a NOT AM-formatted description that can be 

transmitted by clicking the "Transmit" button. The whole 

process can be completed in a few minutes. 

Cl 

w 1-

u 

-o 

C:LU 1-a: 

~<( a:::J 

u.d 

QCJ) 

<((/) 

wa: a:W 

<(1- LU 

~~ 

zz 

o-, 

i=Z 

uo 

wCJ)<.9 

I LU (f.) a: (/) 

0 

a: 

u 

-------- ~~-

1 ~A,,~~T'',--~~:~~i~~;~:· 10 L-~~~~~~~~~~~~~~~~~ 

0 15 30 45 60 75 90 

BASELINE ANGLE, IN DEGREES 

Figure 5. The cross-sectional area of the restricted region as a 

function of the baseline angle, a, for two elapsed times. This shows 

that a minimum region can be up to 50 percent smaller than some 

arbitrary region. Inset shows definition of baseline angle. 

Figure 6. Map of Cook Inlet area, Alaska, showing the keep-out 

region at two times for a hypothetical eruption of Iliamna Volcano. 

CONCLUSIONS AND 

RECOMMENDATIONS 

We have described an approach that could provide 

timely information to the air traffic industry to assist them in 

avoiding potentially hazardous areas contaminated with volcanic ash. Using existing methods, we have demonstrated 

computations for particle transport and settling and for defining the restricted airspace. While the whole process has been 

assembled by hand-the methodology can easily be implemented on low-end computer workstations, high-end personal computers, and using available graphical-userinterface building tools. 

To transform the suggested approach into an operational tool will require additional development work. Specifically, workable interfaces adapted to potential users must be 

developed; interfaces with wind-data sources and the optimal interpolation of such data into a consistent wind field 

must be developed; the initial conditions must be relevant to 

the different types of volcanoes that are of interest; the hardware and software to generate and update the NOT AM must 

be designed and written. None of these are insurmountable 

problems. They require straightforward engineering work. 
DEFINING A KEEP-OUT REGION FOR AIRCRAFT AFTER A VOLCANIC ERUPTION 303 

llfH HDBO:MNC f:Uolc:eno Wort f:HC_JJolteno 

Spurr e 

Dlala 

Augustine . e 

Click on tbe ErupdiJI Volcaoo 

Figure 7. Startup screen for the Cook Inlet area, Alaska, example 

described in the text. 

rm 

~ 

llfH HOBO:MNC f:Uoltano Wort f:HC_Uoltano 

Mt Diamna Definition 

Width (km)} 

Figure 8. The screen that lets the user define cloud parameters 

that are needed for transport calculations. 

ACKNOWLEDGMENTS 

Elements of the software used to generate the demonstration was developed under the Defense Nuclear Agency 

funding. John Cockayne of Science Applications International Corporation provided useful comments and insights 

into the problem of aircraft encounters with dust. We also 

appreciate comments from the reviewers. 

II fH HDBO:MNC f:Uoltano Wort f:HC_JJolteno 

Display of Restricted Airspace 

Figure 9. The restricted region for the Cook Inlet area, Alaska, as 

calculated by the software screen for the example. 

llfH H080:MNC f:Uoltano Work f:HC_Uoluno 

Two Hour Restricted Region 

Corners: 

59.83°N/-153.06°E 

60.27°N/-152.17°E 

59.27°N/-150.25°E 

58.83°N/-151.15°E 

CUck Here to Trallsmit 

~ CUck Here to Print 

Verbal description of region. 

Format to follow NOTAM 

Figure 10. The NOT AM screen for the example. 

REFERENCES CITED 

Beard, K. V., 1979, Terminal velocity and shape of cloud and precipitation drops aloft: Journal of Atmospheric Sciences, v. 33, 

p. 851-854. 

Casadevall, T.J., 1992, Volcanic hazards and aviation safety, lessons of the past decade: Federal Aviation Administration, Aviation Safety Journal, v. 2, p. 3-11. 
304 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Cockayne, J.E., and Singer, H.A., 1991, Multiburst environments 

and fratricide effects. Volume I -Cluster analysis of wind profiles for fratricide effects: Defense Nuclear Agency Report 

DNA-TR-90-122, v.l, 51 p. 

Davies, C.N., 1945, Definitive equations for the fluid resistance of 

spheres: Proceedings of the Physical Society, pt. 4, v. 57, no. 

322, p. 259. 

Flanigan, V.P.R., and Taylor, P., 1966, Tables of aerosol physics 

functions: Central Electricity Generating Board, Berkeley Nuclear Laboratories, United Kingdom, tables 1-3. 

Gifford, F.A., Barr, S., Malone, R.C., and Mroz, E.J., 1988, Tropospheric relative diffusion to hemispheric scales: Atmosphere 

Environment, v. 22, no. 8, p. 1871-1879. 

Heffter, J.L., 1983, Branching atmospheric trajectory (BAT) model: Rockville, Md., NOAA Air Resources Laboratory Technical Memorandum ERL, ARL-121, 16 p. 

Hopkins, T.H., and Bridgeman, C.J., 1985, A volcanic ash transport 

model and analysis of Mount St. Helens ashfall: Journal of 

Geophysical Research, v. 90, p. 10620-10630. 

Kuo, Y.H., Skumanich, M., Haagenson, P.L., and Chang, J.S., 

1985, The accuracy of trajectory models as revealed by the 

observing system simulation experiments: Monthly Weather 

Review, v. 113, p. 1852-1867. 

Leifer, R., Hinchliffe, L., Fisenne, 1., Knutson, E., Olden, M., Sedlacek, W., Mroz, E., and Cahill, T., 1981, Measurements of the 

stratospheric plume from the Mount St. Helens plume: Radioactivity and chemical composition: Science, v. 214, p. 

904-907. 

Newell, R.E., and Deepak, A., eds., 1982, Mount St. Helens eruptions of 1980; atmosphere effects and potential climate impact: 

A Workshop Report: National Aeronautics and Space Administration Report NASA SP-458, 119 p. 

Norment, H. G., 1979, DELFIC: DepartmentofDefense fallout prediction system, Volume !-Fundamentals: Defense Nuclear 

Agency Report DNA 5159F-1, 98 p. 

Press, W.H., Flannery, B.P., Teukolsky, S.A., and Vetterling, 1986, 

Numerical Recipes in FORTRAN, the Art of Scientific Computing: New York, Cambridge University Press, 963 p. 

Steenblik, J.W., 1990, Volcanic ash: A rain of terra: Air Line Pilot, 

June/July, p. 9-15, 56. 

Tootell, B., 1985, All Four Engines Have Failed: The True and Triumphant Story of Flight BA 009 and the "Jakarta Incident:" 

Auckland, Hutchinson Group Ltd., 178 p. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

DETECTION AND DISCRIMINATION OF 

VOLCANIC ASH CLOUDS BY 

INFRARED RADIOMETRY-I: THEORY 

By Alfred J. Prata and Ian J. Barton 

ABSTRACT 

Volcanic ash clouds with a high concentration of silicate particles exhibit optical properties in the infrared (8-13 

Jlm) that can be used to discriminate them from normal 

water/ice clouds. In principle, a simple radiometer equipped 

with at least two channels with appropriate passbands may 

be used to identify volcanic clouds. In this paper, we 

develop the theoretical basis for such a radiometer. We solve 

the radiative-transfer problem in a cloudy atmosphere by 

using a discrete-ordinates model and present results for a 

variety of viewing conditions. These include vertical viewing downward (from a satellite), horizontal viewing (from an 

aircraft), and vertical viewing upward (from the ground). 

We also present some LOWTRAN-7 calculations for representative atmospheres, which include height variation of 

temperature, cloudiness, water vapor, and other trace gases. 

INTRODUCTION 

The thermal infrared window between 8 Jlm and 13 Jlm 

has frequently been exploited for remote sensing of clouds 

and the Earth's surface. It has been suggested by Prata 

(1989b) that this region may also be used for detection and 

discrimination of volcanic ash clouds. Theoretical calculations indicate that clouds containing silicate materials 

behave quite differently than ice and water clouds at wavelengths between 10 Jlm and 12 Jlm. There have been anumber of ash-cloud studies using advanced very high resolution 

radiometer (A VHRR) satellite data that demonstrate this 

anomalous behavior (Prata and others, 1985; 1989a; Holasek 

and Rose, 1991). This behavior is due primarily to the much 

stronger dispersive nature of silicate-bearing materials compared to water and ice in the infrared window. Prata (1989b) 

used a radiative-transfer model to explain the difference in 

temperature obtained at wavelengths of 10.8 Jlm and 11.9 

Jlm (appropriate to A VHRR channels 4 and 5) when viewing 

volcanic clouds from space. Here, we will also use the 

model to examine the effects when viewing horizontally 

(i.e., from an aircraft) or when viewing vertically from the 

ground. We are motivated in this work by the expectation 

that a multichannel radiometer when used from an aircraft or 

from the ground will also be able to discriminate ash clouds 

from normal water/ice clouds. Because viewing a cloud 

from the ground or from an aircraft involves paths that 

traverse a large part of the lower atmosphere, we also need 

to take account of absorption and emission by gases, such as 

water vapor. 

In this paper we will present theoretical results, and, in 

part II (Barton and Prata, this volume), we will present some 

preliminary data from ground-based measurements of an 

actual volcanic cloud. 

RADIATIVE TRANSFER WITH 

SCATTERING 

The radiative-transfer equation for a plane-parallel scattering atmosphere may be written (Chandrasekhar, 1960): 

dl 

llat (t, Jl) = /(t, Jl)- (l-tu0 )B(T) 

rn Jl _ _5!. P(Jl;Jl')!(t,Jl')dJl' 

2 -1 

where 

I is the radiance, 

t is the optical depth, 

11 is the cosine of the zenith angle, 

Tis temperature, 

B is the Planck function, 

t'U0 is the single scattering albedo, and 

P is the axially symmetric phase function. 

(1) 

305 
306 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

An illustration of the problem is shown in figure 1. The 

boundary conditions are that the radiances incident at the 

cloud top and base are isotropic, with Planck brightness temperatures of T8 and Tg respectively. That is: 

I (0,-J.L)=B(Ts) 

The discrete-ordinates solution is given by: 

where 

l('t,Jl) = LLjUj(J.Li)e-Kjt+B(T) 

j 

(2) 

-n ~i, j ~n, (2n is the number of discrete radiation 

streams). 

The eigenvalues, Kj, and eigenvectors, ~. are determined 

by using an algebraic eigenvalue equation solver as suggested by Stamnes and Swanson (1981). 

TWO-STREAM SOLUTION 

To gain insight into what processes are important in the 

transport of thermal radiation through the cloud, a twostream (2n = 2) solution is employed. This solution is analytic and can be easily derived (Liou, 1974). In this case, the 

general solution (given by equation 2) is: 

t = 0 .... ---------------.. 

Scattering cloud layer 

"/ 

1\ 

t=tc------------------~-----------------

~' 

Figure 1. Schematic of the plane-parallel scattering cloud model. 

where 

Tc is the cloud temperature. 

Applying the boundary conditions we have: 

L_W_e+K'tc+ L+W+e-K'tc = B(Tg)-B(Tc) 

Where we have made use of the fact (Liou, 1974): 

W_(-J.L) = W+(+J.L) 

W_(+J.L) = W+(-J.L) 

(4) 

(5) 

We have dropped explicit reference to Jl and n for notational 

convenience. Adding and subtracting these equations and 

solving for the L's: 

L+= ~ [B ( Ts) + B ( Tg) - 2B ( Tc) + B ( Tg) + B ( Ts) ] 

2 W+e-Ktc+w_ W+e-Ktc_w_ 

L_ = ~ [B ( Ts) + B ( Tg) - 2B ( Tc) + B ( Ts) - B ( Tg) ] 

2 W +e-Ktc +W- W +e-Ktc_ WThe solution for the upward component at the cloud top is 

then: 

and the downward component at the cloud base is: 

The eigenvalues (±K) and eigenvectors (W _, W +) are: 

The cosine of the scattering angle has the value: 

1 

Jl =-J3 

(8) 

(9) 

We now consider two limiting cases that are of interest 

to the detection problem. 

A. Optically thin limit ( 'tc ~ 0). 

In this case, it may be shown that: 

/(0, +J.L) ~ B(Tg) 
DETECTION AND DISCRIMINATION OF ASH CLOUDS BY INFRARED RADIOMETRY-I: THEORY 307 

and that: 

l('t0 -J.L) ~ B(T8 ) 

B. Optically thick limit ('tc ~ oo). 

From equation 5, we find that: 

(10) 

and, from equation 6: 

(11) 

Note that the factor 

may be interpreted as an effective emissivity of the cloud. It 

is seen that the radiance consists of two components: an 

emitted portion and a reflected portion. In the case of viewing from the ground, the reflected portion may be significant because B(Tg) >> B(Tc). 

OPTICAL PROPERTIES 

Mie calculations are performed to determine the scattering properties and phase function of a polydisperse 

ensemble of particles. These calculations require refractive 

indices, the particle-size distribution, and the particle shape. 

The results are given in terms of efficiency factors: 

f

oo 2 . ( 21tr )dn (r) d 

1tr Q_t\ A' m ---;Jr r A 0 Q = ------- (12) 

f foo 2dn (r) 

where 

1tr ---;Jr dr 

0 

Qf is the Mie efficiency factor for extinction, scattering, 

or absorption, and 

n(r) is the size distribution of particles, with radius r, in 

units of number of particles per unit volume. 

The extinction, absorption, and scattering efficiencies are 

related by: 

(13) 

The single scattering albedo is: 

(14) 

The asymmetry parameter, g, is: 

1Jl 

g = 2 p (J.L) J.LdJ.L 

-1 

(15) 

SIZE DISTRIBUTIONS 

The modified-y size distribution has been used to 

include the effect of mean particle size on the scattering 

properties of the cloud. The distribution is given by: 

dn (r) Nb1 

-- = -r6 exp (-br) dr 6! (16) 

where 

r0 is the mean particle radius, 

N is the total number of particles per unit volume, and 

b=61r0 • 

OPTICAL THICKNESS 

The optical thickness of the cloud depends on the size 

distribution, extinction efficiency, and the geometrical thickness of the cloud. These are related by: 

(17) 

where 

L is the geometrical thickness. 

For a 1-km-thick cloud of particles with a concentration of 

102 cm-3, a mean particle radius of 3 J.Lm, and Qext = 2 (at 

10 J.Lm), 'tc = 5. 

MIE CALCULATIONS 

The scattering parameters required for the radiativetransfer calculations are obtained using Mie theory. A computer program developed by Evans (1988) was used. Refractive indices of quartz, volcanic dust, water, and ice are input 

to the program together with the appropriate size distribution 

and particle shape. The refractive indices of quartz are 

obtained from Petersen and Weinman (1969) and those of 

volcanic dust are from Volz (1973). The modified-ysize distribution was used for these calculations with a mean particle 

radius of 3 J.Lm-the particles were assumed to be spherical. 

Results of the calculations are given in table 1 and figures 2 

and 3. These results show that volcanic substances (quartz 

and dust) have a larger extinction than water and ice and that 

the extinction decreases with wavelength between 10.8 J..Lm 

and 12.0 J..Lm. For water and ice, the extinction increases with 

wavelength in this region. 
308 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Refractive indices, extinction efficiency factor, asymmetry parameter, and single scattering albedo for quartz, volcanic 

dust, ice, and water. 

[Real part of refractive index is in column under nr; imaginary part of refractive index 

is in column under k. Qexr, extinction efficiency factor; g, asymmetry parameter; m0 , 

single scattering albedo. The modified-y size distribution was used, with r 0 = 3 J.UD] 

Wavelength nr k Qext g mo 

Quartz I 

8.6 0.658 1.448 3.171 0.622 0.603 

10.1 2.607 0.048 2.198 0.427 0.976 

10.9 2.140 0.027 3.377 0.405 0.860 

11.8 1.627 0.050 2.832 0.632 0.825 

12.0 1.515 0.063 2.247 0.650 0.766 

12.5 1.526 2.240 3.224 0.491 0.595 

Volcanic dust2 

8.6 1.221 0.650 2.330 0.758 0.411 

10.1 2.078 0.101 3.248 0.561 0.659 

10.9 1.780 0.100 3.259 0.639 0.713 

11.8 1.776 0.218 2.960 0.661 0.577 

12.0 1.756 0.230 2.890 0.660 0.566 

12.5 1.713 0.270 2.718 0.653 0.530 

Ice3 

8.6 1.288 0.039 1.658 0.776 0.758 

10.1 1.185 0.058 0.837 0.731 0.495 

10.9 1.087 0.204 1.126 0.704 0.233 

11.8 1.224 0.395 1.799 0.675 0.322 

12.0 1.280 0.413 1.909 0.670 0.339 

12.5 1.386 0.422 2.070 0.656 0.370 

Water4 

8.6 1.275 0.037 1.557 0.777 0.758 

10.1 1.215 0.052 0.925 0.723 0.596 

10.9 1.172 0.078 0.805 0.702 0.386 

11.8 1.122 0.159 0.955 0.669 0.232 

12.0 1.111 0.199 1.072 0.662 0.228 

12.5 1.123 0.259 1.254 0.643 0.244 

1 Refractive index data from Petersen & Weinman (1969). 2 Refractive index data from Volz (1973). 

3 Refractive index data from Warren (1984). 

4 Refractive index data from Hale & Querry (1973). 

MODEL RESULTS 

The discrete-ordinates model (with 2n = 32) has been 

used to calculate the upward and downward radiation 

streams for the three cases of interest (satellite, ground-based 

sensing, and aircraft). The data given in table 1 were used in 

the calculations. 

SATELLITE SENSING 

The cloud was assumed to have a temperature of -40°C, 

and the ground was assumed to have a temperature of 15°C. 

The optical thickness of the cloud was set to 'tc = 5 at 10.1 

i= 

a: 

<( 

c.. 

.....J 

<( 

UJ 

!;. 

>< 

w 

Cl 

~ 

w 

> 

i= 

u 

<( 

0:: 

u.. 

UJ 

a: 

w 

> 

i= 

u 

<( 

a: 

u.. 

UJ 

0:: 

5 

4 

3 

2 

0.10 

9 

EXPLANATION 

• Quartz 

+ Volcanic dust 

~ Ice 

0 Water 

10 11 12 13 

WAVELENGTH, IN MICROMETERS 

Figure 2. A, Real part of the refractive index of quartz, volcanic 

dust, ice, and water as a function of wavelength between 8.5 J..Lm and 

l3.5J..Lm. B, Imaginary part of the refractive index. 

J.Lm. Figures 4A and 4B show the brightness temperatures as 

a function of zenith angle for quartz, volcanic dust, ice, and 

water. Note that, for all zenith angles, the temperatures at 

10.9 J.Lm are less than those at 11.8 J.Lm for the volcanic substances, whereas the reverse is true for ice and water (except 

at large zenith angles when the limb-darkening effect 

appears to be more pronounced at 10.9 J.Lm than at 11.8 J.Lm). 

Note that at 60° the satellite scan angle is about 50° so this 

effect may be seen from the A VHRR, which scans to ±55 .4 °. 

For optically thick clouds, we have seen from the two-stream 

approximation that the satellite radiometer receives radiation 

at the cloud temperature multiplied by the effective emissivity (which is a function of the optical properties and, hence, 

wavelength) because, in this case, we may assume that the 

radiance of space is effectively negligible. It is not sufficient 

to simply insert the optical parameters from table 1 and take 

the limit 'tc ~ oo because, in reality, the cloud becomes optically thick due to large particles. This implies that, Qext• fil0 , 

and g must be computed for a new size distribution. Clearly, 
DETECTION AND DISCRIMINATION OF ASH CLOUDS BY INFRARED RADIOMETRY-I: THEORY 309 

I- 4 

z 

w 3.5 u 

u:: 3 L.1. 

LU 

0 2.5 u 

z 2 0 

i= 1.5 u 

z 

i= 

X 

w 0.5 

A 

>a: 0.8 a:w 

1-1-

ww 

~~ 0.6 ~< >O: (1)<3:: <C.. 0.4 

(!) 

z 0.8 a: 

w 

~0 0.6 <{0 

uw 

(/)~ 0.4 w<t: 

...J 

(!) 

z 0.2 Quartz • A 

U5 + Volcanic dust 0 

QL-L-L-L_L_L_~~~~~~~~~-L-L-L~ 

8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 

C WAVELENGTH, IN MICROMETERS 

Figure 3. A, Extinction coefficient as a function of wavelength for 

quartz, volcanic dust, ice, and water. B, Asymmetry parameter as a 

function of wavelength. C, Single scattering albedo as a function of 

wavelength. 

we cannot expect to model this situation accurately because 

the cloud structure would be extremely inhomogeneous and 

complex. To give an indication of what to expect, table 2 

shows the results for the poly disperse cloud with r 0 = 3 J.l.m 

and r 0 = 30 J.l.m. Only the 10.9-J.l.m and 11.8-J.l.m brightness 

temperatures are shown along with the effective emissivities. 

These results indicate that, for optically thick clouds, 

A VHRR channel-4 temperatures should be less than or equal 

to channel-5 temperatures. However, when ice and water are 

mixed in with volcanic debris, the temperature difference 

(channel 4 - channel 5) may lead to positive, negative, or 

zero differences. The optically thick case may be the most 

difficult to interpret. 

GROUND-BASED SENSING 

In this case, the radiometer is assumed to be viewing the 

plume at an elevation angle of 26°. The plume temperature 

is set at 5°C, and the ground temperature is set at 15°C. 

Table 2. Brightness temperatures and effective emissivities for 

two size distributions. 

[Cloud-top temperature, Tc, is -40.0°C; tc = l 00 at l 0.1 JJ.m. Values are computed for 

the stream closest to vertical (cos-1JJ. = 4°)] 

z 

~ LU 

~ 

(/) 

w 

w 

a: 

(!) 

w 

0 

~ 

LU~ 

c:::: 

=> 

~ a: 

LU 

c.. 

~ 

w 

I-

(/) 

(/) 

LU 

z 

1-

::r: 

£2 

c:::: 

m 

Wavelength(~ Temperature (

0 C) Effective emissivity 

10.9 

11.8 

10.9 

11.8 

240 

235 

230 

225 

220 

215 

210 

205 

A 

236 

235 

234 

223 

232 

231 

230 

229 

228 

227 

226 

0 

B 

10 

r 0 = 3 J.1111; modified-y 

-45.6 

-43.5 

r 0 = 30 J.LIIl; modified-y 

-40.0 

-40.0 

EXPLANATION 

• Quartz, 1 0.9 f.!m 

o Quartz, 11.8 f.!m 

A Volcanic dust, 10.9 f.!m 

.a. Volcanic dust, 11.8 f.!m 

EXPLANATION 

+ Ice, 10.9 J.lm 

<> Ice, 11.8 f.!m 

,.. Water, 10.9 J.lffi 

v Water, 11.8 JJ.m 

0.935 

0.957 

1.000 

1.000 

20 30 40 50 60 70 80 90 

ZENITH ANGLE, IN DEGREES 

Figure 4. A, Satellite simulated brightness temperature as a function of zenith angle for quartz and volcanic dust clouds at 10.9 flm 

and 11.8 flm. B, As for A, but for water and ice clouds. 
3IO VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

These temperatures are representative of the values measured at Sakurajima Volcano (see Barton and Prata, this volume). Results are given in figure 5 for quartz and water. 

Temperature differences between I0.9 J.lm and Il.8 J.lm are 

positive for the quartz cloud and negative for the water 

cloud. 

These calculations do not include the influences of 

water vapor absorption and emission. These affects must be 

accounted for when viewing at low elevation angles in the 

troposphere. To take them into account, we have used the 

radiance/transmittance code developed by the U.S. Air Force 

known as LOWTRAN-7. We calculate the slant path radiance and transmittance for a radiometer viewing at an elevation angle of 26°. The total path length is governed by the 

location of the target. To simulate our measurements at 

Sakurajima, we assume that the target is at a height of 

between I and 2 km above the radiometer. By varying the 

model atmosphere and target height, a range of slant paths 

and water vapor amounts are obtained. 

LOWTRAN-7 provides radiances and transmittances at 

a maximum resolution of 5 cm-1; these are convolved with 

the filter functions of the airborne volcanic-ash-detection 

system (A V ADS) instrument (Barton and Prata, this volume) to give the simulated radiances. Finally, the slant path 

radiance, Rp, and the slant path transmittance, fp, are combined with the cloud radiance, Rc, that is computed by the 

scattering model to give the radiance at the radiometer, R;. 

This is given by: 

Ri = Rctp + RP (I8) 

280 

z 278 

> ...J 

w 

~ 

(/) 

w 276 w 

cr: 

(.9 

w 

Cl 

~ 274 

L.U~ 

0::: 

::::> 

1-

<( 272 0::: 

L.U 

a.. 

~ 

L.U 

1- 270 

268 

8 9 10 11 12 13 

WAVELENGTH, IN MICROMETERS 

Figure 5. Simulated brightness temperatures as a function of 

wavelength for quartz and water. 

The calculations described above have been done for a 

quartz cloud and a water cloud. Because it appears that only 

the I 0.9-J.lm and II.8-J.lm channels are a good pair for discriminating cloud types, the results are shown for these channels only. Figure 6 shows the variation in the brightness 

temperature difference, LlT, between the I0.9-J.lm and 11.8-

J.lm channels as a function of precipitable water. For the 

quartz cloud, the positive differences decrease with increasing precipitable water, and, for water clouds, the difference 

becomes more negative. Thus, water-vapor affects will tend 

to reduce the discrimination. 

AIRCRAFT SENSING 

This situation is modeled by assuming that the plane 

parallel sides of the cloud are oriented in the vertical. The 

radiation entering the cloud is the same on both sides (i.e., 

B(T8 ) = B(Tg)). For simplicity, we assume that the radiation 

is isotropic and composed of equal portions from the background sky and from the warm surface. A value of T8 = 

-30°C is assumed, and the cloud temperature, Tc, equals 

-50°C. This temperature is equivalent to an aircraft cruising 

height of about 30,000 ft. Results are presented in table 3. 

We notice that, for optical thicknesses greater than 'tc = 5, 

(/) 

::::> 

U5 

...J 

w 

u 

(/) 

L.U 

L.U 

0::: 

(.9 

w 

Cl 

~ 

ui 

u 

z 

L.U 

0::: 

w 

u.. 

u.. 

i5 

w 

5 ! I 

4~ • 

3 -

2-

-1 f.-

I 

• 

• • 

• 

I I 

EXPLANATION 

o Water 

• Ash 

-

-

-

-

cr: : • ~ 0 f-----~---------------------------------------------------~-----------

0::: 

w 

a.. 

~ -1 - 0 0 0 -

~ ¢ 0 • 

(/) 

(/) 

L.U 

z -2- 0 0 

1-

::I: 

(.9 

-

0 

0: 

~ -3L_~ i __ _L __ J_ I __ L-~~~---L--~--~~~~ I I I 

0 2 3 4 5 

PRECIPITABLE WATER, IN CENTIMETERS 

Figure 6. Simulated temperature differences (temperature at 10.9 

Jlm minus that at 11.8 J.lm) as a function of water-vapor loading for 

a ground-based instrument viewing a cloud of ash (quartz) and a 

cloud of water. 
DETECTION AND DISCRIMINATION OF ASH CLOUDS BY INFRARED RADIOMETRY-I: THEORY 311 

pairs of channels can be selected that give very good discrimination between quartz and ice clouds. For example, the 

pairs 10.9 J.tm/11.8 J.tm and 10.1 J.tm/12.0 J.tm give positive 

temperature differences for the quartz cloud and negative 

differences for the ice cloud. It appears that the 10.1 J!rnl 

12.0 J.tm pair is a better discriminator. Calculations of the 

atmospheric path radiance have also been done using 

LOWTRAN-7 and assuming a view with an elevation of 4°, 

but these do not change the results noticeably. 

CONCLUSION 

Radiative-transfer calculations for an idealized scattering cloud indicate that quartz and volcanic ash behave differently than water and ice between wavelengths of 10 J.tm and 

12 J.tm. We have found that, for a ground-based radiometer 

viewing a volcanic cloud, the brightness temperature at 10.9 

J.tm is greater than that at 11.8 J.tm. For water and ice clouds, 

the reverse is true. Absorption and. emission by atmospheric 

gases, principally water vapor, causes the difference 

between the brightness temperature at 10.9 J.tm and 11.8 J.tm 

Table 3. Cloud temperatures derived from the scattering model 

for quartz and ice particles at different optical thicknesses. 

[tc, optical thickness; temperatures shown are in °C) 

Wavelength tc= 5 tc= 10 tc= 50 tc = 100 

Quartz 

8.6 -32.00 -48.76 -49.06 -50.00 

10.1 -37.05 -36.23 -7.12 -38.21 

10.9 -37.40 -44.37 -44.78 -44.81 

11.8 -37.01 -46.77 -47.07 -47.25 

12.0 -37.91 -47.64 -47.96 -48.21 

12.5 -39.19 -48.44 -48.83 -50.00 

Ice 

8.6 -39.33 -48.99 -49.20 -50.00 

10.1 -39.33 -49.46 -49.58 -49.73 

10.9 -39.56 -49.20 -49.47 -50.00 

11.8 -36.53 -43.30 -43.58 -43.58 

12.0 -36.46 -43.04 -43.29 -43.29 

12.5 -36.19 -42.33 -42.56 -50.00 

to decrease. Similar results are found for near-horizontal 

viewing of a cloud at 8 km. We also note that pairs of channels at 10.9 J.tm/11.8 J.tm and 10.1 J.tm/12.0 J.tm should give 

good ash-cloud discrimination from the ground and from aircraft. Further modeling studies are in progress to assess the 

affects of particle shape and cloud composition on radiative 

transfer. 

REFERENCES CITED 

Chandrasekhar, S., 1960, Radiative Transfer: New York, Dover 

Publications, Inc., 303 p. 

Evans, B.T.N., 1988, An interactive program for estimating extinction and scattering properties of most particulate clouds: Australia Defense Science and Technology Organization, 

Materials Research Laboratory, Department of Defense Report 

MRL-R-1123. 

Hale, G.M., and Querry, M.R, 1973, Optical constants of water in 

the 200 nm to 200 J..lm wavelength region: Applied Optics, v. 

12, p. 555-563. 

Holasek, R.E., and Rose, W.I., 1991, Anatomy of 1986 Augustine 

Volcano eruptions as recorded by multispectral image processing of digital AVHRR weather satellite data: Bulletin of Volcanology, v. 53, p. 420-435. 

Liou, N-K., 1974, Analytic two-stream and four-stream solutions 

for radiative transfer: Journal of Atmospheric Sciences, v. 31, 

p. 1473-1475. 

Peterson, J.T., and Weinman, J.A., 1969, Optical properties of 

quartz dust particles at infrared wavelengths: Journal of Geophysical Research, v. 74, no. 28, p. 6947-6952. 

Prata, A.J., 1989a, Observations of volcanic ash clouds using 

A VHRR-2 radiances: International Journal of Remote Sensing, v. 4, p. 751-761. 

---1989b, Radiative transfer calculations for volcanic ash 

clouds: Geophysical Research Letters., v. 16, p. 1293-1296. 

Prata, A.J., Wells, J.B., and Ivanac, M., 1985, A "satellite's eyeview" of volcanoes on the Lesser Sunda Islands: Weather, v. 

40, p. 245-250. 

Stamnes, K., and Swanson, R. A., 1981, A new look at the discrete 

ordinates method for radiative transfer calculations in anisotropically scattering atmospheres: Journal of Atmospheric Sciences,v.38,p.387-399. 

Volz, F.E., 1973, Infrared optical constants of ammonium sulfate, 

Sahara dust, volcanic pumice, and fly ash: Applied Optics, v. 

12, p. 564-568. 

Warren, S.G., 1984, Optical constants of ice from the ultraviolet to 

the microwave: Applied Optics, v. 23, p. 1206-1225. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Avia~ion Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

DETECTION AND DISCRIMINATION OF 

VOLCANIC ASH CLOUDS BY 

INFRARED RADIOMETRY-II: EXPERIMENTAL 

By Ian J. Barton and Alfred J. Prata 

ABSTRACT 

An airborne multichannel radiometer has been built to 

test the feasibility of using infrared radiation to detect and 

discriminate volcanic ash clouds. The radiometer has five 

selectable filters and two temperature-controlled precision 

black bodies for internal calibration. The instrument has 

been flight tested up to an altitude of 8,000 m and has performed well. During the flight tests, measurements were 

made in both clear and cloudy skies at varying heights and 

viewing angles. Results from these tests will be presented 

and compared to theoretical calculations. The radiometer has 

also been used to view the volcanic plume emanating from 

Mt. Sakurajima, on the Japanese island ofKyushu. For these 

tests, the radiometer was ground based and pointed upward, 

either toward the ash plume, water clouds, or the clear sky. 

The radiometer measurements support the concept of using 

an airborne radiometer to detect volcanic ash clouds ahead of 

an aircraft. The advantages of this detection technique over 

others are discussed. 

INTRODUCTION 

In the first paper of this pair (Prata and Barton, this volume), theoretical calculations indicated that it should be possible to discriminate between water/ice clouds and volcanic 

ash clouds using infrared radiometry. This possibility is also 

evident when satellite instruments are used to investigate the 

infrared properties of volcanic ash clouds. It has been shown 

by Prata (1989) that the two thermal infrared channels of the 

advanced very high resolution radiometer (A VHRR) flying 

on the NOAA-7 operational meteorological satellite can be 

used to discriminate between normal clouds and volcanic ash 

clouds. 

The major danger of volcanic ash clouds to commercial 

aircraft is the stalling of engines due to the ingestion of silicate rock particles. Because these particles have different 

optical properties to water droplets at 11 and 12 jlm, a 

radiometer operating at these wavelengths should be able to 

discriminate between volcanic ash and water clouds. 

To test this hypothesis, an infrared radiometer has been 

built and used to view both water/ice clouds and volcanic ash 

clouds in the thermal infrared band. The results of some airborne tests in Australia and some ground-based observations 

of volcanic ash clouds in Japan will be presented here. 

THE RADIOMETER 

A diagram of the radiometer is shown in figure 1. The 

instrument has a single beam with a beam width of 3° and 

can sample incident thermal radiation in one of five wavelengths selected by choosing an appropriate interference filter (see fig. 2 and table 1). The filters included in the 

radiometer were varied depending on the location of the tests 

and the physical properties under investigation. The radiometer includes two internal black-body targets for accurate 

calibration. A mechanical chopper alternates the signal 

received by the detector between a known temperature and 

the incoming radiation; then a phase-locked loop ensures 

that background radiation is not detected. The incident radiation is focused onto the pyroelectric detector by a rightangle parabolic reflector. The radiometer has a typical noise 

temperature near 0.1 °C, depending on the integration time 

used (normally 2 s) and the band width of the filter. For the 

airborne tests, the incoming radiation was first passed 

through a germanium window that has a transmission nearly 

equal to unity at the wavelengths of interest (see fig. 2). 

The filter at 6.4 jlm was included to investigate the possibility of detecting clear-air turbulence by observing watervapor intrusions into the upper atmosphere (Kuhn and 

others, 1977). Unfortunately, the detector response at this 

lower wavelength was not sufficient to give a useful signal. 

The 8.6-j..lm filter was included for the detection of S02, 

which has a broad absorption band in this region of the 

spectrum. 

313 
314 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Details of filters used in the radiometer. 

[CAT, clear-air turbulence] 

Central Band 

wavelength width Function 

().l.ffi) ().l.ffi) 

6.4 0.3 Water-vapor emission for CAT. 

8.6 0.5 so2 emission. 

10.1 0.5 Water cloud-ash cloud discrimination. 

10.8 0.6 Water cloud-ash cloud discrimination. 

12.0 0.6 Water cloud-ash cloud discrimination. 

10.91 1.0 Water cloud-ash cloud discrimination. 

11.8 1.4 Water cloud-ash cloud discrimination. 

Data from the radiometer were recorded on an IBMcompatible personal computer using a commercial analogto-digital board. 

THE AIRBORNE EXPERIMENT AND 

RESULTS 

Aircraft tests of the radiometer were carried out near 

Hobart, on the island of Tasmania. The radiometer was 

mounted in a pod that was fitted under the wing of a Navajo 

aircraft so that it looked directly ahead of the aircraft. A second pod, which included a forward-looking video camera, 

was fitted under the other wing. The video tape recording for 

Hot black body Reference black body 

assembly 

Sensor 

Filter 

holder 

Chopper 

Cold black body assembly 

Figure 1. Diagram of the multichannel radiometer. 

each flight was later used to determine the target in the field 

of view of the radiometer. The radiometer electronics and 

data-logging system were included in the aircraft cabin. 

Flight data were also recorded on a second computer. 

Initially, the radiometer included the five narrow-band filters 

centered at wavelengths of6.4, 8.6, 10.1, 10.8 and 12.0 Jlm. 

During the aircraft campaign, for the reason explained 

above, the 6.4 Jlm filter was replaced with a wider filter at 

10.9 Jlm and, because no large concentrations of so2 were 

expected in the Tasmanian atmosphere, the filter at 8.6 Jlm 

was also replaced by a second broad filter at 11.8 Jlm. 

The aircraft was flown at various altitudes up to 8,000 

m, and measurements of the infrared radiation emitted by 

different water-and-ice clouds and the clear sky were taken. 

For each channel (filter), the signals measured by the radiometer were converted to temperatures using the inverse 

Planck function at a wavelength determined from a combination of the filter's spectral response, the germanium-window transmission, and the detector response. Figure 3 shows 

these "brightness" temperatures for the clear sky for level 

flight at 4,000 m. The measurements are as predicted from 

theoretical calculations. The temperatures at 10.8 Jlm are 

colder because there is less water-vapor absorption at this 

wavelength compared to that at 11.8 Jlm. The temperature at 

10.1 Jlm is warmer due to the radiometer receiving radiation 

from the strong 9.6-Jlm absorption band of ozone in the 

warm stratosphere. For comparison, measurements taken 

from the ground looking at a clear sky are included in 

figure 3. 

Stepper motor drive circuitry housing 

and front end electronics 
DETECTION AND DISCRIMINATION OF ASH CLOUDS BY INFRARED RADIOMETRY-II: EXPERIMENTAL 315 

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WAVELENGTH, IN MICROMETERS 

Figure 2. Relative spectral responses of the detector and transmittances of filters and the germanium window. Heavy lines indicate spectral response of broad filters; light lines indicate spectral 

response of narrow filters. 

Figure 4 shows brightness temperatures measured when 

the aircraft was flying horizontally toward a cumulus cloud 

at 3,300 m. Again, the temperatures at 10.8 f.Lm are less than 

those at 11.9 f.Lm, as predicted by theory. In this case, the 

1 0.1-f.Lm channel shows a colder temperature due to the 

cloud obscuring warm stratospheric ozone. 

The tests at Hobart showed that the radiometer could 

operate well in an aircraft flying at levels up to 8,000 m. All 

measurements with the radiometer agreed with theoretical 

calculations. 

VOLCANIC-ASH-CLOUD 

MEASUREMENTS 

Having fully tested the radiometer on an airborne platform, it was then necessary to use the instrument to study the 

infrared characteristics of a real volcanic ash cloud. For this 

reason, the radiometer was taken to Mt. Sakurajima, on the 

southern Japanese island of Kyushu. Funds were not available to mount an aircraft campaign, but there were several 

advantages in operating the radiometer from the ground. Mt. 

Sakurajima has an altitude of 1,118 m and is an active volcano that erupts between 100 and 200 times annually. 

Between eruptions, there is almost continual ejection of volcanic ash into the atmosphere. During these passive ejections, the ash is usually carried to no more than 1,000 m 

above the crater. When the volcano erupts, however, ash can 

reach altitudes of several thousands of meters (Onodera and 

Kamo, this volume). 

Observations of clear skies, water/ice clouds, and volcanic ash clouds were taken from different locations in the 

vicinity ofMt. Sakurajima. For the Japan measurements, the 

8.6-f.Lm SOz filter was used along with the narrow filters at 

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EXPLANATION 

• Ground-based measurements, 

Melbourne, Australia 

+ Airborne measurements 

x Ground-based measurements, Japan 

0 LOWTRAN calculations 

9 10 11 

WAVELENGTH, IN MICROMETERS 

12 

Figure 3. Clear-sky measurements using the infrared radiometer. 

LOWTRAN, a radiance/transmittance code developed by the U.S. 

Air Force. See Prata and Barton (this volume). 

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WAVELENGTH, IN MICROMETERS 

Figure 4. Airborne measurements of a cumulus cloud made near 

Mt. Sakurajima, Japan. Vertical bars indicate measurement 

uncertainty. 
316 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

10.1 and 12.0 J.Lm and the wider filters at 10.9 and 11.8 J.Lm. 

The germanium window was not used in the measurements 

made in Japan. 

The radiometer was operated under computer control 

with a calibration cycle for all channels used at the start and 

end of a measurement period. In between calibration cycles, 

the radiometer cycled between the selected filters. Typically 

the radiometer viewed at one wavelength for about 10 s 

before cycling to the next filter. 

The results of clear-sky measurements have already 

been shown in figure 3. Of particular interest is the warmer 

signal in the 8.6- and 1 0.1-J.Lm channels, presumably due to 

increased concentrations of S02 and C02 from the volcanic 

emissions. The other interesting feature is the difference 

between the 11.8- and 12.0-J.Lm measurements. This is 

assumed to be due to excess sulfuric-acid particles in the 

hazy atmosphere near the volcano. Sulfuric acid has a much 

stronger absorption at 11.8 J.Lm than at 12.0 J.Lm. 

On several days, the radiometer was used to view the 

volcanic ash cloud emanating from Mt. Sakurajima. On most 

occasions, there were sufficient water clouds in the vicinity 

to enable measurements of both volcanic ash clouds and 

water clouds from the same location under the same conditions. The results of measurements taken from the Sakurajima Volcanological Observatory on March 10, 1991, are 

shown in figures 5 and 6. In figure 5, the brightness temperatures of a cumulus cloud are shown as measured by the 

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Central wavelength 

! 10.9j..lm 

2 11.81lm 

200 300 400 500 

TIME SINCE START OF EXPERIMENT, IN SECONDS 

Figure 5. Ground-based measurements of a cumulus cloud near 

Mt. Sakurajima, Japan, March 10, 1991. Radiometer looking at an 

elevation of21 °. Vertical bars indicate measurement uncertainty. 

radiometer looking at an elevation of 21°. As with the airborne measurements, the temperature at 11.8 J.Lm is warmer 

than that at 10.9 J.Lm. Figure 6 shows the brightness temperatures in the five channels obtained at an elevation of 13.5° 

and looking toward the volcanic cloud. In contrast to the 

cloud observations and the clear-sky measurements, the temperature at 11.8 J.Lm is cooler than that at 10.9 J.Lm. Also, the 

figure shows that the same characteristic is true for the narrow-band channels: the temperature at 12.0 Jlm is cooler than 

that at 10.1 J.Lm (fig. 4). In fact, these measurements show 

that the narrow-band channels give a better discrimination 

than the broader channels. However, this improved discrimination was not always observed in the radiometer data, perhaps due to changing concentrations of carbon dioxide and 

sulfuric-acid particles in the intervening atmosphere. Nevertheless, in all cases when viewing water and volcanic ash 

clouds, the radiometer was easily able to discriminate 

between the two cloud types. 

CONCLUSIONS 

The multichannel infrared radiometer has been tested 

on both a high-flying aircraft in Australia and on the ground 

in the vicinity of a Japanese volcano. The results from these 

tests support the theoretical calculations of the spectral characteristics of the infrared radiance emitted by clear skies, 

water/ice clouds, and volcanic ash clouds. Radiometer measurements indicate that water clouds and volcanic ash clouds 

have markedly different optical properties at wavelengths 

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EXPLANATION 

Central wavelength 

• 8.6f.Lm 

+ 10.1 f.Lm 

1::. 12.0f.Lm 

0 10.9f.Lm 

x 11.8Jlm 

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600 800 1,000 1,200 

TIME SINCE START OF EXPERIMENT, IN SECONDS 

Figure 6. Ground-based measurements of volcanic ash cloud 

emanating from Mt. Sakurajima, Japan, March 10, 1991. Radiometer looking at an elevation of 13.5°. 
DETECTION AND DISCRIMINATION OF ASH CLOUDS BY INFRARED RADIOMETRY-II: EXPERIMENTAL 317 

near 11 and 12 J.lm. This contrast in the behavior of the two 

types of clouds clearly identifies a means whereby an airborne instrument can be used to successfully detect hazardous volcanic ash clouds in the flight path of commercial 

aircraft. 

CONSIDERATIONS FOR AN 

AIRBORNE DETECTION SYSTEM 

The infrared technique for the airborne detection of volcanic ash clouds has several advantages over other systems. 

1. An infrared instrument detects the presence of silicate 

particles, which are the actual constituents of volcanic 

ash clouds that cause aircraft engines to stall. 

2. The instrument relies on passive remote sensing to 

detect the naturally emitted radiation from the ash 

cloud and does not rely on the reflection of energy 

transmitted from the aircraft itself. 

3. The instrument would detect volcanic ash clouds well 

ahead of an aircraft (1 00-200 km), giving ample time 

for evasive action. 

4. If infrared-detector arrays are used, the instrument 

could operate without any moving parts. This would 

be a great boon for reliability and maintenance. 

5. The technique is ideally suited for incorporation into a 

multifunction instrument. Similar technology can be 

used to detect clear-air turbulence (Kuhn and others, 

1977) as well as wind shear in the landing and takeoff phases of flight (Sinclair and Kuhn, 1991). 

RECOMMENDATIONS 

In view of the results presented in this paper it is recommended that: 

1. Research work continues in order to identify the optimum wavelengths and bandwidths for an operational 

instrument, 

2. Further tests are undertaken to investigate a volcanic 

ash cloud at aircraft-cruise altitudes, 

3. Financial and other support be given to the development of a full airborne prototype instrument, and 

4. Collaborative programs be developed to work toward 

a multifunction instrument using infrared radiometry. 

ACKNOWLEDGMENTS 

Funding for the radiometer development and the airborne trials in Hobart was provided by the Commonwealth 

Scientific and Industrial Research Organization (CSIRO), 

Office of Space Science and Applications. The instrument 

was built in the CSIRO workshops by Mr. John Bennett and 

his staff. The field trip to Mt. Sakurajima was sponsored by 

the Australian Department of Industry, Technology, and 

Commerce under their bilateral science and technology program with Japan. The field program at Sakurajima would not 

have been possible without the enthusiastic support of Professor Kosuke Kamo and his staff at Sakurajima Volcanological Observatory. The authors would like to express their 

deep thanks to these colleagues who have made such a valuable contribution to this program. 

REFERENCES CITED 

Kuhn, P., Carcena, F., and Gillespie, C.M., Jr., 1977, Clear air turbulence; detection by infrared observations of water vapor: 

Science, v. 196, p. 1099-1100. 

Prata, A.J., 1989, Observations of volcanic ash clouds in the 10-12 

J.Lm window using A VHRR/2 data: International Journal of Remote Sensing, v. 10, p. 751-761. 

Sinclair, P.C., and Kuhn, P.M., 1991, Aircraft low altitude wind 

shear detection and warning system: Journal of Applied Meteorology, v. 30, p. 3-16. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

SATELLITE MONITORING OF VOLCANOES 

USING ARGOS 

By J.P. Cauzac, Christian Ortega, and Laurel Muehlhausen 

ABSTRACT 

The Argos satellite system has been used for environmental data collection for more than 10 years. It was first 

used on a volcano in 1982, collecting data from field experiments on Mt. Etna. Since then, many more volcanoes have 

been monitored with portable data loggers transmitting 

through Argos. These provide year-long observations and 

give users regularly updated data sets for a better understanding of complex volcanic phenomena. 

Argos stations provide permanent monitoring and help 

to detect increases in activity on remote volcanoes. Specialists can be brought in before the volcano erupts so that airline 

companies have information more quickly. For civil aviation, the most useful feature of Argos is its worldwide coverage. Orbiting satellites reach the world's most remote 

areas. Processing centers in Toulouse, France; Landover, 

Md.; Melbourne, Australia; and Tokyo, Japan, distribute all 

collected data to users. They also allow several users to share 

information simultaneously. 

In collaboration with scientists from INSU (French 

Institute for Earth and Planetary Sciences), Collecte Localisation Satellites (CLS) Argos has recently developed two 

types of stations: one for monitoring seismic tremors and 

events (SISMO 1 ), and one for monitoring physical-chemical 

parameters (MONOA). Along with the stations, users are 

provided with dedicated PC software that can automatically 

download data from one of the processing centers, put them 

in a database, and display the results graphically. 

INTRODUCTION 

Most volcanologists agree that active volcanoes should 

be more widely monitored. But the significant eruptions in 

the 1980's were mostly at volcanoes with few previously 

observed eruptions. This is why volcanologists are now calling for permanent systems on more volcanoes (Tilling, 1990; 

Ward, 1990). Continuous monitoring of volcanoes would 

provide a way of recording early signs of activity and provide information on the physical-chemical processes that 

trigger and sustain eruptive activity. Monitoring more volcanoes would increase the probability of observing eruptions. 

Owing to high investment and maintenance costs, it is 

not feasible to establish permanent, sophisticated observatories on each active volcano. It is even less feasible in remote, 

scarcely inhabited areas where the risk for local populations 

is low. The problem is that events at these unmonitored volcanoes can affect air traffic. 

Remotely monitored data-collection platforms are a 

cost-effective alternative to large observatories. Data are 

relayed through the satellite to one or more institutes in 

charge of long-term monitoring and responsible for detecting early signs of increases in volcanic activity. If required, 

these institutes may decide to do more accurate observations 

using satellite images or by installing additional instruments. 

This continuous monitoring would help to protect civilian 

populations and would provide input data for scientific studies. For airline companies, this may help to save days in the 

decision process when air routes are to be modified. 

Among other telemetered platforms, those reporting via 

the Argos satellites have many attractive features. They are 

easy to install and maintain and require little on-site equipment. Because they are reliable and use little power, they can 

be left unattended for a year or more while transmitting data 

several times per day. Finally, they benefit from the worldwide 

dissemination network operated by Argos, which has already 

been chosen to distribute data collected by thousands of environmental platforms (drifting buoys, fishing vessels, etc.). 

This document outlines a global system for volcano 

observation using satellite transmission by Argos. 

ARGOS EXPERIENCE IN 

MONITORING VOLCANOES 

The first application of Argos on a volcano was in 1982, 

when scientists from different earth-science agencies cooperated and developed common monitoring tools in the 

French PIRPSEV program (Interdisciplinary Research Program for the Forecasting of Volcanic Eruptions). Argos 

platforms are now installed on more than one dozen volcanoes worldwide (fig. 1). 

319 
320 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

-c:,_. ~2 ~ ~ _, ~::> ~/re_ ~..- --~ 60 ~ kl. .......,_> ""l,~ b2 ;n::t ... r-~ ~ <~,, (/ 

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• Etna monitored by LGIT & lPG for PIRPSEV 

EXPLANATION • Ambrym, Hunter, Matthew, Vanuatu monitored by ORSTOM for PIRPSEV 

• Seismic and multisensor platform 

• Colima, Momotombo, Nyos, Kelud, Merapi, Ruapehu, Soputan, Taal 

monitored by Universite de Savoie • Multisensor platform for lake buoy 

LGIT: Laboratoire de Geophysique Interne et Tectonophysique 

PIRPSEV: Programme lnterdisciplinaire de Recherche sur Ia Prevention 

des Eruptions Volcaniques 

.A. MONOA test platform for temperature 

lPG: lnstitut de Physique du Globe 

Figure 1. Volcanoes monitored using Argos platforms. MONO A, Argos station for monitoring physical-chemical 

parameters. 

A 1 0-station seismic network was installed on Mt. Etna, 

Italy, in the early 1980's and operated continuously for several years with practically no maintenance, even though certain stations were at altitudes of over 3,000 m. Seismologists 

(Glot and others, 1984) developed on-site filtering of data to 

transmit significant seismic parameters in short Argos messages. The time-tag provided by the Argos satellites synchronized all stations down to 10 ms (milliseconds) and 

helped to locate seismic epicenters. 

Further experiments led by ORSTOM (French 

Research Institute for Cooperative Development) at volcanic 

islands in the New Hebrides showed Argos to be a very adequate tool for monitoring remote and uninhabited sites on a 

long-term basis. Fumarole temperatures, heat-flux measurements, and local seismicity are among 15 parameters that are 

transmitted nine times per day. The first platforms were 

installed in 1986, and most are still reporting (Michel Lardy, 

unpub. data). 

The February 1990 eruption of the Kelut Volcano, East 

Java, Indonesia, showed how permanent monitoring can 

help to mitigate the effects of an eruption. A single Argos 

buoy in the middle of the crater lake collected precursory 

signs months before the eruption. Some slowly varying 

effects would not have been easily monitored with discrete 

measurements. The buoy was designed by the University of 

Chambery, France, as part of a cooperative program with the 

Volcanological Survey of Indonesia (VSI). Sensors included 

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10 20 31 10 20 30 10 20 31 10 20 31 10 20 

OCT NOV DEC JAN FEB 

1989 1990 

DATE 

Figure 2. Kelut Volcano, Indonesia-Lake temperature before 

the eruption of February 1990 as transmitted via Argos and monitored by the Volcanological Survey of Indonesia. Temperature 

measurement ceased at the time of eruption. 

thermistor strings and hydrophones to detect the bubbling 

noise; data were transmitted via Argos. Surface-temperature 

measurements increased constantly by about 1 °C every 10 

days from November 10, 1989, to February 10, 1990 (just 

before the eruption). The lake-bottom measurement showed 

a sharp increase, from 43°C to 58.5°C, within 10 days in 

November and remained the same until the first phreatic 
SATELLITE MONITORING OF VOLCANOES USING ARGOS 32I 

Figure 3. Satellite passes and ground coverage. Shaded area in A 

indicates the area of ground coverage. Shaded area in B indicates 

overlap between successive passes. 

eruption (fig. 2). The low- and medium-frequency recordings of the hydrophone showed an increase of gas bubbles 

from January I5 to 20. Because of the ability to detect precursory signs, the alert was issued several months before the 

eruption, and large-scale engineering works were quickly 

carried out to prevent a major catastrophe. The combination 

of intensive volcano monitoring, warning systems, and volcanic-hazard assessment significantly reduced the number of 

victims (Sudradjat, I99I). 

New joint studies with the Volcanological Survey of 

Indonesia are scheduled early in I993 to monitor Merapi 

Volcano, Central Java, Indonesia. This program, funded by 

the French Deh~gation aux Risques Majeurs, includes installation of Argos platforms with extensometers (MONOA) 

and seismic recorders (SISMO I). The development of these 

platforms was funded by CLS, the operator of the Argos 

system. 

OVERVIEW OF THE ARGOS SYSTEM 

Argos has been operational since I978 and is the result 

of a cooperative program by National Aeronautics and Space 

Administration (NASA), National Oceanic Atmospheric 

Table 1. Variation of Argos satellite "visibility" from the ground 

as a function of latitude. 

[PIT, platform transmitter terminal (latitude shown in degrees); cum. visibility, cumulative visibility over a 24-hour period (in time units of minutes); min. passes, minimum 

number of passes per 24-hour period; mean passes, mean number of passes per 24-hour 

period; max. passes, maximum number of passes per 24-hour period. See text for 

additional explanation] 

PTT Cum. Min. Mean Max. 

latitude visibility passes passes passes 

0 80 6 7 8 

±15 88 8 8 9 

±30 100 8 9 12 

±45 128 10 11 12 

±55 170 16 16 18 

±65 246 21 22 23 

±75 322 28 28 28 

±90 384 28 28 28 

Administration (NOAA), and the Centre National d'Etudes 

Spatiales (CNES, the French space agency). The Argos system offers two capabilities with worldwide coverage: (I) 

collecting environmental data from remote platforms, and 

(2) locating the platforms. 

The first satellite was launched in I978, and new satellites are launched every I or 2 years. The space segment is 

comprised of two NOAA satellites in a low Earth orbit (fig. 

3). They receive all transmissions from platforms that are 

visible from the satellites during the entire orbital revolution. 

The signals are stored by tape recorders on board the satellites and are downloaded to three ground stations. The 

onboard equipment also retransmits the data in real time. 

Presently, two Argos satellites are in operation (NOAA-H 

and NOAA-D), and two others are backups. 

The satellites provide worldwide coverage with polar 

orbits at 830 km and 870 km altitude. The orbital period is 

approximately I 0 I minutes; this gives I4 orbital revolutions 

per satellite per day. 

Each satellite simultaneously sees all platforms within 

a 5,000-km-diameter circle. As the satellite orbits, the visibility zone sweeps a 5,000-km-wide swath around the Earth 

that passes over the North and South Poles. As a result of the 

Earth's rotation, the ground tracks and swath shift 25° west 

about the polar axis, with sidelap between successive swaths. 

Because sidelap increases with latitude, the number of daily 

passes over a given platform depends on latitude, from six 

messages per day at the equator, to more than twenty at the 

poles (table I). 

Argos platforms consist of data loggers with a 40 I.650-

MHz platform transmitter terminal (PTT). Each PTT transmits a short message (up to 256 bits) that is repeated regularly (every 200 s, for example). Several messages can thus 

be received on a single pass, increasing transmission 
322 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 4. Argos worldwide coverage and areas processed in regional mode with shorter throughput times. Thick 

circles show area where 50 percent of all received messages are also processed in regional mode. Thin circles show 

area where 30 percent of all received messages are also processed in regional mode. 

reliability. For mobile platforms, location can be calculated 

from the Doppler shift on the signal received by the satellite. 

The Argos onboard equipment receives all messages 

transmitted by platforms within the satellite-visibility area. 

Messages are received, processed, and retransmitted back to 

Earth when the satellite is in view of one of the three ground 

stations (Lannion, France; Wallops Island, Va.; and Fairbanks, Alaska). 

Data is processed in two manners: regional and global. 

Regional processing uses the real-time downlink and occurs 

when the satellite sees the platform and the receiving station 

simultaneously. Because the data from these platforms are 

received in real time, they are available to users more quickly 

(fig. 4). Global processing occurs for all platforms, even if 

they have been processed regionally, and uses the recorded 

data. Global and regional data flows are received by ground 

stations and are then sent to one of the Argos processing centers: either Toulouse, France, or Landover, Md. The two centers are linked by a dedicated line in order to back each other 

up and allow dual processing of data. Each center operates 

around the clock every day of the week and features full 

internal redundancy. A center has recently been opened in 

Melbourne, Australia, and provides regional coverage for 

platforms in that area. A similar center in Tokyo distributes 

data collected in the global mode. 

The centers check and time-tag the messages and sort 

them by platform. On request, sensor data can be converted 

into physical values. Users access their results via an online dissemination system, supplying the last 4 days of data 

plus data for the current day. Data are also archived and 

can be recovered off line (tapes and floppy disks). Most 

users connect to the closest distribution center through public networks (Tymnet or Internet in the United States), 

using desktop computers with modems. They receive new 

messages upon interrogation or automatically at defined 

intervals. 

Throughput time (the delay from when a message is 

received by satellite to when it is available to users) 

improves constantly due to frequent upgrades at the processing centers. In global mode, 60 percent of the messages are 

available in less than 3 hours. In regional mode, 60 percent 

of data are available in less than 45 minutes and 95 percent 

are available in less than 1 hour. 

AN ARGOS VOLCANOLOGICAL 

SYSTEM 

CLS Argos has worked with seismologists and volcanologists to define a basic volcano-monitoring system. The 

system includes field stations with Argos transmitters and 

dedicated software to access the data (fig. 5). The main 

objective is to provide both local teams and cooperating scientists in other countries with continuously updated information on volcanoes where permanent laboratories cannot be 

installed. 

The user has continual access to transmitted data in near 

real time (results available in less than 1 hour when the platform is served by regional processing mode). Several times 

per day, the user knows the status of scientific measurements 

and station-operating status (housekeeping parameters), 

which allow efficient scheduling of field work. Finally, 

many scientists worldwide can have access to the data 

through computer networks. 
SATELLITE MONITORING OF VOLCANOES USING ARGOS 323 

Figure 5. The Argos volcanological system provides two ways to access data: (I) locally, with full data set on removable memory card, and (2) by means of the Argos dissemination network. 

In addition to remote monitoring via satellite, data can 

be accessed locally. The stations developed by CLS Argos 

have programs for configuring instruments and retrieving 

data. This can be done in the observatory or on site using a 

portable personal computer (PC)-this insures that local 

teams are fully involved in processing the data from their 

volcano. The software downloads all the data from global 

and regional Argos processing centers and displays graphics 

and tables on a PC. Data from several stations can be read 

with a single program. 

The current Argos volcano-monitoring stations are 

SISMO 1 and MONOA. The SISMO 1 is dedicated to seismology. The MONOA records slowly varying parameters, 

such as fumarole temperature, extension of faults, etc. Both 

stations have high memory capacity, low power consumption, and include a miniature Argos transmitter. They are 

powered by solar panels and batteries. 

The PC-based program to retrieve Argos data performs 

the following functions: interrogation via modem of the 

Argos processing center, access to the latest data, and storage on the PC hard disk. The program manages a database 

consisting of months of collected data for each platform; the 

program is built around the Novell XTrieve structure and is 

compatible with many scientific programs. Parameters can 

be displayed as curves or bar graphs; several parameters can 

be monitored on the same screen when correlation is useful. 

The cost of the monitoring system is within reach of 

volcanological institutes. The basic MONOA station, ready 

to use with its Argos transmitter, starts at approximately 

$2,500; the SISMO 1 starts at $5,000. With $25,000, one can 

set up a basic volcano observatory that has several stations 

and several years of transmission via satellite. 

TECHNICAL DESCRIPTION 

OF THE FIELD EQUIPMENT: 

SISMOl AND MONOA 

TECHNICAL CHARACTERISTICS OF SISMOl 

SISMO 1 is a portable data logger that digitizes, processes, and stores the ground-velocity signal recorded by 

geophone. It also transmits significant data via Argos. It is 

for two types of applications: (1) long-term monitoring with 

a few stations per volcano, with transmission of mean 

energy, number of seismic events relative to given thresholds, and duration of tremors relative to given thresholds; (2) 

short-term, comprehensive, seismic studies, such as installation of large networks of stations for locating and tracking 

seismic events. The network can easily be synchronized by 

accurate time-coding done by the Argos satellite. 

• The analog-input stage features adjustable gain (from 

1 to 2,048) and sampling rates up to 200Hz. A 12-bit 

analog-to-digital converter is used. 

• The input signal is permanently processed. It triggers 

acquisition and storage according to one of three 

modes: (1) automatic seismic-event detection by 

short-term to long-term average ratio (STAILTA); (2) 

time triggered, the signal being stored during up to 30 

programmable time slots; (3) wired remote start up. 

• Signal processing based on algorithms tested by Institute of Geophysics in Ziirich (Baer and Kradolfer, 

1987). 

• Data are stored on a removable Flash memory card 

(credit-card size), with 4-megabyte capacity. A 
324 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

64-megabyte version has been announced by card 

manufacturers. The Argos message warns when the card 

memory is 80 percent full. This helps to help to schedule 

card replacement. SISMO 1 controls the card status and 

protects from overwriting data. 

• The internal clock tags arrival of seismic events to 5 

ms and can be synchronized with an external radio 

signal. Also, several stations can be externally synchronized by comparing their time with the accurate 

Argos satellite clock. 

• The Argos message, transmitted at 401.650 MHz, 

includes a platform identifier plus 256 bits of data. 

The number of Argos messages received depends on 

station latitude (minimum of eight messages per day 

at equator; maximum of 28 at the poles). 

• SISM01 is powered by external12-V de supply, with 

an average current drain of less than 20 rnA. 

TECHNICAL CHARACTERISTICS OF MONOA 

MONOA is a single-input data logger with an Argos 

transmitter. Another version accommodates eight sensors. It 

is compatible with a broad range of sensors with voltage or 

current outputs (0-1 V, 0-15 V (±1 V), 4-20 rnA). MONOA 

has a proven capability to immediately adapt to users' dedicated sensors, such as tiltmeters or extensometers. 

• Data-acquisition rates are programmable for 5, 10, 15, 

20, 30, or 60 seconds or minutes. Averaging periods 

are also user defined. A 1 O-bit analog-to-digital converter is used. 

• Data is stored on a 128-Kbyte memory board. (One 

megabyte with 8-sensor version.) 

• MONO A is powered by external 12-V de supply, with 

an average current drain of less than 3 rnA. 

• The Argos message includes the last 12 measurements, time and date, and memory occupancy for the 

single-sensor version. 

A POTENTIAL APPLICATION: 

MONITORING VOLCANOES 

IN THE ALEUTIANS 

Akutan Volcano is one of approximately 40 historically 

active volcanoes in the Aleutian Islands that lie close to busy 

northern Pacific air routes. Its most recent eruptions, in 1992, 

confirmed that volcano ash plumes may disrupt and endanger air traffic. However, at present, no Aleutian volcanoes 

are under surveillance by the Alaska Volcano Observatory. 

Akutan is not yet fitted with Argos transmitters. However, the geographical position of volcanoes in the Aleutian 

Islands is favorable for the Argos system. At these high latitudes, there are an average of twenty Argos satellite passes 

every day, thereby providing frequently updated data. In 

addition, the proximity of these platforms to the ground station in Fairbanks means that data from these platforms 

would be processed in regional mode, and results would be 

available to users within 30 minutes to 1 hour of being generated. Collected data would be readily available, whatever 

the weather conditions. 

CONCLUSIONS 

Many systems can now monitor volcanic activity 

remotely. Of these, Argos satellite-based data collection has 

unique strengths, including worldwide coverage and a 

proven dissemination network. Recently, CLS, the Argos 

system operator, has contributed to developing an end-toend system that includes volcanological platforms and processing software. Volcanologists can now install platforms 

for years to sense, store, and transmit significant parameters. 

The data are available to: (1) cooperating organizations 

around the world via the Argos data network, and (2) to local 

volcanologists, straight from the data logger. 

Argos data transmission is not hampered or degraded by 

cloud cover or darkness, as in some remote-sensing techniques. Argos provides advance information on volcanicactivity patterns and may be used to schedule further observation using remote sensing. Compared to permanently 

manned observatories, Argos volcano-monitoring stations 

and satellite telemetry are cost effective, and a budget of 

$25,000 would allow the monitoring ofuninstrumented volcanoes. 

The benefits of volcano monitoring for aviation are: 

• Once long-term global databases are established, volcanoes will be better characterized and understood. 

Scientists may then be able to access the risk of eruptions from historical trends and current conditions. 

• Argos can provide remote notification of increased 

volcanic activity, as it did on Kelut, Indonesia, in February 1990. 

• Argos data can be accessed, via the operational Argos 

distribution network, anywhere in the world. 

REFERENCES CITED 

Baer, M., and Kradolfer, U., 1987, An automatic phase picker for 

local and teleseismic events: Bulletin of the Seismological Society of America, v. 77, p. 1437-1445. 

Glot, J.P., Gresta, S., Patane, G., and Poupinet, G., 1984, Earthquake activity during the 1983 Etna eruption: Bulletin of Volcanology, v. 47, p. 953-963. 

Sudradjat, A., 1991, A preliminary account of the 1990 eruption of 

the Kelut Volcano: Geologische Jahrbuch, v. Al27, p. 

447-462. 

Tilling, R.I., 1990, Coping with volcanic hazards: A global perspective: Earthquakes & Volcanoes, v. 22, p. 154-160. 

Ward, P.L., 1990, Global data collection and the surveillance of 

active volcanoes: Palaeogeography, Palaeoclimatology, and 

Palaeoecology (Global and Planetary Change Section), v. 89, 

p. 263-267. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

CURRENT AND FUTURE CAPABILITIES IN FORECASTING 

THE TRAJECTORIES, TRANSPORT, AND DISPERSION OF 

VOLCANIC ASH CLOUDS AT THE CANADIAN 

METEOROLOGICAL CENTRE 

By Real D' Amours 

ABSTRACT 

The Canadian Meteorological Centre (CMC) Dorval, 

Quebec, is the main Canadian center for processing weather 

information. Because of its computer and communication 

facilities and because of its numerical weather-analysis and 

prediction models, CMC is the Canadian agency that can 

most rapidly respond to information requests about the largescale evolution of pollution clouds. For that purpose, a 3-D 

trajectory model and a 3-D transport/diffusion model are in 

operation. These models are also used to estimate the motion 

of volcanic ash clouds. This paper briefly describes the CMC 

and the numerical models available for atmospheric transport. Application to volcanic ash clouds is illustrated by the 

simulation of a hypothetical eruption at Mt. Meager in British Columbia. Forthcoming improvements and direction of 

future developments for the models are presented. 

INTRODUCTION 

The Canadian Meteorological Centre, in Dorval, Quebec, is part of Environment Canada and is the main Canadian 

center for processing weather information. It supports the 

nine regional weather centers of Atmospheric Environment 

Service (AES), plus the National Defense Weather Centres. 

CMC operates the AES supercomputer, a NEC SX-3/44, 

plus a variety of other mainframe computers, and the AES 

communication systems. CMC runs numerical weatheranalysis and prediction models for AES. Weather observations from the world are continuously arriving at CMC 

through the global telecommunication system (GTS) as well 

as through the AES telecommunication network. 

Weather analysis is performed automatically for the 

global atmosphere through a data-assimilation system. Analyses are done for four main synoptic times: 00:00 UTC, 

06:00 UTC, 12:00 UTC, and 18:00 UTC. The data-assimilation system consists of an objective-analysis (OA) procedure 

based on a multivariate optimum interpolation method and 

on global and regional spectral numerical weather-prediction 

models. The prediction models produce 6-hour forecasts, 

which serve as initial guesses; those guess fields are then 

corrected with observational data by the OA. Analyses are 

done for temperature, geopotential height, wind, and humidity at 15 vertical levels, extending from the Earth's surface to 

about 100,000 ft. The analyzed fields are used as initial conditions for various forecast models. 

Two numerical weather-prediction (NWP) models are 

currently in operation at CMC: a regional fmite-element 

model and a global spectral model. The regional fmite-element (RFE) model is a hemispheric model with variable resolution; the high-resolution (100 km) area covers North 

America. The model is executed twice a day, at 00:00 UTC 

and 12:00 UTC, and produces forecasts for up to 48 hours 

into the future. The global spectral model is also executed 

twice a day: into the future up to day 6 at 00:00 UTC and up 

to day 3 at 12:00 UTC. The accuracy of the forecasts produced by these models is comparable to forecasts produced 

by other national meteorological centers (table 1). 

At all times, CMC has an accurate knowledge of the 

actual state of the synoptic-scale flow of the atmosphere and 

of its most probable evolution for the next few days. CMC is 

therefore the Canadian agency that can most rapidly respond 

to information requests about the large-scale evolution of 

pollution clouds during environmental emergencies. For that 

reason, a 3-D trajectory model and a 3-D transport/diffusion/ 

deposition model have been implemented in CMC's operations. The primary purpose for implementing these models 

was to increase preparedness for nuclear emergencies. The 

models are also used to estimate the motion of volcanic ash 

plumes. 

THE TRAJECTORY MODEL 

CMC's trajectory model is a simple 3-D Lagrangian 

model. Given a 3-D wind field, the model will calculate the 

motion of a neutrally buoyant air parcel, starting from a 

325 
326 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. RMS (root-mean-square) error of wind vector, 24-hour 

forecast for North America, January 1, 1992, to April 30, 1992. 

[Verifications were done by the issuing Canadian Meteorological Centre, Dorval, 

Quebec, following the World Meteorological Organization (WMO) recommendations 

for a standard set of radiosonde stations. UKMO, United Kingdom Meteorological 

Office] 

Models 500 hPa 

(:::18,000 ft) 

Canadian global spectral model ....... 11.7 knots 

U.S. global model (aviation run) ...... 11.5 knots 

UKMO global model ....................... 12.6 knots 

200 hPa 

(:::35,000 ft) 

17.1 knots 

16.8 knots 

18.7 knots 

specified point of origin. The model considers no other process than advection by the wind. CMC's trajectory model 

operates on a polar stereographic grid in the horizontal plane, 

and in pressure coordinates in the vertical plane. It was 

designed mostly for use over North America (fig. 1). 

The model can be executed in forecast or hindcast 

mode. It uses interpolated wind fields and vertical motions 

produced by the global data-assimilation and forecast systems. Trajectories are calculated for three air parcels originating from a single location but from three different vertical 

levels, all user specified. 

Figure 1. Window for the trajectory model. Trajectories for parcels exiting the window will terminate at the point of exit. CMC's trajectory 

model operates on a polar stereographic grid in the horizontal plane and on pressure coordinates in the vertical plane. It was designed for use 

over North America. 
ASH CLOUD FORECASTING AT THE CANADIAN METEOROLOGICAL CENTRE 327 

040CISI 

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HAUTEURS 80-DISSDS DO HIVEAU Dl Lft IIIR 

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:1---:.-------J: 300 118 

TR8JECTOR\' lORICftSTS FOJt 11 E fl G E R PREVISIOI!S DE_TRftJICTOIRI POUR. +------1- 250 liB 

Figure 2. · Sample output of trajectory model as it is made available to the user. Positions are plotted at 3-hour intervals. Heights along 

the trajectories are given on the left side of the map, in meters above mean sea level. The map is centered on the origin of the parcels for 

the north-south direction, but it is somewhat displaced to the west. As in most circumstances, parcels move rapidly eastward. Solid triangles, trajectory at 400 hPa; X's, trajectories at 300 hPa; crosses, trajectories at 250 hPa. 

Results from the trajectory model can be made available to the users within 1 0 minutes of request. The results 

may be transmitted in chart form through the AES meteorological satellite information system (METSIS) or via telecopier. Positions calculated at 3-hour or 6-hour increments 

(latitude, longitude, and height) along the trajectories are 

also available in the form of alphanumeric messages on AES 

telecommunications networks. 

The trajectory model can be useful for emissions of 

short duration. However, it does not provide any information 

on plume dimensions or size, on air concentrations, or on 

surface deposition. 
328 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

THE CANADIAN EMERGENCY 

RESPONSE MODEL (CANERM) 

The Canadian emergency-response model (CANERM) 

was developed by J. Pudykiewicz of Environment Canada 

following the Chernobyl nuclear accident (Pudykiewicz, 

1989). CANERM is a 3-D advection/diffusion model that 

simulates the effects of wet and dry scavenging, estimates 

wet and dry deposition, and models the mixing effects within 

the planetary boundary layer. Although the model was 

designed to assess the motion of radioactive clouds resulting 

from large nuclear accidents, it can be used to model volcanic ash clouds. 

In the current operational setup, CANERM can execute 

on either the Northern or Southern Hemisphere. Three configurations are available: (1) a hemispheric domain at a horizontal resolution of 150 km, (2) a continental domain with a 

resolution of 50 km, and (3) a regional domain at a 25-km 

resolution. The continental domain covers a square area 

roughly l.Ox108 km2 that is centered on the source of emission. The regional domain is also centered on the source and 

covers about 3.0x107 km2. The vertical coordinate is the terrain-following a-coordinate ( cr is the ratio of the atmospheric pressure at a given vertical level to the surface 

pressure at that location). The model has 11 vertical levels up 

to about 50,000 ft above sea level (a = 0.1; this is approximately equal to 100 hPa). Winds, temperature, moisture, 

and geopotential must be provided to the model. These may 

come from an historical sequence of objective analyses 

(hindcast mode) or from the output of the global spectral 

model (forecast mode). The hindcast mode is used to obtain 

the best estimate of the actual state of the plume, and the 

forecast mode is used to obtain the expected state. The two 

modes can be used in sequence for events of extended duration. 

The release to the model atmosphere near the source is 

modeled by a Gaussian function. The standard deviation is 

one grid length in the horizontal plane, and 0.1 cr in the vertical plane. The height, intensity, and duration of the release 

are specified by the user. To simulate volcanic ash, an inert, 

neutrally buoyant gas tracer, not subject to washout, is used. 

CANERM produces estimates of the 3-D shape of the ash 

plume as it evolves in the atmospheric flow. Results can be 

made available to users in chart form via telecopier about 30 

minutes after request. 

AN EXAMPLE: HYPOTHETICAL 

ERUPTION AT MT. MEAGER, 

BRITISH COLUMBIA 

Mt. Meager volcano is part of the Garibaldi volcanic 

belt in British Columbia, where a volcanic eruption of consequence is possible (Hickson, this volume). A simulation 

was done for a hypothetical eruption at 12:00 UTC, June 20, 

1991. Sample outputs of the trajectory and CANERM models are illustrated in figures 2 and 3 as they would be made 

available to users. An experimental run of CANERM was 

also done, at a resolution of 10 km, using interpolated fields 

produced by CMC' s operational RFE model. 

The meteorological situation for the simulation was 

characterized by a weak wind circulation over western North 

America at all levels. This is apparent in the unusual behavior of the trajectories (fig. 2), which indicate a northwestward motion immediately following the hypothetical 

eruption. The trajectories at 400 hPa and 300 hPa recurve 

northeastward after about 18 hours; the 250 hPa trajectory 

trends southeast after the same elapsed time. Figure 3 shows 

the ash plume produced by the CANERM run at 50-km resolution, after 48 hours, at 250 hPa. The modeled plume 

reaches far inland over Oregon and Idaho, but the end point 

of the trajectory at 250 hPa, which should indicate the position of an air parcel originating from above the volcano 48 

hours later, is still over the ocean. The plume has also spread 

over northern British Columbia; this is not indicated from 

the trajectory at 250 hPa, but is hinted at by the trajectories 

at 300 and 400 hPa. The extent of the plume produced by 

CANERM is greater than what could be inferred from the 

trajectories. This can be explained by the fact that (1) the trajectory model has no diffusion in its formulation, and it 

tracks an air parcel that has, in fact, no dimensions, whereas 

CANERM has a well-developed ash column to begin with 

because of the Gaussian source model, and (2) the plume 

continues to spread throughout the simulation because of diffusion. 

A test run of CANERM at a resolution of 10 km, based 

on interpolated wind fields produced by the RFE model was 

also performed for Mt. Meager for the same time. At that resolution, about 96 percent of the plume at 400 hPa is within a 

radius of 20 km at the first interval of 3 hours; this is comparable to the size of the umbrella cloud generated shortly after 

an eruption (Woods and Kienle, this volume). The winds 

provided to CANERM do not permit resolution of features 
ASH CLOUD FORECASTING AT THE CANADIAN METEOROLOGICAL CENTRE 

0 

0 

' N 

-t 

' 0 

N 

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0 

' -t 

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CV 22 JUN 91 122 FP 48HR TRACER 

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SOURCE DESCRIPTION 

STANDaRD DEVIATION CHOR) : 1 GRID LENGTH 

STANDaRD DEVIaTION CVERT): .1 SIGna COORDINftTES 

STaNDaRD DEVIaTION CTinE): 03H 

329 

Figure 3. Sample output ofCANERM as it would be transmitted to the user. This is a 48-hour forecast of the instantaneous plume, at 250 

hPa (::: 35,000 ft) from an execution with a resolution of 50 km. Ash concentration units are in Jlglkg of air (ppbm-parts per billion by mass), 

given an emission of 1.3 megatons. In this simulation an inert gas tracer is used. Deposition and washout are not simulated. Release height 

is at 25,000 ft, and release duration is about 6 hours. 
330 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

c 

B· 

EXPLANATION 

Ash concentration·. 

i .. 11},000 !lg/kg 

lOO~g 

- l).lg/kg 

Figure 4. Forecasts of the instantaneous plume at 250 hPa (::: 35,000 ft) from a test CANERM run at 1 0-km resolution using interpolated 

winds produced by the regional finite-element model for hypothetical eruption ofMt. Meager at 12:00 UTC, June 20, 1991. The geographical area shown on the map constitutes the total domain of the model for this run. Ash concentration units are Jlg/kg of air (ppbm), given an 

emission of 1.3 megatons. In this simulation, an inert gas tracer is used. Deposition and washout are not simulated. Release height is at 

25,000 ft, and release duration is about 6 hours. Cross symbol, which is barely visible in A, indicates approximate location of Mt. Meager. 

A, 3-hour forecast; B, 18-hour forecast; C, 36-hour forecast; D, 48-hour forecast. 
ASH CLOUD FORECASTING AT THE CANADIAN METEOROLOGICAL CENTRE 331 

of less than 100 km in size. It can be argued, however, that, 

at upper levels (which are of interest for aviation), the flow 

is relatively smooth and most of the variability is in the synoptic scales, which are adequately resolved by the RFE. The 

evolution of the plume at 250 hPa is depicted in figure 4. At 

3 hours (fig. 4A), a tendency for the plume to bifurcate is evident. At 18 hours (fig. 4B), the cloud has spread considerably 

and the maximum concentrations are well detached from the 

source. At 36 hours (fig. 4C), extensive stretching has 

occurred and a branch is moving rapidly southward. From 36 

to 48 hours (fig. 4D), it can be seen that the whole cloud over 

the Pacific has started to translate eastward as the atmospheric flow aloft begins to reorganize. The final shape of the 

cloud at 250 hPa could not have been easily deduced from 

the trajectories alone. 

FUTURE CAP ABILITIES 

The NEC SX-3/44 supercomputer was installed at 

CMC in early October 1991, and the conversion ofCMC's 

operational system was completed on December 15, 1992, 

resulting in a reduction of the response time by a factor of 

two for CANERM. A global mode for the trajectory model 

and CANERM will be implemented in early 1994. 

Development work to account for particle-size distribution and settling velocities is in progress. CANERM's capacity to provide estimates of ash surface deposition will be 

activated in mid-1994. Improved wet scavenging will also be 

possible using available precipitation fluxes from NWP 

models. 

Over the next few years, estimates of air concentrations 

and of surface deposition very near the source will improve 

with the introduction of more sophisticated sub-models to 

better estimate initial plume rise, vertical distribution of 

ejected materials, and other sub-grid-scale effects. Eventually a dedicated, high-resolution, non-hydrostatic meteorological model will be included to resolve the detailed 

structure of atmospheric motions in the vicinity of the 

source. 

REFERENCE CITED 

Pudykiewicz, J., 1989, Simulation of the Chernobyl dispersion with 

a 3-D hemispheric tracer model: Tellus, v. 41B, p. 391-412. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

AN AIRCRAFT ENCOUNTER WITH A 

REDOUBT ASH CLOUD (A SATELLITE VIEW) 

By Kenneson G. Dean, Lawrence Whiting, and Haitao Jiao 

ABSTRACT 

Satellite images, wind measurements, and ground 

observations were used to track and map gas clouds and ash 

clouds emitted by Redoubt Volcano, Alaska, on 15 December 1989. This eruption resulted in a nearly catastrophic 

encounter between airborne ash and a Boeing 747 jet aircraft 

(most of southern Alaska was completely covered by clouds 

on that day). Four satellite images were analyzed using complex digital-processing techniques to locate geographic features and to distinguish eruption-related gas clouds from 

meteorological clouds. The technique of subtracting thermal 

infrared bands to detect ash clouds was applied to three 

images but was only successful on the 13:42 Alaska Standard Time (AST) image. The 13:42 image revealed the presence of two ash clouds near Fairbanks and Delta Junction 

that may have been involved in the encounter with the 747 

aircraft earlier that morning. Ground samples from the two 

ash clouds help quantify the characteristics of ash clouds 

detected by satellite sensors. The eruption at 10: 15 AST 

appears to be the origin of the ash involved in the aircraft 

encounter. 

INTRODUCTION 

On 14 December 1989, Redoubt Volcano, located 177 

km southwest of Anchorage, Alaska (fig. 1), erupted and 

expelled a huge eruption cloud composed of ash and gas to 

altitudes greater than 10 km (Brantley, 1990). For the next 4 

months, 24 additional eruptions resulted in the deposition of 

ash throughout southern Alaska (Scott and McGimsey, 

1991 ). Clouds of ash and gas from Redoubt Volcano drifted 

hundreds of kilometers to locations beyond Fairbanks, Delta 

Junction, and Glennallen. 

The danger to airline traffic posed by airborne ash was 

exemplified on 15 December at 11 :45 Alaska Standard 

Time, when a Boeing 747 jet flew into an ash cloud at an altitude of 7,600 m (25,000 ft) northeast of Talkeetna, Alaska. 

All four engines shutdown within minutes after the aircraft 

entered the cloud but were restarted about 8 minutes later, 

narrowly averting a catastrophe (Brantley, 1990; Casadevall, 

in press). The ability to detect, monitor, and predict the 

movement of volcanic plumes and ash clouds would help to 

minimize the possibility of aircraft encounters with ash. Satellite images are one potential source of this information. 

The 15 December 1989 chronology of events and National 

Oceanographic and Atmospheric Administration (NOAA) 

advanced very high resolution radiometer (A VHRR) satellite images used in our analysis are given in table 1. 

NOAA AVHRR satellite images have been used to 

monitor and analyze eruption clouds from Redoubt (Dean 

and others, 1990; Kienle and others, 1990); from Augustine 

(Holasek and Rose, 1991); from Colo, Indonesia (Maligreau 

and Kaswanda, 1986); from Mt. Galunggung, Indonesia 

(Hanstrum and Watson, 1983); from El Chich6n, Mexico 

(Matson, 1984); and from Mount St. Helens (Matson and 

Staggs, 1981). Techniques have been developed to distinguish ash clouds from meteorological clouds and other airborne volcanic constituents (Prata, 1989; Holasek and Rose, 

1991 ). Images from the Earth observing system (EOS) 

spacecraft will become an additional source of data for analyzing volcanoes in the near future (Mouginis-Mark and others, 1991). 

Images from the A VHRR sensor aboard the polar-orbiting NOAA-10 and NOAA-11 (N-10, N-11) satellites are 

recorded for the Cook Inlet region more than 10 times per 

24-hour period. This high temporal resolution is unique to 

high latitudes due to extensive overlap on each image swath 

from adjacent orbits. The data have a spatial resolution of 1 

km and a swath width greater than 2,000 km. The images are 

recorded in five wavelengths: visible band 1 (0.58-0.68 

~m), near-infrared band 2 (0.72-1.1 ~m), thermal-infrared 

band 3 (3.55-3.93 ~m), thermal-infrared band 4 (10.3-11.3 

~m), and thermal-infrared band 5 (11.5-12.5 ~m). However, on even-numbered NOAA satellites up to but not 

including N-12, band 5 is a duplicate of band 4. The fiveband coverage can detect both volcanic and non-volcanic 

cloud formations during both day and night. 

In this paper, clouds composed of gas and ash emitted 

by a volcano are referred to as eruption clouds. Eruption 

clouds may have a conical shape with an apex ending at the 

333 
334 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

• Delta Junction 

0 

Figure 1. Location map of south-central Alaska. 

';);> ("') 

t;\~ 

Ul\~ 

~r 

' ' \ 

' ' ~ ' \ 

\ 

volcano indicating that it is still being emitted, or the apex 

may be adrift and not connected to the volcano. An ash 

cloud is that portion of an eruption cloud containing volcanic 

ash that damages aircraft and other mechanical devices. 

Both ash and gas components of eruption clouds can be 

detected on satellite images, but they may not always be distinguishable from each other. 

OBJECTIVES 

The objective of this analysis is to use satellite images 

to identify and monitor eruption clouds, including the ash 

clouds responsible for the near-downing of an aircraft on 15 

December 1989. A VHRR images are used to distinguish 

eruption clouds from surrounding meteorological clouds, to 

map the trajectory and distribution of eruption clouds, and to 

detect and track the movement of the ash cloud that the aircraft encountered. 

METHODS 

SATELLITE ANALYSIS 

Three eruptions occurred on the morning of 15 December: at 01:40, 03:48, and 10:15 AST. Four satellite images 

were recorded at 03:28, 05:09, 09:28, and 13:27 AST (table 

1) and show that most of southern Alaska was completely 

covered by clouds. To relate cloud structures to ground locations, the images were registered to an Albers equal-area 

map projection, and geographic features were digitally 

superimposed. The values of individual pixels were 

Table 1. Chronology ofEvents on 15 December 1989. 

[AST, Alaska Standard Time] 

Time(AST) Event 

01:40 .. .................. . Eruption, 12 minutes duration 

03:28 ....... .... .... .. ... . Image: NOAA-11; orbit no. 6305 

03:48 .. .. .... ... ...... .... Eruption, 10 minutes duration 

05:09 .... ... ......... .. ... Image: NOAA-11; orbit no. 6306 

09:28 ...... ........ ... .... Image: NOAA-10; orbit no. 16851 

10:15 .. .. .. .... ...... .. ... Eruption, 40 minutes duration 

11 :45 .... .... .... .. ....... Aircraft-ash cloud encounter 

13:27 .. ..... ....... .. ..... Image: NOAA-11; orbit no. 6311 

transformed to temperature and albedo using coefficients 

provided with the data as described in the NOAA polar 

orbiter data users guide (Kidwell, 1991 ). Contrast was 

enhanced to optimize the detection of eruption-related gas 

clouds and ash clouds. Individual bands of satellite data were 

combined to distinguish gas clouds, ash clouds, and other 

plume constituents from meteorological clouds using established experimental techniques. These included: 

• Subtraction between bands 5 and 4 to distinguish ash 

clouds from meteorological clouds, 

• Subtraction between bands 2 and 1 to help distinguish 

the water-vapor portion of eruption clouds from other 

plume constituents, and 

• Principal-component analysis to distinguish eruption 

clouds from meteorological clouds. 

Color composite images were generated using various combinations of raw images, band subtractions, and principal 

component images. 

Images that result from the subtraction of two bands of 

data may detect distinct properties of eruption clouds. The 

image that results from subtracting the two thermal infrared 

bands on AVHRR data (bands 4 and 5 on NOAA-9, 11, and 

12 satellites) detects ash clouds (Prata, 1989; Holasek and 

Rose, 1991 ). The image that results from subtracting visible 

and near-infrared bands may help to distinguish water vapor 

from other plume constituents (Dean and others, in press). 

These band-subtraction techniques were used in this analysis 

to help distinguish plume components. 

The principal-component-analysis technique creates 

new images by performing coordinate transformations that 

recognize the maximum variance in multispectral data. This 

technique generates new images referred to as "principalcomponent images" (PCI, PC2, PC3, etc.). The first principal-component image is a weighted-average picture: the 

remaining principal-component images are similar to pairwise differences between bands (Sabins, 1987; Siegal and 

Gillespie, 1980). The principal-component images were 

used to help distinguish subtle eruption-cloud signatures 

from meteorological clouds. 

Altitudes of the eruption clouds were estimated by comparing their temperatures with the temperature profile of the 
AN AIRCRAFT ENCOUNTER WITH A REDOUBT ASH CLOUD (A SATELLITE VIEW) 335 

atmosphere. The eruption cloud, which is hot when first 

emitted by the volcano, will rise due to buoyancy but is also 

mechanically lifted by the force of the eruption. These two 

factors often propel eruption clouds to altitudes higher than 

many cloud masses (Sparks and others, this volume; Woods 

and Kienle, this volume; Dean and others, in press) where 

they rapidly cool to the temperature of the surrounding air. 

The temperature of the upper surface of the eruption cloud is 

derived from the thermal-infrared (band 4) satellite images. 

The thermal profile of the atmosphere is derived by the 

National Weather Service (NWS) from radiosonde observations and compared to the eruption-cloud temperature to 

determine an estimate of eruption-cloud height. These estimates are subject to errors (Woods and Self, 1992). The perspective view of the upper cloud surface was generated 

based on these principles and is shown in figure 2. 

Eruption clouds have some attributes that distinguish 

them from many meteorological clouds. They are often 

higher and, hence, colder; they often have a larger albedo 

and are thus brighter; and, eruption clouds often have an 

apex starting at a volcano. A perspective view to the northeast was generated to show some of these differences (fig. 2) 

based on the 13:27 AST satellite image using a combination 

of the visible (band 1) and thermal-infrared (band 4) bands. 

In this example, the volcanic plume seen emanating from 

Redoubt Volcano was not at a greater height than the surrounding clouds, even though it is shown that way on this 

image, but it was brighter due to its high albedo on the visible-band data. 

Figure 2. Perspective view, looking approximately northeast, of 

cloud tops generated from an A VHRR satellite image of south-central Alaska, 13:27 AST, 15 December 1989. The plume extends 

from Redoubt Volcano to the northeast and is brighter (high albedo) 

than most of the surrounding clouds. Cook Inlet is outlined on the 

right-hand side of the figure; refer to figure 1. 

Figure 3. AVHRR satellite image of south-central Alaska, 03:28 

AST, 15 December 1989. Suspected eruption clouds appear as 

green and red across the center of the image. The image is approximately 500 km on a side. The flight of the aircraft that encountered 

the ash cloud is shown as straight line segments in the upper and 

central parts of the figure. See text for explanation of A, B, C, D, 

and E. 

The flight path of the aircraft that encountered the ash 

cloud is shown on figures 3 through 7. Labels along the flight 

path indicate the position of the aircraft at the time of critical 

events (Casadevall, in press): 

• A-(11 :46 AST)-Ash cloud encountered at 7,600 m 

(25,000 ft), 

• B-(11 :48 AST)-Engine shutdown at 7,600 m 

(25,000 ft), 

• C-(11 :50 AST)-Exit ash at 6,000 m (20,000 ft), 

• D-(11 :52 AST)-Restart two engines at 5,200 m 

(17,200 ft), 

• E-(11:55 AST)-Restart two engines at 4,100 m 

(13,300 ft). 

RESULTS 

The first AVHRR image (NOAA-11, orbit no. 6305), 

was recorded at 03:28 AST, 2 hours after the 01:40 AST 

eruption. A color composite image was generated to optimize differences in morphology and spectral response within 

the overlying cloud layer using PC3 as red, thermal-infrared 

band 3 as green, and PCI as blue (fig. 3). This image shows 

a cloud structure (green and red) that may be an eruption 
336 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 4. AVHRR satellite image of south-central Alaska, 05:09 

AST, 15 December 1989. The suspected eruption cloud has an 

apex at Redoubt Volcano and appears as yellow across the center of 

the image. The image is approximately 500 km on a side. The flight 

path of the aircraft that encountered the ash cloud is shown as 

straight line segments in the upper and central parts of the figure. 

See text for explanation of A, B, C, D, and E. 

cloud that starts northeast of Redoubt Volcano and extends 

to the east over Anchorage and beyond, to Prince William 

Sound, south of Valdez. The suspected eruption cloud was 

presumably emitted by the OI :40 AST eruption and appears 

to be in three segments, possibly indicating a discontinuous 

event comprised of three distinct eruptions. A subtraction of 

bands 5 and 4 was not successful in detecting the ash clouds. 

The second A VHRR image (NOAA-II, orbit no. 6306) 

was recorded at 05:09 AST, I.5 hours after the 03:48 AST 

eruption. A color composite image was generated to optimize differences in the morphology and spectral response 

within the overlying cloud layer. The optimal combinations 

used the thermal-infrared band 3 as red, thermal-infrared 

band 4 as green, and PCI as blue (fig. 4). This band combination shows a suspected eruption cloud (yellow), with an 

apex near Redoubt Volcano, extending to the northeast and 

east, beyond Valdez. The eastern portion of this cloud is 

slightly detached and may be a remnant from the 01:40 AST 

eruption. A subtraction of bands 5 and 4 was not successful 

in detecting the ash clouds. 

The third AVHRR image (NOAA-10, orbit no. 16851) 

was recorded at 09:28 AST, 6 hours after the 03:48 AST 

eruption and about 45 minutes before the 10:15 AST eruption. A color composite image was generated to optimize differences in the morphology and spectral response within the 

overlying cloud layer with PC 1 as red, thermal-infrared band 

4 as green, and thermal-infrared band 5 as blue (fig. 5). This 

image shows a suspected eruption-cloud (green and yellow) 

northeast of Redoubt Volcano that extends beyond Talkeetna and across the flight path of the aircraft that encountered an ash cloud. This cloud does not have an apex at 

Redoubt Volcano. Two possible volcanic-related clouds 

(yellow) can also be seen south of Glennallen and between 

Talkeetna and Fairbanks. Detection of ash clouds using the 

subtraction between bands 4 and 5 could not be applied 

because these bands are identical on the NOAA -10 satellite. 

The fourth A VHRR image (NOAA-11, orbit no. 6311) 

was recorded at 13:27 AST, 3.25 hours after the start of the 

10: 15 AST eruption. A color composite image was generated to detect the plume and ash clouds using PC3 as red, 

subtraction of band 1 from 2 as green, and subtraction of 

band 4 from 5 as blue (fig. 6). This is the first 15 December 

image that unquestionably shows a volcanic plume despite 

the cloud layer and reveals an eruption cloud still emanating 

from Redoubt Volcano (yellow and green in the lower left 

portion of fig. 6) 2.5 hours after the end of the seismic event 

defining the I 0: 15 AST eruption. This plume trends northeast and east, ending just short of Anchorage, and is brightest 

Figure 5. A VHRR satellite image of south-central Alaska, 09:28 

AST, 15 December 1989. The suspected eruption clouds are green 

and yellow features that extend from Redoubt Volcano to Glennallen. The yellow features across the upper third of the figure may 

also be volcanic emissions. The image is approximately 500 km on 

a side. The flight path of the aircraft that encountered the ash cloud 

is shown as straight line segments in the central part of the figure. 

See text for explanation of A, B, C, D, and E. 
AN AIRCRAFT ENCOUNTER WITH A REDOUBT ASH CLOUD (A SATELLITE VIEW) 337 

Figure 6. AVHRR satellite image of south-central Alaska, 13:27 

AST, 15 December 1989. The eruption cloud (light green) has an 

apex at Redoubt Volcano and extends to Anchorage. The ash clouds 

(purple), which are south of Fairbanks and Delta Junction, may 

have been involved in the aircraft encounter. The image is approximately 500 km on a side. The flight path of the aircraft that encountered the ash cloud is shown as straight line segments in the central 

part of the figure. See text for explanation of A,B, C, D, and E. 

on the band-2-minus-band-1 image, suggesting that its composition is something other than water vapor (Dean and others, in press). To the north, near Fairbanks and Delta 

Junction, two clouds (purple and pink) were observed in the 

band-5-minus-band-4 image, suggesting that they are composed of ash, as indicated by the signature generated by this 

band combination (Prata, 1989; Holasek and Rose, 1991). 

DISCUSSION 

GROUND ASH DISTRIBUTION AND 

ERUPTION-CLOUD TRAJECTORIES 

To show more clearly the scenario of events on 15 

December 1989, a summary image was compiled that integrated all of the "eruption clouds" observed on satellite data. 

The maximum extent of these clouds was extracted from 

individual images and transferred to a cloud-free reference 

image (fig. 7). Colors designate the image from which the 

suspected eruption clouds were extracted: green, 03:28 AST 

image; red, 05:09 AST image; blue, 09:28 AST image; yellow, 13:27 AST image. This integrated image shows that 

Figure 7. Artificially integrated satellite image that shows all of 

the possible eruption clouds on 15 December 1989. Colors designate the image from which the eruption clouds were extracted: 

green, 03 :28 AST image; red, 05:09 AST image; blue, 09:28 AST 

image; yellow, 13:27 AST image. The flight path of the aircraft that 

encountered the ash cloud is shown as straight line segments in the 

upper and central parts of the figure. See text for explanation of A, 

B, C, D, and E. 

three of the four suspected eruption clouds have an eastward 

trajectory and that there is a northward progression in the trajectory of the early-morning eruption cloud, a northeast 

trend at 09:28 AST, and a northeast to eastward trend at 

13:27 AST. 

The predominantly eastward trajectory of the suspected 

eruption clouds does not agree with the distribution of surface ash collected by the U.S. Geological Survey (Scott and 

McGimsey, 1991). Surface ash deposited by the 15 December 1989 eruption is found northeast of Redoubt Volcano, 

not to the east, as the eruption cloud seen on the images 

would indicate. This suggests that either the suspicious 

clouds are not volcanic or that, as the ash falls from the 

plumes, it is swept northward by winds at a different altitude 

and that the clouds seen on the images do not contain ash. 

The elongated shape of the clouds with apexes at Redoubt 

Volcano (possibly two of four suspected plumes), geographic position, soft texture, and spectral signatures of these 

cloud structures indicate that they may be plumes, although 

absolute quantifying data is not available. 

The second explanation is possible because winds 

below about 7-km altitude are to the north; at 7 to 12 km, the 

winds are to the northeast; and at 12 to 28 km, the winds are 
338 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

to the northeast and east (03:00 AST, 15 December 1989, 

Anchorage radiosonde data). The wind directions indicate 

that the ash is in the lower air mass (below 7 km) and is being 

swept northward, whereas the eruption clouds seen on the 

images are in a higher air mass and are being transported 

northeast and east. 

AIRCRAFT-ASH CLOUD ENCOUNTER 

Redoubt Volcano erupted three times during the morning of 15 December 1989: at 01:40, 03:48, and 10:15 AST. 

In order to identify which eruption cloud was involved in the 

encounter with the jumbo jet, we compare the velocity 

required to transport an ash cloud from Redoubt Volcano to 

the site where the encounter occurred to the wind velocity 

and direction obtained from radiosonde data from Anchorage International Airport. The required azimuth from 

Redoubt Volcano is approximately 40°, and the encounter 

occurred at an altitude of 7.6 km (25,000 ft). 

The 10:15 AST eruption occurred 90 minutes prior to 

the aircraft-ash encounter at a point approximately 280 km 

northeast of Redoubt Volcano (Casadevall, in press). Based 

on these conditions, the ash cloud requires a velocity of 55 

m/s to reach the site. The wind at 8 km altitude has a velocity 

of 55 m/s and a heading of 47° (15:00 AST sounding, 15 

December 1989, Anchorage). Thus, measured wind parameters closely correlate with the transport of ash emitted by 

the 10:15 AST eruption. 

ASH CLOUD AT FAIRBANKS AND DELTA 

JUNCTION 

The 13:27 AST A VHRR image (fig. 6) shows two ash 

clouds near Fairbanks and Delta Junction, approximately 3 

hours after the 10: 15 AS T eruption. One or both of these ash 

clouds may be the one that the aircraft encountered near Talkeetna, 1.75 hours earlier. Back-tracking of cloud movement 

using wind data from Fairbanks atmospheric soundings were 

used to test this hypothesis. 

The aircraft encountered ash at 7.6 km (25,000 ft) altitude (point A, figs. 3-7), 200 km from Fairbanks and Delta 

Junction. Temperature-height correlations of the cloud in the 

Fairbanks area range from 1.5 to 7 km (5,000 to 23,000 ft), 

and the height of the Delta cloud range from 2.5 to 13.5 km 

(8,000 to 44,500 ft) (15:00 AST sounding, 15 December 

1989, Fairbanks). The range of heights of the cloud at Delta 

Junction spans the height of the encounter, and the upper 

height of the cloud near Fairbanks is slightly lower. 

To transport the ash clouds from point of the encounter 

with the aircraft, to the Fairbanks and Delta Junction area, a 

velocity of 32 m/s and a northeast-blowing wind are 

required. Velocity calculations based on ground reports of 

ash fall are 31 m/s and show a northeast direction of movement (R. McGimsey, oral commun., 1992). 

Meteorological measurements indicate that wind direction at approximately 7-km altitude would move the ash 

cloud that the aircraft encountered to either the Fairbanks or 

Delta Junction position. Wind at that altitude has a velocity 

of 31 m/s, with the wind blowing to the northeast. It does 

appear that either or both of these ash clouds were involved 

in the aircraft encounter, although the height of the cloud 

near Fairbanks is slightly lower than the altitude of the 

encounter. 

Ground samples of ash from these ash clouds collected 

in the Fairbanks area had a mass of 0.1 g/m2 (C. Nye, oral 

commun., 1991). Approximately 85 percent of the ash particles that fell from the Delta Junction cloud were in the 

0.0039- to 0.0625-mm size range, based on two samples (R. 

Combellick, oral commun., 1991), and were composed predominantly of very angular glass and plagioclase (C. Nye, 

oral commun., 1991). The glass shards made up greater than 

7 5 percent of the total ash weight. 

CONCLUSIONS 

The 15 December 1989 eruption of Redoubt Volcano 

resulted in a near-fatal encounter of a jumbo jet passenger 

aircraft (Boeing 747) with the ash cloud from the 10:15 AST 

eruption. Despite the almost total cloud cover over south and 
AN AIRCRAFT ENCOUNTER WITH A REDOUBT ASH CLOUD (A SATELLITE VIEW) 339 

central Alaska, eruption clouds were observed on several 

satellite images. However, the position of the clouds seen on 

the images did not always agree with ground observations of 

fallen ash, probably due to height differences between the 

ash component and gas component of the eruption cloud 

(and the air masses that transported those parts). A technique 

of using multiple thermal bands to distinguish ash clouds 

from other clouds was successful on only one out of three 

possible images (fig. 6). This image, recorded at 13:27 AST, 

detected ash clouds near Fairbanks and Delta Junction. One 

or both of these ash clouds were very likely involved in the 

aircraft encounter at 11:45 AST. 

Validation analyses of eruption clouds observed on satellite images have been minimal. It is not known how opacity, plume composition, particle size, and particle density 

affect the signatures observed on the satellite images. A 

thorough understanding of these factors would significantly 

improve the utility of satellite images for tracking and monitoring eruption clouds. 

REFERENCES CITED 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14, 1989-August 31, 1990: U.S. Geological Survey Circular 1061, 33 p. 

Casadevall, T. J., in press, The 1989-1990 eruption of Redoubt 

Volcano, Alaska: Impacts on aircraft operations: Journal of 

Volcanology and Geothermal Research. 

Dean, K.G., Bowling, S.A., Shaw, G., and Tanaka, H., in press, Satellite analysis of movement and characteristics of the Redoubt 

Volcano plume: Journal of Volcanology and Geothermal Research. 

Dean, K.G., Guritz, R., and Garbeil, H., 1990, Near-real time acquisition and analysis of satellite images of Redoubt Volcano 

[abs.]: Eos, Transactions, American Geophysical Union, v. 71, 

p. 1701. 

Hanstrum, B.N., and Watson, A.S., 1983, A case study oftwo eruptions of Mount Galunggung and an investigation of volcanic 

cloud characteristics using remote sensing techniques: Australian Meteorological Magazine, v. 31, p. 171-177. 

Holasek, R.E., and Rose, W.I., 1991, Anatomy of 1986 Augustine 

Volcano eruptions as recorded by multispectral image processing of digital AVHRR satellite data: Bulletin of Volcanology, 

v. 53, p. 420--425. 

Kidwell, K.B., ed., 1991, NOAA polar orbiter data users guide 

(TIROS-N, NOAA-6, NOAA-7, NOAA-8, NOAA-9, NOAA10, NOAA-11, and NOAA-12): Washington D.C., National 

Oceanic and Atmospheric Administration, National Environmental Satellite Data and Information Service, National Climatic Data Center, Satellite Data Services Division. 

Kienle, J., Dean, K.G., Garbeil, H., and Rose, W.l., 1990, Satellite 

surveillance of volcanic ash plumes; application to aircraft 

safety: Eos, Transactions, American Geophysical Union, v. 71, 

p. 266. 

Maligreau, J-P., and Kaswanda, 0., 1986, Monitoring volcanic 

eruptions in Indonesia using weather satellite data: The Colo 

eruption of July 28, 1983: Journal of Volcanology and Geothermal Research, v. 27, p. 179-194. 

Matson, M., 1984, The 1982 El Chich6n eruptions-A satellite perspective: Journal of Volcanology and Geothermal Research, v. 

23, p. 1-10. 

Matson, M., and Staggs, S.J., 1981, The Mount St. Helens ash 

cloud: Bulletin of the American Meteorological Society, v. 62, 

p. 1486. 

Mouginis-Mark, P., Rowland, S., Francis, P., Friedman, T., Garbeil, H., Gradie, J., Self, S., and Wilson, L., 1991, Analysis of 

active volcanoes from the Earth observation system: Remote 

Sensing of the Environment, v. 36: p. 1-12. 

Prata, A.J., 1989, Observations of volcanic ash clouds in the 10-12 

Jlm window using A VHRR/2 data: International Journal of 

Remote Sensing, v. 10, p. 751-761. 

Sabins F.F., 1987, Remote Sensing: Principals and Interpretations 

(2nd ed.): New York, W.H. Freeman and Company, 449 p. 

Scott, W.E., and McGimsey, R.G., 1991, Mass, distribution, grain 

size, and origin of 1989-1990 tephra-fall deposits of Redoubt 

Volcano, Alaska [abs.], in Casadevall, T.J., ed., First International Symposium on Volcanic Ash and Aviation Safety, U.S. 

Geological Survey Circular 1065, p. 39. 

Siegal, B.S., and Gillespie, A.R., 1980, Remote Sensing in Geology: New York, John Wiley and Sons, 702 p. 

Woods, A.W., and Self, S., 1992, Thermal disequilibrium at the top 

of volcanic clouds and its effect on estimates of the column 

heights: Nature, v. 355, p. 628-630. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

GEO-TOMS: TOTAL-OZONE MAPPING SPECTROMETER FOR 

OZONE AND SULFUR-DIOXIDE MONITORING 

FROM A GEOSTATIONARY SATELLITE 

By Ulli G. Hartmann, Robert H. Hertel, Herbert A. Roeder, and J. Owen Maloy 

ABSTRACT 

GEO-TOMS is a proposed ozone and sulfur-dioxide 

mapping spectrometer designed to fly on a geostationary satellite platform. It is an adaptation of the Nimbus-7 total 

ozone mapping spectrometer (TOMS), that is capable of 

imaging the whole Earth on a charge-coupled detector 

(CCD) array. The instrument will provide 12.2-km spatial 

resolution at nadir and will provide a complete multiband 

image every 10 minutes in 6 to 12 wavelength bands. Based 

on the performance of the Nimbus TOMS, GEO-TOMS will 

be capable of detecting volcanic eruptions and plumes and 

monitoring their progress in near real time, providing early 

warning of volcanic hazards to aviators and others. 

INTRODUCTION 

Eruptions pose a hazard not only to people living 

nearby but also to aircraft and people in the path of ash fallout. Volcanic sulfur dioxide (S02) is an important component in volcanic plumes, and satellite-based instruments 

sensitive to sulfur dioxide can detect volcanic eruptions from 

space. Satellite weather instruments that respond primarily 

to temperature differences and cloud cover are not nearly as 

sensitive for detecting volcanic clouds as instruments that 

are sensitive to sulfur dioxide (Matson, 1984). 

The total ozone mapping spectrometer (TOMS) was 

launched on the Nimbus-7 in 1978. The instrument monitors 

the state of the Earth's protective ozone layer by mapping the 

global ozone. TOMS measures sunlight reflected from the 

atmosphere at six wavelengths near the edge of the strong 

ozone absorption band in the ultraviolet. Stronger absorption 

at shorter wavelengths indicates a higher ozone concentration. TOMS has provided extensive and frequently cited data 

on the gradual deepening of the Antarctic ozone hole. In the 

years of operation of the first TOMS on the Nimbus polarorbiter, users of TOMS data found that it had other unexpected capabilities and uses. TOMS not only maps ozone 

accurately, but it also can detect transients in total ozone and 

sulfur dioxide and track volcanic plumes over large distances 

(Bluth and others, 1992; Krueger, 1983, 1985; Krueger and 

others, 1990, this volume). 

TOMS can detect S02 because this gas has an ultraviolet absorption band in the same wavelength region as ozone. 

The Nimbus-7 TOMS has detected 37 volcanic eruptions 

since 1978, including the S02 cloud from the May 18, 1980, 

eruption of Mount St. Helens as it drifted across the United 

States (Kerr and Evans, 1987; Krueger and others, this volume). An instrument that measures atmospheric ozone from 

space can also observe ozone discontinuities produced by 

severe storms and jet-stream winds and is potentially useful 

for warning aircraft of dangerous flight conditions (Shapiro 

and others, 1982). 

NEED FOR GEOSYNCHRONOUS 

OBSERVATIONS 

At a conference for users of TOMS data held at Goddard Space Flight Center (GSFC) in 1986, the scientific contributors identified several uses for Nimbus-7 TOMS data 

beyond the daily ozone-mapping function. Some of these 

uses require observation of the Earth with higher time resolution, such as half-hourly or better. Table 1 lists the requirements for the principal time-critical applications (adapted 

from Schenk, 1987). 

Measurements from a polar-orbiting satellite provide 

only one or two observations of the globe each day, not 

enough to provide a useful early-warning capability. Smaller 

eruptions may be missed by a single polar-orbiting satellite 

because the plume can be dispersed in less than 1 day. Many 

instruments would be needed in low-altitude polar orbits to 

provide sufficient time resolution. On the other hand, only a 

few instruments in geostationary orbit at an altitude of more 

than 35,800 km can provide a worldwide operational warning and monitoring network. For a geostationary TOMS to 

be fully useful, the ground resolution at nadir should be in 

the 10-30-km range (i.e., better than the 50-km resolution of 

the polar-orbiting TOMS). The time resolution should be at 

least 30 minutes. 

341 
342 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Applications requiring geostationary orbit. 

[Achieving high temporal resolution and global coverage requires many instruments 

in low-altitude orbit but only a few in geostationary orbit. res., resolution. Adapted 

from Schenk (1987)] 

Phenomenon or 

feature 

Hurricanes 

Temporal res. 

(minutes) 

Spatial res. 

(kilometers) 

Eye ................................ 5-10 ........................... 5-10 

Environs .......................... 30 ............................ 10-30 

Convection-environment 

interaction ...................... 5-10 ............................ 510 

Jet streams ......................... 10-30 ............................ 10 

Volcanoes 

First 12 hours ................. S-10 ........................... 5-10 

After first 12 hours ........... 30 ............................... 30 

Full Earth-disk coverage ........ 30 ............................ 10-30 

A geostationary version of TOMS must either scan or 

image the entire Earth. Some ozone-detection capability can 

be obtained through use of a filter photometer following the 

main infrared and visible Earth scanner of a meteorological 

satellite. The stability and sensitivity of a filter system is 

unlikely to meet the quantitative specifications required for 

detecting volcanic plumes. In addition, the scan time is 

longer than 10 minutes. A resolution of 10 km implies an 

image with more than 1 million pixels. From a signal-tonoise standpoint, it is better to scan the few wavelength 

bands used than to scan so many pixels. This consideration 

led us to study an imaging spectrometer called GEO-TOMS. 

We presented a preliminary version of the GEO-TOMS 

design in 1986 (Krueger and others, 1987), and, since then, 

we have further refined the design. No prototype has yet 

been built, however. The main goal in the GEO-TOMS 

Table 2. Comparison of TOMS and GEO-TOMS spectral and radiometric requirements. 

[TOMS, total ozone mapping spectrometer. The GEO-TOMS, in geostationary orbit, has similar spectral and radiometric requirements but has a smaller field of view and longer observing time per pixel. TOMS FM-l/2 is the original TOMS design; TOMS 

FM-3/4 is an improved design. deg., degrees; max. maximum; N/S, not specified] 

Design requirement TOMS TOMS GEO- Units 

FM-112 FM-3/4 TOMS 

General requirements 

Observing time per wavelength band 0.014 0.010 50 s 

Pixel size at nadir 50x50 50x50 12.2 km 

Pixels per field-of-view I I 1,024xl,024 

Pixel size (square) 3x3 3x3 0.02x0.02 de g. 

Instrument overall field-of-view 3x3 3x3 20x20 de g. 

Spectral requirements 

Wavelength range 312.5-380.0 308.6-360.0 308.6-360.0 nm 

Spectral bandpass (full-width at half-max.) 1±0.1 1+0.3-0.0 1+0.3-0.0 run 

Wavelength accuracy (/...<340 run, l5°-35°C) 0.05 0.1 0.1 run 

Wavelength calibration accuracy N/S 0.005 0.005 run 

Wavelength stability/repeatability 0.02 0.005 0.005 run 

Wavelength monitoring caEabili~ 0.1 0.01 0.01 run 

Radiometric requirements 

Full-scale radiance 500 500 500 W/cm3-sr 

Maximum radiance 320 400 400 W/cm3-sr 

Minimum radiance 0.32 0.4 0.4 W/cm3-sr 

Radiometric resolution 1.0 0.2 0.2 %precision 

Minimum-radiance signal-to-noise ratio 301 301 301 

Signal dynamic range 1.56x 105 6.25x 105 6.25x105 

Radiometric repeatability N/S 0.004 0.2 %/hr 

Detector stability 5 5 5 %/yr 

Radiometric linearity 2 I 2 %signal 

Spectral stray light 1000:1 0.5 0.5 %signal 

Band-to-band crosstalk N/S 0.1 1 %signal 

Residual polarization sensitivity 5 5 5 % 

Reflectance calibration capability N/S 0.1 5 %/yr 

1 Goal is 100. 
GEO-TOMS: TOTAL-OZONE MAPPING SPECTROMETER FOR OZONE AND SULFUR-DIOXIDE MONITORING 343 

design has been to develop a baseline for a future operational 

instruments by providing near-real-time global imaging 

capability while still meeting the stringent TOMS performance specifications. Table 2 lists the design requirements 

for the original TOMS (FM-1/2), the new improved TOMS 

(FM-3/4), and GEO-TOMS. 

PRELIMINARY DESIGN OF 

GEO-TOMS 

GEO-TOMS is an ozone and sulfur-dioxide mapping 

instrument specifically designed to fly on a geostationary 

platform. GEO-TOMS will be a new member of a family of 

already-proven instruments that map atmospheric ozone distribution by measuring the solar ultraviolet radiation backscattered from the atmosphere. The first member of the 

family was the backscattered ultraviolet instrument (BUV), 

launched in 1970 on Nimbus-4. The solar/backscatter ultraviolet instrument (SBUV) and the total ozone mapping spectrometer (TOMS FM-1) were launched as a combined 

package on Nimbus 7 in 1978. These instruments demonstrated exceptional life: 8 years in orbit for BUV and 

SBUV-TOMS continues to operate after more than 15 

years. Later versions of the spectrometer include the SBUV2 series, flying on National Oceanic and Atmospheric 

Administration (NOAA) satellites, and TOMS FM-2, 

launched on a Soviet Meteor satellite in August, 1991. Perkin-Elmer is building a new version of the TOMS sensor to 

fly on the Japanese advanced Earth observing satellite 

(ADEOS). 

The design of such instruments must provide solutions 

to several technical problems. Here is how the GEO-TOMS 

design solves the principal problems: 

Problems Solutions 

Light collection ............. Long observing time ( 10 minutes). 

Parallel observation of all pixels. 

Wavelength stability 

and resolution .......... Diffraction-grating spectrometer. 

Unwanted (stray) 

Cam-driven grating positioning 

mechanism. 

light rejection ........... Visible-light-absorbing coatings. 

High-quality grating. 

Image readout 

and processing ......... On-board microprocessor, 

large memory. 

GEO-TOMS uses the technology of both SBUV and 

TOMS but images the whole Earth disk onto a silicon-array 

detector in one wavelength band at a time, without a spatial 

scanner. A diffraction grating rotates to select from six to 12 

wavelength bands for imaging, as in the Nimbus-4 BUV, the 

Nimbus-7 SBUV, and SBUV-2. The wavelength bands will 

be selected to optimize both ozone and S02 detection. The 

proposed wavelength-scanning mechanism is essentially the 

same as the motor-driven mechanical cam proven on BUV 

and SBUV. 

Figure 1 shows the optical layout of the GEO-TOMS. 

The field of view is 20°, so that the whole Earth is imaged at 

one time. The optical design is similar to the original TOMS 

except that there are two parabolic collimating mirrors 

instead of one spherical mirror. Optical ray traces show that 

a single mirror will not provide the needed image quality for 

the wide field. Light reflected from either the atmosphere or 

a calibration diffuser passes through a depolarizer and enters 

a diffraction-grating monochromator. Light from the grating 

passes through a single exit slit onto a 1,024x1,024 chargecoupled detector (CCD) through an optical system that corrects monochromator aberrations. A shutter provides optical 

zeroing. As in the previous instruments, in-flight wavelength 

calibration will use a mercury lamp. 

RADIATOR I COOLER 

CCC DETECTOR AND DETECTOR ELECTRONICS 

EXrTSUT 

THREE DIFFUSER PLATES 

AND ONE COVER PLATE 

Figure 1. GEO-TOMS optical layout. The grating spectrometer 

collimates and diffracts light reflected from the Earth, forming an 

image of the entire Earth in one narrow-wavelength band at a time 

on the charge-coupled detector (CCD). The diffraction grating rotates, imaging the Earth at different wavelengths to determine ~he 

amounts of ozone and sulfur dioxide in the scene. A movable scene 

mirror permits the instrument to view the calibration diffuser. 
344 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

With such faint signals and high spectral resolution, the 

rejection of radiation at unwanted wavelengths, or "stray 

light," must be excellent. GEO-TOMS needs a high-quality 

grating like that used for the newer TOMS models, because 

stray light increases when only a small part of the grating is 

used for each pixel. To reduce stray light, the GEO-TOMS 

will use mirrors coated to reflect the ultraviolet, but not the 

visible radiation. 

DETECTOR SELECTION 

The ultraviolet sensitivity of CCD detectors has now 

advanced sufficiently so that such detectors can be planned 

on for GEO-TOMS. The use of a single, stable silicon CCD 

detector reduces drift problems. Reading out the image often 

enough to prevent saturation permits covering the wide 

dynamic range. Shielding will be used to prevent damage 

from charged particles. Even though the current design plans 

on an ultraviolet-sensitive CCD detector, the GEO-TOMS 

concept does not depend on the availability of such a detector. The Voyager ultraviolet spectrometer observed the 

atmospheres of the outer planets using a silicon-array detector with a microchannel plate for ultraviolet image intensification. Since then, many such detectors have been fabricated 

using higher resolution arrays. These are commercially 

available for space use with integrated detector arrays and 

fiber optics. 

DETECTOR COOLING 

Because it is not necessary to cool the detector to cryogenic temperatures, a simple passive radiator cools the CCD 

detector to -40°C to reduce leakage current. There is evidently a weight and cost optimum, because a large instrument needs no cooler, whereas a small instrument must have 

a large cooler. As a baseline, we have made the monochromator the same size as in the present TOMS, but this choice 

does not necessarily provide the minimum weight or cost. 

LAYOUT 

The baseline mechanical layout appears in figure 2. The 

mirrors will be mounted on lapped surfaces, as for TOMS. 

The rigid structure keeps the pixels in place on the detectors 

and assures the required wavelength stability. The monochromator and other optical components and mechanisms 

form an assembly that is mounted inside the housing. The 

stiff box structure of the mount incorporates the electronics 

as a structural element, providing part of the structural rigidity and reducing weight. One side of the instrument continually faces north, and the opposite side faces south. These 

sides provide locations for thermal radiators with a 

continuous space view. Separate radiators cool the detector 

(-40°C) and the electronics (+25°C). The detector temperature will be regulated by a small heater. 

ELECTRONICS 

GEO-TOMS is mainly a digital instrument with few 

critical analog circuits and, therefore, does not need most of 

the sophisticated electronics components required for the 

polar-orbiting TOMS instruments. The instrument contains 

an image processor with a separate microprocessor for interfacing and control. 

DATA RATES 

The noon data rate for the GEO-TOMS is about 409 

kbits/s at maximum spatial resolution. This rate is comparable to other geostationary imaging instruments. On-board, 

Figure 2. GEO-TOMS mechanical arrangement. The monochromator and scanner mounts into a frame that also supports the electronics assemblies. The instrument views the diffuser through a side 

port. 
GEO-TOMS: TOTAL-OZONE MAPPING SPECTROMETER FOR OZONE AND SULFUR-DIOXIDE MONITORING 345 

real-time event processing with detection of affected region 

with deletion of uninteresting data could reduce the realtime rate. 

DIFFUSER CALIBRATION 

Calibration of the GEO-TOMS will use techniques borrowed from TOMS, SBUV, and SBUV-2, incorporating the 

benefit of the improved diffuser system used in later instruments. All backscattered-ultraviolet instruments, including 

TOMS and GEO-TOMS, measure the reflectance of the 

atmosphere. The absolute radiance is not of primary interest. 

The reflectance standard is a diffuse-reflecting plate, or diffuser, periodically exposed to sunshine and viewed by the 

instrument. So far, nothing surpasses the stability and uniformity of the simple, ground aluminum plate originally used 

on the first BUV instrument that was launched over 20 years 

ago, although the plate's reflectance declines with prolonged 

exposure to the sun. The diffuser calibration employs an 

ultraviolet light source to compare the reflectance of a protected reference diffuser and the active diffuser. The light 

source itself needs to be stable only during the comparison. 

By using more than one diffuser, the effects of sun exposure 

and vacuum exposure can be disentangled. Although less 

elaborate than the diffuser-calibration systems used in 

TOMS instruments designed for quantitative mapping, the 

GEO-TOMS system should be adequate for transient 

mapping. 

RESULTS 

Our design study shows that the GEO-TOMS concept 

is feasible. Optical ray-trace results demonstrate that such a 

wide-field monochromator will work as an imager. The 

width of the nadir point-spread function is smaller than the 

desired resolution. Thus, the detectability for a point source 

is almost the same as for a cloud several pixels across. The 

inherent GEO-TOMS spectral resolution is somewhat better 

than 0.7 nm full-width at half-maximum and meets the 

TOMS specification. Because each pixel uses only a small 

part of the grating, the inherent resolution is comparable to 

the desired resolution and varies somewhat over the field of 

view. The longer integration time and larger entrance aperture compensate for the reduced solid angle of the field of 

view in the GEO-TOMS, as compared to the existing TOMS 

aboard Nimbus-7. The estimated signal-to-noise ratio of 

GEO-TOMS is 40: 1 at minimum radiance, about the same as 

the Nimbus TOMS, including the effects of space radiation. 

This estimate assumes the use of 12 wavelength bands and 

the same 50-second integration time for each wavelength. In 

practice, exposure time will be optimized for each wavelength depending on current cloud and lighting conditions. 

CONCLUSIONS 

Imaging of ozone and sulfur dioxide in the upper atmosphere from geostationary satellite orbit can provide early 

warning and monitoring of volcanic events and severe 

storms for the benefit of aviators and others. GEO-TOMS is 

a proposed geostationary instrument, based on the proven 

polar-orbiting TOMS, that can provide this imaging capability by detecting backscattered solar ultraviolet radiation. 

Analysis of the GEO-TOMS design has shown that the 

instrument concept can provide near-real-time maps of 

ozone and sulfur dioxide. 

REFERENCES CITED 

Bluth, G.J.S., Doiron, S.D., Krueger, A.J., Walter, L.S., and 

Schnetzler, C. C., 1992, Global tracking of the S02 clouds from 

the June 1991 Mount Pinatubo eruptions: Geophysical Research Letters, v. 19, p. 151-154. 

Kerr, J.B., and Evans, W.J., 1987, Comparison of ground-based and 

TOMS measurements of S02 from volcanic emissions: NASA 

Conference Publication 2497, p. 60--69. 

Krueger, A.J., 1983, Sighting of El Chich6n sulfur dioxide clouds 

with the Nimbus 7 total ozone mapping spectrometer: Science, 

v.220,p. 1377-1378. 

--1985, Detection of volcanic eruptions from space by their 

sulfur dioxide clouds: American Institute of Aeronautics and 

Astronautics, AIAA 23rd Aerospace Sciences Meeting, January 14-17, Reno, Nev., Report AIAA-85-0100, 4 p. 

Krueger, A.J., Maloy, J.O., and Roeder, H.A., 1987, A geostationary imaging spectrometer TOMS instrument: NASA Conference Publication 2497, p. 88-89. 

Krueger, A.J., Walter, L. S., Schnetzler, C.C., and Doiron, S.D., 

1990, TOMS measurements of the sulfur dioxide emitted during the 1985 Nevado del Ruiz eruptions: Journal of Volcanology and Geothermal Research, v. 41, p. 7-15. 

Matson, M., 1984, The 1982 El Chich6n volcano eruptions-A satellite perspective: Journal of Volcanology and Geothermal Research, v. 23, p. 1-10. 

Shapiro, M.A., Krueger, A.J., and Kennedy, P.J., 1982, Nowcasting 

the position and intensity of jet streams using a satellite-borne 

total ozone mapping spectrometer, in Browning, K.A., ed., 

Nowcasting: New York, Academic Press, p. 137-145. 

Schenk, W.E., 1987, Observation guidelines for a total ozone mapping spectrometer (TOMS) in geostationary orbit: NASA Conference Publication 2497, p. 86-87. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

PASSIVE, TWO-CHANNEL, THERMAL-INFRARED 

IMAGING SYSTEMS FOR DISCRIMINATION 

OF VOLCANIC ASH CLOUDS 

By Frank R. Honey 

ABSTRACT 

The National Oceanic and Atmospheric Administration's advanced very high resolution radiometer image data, 

recorded and displayed in Perth, Australia, in June 1982, dramatically demonstrated a capability for satellite observation 

of the volcanic ash from the eruption of Galunggung Volcano, Indonesia. Analysis of the data, based on an understanding of the spectral-emissivity properties of silica-rich 

materials, and of water clouds, resulted in discrimination and 

display of the ash cloud over a period of several days. 

Interest in the techniques that were used for this discrimination procedure led to the proposal in 1982 of a passive, two-channel, thermal imaging system that could be 

mounted in an aircraft. Display of the enhanced data from the 

proposed imaging system could be multiplexed into existing 

aircraft avionics and could alert the crew to the presence of 

silica-rich materials in the flight path over ranges up to or 

exceeding 100 km, assuming a clear line of sight. The initial 

instrument design is discussed, and several improvements on 

the original concept and limitations to the application of such 

an instrument are outlined. 

INTRODUCTION 

Encounters of aircraft with ash plumes from volcanic 

eruptions have caused considerable damage and, in several 

cases, have had near-fatal consequences. The development 

of sensors for the detection of hazardous materials and other 

atmospheric phenomena in the flight paths of aircraft is 

assuming a high priority for agencies involved in enhancing 

aviation safety. 

Opportunistic recording of data from the polar-orbiting satellites of the National Oceanic and Atmospheric 

Administration (NOAA) at the time of the eruption of 

Galunggung Volcano in Indonesia in June 1982, and the 

subsequent development of enhancement and display procedures, enabled a positive discrimination of volcanic ash 

and dust clouds from normal water and ice clouds. This 

research also provided an indication of the requirements for 

geosynchronous satellite sensors with appropriate thermal 

infrared channels and led to the proposal of a passive, twochannel, thermal-infrared imaging sensor that could be 

mounted in aircraft to alert the crew to potential hazard, 

with sufficient time to take nonviolent, evasive maneuvers. 

The enhancement and discrimination procedures developed were based on an understanding of the spectral emissivity properties of silicate minerals expected to be present in 

the dust and ash plumes. Subsequent modeling by other 

workers using radiative-transfer theory provided an alternative mechanism to explaining the spectral discrimination 

(Prata, 1989; Prata and Barton, this volume). 

SATELLITE DATA COLLECTION AND 

ANALYSIS 

The NOAA satellites are near-polar-orbiting environmental and meteorological satellites that are operated by the 

U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration (Sabins, 1987). In general, two 

satellites are operational at any one time, giving a potential 

for coverage of an area four times per day (twice during daylight hours, twice during the night). In practice, however, 

there are gaps in coverage of any location due to the orbital 

characteristics of the spacecraft. 

The advanced very high resolution radiometer 

(A VHRR) sensor on the NOAA satellite series has five spectral channels, with wavelength ranges of 0.55-0.68, 

0.725-1.1, 3.55-3.95, 10.5-11.5, and 11.5-12.5 j..lm. The 

ground spatial resolution of the sensor is 1.1 km. Data are 

transmitted and recorded to 1 O-bit precision, providing sufficient dynamic range to accommodate targets ranging from 

sea surfaces to clouds and snow. 

In late 1981, data from the NOAA-7 AVHRR sensor 

were being recorded on an irregular basis under a joint 

research effort between the Commonwealth Scientific and 

Industrial Research Organization (CSIRO) and the staff 

from the Western Australian Institute of Technology 

(WAIT) (now Curtin University of Technology). The 

CSIRO/W AIT team had developed a low-cost satellite 

347 
348 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

tracking and receiving facility (Carroll and others, 1981) to 

provide near-real-time access to the A VHRR data for application to research projects on oceanography, land use, geology, flooding, and fires. 

The tracking and receiving facility in Perth had the 

capability to record data from the satellites down to elevations above the horizon of approximately 3 °. Depending on 

the orbital position of the satellite, this enabled some data 

acquisition over the island of Java, Indonesia. Data from the 

NOAA-7 satellite were not recorded for the area around and 

to the southeast of Galunggung until29 June 1982; however, 

ash plumes of sufficient concentrations and extent for satellite detection were likely emitted by the volcano for several 

weeks previous to that time. Data from earlier overpasses by 

the NOAA-7 spacecraft had either not been recorded or the 

satellite was too far to the east to provide coverage of the 

area. 

Unfortunately NOAA-6, the only other operational 

NOAA satellite in orbit at that time, did not have channel 5 

(11.5-12.5 ~m) functioning. Thus, the two-thermal-channel 

technique could not be applied to the NOAA-6 data. 

DATA ANALYSIS, ENHANCEMENT, 

AND DISPLAY 

The initial approach to data analysis was similar to the 

analysis applied to data from the Japanese geostationary 

meteorological satellite (GMS-2) by the Australian Bureau 

ofMeteorology (Hanstrum and Watson, 1983). In that study, 

eruptions of Galunggung on 24 June and 13 July 1982 were 

observed using GMS-2 imagery. Enhanced infrared imagery 

revealed signatures for the volcanic ash clouds produced by 

these two eruptions that were similar to growing thunderstorms. The GMS-2 images were used to estimate cloud-top 

height, and cloud movement was monitored. 

In the analysis by the CSIRO/W AIT team, individual 

thermal channels 3, 4, and 5 of the NOAA-A VHRR data 

were enhanced individually to accentuate radiometric variations due to areas of different temperature within clouds in 

the images. Although radiometric differences were 

observed, the area suspected of being the volcanic ash plume 

was not positively discriminated from the normal water 

clouds in the area. In an attempt to discriminate the clouds 

using possible albedo differences, the reflected bands on the 

daytime images were enhanced. However, this technique 

was also inconclusive, as were color combinations of contrast-enhanced single bands. 

At the time of the Galunggung eruption, the author was 

designing an airborne multispectral scanner to be applied 

primarily for minerals exploration, based on the different 

reflectance and emittance spectra of various minerals 

(Honey and Daniels, 1985). The 13 spectral bands of this 

scanner included four thermal-infrared channels (8.5-8.9, 

9.7-10.1, 10.8-11.2, 11.5-12.0 J.Lm) that were specifically 

selected to discriminate rocks using differences in their silicate emission spectra (Lyon, 1964; Salisbury and others, 

1987). The position of the emission minima, which is due to 

the asymmetric stretching modes of the 0-Si-0 units, is 

related to the structure of particular silicate minerals and 

ranges from approximately 8.5 J.Lm for quartz to 10.7 J.Lm for 

Fe-Mg minerals such as olivine. 

Because ash from volcanic eruptions contains large 

proportions of silicate materials, particularly the ferromagnesian silicates whose emission minima overlap with the 

wavelength range of the NOAA-AVHRR band 4 (10.5-11.5 

J..Lm), differences and ratios between bands 4 and 5 of the 

A VHRR data were generated to provide a more definite discrimination between the plume of volcanic ash and normal 

water clouds in the area. These images display band 4 in 

blue, band 5 in green, and the difference between band 4 and 

band 5 in red-they show normal water clouds as black, the 

sea surface as blue-cyan, and volcanic ash plumes as orange 

to pink. The results of this method show positive discrimination of the volcanic ash plume from normal water clouds. 

The procedures and displays developed by the CSIRO/ 

WAIT team aroused the interest of the Australian aviation 

authorities and the media, and data collection and analysis 

activities continued for several weeks. The results of the 

analysis, enhancement, and display of the A VHRR data 

clearly demonstrated the potential for detecting and monitoring volcanic ash plumes using thermal channels similar to 

channels 4 and 5 of the NOAA-AVHRR sensors. However, 

following the period of intense data collection and analysis, 

it was considered that the low frequency of coverage by the 

NOAA-AVHRR satellites precluded their application to an 

operational monitoring and warning capability. 

ALTERNATIVE SENSOR SYSTEMS 

During discussions in 1982 with Australian aviation 

authorities, the limitations of the polar-orbiting satellites as a 

means of monitoring eruptions of volcanoes, and for tracking ash and dust plumes, were reviewed. The possibility of 

applying geosynchronous meteorological sensors was considered, although the Japanese geostationary meteorological 

satellite (GMS-2) then operating only had one thermal channel, and the two-channel discrimination procedures could 

not be applied. Geosynchronous satellites, with their high 

frequency of coverage over large areas, could provide a 

capability for monitoring and tracking, assuming that futuregeneration systems have two thermal infrared channels: 

preferably one from approximately 10.0-11.0 J..Lm and the 

second from 11.5-12.5 J..Lm. 

The second, more direct means of determining the presence of volcanic ash plumes in or near the path of aircraft 

would utilize a two-thermal-channel imaging system, with 

moderate spatial resolution, mounted on an aircraft. 
THERMAL-INFRARED IMAGING SYSTEMS FOR DISCRIMINATION OF VOLCANIC ASH CLOUDS 349 

TWO-CHANNEL THERMALINFRARED IMAGING SENSOR 

The infrared imaging sensor proposed to Australian 

aviation authorities in 1982 comprised an optical window 

transmitting in the 10-12.5-~m region; scanning optics; dispersion optics to split out the 10.0-11.0- and 11.5-12.5-~m 

regions; infrared camera optics; cooled infrared detectors; 

amplification, data storage, analysis, and display hardware; 

and an interface to aircraft avionics to enable the pilot and 

crew to view the imagery. The estimated maximum weight 

of the imaging sensor was 25 kg. The amplification, storage, 

analysis, and display electronics, together with the interfaces 

to aircraft avionics, would provide the crew with a real-time 

display of the region in front of the aircraft as well as providing an alarm capability upon detection of anomalous infrared 

signatures associated with silicate materials. 

The scanning optics would acquire energy over a field 

of view of approximately ± 10° in the horizontal direction 

(relative to the direction of flight) and would acquire energy 

from 2° above horizontal and 8° below horizontal in the vertical direction. At 1 00-km range, this system images an area 

35 km wide, extending from 3.5 km above to 14 km below 

the aircraft's projected track. Assuming that each scan line 

comprises 64 picture elements and that 32 lines are scanned, 

the spatial resolution at 100 km would be 550 m. At 10-km 

range, the resolution would be 55 m. 

Since the original design proposal in 1982, there have 

been a number of technical advances that would reduce both 

the weight and bulk of the original sensor. For example, the 

dispersion optics originally considered used a dichroic beam 

splitter to separate the two infrared regions, with cold infrared band-pass filters in front of the detectors limiting the 

energy to 10.0-11.0 and 11.5-12.5 Jlm. Other dispersion and 

multisensor systems developed in the past decade may now 

be more practical and compact. 

When the initial concept was being developed, focalplane-array technology for mercury-cadmium detectors was 

not readily available for commercial purposes. As this technology has developed, these arrays have become available so 

that the early imaging technique using two-axis scanning of 

mirrors is no longer necessary-this simplifies the mechanical construction of such imaging systems and increases their 

mechanical reliability. 

The infrared camera optics, which focus energy onto 

detector elements or arrays, must pass through the entrance 

window of a liquid-nitrogen-filled Dewar cooling vessel 

within which the cold infrared band-pass/blocking filters are 

mounted in order to minimize the level of background 

energy. The requirement for the sensor's detector elements 

or arrays to be cooled to 78° Kelvin (liquid nitrogen) was a 

potentially limiting factor because either liquid-nitrogenfilled Dewar cooling vessels or in situ coolers, such as JouleThomson cryostats, were required. Commercially available 

cooling technology has matured considerably since 1982, 

with compact, reliable, closed-cycle Stirling coolers now 

capable of providing the necessary cooling. 

Even though the concept of developing a forward-looking, imaging, two-channel volcanic ash discriminator is now 

a reality (Prata and others, 1991; Barton and Prata, this volume), considerable research is necessary to determine the 

limitations of such a system, particularly the sensitivity, 

range, and the influence of poor visibility due to other clouds 

in the area and field of view. Such instruments should never 

be assumed to provide a fail-safe means of detecting the 

presence of hazardous levels of volcanic dust and ash in the 

path of aircraft. They should only be considered as aids to the 

pilot and crew. 

RESEARCH SINCE 1982 

Since 1982, the author has focused his research on the 

development of other advanced multispectral sensors 

(Honey and Daniels, 1985). However, activity to advance 

research and development of operational techniques for 

detecting and tracking volcanic ash clouds commenced 

again in CSIRO in 1984-85 with the work of A.J. Prata. Subsequent modeling of the volcanic ash phenomenon using 

scattering theory (Prata, 1989) reinforced the logic of the 

earlier analysis of A VHRR data. This earlier analysis was 

based on the assumption that the energy was being emitted 

by the dense volcanic ash cloud rather than considering the 

energy as being scattered and differentially absorbed, as in 

Prata's (1989) analysis. Prata (1989) also used the refractive 

indices of quartz in his modeling rather than the refractive 

indices for more basic mineral or rock types, such as the rhyolite, andesite, and basalt that are typical of volcanic materials. The complex refractive indices of volcanic ash (Volz, 

1973) differ significantly from the values for quartz (Peterson and Weinman, 1969). 

A third phenomenon may contribute to negative "temperature" differences, leading to the discrimination of a volcanic plume from normal water clouds. The temperature of 

the ash cloud from Galunggung was estimated at approximately -7 5°C, and the lowest temperature of water clouds in 

the area was calculated as-15°C (Scarone, 1987). For blackbody emission at 203 ° Kelvin, the emission maximum 

occurs at 14.28 ~m, whereas for a black body at 263° Kelvin, 

the emission maximum occurs at 11.02 Jlm. Thus, for the 

warmer water-cloud masses in the area of the eruption, in the 

absence of any other factors and assuming an emissivity of 

1.0, the difference of band 4 minus band 5 would be positive, 

whereas the difference would be negative for the volcanic 

plume. Further modeling and research will be necessary to 

determine the relative contributions of the phenomena outlined above. The most encouraging feature of all of the phenomena, however, is that the band differences, either 

expressed as radiance or as temperature, provide a means of 

discriminating cloud types. 
350 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

The CSIRO group involved in research into the detection of hazardous material and phenomena has developed a 

two-thermal-channel radiometer to test the spectral and radiometric design criteria for an airborne imaging sensor (Prata 

and others, 1991; Barton and Prata, this volume; Prata and 

Barton, this volume). 

CONCLUSIONS 

Image data from the A VHRR sensors on the operational 

NOAA satellite series have the appropriate spectral channels 

to enable discrimination of volcanic ash clouds from regular 

water and ice clouds. The limited frequency of overpass of 

these polar-orbiting satellites precludes their application for 

monitoring and tracking of the clouds to provide aircraft 

crews with warning of potential hazardous features in their 

flight path. The possibility of dual-channel thermal-infrared 

sensors being implemented on geosynchronous weather satellites offers some potential for developing procedures for 

locating and monitoring of volcanic eruptions and the tracking of their plumes. 

More direct and immediate capability may be provided 

using dual-infrared-channel imaging instruments mounted in 

aircraft. The principles upon which such sensors will operate 

have been established from the analysis of the NOAAA VHRR data and from modeling of the emission and radiative transfer processes. Further study is necessary to test 

models that lead to analysis and enhancement procedures 

and to the design of the appropriate instruments. It will be 

important to establish the limitations that apply to these sensors, in terms of the minimum detectable quantities of ash 

and dust, the range over which they will provide an effective 

early-warning adjunct, and the factors that will restrict or 

completely negate their capability. 

ACKNOWLEDGMENTS 

The author gratefully acknowledges the effort, support, 

and enthusiasm of Professor Bill Carroll and the devoted 

team of CSIRO scientists and technicians who made this 

project both achievable and enjoyable. The author also 

acknowledges the effort of the team of WAIT engineering 

students who worked so diligently to collect much of the data 

upon which this work was based. 

REFERENCES CITED 

Carroll, W., Honey, F.R., and Cargill, R.D., 1981, Real time multispectral imagery from the NOAAffiROS A VHRR system, in 

Proceedings, 2nd Australasian Remote Sensing Conference-LANDSAT 81: Canberra, Australia, p. 721-726. 

Hanstrum, B.N., and Watson, A.S., 1983, A case study of two eruptions of Mount Galunggung and an investigation of volcanic 

eruption cloud characteristics using remote sensing techniques: 

Australian Meteorological Magazine, v. 31, p. 171-177. 

Honey, F.R., and Daniels, J.L., 1985, Application of Carr Boyd 

Minerals Limited airborne multispectral scanner to spectral 

discrimination of hydrothermally altered areas, in Proceedings 

of the International Symposium on Remote Sensing of the Environment, 4th Thematic Conference (Remote Sensing For Exploration Geology), San Francisco, v. 1, p. 227-231. 

Lyon, R.J.P., 1964, Evaluation of infrared spectrophotometry for 

compositional analysis of lunar and planetary soils, part II, in 

Rough and Powdered Surfaces: Washington, D.C., National 

Aeronautics and Space Administration, NASA Contractor Report NASA CR-100. 

Peterson, J.T., and Weinman, J.A., 1969, Optical properties of 

quartz dust particles at IR wavelengths: Journal of Geophysical 

Research, v. 74, p. 6947--6952. 

Prata, A.J., 1989, Radiative transfer calculations for volcanic ash 

clouds: Geophysical Review Letters, v. 16, p. 1293-1296. 

Prata, A.J., Barton, I.J., Johnson, R.W., Kamo, K., andKingwell, J., 

1991, Infrared radiometric detection of volcanic ash clouds: 

Nature, v. 354, p. 25. 

Sabins, F.F., Jr., 1987, Remote Sensing: Principles and Interpretations: New York, W.H. Freeman and Company, 449 p. 

Salisbury, J.W., Walter, L.S., and Vergo, N., 1987, Mid-infrared 

(2.1-25 J.lm) spectra of minerals: U.S. Geological Survey 

Open-File Report 87-263, 26 p. 

Scarone, Hugo, 1987, Volcanic ash clouds-A continuing threat to 

international aviation: Earthquakes & Volcanoes, v. 19, p. 

65-73. 

Volz, F.E., 1973, Infrared optical constants of ammonium sulphate, 

Sahara dust, volcanic pumice and flyash: Applied Optics, v. 12, 

p. 564-568. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

SEISMIC IDENTIFICATION OF 

GAS-AND-ASH EXPLOSIONS AT 

MOUNT ST. HELENS-CAPABILITIES, 

LIMITATIONS, AND REGIONAL APPLICATION 

By Chris Jonientz-Trisler, Bobbie Myers, and John A. Power 

ABSTRACT 

Since 1980, analysis of seismic signals recorded by the 

University ofWashington (UW) and U.S. Geological Survey 

(USGS) Mount St. Helens seismic network have been analyzed and correlated with observations made by field crews, 

pilots, radar operators, and the general public. These analyses have led to the development of criteria that enable identification of most kinds of seismic events that occur at Mount 

St. Helens. These events include gas-and-ash explosions, 

volcanic earthquakes, volcanic tremor, rockfalls, debris 

flows, dome-building eruptions, and many types of manmade seismic noise. Identification criteria are based on comparison of signal envelope, dominant frequencies, and relative amplitudes and timing among stations. 

In general, gas-and-ash explosions (vigorous venting 

of steam and (or) other gases and volcanic ash) at Mount 

St. Helens are characterized by emergent, low-frequency 

signals of extended duration, often with pulsating amplitude changes. The signal amplitudes from stations in the 

crater are much higher than those from stations on the volcano's flanks. The amplitudes from different flank stations 

are approximately equal. 

Several factors may complicate signal identification. 

These include: (1) evolution of the volcanic system with 

time, (2) overlap of signals that are recorded close together 

on seismograms, and (3) the temporary loss of data from key 

stations. Nevertheless, we have had considerable success 

identifying explosions within minutes of their occurrence. 

The criteria used to identify gas-and-ash explosion signals at 

Mount St. Helens and the techniques used to develop those 

criteria provide a foundation for signal identification at other 

active volcanoes. 

INTRODUCTION 

Although Mount St. Helens is the only Cascade volcano to have erupted while the Washington-Oregon 

regional seismic network (fig. 1) has been in operation, 

there are about a dozen potentially hazardous volcanoes in 

the Cascade Range. This volcanic chain stretches from 

British Columbia (Hickson, this volume) southward 

through Washington and Oregon and into northern California. The proximity of these volcanoes to airports (fig. 1) 

means that any aircraft operating in the Pacific Northwest 

could be at risk from volcanic ash in the air or on an airport 

surface. This risk is regional because an ash cloud erupted 

from any of the Cascade volcanoes can drift in the direction 

of the wind for hundreds of kilometers. 

On May 18, 1980, the eruption plume from Mount St. 

Helens climbed to approximately 60,000 ft (18,300 m) 

within 1 0 minutes of the start of the eruption (Rosenbaum 

and Waitt, 1981). The ash plume spread rapidly eastward, 

passing Yakima, Wash. (135 km downwind), 1 hour later 

and reaching midcontinent by the morning of May 19. 

Heaviest ash fall occurred in eastern Washington (SarnaWojcicki and others, 1981 ). The ash plume disrupted air traffic throughout the region, and hundreds of commercial operations in eastern Washington were canceled owing to 

accumulations of ash on airport surfaces (Schuster, 1981 ). 

The May 18 eruption clearly demonstrated how major 

volcanic activity can affect air traffic. But even small, shortlived, gas-and-ash explosions can create a hazard for airports 

and air traffic within the approach and departure paths to 

major metropolitan areas such as Portland and Seattle. Hundreds of gas-and-ash explosions have occurred at Mount St. 

Helens since 1980. These varied in size and intensity from 

minor events, in which small amounts of steam and entrained 

ash rose less than 1,000 ft above the dome (to approximately 

6,800 ft above sea level), to energetic events that generated 

large ash plumes, which rose as high as 20,000 ft above the 

dome. Minor ash fall from these events was reported as far 

as 1 00 miles ( 160 km) downwind. 

The seismic and volcanic activity at Mount St. Helens 

since 1980 has provided an ideal opportunity to make realtime or near-real-time correlations between seismicity and 

field observations. From these correlations, criteria for 

351 
352 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

EXPLANATION 

~ Major airports 

• Seismic station 

6. Volcano 

Ash fall 

May 18, 1980 a May 25, 1980 

~ June 12. 1980 

0 40 

L.......J 

KILOMETERS 

Figure 1. Map showing location of volcanoes, seismic stations, 

and major airports in Washington and Oregon. Many smaller airports 

(not shown) are also close to Cascade volcanoes. Areas of ash fall 

shown are from Mount St. Helens; dates of eruption are also shown. 

identifying various types of events from their seismic signature were developed. The capability to recognize specific 

events when the mountain is not visible, such as during bad 

weather or at nighttime, greatly improves our ability to 

issue timely warnings about potential ash plumes. 

METHODS 

In response to increased seismicity at Mount St. Helens 

in 1980, seismologists installed additional stations near the 

volcano to supplement data from the UW regional seismic 

network. The UW and USGS currently maintain a combined 

network of 18 seismic stations within 11 miles (18 km) of 

Mount St. Helens. At times, fewer or more stations have 

existed, depending on operational and research needs. Most 

of the stations are vertical-component seismometers with a 

1-Hz response. A few stations are monitored only by the 

USGS Cascades Volcano Observatory (CVO) or by the UW, 

but most stations are monitored by both groups. 

The data from all stations are recorded digitally on 

computer. Data from 20 to 40 percent of the stations are 

recorded in analog form on rotating drums called "helicorders." Although digital analysis is best for accurate location 

of earthquakes and some rockfalls, analog data permits 

rapid visual analysis of individual events and the overall 

pattern of seismicity. 

Between 1981 and 1986, more than 3,070 seismic signals recorded on helicorders were correlated with field 

observations. These events included 1,376 rockfalls and avalanches (mostly in the crater), 1,277 earthquakes, and 394 

gas-and-ash explosions (fig. 2). Most correlations were 

made by real-time radio communication with USGS-CVO 

field crews and pilots. Near-real-time communication with 

Federal Aviation Administration personnel, U.S. Forest Service observers, radar operators, the media, and the general 

public also provided valuable information. 

By carefully observing and analyzing the seismic signals, identification criteria were developed for most event 

types. These criteria are based on comparisons of the shape 

of the signal envelope, dominant frequencies, and relative 

amplitudes and timing among stations located at various distances from the volcano (fig. 3). 

RESULTS AND DISCUSSION 

Gas-and-ash explosion signals are usually characterized by emergent onset, whereby the amplitude of the signal 

builds over seconds to minutes; however, some events have 

more impulsive onsets or are preceded by small earthquakes. 

Signal frequency is relatively low and signal duration is 

long, lasting from a few minutes to about 30 minutes on 

flank stations. Occasionally, explosions are followed by 

hours of increased background noise and small earthquakes. 

Signal amplitude often increases and decreases in pulses during the event. Signal amplitudes recorded by stations located 

on the flanks of the volcano are roughly equal. In contrast, 

rockfalls from the lava dome and (or) the walls of the crater 

usually record at widely varying amplitudes on flank stations-the signal being largest at the station closest to the 

rockfall. During an explosion, signal amplitudes on stations 

in the crater, tens to hundreds of meters from the vent, are 

higher than those from stations on the flanks (fig. 4). 

CAP ABILITIES 

To identify a gas-and-ash explosion, the best results 

were obtained using four stations: one crater station, two 

flank stations, and one off-volcano station at least 11 miles 

(18 km) away. Using these stations and the above criteria, 

we became sufficiently skilled to recognize most gas-andash explosions from the seismic records during the first few 

minutes of the event. 

During the fall and winter of 1983-84, an experienced 

seismic observer was stationed by the helicorders for several hours per day on most days that crews were working in 

the crater. The observer was responsible for rapidly evaluating all incoming signals and notifying crews of any 
SEISMIC IDENTIFICATION OF GAS-AND-ASH EXPLOSIONS AT MOUNT ST. HELENS 353 

Figure 2. Seismic signal from gas-andash explosion on June 16, 1982. Tick 

marks on seismogram are at !-minute intervals, beginning in the upper left part of 

the figure. Letters A, B, C, and D on seismogram mark the approximate time at 

which the corresponding photographs (A, 

B, C, and D) were taken. Times shown on 

seismogram are Pacific Daylight Time. 
354 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

L 1 minute _j 

4 

--T 

1 - _.--..-·--- 3 ~ 

-- ---~ 

Figure 3. Seismic signal recorded at "yellow rock" (YEL) seismometer, which is located within the crater of Mount St. Helens 

(see fig. 4). Identification criteria for type of event are based on 

comparison of signal characteristics as follows (numbers keyed to 

figure): I, shape of the signal envelope; 2, signal frequency (measured approximately by the number of times the pen crosses the 

"zero line"-the horizontal line traced by an undisturbed 

pen-during I minute (this is not labeled on the figure); 3, relative 

amplitudes among stations; and 4, relative timing of the first arrival among stations. 

suspected gas-and-ash explosions. During this time, all gasand-ash explosions that occurred were correctly identified 

from their seismic signals while they were occurring. In 

many cases, events were identified during the first 5-20 

seconds, and warning was radioed to field crews before the 

gas-and-ash actually exited the top of the dome. Two less 

experienced observers who were taught to recognize these 

signals also had reasonable success: they did not miss any 

explosions, but they did radio several false alarms to field 

crews in the crater. 

This type of continuous monitoring requires the constant surveillance by a trained observer and is too demanding to be practical on a regular basis. Normally, the 

helicorders are only monitored visually when USGS or UW 

crews are flying in or working in or near the crater or when 

overall levels of seismicity are elevated. A seismic alarm 

system (Myers and Theisen, this volume) is used to alert 

the scientist on duty to possible explosions at other times. 

Since 1984, we have continued to correctly identify most 

gas-and-ash explosions from seismic records, either in real 

time, when helicorders are visually monitored, or within 

minutes of checking the records, when the seismic-alarm 

system is used. 

LIMITATIONS AND COMPLICATIONS 

Reliable signal recognition depends on experienced 

observers who are familiar with the character of a variety of 

signals from the network stations (Malone and others, 1981). 

During the past 10 years, a few gas-and-ash explosions have 

been missed or incorrectly identified, even by experienced 

observers. Several factors complicate rapid signal identification, including: (1) evolution of the volcanic system with 

time, (2) overlap of signals on the helicorder record, and (3) 

the temporary loss of data from key stations. 

EVOLUTION OF THE VOLCANIC 

SYSTEM WITH TIME 

Signals generated by gas-and-ash explosions during 

1982-85 tended to be more emergent and lower in amplitude than signals generated by gas-and-ash explosions of 

comparable height in 1986 and during 1989-91. Between 

October 1980 and October 1986, the lava dome grew in 16 

distinct, dome-building eruptions (Swanson, 1990). The 

frequency of these eruptions probably helped keep the volcanic conduit relatively open. The March-April 1986 

explosions, which generally had higher amplitudes and 

more impulsive (less emergent) signals than previous 

events, occurred near the end of a 1-year lull between 

dome-building eruptions. The 1989-91 gas-and-ash explosions (Myers, 1992), which were even higher in amplitude 

relative to plume height, occurred after nearly 3 years of 

quiescence. At least four explosion-like signals during the 

1989-91 series did not generate a plume. 

These changes in seismic characteristics may be associated with cooling of the dome and blocking of the conduit. 

Perhaps the higher amplitudes and more impulsive onsets 

reflect the higher energies and gas pressures required for 

magma to break through to the surface. 

OVERLAP OF SEISMIC EVENTS 

Another factor that can complicate rapid signal identification is the overlapping of seismic signals on the helicorder. 

Overlap can obscure the onset, maximum signal amplitude, 

and shape of the seismic envelope. This overlap can be 

caused by ( 1) a single, long event that writes over portions of 

itself that were recorded 15 or 30 minutes earlier (one full 

revolution of the helicorder), (2) other events that were 

recorded 15 or 30 minutes before or after the event in question, or (3) several events that occur simultaneously. 

Events that occur simultaneously can combine frequencies and amplitudes, producing signals that are atypical 

or that mimic other types of events. In the fall of 1990, the 

combined signal from a small distant earthquake (teleseism) 

and crater rockfall, which began a few seconds later, was 

misidentified as a gas-and-ash explosion. The distant earthquake gave the signal a low-frequency onset and similar 

amplitudes on the flank stations while the rockfall increased 

the amplitude on the crater stations. High-frequency, lowamplitude signals from an ongoing storm further complicated identification. The misidentification was recognized 

when the earthquake signal was identified on a regional 

seismic station more than 10 miles from the volcano. 
SEISMIC IDENTIFICATION OF GAS-AND-ASH EXPLOSIONS AT MOUNT ST. HELENS 355 

Gas-and-ash explosion 

VEL 

--------------_;·------------------~---- EDM .. 

Volcanic 

earthquake 

~VEL 

SHW 

EDM 

.!:2 

rn 

Q) 

:§ 

0 

~ c 

Q) 

Q) 

~ Q) 

..0 

Q) 

(.) 

c 

e 

Q) 

:t: 

:0 

Q) 

E 

f= 

Local (non"volcanic) 

earthquake 

----· 

___ __....._ 

-----

-.--.--.- _.._ ___ _ ----~- -----:-

VEL 

____,_ ~ 

____,_ 

-~ 

_ ____,_ b-~ 

--1 't .; ~ 

____,_ 

____...____ 

~ 

SHW 

- ___..__ ·- ---A-

---A-

~ 

~ 

·-·-·-

EDM --

Rockfall 

~·IIJliiFI VEL 

--J~--------------------------­

~----~------------------- . "' ..... -J, •____. 

- SHW 

122°16' 12" 

EXPLANATION 

Mount St. Helens 

seismograph stations 

A VEL, Crater station 

A SHW, Flank station 

A EDM, Flank station 

46°15' r---------------------t 

45°09' 

SHW 

.. 

0 

6562-ft contour 

(2000 m) 

EDM .. 

5 KILOMETERS 

Figure 4. Examples of characteristic seismic signals for gas-and-ash explosions, rockfalls, and earthquakes at Mount St. Helens. Tick marks 

are at 1-minute intervals. Note the differences in signal amplitudes and relative timing at flank and crater stations during the explosion compared to the rockfall. Explosion signals have a higher amplitude at the crater station (YEL) than at flank stations; flank stations (EDM, SHW) 

show similar amplitudes. The amplitude of a rockfall signal is highest at the station closest to the rockfall. It is often possible to see differences 

in first-arrival times among stations during a rockfall-this is rarely possible with close stations during explosions. Explosion and rockfall 

signals are normally more emergent than earthquake signals. 
356 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Approximate event counts, by event type, at five Cascade 

volcanoes, 1989-90. 

Volcano Ex- Earth- Rock- Ice Lahars 

plosions quakes falls quakes 

Mount St. Helens 102 104 104 0 101 

Mt. Rainier 0 102 102 103 101 

Mt. Hood 0 101 0 101 0 

Mt. Baker 0 101 101 103 0 

Mt. Adams 0 101 101 101 101 

LOSS OF DATA FROM KEY STATIONS 

If data are lost from one or more stations normally 

used to identify differences among signal characteristics, 

identification can be difficult. For example, loss of data 

from either of the flank stations "east dome" (EDM) or "St. 

Helens west" (SHW) (see fig. 4) prevents comparison of 

their relative signal amplitudes, making it hard to distinguish explosions from rockfalls. Without data from a distant station, the misidentification of the small teleseism 

mentioned above would not have been corrected. 

REGIONAL APPLICATIONS 

The UW also operates one or more seismic stations at 

or near nine other Cascade volcanoes, and, during the past 

few years, seismologists have established and compared 

"background" levels of seismicity at several of these volcanoes (table 1). At each volcano, signals that are larger than a 

pre-set threshold are categorized using the identification criteria discussed in this paper. Correlation of signals and field 

observations is done when practical; signals from debris 

flows and rockfalls exhibit similar characteristics at different 

volcanoes (Jonientz-Trisler and Qamar, 1989; R.D. Norris, 

oral commun., 1992). Even though the skill to interpret seismic signals at one volcano can be successfully applied to 

another volcano (Weaver and others, 1990), the cause may 

differ from volcano to volcano. If levels of seismicity 

increase above background at a volcano, more stations can 

be installed to improve the ability to interpret signals and 

locate events. 

CONCLUSIONS 

By careful correlation of seismic events with field 

observations at Mount St. Helens, criteria have been developed for identifying gas-and-ash explosions and other volcanic or seismic events from the analog seismic record. Several 

seismic stations are needed to compare signal characteristics 

among stations. Use of the criteria allows rapid, accurate 

identification of events when the volcano is not visible 

owing to weather conditions or darkness. 

The technique can be used by inexperienced observers 

if guidelines and samples of characteristic seismic signals 

from several stations are provided. But when signals are 

obscured by other events or data is missing from key stations, 

interpretation can be difficult, even for experienced observers. 

Seismic signals at other Cascade volcanoes have been 

compared to visual observations when possible. These signals display similar characteristics to signals of similar 

events at Mount St. Helens. The criteria used to identify gasand-ash explosion signals at Mount St. Helens and the techniques used to develop those criteria will help provide a 

foundation for signal identification at other active volcanoes. 

REFERENCES CITED 

Jonientz-Trisler, Chris, and Qamar, A., 1989, Debris flow seismograms from Mount Rainier and Mount Adams [abs]: Eos, 

Transactions, American Geophysical Union, v. 70, p. 1190. 

Malone, S.D., Endo, E.T., Weaver, C.S., and Ramey, J.W., 1981, 

Seismic monitoring for eruption prediction, in Lipman, P.W., 

and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. 

Helens, Washington: U.S. Geological Survey Professional Paperl250,p.803-813. 

Myers, Bobbie, 1992, Small explosions interrupt 3-year quiescence 

at Mount St. Helens, Washington: Earthquakes & Volcanoes, 

v.23,no.2,p.58-72. 

Rosenbaum, J. G., and Waitt, R.B., 1981, Summary of eyewitness 

accounts ofthe May 18 eruption, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. Helens, 

Washington: U.S. Geological Survey Professional Paper 1250, 

p. 53--67. 

Sarna-Wojcicki, A.M., Shipley, S., Waitt, R.B., Dzurisin, D., and 

Wood, S.H., 1981, Areal distribution, thickness, mass, volume, 

and grain size of air-fall ash for the six major eruptions of 1980, 

in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 577--600. 

Schuster, R. L., 1981, Effects of the eruptions on civil works and 

operations in the Pacific Northwest, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. Helens, 

Washington: U.S. Geological Survey Professional Paper 1250, 

p. 701-718. 

Swanson, D.A., 1990, A decade of dome growth at Mount St. 

Helens, 1980--1990: Geoscience Canada, v. 17, no. 3, p. 

154--157. 

Weaver, C.S., Norris, R.D., and Jonientz-Trisler, C., 1990, Results 

of seismological monitoring in the Cascade Range, 

1962-1989: Earthquakes, eruptions, avalanches and other curiosities: Geoscience Canada, v. 17, no. 3, p 158-162. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

INFRASONIC AND SEISMIC DETECTION 

OF EXPLOSIVE ERUPTIONS AT 

SAKURAJIMA VOLCANO, JAPAN, AND 

THE PEGASAS-VE EARLY-WARNING SYSTEM 

By Kosuke Kamo, Kazuhiro Ishihara, and Makoto Tahira 

ABSTRACT 

More than 6,000 explosive, summit eruptions have 

taken place at Sakurajima Volcano, Kyushu, Japan since 

1955. The explosions can be predicted using tilt and strain 

data obtained near the summit area and from swarms of shallow seismic events generated beneath the active crater. The 

onset of explosions is detected by explosion earthquakes, by 

the air-shocks accompanying them, and by visual observation. The success rate of the automated warning system for 

strong eruptions is more than 80 percent. 

Explosive eruptions at Sakurajima Volcano also have 

been detected frequently by infrasonic waves using an array 

of low-frequency microphones at Kariya, Aichi, 710 km 

from the volcano. The infrasonic system at Kariya is capable 

of detecting air waves generated by eruptions from volcanoes at distances of as much as I ,200 km. This capability 

forms the basis of a proposal for a worldwide network of airwave sensors to monitor volcanic explosions. A scheme, 

PEGASAS-VE (pressure gage system for air-shocks by volcanic eruptions), is proposed for the acquisition of information on eruption locations and their estimated magnitudes. 

The scheme would be a very effective means of enhancing 

aviation safety and would be similar to the tsunami warning 

system, which is in worldwide operation. 

INTRODUCTION 

Extensive studies have been undertaken at Sakurajima 

Volcano since 1960 to investigate the eruption mechanisms 

and to identify the precursors necessary for reliable prediction of the explosive eruptions (Kamo, 1978). Recent 

progress has made possible the prediction of explosive eruptions with high precision. The prediction techniques at 

Sakurajima, therefore, should provide useful information for 

aviation safety. Recent results from these studies of detection and prediction of summit eruptions at Sakurajima by the 

Sakurajima Volcanological Observatory of Kyoto University, are discussed in the first part of this paper. 

One notable aspect of explosive eruptions is the 

release of air-shock waves. Detection of such waves is, 

therefore, an important way to record explosive, ash-producing eruptions. A combination of pressure sensors and 

seismographs at Sakurajima is used for identification of 

explosive eruptions. The air-shocks are also detectable at 

very large distances because they propagate in the atmosphere as infrasonic waves. Air-shocks generated by eruptions at Sakurajima have been observed frequently at 

Kariya, 710 km from the volcano (Tahira, 1981, 1988). The 

possibility of detecting volcanic eruptions using a system of 

infrasonic microphones within a large area has been discussed by Tahira and others (1988). Remarkable infrasonic 

signals associated with the eruptions of Mt. Pinatubo, in 

June 1991, were recorded by the infrasonic system at 

Kariya. A brief description of the recorded signals from 

Pinatubo is presented in this paper. The principles and 

results of observations at Kariya are described in the second part of this paper, and a system called PEGASAS-VE 

is proposed for simultaneous monitoring of many volcanoes and is suggested as a possible technique to reduce the 

threat that volcanic eruptions pose to aviation. 

DETECTION AND PREDICTION OF 

EXPLOSIVE ERUPTIONS AT 

SAKURAJIMA 

An explosive eruption is accompanied not only by the 

ejection of volcanic bombs and ash but also by air-shocks 

and an explosion earthquake that originates beneath the 

active crater. The onset time and intensity of volcanic explosions at both Sakurajima and Suwanosejima Volcanoes have 

been monitored using a combination of seismometers and 

infrasonic microphones installed at distances of2-5 km from 

the active craters (Iguchi and Ishihara, 1990). Data collected 

357 
358 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

1~------ ... '1 0 seconds] -,11 -.~ B 

1.::~ c 

I 1----' .. -, I I -~--: -----1] 

10 seconds 

Figure 1. Examples of records of ( 1) the vertical component of explosion earthquakes, which originate beneath the summit crater, and 

(2) air-shocks. A, Explosion-earthquake record at Sakurajima Volcano (seismograph located 2.9 km from summit crater); B, Air-shock 

record at Sakurajima Volcano (infrasonic microphone located 5.5 km 

from summit crater); C, Explosion-earthquake record at Suwanosejima Volcano; D, Air-shock record at Suwanosejima Volcano. Both 

the seismograph and infrasonic microphone at Suwanosejima ( C and 

D, respectively) are located 3.3 km from summit crater. 

at Suwanosejima Volcano are transmitted through telephone 

networks to the Sakurajima Volcanological Observatory 

using a personal-computer communication system. Examples of seismic and infrasonic records at Sakurajima and 

Suwanosejima Volcanoes are shown in figure 1. 

Kamo (1978) noticed from a series of observations at 

Sakurajima that successive explosive eruptions are preceded by a swarm of shallow, B-type earthquakes, and prediction of explosive eruptions has been attempted by 

monitoring these volcanic earthquakes. Ishihara and Iguchi 

(1989) classified B-type earthquakes into two types, BH 

and BL, by the dominant frequency of the seismic waves. 

BH earthquakes are related to the intrusion of magma into 

the conduit, and BL earthquakes are related to the movement of magma up to the summit crater. There is a good 

correlation between swarms of B-type earthquakes, in July 

to November 1987, with increases of explosion events at 

Sakurajima (fig. 2). Nineteen swarms and 87 explosions 

were observed during this period. Seventy explosions out 

of 87 occurred within a week after swarms of B-type earthquakes. Note that no swarms or explosions were observed 

from the end of September through October 1987. Uhira 

and Ueda (1988) examined the correlation between explosions at Sakurajima and swarms of B-type earthquakes for 

a longer period, from 1984 to 1988. They found that more 

than 80 percent of explosions originated within a week 

after swarms of B-type earthquakes. 

To investigate eruption mechanisms and to establish a 

reliable prediction technique, Kamo and Ishihara (1989) have 

made detailed measurements of tilt and strain of the summit 

area of Sakurajima Volcano. An underground tunnel was 

constructed in a lava dome 2.8 km northwest of the summit 

crater, and a two-component water-tube tiltmeter and a threecomponent extensometer were installed inside the tunnel. 

A characteristic inflation, which occurs shortly before 

summit eruptions, followed by deflation after eruption, has 

been noted. The duration of inflation ranges from several 

minutes to several hours. The inflation is interpreted to be 

caused by intrusion of magma into a shallow magma reservoir beneath the crater. The amount of ground deformation 

does not correspond necessarily to explosivity, but it is 

related to the total amount of volcanic ejecta (Ishihara, 1988). 

An automated warning system has been developed, on 

the basis of the above-mentioned relationships, to assess 

eruptive activity at Sakurajima Volcano from the trend of 

deformation (fig. 3). The ground-deformation data are 

recorded continuously by a personal computer, and one of 

three levels of alarm (caution, critical, and warning) are 

issued when the amount of ground-tilt reaches 0.01, 0.05, 

and 0.1 microradians, respectively. The data and results of 

the assessment are displayed on a computer monitor screen 

in real time. The results of the automated warning system are 

shown in table 1 for the period from January 1987 through 

May 1991. Using this system, the prediction rate for the 

strong explosions with air-shocks that exceed 200 Pa (2 mb) 

is exceptional (87 percent). The exact onset time of eruption 

cannot be predicted at present because the amount of inflation that triggers an eruption changes from case to case. 

DETECTION OF DISTANT VOLCANIC 

EXPLOSIONS WITH INFRASONIC 

TECHNIQUE 

Shock waves released into the air by explosive eruptions propagate without substantial loss of energy for long 

distances in the atmosphere as infrasonic waves. Infrasonic 

waves can be detected by using a set of sensitive infrasonic 

microphones at a station hundreds of kilometers away from 

the volcano (Goerke and others, 1965; Wilson and others, 

1966; Wilson and Forbes, 1969). Infrasonic waves from 

summit eruptions at Sakurajima Volcano have been 

recorded frequently at Kariya (Tahira, 1982, 1988; Ishihara 

and others, 1986). 

The infrasonic observation system operating at Kariya 

(fig. 4) consists of an array of three, low-frequency capacitor microphones installed on the ground at a spacing of 
8 

6 

4 

2 

0 

1,200 

CJ) 1,000 Iz 

w 800 

> w 

u. 600 

0 

a: 400 

w 

llJ 200 ~ 

::::> 0 z 

10 

8 

6 

4 

2 

0 

INFRASONIC AND SEISMIC DETECTION OF EXPLOSIVE ERUPTIONS AT SAKURAJIMA VOLCANO, JAPAN 359 

JAN FEB 

EXPLANATION 

~~~ BL-type swarm (BH-type 

swarms are labeled) 

MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC 

MONTH 

Figure 2. Number of events at Sakurajima Volcano during 1987. A, volcanic explosions; B, shallow, B-type volcanic earthquakes (depth 

< 3 km); C, deep, A-type earthquakes (depth between 1 km and 15 km). 

Table 1. Results of automated warning system at Sakurajima Volcano, Japan, for the period from January 1987 

through May 1991. 

[Prediction rate refers to prediction rate for explosive eruptions. Comments in "remarks" colwnn refer to level of alarms issued prior to explosive 

eruption. min., minimal] 

E~losive eru~tions State of deformation at time of e~losion 

Intensity of Number of Eruption Non-eruption Pre-eruption Prediction 

air-shocks 1 explosions (deflation) (min. change) (inflation) rate Remarks 

(mb) (%2) (%2) (%2) (%) 

~ 0.9 169 4 16 80 34 "Caution" for 37 explosions. 

"Critical" for 11 explosions. 

"Warning" for 9 explosions. 

1.0-1.9 129 2 7 91 61 "Caution" for 63 explosions. 

"Critical" for 12 explosions. 

"Warning" for 4 explosions. 

2.0-2.9 65 0 0 100 81 "Caution" for 43 explosions. 

"Critical" for 8 explosions. 

"Warning" for 2 explosions. 

3.0-3.9 27 0 0 100 100 "Caution" for 15 explosions. 

"Critical" for 11 explosions. 

"Warning" for 1 explosion. 

~4.0 3 0 0 100 100 "Critical" for 2 explosions. 

"Warning" for 1 explosion. 

1 Approximate. Observed at 2.7 km from the summit crater. 

2 Percent of number of explosions. 
360 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Water-tube tiltmeter and 

II 

D ___.. 

D 

D 

Telemeter Personal computers 

Eruption 

(deflation) 

Level of alarms 

Warning 

Critical 

Caution 

Pre-eruption 

(inflation) 

High 

t 

Low 

Assessment of 

volcanic activity 

Non-eruption 

(minimal change) 

Figure 3. Schematic diagram of underground installation of tiltmeter and extensometer at Sakurajima Volcano. Alarm system is 

also shown. 

470-580 m and a system for recording and analysis. The 

frequency range of the microphone is 0.04-1 Hz. Because 

the amplitude of the infrasound signals from distant 

volcanoes is commonly, but not always, well below the 

level of irregular noise caused by local atmospheric 

turbulence such as wind noise, a "line microphone" 

(Tahira, 1981) is attached to each microphone to reduce 

wind noise. The line microphone is made up of a number of 

vinyl-chloride pipes, 5 em in diameter, arranged parallel to 

each other and connected to the central box containing the 

infrasonic microphone (fig. 5). The ends of each pipe are 

terminated by a capillary inlet opening, and the pressure 

fluctuations at the openings are propagated in the pipe and 

mixed in the central box, thus yielding spatially averaged 

pressure changes. Irregular wind noise is weakened 

considerably by this averaging process, but infrasonic 

waves of much longer wavelengths can survive the spatial 

averaging effect of the line microphone, thereby improving 

the signal-to-noise ratio. 

The noise reducer used at Kariya takes a line average of 

the pressure field over a length of 100 m along the ground. 

Infrasonic signals transmitted to the recording room by wire 

transmission lines are recorded continuously on a magnetic, 

analog data recorder together with the time-code signal. The 

data also are recorded on a pen oscillograph for the purpose 

of visual monitoring. The corresponding portion of the magnetic tape is replayed and analyzed in detail by a personal 

computer when a similar waveform is found in the three 

channels. A computer program is provided to calculate the 

cross-correlation coefficient between every pair of channels 

from which optimum time lags of the signal traversing the 

microphone array are obtained. The speed and direction of 

arrival of the signals then are computed, taking into account 

the geometry of the tripartite array of the microphones. The 

association of the recorded infrasonic signals with an eruption is established easily from information on the direction of 

arrival once the source volcano and its eruption time are 

identified from other information. The association is also 
INFRASONIC AND SEISMIC DETECTION OF EXPLOSIVE ERUPTIONS AT SAKURAJIMA VOLCANO, JAPAN 361 

/ 

/ 

Line microphone 

/ 

/ 

/ 

/ 

/ 

\ 

/ 

/ 

/ 

Time-code generator 

0 0 

0 0 

0 0 

/ 

/ Analog data recorder Pen monitor 

/ 

D Maximum amplitude 

Cross correlation 

Direction of arrival 

Horizontal phase 

velocity 

0 100 200 300 METERS 0000000 

0000000 

Tape player Microcomputer Printout 

Figure 4. Infrasonic observation system currently operating at Kariya, Japan (lat 35.05°N., long 137.05°E.). A map of the microphone 

array is shown on the left, and a schematic diagram of the recording and analyzing system is on the right. IGN, IGW, and IGE are infrasonic 

microphone stations at Kariya. 

INFRASONIC MICROPHONE 

---~~~;;;;;;;;;;;~~~~~~~~~::-a~.~--~~i_~f=rf~~CA~~PI~L~L~A~RY~I~N~LE~~;;O;P;E;N;IN;G;S;;~~~---

Figure 5. Schematic view of the multi-pipe line microphone used in the Kariya infrasonic system. Only a few pipes are illustrated here for 

simplicity, but the prototype has 13 pipes on each side and takes the spatial average of the pressure field over a length of I 00 m. 

checked from the arrival time of the infrasonic signals by 

seeing if this is reasonable for the source-receiver distance 

and speed of sound in the atmosphere. An example of the 

infrasonic wave generated by a summit explosion of Sakurajima Volcano is shown in figure 6. 

The detection rate of the infrasonic system at Kariya 

for explosions at Sakurajima Volcano increases with the 

strength of explosion and reaches 81 percent for strong 

explosions that produce air-shocks greater than 400 Pa at 

the seismic station HAR, which is located about 2. 7 km 

from the active crater (Tahira and others, 1988). One of the 

notable aspects of the infrasonic waves recorded at Kariya 

from explosive eruptions at Sakurajima is that two or more 

wave packets are frequently observed from a single eruption. Propagation paths for these infrasonic signals were 

studied by Tahira (1982) using a ray-tracing technique, and 

it has been shown that three different sound channels are 

possible from Sakurajima to Kariya, depending on the vertical profile of atmospheric temperature and winds. The 

lowest channel is formed between the ground and upper 

troposphere in which acoustic signals are propagated at a 

speed of 340-350 rn/sec. Infrasonic waves take longer 

when propagated by downward refraction at higher altitudes, giving rise to apparent speeds of approximately 310 

rn/sec for stratospheric refraction and 260-280 rn/sec for 

lower tropospheric refraction. 
362 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

~ U5 

aJ lni""""''VVVVV-.J'-'\1"\/V" 

1-

z 

.....J 

<( 

Z ltiT\"""""'\/\/11/V\.,-..r....., 

(.!) 

U5 

u 

0 z H-\"J\AJ'\/\/\/\,.,1-\Ao.. 

(/') 

<( 

0:: 

LL. 

z 

07:58 07:59 0&00 

TIME (JAPAN STANDARD TIME) 

Figure 6. An example of the infrasonic signal at Kariya originating from a summit explosion of Sakurajima Volcano on November 

21, 1986. Kariya is 710 km from Sakurajima. IGN, IGW, and IGE 

are infrasonic microphone stations at Kariya. Scale divisions on 

vertical axis are in 1-~b increments. 

Infrasonic signals from eruptions of other volcanoes in 

Japan have been recorded by the microphone array at Kariya, 

including the 1983 eruption of Asamayama (200 km away), 

the 1986 eruption of the submarine volcano at FukutokuOkanoba (1,270 km away), the 1986 and 1987 eruptions of 

Izu-Oshima (215 km away) (Tahira and others, 1990), and 

the 1989 eruption of the submarine volcano near Ito (190 km 

away from Kariya). 

INFRASONIC SIGNALS FROM 

PINATUBO 

Remarkable infrasonic signals were recorded at Kariya 

during the eruptions of Mt. Pinatubo in the Philippines on 

June 14--15, 1991. The direction of arrival of these infrasonic signals is SSW.-SW. and roughly coincides with the 

great-circle bearing of Pinatubo (i.e., 221° as measured 

clockwise from north). The time sequence (in Universal 

Time Code-UTC) of the infrasonic events at Kariya was 

examined by analyzing recorded data at successive 2-

minute intervals. The results are shown in figure 7. The 

arrival of infrasonic waves is evident on figure 7 during the 

following intervals (in UTC): (A), June 14, 18:16-18:38; 

(B), June 14, 20:02-20:42; (C), June 14, 21 :42-22: 18; (D), 

June 15, 00:46-00:58; (E), June 15, 08:26-19:02. Additional infrasonic signals are observed also around 06:08, 

06:52, 07:46, and 08:02 (UTC) on June 15. However, no 

further analyses for these signals were attempted because 

their exact onset times are not clear due to wind noise. The 

time sequence of infrasonic events (AHE) were compared 

with that of reported eruptions at Pinatubo (Smithsonian 

Institution, 1991 ). Eruption times are shown by the arrows 

in the left-hand column of figure 7. The onset of infrasonic 

VOLCANIC ACTIVITY 

!JUNE 141 

SMALL 

STRONG 

ONSET OF STRONG, 

SUSTAINED ACTIVITY 2211 

I JUNE 151 ooos ....... -----.,------'· 0031 

ONSET OF THE 

STRONGEST ACTIVITY 

ASH COLUMN FIXED 

OVER THE VOLCANO 

LESS VIOLENT ACTIVITY 

INFRASONIC AMPLITUDE (Pa) 0.0 0.5 1.0 1.5 2.0 

STATION NOISY 

TIME (GMT) 

Figure 7. Association of the infrasonic events at Kariya with explosions ofMt. Pinatubo, Philippines, on June 14-15, 1991. Thick 

bars perpendicular to the time axis on right-hand part of figure indicate infrasonic arrivals; bar length shows amplitude. Hachured 

parts indicate the time during which reliable infrasonic observations were not possible due to severe wind noise. Actual eruption 

times are shown by arrows on the left-hand side of the figure. Onset times of infrasonic events are connected with corresponding 

eruptions by dotted lines. 

events at Kariya are preceded by notable eruptions by 

between 2 hours 44 minutes and 2 hours 55 minutes, except 

for one case. The onset times of infrasonic events are connected with corresponding volcanic eruptions by dotted 

lines in figure 7. 

The travel speed computed using these time lags and 

the distance between Kariya and Pinatubo (2,770 km) falls in 

the range from 264 to 282 m/sec. These speeds are commonly observed for infrasonic signals from the eruptions of 

Sakurajima Volcano in summer months when they are propagated by repeated reflections and refractions between the 

Earth's surface and lower thermosphere (Tahira, 1988). 

The correspondence of infrasound with volcanic activity is questionable for signal (C). Its travel time would be 3 

hours 22 minutes if the signal was generated by the eruption 
INFRASONIC AND SEISMIC DETECTION OF EXPLOSIVE ERUPTIONS AT SAKURAJIMA VOLCANO, JAPAN 363 

6 

3 

b 

~ 0 

~ -3 

<( 

~ -6-L--~----~------~----~~-----L------L-----~------~------~-----L------._----~~-- <( 

a.. 

z A 

w 

0::: 

::J 

(/) 

(/) 

w 

0::: 

a.. 

z 

6 

w 3 

(9 

~ 0 

0-3 

20:10 20:15 20:20 

08:25 08:30 08:35 

B TIME (UTC) 

Figure 8. Examples of infrasonic signals recorded at Kariya, Japan, from the 1991 eruptions ofMt. Pinatubo, Philippines. Traces ofthe 

output data from three microphones are superposed after shifting the time axis to achieve the best phase match. See text for discussion. A, 

infrasonic signals for June 14, 1991; B, infrasonic signals for June 15, 1991. 

reported to have occurred at I8:20 UTC. However, this is 

somewhat too long, and we believe that the explosion causing this infrasonic signal must have taken place between 

I8:47 UTC and I8:58 UTC on June I5. A major eruption 

was recorded at I8:57 UTC on June I5, according to eruption data based on the observations at a temporary station by 

PHIVOLCS (R. Punongbayan, oral commun., I99I). This 

occurrence time is well within the reasonable range to interpret our infrasonic signal (C). 

The highest infrasonic activity was recorded from 

08:26 UTC through II: I 0 UTC on June I5, when amplitudes 

frequently exceeded I Pa. The activity then began to 

decrease, and the amplitude decreased to as low as O.I Pa by 

I9:00. The infrasonic signals, starting at 08:26 UTC is reproduced in figure SA and may be compared with a less intense 

signal, at an early stage, at about 20: I5 UTC on June I4 (fig. 

8B). The onset time of the strongest eruptions of Pinatubo 

was 05:42 UTC on June I5. This time corresponds well with 

the onset of the largest infrasonic disturbances. The ash column was reported to have remained fixed over the volcano 

until 13:30 UTC, but our infrasonic data suggest that the climactic eruptions lasted only until around 08:00 UTC and 

that, thereafter, the eruption subsided gradually. Weak infrasonic signals were again recorded at Kariya about 36 hours 

after the onset of the strong eruption, at 05:42 UTC, and 

lasted about 8 hours. These later signals are inferred to be the 

ones propagated to Kariya via an antipodal path (A2 waves). 

More detailed analyses of the Pinatubo infrasonic waves will 

be published separately. 

PEGASAS-VE 

Two or more infrasonic microphone arrays, operated 

500-I ,000 km apart, permit independent determination of 

the source location by extrapolation of the direction of 

arrival at different arrays. This leads to the proposal for a 

worldwide network of infrasonic microphone arrays to continuously monitor the volcanic eruptions in a wide area. The 

proposed system is called pressure gage system for airshocks by volcanic eruptions (PEGASAS-VE) and is shown 

diagramatically in figure 9. 

Each array consists of three or more infrasonic microphones with wind-noise-reducing pipes, a time-code generator, and a personal computer. The personal computer 

continuously records small pressure changes picked up by 

the microphones. The incidence of the traveling signal is 

confirmed, and then the direction of arrival, horizontal phase 

velocity, occurrence time, and signal amplitude are computed. The results are transmitted automatically to a central 

station where the source location of the signal is estimated 

from data sent by other array stations. 

Appropriate information would be given to the aviation 

system when a large eruption is detected. The information 

includes the time and place of the possible eruption and its 

explosivity. A satellite telemetry system such as Argos, making use of NOAA polar-orbiting satellites, can be useful to 

collect information from each infrasonic station and to transmit the result of analysis to the aviation system (Cauzac and 

others, this volume). The PEGASAS stations should be 
364 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

PERSONAL COMPUTER 

MIC 1 

ISOLATION 

AMPLIFIER 

TIME CODE 

GENERATOR 

ISOLATION 

AMPLIFIER 

TIME CODE 

GENERATOR 

( 

VOLCANIC ERUPTION J ~· --~W~~~--G--C~~------~ 

PERSONAL COMPUTER 

PERSONAL COMPUTER 

ISOLATION 

AMPLIAER 

TIME CODE 

GENERATOR 

Figure 9. The PEGASAS-VE system consists of a number of infrasonic microphone arrays that are 500-1,000 km apart. Each array continuously monitors the incidence of traveling signals and computes the direction of arrival, horizontal phase velocity, signal amplitude, and 

dominant frequency. All of these data are transmitted to a data center where the source location, occurrence time, and source intensity are 

calculated. Appropriate information is given to the aviation system when the source of a significant eruption is identified. 

located within a distance of about 500 km from the volcano 

to acquire the information of eruption within 30 minutes, 

taking into account the travel speed of infrasonic signals in 

the atmosphere. 

CONCLUSIONS 

Many of the summit eruptions at Sakurajima Volcano 

are predicted by monitoring seismic activity at the volcano. 

The eruptions tend to occur within 1 week after swarms of 

B-type earthquakes. A prediction in the shorter term is also 

possible at Sakurajima by instrumental monitoring of inflation of the ground. These prediction techniques can provide 

a primary way to reduce the threat of volcanic eruptions to 

aviation safety. 

Once an eruption has occurred, however, the most 

important thing is to detect the eruption as soon as possible. 

The combination of a seismograph with an infrasonic 

microphone has proved to be a useful technique to detect 

explosive eruptions, when installed at the volcano (Onodera 

and Kama, this volume). In this paper, we have proposed 

an extension of this system, which we call PEGASAS-VE, 

that is essentially a set of infrasonic microphone arrays to 

detect infrasonic waves generated by volcanic eruptions. 

This system would be capable of detecting explosive volcanic eruptions within 30 minutes when the spacing of the 

station is on the order of 500 km from the volcano. It merits 

the attention of the world aviation community because of 

its ability to provide coverage, at relatively low expense, of 

a large number of unmonitored volcanoes, such as those of 

the Kurile-Kamchatka-Aleutian region. 

ACKNOWLEDGMENTS 

The authors express their hearty thanks to Drs. Wally 

Johnson, Thomas Casadevall, and Steven McNutt for 

reviewing the manuscript and offering helpful suggestions. 

REFERENCES CITED 

Goerke, V.H., Young, J.M., and Cook, R.K., 1965, Infrasonic observations of the May 16, 1963, volcanic eruption on the island 

ofBali: Journal of Geophysical Research, v. 70, p. 6017-6022. 
INFRASONIC AND SEISMIC DETECTION OF EXPLOSIVE ERUPTIONS AT SAKURAJIMA VOLCANO, JAPAN 365 

Iguchi, M., and Ishihara, K., 1990, Comparison of earthquakes 

and air-shocks accompanied with explosive eruptions at 

Sakurajima and Suwanosejima Volcanoes: Kyoto University, 

Disaster Prevention Research Institute, Annual Report, v. 

33B-1, p. 1-12. 

Ishihara, K., 1988, Prediction of summit eruption by tilt and strain 

data at Sakurajima Volcano, Japan, in Proceedings, Kagoshima 

International Conference on Volcanoes, p. 207-210. 

Ishihara, K., and Iguchi, M., 1989, The relationship between microearthquake swarms and volcanic activity at Sakurajima Volcano: Kyoto University, Disaster Prevention Research Institute, 

Annual Report, v. 32B-l, p. 1-11. 

Ishihara, K., Iguchi, M., and Tahira, M., 1986, [Observations of air 

waves associated with volcanic explosions]: Report of the 

Sakurajima Volcano Observatory (October-December, 1982), 

p. 131-138. [In Japanese.] 

Kamo, K., 1978, Some phenomena before the summit eruptions at 

Sakurajima Volcano: Bulletin of the Volcanological Society of 

Japan,v.23,p. 53-64. 

Kamo, K., and Ishihara, K., 1989, A preliminary experiment of 

automated judgment of the stages of eruptive activity using 

tiltmeter records: lA VCEI Proceedings in Volcanology, v.1, 

p. 585-598. 

Smithsonian Institution, 1991, Pinatubo: Bulletin, Global Volcanism Network, v.16, no. 5, p. 2-8. 

Tahira, M., 1981, A study ofthe infrasonic wave in the atmosphere, 

multi-pipe line microphone for infrasonic observation: Journal 

ofthe Meteorological Society of Japan., v. 59, p. 477-486. 

---1982, A study of the infrasonic wave in the atmosphere. (II) 

Infrasonic waves generated by the explosions of the volcano 

Sakura-jima: Journal of the Meteorological Society of Japan, v. 

60, p. 896-907. 

---1988, A study of the long-range propagation of infrasonic 

waves in the atmosphere. (I) Observation of the volcanic infrasonic waves propagating through the thermospheric duct: Journal ofthe Meteorological Society of Japan, v. 66, p. 17-26. 

Tahira, M., Ishihara, K., and Iguchi, M., 1988, Monitoring volcanic 

eruptions with infrasonic waves, in Proceedings, Kagoshima 

International Conference on Volcanoes, p. 530-533. 

Tahira, M., Ishihara, K., and Ukai, E., 1990, [Infrasonic waves 

observed at Kariya in association with the 1986 and 1987 

eruptions of Izu-Oshima Volcano]: Kazan, v. 35, p. 11-25. 

[In Japanese.] 

Uhira, K., and Ueda, Y., 1988, Volcanic monitoring at Kagoshima 

local meteorological observatory of the Japan Meteorological 

Agency, in Proceedings, Kagoshima International Conference 

on Volcanoes, p. 227-229. 

Wilson, C.R., Nichparenko, S., and Forbes, R.B., 1966, Evidence of 

two sound channels in the polar atmosphere from infrasonic 

observations of the eruption of an Alaskan volcano: Nature, v. 

211, p. 163-165. 

Wilson, C.R., and Forbes, R.B., 1969, Infrasonic waves from Alaskan volcanic eruptions: Journal of Geophysical Research, v. 

74, p. 4511-4522. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC HAZARD DETECTION WITH 

THE TOTAL OZONE MAPPING SPECTROMETER (TOMS) 

By Arlin J. Krueger, Scott R. Doiron, Gregg S.J. Bluth, Louis S. Walter, 

and Charles C. Schnetzler 

ABSTRACT 

Volcanic clouds can be uniquely discriminated from 

weather clouds with the total ozone mapping spectrometer 

(TOMS) instrument on the Nimbus-7 and Meteor-3 satellites. Sulfur dioxide, which is carried along with water and 

ash in volcanic eruptions, is measured by TOMS as a byproduct of ozone mapping. Eruptions are easily detected in 

sulfur dioxide maps because the background so2 amounts 

are relatively small and uniform, whereas visible and infrared satellite images must be searched manually for distinctive cloud shapes. The TOMS technique also produces a 

quantitative estimate of eruption size based on sulfur dioxide 

content. Sulfur dioxide data from polar-orbiting satellites, 

coupled with a short-term trajectory forecast, can be used to 

prepare volcanic aviation-hazard maps. 

The detection and tracking capability of TOMS is illustrated with examples from the June 1991 Pinatubo and May 

1980 Mount St. Helens eruptions. The 50 volcanic eruption 

clouds detected with TOMS since 1978 include: Pinatubo, 

Mount St. Helens, El Chich6n, Cerro Hudson, Alaid, Nyamuragira, Galunggung, Una Una, Ruiz, Redoubt, Hekla, and 

several Galapagos volcanoes. 

INTRODUCTION 

The detection of volcanic ash clouds for aviation 

safety currently depends on reports from the ground and air 

and manual screening of visible and infrared cloud images 

from satellites. Damage to aircraft from flying through ash 

clouds has cost the aviation industry hundreds of millions 

of dollars (Steenblik, 1990) since the first serious incidents 

during the 1982 eruptions of Galunggung. During the June 

1991 eruptions of Mt. Pinatubo in the Philippine Islands, at 

least 16 aircraft were exposed to ash at distances up to 

1,000 km from the volcano (Casadevall and De Los Reyes, 

1991 ). Further aircraft damage results from the sulfuric 

acid haze that remains in the stratosphere long after the 

eruption. Thus, it is clear that the methods of detection of 

volcanic-hazard areas, as well as the communication of 

warnings, need improvement if future incidents are to be 

prevented. In this paper we discuss a satellite method for 

detection of explosive eruption clouds using sulfur dioxide 

gas as a tracer. 

DISCRIMINATION OF ERUPTION 

CLOUDS FROM METEOROLOGICAL 

CLOUDS 

Earth-orbiting satellites provide an excellent platform 

for detection of volcanic eruptions because of the global 

coverage and the potential for rapid transmission of data. 

Presently, the National Oceanic and Atmospheric Administration (NOAA) operational polar and geostationary satellites carry visible and infrared imaging instruments, such as 

the advanced very high resolution radiometer (A VHRR), in 

which the primary products are cloud images and temperature-distribution maps. Eruptions can be detected by manual inspection of images for evidence of plumes (Matson, 

1984; Sawada, 1987). This generally requires that the eruption column be sheared by winds into a plume, and, of 

course, the method fails if there is no contrast between the 

plume and underlying clouds. For example, Nevada del 

Ruiz Volcano, Columbia, produced no visible or infrared 

signature in its November 1985 eruption (M. Matson, 

NOAA, oral commun., 1986). 

Manual searches of satellite images could be avoided if 

cloud-composition differences are exploited. Volcanic 

clouds are primarily water, with carbon dioxide, silicate rock 

particles, and sulfur dioxide, with trace gases, such as HCl, 

present in smaller amounts. A relatively weak silicate signal 

at infrared wavelengths has been detected in eruption clouds 

using multispectral data from the A VHRR (Prata, 1989; 

Holasek and Rose, 1991; Dean and others, this volume; 

Schneider and Rose, this volume). Sulfur dioxide also has a 

very strong absorption band in the near-ultraviolet portion of 

the spectrum. This has been successfully exploited in detection of eruption clouds with the TOMS instrument on the 

Nimbus-7 satellite (Krueger, 1983), as reported here. 

367 
368 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

TOMS CAP ABILITIES FOR 

DETECTION OF ERUPTIONS 

TOMS measures the radiance of the atmosphere, as 

does A VHRR, but adds to this a measurement of the solar 

flux. From this measurement, the albedo (the ratio of 

reflected radiance to incident solar irradiance) of the atmosphere is computed. The albedo of the sunlit atmosphere is 

a result of scattering by air molecules; reflection from clouds 

or surface features, such as oceans, vegetation, soil, and 

snow or ice; and by absorption by specific atmospheric constituents. If narrow spectral bands are used, the quantity of 

absorbing gases (ozone and sulfur dioxide) below the spacecraft can be derived. 

The TOMS instrument is an ultraviolet spectrometer 

with six narrow wavelength bands designed for measurement of total ozone. Four of the wavelengths are used in 

pairs (312.5-331.2 nm and 317.5-339.8 nm) in a differential-absorption mode. The two longest wavelengths (360 and 

380 nm) are used to determine surface reflectivity. 

Ozone strongly absorbs light at wavelengths less than 

330 nm. To measure ozone from space, it is necessary to 

account for all the components of the system, including 

clouds and the reflectivity of the surface. If this were not 

done, clouds would produce artifacts in ozone maps. The success can be judged from the final ozone product, where the 

errors in total ozone from cloud effects are less than 1 percent. 

Sulfur dioxide has larger absorption coefficients than 

ozone at wavelengths less than 320 nm, but the background 

concentrations of this gas are so low that it is virtually undetectable in the ultraviolet Earth albedo, except in volcanic 

eruptions. When sulfur dioxide is present, differences in the 

absorption spectra of ozone and sulfur dioxide allow separation of the two species (Krueger, 1985). Volcanic clouds 

have been detected by this method at all altitudes above the 

boundary layer, but the observations are limited to day time. 

In addition, volcanic clouds below the upper stratosphere 

may be masked by large ozone amounts and long slant paths 

for the sunlight during winter. 

Horizontal structure in ozone and sulfur dioxide is 

resolved by scanning the field of view of the spectrometer 

perpendicular to the motion of the satellite. The width of the 

scan is designed for full global coverage on each day. The 

spatial resolution of 50x50 km on the ground directly below 

the satellite is crude by comparison with A VHRR. However, 

spatial resolution is not critical because the TOMS technique 

depends on identification of the sulfur dioxide rather than 

resolving the detailed shape of a volcanic cloud. 

TOMS is on the National Aeronautical Space Administration (NASA) Nimbus-7 satellite that was launched into a 

polar, noon-midnight, sun-synchronous orbit in October 

1978. A second TOMS instrument was launched on August 

15, 1991, into polar orbit on a Russian Meteor-3 spacecraft. 

Data continuity is assured through new TOMS instruments, 

which are planned for launch on a U.S. Earth Probes satellite 

in 1994, on a Japanese advanced Earth observing satellite 

(ADEOS) in 1996, and on an undesignated satellite in 1998. 

NOAA plans to fly TOMS instruments on operational polarorbiting satellites after the tum of the century. 

The TOMS data-production system at NASA/Goddard 

Space Flight Center normally takes 3-5 weeks for release of 

archival data. These historical data are used in ozone 

research, for assessment of volcanic sulfur dioxide production, and for confirmation of reports of eruptions in remote 

areas. However, the capability for routine, near-real-time 

data production (release in hours after playback from the satellite) has now been developed, and the data can be provided 

to users on a best-effort basis. Some satellites carrying 

TOMS instruments can also transmit data in real time if 

ground-receiving stations are available. 

The existing TOMS instrument design is optimized for 

ozone detection. Sulfur dioxide detection could be improved 

by changes in the field of view to improve ground resolution 

and by selecting the wavelengths for sulfur dioxide. Polarorbiting satellites are limited to one or two overpasses of 

each volcano each day. This limitation can be averted by 

development of a modified TOMS for flight on geostationary satellites (Hartmann and others, this volume). 

EXAMPLES OF ERUPTION 

DETECTION WITH TOMS 

Over the past 13 years, eruptions of 50 volcanoes have 

been measured with TOMS. The technique was devised following the eruption ofEl Chich6n in 1982 (Krueger, 1983), 

then it was extended to all other known eruptions to make a 

comparison of cloud properties. The volcanoes include 

Alaid, Galunggung, Nyamuragira, Mauna Loa, Una Una, 

Nevado del Ruiz, Redoubt, Hekla, Cerro Hudson, and several Galapagos volcanoes. The 1985 Ruiz eruption (Krueger 

and others, 1990) is an example of a sulfur dioxide cloud 

without visible or infrared signatures. On the other hand, not 

all eruptions produce measurable amounts of sulfur dioxide. 

For example, phreatic (steam-driven) eruptions are not 

accompanied by large amounts of sulfur dioxide; however, 

they do not appear to present the same problem to aviation as 

magmatic eruptions because of their smaller size. 

PINATUBO 

The 1991 eruptions of Mt. Pinatubo in the Philippines 

contain the largest masses of sulfur dioxide measured by 

TOMS (Bluth and others, 1992). They also produced the 

largest number of volcanic ash-aircraft incidents ever 

recorded (Casadevall and De Los Reyes, 1991). Twenty million tons of sulfur dioxide were injected into the atmosphere 

in a series of Plinian eruptions beginning on June 12, 1991, 
VOLCANIC HAZARD DETECTION WITH THE TOTAL OZONE MAPPING SPECTROMETER (TOMS) 369 

Figure 1. TOMS images of the Mount Pinatubo sulfur dioxide clouds on June 12-16, 1991. Sulfur dioxide amounts, in milli-atmospherecentimeters (m-atm-cm), are represented by a false-color scale, as shown on the right of each image. The diagonal white line is a flight corridor from Singapore to Hong Kong, which was affected by ash from Pinatubo. A, Initial magmatic eruption on June 12, 1991, observed 

about 90 minutes after the eruption began at 08:51 Manila time (00:51 UTC). The cloud is the white-red spot near Luzon Island, Philippines. 

B, Pinatubo sulfur dioxide clouds on June 13, 1991. An eruption at 08:45 Manila time (00:45 UTC) has produced the yellow-red spot near 

the Philippines, and the cloud from the prior day's eruption is the green-yellow patch over Vietnam. C, Sulfur dioxide image from TOMS 

at 11:30 Manila time (03:30 UTC) on June 15, 1991. Increased activity has produced a plume extending across the South China Sea. D, The 

sulfur dioxide cloud produced by the paroxysmal eruption of Pinatubo on the afternoon of June 15, 1991. Note that the range of the color 

scale is an order of magnitude greater than in A- C. The cloud, observed at 11 :45 Manila time (03 :45 UTC) on June 16, covers much of the 

South China Sea. Numerous aircraft incidents took place along the Singapore-Hong Kong flight route. 

and culminating in a paroxysmal explosion on June 15 

(Pinatubo Volcano Observatory Team, 1991 ). 

Figure IA illustrates the initial June 12 eruption of 

Pinatubo as a bright white-red spot of sulfur dioxide just 

west of the volcano at lat l5°N., long 120°E. The Nimbus-7 

satellite overpass of the Philippines was about 90 minutes 

after the eruption at 08:51- 09:26 Manila time (00:51-01 :26 

UTC) (Pinatubo Volcano Observatory Team, 1991 ). The 

sulfur dioxide amounts at each geographic location are portrayed with a false-color scale, shown on the right-hand 

side of the figure. Sulfur dioxide amounts are given in units 

of milli-atmosphere-centimeters (m-atm-cm), a measure of 

the equivalent thickness of a layer of pure sulfur dioxide 

gas at standard temperature and pressure conditions. The 

peak so2 amounts in this cloud are about 60 m-atm-cm, 

and the total amount of so2 in the cloud is 100,000 metric 

tons, as determined on June 13 when the cloud was optically thin. The scattering of light and dark blue spots 

throughout the image are noise in the data. The black band 

over northwest China is an artifact due to two missing scan 
370 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

lines. The diagonal white line over the South China Sea 

india~tes the heavily traveled flight corridor from Singapore to Hong Kong which was the site of numerous aircraft incidents following the June 15 eruption. 

The first reported aircraft incident was at 12:20 Manila 

time (04:20 UTC), about 2 hours after the Nimbus-7 overpass, at a location about 200 km southwest of the volcano 

(Casadevall and De Los Reyes, 1991). The NOAA-II 

AVHRR image taken at 13:30 Manila time (05:30 UTC), 70 

minutes after the incident, clearly shows an ash plume 

extending 330 km southwest of the volcano (Smithsonian 

Institute, 1991 ). This episode illustrates the importance of 

timing and communications in aviation safety. 

Throughout the next 24 hours, this cloud was carried 

across the Singapore-Hong Kong flight corridor by tropical 

easterly winds. At the June 13 TOMS overpass, the S02 

cloud from the June 12 eruption is already over Vietnam, 

some 1,300 km west of Manila (fig. lB). Another eruption, 

which occurred at 8:41-8:46 Manila time (00:41-00:46 

UTC) (Pinatubo Volcano Observatory Team, 1991), is visible as a yellow-red spot near Luzon. This eruption began 

two hours before the TOMS overpass. The first aircraft 

incident in the Singapore-Hong Kong corridor took place 

at 00:30 Manila time on June 14 (16:30 UTC, June 13) over 

the South China Sea. 

Larger eruptions, which began on the morning of June 

14, are observed on the 11 :30 (03:30 UTC) June 15 overpass 

(fig. 1 C) as a series of volcanic clouds extending 1,600 km 

WSW. from Pinatubo to Vietnam. 

The paroxysmal eruption began in early morning on 

June 15 and continued for more than 12 hours. This eruption 

produced a massive cloud, which was observed with TOMS 

at 11:45 (03:45 UTC) on June 16 to be covering much of the 

South China Sea (fig. lD). Note that the color scale has been 

expanded by more than a factor of ten from figures IA-1 C to 

display the approximately 20 million metric tons of sulfur 

dioxide produced in this eruption. This cloud was responsible for most of the aircraft encounters along the Singapore-Hong Kong flight corridor. 

MOUNT ST. HELENS 

The eruption of Mount St. Helens on May 18, 1980, 

provides a second example of a volcanic cloud drifting 

across an area with a high volume of air traffic. Mount St. 

Helens produced only about 3 percent of the sulfur dioxide 

of Pinatubo, but the cloud drifted across the United States in 

less than 3 days. This eruption produced a diffuse, lower tropospheric dust cloud, which moved east and north, and an 

upper tropospheric ash and sulfur dioxide cloud, which 

drifted east and south (Newell and Deepak, 1982). 

The sulfur dioxide cloud on May 19 is shown in figure 

2A as an image produced during reanalysis of archived 

TOMS data. About 27 hours after the eruption, a trail 

extends from the volcano location in southwest Washington 

to central Wyoming. The bulk of the cloud is found in a 

plume extending to the southwest corner of South Dakota, 

then southeast across Nebraska and Kansas to the panhandle 

of Texas. On May 20, the trail of volcanic material extends 

from northern Oregon, across Idaho, Colorado, Kansas and 

Missouri, to the vicinity of Detroit (fig. 2B). At this time, 

the most dense part of the sulfur dioxide cloud was over Illinois, Indiana, Ohio, and Michigan. On succeeding days, the 

northern part of this cloud was sheared by jet stream winds 

into an elongated stream, whereas the remainder of the ash 

cloud stagnated in a ridge over the Central States. Based on 

radiosonde winds and other observations, the cloud was 

located primarily between the 100-mb (16-km) and 200-mb 

(12-km) surfaces. 

Analyses ofthe ash-cloud trajectory, based on meteorological data, were prepared by the NOAA Air Resources 

Laboratory (see fig. 12-10 in McClelland and others, 1989) 

and by Ed Danielson of the Ames Research Center (Newell 

and Deepak, 1982). Figure 3 illustrates the Danielson trajectory for the 200- and 300-mb (9-km) levels. The general path 

is similar to the TOMS trajectories shown in figure 2; however, the actual cloud has a compact form with significant 

differences in timing and location. At the TOMS overpass 

time on May 19, the ash cloud is predicted to be over Arkansas at 9-km altitude (300 mb ), over central Colorado at 12 

km (200mb), and (not shown here) over the Utah-Wyoming 

border at 16 km (1 00 mb ). The actual cloud location from 

TOMS data is north and west of the forecast locations. On 

May 20, the trajectory forecast placed the ash south and east 

of the TOMS cloud. The differences illustrate the need for 

both a high degree of vertical and temporal resolution in 

meteorological data for trajectory forecasting. 

CONCLUSIONS 

A voidance of volcanic ash by aircraft requires use of 

all available sources of information. Once the plume is in 

the upper troposphere or lower stratosphere, the problem is 

detection and prediction of its motion. Meteorological data 

are needed to infer the height of a sulfur dioxide cloud 

based on measured wind speeds as a function of altitude. 

With only one satellite observation of cloud location per 

day, a forecast is required to estimate the location at intervening hours. Trajectory forecasts appear to need updating 

with volcanic-cloud information more than once per day 

due to weaknesses in the models and limitations in the 

meteorological database. However, good results have 

recently been obtained in forecasting the trajectory of Cerro 

Hudson under Southern Hemisphere polar-vortex conditions (Schoeberl and others, 1993). 

The TOMS technique produces unequivocal information about sulfur dioxide clouds produced during magmatic 

eruptions. Data from the present class of TOMS instruments on polar-orbiting satellites will be collected for at 

least the next decade. 
VOLCANIC HAZARD DETECTION WITH THE TOTAL OZONE MAPPING SPECTROMETER (TOMS) 371 

Figure 2. A, TOMS observations near local noon on 

May 19, 1980, of the sulfur dioxide cloud from the May 18, 

1980, eruption of Mount St. 

Helens. The cloud appears as a 

red-white patch over the 

central Western States. A trail 

of smaller so2 amounts extends westward back toward 

the volcano, which is located 

in southern Washington State. 

B, The sulfur dioxide cloud 

from Mount St. Helens on 

May 20, 1980. The bulk ofthe 

cloud is now over 111inois, 

Indiana, Ohio, and Michigan. 
372 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 3. Trajectory analysis based on meteorological data indicating the predicted path of the Mount St. Helens cloud (May 18, 

1980) at 200 and 300mb. Note the general agreement with the actual 

locations shown in figure 2, but note also the differences in detail, 

such as a more northerly trajectory than predicted. Prepared by E. 

Danielson of the Ames Research Center (Newell and Deepak, 1982). 

REFERENCES CITED 

Bluth, G.J.S., Doiron, S.D, Krueger, A.J., Walter, L.S., and Schnetzler, C.C, 1992, Global tracking of the S02 clouds from the 

June 1991 Mount Pinatubo eruptions: Geophysical Research 

Letters, v. 19, p. 151-154. 

Casadevall, T.J., and De Los Reyes, P.J., 1991, Impact ofJune 1991 

Pinatubo eruptions on aircraft operations in the western Pacific 

and southeast Asia [abs.]: Eos, Transactions, American Geophysical Union, v. 72, no. 44 [Supplement], p. 95. 

Holasek, R.E., and Rose, W.l., 1991, Anatomy of the 1986 Augustine Volcano eruptions as revealed by digital AVHRR satellite 

imagery: Bulletin of Volcanology, v. 53, p. 529-544. 

Krueger, A.J., 1983, Sighting of El Chich6n sulfur dioxide clouds 

with the Nimbus 7 total ozone mapping spectrometer: Science, 

~22~p. 1377-1378. 

---1985, Detection of volcanic eruptions from space by their 

sulfur dioxide clouds: American Institute of Aeronautics and 

Astronautics, 23rd Aerospace Sciences Meeting, January 

14-17, Reno, Nev., Report AIAA-85-0100, 4 p. 

Krueger, A.J., Walter, L.S., Schnetzler, C.C., and Doiron, S.D., 

1990, TOMS measurements of the sulfur dioxide emitted during the 1985 Nevado del Ruiz eruptions: Journal of Volcanology and Geothermal Research, v. 41, p. 7-15. 

Matson, M., 1984, The 1982 El Chich6n volcano eruptions-A satellite perspective: Journal of Volcanology and Geothermal Research, v. 23, p. 1-10. 

McClelland, L., Simkin, T., Summers, M., Nielsen, E., and Stein, 

T.C., 1989, Global Volcanism 1975-1985: Englewood Cliffs, 

N.J., Prentice-Hall, Inc., 655 p. 

Newell, R.E., and Deepak, A., 1982, Mount St. Helens eruptions of 

1980: Atmospheric effects and potential climatic impact: 

NASA Workshop Report SP-458, 119 p. 

Pinatubo Volcano Observatory Team, 1991, Lessons from a major 

eruption: Mt. Pinatubo, Philippines [abs.]: Eos, Transactions, 

American Geophysical Union, v. 72, no. 44 [Supplement], p. 

545- 553. 

Prata, A.J., 1989, Observations of volcanic clouds in the 10-12 Jlm 

window using AVHRRJ2 data: International Journal of Remote 

Sensing, v. 10, p. 751- 761. 

Sawada, Y., 1987, Study on analyses ofvolcanic eruptions based on 

eruption cloud image data obtained by the geostationary meteorological satellite (GMS): Technical Report of the Meteorological Research Institute No. 22, Tsukuba, Japan, 335 p. 

Smithsonian Institute, 1991, Pinatubo: Bulletin of Global Volcanism Network, v. 16, no. 5, p. 2-8. 

Schoeberl, M.R., Doiron, S.D., Lait, L.R., Newman, P.A., and 

Krueger, A.J., 1993, A simulation of the Cerro Hudson S02 

cloud: Journal of Geophysical Research, v. 98, p. 2949- 2955. 

Steenblik, J.W., 1990, Volcanic ash: A rain of terra: Air Line Pilot, 

June/July, p. 9- 15 and p. 56. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

MONITORING VOLCANIC ERUPTIONS 

USING NOAA SATELLITES 

By Michael Matson, James S. Lynch, and George Stephens 

ABSTRACT 

National Oceanic and Atmospheric Administration 

(NOAA) meteorological satellite data have been used to 

detect volcanic eruptions and monitor the subsequent ash 

clouds since 1976. Imagery (analog or digital) can be used in 

conjunction with conventional radiosonde data to determine 

the altitude of a volcanic eruption column; the size, speed, 

and position of the eruption cloud; and the direction in which 

the cloud is moving. This information can be used to provide 

guidance to pilots flying in areas near active eruptions. 

INTRODUCTION 

Many active volcanoes are located in remote areas of 

the globe, far from human habitation but near major flight 

routes (e.g., Aleutian and Kamchatkan volcanoes). Because 

of their remoteness, these volcanoes are often not monitored, 

and it is almost impossible to provide pilots with information 

about volcanic activity along the flight route. However, satellite systems, with their global coverage, can provide information on erupting volcanoes in virtually any part of the 

world (Sawada, 1987, this volume; Sudradjat, 1989). 

METHODS OF STUDY 

POLAR-ORBITING SATELLITES 

The National Oceanic and Atmospheric Administration 

(NOAA) normally operates two weather satellites in polar 

orbits and two weather satellites in geostationary orbits (currently, four polar-orbiting satellites and one geostationary 

satellite are operational). The NOAA polar-orbiting satellites operate at 833 to 870 km above the Earth in near-circular sun-synchronous orbits with 98.89° inclination, which 

results in 14.25 revolutions per day and obtains complete 

global coverage every 24 hours. 

The primary imaging system aboard the polar-orbiting 

satellites is the advanced very high resolution radiometer 

(A VHRR), a cross-track multispectral scanner with a nadir 

resolution of 1.1 by 1.1 km and an image swath width of 

2,600 km. The A VHRR offers five spectral channels-two 

visible and three infrared (see table 1). Experimental multispectral techniques based on A VHRR imagery (channels 3, 

4, and (or) 5) have been developed for monitoring volcanic 

plumes (Prata, 1989; Holasek and Rose, 1991; Potts and 

Whitby, this volume; Schneider and Rose, this volume). 

The A VHRR imagery is available at full resolution to 

direct-readout stations acquiring automatic picture transmission data (frequencies of 137.50 or 137.62 MHz) or high-resolution picture transmission data (frequencies of 1,698.0 and 

1,707.0 MHz). Data is also tape recorded on board the satellites and downloaded each orbit to the command and dataacquisition facilities in Fairbanks, Alaska, and Wallops 

Island, Va. The global data, resampled to 4-km resolution, 

are known as global area coverage or GAC data. Pre-specified, tape-recorded scenes, recorded at 1.1-km resolution, 

are known as local area coverage or LAC data. The two 

images in this paper (figs. 1 and 2) are from the A VHRR 

LAC coverage of the Philippines, which was established 

about June 1, 1991, 2 weeks prior to the paroxysmal eruption 

of Mt. Pinatubo. 

Currently, imagery from two polar-orbiting satellites, 

NOAA-II and NOAA-12, are operationally available. During any 24-hour period, the satellites will pass over any part 

of the world at least twice; once during the day, and 12 hours 

later at night. Coverage over the polar areas can be up to 9 

times per day due to orbital overlaps at these latitudes. With 

two satellites, repetitive coverage of any area of the world is 

obtained at least 4 times daily at the equator and up to 18 

times daily over the polar areas. 

GEOSTATIONARY OPERATIONAL 

ENVIRONMENTAL SATELLITE (GOES) 

The geostationary operational environmental satellite 

(GOES-7) is in orbit 35,800 km above the Western Hemisphere equator and orbits around the Earth at the same rotation rate as the Earth. Thus, it is always viewing a constant 

portion of the Western Hemisphere between lat 60°N. and lat 

60°S., providing repetitive coverage of the area as often as 

373 
374 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Spectral channels of the advanced very high resolution 

radiometer (AVHRR). 

Channel Wavelength ().!m) Primary uses 

0.58--0.68 Daytime cloud mapping. 

Snow/ice analysis. 

2 0.725-1.10 Surface-water delineation. 

Vegetation analysis. 

3 3.55- 3.93 Forest fire monitoring. 

Nighttime cloud mapping. 

4 10.30-11.30 Sea-surface temperature. 

Day/night cloud mapping. 

5 11 .50- 12.50 Sea-surface temperature. 

Day/night cloud mapping. 

every 30 minutes. The scanner imaging system aboard 

GOES acquires one band of visible data (0.55- 0.70 !liD) with 

a 1-km resolution, and one band of thermal-infrared (IR) 

data (1 0.5-12.6 !lm) is acquired at a resolution of 8 km 

(Sabin, 1987). 

Because of the complete coverage between lat 60°N. 

and lat 60°S. provided by GOES-7, it is possible to monitor 

many volcanic eruptions in the Western Hemisphere. The 

imagery .can be received as often as every 30 minutes, making near-real-time tracking of volcanic ash clouds possible. 

This tracking information can include plume altitude, position, size, speed, and directional movement. NOAA-11 and 

NOAA-12 can provide the same information for volcanic 

eruptions worldwide but only as often as every 6 hours near 

the equator and every 1 112 hours near the poles. 

PINATUBO ERUPTION 

The Mt. Pinatubo eruption provides examples of the 

NOAA satellite capability to monitor such events. The largest and most violent of the eruptions began on the morning 

of 15 June 1991. The most violent eruptive phase is shown 

in figure 1. An extensive ash plume achieved heights of 

25-30 km and, in the immediate vicinity of the volcano, 

attained altitudes of approximately 35-40 km. An overshooting top was fixed over the volcano for a 12-hour period. 

The ash from this phase of activity accounted for more than 

95 percent of the resultant 2, 700,000-km2 plume. 

The final phase of the eruption on June 16 was noted by 

a "wedge shaped" plume fixed on the volcano. During this 

phase (fig. 2), ash reached heights of 23-25 km. It is apparent from these satellite images that the areal extent and 

movement of the eruption cloud can be monitored. In addition, by comparing the satellite-derived black-body temperature of the eruption cloud to a nearby radiosonde station 

taking upper air temperature and wind profiles, it is possible 

to assign an altitude to the cloud. 

DRAWBACKS TO SATELLITE 

METHODS 

There are two problems with utilizing satellite data for 

volcanic eruptions. First, it is often difficult, in early stages 

of an eruption, to distinguish a volcanic eruption from a 

meteorological cloud. Often, the spectral signature and 

shape of each are similar; however, multispectral image processing using A VHRR data can be useful in discriminating 

ash clouds from meteorological clouds (Prata, 1989; Holasek 

and Rose, 1991 ; Dean and others, this volume; Schneider 

and Rose, this volume). It is easier to look for a reported 

eruption on satellite imagery than it is to detect an eruption 

by using the imagery alone. Despite this difficulty, several 

volcanic eruptions have initially been detected by trained 

analysts using satellite data alone. 

The second problem is assigning an altitude to the 

eruption cloud during the early stages of an eruption. 

Using satellite-derived temperature data alone and comparing it to nearby radiosonde temperature data may result in 

Figure 1. Mt. Pinatubo volcano, Philippines, NOAA-I 0 multispectral (infrared) image processed from 1.1-km data (reduced to 2.2 

km) at 6:30p.m. (local time) on 15 June 1991 . The extensive canopy 

of ash over Luzon and the South China Sea was produced after nearly 8 hours of continuous eruption during the "paroxysmal" event, 

which lasted a total of21 hours. The "overshooting top" can be seen 

over the volcano. Even though prevailing winds are from the northeast, the force of the eruption was great enough so that some ash was 

forced upwind. The concentric rings around the central core appear 

to be gravity waves propagating outward. Temperatures derived 

were as low as -80°C, and components of the ash cloud tracked 

west-southwestward at nearly 45 m/s at altitudes of 30 to 35 km. 
MONITORING VOLCANIC ERUPTIONS USING NOAA SATELLITES 375 

- • -~ ~.;,~~ 4' " ~'-

.. "'u· 

Figure 2. Mt. Pinatubo volcano, Philippines, NOAA-I 0 false-color, multispectral (visible and infrared) composite processed from 1.1-km 

data at 7:00a.m. (local time) on 16 June 1991 . A "wedge shaped" ash cloud, locked over the volcano (X), is depicted during the third phase 

of the "paroxysmal" eruption. Material can be seen rising from the volcano, spreading to form the blue-gray plume and ash cloud. 
376 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

two altitude assignments due to atmospheric temperature 

inversions. The problem can be resolved after the ash 

cloud starts to spread by comparing the ash-cloud speed 

and direction to radiosonde wind speed and direction. An 

additional problem can arise if the cloud is not in thermal 

equilibrium with the atmosphere (Self and Walker, this 

volume; Woods and Kienle, this volume), which will cause 

incorrect altitude calculations. 

CONCLUSIONS 

Although NOAA satellite data do have their limitations, 

used in conjunction with other sources of volcanic-eruption 

information, these data can provide near-real-time information on the altitude, size, speed, and direction of ash clouds. 

This information, along with trajectory forecasts, is now 

being operationally supplied by NOAA to the U.S. Federal 

Aviation Administration to provide volcanic-hazard alerts to 

aircraft in flight-information regions for which the United 

States is responsible. Operators of other national satellite 

systems could make similar information available to pilots 

flying near active volcanoes in areas covered by their meteorological satellites. 

REFERENCES CITED 

Holasek, R.E., and Rose, W.I., 1991, Anatomy of 1986 Augustine 

Volcano eruptions as recorded by multispectral image processing of digital AVHRR satellite data: Bulletin of Volcanology, 

V. 53, p. 420-435. 

Prata, A.J., 1989, Observations of volcanic ash clouds in the I 0-12 

~m window using A VHRR/2 data: International Journal of Remote Sensing, v. 10, p. 751-761. 

Sabin, Jr., F.F., 1987, Remote Sensing: Principles and Interpretation: New York, W.H. Freeman and Co., 449 p. 

Sawada, Y., 1987, Study on analyses of volcanic eruptions based on 

eruption cloud image data obtained by the geostationary meteorological satellite (GMS): Technical Reports of the Meteorological Research Institute, no. 22, 335 p. 

Sudradjat, A., 1989, Volcanic eruption monitoring using space platforms: Journal of the Indonesian Association of Geologists, v. 

12, p. 437-448. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

VOLCANIC TREMOR AMPLITUDE CORRELATED WITH 

ERUPTION EXPLOSIVITY AND ITS POTENTIAL USE IN 

DETERMINING ASH HAZARDS TO AVIATION 

By Steven R. McNutt 

ABSTRACT 

New data on volcanic tremor define an empirical relation between tremor amplitude or strength and eruption 

explosivity: as explosivity increases, tremor amplitude 

increases. Tremor data from 21 eruptions at 14 volcanoes 

were normalized to their reduced-displacement amplitudes, 

thereby permitting quantitative comparison. A linear regression of amplitudes plotted versus volcano explosivity index 

(VEl) yielded the formula: 

log10(reduced displacement)= 0.46(VEI) + 0.08 

Similarly, amplitudes plotted versus ash-column height 

yielded the formula: 

log10(reduced displacement) = 

(1.80) log10(ash-cloud height)- 0.08 

Both regressions are significant at the 95 percent level, 

although the VEl data fit slightly better. 

A rapid assessment of a volcano's explosivity could 

help determine hazards from airborne ash. Thus, tremor 

amplitudes could form one component of a warning system. 

The tremor amplitudes are recorded in near real time as the 

volcanic materials exit the vent. It then takes at least several 

minutes for the ash to reach altitudes where it poses a hazard 

to aircraft. Therefore, in the best case, tremor amplitudes 

could help determine the size of an eruption and the amount 

of ash before the ash reached altitudes where it poses a hazard to aircraft. In terms of aviation hazards, the threshold or 

critical amplitude oftremor is 10 cm2. 

INTRODUCTION 

A fundamental problem with respect to volcanic ash and 

aviation safety is the prediction of the volume of tephra and 

the column height resulting from volcanic eruptions. Numerous jet aircraft have been adversely impacted by airborne volcanic ash over the past 10 years. For example, the recent 

eruptions of Mt. Pinatubo, Philippines, caused damage to 

more than 14 jet aircraft (Casadevall and De Los Reyes, 

1991 ). Clearly, solutions to the problem of aircraft encounters 

with airborne ash need to be addressed before tragedy occurs. 

A main part ofthe problem has been the inability of monitoring teams to identify the presence and amount of ash resulting 

from a volcanic eruption at the time it occurs. 

This paper describes new results based on analyses of 

volcanic tremor, a type of seismicity, and its relation to the 

explosivity of a volcanic eruption. It will be shown that the 

amplitude of volcanic tremor, as recorded on a seismogram 

and normalized to a common scale, is proportional to the 

explosivity of eruptions based on such parameters as ashcolumn height, volume of tephra, and eruption style. The 

paper describes the data and its limitations and recommends 

how seismological data on volcanic tremor may be used to 

help reduce aviation hazards caused by volcanic ash. 

METHOD OF STUDY 

VOLCANO EXPLOSIVITY 

To compare the explosivity of eruptions to the amplitude of volcanic tremor accompanying them, the volcano 

explosivity index (VEl) of Newhall and Self (1982) is used 

(table 1 ). The VEl uses nine parameters to ascribe a numerical index, ranging from 0 to 8, to an eruption: general eruption description, volume of tephra, ash-column height, 

qualitative description, classification, duration, CA VW 

(Catalog of Active Volcanoes and Solfatara Areas of the 

World-see References Cited) maximum explosivity, tropospheric injection, and stratospheric injection. Of these 

parameters, ash-column height is the one of most concern to 

aviation safety. 

VEl values are normally determined as whole units. In 

this respect, they are similar to earthquake intensities, such 

as Modified Mercalli intensities, rather than to earthquake 

magnitudes. In this study, both published values and values 

determined by the author were used. Selected component 

information is shown in table 2. 

The VEl has several shortcomings; for example, ashcolumn height plotted versus the logarithm of total erupted 

mass shows some eruptions whose values fall outside 

377 
Table 1. Criteria for estimation of volcanic explosivity index. 

[After Newhall and Self (1982). VEl, volcanic explosivity index. Criteria are listed in decreasing order of reliability. Mod, moderate; column height given in kilometers above vent for VEl 0-2 and in kilometers above sea level for VEl 

~ 3; CAVW, Catalog of Active Volcanoes and Solfatara Areas of the World] 

Criteria 

Description 

Volume of ejecta (m3) 

Classification (Tsuya, 1955)1 

Column height (km) 

Qualitative description 

Classification 

Duration2 

CA VW maximum explosivity3 

Tropospheric injection 

Stratospheric injection 

0 

Non-explosive 

<104 

I 

<0.1 

Small 

104-106 

II-III 

0.1-1 

2 

Moderate 

106-107 

IV 

1-5 

3 

Mod-large 

107-108 

v 

3-15 

VEl 

4 5 6 7 8 

Large Very large-----------------------------------------------------

108-109 109-1010 1010_1011 1011-1012 >1012 

VI VII VIII IX ----------------

10-25 > 2 5 ---------------------------------------------------------· 

-------"Gentle, effusive"---- -----------"Explosive"--------- -------"Cataclysmic, paroxysmal, colossal"--------------------------------· 

"Severe, violent, terrific"-----------------------------------------------------------------------· 

-----------"Strombolian"----- ---------"Plinian"---------------------------------------------------------------· 

---------"Hawaiian"------- --------------------"Vulcanian" -------- ---------------------"Ultra-Plinian"----------------------------------------

-----------------------> 12-----------------------------------------------------------

---------------<i--~:::~-~~~::::==~=~~~~=~~=~~~==;;~-12-----------

---Lava flows--- ----------------Explosions or nuees ardentes-------------------------------------------------------------------------------------------

---------Phreatic----------.............................. . 

----Dome or mudflow-----

Negligible 

None 

Minor 

None 

Moderate 

None 

Substantial ----------------------------------------------------------------------------------------------

Possible Definite Significant-----------------------------------------------------· 

1 If all eruptive products were pyroclastic ejecta. 

2 In hours of continuous blast. 

3 The most explosive activity indicated for the eruption in CA VW. 

w 

-l 

00 

< 0 

h 

> z 

(5 

> 

1/J 

::c: 

~ tJ 

> 

< 

> ....., 

~ 1/J 

> "Tj 

t'TJ 

....., 

~ 

'"C 

25 

(') 

t'TJ 

t'TJ 

tJ 

z 

0 

~1/J 

"Tj 

:;;;; 

1/J 

....., 

z ....., 

t'TJ 

~ > ....., 

0 

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--< 

~ '"C 

0 

1/J 

2 

~ 
VOLCANIC TREMOR AND ITS USE IN DETERMINING ASH HAZARDS TO AVIATION 379 

Table 2. Eruption and tremor parameters. 

[VEl, volcano explosivity index (see table l); ash-cloud height given in kilometers above vent for VEl 0-2 and in kilometers above sea level for VEl~ 3; tephra volume refers to 

volume of uncompacted ash; leaders ( --) indicate no data; Vole. Obs., Volcano Observatory] 

Volcano 

name 

Elevation 

(m) 

Eruption 

date 

Tremor Ash-cloud Tephra 

amplitude VEl height volume References 

(cm2) (km) (xi06 km3) 

Augustine ............... 1,227 .... 1976, January .................. 140 ........ 4 ........... 13 ............. -- ............. Reeder and Lahr, 1987 

Simkin and others, 1981 

McClelland and others, 1989 

Fuego ..................... 3,763 .... 1973, April27 .................. 24 ......... 3 ........... >2 .............................. D. Harlow, unpub. data 

Fuego ..................... 3,763 .... 1975, July-September ....... 8 ........ 2 .......... 1-2 ............ -- ............. Simkin and others, 1981 

D. Harlow, unpub. data 

Gal eras .................. 4,482 .... 1989, May 4-5 ................. 17 ......... 2 ............ 3 .............. -- ............. D. Harlow, unpub. data 

Kilauea .................. 1,222 .... 1983, January 5-12 ........ 18.3 ....... 2 .......... 1-2 ............ 14 ............. Koyanagi and others, 1988 

Masaya ..................... 635 .... 1977, February ................ 2.5 ........ 0 ........... <1 ............. -- ............. Simkin and others, 1981 

D. Harlow, unpub. data 

Mount St. Helens ... 2,549 .... 1980, May 18 .................. 260 ........ 5 .......... >24 ......... 1,100 .......... Fehler, 1983 

Simkin and others, 1981 

Sarna-Wojcicki and others, 1981 

Mount St. Helens ... 2,549 .... 1980, August 7 ................. 20 ......... 3 .......... 13.4 ........... 4.5 ............ Fehler, 1983 

· Harris and others, 1981 

McClelland and others, 1989 

Scandone and Malone, 1985 

Mount St. Helens ... 2,549 .... 1980, October 16-18 ........ 10 ......... 3 .......... 14.3 ........... 3.0 ............ Fehler, 1983 

Harris and others, 1981 

McClelland and others, 1989 

Scandone and Malone, 1985 

Pacaya .................... 2,552 .... 1973, May 7 ...................... 5 .......... 1 ........... <1 ............. -- ............. McNutt and Harlow, 1983 

Simkin and others, 1981 

Pacaya .................... 2,552 .... 1979, October 6-7 ............. 9 .......... 2 ........... >1 ............. -- ............. D. Harlow, unpub. data 

Pavlof .................... 2,518 .... 1980, November 12-13 .... 11.. ....... 3 ........... 11 .............. 6 .............. McNutt, 1987 

Simkin and others, 1981 

Pavlof .................... 2,518 .... 1983, November 14-16 .... 16 ......... 3 ........... 7.5 ............. 12 ............. McNutt, 1987 

McClelland and others, 1989 

Pavlof .................... 2,518 .... 1986, April18-19 ............ 54 ......... 3 ........... 15 .............. 8 .............. McNutt, 1987 

McClelland and others, 1989 

Pinatubo ................. 1,760 .... 1991, June 15 ................ 1,070 ...... 6 ........... 30 .......... 3,000 .......... R. White, written commun., 1991 

Pinatubo Vole. Obs. Team, 1991 

Plosty Tolbachik .... 3,085 .... 1975, July 9-26 ............... 146 ....... .4 ........... 13 .......... 1,000 .......... Fedotov and Markhinin, 1983 

Gorel'chik and others, 1983 

Simkin and others, 1981 

Redoubt ................. 3,108 .... 1989, December 15 .......... 39 ......... 3 .......... > 12 .......... 9-16 ........... Miller and Davies, 1990 

Brantley, 1990 

Scott and McGimsey, in press 

Redoubt ................. 3,108 .... 1990, April21 .................. 15 ......... 3 ........... >8 ......... 0.6-1. 3 ......... Miller and Davies, 1990 

Brantley, 1991 

Scott and McGimsey, in press 

San Cristobal ......... 1,745 .... 1976, March .................... 2.4 ........ 1 ........... > 1 ............. -- ............. Simkin and others, 1981 

D. Harlow, written commun.,l991 

Sheveluch .............. 3,395 .... 1964, November 12 ......... 152 ........ 4 ........... 15 ............ 300 ............ Gorshkov and Dubik, 1970 

Simkin and others, 1981 

Veniaminof. ........... 2,507 .... 1983, June 28 ................... 17 ......... 3 ............ 8 ............... 9 .............. McClelland and others, 1989 

S.McNutt,unpub.data 
380 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Cl 

w 

a: 

<( 

:::> 1,000 0 

C/) 

C/) 

a: 

w 

r 

w 

~ 

i= 

~ 100 

u 

z 

r~ 

z 

w 

~ 

w 

u 

~ 10 

C/) 

iS 

Cl 

w 

u 

:::> 

Cl 

w 

a: 

0 

• 

2 3 4 5 6 7 8 

VOLCANO EXPLOSIVITY INDEX (VEl) 

Figure 1. Volcanic tremor reduced displacement versus volcano explosivity index (VEl) of Newhall and Self (1982). The plotted line is a linear regression fit to the data. The correlation 

coefficient, r, is 0.93. 

current VEl boundaries (Carey and Sigurdsson, 1989). 

Also, VEl = 3 is too broad a category in terms of aviatioJJ. 

because it includes both eruptions that are hazardous to aviation as well as those that are not. VEl = 3 is also the unit 

that has the greatest scatter in figure 1. Despite these shortcomings, the VEl is well known and widely used in the volcanological community. 

VOLCANIC TREMOR 

Volcanic tremor is a type of seismicity associated with 

active volcanoes. Its typical appearance on a seismic record, 

or seismogram, is that of an irregular sine curve or sine wave, 

and its key distinguishing feature is its long duration compared with earthquakes of the same amplitude or strength as 

recorded on a seismogram (McNutt, 1992). Terms such as 

"eruption signals" and "blast events" have also been used for 

some signals that are here referred to as volcanic tremor. 

Because terminology is not standardized and the purpose 

here is merely descriptive, the most general term has been 

used in this paper. 

An example of a tremor seismogram is shown in figure 

2, which shows data from Pacaya Volcano (Guatemala), 

recorded on a station 10 km from the vent. Tremor occurs for 

1 hour, stops for 1 hour, then resumes for 2 hours. This is 

followed by an amplitude reduction for 1/2 hour, then strong 

tremor that nearly saturates the seismograms. This strong 

tremor was accompanied by an eruption of steam-and-ash 

clouds to a height of several kilometers. The seismogram 

shows several typical features of tremor: (1) long signal 

duration, (2) nearly monotonic low frequencies, and (3) 

amplitudes that vary over several time scales. 

The Pacaya tremor was recorded at several seismic stations. In general, it is necessary to use a network of six to 

eight well-distributed stations, ranging in distance from 1 to 

20 km from the volcanic vent. This permits the recording of 

both weak and strong volcanic tremor on-scale and the ability to discern tremor and other signals of volcanic origin 

from regional or distant earthquakes. 

Volcanic tremor is nearly ubiquitous at active volcanoes. However, tremor occurs both during eruptions and during non-eruptive periods, so false alarms are possible. In 

general, eruption tremor is stronger and is oflonger duration 

than non-eruption tremor. Otherwise, there are no known 

methods to distinguish eruption tremor from non-eruption 

tremor. Some data suggest that strong tremor has a longer 

period or lower frequency than weak tremor (Aki and Koyanagi, 1981), but the effect is slight. 

The primary interest of this paper is to examine volcanic-tremor amplitudes or strengths during eruptions. For 

proper comparison between episodes of tremor at different 

volcanoes, the amplitudes are normalized to a common reference using a procedure called reduced displacement 

(R.D.). Two formulas are commonly used. For body waves 

(e.g., P-waves and S-waves) the formula of Aki and Koyanagi (1981) is: 

A (r) 

R.D.= 2Ji·M (1) 

For surface waves (e.g., Rayleigh waves, Love waves, 

and PL-waves) the formula ofFehler (1983) is: 

where 

AJ):iR.D.= 2JiM 

A is the amplitude, in centimeters, peak-to-peak, 

(2) 

r is the distance from source to seismic station, in centimeters, 

M is the seismograph magnification at the tremor frequency, 

'A is the tremor wavelength, in centimeters, and 

2Ji is the root-mean-square (rms) amplitude correction. 

Where possible, it is best to use values determined from 

several seismic stations located at a given volcano because 

these permit redundancy and error resolution. Such calculations have been performed for about 40 volcanoes; a subset 

ofwell-determined values from 21 eruptions at 14 well-studied volcanoes is shown in table 2 and figures 1 and 3. Note 
VOLCANIC TREMOR AND ITS USE IN DETERMINING ASH HAZARDS TO AVIATION 381 

1 minute 

Figure 2. Portion of a -seismogram from Pacaya Volcano, Guatemala, recorded on October 7, 1979. Time marks are at 1-minute intervals, 

and each line is 15 minutes apart from adjacent lines. Time increases from top to bottom and from left to right. Volcanic tremor of variable 

amplitude occurs for about 4.5 hours of the middle 6 hours of the record. A steam-and-ash eruption occurred during the strongest part of 

the signal (large arrow). The frequency of the tremor is about 1.5 Hz. Several nearby earthquakes are also recorded (small arrows). 

that the tables and figures show one value per eruption. 

These are the tremor values that correspond to the peak VEl 

during each eruption. 

DATA SELECTION 

Data used in this study are primarily published data 

from the last 20 years. A number of values were determined 

by the author from unpublished data that are part of an ongoing investigation (McNutt, 1992). For these cases, to assure 

quality control, it was necessary to examine the time series 

for both tremor and the eruption parameters so that details of 

the temporal relation between the two could be assessed. 

Other studies have examined tremor amplitudes versus 

eruption parameters for many different times within single 

eruptions (Eaton and others, 1987; Koyanagi and others, 

1988; McNutt and others, 1991). The present study, however, 

is concerned with establishing a general relationship between 

various volcanoes, assuming similarity of eruptions. Thus, 

plotting one value per eruption-the maximum tremor 

amplitude accompanying the maximum VEl-implies equal 

weighting of each eruption. VEl is the independent variable 

(x-axis). The accompanying tremor reduced displacement is 

plotted as the dependent variable (y-axis). The regression formula minimizes they errors. To use the data in the opposite 

sense-to forecast VEl from the tremor amplitude-the 

regression must be done with the variables reversed. For the 

data set of this paper, however, the difference is slight. An 

enlightening discussion of the issue of regression polarity is 

given by Bolt (1978). 

A strength of the data set is that it spans six orders of 

magnitude in VEL This is possible due to inclusion of data 

on Mt. Pinatubo (R. White, oral commun., 1991; White and 

others, 1992), which, at VEl = 6, is the largest eruption 

worldwide since the 1912 eruption ofKatmai, Alaska. A limitation of the data set is that it consists of a relatively small 

number of eruptions. As more data are added, the derived 

parameters may change somewhat, although they will not 

change much because the six orders of magnitude of VEl provides stability. Roughly speaking, the VEI-5 and -6 data 

points "anchor" the upper end of the correlation; adding more 

data at the lower end will not significantly change the slope. 
382 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

RESULTS 

TREMOR AMPLITUDE VERSUS VEl 

The primary result of this study is that tremor amplitudes increase as eruptions become more explosive. This is 

seen clearly in figure 1, which plots reduced displacement 

tremor amplitude versus VEL A linear regression fit to the 

data yields the relation: 

log10(reduced displacement)= 0.46(VEI) + 0.08 

The correlation coefficient is r = 0.93, which is significant at greater than the 95 percent level. The derived relation spans six orders of magnitude of VEl and three orders 

of magnitude of tremor amplitude; hence, it is robust. 

There is scatter in the data of a factor of approximately 2 

to 3, most of which is probably due to stochastic variation 

in parameters, similar to scatter shown in Carey and 

Sigurdsson (1989, their fig. 7). 

ASH-CLOUD HEIGHT VERSUS 

TREMOR AMPLITUDE 

Tremor amplitudes increase as ash-cloud heights 

increase (fig. 3). A linear regression fit to the data for eruptions with ash-cloud heights of 3 km or more yields the 

relation: 

log10(reduced displacement)= 

(1.80) log10(ash-cloud height)- 0.08 

The correlation coefficient is r = 0.75, which is lower 

than for the VEl, but still significant at greater than the 95 

percent level. For this plot, ash-cloud heights were measured 

above the vent, as opposed to above sea level (see tables 1 

and 2). The derived relation spans two orders of magnitude 

in both tremor amplitude and cloud height. The scatter 

appears to be greater than in figure 1, and the correlation 

coefficient is lower, implying a worse fit. Further, there is a 

gap or offset in the data between about 1.5- and 3-km height. 

Four of the seven eruptions with cloud heights below 2 km 

are effusive eruptions of basaltic lava. Thus, the volumes are 

high, whereas the ash-column heights are low. The VEl is an 

aggregate index that averages these effects. This is probably 

the reason that no similar gaps are seen in figure 1. 

GENERAL FEATURES AND 

LIMITATIONS OF THE RELATIONSHIPS 

Although volcanic tremor occurs during nearly all eruptions, specific features of tremor may be difficult to forecast 

in advance. Furthermore, physical conditions, such as vent 

geometry, may change as a function of time. Typically, the 

strongest tremor recorded at each volcano occurs during its 

largest or most explosive eruptions. Weaker tremor accompanies weaker or less explosive activity at the same volcano. 

0 

w 

0:: 

<( 

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(/) 

0:: 

w 

1-

w 

:2 

i= 

~ 100 

u 

z 

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z 

w 

:2 

w 

u 

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(/) 

0 

0 

w 

u 

:::> 

0 

w 

0:: 

0 

0 

8 

0 

• 

• 

• 

• 

• • 

• • 

1~----------------~10----------------~100 

ASH-COLUMN HEIGHT, IN KILOMETERS 

Figure 3. Volcanic tremor reduced displacement versus ashcloud height above the vent. The plotted line is a linear regression 

fit of the data for eruptions in which the ash cloud reached a height 

of 3 km or more above the vent (solid symbols). Values below 3 km 

(open symbols) were not used in the regression. The correlation coefficient, r, is 0.75. 

This assumes that the style of eruption remains similar. At 

some volcanoes, the first or "vent-clearing" phase of an 

eruption may be more explosive than later phases of activity. 

The vent-clearing phases are generally accompanied by 

strong tremor, whereas later phases are accompanied by 

weaker tremor. For example, many of the post-May 18, 

1980, eruptions of Mount St. Helens, especially the domebuilding eruptions, were very similar to each other; in fact 

the similarity of precursors permitted accurate forecasting of 

many of these events (Swanson and others, 1983). At 

Redoubt Volcano, Alaska, several of the later eruptions of 

the 1989-90 eruption sequence were forecast, whereas the 

earlier ones were not (Brantley, 1990; J.A. Power, written 

commun., 1992). At Mt. Spurr, Alaska, it took scientists 11 

minutes to recognize the onset of the first eruption in June 

1992, but only 3 minutes each for the second and third eruptions (Miller and others, 1992). Clearly, as volcanologists 

become more familiar with the characteristics of a specific 

volcano, a better job can be done in forecasting its eruptions 

and determining when an eruption is in progress. 

Vent geometry and vent size can each affect tremor 

amplitudes for a given VEL For example, at Kilauea Volcano (fig. 4) (Eaton and others, 1987), when the vents are 
VOLCANIC TREMOR AND ITS USE IN DETERMINING ASH HAZARDS TO AVIATION 383 

Cylindrical conduit 

EXPLANATION 

e Kilauea volcano 

.A. Pavlof volcano 

FOUNTAIN HEIGHT, IN METERS 

10 

~o 

8 ~ ~ W<( 

~:::> 

wo 

UCI) 

6 ::s (/) a.. a: ~~ Ow 

4 0 ~ 

~i= 

=>rE 

2 fa u a:~ 

Figure 4. Volcanic tremor reduced displacement versus lavafountain height. The solid line represents a linear regression fit to 

the Kilauea data. Points I and 2 are from fissures rather than cylindrical conduits. The dashed line fits these two points and is forced 

to intersect they-axis at 1.7 cm2. Figure modified from Eaton and 

others ( 1987). 

more fissure-like, or less cylindrical, the tremor amplitudes 

are higher by about a factor of 7 for the same height of lava 

fountaining. Thus, knowledge of vent geometry prior to 

eruptions can be used to help estimate explosivity based on 

tremor amplitude, but the fact that many vents change size or 

shape during the course of eruptions may require frequent 

updating of such information. For many stratovolcanoes, 

vent geometry remains relatively unchanged for periods of 

years, such as PavlofVolcano from 1973 to 1984 (McNutt, 

1987). Other factors that may affect amplitudes are attenuation, coupling, and nonlinearity. 

NON-ERUPTION TREMOR 

This study has focused on tremor that occurred during 

known eruptions. At a number of volcanoes, however, 

tremor occurs during times of no eruptions, although this 

tremor is generally weak. The strongest known non-eruption 

tremor is a deep(> 40 km) tremor at Kilauea (Aki and Koyanagi, 1981). Such non-eruption tremor could contribute 

substantially to the false-alarm rate of a warning system 

based on the detection of volcanic tremor. A threshold value, 

or critical amplitude of tremor, must be defined. 

A recent study based on a worldwide sample of 

tremor from more than 80 volcanoes (McNutt, 1992) 

showed that about 60 percent of tremor episodes accompanied eruptions of gas, ash, or lava. About half of the 

remaining tremor episodes, or 20 percent, occurred within 

the 10 days immediately preceding or following eruptions. 

These data probably represent the upper range of the falsealarm rate: 20 to 40 percent of tremor episodes occur with 

no eruption. Combining information on amplitudes, frequencies of tremor, and durations of tremor episodes could 

reduce that rate significantly. It is not known whether the 

amplitude of precursory tremor can be used to forecast the 

size of an upcoming eruption. 

DISCUSSION AND CONCLUSIONS 

The results of this paper can be thought of physically as 

an application of Newton's second law: for every action, 

there is an equal and opposite reaction. Ash, magma, and gas 

move up, and the ground deforms and vibrates in response. 

Thus, the observed relations translate the second law into 

volcano-seismology terms. The observed scatter is considerable, however, and is probably caused by stochastic variation 

as well as factors including vent size, vent geometry, attenuation, coupling, and possible nonlinearity. At volcanoes, we 

seldom know the size or shape of the vent at the time of eruption, and our knowledge of coupling of gas-charged magma 

to wallrock is very poor. A recent example is dome-collapse 

events at Unzen Volcano, some of which were nearly aseismic, although the events produced ash clouds (H. Okada, 

oral commun., 1991 ). 

Despite these limitations, however, the derived relationships provide useful information, which must be applied 

with an appropriate level of conservatism. Two key factors 

are the threshold or critical amplitude of tremor and the 

false-alarm rate. Figures 1 and 3 show that ash typically does 

not reach altitudes hazardous to aircraft unless the tremor 

amplitude is;::: 10 cm2. Therefore, this is the critical amplitude of tremor (the amplitude above which appropriate hazard-mitigation actions would be taken). Regarding false 

alarms, it was stated above that, in the worst case, the falsealarm rate is between 20 and 40 percent based on study of a 

worldwide sample (McNutt, 1992). Thus, if the critical 

amplitude of tremor is reached, results suggest that there is a 

60 to 80 percent chance that a hazardous, ash-producing 

eruption is taking place, but there is a 20 to 40 percent chance 

that one is not. 

Clearly, some sort of confirmation is needed. This 

might be visual confirmation, if weather conditions permit, 

or a signal observed on a microbarograph, lightning detector, slow-scan TV, hydrologic sensor, or other device. It is 

important to note that the onset of the tremor signal either 

precedes or occurs at the time the eruption begins, so it is 

the first geophysical signal to be recorded because seismic 

waves travel at speeds of several kilometers per second. 

Once confirmation is achieved, the tremor amplitude and 

duration together may be used to estimate the likely size of 

the eruption, including estimates of the tephra volume and 

height of ash clouds. Data published by Scandone and 
384 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Malone (1985) for Mount St. Helens illustrate one example 

of how this might work. 

In practice, there would generally be a time delay of 

several minutes between the onset of tremor and the time that 

a warning could be issued. This is because tremor and some 

low-frequency or long-period discrete earthquakes share 

common onsets (Fehler, 1983). Because, by definition, discrete earthquakes will end whereas tremor is continuous, it 

may take several minutes to determine if the event ends. In 

general, discrete earthquakes have longer durations as their 

magnitudes increase, so the verification time increases with 

event size. For magnitude 2 events, typical durations are 50 

seconds, increasing to 300 seconds for magnitude 4. However, since the rate of ascent of ash clouds is on the order of 

20 to 100m/sec (Voight, 1981), this would still give at least 

several minutes lead time before the ash reached altitudes 

hazardous to aircraft. Nevertheless, a procedure would need 

to be developed to tum off an alarm if an event thought to be 

tremor turned out to be a low-frequency earthquake instead. 

Eruptions are not uniform processes, so tremor amplitudes and other parameters often vary by about an order of 

magnitude during a single eruption phase. In some cases, 

tremor amplitude is high at the beginning and end of an episode but low in the middle (e.g., Pinatubo-R. White, oral 

commun., 1991 ), whereas, in many others, amplitudes begin 

small, grow large, then decline (such as Puu Oo-Koyanagi 

and others, 1988; and Pavlof-McNutt, 1987). These observations suggest that estimates of tephra volume and ashcloud height based on tremor amplitudes may need to be 

revised several times over the course of a single eruption. 

These features suggest a practical approach consisting 

of warning, confirmation, and updates. The warning would 

be that an eruption producing tephra may be in progress 

based on the identification of volcanic tremor. Then the 

reduced displacement would be calculated, the duration 

measured, and the event detected using field observations 

and other monitoring techniques, such as microbarographs, 

lightning detectors, or slow-scan television. A confirmation 

would state that an eruption is taking place and would provide first estimates of ash-column height and tephra volume. 

Alternatively, this would be the time to cancel the warning if 

the suspected eruption was not confirmed or if a low-frequency seismic event occurred instead of tremor. Later 

updates would estimate ash-cloud height and tephra volume 

based on variations in tremor amplitude. Finally, a last notification would indicate that the eruption was over. As more 

experience is gained with a given volcano, it would be 

expected that the false-alarm rate would decline and the estimates of eruption parameters would improve. 

RECOMMENDATIONS 

1. For volcanoes where we have no observational capability but where we have a seismic network, the 

method described in this paper offers an important 

chance to determine if an eruption has occurred and if 

that eruption produced ash that could threaten aircraft. 

Thus, it is necessary for seismologists to install a sufficient number of seismic stations, typically six to 

eight stations at each monitored volcano, to determine 

earthquake and tremor source locations and amplitudes with confidence and to permit error resolution. 

2. Information on tremor could be important to giving 

early warnings and to developing a probabilistic format for information dissemination from volcano 

observatories to emergency management agencies. A 

warning only a few minutes after tremor is recorded 

could be based on seismic data alone, then confirmed 

and updated approximately every 20 to 30 minutes. 

Such a message might read, "Based on the recording 

of volcanic tremor of amplitude 10 cm2, we believe 

that there is a 60 to 80 percent chance that an eruption 

began at 08:00 hours and may have produced ash 

clouds to heights of 10 km and a tephra volume of 

approximately 107m3." 

3. Volcano observatories need to standardize the reporting of volcanic tremor so that reduced displacements are routinely used. Reports of tremor should 

state the onset time, duration in minutes, frequency 

in hertz, and reduced tremor amplitude displacement 

in cm2. Seismograph type and location should also 

be stated explicitly. 

4. Volcanologists need to increase the observational 

database to make the results more robust and to better 

interpret scatter or trends depending on factors such 

as composition of the magma, vent geometry, and 

amplitude versus duration of individual tremor episodes. The VEl scale needs to be modified so that 

more eruptions fall within the parameter boundaries, 

such as ash-column height and volume. Further, a 

weighted VEl needs to be developed for use in aviation problems, with extra weight given to ash-column 

height and to suspended-ash volume. 

ACKNOWLEDGMENTS 

I thank Thomas J. Casadevall, John A. Power, and 

Robert A. Page for reviewing the manuscript, William E. 

Scott for sending me a preprint of his Redoubt manuscript, 

and David H. Harlow for generously providing his unpublished data over the years. 

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VOLCANIC TREMOR AND ITS USE IN DETERMINING ASH HAZARDS TO AVIATION 385 

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and Wood, S.H., 1981, Areal distribution, thickness, mass, volume, and grain size of air-fall ash from the six major eruptions 

of 1980, in Lipman, P.W., and Mullineaux, D.R., eds., The 

1980 Eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 577-600. 

Scandone, R., and Malone, S.D., 1985, Magma supply, magma discharge and readjustment of the feeding system of Mount St. 

Helens during 1980: Journal of Volcanology and Geothermal 

Research., v. 23, p. 239-262. 

Scott, W.E., and McGimsey, R.G., in press, Character, mass, distribution, and origin of tephra-fall deposits of the 1989-1990 

eruption of Redoubt Volcano, south-central Alaska: Journal of 

Volcanology and Geothermal Research. 

Simkin, T., Siebert, L., McClelland, L., Bridge, D., Newhall, C., 

and Latter, J.H., 1981, Volcanoes of the World: Stroudsburg, 

Pa., Hutchinson Ross Co., 232 p. 

Swanson, D.A., Casadevall, T.J., Dzurisin, D., Malone, S.D., Newhall, C.G., and Weaver, C.S., 1983, Predicting eruptions at 

Mount St. Helens, June 1980-December 1982: Science, v. 221, 

p. 1368-1376. 

Tsuya, H., 1955, Geological and petrological studies of volcano 

Fuji 5: Tokyo Daigaku Jishin Kenkyusho Iho, v. 33, p. 

341-382. 

Voight, B., 1981, Time scale for the first moments of the May 18 

eruption, in Lipman, P.W., and Mullineaux, D.R., eds., The 

1980 Eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 69-86. 

White, R.A., Harlow, D.H., and Chouet, B.A., 1992, Long period 

earthquakes preceding and accompanying the June 1991 

Mount Pinatubo eruptions [abs.]: Eos, Transactions, American 

Geophysical Union, v. 73, no. 43 [supplement], p. 347. 

VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

AIRBORNE RADAR DETECTION OF VOLCANIC ASH 

By Mark E. Musolf 

ABSTRACT 

Detection of volcanic ash clouds by both ground-based 

and airborne radar systems is highly desirable. Airborne 

radars would provide in-flight detection of ash clouds for 

regions where ground-based radar coverage is not available, 

allowing for real-time pilot reaction to a potentially dangerous situation. Present airborne weather radars are insufficient for detection of volcanic ash particles or clouds due to 

the power/aperture and sensitivity limitations of these systems. Three different airborne radar configurations, X-band 

(9.5 GHz), Ku-band (16 GHz), and millimeter (95 GHz), are 

analyzed to determine their effectiveness for detection of 

volcanic ash. Volcanic-ash-cloud detection and signal-tonoise ratio are evaluated as a function of operating frequency, radar cross section, and range. Along with performance evaluation, antenna parameters (gain, beam widths) 

and waveform parameters are addressed. 

The results of the volcanic-ash-detection analysis 

revealed that a high-power Ku-band airborne radar could 

provide the necessary detection performance against light 

ash, given some prior knowledge of a volcanic eruption. The 

analysis also confirmed the inadequacy of existing X-band 

weather radars for detection of light volcanic ash. 

INTRODUCTION 

For the past decade, volcanologists, meteorologists, 

and engineers have studied the effect of volcanic ash on air 

traffic safety. It has been well documented that aircraft flying into a volcanic ash cloud increase the risk of a major 

accident due to engine failure (Brantley, 1990). The airborne detection of a volcanic ash cloud would warn the 

pilot of potential danger ahead. During daylight hours, ash 

clouds can be visually distinguished from normal rain 

clouds; however, during night operations, pilots have no 

means of ash-cloud detection. Conventional X-band airborne weather radars (table 1) are specifically designed for 

detection of severe natural weather phenomena rather than 

clouds of very small dielectric particles. 

This study addresses the limitation of existing radar 

systems and suggests an ideal, conceptual radar design based 

on the technology that exists today and will exist in the 

future. The radars selected for analysis contain parameters 

(power, antenna gain, beam widths) that are typical of many 

weather radars in existence today. 

APPROACH 

A detailed radar analysis was performed for the detection of volcanic ash clouds. The study was subdivided into 

the following areas: 

A. Ash detection design considerations.-Areas of 

study included (1) operating-frequency selection, based on 

reflectivity per unit volume and atmospheric attenuation, and 

(2) power/aperture limitations. 

B. Detection-range performance.-Typical radar 

parameters from existing commercial and military weather 

radar systems were used in the analysis. Signal-to-noise ratio 

was calculated to determine detection-range performance 

based on the reflectivity of volcanic ash. 

C. Configuration summary matrix.-Advantages and 

disadvantages of each of the radar operating frequencies that 

were analyzed for volcanic ash detection were summarized. 

D. Airborne radar technology advances.-Applicability of the latest airborne radar technology advances to volcanic ash detection was addressed. 

E. Ideal conceptual-design requirements.-Airborne 

radar conceptual-design requirements were developed based 

on existing technologies. 

ASH-DETECTION 

CONSIDERATIONS 

The detection of volcanic ash clouds is very difficult for 

an airborne weather radar due to the very low reflectivity of 

ash-particle clouds. The reflectivity is orders of magnitude 

smaller than the reflectivity of light rain. Ash-cloud detection is also limited by the very low power/aperture products 

of existing airborne weather radars. This section will address 

each of these effects. 

The detection of volcanic ash is highly dependent on the 

operating frequency of the radar because the reflectivity per 

387 
388 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 1. Conventional airborne weather radars. 

[From Business and Commercial Aviation, 1989; Blake, 1990] 

Radar type Existing sensors Frequency band 

Commercial Primus 500 X-band 

Primus 708 X-band 

WXR-700 X-band 

Military AN/APS-133 X-band 

unit volume of ash is inversely proportional to wavelength. 

The reflectivity per unit volume (Tt, in units of m-1

) is computed using the following equation (Nathanson, 1991): 

5 

1t 2 

11 = -IK1 z (1) A-4 

IK1 2 = ~£- =0.36=(lightashfall); Z = I.D6 (2) 

£+1 

where 

'A is the radar wavelength, 

£ is the dielectric constant of a spheroid, and 

D is the diameter of a droplet or particle. 

The reflectivity for three rainfall rates ( 16 mmlhr, 4 

mmlhr, and 1 mm/hr), dense ash cloud, and light ashfall were 

computed as a function of the radar operating frequency, 

based on parameters given in Harris and Rose (1983) for 

dense ash cloud, Harris and others (1981) for light volcanic 

ash, and Nathanson (1991) for rain. The results are given in 

figure 1. Note, for rain, Z is expressed as Z = ari.6, where r 

is the rainfall rate in mmlhr and a is approximately 200. For 

frequencies above 35 GHz, the data were extrapolated from 

data of R. Crane and H. Burke, presented in Nathanson 

(1991, p. 216-218 and 232-234). 

The reflectivity of light ash fall is approximately 40 

dB (1 04 times) to 25 dB (320 times) smaller than the light 

rain (1 mmlhr) condition. Based on reflectivity alone, 

higher frequency radars will yield better detection due to 

stronger backscatter. 

Atmospheric attenuation is also a function of operating 

frequency. Attenuation is inversely proportional to operating 

frequency. The round-trip atmospheric attenuation for Xband, Ku-band, and 95 GHz is given in table 2. 

Both reflectivity and atmospheric-attenuation results 

for the selected operating frequencies were incorporated into 

the detection-range-performance analysis. 

The airborne radar systems power/aperture product 

also contributes to detection performance. The power/aperture product is the product of the radiated average power 

and antenna gain of the radar. The larger the power/aperture product, the greater the detection performance. The 

power/aperture product of airborne weather radar systems 

are limited by the size, weight, and cost of the sensor. Conventional airborne weather radars utilize high-peak-power, 

Table 2. Atmospheric attenuation at 4-km altitude. 

[From Nathanson, 1991; Norden Systems, Inc., unpub. data] 

Operating Two-way atmospheric 

frequency attenuation ( dB/km) 

X-band ......................................... 0.02 

Ku-band ....................................... 0.03 

95 GIIz ......................................... 0.2 

low-duty-cycle transmitters producing very low average 

power. High-average-power transmitters, which are used 

on advanced military multi-mode radars, are heavy and too 

expensive for commercial application. As technology 

progresses, the weight and cost of high-average-power 

transmitters may be reduced to a level that is acceptable for 

future airborne weather radars. 

Maximum antenna gain is determined by the largest 

physical area available for the antenna aperture. Conventional weather radars are located in the nose of the aircraft 

to p.rovide for maximum forward-looking surveillance coverage. The physical dimensions available for the antenna 

aperture is 10 by 10 inches in small aircraft and 30 by 30 

inches in larger aircraft. For a constant area, antenna gain 

is only a function of operating frequency. The gain is 

inversely proportional to wavelength. Therefore, higher 

operating frequencies will yield a higher antenna gain. 

Antenna gain as a function of operating frequency was considered in the detection analysis. 

DETECTION-RANGE PERFORMANCE 

To determine the detection-range performance of volcanic ash clouds, the signal-to-noise ratio is computed. The 

generic signal-to-noise ratio (SNR) equation is given by 

(Barton, 1976, p. 110--114): 

en 0 

....J 

w 

Ill -20 

u 16 mm/h Rainfall 

w 

Cl -40 

z 

~~ -60 

> -80 ~ 

Dense ash cloud--::-:..---------

------ ---- ------

u 

w 

....J -100 u.. 

w 

0:: 

95 

OPERATING FREQUENCY, 

Ku-band IN GIGAHERTZ 

Figure 1. Reflectivity versus radar operating frequency for rain 

and volcanic ash. 
AIRBORNE RADAR DETECTION OF VOLCANIC ASH 389 

2 2 Pp'tNG A a 

SNR=--------------

3 4 ( 4n) KTFnLhpLaR 

where 

P P is peak power, 

't is the transmitted pulse width, 

N is the integration gain, 

G is the antenna gain, 

A is the wavelength, 

0' is the radar cross section in resolution cell, 

(3) 

KT is the thermal noise factor (K is the Boltzmann constant; Tis the absolute temperature), 

Fn is the noise figure, 

Lhp is the hardware and processing loss, 

La is the atmospheric attenuation (two-way), and 

R is the range to target or clutter. 

For a point target, such as an aircraft, truck, or building, cr is 

the radar cross section of the specific target. Because volcanic-ash-cloud detection is based on a distributed target, cr is 

a volumetric radar cross section. Therefore, the volumetric 

signal-to-noise ratio equation is required. 

The volumetric radar cross section equation is given by 

(Eaves and Reedy, 1987): 

0' = ,v 

where 

cr is the radar cross section in the resolution cell, 

11 is the radar reflectivity per unit volume, and 

Vis the volume of the resolution cell. 

(4) 

The volume of the resolution cell is computed by (Eaves 

and Reedy, 1987): 

1t 2 

V = 4R 9az9e/Wr 

where 

9az is the azimuth beam width, 

9e/ is the elevation beam width, and 

Wr is the range resolution. 

(5) 

The volumetric signal-to-noise ratio equation is given by: 

3 2 2 

1t Pp'tNG 9az9elWriKI Z 

SNRv 2 2 256A R KTFnLhpLa 

(6) 

The conventional airborne radar configuration parameters that were utilized in the detection analysis are given in 

table 3. 

The signal-to-noise ratio was calculated as a function of 

detection range for the four radar configurations based on the 

light-ash reflectivity previously computed. To achieve 

detection of the ash cloud, a signal-to-noise ratio (SNR) of at 

least 6 dB is required. The SNR detection plot is given in figure 2. The performance of the 95-GHz radar is very poor due 

Table 3. Conventional airborne radar parameters. 

[Radar parameters are based on various, existing airborne radar systems. Az, azimuth; 

elev., elevation; proc., processing; Atmos., Atmospheric] 

Parameter X-band1 X-band2 Ku-band3 95 GHz 

Average power (W) 3.4 65 65 4.5 

Antenna gain (dB) 34 33 37 49 

Az. & elev. beam width (

0 ) 4 2.9 1.7 0.35 

Range resolution (m) 525 750 750 60 

Reflectivity factor (mm6/m3) 0.1 0.1 0.1 0.1 

Refractive index 0.36 0.36 0.36 0.36 

Noise figure (dB) 7 8 8 9.5 

Hardware & proc. loss (dB) 4 4 4 4 

Atmos. loss (dB/km) 0.02 0.02 0.03 0.2 

1 Commercial weather radar. 2 APS-133. 

3 Scaled APS-133. 

to the low average power, large atmospheric attenuation, and 

small azimuth beam width. The commercial X-band radar 

has very low SNR due to very low reflectivity and low average power. The military X-band radar has better performance than the commercial radar due to 13 dB of greater 

average power. This radar would be able to detect ash clouds 

at approximately 10 km-this is too close to prevent penetration into the cloud. The best performance would be achieved 

with a scaled Ku-band weather radar, due to greater antenna 

gain and larger ash reflectivity. This radar would detect ash 

clouds out to approximately 25 km. For the desired detection 

range of75 km, 10 dB in additional power/aperture and (or) 

integration gain would be required. To achieve 10 dB of integration gain, the radar scan rate would be reduced to approximately 1/18th of the normal scan rate. This new scan rate 

could be utilized in a special ash-detection radar mode. 

Based on detection-range-performance analysis, existing 

conventional airborne weather radar falls well short of 

achieving acceptable ash detection. 

CONCLUSIONS 

The results of this detection analysis reveal that severe 

problems exist with the airborne detection of volcanic ash 

clouds. Each of the radar operating frequencies analyzed 

offers advantages and disadvantages for detection. A configuration summary is given in table 4. 

Even though most conventional airborne weather radars 

are at X-band, this may not be the optimal frequency band 

for volcanic ash detection. Based on the results of this study, 

a high-average-power (at least 500 watts) Ku-band radar 

could provide the necessary detection performance. However, to insure detection, the airborne radar sensor would 

require a prior knowledge of a volcanic eruption. The radar 

would initiate a special radar mode of operation when volcanic ash is expected in the area. The antenna would be tilted 
390 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 4. Summary of radar operating frequencies. 

Configuration Advantage Disadvantage 

X-band •Existing commercial and military 

equipment. 

•Small reflectivity per unit volume. 

•High power transmitters used on 

military multimode airborne radars. 

•Light atmospheric and rain attenuation. 

Ku-band •Existing military equipment. 

•High-power transmitters used on 

•No commercial weather radars at 

this band. 

military multimode airborne radars. •Heavy atmospheric and rain 

attenuation. 

95 GHz •Large reflectivity per unit volume. 

•Light weight. 

•Low average power transmitters. 

• Very heavy rain attenuation. 

•Narrow beam widths. 

up to eliminate ground-clutter effects, and an optimized 

waveform for close-in range surveillance (about 75 km) 

would be transmitted. The antenna scan rate would be 

reduced to allow for maximum integration gain. Advanced 

signal processing techniques could also be employed for volcanic-ash-cloud discrimination. Doppler processing, waveform pulse-code matching, and polarization diversity could 

be utilized for particle detection and identification. These 

areas will be a topic for further study. 

en 

_.J 

w 

al 

u 

~ 10 

z 

0 

~ a: 0 w 

en 

6 

z 

6 

1- ....J -10 

<( 

z 

(!) 

U5 

I 

I 

I 

\ 

\ 

\ 

\ 

\ 

' ' ' 

Ku-band (scaled) 

SNR REQUIREMENT 

------,_ / X-band (military 

\ '',,,',,, 

', .... , 

',,<__ configuration) 

\ '................ / X-band (commercial 

' 95-GHz radar ........ < configuration) 

10 

'< ........ ' ................ ' ........ 

' ' 

20 30 40 50 60 

RANGE, IN KILOMETERS 

70 80 

Figure 2. Signal-to-noise ratio (SNR) versus range for airborne 

detection of volcanic ash by radar. 

ACKNOWLEDGMENTS 

The author would like to thank Dr. Lester Kosowsky, 

Dr. Dan Held, and Mr. Robert Guarino for their support and 

technical contributions in the area of volumetric detection. 

REFERENCES CITED 

Barton, D.K., 1976, Radar System Analysis [Artech Radar Library]: Englewood Cliffs, N.J., Prentice-Hall, 608 p. 

Blake, B., 1990, Radar and electronic warfare systems, in 

Jane's-Radar and Electronic Warfare Systems 1990-91: Alexandria, Va., Jane's Information Group, p. 213. 

Brantley, S.R., 1990, The eruption of Redoubt Volcano, Alaska, 

December 14, 1989-August 31, 1990: U.S. Geological Survey 

Circular 1061, 33 p. 

Business and Commercial Aviation, 1989, May, p. 208-213. 

Eaves, J.L., and Reedy, E.K., 1987, Principles of Modem Radar: 

New York, Van Nostrand Reinhold Company, 712 p. 

Harris, D.M., and Rose, W.I., 1983, A radar method for estimating 

particle sizes, concentrations and total ashfall mass in volcanic 

ash clouds: Applications and comparisons with ashfall data: 

Journal of Geophysical Research, v. 88, p. 10969-10983. 

Harris, D.M., Rose, W.I., Roe, R., and Thompson, M.R., 1981, Radar observations of ash eruptions, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. Helens, 

Washington: U.S. Geological Survey Professional Paper 1250, 

p. 323-333. 

Nathanson, F.E., 1991, Radar Design Principles: Signal Processing 

and the Environment: New York, McGraw-Hill, 720 p. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

RADAR REMOTE SENSING OF VOLCANIC CLOUDS 

By William I. Rose and Alexander B. Kostinski 

ABSTRACT 

Ground-based meteorological radar systems have been 

very useful at tracking ash clouds for distances of several 

hundred kilometers from the radar station; however, aircraftbased radar with wavelengths of several centimeters does not 

detect volcanic ash clouds because ash particles are generally smaller than raindrops. Of even greater importance, 

ground-based radars represent the best known method for 

determining the height of ash clouds-these data are central 

to mitigating ash-cloud hazards. Although radar observations of ash clouds have been made only with radar systems 

designed for thunderstorms, it may be possible to design a 

volcanic-cloud radar system that would optimize parameters 

for volcanic clouds. An optimal system should have a wavelength range of 3 mm to 3 em, a range of about 300 km, a 

Doppler capability, and it should be portable. A principal 

contribution of ground-based radar could be the real-time 

determination of volcanic-cloud locations in three dimensions. Such data could be overlain on air traffic control monitors and could serve as initial input to cloud-dispersal 

models to allow trajectory forecasts for the first few hours 

after detection. 

INTRODUCTION 

Meteorological radar is a familiar tool for aviation. 

Ground-based meteorological radar systems exist at many 

airports to locate major storm clouds, and airborne radar systems help pilots avoid rain clouds. Recently, Doppler radar 

systems have been installed at airports to help identify windshear hazards. This paper is directed to the problem of how 

radar systems can help with the mapping of volcanic ash 

clouds. We review some uses of ground-based radar systems 

during ash eruptions and make recommendations about how 

radar systems can best contribute to a comprehensive plan 

for mitigating aviation hazards from ash clouds. 

METHODS OF STUDY 

The use of radar to observe ash eruptions is not widespread. In the United States, radar was used during the 1976 

eruptions of Augustine Volcano, Alaska (Johnston, 1976; 

Kienle and Shaw, 1979). During the Mount St. Helens activity of 1980-82, we had the opportunity to collect observations using National Weather Service (NWS) and Federal 

Aviation Administration (FAA) radar systems. These results 

were reported in detail by Harris and others (1981) and Harris and Rose (1983). A summary of those results is useful 

here to provide a basis for recommendations. 

SUMMARY OF RESULTS 

The May 18, 1980, eruption of Mount St. Helens produced an extensive ash cloud that was detected and mapped 

by the geostationary operational environmental weather satellites (GOES) and FAA radar systems (fig. 1). As the data 

show, the radar detects a smaller, presumably denser, portion 

of the ash cloud than that detected in the GOES image. Subsequent eruptions of Mount St. Helens during 1980-82 produced ash clouds that were much smaller than the May 18 

cloud. Some of these ash clouds were mapped by NWS radar 

at Portland, Oreg. The smallest eruption detected was the 

March 19, 1982, event, which was estimated to have produced about 4x1011 g of ash and, more importantly, lasted 

only 30-40 seconds (Harris and Rose, 1983). This eruption 

duration is 1,000 times shorter and its ash volume is more 

than 1,000 times smaller than the 5x1014-6x1014 g of ash 

produced on May 18, 1980. These data attest to the ability of 

meteorological radars to detect ash clouds that span a wide 

range of scales. Both of these eruptions probably had radar 

reflectivities that lie near the lower end of the wide dynamic 

range that is detectable by ground-based meteorological 

radar systems. 

ASH-CLOUD DETECTION 

Ash clouds and thunderstorms cause backscatter of 

some of the radar energy that is incident upon them. The 

reflectivity of a radar target is a function of the abundance of 

particles and their scattering cross section within the target. 

The reflectivity, T\, is the summation of the backscatter cross 

sections of the particles per unit volume averaged over the 

radar pulse volume (Atlas, 1964). For solid spherical 

391 
392 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

particles small enough to obey Rayleigh scattering, the backscattered reflectivity is equal to: 

6 5 I 

1

21t E-1 2 ~6 T\ = -- X -- £..Y A4 E+2 (1) 

where 

'A is the wavelength, 

E is the dielectric constant of the reflecting particles, and 

r is the radius of spherical particles. 

The expression for the received power (Pr) from a target composed of randomly distributed particles (ProbertJanes, 1962; Serafin, 1990) is: 

where 

P 0 is the peak transmitted power, 

h is the radar pulse length in space (distance), 

G is the actual gain of antenna, 

(2) 

e is the horizontal beam width to the -3-dB level for oneway transmission, 

<1> is the vertical beam width to the -3-dB level for oneway transmission, and 

R is the range. 

Some of the fundamental characteristics of ash clouds 

from the aviation perspective were reviewed by Rose 

(1987). Radar-target parameters calculated for a thin ash 

cloud that was sampled by a research aircraft (Rose and 

others, 1980) were compared by Harris and others (1981) 

with analogous parameters for warm orographic rain and 

thundershowers. The refractive index factor in equation 2 

(IE-1/£+212) for ash (0.36) is higher than for ice (0.197) and 

lower than for water droplets (0.93), and the sizes of particles in ash clouds are probably generally smaller than water 

droplets in rain clouds. Because of the r6 term in both 

equations, ash clouds generally are not as pronounced a 

radar reflector as storm clouds (the reflectivity factor is 

equal to L(2r)6, the summation of the sixth power of the 

particle radius for all the particles in a unit volume of target 

space). It is also for this reason that airborne radars, which 

have much lower transmitted power than ground-based systems, do not detect ash clouds well. 

CLOUD HEIGHT 

In addition to being useful for mapping the dense interiors of ash clouds, ground-based radar systems have also 

produced data about the heights of ash clouds (fig. 2). This 

data is obtained by observation of the range-height indicator 

(RHI) on the radar system, which can detect a sharp top 

boundary of the eruption cloud, particularly above the vent. 

This data is very valuable because the eruption-column 

height is a measure of the rate of eruption of magma (Wilson 

and others, 1978). Thus, a series of column-height measurements allow the mass and dynamics of an eruption to be 

directly monitored. 

When an ash cloud is dispersing in the atmosphere, the 

altitude of the cloud top above the vent represents information that is essential to aviation. Other methods of obtaining 

this data are flawed, particularly at stratospheric heights. 

Satellites are a proven way to track volcanic clouds (Krueger, 1983; Matson, 1984), and the satellite remote thermal 

sensing data of the temperature of cloud tops is very useful 

for determining the heights of clouds in the troposphere, 

where temperatures decrease regularly with height 

(Holasek and Rose, 1991 ). However, satellite remote-sensing methods do not always result in a unique solution for 

cloud-top heights at stratospheric levels, where temperatures do not decrease regularly with height (Schneider and 

Rose, this volume). Thus, radar systems appear to offer one 

of the best ways to obtain dependable column-height data. 

Because these data are vital inputs to dispersal models that 

forecast the movements of drifting clouds (Carey and Sigurdsson, 1982) and are needed for volcanologic reasons, a 

radar system appears to offer an important capability to 

address the ash cloud-aviation problem. 

CLOUD STRUCTURE 

A potentially critical contribution of radar systems to 

volcanology is the possibility of doing detailed study of the 

proximal structure of volcanic clouds. It is likely that direct 

observations of the "umbrella" region of eruption clouds 

(Sparks and others, 1986; Self and Walker, this volume) can 

be made using radar and that variations in eruptive activity 

can be directly monitored. Radar can also detect high-reflectivity regions below the main volcanic clouds that represent 

early fallout of coarse particles. It can also be used to measure apparent wind speed by detecting ash-cloud drifting and 

using a Doppler capability. 

Mapping and height determinations are the two simplest measurements that have been demonstrated by groundbased radar. It is also possible to recognize levels of reflection, as shown in the 16:40, 17:40, and 18:40 PDT (Pacific 

Daylight Time) images for the May 18, 1980, Mount St. 

Helens eruption (fig. 1 ). From these basic radar data, it is 

possible to determine or estimate a number of useful parameters such as: ( 1) the duration and rate of the eruption as a 

function of time, (2) the three-dimensional distribution of 

particle concentrations in the ash cloud, (3) the total mass of 

ash in the cloud, and ( 4) the locations and amounts of ashfall 

(Harris and Rose, 1983). 
,--·--------r 

j : 

WASHINGTON 

Sea ttl~ 

Spokane 

oJ 

I 

I 

\ \ ------\ 0'-/-..._;...--..../ 

Portland 0940 

RADAR REMOTE SENSING OF VOLCANIC CLOUDS 

,~---------r 

j : 

WASHINGTON I 

I 

I 

\ 

---\ 

,--·--------r 

j I 

I 

I 

393 

1240 

,-·- ·--------r-r---- J I 

I 

I 

r' 

'-./' 

,--·--------r-r------- J I 

,-------,----r-r--·---·-- J I 

OREGON 

MOU 

xST HELE 

'\ ------\ \ /-...__;....-..../ '\ ...... 1840 

I 

-' I 

\ 

1640 

,--·--------r-T 

j : I 

WASHINGTON I ' 

1-

-;WYO 

OREGON 

I 

,----------r-r 

j : I 

I WASHINGTON ' \ 

I \" 

I , \ 

MOUNT \ I '\ x ST HELENS IDAHO I 

\ /------\ r' 

.._/-...__;....-.... 2240 '\ 

/ 

I 

\ 

1740 

WASHINGTON 

MOUNT 

ST HELENS 

\ X ------\ 

.._/-...__;....-..../ 2040 '\ 

200 KILOMETERS 

I I 

Figure 1. Shape and structure of May 18, 1980, eruption cloud from Mount St. Helens (X), as depicted by Seattle and Spokane radar 

systems and NOAA geostationary weather satellite. The solid line outlines the visible cloud as observed by the weather satellite. Hourly 

tracings of radar reflections at level 1 are shown as light patterned areas; level-2 reflections are shown as dark patterned areas. Times 

shown are Pacific Daylight Time (PDT). Figure from Harris and others (1981). 
394 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

A RADAR SYSTEM FOR 

VOLCANIC ASH CLOUDS 

We now consider the feasibility of designing a radar 

system capable of detecting and monitoring volcanic ash 

clouds. In order to focus on the essential physics, we concentrate on the scattering process. The natural approach is to 

analyze the scaling allowed by the scattering equation ( eq. 

1). For a single particle, and in the Rayleigh regime appropriate for small particles, the backscattered reflectivity, 11, is: 

(3) 

where 

Dis the diameter of the scattering particle. 

There are three factors to consider here: 1/A. 4 wavelength 

dependence, D6 particle-size dependence, and the quadratic dependence on the dielectric constant (£) of the 

reflecting particles. 

Because we argue here that a shorter wavelength radar 

will be needed for volcanic applications, we need the£ values for these wavelengths. A representative value at 35 

GHz (about 8.6 mm) can be found in Ulaby and Elachi 

(1990). The permittivity (real part of£) is given between 

2.6 and 9.6 for volcanic materials (the imaginary part of£, 

the loss tangent-Ulaby and Elachi (1990)- is generally 

between 0.01 and 0.05). Calculation of the (£-1)/(£+2) factor shows that the volcanic-ash echo is about 1. 7 to 4.4 

times weaker than that of water, the rest of the conditions 

(size, distance, and wavelength) being the same. Let us 

therefore assume that the ash-detection system has a better 

sensitivity (e.g., a three-times-smaller minimal detectable 

signal) than a typical weather radar, and go on to consider 

the wavelength and size dependence. 

In the dipole (small-particle or Rayleigh) approximation, the backscattered intensity is proportional to the sixth 

power of the diameter (eq. 3). Thus, the largest ash particles 

present in the cloud are the main scatterers. The size distribution usually contains many fewer large particles than 

small ones because they typically have a lognormal distribution. The number of small particles does not increase fast 

enough to counteract the dependence on D6. Therefore, for 

this discussion, it is sufficient to assume that we deal with 

particles of a single size in the cases to be compared (e.g., 

rain and volcanic ash). 

Even in the heaviest of rains (150 mmlhr) there are no 

more than a 1,000 large drops between 4 and 5 mm in diameter per cubic meter. However, a volcanic ash cloud with an 

ash concentration of 1 g/m3 might have about 100,000 particles per cubic meter with sizes of 40 to 50 j.lm. The maximum size depends on the stage of cloud development, 

among other factors. 

I-~ en 

24 i~ ! 1 Maximum height exceeded 

I a: 20 1: limit of radar system <.9LU II -I- ~I LULU 16 I 

I~ I 

zo 12 I 

I 

~_J I 

I 3Q 8 I 

I 

oz I 

4 I u- 1::.. 

0 

0800 1000 1200 1400 1600 1800 2000 2200 

TIME 

Figure 2. Heights of the May 18, 1980, eruption column at 

Mount St. Helens, as determined by Portland radar. Heights are 

relative to sea level. Base value (triangle) is plotted at time eruption began at approximate altitude of the vent; it is followed by a 

value that exceeded the limit of the radar system (dashed line). 

Times shown are Pacific Daylight Time (PDT). Figure adapted 

from Harris and others ( 1981 ). 

In order to demonstrate the extreme sensitivity of radar 

observations to D6!A. 4, consider the following two cases: (1) 

largest raindrops of 5 mm and ash particles of 0.05 mm (size 

ratio, SR, equals 1 00), and (2) largest rain drops of 2 mm 

along with 200-j..lm (0.2-mm) ash particles (SR = 10). We 

assume, for simplicity, that the number of ash particles per 

unit volume in both comparisons is 100,000. 

In case 1 (SR = 1 00), the reflectivity per particle is 

lower by a factor of 1 o-12 for the ash than for rain because of 

the D6 factor. There are 100 times more ash particles per unit 

volume, which leaves a factor of 10-10. In order to compensate for this lowered reflectivity with the A. 4 dependence, one 

must take a fourth root of 1 o-1 0, which yields a wavelength 

(0.6 mm) that is 178 times smaller than that of a typical 

weather radar (10 em). 

However, repeating the same calculations for case 2 

(SR = 1 0) yields the decrease of A. by a factor of only 10 

(i.e., 5-mm radar). This is encouraging and probably 

explains the reasons for using millimeter radar in cloudphysics research (Atlas, 1990; Sauvegeot, 1992). Thus, at 

the number density of 100,000 particles per m3 for ash, 

200-j..lm ash particles can be detected 50- 100 km away (in 

the clear troposphere) by a millimeter weather radar system, but 20-j..lm particles cannot be similarly detected. This 

explains previous observations that describe the visibility 

of an ash cloud on a radar monitor and its gradual disappearance as larger particles fall out of the plume. The major 

disadvantage of millimeter-wavelength radars as opposed 

to centimeter radars is the high atmospheric absorption by 

oxygen and water vapor (Sauvegeot, 1992, p. 1 03). However, the range can be improved considerably by operating 

in atmospheric "windows" of 35, 95, 140, and 220 GHz, 

especially for near-vertical-pointing radars. 

Ideally, a ground-based radar should be placed at a site 

within range of the volcano and nearby airports where 
RADAR REMOTE SENSING OF VOLCANIC CLOUDS 395 

aircraft would be landing and taking off. An operating 

range of 300 km would be very useful and would allow 

flexibility for installation at a site with power and road 

access. Portability would be desirable because permanent 

siting of a radar would experience the disadvantage of long 

reposes between periods of activity. For example, a mobile 

radar in Alaska could be placed at Kenai (between Redoubt 

Volcano and Anchorage) during Redoubt or Spurr activity 

and could be moved to Homer (between Augustine Volcano and Anchorage) in the event of activity at Augustine 

(Hufford, this volume). 

Radar operators can be trained to identify ash clouds. 

Positions of potentially active volcanoes should be displayed as an overlay on radar monitor screens. Coordination with volcano observatories that monitor seismicity 

should be arranged so that radar operators are informed 

when eruptions are expected. Periodic, automated azimuthal and elevation scanning using an algorithm to eliminate ground clutter and to detect change could be 

performed as a useful routine procedure at radar systems 

with active volcanoes in range. Routine schemes should be 

designed to measure and track ash clouds automatically or 

semi-automatically once they are detected. 

Other useful features of a volcanic-cloud radar system 

would be Doppler and polarimetric capabilities. If the system were equipped with Doppler features, signal processing 

could extract radial-velocity information in the form of a 

Doppler power spectrum, which is related directly to the particle-size distributions in the ash cloud. The lack of information about grain size of the particles in the cloud presents a 

serious uncertainty that has been ignored in previous discussions. Thus, a Doppler radar would clarify an important 

uncertainty about ash clouds. Polarimetric radars are useful 

in shape analysis of particles. Because we are uncertain 

about the shapes of particles as they move in the drifting 

cloud, polarimetry could be a potentially important capability for a volcanic-ash-cloud radar system. 

CONCLUSIONS AND 

RECOMMENDATIONS 

Ground-based meteorological radar systems can provide valuable tracking information on drifting volcanic 

clouds at ranges of 50 to more than 500 km from the radar 

unit. Such ground-based radar systems currently offer the 

best known method of determining eruption-cloud heights, 

particularly if the ash cloud reaches the stratosphere. During 

eruptions this information is vitally needed in real time for 

accurate plume-dispersion forecasts and aviation routing. 

A radar system designed for volcanic-cloud detection 

and tracking should probably have a wavelength in the 

range of 3 mm to 3 em and a range of at least 300 km. Volcanic-cloud radar systems should be portable because long 

volcanic repose periods will likely occur during the life of 

the instrument, and relocation may be desirable to monitor 

other eruptions. 

Doppler radar systems now available offer the possibility of sensing the particle-size distribution in a volcanic 

cloud, information that cannot be easily obtained in other 

ways and that is important in assessing ash-cloud hazards 

and dispersion forecasts. 

ACKNOWLEDGMENTS 

The radar observations that formed much of the basis 

for this review came from papers by Harris and others (1981) 

and Harris and Rose (1983). The interest of Robert Roe of 

the National Weather Service at Portland, Oreg., and Martin 

Thompson at the NWS in Auburn, Wash., was essential to 

the observations. David M. Harris thoroughly reviewed the 

manuscript and made many helpful suggestions. 

REFERENCES CITED 

Atlas, D., 1964, Advances in radar meteorology, in Landsberg, 

H.E., and Van Mieghem, J., eds., Advances in Geophysics, 

Volume 10: New York, Academic Press, p. 317-479. 

--ed., 1990, Radar in Meteorology: Boston, American Meteorological Society, 806 p. 

Carey, S.N., and Sigurdsson, H., 1982, Influence ofparticle aggregation on deposition of distal tephra from the May 18, 1980 

eruption of Mount St. Helens volcano: Journal of Geophysical 

Research., v. 87, p. 7061-7072. 

Harris, D.M., and Rose, W.I., 1983, Estimating particle sizes, concentrations, and total mass of ash in volcanic clouds using 

weather radar: Journal of Geophysical Research, v. 88, p. 

10969-10983. 

Harris, D.M., Rose, W.I., Roe, R., and Thompson, M., 1981, Radar 

observations of ash eruptions, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. Helens, 

Washington: U.S. Geological Survey Professional Paper 1250, 

p. 323-333. 

Holasek, R.E., and Rose, W.l., 1991, Anatomy of 1986 Augustine 

Volcano eruptions as recorded by multispectral image processing of digital A VHRR weather satellite data: Bulletin of Volcanology, v. 53, p. 420-435. 

Johnston, D.A., 1976, Volatiles, magma mixing and the mechanism 

of eruption of Augustine Volcano, Alaska: Seattle, Wash., University ofWashington, unpub. Ph.D. dissertation, 177 p. 

Kienle, J., and Shaw, G.E., 1979, Plume dynamics, thermal energy 

and long-distance transport ofVulcanian eruption clouds from 

Augustine Volcano, Alaska: Journal of Volcanology and Geothermal Research, v. 6, p. 139-164. 

Krueger, A.J., 1983, Sighting of the El Chich6n sulfur dioxide 

clouds with the Nimbus 7 total ozone mapping spectrometer: 

Science, v. 220, p. 1377-1379. 

Matson, M., 1984, The 1982 El Chich6n volcano eruptions-A satellite perspective: Journal of Volcanology and Geothermal Research, v. 23, p. 1-10. 
396 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Probert-Jones, J.R., 1962, The radar equation in meteorology: 

Quarterly Journal of the Royal Meteorology Society, v. 88, p. 

485-495. 

Rose, W.I., 1987, Interaction of aircraft and explosive eruption 

clouds, a volcanologist's perspective: American Institute of 

Aeronautics and Astronautics Journal, v. 25, p. 52-58. 

Rose, W.I., Chuan, R.L., Cadle R.D., and Woods, D.C., 1980, 

Small particles in volcanic eruption clouds: American Journal 

of Science, v. 280, p. 671-696. 

Sauvegeot, H., 1992, Radar Meteorology: Boston, Artech House, 

366p. 

Serafin, R.J., 1990, Meteorological radar, in Skolnik, M., ed., Radar 

Handbook (2d ed.): New York, McGraw-Hill, p. 23.1-23.33. 

Sparks, R.S.J., Moore, J.G., and Rice, C., 1986, The initial giant 

umbrella cloud of the May 18, 1980 explosive eruption of 

Mount St. Helens: Journal of Volcanology and Geothermal Research, v. 28, p. 257-274. 

Ulaby, F.T., and Elachi, C., eds., 1990, Radar Polarimetry for Geoscience Applications: Norwood, Mass., Artech House, 364 p. 

Wilson, L., Sparks, R.S.J., Huang T.C., and Watkins, N.D., 1978, 

The control of volcanic column heights by eruption energetics 

and dynamics: Journal of Geophysical Research, v. 83, p. 

1829-1836. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

TRACKING OF REGIONAL VOLCANIC ASH CLOUDS 

BY GEOSTATIONARY METEOROLOGICAL 

SATELLITE (GMS) 

By Yosihiro Sawada 

ABSTRACT 

Visible and infrared images from the Japanese geostationary meteorological satellite (GMS) have detected ash 

clouds generated by large volcanic eruptions in Kamchatka, 

Kurile Islands, Japan, Philippines, Indonesia, and Marianas 

since its launch in late 1977. Even though the GMS detection 

rate of ash clouds for eruptions that occurred within the GMS 

field of view was around 13 percent, ash clouds that are 

ejected to high altitudes, are widely dispersed, and may 

threaten aviation safety, have been tracked well in GMS 

images. Discrimination of ash clouds from atmospheric 

clouds and the tracking of small, thin ash clouds were not possible due to the limitations of the GMS' s detector for spectrum analyses and ground resolution. Tentative estimations 

of altitudes of cloud tops and thermal energy releases of eruptions have been made from analyses of the imagery data. 

INTRODUCTION 

Using visual observations from the ground or air, it is 

very difficult to observe and track the extent of volcanic ash 

clouds that are widely dispersed at high altitudes. Satellite 

imagery offers the opportunity for viewing large regions 

covered by ash clouds (Sudradjat, 1989). The GMS carries a 

detector known as the visible and infrared spin-scan radiometer (VISSR). The ground resolution of VISSR is 1.25 km 

and 5 km in the visible and infrared bands, respectively, and 

the wavelength is 0.5-0.75 j.lm for the visible band and 

10.5-12.5 j.lm for the infrared band. Whereas the GMS 

detector's ground resolution is limited, it has a very wide 

field of view, and its short time interval between images 

compared to that of polar-orbiting satellites makes it very 

effective for tracking eruption clouds. 

Through careful examination of GMS images, the rate 

of detection of ash clouds within the field of view of GMS 

has been evaluated. Estimates of the heights of tops of ash 

clouds were determined by analyses ofGMS's digital data of 

infrared images. The results are applied to estimates of thermal energy release by ash clouds in order to evaluate the 

strengths of volcanic eruptions. Variations in eruption intensity are judged by evaluating intensified or weakened ash 

clouds over the volcano. Heights of cloud tops, estimated 

from image data, are compared to those observed from the 

ground, and discrimination of ash clouds from ambient atmospheric clouds is attempted using combinations of visible and 

infrared digital data from ash clouds and atmospheric clouds. 

METHODS OF STUDY 

Detection and tracking of ash clouds for a number of 

eruptions between 1977 and 1991 were conducted by carefully examining successive GMS images near volcanoes, 

following notification of big volcanic eruptions (e.g., 

Sawada, 1987). At first, existence of volcanic-like clouds 

very near or over the volcano is sought in infrared images, 

then it is checked whether the volcanic-like cloud appears in 

the visible image during day time-in this case, the top surface of an eruption cloud containing ash particles may show 

a dark-toned surface compared to ambient atmospheric 

clouds. Drift direction of the ash cloud is determined by 

examining a sequence of images, and the width and length of 

the ash cloud are measured. Duration of the volcanic eruption can be judged by inspecting whether the ash cloud continues to originate at the site of the volcano or whether it has 

already detached and moved away from the volcano. 

Estimation of the altitude of the ash cloud is made using 

the assumptions that the top of an ash cloud under the tropopause shows the coldest temperature and the surface temperature at high altitude coincides with ambient air temperature. 

Therefore, the height of the top of an ash cloud can be estimated using the air-temperature profile from radio-sounding 

observations near the volcano (Sawada, 1983a, 1983b, 

1985a, 1985b, and 1987). 

Evaluation of the strength of a volcanic eruption was 

made by estimating the thermal energy released by the ash 

cloud and by applying the following experimental equation 

proposed by Briggs (1969) for the case of a thermal plume: 

397 
398 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

(1) 

where 

Q is the thermal energy release rate in megawatts, 

llh is the height of ash cloud in meters above the crater, 

u is the mean wind velocity in meters per second at the 

top altitude, and 

x is the horizontal distance from the crater in meters. 

The horizontal distance is used under the condition of x ~ 

50h, where h is the altitude of the plume source, even 

though the limiting condition for applying Briggs's equation 

is x ::;; 1 Oh. The duration time of the volcanic explosion was 

estimated based on analyses of eruption-cloud data and 

from published information from the bulletins of the Global 

Volcanism Network (GVN) of the Smithsonian Institution 

(McClelland, this volume; McClelland and others, 1989) 

and from the Bulletin of Volcanic Eruptions (BYE) published by the Volcanological Society of Japan. The thermal 

energy release (Eth, in ergs) by ejected materials was calculated in the case of juvenile materials by the following equation, proposed by Yokoyama (1957), using abbreviated 

values for the parameters in the equation proposed by Nakamura (1965): 

Eth = (M) ((TC) +H) (4.18x107) (2) 

where 

M is the total mass of ejecta in grams, 

T is the difference in temperature (assumed to be 600°C) 

between ejected materials and ambient air temperature, 

Cis the specific heat (0.25 cal/g°C), and 

His the latent heat of melting (10 cal/ g). 

Discrimination of ash clouds from ambient atmospheric 

clouds was tried using numerical data for albedo and the 

temperature of surfaces for both ash clouds and atmospheric 

clouds because several examples of ash clouds showed darktoned surfaces in visible-band GMS images. 

RESULTS AND OBSERVATIONS 

Ash clouds produced by strong eruptions at 23 volcanoes have been detected in GMS images through 1985 

(Sawada, 1987). Thereafter, ash clouds from large eruptions at nine volcanoes were detected through June 1991 

(fig. 1). Table 1 is a list of eruption clouds detected in GMS 

images. Examples of ash clouds detected after 1986 are 

shown in figures 2-7. 

Table 1. List ofmajor ash clouds detected with OMS images, December 1977 through June 1991. 

[OMS, geostationary meteorological satellite. a.s.l., above sea level] 

Data nertaining to highest ash cloud 

Date Volcano Cloud top Length Width 

(kma.s.L2 (km) (km) 

1981 

Apr. 27-May 25 Alaid, Kurile Is. 12 2300 270 

May 14-15 Pagan, Mariana Is. 16 250 220 

Apr. 5-0ct. 14 Galunggung, Java 18 150 90 

Aug. 26-Nov. 10 Soputan, Sulawesi 15 170 70 

Oct. 24-25 Lopevi, New Hebrides 13 190 80 

July 23-Aug. 26 Una Una, Sulawesi 17 160 120 

May 25-26 Soputan, Sulawesi 16 260 170 

Aug. 31 Soputan, Sulawesi 15 410 310 

Sep. 10-0ct. 2 Mayon, Luzon 16 200 70 

Jul~ 30 Sangeang AEi ~Sunda Is.) 14 130 100 

1986 

Nov. 19-20 Chikurachiki, Kurile Is. 8 380 90 

Nov. 21 Izu-Oshima, Izu Is. 8 150 40 

1988 

May 8-9 Banda Api, Banda Sea 17 80 80 

Jul~ 29-31 Makian, Halmahera ~Kie Besi) 16 120 50 

1990 

Feb. 10 Kelut, Java 17 300 230 

1991 

June 12 Pinatubo, Luzon 14 140 130 

June 14-15 Pinatubo, Luzon ~28 2,800 1,700 
TRACKING REGIONAL VOLCANIC ASH CLOUDS BY GEOSTATIONARY METEOROLOGICAL SATELLITE 399 

s 

Figure 1. Distribution of volcanoes for which ash clouds have 

been detected in GMS images (December 1977-June 1991). Bold 

line denotes limits of GMS ground coverage. 

Most ash clouds do not show clear differences in GMS 

images from atmospheric clouds. However, several examples do show the dark-toned surfaces of ash clouds in visibleband images, as in the cases of ash clouds of the 1988 eruption of Banda Api, the 1988 eruption of Makian, and the 

1991 eruption of Pinatubo (figures 4, 5, and 7). The ash 

clouds of the 1981 Alaid eruption were well discriminated 

from ambient atmospheric clouds in visible-band images 

because of their dark-toned surfaces-this may be due to 

ash-rich contents (Sawada, 1983a, 1987). 

The ash clouds show various shapes in GMS images 

under the influence of different prevailing winds at different altitudes. In general, the extent of an ash cloud influenced by slow wind velocities (<about 10 m/s) appears as 

a wide, fan-shaped region, but the cloud extent becomes 

narrow with strong winds(> about 20 m/s) (Sawada, 1987). 

In the case of the ash cloud from the 1990 Kelut eruption, 

very large scale ash clouds were seen over and around the 

volcano in GMS images (fig. 6). The eruption was a very 

large event (Sudradjat, 1991 ), but this large-scale cloud 

may have developed due to active convection by rising ash 

clouds over the volcano. 

The ash cloud during the 1986 Izu-Oshima eruption 

was detected in GMS images (fig. 3). The height of the cloud 

top estimated from image data was 8-9 km, but the observations from the ground and photographic data showed the top 

altitude to be 12-14 km. The reason for the difference was 

due to the warm surface temperature of the cloud top compared to the ambient air temperature at that altitude, which 

Figure 2. Eruption cloud from the November 1986 eruption of 

Chikurachiki Volcano, Russia. Cloud is drifting to the east from the 

volcano. A, Infrared-band image at 22:30 UTC, November 19, 

1986. B, Infrared-band image at 00:00 UTC, November 20, 1986. 

C, Visible-band image taken at 00:00 UTC, November 20, 1986. 

Note dark-toned eruption cloud in C. Eruption clouds are indicated 

by white arrows. 
400 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 3. Eruption cloud from the November 1986 eruption of 

Izu-Oshima, Japan. Cloud is drifting to the east. A, Infrared-band 

image at 09:00 UTC, November 21, 1986. The north rim of the 

cloud appears over the tip of the Boso Peninsula due to GMS's parallax angle. B, Infrared-band image at 10:30 UTC, November 21, 

1986. Eruption clouds are indicated by white arrows. 

leads to an underestimation of the altitude of the cloud top. It 

may be possible that very active thermal emissions were 

occurring on the surface of the developing ash clouds. The 

northern edge of the ash cloud seen in the GMS image was 

located on the tip of the Boso Peninsula, but the same cloud 

was observed at almost the same time in imagery from the 

National Oceanic and Atmospheric Administration (NOAA) 

polar-orbiting satellite that was obtained over the volcano. In 

the NOAA imagery, the edge of the cloud was about 14 km 

off the tip of the peninsula. Therefore, the underestimated 

cloud top determined from the GMS imagery could be corrected by using the parallax of GMS. 

The ash clouds of the 1986 Izu-Oshima eruption were 

also well detected by Japan Meteorological Agency's 

(JMA's) weather radars at Fuji, Haneda, Tokyo, and 

Nagoya. Fuji radar has a wavelength of 10 em, whereas the 

Figure 4. Eruption cloud from the May 1988 eruption of Banda 

Api, Indonesia. A, Infrared-band image at 23:00 UTC, May 8, 1988. 

B, Visible-band image at 23:00 UTC, May 8, 1988. Circular and 

dark-toned eruption cloud showing ring-shaped textures can be seen 

in B. Eruption clouds are indicated by white arrows. 
TRACKING REGIONAL VOLCANIC ASH CLOUDS BY GEOSTATIONARY METEOROLOGICAL SATELLITE 401 

Figure 5. Eruption cloud from the July 1988 eruption ofMakian, Indonesia. Infrared-band images taken on July 29, 1988 at A, 03:00 UTC 

and B, 06:00 UTC. Visible-band images taken on the same date at C, 03:00 UTC and D, 06:00 UTC. Cloud is drifting to the southwest from 

the volcano in the 03:00 UTC images (A and C). The detached cloud, southwest of the volcano, extended to the south, as shown in 06:00 

UTC images (B and D). Dark-toned eruption cloud is seen in C and D. Eruption clouds are indicated by white arrows. 

other stations have 5-cm radar (fig. 8). The ash clouds appear 

as dense rain clouds in these weather radars, and the top 

height of the clouds was determined to be at altitudes of9-12 

km (fig. 9). Although the number of examples is limited, 

dense ash clouds can be measured with weather radars; however, thin ash clouds are not observed. Detection of these 

dense ash clouds depends on ash content. 

During day time, visible-band images can sometimes 

identify individual eruption clouds that are generated by 

intermittent eruptions: ash clouds appear as dark-toned surfaces owing to high ash content. For example, GMS visibleband images detected many large, discrete, dark-toned ash 

clouds from the June 15, 1991, Pinatubo eruption, showing 

strong individual eruptions (fig. 7). There were clear circular 

and linear textures on the surfaces of the giant eruption 

clouds (Tokuno, 1991 ). 

Based on the number of volcanoes that erupted and the 

number of eruption clouds detected in GMS images during 

the period from December 1977 through June 1991, the 

detection rate of eruption clouds with OMS was 13.3 percent 

(table 2) (Sawada, 1989a, 1989b ). For GMS, the detection 

limit of the extent of ash clouds was 20 by 30 km under very 

good weather conditions for visible-band imagery, and the 

detection limit of the altitude of ash clouds was 4--5 km 

(Sawada, 1989b ). This low detection rate is due largely to the 

limitation of ground resolution and the difficulty in discriminating ash clouds from atmospheric clouds with VISSR data. 

The thermal energy releases calculated from analyses 

of ash-cloud data and the mass of ejected materials show 

good agreement (fig. 1 0) and suggest the possibility that the 

strength of volcanic eruption may be estimated from ashcloud data. 

Table 2. Detection rate of ash clouds with GMS images within 

the GMS field ofview, December 1977 through June 1991. 

[GMS, geostationary meteorological satellite. Data from Bulletin of Volcanic Eruptions (Volcanological Society of Japan), Scientific Event Alert Network Bulletin 

(Smithsonian Institution), and Global Volcanism Network Bulletin (Smithsonian 

Institution)] 

Number of eruptions 

Number of eruption clouds detected 

Detection rate 

332 

44 

13.3% 
402 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 6. Eruption cloud from the February 1990 eruption ofKelut, Indonesia. Infrared-band images taken on February 10, 1990, at A, 

06:00 UTC; B, 09:00 UTC; C, 15:00 UTC; and, D, on February 11, 1990, at 00:00 UTC. Initial, small eruption cloud rapidly expanded-this 

can be seen in A, B, and C. Eruption clouds are indicated by white arrows. 

Discrimination of ash clouds from atmospheric clouds 

and the evaluation of ash content in ash clouds have been 

attempted, but good resolution has still not been achieved 

(Sawada 1987) because GMS' s detection of single bands in 

infrared and visible wavelengths cannot separate the optical 

features of eruption clouds from those of atmospheric clouds. 

CONCLUSIONS AND 

RECOMMENDATIONS 

GMS images can detect and track widely dispersed 

ash clouds from large volcanic eruptions. Due to the short 

time interval (30 minutes to 1 hour) between images, 

dynamic assessment of ash-cloud development is possible. 

The detection rate for low-altitude clouds (below about 10 

km) is only about 13 percent, due largely to the limitation 

of the imaging system and the characteristics of the radiometer. However, widely dispersed ash clouds reaching altitudes higher than 10 km were almost always detectable and 

were well tracked in GMS images. 

Under the influence of strong prevailing winds, ash 

clouds that had detached from the site of a volcano after major 

activity faded and became elongated in the wind direction. 

There are differences between maximum altitudes of ash 

clouds estimated based on the temperature of the top surface 

of the cloud and those altitudes as observed from the ground. 

Some of the differences may be due to active thermal emissions on the top surface of ash clouds-this will cause underestimation of cloud-top altitudes. The underestimated cloud 

top of the 1986 Izu-Oshima eruption could be corrected using 

the GMS's parallax. 
TRACKING REGIONAL VOLCANIC ASH CLOUDS BY GEOSTATIONARY METEOROLOGICAL SATELLITE 403 

Figure 7. Eruption cloud from June 1991 eruption ofMt. Pinatubo, Philippines as seen on visible-band images taken at A, 01:00 UTC, 

June 15, 1991, and B, 02:00 UTC on the same date. Dark-toned ash clouds drifting to the west from the volcano were obtained at short 

time intervals during maximum activity- these images show the frequent occurrence of strong explosions. Eruption clouds are indicated 

by white arrows. 

Figure 8. Ash cloud from the November 1986 eruption of IzuOshin:a, Japan (located at tip of white arrow), obtained at 08:30 

UTC on November 21 with the weather radar at Haneda station 

(white circle), which is about 90 km NNE. of the crater. VS, S, M, 

and W in "gray" scale refer to the intensity of radar echo as very 

strong, strong, medium, and weak (this relative scale is applicable 

to rain clouds). The intensity of the radar echo from the eruption 

cloud grades from weak at the outer edge of the cloud to areas of 

medium and strong intensity near the center of the cloud. 

Figure 9 (facing column). Observations of the altitude of ashcloud tops for the November 21, 1986, eruption of Izu-Oshima, 

Japan. A, Data at 08:10 UTC, November 21, 1986, from weather radar at Fuji, which is about 96 km NW. of the crater. B, Data at 08:14 

UTC on the same date from weather radar at Tokyo, which is about 

105 km NNE. of the crater. Cloud tops are indicated by white arrows. 

20 

10 

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404 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

z 

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EXPLANATION 

1 Alaid (1981) 

2 Pagan (1981) 4 

3 Asama (1982) • 4 Galunggung (1982) 

5 Soputan (1982) 7 

6 Lopevi ( 1982) • 

7 Una Una (1983) 9 1 

8 Soputan (1984) • • 2. 

9 Mayan (1984) 5 

• 8 

• 

6 

• 

3 

• 

I I I I 

1021 1022 1023 1024 

THERMAL ENERGY RELEASE BASED 

ON TOTAL MASS OF EJECTED 

MATERIAL, IN ERGS 

1025 

Figure 10. Relationship between thermal energy release based on 

ash-cloud data from GMS visible and infrared imagery (vertical axis) and thermal energy release based on total mass of ejected material reported in McClelland and others (1989) and by the annual 

Bulletin of the Volcanological Society of Japan (horizontal axis). 

Weather radar can detect dense ash clouds and can 

determine their height; however, the detection rate is very 

low. Thermal energy release estimated from ash-cloud data 

was in good agreement with estimates based on the volume 

of erupted materials. This indicates the possibility of evaluating the strength of volcanic eruptions from eruption-cloud 

data obtained from satellite imagery. 

Discrimination of ash clouds from ambient atmospheric 

clouds was usually not possible using GMS' s visible and 

infrared data, except for dark-toned clouds in visible-band 

images in which ash content was high. Further acquisition of 

data on optical features of ash clouds are needed for discrimination of ash clouds from atmospheric clouds and for estimation of ash content in ash clouds. Further improvement of 

ground resolution and the establishment of a multispectraldetector capability for VISSR are needed to improve the 

detection rate of ash clouds. 

ACKNOWLEDGMENTS 

The author expresses his cordial thanks to Dr. Christopher G. Newhall and Dr. Thomas J. Casadevall of the 

U.S. Geological Survey for providing the opportunity to 

attend the Seattle Symposium. He also expresses cordial 

thanks to the reviewers for their careful and scientific revisions of his manuscript. 

REFERENCES CITED 

Briggs, G.A., 1969, Plume rise: Springfield, Va., U.S. Department 

of Commerce, National Technical Information Service, AEC 

Critical Review Series, TID-25075, 81 p . 

McClelland, L., Simkin, T., Summers, M., Nielsen, E., and Stein, 

T.C., 1989, Global Volcanism 1975-1985: The First Decade of 

Reports from the Smithsonian Institution's Scientific Event 

Alert Network (SEAN): Englewood Cliffs, N.J., Prentice Hall, 

655 p. 

Nakamura, K., 1965, Energies dissipated with volcanic activities-Classification and evaluation: Bulletin of the Volcanological Society of Japan, 2nd ser., lOth Anniversary, p. 81-90 

[in Japanese with English abstract]. 

Sawada, Y., 1983a, Analysis of eruption clouds by the 1981 eruptions of Alaid and Pagan Volcanoes with GMS images: Papers 

in Meteorology and Geophysics, v. 34, no. 4, p. 307-324 [in 

Japanese with English abstract]. 

---1983b, Attempt on surveillance of volcanic activity by eruption cloud image from artificial satellite: Bulletin of the Volcanological Society of Japan, 2nd ser, v. 28, no. 4, p. 357- 373 [in 

Japanese with English abstract]. 

---1985a, Detection capability of eruption clouds and observations of eruption sequences by GMS images: Journal of theRemote Sensing Society of Japan, v. 5, no. 3, p. 207-224 [in 

Japanese with English abstract]. 

--- 1985b, GMS observation of eruption clouds of the 1984 

September-October Mayon eruption: Philippine Journal of 

Volcanology, v. 2, p. 143-155. 

---1987, Study on analyses of volcanic eruptions based on 

eruption cloud image data obtained by the geostationary meteorological satellite (GMS): Technical Reports of the Meteorological Research Institute, no. 22, 335 p. 

---1989a, Regional monitoring of eruption clouds, and estimation of amount of air-borne ejecta, using satellite imagery: Proceedings of Kagoshima International Conference on 

Volcanoes, p. 539- 542. 

---1989b, The detection capability of explosive eruptions using 

GMS imagery, and the behavior of dispersing eruption clouds, 

in Latter, J.H., ed., IAVCEI Proceedings in Volcanology 1, 

Volcanic Hazards: International Association of Volcanology 

and Chemistry of the Earth's Interior, p. 233- 245. 

Sudradjat, A., 1989, Volcanic eruption monitoring using space platforms: Journal of the Indonesian Association of Geologists, v. 

12, p. 437-448. 

----1991, A preliminary account of the 1990 eruption of the Kelut Volcano: Geologische Jahrbuch, v. Al27, p. 447-462. 

Tokuno, M., 1991, GMS-4 observations of volcanic eruption 

clouds from Mt. Pinatubo, Philippines: Meteorological Satellite Center Technical Note, no. 23, p. 1-14. 

Yokoyama, 1., 1957, Energetics in active volcanoes: Bulletin of 

Earthquakes Research Institute, 2nd paper, no. 35, p. 75-97. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

OBSERVATIONS OF THE 1989-90 REDOUBT 

VOLCANO ERUPTION CLOUDS USING AVHRR 

SATELLITE IMAGERY 

By David J. Schneider and William I. Rose 

ABSTRACT 

The 1989- 90 eruptions of Redoubt Volcano, Alaska, 

generated ash clouds that reached altitudes of as much as 

12 km and provided an opportunity to test and refine the 

use of the advanced very high resolution radiometer 

(A VHRR) for satellite remote sensing of volcanic eruption 

clouds. Several aircraft encountered dispersed volcanic 

clouds, including a Boeing-747 that temporarily lost power 

from all four engines. Such near-tragic incidents highlighted the need for improved methods of discriminating 

and tracking volcanic clouds. 

Thirty-one A VHRR images from various stages of the 

Redoubt eruption were examined. In the early, more energetic phases of the eruption, the Redoubt volcanic clouds 

could be discriminated by a technique that employs an 

apparent temperature difference between bands 4 and 5 of 

A VHRR. This method was particularly successful in clouds 

that were older than 1 hour, demonstrating that slight aging 

of the cloud during dispersal enhances its discrimination by 

this method. In the later stages of Redoubt activity, this 

method fails, probably because of environmental variables 

associated with the changing character of the eruption. The 

ash clouds associated with dome collapses that marked the 

later Redoubt clouds were of small volume and may not have 

contained as high a proportion of fine ash particles. 

Laboratory biconical reflectance measurements were 

conducted to determine the spectral variability of ash that 

fell out of the Redoubt clouds. The results show that ash 

reflectance is controlJed more by particle size than by particle composition, but these alone do not explain the variability we observed in the satellite data. 

INTRODUCTION 

Satellite remote sensing of volcanic clouds is an important tool for scientists and those engaged in mitigating natural hazards. The total ozone mapping spectrometer (TOMS) 

has been used to measure the so2 released by eruptions 

(Krueger, 1983; Krueger and others, this volume), and 

multispectral image processing of advanced very high resolution radiometer (A VHRR) data has succeeded in discriminating volcanic clouds from weather clouds (Hanstrum and 

Watson, 1983; Prata, 1989a; Holasek and Rose, 1991). Perfection of image-processing algorithms and identification of 

primary physical parameters controlling success of the algorithms could lead to operational use of A VHRR data in 

reducing dangerous encounters between aircraft and volcanic clouds (Rose, 1987; Casadevall, 1990; Steenblik, 1990) 

and for monitoring the global dispersion of large atmospheric injections by volcanoes. 

This paper attempts to advance satellite-based volcaniccloud sensing through analysis of A VHRR data collected 

during the Redoubt eruptions of 1989-90. In particular, it 

tests a volcanic-cloud-discrimination algorithm developed 

by Holasek and Rose (1991) for the 1986 eruption of Augustine Volcano. Redoubt and Augustine Volcanoes, located in 

the Cook Inlet area of Alaska (Kienle, this volume), both 

erupted during the winter and early spring and have similar 

·chemical compositions. 

A VHRR satellite images collected during various 

stages of the Redoubt eruption were analyzed to test the utility of cloud-discrimination algorithms. In addition, the spectral variability of the Redoubt volcanic clouds were 

investigated through analysis of biconical reflectance measurements of samples of ash fallout and crushed pumice, 

glass, and minerals separated from Redoubt Volcano. 

AVHRRSENSOR 

The AVHRR sensor, aboard the National Oceanic and 

Aeronautics Administration (NOAA) polar-orbiting weather 

satellites since 1978, has been used in the study of several 

eruptions (Kienle and Shaw, 1979; Hanstrum and Watson, 

1983; Matson, 1984; Malingreau and Kaswanda, 1986; 

Glaze and others, 1989; Holasek and Rose, 1991 ). A VHRR 

data from NOAA-10 and NOAA-11 were used to study the 

Redoubt eruptions. This sensor images a 2,800-km-wide 

swath with a spatial resolution of 1.1 km at the nadir. The 

AVHRR sensor aboard NOAA-10 has four bands: band 1, 

405 
406 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

visible (0.58-0.68 jlm); band 2, near-infrared (0.73-l.IO 

jlm); band 3, mid-infrared (3.55- 3.93 jlm); and band 4, thermal-infrared (1 0.3-I1.3 jlm), whereas the A VHRR sensor 

aboard NOAA-II contains the previous bands plus band 5, 

thermal-infrared (11.5- I2.5 jlm). Each satellite passes over 

a point on the ground twice per day, with more frequent coverage occurring at high latitudes where the orbits converge at 

the poles. The large swath width, frequent coverage, and 

multispectral capability make the A VHRR sensor a useful 

instrument for studying volcanic clouds. 

THE 1989-90 ERUPTION OF 

REDOUBT VOLCANO 

Redoubt Volcano is an andesitic composite volcano 

located in the Cook Inlet region of Alaska, approximately 

200 km southwest of Anchorage (fig. 1). In mid-December 

1989, Redoubt erupted for the first time since I966. During 

the next 5 months, there were more than 20 eruptive episodes, which produced ash clouds reaching greater than 12-

km altitude (table I) (Brantley, I990). Scott and McGimsey 

(in press) estimate the total tephra-fall volume to be 

2xi07-4xi07 m3, dense-rock equivalent, and note that two 

different tephra types were produced. Pumiceous tephra was 

generated by magmatically driven explosions on December 

I4 and I5, and fine-grained lithic-crystal tephra was erupted 

starting on December I6 and during all later events. The 

lithic-crystal tephra was generated by two processes: hydrovolcanic explosions dominated from December I6 to 19, and 

pyroclastic flows, resulting from dome collapse, became an 

increasingly important process from January 2, I990, to the 

end of eruptive activity in April. Pyroclastic flows were the 

only mechanism generating tephra during the last five eruptive episodes (Scott and McGimsey, in press). 

More than 60 percent of Alaska's population lives in the 

Cook Inlet region. Major oil facilities are also located in this 

region, and Anchorage is a major hub of air traffic between 

Asia and Europe. There were four incidents of commercial 

aircraft encountering volcanic clouds, including one incident 

in which a Boeing 747 carrying 246 people lost power from 

all four engines after flying through a cloud (Casadevall, 

1990). The aircraft lost more than 4 km of altitude before two 

engines were restarted at 5.2 km- the remaining engines 

were restarted at about 4.1 km (Przedpelski and Casadevall, 

this volume). The aircraft was extensively damaged (Steenblik, 1990), and the incident highlighted the need for new 

techniques to detect and track volcanic clouds. 

MULTISPECTRAL IMAGE 

PROCESSING OF THE A VHRR IMAGES 

More than 30 images of the Redoubt region were collected from the archive at the NOAA National Environmental 

Table 1. Chronology of the 1989- 90 eruption of Redoubt Volcano. 

[Modified from Brantley (1990). X, volcanic activity occurred; na, not applicable; ?, 

volcanic activity uncertain; cont., continuous; fr., from] 

TY£e of volcanic activity 

Da!: Time1 E~losion2 Dome collaEse Plume hei~t 

December 1989 

14 9:47 X(l7) na >IOkm 

15 1:40 X(12) na ? 

3:48 X(10) na ? 

10:15 X(40) na >12 km 

16-18 (Nearly cont. ejection of tephra fr. crater) <7 km 

19 6:30 X~92 na >9km 

January 1990 

2 17:48 X(26) X >12km 

19:27 X(61) X >12 km 

8 10:09 X(15) X >12 km 

11 10:01 X(5) ? >9km 

13:42 X(12) ? ? 

16 22:48 X~132 ? >11 km 

February 1990 

15 4:10 X(20) X >10km 

21 12:32 X(6) X 9km 

24 5:05 X(4) X 9km 

28 9:47 X~ 52 X 8km 

March 1990 

4 20:39 X(8) X 12 km 

9 9:51 X(IO) X IOkm 

14 9:47 X(14) X 12km 

23 4:04 X(8) X >IOkm 

29 10:33 X~72 X ? 

April1990 

6 17:23 X(7) X 9km 

15 14:49 X(8) X >IOkm 

21 18:11 X(4) X >8km 

1 Alaska Standard Time. 2 Numbers in parentheses indicate duration of explosive 

activity in minutes, based on seismicity. 

Satellite Data and Information Service (NESDIS) and from 

the University of Alaska's Geophysical Institute following 

the eruption; 11 images are described in detail in this paper 

(table 2). In several cases, eruptive episodes are recorded in 

multiple images, providing an opportunity to track the ash 

clouds from the initial eruption through the dispersion of the 

volcanic clouds. 

Image processing of the AVHRR scenes was conducted 

using Erdas and Terascan on a Sparc-1 +workstation. Images 

of the Redoubt region were extracted from the full scene; the 

thermal channels were calibrated using the procedure of Kidwell (1991 ); and the images were georeferenced to a common projection. Following the technique of Prata (1989a) 

and Holasek and Rose (1991), algebraic manipulations were 
OBSERVATIONS OF REDOUBT VOLCANO ERUPTION CLOUDS USING A VHRR SATELLITE IMAGERY 407 

Table 2. Satellite images of Redoubt volcanic clouds used in this 

study. 

[LUT (look-up table) represents image channel color rendition in red (R), green (G), 

and blue (B)] 

Date and Color, LUT Satellite Cloud type2 

start time (GMT1) R G B 

12/16/89 12:18 4m5 3 4 NOAA-11 

12116/89 13:59 4m5 3 4 NOAA-11 

12118/89 21:55 4m5 3 4 NOAA-11 

12118/89 23:37 4m5 3 4 NOAA-11 

01/08/90 19:28 4 4 4 NOAA-10 2 

01/08/90 23:13 3m4 3 4 NOAA-11 3 

02115/90 13: 17 4 4 4 NOAA-11 2 

02115/90 18:26 3m4 2 NOAA-10 3 

03/23/90 13:25 4 4 4 NOAA-11 2 

03/23/90 18:11 3m4 2 NOAA-10 3 

03/23/90 23:24 3m4 2 NOAA-11 3 

1 Greenwich Mean Time. Local time is GMT minus 9 hours. 2 See text for discussion of cloud types. 

performed on A VHRR bands 4 and 5 to enhance the volcanic 

clouds and distinguish them from weather clouds. Ratios of 

band 4 to band 5 and differences between band 4 and band 5 

were calculated and evaluated. The subtraction process 

results in an "apparent temperature difference," which we 

find particularly useful. The term "apparent temperature difference" is defined as the difference between temperature 

values derived from emitted energy measured at 10.5-11.3 

!J.m (band 4) and 11.5- 12.5 !J.m (band 5). The temperature 

difference is not real, but rather it is the result of differential 

emission of energy at these two wavelengths. When the emittance is converted to a temperature value, it produces an 

apparent temperature difference. An example of the band-4-

minus-band-5 operation is shown in figure 2. In figure 2A- B, 

the single-band images are quite similar, and the volcanic 

plume is not very distinct. The plume is greatly enhanced by 

the band subtraction operation (fig. 2C), which generally 

produced better results, in terms of plume discrimination, 

than the ratio operation. When these operations were not successful, or when using data from NOAA-I 0 (which does not 

contain band 5), ratios and differences of band 3 and band 4 

were calculated. 

The results of these mathematical operations were 

visually evaluated to determine their ability to enhance volcanic clouds. False-color composites were generated on 

24-bit graphic monitors by displaying algebraic enhancements along with several of the A VHRR bands in the red, 

green, and blue image planes of the monitor. False-color 

composites are helpful in interpreting the extent of the volcanic cloud because data from the individual bands interact 

to increase enhancement of the cloud. The various band 

combinations used to produce the false-color composites 

are shown in table 2. 

OBSERVATIONS OF THE 

A VHRR IMAGES 

For the purpose of description and discussion, the 

Redoubt volcanic clouds shown in the satellite images are 

divided into three classes that are chosen on the basis of cloud 

spectral properties, morphology, and size. It is not implied 

that these cloud types will be produced by eruptions of other 

volcanoes or that they are the only type that will be produced. 

The classes include: 

Type-] volcanic c/ouds.-Clouds generated by magmatic explosions during the first week of activity (while there 

was a nearly continuous ejection of tephra from the crater). 

These clouds were low ( < 7 km) and extended for hundreds 

of kilometers from the vent. Examples of this cloud type are 

shown in figure 3. 

Type-2 volcanic c/ouds.-Clouds generated in part by 

dome collapse and subsequent pyroclastic flows (Scott and 

McGimsey, in press). These short-duration, discrete eruptive 

events were imaged within minutes of the onset of eruption. 

The type-2 clouds are higher(> 10-12 km) than type-1 clouds 

and have a distinctive, circular morphology. Examples of 

these clouds are shown in figure 4. 

Type-3 volcanic c/ouds.-Dispersed type-2 clouds. 

These clouds were imaged several hours after the initial 

eruptive event and show the dispersion of clouds produced 

by a single eruptive pulse. Examples of these clouds are 

shown in figure 5. 

Although volcanic clouds were discriminated from 

weather clouds in many cases, no single algorithm was successful in enhancing all three cloud types. For the type-1 

clouds, the band-4-minus-band-5 operation of Prata (1989a) 

and Holasek and Rose ( 1991) worked to discriminate portions 

of the volcanic cloud from the weather clouds (fig. 3A-D). 

This operation was successful for both daytime and nighttime 

images, but the discrimination is enhanced in the daytime 

images when band 3 data are included. All of the false-color 

composites in figure 3 were produced using identical band 

combinations (table 2), but a dramatic difference can be seen 

between the nighttime images from December 16 (fig. 3A-B) 

and the daytime images from December 18 (fig. 3C-D). Band 

3 of the A VHRR sensor (3.53-3.93 !J.m) is a hybrid band, 

measuring thermal emittance at night and a combination of 

reflectance and emittance during the day. In the nighttime 

images, the enhanced portion of the volcanic cloud is red, 

indicating that the enhancement is solely caused by the band4-minus-band-5 subtraction operation. By contrast, the volcanic cloud in the daytime images is yellow, indicating that the 

enhancement is a result of both the subtraction operation and 

high band 3 reflectance of the volcanic cloud with respect to 

the weather clouds. 

The distal portions of two of the type- I volcanic clouds 

were enhanced more than the proximal portions (fig. 3A-B). 

Near the vent, the volcanic cloud is spectrally similar to the 

weather clouds seen at the bottom of the image-the 
408 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

60 

• HAYES 

MT SPURR 

~ CRATER 

PEAK 

LAKE CLARK • 

NATIONAL PARK L ~- ] ~c . .r 

AND PRESERVE ~ •

1 

REDOUBT 

VOLCANO. 

0 

I 

0 

12/25/89-38 

12/25/89-2a 

GULF 

0 F 

ALASKA 

50 MILES I I 

50 KILOMETERS 

Figure 1. Index map of the Cook Inlet Region of Alaska. Sample locations of the ash spectra shown in figure 6 are indicated by solid 

circles. Figure modified from Brantley ( 1990). 
OBSERVATIONS OF REDOUBT VOLCANO ERUPTION CLOUDS USING AVHRR SATELLITE IMAGERY 409 

subtraction operation is successful once the cloud disperses. 

Note that, in both cases, the subtraction operation is successful once the cloud has been transported approximately 

100 km, or about 1 hour, from the vent. A z-shaped bend in 

the unenhanced portion of the volcanic cloud (east of 

Kenai) seen in figure 3A can be seen in figure 3B as an 

enhanced portion of the volcanic cloud. This image was 

collected about 1 hour after the previous image (fig. 3A) 

and shows that the discrimination becomes more distinctive 

as the volcanic cloud disperses. 

In some cases, the effectiveness of the band-4-minusband-5 operation in discriminating dispersed volcanic 

clouds is influenced by the underlying surface. Holasek and 

Rose (1991) found that their algorithm was more successful 

in discriminating volcanic clouds over water than over 

land, and effects of the underlying surface are observed in 

several images from Redoubt. In figure 3A, the discrimination of the volcanic cloud is distinct where the cloud passes 

over the western Kenai Peninsula and over the water of 

Prince William Sound, but the cloud is not apparent where 

it passes over the snow-covered mountains. In figure 3C, 

the discrimination of the cloud is reduced where it overlies 

low clouds over land. 

Whereas the band-4-minus-band-5 difference was successful in discriminating type-1 volcanic clouds, this operation was not successful with type-2 clouds. These clouds are 

shown in figure 4 as band-4 thermal images, and they were 

identified by their anomalously low temperature 

(220°- 230°K), their circular morphology, and their location 

relative to the vent. An inverted grayscale has been applied 

to the images in figure 4 so that details of the cold volcanic 

clouds are discernible. 

These images were collected between 7 and 21 minutes 

after the onset of the eruption, as determined by seismicity 

(Brantley, 1990), and show that the cloud is detached from 

the vent, supporting the interpretation of Scott and McGimsey (in press) that these volcanic clouds were generated by 

Figure 2 (right). NOAA-11 A VHRR images demonstrating the 

discrimination of a volcanic eruption cloud from weather clouds. 

Image was collected on December 18, 1989, at 23:37 GMT. All images are shown with an inverted grayscale, so that cold objects are 

bright and warm objects are dark. A, AVHRR band-4 image showing an indistinct plume from Redoubt and weather clouds throughout the scene. B, A VHRR band-5 image. C, The result of a band-4-

minus-band-5 operation. Note that the volcanic plume is a bright 

feature and that the weather clouds appear gray to black. 
410 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 3. False-color composite A VHRR images oftype-1 eruption clouds from Redoubt Volcano. All of the color composites were produced using band 4 minus band 5 in red, band 3 in green, and band 4 in blue. See text for description of cloud types. A, NOAA-11 image 

collected on December 16, 1989, at 12:18 GMT. B, NOAA-II image collected on December 16, 1989, at 13:39 GMT. C, NOAA-11 image 

collected on December 18, 1989, at 21:55 GMT. D, NOAA-11 image collected on December 18, 1989, at 23:37 GMT. 
OBSERVATIONS OF REDOUBT VOLCANO ERUPTION CLOUDS USING AVHRR SATELLITE IMAGERY 411 

dome collapse and pyroclastic flows. Dispersal of these 

clouds and transformation into type-3 clouds are monitored 

in subsequent images, and the observations of these clouds 

are discussed below. 

Even though it appears that the volcanic clouds show 

variation in cloud-top topography, this cannot be quantified. It is possible to determine cloud-top elevation and 

topography by relating the temperature of the cloud, as 

determined by one or more thermal bands of the satellite 

sensor, with a temperature profile of the atmosphere as 

determined by radiosonde or other methods. Altitude values 

for each cloud pixel can be determined in this manner. 

Whereas this method is useful for tropospheric clouds, it is 

unsuccessful at higher altitudes due to the temperature 

inversion that defines the tropopause. All of the type-2 volcanic clouds penetrated the stratosphere, which starts at 

about 1 0-km altitude during the Arctic winter, limiting 

height estimates of clouds to a minimum value and preventing the determination of cloud-top topography. 

The frequent coverage of the NOAA satellites provided 

opportunities to observe the transport and dispersion of the 

Redoubt volcanic clouds. These dispersed, type-3, volcanic 

clouds were enhanced by a band-3-minus-band-4 operation. 

The dispersed volcanic cloud from the January 8, 1990, 

eruptive episode is seen in figure 5A. This image was collected about 5 hours after the start of the eruption seen in figure 4A and shows a yellow, comma-shaped cloud extending 

from north of Anchorage to the southern coast of the Kenai 

Peninsula and a more dilute, hazy cloud extending back 

toward the vent. The volcanic cloud is shown in yellow, indicating that the enhancement results from a combination of 

the band-3-minus-band-4 operation and high band-3 reflectance of the volcanic cloud with respect to weather clouds. 

Figure 4 (left). Inverted grayscale AVHRR band-4 thermal images oftype-2 eruption clouds from Redoubt Volcano. See text for 

description of cloud types. A, NOAA-10 image collected on January 8, 1990, at 19:28 GMT. B, NOAA-11 image collected on February 15, 1990, at 18:26 GMT. C, NOAA-11 image collected on 

March 23, 1990, at 13:25 GMT. 

Figure 5 (following pages). False-color composite A VHRR images oftype-3 eruption clouds from Redoubt Volcano. See text for 

description of cloud types. All of the color composites, except A, 

were produced using band 3 minus band 4 in red, band 2 in green, 

and band 1 in blue. A, NOAA-11 image collected on January 8, 

1990, at 23:13 GMT. This color composite was produced using 

band 3 minus band 4 in red, band 3 in green, and band 4 in blue. B, 

NOAA-10 image collected on February 15, 1990, at 18:26 GMT. 

C, NOAA-10 image collected on March 23, 1990, at 18:11 GMT. 

D, NOAA-1 I image collected on March 23, 1990, at 23:24 GMT. 
412 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 
OBSERVATIONS OF REDOUBT VOLCANO ERUPTION CLOUDS USING A VHRR SATELLITE IMAGERY 413 
414 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

The band-4-minus-band-5 operation was not successful in 

discriminating this cloud, and theories regarding the failure 

of this operation are included in the discussion. 

Another type-3 cloud, from the February 15, 1990, 

eruptive episode, is seen in figure 5B. The image was collected about 5 hours after the initial eruption seen in figure 

4B and consists of a linear, light-red cloud extending from 

the bottom of the image back toward the volcano, in the 

upper left of the image. At this time, the cloud front had traveled more than 800 km to the southeast over the Gulf of 

Alaska. Even though the band-3-minus-band-4 operation 

was useful in enhancing the volcanic cloud, some of the 

weather clouds have a similar spectral signal. In this case, 

manual image interpretation is needed to define the limits of 

the volcanic cloud. This image was collected by NOAA-1 0, 

which contains one thermal band, so it was not possible to 

attempt the band-4-minus-band-5 operation. 

A third type-3 volcanic cloud, from the March 23, 

1990, eruption, is seen in two successive images, one 

NOAA-10 image collected 5 hours after the initial eruption 

(fig. 5C) and a NOAA-11 image collected 5 hours later 

(fig. 5D). In figure 5C, the circular volcanic cloud front has 

traveled about 450 km, and a tail trails back toward the 

vent. The band-3-minus-band-4 operation was used to 

enhance the volcanic cloud, but the clarity of the enhancement is diminished by multiple data line dropout along the 

northern boundary of the volcanic cloud. 

In the NOAA-11 image acquired 5 hours later (fig. 5D), 

the continued dispersal of the volcanic cloud can be seen. 

The cloud front now extends for more than 825 km, from 

near the vent to the Bering Sea. Once again, the band-3-

minus-band-4 operation helped to enhance the volcanic 

cloud, but it did not discriminate it from the weather clouds 

along the top of the scene. The northward bend in the cloud 

seen in this image is also apparent in the previous image (fig. 

5C) and may be due to wind shear. Ash fallout from this 

eruption is visible as a dark band that trends west for about 

300 km and is correlated to the distribution of ash on the 

ground as mapped by Scott and McGimsey (in press). 

REFLECTANCE SPECTRA OF 

VOLCANIC ASH 

The reflectance properties of 19 volcanic ash samples 

from Redoubt were investigated to see how they varied with 

transport, and how they varied throughout the eruption. 

These samples were collected by personnel of the Alaska 

Volcano Observatory in the weeks to months following the 

eruption. All of the ash samples used in this study were collected from snowpits throughout Alaska (fig. 1) and were 

correlated by Scott and McGimsey (in press) to eruptive 

events by their stratigraphic position. The ash was separated 

from the snow by melting and filtration, eliminating any sulfuric-acid coatings that may have been present. 

To aid in interpretation of the ash reflectance spectra, 

glass and mineral separates were also prepared. Pumice fragments from the December 15, 1989, eruptive event were 

crushed mechanically, and glass and crystals were separated 

using heavy-liquid-separation techniques. The pumice, crystal, and glass separates were sieved to produce a 0.25-mm to 

0.088-mm sample, and subsets of these samples were 

crushed to produce a sample ofless than 0.088 mm. This was 

done to reflect the reduction in grain size and the fractionation of the crystals with respect to glass that occurs as volcanic clouds age and are transported. The crystal separates 

were composed primarily of plagioclase, with lesser 

amounts of hornblende and pyroxene. 

Laboratory biconical reflectance measurements were 

conducted on the ash samples and mineral separates by the 

Jet Propulsion Laboratory (JPL) (J. Crisp, JPL, oral commun., 1991). Although the AVHRR sensor measures emitted 

energy, reflectance measurements can be related to emittance, which is difficult to measure in the laboratory (Bartholomew and others, 1989). Kirkoff's law states that, for a 

given temperature and wavelength, emittance and reflectance are complementary. This law only applies to solid 

objects because scattering is ignored. Although this is a 

major simplification, we use it to correlate reflectance measurements to the emittance recorded by the satellite sensor. 

Biconical reflectance spectra of ash fallout from eruptions on December 15, 1989, December 16, 1989, and from 

January 8, 1990, are shown in figure 6A-C. These reflectance spectra are typical ofthe 19 ash samples that were measured and show two reflectance peaks of interest to this 

study. The first peak extends from 3 J.Lm to 5 J.Lm and contains 

AVHRR band 3, whereas the second peak extends from 8 

J.Lm to 12 J.Lm and contains A VHRR bands 4 and 5. In the 

region containing A VHRR band 3, the reflectance varies by 

10- 15 percent between eruptive episodes, and, for the 

December 15, 1989, event, the reflectance increases by 20 

percent as the distance from the vent increases. In contrast, 

all of the samples show a broad similarity in reflectance in 

the region containing A VHRR bands 4 and 5, except for the 

sample suite from the December 15, 1989, event, where the 

reflectance increases by 1- 2 percent with increasing distance 

from the vent. 

The reflectance spectra of the pumice and the glass and 

crystal separates are shown in figure 7A-B. All ofthe coarsegrained samples (fig. 7A) show a reflectance peak at 9 J.Lm. 

The reflectance at 9 J.Lm is less prominent for the crystal separate and the pumice sample, and the glass separate has a 

smaller reflectance peak at 11.5 J.Lm. The fine-grained samples (fig. 7 B) show a much-diminished reflectance peak at 9 

J.Lm for the glass separate and none for the pumice sample 

and crystal separate. The peak at 11.5 J.Lm is most prominent 

for the glass sample, but the pumice and crystal separates 

also have a broad peak in this region. These spectra show 

that reflectance is influenced more by particle size than by 

particle composition. 
OBSERVATIONS OF REDOUBT VOLCANO ERUPTION CLOUDS USING AVHRR SATELLITE IMAGERY 415 

60 

50 

40 

30 

20 

10 

0 

A 

60 

Iz 

w 50 u 

0:: 

w 

a... 40 

z 

w~ 30 

u 

z 

<( 20 Iu 3 w 

....J 10 u.. 

w 

0:: 

0 

B 

60 

50 

40 

30 

20 

10 

4 6 

C WAVELENGTH, IN MICROMETERS 

Figure 6. Biconical reflectance plot of ash samples from three 

eruptions of Redoubt Volcano. The band widths of A VHRR bands 

3, 4, and 5 are indicated. Sample locations are shown in figure 1. A, 

Four ash samples from the December 15, 1989, eruption. B, Three 

ash samples from the December 16, 1989, eruption. C, Four ash 

samples from the January 8, 1990, eruption. 

1-

z 

w 

u 

0:: 

w 

a... 

z 

10 

8 

6 

4 

2 

0 

I I 

- ,.,.. 

/ '" .. I,,~""\--·, ( '" .... \ 

I I ·, \ - I, \ ', ' 

I ·'; "' '._ I ' I 

/// \ I 

,, I: I \ .... 

- tj"" 

I 

f- EXPLANATION 

---- Glass 

-- Crystals 

------- Pumice 

I I 

w~ A 

~ 10 

~ u 

w 

....J 

u.. 

w 

0:: 8 

6 

4 

2 

0 

I I 

-

fI'"""' 

I \..,_r~ 

f--- (_, f'...:/ \: .,f/"-

~ rlr 

j 

I I 

8 9 10 

I I 

., ''"' 

·-, \ 

'-,\ -~ 

'\, 

"\. ".: 

\.Jv, v~ '~ 

'~\ ~\: ·e.~ 

4 5 

I I 

I I 

If, ~'---"' 

'. \ 

I v ''\ 

r.t'-t-:~ ;? f(;-:s:;.. \ I\ \ ', 

'\ \ . 

\':~ 

\ 

4 5 

I I 

11 12 

B WAVELENGTH, IN MICROMETERS 

-

-

-

~= 

-

-

-

\ '-'2 -

13 

Figure 7. Biconical reflectance plots of pumice, glass, and crystal 

separates from Redoubt Volcano. A, Sieved 0.25-0.88-mm samples. B, Sieved> 0.088-mm samples. The band widths of A VHRR 

bands 4 and 5 are indicated. 
416 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

DISCUSSION 

The spectral discrimination of volcanic clouds is complicated by dynamic processes that occur during the eruption, transport and dispersion of the cloud-these processes 

may prevent the use of a single image-processing algorithm 

for use on all volcanic clouds. Previous researchers (Prata, 

1989a, 1989b; Holasek and Rose, 1991) have utilized differences and ratios of A VHRR bands 4 and 5 to discriminate 

volcanic clouds from weather clouds, but these operations 

were only partially successful at Redoubt. It has been shown 

that the band-4-minus-band-5 subtraction operation produces positive apparent temperature differences (.Ll T) for 

weather clouds and negative apparent temperature differences for volcanic clouds (Yamanouchi and others, 1987; 

Prata, 1989b). However, positive apparent ~T's can occur 

for volcanic clouds if the cloud contains a large amount of 

water or if the particle size is large (Prata, 1989b ). 

The early eruptions of the Redoubt series (type-1 

clouds) more closely resemble the kinds of ash clouds that 

are likely to be of most concern to aviation safety than do 

the later ones. Two important features of these early clouds 

are the success of the discrimination algorithm based on 

apparent ~ T determined from bands 4 and 5 and the indication that, for success of the algorithm, the cloud must have 

aged (dispersed freely in the atmosphere) for 1 hour or 

more. Several observations point to the role of fine silicate 

particles in explaining these phenomena. Biconical reflectance data suggest that fine particle size may enhance the 4-

minus-5 effect, and magmatic explosions resulting from 

explosive vesiculation may be more likely to produce fine 

ash than dome collapse. Aging of a volcanic cloud will 

result in decreasing the grain size of suspended ash because 

fallout will remove larger particles, and it will also tend to 

reduce the water or ice in the cloud, thereby enhancing the 

relative importance of the fine ash particles. Because the 

largest and most broadly hazardous ash clouds are magmatic (and are likely to generate drifting ash clouds that 

contain significant concentrations of fine ash) these observations are likely to be of general applicability. 

The band-4-minus-band-5 operation produced positive 

Ll T's for both volcanic and weather clouds in images oftype2 volcanic clouds from Redoubt, which were collected 

within 30 minutes ofthe start of the eruption. These volcanic 

clouds probably contained large amounts of water, due to the 

entrainment of moist air from the lower atmosphere, and 

were identified in band-4 thermal images by their proximity 

to Redoubt, their circular morphology, and cold temperature 

(fig. 4A-C). Volcanic clouds of this type could be confused 

with convective weather clouds, but this is unlikely in winter 

Arctic images. In two of the images (fig. 3A-B) of type-1 

clouds, the band-4-minus-band-5 operation produced positive ~T's for the proximal portion of the cloud and negative 

~T's for distal portions of the cloud. The region of negative 

.LlT is shown in red in figure 3A-B. We attribute the change 

in the spectral signature of this volcanic cloud to a decrease 

in particle size and water content during transport. Analysis 

of wind-speed data for this eruption indicates that the transition from positive to negative difference values in the volcanic cloud took about 1 hour. 

Type-3 volcanic clouds were difficult to discriminate, 

perhaps due to their relatively small volume and the dispersion and sedimentation of ash that occurred before they 

were imaged. Whereas many volcanic clouds can be discriminated using the band-4-minus-band-5 operation, the 

concentration of ash required to produce a detectable signal 

is unknown. Another factor that affects the subtraction 

operation is particle size. The type-3 clouds may have contained fewer fine particles than the type-1 clouds because 

they were produced as part of a dome collapse, rather than 

from a purely explosive, volatile, effervescent mechanism, 

thus reducing the ash signal. 

The band-3-minus-band-4 operation was useful in 

enhancing type-3 clouds, but it did not discriminate them 

from weather clouds. This operation was more successful 

during the daytime hours, when band-3 backscatter is important, than at night, when this band has a larger thermal component. Although this is a useful operation, it is difficult to 

make general observations regarding its success because the 

reflectance is dependent on a number of factors, including 

particle size, shape and abundance, sun azimuth and elevation, and the location of the cloud and the satellite relative to 

the sun. However, this operation, used in conjunction with 

observations of cloud morphology, can be used to interpret 

the extent of probable volcanic clouds. 

The use of ash fallout reflectance measurements as 

"ground truth" for interpreting satellite imagery has several 

shortcomings. One fundamental problem is that the reflectance measurements were made on ash fallout, which by definition is not what is in the volcanic cloud. Very fine 

particles are probably the most important, yet their collection 

is difficult because their fallout may be too light to be distinguished on the ground, and the particles fall out long distances from the vent over very broad areas. Another problem 

lies in relating the reflectance measurements to the emittance 

recorded by the sensor. Volcanic clouds are heterogeneous 

assemblages of particles and gases; therefore, subtracting the 

reflectance measurements from a black body of the appropriate temperature is a poor approximation. Additional work 

needs to be done to determine the most effective way of 

· using reflectance measurements of ash fallout as "ground 

truth" for image interpretation. 

In spite of these difficulties, the mineral separate spectra show that reflectance is controlled more by particle size 

than by the particle composition. In a volcanic cloud, this 

would imply that the discrimination of distal clouds would 

be controlled more by the reduction in the size distribution of 

the particle with transport than by the increase in the proportions of volcanic glass in the cloud due to eolian fractionation. Although the exact relationship of reflectance to 
OBSERVATIONS OF REDOUBT VOLCANO ERUPTION CLOUDS USING A VHRR SATELLITE IMAGERY 417 

emittance is unknown, the effects of particle size, particle 

shape, and particle composition would probably be enhanced 

for suspended particles. In this case, the complex shape of 

glass particles compared to crystals may have an important 

effect on the emittance of volcanic clouds. 

This study has shown that the discrimination of volcanic clouds using A VHRR imagery is more complex than 

previously thought and has identified several parameters 

that contribute to this complexity. These include cloud 

water content and particle size, concentration, and composition. Additional factors not included in this study include 

the role of acid aerosols (Prata, 1989a) and sensor viewing 

geometry. The relative importance of each of these parameters can be investigated in laboratory experiments utilizing 

an imaging radiometer to observe simulated volcanic 

clouds. Images can be collected at the same wavelength 

intervals as the A VHRR sensor, and image-processing 

operations similar to the ones described in this paper can be 

conducted. Results of the laboratory studies can be used to 

guide future work on thermal imaging and particle and gas 

sampling of actual volcanic clouds. 

CONCLUSIONS 

Volcanic clouds of a variety of types and scales were 

observed and mapped by A VHRR images during the 

Redoubt eruptions of 1989-90. These examples broaden the 

experience on volcanic cloud tracking and discrimination 

using multispectral image-processing techniques and provide insight on additional work that needs to be conducted. 

A major conclusion of this paper is that volcanic clouds 

have natural variability that is reflected in satellite images 

and that affects the methods used to discriminate and map 

their dispersion. This variability is magnified for activity 

like that of Redoubt Volcano, which changed eruptive mechanism during its period of activity. Most ash-producing 

eruptions from other volcanoes, particularly the larger ones, 

are more likely to resemble the early (type-1) clouds of 

Redoubt. This is encouraging because the simple method of 

discrimination of volcanic clouds using apparent temperature differences between A VHRR bands 4 and 5 works well 

on type-1 clouds; therefore, the simplest methodology is 

likely to be useful in many of the most serious cases. Discrimination of volcanic clouds using the band-4-minusband-5 operation is difficult or impossible for very young 

clouds with high water content and (or) a large particle size, 

but it is very useful for drifting volcanic clouds. A major 

uncertainty of this method is the particle concentration 

required to produce a measurable signal. 

Ash reflectance is controlled more by particle size than 

by particle composition. The fractionation of glass and crystals in a volcanic cloud are not likely to produce reflectance 

and emittance differences on their own, but fractionation 

will operate in conjunction with the proportional increase of 

fine particles as the cloud disperses. Laboratory reflectance 

measurements are inadequate to explain the spectral variability observed in the imagery of the Redoubt volcanic 

clouds. Emittance measurements need to be made of simulated volcanic clouds in the laboratory and in situ measurements and particle sampling need to be conducted on actual 

volcanic clouds to provide "ground truth" for interpretation 

of satellite imagery. 

ACKNOWLEDGMENTS 

We would like to thank the following people and organizations for their cooperation and support for this study. 

Mike Matson of NOAA/NESDIS provided most of the 

A VHRR data, and Ken Dean of the University of Alaska's 

Geophysical Institute provided several AVHRR scenes. Joy 

Crisp of the Jet Propulsion Lab made the ash reflectance 

measurements, and the Alaska Volcano Observatory furnished field support. This study was funded in part by NSF 

Grant 91-17726 and NASA Grant 1442-VC1P-011-91. 

REFERENCES CITED 

Bartholomew, M.J., Kahle, A.B., and Hoover, G., 1989, Infrared 

spectroscopy (2.3-20 J.Lm) for the geological interpretation of 

remotely sensed multispectral infrared data: International Journal of Remote Sensing, v. 10, p. 529-544. 

Brantley, S.R., ed., 1990, The eruption of Redoubt Volcano, Alaska, December 14,1989-August 31, 1990: U.S. Geological Survey Circular 1061, 33 p. 

Casadevall, T.J., 1990, The 1989-90 eruption of Redoubt Volcano, 

Alaska, impacts on aircraft operations in the vicinity of Anchorage [abs.]: Eos, Transactions, American Geophysical 

Union, v. 71, p. 1701. 

Glaze, L.S., Francis, P.W., Self, S., and Rothery, D.A., 1989, The 

16 September 1986 eruption of Lascar Volcano, north Chile, 

satellite investigations: Bulletin of Volcanology, v. 51, p. 

911-923. 

Hanstrum, B.N., and Watson, A.S., 1983, A case study of two eruptions of Mount Galunggung and an investigation of volcanic 

cloud characteristics using remote sensing techniques: Australian Meteorological Magazine, v. 31, p.l71-177. 

Holasek, R.E., and Rose, W.I., 1991, Anatomy of 1986 Augustine 

Volcano eruptions as revealed by digital A VHRR satellite imagery: Bulletin of Volcanology, v. 53, p. 420--435. 

Kidwell, K.B., ed., 1991, National Oceanic and Atmospheric Administration Polar Orbiter Data Users Guide: Washington, 

D.C., National Oceanic and Atmospheric Administration/National Environmental Satellite Data and Information Service, 

294p. 

Kienle, J., and Shaw, G.E., 1979, Plume dynamics, thermal energy 

and long-distance transport ofVulcanian eruption clouds from 

Augustine Volcano, Alaska: Journal of Volcanology and Geothermal Research, v. 6, p. 139-164. 
418 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Krueger, A.J., 1983, Sighting of the El Chichon sulfur dioxide 

clouds with the NIMBUS 7 total ozone mapping spectrometer: 

Science, v. 220, p. 1377-1379. 

Malingreau, J.P., and Kaswanda, 1986, Monitoring volcanic eruptions in Indonesia using weather satellite data: The Colo eruption of July 28, 1983: Journal of Volcanology and Geothermal 

Research, v. 27,p. 179-194. 

Matson, M., 1984, The 1982 El Chichon Volcano eruptions-A satellite perspective: Journal of Volcanology and Geothermal Research, v. 23, p. 1-10. 

Prata, A.J., 1989a, Observations of volcanic ash clouds in the 10--12 

J..Lm window using A VHRR/2 data: International Journal of Remote Sensing, v. 10, p. 751-761. 

---1989b, Infrared radiative transfer calculations for volcanic 

ash clouds: Geophysical Research Letters, v. 16, p. 

1293-1296. 

Rose, W.I., 1987, Interaction of aircraft and explosive eruption 

clouds: A volcanologist's perspective: American Institute of 

Aeronautics and Astronautics Journal, v. 25, p. 52-58. 

Steenblik, J.W., 1990, Volcanic ash: A rain of terra: Air Line Pilot, 

v.59,p.9-15,p.56. 

Salisbury, J.W., and Walter, L.S., 1989, Thermal infrared (2.5-13.5 

J..Lm) spectroscopic remote sensing of igneous rock types on 

particulate planetary surfaces: Journal of Geophysical Research, v. 94, p. 9192-9202. 

Scott, W.E., and McGimsey, R.G., in press, Character, mass, distribution, and origin of tephra-fall deposits of the 1989-90 eruption of Redoubt Volcano, south-central Alaska: Journal of 

Volcanology and Geothermal Research. 

Yamanouchi, T ., Suzuki, K., and Kawaguchi, S., 1987, Detection of 

clouds in Antarctica from infrared multispectral data of 

A VHRR: Journal of the Meteorological Society of Japan, v. 

65, p. 949-961. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

APPLICATION OF CONTEMPORARY GROUND-BASED 

AND AIRBORNE RADAR FOR THE OBSERVATION OF 

VOLCANIC ASH 

By Melvin L. Stone 

ABSTRACT 

Radar detection and tracking of volcanic ash from 

Mount St. Helens demonstrated the usefulness of real-time 

surveillance of ash clouds. The radars used were operational 

National Weather Service (NWS) magnetron systems. The 

low radar reflectivity reported for volcanic ash clouds makes 

the detection and characterization of the potential threat to 

aviation a formidable task. The NWS is procuring pulsed 

Doppler radars with enhanced sensitivity that may find 

application in volcanic ash cloud surveillance. Contemporary airborne weather radars lack the capability to detect volcanic ash and provide warning information. An overview of 

radar principles and technical issues related to observing volcanic ash illustrates the capabilities and limitations of radar 

in this application. Azimuth and elevation scanning strategies are presented. A technique is discussed for measuring 

wind speed and particle fall velocity when an ash cloud 

passes over the radar. The functional elements of a digital 

radar processor are described to acquaint users with their 

potential. The WSR-88D (NEXRAD) is recognized as the 

most suitable candidate for volcanic ash cloud surveillance, 

both because of its sensitivity and its planned deployment in 

the vicinity ofthe Cascade Range and in Alaska. A candidate 

radar for research on volcanic ash is suggested. 

INTRODUCTION 

Recent aircraft encounters with volcanic ash have 

renewed interest in the examination of the capability of 

radar to detect and characterize ash clouds. Successful use 

of National Weather Service (NWS) and Federal Aviation 

Administration (FAA) radars during the Mount St. Helens 

eruptions (fig. 1) demonstrated their ability to generate 

information of scientific value and their potential use in 

providing warnings to aviation (Harris and others, 1981; 

Harris and Rose, 1983; Rose, 1987). This report considers 

the capabilities and limitations of ground-based radars that 

will become operational during the 1990's as they apply to 

providing data useful in generating aviation warnings of 

volcanic ash. The inability of airborne weather radar to 

detect volcanic ash is noted. 

The scientific and aviation interests in applying radar 

to the monitoring of volcanic activity include determining 

(1) whether an eruption is occurring, (2) the eruption height 

versus time (to use in estimating the rate of eruption), (3) 

cloud dimensions and altitude range as a function of time, 

( 4) estimates of successive cloud positions and boundaries 

and initial trajectories (i.e., tracking and prediction), and (5) 

when the initial explosive pulse has ended (Harris, this volume; Rose, 1987). 

Volcanic ash detection must be capable of providing 

wide area coverage to serve the needs of aviation. Owing to 

its small particle size, density, and dielectric constant, the 

low radar reflectivity of ash clouds may limit the range of 

ground-based radars to a few hundred kilometers. Noting 

that ash fall and aircraft damage have been reported more 

than 1,000 km from Mt. Pinatubo (Casadevall and De Los 

Reyes, 1991), it is clear that hazard-area coverage by direct 

detection of the ash cloud by a single, ground-based, 

100-200-km-range radar is not possible. 

Eruptions of Mt. Pinatubo (Pinatubo Volcano Observatory Team, 1991) and Mount St. Helens (Newell and 

Deepak, 1982) produced ash layers at several different altitudes that traveled in different directions. Because it is 

unlikely that distal ash clouds, which might be a threat to jet 

aircraft, will have sufficient particle size and density to be 

detectable by radar, it is necessary that proximal observations be made to determine the disposition of clouds for use 

in long-range forecasting. It should be noted that clouds that 

are several hours old still can have particle concentrations of 

1 g/m3 or higher in the cloud core along the plume axis, 

which will aid in radar detection (Harris, this volume). 

If appropriately located with respect to the erupting volcano, the radar can detect and track the ash cloud and provide 

data to a warning network (Rose and Kostinski, this volume). Owing to the varied winds aloft, an important role for 

a radar operating near an erupting volcano is to report the 

altitude of ash cloud layers to the meteorological and aviation forecasting centers where the information can be combined with wind profiler (Leary, 1992) and satellite 

observations to develop an operationally useful two- or 

three-dimensional record of the disposition and motion of 

419 
420 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

0 

OREGON 

I ' ... 200 KILOMETERS 

EXPLANATION 

Extent of eruption cloud as observed by: 

B NWS level-1 radar 

NWS level-2 radar 

0 NOAA weather satellite 

Figure 1. Radar and satellite depictions of Mount St. Helens eruption clouds on 18 May 1980 at 17:40 PDT as observed by Seattle 

and Spokane radar systems and NOAA weather satellite. The disparity in coverage between the two sensor systems indicates the 

need for multiple-radar and multi-sensor surveillance of volcanic 

ash. The radar reports may be understated due to omission of echoes 

whose signal strength was less than NWS (National Weather Service) level 1 and may be due to possible blockage by mountains east 

of Spokane. From Harris and others (1981). 

the volcanic ash. Satellites such as NOAA-11 and NOAA12, which carry the advanced very high resolution radiometer (AVHRR) (Holasek and Rose, 1991; Hastings and 

Emery, 1992; Matson and others, this volume) provide 

observations that can be useful in tracking and forecasting 

movement of volcanic ash. A recent example is the use of 5-

cm radar to obtain timely vertical profiles of the erupting column from Mt. Spurr (Alaska Volcano Observatory, 1993). 

Heffler and others ( 1990) have reported a forecast error 

of less than 25 percent of the downwind range (for distances 

often beyond 5,000 km) for 90 percent of the cases verified 

at 300 mb and less than 50 percent at 500 mb. Even though 

this is a significant accomplishment, better long-range forecasts are needed to support air traffic operations: damaging 

ash particles have been reported at 1,200 km from the erupting volcano (Casadevall and De Los Reyes, 1991). Forecasting will be enhanced by new radar facilities, which are 

planned or under evaluation (Hufford, this volume). The 

National Weather Service is installing a network of Doppler 

weather radars that will cover the conterminous United 

States, Alaska, and Hawaii. The locations of radars to be 

installed in the vicinity of the Cascade Range and in southern 

Alaska are shown in figure 2. If the current National Oceanic 

and Atmospheric Administration (NOAA) demonstration 

network of wind pro filers is expanded to cover conterminous 

United States and Alaska, the winds from 1,600 to 53,000 ft 

will be measured 10 times per hour to provide data that will 

enhance the accuracy of prediction of cloud trajectories at 

different altitudes. 

The remainder of the report will describe radar detection theory, the architecture and functions of a typical modem weather radar system, and the parameters and 

applicability to volcanic ash detection of both ground-based 

and airborne systems that are being deployed. Finally, a 

transportable radar will be recommended for emplacement 

near a volcano that is active or anticipated to erupt. 

DETECTION THEORY 

Radar detection of volcanic ash is comparable to 

detection of precipitation and clouds-i.e., it involves a 

volumetric target of many, small, moving particles. One of 

the major challenges results from the difficulty in distinguishing ash cloud echoes from hydrometeor and clear-air 

reflections. Comparison of the position of the origin of 

clouds with the position of the volcano and correlation with 

current meteorological data provides information for identifying ash echoes. 

Because the ash cloud is a volumetric target, the Probert-Jones (1962) equation (eq. 1), which is widely used by 

meteorologists, can be applied to calculate the effective 

reflectivity of the volcanic ash cloud. 

where 

Pr is the received echo power (watts), 

Pt is the peak transmitter power (watts), 

G is the antenna gain ([n2k2]/[8<!>], where k:: 1), 

A. is the wavelength (em), 

8 is the horizontal3-dB beamwidth (radians), 

<1> is the vertical 3-dB beamwidth (radians), 

't is the pulse length (s ), 

c is the velocity of light, 

r is the range (m), and 

N L cri is the reflectivity per unit volume(= 11), 

i= l 

where 

D; is the diameter of the ith drop, and 

(1) 
APPLICATION OF GROUND-BASED AND AIRBORNE RADAR FOR OBSERVATION OF VOLCANIC ASH 421 

!:::, =VOLCANO 

0 =CITY 

ALASKA 

e = WSR-880 RADAR 

~ FAIRBANKS 

MT. 

WRANGELL 6 

Figure 2. Location of planned National Weather Service radars (WSR-88D) in Alaska and in the vicinity of the Cascade Range. 

IR1 2 = I m 

2

-

1

1 (where m is the complex index of 

m2 +2 

refraction). 

N 

The reflectivity factor, Z = :I, n1 . If metric units are 

i= I 

used, Zhas the dimensions ofm6/m3. 

The Probert-Janes equation applies well to the beamfilled case. For spherical particles whose diameters are less 

than 0.07/... over a range of wavelengths from 0.9 to 10.0 em, 

the Ray leigh backscattering approximation can be used in 

calculating cri. The reflectivity factor, Z, used by meteorologists is related to the summation of the sixth power of the 

diameter of spherical particles in a unit volume. When the 

scatterers are small with respect to the radar wavelength (i.e., 

when the Rayleigh approximation for backscatter is applicable), the index of refraction is known, and the beam is known 

to be filled, measurement of reflected power and range permit the calculation of Z, the reflectivity factor. In the case of 

volcanic ash, particle shape and concentration, and the extent 

of beam filling are generally unknown. Because all of the 

requirements of the formula for the reflectivity factor are not 

met, the effective reflectivity factor, Ze, is used in place of Z. 

The value of1Kl2 for water is 0.93, whereas for ash composed of silicate glass, 1Kl2 is 0.36. Measurements of silicate 

glass made at frequencies of 0.450 and 35 GHz differ only 

slightly (Campbell and Ulrichs, 1969). 

Estimates have been made of particle sizes based on 

falling velocities inferred from the decrease in ash cloud 

altitude with time (Harris and Rose, 1983). Owing to sixth 

power dependence of the reflectivity, the larger particles 

dominate in determining reflectivity. The shape of the airborne ash is complex due to agglomeration of the particles (Rose and Hoffman, 1980; Harris and Rose, 1983). 

However, the large particles tend to be equant and, 

because of their dominance in contributing to the total 

reflectivity, the asymmetry associated with the smaller particles is not of significance. 

An example of cloud parameters that illustrate a taxing 

case for detecting light ash cloud from the Fuego Volcano is 

presented by Harris and others (1981 ). The ash cloud measurement compares with that of warm orographic rain (0.02 

mrn/h). Differences in particle size and number can significantly increase reflectivity. For example, Mount St. Helens 

had an equivalent reflectivity in the downwind ash cloud of 

29-40 dBZe (Harris and others, 1981). Harris (this volume) 

assumed that the lower reflectivity portion of the ash cloud 

was 10 dB weaker, corresponding to an effective reflectivity 

range of 20 to 30 dBZe. 
422 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Harris and Rose (1983) calculated reflectivity values 

for Mount St. Helens clouds based on particle size distributions and estimated accumulation rates of ash deposits. They 

provide an independent method of assessing ash cloud 

reflectivity that can be used in estimating radar detection 

performance. 

REFLECTIVITY AND DOPPLER 

VELOCITY MEASUREMENT 

Weather radar techniques have been used effectively 

in the observation of volcanic ash, as noted above. Future 

observations will benefit from significant advances that 

have been made in microwave equipment, computers, Doppler and reflectivity signal processing, data-extraction algorithms, and automated operations in making quantitative 

weather measurements. Doppler radar facilitates direct 

measurement of the radial component of velocity, coherent 

signal integration, and removal of interfering ground-clutter 

echoes. The same techniques enhance the observation of 

volcanic ash whenever an eruption deposits measurable 

quantities of ash within the surveillance volume of the 

radar. This section describes the features of a generic Doppler weather radar. Doviak and Zrnic' (1984) present a 

comprehensive treatment of the measurement of reflectivity 

and Doppler velocity. 

It is assumed that a weather radar operating at a 5- to 

1 0-cm wavelength is used for volcanic ash surveillance. In 

the most commonly used volumetric observing mode, taking 

3 to 5 minutes, its pencil-beam antenna is programmed to 

scan continuously in azimuth while stepping in elevation 

after each scan to cover the altitudes of interest. As an example, a 360° azimuth scan of a radar with a 1.5° beam width at 

an elevation angle close to the horizon, processing 64 samples per resolution cell (one beam width by one 150-m-range 

sample), takes approximately 40 seconds. Using the same 

radar parameters, observing in the range-height indicator 

mode with the antenna scanning over a range of elevation 

angles from the horizon to 30° takes about 3 seconds. The 

exact time to achieve the desired coverage is a function of the 

volume to be scanned, the radar parameters, and the signal 

integration employed. Variants of these scanning strategies 

are used to accommodate different meteorological situations. Others will be required for observation of volcanic ash 

and ejecta. 

Figure 3 is a the generic block diagram of a radar system that employs a coherent transmitter and receiver to support Doppler processing of echoes. Transmission and 

reception use the same parabolic antenna. A transmit-receive 

(T/R) switch isolates and protects the receiver during the 

time that the transmitter is operating. Upon reception, the 

signal is translated to a lower frequency where filtering and 

detection take place. The detected signal is quantized using 

a sampling interval corresponding to a range of 0.15 to 1 km. 

Subsequent calculations of reflectivity, Doppler (radial) 

velocity, and spectral width are performed by a high-speed, 

digital processor. Ground clutter is substantially eliminated 

in the signal-processing operation. Spatial and temporal 

smoothing are applied to the reflectivity and radial velocity 

fields prior to transmitting the data to the display processor. 

Owing to the height extent, the variability in the effective reflectivity of the desired signals as a function of the size 

distribution and composition, range to the scatterers, and the 

presence of intense ground-clutter echoes, the strength of the 

received signals can range over 90 dB. To accommodate a 

large range of signal intensity within the linear range of the 

receiver and analog-to-digital converter, appropriate gaincontrol circuits are employed. 

A number of operational modes employing different 

scan strategies are used to accommodate different meteorological situations. Currently planned precipitation surveillance modes for the weather surveillance radar-88 Doppler 

(WSR-88D) take 5 to 6 minutes to provide range unambiguous coverage up to an altitude of 21 km. The dynamics of 

eruptions should be factored into the scan strategies designed 

for ash surveillance. For example, normal weather scans may 

be automatically interrupted in the interest of executing 

range-height scans around the plume. The volcanic observations could be cued by the detection of ejecta above a volcano or by an increase in seismic activity. 

A radar located close enough to a volcano to observe 

the updraft of the plume would be both useful in identifying 

an event and in providing the volcanologist with important 

dynamic information on the ejecta. Doppler radar measures 

the radial component of velocity; hence, when situated close 

to a volcano, it may be capable of measuring the vertical 

velocity of the plume. As shown in figure 2, radars planned 

for installation in Alaska and in the vicinity of the Cascade 

Range are generally located beyond 100 km from volcanoes 

(Hufford, this volume) and may not provide reliable observation of the plume. A dedicated radar, located near the vol- . 

cano, would characterize the plume and initiate generation of 

aviation hazard warnings. 

With the advent of relatively inexpensive computers, 

automated weather radar algorithms have been implemented for identifying severe storms, measuring echo tops, 

calculating wind shear, tracking and predicting storm-cell 

and gust-front motion, and eliminating echoes due to anomalous propagation (Noyes and others, 1991; Weber and others, 1991 ). The results are automatically presented 

concisely to observers on a geographic situation display 

and can be readily transmitted over commercial telephone 

lines. Similar algorithms and facilities can be employed for 

volcanic ash observations. 

Figure 4 is an example of a Doppler weather radar 

range-height display of a large sheared convective storm 

(S.G. Geotis and E. Williams, MIT Weather Radar Laboratory, written commun., 1991 ). This storm is morphologically 

similar to the volcanic plume distortion caused by wind 

shear shown in figure 5 (Newell and Deepak, 1982). 
APPLICATION OF GROUND-BASED AND AIRBORNE RADAR FOR OBSERVATION OF VOLCANIC ASH 423 

TRANSMITTER ~ ca-ERENT 

DRIVER 

I 

MIXER 

IF AMP 

QUAD 

V[)E() 

DETECTORS 

I ! la 

AID 

CXJNVERTER 

La 

GO..N) f---.+ 

STABLE 

LOCAL 

OSCILLATOR 

~ 

CXl-IEFI:NT 

OSCILLATOR 

~ RADIAL h SPATIAL r-+ TEMPORAL ~ V 

VELOCITY FILTERS FILTER 

AUTO 

CLUTTER CORRELATOR 

FILTERS R{O), R{1) 

~ st\R 

TI-lRESHOLDING 

~ f--.+ ~ SPATIAL TEMPORAL L------.....lf-~ REFLECTIVITY ~~ FILTERS ~ FILTER ~ Z 

CLUTTER 

RESIDUE 

MAP 

Figure 3. Generic block diagram of a modem Doppler weather radar system (modified from Weber and others, 1991 ). 

A TECHNIQUE FOR PROXIMAL 

OBSERVATION OF ASH CLOUDS 

The wind velocity at the altitude of the ash clouds is 

essential to volcanologists and to forecasters in providing 

aviation hazard warnings. Doppler radar can determine only 

the radial component of the wind from a stand-off location. 

When the ash cloud passes over the radar, it is possible to 

determine the vertical profile of the horizontal wind within 

the cloud (L 'hermitte and Atlas, 1961 ). The needed data are 

collected by holding the antenna at a constant elevation 

angle and by recording the radial velocity at several ranges 

while the antenna is scanned 360° in azimuth. The mean 

Doppler velocity varies sinusoidally as the antenna scans a 

volume of particles that have uniform wind velocity and particle fall speed. Maxima and minima are observed when the 

beam azimuth passes upwind(~= 0) and downwind(~= 1t). 

Using the following equations (from Atlas, 1964; L'hermitte 

and Atlas, 1961 ), the horizontal winds and terminal velocity 

of the precipitation particles are calculated. 

When~= 0, 

(2) 

When~ =n, 

-

V1 = V1sina- Vhcosa 

The wind speed at altitude, h, is: 

- - v1- v2 

Vh=--

2cosa. 

and the particle fall speed is: 

- -

(3) 

(4) 

v = v1 + v2 (S) 

1 2sina 

This processing, referred to as the velocity azimuth display 

(VAD), has been extended (Waldteufel and Corbin, 1979) to 

produce wind fields over a three-dimensional volume (volume velocity processing-VVP). Whenever the disposition 

of the radar and ash clouds are favorable for the performance of the 360° scan, the VAD or its later realization provides a capability to measure horizontal winds and the 

terminal velocity of ash particles. 

COMPARISON OF CANDIDATE 

RADAR SYSTEMS 

The parameters of four radars (three ground-based and 

one airborne) are presented in table 1 for comparison. The 
424 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Figure 4. A two-dimensional representation of a sheared thunderstorm on a Doppler weather radar display, as viewed in real time. The 

upper panel shows the radial component of the velocity of the storm cloud. The velocity profile indicates Doppler folding as the wind exceeds 

16m/sin the range of30 to 70 km from the radar. The lower panel shows the intensity of the sheared thunderstorm. Range label on horizontal 

scale indicates range from NEXRAD station. This type of large, sheared thunderstorm bears a strong resemblance to the schematic cross 

section of the volcanic ash cloud that is shown in figure 5. For additional information about Doppler radar, see Doviak and Zmic' (1984). 

Figure 5. Schematic cross section of volcanic ash plume distortion caused by wind shears. Altitudes expressed in thousands of 

feet. From Newell and Deepak (1982). 

three ground-based radars will be in widespread use for 

meteorological purposes in the 1990's. The WSR-88D is 

used by the NWS, the FAA, and the Department of Defense 

for long-range surveillance and severe storm detection. The 

terminal Doppler weather radar (TDWR) is used by the 

FAA for detecting thunderstorms and micro bursts in the 

vicinity of an airport. The transportable C-band radar is 

used by a number of universities for research purposes and 

also finds widespread use in general weather radar service 

by governments and industry. The RDR-4A is typical of the 

small, lightweight units in use on commercial jet aircraft. 

Note that the performance of the RDR-4A radar is orders of 

magnitude lower than that of the ground-based radars, and 

this radar as well as other airborne radars in its size class 

should not be relied upon to detect the presence of hazardous volcanic ash. 
APPLICATION OF GROUND-BASED AND AIRBORNE RADAR FOR OBSERVATION OF VOLCANIC ASH 425 

Table 1. Parameters of various radar systems. 

[NEXRAD, next-generation weather radar; TDWR, terminal Doppler weather radar. Sources of information: Heiss and others 

(1990), S.G. Geotis and E. Williams, MIT Weather Radar Laboratory, written commun. (1991 )] 

Parameter 

Frequency (MHz) 

Wavelength (em) 

Transmitter output power 

(Kwpeak) 

Antenna gain (dB) 

Horizontal and vertical 

antenna beamwidth (

0 ) 

Noise figure (dB) 

Pulse width (J..Ls) 

Transportable 

C-hand 

5,550 

5.40 

250 

43.75 

1.6 

1.8 

1 

Pulse repetition frequency (Hz) 250-1,200 

Minimum discernible signal (dBm) -106 

Approximate reflectivity detectable2 

at 100 km ( dBZe) 12 

1 WSR-74 modified for Doppler processing. 2 Depends on scanning and processing. 

To illustrate the relative performance of the four radars, 

signal-to-noise ratios as a function of range have been calculated for a reflectivity of 10 dBZe and are shown in figure 6. 

The effects of propagation, target characteristics, signal integration, and specific radar system losses omitted from this 

simplified illustration must be included in estimating performance. The factors affecting detection are discussed in 

Doviak and Zmic' (1984) and in Echard (1987). 

It is clear from figure 6, which is drawn for a 10 dBZe 

reflectivity value, that the WSR-88D and TDWR are capable 

of achieving reasonable detection performance. When it is 

located near the erupting volcano, the transportable C-hand 

radar is useful in detecting volcanic ash clouds both for 

research and for generating hazard warning information. 

The features of the WSR-88D radar are presented in 

table 2. This radar will be widely installed in the United 

States. Five systems will be located in the Washington-Oregon area near the Cascade Range; two will be installed at 

Anchorage and King Salmon, Alaska, within approximately 

115 krn or less of the volcanoes located to the west and 

southwest of Anchorage. The radar locations are listed in 

table 3. In order to serve many users, the system is partitioned so that the base data (comprising radar reflectivity, 

Doppler frequency, and spectrum width) are sent via telephone lines to the user's data-processing facility. The WSR88D weather radar is the most powerful system being widely 

deployed and should give the best performance in detecting 

volcanic ash. 

Even though the TDWR has a useful detection capability, the systems are programmed for installation in regions 

(/) 

_J 

w 

ca 

u 

w 

0 

z 

WSR-88D 

NEXRAD 

2,700-3,000 

10.50 

750 

45.50 

0.95 

4.07 

1.57 

4.50 

318-1,304 

-110 

-2 

-10 

50 

40 

6 30 f= 

<( 

0:: 

w 

(/) 20 0 

z 

6 

I-

_j 10 

<( 

z 

(!) 

U5 

TDWR 

5,600-5,650 

5.30 

250 

50.00 

0.50 

1.80 

1.10 

300-2,100 

-110 

-6.2 

RDR-4A 

9,345 

3.20 

0.13 

35.00 

3.40 

5.00 

6.00 

363 

-112 

22 

100 

RANGE, IN KILOMETERS 

400 

Figure 6. Comparison of the signal-to-noise performance of contemporary weather radars calculated for an equivalent reflectivity of 

10 dBZe (see text). Actual performance will depend on losses and 

processing gain. Note that the air-carrier radar (RDR-4A) is almost 

three orders of magnitude less capable than the WSR-88D 

(NEXRAD) system. 
426 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Table 2. Characteristics WSR-88D. 

[After Heiss and others (1990). Reprinted with permission] 

Radome 

Diameter 

RF loss (two way) 

Pedestal 

Steerability 

Rotational rate (maximum) 

Acceleration 

Mechanical limits 

Antenna 

Polarization 

Reflector diameter 

Gain (at 2,800 :MHz) 

Beam width 

First sidelobe level 

Antenna subsystem 

Fiberglass skin foam sandwich. 

39ft 

0.3 dB at 2,800 :MHz. 

Elevation over azimuth. 

Azimuth Elevation 

360° 

36° s-1 

15° s-2 

Parabola of revolution. 

Circular. 

29ft 

45.5 dB 

0.95° 

29d.B 

-1 o to 45° 

36° s-1 

15° s-2 

-1 o to +60° 

Transmitter and receiver subsystem 

(coherent-chain design) 

Transmitter 

Frequency 

Peak power 

Pulse widths (nom.) 

RF duty cycle 

PRF's 

Receiver 

Dynamic range 

Noise temperature 

Intermediate frequency 

Bandwidth (3 dB) 

Clutter canceller 

Suppression 

Notch half widths 

Reflectivity bias 

Minimwn usable velocity 

Range sampling 

Azimuth sampling 

Velocity calculation 

Algorithm 

Estimation accuracy (nom.) 

Number of pulses averaged 

Range increment 

Azimuth increment 

Spectrum width calculation 

Algorithm 

Estimate accuracy (nom.) 

Number of pulses averaged 

Range increment 

Azimuth increment 

Reflectivity calculation 

Algorithm 

Estimate accuracy (nom.) 

Number of pulses averaged 

Range increment 

Azimuth increment 

2,700 :MHz to 3,000 :MHz 

750kW 

1.57 JlS and 4.5 JlS 

0.0021 (max.) 

(Short pulse) 318Hz to 1,304 Hz 

(Long pulse) 318Hz to 452Hz 

95 dB 

450° K 

57.6 :MHz 

0.79 :MHz 

Signal Processor Subsystem 

Infmite impulse-response design. 

30 dB to 50 dB 

0.5 to 4 ms-1 

0 to I dB (on 4 ms-1 width signal). 

0 to4 ms-1 

0.25 km 

10 

Complex covariance argument. 

Pulse-pair processing. 

1 ms-1 

40 to 200 

0.25 km 

10 

Autocorrelation. 

Single lag correlation. 

I ms-1 

40 to 200 

0.25 km 

10 

Return power average. 

Linear power average. 

I dB 

6 to64 

I km 

10 
APPLICATION OF GROUND-BASED AND AIRBORNE RADAR FOR OBSERVATION OF VOLCANIC ASH 427 

Table 3. WSR-88D locations planned as of December 4, 1992. 

[Est., Estimated; Seaffac, Seattle!facoma; TBD, to be determined] 

Area Est. delivery date Latitude (N.) Longitude (W.) 

Cascades 

Eureka, Calif. Nov. 1994 40°29'55" 124°17'27" 

Medford, Oreg. Aug. 1995 42°04'52" 122°42'58" 

Pendleton, Oreg. Oct. 1995 45°41'26" 118°51 '09" 

Portland, Oreg. Nov. 1994 45°42'53" 122°57'56" 

Sea/Tac, Wash. Feb. 1994 48°11'40" 122°29' 45" 

SEokane, Wash. Nov. 1995 47°40'52" 117°37'42" 

Alaska 

Anchorage June 1995 60°43'33" 151 °21'05" 

Bethel May 1996 TBD TBD 

Fairbanks Sep. 1995 65°02'05" 147°30'04" 

King Salmon Apr. 1996 58°40'45" 156°37'48" 

Middleton Island July 1995 59°26'02" 146°19'57" 

Nome May 1996 TBD TBD 

Sitka Aug. 1995 56°51'11 II 133°31'38" 

having frequent thunderstorm activity and associated 

microbursts, which are hazardous to flight. No TDWR systems will be installed in the vicinity of the Cascade Range or 

in Alaska. 

The transportable C-hand radar, designated WSR-74, 

has proven to be a highly versatile research instrument as well 

as an operational system. The Massachusetts Institute of 

Technology weather radar group has installed their unit in sea 

containers for deployment in the South Pacific. Over the past 

5 years, the radar has moved once or twice a year in support 

of operations in the United States and Australia. This radar, 

outfitted with a 10-m antenna, is the least expensive system 

for research. It can be rapidly deployed near a volcano when 

activity indicates an imminent eruption. Emplacement of a 

carefully packaged unit should take less than a week. Consideration should be given to acquiring such a system for use 

by volcanologists for basic research and for the further development of aviation-hazard-warning techniques. 

SUMMARY 

Radar has proven to be useful in locating volcanic ash 

clouds and can be used in aviation hazard forecasting, particularly if the radar is located close to the erupting volcano and 

if hydrometeors can be identified independently during the 

eruption. Under these circumstances, any echo originating at 

the location of the volcano may be presumed to be an ash 

cloud and can be tracked in position and altitude. The altitude information, coupled with winds aloft data, can be used 

to infer trajectories for ash clouds at different altitudes-a 

valuable input to the aviation hazard warning system. 

A brief overview of radar detection of volcanic ash, 

based on weather radar practice, highlights the potential of 

ground-based radar observations. The reduction of the effective reflectivity factor with time as a result of the precipitation of the larger ash particles, the location of the radar with 

respect to the ash cloud, and detection capability of a radar 

set a limit in the hazard warning area that may be served by 

a single radar. 

Performance estimates show that the WSR-880 

weather radar has a potential to perform volcanic ash surveillance. A program is underway to install a network of these 

radars covering all 50 States. Means to exploit the observational capability of the WSR-880 radars for volcanology and 

aviation-hazard-related applications should be investigated. 

It is anticipated that appropriate operating strategies, communications, processing data recording, and display equipment, as well as processing algorithms, will be specified 

(Evans, this volume). 

A dedicated, transportable research radar is suggested 

for further study of volcanic ash clouds and for the perfection 

of automated algorithms for generating hazard warnings. 

Techniques for radar sensing that may be useful for enhancing radar surveillance of volcanic activity should be investigated. Spectral characteristics of echoes, dual-polarization 

observations, and multiple-frequency observations are 

among the candidates that may be considered. 

ACKNOWLEDGMENTS 

The comprehensive review and valuable suggestions 

made by Dr. David M. Harris, Utah State University, are 

appreciated. This work was sponsored by the Federal Aviation Administration under contract no. DTF AO 1-89-Z-02033. 

REFERENCES CITED 

Alaska Volcano Observatory, 1993, Mt. Spurr's 1992 eruption: 

Eos, Transactions, American Geophysical Union, v. 74, p. 217, 

221-222. 

Atlas, D., 1964, Advances in Radar Meteorology: Advances in 

Geophysics, Volume 10: New York, Academic Press, p. 

317-478. 

Campbell, M.J., and Ulrichs, J., 1969, Electrical properties of rocks 

and their significance for lunar radar observations: Journal of 

Geophysics, v. 74, no. 25, p. 5867-5881. 

Casadevall, T.J., and De Los Reyes, P.J., 1991, Impact of June 1991 

Pinatubo eruptions on aircraft operations in the western Pacific 

and southeast Asia [abs.]: Eos, Transactions, American Geophysical Union, v. 72, no. 44 [supplement], p. 95. 

Doviak, R.J., and Zrnic', D.S., 1984, Doppler Radar and Weather 

Observations: Orlando, Fla., Academic Press, Inc., 458 p. 

Echard, J.D., 1987, Target detection in noise and clutter, in Currie, N.C., and Brown, C.E., eds., Principles and Applications 

of Millimeter Wave Radar: Norwood, Mass., Artech House, 

p. 75-129. 
428 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Hastings,D.A.,andEmery, W.J., 1992, Theadvancedveryhighresolution radiometer: A brief reference guide: Photogrammetric 

Engineering and Remote Sensing, v. 58, no. 8, p. 1183-1188. 

Harris, D.M., and Rose, W.I., 1983, Estimating particle sizes, concentrations, and total mass of ash in volcanic clouds using 

weather radar: Journal of Geophysical Research, v. 88, no. 

CIS, p 10969-10983. 

Harris, D.M., Rose, W.l, Roe, R., and Thompson, M.R., 1981, Radar observations of ash eruptions, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 Eruptions of Mount St. Helens, 

Washington: U.S. Geological Survey Professional Paper 1250, 

p. 323-333. 

Heffter, J.L., Stunder, B.J.B., and Rolph, G., 1990, Long-range 

forecast trajectories of volcanic ash from Redoubt Volcano 

eruptions: Bulletin of the American Meteorological Society, v. 

71' p. 1731-1738. 

Heiss, W.H., McGrew, D.L., and Sirmans, D., 1990, NEXRAD: 

Next generation weather radar (WSR-88D): Microwave Journal, v. 33, p. 79-80, 84--98. 

Holasek, R.E., and Rose, W.l., 1991, Anatomy of 1986 Augustine 

Volcano eruptions as recorded by multi-image spectral processing of digital A VHRR weather satellite data: Bulletin of 

Volcanology, v. 53, p. 42~35. 

Leary, W.E., 1992, Radar system gives forecasters more data on 

wind more often: New York Times-The Environment, July 

21, 1992, section C, p. 4. 

L'hermitte, R.M., and Atlas, D., 1961, Precipitation motion by 

pulse Doppler radar: Proceedings, Ninth Weather Radar 

Conference: Boston, Mass., American Meteorological Society, p. 218-223. 

Newell, R.E., and Deepak, A., eds., 1982, Mount St. Helens eruptions of 1980: Atmospheric effects and potential climatic impact: NASA Special Publication SP-458, 119 p. 

Noyes, T.A., Troxel, S.W., Weber, M.E., Newell, O.J., and Cullen, 

J., 1991 , The 1990 airport surveillance radar wind shear processor (ASR-WSP) operational test at Orlando International 

Airport: Lexington, Mass., MIT Lincoln Laboratory, Project 

Report ATC-178, 68 p. 

Pinatubo Volcano Observatory Team, 1991, Lessons from a major 

eruption: Mt. Pinatubo, Philippines: Eos, Transactions, American Geophysical Union, v. 72, no. 49, p. 545, 552-553, 555. 

Probert-Jones, J.R., 1962, The radar equation in meteorology: 

Quarterly Journal of the Royal Meteorological Society, v. 88, 

p. 485-495. 

Rose, W.l., 1987, Interaction of aircraft and explosive eruption 

clouds: A volcanologist's perspective: American Institute of 

Aeronautics and Astronautics Journal, v. 25, p. 52-58. 

Rose, W.l., Jr., and Hoffman, M.F., 1980, Distal ashes of the May 

18, 1980, eruption of Mount Saint Helens [abs]: Eos, Transactions, American Geophysical Union, v. 61, p. 1137. 

Waldteufel, P., and Corbin, H., 1979, On the analysis of single Doppler data: Journal of Applied Meteorology, p. 18532-18542. 

Weber, M., Stone, M., Primeggia, C., and Anderson, J., 1991, Airport surveillance radar based wind shear detection: Proceedings, Fourth International Conference on Aviation Weather 

Systems, Paris, p. Jll-J20. 
VOLCANIC ASH AND AVIATION SAFETY: 

Proceedings of the First International Symposium 

on Volcanic Ash and Aviation Safety 

U.S. GEOLOGICAL SURVEY BULLETIN 2047 

THE POTENTIAL FOR USING GPS FOR 

VOLCANO MONITORING 

By Frank H. Webb and Marcus I. Bursik 

ABSTRACT 

Volcanic eruptions can adversely impact aircraft 

safety by ejecting vast quantities of ash into the atmosphere. The eruption of ash may go undetected by observers both on the ground and in the air, especially at remote 

volcanoes, at night, and in poor weather. It is therefore 

important to develop a system capable of monitoring the 

eruptive state of volcanoes that does not depend on visual 

ash-cloud sighting. Numerous geological techniques are 

being developed for this purpose, some of which depend on 

making careful measurements of ground movements at volcanoes. Ground deformation preceding volcanic eruptions 

occurs at relatively high strain rates, which can change on 

time scales of hours and perhaps minutes in the days 

directly before eruption. Geodesy using the global positioning system (GPS) is perhaps the most promising technique 

for autonomously monitoring volcanic ground deformation 

with daily and sub-daily time resolution. Recent launches 

of additional GPS satellites and increased tracking-station 

distribution have resulted in an increase in the number of 

short intervals during the day with strong satellite and 

ground-station geometry, making it possible to investigate 

high-strain-rate phenomena over sub-daily time scales that 

accompany volcanic eruptions. Once rapid volcanic ground 

movements are better understood, it may be possible to 

develop a relatively inexpensive GPS system that can be 

used in conjunction with other monitoring techniques to 

warn aircraft of an ash eruption. 

INTRODUCTION 

Volcanoes present the most severe geological hazard 

to aviation because they can inject huge quantities of rock 

debris and fine particles and corrosive aerosols into the 

atmosphere. This debris can be directly ingested by aircraft 

engines and can cause flameout or serious malfunction, or 

the debris can remain for months in the atmosphere and 

contribute to the gradual deterioration and erosion of aircraft components. 

Hazards to aircraft posed by volcanoes can be mitigated by a system for warning aviators of an impending or 

ongoing eruption, even when visual corroboration of eruptive activity is not available. Visual sightings are difficult 

during the night and poor weather or when a relatively 

remote active volcano lies along a flight path. In addition, 

very diffuse ash clouds can drift hundreds or even thousands of kilometers from their source and pose a hazard to 

aircraft. Therefore, an effective warning system must be 

based on the ability of earth scientists to gather and correctly interpret information regarding the status of a 

volcano's activity. 

A variety of volcano-monitoring techniques have been 

devised in the hope that a clear indication of an impending 

eruption can be determined. The most commonly used techniques of volcano monitoring fall into three categories: (1) 

analysis of seismic patterns (McNutt, this volume), (2) analysis of the patterns of deformation of the Earth's surface, and 

(3) chemical analysis of the gas emissions from vent regions. 

As magma rises toward the surface, the Earth's crust is distorted or deformed to accommodate magma movements. The 

movements at the surface may be only as large as a few centimeters, but modem instrumentation is sufficiently precise 

to measure them. 

The global positioning system (GPS) is one of several 

geodetic techniques that can be used to measure deformation 

at the Earth's surface associated with magma movement. 

Other techniques involve the use of: (1) leveling, in which 

vertical motions are measured with precise optical-level 

instruments, (2) laser geodimeters, or electronic distance 

meters (EDM's), which measure horizontal motions over 

distances up to approximately 10 km, (3) tilt meters, and (4) 

strainmeters, which record small changes in the dimensions 

of crustal rock that are induced by deformation. 

Although most of the above monitoring methods are at 

least as precise as a GPS-based system, GPS has several 

important characteristics that are not shared by the others 

that suggest it could provide the most effective monitoring 

capability. GPS receivers are readily available and are 

becoming reasonably priced. In contrast, laser geodimeters 

and strainmeters are custom built and are expensive. GPS 

429 
430 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

data-collection and analysis costs are also becoming competitive and will decrease with time. Once a GPS receiver is in 

place, the only labor costs are those associated with data 

analysis and site maintenance. Most other monitoring methods, such as leveling, require many hours in the field by a 

crew of several people to collect data. In addition, as GPS 

monitoring is a remote technique-there is little risk to 

human life in a potentially hazardous geological environment. Probably the greatest advantage of GPS is that it can 

provide complete spatial positioning over a vast range of distances without a line-of-sight requirement among the stations. Although geodimeters measure distances with high 

precision, the lack of three-dimensional control means that 

interpretation of length changes becomes increasingly difficult as baseline slope increases (Savage and Lisowski, 

1984). This contribution explores the use of GPS for a volcano-aviation warning system. 

RELATIONSHIP OF GROUND 

DEFORMATION TO ERUPTIONS 

GPS techniques are commonly applied to the investigation of crustal deformation resulting from plate-tectonic 

motion. However, strain of the Earth's surface in volcanic 

environments differs markedly from tectonic strain associated with faults along and within plate boundaries. Spatially, 

volcanic signals are often characterized by large, local, vertical and dilatational (stretching) components (fig. 1). Temporally, the signals are transient, generally remaining nearly 

constant for long periods and sometimes increasing by the 

hour or minute in the days before an eruption. These unique 

characteristics are the direct result of the primary source of 

strain in volcanoes-pressurized magma migrating toward 

the Earth's surface. Dramatic examples of the peculiar features of volcanic deformation are provided by Iwo Jim a and 

Mount St. Helens. At Iwo Jima, a volcanic island only 10 km 

across in its longest dimension, the shoreline on which Captain Cook landed in 1779 is now 40 m above sea level 

(Newhall and Dzurisin, 1988). In the month prior to the catastrophic sector collapse and eruption on May 18, 1980, the 

north flank of Mount St. Helens moved outward at a rate of 

1.5-2.5 m/day (Lipman and others, 1981 ). 

Not all ground deformation episodes in volcanic 

regions culminate with an eruption. Hill and others (1991) 

have summarized some of the most recent episodes of volcanic unrest that have been monitored with geodetic techniques. In the best known examples, volcanoes deform at 

rates ranging from centimeters per day to meters per day in 

the hours or days before eruption, whereas magma movement at depth can cause strain rates of centimeters per year 

for years or decades with no eruption. It is necessary for an 

aviation-warning capability to distinguish the rapid deformation that may culminate in the eruption of an ash column 

,( -.,., I' ' ' / ,.. \ J. -\ I ..J, 

~~ ,. \ 

\ 

-1 

~ I 

\ '1 

~ I 

\ - ' '--(, 

......... 30--:- ''-c. 

-· -20-:- ...... ~ __ l.-...... 

0 5 KILOMETERS 

65° 

40'~~----------------------------------~ 

Figure 1. An example of a type of deformation found at volcanoes. This example is from Krafla caldera, Iceland, November 5, 

1976, to January 8, 1977. Heavy lines indicate the amount of vertical uplift in centimeters. Note the distinct "bull's eye" pattern associated with magma at depth pushing the rock above it. Dashed lines 

indicate the rim of the caldera, a large crater formed previously by 

collapse of a partially emptied magma chamber. Modified from 

Ewart and others (1990). 

from the slower "background" deformation caused by noneruptive processes. 

To date, there is no known method for unambiguously 

distinguishing deformation leading to eruption. Swanson 

and others (1983) summarized the success of eruption prediction at Mount St. Helens in the period after the catastrophic May 18, 1980, event. A pattern of precursory 

seismic and geodetic events developed during a series of 

dome-building eruptions following May 18. Some of these 

eruptions also produced explosive emission of volcanic ash 

into the atmosphere. Because of the pattern of activity preceding eruptions, most of the events were successfully predicted in the days or weeks preceding the event. Swanson 

and others (1983) concluded that these smaller, quasi-periodic events that frequently occur after a paroxysmal blast are 

amenable to monitoring and prediction. These authors felt 

that the short-term prediction of a major ash-forming event 

that poses a serious aviation hazard, such as that of May 18 

at Mount St. Helens, was a rather distant goal. 

THE GLOBAL POSITIONING 

SYSTEM 

The global positioning system was developed and is 

being deployed by the United States Department of Defense 

(DOD) for worldwide, continuous, real-time point positioning. It is a satellite-based navigational system that is increasingly being used by the civilian and scientific communities 
THE POTENTIAL FOR USING GPS FOR VOLCANO MONITORING 431 

Figure 2. For three dimensional point positioning, the GPS receiver estimates four unknowns: its three-dimensional station coordinates and its clock offset from GPS time. This requires 

observations from four satellites. The geometry of the satellites determines the strength with which the receiver can estimate these parameters. The term PDOP (position dilution of precision) is a 

measure of the strength of the satellite geometry to estimate these 

unknown parameters (Wells and others, 1986). An example of good 

satellite geometry for 3-D positioning would be three receivers 

equally spaced on the horizon and one receiver directly overhead. 

Poor 3-D positioning geometry would have all the satellites directly 

above the receiver or all of the satellites clustered on the horizon. 

During 1 day, satellite geometry varies continuously at every station 

and so does the strength of point positioning. 

for surveying and precise geodetic applications. GPS satellites orbiting the Earth passively broadcast timing codes and 

orbital information that receivers on the ground or in aircraft 

can use to determine their positions. The information is 

broadcast by the satellites on two L-band carrier frequencies, 

L 1 and L2. These carriers, the timing codes, and the orbital 

information can be used in a number of ways to position one 

or more GPS receivers. The method implemented depends 

on the user's required precision, solution frequency, and the 

sophistication of the user's receiver. Processing algorithms 

can vary from independent point positioning of a single 

receiver in real time with 10-m accuracy to differential positioning using data from a global network of receivers for millimeter to centimeter accuracy and precision. 

Real-time point positioning with GPS is the determination of the position of one receiver using signals broadcast by 

several GPS satellites. Each GPS satellite broadcasts ephemerides (orbital information) and timing information on the 

two L-band carrier frequencies. The receiver uses the timing 

information to determine its range to each of the satellites 

that are in view. These ranges and the ephemerides of the 

satellites are used to estimate the receiver's position vector 

in an Earth-centered reference frame and the offset of the 

receiver's clock from GPS time (fig. 2). To estimate these 

parameters, the receiver needs to collect data from at least 

four satellites simultaneously. The precision with which it 

can determine its position depends on the accuracy of the satellite ephemerides, the satellite geometry, and the accuracy 

of the ranges to the satellites. 

There are three types of ranging information that can 

be extracted from the GPS signal: P-code on each of the Lband carriers (P1 and P2) and CIA code on the L1 carrier. 

C/ A code provides a coarse estimate of the range to the satellite. Many receivers are commercially available that use 

the C/ A code to provide 50-100-m positioning accuracy. 

More sophisticated receivers use the precise P-code for 

determining the range to the satellites to about 10 m. 

Receivers capable of using these codes have a greater realtime positioning capability; however, the P-code is subject 

to encryption by the DOD. This encryption, called antispoofing (AS), prevents unauthorized users from taking full 

advantage of the precise ranging information. The DOD 

can also degrade the real-time positioning capability with 

selective availability (SA), which consists in adding signal 

noise to the carriers and degrading the accuracy of the 

broadcast ephemeris message. 

Even in the absence of SA and AS, P-code ranges are 

actually "pseudo ranges" to the satellites because they are 

contaminated by clock errors, atmospheric delay errors, and 

orbital errors-this limits the accuracy of point positioning 

to approximately 10 m. If real-time positioning is not 

required, the effects of these errors on the precision of the 

positioning can be reduced by processing the data after the 

fact (i.e., post-processing). Most post-processing algorithms 

exploit the information contained in tracking the L 1 and L2 

carriers. When the satellites are tracked over some time 

interval, satellite ranges to the receiver change. These 

changes can be coarsely determined by the pseudo range, but 

high-accuracy geodetic measurements require the more precise measurements of the receiver's accumulated phase 

observations. Ionospheric delays are removed by using an 

ionosphere-free linear combination of the dual-frequency 

observables. These phase observables, and the pseudo 

ranges if present, are used from a network of ground receivers to simultaneously estimate the positions, atmospheric 

corrections, and clock errors for the network and the clock 

errors and orbit errors of the GPS satellites. For the highest 

precision applications, 8 to 24 hours of data from a global 

network of receivers are used to estimate satellite and 

receiver parameters. In this global reference frame, relative 

station positions can be determined to a few millimeters in 

the horizontal and about 2 em in the vertical over distances 

of approximately 1,000 km (Heflin and others, 1992; Blewitt 

and others, 1992). 

Because near-real-time positioning is required for a 

volcano-monitoring and warning system, the attendant 

accuracy will be somewhat better than the current real-time 

accuracy but not necessarily as good as that obtained by 
432 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

extensive post-processing. In addition, to clearly define 

rapid strain events preceding eruptions, it may be necessary 

to obtain solutions at sub-daily intervals. By combining postprocessing estimation techniques with real-time data acquisition, relatively high precision positioning at sub-daily 

intervals can be obtained. It is possible to calculate nearly 

continuous relative positions of a receiver on a volcano at a 

precision level better than 1 em, as we demonstrate in the 

next section. 

A DEMONSTRATION OF GPS 

CAPABILITY 

A worldwide network of 31 continuously operating Pcode receivers is currently being deployed for routine geodetic observations. A subset of 21 stations within the network was deployed in 1991 during a 3-week GPS 

experiment (Heflin and others, 1992) to test the ability of 

GPS to measure global geophysical parameters, such as 

polar motion and tectonic strain accumulation. Data from 

many of these receivers were remotely retrieved over commercial phone lines on a daily basis. Analysis of the data to 

determine station locations was performed after the entire 

data set had been accumulated. 

There were 210 baselines within the network having 

lengths ranging from about 100 km to nearly the diameter of 

the Earth. All of the data were analyzed at the Jet Propulsion 

Laboratory (JPL) with an automated version of the GIPSY 

processing software (see Sovers and Border, 1987, for a 

mathematical description) on Micro-VAX computers. Central processing unit (CPU) speed limited the processing efficiency to more than 1 day of CPU per day of global network 

data. With currently available state-of-the-art workstations, 

processing time would be reduced to a few hours. Daily measurement precisions for baselines (of 4 parts in 109 of the 

baseline length) were obtained from the global network 

(Heflin and others, 1992). This level of precision was the 

highest yet obtained with GPS over such a wide range of 

baseline lengths and has been attributed to the strength of the 

global receiver network and the satellite constellation. 

Although the precise solutions discussed above were 

obtained daily, the temporal spacing of GPS baseline solutions can be adjusted according to the rate at which data are 

accumulated at the processing station and the precision that 

is required for a particular application. In the case of volcanoes, daily solutions collected over a period of 1 week would 

be sufficient to discern strain rates greater than a few millimeters per day. If such a week-long survey suggested that 

this several-millimeter-per-day threshold was being 

exceeded, as for example during increased activity preceding 

an eruption, solutions could be calculated more frequently 

than once per day. However, as the frequency at which 

solutions are calculated increases, the resolution of the position estimates decreases, but not dramatically. 

There is another limit to the frequency at which solutions can be usefully calculated. Independent solutions at 

every data point (usually every 30-120 s) are currently not 

possible on a continuous basis because of the limitations of 

the present satellite constellation. At least four satellites are 

required for independent solutions to be derived at every 

data point because, at every observation, the data from one 

station are used to estimate its position in three dimensions 

and its time offset from GPS time. With the current GPS constellation, there are periods during the day when fewer than 

four satellites are visible. (Global 24-hour coverage with 

four-satellites is expected to be available in 1993 when GPS 

becomes fully operational.) Positions can be calculated during periods when fewer than four satellites are visible by 

assuming that a station's position is not completely independent from solution to solution. Because virtually all movements of the Earth's crust occur at rates that are less that 

centimeters per hour, even on volcanoes, it is generally reasonable to assume that a station's position is not excessively 

different from its position at earlier times or data points. That 

is, position estimates from one GPS observation to the next 

are not independent and can be modeled using processnoise-estimation techniques (Bierman, 1977). 

Process-noise-estimation techniques have been applied 

to the estimation of static baselines of 22, 179, and 1,500 km 

with GPS field data to investigate strategies necessary to 

obtain relatively precise sub-daily solutions. Results show 

that solution strength, as measured by the formal error of the 

solution and the accuracy of the estimate, is dominated by 

satellite geometry. Because the satellite geometry (fig. 2) 

varies throughout the day, there are times during which baselines cannot be estimated independently at every observation 

epoch (figs. 3A, B). This results in noncontinuous estimates 

of the baseline throughout the day. If a process-noise model 

is used to apply a weak constraint between the estimates, 

baseline estimates can be obtained during periods of poor 

satellite geometry (fig. 3C). This model relies on the fact that 

the station does not move an excessive amount between 

observations. In the example, a random-walk process-noise 

constraint for a rate of change of the receiver coordinates of 

40 em/ Jhf was used to estimate the station position of one 

of the stations. Solutions were estimated continuously using 

a 6-minute data interval. With this constraint and during the 

periods of the best satellite geometry, the formal errors indicate that motions < 1 cm/hr should be detectable in the 

length, transverse, and vertical components with two hours 

of observations. This rate is an order of magnitude less than 

that observed during the month preceding the May 18 eruption of Mount St. Helens (Lipman and others, 1981). 

Based on the Mount St. Helens example, volcano monitoring for eruption prediction and aircraft warning may 

often require almost continuous calculation of receiver positions. In certain instances, it may even be useful to calculate 
THE POTENTIAL FOR USING GPS FOR VOLCANO MONITORING 433 

positions hourly, or even within fractions of an hour. The 

above results and those from the 1991 experiment suggest 

that precursory volcanic deformation at sub-daily and daily 

intervals could be monitored with high precision with a GPS 

volcano-monitoring network. On short baselines, an increase 

in the precision by a factor of about 2 could be obtained 

using ambiguity resolution (Blewitt, 1989). The outlook for 

less correlated solutions and increased sub-daily precision is 

good, given the continued filling ofthe GPS satellite constellation and increased ground-station distribution. 

A SYSTEM FOR IMPLEMENTATION 

OF REAL-TIME 

GPS MONITORING 

GPS provides the most realistic possibility for eruption 

prediction based on monitoring surface deformation. The 

most important issues that need to be considered for realtime volcano monitoring with GPS are: (1) the hardware 

necessary for collecting, retrieving, and analyzing the data in 

real time, (2) the analysis strategy used to detect ground 

deformation, and (3) the scientific insight required to interpret the deformation signals in terms of volcanic processes. 

The hardware necessary for the monitoring system is 

rather simple (fig. 4). A network of receivers is stationed on 

Figure 3 (right). Sub-daily GPS baseline length obtained for a 22-

km baseline in California between station M7115a and GOLD (at 

the Goldstone Deep Space Network facility). A, The plot shows the 

residual from a nominal value for baseline length. Solutions were estimated each time a GPS measurement was saved by the receiver. 

Each estimate for the position of M7115a is uncorrelated with the 

previous estimate. That is, the position of M7115a is modeled as a 

white-noise process. Shaded regions are regions when the satellite 

geometry was insufficient to estimate the station position and clock. 

Vertical bars indicate ± 1 sigma formal error in the baseline solution. 

B, Formal errors (dashed line) in the solutions from A track the position dilution of precision (PDOP, solid line) for these stations 

closely, suggesting that satellite geometry is the dominant error 

source for sub-daily solution strength. (The tail in the formal error 

at the beginning of the data arc is caused by no data being collected 

at M7115a for the first I 00 minutes of the day.) C, Periods of bad 

satellite geometry can be spanned if the station position is modeled 

as being correlated from one GPS observation to the next. In this example, only baseline length is plotted for a random-walk model of 

the station position. Vertical bars indicate ± I sigma formal error in 

the baseline solution. This model is applied with process noise being 

added to the variance at a rate of 40 em/ Jhr , resulting in solutions 

being obtained at every sample point, with a weak correlation from 

solution to solution. Periods when the station position could not be 

estimated with the white-noise model are now spanned. The usefulness of observations during these periods depends on the magnitude 

of the signal and the strength of the satellite constellation. 

the volcano to be monitored. There are two types of receivers 

available: coded and codeless. The main drawback of 

codeless receivers is their lack of tracking the P-code (pseudo 

range), resulting in more frequent losses of lock by the 

receiver on the satellite signals. When losses of lock (cycle 

slips) occur, they must be repaired in the analysis of the data. 

For codeless receivers, this is a time-consuming process that 

usually involves bringing together data from several receivers in order to detect the cycle slip and properly correct for it 

(Blewitt, 1990). Communication links between the volcano 

receivers and a central processing station, and between the 

central processing station and other global receivers, must 

rely on telemetering of data, either via communications satellite or telephone lines. The link between the central processing station and the volcano receiver needs to be real time, 

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IN MINUTES 
434 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

,_j 

,_1 J • .. ,. J • ,- ,.J 

,..),.) 

, .. ,.) L1 and L2 

,-) c .. ,.J .. 1.) 

L 1 and L2 carrier, 

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Satellite Orbits, clock qffsets 

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Station Positions: 

Remote station as constant over a day 

Volcano station at' daily and sub-daily 

intervals 

______ rJ 

Add new solution 

to time series 

Time • 

Figure 4. One possible design for a real-time, continuous, GPS volcano-monitoring system. Data 

collected at a volcano receiver are transmitted via modem to a central processing facility This facility 

also collects data from other global and (or) local receivers. Data from all receivers are "added" to the 

estimation of the baselines between the volcano monitoring stations and the local and (or) global receivers. The processing facility monitors the GPS baseline results for strain accelerations. This information is used to adjust the frequency with which data are obtained from the volcano station for 

estimating relative motion. 

especially during high-strain-rate events. It is not necessary 

that data from the global stations, and from the volcano 

stations in times of quiescence, be retrieved in real time. This 

information can be added to the solution as it is acquired by 

the processing facility. 

The particular analysis strategy pursued at any one 

time represents a trade-off between a desired precision and 

the frequency at which solutions are calculated. Fortunately, the trade-off between precision and solution spacing 

is mirrored in the physics relating ground deformation and 

eruptive events. In the time period leading up to an 

eruption, strain rates are expected to be relatively high and 

strain magnitudes to be relatively large. During these 

periods, more useful information will be derived by calculating more frequent, less precise positions than less frequent, more precise positions. When deformation is slow 

and an eruption is more likely to occur in the distant future, 

more precise solutions can be calculated less frequently. It 

is thus useful to exploit a flexible analysis strategy. 

Changes in the relatively infrequent, yet precise, positions 

together with other eruptive precursors could be used to 

trigger higher time resolution analysis strategies. 
THE POTENTIAL FOR USING GPS FOR VOLCANO MONITORING 435 

The GPS receivers must be judiciously stationed on a 

potentially active or hazardous volcano. Because of the 

impossibility of monitoring all volcanoes that might erupt 

explosively, the system must be based on portable receivers 

that can be deployed temporarily at potentially destructive 

volcanoes. At least two receivers should be deployed near 

the possible eruptive center, if this can be determined 

through seismic or geological methods, to exploit the magnitude of the deformation signal there. Data from these receivers are down-loaded daily to a central processing center. 

These data and data from other nearby stations and (or) global networks are then used to estimate baselines to the volcano stations, which are interpreted to discern accelerations 

in the movement of the positions of the volcano stations. 

This information is combined with other observations indicating increased activity and is used to alert the system to 

increase the frequency of solution calculation. Thus, the system must be sufficiently flexible to allow changes in the temporal spacing between baseline solutions. GPS analysis 

systems, currently in operation, facilitate and streamline the 

process of changing the frequency of solution calculation. 

Solutions can be rapidly calculated and included in a new 

solution time line at the expense of older, outdated solutions. 

Efforts using GPS to monitor deformation at volcanoes 

have already been initiated. Many of these involve application of GPS techniques developed for measuring plateboundary deformation to understanding regional crustal 

movements related to volcanism. Marshall and Stein (1991) 

and Meertens and Smith (1991) have reported somewhat 

ambiguous results of regional GPS geodetic surveys at Long 

Valley and Yellowstone calderas in the United States. There 

have also been important advances in developing systems 

useful for eruption prediction. Data from Unzen Volcano 

and Teshi Volcano (Shimada and others, 1990) were analyzed using standard post-processing techniques and showed 

that a geodetic signal was measured by GPS receivers that 

may have been useful for prediction purposes if real-time 

processing had been available. At Long Valley caldera and 

Augustine Volcano, Alaska, the U.S. Geological Survey and 

National Aeronautics and Space Administration are developing near-real-time GPS monitoring systems for eruption prediction. Any standardized GPS volcano-monitoring 

technique is still in the future, however. Receivers and telecommunications equipment are still too expensive for routine deployment. In addition, as described above, the 

analysis techniques necessary to obtain near-real-time, precise positions are still in the research-and-development 

stage. Rapid progress on these two fronts suggest that realtime GPS monitoring is not an unrealistic goal. 

CONCLUSIONS 

Although volcanoes represent an inherently complex 

physical system, earth scientists have identified several types 

of phenomena, including ground deformation, that indicate 

an eruption may be imminent. Moreover, progress has been 

made in identifying how these features can be interpreted to 

obtain a near-real-time eruption-prediction capability. Our 

results suggest that the global positioning system will soon 

be able to provide precise, sub-daily, three-dimensional 

positioning information to monitor rapid ground deformation preceding an eruption. In addition, GPS hardware technology is sufficiently evolved that relatively inexpensive Pcode receivers will be available in the near future to enable 

near-real-time data analysis. It is the combination of a flexible precision and solution-calculation interval with nearreal-time analysis and communication that will define the 

optimum system for geodetic volcano monitoring, prediction, and aviation warning using GPS. 

ACKNOWLEDGMENTS 

The research described in this publication was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National 

Aeronautics and Space Administration. M.B. acknowledges the receipt of a National Research Council/Jet Propulsion Laboratory Research Associateship. Dan Dzurisin, 

Geoff Blewitt, and Steve Lichten provided useful comments to improve the manuscript. 

REFERENCES CITED 

Bierman, G.J., 1977, Factorization Methods for Discrete Sequential 

Estimation: New York, Academic Press, 241 p. 

Blewitt, G., 1989, Carrier phase ambiguity resolution for the global 

positioning system applied to geodetic baselines up to 2,000 

km: Journal of Geophysical Research, v. 94, p. 10187-10203. 

---1990, An automatic editing algorithm for GPS data: Geophysical Research Letters, v. 17, p. 199-202. 

Blewitt, G., Heflin, M.B., Webb, F.H., Lindqwister, U.J., and MalIa, R.P., 1992, Global coordinates with centimeter accuracy in 

the International Terrestrial Reference Frame using GPS: Geophysical Research Letters, v. 19, p. 853-856. 

Ewart, J.A., Voight, B., and Bjorneson, A., 1990, Dynamics of 

Krafla caldera, north Iceland: 1975-1985, in Ryan, M.P., ed., 

Magma Transport and Storage: New York, John Wiley and 

Sons, p. 225-276. 

Heflin, M., Bertiger, W., Blewitt, G., Freedman, A., Hurst, K., Lichten, S., Lindqwister, U., Vigue, Y., Webb, F., Yunck, T., and 

J. Zumberge, 1992, Global geodesy using GPS without fiducials: Geophysical Research Letters, v. 19, p. 131-134. 

Hill, D.P., Johnston, M.J.S., Langbein, J.O., McNutt, S. R., Miller, 

C.D., Mortensen, C.E., Pitt, A.M., and Rojstaczer, S., 1991, 

Response plans for volcanic hazards in the Long Valley caldera 

and Mono Craters area, California: U.S. Geological Survey 

Open-File Report 91-270, 65 p. 

Lipman, P.W., Moore, J.G., and Swanson, D.A., 1981, Bulging of 

the north flank before the May 18th eruption-Geodetic data, 

in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 
436 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Eruptions of Mount St. Helens, Washington: U.S. Geological 

Survey Professional Paper 1250, p. 143-156. 

Marshall, G., and Stein, R., 1991, Monitoring ground deformation 

at Mono Craters, California, using a dense GPS network [abs.]: 

Eos, Transactions, American Geophysical Union, v. 72, p. 118. 

Meertens, C.M., and Smith, R.B., 1991, Crustal deformation of the 

Yellowstone Caldera from first GPS measurements, 

1987-1989: Geophysical Research Letters, v.18, p. 

1763-1766. 

Newhall, C.G., and Dzurisin, D., 1988, Historical unrest at large 

calderas of the world: U.S. Geological Survey Bulletin 1855, 

1108 p. 

Savage, J., and Lisowski, M., 1984, Deformation in the White 

Mountains seismic gap, California-Nevada, 1972-1982: Journal of Geophysical Research, v. 89, p. 7671-7687. 

Shimada, S., Fujinawa, Y., Sekiguchi, S., Ohmi, S., Eguchi, T., and 

Okada, Y., 1990, Detection of a volcanic fracture opening in 

Japan using global positioning system measurements: Nature, 

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Sovers, O.J., and Border, J.S., 1987, Observation model and parameter partials for the JPL geodetic GPS modeling software "GPSOMC:" Jet Propulsion Laboratory Publication JPL 87-21. 

Swanson, D.A., Casadevall, T.J., Dzurisin, D., Malone, S.D., Newhall, C.G., and Weaver, C.S. 1983, Predicting eruptions at 

Mount St. Helens, June 1980 through December 1982: Science,v.221,p. 1369-1376. 

Wells, D.E., Beck, N., Delikarao1ou, D., Kleusberg, A., Krakiwsky, E. J., Lachapelle, G., Langley, R.B., Nakiboglu, M., 

Schwartz, K., Tranquilla, J.M., and Vanicek, P., 1986, Guide 

to GPS positioning: Fredricton, New Brunswick, Canada, Canadian GPS Associates. 
SELECTED GLOSSARY OF VOLCANOLOGY 

AND METEOROLOGY 

Active volcano. A volcano that is erupting or has erupted in recorded history. 

Ash. Finely fragmented particles of rocks and minerals less than 2 mm in diameter (less 

than 0.063-mm diameter for fme ash) produced by explosive volcanic eruption. See 

also tephra, pyroclast, ejecta. 

Ash cloud. A cloud of volcanic ash and pyroclastic fragments, often containing gases and 

aerosols of volcanic origin, formed by volcanic explosion and carried by winds away 

from an eruption column. Ash clouds are often dark colored-brown to gray. Ash 

clouds may drift for hundreds to thousands of kilometers from their volcanic source. 

As ash clouds become more dilute, they may be difficult to distinguish from 

meteorological clouds. See also eruption cloud. 

Ash flow. A mixture of hot gases and ash, which may move down the flanks of a volcano 

or along the ground surface at high speed. See also pyroclastic flow. 

Composite volcano. A steep-sided volcano composed of many layers of volcanic rocks, 

usually lava flows and ash and pyroclastic deposits; also known as a stratovolcano. 

Dormant volcano. A volcano that is not presently erupting but is considered capable of 

doing so in the future. 

Earthquake. A sudden motion or trembling in the Earth caused by the sudden fracturing 

of a part of the Earth's crust. See also tremor. 

Ejecta. General term for material thrown out by a volcano. See also pyroclast and tephra. 

Eruption cloud. A cloud of volcanic ash and other pyroclastic fragments, and volcanic 

gases and aerosols, that forms by volcanic explosion. Eruption clouds are often dark 

colored-brown to gray. Often used interchangeably with plume or ash cloud. 

Eruption column. The vertical pillar of ash and gas that forms above a volcano at the 

time of eruption. Eruption columns from energetic eruptions may rise to altitudes in 

excess of 100,000 ft (30 km). 

Fumarole. A vent on a volcano from which gases and vapors are emitted. 

Hawaiian eruption. An eruption characterized by the non-explosive eruption of fluid 

lava of basaltic composition. Hawaiian eruptions generally pose no threat to aviation 

safety. 

Isobars. Lines on a weather map or chart connecting points of equal pressure. 

Lapilli. Pyroclastic fragments with diameters between 2 and 64 mm. 

Lava. Molten rock that erupts from a volcano. 

Magma. Naturally occurring molten rock generated within the Earth that can be erupted 

as lava or pyroclasts. 

Mesoscale. Term used to refer to weather phenomena with systems of length of about 

100 km, of velocity of about 10 m/s, and with time scales of about 3 hours. 

Millibar. A unit of atmospheric pressure equal to 1/1000 bar, or 1,000 dynes per square 

centimeter. 

Mudflow. A general term for a flowing mass of predominantly fine-grained earth 

material mixed with water and possessing a high degree of fluidity during movement. 

The Indonesian term lahar is often used interchangeably with mudflow. 

437 
438 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Phreatic eruption. A volcanic eruption or explosion of steam, mud, or other non-juvenile 

material, generally caused by the heating and expansion of ground water due to 

underlying magma. 

Plinian eruption. A large explosive eruption that ejects a steady, turbulent stream of 

fragmented magma and magmatic gas to form an eruption column that may reach 

altitudes in excess of 100,000 ft (30 km). 

Plume. Term often used to describe the elongated, downwind, dispersed portion of an 

eruption cloud and ash cloud. 

Pyroclast. An individual volcanic particle ejected during an eruption. For example, ash, 

lapilli, and volcanic bombs are pyroclasts. 

Pyroclastic flow. A turbulent flowing mass of fragmented volcanic materials mixed with 

hot gases that may move downhill at high speed. Pyroclastic flows may result from the 

collapse of tall eruption columns or from spillover of ejected materials from erupting 

vents. See also ash flow. 

Rawinsonde. Observations of upper-air conditions, including wind direction and speed, 

temperature, pressure, and relative humidity using signals from a radiosonde that is 

tracked with radar or a radio-direction finder. 

Seismometer. An instrument that detects earthquakes. 

Stratosphere. The outer layer of the atmosphere that overlies the tropopause and is above 

an altitude of about 10 to 20 km. 

Stratovolcano. A volcano that is constructed of alternating layers of lava and pyroclastic 

deposits; also known as a composite volcano. 

Strombolian eruption. An eruption consisting of short, discrete, explosions which may 

eject pyroclasts for a few tens to a few hundreds of feet into the air. Each explosion may 

last for only a few seconds, and there may be pauses of tens of minutes between 

explosions. 

Tephra. A collective term for all violently ejected materials from craters or vents during 

volcanic eruptions. These materials are either airborne momentarily or for a longer 

period of time depending primarily on the vigor of the eruption and the size of ejected 

fragments. Generally, coarser tephra are deposited closer to the erupting crater or vent 

and finer grained tephra are deposited farther away. Tephra includes volcanic dust, ash, 

cinder, lapilli, bombs, and blocks. See also ejecta. 

Tremor. A type of seismicity characterized by continuous vibration of the ground related 

to the movement of magma and volcanic gas within or beneath a volcano. 

Tropopause. An atmospheric transition zone located between the troposphere and the 

stratosphere at an altitude of about 10 to 20 km. In this region, temperatures and 

atmospheric stability begin to increase with increasing altitude. 

Troposphere. That portion of the atmosphere next to the Earth's surface in which 

temperature generally decreases with altitude, clouds form, and weather systems and 

convection are active. 

Volcanic gas. Volatile material, released during a volcanic eruption, that was previously 

dissolved in magma. The principal volcanic gases include water vapor, carbon dioxide, 

and sulfur dioxide. 

Volcano. A vent or opening at the surface of the Earth through which magma erupts. Also 

the landform that is produced by the erupted material accumulated around the vent. 

Vulcanian eruption. A type of volcanic eruption characterized by short-duration, violent, 

explosive ejection of fragments of lava. Vulcanian eruption columns may reach 

altitudes of 45,000 ft (15 km) or more. 
A/C 

A CARS 

ACC 

ACMS 

ADEOS 

AD PIC 

AEROS 

AES 

AFGWC 

AFSS 

AFTN 

AGFS 

AGSO 

AGU 

AlA 

AIAA 

AlP 

ALPA 

AMIC 

AOPA 

APU 

ARAC 

ARINC 

ARL 

ARO-NET 

ARSI 

ARTCC 

AS 

ASD 

AST 

ATA 

ATC 

ATCSCC 

ATS 

AVADS 

AVHRR 

AVN 

AVO 

AWPG 

BOM 

BUV 

BVE 

CAA 

CANERM 

CAT 

CAVW 

CCD 

CLS 

CMC 

LIST OF SELECTED ACRONYMS 

air conditioning; also used as shorthand for "aircraft" 

aircraft communications addressing and reporting system 

area control center 

aircraft condition monitoring systems 

advanced Earth observing satellite (Japan) 

atmospheric diffusion particle-in-cell model (Lange, 1978) 

ARAC emergency response operating system; see ARAC 

Atmospheric Environment Service (Canada) 

see GWC 

aircraft flight service stations 

aeronautical fixed telecommunications network (Australia) 

aviation gridded forecast system 

Australian Geological Survey Organization 

American Geophysical Union 

Aerospace Industries Association of America 

American Institute of Aeronautics and Astronautics 

aeronautical information publication 

Air Line Pilots Association 

area manager-in-charge 

Aircraft Owners and Pilots Association 

auxiliary power unit 

atmospheric release advisory capability (U.S. Department of Energy) 

Aeronautical Radio, Inc. 

Air Resource Laboratory (NOAA) 

Alaska region operational (computer and) communications network 

Atmospheric Research Systems, Inc. 

air route traffic control center 

anti-spoofing (DOD encryption of GPS P-code information) 

aircraft situation displays 

Alaska Standard Time 

Air Transport Association 

air traffic control; air traffic center 

Air Traffic Control System Command Center (Washington, D.C.) 

air traffic service; also air traffic system 

airborne volcanic-ash-detection system 

advanced very high resolution radiometer 

aviation run of the medium-range forecast model 

Alaska Volcano Observatory 

aviation weather product generator 

Bureau of Meteorology (Australia) 

backscattered ultraviolet instrument 

Bulletin of Volcanic Eruptions (Volcanological Society of Japan) 

Civil Aviation Authority (Australia) 

Canadian emergency-response model 

clear-air turbulence 

Catalog of Active Volcanoes and Solfatara Areas of the World 

charge-coupled detector 

Collecte Localisation Satellites (France) 

Canadian Meteorological Centre 

439 
440 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

CNES 

COS SA 

CSIRO 

CSLP 

cvo 

CWA 

cwsu 

DFDR 

DIS 

DMSP 

DOD 

DOE 

DUAT 

DVI 

ECC 

ECS 

EDM 

EFIS 

EGT 

EOS 

EPR 

ETA 

ETMS 

FAA 

FADEC 

FAR 

FIR 

FSF 

FfiT 

GAC 

GMS 

GMT 

GOES 

GOSTA 

GPS 

GRIB 

GSFC 

GTS 

GVN 

GWC 

HARS 

HIPS 

HIRS 

HPC 

HPT 

lATA 

IAVCEI 

IAVW 

ICAO 

IF ALP A 

IFC 

IFR 

IFSD 

IMC 

Centre National d'Etudes Spatiales (the French space agency) 

Office of Space Science and Application (Australia) 

Commonwealth Scientific and Industrial Research Oraganization 

Center for Short-Lived Phenomena (Cambridge, Mass.) 

Cascades Volcano Observatory (U.S. Geological Survey) 

center weather advisory 

Central (Center) Weather Service Unit 

digital flight-data recorder 

dust-injection system 

defense meteorological satellite program (United States) 

Department of Defense (United States) 

Department of Energy (United States) 

direct-user-access terminal 

dust veil index 

emergency coordination center 

environmental control system 

electronic distance meter 

electronic flight instrument system 

exhaust-gas temperature 

Earth observing system (spacecraft) 

engine pressure ratio 

estimated time of arrival 

enhanced traffic management system 

Federal Aviation Administration (United States) 

full-authority digital electronic controls 

Federal Aviation Regulation 

flight-information region 

Flight Safety Foundation 

turbine inlet temperature 

global area coverage (data) 

geostationary meteorological satellite 

Greenwich Mean Time (equivalent to UTC) 

geostationary orbiting (operational) environmental satellite 

Global Ocean Surface Temperature Atlas 

global positioning system 

gridded binary format 

Goddard Space Flight Center 

global telecommunication system 

Global Volcanism Network (Smithsonian Institution-formerly SEAN) 

Global Weather Central (U.S. Air Force); also AFGWC 

high-altitude routing system 

high-resolution image-processing system 

high-resolution infrared radiation sounder 

high-pressure compressor 

high-pressure turbine 

International Air Transport Association 

International Association of Volcanology and Chemistry of the Earth's Interior 

International Airways Volcano Watch 

International Civil Aviation Organization 

International Federation of Air Line Pilots' Associations 

instrument flight conditions 

instrument flight rules; see also VFR 

(engine) in-flight shut down 

instrument meteorological conditions 
INSU 

IR 

ITWS 

JAL 

JMA 

JPL 

KLM 

KLMO 

LAC 

LLNL 

LOWTRAN 

LPT 

MAPS 

MciDAS 

MEDIC 

METSIS 

MONO A 

MOU 

MSU 

MWO 

MWP 

Nt 

N2,N2 

NASA 

NAWAU 

NESDIS 

NEXRAD 

NGM 

NGV 

NMC 

NOAA 

NO TAM 

NVM 

NWP 

NWS 

OA 

ORSTOM 

PB 

PDOP 

PDT 

PEGASAS-VE 

PIREP 

PIRPSEV 

PLA 

Ps3 

Ps3 

PT2 

PT2.5 

RAWPG 

RFC 

RFE 

RHI 

RISC 

RSAM 

LIST OF SELECTED ACRONYMS 

Institute for Earth and Planetary Sciences (France) 

infrared 

integrated tenninal weather system 

Japan Air Lines 

Japan Meteorological Agency 

Jet Propulsion Laboratory (California Institute of Technology) 

Royal Dutch Airlines 

Kagoshima Local Meteorological Observatory (part of JMA) 

local area coverage (data) 

Lawrence Livennore National Laboratory (Livennore, Calif.) 

radiance/transmittance code developed by the U.S. Air Force 

low-pressure turbine 

mesoscale analysis and prediction system 

man-computer interactive data access system 

meteorological data interpolation code 

meteorological satellite information system (Canada) 

Argos station for monitoring physical-chemical parameters 

memorandum of understanding 

microwave sounding unit 

meteorological watch office 

meteorological weather processor 

fan speed 

core (rotor) speed 

National Aeronautics and Space Administration (United States) 

national weather advisory unit 

National Environmental Satellite Data and Infonnation Service (NOAA) 

next-generation weather radar 

nested grid model 

nozzle guide vane 

National Meteorological Center (Canada; Camp Springs., Md.; Melbourne, Australia) 

National Oceanic and Atmospheric Administration (United States) 

notice to ainnen 

non-volatile memory (feature ofFADEC) 

numerical weather-prediction (model) 

National Weather Service 

objective analysis 

Research Institute for Cooperative Development (France) 

burner pressure; burner static pressure 

position dilution of precision 

Pacific Daylight Time; also abbreviation for Pendleton, Oreg. 

pressure gage system for air-shocks by volcanic eruptions 

(also Pirep) pilot report 

interdisciplinary research program for the forecasting of volcanic eruptions (France) 

power lever angle 

compressor discharge pressure; high-compressor static-discharge pressure 

compressor-discharge pressure 

inlet total pressure 

fan-exit total pressure 

regional aviation weather product generator 

Regional Forecasting Center (part ofBOM) 

regional finite-element (model) 

range-height indicator 

reduced instruction set chip 

real-time seismic-amplitude monitoring system 

441 
442 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

SA 

SAB 

SBUV 

SEAN 

SIGMET 

SIGWX 

SISMOI 

SNR 

SOl 

svo 

TDWR 

TIROS 

TMU 

TOMS 

TOVS 

TRACON 

TSC 

UAV 

UCAR 

USFS 

USGS 

UTC 

uw 

VAD 

VADAS 

VAFTAD 

VAR 

VARTAM 

VAW 

VAWS 

VEl 

VFR 

VISSR 

VOR 

VSI 

VULCAN 

VULCAN-AUS 

VULCAN-IND 

VVP 

vws 

WAFS 

WAIT 

WFO 

WMO 

wovo 

WSFO 

wso 

www 

Zulu 

selective availability (GPS term) 

Synoptic Analysis Branch (of the NWS) 

solar/backscattered ultraviolet instrument 

Scientific Event Alert Network (Smithsonian Institution-now called GVN) 

significant meteorological advisory 

significant weather chart 

Argos station for monitoring seismic tremors and events 

signal-to-noise ratio 

southern oscillation index 

Sakurajima Volcanological Observatory (Kyoto University, Japan) 

terminal Doppler weather radar 

television and infrared observing (observation) satellite 

traffic management unit 

total ozone mapping spectrometer 

TIROS observational vertical sounder 

terminal radar approach control 

transportation system center 

unmanned aircraft vehicle 

University Corporation for Atmospheric Research 

U.S. Forest Service 

U.S. Geological Survey 

Coordinated Universal Time (also Universal Time Code; see also GMT, Zulu) 

University ofWashington 

velocity azimuth display (feature ofNEXRAD) 

volcanic ash detection and aviation safety (study group) 

volcanic ash forecast transport and dispersion model 

volcanic activity report (form); cf., Fox, this volume, fig. 1 

volcanic ash report to airmen 

volcanic ash warning 

volcanic ash warning system 

volcanic explosivity index 

visual flight rules; see also IFR, IFC 

visible and infrared spin-scan radiometer 

very high frequency omnidirectional radio range 

Volcanological Survey of Indonesia 

Volcanological/ Airspace Liaison Committee-Australia/Indonesia 

Australia-based working group of VULCAN 

Indonesia-based working group of VULCAN 

volume velocity processing 

volcano watching system 

world-area forecast system 

Western Australia Institute of Technology (now Curtin University of Technology) 

weather forecast office 

World Meteorological Organization 

World Organization of Volcano Observatories 

Weather Service Forecast Office 

Weather Services Office (Australia) 

World Weather Watch 

Coordinated Universal Time 
AUTHORS' ADDRESS LIST 

Mr. Jorge Barquero 

Observatorio Vulcanologico y Sismologico de Costa Rica 

Universidad Nacional 

Apartado 86-3000, Heredia 

Costa Rica 

374570-377023-376363,ext.2304,2405 

FAX: (506) 238-0086 

Dr. Ian J. Barton 

CSIRO Division of Atmospheric Research 

Private Bag No. 1 

Mordialloc, Victoria 3195 

Australia 

61-3-586-7668 

FAX: 61-3-586-7600 

Mr. Craig I. Bauer 

National Weather Service 

701 C Street, Box 23 

Anchorage, AK 99513 

(907) 271-5107 

FAX: (907) 271-3711 

Mr. Gregory K. Bay hurst 

INC-7 MS J-514 

Los Alamos National Laboratory 

Los Alamos, NM 87545 

(505) 667-4534 

FAX: (505) 665-5688 

Dr. James E. Beget 

Department of Geology and Geophysics 

University of Alaska 

Fairbanks, AK 99775 

(907) 474-7565 

FAX: (907) 474-5163 

Mr. Stanley G. Benjamin 

NOAA Forecast Systems Laboratory 

NOAAIERL/FSL R/E/FS 1 

325 Broadway 

Boulder, CO 80303 

(303) 497-6938 

FAX: (303) 497-6750 

Dr. Gregg S.J. Bluth 

Department of Geological Engineering 

Michigan Technological University 

1400 Townsend Dr. 

Houghton, MI 49931 

(906) 487-2531 

FAX: (906) 487-2943 

Dr. Marcus I. Bursik 

Department of Geology 

State University ofNew York at Buffalo 

Buffalo, NY 14268 

(716) 645-3992 

FAX: (716) 645-3999 

Captain Ernest E. Campbell 

Boeing Commercial Airplane Group 

P.O. Box 3707, MIS 2T-61 

Seattle, WA 98124-2207 

(206) 662-7886 

FAX: (206) 662-7575 

Dr. Thomas J. Casadevall 

U.S. Geological Survey 

Box 25046, MS 903 

Denver Federal Center 

Denver, CO 80225 

(303) 236-1080 

FAX: (303) 236-1414 

Dr. Steven N. Carey 

University ofRhode Island 

School of Oceanography 

Kingston, RI 02881 

( 401) 792-6222 

FAX: (401) 792-6160 

Mr. J.P. Cauzac 

North American CLS, Inc. 

9200 Basil Court, Suite 306 

Landover, MD 20785 

(301) 341-1814 

FAX: (301) 341-2130 

443 
444 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Dr. Real D' Amours 

Canadian Meteorological Centre 

2121 North Service Rroad, Suite 200 

Trans Canada Highway 

Dorval, Quebec H9P 1J3 

Canada 

(514) 421-4684 

FAX: (514) 421-4639 

Mr. Douglas D. D' Autrechy 

Science Applications International Corporation 

1710 Goodridge Dr. 

McLean, VA 22102-1302 

(703) 556-7142 

FAX: (703) 356-8408 

Mr. Kenneson G. Dean 

Geophysical Institute 

University of Alaska Fairbanks 

Fairbanks, AK 99775-0800 

(907) 4 7 4-4 7 64 

FAX: (907) 474-7290 

Mr. Scott R. Doiron 

ST Systems Corporation 

4400 Forbes Boulevard 

Lanham, MD 20706 

(301) 286-8036 

FAX: (301) 286-3460 

Dr. Michael G. Dunn 

Calspan Advanced Technology Center 

4455 Genesee St. 

Buffalo, NY 14225 

(716) 631-6747 

FAX: (716) 631-6815 

Dr. James S. Ellis 

Lawrence Livermore National Laboratory 

Box 808 (L-262) 

Livermore, CA 94551 

(510) 422-1808 

FAX: (510) 423-4527 

Mr. Donald D. Engen 

809 Duke St. 

Alexandria, VA 22314 

(703) 548-6750 

FAX: (703) 548-6886 

Dr. James E. Evans 

Weather Sensing Group 

Room HW29-119B 

M.l. T. Lincoln Lab 

P.O. Box 73 

Lexington, MA 02139 

(617) 981-7433 

FAX: (617) 981-0632 

Captain Peter M. Foreman 

Air Traffic Services Committee 

5351 Parker Avenue 

Victoria, B.C., V8Y2N1 

Canada 

(604) 658-8045 

FAX: (604) 276-8923 

Mr. TomFox 

International Civil Aviation Organization (ICAO) 

1000 Sherbrooke St. West 

Montreal, Quebec H3A 2R2 

Canada 

(514) 285-8194 

FAX: (514) 285-6759 

Dr. Charles R. Gallaway 

Department of Defense 

680 1 Telegraph Road 

Alexandria, VA 22310-3398 

(703) 325-1282 

FAX: (703) 325-2957 

Dr. Jennie S. Gilbert 

Department of Geology 

University of Bristol 

Wills Memorial Building 

Queens Road, Bristol BS8 1RJ 

United Kingdom 

(0272) 303030, ext. 4795 or 0272 

FAX: (0272) 253385 

Mr. Robert F. Hamley 

National Weather Service 

FAAARTCC 

3101 Auburn Way South 

Auburn, WA 98002 

(206) 931-5401 

FAX: (206) 931-5208 
Dr. David M. Harris 

Department of Forestry 

Utah State University 

Logan, UT 84321-5215 

(801) 750-2585 

FAX: (801) 750-3798 

Dr. Ulli G. Hartmann 

Perkin-Elmer Corporation 

2771 N. Garey Ave. 

Pomona, CA 91767 

(714) 593-3581 

FAX: (714) 596-2301 

Dr. Jerome L. Heffter 

NOAA Air Resources Laboratory 

1325 East-West Highway, Room 9358 

Silver Spring, MD 20910 

(30 1) 713-0295 

FAX: (301) 713-0119 

Dr. Grant Heiken 

ESS-1, Geology /Geochemistry 

MIS D-462 

Los Alamos National Laboratory 

Los Alamos, NM 87545 

(505) 667-8477 

FAX: (505) 667-3494 

Dr. Robert H. Hertel 

Perkin-Elmer Corporation 

2771 N. Garey Ave. 

Pomona, CA 91767 

(909) 593-3581 

FAX: (909) 596-2301 

Dr. Catherine J. Hickson 

Geological Survey of Canada 

100 West Pender Street 

Vancouver, B.C. V6B 1R8 

Canada 

(604) 666-3955/0539 

FAX: (604) 666-1124 

Dr. Frank R. Honey 

SpecTerra Systems Pty Ltd. 

43 Hobbs Avenue 

Dalkeith, Western Australia 6009 

Australia 

61 (9) 389-8050 

FAX: 61 (9) 386-7935 

AUTHORS' ADDRESS LIST 

Mr. Gary L. Hufford 

National Weather Service 

222 W. 7th Ave., #23 

Anchorage, AK 99513 

(907) 271-3886 

FAX: (907) 271-3711 

Dr. Lee Huskey 

School of Public Affairs 

University of Alaska Anchorage 

3211 Providence Drive 

Anchorage, AK 99508 

(907) 786-1916 

FAX: (907) 786-7739 

Dr. Kazuhiro Ishihara 

Sakurajima Volcano Observatory 

Yokoyama, Sakurajima 

Kagoshima 891-14 

Japan 

81-992-93-2058 

FAX: 81-992-93-4024 

Mr. Haitao Jiao 

Geophysical Institute 

University of Alaska Fairbanks 

Fairbanks, AK 99775-0800 

(907) 474-4764 

FAX: (907) 474-7290 

Dr. R. Wally Johnson 

Australian Geological Survey Organization 

GPO Box 378 

Canberra ACT 2601 

Australia 

61-62-49-93 77 

FAX: 61-62-49-9983 

Ms. Chris Jonientz-Trisler 

Federal Emergency Management Agency 

Federal Regional Center 

130 - 228th sw 

Bothell, WA 98021-9796 

(206) 487-4645 

FAX: (206) 487-4613 

Dr. Kosuke Kamo 

Sakurajima Volcanological Observatory 

Koyto University 

Yokoyama, Sakurajima 

Kagoshima 891-14 

Japan 

81-992-93-2058 

FAX: 81-992-93-4024 

445 
446 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Dr. Juergen Kienle 

Geophysical Institute 

University of Alaska 

Fairbanks, AK 99775-0800 

(907) 474-5681 

FAX: (907) 474-5618 

Dr. Vladimir Yu. Kirianov 

Institute of Volcanic Geology and Geochemistry 

9 Piip Avenue 

Petropavlovsk-Kamchatsky, 683006 

Russia 

415-00-59194 

Dr. Alexander B. Kostinski 

Department of Geological Engineering 

Michigan Technological Univesity 

Houghton, MI 49931 

(906) 487-2531 

FAX: (906) 487-2943 

Dr. Arlin J. Krueger 

Earth Sciences Directorate 

NASA, Goddard Space Flight Center 

Greenbelt, MD 20771 

(301) 286-6358 

FAX: (301) 286-3460 

Dr. J.R. Labadie 

JAY COR 

1212 N.E. 62nd St 

Seattle, WA 98115 

(206) 526-5125 

FAX: (206) 526-5531 

Dr. Stephen J. Lane 

Department of Geology 

University of Bristol 

Wills Memorial Building 

Queens Road, Bristol BS8 1RJ 

United Kingdom 

(0272) 303030, ext. 4795 or 0272 

FAX: (0272) 253385 

Mr. James S. Lynch 

NOAA/NESDIS 

World Weather Building, Room 410 

Washington, DC 20230 

(301) 763-8444 

FAX: (301) 763-8142 

Dr. Giovanni Macedonia 

Centro di Studi per Ia Geologia e Dinamica 

dell' Appennino-CNR 

via Santa Maria 53 

I-56100 Pisa 

Italy 

050-47383-6 

FAX: 050-43163 

Mr. J. Owen Maloy 

Mountain Instruments Corporation 

P.O. Box 2083 

Mammoth Lakes, CA 93546 

(619) 934-9511 

FAX: (619) 934-4553 

Dr. Allen S. Mason 

INC-7 MS J-514 

Los Alamos National Laboratory 

Los Alamos, NM 87545 

(505) 667-4534 

FAX: (505) 665-5688 

Mr. Michael Matson 

NOAA/NESDIS 

World Weather Building 

5200 Auth Road 

Washington, DC 20230 

(301) 763-8142 

FAX: (301) 763-8131 

Mr. Lindsay McClelland 

National Park Service 

Wildlife and Vegetation Division 

800 N. Capital St. N.W., Room 500 

Washington, DC 20002 

(202) 343-1004 

FAX: (202) 343-8137 

Dr. Stephen R. McNutt 

Alaska Volcano Observatory 

Geophysical Institute 

University of Alaska 

Fairbanks, AK 99775-800 

(907) 474-7131 

FAX: (907) 474-5618 

Captain Edward Miller 

Aviation Weather Committee 

Air Line Pilots Association 

535 Herndon Parkway 

Herndon, VA 22070 

(703) 689-4200 

FAX: (703) 689-4370 
AUTHORS' ADDRESS LIST 

Mr. Michael C. Monteith 

Science Applications International Corporation 

1710 Goodridge Dr. 

McLean, \'A 22102-1303 

(703) 821-4517 

FAX: (703) 356-8408 

Ms.LaurelMuehlhausen 

North American CLS, Inc. 

9200 Basil Court, Suite 306 

Landover, MD 20785 

(301) 341-1814 

FAX: (301) 341-2130 

Mr. Thomas L. Murray 

U.S. Geological Survey 

5400 MacArthur Blvd. 

\'ancouver, WA 98661 

(206) 696-7549 

FAX: (206) 696-7866 

Mr. Mark E. Musolf 

United Technologies- Norden Systems 

P.O. Box 5300 

Norwalk, CT 06856 

(203) 852-7533 

FAX: (203) 852-7423 

Ms. Bobbie Myers 

U.S. Geological Survey 

5400 MacArthur Blvd. 

\'ancouver, WA 98661 

(206) 696-7908 or 7906 

FAX: (206) 696-7866 

Dr. Reginald E. Newell 

Department of Earth, Atmospheric and Planetary Sciences 

Massachusetts Institute of Technology 

Cambridge, MA 02139 

(617) 253-2940 

FAX: (617) 253-6208 

Mr. Saburo Onodera 

Meteorology Section, Flight Operations Dept. 

Japan Air Lines Co., Ltd. 

JAL Operation Center Bldg. 

1-1 Hanedakuko 2 Chome 

Ota-Ku, Tokyo 144 

Japan 

81-3-3747-3357 

FAX: 81-3-3747-4619 

Mr. Christian Ortega 

North American CLS, Inc. 

9200 Basil Court, Suite 306 

Landover, MD 20785 

(301) 341-1814 

FAX: (301) 341-2130 

Mr. Donald H. Parkinson 

National Weather Service 

FAAARTCC 

3101 Auburn Way South 

Auburn, WA 98002 

(206) 390-5401 

FAX: (206) 931-5208 

Dr. P. Papale 

Istituto Nazionale di Geofisics 

via di \'ilia Ricotti 42, 

1-00100 Roma 

Italy 

Dr. M. Teresa Pareschi 

Centro Ricerca IBM, 

via Santa Maria 67 

1-56100 Pisa 

Italy 

Mr. John F. Paskievitch 

U.S. Geological Survey 

4200 University Dr. 

Anchorage, AK 99508 

(907) 786-7454 

FAX: (907) 786-7450 

Mr. John A. Power 

U.S. Geological Survey 

Geophysical Institute 

University of Alaska Fairbanks 

Fairbanks, AK 99775-0800 

(907) 474-5333 

FAX: (907) 474-5618 

Mr. Rodney J. Potts 

Bureau of Meteorology 

GPO Box 1289K 

Melbourne, \'ictoria 3001 

Australia 

61-3-6694584 

FAX: 61-3-6694695 

Dr. Alfred J. Prata 

CSIRO, Division of Atmospheric Research 

Private Bag No. 1 

Mordialloc, \'ictoria 3195 

Australia 

61-3-586-7681 

FAX: 61-3-586-7600 

447 
448 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Mr. Zygmunt J. Przedpelski 

24 Quartermaster Dr. 

Salem, SC 29676 

(803) 944-5622 

Dr. Herbert A. Roeder 

Perkin-Elmer Corporation 

2771 N. Garey Ave. 

Pomona, CA 91767 

(909) 593-3581 

FAX: (909) 596-2301 

Dr. William I. Rose 

Department of Geological Engineering 

Michigan Technological University 

1400 Townsend Dr. 

Houghton, MI 49931 

(906) 487-2531 

FAX: (906) 487-2943 

Dr. Mauro Rosi 

Dipartimento di Scienze della Terra 

via Santa Maria 53 

1-56100 Pisa 

Italy 

Dr. Yosihiro Sawada 

Sendai District Meteorological Observatory 

1-3-15 Gorin, Miyagino-ku 

Sendai 983 

Japan 

022-291-8171 (ext. 140) 

FAX: 022-291-8110 

Dr. Roberto Santacroce 

Dipartimento di Scienze dalla Terra 

via Santa Maria 53 

1-56100 Pisa 

Italy 

Dr. Thomas W. Schlatter 

NOAA Forecast Systems Laboratory 

NOAA/ERL/FSL R/E/FS 1 

325 Broadway 

Boulder, CO 80303 

(303) 497-6938 

FAX: (303) 497-6750 

Mr. David J. Schneider 

Department of Geological Engineering 

Michigan Technological University 

1400 Townsend Dr. 

Houghton, MI 49931 

(906) 487-2531 

FAX: (906) 487-2943 

Dr. Charles C. Schnetzler 

Earth Sciences Directorate 

NASA, Goddard Space Flight Center 

Greenbelt, MD 20771 

(301) 286-3532 

FAX: (301) 286-4098 

Dr. Stephen Self 

Department Geology and Geophysics 

University of Hawaii 

2525 Correa Road 

Honolulu, HI 96822 

(808) 956-5996 

FAX: (808) 956-2538 

Dr. Tom Simkin 

NHBMS 119 

Smithsonian Institution 

Washington, DC 20560 

(202) 357-2786 

FAX: (202) 357-2476 

Dr. R.S.J. Sparks 

Department of Geology 

University ofBristol 

Wills Memorial Building 

Queens Road, Bristol BS8 lRJ 

United Kingdom 

(0272) 303030, ext. 4795 or 0272 

FAX: (0272) 253385 

Mr. George Stephens 

NOAA/NESDIS 

5200 Auth Road, Room 510 

Camp Springs, MD 207 46 

(301) 763-8142 

FAX: (301) 763-8131 

Dr. Melvin L. Stone 

ATC Surveillance Group 

M.I. T. Lincoln Laboratory 

Lexington, MA 02173-9108 

(617) 981-7426 

FAX: (617) 981-3495 

Dr. Barbara J.B. Stunder 

NOAA/ Air Resources Laboratory 

1325 East-West Highway, Room 9358 

Silver Spring, MD 2091 0 

(301) 713-0295 

FAX: (301) 713-0119 
Dr. Thomas J. Sullivan 

Lawrence Livermore National Laboratory 

Box 808 (L-262) 

Livermore, CA 94551 

(510) 422-1808 

FAX: (510) 423-4527 

Dr. Samuel E. Swanson 

Department of Geology and Geophysics 

University of Alaska 

Fairbanks, AK 99775 

(907) 474-7565 

FAX: (907) 474-5163 

Dr. Makoto Tahira 

Koyto University 

Yokoyama, Sakurajima 

Kagoshima 891-14 

Japan 

81-992-93-2058 

FAX: 81-992-93-4024 

Dr. Hiroshi L. Tanaka 

Institute of Geoscience 

University of Tsukuba 

Tsukuba, Ibaraki 305 

Japan 

0298 53 4502 

FAX: 0298 51 9764 

Mr. George J. Theisen 

U.S. Forest Service 

Gifford Pinchot National Forest 

Vancouver, WA 98668 

(206) 696-7856 

FAX: (206) 696-7863 

Dr. Bradford H. Tuck 

School of Public Affairs 

University of Alaska Anchorage 

3211 Providence Drive 

Anchorage, AK 99508 

(907) 786-1915 

FAX: (907) 786-7739 

Mr. Jerald Uecker 

NOAA-National Weather Service 

Aviation Services Branch 

1325 East-West Highway 

Silver Spring, MD 20910 

(301) 713-1726 

FAX: (301) 713-1598 

AUTHORS' ADDRESS LIST 

Dr. Peter L. Versteegen 

Science Applications International Corporation 

1710 Goodridge Dr. 

McLean, VA 22102-1303 

(703) 821-4517 

FAX: (703) 356-8408 

Major Douglas P. Wade 

Headquarters, Defense Nuclear Agency 

6801 Telegraph Road 

Alexandria, VA 22310-3398 

(703) 325-1054 

FAX: (703) 325 2957 

Dr. George P. L. Walker 

University of Hawaii at Manoa 

Dept. of Geology and Geophysics 

2525 Correa Road 

Honolulu, HI 96822 

(808) 956-5996 

FAX: (808) 956-2538 

Dr. Louis S. Walter 

Laboratory for Terrestrial Physics 

NASA, Goddard Space Flight Center 

Greenbelt, MD 20771 

(301) 286-2538 

FAX: (301) 286-9200 

Dr. Frank H. Webb 

Jet Propulsion Laboratory 

4800 Oak Grove Laboratory 

MS 238-625 

Pasadena, CA 91109 

(818) 354-4670 

Mr. Frank Whitby 

Bureau of Meteorology 

GPO Box 1289K 

Melbourne 

Victoria 3001, Australia 

61-3-6694584 

FAX: 61-3-6694695 

Mr. Lawrence Whiting 

Geophysical Institute 

University of Alaska Fairbanks 

Fairbanks, AK 99775-0800 

(907) 474-4764 

FAX: (907) 474-7290 

449 
450 VOLCANIC ASH AND AVIATION SAFETY: PROCEEDINGS, FIRST INTERNATIONAL SYMPOSIUM 

Dr. Colin J.N. Wilson 

Institute of Geological and Nuclear 

Sciences Ltd. 

Wairakei Research Centre 

Private Bag 2000, Taupo 

New Zealand 

64 7 374-8211 

FAX: 64 7 374-8199 

Dr. Andrew W. Woods 

Institute of Theoretical Geophysics 

J 

Department of Applied Mathematics and Theoretical Physics 

University of Cambridge 

Cambridge CB3 9EW 

United Kingdom 

44-223-33-7095 

FAX: 44-223-33-7918 

Published in the Central Region, Denver, Colorado 

Manuscript approved for publication May 4, 1994 

Edited by Richard W. Scott, Jr. 

Graphics prepared by Denny Welp, Roger Highland, Gayle 

Dumonceaux, Art Isom, and Springfield & Springfield. In 

places, extensive use has been made of author-drafted 

material. 

Photocomposition by Joan Nadeau, Carol Quesenberry, and 

Mari L. Kauffmann 

Additional proofing and review by Robert K. Wells 

Printing contract administration by Debra Sokol 

Dr. Kenneth H. Wohletz 

INC-7 MS J-514 

Los Alamos National Laboratory 

Los Alamos, NM 87545 

(505) 667-4534 

FAX: (505) 665-5688 

Dr. Zhong Xiang Wu 

Department of Earth, Atmospheric, and Planetary Sciences 

Massachusetts Institute of Technology 

Cambridge, MA 02139 

(617) 253-2940 

FAX: (617) 253-6208 

Mr. Lester M. Zinser 

351 W. North 

Ajo, AZ 85321-2153 

(602) 245-2936 

>:r U.S. ~ PRl:Nl'IRi OFFICE: 1994-573-038/86047 
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