Airborne Volcanic Ash—A Global Threat to Aviation

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2010-3116

December 2010

U.S. GEOLOGICAL SURVEY—REDUCING THE RISK FROM VOLCANO HAZARDS

T he world’s busy air traffic 

corridors pass over or downwind 

of hundreds of volcanoes capable of 

hazardous explosive eruptions. The 

risk to aviation from volcanic activity is 

significant—in the United States alone, 

aircraft carry about 300,000 passengers 

and hundreds of millions of dollars of 

cargo near active volcanoes each day. 

Costly disruption of flight operations in 

Europe and North America in 2010 in 

the wake of a moderate-size eruption 

in Iceland clearly demonstrates how 

eruptions can have global impacts 

on the aviation industry. Airborne 

volcanic ash can be a serious hazard 

to aviation even hundreds of miles 

from an eruption. Encounters with 

high-concentration ash clouds can 

diminish visibility, damage flight 

control systems, and cause jet 

engines to fail. Encounters with lowconcentration clouds of volcanic ash 

and aerosols can accelerate wear 

on engine and aircraft components, 

resulting in premature replacement. 

The U.S. Geological Survey (USGS), 

in cooperation with national and 

international partners, is playing a 

leading role in the international effort 

to reduce the risk posed to aircraft by 

volcanic eruptions.

Airborne volcanic ash is a serious hazard to aviation and can cause 

jet engines to suddenly fail in flight. Explosive volcanic eruptions 

can send ash to flight levels at speeds of 5,000 to 8,000 feet per minute; given the speed of aircraft and 

such rapid rise rates for ash clouds, the industry has challenged authorities to notify cockpit crews within 

5 minutes of eruption detection worldwide. This image taken from space shows a vertical column of ash 

and an ash-cloud rising 60,000 feet above Rabaul Volcano, Papua New Guinea, in September 1994 (Space 

Shuttle STS-064 image). Carried westward by the winds, the ash cloud spread rapidly over busy air routes 

near Indonesia. The inset photo shows a 1990 eruption cloud from Redoubt Volcano, Alaska (photo courtesy 

of W. Rose, Michigan Technological University). Taken from an aircraft descending into Anchorage, about 

50 miles (80 km) from the volcano, it shows just how similar weather and ash clouds can appear when 

viewed from the cockpit.

Volcanic eruptions pose a serious 

hazard to aviation when highly abrasive, 

pulverized rock debris (ash) and gas are 

ejected explosively into the atmosphere 

and dispersed over long distances. Worldwide, more than 100 reported encounters 

of aircraft with volcanic ash have resulted 

in hundreds of millions of dollars in damage and, in three dramatic cases, caused 

the near loss of wide-body passenger 

jets. For aircraft to avoid encounters with 

volcanic ash, air traffic controllers, pilots, 

and dispatchers must be rapidly notified 

when explosive eruptions occur and ash is 

in the atmosphere.

In cooperation with national and international partners, the U.S. Geological Survey (USGS) Volcano Hazards Program is 

playing a leading role in the global effort 

to reduce the risk of aircraft encounters 

with ash through timely eruption forecasts 

and warnings, education about the hazard, 

and scientific investigation of volcanic 

processes and ash-cloud properties. Hundreds of active volcanoes around the globe 

have the potential to severely affect aviation operations, and each year dozens of 

these volcanoes erupt explosively. On a 

global basis, volcanic ash is a daily conIn the United States alone, aircraft carry about 

300,000 passengers and hundreds of millions of 

dollars of cargo near active volcanoes each day. 

This photo shows a jet on approach into SeattleTacoma International Airport in Washington. Mount 

Rainier, one of more than a dozen potentially active 

Cascade volcanoes in the Pacific Northwest of 

the United States, looms in the distance. (Image 

courtesy Alaska Airlines.) 
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cern to aviation. Volcanic ash clouds are 

carried by prevailing winds and can drift 

in different directions at many flight levels 

for thousands of miles from the erupting 

volcano. The hazard is complicated by the 

fact that ash and aerosol clouds from volcanoes can remain aloft at cruise altitudes 

for days to weeks. These clouds are difficult to distinguish visually from weather 

clouds and are invisible to air traffic 

control and aircraft radar. Volcanic activity can also have serious impacts on lowaltitude aircraft and on airport operations.

Hazards and Risks

Volcanic ash consists of small (less 

than 2 mm or 0.08 inch across) solid, 

sharp-edged fragments of quickly cooled 

volcanic glass and minerals blasted at high 

velocity into the atmosphere during explosive eruptions. This material is abrasive 

and melts at the high operating temperatures of modern jet engines. When ingested 

into a jet engine, volcanic ash erodes turbine blades, and the melted ash can adhere 

to critical parts, causing engine failure 

(“flameout”). Any forward-facing surface 

of an airplane engulfed in a volcanic ash 

cloud is likely to be eroded, including the 

cockpit and forward cabin windows and 

landing-light covers. Cockpit windows 

may become so abraded that pilots have 

a serious loss of forward visibility. Ash 

entering sensitive aircraft electronics can 

interfere with navigation and other onboard systems. As a result of electrical 

disturbances within the ash cloud, a flight 

crew may also lose the ability to transmit a 

distress call.

Sulfur and other gases released in large 

eruptions also affect aircraft and their occupants. Acidic aerosols formed by the 

hydration of these volcanic gases produce 

a corrosive mist that may cause respiratory 

problems for passengers and flight crews 

and accelerate deterioration of vulnerable 

aircraft components. Over a period of 

many years, such exposure can significantly increase aircraft maintenance costs. 

Chronic “degassing” of nearby volcanoes 

upwind of airports can also affect ground 

operations or even close airfields for years.

Volcanic ash and aerosol clouds above 

airports and ash falling on and near airports 

can be hazardous to aircraft on approach 

and departure, as well as to operations on 

the ground. Ash on runways reduces braking effectiveness of aircraft, and wet ash is 

extremely slippery. The fine particles can 

be resuspended by surface winds and airGlassy—melted and then resolidified—volcanic ash adheres to 

the leading edge of a high-pressureturbine stage-1 nozzle guide vane 

inside a jet engine that encountered 

a volcanic ash cloud at 25,000 feet. 

The patch of dark glass shown here 

is about 1 inch across. (Photo courtesy of General Electric.)

ONE AIRCRAFT’S HARROWING ENCOUNTER WITH VOLCANIC ASH

For more than 4 terrifying minutes on December 15, 1989, a powerless Boeing 747 with 231 passengers aboard plunged in 

silence towards the rugged, snow-covered mountains 90 miles north of Anchorage, Alaska. Fine ash and a strong odor 

of sulfur filled the cockpit and cabin as the flight crew donned oxygen masks and initiated emergency procedures to restart all four engines, which had flamed out when the aircraft inadvertently entered an eruption cloud from Redoubt Volcano 150 miles away. Radio transmissions to Anchorage Air Route Traffic Control Center record the severity of the event:

“KLM 867, we have flame out...all engines....and we are descending now.”

“KLM 867 heavy, we are descending now....we are in a fall!”

Although the crippled jet’s engines were 

restarted, and it ultimately landed safely 

in Anchorage, it suffered more than 

$80 million in damage ($140 million in 

today’s dollars, about half the price of a 

new Boeing 747). This incident was another “wake-up call” to volcanologists, 

industry representatives, and aviation 

officials worldwide. Following this encounter, coordinated efforts to address 

the hazard of airborne volcanic ash and 

implement more effective detection 

tools and warning systems around the 

globe accelerated.

KLM Flight 867 after landing safely.
The sulfur dioxide (SO2

) cloud produced 

by the August 7, 2008, eruption of Kasatochi Volcano (red triangle) in the central 

Aleutian Islands of Alaska remained 

fairly coherent for a few days, drifting 

south and east across North America 

and the Atlantic Ocean. Eventually it 

split into multiple streams and circled 

the northern hemisphere between 35,000 

to 45,000 feet above sea level, as shown 

in this composite satellite image from 

August 16. Colors represent the relative 

amount of gas, with red being the highest and blue the lowest. There may or 

may not be detectable ash associated 

with such sulfur dioxide clouds. Data 

are from NASA’s EOS-Aura satellite and 

its Ozone Monitoring Instrument (OMI), 

courtesy of Dr. Simon Carn, Michigan 

Technological University. (DU represents Dobson Units, a measure of the 

mass of SO2

 per unit area of atmosphere.)

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port ground operations until removed from 

the tarmac, an expensive and difficult process. When an airport is closed or operations curtailed because of the presence of 

ash, significant and costly disruptions result, including the loss of required alternate 

landing sites for aircraft aloft. This is particularly a concern for twin-engine aircraft 

operating under ETOPS (Extended-range 

Twin-engine Operational Performance 

Standards) flight rules on oceanic flights.

Development of U.S. and International 

Warning Systems

In response to in-flight engine failure 

incidents in 1982, the International Civil 

Aviation Organization (ICAO) created 

the International Airways Volcano Study 

Group, which later became the International Airways Volcano Watch program 

(IAVW). A major goal of the IAVW is to 

improve global ash detection and warning systems for air traffic controllers, 

dispatchers, and pilots. Major accomplishments of the IAVW include development 

of standards for in-flight ash warning 

messages from the worldwide system of 

Meteorological Watch Offices and the 

creation of nine Volcanic Ash Advisory 

Centers in the mid-1990s. The eruptions 

of Redoubt (1989–90) and Mount Spurr 

(1992) volcanoes in Alaska, both of 

which had a profound impact on regional 

aviation operations, prompted significant 

growth of the Alaska Volcano Observatory (AVO), increased monitoring along 

the Aleutian chain, and development of 

the first Interagency Operating Plan for 

Volcanic Ash Episodes. The United States 

has recently strengthened the ash-cloud 

warning program for aviation within its 

airspace by preparing a National Volcanic 

Ash Operations Plan for Aviation. This 

plan documents responsibilities, communication protocols, and hazard message 

formats for the Federal Aviation Administration (FAA), National Oceanic and 

Atmospheric Administration (NOAA), 

USGS, and the U.S. Air Force Weather 

Agency. The plan is available online at 

http://www.ofcm.gov/p35-nvaopa/pdf/

FCM-P35-2007-NVAOPA.pdf. 

Role of the Aviation Community

Pilot education is a key factor in mitigating the hazard from aircraft encounters 

with volcanic ash. (continued on page 5)

The weight of rain-soaked 

ash fall from the 1991 eruption 

at Pinatubo Volcano in the 

Philippines caused this DC-10 

to fall back on its tail at Cubi 

Point Naval Air Station (photo 

courtesy of R.L. Rieger/U.S. 

Navy). An inch of wet ash can 

weigh as much as 10 pounds 

per square foot. 

VOLCANIC ASH CAN IMPACT AIRPORT OPERATIONS

Volcanic ash falling on and near airports is a hazard to aircraft on approach and 

departure, as well as to operations on the ground. Ash accumulation of more than 

a trace amount (~1 mm or the thickness of a dime) requires complete removal for 

airports to resume full operations. Ash does not simply blow away and disappear; it 

must be disposed of in a manner that minimizes remobilization by wind and aircraft. 

Case studies of cleanup methods are online at http://www.avo.alaska.edu/pdfs/cit2773.

pdf. Recommended procedures for the protection and cleanup of ash-contaminated 

airports are given by the International Civil Aviation Organization (ICAO) in the Manual 

on Volcanic Ash, Radioactive Material, and Toxic Chemical Clouds (Document 9691-

AN/954, 2002), available online at http://www2.icao.int/en/anb/met-aim/met/iavwopsg/

Documents/Forms/Allitems.aspx.

Workers clean ash 

at Mariscal Sucre 

International Airport in 

Quito, Ecuador. (Photo 

courtesy of El 

Commercio, Quito, 

Ecuador.)
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Volcano observatories are a source of important hazard information for aviation users. Airlines can use warnings of impending or ongoing volcanic activity 

to select safe and efficient routes that avoid ash-contaminated airspace. Aviation Color Codes are used by all U.S. Volcano Observatories to indicate the 

status of volcanoes and are recommended for use worldwide by the International Civil Aviation Organization (ICAO).

EDUCATION AND COORDINATION 

To inform the aviation industry and flight crews about the hazards of volcanic ash, the International Civil Aviation Organization (ICAO) has 

produced a variety of educational and resource materials, including the poster below. In addition, professional aviation organizations, 

such as the Air Line Pilots Association, have also made a sustained effort to promote understanding of the hazard and of methods of 

ash avoidance—http://www.alpa.org/Portals/Alpa/VolcanicAsh/VolcanicAsh.htm. Scientists with the USGS Volcano Hazards Program 

also give briefings to pilots, dispatchers, controllers, and others in order to familiarize the aviation community with volcano monitoring, 

hazards, and warning systems. In addition to the education of aviation personnel, effective coordination among volcano observatories, 

air traffic control authorities, and aviation meteorology services is essential to reduce aircraft encounters with ash clouds.

Volcano is in typical background, noneruptive state 

or, after a change from a higher level,

volcanic activity has ceased and volcano has returned to noneruptive background state.

YELLOW

ORANGE

RED

Eruption is imminent with significant emission of volcanic ash into the atmosphere likely

OR

eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].

GREEN

Color Description

Volcano is exhibiting signs of elevated unrest above known background level

or, after a change from a higher level,

volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain,

OR

eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].

Color codes, which are in accordance with recommended International Civil Aviation Organization (ICAO) procedures, are intended to inform the aviation sector about a volcano’s status and 

are issued in conjunction with an Alert Level. Notifications are issued for both increasing and decreasing volcanic activity and are accompanied by text with details (as known) about the 

nature of the unrest or eruption, especially in regard to ash-plume information and likely outcomes. 

Aviation Color Code Used by U.S. Geological Survey Volcano Observatories
Tokyo

VAAC

Darwin

VAAC

London

VAAC

Toulouse

VAAC

Montreal

VAAC

Anchorage

VAAC

Wellington

VAAC

Washington

VAAC

Buenos Aires

VAAC

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VOLCANIC ASH ADVISORY CENTERS (VAAC)

Because volcanic ash clouds travel long distances, official response to an ash-cloud threat must be coordinated internationally. 

Under the auspices of the World Meteorological Organization (WMO) and the International Civil Aviation Organization (ICAO), nine 

regional Volcanic Ash Advisory Centers (VAACs) provide advisories to international Meteorological Watch Offices (MWOs) about 

the location and movement of ash clouds. The VAACs are located in Anchorage, Buenos Aires, Darwin, London, Montreal, Toulouse, 

Tokyo, Washington, D.C., and Wellington. VAACs use volcano-observatory reports, pilot reports, geostationary and polar-orbiting 

satellite data, and ash-dispersion models as the bases for their advisories. As an ashcloud drifts downwind, responsibility for issuing 

advisories generally passes from one VAAC to the next. The map shows volcanoes of the world (red triangles), areas of responsibilities 

for VAACs, and simplified major global air routes (white lines). Dotted regions are not covered by any VAAC because of satellite or 

other infrastructure limitations.

(continued from page 3) To address this, 

a consortium of pilot organizations, the 

FAA, aircraft manufacturers, and other 

aviation interests have developed and 

promoted operating procedures for flight 

crews whose planes inadvertently enter a 

volcanic ash cloud. This guidance is now 

part of flight crew training and emergency 

checklists for many airlines.

During a volcanic eruption, flight crews 

are important partners in disseminating 

warning information to keep aircraft safe. 

Often pilot reports are the first direct observations of a volcanic event. Details of 

such observations are of great help to volcanologists trying to interpret data from 

distant eruptions and to meteorologists 

and aviation managers who issue warnings and may have to restrict air space. 

Flight crews can greatly assist in these 

efforts by relaying key descriptive information contained in the Volcanic Activity 

Report Form (VAR) to air traffic control 

(ATC) centers.

Communicating the Hazard—The Aviation 

Color Code and the VONA

Volcano observatories provide important 

volcano hazard information for meteorological and aviation authorities who are responsible for issuing SIGMETs (advisories 

of Significant Meteorological information), 

NOTAMs (Notices To Airmen), and other 

warning products. Airlines can use warnings of impending or ongoing volcanic 

activity to select safe and efficient routes 

that avoid ash-contaminated airspace. In 

1990, USGS scientists at AVO developed a 

four-color alert system for volcanic activity. This system was used to quickly inform 

the aviation community about the severity 

of hazard and level of activity at a volcano. 

ICAO has adopted a modified version of 

this color code system as the recommended 

guideline for volcano observatories worldwide. A change in the color code (either up 

or down) or a significant change within a 

color code prompts USGS volcano observatories to issue a specialized message for 

aviation users called a VONA—Volcano 

Observatory Notice for Aviation—that 

summarizes hazard information for pilots, 

aviation managers, controllers, and dispatchers in concise text.
The Future 

The worldwide growth of air traffic, 

especially in volcanically active regions 

such as the Pacific Rim, means that volcanic ash will remain a serious hazard 

to aviation. Furthermore, the expected 

introduction of “free-flight” air traffic operations by the FAA and increased use of 

twin-engine aircraft across remote areas 

of the planet (areas having few alternate 

landing sites) make timely detection and 

reporting of eruptions, ash-cloud movement, and anticipated ash fall essential to 

flight safety. The 2010 Icelandic eruption 

highlighted this and many other remaining challenges facing safe and efficient 

aviation operations during an explosive 

volcanic event. 

Keys to reducing the risk to aviation are 

(1) increased ground-based volcano monitoring (only a very small percentage of volcanoes that threaten aviation are currently 

considered well-monitored with modern 

instrumentation) and improved eruption 

forecasts; (2) development of new and 

improved tools and techniques to detect, 

track, and characterize volcanic clouds 

that are a hazard to aviation; (3) improved 

forecasting of ash-cloud movement and expected ash fall; (4) research and education 

to better quantify and build awareness of 

the hazard; and (5) refinement of protocols 

to ensure rapid communication of ashhazard warnings to flight crews. Scientists 

in the USGS Volcano Hazards Program are 

continuing to work with national and international partners to accomplish these goals 

and improve flight safety and efficiency 

around the world.

Christina A. Neal and Marianne C. Guffanti

Edited by James W. Hendley II 

and Peter H. Stauffer

Graphic design by Judy Weathers

COOPERATING ORGANIZATIONS

Airline Pilots Association

Alaska Division of Geological and 

Geophysical Surveys

Environment Canada, Canadian Meteorological 

Center, Montreal Volcanic Ash Advisory Center

Federal Aviation Administration

International Air Transport Association

International Civil Aviation Organization

National Oceanic and Atmospheric Administration/

National Environmental Satellite Data and 

Information Service/

Satellite Services Division

National Oceanic and Atmospheric Administration /

National Weather Service

 University of Alaska Fairbanks 

Geophysical Institute

World Meteorological Organization

For more information contact:

U. S. Geological Survey

Alaska Volcano Observatory

4200 University Drive

Anchorage, AK 99508

Tel. (907) 786-7497

http://www.avo.alaska.edu

http://volcanoes.usgs.gov

http://www.ssd.noaa.gov/VAAC/

http://www.icao.int/icao/en/anb/met/index.

html#Doc9766

See also U.S. Geological Survey’s Alert Notification 

System for Volcanic Activity 

(USGS Fact Sheet 2006-3139); 

What are Volcano Hazards? 

(USGS Fact Sheet 002-97); 

and 

Volcanic Ash Fall—A Hard Rain of Abrasive Particles 

(USGS Fact Sheet 027-00)

This Fact Sheet and any updates 

 to it are available online at 

 http://pubs.usgs.gov/fs/2010/3116/

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REMOTE SENSING OF VOLCANIC ASH CLOUDS

Remote sensing by satellite is a powerful tool used to detect and quantify volcanic clouds, 

especially in remote areas of the globe. Volcanic clouds containing ash (mineral and glass 

fragments) and gases such as sulfur dioxide (SO2

) absorb energy from different wavelengths of the electromagnetic spectrum in different amounts than weather clouds—this 

allows satellite sensors to differentiate the various cloud constituents. Volcanic ash is 

detected by comparing the intensity of radiation at two thermal infrared wavelengths, 

creating images of “brightness temperature difference,” while SO2

 is typically detected 

using several wavelengths of ultraviolet energy. Limitations of these techniques are 

frequency of image acquisition (geostationary satellites provide images approximately 

every 15 minutes, but others may provide data only a few times a day), the amount of 

water vapor in the atmosphere, daylight (for ultraviolet satellite data), and masking effects of weather clouds for some sensors. New sensors developed in the past decade 

hold great promise for better real-time tracking and characterization of volcanic clouds.

Satellite images showing the usefulness of the thermal infrared brightness temperaturedifference technique and the ultraviolet absorption technique for discriminating volcanic ash 

and SO2 

, respectively, in volcanic clouds that are physically mixed and visually indistinguishable 

from weather clouds. These images from August 2008 show an ash cloud from Alaska’s 

Kasatochi Volcano over the northern Pacific, about 2 days after the eruption. Shorelines (red) 

are enhanced for reference. A shows a thermal infrared brightness-temperature image. B is 

an enhanced image showing volcanic ash detected using a two-wavelength thermal infrared 

brightness temperature difference. C shows the corresponding SO2

 cloud as indicated by the 

ultraviolet wavelength absorption technique. (Images processed by D. Schneider, USGS.)