.

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1022-A
ASSESSMENT OF

INCREASED THERMAL ACTIVITY

AT MOUNT BAKER, WASHINGTON

MARCH 1975-MARCH 1976
Frontispiece. Mount Baker Volcano. Mount Baker stands more than 3 km above Baker Lake. Acidic water drains through the breach in the 

east rim of Sherman Crater (top center), flows beneath Boulder Glacier and into Boulder Creek, and eventually empties into Baker Lake 

(foreground), 12 km east of the crater. Aerial photograph taken March 4, 1976.
Assessment of 

Increased Thermal Activity 

at Mount Baker, Washington, 

March 1975-March 1976

By DAVID FRANK, MARK F. MEIER, and DONALD A SWANSON

with contributions by JAMES W. BABCOCK, MARVIN O. FRETWELL,

STEPHEN D. MALONE, CHARLES L. ROSENFELD, RONALD L SHREVE, and RAY E. WILCOX

VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1022-A

A summary of geothermally induced changes, 

progress report on geophysical and geochemical 

monitoring, and analysis of hazards at Mount Baker

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Frank, David.

Assessment of increased thermal activity at Mount Baker, Washington, March 1975-March 1976.

(Volcanic activity at Mount Baker, Washington)

(Geological Survey Professional Paper 1022-A)

Bibliography: p.

Supt.ofDocs.no.: I 16:1022-A.

1. Baker, Mount, Wash. 2. Earth temperature Washington (State) Baker, Mount.

I. Meier, Mark F., joint author. II. Swanson, Donald A., joint author. III. Title. IV. Series. V. Series: United States Geological

Survey Professional Paper 1022-A. 

QE523.B18F7 551.2'l'0979773 76-608347

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 

Stock Number 024-001-02981-2
CONTENTS

Page

Abbreviations ........................................... VI

Terminology ............................................ VII

Abstract ................

Introduction ............

Acknowledgments .......

Pre-1975 thermal activity 

1975-76 thermal activity .

Visual observations ..........................

New areas of heat emission ..............

Expansion of old areas of heat emission ...

Thermal infrared observations ................

Summary of thermal infrared observations, 

by Charles L. Rosenfeld ................

Estimates of heat flow ...............

Structural implications of heat pattern

Geophysical and geochemical monitoring ... 

Summary of seismicity and gravity, 

by Stephen D. Malone ...............

Seismicity........................

Gravity ..........................

Tilt .............................................

Petrography .....................................

Results of petrographic examination of samples, 

by James W. Babcock and Ray E. Wilcox ....

Gas ............................................

Hydrology .......................................

Al

1

2

2

8

8

8

9

10

12

14

16

17

19

19

20

23

25

25

26

27

Geophysical and geochemical monitoring Continued 

Hydrology Continued

Monitoring of water quality, by Marvin O. Fretwell. A27 

Hazard analysis ......................................... 30

Pollution ............................................ 31

Avalanche and mudflow hazard ...................... 32

Hazard analysis based on historical record ........ 35

Hazard analysis based on present conditions ....... 36

Sources of mudflows or rock avalanches ....... 36

Motion of possible avalanche or mudflow ...... 36

Summary of evaluation of air-cushioned 

avalanche or mudflow at Boulder Creek, 

by Ronald L. Shreve .................. 36

Effect of possible rock avalanche 

or mudflow on Baker Lake ................. 39

Discussion of hazard analyses .................... 39

Response to Mount Baker activity .................... 39

Initial response .................................. 39

History of Baker Lake closure action .............. 41

Lifting of Baker Lake closure ..................... 41

Conclusions ............................................. 42

References cited ......................................... 43

Appendix 1: U.S. Geological Survey statement on Mount Baker 

situation, June 19, 1975 ................................ 46

Appendix 2: Evaluation of possibility of air-cushioned rock

avalanche or mudflow from Mount Baker, by R. L. Shreve 46 

Appendix 3: U.S. Geological Survey statement on Mount Baker 

situation, April 6, 1976 ................................ 49

ILLUSTRATIONS

FRONTISPIECE. Aerial photograph of the east slope of Mount Baker, March 1976. Page

FIGURE 1. Index map of Mount Baker ...................................................................................... A2

2. Aerial photograph of Dorr Fumarole Field, August 1969 .......................................................... 3

3. Vertical photograph of Dorr Fumarole Field, July 1975 ........................................................... 4

4 7. Photographs of Sherman Crater:

4. Taken from the summit in 1908 ....................................................................... 5

5. Fumarolic activity on the west rim, 1909 ............................................................... 6

6. Fumarolic activity on the west rim, 1914 ............................................................... 6

7. Old main fumarole at south base of Lahar Lookout, August 1974 ......................................... 6

8. Aerial photograph of ice depression in center of Sherman Crater, September 1960 .................................. 7

9. Photographs of Sherman Crater taken from Lahar Lookout, August 1974 and August 1975 ......................... 10

10. Vertical photographs of Sherman Crater, September 1963, September 1975, and April 1976 ......................... 12

11. Aerial photograph of Sherman Crater, March 1975 ............................................................... 15

12-14. Photographs showing:

12. Site of the new main fumarole at the south base of Lahar Lookout, taken from Sherman Peak, August 1974, July

1975, and February 1976 ............................................................................ 18

13. Ice pits in Boulder Glacier, March 1976 ................................................................ 21

14. Superheated fumarole in east breach, September 1975 .................................................. 22

15. Aerial photograph showing upwelling within the crater lake, April 1976 ........................................... 22
VI CONTENTS

Page

FIGURE 16. Photograph of high-pitched fumarole in southwest pit, July 1975 ................................................... A22

17. Infrared image of Sherman Crater, September 1975

18. Stereopair of aerial photographs of Sherman Crater, August 1975 ..............

19. Maps of thermal area, 1900 to 1975 and March to September 1975 .............

20. Graph of thermal area in Sherman Crater, 1900 to 1976 ......................

21. Diagram of method for estimating snow and ice loss ...........................

22. Map of seismic, tilt, and gravity stations .....................................

23. Graph showing spirit-level tilt and gravity measurements .....................

24. Graph showing tiltmeter data at sites A and B ...............................

25. Map of sampling sites for ejecta and locations of profiles through Lahar Lookout

26. Photograph of layers of ejecta in wall of crevasse, March 1975 .................

27. Photograph of gas sensor site ................................................

28. Diagram of profiles through Lahar Lookout ...................................

29. ERTS-1 image of the regional setting of Mount Baker .........................

23

24

28

30

31

31

32

33

34

35

35

37

40

TABLES

Page

TABLE 1. Thermal area at Sherman Crater ................................................................................ A16

2. Different estimates of heat flux from core areas of thermal ground ................................................ 16

3. Heat flux estimated by loss of snow and ice ...................................................................... 17

4. Summary of snow and ice loss and heat-flow estimates ........................................................... 17

5. Seismometers at Mount Baker .................................................................................. 20

6. Summary of >10 jam constituents in debris samples from Sherman Crater area, collected March 31,1975, to February 6,

1976........................................................................................................ 26

7. Characteristics of observed and probable air-cushioned rock avalanches compared with a prehistoric mudflow and

avalanche at Mount Baker ................................................................................... 38

8. Calculated height of waves at Upper Baker Dam ................................................................. 39

ABBREVIATIONS

A ......................... area

BM ....................... bench mark

cm ....................... centimeter

ft3 ........................ cubic foot

m3 ........................ cubic meter

°C ........................ degree Celsius

db ........................ decibel

d ......................... day

D ......................... average snow and ice thickness

FM ....................... frequency modulation

ft......................... foot

H ........................ heat flux

h ......................... water equivalent thickness

hr ........................ hour

Hz ....................... hertz

J ......................... joule

kg ........................ kilogram

km ....................... kilometer

L ......................... latent heat of melting

1 ......................... liter

m ........................ meter

mGal ..................... milligal

ML ....................... local earthquake magnitude

approximated by coda length 

mm ...................... millimeter

mo ....................... month

MW ...................... megawatt

jam ....................... micrometer

jurad...................... microradian

ppb ....................... parts per billion

ppm ...................... parts per million

p ......................... density

s ......................... second

ft2 ........................ square foot

m2 ........................ square meter

t ......................... time

W ........................ watt

yr ........................ year

103 ....................... thousand

105 ....................... hundred thousand

106 ....................... million

107 ....................... ten million

109 ....................... billion
CONTENTS

TERMINOLOGY

VII

Air-cushioned avalanche. An avalanche of debris that moves at 

high speed on a cushion of trapped air.

Avalanche. A large mass of snow, ice, soil, or rock, or mixtures of 

these materials, that falls or slides at high speed under the force of 

gravity.

Debris flow. A mudflow; also used as a rapid mass flowage of coarse 

rock debris.

Ejecta. In this report, fragmental airfall debris produced by 

fumarolic activity.

Eruption. The ejection of volcanic material by a process triggered by 

a magmatic source.

Firn. Snow that remains after at least one melting season.

Friction coefficient. A characteristic of mass movements, such as 

avalanches or mudflows; the vertical drop divided by the horizontal distance of travel.

Fumarole. A vent having a diameter of a few centimeters to several 

meters at the ground surface, from which volcanic gases and water 

vapor or steam are exhaled, often at high temperatures.

Fumarole field. A cluster of fumaroles and associated warm ground.

Fumarolic activity. The surficial expression of noneruptive heat 

emission from a subsurface source, which may be a recent lava 

flow, a cooling body of magma or hot rock (either rising or already 

in place), or a hydrothermal system of hot water or steam.

Geothermal. Pertaining to heat from beneath the earth's surface.

Heat flux. The flow of heat per unit time.

Heat flux density. The heat flux per unit area.

Hydrothermal activity. The action of heated water within the 

earth.

Hydrothermal alteration. The chemical and physical transformation of rock by reaction with heated water.

Lahar. A mudflow which originates on a volcano.

Lava. Molten rock near or on the ground surface, relatively poor in 

gas content; also the same material after it has cooled and 

solidified.

Magma. Molten rock at some depth. Differs from lava in that it contains more gases, which are lost as magma nears the surface and 

changes to lava.

Mudflow. A mass of water-saturated rock debris that moves downslope under the force of gravity.

Pyroclastic flow. A hot, dry mass of volcanic rock debris that moves 

away from an active volcanic vent.

Radiant flux. The flow of radiated heat per unit time.

Stratigraphic. Pertaining to layered deposits of rock.

Tephra. General term for airfall debris produced by a volcanic eruption. Includes but is not limited to ash, pumice, and bombs.

Thermal area. Spatial area of thermal ground.

Thermal ground. In this report, ground heated by a volcanic source.

Water equivalent. The amount of water that would result from the 

complete melting of a body of deposited snow, firn, or ice, expressed 

as thickness (depth) or volume.
VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

ASSESSMENT OF INCREASED THERMAL ACTIVITY

AT MOUNT BAKER, WASHINGTON,

MARCH 1975-MARCH 1976

By DAVID FRANK, MARK F. MEIER, and DONALD A. SWANSON

With contributions by JAMES W. BABCOCK, MARVIN O. FRETWELL, STEPHEN D. MALONE,l 

CHARLES L. RosENFELD, 2 RONALD L. SnREVE,3 and RAY E. WILCOX

ABSTRACT

In March 1975 Mount Baker showed a large increase in thermal 

emission, which has persisted for more than 1 year. Fumarole ejecta 

accompanied the thermal activity from March to September, but the 

ejecta had no constituents that suggest a magmatic source. Estimates of that part of the total heat flux that would account for the 

observed snow and ice loss show that the heat-flow increase was 

roughly one order of magnitude, from about 2 megawatts at 10 watts 

per square meter, averaged over Sherman Crater before 1975, to 

about 30 megawatts at 180 watts per square meter, during 1975. 

Almost half of the glacier that occupied the basin of Sherman Crater 

was melted in 1975.

The new activity generated great concern among the public and 

the government agencies responsible for geological evaluation of potential hazards and for protection of life and property. The past 

geologic history, current topography, rock alteration, and location of 

major fumarolic activity indicate that large rock avalanches and 

mudflows on the east slope in Boulder Creek valley are the potential 

hazards of most significance related to present conditions. The most 

probable types of large mass movements would be mudflows, having 

speeds of as much as 50 kilometers per hour, that would originate 

from mixtures of snow, ice, and melt water and avalanches of structurally weak clay-rich rocks that make up the rim of Sherman 

Crater. Similar mudflows from the volcano have traveled at least 12 

kilometers 8 times during the past 10,000 years. A possible worst 

case event, however, might be a larger, air-cushioned avalanche of as 

much as 20 to 30 million cubic meters that could hit Baker Lake at 

speeds of more than 300 kilometers per hour and generate a wave of 

water large enough to overtop Upper Baker Dam.

At least 30 million cubic meters of potentially unstable material 

occurs as hydrothermally altered remnants of the rim of Sherman 

Crater and could provide the required volume for the estimated worst 

case event or for smaller avalanches and mudflows. An earthquake, 

steam explosion, or eruption could provide a suitable trigger to initiate movement. Although such triggering events were possible before 

1975, the probability might have been as much as 10 times greater in

"University of Washington.

2Oregon State University.

"Consulting Geologist, Los Angeles, Calif.

1975 because of the increased thermal activity. The threat of 

avalanches and mudflows on Boulder Creek valley and Baker Lake 

prompted the closure by management agencies of the Boulder Creek 

drainage and of Baker Lake and its shoreline in the summer of 1975. 

Additionally, Baker Lake was kept below full pool at a level calculated to prevent overtopping of Upper Baker Dam by waves which 

could result from a worst-case avalanche.

In 1975 an interdisciplinary program of seismic, tilt, gravity, gas, 

hydrologic, petrologic, thermal infrared, and photographic studies by 

Federal and university scientists was initiated to evaluate the impact 

of the current thermal activity and to monitor changes that might indicate an impending eruption. By March 1976 only one small earthquake had been identified beneath Mount Baker. Tilt and gravity 

changes have been observed but cannot be attributed solely to 

volcanic causes. The data available thus far provide no evidence of an 

impending eruption, but they cannot be fully interpreted without 

many additional geophysical and geochemical measurements, as it is 

not yet possible to clearly distinguish volcanic effects from nonvolcanic background effects.

Inasmuch as current activity continues unchanged without 

steam explosions, eruptions, or frequent or large earthquakes the 

probability of a suitable trigger for large avalanches and mudflows 

should decrease and should approach that of a more average year. 

Such an average year would have a hazard probability at least as 

great as that which existed before 1975, although that level of 

hazard was not recognized at the time by the public or by administrative agencies. The potential hazard and the uncertainties of future 

activity at Mount Baker necessitate continued observation and instrumental monitoring.

INTRODUCTION

Thermal activity at Mount Baker, Wash., increased 

drastically in March 1975 and led to speculation that a 

volcanic eruption might be imminent. Through the next 

12 months, Mount Baker was the site of the most intensive monitoring ever applied to a volcano in the Cascade

Ai
A2 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

Range. By spring of 1976 the thermal activity had remained strong, but no further evidence of an impending 

eruption had surfaced; however, the collected data provide valuable insights into potentially hazardous processes that might be expected in the future at any quiescent volcano.

Mount Baker (48°47' N., 121°49' W.) is the northernmost of the Quaternary stratovolcanoes of the 

Cascade Range of northern California, Oregon, and 

Washington (Coombs, 1939). The summit is 3,285 m 

above mean sea level and 48 km east of Bellingham 

Bay. The volcano is drained on the east and south by 

tributaries of the Skagit River and on the west and 

north by headwaters of the Nooksack River (fig. 1). 

Owing to high precipitation and to the high latitude of 

the volcano, it is almost completely covered by glaciers.

122°00'

CJVIT BAKER^X

Sherman 

Crater (

FIGURE 1. Index map of the Mount Baker, Wash., area. Glaciers are 

outlined by dashed lines.

This report provides a compilation and discussion of 

thermal changes that occurred on Mount Baker between March 1975 and March 1976. Because many of 

the changes were detected primarily by visual observation, the historic record of the past 75 years is first 

reviewed to place current activity into perspective with 

older thermal features. Geochemical and geophysical 

monitoring activities during the past year are then

summarized, and significant results are discussed. 

Finally, existing and potential hazards are evaluated, 

and the resultant administrative and public responses 

are described.

ACKNOWLEDGMENTS

Data concerning pre-1975 activity were derived from 

photographs and reports from various mountaineering 

sources; from aerial photographs, primarily by Austin 

Post, taken from glacier research and kept at the U.S. 

Geological Survey Project Office, Tacoma; from recent 

field and infrared remote sensing studies by the U.S. 

Geological Survey; and from the University of 

Washington investigations of volcanic seismicity. 

Special appreciation is extended to Alex Horstman, 

S. M. Lea, Peter Shreve, M. A. Spiers, and I. J. 

Virsnieks, who, without any foreknowledge that we are 

aware of, provided assistance in acquiring valuable 

field data during 1972-74 that established much of the 

basis on which to judge the extent of recent changes.

Data on 1975 76 activity were drawn from interdisciplinary studies by researchers of the U.S. Geological Survey, U.S. Forest Service, Los Alamos Scientific 

Laboratory, University of Washington, Eastern Washington State College, Western Washington State College, Oregon State University, and Central Oregon 

Community College. Some of those most involved in the 

present monitoring programs at Mount Baker include 

S. D. Malone, seismicity and gravity; R. M. Krimmel 

and Austin Post, aerial photography; Motoaki Sato, gas 

chemistry; J. E. McLane, J. W. Babcock, and R. E. 

Wilcox, petrography; D. A. Swanson and W. T. 

Kinoshita, spirit-level tilt; Rex Alien, Anselmo Rodriquez, J. D. Unger, and D. H. Harlow, borehole 

tiltmeters; Bruce Nolf, tilt-bar stations; C. L. Rosenfeld, 

infrared studies; and G. C. Bortleson, M. O. Fretwell, 

and A. D. Zander, water quality. The sections on 

monitoring in this report were compiled from summaries prepared by many of these individuals.

PRE-1975 THERMAL ACTIVITY

The history of volcanic activity during the past 

10,000 years has been reviewed by Hyde and Crandell 

(1975,1977), who found stratigraphic evidence of a major eruptive episode of pyroclastic flows, lava flows, and 

tephra during the early part of this time period. These 

eruptions were followed by at least two small eruptions 

of tephra, the most recent of which was within the past 

few hundred years. Historic reports of eruptive activity 

were reviewed by Malone and Frank (1975), who found 

references to eruptions of tephra and, possibly, lava 

flows during the mid 1800's. However, no definite correlation has been made between the most recent
ASSESSMENT OF INCREASED THERMAL ACTIVITY A3

FIGURE 2. Dorr Fumarole Field, on the northeast slope of Mount Baker. A vapor plume (arrow) can be seen in this August 2,1969, view of 

the field, which lies in a small cirque at the head of Mazama Glacier. Sherman Crater lies to the south, behind and to the left of the summit. Aerial photograph K692 16, by Austin Post.

deposits found by Hyde and Crandell (1975, 1977) and 

the 19th-century eruptions.

Reports by observers show that fumarolic activity 

has been common since the mid-1800's. Coleman (1869) 

reported fumarolic activity in 1868 in Sherman Crater 

about 1 km south of the volcano's summit, and William 

Henry Dorr4 reported vapor emission on the north slope 

of the volcano in 1884 in an area now called the Dorr 

Fumarole Field (fig. 1).

Although no large changes have occurred recently at 

the Dorr Fumarole Field, it is described here because it 

has been overlooked in most of the literature concern4 Reported in C. F. Easton's "Mt. Baker, Its Trails and Legends," an unpublished 262-page 

compilation of photographs, newspaper articles, and manuscript commissioned in 1911 by 

the Mount Baker Club and kept in archives at the Whatcom County Museum of Natural 

History, Bellingham, Wash.

ing Mount Baker. In 1884 W. H. Dorr viewed what he 

thought was "a steaming crater on the northeast slope" 

of the volcano (fig. 2).

In 1906 a more extensive examination was made by 

Landes (1907, p. 6-7), State Geologist, who wrote:

The steam vents occur over about 2 acres and this area is now wholly 

bare and free from ice. There are hundreds of vents from which 

steam is constantly escaping and in the summer air the vapor rises 

forty or fifty feet before it becomes invisible * * *. Along with the 

steam much sulphur is escaping, and for several miles away the odor 

of it may be detected. The sulphur in a variety of colors is being 

deposited upon the rocks about the vents. From many of the vents 

small streams of boiling water flow, and these unite in a brook that 

soon plunges beneath ice.

Landes' (1907) description could equally apply to present conditions. Aerial photographs taken since 1940, as
VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

FIGURE 3. Vertical view of Dorr Fumarole Field. About 4,900 m2 of heated, snow-free ground (circled) is visible. Aerial photograph

75MB1-25, by R. M. Krimmel, June 10,1975.

well as infrared thermographs made from 1970 to 1975, 

show little change in the area of snow-free thermal ground at the Dorr Field.5 The midsummer size of 

the area, as measured from a 1975 photograph (fig. 3),

6 A report containing the results of an experiment to monitor temperature by satellitetransmitted data during 1973 74 at the Dorr Fumarole Field and an analysis of aerial infrared surveys of Mount Baker during 1970-73 is now being prepared by J. D. Friedman.

is 4,900 m2 . Typically, the Dorr Field contains small 

fumaroles, generally a few centimeters across but in 

places as much as 20 cm, that have temperatures of 

about 90°-91°C, the approximate boiling point of water 

at that altitude. Vapor plumes from the area are 

usually visible from the air, and sometimes they may be 

seen from north of the volcano at Austin Pass.
ASSESSMENT OF INCREASED THERMAL ACTIVITY A5

FIGURE 4. Sherman Crater, viewed to the south from near the summit of Mount Baker, July 20,1908. Reports of mountaineers as early as 

the 1890's mention sulfurous vapors which issue from an ice pit within Sherman Crater. The same prominent ice pit (arrow) as that of 

late 19th-century reports lies between Sherman Peak to the south and Lahar Lookout in the left foreground. Asahel Curtis photographed 

this early view.

Newspaper accounts record several climbers' reports 

of steam emission at Sherman Crater in the 1890's. A 

photograph taken in 1900, viewed southward from the 

top of Lahar Lookout, shows vapor issuing from a large 

ice pit near the east breach of the crater rim (Rusk, 

1924, p. 130). The surface of the snow in the crater is 

otherwise very smooth; only a few crevasses are on the 

upper slopes of Sherman Peak, the highest part of the 

south rim of the crater. Figure 4 is one of a series of 

photographs with a similar view that were taken in late 

summer, in the early part of this century. These photographs all show a large ice pit near the east breach. By 

the time of our first field investigations, in 1972, the 

general ice cover in the crater was markedly lower than 

it was in 1900, either because of increased subglacial 

melting from volcanic heat or because of a decrease in 

glacier thickness generated by climatic conditions;

however, the large ice pit was still present. Elsewhere 

in Sherman Crater, photographs taken during the early 

part of the century show small clusters of fumaroles 

(figs. 5, 6). Rough estimates of the amount of heated 

snow-free ground, as represented by the features visible in early photographs, indicate at least several 

hundred square meters of thermal area prior to 1940. 

These are minimum estimates because not all of the 

crater can be seen in early photographs.

The earliest available photographs that show the 

whole crater were taken in 1940 (Frank and others, 

1975, fig. 3), a time that coincides approximately with a 

20th-century minimum in glacial extent in the North 

Cascades (Hubley, 1956). If volcanic heat had been constant and in equilibrium with ice thickness in Sherman 

Crater since 1940, the extent of the snow-free thermal
A6 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

FIGURE 5. Fumarole cluster on the west rim of Sherman Crater, 

1909. Photograph by Henry Engberg.

FIGURE 6. Part of the west-rim thermal area, 1914. Photograph by 

Clyde Banks.

area would have decreased after 1940 as the glacial 

cover increased at high altitudes. Instead, aerial photographs taken during late-summer snow conditions in 

1940 and almost every year since 1956 show that the 

snow-free thermal ground in Sherman Crater has inFIGURE 7. Northward view of the old main fumarole near the east 

breach of Sherman Crater, August 16, 1974. This fumarole lies at 

the south base of Lahar Lookout.

creased from about 5,500 m2 in 1940 to almost 10,000 

m2 during the past decade. A thermal-infrared survey 

in November 1972 found 8,800 m2 of infrared anomalies 

warmer than 0°C in Sherman Crater (Frank and 

others, 1975, p. 84). This value is in good agreement 

with our estimates of the thermal area made from the 

more recent aerial photographs (1966 and later).

Field investigations in 1972 74 showed that thermal 

features consisted of warm ground and small 

fumaroles. The fumaroles were generally a few centimeters across, although some were as large as 50 cm, 

and all had temperatures at or below 90°C. Fumaroles 

occurred in clusters along the southwest, west, and 

northwest rims and near the east breach area of the 

crater rim. One particularly loud, pressurized fumarole 

(fig. 7) near the east breach bordered a stream that 

drained surface water from Sherman Crater. This 

fumarole, referred to as the old main fumarole, appeared to produce the largest vapor plume in Sherman 

Crater not only during pre-1975 field investigations 

but also in most aerial photographs of the crater taken 

before 1975. A temperature of 84°C measured at the old 

main fumarole in August 1974 was distinctly lower
ASSESSMENT OF INCREASED THERMAL ACTIVITY A7

FIGURE 8. Prominent depression (arrow) in ice surface in middle of 

Sherman Crater. In this late afternoon view, shadow accentuates 

the depression. Other pre-1975 thermal features mentioned in text 

are as follows: EB, two clusters of fumaroles near the east breach;

than temperatures in nearby, less pressurized 

fumaroles. The lower temperature at the time may 

have reflected a large input of cooler creek water. Other 

fumaroles near the east breach occurred in two main 

clusters, in the area of the old main fumarole and 

upstream near a small water fountain (perforations d 

and e, respectively, of Frank and others, 1975). 

The drainage creek from Sherman Crater was inWR, west-rim fumaroles; NWR, northwest-rim fumaroles; and 

NWP, northwest pits. The prominent plume in the lower right 

originates from the old main fumarole. Aerial photograph 

FR6025-135, by Austin Post, September 27, 1960.

vestigated in 1973 with tracer dye (Frank, 1975). It was 

found to travel beneath Boulder Glacier and to affect 

the pH and sulfate content of Boulder Creek. As 

described later in this report under "Hydrology," the 

monitoring of Boulder Creek during 1975 showed 

degradation of water quality to be a major environmental result of increased fumarolic activity.

Photographs taken after 1956 show a prominent
A8 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

depression in the surface of the ice in the central part of 

the crater (fig. 8). Frank, Post, and Friedman (1975, p. 

86) interpreted this depression to be a surficial expression of some subglacial source of heat, possibly a warm 

lake. Subglacial exploration in ice caves by Kiver (1975, 

p. 87) revealed that in 1974 a pond only 10 m long was 

evident beneath the depression.

Thermal activity in the southwestern part of the 

crater was first noted in photographs taken in 1956. 

One pit, and sometimes two, persisted in this area 

throughout the 1960's. Photographs show that these 

pits were often completely covered by snow during the 

winter but that they always melted open in the summer.

Fumaroles have been present along the west rim of 

the crater since the early 1900's. Although photographs 

taken intermittently from 1909 through the 1930's 

show some of the fumaroles, the total extent of activity 

was first revealed by 1940 aerial photographs, which 

show a linear zone of fumarole clusters about 100 m 

long midway across the inner slope of the west rim. The 

fumaroles along the west rim are the most accessible 

and have been the most closely observed in the crater.

Early 20th-century photographs show little of the 

northwest area of the crater. However, by 1940 thermal 

ground occurred at two locations along the rock-ice 

margin at the base of the steep northwest rim and in a 

shallow ice pit about 50 m downslope from the rim. 

These features changed little in subsequent years, 

although at times two adjacent shallow ice pits formed 

instead of one. Since 1956 the northwest ice pits have at 

times been completely covered by winter snow, as have 

the southwest pits, but they, also, have always melted 

open during the summer.

1975-76 THERMAL ACTIVITY 

VISUAL OBSERVATIONS

An important feature of all pre-1975 photographs of 

Sherman Crater is the small number of crevasses and 

the general smoothness of the crater glacier (fig. 9 A). 

The change in thermal activity in 1975 was accompanied by a tremendous increase in the area of heated, 

snow-free ground and by an increase in the number and 

size of crevasses as ice in the crater began to accelerate 

downslope toward the east breach and the new thermal 

areas (fig. 9fi).

The first observations of abnormal activity were 

made on March 10, 1975, when personnel at Upper 

Baker Dam (fig. 1) and residents of towns south and 

west of Mount Baker noted unusually high, dark vapor 

plumes. During subsequent overflights of the crater, 

two major changes were most evident the appearance of new, larger fumaroles, and the emission of

fine-grained ejecta. Later effects of increased thermal 

activity were the massive breakup of snow and ice and 

the development of a crater lake. New thermal features 

developed in areas which had not previously shown 

thermal activity. In addition, virtually all the preexisting thermal features had enlarged (figs. 10A, B,C).

NEW AREAS OF HEAT EMISSION

Photographs and infrared images taken during the 

few weeks following March 10 showed the initial 

development of three new clusters of thermal activity 

 the north pit, the new main fumarole, and the 

Boulder Glacier pits (fig. 11). The north pit formed in a 

previously smooth ice slope that descended the north 

rim of the crater from the mountain's summit (fig. 

10A). The pit enlarged through the spring, mostly as a 

result of ice calving, and has consistently been the 

source of a large vapor plume. Because of the pit's inaccessibility, little is known of the areal extent or the temperatures of fumaroles that feed this prominent plume. 

From the location of ice-cave entrances, it is judged 

that water drains subglacially from the north pit 

downslope to the east breach.

A new main fumarole had developed by March 10 on 

a ridge near the base of Lahar Lookout (fig. 12). The 

plume from this fumarole has consistently been the 

largest single fumarole plume during the past year, 

although the combined vapor from clusters of other 

fumaroles has at times produced more prominent 

plumes. The orifice of the new main fumarole was about 

1 m in diameter when first observed in March; it 

developed into a 1- x5-m fissure by summer and has remained about the same size through March 1976 

(fig. 12C). Attempts at temperature measurement were 

never completely successful, giving only a minimum 

value of 86°C along the inside margin of the fumarole in 

September.

Most of the particulate matter ejected from Sherman 

Crater during 1975 apparently came from this single 

fumarole, although during at least one period, July 

10 11, many of the other fumaroles also emitted ejecta. 

Ejecta in the main fumarole plume was noted in many 

field investigations and overflights between March 27 

and September 30 and probably was emitted continuously through the spring and summer of 1975. Mud 

streams from the lower lip of the main fumarole were 

noted in August and September and indicated that part 

of the fumarole consisted of a mudpot during this 

period. Analyses of ejecta and mud are summarized 

under "Petrography" later in this report.

After heavy snowfall began in October, no more ejecta from the new main fumarole were observed on the 

snow surface. The first winter field investigations, in
ASSESSMENT OF INCREASED THERMAL ACTIVITY A9

February 1976, revealed two additional changes that 

had occurred after late September. Mud extrusion had 

stopped, and the inside lip of the fumarole had been 

lightly coated with yellow sublimates probably 

sulfur. These changes suggest that vapor in the new 

main fumarole became considerably drier after September 1975.

Photographs and infrared images made in March 

1975 showed the presence of two small ice pits in the 

upper part of Boulder Glacier at the northeast base of 

Sherman Peak (fig. 11). By summer, the two pits 

coalesced into a single trough between ice in the east 

breach and a rock outcrop on Sherman Peak, and a second trough developed nearby within a crevasse in 

Boulder Glacier. Both troughs persisted through the 

winter of 1975-76 (fig. 13), and infrared images show 

that they have been warmer at times than other nearby 

crevasses. Small amounts of vapor have occasionally 

been observed within the troughs. Possible sources of 

subglacial heat responsible for the troughs are either 

local fumarolic activity or warm water (perhaps 

ponded) from the subglacial stream that drains the 

crater.

EXPANSION OF OLD AREAS OF HEAT EMISSION

In addition to activity in new areas, all pre-1975 sites 

of thermal activity have changed to some extent. The 

most prominent changes occurred near the east breach 

in the central part of the crater, and along the southwest, west, and northwest rims.

In 1975 the two large clusters of fumaroles near the 

east breach expanded into a single cluster of activity 

that included the new main fumarole. Many other 

fumaroles were superheated, reaching temperatures of 

as much as 131°C when measured in September 1975 

and February 1976. The hotter fumaroles were typically associated with greater amounts of sulfur 

deposits and higher vapor pressures (fig. 14). A water 

fountain, which had been in a pool about 2 m across and 

30 cm deep in 1973 and 1974, had dried up by September 1975. The greatest density of superheated 

fumaroles occurred in the area of this old water fountain, which corresponds to the site of the large ice pit in 

early 20th-century photographs (fig. 4). This location 

has consistently been the site of the hottest and largest 

cluster of heat emission in Sherman Crater in this century.

During the summer of 1975, as the ice margin 

receded upstream from the superheated area toward 

the north pit, a flat alluvial deposit of sand and silt was 

revealed that appeared to be sediment washed down 

from the area of the north pit. A pond was observed to 

be temporarily dammed here on July 3, but it had

drained by September. Streams from this area merged 

with a stream from the central part of the crater. 

Drainage then skirted the superheated area, cut 

through the bank on which the old main fumarole was 

located, and cascaded about 20 m down into the narrow 

ice-covered gorge of the east breach, between Sherman 

Peak and Lahar Lookout. Stream discharge was not 

measured in 1975, but it appeared to be similar to that 

observed in September 1973 and August 1974. The apparently similar discharge, despite obviously increased 

ice melt, suggests that a significant amount of water is 

lost from the crater either underground or, more probably, by evaporation. Stream temperatures near the old 

main fumarole in September 1975 were 18° 21°C, in 

comparison to 7°-8°C in August 1974.

The depression in the central part of the crater 

quickly deepened in March 1975 as crevasses formed 

around it. In April ice collapsed and melted into a 

shallow oval lake about 50x70 m across at the bottom 

of a 40-m-deep ice pit. Fumaroles occurred both on the 

shore and within the lake. As many as 5 patches of upwelling developed in the north-central part of the lake 

from May through August, but only one major area persisted through March 1976 (fig. 15). The lake depth was 

less than 50 cm at 2 points about 10 m from shore, and 

the maximum depth was probably not much greater. If 

an average depth of 1 m is assumed for the lake, about 

2,600 m3 of water was impounded on the floor of the 

central pit. The lake has drained continuously since 

April 1975 beneath ice at its eastern margin, where it 

presumably feeds the main creek in the east breach. 

Lake temperatures varied between 26° and 34° C in the 

summer of 1975 and were probably strongly affected by 

the amount of ice which fell intermittently from the 

walls of the central pit. The lake level and shape has 

fluctuated somewhat since that time, but ice has failed 

to dam the lake outlet during the past year.

The southwest pit enlarged greatly in 1975, and investigation revealed an area of hot ground surrounding 

a small fumarole that was highly pressurized (fig. 16). 

This fumarole has consistently produced the highest 

pitched sound of any in the crater. By September, ice 

collapse was noted nearby, next to a prominent rim 

remnant (fig. 10.6). Vapor issued, at times, from enlarging crevasses in this area, and by December 1975 a 

large new pit had developed between the southwest pit 

and the west rim (fig. 10C, NSWP). This new pit is one 

of the few major changes since the summer of 1975 and 

represents further expansion of fumarolic activity in 

the southwestern part of the crater.

A major expansion of the preexisting linear zone of 

thermal activity along the west rim occurred in 1975 as 

new fumarole clusters formed downslope from it. 

Because of accessibility, the west rim has been the site
A10 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

FIGURE 9. — Southwestward view of Sherman Crater, from Lahar Lookout. A, August 1974, signs of thermal activity are the west-rim

fumaroles and southwest pit have expanded, the central pit has

of repeated temperature measurements and gas sampling. Temperatures in 1975 were 89°-91°C. During at 

least one period — June 10-11, 1975 — many of the 

west-rim fumaroles emitted clayey ejecta similar to 

that from the new main fumarole.

The northwest thermal area also expanded in 1975. 

Two adjacent but distinct clusters of activity developed 

within the ice pits; however, much — but not all— of

the hot ground was covered by snow during the winter 

of 1975—76. Fumarolic activity along the northwest rim 

occurs in a breccia layer which is a continuation of the 

same layer that contains much of the west-rim activity.

THERMAL INFRARED OBSERVATIONS

Infrared studies made during 1975 were conducted 

by several groups. A cooperative University of
ASSESSMENT OF INCREASED THERMAL ACTIVITY All

fumaroles (right middle) and the southwest pit (behind snowdrift). A tent and standing man provide scale. B August 1975, the west-rim 

appeared, and the glacier has broken up considerably.

Washington—U.S. Forest Service infrared survey was 

made March 26, 1975, shortly after the onset of increased activity. These initial infrared images confirmed that the major areas of new thermal activity 

were near the east breach and in the north pit. The 

survey also detected anomalous heat in the two small 

ice pits at the northeast base of Sherman Peak (fig. 13).

In April, Los Alamos Scientific Laboratory also began 

to acquire infrared data (Eichelberger and others, 

1976), and in May the Oregon Army National Guard 

and the Geography Department at Oregon State 

University (OSU) undertook a cooperative remote sensing program. The OSU program was headed by Charles 

L. Rosenfeld, who prepared the following summary.
A12 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

FIGURE 10. — Vertical views of Sherman Crater. A, Thermal features all visible in this photograph. These features remained virtually 

on September 3, 1963. Snow-free areas which resulted from ther- unchanged until 1975. B, By September 24, 1975, all the old thermal activity are near the east breach (EB), southwest pit (SWP), mal features had expanded. A single dense plume issued from the 

west rim (WR), northwest rim (NWR), and northwest pit (NWP), new main fumarole at the south base of Lahar Lookout (arrow),

SUMMARY OF THERMAL INFRARED OBSERVATIONS

By CHARLES L. ROSENFELD

Beginning in mid-May, thermographic images were 

obtained at 10-day intervals by use of an infrared line 

scanner aboard OV—1C Mohawk aircraft. These 

aircraft (part of the 1042d Military Intelligence Company (Aerial Surveillance)), based at the Army Aviation Facility at Salem, Oreg., were also used to obtain 

aerial photographs at 20-day intervals. Special flights 

were also flown in response to signals from the groundbased monitors operated by other groups.

This infrared monitoring program was designed to 

provide high-resolution images for interpretation of 

thermal activity and to aid in evaluation of thermal 

changes and potential hazards associated with them. 

Flights were designed to provide both day and night

coverage. A series of experimental flights was initially 

conducted to determine the best spectral response 

regions for the observation of thermal activity. Two infrared detector heads were used for the AN/AAS-14A 

line scanner employed in this project:

Detector Spectral range

Mercury, Cadmium 8-14 ^m (10-13 peak

Telluride (MCT). response). 

Indium Arsenide (InAs) ----- 1-3.4 fjan (3-3.2 peak

response).

In addition, a selection of band-pass and cutoff filters 

were used. Images acquired by use of the MCT detector 

and the appropriate cutoff filter show a large 

anomalous area that is hotter than 15°C but obscured 

in some places by rising steam plumes. Figure 17 shows 

an image obtained on September 26, 1975, with the 

InAs detector, which was also used to pinpoint the loca-
ASSESSMENT OF INCREASED THERMAL ACTIVITY

4 "

and a thin cover of ejecta blanketed the snow surface. Other new 

features included the Boulder Glacier pits (BGP), the north pit 

(NP), and the crater lake in the central pit (CP). C, On April 3, 

1976, the newly developed thermal features were still present

tion of major "hotspots" and reduce the level of atmospheric attentuation by steam. The differences in 

image resolution make simultaneous acquisition 

desirable, in that the MCT detector shows pertinent terrain features that facilitate easy location of major 

anomalies, whereas the In As detector (sometimes used 

with a cutoff at 80°C) resolves the exact location of 

fumarole vents but subdues locational information. 

Good fumarole locations can be identified by optically 

superimposing the InAs on the MCT imagery. Dual sensors were operated in a simultaneous mode throughout 

the monitoring program.

A log of all anomalies was maintained and updated at 

10-day intervals. Daytime stereographic photographs 

(fig. 18) were then related to the thermal images, which 

were acquired at night to minimize anomalies due to 

solar heating. In figure 18, 7 major fumarole clusters

despite peak accumulation of seasonal snowpack. In addition, a 

new pit, full of steam, developed in the southwestern part of the 

crater (NSWP). Aerial photography by Austin Post (A, V635-8; B, 

75V5-262) and R. M. Krimmel (C, 76NC2-13).

can be identified. Each infrared "hotspot" has been 

assigned to a cluster, and its position and its initial observation date have been recorded.

Early attention was focused on the growth of thermal 

activity near the east-breach and north-pit areas, but 

the dramatic formation of the central pit between April 

12 and April 20 demonstrated that sudden changes 

could also occur elsewhere within the crater. The total 

surface area of the crater was calculated to be 185,700 

m2 , of which 35,200 m2 (19 percent of the crater area) 

was free of snow and ice in August 1975. Infrared thermographs indicated that 12,600 m2 (or more than onethird of the snow-free area) was heated to more than 

15°C on August 24, 1975. Few changes were observed 

between August 1975 and March 1976. The 1975-76 

winter snowfall has outlined a heated area of nearly 

12,000 m2 of persisting snow-free ground which approx-
A14 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

% .^

FIGURE 10. -

imately coincides with the summer surface that is hotter than 15°C. Some new ice perforations have appeared since summer, most notably along the southwest rim.

ESTIMATES OF HEAT FLOW

The change in area of heated snow-free ground (thermal area) was mapped (fig. 19) by discrimination of 

anomalously steep snow margins in aerial photographs 

and by field observations (Frank and Post, 1976). This 

method estimates the area of geothermally heated 

ground during late summer snow conditions. The major 

source of error is lack of differentiation between 

geothermal areas and solar-heated ground where snow 

is absent. Such error can be minimized by nighttime 

thermal infrared surveys. Nevertheless, photographs 

and several temperature measurements below the 

ground surface permit rough estimates of the thermal 

area to within a few hundred square meters.

Table 1 lists the amount of thermal area as mapped 

from vertical photographs taken after 1940 and as esti-

__JI.

Continued.

mated from ground photographs taken prior to 1940. 

The chronological change in thermal area is displayed 

in figure 20. Generally, a small but consistent increase 

in thermal area occurred prior to 1975. In 1975 the 

thermal area expanded by a factor of 3 from conditions 

of the previous year. By late summer 1975, about 28,000 

m2 of thermal ground was apparent in photographs. At 

the same time, about 12,600 m2 of infrared anomaly 

above 15°C occurred within this area, as previously 

described by Rosenfeld. The 1975 increase was by far 

the greatest change during the last 75 years. This 

threefold increase in thermal area, however, represents 

only part of the total heat increase. A lower limit for ' 

total heat flux from Sherman Crater can be calculated 

from the volume of newly melted snow and ice.6 This 

method produces a minimum value because it neglects 

heat flux involved in evaporation and radiation from 

snow-free areas, as well as advection in water and 

vapor discharge.

6 As used in this report, "snow and ice" includes firn.
ASSESSMENT OF INCREASED THERMAL ACTIVITY A15

/' 

.**

-offm

FIGURE 11. — Early westward view of increased thermal activity, March 27, 1975. Initial signs of new activity were the north pit (not shown), 

main fumarole (arrow), increased crevassing, and Boulder Glacier pits (BGP). For scale, the distance across the east breach from the top 

of Sherman Peak (upper left) to the top of Lahar Lookout (middle right) is about 500 m. Aerial photograph by Austin Post.

Figure 21 illustrates the method by which heat-flow 

estimates can be made. Core areas of intense heat flow 

are free of snow even in winter (fig. 21 A); areas of 

moderate heat flow become snow free during the summer (fig. 21fi); and the remaining snow, firn, and ice 

mass of Sherman Crater thins from year to year (fig. 

21C), presumably owing to melting at the base or to 

extension toward thermal areas. The development of 

new thermal areas in 1975 caused intense local extension and crevassing toward these areas (fig. 21D) 

because additional heat went into melting of nearby 

snow and ice.

Heat flux from the core thermal areas (fig. 21A ) is 

difficult to estimate. Two approaches are used in this 

estimation: First, these areas remain free of snow and 

probably are hot enough to melt snow as fast as it falls 

or drifts in. White (1969) estimated that 419 W/m2 of 

heat flux was necessary for such rapid snowmelt. This 

flux density is sufficient to melt snow at a rate of 11 

cm of water (equivalent thickness) per day, which is 

not an unreasonable limit at Mount Baker, considering the high precipitation and rapid wind-drifting environment. The actual heat-flux density could be 

slightly lower or considerably higher. Second, some 

areas, such as the central pit, had flux densities as 

high as 2,400 W/m2, as judged by snowmelt and 

icemelt in the spring of 1975. If one assumes that the 

heat flux does not vary seasonally, such maximum 

values of observed flux densities can be used to estimate heat flux in adjacent areas that are free of snow 

during times of peak snowpack, as these areas cannot 

have had lower flux densities. These various estimates 

of core-area heat flux are given in table 2. Pre-1975 

values are less than 1 MW; 1975-76 values are considerably greater than 1 MW.

Heat flow marginal to the core geothermal areas 

(figs. 215, C, D) can be estimated somewhat more precisely from the anomalous loss of snow and ice in summer. The heat flux is given by

H = pDALIt

where p is average density (600 kg/m3 for snow; 700 

kg/m3 for snow and ice undifferentiated), Dis average
A16 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

TABLE 1. — Snow-free thermal area, in square meters, at Sherman Crater

[Areas not completely shown in photographs are indicated by a query (?). Zero indicates area was snow covered at the time photograph was

made]

Old New 

south- south- North- NorthDate of East west west Central West west west North Boulder 

photograph breach pits pit pit rim rim pits pit Glacier Total

1900.... 300? 000???0? 300? 

1908-14.... 300? 000 800? ? ? 0 ? 1,100? 

Sept. 1933.. 2,000? ? ? ? 2,400 500 0 0 ? 4,900? 

Sept. 1940.. 2,000 000 2,800 500 200 0 0 5,500 

Aug. 22, 1956.. 2,300 200 0 0 3,100 500 300 0 0 6,400

Sept. 27, I960.. 2,800 400 0 0 3,800 500 100 0 0 7,600 

Sept. 3, 1963.. 2,200 500 0 0 4,300 900 200 0 0 8,100 

Aug. 1965.. 3,000 1,000 0 0 4,900 900 400 0 0 10,200 

Sept. 22, 1966.. 2,300 700 0 0 4,800 900 100 0 0 8,800

Aug. 22, 1969.. 3,000 600 0 0 4,500 900 400 0 0 9,400 

Mar. 1, 1971.... 800 0 0 0 1,000 200 0 0 100 2,100 

Apr. 22, 1972. '1,100 0 0 0 800 200 0 00 2,100 

Aug. 27, 1972.. 3,400 900 0 0 4,400 900 200 0 100 9,900

Aug. 16, 1974.. 3,100 1,000 0 0 4,200 900 300 0 100 9,600 

Mar. 24, 1975.. 3,800 200 0 0 1,400 300 100 800 100 6,700 

June 10, 1975.. 7,100 300 0 2,600 6,600 900 600 4,000 100 22,200 

July 20, 1975.. 8,100 500 0 2,700 9,800 900 700 2,900 100 25,700

Sept. 7, 1975.. 8,900 500 100 2,800 9,900 900 1,700 3,900 200 28,900 

Sept. 24, 1975.. 9,000 500 400 2,900 9,900 900 2,000 3,900 200 29,700 

Dec. 5, 1975.. 1,100 100 100 1,500 1,200 500 100 400 200 5,200 

Mar. 4, 1976.. 2,600 100 200 1,500 2,200 900 200 2,700 200 10,600 

Apr. 3, 1976.. 3,300 100 200 1,600 2,500 900 200 2,700 200 11,700

1 Area measured from infrared image.

TABLE 2. — Estimates of heat flux from core areas of thermal 

ground

[Data are in megawatts]

Flux estimated 

Flux estiamted from highest 

Date by assuming a flux observed 

density of 419 W/m2 flux density

Mar. 1, 1971 .............. 0.9 (0

Apr. 22, 1972 ............. .9 0.2

Mar. 24, 1975 ............ 2.5 5.8

Mar. 4, 1976 .............. 4.3 10.0

Apr. 3, 1976 .............. 4.7 11.2

1 No estimate made.

snow and ice thickness, A is area, L is latent heat of 

melting (336X103 J/kg), and t is time required for thickness, D, to melt. This simple equation, however, underestimates the heat flow from areas shown as Bin figure 

21 because near the core geothermal regions the snow 

and ice melt more rapidly than in outlying areas, 

whereas t in the above equation is the total time required to completely clear an appreciable area of ice 

and snow. Furthermore, this method neglects heat lost 

by advection in steam plumes or through warm streams 

in subglacial tunnels. 

Table 3 lists the heat -flux values estimated from 

loss of snow and ice between spring and summer in 

geothermal areas that are marginal to the core areas 

used in table 2. Areas and times are derived from data 

in table 1, and the water equivalent thickness of 

melted snow and ice is estimated from field observations (where water equivalent thickness, h, is equal to 

pD divided by the density of water). Heat flux during 

1975 in these areas is more than 10 times greater 

than before 1975.

Table 4 summarizes estimates of heat flow from snow 

and ice melt in the various regions (A, B, C, D) represented in figure 21. Before 1975 an estimated minimum 

of about 2 MW of heat was released from Sherman 

Crater at an average heat-flux density of about 10 

W/m2 . In 1975 a minimum of about 30 MW of heat was 

released at an average flux density of about 180 W/m2 . 

Thus, the heat flow required to melt snow and ice increased roughly by one order of magnitude in 1975. 

Implicit in this discussion of heat flow is that, except 

for the spring of 1975, H did not change significantly 

with time over periods of about 1 year. Such an assumption presently seems reasonable for 1975—76 because 

visual observations have not indicated any marked 

change in the overall level of fumarolic activity since 

the spring of 1975. Although activity increased slightly 

before 1975, as reflected by retreating snowlines, the 

yearly change from 1971 to 1972, for which pre-1975 

heat-flow estimates were made, and in 1974 is probably 

not significant.

STRUCTURAL IMPLICATIONS OF HEAT PATTERN

Surficial thermal features represent locations of conduits from the deeper thermal system of the volcano. 

Four possible controls on heat flow can be inferred from 

the fumarole pattern: 

1. At the west and northwest rims, much of the activity is confined to breccia that is interlayered 

with lava flows. As rising heat nears the ground 

surface, a preferred path of convective flow is evidently through the more permeable breccia.
ASSESSMENT OF INCREASED THERMAL ACTIVITY A17

TABLE 3. — Heat flux estimated by loss of snow and ice

[Zero indicates area was snow covered at the time observation was made. Leaders (...) indicate no estimate was made.]

Location

Old southwest pits ............

New southwest pit ............

North pit .....................

Local crevasse extension .......

Central pit ...................

Remainder of crater ...........

Area, 

A (in*)

Water „ 

equivalent TMTM

"fctoT" H(MW)

Apr. 22 to Aug. 27, 1972

2,300 

900 

0

3,600 

700 

200 

0 

0

0

4 0.28

4 .11 

0 0 

3 .33 

1 .022 

1 .006 

0 0 

0 0

0 0

1925 to July 27, 1974

156.000 !13 0.44

Water 

Area, equivalent 

A (m2) thickness, 

Mm)

Mar. 10 to June 10,

3,300 28

100 4 

0 0 

5,200 4 

600 1 

500 2 

3,200 14 

8,200 10

Mar. 10 to Apr. 21,

2,600 25

Heat 

flux,

W(MW)

1975

3.9

.02 

0 

.88 

.03 

.04 

1.9 

3.4

1975

6.3

July 27, 1974, to July 4, 1975

137.000 14 6.2

Area, 

A(m2)

Water 

equivalent 

thickness, 

Mm)

Heat 

flux, 

tf(MW)

June 10 to Sept. 24, 1975

1,900 

200

400 

3,300

1,400

28 

4 

28 

4

2

2.0 

.03 

.41 

.49 '.ib

Apr. 21 to Sept. 24, 1975

300 28 0.21

1 These values for h were derived from summer photographs of the crater center, taken from the same position on the west rim in 1925,1974, and 1975. 

The 1974-75 figure was increased by 2 m to account for observed thinning of 7-15 m near the west and south rims.

TABLE 4. — Summary of snow and ice loss and heat-flow estimates for 

Sherman Crater

Pre-1975 1975

Water equivalent volume of total snow and ice

in crater (millions of m3) ................. '2.2-2.7 1.2-1.7

Water eqiuivalent volume of snow and ice lost

from crater (millions of m3): 

By expansion of thermal ground ........ (2) 0.47

By thinning of remaining snow and ice .. (2) .55 

Percentage of snow and ice loss ............. (2)____37—46

Heat flux, H (MW) :

A. 3 Core thermal area free of snow in

winter ........................ 0.3-0.9 2.5-11.2

B.3 Thermal ground where snowcover

melted in summer ............. 0.8 16.3

C.3 Thinning of remaining snow and

ice ........................... .4 6.2

D. 3 Localized extension of crevasses

into central and north pits ...... ___(*)_____3.4

Total ....................

Average of minimum heat-flux density4 for 

Sherman Crater (W/m2) ...............

1.5-2.1 28-37

8-11 150-200

1 Calculated for a paraboloid of revolution with a maximum water-equivalent depth of 28 

to 35 m.

2 Not estimated.

3 Letters refer to areas illustrated in figure 21.

4 Average worldwide heat flow in nonvolcanic areas is 0.06 W/m2 .

2. Fumarole clusters form a discontinuous semicircle 

of activity along the inside rim of Sherman 

Crater, except where hydrothermal activity 

seems to be absent along the south rim. (See fig. 

19C.) Such a pattern suggests that most of the 

hydrothermal emission is controlled by concentric fractures that might be associated with 

the initial formation of the crater. Surface displacements related to such structural features, 

however, have not been identified.

3. The location of some of the new activity suggests an 

east-west structural control across the center of 

Sherman Crater. For example, two long easttrending lobes of activity extend downslope from 

the west rim, and an east-west line of fumaroles 

occurs along the north shore of the lake and the 

north bank of the outlet stream.

4. The east breach apparently overlies the most direct 

permeable path from the volcanic heat source

because this area has the hottest and largest 

fumaroles. Furthermore, heat activity has 

historically been concentrated in this area since 

at least 1900. The presence of the breach itself indicates that at some time in the past either local 

hydrothermal or volcanic activity or erosion 

facilitated by hydrothermal alteration removed a 

section of the crater rim.

Thus, the fumarole pattern provides a hint of underlying structures. The distribution of hydrothermal 

activity can be summarized as a central core of heat 

emission, 60—80 m in diameter, near the east breach, 

on which is superimposed a semicircular zone of activity, about 400 m in diameter, along the inside crater 

rim and possibly an east-west crosscutting zone 

through the center of the crater. In some areas, zones of 

heat convection come to the ground surface along 

relatively permeable layers of breccia rather than along 

lava flows.

All these thermal features are apparently related to 

structures associated with Sherman Crater, although 

the dips of many of the units that form the north half of 

the crater rim suggest that much of the material there 

was erupted from an older vent to the north, now buried 

by snow and ice. The extent and composition of deposits 

in Boulder Creek valley (Hyde and Crandell, 1977) indicate that eruptions occurred during the past 10,000 

years at Sherman Crater, but no products known to be 

from other vents in the summit area have been dated.

GEOPHYSICAL AND GEOCHEMICAL 

MONITORING

Visual monitoring of thermal activity provides important information on changes that have taken place or 

are currently in progress but supplies little evidence of 

where or when future changes will occur. Because the 

timing, as well as location, of future eruptive activity 

should be known for proper protection of life and prop-
A18 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

FIGURE 12. — View from Sherman Peak of the site of the new main fumarole at the south base of Lahar Lookout. A, August 17, 1974, the two 

clusters of activity are evident near the east breach, including a prominent plume from the old main fumarole. B, July 6, 1975, a dense 

particle-laden plume extends from the 1- X 5-m opening of the new main fumarole, which occurs on a rock rib that had no sign of vapor

erty, other types of monitoring are necessary — in 

particular, geophysical and geochemical investigation 

of the volcanic processes. Such investigation provides 

many clues to the basic cause of volcanic processes, 

which should be understood for eventual eruption prediction.

No one method of volcano monitoring has yet proved 

to have sure predictive capability for eruptions. 

However, many different monitoring methods in other 

volcanic areas have at times successfully anticipated 

eruptions in a general way and may eventually lead to 

more precise predictions. Prediction of Cascade volcanism is complicated, in part because past monitoring in 

the Cascade Range has generally been of a reconnaissance nature and in part because no recent eruptions 

have occurred to provide data on precursory patterns.

Personnel of the U.S. Geological Survey, other 

government agencies, and several colleges and universities have initiated various types of monitoring

programs. Most of the programs were designed to 

evaluate the potential for a future eruption. The 

programs involved six broad types of study: seismicity, 

gravity, tilt, petrography, gas, and hydrology. All these 

programs provided useful information on the state of 

the volcano.

Most eruptions are preceded by increased seismicity 

at the volcano. Consequently, monitoring of seismicity 

is probably the single most effective means of evaluating the potential for an eruption in the near future. A 

seismometer was installed near Mount Baker by the 

U.S. Geological Survey in the summer of 1972 (fig. 22, 

MBW) and is currently operated by the Geophysics 

Program of the University of Washington.

Grants from the U.S. Geological Survey and National Science Foundation enabled the Geophysics 

Program to increase its seismic coverage of Mount 

Baker in the spring and summer of 1975. This work 

was done under the supervision of Stephen D. Malone, 

who supplied the following summary.
ASSESSMENT OF INCREASED THERMAL ACTIVITY A19

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4

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emission in 1974. C, February 6,1976, vapor still issues from this fumarole, but without ejecta. The snowmelt pattern delineates the area 

of thermal ground around the fumarole.

SUMMARY OF SEISMICITY AND GRAVITY

By STEPHEN D. MALONE 

SEISMICITY

On March 30, 1975, 3 weeks after increased 

fumarolic activity at Mount Baker was first observed, a 

short-period telemetered seismic station was installed 

on the south rim of Sherman Crater, less than 500 m 

from the center of the fumarolic activity. This station 

has been in almost continuous operation since then. In 

late summer 1975, 5 additional stations were installed 

on and near the mountain to increase the coverage. Table 5 and figure 22 specify the stations that form the expanded Mount Baker network.

The characteristics of the Mount Baker seismic stations are similar to those of the standard short-period 

station used by the U.S. Geological Survey: 1 Hz 

seismometer, nominal magnification of 100,000 to 

500,000 at 20 Hz, and conversion to FM subcarriers for 

telemetry over radio and (or) telephone communication

links. Data are recorded on Geotech develocorders with 

a single channel being monitored on a helicorder. The 

records thus produced are reviewed daily for changes in 

seismic activity. Photographic copies of selected events 

are made for additional analyses.

The severe environmental conditions found high on 

Mount Baker have placed a number of limitations on 

seismic research. Special effort was made when installing the seismic stations to prepare the site to withstand 

very cold temperatures, high snow accumulation, and 

heavy rime-ice formation. Ice presents the worst 

problem, as it can produce very high loads on antenna 

structures and cannot be avoided. Despite these 

difficulties, the crucial stations MBW, SCW, AAB, and 

LLB kept operating through the winter.

Data from the Mount Baker array have been very interesting because they show an almost complete lack of 

earthquakes local to the volcano both before and after 

March 1975. The seismic events recorded seem to be of 

the type produced by ice movement (Weaver and
A20

WRB

LLB . 

MLB. 

LYW

VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON 

TABLE 5. — Seismometers at Mount Baker

NOTE: — All data are telemetered to the University of Washington for recording and analysis.

Symbol

MBW ........

sew .........

BBB .........

AAB .........

Location 

Gat and long)

48.7847° N.,

121. 9008° W. 

48.7677° N.,

121.8155° W. 

48.8035° N.,

121.7837° W. 

48.7367° N.,

121.8112° W.

Description

Grouse Ridge, 7 km W.

of Sherman Crater.

Crater,

N.-NE. of Sherman 

Crater. Site of tUt 

station B. 

Crag View, 3 km S. of

Sherman Crater. Site 

of tilt station A.

Start date

Summer 1972 . . .

March 30, 1975 .

Sept. 20, 1975 . . .

Sept. 30, 1975 . . .

Reliability as 

of March 1976

25 percent useless 

data due to wind.

5 percent useless 

data due to radio 

interference.

not repair because 

of weather and 

snow conditions.

5 percent useless 

data, unknown

48.7685° N., 

121.8187° W.

48.7718° N., 

121.8115° W.

48.6889° N., 

121.6867° W.

48.5353° N., 

122.1017° W.

West rim of Sherman 

Crater.

Sept. 19,1975

Top of Lahar Lookout, ........ do.

NE. corner of crater.

Near Marten Lake, 8 

km E. of Sherman 

Crater.

34 km SW. of crater. 

Part of western 

Washington regional 

net.

Sept. 30,1975

April 1975

. Failed Jan. 5,1976,

due to ice

destroying the

antenna. 

. Currently operating;

almost no down

time. 

. Intermittent until

January 1976; 25

percent no data. 

. Currently operating;

5 percent useless

data.

Malone, 1976). The main reasons for this interpretation 

are the rapid dispersive characteristic of a very shallow 

source in a highly stratified medium, the low phase 

velocity, and the similarity to events on Mount St. 

Helens, where additional evidence for a glacier source is 

available. A possibility remains that some or even 

many of these events on Mount Baker are very shallow 

earthquakes, although the evidence is against it. Even 

if they were earthquakes, their rate of occurrence is not 

high and seems to have decreased during the fall and 

winter months. The level of earthquake activity at 

Mount Baker contrasts sharply with the moderate 

seismicity at three other Cascade volcanoes to the 

south, Glacier Peak, Mount Rainier, and Mount St. 

Helens.

In addition to the glacier-source events observed on 

the seismic records, there have been periods of high 

seismic noise that last from tens of minutes to half a 

day. These noise periods are characterized by rather 

monochromatic bursts of about 5 Hz from 5 to 10 seconds apart that vary from 6 to 24 db above the background level for quiet times. They do not appear to be 

caused by wind, for there seems to be no correlation between weather activity and their presence. The noise 

bursts appeared mostly during the spring and early 

summer of 1975 and have not occurred since July 1975.

These periods of increased noise may have been 

fumarolic venting which occurred only when the new 

fumaroles were young, or perhaps this is a different 

form of glacier noise, being produced by short continuous ice motion rather than discrete slips.

On February 27,1976, a small earthquake (ML=^1) occurred at Mount Baker, the only definitely identifiable 

earthquake to occur locally since seismic coverage extended to the region in 1972. The earthquake was about 

1 km east-southeast of Sherman Crater at a depth of 

3—6 km. Inasmuch as this has been the only local 

earthquake of record since March 1975, there is no 

compelling seismic evidence to suggest an increase in 

stress within the volcano, such as might occur prior to 

an eruption.

GRAVITY

Both a change in mass near a point and a change in 

elevation of a point can cause changes in the acceleration of gravity as measured at the point. Such changes 

measured on an active volcano could signify, among 

several possibilities, the influx of magma into the 

volcano's reservoir system. The University of 

Washington has been testing this concept since May 12, 

1975, when two gravity stations were established on the 

south and west rims of Sherman Crater and another 

was located 29 km to the south at the Concrete Airfield.
ASSESSMENT OF INCREASED THERMAL ACTIVITY A21

FIGURE 13. — Two ice pits (arrows) in upper Boulder Glacier just outside Sherman Crater, March 4, 1976.

Data from these stations are shown in figure 23. A 

Lacoste and Romberg G gravity meter was used. A set 

of gravity readings was repeatable within 0.05 mGal, 

and instrument drift relative to an assumed stable base 

at the University of Washington was linear and less 

than 0.1 mGal/mo.

Gravity was remeasured at these stations several 

times throughout the summer, and again at the southrim station on February 6, 1976 (fig. 23). The readings

were corrected for Earth tides and show that the gravity decreased at the two Sherman Crater stations during the summer, about 0.46 mGal on the west rim and 

0.61 mGal on the south rim. This trend reversed at the 

south-rim station during the fall and winter, with an increase in gravity of about 0.13 mGal between late September 1975 and February 6, 1976. Gravity fluctuations at Concrete remained within experimental error. 

At the end of the summer of 1975, seven additional gra-
A22 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

y*. - r -

^^"^pp^r^iP^i^ £*=•• :,**#• ^^W-Srffe*

FIGURE 14. — Superheated fumarole in the eastern part of Sherman 

Crater. Large deposits of sulfur have formed around the hottest 

fumaroles. Photograph by S. D. Malone, September 5, 1975.

vity stations were established at various elevations, but 

they were not resurveyed prior to spring 1976.

Interpretation of the gravity data is presently ambiguous and must await the acquisition of measurements for at least 1 more year. Correcting for snowmelt 

is a difficult problem because little is known about the 

amount of water lost to evaporation and runoff over the 

upper reaches of the mountain. In the immediate area 

of the two gravity stations on the crater rim, estimates 

of the amount of lost mass have been made from the observed decrease in the snow level and measured snow 

density. Corrections for these local effects reduce the 

gravity change over the summer to about 0.4 mGal at 

both stations.

The gravity decrease can be explained several ways. 

The most obvious is an elevation increase. A change of 

0.4 mGal represents a free-air change of 1.3 m. Uplift of 

this amount, if present, must be local to the crater or 

purely pluglike in form, as tilt data show too little deforFIGURE 15. — Main area of upwelling within the crater lake. The lake 

was about 50 m across at this time, and the upwelling was about 2 

m in diameter. Aerial photograph taken from the south, April 3, 

1976.

FIGURE 16. — Highly pressurized high-pitched fumarole in the southwest pit (SWP), July 16, 1975. The fumarole opening is about 15 

cm wide, and the ice pit is about 20 m wide, from left to right.

mation to be consistent with large elastic inflation of

the volcano.

Mass withdrawal from within the volcano is another

possible cause of gravity change. Two calculations 

which assume a point mass distribution 100 m below
ASSESSMENT OF INCREASED THERMAL ACTIVITY A23

FIGURE 17. — Infrared image of Sherman Crater, September 26, 

1975, acquired by Oregon Army National Guard. The brightest 

spot (arrow) in the east breach (EB) corresponds to the new main 

fumarole. Bright spots along the north margin of the central pit 

(CP) correspond to fumaroles grouped on a mound above waterline 

along the north shore of the lake. Two particularly strong groups of 

fumaroles are evident on the west rim (WR). The north pit (NP) 

and southwest pit (SWP) are not very bright because of vapor and 

partly overhanging ice which shield the fumaroles from the infrared sensor. Other fumarole clusters are the northwest pits 

(NWP) and northwest rim (NWR).

each gravity station or 100 m below the center of the 

crater require masses of 6X108 or 4X109 kg, respectively. Withdrawal of magma of these amounts would 

reasonably be accompanied by seismicity. Mass discharge of sulfur, other gases, and dust into the air is 

thought to be less than 108 kg.

The observed increase in gravity in midwinter 1976 

suggests that changes in mass due to snowmelt and accumulation over the entire mountain may be more important than the very local effects near the crater. A 

0.4-mCJal gravity decrease over the summer due to 

snow lost over the entire mountain requires loss of 4.4 

m of water equivalent thickness (about 7.3 m of snow 

and ice) distributed evenly on the surface of a cone at 

an angle of 28° to the horizontal (the average slope of 

Mount Baker). The snow accumulation and summer 

melt rates on Mount Baker are unknown but probably 

are about half this figure. Furthermore, the mountain 

as a whole should have gained during the winter at 

least as much snow as it lost during the summer. The 

gravity results do not show this relation although the 

only winter measurement (fig. 23) was made about 2 

months before the peak in snow accumulation. Snow 

effects still do not seem to account for all the gravity 

change, but it will take at least 1 complete year of data 

to resolve this question.

TILT

Many volcanoes are known to have inflated before 

eruptions and to have deflated after eruptions, 

presumably in response to filling and emptying of a 

magma reservoir system. Probably the best way to 

detect such deformation is by determining the changes 

in inclination (tilt) of the ground surface at several 

points on the cone. Three different systems for measuring tilt, one of which is still experimental, have been installed at Mount Baker. Results to date have been 

somewhat conflicting but probably indicate no significant inflation of the volcano.

Three spirit-level tilt stations were installed and 

measured on July 8-9, 1975, and were subsequently 

reoccupied on August 2—5 and on September 30, 1975; 

locations are given in figure 22. This type of tilt station 

involves precise leveling between fixed points that are 

20-40 m apart. Comparison of elevation for leveling 

surveys made at different times indicates whether the 

ground has tilted. Tilts of about 5 /urad (5 ppm, or 5 

mm/km) or more are resolvable by this method. Under 

favorable conditions of site stability, such tilt can be interpreted in terms of volcano deformation. However, 

site conditions at Mount Baker are not considered to be 

favorable, owing to freeze-thaw problems and the highly fractured nature of the lava flows and breccia in 

which the stations are located.

The net tilt from July 8-9 to September 30 was: Site 

A, 7.5 fjirad toward the south-southeast; site B, no 

change; site C, 7 /urad toward the west (fig. 23). The 

tilts at sites A and C are directed away from the summit 

area and are marginally greater than the expected error. The tilts are not considered to be significant, 

however, in view of their small magnitude, the 3-month 

period over which they accumulated, and the problems 

of site stability. Furthermore, small tilts directed away 

from the cone would be expected to develop during the 

summer, owing to unloading of the cone by loss of snow 

and ice. The spirit-level tilt data are, in all probability, 

in accord with the seismic data in suggesting little if 

any intrusive activity during July through September

1975.

Two continuously recording borehold tiltmeters were 

installed near sites A and B in early August 1975. 

These electronic instruments, each placed about 1.5 m 

underground in a 9-cm-diameter hole drilled in an andesite flow, are capable of continuously recording tilts 

of a fraction of a microradian. Data from the batteryoperated meters are relayed via satellite telemetry and 

are eventually recorded at an office of the U.S. Geological Survey in Menlo Park, Calif. The two instruments 

operated successfully through the winter.

Data from the two borehole tiltmeters from August 

10, 1975, to March 10, 1976, are plotted in figure 24.
A24 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

FIGURE 18. — Stereophotographs of Sherman Crater, August 20, 

1975, acquired by Oregon Army National Guard. Seven major 

clusters of fumaroles can be correlated with those listed in figure 

17. The initial breakup of ice which eventually resulted in the formation of an eighth cluster—the new southwest pit—is evident

Breaks in the curves represent missing data, owing to 

equipment malfunction or telemetry loss. Tiltmeter A 

was rezeroed in early September following a period of 

equipment failure; this accounts for the prominent 

offset in the curves.

Data from the two tiltmeters show a consistent pattern of subsidence north of site A from August to early 

December, west of Site B from October to December, 

and only slight change at both sites thereafter. The 

cumulative tilt before December is approximately 100 

/u,rad on a bearing of about S. 84° W. at site B and at 

least 50 /urad on a bearing of about N. 7° E. at site A. 

Projections of the two tilt vectors intersect in the region 

of the upper Mazama Glacier, north of the Dorr Fumarole Field. The data are far "noisier" before December 

than after, particularly those from site B. Some of this 

noise occurred at both sites simultaneously, whereas 

other noise affected only one site. From August to October the data at site B are less consistent and might 

reflect a settling period in the instrument site or a combination of different processes.

The data can be interpreted in two quite different 

ways, and it is not known which is preferable. One 

possibility is that the data indicate deformation of the 

volcano during the August—December period and lack 

of deformation during the December—March period. 

Under this interpretation, the pre-December deformation could have been related to withdrawal of magma

against the crater rim between SWP and WR. Ice in Sherman 

Crater and upper Boulder Glacier appears to be almost black in 

these photographs because of the thin but dark blanket of 

fumarole ejecta.

from a high-level storage system centered beneath upper Mazama Glacier. Such an explanation would account for the synchronous changes in tilt at both sites 

between October and December, but the evidence is less 

conclusive for the period from August to October.

Two other sets of data appear to be inconsistent with 

the subsidence shown by tiltmeter data at site A from 

August to October: (1) the gravityreadings, which suggest the possibility of uplift of the summit region extending until at least late September, when the last 

1975 field measurement was made; and (2) the spiritlevel tilt data, which suggest little, if any, outward tilt 

until at least late September.

A nonmagmatic process that could explain subsidence between October and December is loading by 

winter snow accumulation, which began in the first 

week of October. This explanation, however, would also 

conflict with tiltmeter data at site A between August 

and October, a period when summer snow ablation was 

still in progress.

An alternative interpretation of the tiltmeter data involves the more localized effects of weather and snow 

accumulation superimposed on slightly unstable sites. 

In this interpretation, the tilt before December would 

result from local differential movement of either the 

tiltmeter relative to the wallrock or a small block in 

which the meter is emplaced relative to the mountain 

as a whole. The azimuth of tilt could be largely for-
ASSESSMENT OF INCREASED THERMAL ACTIVITY A25

tuitous, although the azimuth at site B is nearly perpendicular to a high cliff overlooking Mazama Glacier 

and could be strongly influenced by rotation toward the 

free face. The decrease in noise in early December could 

record the accumulation of a heavy snow blanket that 

damps out thermal and storm effects. This alternative 

interpretation may be somewhat limited in application, 

but it does not conflict with any other observations, nor 

does it require explanation of inconsistencies in 

August—October data. Whatever the interpretation, 

the data provide no evidence of significantly large inflation of the volcano, as might be expected prior to an 

eruption.

A third type of tilt-measuring system, using a 1.2-m 

base Sylvester model tilt bar, was installed at several 

locations by Bruce Nolf (Central Oregon Community 

College). It is experimental and, so far, has given data 

that conflict with both the spirit-level and the borehole 

data (Nolf, 1976). This method is promising, however, 

and may eventually become an inexpensive and reliable 

means of monitoring ground tilt.

PETROGRAPHY

The nature of the material ejected from the 

fumaroles within Sherman Crater was of utmost importance, for, if it contained juvenile volcanic ash, the presence of an eruptible molten body of magma would be 

implied. With this in mind, the coarse fractions of samples of ejecta collected at intervals from March 31, 

1975, to February 6, 1976, were examined 

petrographically by James W. Babcock and Ray E. 

Wilcox, who provided the following summary.

RESULTS OF PETROGRAPHIC EXAMINATION OF SAMPLES

By JAMES W. BABCOCK and RAY E. WILCOX

For petrographic examination, a fraction coarser 

than about 10 /mi was obtained from each sample by 

repeated settling in water and decanting of fines. The 

constituents were identified in immersion mounts 

under the polarizing microscope; some constituent 

identifications were also supplemented by spindle-stage 

and X-ray methods of analysis.

Results of the petrographic examination are summarized in table 6 for 24 samples of the 1975 ejecta, 5 

samples of pre-1975 surficial debris, and 1 sample of 

suspended sediment in the crater lake. Collection sites 

are shown in figure 25. Samples of 1975 ejecta are arranged in order of probable time of ejection. For many 

samples this could be narrowed to periods of a few days 

or less because of the known times of snowfall with 

which the samples were mixed (fig. 26) or because of 

collection directly from the plume. Other samples 

represent undifferentiated mixtures of ejecta expelled 

from March 10 to the time of collection. The pre-1975

deposits include a 10-cm-thick white tephra layer 

(Bd-30-1) from the top of Lahar Lookout, a black sand 

deposit (Bd—15-1) from near the summit, and other 

mixed surficial debris that contains no 1975 ejecta. The 

sample of lake sediment probably contains 1975 fumarole ejecta as well as older material.

In every sample of the 1975 ejecta, opaline silica 

minerals (including tridymite and cristobalite) are 

present as major constituents — greater than 10 percent by volume. Large amounts of opaque sulfides 

(designated as pyrite in table 6) and lithic and 

scoriaceous fragments are also present in many of 

these samples. Minor constituents (less than 10 percent 

by volume) include old glass shards, sulfur, alunite, 

anhydrite, gypsum, opaque oxides (mainly magnetite), 

plagioclase, orthorhombic and monoclinic pyroxene, 

chalcedony, and, rarely, quartz. Four samples in which 

the clay fraction was analyzed contained more than 10 

percent by weight of clay minerals.

Spheroids of pyrite, opal, and sulfur, ranging in 

diameter from 0.07 to 0.5 mm, are common among the 

predominantly irregularly shaped particles. The pyrite 

spheres average about 0.2 mm in diameter; those of 

opal and sulfur are generally smaller and less abundant. Some spheroids are composite and consist of a 

thin rind of pyrite crystals that coats a core of opal or 

sulfur. Other spheroids are mainly opal with included 

pyrite crystals, or mainly sulfur with a filamentous 

meshwork of opal. One apparent change in ejecta composition through time is a decrease in pyrite from a 

major to a minor constitutent in early July.

None of the constituents of the 1975 ejecta is attributed to the eruption of fresh magma during the current activity. Rather, all are logically to be expected in 

this setting and represent debris that was torn off the 

walls of the fumaroles or that slid into the fumaroles as 

small mudflows triggered by snowmelt. Although 

Radke, Hobbs, and Stith (1976) found fibers which they 

suggested were fresh volcanic glass (Pele's hair) in ejecta collected by aerial methods, their analyses of the 

fibers did not include elemental or mineralogical composition. U.S. Geological Survey studies found no evidence of Pele's hair in 1975 ejecta from Mount Baker. 

Scoria fragments and glass shards, which have refractive indices implying compositions of andesite to dacite, 

are encrusted with opaline silica and, therefore, predate at least the most recent fumarolic activity. The 

sulfur-bearing minerals are typical of the suite found at 

various levels in the throats of fumaroles.

The results of this petrographic examination are in 

general accord with those of others (Eichelberger and 

others, 1976; McLane and others, 1976a, b), although 

the proportions of some constituents differ. This, no 

doubt, reflects the complicated mixed nature of the
A26 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

TABLE6. — Summary of> 10 n m constituents in debris samples from Sherman Crater area; collected March 31, 1975, to February 6, 1976 

[M, major constituent (greater than 10 percent); x, minor constituent; ?, trace amount suspected but not established]

Collection 

date in 1975 . .

Probable time 

of ejection 

in 1975 .......

Opal, tridymite, and 

(or) cristobalite . . . 

Quartz and (or) 

chalcedony ........

Pyrite ..............

Sulfur ..............

Pyroxene ...........

Scoria and (or) 

lithics ............

Glass ...............

Re,fTtiW ^25 

Index 1.500

1975 ejecta

Snow surface

CO(-'

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1

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V 

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>, 

3

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3>-8 

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1

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CO

M

X 

X

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X

X 

X 

X

I

Tf

jj> 

3

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jj, 

3"-8

i O

t*to

1 O

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m

M

X

M

X

X

X 

X

X 

X

01

j^, 

3

_>, 

3'-B

7

i

to

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M

?

X

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9

X 

X

1 o

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3

To

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3'-B

i

i to CQ

M

X 

X

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X

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X

•

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_>, 

3"-8

V

1 to

CO

M

X

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X 

X 

X

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3

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f

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X

ac

<

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1

1

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CO

M

X

M

X 

X

X

M

X 

V

X 

X 

V

•

01

"E. 

*

Ol

-M 

O.

«

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1 to CO

M

X 

X

X

X

M

X

X

Ol

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*

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H

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M

X

X 

X

X

M

X

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1 Collected in 1976.

2 Contains a trace of microcline feldspar.

3 Tephra layer (10 cm thick).

ejecta. Electron microprobe analyses by McLane, 

Finkelman, and Larson (1976b) of 7 glass samples from 

the ejecta showed an average composition, in weight 

percent, of SiO2 , 65.4; A12O3 , 14.1; Fe2O3 , 3.5; K2 O, 4.0; 

Na2O, 4.4; CaO, 1.5; MgO, 0.9; and TiO2 , 0.6.

Samples of pre-1975 material contain a suite of 

minerals similar to that in 1975 ejcta, although some 

differences in proportion are distinguishable. In particular, major amounts of glass are present in four of 

the pre-1975 samples, and major amounts of quartz are 

present in the fifth sample. Glass and quartz are either 

absent or present in only minor amounts in samples of 

1975 ejecta.

GAS

There is a theoretical basis for believing that the concentration of reducing gases, such as hydrogen, hydrogen sulfide, and sulfur dioxide, emitted from 

fumaroles increases before a magmatic eruption. As an

experiment designed to test such theory, Sato, Malone, 

Moxham, and McLane (1976) designed a continuously 

recording sensor and installed it in one of the fumaroles 

on the west rim of Sherman Crater (figs. 25, 27) in May 

1975. The sensor, which monitors temperature as well 

as reducing capacity of the fumarole gas, was connected 

via radio to the University of Washington, where data 

were compiled. Various instrument problems hampered 

operation of the device, but data were obtained successfully from mid-July to mid-October. Changes in gas 

composition were observed; however, at no time did the 

data suggest an impending eruption.

Aerial surveys of gases and aerosols were made by 

Radke, Hobbs, and Stith (1976), who measured 0.35 and 

1.3 kg/s of gaseous sulfur in the fumarole plume on 

March 27 and June 30, 1975, respectively. They further 

found that the 10-ppb contour of gaseous sulfur could 

extend as far as 90 km downwind, as it did on March 27, 

when the plume was traced southward above Everett,
ASSESSMENT OF INCREASED THERMAL ACTIVITY A27

Wash. A later flight, on November 18, recorded a rate of 

sulfur emission similar to that recorded during the 

June flight (L. F. Radke, oral commun., 1975).

HYDROLOGY

Much of the concern about Mount Baker's increased 

thermal activity after March 1975 has focused on the 

possible occurrence of lava eruptions, pyroclastic flows, 

and mudflows and associated flooding. However, to date 

(March 1976), the greatest undesirable effects of the increased activity have been an increase in atmospheric 

pollution and a decrease in the quality of some local 

waters (Wilson and Fretwell, 1976). The water-quality 

monitoring relative to Mount Baker's increased activity 

is summarized by Marvin O. Fretwell.

MONITORING OF WATER QUALITY

By MARVIN O. FRETWELL

Water-quality data from the Mount Baker area were 

very meager before heat emission increased in March 

1975. Since then, however, a considerable amount of 

water-quality data has been collected by several agencies, including the U.S. Forest Service, U.S. Geological 

Survey, Washington State Department of Game, 

Washington State Department of Ecology, and the 

University of Washington. The need for a background 

data base and a compilation of all pertinent waterquality data prompted Wilson and Fretwell (1976) to 

prepare a table of data listing all the historic and current water-quality data available through December 

31, 1975, for Sherman Crater, Boulder Creek, Park 

Creek, Sandy Creek, Sulphur Creek, Rocky Creek, and 

Baker River (below Baker Lake). Bortleson and Wilson 

(1976) tabulated the data for the detailed survey of 

Baker Lake made in September 1975. These two 

reports were later expanded and updated by Bortleson, 

Wilson, and Foxworthy (1976).

The increased thermal activity has apparently produced additional flow of acidic water into Boulder Creek 

(fig. 1), which drains Sherman Crater. The discovery of 

acidic water in Boulder Creek raised questions about 

possible detrimental effects on Baker Lake, into which 

Boulder Creek discharges, and on the Skagit River, 

farther downstream. Therefore, a preliminary reconnaissance was made by personnel of the U.S. Geological 

Survey in March 1975 to measure various water-quality 

parameters in Boulder Creek, Baker Lake, Baker River, 

Skagit River, and several unaffected streams near 

Boulder Creek that flow into Baker Lake. The reconnaissance indicated that the acidity problem was confined to Boulder Creek and Baker Lake and was not 

detectable below the lake. Also, in this and later surveys, the toxic-metal content in the outflow of Baker 

Lake was found to be no higher than that in the 

unaffected streams flowing into Baker Lake.

A more detailed survey of Baker Lake's water quality 

was conducted in September 1975. Measurements were 

made of specific conductance, pH, temperature, and dissolved oxygen. Data from this survey, tabulated by 

Bortleson and Wilson (1976), indicate that the acidic 

water at that time was moving downstream close to the 

lake bottom in the shallower part of the lake until it 

reached deeper waters of the same density, at which 

depth it fingered out into the lake as an acidic wedge. 

Although the exact areal extent of the acidic wedge is 

not known, it did not extend beyond a sampling transect 1.8 km downlake. The acidic water at this time was 

established as neither being pooled in large quantities 

on the bottom nor corroding the concrete in the dam. 

Concentration and movement of acidic water in Baker 

Lake is expected to vary according to the Boulder Creek 

discharge and according to the seasons of the year. Additional surveys are planned in 1976 to maintain observation of the lake conditions.

A joint-agency monitoring program was initiated to 

maintain surveillance of the Boulder Creek—Baker 

Lake—Baker River system. U.S. Forest Service personnel measured pH, specific conductance, temperature, 

and water stage approximately every 3 to 5 days during 

the summer of 1975 at the bridge crossings of Boulder 

and Park Creeks. Also, about every 2 weeks Forest Service personnel collected samples for chemical analysis 

of common constituents and toxic metals at these two 

sites and at Baker River, below Baker Dam. Chemists 

of the U.S. Geological Survey analyzed these samples. 

Sampling frequency was sharply reduced during the 

winter, owing to access problems.

Data from this program show that average concentrations of sulfate, iron, manganese, aluminum, arsenic, and fluoride in Boulder Creek are 10 to 100 times 

higher than in nearby streams. Average summertime 

pH in 1975 in Boulder Creek was about 3.9, and in nearby streams, about 7.2. Immediately downstream from 

Baker Lake, the pH averaged about 7.0. After fall and 

winter freezeup at higher elevations, the average pH of 

Boulder Creek rose to about 5. Acid loads from Boulder 

Creek in the summertime ranged from a few thousand 

to several thousand kilograms of H2SO4 per day. To 

date (March 1976), no significant acidity has been 

detected downstream from Baker Lake.

In an attempt to maintain surveillance of this potential problem, a radiotelemetering monitor was installed 

in early 1976 on Boulder Creek to warn of sudden 

changes in streamflow or in pH, either of which may be 

early indicators of undercutting or damming of the 

breach or of a mudflow. The monitor, which was not yet 

fully operational by March, measures water stage, pH, 

temperature, specific conductance, and dissolved 

oxygen. These data are relayed hourly by radiotelemetry to the Tacoma office of the U.S. Geological Survey.
A28 VOLCANIC ACTIVITY AT MOUNT BAKER, WASfflNGTON
121°49'

CONTOUR INTERVAL 10 METERS

FIGURE 19. — Thermal area as mapped from photographs. A, Thermal area during late to photograph dates. Dashed areas around the north pi

summer snow conditions from 1900 to 1975 was mapped by interpretation of high heat flow, where ice did not melt completely 

anomalous snowline margins in conjunction with 1972-75 field data. Thermal areas replenishment by ice calving into the north pit. B

for 1908-14 represent minimum areas because only part of the crater was visible in 1:24,000, 1975. 

available photographs. B, Thermal area from March to September 1975. Letters refer
A30 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

30

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£15

I- 

< 

EC 

U

10

• Summer

o Winter or spring

oo

1900 1910 1920 1930 1940 1950 1960 

YEAR

1970 M A M J JASONDJ FMA 

1975 1976

FIGURE 20. — Change in snow-free thermal area through the 20th century. Values of thermal area prior to 1940 (dashed) may be somewhat 

low because not all of Sherman Crater was visible in the earlier photographs. A small general increase in area is apparent from 1900 to 

1974; a threefold increase occurred in 1975. The 1976 winter thermal area remains almost 3 times greater than the late winter areas of 2 

previous years.

HAZARD ANALYSIS

Quiescent volcanoes often create interest only as 

scenic wonders or opportune watersheds, and not as 

having potentially destructive capabilities. Active 

volcanoes, on the other hand, draw more serious considerations. Because many of the Cascade Range 

volcanoes erupted at various times during the last few 

thousand years, the verbal record of Native Americans 

is permeated with legends of volcanic catastrophies. Indeed, the most explosive postglacial eruption of the 

North American Continent, which culminated in the 

collapse of Mount Mazama about 6,600 years ago to 

form Crater Lake, Oreg., was probably witnessed by 

local residents.

Twentieth-century civilization in the Pacific Northwest, however, has not had the opportunity to fully appreciate the hazards associated with volcanic eruptions. 

Explorers of the 1800's recorded accounts of eruptions 

as seen from great distances, and, to be sure, the explosive eruptions of Lassen Peak in 1914—17 generated

some excitement, but the low density of nearby civilization resulted in recognition of these events mostly as 

curiosities.

For many decades society has been building its structures ever closer to the Cascade volcanoes. Only in the 

past 15 years, however, have stratigraphic studies of 

postglacial volcanic deposits prompted serious consideration of the risk presented by the volcanoes. So, 

not only do we face the volcanic threat to future land 

use, but also we must confront the unforseen dilemma 

of the already established, economically important 

structures — such as hydroelectric power reservoirs — 

that lie in the path of potential danger. In such circumstances, it is not enough to make a simple scientific estimate of risk; it is also necessary to weigh the risk to life 

and property against the socioeconomic advantages of 

taking some, part, or all of the risk. The latter problem 

certainly should not be dealt with solely by scientists 

but should be addressed by all people threatened by 

volcanic hazards.
ASSESSMENT OF INCREASED THERMAL ACTIVITY A31

Winter level

Thermal

Pre-1975

Winter level

Summer level

1975

FIGURE 21. — Diagrammatic cross section of part of Sherman Crater, 

showing how heat flow can be estimated from snow and ice loss. A 

represents the volume of snow melted to keep the area snow free in 

winter. Heat-flux estimates for A were derived in two ways: (1) 

Heat-flux density was assumed to be 419 W/m2 , or (2) the maximum heat-flux density measured elsewhere in the crater was 

used. B represents the volume of snow (pre-1975) or of snow, ice, 

and firn (1975) melted as thermal ground becomes snow free in 

summer. C shows the volume lost from thinning of remaining snow 

and ice from year to year because of either local melting or gradual 

extension toward the thermal areas. D is crevasse volume due to 

local extension toward new thermal areas and was measured only 

west of the central pit and north and east of the north pit. For B, C, 

and D, densities were assumed to be 600 kg/m3 for snow and 700 

kg/m3 for snow and ice undifferentiated, and heat flux was calculated on the basis of the rate of removal of snow and ice.

Should Mount Baker erupt in the future, certain 

areas would be threatened by a variety of volcanic 

phenomena (Hyde and Crandell, 1977). Even though 

Mount Baker is now dormant, the current hydrothermal activity presents some hazards, which include 

pollution by gaseous and liquid effluents and possible 

avalanches of rock debris and mudflows. The following 

section discusses present hazards and responses to 

them by administrative agencies.

POLLUTION

To date, effluents of volcanic gases and acidic waters 

have been a major hazard at Mount Baker. An abundant gas from fumaroles in Sherman Crater is toxic hydrogen sulfide (H2S). A concentration of only 1 ppm is 

detectable as a rotten-egg smell, but the human sense 

of smell can be quickly destroyed by H2S. Thus, smell 

alone is not a suitable warning of overdose. The OcFIGURE 22. — Locations of seismic, tilt, and gravity stations on 

Mount Baker.

cupational Safety and Health Administration recommends protective breathing apparatus for H2S concentrations greater than 10 ppm. Analyses by J. E. 

McLane (oral commun., 1975) of several samples of 

vapor from fumaroles in Sherman Crater during 1975 

indicated H2 S concentrations of several percent, 

enough to cause death in minutes. Monitoring of H2S in 

the open air along the rim of Sherman Crater during 

the summer of 1975 showed that concentrations 

greater than 50 ppm are to be expected, even tens of 

meters downwind from fumarole openings. At times, 

H2S has been smelled at lower altitudes, particularly in 

the Boulder Creek valley but also as far as 30 km to the 

west at the community of Deming. Although not yet 

studied in detail, current levels of H2S concentration at 

such great distances are probably too low to cause much 

harm to people. However, the physiological effect of 

sulfur gases on plants—timber in particular—has 

been significant in other areas (Carlson, 1974) and 

bears further study at Mount Baker. From aerial surveys in June 1975, Radke, Hobbs, and Stith (1976, p. 

96) concluded that Mount Baker at that time produced 

Washington's largest single plume of gaseous sulfur, 

natural or industrial.

Another abundant fumarole gas at Sherman Crater 

is carbon dioxide (CO2). Although not toxic, CO2 is 

heavier than air and has caused animal suffocation in 

enclosed basins near fumaroles in Iceland (Thorarinsson, 1970, p. 36-37). Other common toxic gases in 

fumaroles at other volcanoes (but which are not pre-
A32 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1 

0

-0.2

-0.1 

0

10

0

•3Z Tilt change, in microradians. Error bar S/JL rad wide

-31 Gravity change, in milligals. Error bar 0.05 mGal

—— —— —X Gravity change, in milligals, corrected for 

local loss of snow and ice. 

Error bar 0.05 mGal

Concrete, Wash.

_^. W_dpw[!___-• Tilt site C 

J_____

Tilt site B

J

-> SSEdqwn____. Tilt site A 

J_____

May June July August September October November December

1975

FIGURE 23. — Spirit-level tilt and gravity measurements.

January February 

1976

dominant in the 1975 analyses of gas from Sherman 

Crater (J. E. McLane, oral commun., 1975)) are sulfur 

dioxide (SO2 ), carbon monoxide (CO), ammonia (NH3 ), 

flourine (F), and chlorine (Cl). The precautions taken 

during the recent field investigations at Mount Baker 

limited the observed effects of fumarole gas to occasional nausea, headache, and eye irritation. However, 

the hazardous potential of such gases was shown in 

1934, when either toxicity or displacement of oxygen by 

fumarole gas in a hydrothermal area on Mount Hood, 

Oreg., resulted in one of the few known human deaths 

from a volcanic cause in the United States (McNeil, 

1937, p. 178-191).

Acidification of surface water and ground water commonly occurs in fumarole fields by oxidation of 

fumarole gases (Schoen and others, 1974, p. 4). Fretwell 

previously described the flow path and chemistry of 

acid-charged water that drains from Sherman Crater. 

Acid can be toxic to aquatic life and can cause structural deterioration, particularly of concrete. The degree 

of hazard depends primarily on the initial concentration and dilution downvalley of toxic substances in 

water discharged from the crater. Because the present 

drainage from Sherman Crater flows into Boulder 

Creek, the major effect on water quality is limited to 

Boulder Creek and downvalley areas. High levels of 

acidic water in 1975 did not extend farther downstream

than Baker Lake. Bortleson, Wilson, and Foxworthy 

(1976) provide a more detailed analysis of the water 

quality implications of present hydrothermal activity.

Tests of water samples from the drainage system of 

the Dorr Fumarole Field in 1974 indicated that the 

water did not flow freely through Mazama Glacier into 

Bar Creek at that time. Because there was no evidence 

of increased fumarolic activity at the Dorr Field in 

1975, acid waters probably still do not appreciably 

affect Bar Creek. Future increases in activity, however, 

might be reflected in high acidity in Bar Creek, Wells 

Creek, and possibly the North Fork Nooksack River.

AVALANCHE AND MUDFLOW HAZARD

Hydrothermal activity in fumarole fields typically 

consists of hot fluids that rise to the ground surface and 

penetrate interstices of the surrounding rocks. Chemical equilibration of rocks with the hydrothermal environment produces various alteration products, depending on the temperature, pressure, and chemical 

composition of the fluids. Under the strongly reactive 

conditions that usually accompany hot fluids, rock 

alteration can first cause physical and chemical 

changes along fissures and cavities and eventually can 

affect the entire mass.

The mechanical stability of rock that has been 

altered depends largely on fluid pressure, on fracturing
ASSESSMENT OF INCREASED THERMAL ACTIVITY A33

N-S

50-

25

CO

Q

< 0

cc 

O 

cc

O

H 

H 

150

E-W

N-S O 

Q

I 

H

cc 

O

O 

Q

fe

Tilt site

100

50

N-S O 

Q

T. \- 

QC 

O

O 

Q

CO

August September October November December

1975

January February March 

1976

FIGURE 24. — Tiltmeter data at sites A and B.
121°49'

CONTOUR INTERVAL 10 METERS

FIGURE 25. — Sampling sites (dots) of ejecta in the Sherman Crater area, and location of profiles across Lahar Lookout. Gas sensor 

cated at G.
ASSESSMENT OF INCREASED THERMAL ACTIVITY A35

FIGURE 26. — Two layers of ejecta (samples Bd-1-2 and Bd-1-3, 

table 6) in crevasse wall 100 m west of the new main fumarole. 

Ejecta was being deposited on the snow surface at the time this 

photograph was taken, March 31, 1975.

FIGURE 27. — Location of gas sensor on west rim, February 6,1976.

generated by crystal growth and thermal and (or) tectonic stresses, and on the physical properties of the 

mineral products of alteration. Clay is a common alteration product at the ground surface, as well as at depth,

in hydrothermal systems. In some geothermal areas, 

clay has been found to be a major rock component at 

depths of as much as 900 m. (For example, see Sumi, 

1970.) Old volcanoes, such as Mount Baker, at which 

fumarolic activity has been going on for thousands of 

years, might be expected to contain large, structurally 

weak bodies of clay-rich material. Montmorillonite and 

kaolinite clay are abundant on the surface of Sherman 

Crater (Bockheim and Ballard, 1975) and reflect the 

alteration to various degrees of virtually all the rock 

rimming the crater. Although the extent of alteration 

beneath the surface is unknown, its presence at depth 

is indicated by major concentrations of clay minerals in 

the 1975 ejecta.

Hydrothermally altered material is a prime source of 

rock debris for avalanches and mudflows. Mass movements of such debris can be initiated by the opening of 

large new fumarole conduits, as well as by other 

volcanic-related events, such as earthquakes, eruptions, or steam explosions. In order to examine the potential hazard presented by large mass movements at 

Mount Baker, two approaches have been taken: investigation of the recent geological record and appraisal of current conditions.

HAZARD ANALYSIS BASED ON HISTORICAL RECORD

The time, place, or magnitude of a natural-hazard 

event usually cannot be predicted. However, the probability of its occurring at a specific place and having a 

specific magnitude can be estimated if a relatively complete history of occurrences is available. Probability 

estimates for future events, then, rest only on the 

assumption that the statistical characteristics which 

describe past events carry on into the future. This procedure is widely used in regard to certain other natural 

hazards, such as floods, droughts, and severe storms.

Data gathered by Hyde and Crandell (1977) were 

used to estimate probabilities in 1975 for two types of 

events: (1) a mudflow sufficiently large to reach Baker 

Lake, having an estimated probability of 1 in 100 in a 

given year, and (2) an air-cushioned avalanche into 

Baker Lake, having an estimated probability between 1 

in 1,000 and 1 in 10,000 in a given year. (See app. 1.) 

These probability figures are only estimates because of 

the small sample of data; the uncertain conditional 

probability that a given mudflow would occur in the 

Baker Lake drainage, and not elsewhere; the quantitatively unknown influence of the 1975 thermal activity as a mudflow trigger; and the possibility (which 

was not considered) that the frequency of mudflows 

may have increased, as shown by the geologic record of 

the last 500-600 years (Hyde and Crandell, 1977).
A36 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

HAZARD ANALYSIS BASED ON PRESENT CONDITIONS

Although the probability of occurrence of large 

mudflows can be estimated by analyzing the frequency 

of similar events in the past, this type of study yields little information on such important parameters as the 

shape and velocity of the mudflow. Good estimates of 

these parameters are necessary before any analysis can 

be made of the most important hazard from such a 

flow — its effect on Baker Lake. These estimates can be 

made by determining the present conditions at Mount 

Baker and by comparing these conditions with those 

where mudflows and avalanches have been observed 

elsewhere.

If a large mass from the rim of Sherman Crater were 

set in motion, it could begin as an avalanche of rock, 

snow, and ice. After descending the steep slopes of 

Mount Baker, its motion might continue downvalley as 

a wet slurry (mudflow), as an air-cushioned avalanche 

of broken rock, or, possibly, as a fluidized mass with intermediate characteristics. Air-cushioned avalanches 

are known to travel much faster than mudflows, but 

they cannot form unless a certain critical volume of 

debris is involved and other specific conditions are met. 

Thus, evaluation of this hazard includes ascertaining 

whether unstable rock masses exist which could be set 

in motion and whether the volume of rock would be 

sufficient and other conditions met so that an air 

cushion would form and be retained under the sliding 

rock debris.

SOURCES OF MUDFLOWS OR ROCK AVALANCHES

Large steep masses of altered and weakned rock currently exist high on Mount Baker. Almost all of the rim 

of Sherman Crater is composed of highly altered lava 

flows and breccias. Favorable topography outside Sherman Crater, which would allow rapid downslope movement of rock debris, exists at Sherman Peak and Lahar 

Lookout. At both places, the rock debris would probably 

descend the Boulder Creek valley and could reach 

Baker Lake (frontispiece).

Sherman Peak (altitude 3,089 m) stands about 220 m 

above the east breach and is mostly sheathed by snow 

and ice. The slope toward the notch is about 40°; toward 

Boulder Glacier, about 43°; and toward Talum Glacier 

(also tributary to Boulder Creek), about 39°. Small avalanches of about 35 X 103 m3 of snow, firn, and altered 

rock from Sherman Peak have occurred at least 6 times 

since 1958 (Frank and others, 1975). Much larger avalanches seem possible. Frank, Post, and Friedman 

(1975) estimated that an avalanche of about 5X106 m3 

was conceivable if additional material undercut by the 

smaller avalanches also broke off. If all of Sherman 

Peak slid off to the east, possibly as a result of a 

massive steam explosion or earthquake, as much as

16X106 m3 of material could be set in motion. Such a 

volume is represented by the material above a hypothetical surface dipping 24.5° E., originating on the 

south rim of Sherman Crater about 170m west of Sherman Peak and emerging east of the peak at an altitude 

of 2,590 m. The slope of this possible shear surface is 

somewhat less than the average angle of repose of disaggregated dry rock, so an additional mobilizing agent 

— steam, water, or explosion — probably would be required to move a mass this large. The present distribution of fumaroles does not appear to coincide with the 

hypothetical fracture surface.

Lahar Lookout is a more likely source for a huge 

avalanche or mudflow because (1) a larger mass of 

altered rock is present above a possible shear surface; 

(2) rock exposed there is thoroughly altered and cut by 

several structures which might expedite failure; and (3) 

existing steam conduits pass close to or through the 

possible shear surface. Profiles through Lahar Lookout 

(fig. 28) suggest that, for a width of 490 m, the volume 

above a possible curved shear surface beneath Lahar 

Lookout is about 33x 106 m3 , and the volume above a 

planar shear surface that slopes 34° (angle of repose of 

dry rock fragments) is about 16x 106 m3 . An additional 

amount should be added to these figures because of 

snow and ice beside or below the outcrop of the hypothetical shear surface, perhaps equal to 30 percent of 

the rock volume. Although extremely unlikely, it is 

possible that an even larger mass could break up.

MOTION OF POSSIBLE AVALANCHE OR MUDFLOW

Air-cushioned rock avalanches are known to travel 

very fast, so the possibility of one of these reaching 

Baker Lake and delivering a large impulse to the lake is 

clearly the worst possible hazard to consider. Table 7 

lists dimensions and other parameters of large debris 

slides elsewhere which are believed to have traveled, at 

least in part, on an air cushion, together with relevant 

information on a previous avalanche and mudflow at 

Mount Baker. A possible 20 to 30X106 m3 avalanche 

down the Boulder Creek valley would drop 2,800 m 

within a distance of 12,500 m, and would have a "friction coefficient" of 0.22. It would therefore have 

parameters similar to those of the air-cushioned avalanches at Frank, Alberta; Sherman Glacier, Alaska; 

Little Tahoma Peak, Washington; and Huascaran, 

Peru. Thus, rapid motion is considered possible.

The following analysis of such an air-cushioned avalanche at Boulder Creek is a statement by Ronald L. 

Shreve; his complete statement is given as appendix 2.

SUMMARY OF EVALUATION OF AIR-CUSHIONED 

AVALANCHE OR MUDFLOW AT BOULDER CREEK

By RONALD L. SHREVE

Air-cushioned avalanches of the sort considered here 

do not occur frequently in nature and cannot be studied
ASSESSMENT OF INCREASED THERMAL ACTIVITY A37

3100

A 

3000

C/5

DC 

UJ

hLLJ

LLJ 

Q

ID

P 

<

2900

2800

2700

FIGURE 28. — Four parallel profiles across Lahar Lookout. Profiles 

are spaced approximately 120 m apart; their locations are shown 

in figure 25. Hachures indicate rock outcrops; dashed lines indicate snow. Heavy line is a possible curved shear surface; and heavy

in the laboratory. Therefore, relatively few comparable 

case histories exist, and even fewer established principles are available for use as a basis for prediction. The 

uncertainty is further compounded by the unpredictable effects of volcanic activity on a glacier-clad mountain. Thus, estimates given here must be viewed with 

caution.

Formation of an air-cushioned avalanche with long 

runout requires that the avalanche override and trap 

sufficient air to significantly reduce contact with the 

ground. This, in turn, requires a suitable break in slope 

to launch the avalanche into the air, high speed to enable it to override enough air, and sufficient thickness of 

the debris and smoothness of the ground to prevent excessive loss of air. An adequate slope break for launching is present at the 1,000-m level in the canyon of 

Boulder Creek. The speed of a hypothetical avalanche 

at this launch point would probably be at least 270 

km/hr, which corresponds to conversion of one-eighth

A' 

B'

C' 

D'

dashed line is a possible planar shear surface sloping 34°. Major 

new fumaroles in the Lahar Lookout mass emerge at dots; locations of heat emission which possibly are fumaroles emerge at x.

of the available potential energy to kinetic energy; observations at other areas suggest a somewhat higher 

fraction — possibly one-fifth —would be converted. 

Even at the speed of 270 km/hr, enough air could be 

trapped to form a layer about 2 m thick if compressed 

under 6 m of debris over the whole area of the 

avalanche down to the lakeshore.

The most important consideration is the probable 

thickness of the avalanching debris. On the basis of 

other observations it seems reasonable to assume that a 

minimum debris thickness of 5 m is necessary for long 

runout. In other avalanches, 75 to 85 percent of the 

debris was deposited beyond the launch point. At 

Mount Baker, the area of the probable avalanche path 

is 6.6x 106 m2 from the 1,000-m level to the lakeshore. If 

debris were to be spread over this area to a depth of 5 m, 

and if corrections were made for the amount left above 

the launch point and for the increase in volume of the 

rock as it disaggregates in the initial fall, the required
A38 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

TABLE 7. — Characteristics of observed and probable air-cushioned rock avalanches compared with a prehistoric mudflow and avalanche at

Mount Baker

[Leaders (....) indicate no data available]

Blackhawk, California (Shreve, 1968) ..............

Elm, Switzerland (Heim, 1882) ....................

Frank, Alberta, Canada 

(McConnell and Brock, 1904) ....................

Sherman Glacier, Alaska (Shreve, 1966) ............

Little Tahoma Peak, Washington 

(Crandell and Fahnestock, 1965) .................

Huascaran, Peru: 

(McDowell andFletcher, 1962; Morales, 1966) . . . 

(Plafker and others, 1971) .....................

Mount Baker (Hyde and Crandell, 1977): 

Middle Fork Nooksack River mudflow ..........

Rainbow Creek avalanche .....................

Year

(3)

1881

1903

1964

1963

1962 

1Q70

(3)

(3)

Volume 

(m3 x 106)

300

11

37

30

11

13 

>50

40

13

Vertical 

drop

(m)

1,200

600

670

1,100

1,900

3,500 

3,500

2,800

1,700

Horizontal 

distance

(m)

9,000

2,000

2,700

5,000

6,400

14,500 

14,500

27,000

9,000

Friction 

coefficient1

0.13

.30

.26

.22

.30

.24 

.24

.10

.19

Observed Calculated 

speed speed2 

(km/hr) (km/hr)

120

160

175

185

. . . 100-150

123 

280-335

Air 

cushion

Probable

Observed

Do.

Probable

Do.

Do.

Unknown.

Do.

1 Vertical drop divided by horizontal distance; values given by original authors may not coincide exactly with values or ratios given in this table.

2 Minimum speed computed on assumption of conservation of energy.

3 Prehistoric.

(minimum) original volume of undisaggregated rock 

would be 25x 106 m3 .

During runout, the trapped air must spread out more 

or less uniformly under the advancing debris. This 

process depends strongly on the variation with time of 

the thickness of the debris passing the launch point. 

Judging from other air-cushioned avalanches, long 

runout seems to require a thickness that tapers slightly 

toward the rear so as to partly compensate for the rapid 

removal of air from the launch region by shearing. At 

Mount Baker, the thickness could conceivably vary in 

such a way that the air layer would be unstable and 

break up rapidly, even though other factors, such as 

forward speed, air volume, and debris thickness, were 

favorable for development of an air cushion. A further 

requirement for a stable air cushion is that the product 

of permeability and bulk density of the debris at the 

base of the avalanche be less than about 0.7 times the 

product of harmonic mean permeability and arithmetic 

mean density for the whole thickness of the debris. In 

practical terms, a thin basal layer of finer, tighter 

material would suffice. At Mount Baker, this requirement would doubtless be satisfied by snow picked up 

from Boulder Glacier. An air-cushioned avalanche 

debouching from the narrow canyon of Boulder Creek 

onto the convex alluvial cone between the main road 

and Baker Lake very likely would tend to split into 

multiple lobes. This would lead to loss of air that, if 

great enough, might disrupt the air cushion short of the 

lake. Slowing of the avalanche and increased air loss 

would also occur if the surface of the alluvial cone had 

rough local relief greater than the thickness of the air 

cushion.

Thus, a rock mass having a volume of 20 to 30x 106 

m3 that breaks off Lahar Lookout might travel down the 

Boulder Creek valley on an air cushion; if so, it might 

lose its air cushion before striking Baker Lake.

An air-cushioned avalanche large enough to reach

Baker Lake would probably be about 350 to 450 m wide 

at the point where the main road crosses Boulder Creek. 

Also, it would spread laterally as it crossed the convex 

surface of the alluvial cone to the lakeshore, where it 

would most likely have a width of about 2,400m. Speed of 

the avalanche on entering the lake would probably be in 

the range of 160 to 320 km/hr; its thickness on entering 

the lake would most likely be about 6 m.

If the avalanche did not capture and retain an air 

cushion, it could travel entirely as a mudflow, or it could 

travel part of the distance on an air cushion and the remainder of the way as a mudflow. A mudflow would 

tend to be narrower, thicker, and slower than an aircushioned avalanche of the same volume. A mudflow 

down Boulder Creek that originated in a fall of 30x 106 

m3 of rock from the vicinity of Lahar Lookout would 

probably have a width of about 800 m, a thickness of 

about 12 m, and a speed of about 50 km/hr as it entered 

Baker Lake.

Note that, unlike air-cushioned avalanches, there is 

no minimum thickness or minimum speed for a 

mudflow that could reach the lake. Hyde and Crandell 

(1977) found remnants of prehistoric mudflows that are 

less than 0.6 m thick along Boulder Creek between the 

main road and Baker Lake. Thinner flows will be 

slower, generally narrower, and occur more frequently 

than thicker ones. In addition, an air-cushioned 

avalanche too small to reach the lake could continue on 

as a high-speed mudflow, as did the Huascaran 

avalanche near Matacoto, Peru (Plafker and others, 

1971). That mudflow traveled 150 km down the Rio 

Santa below Matacoto at an average speed of about 35 

km/hr; its initial speed near Matacoto probably was 

several times higher. Thus, rock debris moving down 

Boulder Creek valley could enter Baker Lake at speeds 

ranging from almost zero to a few hundred kilometers 

per hour, depending on size of fall and mode of transport.
ASSESSMENT OF INCREASED THERMAL ACTIVITY A39

EFFECT OF POSSIBLE ROCK AVALANCHE 

ORMUDFLOW ON BAKER LAKE

As it is possible for a fast-moving avalanche to enter 

Baker Lake, the consequences should be assessed with 

respect to human life and property damage. Three 

possible effects of a large wave on the lake have to be 

considered: (1) safety of people on the lake, in public 

campgrounds, and in a private resort on the lakeshore; 

(2) safety of Upper Baker Dam (a concrete gravitational structure that impounds Baker Lake); and (3) 

safety of Lake Shannon (and Lower Baker Dam) and 

the populated Skagit River valley downstream from 

Baker Lake (fig. 29) . An estimate of the possible wave 

height at the campgrounds and at Upper Baker Dam is 

an essential part of this analysis.

Puget Sound Power and Light Co. (Puget Power), 

managers of the Baker Lake hydroelectric power project, commissioned Tetra Tech, Inc., to estimate the 

effect of a possible avalanche or mudflow on the lake. 

The following analysis of possible wave heights is based 

on information contained in the report made to Puget 

Power.

The avalanche or mudflow is considered to be a rigid 

body, causing displacement of the lake surface. The 

energy dissipation due to impact of debris on the lake 

surface is neglected, and the lake margin is considered 

to be vertical. These two assumptions are conservative 

— that is, the real waves will be lower than those predicted. Wave propagation can then be described by the 

usual two-dimensional nonlinear long-wavelength 

wave equations. These equations can be solved by making finite-difference approximations and using any one 

of several solution techniques. As a result, time histories of water-surf ace elevation can be calculated at 

various points along Baker Lake and for any specified 

stage of the lake. Typical results are shown in table 8 

for a wave arriving at Upper Baker Dam.

TABLE 8. — Calculated height of waves at Upper Baker Dam in the 

event of an avalanche or mudflow

[Overtopping of the dam was not considered in calculating wave height. Normal "full-pool"

stage is 2.4 m below dam crest. Leaders (...) indicate no calculation was made. Information

supplied by Puget Sound Power and Light Co. Data are in meters]

Wave height above lake stage

Assumed 

avalanche or 

mudflow speed

Do ........

Do ........

219km/hri ....

49.4km/hr1 ...

Lake stage 

below dam 

crest

........ 2.4

........ 5.5

........ 8.5

........ 2.4

........ 2.4

For flow 

2,400 m wide 

and 6.1 m thick

10.0 

8.3 

7.1 

9.4

For flow 

800m wide and 

12.2m thick

5.2 

4.1

3.4 

0.8

1 Corrected avalanche and mudflow parameters; these figures were misplaced in the 

original table in the Tetra Tech report to Puget Power.

These results show that holding the reservoir stage 

about 7 m below the dam crest (4.6 m below normal fullpool elevation) is sufficient to prevent overtopping and 

any damage downstream resulting from an aircushioned avalanche into the lake. Also, the difference

in calculated wave heights between an instantaneous 

debris impact having infinite speed and a fast 

avalanche having a more realistic, finite speed is small 

(6 percent). For a slower mudflow, the actual speed 

must be used to calculate wave height.

Comparison of the present state of knowledge of 

avalanche or mudflow dynamics and that of waterwave dynamics is interesting. The propagation of a 

wave in water is described by known laws (the NavierStokes equations). Procedures for solving these equations numerically for specified conditions, such as a 

wave on Baker Lake, are well known. With the assignment of appropriate parameters and boundary conditions, solutions can be obtained in a straightforward 

manner and to almost any level of precision.

By way of contrast, very little is known about the 

dynamics of large mudflows or rock avalanches. Very 

few quantitative observational data have been obtained 

anywhere in the world. Even the appropriate flow law 

(rheology) is virtually unknown. Thus, simple questions, such as how fast would a specified debris mass 

move on a specified surface, cannot be answered. Certainly, this is a field ripe for research.

DISCUSSION OF HAZARD ANALYSES

The worst plausible geologic event at Mount Baker, 

assuming no volcanic or phreatic eruption, is a huge 

rock mass breaking from the rim of Sherman Crater, 

descending into Boulder Creek valley as a fast-moving 

avalanche, entering Baker Lake, and generating a 

large water wave. The geologic record of prehistoric 

events allows certain probabilities of occurrence to be 

estimated without reference to specific locations. On 

the other hand, study of present conditions and their 

relation to conditions of known avalanches in other 

areas allows estimates of likely parameters of an 

avalanche or mudflow moving down Boulder Creek 

valley to be made but does not allow the probability of 

occurrence of such an event to be calculated. The combination of these two methods adds somewhat to our 

knowledge. But a useful prediction cannot be made; 

probabilities of occurrence of specific avalanches or 

mudflows indicated by study of current conditions cannot be assigned with a high level of confidence, and no 

predictions of the time of occurrence can be made. 

Thus, only a generalized hazard probability can be 

stated, along with estimates of parameters of possible 

avalanches or mudflows.

RESPONSE TO MOUNT BAKER ACTIVITY

INITIAL RESPONSE

The dust-laden steam clouds at Mount Baker on 

March 10 and 11, 1975, caused considerable local apprehension and scientific interest. By midday, on 

March 11 (about 20 hours after the initial observa-
A40 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

FIGURE 29. — This satellite view of northwestern Washington shows how drainage from Sherman Crater at the east slope of Mount Baker 

flows through two reservoirs and into the Skagit River. Cultvated areas in the region are illustrated by the checkerboard patterns of farms 

in the valleys and deforested clearcuts in the mountains. Except for seasonal resorts, Concrete, Glacier, and Kulshan are the nearest small 

communities in valleys which drain Mount Baker. Bellingham and Mount Vernon are major population centers, ERTS satellite image 

E-1258-18322, April 7, 1973.

tions), the University of Washington, Western Washington State College, Washington State Department of 

Emergency Services, Federal Disaster Assistance Administration, and the U.S. Geological Survey had been 

alerted, and several trips by aircraft had been made to 

observe and photograph the volcano. After a period of

cloudy weather on March 12 and 13, continuing abnormal discharge of steam and ejecta was observed. Large 

steam plumes had been seen before, as on February 28, 

1971, but they did not issue from new fumaroles nor did 

they contain ejecta, and the activity returned to normal 

within a day or so. In March 1975 it was obvious that
ASSESSMENT OF INCREASED THERMAL ACTIVITY A41

there had been a major change in the steam activity of 

the mountain, and a number of scientists began to plan 

field investigations. At least initially, the various 

groups acted independently, depending on their 

resources and subjects of interest. By March 31 a 

seismometer and telemetry link has been installed on 

the rim of Sherman Crater.

On April 8 the first of many iiiteragency meetings 

concerning Mount Baker's activity was held. This was 

arranged by the U.S. Forest Service to collect available 

scientific data, to prepare contingency plans, and to obtain advice on possible administrative actions needed to 

protect the public. An important result of this meeting 

was to bring together the various scientific investigators so that a more coherent picture of the steam activity was possible. Specialists were informally assigned 

for each critical monitoring activity, to keep track of 

developments in their fields of interest, and to communicate results to the U.S. Forest Service and to 

others. As a result of this meeting, the Forest Service 

closed Sherman Crater and the Boulder Creek drainage 

to public access. The U.S. Geological Survey assigned 

personnel to conduct and coordinate monitoring activities and to represent the agency at future meetings 

with public officials.

HISTORY OF BAKER LAKE CLOSURE ACTION

Briefings regarding potential hazards were presented 

by the U.S. Geological Survey to concerned governmental agencies during May 12-29. These included 

Federal, State, and local agencies: U.S. Forest Service, 

Federal Disaster Assistance Administration, U.S. Army 

Corps of Engineers, and National Park Service, the 

Washington Governor's Office and Washington State 

Departments of Ecology, Emergency Services, Community Relations, and Natural Resources, and the 

Skagit Regional Council, which included county commissioners, mayors, and city managers of the communities downstream from the Baker Lake area. The 

Department of Ecology, because of their concern with 

dam safety, requested information from the U.S. 

Geological Survey on the "maximum plausible" 

mudflow or avalanche that might be expected to enter 

Baker Lake. Consequently, data similar to those shown 

in table 7, together with estimates of speeds (20-50 

km/hr for a mudflow, 150 km/hr for an air-cushioned 

avalanche) for a "maximum plausible" debris flow 

(volume 30x 106 m3), were furnished by the U.S. 

Geological Survey to the Washington State Department 

of Ecology and to Puget Power on May 30. This action 

triggered an important series of events.

Puget Power, recognizing that a fast-moving 

avalanche might cause a disastrous wave on the reservoir, met with U.S. Geological Survey personnel and 

shortly thereafter engaged a consulting firm, Tetra

Tech, Inc., to analyze the possible wave. On June 16 the 

consultants' preliminary results were delivered to 

Puget Power and were divulged to the Federal Power 

Commission, the U.S. Forest Service, and the U.S. 

Geological Survey. The preliminary calculations were 

based on a greatly oversimplified model and suggested 

a wave higher than that indicated by a subsequent, 

more thorough analysis by the same firm. Drawing 

down the reservoir to prevent damage from such a large 

wave would mean an appreciable loss of hydroelectric 

power generation; such a potential wave could also 

cause loss of life to persons on the lake or shoreline. The 

U.S. Geological Survey was asked to evaluate the probability of hazard and to estimate the width, thickness, 

and speed of the "worst possible" avalanche as the basis 

for more refined analysis and action.

A statement by the U.S. Geological Survey as to the 

probability of the occurrence of mudflows or avalanches 

(app. 1) was presented at interagency meetings, which 

included representatives from Puget Power and Tetra 

Tech, on June 20 and 23. A task force was created on 

June 23, consisting of representatives of the agencies 

responsible for public safety in the area: U.S. Forest 

Service, Washington State Department of Ecology 

(representing the Governor's Office), County Commissioners of Skagit and Whatcom Counties, and Puget 

Power. The Federal Power Commission, the U.S. Army 

Corps of Engineers, and the U.S. Geological Survey were 

advisors to the task force.

On June 23 the task force recommended to the appropriate agencies that the Baker Lake area be closed 

to public access and that the reservoir be maintained at 

a safe level (initially 10 m below full pool) to accommodate the "worst possible" debris flow. The U.S. Forest 

Service and Puget Power announced these actions on 

June 25.

Subsequent task force recommendations included (1) 

upward adjustment of reservoir level, as more refined 

calculations by Tetra Tech indicated somewhat lower 

potential wave heights; (2) additional studies of a possible air-cushioned avalanche (performed by R. L. 

Shreve, app. 2) and the stability of Lahar Lookout; (3) 

studies by a consulting firm (Stone and Webster, Inc.), 

which concluded that Upper Baker Dam should not be 

allowed to be overtopped; (4) creation of an information 

committee (with representatives from the U.S. Forest 

Service, U.S. Geological Survey, University of Washington, and Puget Power), which issued weekly news 

bulletins about Mount Baker throughout the summer of 

1975; and (5) development of contingency plans by the 

U.S. Forest Service, Puget Power, and the two counties.

LIFTING OF BAKER LAKE CLOSURE

Closure of Baker Lake during the summer of 1975 

caused loss of revenue at a private resort, diverted
A42 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

recreationists from the area (with attendant loss of 

business revenue in the nearby town of Concrete), and 

diminished production of electrical power. By the 

winter of 1975—76 the monitoring activities had shown 

no unequivocal evidence that an eruption was 

forthcoming, nor had any mudflows or large rock 

avalanches occurred. It was evident to the U.S. Forest 

Service and Puget Power that the closure needed 

reevaluation. A series of task force meetings, beginning 

on January 29, 1976, considered the effects of continued closure, monitoring evidence, possible changes 

in the mudflow or avalanche hazard, and how additional data on slope stability or avalanche parameters 

might be obtained.

Independently, the U.S. Geological Survey reconsidered the hazard probability. A new statement (app. 

3) pointed out (1) that there was now no clear evidence 

of forthcoming eruption, whereas an eruption could 

have been imminent at the time of the earlier statement; (2) that the degree of mudflow or avalanche 

hazard now probably approached the level of that in an 

"average year" within the last 10,000 years; and (3) 

that the probability of the occurrence of a large fast 

avalanche had therefore somewhat diminished. Drafts 

of this statement were presented to the task force.

During a meeting on March 23, 1976, the task force 

accepted the Survey's draft statement and studied 

possible management alternatives. Public safety, 

generation of electrical power, preservation of the 

economic base of the local community, economy of the 

private resort, safety of structures, such as dams and 

highway bridges, public use, scientific research, and 

natural resources, such as fish and timber, were all considered. The group recommended opening Baker Lake 

to the public but keeping Sherman Crater and the 

Boulder Creek drainage closed — an action that recognized the apparent decrease in hazard by permitting 

public use of the lake, yet drew attention to a continuing hazard by keeping some areas closed. It was also 

recommended that Puget Power be allowed to operate 

the reservoir at a normal stage and that the various 

contingency plans (including possible reimposition of 

complete closure) be kept in readiness. The Survey's 

statement and a Forest Service-Puget Power-task 

force statement rescinding closure were announced at a 

press conference on April 6, 1976.

CONCLUSIONS

Fumarolic activity can have different meanings at 

different volcanoes. Fumaroles can represent the waning release of heat from a cooling magma chamber that 

last erupted hundreds or thousands of years ago. Alternatively, fumaroles can reflect the initial release of 

heat through new fractures that emanate from a rising

body of magma. Any gradation between these two extremes is also possible, so that fumaroles might bear little relation to an increase or decrease in activity of a 

magma source but, instead, simply mark the background heat emission during a volcano's repose period 

between eruptions — a period that can last from days to 

centuries.

Increased thermal activity has been the first (and 

sometimes the only) observed sign of an oncoming 

eruption, as at Soufriere in 1971 (Aspinall and others, 

1973) and at Taal in 1965 (Moxham, 1971, p. 104). 

Many, if not most, other volcanoes have been observed 

to have additional precursors, particularly seismic activity. Lack of a long period of baseline data, both visual 

and instrumental, during the repose period of a volcano 

greatly detracts from the ability to interpret new data. 

Under such limitations, eruption precursors can best be 

detected by conducting many different types of 

monitoring side by side over long periods of time.

The lack of a sufficient data base is clearly evident 

with respect to interpretation of present fumarolic activity at Mount Baker. A single year of intensive 

monitoring serves to show that a longer period of observation is necessary for rigorous examination and prediction of the future behavior of a volcano which obviously is in some state of change. Nevertheless, data 

acquired so far do support four conclusions:

1. The level of thermal activity has had a small upward trend for many decades.

2. In 1975, an increase in heat flux of roughly one 

order of magnitude occurred and represents the 

greatest change in thermal activity during the 

20th century.

3. Despite the increased heat emission, other 

geophysical and geochemical data acquired during the past year have not provided evidence of 

an impending eruption.

4. Continuing hydrothermal activity provides some of 

the conditions necessary for the occurrence of 

avalanches of rock debris and potential 

mudflows, whether or not the volcano erupts. 

This hazard existed to some degree prior to 1975, 

although it was not fully recognized by the public 

or by agencies responsible for land management.

Less conclusive or presently uninterpretable results 

are much more numerous. What caused the gradual 

thermal increase prior to 1975 and the sudden jump in 

heat emission beginning in 1975? Exactly what does 

the past year's monitoring show? Are there signs of additional volcanic change hidden by the background 

noise that snow and weather imprint on seismic, tilt, 

and gravity data, or are virtually all of the instrumental
ASSESSMENT OF INCREASED THERMAL ACTIVITY A43

changes due to nonvolcanic causes? Answers at this 

point are certainly premature, but presentation of the 

data acquired so far provides a useful base for future 

scientific work and administrative decisions.

As a quiescent volcano, Mount Baker will surely 

erupt at some time in the future. We cannot be certain 

that the time of that eruption will be predictable, 

regardless of the amount of monitoring, but we can anticipate the types of hazards which might accompany 

an eruption (Hyde and Crandell, 1977). We can also anticipate hazards that accompany thermal activity on 

Mount Baker, regardless of an eruption. These hazards 

range from localized volcanic gases around the 

fumarole fields to water pollution and potential 

mudflows and rock avalanches in the drainage system 

below Sherman Crater — primarily in Boulder Creek 

and Baker Lake. Perhaps the most significant result of 

increased activity at Mount Baker has been the increase in public awareness of these hazards.

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Shreve, R. L., 1966, Sherman landslide, Alaska: Science, v. 154, no. 

3757, p. 1639-1643.
A44 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

— 1968a, The Blackhawk landslide: Geol. Soc. America Spec. 

Paper 108, 47 p.

1968b, Leakage and fluidization in air-layer lubricated

avalanches: Geol. Soc. America Bull., v. 79, p. 653-658.

Sumi, Kiyoshi, 1970, Zonal distribution of clay minerals in the Matsukawa geothermal area, Japan: Internat. Clay Conf., Tokyo, 

Proc., v. 1, p. 501-512.

Thorarinsson, Sigurdur, 1970, Hekla — A notorious volcano: Reykjavik, Almenna Bokafelagio", 110 p.

Weaver, C. S., and Malone, S. D., 1976, Mt. Saint Helens seismic

events — Volcanic earthquakes or glacial noises?: Geophys.

Research Letters, v. 3, no. 3, p. 197-200. 

White, D. E., 1969, Rapid heat-flow surveying of geothermal areas

utilizing individual snowfalls as calorimeters: Jour. Geophys.

Research, v. 74, no. 22, p. 5191-5201. 

Wilson, R. T., and Fretwell, M. O., 1976, Table of data on quality of

surface waters and of snowpack draining to Baker River from

Mount Baker, Washington: U.S. Geol. Survey open-file report,

3 p.
APPENDIXES 1 - 3
A46 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

APPENDIX 1: U.S. GEOLOGICAL SURVEY

STATEMENT ON MOUNT BAKER

SITUATION, JUNE 19, 1975

Geologic hazard studies by the U.S. Geological Survey 

at Mount Baker indicate that there have been at least 2 

major eruptive periods at the volcano during the last 

10,000 years, as well as several additional minor eruptions which produced small amounts of volcanic ash 

and, probably, many others which left no recognizable 

deposits. The increased thermal activity that began 

March 10 at Mount Baker does not necessarily mean 

that an eruption is about to occur. However, this thermal activity does increase the likelihood of an 

avalanche of hydrothermally altered rock from the upper part of the volcano. During the last 10,000 years, 

such avalanches have caused at least 10 mudflows 

which probably were large enough to travel at least 13 

km, the distance from the summit area to Baker Lake. 

One or more of these mudflows moved down each of five 

different valleys. The history suggests a probability of 1 

in 1,000 that a mudflow of this type will occur in an 

average year. However, thermal activity on the scale of 

that since March 10 has not been observed for the previous 100 years, and, therefore, 1975 cannot be considered an average year. The probability of a mudflow 

traveling at least 13 km may now be as much as 10 

times greater than during an average year, or 1 in 100. 

Such a mudflow could enter Baker Lake at a speed of 

30- 50 km/hr.

The 10 mudflows mentioned above range in volume 

from several million to 40 or 50 X 106 m3 . Flows as large 

as 25 X 106 m3 occurred only twice during the past 

10,000 years. Thus, the probability for a flow as large as 

this happening in any average year is only 2 in 10,000. 

In 1975, because of the increased thermal activity, it is 

perhaps 2 in 1,000. Mudflows are most likely to descend 

Boulder Creek but could go down Sulphur Creek, the 

Middle Fork Nooksack River, or other drainages.

The worst avalanche under existing conditions would 

be a very large one at the head of Boulder Creek which 

would trap a cushion of air and move rapidly downslope 

toward Baker Lake. The probability that such a high 

speed avalanche (more than 100 km/hr) would enter 

Baker Lake during 1975 would probably be less than 1 

in 1,000, perhaps as low as 1 in 10,000.

It is not possible now to predict how long the thermal 

activity will continue at the present scale; it may subside, or it may progress into some kind of eruptive activity. If an eruption does occur, the chances of a 

mudflow or other hazardous event would be greatly increased.

APPENDIX 2: EVALUATION OF 

POSSIBILITY OF AIR-CUSHIONED

ROCK AVALANCHE OR 

MUDFLOW FROM MOUNT BAKER

By RONALD L. SHREVE, 

Consulting Geologist, Los Angeles, Calif.

[Report to Mark F. Meier, U.S. Geological Survey, July 21, 1975. All references cited in 

appendix 2 are listed in "References Cited" on p. A43-A44]

This is the report that you requested in our telephone 

conversation on 16 July. It summarizes my responses to 

the principal questions put to me as your consultant in 

connection with the possibility that a large rock avalanche or debris flow originating in the collapse of 

Lahar Lookout on Mount Baker might reach Baker 

Lake. I have responded to essentially four questions:

Question 1. — What is the likelihood that a large rockfall from 

Lahar Lookout might develop into an air-cushion avalanche that 

would reach Baker Lake?

Question 2. — In the event of such an avalanche, what would be its 

most likely width, thickness, and speed as it entered Baker Lake?

Question 3. — If, instead, a rockfall of comparable size developed 

into a debris flow, what would be its most likely width, thickness, and 

speed as it entered Baker Lake?

Question 4. — Could the estimates of probability of various possible 

debris flows and rock avalanches given in the "U.S. Geological 

Survey Statement on Mount Baker Situation" released on 23 June 

1975 be improved?

I must emphasize at the outset that, in the present 

state of knowledge, none of these questions can be 

answered with much certainty. Large debris flows and 

rock avalanches of the sort contemplated in the questions do not occur frequently in Nature and cannot be 

studied in the laboratory. Therefore, there are 

relatively few comparable cases and even fewer 

established principles available as a basis for prediction. Moreover, the uncertainty is compounded at 

Mount Baker by the unpredictable effects of volcanic 

activity on a glacier-covered mountain. The estimates 

given in this report must accordingly be used with appropriate caution.

My previous report to you (letter dated 18 June 1975) 

dealing with questions 1 and 2, which was an emergency rush job that this report supersedes, was based on 

the l:62,500-scale U.S. Geological Survey quadrangle 

maps of the Mount Baker area. I have since completely 

repeated all measurements and calculations using the 

much clearer l:24,000-scale Interim Topographic Map 

of Mount Baker which you sent me a week ago. 

Although there are minor differences in some of the 

numbers, there are no significant changes in the conclusions.

Question 1. — Formation of an air-cushion avalanche 

with long runout requires that the avalanche override 

and trap sufficient air to reduce contact with the 

ground significantly. This, in turn, requires a suitable
ASSESSMENT OF INCREASED THERMAL ACTIVITY A47

break in slope to launch the avalanche into the air, high 

speed to enable it to override enough air, and sufficient 

thickness of the debris and smoothness of the ground to 

prevent excessive loss of air.

In the case of the potential avalanche from Lahar 

Lookout, significant air launch is unlikely to occur anywhere along the likely path of the avalanche, except at 

the lip of the pronounced bench at the 3,000-foot level 

in the canyon of Boulder Creek. The speed of the 

avalanche at this point is likely to be at least 240 ft/s 

(75 m/s), which corresponds to conversion of one-eighth 

of the available potential energy (7,000 ft, or 2,100 m, of 

fall) to kinetic energy. The observations by Heim in the 

Alps (Shreve, 1968a, p. 41) and by myself of the Elm, 

Sherman, and Frank landslides (Shreve, 1966, p. 1639; 

1968a, p. 4, 32, 35), which involved from 0.4 to 1.3 x 109 

ft3 (10 to 35 x 106 m3) of debris, suggest a somewhat 

higher fraction, roughly one-fifth. Nevertheless, even 

at the lower speed, enough air could be trapped to form 

a layer about 6 feet (2 m) thick if compressed under 20 

feet (6 m) of debris over the whole area of the avalanche from the 3,000-foot level down to the lake shore, 

assuming a water-surface elevation of 724 feet, the fullpool elevation. Even elevations as low as 700 feet, 

however, would not significantly change this figure. 

The thickness would be greater if the launch speed 

were higher. By way of comparison, I have computed an 

air-layer thickness of a couple of feet (0.6 m) for the 

Blackhawk landslide (Shreve, 1968a, p. 42). Thus, 

entrapment of sufficient air to provide an air cushion 

seems probable if a large avalanche travels down 

Boulder Creek.

The most important consideration is the probable 

thickness of the avalanching debris. The average thickness of the portion of the Little Tahoma Peak landslide 

that passed beyond the launch point at the terminus of 

the Emmons Glacier was about 15 feet (5 m; from 

figures given by Crandell and Fahnestock, 1965, p. 

A12- A13), of the Sherman was more than 10 to 20 feet 

(3 to 6 m; Shreve, 1966, p. 1639), and of the Huascaran 

was 15 feet (5 m) or more (Plafker and others, 1971, p. 

556). The other probable air-cushion avalanches I have 

studied all had similar or greater thicknesses. Thus, it 

appears reasonable to assume that a minimum debris 

thickness of at least 15 feet (5 m) is necessary for long 

runout.

In the Little Tahoma Peak avalanche (or 

avalanches), 75 to 85 percent of the debris was 

deposited beyond the launch point (Crandell and 

Fahnestock, 1965, p. A12), and a similar figure would 

apply to all other probable air-cushion avalanches that 

I have studied. At Mount Baker the area of the probable 

avalanche path is 7.1 x 107 ft2 (6.6 x 106 m2) from the 

3,000-foot level to the lake shore at 724 feet. If debris

were spread over this area to a depth of 15 feet (5 m), it 

would have a volume of 1.1 x 109 ft3 (30 x 106 m3). Correcting for the approximately 20 percent left above the 

launch point and for the roughly 50-percent increase in 

volume of the initially solid rock as it disaggregates in 

the initial fall, gives a required volume of undisaggregated rock of 0.9 x 109 ft3 (25 x 106 m3).

Looking at the problem another way, the debris left 

above the launch point by the Little Tahoma Peak 

avalanche averaged about 3 feet (1 m) thick (Crandell 

and Fahnestock, 1965, p. A12), and, as before, a similar 

figure would apply to other probable air-cushion 

avalanches. At Mount Baker, the area of the probable 

avalanche path down to the 3,000-foot level is about 

9 x 107 ft2 (8.4 x 106 m2). If covered to a depth of 3 feet 

(1 m), this would require 0.3 x 109 ft3 (8x 106 m3) of 

debris. Adding this to the 1.1 x 109 ft3 (30 x 106 m3 ) required to cover the lower part of the path to a depth of 

15 feet (5 m), and correcting for the 50-percent volume 

increase on disaggregation, gives 0.9 x 109 ft3 (25 x 106 

m3) as the minimum volume of undisaggregated rock 

that would have to fall, in good agreement with the previous figure.

Thus, both lines of reasoning lead to 0.9 x 109 ft3 

(25 x 106 m3) as the minimum volume of undisaggregated rock (and ice) that would have to fall at one time 

in order to produce an air-cushion avalanche that could 

reach Baker Lake. Water-surface elevations as low as 

700 feet will not significantly change this result.

Assessing the likelihood of a single fall of this size 

from the vicinity of Lahar Lookout under present 

circumstances is, in my opinion, essentially impossible. 

According to the l:24,000-scale map, which probably is 

not entirely accurate, roughly the required 0.9 x 109 ft3 

(25 x 106 m3) of rock could be released from Lahar 

Lookout and Sherman Peak by failure along a curved 

surface of rupture sloping downward at an average 

angle of about 30 degrees and emerging at the 8,500- 

foot level at the head of Boulder Glacier. This may be 

compared with the angle of repose of loose, dry, disaggregated rock, which is 34° and with the average inclinations of the surfaces of rupture of the Sherman, 

the Frank, and, probably, the Little Tahoma Peak landslides, which were around 40° (Plafker, 1968, p. 377; 

Shreve, 1968a, p. 35; Crandell and Fahnestock, 1965, p. 

A18, A19). Thus, in ordinary circumstances a single fall 

of the required volume would not be very likely. For 

Mount Baker, however, account must also be taken of 

the potentially important and largely unpredictable 

effects of the weakening and undermining of Lahar 

Lookout and Sherman Peak and the possible steam explosions, or other disturbances, near or under them 

that might be caused by the current increased 

fumarolic emissions and glacial melting, not to mention 

possible future intensified volcanic activity.
A48 VOLCANIC ACTIVITY AT MOUNT BAKER, WASHINGTON

During runout the trapped air must spread out more 

or less uniformly under the advancing debris. This 

process depends strongly on the variation with time of 

the thickness of the debris passing the launch point. 

Longitudinal and lateral variations in thickness- cause 

pressure gradients in the air layer that, combined with 

the shearing due to the forward motion of the debris, 

redistribute the air. Judging from other air-cushion 

landslides, such as the Blackhawk (Shreve, 1968a, p. 

27), long runout seems to require a thickness that 

tapers slightly toward the rear so as to compensate partially the rapid removal of air from the launch region by 

the shearing. For Mount Baker, I am unable even to 

guess the likely thickness variation, but it conceivably 

couid be such that the air layer would be unstable and 

rapidly break up, even though other factors, such as 

forward speed, air volume, and debris thickness, were 

favorable for air-cushion avalanching.

A further requirement for a stable air-cushion is that 

the product of the permeability and the bulk density of 

the debris at the base of the avalanche be less than 

about 0.7 times the product of the harmonic mean permeability and the arithmetic mean density for the 

whole thickness of the debris (Shreve, 1968b, p. 

655—656). In practical terms, a thin basal layer of finer, 

tighter material will suffice. In the Little Tahoma Peak, 

Sherman, and Huascaran landslides, the required basal 

layer was probably snow picked up from the glaciers 

onto which they fell (Crandell and Fahnestock, 1965, p. 

Al; Shreve 1966, p. 1639; 1968b, p. 656; Plafker and 

others, 1971, p. 550). At Mount Baker, this requirement 

would doubtless be satisfied by snow picked up from 

Boulder Glacier.

An air-cushion avalanche debouching from the narrow canyon of Boulder Creek onto the convex alluvial 

cone between the main road and Baker Lake very likely 

would tend to split into multiple lobes, like the Sherman 

landslide (Shreve, 1966, p. 1641). This would lead to loss 

of air that, if severe enough, might disrupt the aircushion short of the lake. Slowing and increased air loss 

would also occur if the surface of the alluvial cone has 

rough local relief greater than the thickness of the air 

cushion — that is, greater than a few feet (a couple of 

meters).

Question 2. — An air-cushion avalanche big enough 

to reach Baker Lake from Lahar Lookout would be 

about 1,200 to 1,500 feet (350 to 450 m) wide at the 

point where the main road crosses Boulder Creek (at 

BM 1056) and would spread laterally as it crossed the 

convex surface of the alluvial cone to the lake shore. 

Judging from the behavior of the Sherman, Little 

Tahoma Peak, and Huascaran landslides (Shreve, 

1966, p. 1640, fig 2; Crandell and Fahnestock, 1965, p. 

A2, fig. 1; Plafker and others, 1971, p. 551, fig. 3) and 

making allowances for inertia, it would most likely

spread to a width of about 1.5 miles (2.4 km) at the lake 

shore, covering it from near the mouth of Little Sandy 

Creek on the southwest to a point about a third of a mile 

(0.5 km) north of the mouth of Boulder Creek on the 

north. Judging from the speeds computed from runup 

of the three previously mentioned landslides on adjacent slopes (Shreve, 1966, p. 1640; Crandell and 

Fahnestock, 1965, p. A19; Plafker and others, 1971, p. 

558), its speed on entering the lake would probably be 

in the range from 150 to 300 ft/s (45 to 90 m/s), with 

200 ft/s (60 m/s) the most likely. Judging again from 

the other three landslides and from the calculations 

given in the response to question 1, its thickness on entering the lake would probably be a minimum of 15 feet 

(5 m) and would most likely be about 20 feet (6 m).

These estimates assume that the volume of rock falling will be near the minimum required to reach Baker 

Lake, because the smallest falls are the most likely. 

Air-cushion avalanches from larger falls would have 

about the same width, greater thicknesses in direct proportion to volume, and somewhat greater speeds on entering the lake.

In summary, if a rockfall from the vicinity of Lahar 

Lookout were to develop into an air-cushion avalanche 

that reached Baker Lake, its width, thickness, and 

speed on entering the lake would most probably be 

about 1.5 miles (2.4 km), 20 feet (6 m), and 200 ft/s (60 

m/s), respectively.

Question 3. — A debris flow would tend to be narrower, thicker, and slower than an air-cushion 

avalanche of the same volume. My opinion is that a 

debris flow down Boulder Creek that originated in a fall 

of lx 109 cubic feet (30 x 106 m3) of rock from the 

vicinity of Lahar Lookout would have a width of roughly 

0.5 mile (0.8 km), a thickness of about 40 feet (12 m), 

and a speed of about 50 ft/s (15 m/s) as it entered Baker 

Lake. This estimate of speed accords with that given in 

the "U.S. Geological Survey Statement on Mount Baker 

Situation," whereas I originally suggested a speed of 

100 ft/s (30 m/s), based on the apparent speed of the 

debris-flowlike part of the Huascaran landslide which 

ran upslope near Matacoto (Plafker and others, 1971, p. 

553, 556). After further discussion, however, I have 

concluded that the lower estimate is better. The estimated thickness is based on the thicknesses of 

prehistoric debris flows of comparable size from Mount 

Baker reported by Hyde and Crandell (1975, p. 8, 9, 11, 

13), which would have approximately the same composition as one from Lahar Lookout and, hence, 

presumably similar properties.

An important point to note is that, unlike air-cushion 

avalanches, there is no minimum cutoff in the likely 

thickness and speed of a debris flow that could reach 

the lake. Hyde and Crandell (1975, p. 10) found remnants of prehistoric debris flows ranging down to less
ASSESSMENT OF INCREASED THERMAL ACTIVITY A49

than 2 feet (0.6 m) thick along Boulder Creek between 

the main road and Baker Lake. Thinner flows will be 

slower, generally narrower, and more probable than 

thicker ones. In addition, an air-cushion avalanche too 

small to reach the lake could continue onward as a 

high-speed debris flow, as did the Huascaran landslide 

near Matacoto (Plafker and others, 1971, p. 553).

Question 4. — I can add little beyond concurrence to 

the estimates of probability given in the "U.S. Geological Survey Statement on Mount Baker Situation." The 

estimates appear to me to be derived by methods appropriate in the circumstances, to be based on the best 

available input data, and to be adequately qualified as 

to their limitations. Despite the considerable uncertainty that must be attached to them, they cannot, in my 

opinion, realistically be improved very much because of 

the uncertainties in the processes and materials involved, the highly incomplete geological record, and the 

present abnormal situation on Mount Baker.

APPENDIX 3: U.S. GEOLOGICAL SURVEY

STATEMENT ON MOUNT BAKER

SITUATION, APRIL 6, 1976

In early March 1975 increased thermal activity was 

reported at Mount Baker, Washington. This activity 

gave rise to concern that the volcano might pose an increased threat to life and property in the Mount Baker 

area. In June 1975 the U.S. Geological Survey issued a 

statement estimating that the chance of a destructive 

mudflow or avalanche was about 10 times greater than 

it had been prior to the onset of the increased thermal 

activity. The Survey, in collaboration with the University of Washington, intensified a program of geophysical, geological, geochemical, and hydrological monitoring of Mount Baker in an effort to document whether or 

not the volcano was building toward an eruption.

These monitoring activities have indicated that the 

thermal emissions, after increasing in intensity in 

March 1975, have remained at about the same level to 

the present time. Geophysical observations have not indicated abnormal local seismicity, and deformation 

measurements have not indicated inflation of the 

volcanic edifice, which commonly precedes volcanic 

eruptions. Thus, there have been no observed indications of an impending eruption at Mount Baker.

The Geological Survey statement of June 1975 

pointed out that "It is not possible now to predict how 

long the thermal activity will continue at the present 

scale; it may subside, or it may progress into some kind 

of eruptive activity." A chief concern at that time was 

that the increased thermal activity was related to magma rising in the volcano and would be followed by an 

eruption. Mount Baker's present behavior, however,

does not indicate that the chance of an eruption is appreciably greater now than it was prior to March 1975. 

Consequently, there now seems to be less need to maintain the intensified volcano monitoring activities that 

were implemented during the past year.

The situation with respect to possible avalanches and 

mudflows of rock debris from the volcano is more 

difficult to assess. In the June 1975 statement, it was 

noted that the geologic history of Mount Baker during 

the past 10,000 years suggested a probability of 1 in 

1,000 that an avalanche or mudflow of sufficient size to 

reach Baker Lake would occur in an average year. It 

was further suggested that the increase in thermal activity, and the possibility that the volcano was building 

toward an eruption, may have multiplied by a factor of 

10 the chance of such an event, so that the probability 

that a large avalanche or mudflow would take place in 

1975 may have been as great as 1 in 100. However, 

thermal activity at the volcano has remained at about 

the same level for about 12 months, during which 

period neither avalanches nor mudflows have been 

recognized. Because of the lack of evidence that the 

volcano is building toward an eruption, the chance that 

a large avalanche or mudflow will be triggered by a 

steam explosion or some other volcanic event in the 

near future seems lessened. Even if the probability of a 

large avalanche or mudflow returned to pre-March 

1975 levels, a certain degree of potential danger would 

remain, but it is one that existed prior to March 1975, 

even though its nature may not have been fully recognized by the public or by agencies responsible for land 

management.

The U.S. Geological Survey statement also suggested 

a probability of between 1 in 1,000 and 1 in 10,000 in 1 

year that a very large rock mass would slide from 

Mount Baker and form an air-cushioned avalanche, 

which would enter Baker Lake at high speed. The probability of such an avalanche also may now be somewhat 

diminished. However, it is not possible to estimate the 

probability of such an event because of uncertainties 

concerning the likelihood that all conditions would be 

met for the formation of a very large air-cushioned 

avalanche.

If the present levels of thermal activity have not 

changed by June 1976, and if the volcano continues to 

show no signs of an impending eruption, the U.S. 

Geological Survey will reduce its monitoring program 

on June 30, 1976.

Other agencies and organizations may also elect to 

reduce their activities on Mount Baker, but it will be advisable to carry out periodic visual observations and to 

continue essential seismic and ground deformation 

measurements. This lower level "volcano watch" should 

be continued as long as the increased thermal activity 

persists.

.S. GOVERNMENT PRINTING OFFICE: 1977-777-034/48