Contributions to 

General Geology 

1965

GEOLOGICAL SURVEY BULLETIN 1221

This volume was published 

as separate chapters A F
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Rockfalls and avalanches from Little Tahoma Peak on Mount Rainier, 

Washington, by Dwight R. Crandell and Robert K. Fahnestock.

(B) Geology of the Hames Valley, Wunpost, and Valleton quadrangles, Monterey 

County, California, by David L. Durham.

(C) Geology of the Florida quadrangle, Puerto Rico, by A. E. Nelson and W. H. 

Monroe.

(D) Geology of the Eldorado Springs quadrangle, Boulder and Jefferson Counties, Colorado, by John D. Wells.

(E) Structure and metamorphism in the Mono Craters quadrangle, Sierra 

Nevada, California, by Ronald W. Kistler.

(F) Igneous geology of the Dry Mountain quadrangle, Jefferson County, Montana, by Harold J. Prostka.
Rockfalls and Avalanches 

from Little Tahoma Peak 

on Mount Rainier 

Washington

By DWIGHT R. CRANDELL and ROBERT K. FAHNESTOCK

CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1221-A

A description of the deposits of seven 

successive rockfalls and avalanches at 

Mount Rainier volcano, and of their 

origin and manner of transport

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price 20 cents (paper cover)
CONTENTS

Page

Abstract ____.________________.________----__-___--__-__--________ Al

Introduction..________________._._____-______--_____._____-._-__._ 1

Geographic and geologic setting.____________________________________ 4

Description of avalanche deposits.____________________________________ 4

Movement and velocity of the avalanches---------------------------- 13

Mudflows__-_---____-______._-_______-----_--_---------________. 22

Dust clouds.-.---------------------------------------------------- 25

Cause of the rockfalls_____-_-___-______--____-________-----___----- 25

References. -. _____________________________________________________ 29

ILLUSTRATIONS

Page 

FIGURE 1. Map of northeast side of Mount Rainier, showing area covered

by avalanches from Little Tahoma Peak____-.--____-_._- A2

2. General view of rockfall-avalanche deposits.________________ 3

3. Surface of avalanche deposits.---------------------------- 5

4. Curved furrow in surface of avalanche unit 4_._._.-.__---.- 6

5. Block of breccia lying on Emmons Glacier..---_--_-_-_---_. 7

6. Aerial photograph of downvalley part of avalanche deposits.-- 8

7. Map of downvalley part of the avalanche deposits...___._.__ 9

8. Damaged pine tree on terminal moraine.___________________ 11

9. Avalanche scar at the base of Goat Island Mountain_________ 12

10. Transverse cross sections of avalanche deposits ------------- 14

11. Lontitudinal section of avalanche deposits.-----------.----- 16

12. View of Little Tahoma Peak from Mount Ruth in 1956------ 18

13. View of Little Tahoma Peak from Mount Ruth, July 9, 1964. _ _ 19

14. Diagram showing expectable points of impact of avalanche

after it left Emmons Glacier.__-_--___----.__--_---._--- 23

15. Cracked mounds on surface of mudflow deposit _____________ 24

16. Water vapor issuing from western base of rockf all scar on

July 9, 1964..._......_..._..-..._____....._...._..... 28

TABLE

Page 

TABLE 1. Comparison of Little Tahoma rockfall-avalanche deposits with

others in the United States and Canada________________ A20

CONTRIBUTIONS TO GENERAL GEOLOGY

ROCKFALLS AND AVALANCHES FROM LITTLE TAHOMA 

PEAK ON MOUNT RAINIER, WASHINGTON

By DWIGI-IT R. CRANDELL and ROBERT K. FAHNESTOCK

ABSTBACT

In December 1963 rockfalls from Little Tahoma Peak on the east side of Mount 

Rainier volcano fell onto Einmons Glacier and formed avalanches of rock debris 

that traveled about 4 miles down the glacier and the White River valley. In 

this distance, the rock debris descended as much as 6,200 feet in altitude. Minor 

lithologic differences and crosscutting relations indicate that the rockfalls caused 

at least seven separate avalanches, having an estimated total volume of 14 

million cubic yards. The initial rockfall may have been caused by a small 

steam explosion near the base of Little Tahoma Peak.

During movement, some of the avalanches were deflected from one side of 

the valley to the other. Calculations based on the height to which the avalanches 

rose on the valley walls suggest that their velocity reached at least SO or 90 miles 

per hour. The unusually long distance some of the avalanches were transported is attributed to a cushion of trapped and compressed air at their base, 

which buoyed them up and reduced friction.

INTRODUCTION

On December 14,1963, and probably on several subsequent occasions 

as well, very large masses of rock fell onto Emmons Glacier from the 

north side of Little Tahoma Peak on the east flank of Mount Rainier 

volcano (figs. 1, 2). As the rock masses struck the glacier, they 

shattered and formed rock avalanches that rushed as much as 4.3 

miles downvalley and came to rest less than half a mile from the 

White River campground in Mount Rainier National Park. As snow 

melted during the summer of 1964, dark rock debris mantling Emmons 

Glacier became visible from a visitor center at Yakima Park, and 

clouds of dust rose almost daily from the rockfall scar. These features 

attracted much interest from park visitors, many of whom wondered 

if they were witnessing volcanic eruptions. This article discusses the 

.avalanche deposits, their manner of transport, and what might have 

caused the rockfalls.

Al
121°45' 121 0 40'

liiiiliilSPIfel

to

FIGURE 1. Map of northeast side of Mount Rainier, showing area covered by avalanches from 

Little Tahoma Peak. Rectangular area at northeastern end of the deposits is shown in 

figures 6 and 7. Arrows indicate inferred direction of movement of the avalanches.
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A3

FIGURE 2. General view of rockfall-avalanehe deposits. Note avalanche debris 

on Enimons Glacier below Little Tahoma Peak. Wooded ridge in center of 

lower valley is a terminal moraine of Emmons Glacier formed between about 

1700 and the early 1900's. The end of an avalanche tongue downvalley from 

the terminal moraine is indicated by a dashed line. Aerial photograph by 

Austin S. Post, U.S. Geological Survey.

The senior author currently is investigating the surficial geology of 

Mount Rainier National Park (Crandell and others, 1962; Crandell, 

1963; Crandell and Miller, 1964); during the periods July 7-12 and 

August 19-September 13, 1964, he studied the avalanche deposits and 

the circumstances that led to their formation. He expresses his 

appreciation to Ranger Naturalists Arthur Haines, William Kagami, 

and Duane Nelson of the National Park Service, each of whom accompanied him in the field in July. The junior author, in a recent study 

of the White River and its flood plain, surveyed 12 profiles across the 

valley floor just downstream from Emmons Glacier (Fahnestock, 

1963). Nine of these profiles were resurveyed in July 1964, with the 

assistance of David Pedersen, University of Texas, to determine the 

thickness of the avalanche deposits. Both of the authors wish to
A4 CONTRIBUTIONS TO GENERAL GEOLOGY

acknowledge the interest and cooperation of John A. Butter, Superintendent of Mount Rainier National Park, and his staff. The Northern 

Forest Fire Laboratory of the U.S. Forest Service at Missoula, Mont., 

provided an aircraft equipped with an infrared sensing device; this 

device was used to examine the north face of Little Tahoma Peak for 

evidence of volcanic heat. The aircraft was piloted by Eldon Down 

and the infrared sensing equipment was operated by Robert A. Cook, 

both of the U.S. Forest Service. Robert M. Moxham of the U.S. 

Geological Survey interpreted the results of the infrared investigation, 

and Austin S. Post of the Geological Survey provided aerial photographs he made of the avalanche deposits on August 20, 1964. The 

authors express their appreciation to J. Hoover Mackin, University 

of Texas, for discussions regarding the rockfalls and avalanches and 

for his critical reading of the manuscript.

Little Tahoma Peak forms the highest part (11,117 ft) of a broad 

wedge pointing toward the top of Mount Rainier, about 2 miles to the 

west (fig. 1). The wedge is made up of volcanic breccia and rubble 

interlayered with lava flows that slope down the flank of the volcano 

in an easterly direction. Both the north and south sides of Little 

Tahoma Peak rise steeply about 2,000 feet above the flanking glaciers. 

The cliffs are largely the result of continuing erosion by a broad sheet 

of ice that flows down the east flank of Mount Rainier. This ice 

splits at Little Tahoma Peak into the southeast-flowing Ingraham 

Glacier and the northeast-flowing Emmons Glacier. Emmons Glacier 

now terminates about 2.5 miles downvalley from Little Tahoma Peak.

Prior to December 1963, the White River just beyond Emmons 

Glacier occupied a valley floor about 500 feet wide, which was flanked 

on the northwest by lateral moraines and stagnant ice and on the 

southeast by Goat Island Mountain. Farther downvalley the valley 

floor is constricted by a large terminal moraine which was formed at 

the front of Emmons Glacier between about 1700 and the early 1900"s 

(Crandell and Miller, 1964) (fig. 2). The White-River still flows 

through this constriction but is now about 300 feet south of its preavalanche course.

DESCRIPTION OF AVALANCHE DEPOSITS

The avalanche.deposits are a jumble of large and small rock fragments in a matrix of grayish-red sand (fig. 3). Many small cracks 

formed in the avalanche deposits during settling and compaction. The 

deposits are loose and porous and they slide and compact underfoot.
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A5

 ' .' Avalanche unitr l ..- ,' '..^ " ''- jB*" , .-^

FIGURE 3. Surface of avalanche deposits is hummocky and strewn with blocks. 

Deposit in front of the man is part of avalanche unit 3 (see fig. 7 and p. A10) ; 

deposit directly behind and to left of the man is part of unit 1.

Most of the rock fragments in the avalanche deposits are light-gray 

to dark-reddish-brown andesite. These fragments came from lava 

flows and from interbedded masses of breccia, both of which were 

erupted during the growth of Mount Rainier and are now exposed on 

the sides of Little Tahoma Peak (see Fiske, Hopson, and Waters, 

1963, p. 73-75). In addition, the avalanche deposits contain blocks 

from an undetermined source. One of these blocks, 15 by 20 by 20 

feet in maximum dimensions, lies on the terminal moraine near the 

northeastern edge of the avalanche deposits. A block of reddishbrown breccia about 1,700 feet upvalley from the terminal moraine 

has maximum dimensions of 24 by 30 by 46 feet (fig. 4), but the 

largest block in the entire deposit (fig. 5) lies on Emmons Glacier 

near the point where the White Kiver flows from the glacier terminus. 

This rock has approximate maximum dimensions of 60 by 130 by 160 

feet, and probably weighs at least 50,000 tons. Many blocks of reddish andesite breccia have disintegrated into piles of rubble since 

the avalanches came to rest; their poor consolidation illustrates the 

weakness of some rock layers in Little Tahoma Peak. Locally, the

782-613 O 65 2 ....--. .--,.. , . : ; . ;.
A6 CONTRIBUTIONS TO GENERAL GEOLOGY

avalanche deposits lie on remnants of glacier ice downvalley from Emmons Glacier; these ice masses probably were present before the avalanche occurred. No glacier ice was seen in the avalanche deposits 

themselves.

Bridges formed of snow mixed with avalanche debris persisted over 

the White Eiver at two places (figs. 6, 7) throughout the summer of 

1964, and the river flowed beneath a third snow bridge between cross 

sections 10 and 12 until late July. The snow in these bridges had 

nearly the density of ice, and about 25 percent of the bridge material 

consisted of rock debris. This mixture probably was formed during 

one or more avalanches and indicates that snow was abundant in the 

debris when it came to rest.

The loose and porous fabric of the avalanche debris probably is due 

to the inclusion and the retention of much air and snow during transport and deposition. According to the records of the National Park 

Service, at White River Ranger Station (7 miles northeast of Little

FIGURE 4. Curved furrow in surface of avalanche unit 4. Furrow is bordered 

on the southwest (left) side by a long curved ridge, which may represent the 

front of a separate avalanche. Pond on floor of furrow drains to the left. 

Block on ridge is about 24 by 30 by 46 feet.
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A7

Tahoma Peak at an altitude of 3,500 ft) 13 inches of snow was on the 

ground on December 14,1963. From December 15 to January 4, 1964, 

snow depth ranged from 7 to 15 inches at the Ranger Station, and from 

January 5 to the end of March, the depth ranged from 23 to 82 inches. 

Thus, at and subsequent to the time of the initial rockfall at least a 

foot of snow probably covered the area crossed by the avalanches.

The surface of the avalanche debris is very rough. If viewed from 

the ground, the surface between Emmons Glacier and the terminal 

moraine has a chaotic appearance, but if seen from above, distinct 

patterns are apparent. One pattern consists of a series of curved 

ridges and furrows between cross sections 6 and 12, just upvalley from 

the terminal moraine (figs. 6, 7). These ridges and furrows lie at 

slight angles to the trend of the valley, are in the thickest part of the 

deposits, and were formed as the avalanches came to rest. Another 

pattern lies between cross sections 3 and 6 and consists of a series of 

straight ridges and furrows that parallel the trend of the valley. 

They may have been formed by debris deposited along the margins of 

avalanche units 4 and 5 during movement. Shallow ponds partly 

occupy some of the furrows in both areas.

FIGURE 5. Block of reddish breccia lying on Emmons Glacier (hidden beneath 

avalanche debris). The block is about 160 feet long and 60 feet high.
IIM

*~a

'B 

"3

"8 'So

0) o

1> 

(rf 

£3

0>

o

g*» 

ago?

»i°
Terminal moraine Gage house before 

and after transport 

by avalanche unit 3 '.' EMMONS'

Moraine 

crests

Moraine crests 

(buried)

Moraine on stagnant ice

Moraine crests

Lateral /moraine .-

FIGUBE 7. Relation of downvalley part of avalanche deposits to moraines of Emmons Glacier and to the former flood plain 

of White River (heavy dashed line). Black areas are shallow ponds. Numbered arrows indicate cross sections shown . 

in figure 10. CD
A10 CONTRIBUTIONS TO GENERAL GEOLOGY

There are also straight ridges and furrows in avalanche debris on the 

lower mile of Emmons Glacier. Farther up, the glacier is steeper and 

extensively crevassed, and the avalanche deposits are thin. Even in 

this area, however, there are parallel strips of fairly clean ice and 

debris-covered ice.

Still another pattern appears if the deposits are studied on the 

ground. Certain areas of the deposits have a distinctive color, texture, 

or topography. If areas of similar characteristics are mapped, it 

becomes apparent that at least seven separate avalanche deposits are 

present; these lap over each other in a series of shinglelike lobes (figs. 

6, 7), which are here called avalanche units.

The earliest two avalanche units lie along the northern edge of the 

deposits; they are both overlapped by a third unit, but as the exposures 

of units 1 and 2 are 1,500 feet apart, the time relation of these two 

early units is not known. For convenience of reference the one farther 

down valley is designated avalanche unit 1, and the other one avalanche 

unit 2. Avalanche unit 1 forms a ridge along the lateral moraine on 

the northwest side of the valley, and blocks of a distinctive light-gray 

andesite litter the ridge. In July a layer of compressed granular snow 

as much as 6 inches thick locally separated the outer margin of this 

unit from the underlying moraine. Avalanche unit 2 has an overall 

reddish appearance, and blocks of light-gray andesite are absent. 

This unit was recognized only in the upper part of the valley; its 

downvalley extent is buried by the younger avalanche deposits.

Avalanche unit 3 cuts across units 1 and 2. It has an overall reddish 

appearance but does not contain as many blocks of light-gray andesite 

as unit 1. Unit 3 represents the largest avalanche of the group. It 

not only reached the terminal moraine but also poured through the 

river gap near the southern end of the moraine and moved about 2,000 

feet farther downvalley as a narrow tongue (figs. 2,6,7). This tongue 

is 300 to 500 feet wide and terminates in a lobate mass of debris 10 

to 15 feet thick. On the south side of the White River, about 1,100 

feet upvalley from the end of the tongue, the deposit rises abruptly 

about 15 feet, and farther upvalley is a series of low transverse ridges 

and furrows. These features may have been formed by a second pulse 

or wave of avalanche debris within unit 3.

On the upvalley side of the terminal moraine, trees and bushes from 

which bark and limbs have been partly removed flank the margin of 

avalanche unit 3 (fig. 8). .This damage was caused by flying rock 

debris that now veneers the crest and flank of the moraine as much 

as 70 feet above the main part of the avalanche deposit. This thin

veneer apparently represents m airborne curtain of sand and small

rock fragments transported by a violent rush of air from beneath 

avalanche unit 3 as it came to rest.
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. All

FIGURE 8. Damaged pine tree on terminal moraine. Tree has been partly 

stripped by airborne debris moving away from viewer. The debris forms a 

veneer only a few inches thick on the moraine and is visible on top of several 

boulders. 

Another noteworthy feature of avalanche unit 3 is a scar 800 feet 

long that the avalanche scraped at the base of Goat Island Mountain 

directly opposite the terminal moraine (fig. 9). The scar is crescentic 

in shape if viewed from the ground, and its highest part, 140 feet above 

the White River, coincides with the narrowest part of the valley. To 

form the scar the avalanche scoured away most of the vegetation and 

the loose rock debris down to solid bedrock.

Avalanche unit 4 resembles unit 3 but contains fewer large blocks. 

Its surface is marked by a series of curved ridges; the most prominent, 

which is about 35 feet high (fig. 4) and 1,400 feet long, may be the 

front of a separate avalanche unit. Unit 5 contains more large blocks 

than unit 4 and cuts across the south end of the most prominent ridge
A12 CONTRIBUTIONS TO GENERAL GEOLOGY

in unit 4. Units 6 and 7 are differentiated by their crosscutting relation to each other and to avalanche unit 5. Neither unit 6 nor unit 

7 had sufficient volume or velocity to move far beyond the terminus 

of Emmons Glacier.

Surveys were made in July 1964 to determine the width and thickness of the avalanche deposits (figs. 10,11). The survey lines followed 

lines surveyed across the valley by Fahnestock in August 1963. Comparison of these two surveys reveals that the avalanche deposits downvalley from Emmons Glacier range in width from 900 to 1,600 feet, 

their broadest part coinciding with the widest and flattest part of the 

old valley floor. The maximum thickness of the avalanche deposits 

is 100 feet, at cross section 7. The greatest mass of debris lies between 

cross sections 10 and 12; at cross section 10, the White River is now 

about 50 feet higher than its pre-avalanche position and about 300 feet 

farther south.

The volume of avalanche debris downvalley from Emmons Glacier, 

estimated from the cross sections, is about 12 million cubic yards.

FIGUKE 9. Avalanche scar, about 140 feet high, at the base of Goat Island Mountain. This scar was formed when part of avalanche unit 3 moved through 

the narrow gap in the terminal moraine (fig. 2). The avalanche deposit downstream (left) from the scar has been partly eroded by the White River. Area 

of avalanche deposits is enclosed by dashed line; arrows show inferred direction of movement of avalanche unit 3.
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A13

In addition, a large volume, perhaps as much as several million cubic 

yards, covers an area of about 1.3 square miles on Emmons Glacier. 

The avalanche debris is estimated to cover a total area of about 2 

square miles and to have a total volume of at least 14 million cubic 

yards. Although the height and the basal width of the rockfall scar 

are estimated to be about 1,700 and 1,800 feet, respectively, the volume 

of the buttress cannot be computed directly because of its irregular 

shape (fig. 12) and a lack of knowledge concerning its original average 

thickness.

MOVEMENT AND VELOCITY OF THE AVALANCHES

Prior to the rockfalls in late 1963, there was a large buttress on the 

north side of Little Tahoma Peak (compare figs. 12,13); the collapse 

of this 'buttress caused the avalanches. The abundance of certain 

kinds of rock in some avalanche units and not in others leads the authors to conclude that different parts of the buttress fell at different 

times, although it is not known whether these separate falls occurred 

at intervals of minutes, hours, or days.

As sections of the buttress fell onto Emmons Glacier, they shattered 

and moved obliquely down the glacier. The avalanche debris was 

moving northeastward when it reached the glacier terminus. Some 

of the avalanches struck the shoulder of Goat Island Mountain, rose 

several hundred feet up its side, and then were deflected northward. 

The avalanches then rose 185 feet up the north lateral moraine and 

were deflected southeastward (fig. 10, cross sections 2-7). After avalanche unit 3 was deflected by the lateral moraine, it flowed into the 

gap near the south end of the terminal moraine. Here it scarred Goat 

Island Mountain, caromed northeastward across the valley, and rose 

a short distance onto the terminal moraine again before continuing 

down valley.

The avalanches represent a type of dry landslide termed "rockfragment flow." During movement, these dry flows are mixtures of 

rock debris and air. Their flowing motion probably is a result of 

buoyancy given to the mass by air trapped and compressed within 

and beneath the rock-fragment flow. Varnes (1958, p. 34) suggested 

that such a mass becomes a kind of density current x of high specific 

gravity and unusual velocity. He also stated that these dry flows of 

rock debris may be caused by volcanic explosions or by very large 

rockfalls or rockslides.

1 Density currents are moving masses of gas or liquid (commonly mixed with pulverized 

solid material) which are of greater density than the gas or liquid in which they are 

enclosed.

782-613'O 65- 3
A14

FEET 

380^

360 

340 

320- 

300 - 

280- 

260- 

240-

W

290 -j 

270- 

250- 

230- 

210- 

190- 

170-

220-i 

200- 

180- 

160- 

140- 

120-

180- 

160- 

140- 

120- 

100- 

80-

500 

I

1000 FEET 

__I

FIGURE 10. Transverse cross sections of avalanche deposits!. Position of Whi 

avalanche topography is based on a survey made by Fahnestock in Augu 

scale is referred to an arbitrary datum. Verticle exaggeration is X
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A15

FEET 

210 1

190 

170-

150-

130-

110 

90-

70-

160- 

140 

120- 

100- 

80- 

60-

SE

110 ~1

90- 

70- 

50 

120-

100-

80-

60 

40-

20 

120 -,

100-

80-

60-

40 

20 

0-

500 

I

1000 FEET

ver before and after the avalanches is indicated by the letter w. Pre- 

(3. Locations of the cross sections are shown in figure 7. The vertical
<u .£

z a os

xavanaav 3Aoav 133d NI 'JLHOGH
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A17

Eyewitnesses of rock-fragment flows tell of a cloud of rock debris 

pouring like a liquid over the land surface, filling depressions and 

being deflected 'by obstacles. A steam explosion that blew out a large 

part of Bandai-san volcano in Japan in 1888 formed a tremendous 

rock-fragment flow that devastated an area of 27 square miles. Sekiya 

and Kikuchi (1889, p. 109 and 106-107, respectively) believed that the 

greater part of the rock-fragment flow was dry during movement, and 

they surmised that its movement was similar to that resulting from 

a large rockfall which they observed in the crater of Bandai-san 

some time after the steam explosion. They described the rockfall as 

follows:

One day, while we were at work in the crater, a huge slice of the precipitous 

wall of rock that had been bared by the explosion fell suddenly and crashed 

with a tremendous uproar down the steep incline beneath. This slab fell from a 

place about 300 metres high. The great masses of earth and rocks were shattered 

as they fell, and broken up into pieces, ever growing smaller as they descended. 

The behaviour of this pulverized mass resembled the rush of a headlong torrent. 

Although boulders measuring 10 metres or more in diameter were mixed up with 

finer matter, as a whole the movement approximated to that of a fluid. No words 

can describe the fierceness and force of that impetuous downpour its mad 

surgings this way and that, and the bold leaps with which it would now and 

then bound over low ridges that hindered its progress, and shoot onward down 

the neighbouring depression.

That the Little Tahoma avalanches moved in a manner like that of 

a fluid is inferred from the way the debris caromed from one side 

of the valley to the other during movement. The heights the avalanches reached on the lateral moraine and on Goat Island Mountain 

are thus explained by centrifugal force, which caused the flowing 

debris to rise higher on the outer side of its curving path.

The path followed by avalanche unit 3 required that the debris move 

at high velocity; some of the speed was attained as masses of rock 

fell vertically as much as 1,700 feet from Little Tahoma Peak. Within 

a distance of 1.3 miles from the base of the rockfall scar, the avalanche 

descended an additional 2,400 feet. It had by then attained enough 

velocity to travel 3 miles farther across the more gentle slope of the 

lower glacier and valley floor to its present resting place.

That a high velocity was attained by avalanche unit 3 is indicated 

by the fact that some of the highest points on the terminal moraine 

were buried by debris and by the fact that the avalanche debris rose 

high on the outside of valley bends (fig. 10). At several places the 

direction of movement of the avalanche was nearly at right angles to 

the valley walls, and debris was deposited high on the valley sides. 

Two tongues of debris ran up on Goat Island Mountain to estimated
A18 CONTRIBUTIONS TO GENERAL GEOLOGY

FIGURE 12. Little Taliomu Peak as viewed from Mount Ruth in 1056.

heights of 250 to 300 feet above the adjacent valley floor, and, farther 

downvalley, the tongue of debris that moved through the gap 

in the terminal moraine reached a height of 140 feet on Goat 

Island Mountain.

If it is assumed that the energy of avalanche unit 3 on the valley 

floor was wholly kinetic energy (mass X velocity2 ) which was com2

pletely transformed into potential energy (mass XgravityX height) 

without frictional loss, a velocity may be computed for the avalanche 

from the height to which it rose on Goat Island Monutain. This computation is made by the following equation, in which g represents the
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A19

PIGUKE 13. Little Tahcnua Peak as viewed from Mount Ruth July 9, 1964. Small 

cloud in front of the peak is formed by water vapor rising from the lower right 

side of the rockfall scar. ( See fig. 1(5.)

 .

value of the acceleration of gravity (32 ft per sec per sec) , v = velocity,

TO = mass, and h = height :

If /i = 300 feet, i> = 139 feet per second, or 95 miles per hour; '"' ' ' ' 

if A=250 feet, v = 127 feet per second, or 87 miles per hour; 

if A =140 feet, i> = 95 feet per second, or 65 miles per hour.

The velocities indicated are probably too small because friction 

caused loss of energy as the debris rose on the flanks of Goat Island 

Mountain. Furthermore, there must have been a substantial downvalley component of movement that would have caused the avalanche to 

travel faster than the computed velocities indicate. If the height is 

decreased by 50 feet to allow for the thickness of the avalanche, veloc-
A20 CONTRIBUTIONS TO GENERAL GEOLOGY

ities should be decreased by roughly 15 feet per second, or by about 

10 miles per hour. It is interesting to compare these calculated velocities with those of other avalanches. For example, the 1881 rockfall 

avalanche at Elm, Switzerland (Heim, 1932, p. 93), had an average 

velocity of about 100 miles per hour, and the 1962 avalanche of ice 

and rock debris from the. northwest face of Nevado Huascaran in 

Peru traveled 9 miles in 7 minutes at an average velocity of 77 miles 

per hour (McDowell and Fletcher, 1962). The estimated minimum 

speed of avalanche unit 3 from Little Tahoma Peak also is similar to 

that computed for other rockfall and rockslide avalanches in North 

America (table 1), using the formula described above.

TABLE 1. Comparison of Little Tahoma rockf all-avalanche deposits with others 

in the United States and Canada

[Thickness of the avalanche deposits is not taken into consideration in computation of velocity]

Location and Reference

Madison Canyon, Mont. (Hadley, 

1964)...-.........................

Gros Ventre, Wyo. (Alden, 1928). .. 

Frank, Alberta (McConnell and 

Brock, 1904)......................

Little Tahoma Peak, Wash, (this

Year

1959

1925 

1903

1963

Volume of 

debris 

(millions of 

cu yds)

07 n

50.0 

47.8

14.0

Maximum 

distance of 

movement 

(miles)

1.0

1.2

2.5

4.3

Approximate 

maximum 

vertical 

drop (feet)

1,300

2,100 

2,860

6,200

Maximum 

runup (feet)

430

350 

400

140

300

Velocity of 

avalanche 

(mph) i

3112

102 

109

65

95

1 Calculated from »=\/20A.

2 A maximum velocity of 100 mph was estimated by Hadley.

The maximum velocity of a rockfall and the subsequent rate of descent of an avalanche on Emmons Glacier can be crudely estimated 

from the acceleration of gravity. A mass of rock falling from a height 

of 850 feet, half the height of the rockfall scar, would have attained 

a velocity of about 160 miles per hour just before it struck Emmons 

Glacier, assuming free fall. The avalanches probably also accelerated 

throughout their first 7,000 feet of travel downglacier, as they descended about 2,400 feet. Although, a loss of velocity must have occurred as falling rock masses struck the glacier, as a cross-glacier 

component of movement occurred after impact, and as sliding on the 

glacier produced f rictional resistance, it seems likely that an avalanche 

would have been traveling at a speed of 100 to 300 miles per hour 

when it left the end of Emmons Glacier.

Some of the avalanches probably were aided in their movement 

beyond the glacier by a cushion of air trapped beneath them which

buoyed them up; this cushion reduced friction and permitted the 

avalanches to be transported a much greater distance than if they had 

traveled in actual contact with the valley floor.
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A21

The formation of a cushion of air beneath moving rock debris has 

been analyzed by Shreve (1959), who studied a large prehistoric rockfragment flow at the northern edge of the San Bernardino Mountains 

in southern California. The deposit is about 2 miles wide and extends 

over a piedmont slope for a distance of about 5 miles beyond the mountain front. Shreve suggested that the rock-fragment flow was caused 

by a large rockslide or rockfall on the northern face of Blackhawk 

Mountain and that, after initial impact, the flow was launched laterally into the air from a rock step near the base of the mountain. 

Lateral movement was at such a high velocity, the maximum was estimated to be 250 miles per hour, that air became entrapped and formed 

a cushion beneath the sheet of rock debris. Escape of air along the 

margins of the rushing mass permitted its outer edges to drop to the 

underlying surface, where they formed marginal ridges that hindered 

further escape of trapped, highly compressed air.

Preservation of a fragile thermograph shelter about 1.5 feet high 

in the gap near the south end of the terminal moraine suggests that a 

cushion of air was trapped beneath avalanche unit 3. Although this 

avalanche did not damage the shelter in passing over it, the shelter 

was subsequently crushed by a 10-inch boulder that rolled down the 

front of avalanche unit 5. A pile of boards that lay on the ground 

near the shelter also was not disturbed by avalanche unit 3 but was 

buried by a few inches of avalanche debris. A protective layer of 

snow seemingly cannot account for the lack of damage, for if the 

avalanche had been traveling in contact with the ground, the leadingpart should have scraped away the snow, and the trailing part should 

then have destroyed the thermograph shelter. Evidently the base 

of the avalanche was not in contact with the ground when it crossed 

this site. A 6-foot-high plywood gage house, less than 10 feet from 

the shelter, was removed by avalanche unit 3. This gage house was 

transported about 300 feet southward in a direction nearly at a right 

angle to the trend of the valley and now lies at the upstream end of 

the scar opposite the terminal moraine (fig.7). This scar (fig. 9), 

produced by the scouring action of the avalanche as it struck the side 

of the valley and caromed back to the northeast, suggests the nature 

of erosion that should have occurred everywhere at the base of the 

avalanche if a cushion of air had not been present.

The existence of an air cushion beneath avalanche unit 3 is also suggested by the distance, about 9,500 feet, the avalanche moved beyond 

the end of Enimons Glacier. Kegardless of its velocity as it left the 

glacier, the avalanche should have struck the valley floor within a time 

interval determined by the acceleration of gravity through the vertical 

distance between the top of the glacier and the valley floor at the point 

of impact. If the avalanche had struck the valley floor at the calcu-
A22 CONTRIBUTIONS TO GENERAL GEOLOGY

lated point of impact, 2,000 feet or less from the end of the glacier 

(fig. 14), it seemingly could not have traveled in contact with the valley 

floor as much as 7,500 feet farther downvalley, nor have risen on the 

side of the lateral moraine and on Goat Island Mountain, nor have 

made a nearly right-angle turn through the gap in the terminal 

moraine. Therefore, it seems unlikely that the avalanche debris 

struck the valley floor within a few thousand feet from the glacier 

and this circumstance can be explained only by the supposition that 

the avalanche was buoyed up by a cushion of compressed air at its base.

The initial impact of a rockfall would not itself create an air 

cushion; the formation of this cushion may require lateral launching 

of a broad sheet of debris into the air parallel to the underlying surface so that the debris as it starts to settle can trap air quickly and 

compress it. Further requirements would be previous pulverization 

of the rock mass to form a sheet of debris and sufficient thickness and 

impermeability of the debris to prevent substantial upward escape of 

air. Air passing upward through the debris, however, would tend 

to fluidize the mass by reducing friction between rock particles and 

thus would increase mobility.

Pulverization of the rock masses from Little Tahoma Peak occurred 

when they struck Emmons Glacier. Sheets of rapidly moving debris 

then descended the glacier and probably were launched laterally into 

the air as they left the terminus of the glacier, which is 200 to 300 feet 

high. Formation and preservation of a cushion of air beneath the 

avalanches in the valley would have been aided by the confining valley 

sides. Marginal ridges comparable to those of the Blackhawk landslide described by Shreve (1959) are not conspicuous, although they 

may be represented by ridges along the north side of the deposits at 

the locations of cross sections 2, 4, 5, and 6.

Because of the distance and the inferred nature of their movement 

downvalley, avalanche units 1, 3, 4, and 5 are thought to have moved 

as rock-fragment flows, probably riding on air cushions. Avalanche 

units 6 and 7 stopped only short distances beyond the glacier and may 

have moved as debris slides in contact with the underlying surface 

throughout most of their distance of transport. The nature of movement of avalanche unit 2 cannot be inferred because of its limited area 

of outcrop.

MUDFLOWS

An interesting side effect of the avalanches was the formation of 

mudflows; they head at channels in the avalanche deposits and 

traveled at least as far downstream as White River campground. The

mudflows thin downstream from about 6 feet to a few inches. Although they have fairly smooth surfaces, some mudflows a foot or
FEET 

1500-1

500-

Trajectory of avalanche debris, assuming 

velocity of 220 ft per sec

-Trajectory of avalanche debris, assumin] 

velocity of 440 ft per sec Narrow gap in 

terminal moraine

End of avalanche unit 3

1000

I

2000 

I

NO VERTICAL EXAGGERATION

FIGURE 14. Diagram showing expectable points of impact of avalanche unit 3 on valley floor if avalanche had not been 

buoyed up by a cushion of air. A speed of 300 miles per hour (440 ft per sec) was the probable maximum velocity of 

the avalanche debris at the end of the glacier, although 150 miles per hour (220 ft per sec) may be a more reasonable 

estimate. The glacier slope was estimated to be 10 percent, and the velocities of 150 and 300 miles per hour were 

assumed to be parallel to the slope of the glacier.

to

CO
A24 CONTRIBUTIONS TO GENERAL GEOLOGY

two thick are dotted with many low mounds, a few inches to a foot 

high and a foot to several feet in diameter (fig. 15). Several mounds 

were excavated, and a large boulder was found beneath each one. 

If the mudflows had come to rest on a layer of snow, the mounding 

and the cracking might have occurred as the supporting snow melted 

and the mudflow settled over the underlying boulders.

The mudflows downvalley from the tongue of avalanche unit 3 

consist of sand and of rock fragments as large as several feet in diameter. In addition, several very large blocks lie on the surface of 

some of these mudflows. The largest of these is a mass of gray 

andesite that has maximum dimensions of 9 by 11 by 16 feet; this 

mass was transported by a mudflow about 4 feet thick. It and other 

blocks like it are excellent evidence of the remarkable ability of mudflows to transport large rock fragments.

FIGURE 15. Cracked mounds on surface of mudflow deposit, probably formed 

as a layer of snow melted under mudflow, permitting mudflow to settle around 

buried boulders.
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A25

The mudflows resulted from the White River spilling over temporary dams of avalanche debris in the narrow gap through the 

terminal moraine and probably upstream from the moraine as well. 

As the water ran across the debris it quickly became loaded with loose 

material and formed masses of bouldery mud that flowed downvalley. 

The paths of the mudflows through the avalanche deposits were subsequently followed by clearer water that cut flat-bottomed channels 

and partly eroded the mudflow deposits (fig. 9).

DUST CLOUDS

Dust clouds frequently veiled the north face of Little Tahoma Peak 

during the winter, spring, and summer months of 1964. These clouds 

were caused by rocks bounding from the rockfall scar onto a long 

dusty apron of debris that bordered the scar base and reached onto 

Emmons Glacier. The rocks apparently were dislodged from the scar 

by freeze and thaw, by melt water from a hanging glacier perched 

on the east side of Little Tahoma Peak, and by wind currents. At 

times, winds would sweep the dust clouds upward and eastward, 

causing the surface of Fryingpan Glacier to become unusually dirty. 

Although rocks continued to fall from the scar during late August 

and early September, dust clouds became rare after this period because 

frequent rains and snows dampened the rockfall debris at the base of 

the cliff.

These dust clouds were small and insignificant in comparison with 

the great palls of dust that accompanied the avalanches. The effects 

of those clouds were still to be seen in July 1964 on the southern 

slope of Mount Ruth, where conifers were still mantled with nearly 

an inch of silt and fine sand that had settled out of the air. Much 

of this sand and silt had been washed off by rains before the following 

September.

CAUSE OF THE ROCKFALLS

The topography and geology of Little Tahoma Peak form an ideal 

setting for rockfalls; in fact, it is surprising that large rockfalls are 

not more common there. Yet, one is led to wonder whether some 

specific event might have triggered the first rockfall from the peak, 

which apparently occurred about noon on December 14. Although 

perhaps not the largest of the series of falls, this first rockfall probably was the most important for it almost certainly removed support 

from other masses of rock, leaving them highly unstable.

A sound heard at the time the first mass of rock is believed to have 

fallen suggests that a steam explosion may have occurred at Little Tahoma Peak. On December 14, Benjamin E. Cottman (oral com num., 

Aug. 25, 1964) and Richard J. Alien (oral commun., Aug. 17, 1964),
A26 CONTRIBUTIONS TO GENERAL GEOLOGY

Forest Bangers of the U.S. Forest Service, were at the Crystal 

Mountain ski area, about 12 miles northeast of Little Tahoma Peak. 

Shortly before noon they both heard a very loud, sharp boom in the 

direction of Mount Rainier. Jet aircraft were not heard before or 

after the loud noise, and Cottman and Alien concluded that the noise 

had originated in some way at Mount Rainier rather than as a sonic 

boom. Although the noise possibly resulted from the rockfall itself, 

the fact that it was a single sharp boom may suggest that it originated 

from an explosion rather than from a rockfall and avalanche. Visibility was poor at the time because of clouds and snow, but as the clouds 

lifted from time to time during the afternoon of the 14th, Cottman cllld 

Alien observed that a large part of Emmons Glacier had become 

covered with dark rock debris below Little Tahoma Peak. According 

to Alien, fresh rock debris also fell from the peak onto new snow 

several times during the following 2 months, but the size of the later 

rockf alls is not known.

If an earthquake had occurred just before or at the same time as the 

first rockfall, one might conclude that the shock triggered the fall. 

According to Prof. Norman Rasmussen (written commun., July 17, 

1964) of the Department of Geology at the University of Washington, 

the most recent quake that preceded the rockfall was recorded on a 

seismograph at Longmire, 8.5 miles south of Little Tahoma Peak, on 

December 13, at about 8 :20 a.m. This earthquake had a duration of 

about 40 seconds and occurred at an estimated distance of about 11 

miles from Longmire in an undetermined direction. No earthquake 

was recorded on the seismograph near noon on December 14, when the 

initial rockfall apparently occurred; however, according to Professor 

Rasmussen, at 4:40 p.m. on that day the seismograph recorded "a 

disturbance not containing the usual character of an earthquake. 

This event is of very small amplitude and short period suggesting a 

local disturbance and may be from sliding rock against rock * * *." 

This small seismic disturbance may have been caused by one of the 

rockf alls and avalanches that followed the initial rockfall, possibly by 

avalanche unit 3, the largest of the group. There is no evidence that 

an earthquake shock was directly responsible for the initial rockfall.

Another possible trigger might have been freezing and thawing of 

ice in cracks in the rock, either of which would have caused a slight 

weakening of the rock. At White River Ranger Station, the maximum 

temperature was 34° on December 14 and the minimum 28°F. It 

seems unlikely that the temperature reached above freezing on that 

day at altitudes of 9,000-11,000 feet on Little Tahoma Peak. Although repeated freeze and thaw undoubtedly contributed to progressive weaking of the rock over many years, these processes probably 

were not the immediate cause of the rockfall on December 14.
ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A27

A third way in which the inital rockf all might have originated could 

have been by a small steam explosion at or near the base of Little 

Tahoma Peak, caused by water beneath the surface coming into contact with hot rock in a confined space.

If one or more steam vents had been active between December 14 and 

the end of January, they probably would not have been observed 

because of the generally cloudy weather during this period; however, 

William Pope and Ross Gregg (oral commun., July 1964), residents 

of Crystal Mountain ski area, observed clouds at Little Tahoma Peak 

from Crystal Mountain on clear days during the winter of 1963-64. 

Some of these appeared to be dust clouds because of their grayishbrown tinge; others were thought to be clouds of water vapor.

Clouds of "steam" also were frequently reported at Little Tahoma 

Peak during July and August 1964 by observers at Yakima Park and 

Burroughs Mountain, but owing to the distance of these points from 

Little Tahoma Peak it was not possible to be sure that these clouds 

were water vapor rather than the dust plumes that were a daily feature 

of the rockfall scar during those months.

On the afternoon of July 9, Crandell and Ranger Naturalist Arthur 

Haines observed the rockfall scar on Little Tahoma Peak through 

binoculars from a point near Mount Ruth. Plumes of water vapor 

could be seen rising from near the base of the west side of the rockfall 

scar (figs. 13, 16), forming a small white cloud that hovered along 

the north side of the peak all afternoon. Meanwhile, no water vapor 

could be detected coming from other obviously moist parts of the scar, 

and no other clouds were visible in the sky. On the basis of this observation, Crandell concluded that an unusual source of heat was present 

at that time near the base of Little Tahoma Peak, and that this source 

of heat might have caused a steam explosion in December 1963.

In the late summer, the U.S. Forest Service was asked to conduct 

an aerial examination of Little Tahoma Peak with infrared heatsensing equipment that is normally used to detect and outline the 

extent of forest fires. The investigation was made on September 3 

and 4,1964, and the results indicated that the temperature of the rockfall scar was then no warmer than normal. Furthermore, snow that 

fell in late August and early September seemed to disappear from all 

parts of the scar at the same rate, indicating approximately equal 

temperatures throughout. Thus, if a source of heat did exist near 

the base of the peak from December 1963 to July 1964, it apparently 

had disappeared by late August or early September.

Small steam explosions probably are not unusual occurrences on 

Mount Rainier, but owing to the inaccessibility of most of the volcano 

during much of the year, they are rarely observed. Such an explosion, 

however, occurred during the summer of 1961. Luther G. Jerstad

ROCKFALLS AND AVALANCHES, MOUNT RAINIER, WASH. A29

(written commun., Sept. 16, 1964) of Eugene, Oregon, was at that 

time guiding parties to the summit. According to Jerstad, he was 

awakened one night at Camp Muir (fig. 1) by a loud noise and shaking 

of the ground. There was bright moonlight, and a great cloud of 

dust could be seen at the south end of Gibraltar Rock, caused by continuing rockfalls which could be plainly heard. The next morning, 

Jerstad observed rock fragments strewn over the surface of Cowlitz 

Glacier for a distance of at least three-quarters of a mile below 

Gibraltar Rock, and in the southern side of Gibraltar Rock there was 

a fresh scar about 150 feet wide, 150 feet deep, and 100 feet high. 

Steam was spouting 200 feet into the air from a vent in the scar, 

apparently under great pressure, and making a noise like a high 

wind. According to Jerstad, the steam continued to issue from the 

vent all summer, although it seemed to decrease in volume and pressure over a period of about 5 weeks. It was no longer active by the 

summer of 1962.

This example demonstrates that small steam explosions are normal 

and expectable phenomena on the flanks of Mount Rainier. Such 

explosions in unstable areas undoubtedly have contributed substantial 

quantities of rock debris to glaciers on the volcano in the past. Although the evidence is not conclusive, the rockfalls and avalanches 

from Little Tahoma Peak possibly were initiated by such a mild steam 

explosion.

REFERENCES

Alden, W. C., 1928, Landslide and flood at Gros Ventre, Wyoming: Am. Inst.

Mining and Metall. Engineers Trans., v. 76, p. 347-361. 

Crandell, D. R., 1963, Paradise debris flow at Mount Rainier, Washington, in

Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper

475-B, p. B135-B139. 

Crandell, D. R., and Miller, R. D., 1964, Post-hypsithermal glacier advances at

Mount Rainier, Washington, in Geological Survey Research 1964: U.S. Geol.

Survey Prof. Paper 501-D, p. D110-D114, [1965], 

Crandell, D. R., Mullineaux, D. R., Miller, R. D., and Rubin, Meyer, 1962,

Pyroclastic deposits of Recent age at Mount Rainier, Washington, m Short

papers in geology, hydrology, and topography: U.S. Geol. Survey Prof.

Paper 450-D, p. D64-D68. 

Fahnestock, R. K., 1963, Morphology and hydrology of a glacial stream White

River, Mount Rainier, Washington: U.S. Geol. Survey Prof. Paper 422-A,

p. A1-A70. 

Fiske, R. S., Hopson, C. A., and Waters, A. C., 1963, Geology of Mount Rainier

National Park, Washington: U.S. Geol. Survey Prof. Paper 444, 93 p. 

Hadley, J. B., 1964, Landslides and related phenomena accompanying the

Hebgen Lake earthquake of August 17; 1959: U.S. Geol. Survey Prof. Paper

435-K, p. 107-138. 

Heim, Albert, 1932, Bergsturz und Menschenleben: Fretz and Wasmuth, Zurich,

218 p.
A30 CONTRIBUTIONS TO GENERAL GEOLOGY

McConnell, R. G., and Brock, R. W., 1904, Report on the great landslide at 

Frank, Alberta: Canada Dept. Interior Ann. Rept. 1902-3, App. to Rept. 

Supt. Mines, pt. 8,17 p.

McDowell, Bart, and Fletcher, J. E., 1962, Avalanche!: Natl. Geog. Mag., v. 

121, no. 6, p. 854-880.

Sekiya, S., and Kikuchi, Y., 1889, The. eruption of Bandai-san: Tokyo Imperial 

Univ., Jour. Coll. Sci., v. 3, pt. 2, p. 91-172.

Shreve, R. L., 1959, Geology and mechanics of the Blackhawk landslide, Lucerne 

Valley, California: California Inst. Technology, unpub. Ph. D. thesis, 79 p.

Varnes, D. J., 1958, Landslide types and processes, Chap. 3 of Eckel, E. B., ed., 

Landslides and engineering practice: Natl. Research Council, Highway Research Board Spec. Rept. 29, p. 20-47.

U.S. GOVERNMENT PRINTING OFFICE: 1965 O 782-613