Postglacial Lahars From 

Mount Rainier Volcano, 

Washington 

By DWIGHT R. CRANDELL 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 677 

A study of the age, extent, and origin of more 

than 55 postglacial mudflows and debris flows 

from Mount Rainier 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director 

Library of Congress catalog-card No. 79-611942 

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

Washington, D.C. 20402 
CONTENTS 

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

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

Geographic setting of the volcano and the lahars ... . 

Climate ...................................... . 

Terminology and distinctive features of lahars .... . 

Ways in which lahars originate .................. . 

Age and lithology of Mount Rainier volcano ...... . 

Dating of lahars ............................... . 

Origin of the clay in some lahars ................. . 

Description of lahars ............................... . 

Lahars in the White River drainage basin ......... . 

Greenwater lahar .......................... . 

Pre-Osceola lahar assemblage ................ . 

Osceola Mudflow .......................... . 

Distribution and volume ................ . 

Texture and mineralogy ................ . 

Origin ................................ . 

Post-Osceola lahar assemblage ............... . 

Post-Osceola lahar assemblage in the West Fork 

valley .................................. . 

Lahars in the Nisqually River valley ............. . 

Paradise lahar ............................. . 

Older lahar at Paradise Park ................ . 

Lahars at Van Trump Park ................. . 

Lahar assemblage A ........................ . 

Lahar assemblage B ........................ . 

Lahar assemblage C ........................ . 

Page 

1 

1 

2 

3 

3 

8 

10 

11 

12 

17 

17 

18 

23 

24 

24 

26 

29 

30 

32 

32 

33 

36 

37 

38 

39 

40 

Description of lahars-Continued 

Lahars in the Nisqually River valley-Continued 

Origin of lahar assemblages in the Nisqually and 

White River valleys....................... 41 

Lahar assemblage D . . . . . . . . . . . . . . . . . . . . . . . . 43 

Lahars in the Nisqually River valley downstream 

from the park. . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

Kautz Creek valley lahar assemblage.............. 45 

Lahars in the valleys of Tahoma Creek and the North 

and South Puyallup Rivers. . . . . . . . . . . . . . . . . . . . 49 

Round Pass Mudflow. . . . . . . . . . . . . . . . . . . . . . . 49 

1, 000-year-old lahar. . . . . . . . . . . . . . . . . . . . . . . . . 56 

Electron Mudflow. . . . . . . . . . . . . . . . . . . . . . . . . . 56 

Lahar assemblage in the Tahoma Creek valley. . 57 

Lahar assemblage in the South Puyallup River 

valley................................... 62 

Block-and-ash flow in the South Puyallup River 

valley................................... 64 

Lahars in the North Puyallup River valley. . . . . . 66 

Lahars in the Mowich River valley. . . . . . . . . . . . . . . 67 

Lahar in the Carbon River valley. . . . . . . . . . . . . . . . . 67 

Lahars in the Muddy Fork of the Cowlitz River and 

Ohanapecosh River valleys. . . . . . . . . . . . . . . . . . . . 68 

The association of lahars with volcanism.......... . . . . . 68 

Hazards from future lahars. . . . . . . . . . . . . . . . . . . . . . . . . . 69 

References cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 

Index............................................. 75 

ILLUSTRATIONS 

:Page 

1. Topographic map of Mount Rainier National Park ______________________________________________ In po,~ket 

2. Profiles and cross sections of the valley floors of the White River, the Nisqually River, and Kautz Creek_ In poflket 

3. Topographic map of the Mount Rainier area showing the Osceola and Electron Mudflows and the 

Paradise lahar_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ In po,~ket 

FIGURE 1. Map showing location of Mount Rainier _________________________________ -- ___ --------------------- 2 

2. Graph showing average annual precipitation at Longmire and Paradise Ranger Station __ ---------------- 3 

3. Graph showing cumulative curves and sorting coefficients of three samples of Evans Creek tilL---------- 6 

4. Graph showing cumulative curves of samples from avalanche deposits on floor of White River valley______ 7 

5. Photograph showing avalanche deposit at and on the terminus of Tahoma Glacier______________________ 18 

6. Map showing distribution of Greenwater lahar----------------------------------------------------- 19 

7-10. Photographs of: 

7. Mounds on the Greenwater lahar ____________________________________ ------ __ ----------------- 20 

8. Mound on the Greenwater lahar __________________________________________ ---- ___ ------------- 21 

9. Large breadcrusted block in a lahar---------------------------------------------------------- 23 

10. Osceola Mudfiow southeast of Greenwater____________________________________________________ 25 

11. Graph showing cumulative curves of size distribution of samples from the Osceola Mudflow_______________ 28 

12. Photograph of lahar exposed near the mouth of Fryingpan Creek______________________________________ 31 

13. Photograph of Paradise lahar above pyroclastic layer 0 east of Ricksecker Point_________________________ 34 

m 
IV CONTENTS 

Page 

FIGURE 14. Graph showing cumulative curves of grain-size distribution of Paradise lahar at three localities and older lahar 

I 

TABLE 

at Paradise Park--------------------------------------------------------------~------------- 35 

15. Photograph of outcrop of Paradise lahar and older lahar at Paradise Park_______________________________ 37 

16. Photograph of lahar in streambank on west side of Nisqually River flood plain__________________________ 39 

17. Graph showing cumulative curves of size distribution of lahars near Longmire___________________________ 41 

18-21. Photographs of: 

18. Fluvial gravel in lahar assemblage C in west bank of Nisqually River___________________________ 42 

19. Deposits in west bank of Kautz Creek______________________________________________________ 47 

20. Bouldery surface of a pre-W lahar assemblage that underlies the floor of Kautz Creek valley__ _ _ _ _ _ 48 

21. Lahars and fluvial sand and gravel deposited near mouth of Kautz Creek in October 1947 _________ 48 

22. Graph showing cumulative curves of size distribution of deposits formed by floods and lahars in the Kautz 

Creek valley in October 1941----------------------------------------------------------------- 49 

23. Photograph of flood in Kautz Creek channel on August 23, 1961______________________________________ 50 

24. Photograph of banks of Kautz Creek shortly after flood of August 23, 1961_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 51 

25. Map showing inferred original extent of Round Pass Mudflow________________________________________ 52 

26. Photograph showing south edge of Round Pass Mudflow at Indian Henrys Hunting Ground_____________ 53 

27. Photograph showing Round Pass Mudflow on top of pyroclastic layer Y above floor of North Puyallup River valley ______________________________________________________________ - _- _ _ _ _ _ _ _ _ _ _ _ _ _ _ n4 

28. Graph showing cumulative curves of size distribution of Electron Mudflow, lahar in the Tahoma Creek Halley, 

1,000-year-old lahar in South Puyallup River valley, and Round Pass Mudflow ___ __ ____ __ __ __ __ __ __ _ 55 

29. Photograph of lahar on top of fluvial cobble-and-boulder gravel in the Tahoma Creek valley __________ -·_____ 59 

30. Photograph showing bouldery deposit left in Tahoma Creek picnic area on August 31, 1967 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 60 

31-35. Photographs showing: 

31. Aerial view of South Tahoma Glacier_______________________________________________________ 61 

32. Rockfall debris above head of South Tahoma Glacier_________________________________________ 63 

33. Bomb-bearing block-and-ash flow deposit along West Side Road near South Puyallup River_______ 64 

34. Outcrop of relatively fine grained facies of block-and-ash flow along West Side Road near South Puyallup 

River_______________________________________________________________________________ 65 

35. Breadcrust bombs from the block-and-ash flow in South Puyallup River valley__________________ 65 

36. Graph showing cumulative curves of size distribution of the block-and-ash flow___________________ _ _ _ _ _ 66 

37. Point diagram of azimuth and dip of north-seeking poles in dense rock fragments and bombs from block-andash flow in South Puyallup River valley_______________________________________________________ 67 

TABLES 

Page. 

1. Average monthly and average annual precipitation at Longmire for the 51-year period preceding 19f6 and 

at Longmire and Paradise Ranger Station for the period 1956 through 1965_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 

2. Size-distribution data on eight lahars, each sampled from two different horizons________________________ 8 

3. Subdivisions of Quaternary time in western Washington ______________________ ----------_____________ 10 

4. Radiocarbon dates pertaining to surficial deposits less than 6,000 years old_____________________________ 11 

5. Source, age, and description of some postglacial pyroclastic deposits___________________________________ 12 

6. Postglacial eruptions, laHars, avalanches, and block-and-ash flows_____________________________________ 14 

7. Mineralogy of clay fractions of Evans Creek tilL _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16 

8. Mineralogy of clay fractions of hydrothermally altered andesite_______________________________________ 17 

9. Sequence of lahar assemblages and their stratigraphic relation to pyroclastic deposits in the White Riv::r and 

West Fork valleys_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 19 

10. Size-distribution data from samples of postglacial lahars and a block-and-ash flow_______________________ 27 

11. Mineralogy of clay-sized fraction of lahars_________________________________________________________ 29 

12. Grain-size distribution data on deposits formed by floods and lahars in the Kautz Creek valley______ _ _ _ _ _ 48 
POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, 

WASHINGTON 

By DwiGHT R. CRANDELL 

ABSTRACT 

More than 55 lahars (mudflows and debris flows from a 

volcano) originated at Mount Rainier during Holocene time. 

These ranged in length from a few miles to 70 miles and in 

volume from a few million cubic yards to more than half a 

cubic mile. Some lahars were created by landsli:des of altered 

volcanic rock; they contain significant amounts of clay, which 

consists of montmorillonite and kaolinite and lesser amounts of 

other clay minerals, which were fo•rmed by hydrothermal alteration of rock within the volcano. Some of these lahars have been 

deep enough, when flowing, to fill valleys to depths of hundreds 

of feet; the fluidity of the lahar permitted most of it to progress 

downvalley and to leave in passing only a thin deposit on valley 

sides and terraces. Smaller laha rs of the same kind seem to have 

progressed downvalley in a single massive wa ve hundreds of 

feet high. Clay-rich lahars originated in massive slides of clayey 

rock that hrud a high moisture content. The slides may have been 

triggered either by strong earthquakes or by volcanic explosions, 

or possibly by swelling that accompanied the ascent of molten 

rock into the volcano. Other lahars were created by the eruption 

of hot volcanic bombs, dense rock fragments, and ash onto ice 

and snow at the summit of the volcano. Rapid melting of snow 

created floods down the volcano's flanks which carried down 

rock debris and a'lso pieked up loose detritus on valley floors 

to form lahars. Still other lahars resulted from precipitation of 

cloudburst proportions and by glacier outburst floods. Some 

outburst floods may have been caused by excessive melting of ice 

around subglacial steam vents. 

There have been repeated episodes of volcanism at Mount 

Rainier within about the last 10,000 years. The last major erurr 

tive period, between about 2,000 and 2,500 years ago, witnessed 

the eruption of pumice and lava flows and the formation of 

many lahars. During this period, erosion alternated with aggradation of lahars and fluvial gravels on the valley floors of 

the White and Nisqually Rivers, and possibly on those of 

some other rivers as well. The last pumice eruption, which 

occurred in the mid-1800's, apparently was on a very small 

scale, and there is no known record of floods or lahars at that 

time. 

If future eruptions of Mount Rainier were to be similar 

in scale and type to those of the last 10,000 years, the greatest 

hazard would be that of lahars. Because of the restriction of 

lahars to the lower parts of valleys away from the immediate flanks of the volcano, valley floors would be especially hazardous. In view of the increased probability of lahar formaltion 

during an eruption, valley floors should be evacuated immediately within a radius of at least 25 miles from the volcano if 

an eruption should begin. It is proposed that permanent residences should not be constructed on certain valley floors near 

Mount Rainier, that consideration be given to the relocation 

of campgrounds that are now in potentially hazardous areas, 

and that future highways and bridges be designed and located 

to minimize destruction by future lahars. Likewise, the planning of all other residential, economic, and recreational developments within valleys that head on the volcano should be 

concerned with lahars as potential geologic hazards. 

Artificial traps that might prevent large lahars from entering densely populated areas now exist in the form of hydroelectric power dams and flood-control dams in some valleys. 

To control a lahar, reservoirs behind these dams would have 

to be empty. No reservoir, however, would be of any avail 

in controlling or diverting a lahar comparable in size with the 

largest that originated at Mount Rainier in [pOstglacial time. 

INTRODUCTION 

Within postglacial (Holocene) time, which constitutes a.bout the last 10,000 years, various events of a 

catastrophic nature have occurred at Mount Rainier. 

These have included repeated eruptions of pumice, 

lava flows, and hot volcanic bombs, and most devastating of all, recurring ·avalanches of rock debris from 

the summit and slopes of the volcano which created 

lahars (mudflows and debris flows from a volcano) 

hundreds of feet deep and many miles long. Within 

the last 10,000 years Mount Rainier has lost a much 

greater volume through these avalanches and other 

erosional processes than it has gained from ithe eruption 

of new lava. 

Some postgla-Cial lahars from Mount Rainier have 

had sufficient volume and mobility to extend into the 

Puget Sound lowland northwest of the volcano (fig. 1) 

and to spread over areas there that are now densely 

populated. Lahars of compara.ble size today would 

doubtlessly be disastrous. My purpose of studying the 

postglacial lahars was to determine their stratigraphy, 

physical chara.cteristics, distribution, and especially 

their manner and place of origin so as to assess the potential hazards presented by future lahars from the 

volcano. 

The study was begun in 1960 as the principal part 

of a broader investigation of surficial deposits in 

Mount Rainier National Park and in selected areas in 

1 
2 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Packwood 

0 

·Gilmore Comers 

Mount St Hele 

0 10 20 30 MILES 

FIGURE I.- Location of Mount Rainier with respect to the Cascade Range and the Puget Sound lowland of western Washington. The dotted line marks the approximate boundary 

'between lowland and mountains. Patterned area around 

Mount Rainier indica,tes glaciers. 

the adjacent mountains. I shared the fieldwork of the 

fir~t two summers with Robert D. Miller, who assumed 

primary responsibility in 1961 for working out the 

glacial history of the upper Nisqually River valley. 

Donal R. Mullineaux joined the projoot in 1962 ·and 

undertook a study of the lithology, distribution, stratigraphy, age, and source of the postglacial pyroclastic 

deposits in Mount Rainier National Park. I was ably 

assisted in the field by my son Thomas D. Crandell (deceased) in 1960, by Jon Koloski in 1962, by Michael P. 

Lane in 1963, and by Jack H. Hyde in 1966. 

Fieldwork in the park was greatly facilitated by the 

cooperation of the Superintendent and staff of the National Park Service, and grateful acknowledgement is 

made of the enthusiastic encouragement and help given 

by Vernon R. Bender, Charles J. Gebler and Norman 

A. Bishop, successive Chief Park Naturalists. Appreciation is also expressed to the St. Regis Paper CO. for 

permission to conduct field investigations on private 

land west of Mount Rainier National Park. 

I profited immeasurably from numerous discussions 

in the field with Richard S. Fiske, Clifford A. Hopson, 

and Aaron C. Waters, who were completing their study 

of the bedrock geology of the park when my investigation was just getting under way. My interest in studying 

the surficial geology of the park was encouraged by 

Professor Waters, who foresaw the desirability of having such a study to supplement their studies of the 

rock formations. 

Unless otherwise specified, all the analyses reported 

here were made in the laboratories of the U.S. Geological Survey. The radiocarbon age determinations 

were supervised by Meyer Rubin, and grain-size analyses were supervised by Thomas C. Nichols and 

Edward E. McGregor. X-ray determinations of the 

mineralogy of silt and clay fractions of lahars and 

other surficial deposits were conducted by Paul D. 

Blackmon, Dorothy Carroll, John C. Hathaway, Edward E. McGregor, and Harry C. Starkey. 

GEOGRAPHIC SETTING OF THE VOLCANO AND LAHARS 

Mount Rainier volcano dominates the landscape of a 

large part of western Washington. rt stands nearly 3 

miles higher than the lowlands to the west and 1% 

miles higher than the surrounding mountains. The base 

of the volcano spreads over an area of about 100 square 

miles, and lava flows that radiate from the base of the 

cone extend to distances of as much as 9 miles. The 

flanks of Mount Rainier are drained by five major rivers 

and their tributaries. Clockwise from the northwest the 

major rivers are the Carbon, White, Cowlitz, Nisqually, 

and Puyallup (fig. 1; pl. 1). Each river flows westerly 

through the Cascade Range and, with the exception of 

the Cowlitz, empties into Puget Sound near Tacoma, 

Wash. The Cowlitz joins the Columbia River in the 

southwestern part of the State to flow to the Pacific 

Ocean. 

Each major river in Mount Rainier National Park 

occupies a deep canyon whose floor is 1,000-3,000 feet 

below the adjacent divides. Valley-floor gradients are 

100-400 feet per mile near the park boundaries and increase markedly upstream. The valley floors of Tahoma 

Creek, the North and South Puyallup Rivers, and 

the Mowich River have gradients of 700-800 feet per 

mile in their upper reaches and are among the steepest 

in the park. The volcano's summit towers 9,000-11,000 

feet above valley floors only 3-6 miles away. The flanks 

of the volcano itself have slopes mostly between 25° 

and 30°, although those of Willis Wall on the north 

side are between 40° and 45°. 
INTRODUCTION 3 

Partly beeause of its position astride a high, dissected part of the Cascade Range, Mount Rainier does 

not have broad peripheral aprons of laharic and 

fluvial deposits like those fringing the base of Mount 

Shasta in northern California and smne large stratovolcanoes elsewhere. Instead, large lahars originating 

on the volcano in Quaternary time repeatedly flowed 

far down the canyons of the Cascade Range, and some 

eame to rest beyond the n1ountain front in parts of 

the adjoining Puget Sound lowland (Crandell, 1963b). 

Within the mountains, lahars typically are found on 

valley floors, although the deposits of some of the largest lahars also veneer valley walls to heights of hundreds of feet. Smne even mantle eli vi des that are a 

thousand feet or 1nore above valley floors near the 

volcano. Lahars that formed within the last thousand 

years cmnmonly form low terraces or veneer other unconsolidated deposits that form the terraces. Older 

lahars are often found interbedded with fluvial terrace 

deposits, duff horizons and stumps that represent old 

forest floors, .and :thin 'layers of pyroclastic mruterial. 

CLIMATE 

The climate of Mount Rainier National Park is cool 

and moist during fall, winter, and spring, hut the summers are relatively wann and dry. Monthly precipitation at Paradise Park, at an altitude of about 5,400 

feet, generally is greater than 10 inches from Oetober 

through March and decreases to an inch or two during 

July (table 1). Within the period from 1956 through 

1965 the highest yearly precipita-tion at Paradise 

Ranger Station was 146.31 inches in 1959, and the lowest 

was 94.56 inches in 1965. As n1uch as 48 feet of snow 

has fallen at Paradise Park in a single winter, and 

snowbanks frequently linger there untH late July or 

August. The average January and July temperatures, 

respectively, at Paradise Park are 26.4° and 53.0°F. 

Minimum daily temperatures below freezing can be 

expected there any month of the year, whereas at Longmire, at an altitude of 2,672 feet, daily minimum temperatures generally ~are above 32°F. during June, July, 

and August. Because of its lower altitude Longmire receives considerably less precipitation than does Paradise 

Park (table 1), and the January and July average temperatures there are 30.2° and 60.6°F., respectively. The 

long-term average annual precipitation at Longmire is 

about 82 inches, but within the last 40 years the annual 

precipitation has ranged from a low of 43.22 inches in 

1952 to a high of 113.60 inches in 1933 (fig. 2). 

Winds throughout the year are generally from the 

west. From May through August, average monthly 

winds are mostly from the west and southwest, and during November through January, they are from the west 

TABLE 1.-Average monthly and average annual precipitat-ion 

(inches) at Longmire (1) for the 51-year period preceding 1£166 

and at Longmire (2) and Paradise Ranger Station (3) for the 

period from 1956 through 1965 

[Compiled from Climatology Data published by the U.S. Weather Bureau] 

January ________________________ _ February _______________________ _ ~arch __________________________ _ ApriL __________________________ _ 

June ~aY---------------------------- ___________________________ _ July ____________________________ _ August _________________________ _ September ______________________ _ 

October---4---------------------

~overnber ______________________ _ I>ecernber _______________________ _ 

Annual average ____________ _ 

10.92 

8. 98 

8. 32 

5. 11 

4. 12 

3. 63 

1. 35 

1. 75 

3. 92 

8. 63 

11.91 

13.79 

82.43 

2 3 

11. 87 

9. 47 

8. 21 

6. 41 

4. 07 

4. 29 

1. 19 

2. 79 

4. 49 

8. 14 

12.69 

11. 75 

85. 37 

17. 21 

13. 82 

11. 89 

8. 87 

4. 60 

3. 95 

1. 71 

4. 09 

6. 33 

11. 26 

18. 20 

17. 94 

119. 87 

and northwest. The directions from which average 

monthly winds come during the other months range 

from northwesterly to southwesterly. One geologic f,£-

fect of these prevailing winds was the deter1nination of 

the fallout pattern of postglaciaJ pyroclastic deposits, 

each of which lies mostly east of the volcano. 

TERMINOLOGY AND DISTINCTIVE FEATURES OF 

LAHARS 

The term "lahar" is an Indonesian word that is usfm 

. in this re·port a,g a general designation for deposits th~tt 

have resulted from rapid mass flowage of rock debris 

mobilized by water and that have originated on the 

slopes of a volcano. The term is also used to refer to the 

flowing 1nixture of rock debris and water. This de:firition follows the usage of van Bemmelen (1949, p. 191) 

and is adopted because of the need for a general term 

·that is independent of reference to the texture of the d~-

150 

CfJ 130 LJ.J 

I 

(.) 120 

~ 110 

~ 100 

z 

0 90 

i= 

<( 80 t0:: 70 u 

LJ.J 60 0::: 

Q_ 

50 

40 

\0 0 N ('t) 

~ ~ 

FIGURE 2.-Average annual precipitation at Longmire from 19<:6 

through 1965 (solid line) and ·average annual preciplitaU'>n 

at Paradise Ranger Station from 1956 through 1965 (dott,~d 

line). 
4 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

posi\t and :the sediment to water ratio during move;ment. 

Thus, use of the term "lahar" a voids the necessity of 

adoping such textural designations as debris flow and 

mudflow, even though these terms are conveniently applied here to certain appropriate lahars. Even though 

all the deposits to be described originated on a volcano, 

it is wetll to emphasize at the outset that not all of them 

originated as the direct and immediate result of volcani"-

activity. 

Most of the lahars described in this report conform to 

the definition of either mudflow or debris flow as used 

by many workers. Sharp and Nobles (1953) used the 

term "debris flow" as a general designation for all types 

of rapid flowage involving rock debris of various kinds. 

They suggested that mudflows are a variety of debris 

flow in which the mud gives the mass a mode of behavior 

which distinguishes it from a flow of wet rock debris 

devoid of mud. Varnes (1958, p. 37) subsequently clarified this usage by restricting the term "mudflow" to 

deposits that have at least 50 percent material of sand 

size and smaller. 

The sand fraction of a lahar may not be as important 

as the silt and clay fraction in imparting certain flowage 

characteristics to a sediment-water mixture. It has been 

experimentally shown that the fall velocity of sandsized material in such a mixture decreases as the clayfraction increases (Simons and others, 1963), and under 

some conditions this has the effect of allowing the coarse 

fraction to be suspended by less turbulence. 

Bull ( 1964) adopted a threefold classification to describe the deposits of alluvial fans in Fresno County, 

Calif. His classification, shown below, was based on 

sorting coefficient (So) , phi standard deviation ( ucp) , 

and phi quartile deviation ( QDcp) •

1 

So uq, Q.Dq, 

Waterlaid sediments (upper limit)___ 3 2. 3 1. 6 

Intermediate sediments (limits)_____ 3-5 2. 9-4. 1 1. 6-2. 3 

Mudflows (lower limit)____________ 5 4. 1 2. 3 

Few grain-size analyses of "waterlaid sediments" 

were made during the present investigation; deposits 

thought to be of this origin are generally referred to in 

this report as fluvial deposits or fluvial sedin1ents, but 

some of then1 tnay also belong in Bull's category of 

"intermediate sediments." Although nearly all the deposits called lahars in this report are mudflows according to BuB's classification, a few samples fall within 

the limits of his "intermediate sediments" category. For 

example, a sample from the fine, graded top of the Elec1 A "sorting coefficient" is the square root of the ratio of the third (larger) quartile 

(the 75 percent value) to the first (smaller) quartile (the 25 percent value). The two 

percentiles refer to the percentage of material that is finer than the grain diameter for 

the percentile on the cumulative curve. As the degree of sorting increases, the two 

quartiles become more nearly equal, and the sorting coefficient approaches 1.0. 

The designation "phi" is equal to the -log2 of the grain diameter in millimeters. 

The formula for the phi standard deviation (uq,) is (4>16-1/>84)/2 and the formula 

r0 r phi quartile deviation (QIJq,) is (4>25-4>75)/2. 

tron Mudflow has a sorting coefficient, phi standard deviation, and phi quartile deviation that fall in the 

"intermediate" category; a sample from the base of 

the Electron at the same locality, however, has paran1eters characteristic of Bull's mudflows. 

Some of the lahars described in this report may have 

been formed by "hyperconcentrated flows" (Beverage 

and Culbertson, 1964), which are water-sediment mixtures that have between 40 and 80 percent E~diment by 

weight. These flows are intennediate between normal 

steamflow, in which there is no more than 40 percent 

sediment by weight, and mudflow, which has more than 

80 percent sediment by weight, according to Beverage 

and Culbertson. Richardson ( 1968) suggestei that some 

of the outburst floods that have originated in Nisqually 

and South Tahoma Glaciers within the la~t 40 years 

(p. 44, 58), have been "hyperconcentra.ted flows." 

Lahars have some features in common with deposits 

of other origins, such as till, fluvial deposits: colluvium, 

and landslides. I know of no single c(nnmon feature that 

serves to distinguish all lahars from all oth~r kinds of 

deposits. Instead, many different characteris .. .ics none of 

which Imt.y be individually definitive, ofter indicate a 

laharic origin when considered collectively. For example, the principal features that led to the recognition of 

the so-called Osceola till of Willis ( 1898) af a mudflow 

were its flat topography and highly digitate pattern of 

distribution in the Puget Sound lowland (G'.'andell and 

Waldron, 1956). These features were considered in conjunction with the deposit's provenance, lack of sorting, 

coarse texture, and vertical distribution on rTalley walls 

in the Cascade Range and at Mount Rainier. We concluded that the Osceola in the Puget Sound lowland 

had been transported and deposited by a medium of 

which no part could have been appreciably higher than 

the present surface of the deposit, a requirement that is 

satisfied only by assuming that the material flowed into 

its present position. 

The distribution of a deposit is very helpful in determining its origin, although the presence of lahars on 

some ridgetops close to the volcano caused ruch initial 

uncertainty concerning their mode of origin. More 

commonly, lahars occur on valley floors, eRpecially at 

some distance away from their source. Their distribution and provenance generally are adequate to distinguish them from local colluvium. 

The texture of some lahars resembles thr,t of coarse 

fluvial sand and gravel deposits, with whicl lahars are 

typically interbedded. Probably the most diagnostic 

feature of a lahar in such a comparison is its lack of 

internal stratification, even though some successions of 

lahars forn1 an assemblage of deposits that i" bedded in 

gross aspect. However, each individual lahar lacks in-
INTRODUCTION 5 

ternal bedding because it 1noved and came to rest as a 

single mass-flowage unit. A fine line cannot be drawn 

between some fluvial deposits that are very crudely 

bedded and some lahars ; in fact, the processes of transportation apparently are gradational. The transport 

ability of a lahar is tremendous because of its relatively 

high viscosity and high specific gravity; thus, large 

blocks of rock are common in the deposits. However, 

large boulders also are present in some crudely stratified 

fluvial deposits (fig. 18). 

Many lahars closely resemble till, and the distinction 

between the two sometimes is not possible in the field. 

The striated, soled, and snubbed stones that are generally regarded as being typical of till are not very helpful in distinguishing tills from lahars. Stones with 

these features were not observed in any of the lahars, 

but neither are they abundant enough in the till to be 

useful criteria at Mount Rainier. Some deposits that I 

initially regarded as till were soon fOlmd to be of postglacial age, and their distance from the present glaciers 

indicates that they cannot have been formed by glacial 

advances of Holocene age. These deposits are interbedded with alluvium in some terraces and form veneers on others, but a laharic origin is inferred because 

all have a distribution that can be explained only by 

mass flowage. 

The size distribution and sorting characteristics of 

some tills (fig. 3) are similar to those of many lahars. 

The sorting coefficients of seven samples of Evans Creek 

till range from 3.16 to 9.5 ( avg. 6.41), and those of the 

lahars discussed in this report range from 3.41 to 17. 

It is nearly impossible to obtain a truly representative 

sample of these coarse deposits, and the true maximum 

sorting coefficient of both kinds of deposits probably is 

greater than 17. 

Some lahars are lithologically similar to the deposits 

of hot dry block-and-ash flows. The high mobility of 

some block-and-ash flows, provided by gas contained in 

the flow, by entrapment, heating, and expansion of cold 

air (McTaggart, 1960), and by the conversion to steam 

of water, snow, and ice incorporated by the flow, would 

permit the flows to move down a valley floor in a manner similar to that of a lahar. One manner of distinguishing between the deposits of these two processes 

is by determining the temperature of the deposits when 

they were emplaced; this can he approximated from a 

study of the orientation of remanent magnetism and 

Curie temperature of the included rock fragments 

(Aramaki and Akimoto, 1957). The orientation is deterlnined by the ferromagnetic mineral or minerals in the 

rock, which is magnetite in the andesites from Mount 

Rainier. As the magnetite in originally molten rock 

cools through its Curie point, it takes on a magnetic 

420-479 0 - 71 - 2 

orientation that is parallel to the earth's magnetic fie] d 

at that 1noment. This is known as thermoremanent magnetisln (TRM). If a deposit came to rest while rorlr 

fragments in it were still above the Curie temperature 

of the magnetite, then the TRM orientations of tl'o, 

fragments should be uniform and parallel. But if tl'o, 

fragments cooled sufficiently before incorporation in a 

n1oving mass, or while the mass was still moving, their 

present TRM orientations would be random. 

It seems possible that a block-and-ash flow could 

grade downvalley into a lahar if the following sequence 

of events occurred (Mullineaux and Crandell, 1962). 

A mass of hot rock fragments, bombs, and ash might accmnulate at the sum1nit of the volcano during an eruption and then might avalanche to form a block-and-a£h 

flow. Snow incorporated by the flow as it crossed snovrfields and glaciers could become water and steam in 

transit; the steam would increase turbulence, and both 

the &ieam and water would dissipate heat and increase 

mobility by decreasing internal friction. If the matr:x 

cooled below the boiling point of water as the flow movrd 

beyond the base of the volcano the mass might become 

a lahar as conversion of water to steam diminishei. 

When the lahar came to rest, possibly as a result of tl'o. 

water and steam evaporating in such quantity that thr.y 

were no longer effective lubricants, many bombs arfi 

dense rock fragments might still be hot enough to carbonize wood. In this regard, Kemmerling ( 1921) r~­

ported a temperature of 92°C at a depth of about 1 foot 

in a lahar a few days after it had been formed durir ~ 

the 1919 eruption of Kelut in Java. About 2 weeks a:fter 

the eruption, the tem'perature had dropped to 50°C, arfi 

2 weeks later the temperature had dropped to 30°C. 

ICemmerling also mentioned a temperature of more th~.n 

360°C in ·a gas vent in the same l~ahar, and 'a temperature 

of 100°C at the same spot a year later. He attribut£oq 

the source of the heat to blocks of pumice which hrd. 

been ejected by the volcano and incorporated in th~ 

lahar. Kemmerling mentioned that a person had boon 

caught and transported some distance in another lahar 

from Kelut without having been burned. On the othqr 

hand, many corpses found later in the same lahar we"':"e 

severely burned. 

The texture of some lahars resembles that of smne 

avalanche deposits. This similarity is not surprising, 

for many lahars originated in avalanch~s, and beca1ne 

lahars only because subs'tantial·amounlts of water were 

present in the rock that formed the avalanches orb~­

cause water was incorporated during movement. Size 

data were obtained on two samples of the avalanche d~­

posits that resulted from rockfalls at Little Tahmna 

Peak in 1963 (fig. 4) (Crandell and Fahnestock, 1965) ~ 

The samples had sorting coefficients of 6.38 and 6.f3. 
6 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

E 

E 

...... 

0 w 0 

N 0 

Cii 100 

Cl 

w 

f-

<( 90 () 

Ci 

~ 80 z 

<( 

I 

f- 70 fI 

C) 

ijj 60 ~ 

>-

m 50 a:: 

w 

z 

Li: 40 (/) 

w 

...J 

() 30 i= 

a:: 

<( 

a_ 

LL. 20 

0 

w 

C) 10 <( 

fz 

w L---: () 0 a:: 

.... 

w 

E 

E 

...... 

0 

c:i 

/ 

vv 

L .... Y v 

---- v p 1-~--' 

f.- v 1-

-i-1-!-I- ~ 

E 

E 

...... 

c:i 

/ 

v ~e~~ 

~ ~~v 

/ Lo\0 "'J/ / 

v f.; 

vv ~n.~ v v ~); 

vV' J..-

~ 

J.--~-"" 

E E 

E E 

E E 0 0 0 q 

...... 8 8 

!--1"" 

------- -; ...... - ~~--- v ,;' 

./ ~ 

/ 

v v v ~~ 1:7' ...... ~---:..-

I.-'" _.,.v 1/ ~ 

~ 

~ v v~ !---'~--' 

~--~ 

v / 

~ v ~/; l.-' v !/ ~/ 

v I 'l ~- I?' 

/ ~ ... ~--~ 

..... .~.-" 

v v 

/ 

v 

a_ CLAY SILT SAND GRANULES PEBBLES COBBLES 

FIGURE 3.-0u:mulative curves and sorting coefficients (So) of three samples of Evans C!reek till. Sample 1 is from a cutbank 

of the Nisqually River in the NWlA, sec. 35, T. 16 N., R. 6 E., 1 mile southeast of Ashford, Wash. Sample 2 is from a 

Roadcut at Round Pass, and sample 3 is from a roadcut 1 mile southeast of Box Canyon. 

Neither sorting index, however, truly represents the degree of sorting in the deposits because of my inability 

to include in the samples a proportionate amount of the 

abundant large rock fragments. 

Two common features of lahars, which may help in 

recognition, are the presence of innumerable air spaces 

within the matrix and a vertical size gradation from 

coarse material at the base to fine material at the top. Air 

spaces seem to be most common in lahars that have a 

fine-grained matrix. Most of the air spaces are of irregular shape and range in size from a fraction of a 

millimeter to several millimeters, but air bubbles of 

spherical shape were noted in the fine-grained, graded 

top of a young lahar from Mount St. Helens. Bull 

(1964, p. A31) described bubble cavities in both waterlaid deposits and mudflows in alluvial fans in California. He noted that they are more common in the 

mudflows and that they are larger and Inore spherical 

if the mudflow has a considerable content of clay or 

silty clay. Air spaces in lahars seem to have been 

for1ned by air bubbles trapped within the n1atrix rather 

than by the draining a way of free water or part of the 

matrix after the lahar came to rest. 

The vertical gradation in texture of lahars is illustrated by data in table 2. This gradation is most conspicuous where the entire thickness of the lahar is 

exposed and commonly it is best shown by the upper 

few feet of a lahar; some lahars grade imperceptibly 

upward from coarse, unsorted material into a silty sand 

that is quite well sorted. An outcrop of the 1niddle third 

of a lahar, in contrast, 1night show no such gradation 

to the eye, and the gradation possibly might not even be 

detected from grain-size analysis. I have seen this vertical gradation in dozens of lahars at many localities in 

the Western United States. These lahars range in age 

from Tertiary to historic and in thickness from a few 

inches to n1any tens of feet. Unfortunately, however, 

the vertical gradation in texture is not present in all 

lahars, nor even in each lahar of a vertical succession 

of several in the same outcrop. 

Size-distribution analyses of several larars indicate 

that the proportion of silt and clay to the w~--ole -2-mm 

(millimeter) fraction is remarkably simHar for any 

given lahar, regardless of the horizon frmn which the 

sample came. This relation seems to be true even though 

the total amounts of the several size fractions change 

considerably from top to bottom of a give--:t deposit. A 

tabulation of data fron1 eight lahars sampled at two 

horizons (table 2) indicates a range in tho proportion 

of silt and clay to the - 2-mm fraction of only 0.4-3.4 
INTRODUCTION 7 

E 

E 

UJ § N . 

- 0 en 100 

0 

UJ 

I-

<( 90 ~ 

0 

~ 80 z 

<( 

I 

I- 70 II 

<!l 

jjj 60 S: 

>- Ill 

a:: 50 

UJ 

z 

i:i: 40 en 

UJ 

_J 

u 30 i= 

a:: 

<( 

c.. 

LL 20 

0 

UJ 

<!l 

<( 10 Iz 

UJ 

u 0 a:: 

UJ 

c.. 

E 

E 

...... 

0 

c:i 

E 

E 

...... 

c) 

c ~v 

v ~'\~ 

v v vv 

v 

vV v 

1..-:~1---

E E 

E E 

E E 0 0 c:i C! 

...... ~ S! 

/~ ~v / 

/ v ~VJ vv 17 J7 I/ 

~)7 vv 

v v 

~~ ~~ '\! ~ 

~e / 

~b v v~ 

CLAY SILT SAND GRANULES PEBBLES COBBLES 

FIGURE 4.-0umulative curves of samples from the avalanche deposits on the floor of the White River valley. (See Orande11 

and Fahnestock, 1965, fig. 3.) Samp1esl and 3 are from unitsl and 3 of the avalanche deposits from Little Tahoma Peal·. 

So, so'l'lting coefficient. 

percent. The siinilarity in proportions of material 

within the -2-mn1 fraction suggests that the matrix is 

nearly uniform in texture and that the textural change 

in the lahar vertically is principally one of an upward 

decrease in the percentage of material larger than 2 1nm. 

Sclnnincke (1967) also caHed a:ttenrtion to the graded 

nature of lahars and, in addition, noted (p. 440) a basal 

zone less than a foot thick of vaguely stratified, fine to 

ooarse sand in the lahars he studied. Basal zones of sand 

like those described by Schmincke were not noted in the 

lahars at Mount Rainier. I ha.ve seen beds of sand 

beneath many lahars of Cenozoic age in western 

Washington, but ,the~se beds seen1 to be genetically 

related to the underlying sequence of fluvial deposits 

rather than to the lahar. 

One interesting and significant relation tha.t was 

found in this study is the propensity of lahars to flow 

down a vaHey and to leave only a thin deposit on the 

valley sides and floor to m'a.rk their passage. Thick fills 

cmnmonly are formed by lahars only at some distance 

from the volcano, mostly at places where the valleys 

widen and become less steep and in areas of the lowland 

beyond the mountain front. During the, passage of some 

lahars of great volume, such as the Osceola Mudflow, 

valleys probably were filled with flowing mud to depths 

of hundreds of feet for many 1ninutes. The Paradise 

lahar, however, probably progressed downvalley ar: a 

single rapidly 1noving wave of fluid nl!aterial hundrrqs 

of feet high, and, except mmnentarily, it did not fill 

valleys to the 1naximum height recorded by its 

remnants. 

Because of the ephemeral character of a deep flowing 

current of mud in a steep and narrow valley and its 

characteristic manner of leaving only a veneer to record 

its passage, smne conventional inferences that can be 

1nade with regard to the aggradation and downcutting 

of fluvial fills are not pertinent to lahars. For example, 

each tert'lace of a flight of several in a valley may be 

veneered with a lahar. According to a conventional 

interpretation, the lahar on each terrace would represent 

a separate event-the lahar on the highest terrace would 

be the oldest, and the formation of each lahar would 

be followed by fluvial downcutting. However, this study 

has demonstrated that each terrace m·ay be veneered 

with the sa.me lahar, which was deep enough to cover 

them all temporarily before the fluid mUJterial drairo.d 

down valley. A corollary is that the same lahar that caps 

a high terrace in a flight of several terraces may lie 

beneath younger lahars and fluvial deposits in a lo~er 

terrace. It is important to recognize, further, that the 
8 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

TABLE 2.-Size-distribution data on eight lahars, each sampled 

from tu·o different horizons 

[In each lahar the proportion of silt and clay to the whole -2-mm fraction is closely similar in both horizons] 

Lahar 

l_--------

2 __ -------

3 ________ _ 

4 ____ -----

5 ____ -----

6.--------

7---------

8 ____ -----

-0.0625mm 

Lahar (percentage thickness Horizon of sample of silt and 

(ft) clay) 

13 Top 1ft__ ________ _ Bottom 1ft ______ _ >9 Top 1ft__ ________ _ 

5-7ft below top __ _ s. 5 Top 1 ft __________ _ Basal4 ft__ _______ _ 6. 5 Top 1 ft __________ _ Bottom 1ft ______ _ 18 Top 1ft __________ _ Bottom 1ft_ _____ _ 25 5-7ft below top __ _ 3-4ft above 

bottom. 9 Top 1ft__ ________ _ Bottom 1ft ______ _ 8 Top 1ft __________ _ 

Bottom 1ft_ _____ . 

13 

8 

15 

12 

19 

7 

36 

20 

25 

24 

18 

20 

8 

11 

6 

6 

-2mm 

(percentage 

of silt, sand, 

and clay) 

59 

37 

68 

50 

83 

28 

93 

57 

70 

66 

54 

63 

37 

52 

34 

31 

-0.0625mm 

-2mm 

(percentage 

of silt and 

clay to whole 

-2mm 

fraction) 

22 

21.6 

22.1 

24 

22.9 

25 

38.7 

35.1 

35.7 

36.4 

33.3 

31.7 

21.6 

21.2 

17.6 

19.4 

1. Uppermost lahar of three exposed in the walls of a gravel pit at Gilmore Corners, 

Wash. (See Mullineaux and Crandell, 1962, p. 859-860, unit 5 in measured sec- tion.) Lahar originated at Mount St. Helens volcano probably within the last 

2,000 years. 2. Lowermost lahar of three at Gilmore Corners (unit lin measured section.) 3. Upper lahar of two in the Alderton Formation of early(?) and middle(?) Pleisto- cene age near Sumner, Wash. (See Crandell, 1963b, p. A78, measured section 6, 

unit 5.) 4. Electron Mudfiow. Samples from outcrop at confluence of Carbon and Puyallup Rivers near McMillin, Wash. (See Crandell, 1963b, p. A5l.) The mudfiow origi- nated at Mount Rainier about 500 years ago. 5. Lahar in the Puyallup Formation of middle(?) Pleistocene age exposed in the 

north wall of the Fennel Creek valley, in the NW~ sec. 8, T. 19 N., R. 5 E., 

about 3.5 miles southeast of Sumner, Wash. 

6. Labar from Mount Hood volcano(?) in the Gresham Formation of middle(?) Pleistocene age. (See Trimble, 1963, p. 55.) Samples taken from roadcut out- crop in the NE~ sec. 14, T. 1 S., R. 4 E., in the valley of the Big Sandy River east of Portland, Oreg. 7. Uppermost lahar of three in sedimentary deposits of Miocene age near Buckley, Wash. (See Mullineaux and others, 1959, p. 689, unit 6 in measured section.) 8. Middle lahar of three in sedimentary deposits of Miocene age. (See above; unit 2 

in measured section.) 

lahar remnants on even the highest terrace do not necessarily mark the maximum height attained by the lahar 

a,t that point while it was moving. 

Despite the remarkable thickness or depth some lahars attained during movement, they evidently did not 

erode deeply even on fairly steep gradients. For example, lahars in some valleys are commonly found on 

top of relatively thin layers of sand and volcanic ash 

that presuma;bly would be easy to erode. These valleys 

have gradients of as much as 700 feet per mile today, 

and they probably ihad comparable slopes when the lahars occurred. The inability of many mudflows to erode 

at their base was recognized by Blackwelder ( 1928). 

This characteristic is particularly well illustrated in 

western Washington by the presence of leaves between 

the base of a poorly consolidated lahar of Miocene age 

and an underlying layer of fine volcanic ash only a few 

inches thick (Mullineaux and others, 1959), and I have 

observed a similar relation in ·the Rocky Mountain foothills near Denver, Colo., where a semiconsolidated lahar 

of the Upper Cretaceous and Paleocene Denver Formation is separated by a thin layer of leaves from an underlying bed of volcanic ash. Schmincke (1967) described thin tubes that extend upward into the basal 

part of a Miocene or Pliocene lahar in centrt'.l Washington; these tubes seem to be the 1nolds of pla,nts that were 

engulfed by the moving lahar. However, Schn1incke regarded these features as low-gradient, low-velocity phenomena, because he inferred (p. 447) that. on steeper 

gradients, closer to the source volcano, sinilar lahars 

had "picked up stream gravels and alluvium ·and uprooted bushes along their way" and (p. 440) that elsewhere one of the lahars was thought to have "possibly 

carved a creek channel in the underlying gravels." 

There can be little question that lahars can and do 

pick up some loose materials from the srrfaces over 

which they flow, and this erosive ability may be related 

not so much to degree of slope as to local turbulence 

caused by channel and valley configuration. Although 

some lahars of Pleistocene age in the soutl' <:';ffi part of 

the Puget Sound lowland seem to have tra.veled 40-50 

miles from rtheir source without appreciable contamination (Crandell, 1963b, p. A10), 1nore than half of the 

pebbles in samples of the Osceola and Electron Mudflows, at comparable distances from their source, are of 

rocks not derived from Mount Rainier (Crandell, 1963b, 

p. A14). 

The apparent inability of many lahars to erode, especially when spreading out on a surface of low slope, 

suggests that the lower part of a lahar is characterized by laminar flow rather than turbulent flow, and 

also that once the front of a lahar has parsed a given 

point, the material immediately above the base at that 

point becomes motionless or nearly so, even though 

movement is continuing in the main mass at higher 

horizons. It is as if the lahar moved :forward as ·a rug 

is unrolled; the immdbilized layer (the rug) then acts 

as a buffer zone immediately above the und~rlying surface to protect it from erosion. 

WAYS IN WHICH LAHARS ORIGINATE 

Lahars can be grouped by origin into nweral categories for the purpose of discussion: (1) trf)se that are 

the direct and immediate results of eruptions, (2) those 

that are indirectly related to an eruption or that occur 

shortly after ·an eruption, ·and (3) those that are not 

related in any way to contemporaneous voles nic activity. 

Lahars that are the direct and immediate results of 

volcanism can be formed in many ways: some of these 

are discussed and a few ·are illustrated by ex-amples that 

have occurred within historic time. 

Floods and lahars are sometimes fonned when a 

crat.er lake is forcefully expelled during an eruption. 

The Indonesian volcano Kelut on the islan1 of Java is 

notorious :for causing lahars in this manner. In 1919, a,n 
INTRODUCTION 9 

eruption through l{elut's crater lake spilled 39 million 

cubic yards of water down the south and southwest 

slopes of the volcano. The water picked up great quantities of loose rock debris and the resulting lahars totally 

or partly de,gtroyed 104 villages and killed 5,500 people. 

Smne lahars reached a distance of 12 miles from the 

volcano (Kemmerling, 1921). A crater lake can also be 

released by the failure of its enclosing walls. During 

eruptions of Smneru ( Smeru) volcano, also on Java, 

magma rising in the cone has repeatedly pushed aside 

parts of the era.ter walls:, ,and this material has avalanched down the sides of the volcano to produce lahws 

(Baak, 1949, p. 5-6). 

Repeated floods of hot water and hot lahars were one 

of the dmninant features of the 1902 eruption of Mount 

Pelee on Ma,rtinique, and some of them were caused by 

emptying of the crater lake (Anderson and Flett, 1903, 

p. 489). Two of the largest hot lahars preceded, by 4 

hours, the nm~e ardente that destroyed the town of St. 

Pierre at the foot of the volcano (Hovey, 1902, p. 346). 

The contmnporaneous eruptions of La Soufriere on the 

island of St. Vincent also caused a crater lake to empty 

and to forn1 a "torrent of 'boiling hot' water and mud" 

(Hovey, 1902, p. 342). The front of this lahar was at 

least 50 feet high as it rushed down a valley that heads 

on the volcano. 

Mud has been extruded directly by some volcanoes. 

According to Oinouye ( 1971) , n1ud consisting of finely 

divided plagioclase, hypersthene, augite, magnetite, 

glass, and hematite was erupted in 1910 frmn five craters 

in the sum1nit of U su volcano in Japan. During an 

eruption of Y ake Dake in Japan in 1962, hot montmorillonite-bearing n1ud ejected from a vent on the 

volcano formed a small mudflow (Morimoto and Ossaka, 

1964). From a study of andesitic breccias of Tertiary 

age in the Cascade Range of northet~l California, Durrell (1944) concluded that mudflows ean be extruded 

directly frmn volcanic fissures. He suggested that the 

solid fraction of the breccias he studied represented a 

highly mobile mass of andesite fragments in a matrix 

of eomminuted andesite ,and alteration products and 

that the water was derived directly frmn the associated 

magma. 

Av,alanches of rock debris can cause lahars by temporarily damming rivers. The water may spill over the 

dam, erode it, and the entire deposit may sweep downstream as a lahar. An event of this kind occurred during 

an eruption of Asama volcano in Japan in 1783 when a 

hot avalanche dammed a nearby river. Within ·an hour 

the river overtopped the dam, eroded it, and caused it to 

collapse. The debris rushed downstream as a hot mudflow that traveled 1nore than 50 miles and killed more 

than 1,300 people ( Aramaki, 1956) . During the 19~Q 

eruption of Santa Maria volcano in Guatemala, glowing 

avalanches moved down into the valleys of the E :lo 

Tamblor and Rio Concepcion and produced boiling-b9t 

lahars. The top of the lahar in the Rio Tamblor was 

covered with incandescent rock debris, and the lahar 

overflowed a cha1mel more than 300 feet deep and 250 

feet wide (Sapper and Termer, 1930, reviewed by Js~­

gar, 1931). 

Avalanches of hot rock debris have also caused lahr.rs 

by melting snow and ice on a large scale. During an 

eruption in 1955 of Bezymianny volcano in Ka,mchat]~a, 

block-and-ash avalanches spread over a broad area at 

the east base of the cone. Snow which was melted by the 

hot debris caused lahars that flowed downvalley more 

than 45 miles (Gorshkov, 1959). During the 19~~ 

eruption of Avacha volcano, also in Kamchatka, lahr.rs 

were caused in pa,rt by the deposition of hot pyroclas+:ic 

material on snow and ice (Meniailov, 1939). Solid nlaterial in the lahars consisted of breadcrusted and scoriaceous bombs in a black sand matrix. 

Volcanic explosions commonly cause landslides in 

rocks that have been weakened by hydrothermal alteration. An explosive eruption of Tokachi-dake volcano in 

Japan caused a large part of the cone to collapse in 19Jl). 

An immense avalanche of hot rock fragments accompanied by steam and possibly by hot water from the 

crater descended the west flank of the volcano and 

melted an accumulation o:f snow. The resulting lab:\,r 

poured down t:he mountain and reached a distance of 

nearly 15 miles (Tada and Tsuya, 1927). An expl~()n 

of the same voleano in 1962 caused a ~slide of about 4 

1nillion eubic 1neters of rock on one side o:f the cone, 

which beca.me a hot l:ahar as it moved downslope. The 

slide occurred in rocks that had been extensively decon1posed by fumarolic activity (Murai, 1963). 

An unusually large avalanche that moved like a lahar 

was caused by ,a phreatic explosion at Bandai-san -volcano in Japan in 1888. The horizontally directed force 

of the explosion caused the failure of a large segm3nt 

of the cone. In all, 1,487 million cubic yards of rock 

debris flowed downslope and covered an area of 27 

square miles at the base of the volcano. The mass ,...,..as 

thought to have been in a relatively dry state durng 

movement (Sekiyo and Kikuchi, 1889). A similar, but 

prehistoric, event occurred at Asama volcano when a 

phreatic explosion destroyed the eastern part of the 

cone and caused a lahar that spread over an area o:f 

•about 35 square miles. The rocks involved had previously 

been extensively altered to clay by solfataric activity 

( Aramaki, 1963) . An even older lahar originated fr'lm 

a catastrophic phreatic explosion of a pre-Asama 

· voloano at the same site ( Aramaki, 1963, p. 267). 
10 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASIDNGTON 

At Lassen Peak in northern California, lahars moved 

down two valleys north of the volcano for a distance 

of 1nore than 20 miles in May 1915. Day and A1len 

( 1925) attributed the lahars to the rapid n1elting of 

snow on the volcano by hot rain, hot volcanic ash, and 

a stean1 blast. It seems 1nore likely, however, that rapid 

1nelting of snow was caused by a lava flow near the summit of the volcano (Finch, 1930). 

Lahars can also result indirectly :from eruptions in 

1nany different ways. A crater lake may be released 

suddenly by failure of part of its restraining embankInent for some reason not associated with simultaneous 

volcanism. In 1953, failure of part of the natural dam 

that impounded Crater Lake on Mount Ruapehu inN ew 

Zealand permitted a large volume o:f water to rush down 

the side of the volcano, where great quantities of loose 

ash and boulders were picked up to :form a lahar. The 

lahar swept away a railroad bridge a :few minutes 

before the arrival of an express passenger train, and 

151 lives were lost (O'Shea, 1954). 

Pyroclastic deposits that are formed during an eruption are especially susceptible to saturation during periods of heavy precipitation, and sliding and flowage 

of these masses commonly cause lahars. These "rain 

lahars" are an almost daily occurrence during the monsoon season following an eruption of the Javanese volcano Kelut (Kmnmerling, 1921). A few weeks after the 

eruptions of La Soufrie.re, in 1902, heavy rains caused 

boiling-hot lahars to flow repeatedly down valleys that 

headed on the flanks of the volcano (Anderson and 

Flett, 1903, p. 422-424, 428-434). The sediment in the 

lahars was principally derived from thick deposits of 

hot sand-sized ash that had been formed during the 

eruption. Between episodes of volcanic activity at 

Vesuvius in 1906, rain and melting snow saturated 

loose rock debris o~ the flanks of the volcano and 

caused re.peated lahars (Perrett, 1924, p. 102). During 

the 1963-1964 eruptions of Irazu in Costa Rica, flash 

floods resulted from runoff whose volume was greatly 

increased by a thin compact layer of newly erupted 

ash. The floods became debris flows as they scoured 

valley sides which were formed by poorly consolidated 

deposits. One d~ebris flow caused great damage and some 

loss of life in the city of Cartago at the south base of 

the volcano (Waldron, 1967) . 

The last general category of lahars consists of those 

that are unrelated to volcanism. Mudflows and debris 

flows can result from saturation of loose rock debris by 

rain and melting snow in an alpine region wherever certain conditions are met-a source of rock debris, adequate moisture, and a steep slope. They may occur 

at volcanoes more often than elsewhere because of the 

combination there of all these conditions. Lahars a.re 

also frequently caused by the sudden release of a body 

of water impounded by a glacier. Although the water 

released n1ay be wholly the product of glacier melting 

related to atmospheric conditions, a flood from a glacier 

on a volcano 1nay also result from rapid, large-scale 

1nelting caused by a stea1n vent or by smne o,..J1er source 

of volcanic heat. 

AGE AND LITHOLOGY OF MOUNT RAINIER VOLCANO 

The ·earliest eviclenee of Mount Rainier volcano is 

present in unconsolidated deposits in the Puget Sound 

lowland to the northwest. These deposits include lahars 

derived fr01n an active volcano at the site of ~I01mt 

Rainier (Crandell, 1963b, p. A10-A11). TL~y are interbedded with glaeial drift deposit~d by a lobe of the 

Cordilleran ice sheet which moved southwarl down the 

Puget Sound lowland. The oldest known lahars were 

formed during the Alderton Interglaciaticn, of middle Pleistocene age (table 3) . Stones in these lahars 

are chiefly hornblende- and hypersthene-ber,ring andesites. A hornblende-hypersthene andesite lava flow is 

known to occur at only one locality in Mount Rainier 

National Park, and its age is unknown (Fiske and 

others, 1963, p. 64). However, lahars that contain 

fragments of a hornblende-hypersthene an.fesite crop 

out in Glacier Basin on the northeast side of Mount 

Rainier (pl. 1) , where they underlie glacial dri'ft ~and 

lava flows of pyroxene andesite. 

The oldest hypersthene-andesite lavas from Mount 

Rainier forn1 thick flows that filled canyons in the 

Caseade Range to depths of as much as 2,000 feet (Fiske 

and others, 1963, p. 66-69). These old resistant flows 

now underlie divides that radiate outward from the 

TABLE a.-Subdivisions of Quaternary time in western Washington 

[The Burroughs Mountain Stade occurred between about 3,000 and 2,500 years ago; the Garda Stade probably began about 800 years ago and exterds to the present (Crandell and Miller, 1964; Porter and Denton, 1967, p. 198-201)] 

Age Geologic-climate unit 

Winthrop Creek Garda Stade 

Glaciation Burroughs MounHolocene tain Stade 

"Hypsithermal interval" 

Suma<>- Stade 

EverP:m Interstade 

Fraser Glaciation Vashon Stade 

Evan1 Creek 

Stade 

Pleistocene Olympia Interglaciation 

Saimon Springs Glaciation 

Puyallup Interglaciation 

Stuck Glaciation 

Alderton Interglaciation 

Orting Glaciation 
INTRODUCTION 11 

base of the volcano, and the sites of smne of the fonner 

canyon walls or divides are now valleys. At a later stage, 

Mount Rainier erupted hundreds of thin lava flows and 

built up its present cone. Fragmental deposits interlayered with lava flows on the flanks of the volcano 

include well-indurated flow breccias as well as loose 

rubbles that may have originated as block-and-ash 

avalanches; pyroclastic deposits interbedded with these 

breccias and rubbles are few (Fiske and othe~rs, 1963, 

p. 75). 

The early canyon-filling lavas, as well as the rocks of 

the modern cone, are chiefly pyroxene andesites; hypersthene is ubiquitous and is the dominant mafic mineral in most flow rocks. Aecording to Fiske, Hopson, 

and Waters ( 1963), augite is generally abundant but 

slightly subordinate to hypersthene, which it encloses 

in some flow rocks. Brown hornblende is a sparse constituent of some flows. Flows of olivine andesite were 

erupted at two small satellite vents at Echo and Observation Rocks relatively late in the history of the volcano, but before the Fraser Glaciation. The most recent 

flows, which 1nake up the present summit cone and 

which probably are no n1ore than 2,000 years old (table 

6), are of an augite-hypersthene andesite (Fiske, Hopson, and Waters, 1963). Smne Holocene pyroclastic 

deposits erupted by Mount Rainier show somewhat 

greater diversity in mafic minerals than some' of the 

flows (D. R. Mullineaux, oral commun., 1969). For example, layer D (table 5) contains variable a1nounts of 

hypersthene, augite, hornblende, and oxyhornblende. 

Mount Rainier volcano seems to have been intermittently active during about the }ast 10,000 years, although 

it has apparently been 1nuch more ructi ve during some 

extended e.pisodes than during others. During this time 

interval the volcano has erupted lava flows at least once; 

bombs, blocks, and ash, which caused hot avalanches, at 

least three times; and pyroclastic material at least 11 

times. In addition, thin layers of fine-grained rock 

debris, which may be lithie ash, are found at 1nany 

horizons in the sequence of pyroclastic deposits and 

may record a dozen or more eruptions that are not 

known to be represented by other deposits (D. R. Mullineaux, oral commun., 1969). 

DATING OF LAHARS 

All the lahars described in this report are of Holocene 

age, except for one that probably was formed during 

a late part of the Fraser Glaciation (table 3). The postglacial age of most lahars can be readily determined 

because they overlie glacial deposits formed during the 

Fraser Glaciation. 

Many of the lahars either contain wood from which 

radiocarbon age determinations could be made or are 

closely associated with other deposits that are wood 

bearing. Age determinations cited here (table 4) of ]c:>Bs 

than 6,000 years ·have been corrected by Meyer Rubin 

(written cmnmlm., 1969) from data provided by H. E. 

Suess. These corrections are based on a 0 14 half life of 

5,730 years and also take into account past variations 

in atn1ospheric 0 14• Ages of less than 6,000 years that 

are given in the following text will be the correc~ed 

ages in 1970 lUlless specified to be uncorrected ages. 

Some lithologically similar lahars have been distinguished, traced, and correlated by their stratigrapltic 

relation to pyroclastic deposits. In some places the pyroclastic deposits are interbedded with the lahars; elsewhere, the age of a given lahar can be bracketed by the 

presence or absence of certain pyroclastic layers on top 

of it. The ages of most of the pyroclastic deposits in 

Mount Rainier National Park are known to within a 

few hundred years frmn radiocarbon age determinations of associated organic matter or from age determinations of such matter from horizons immediately 

above and below e.ach layer of pumice (table 5). All the 

postglacial lahars recognized in the valleys heading at 

Mount Rainier are shown in chronological order in table 

6, together with the pyroclastic deposits which help to 

date them. 

TABLE 4.-Radiocarbon dates pertaining to surficial depcsits 

less than 6,000 years old near Mount Rainier 

[The radiocarbon dates shown in the first column are based on a cu half life of 5,568 

years. The "true" dates shown in the next column are based on a half life of 5,730 

years and are corrected for C14 variations in the atmosphere. (Based on a written commun. from H. E. Suess to Meyer Rubin, 1968.)] 

Radiocarbon 

date (yr) 

"True" Years 

Sample date ago ln 

19701 

Stratigraphic position of sampl~ 

W-1120_____ 290±200 1525 A.D. 

1119_____ 320±200 1500 A.D. 

565_ _____ 530±200 1380 A.D. 

2113 _____ 1,050±350 950 A.D. 

197L ____ 1,100±250 900 A.D. 

1393 _____ 2,040±200 160B.C. 

566 ______ 2,170±200 220 B.C. 

1396 _____ 2,340±200 520 B.C. 

1587. ____ 2, 350±250 530 B.C. 

930 ______ 2,550±200 750 B.C. 

2114. ____ 2, 610±350 850 B.C. 

1972 _____ 2, 710±250 950 B.C. 

1118. ____ 2, 980±250 1300 B.C. 

1115 _____ 3,500±250 2010 B.C. 

564 ______ 4, 700±250 3600 B.C. 

L-223A2 ____ 4,800±300 3640 B.C. 

L-223B2 ____ 4, 950±300 3730 B.C. 

W-2053 _____ 5,020±300 3810 B.C. 

UW-623 _____ 5,040±150 3820 B.C. 

450 Wood from duff above pyroclastic layer 

W from Mount St. Helens. 

450 Wood from duff below pyroclastic layer W. 

600 Wood from Electron Mudflow. 

1, 000 Wood from mudflow in Puyallup r.tver valley. 1, 050 Wood from mudflow in South Puyallup 

River valley. 2,150 Wood from above pyroclastic layer C 

from Mount Rainier. 

2, 200 Wood from mudflow at mouth of Mowich River. 

2, 500 Wood from below pyroclastic layrr C. 

2, 500 Charcoal from block-and-ash florv in 

South Puyallup River valley. 

2, 700 Wood from clay above pyroclastic layer Y. 

2, 800 Wood from Round Pass Mudflo,, in 

Tahoma Creek valley. 

2, 900 Wood from Round Pass Mudflo"V in 

Puyallup River valley. 

3. 250 Carbon from duff above pyroclastic layer Y frolJl Mount St. Helens. 

4, 000 Wood from peat below pyroclastic layer Y. 

5, 550 Wood from Osceola Mudflow. 

5,600 Do. 

5, 700 Do. 

5, 800 Peat from above pyroclastic layH N, 

below layer F, both from M~unt 

Rainier. 

5, 800 Wood from Osceola Mudfl.ow. 

1 Rounded off to the nearest 50 years. 2 Lamont Geological Observatory. 3 University of Washington. 
12 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

TABLE 5.-Source, age, and description of some postglacial pyroclastic deposits in Mount Rainier National Park 

[D. R. Mullineaux, written commun., 1970] 

Pyroclastic layer 

Source 

volcano 

X____________ Rainier---- __ _ W _ _________ __ St. Helens. __ _ C_ _ ________ __ Rainier_------

y ____________ St. Helens ___ _ 

B._---------- Rainier_ _____ _ 

H _________________ do ________ _ F _________________ do ________ _ 

s __________________ do ________ _ 

N _________________ do ________ _ n _________________ do ________ _ L __________________ do ________ _ A. ________________ do ________ _ 

0_ ----------- Mazama __ ---- R_ ___________ Rainier ______ _ 

Approximate 

age (yrs) 

Description 

>UQ--<150 Scattered pumice lapilli. 450 Pumice ash. 

>2, 15Q-<2, 500 Pumice lapilli and scattered 

blocks. 

>3, 25Q-<4, 000 PumicE:' ash. 

>4, OOQ--<5, 800 Pumice ash and scattered 

lapUli. 

>4, OOQ--<5, 800 Scattered pumice lapilli. 

5, 700 Montmorillonite-rich lithic 

ash. 

>5, 7QQ-<6, 600 Sand- to block-sized lithic 

rubble. 

>5,80Q-<6,600 Lithic ash. 

>5, soo--<6, 600 Pumice laptlli. 

>5,8QQ-<6,600 Do. 

>5, 8QQ-<6, 600 Pumice ash and scattered 

lapilli. 

6, 600 Pumice ash. 

>8, 75o-<ll, 000? Pumice and lithic lapilli and 

ash. 

The 1nost distinctive and widespread pyroclastic deposits at. Mount Rainier are :from two other volcanoes. 

Layer 0 (table 5) has mineralogic characteristics that 

correspond to those o:f the pumice and ash that were 

erupted by Mount Mazama volcano at the site o:f Crater 

Lake, Oreg., about 6,600 years ago (Crandell and 

others, 1962; Powers and Wilcox, 1964). This pumice 

layer is especially useful in stratigraphic studies because it blankets the entire park and the adjoining 

region to a depth o:f 1-2 inches and is a distinctive 

yellowish orange. 

The other two exotic pumice deposits are layers Y 

and W, both o:f which were erupted by Mount St. Helens, a volcano about 50 miles south-southwest o:f Mount 

Rainier. Layer Y is a light-yellowish-brown pumice o:f 

1nediun1 to very coarse sand size. It thickens westward 

:frmn about 1 inch near the east edge o:f the park to 

about 12 inches near the southwest corner. Layer Y is 

between 3,250 and 4,000 years old, and :for convenience 

it will be arbitrarily assumed to have an age o:f about 

3,600 years. 

Pyroclastic layer W is a white pumice o:f fine to medimn sand size. It thickens :from about a quarter o:f an 

inch on the west side o:f the park to about 3 inches near 

the southeast corner. A radiocarbon date o:f 320±200 

yea.rs (W-1119) was determined :for charcoal in a horizon o:f duff beneath layer W, and age o:f 290 ± 200 years 

(W -1120) for charcoal in a layer above the pyroclastic 

deposit (Crandell and others, 1962). Radiocarbon ages 

o:f about 300 years ha.ve a "true" age o:f about 450 years 

(table 4). An age o:f about 450 years :for pyroclastic 

layer W is consistent with tree-ring data, because there 

are trees at least 435 years old growing on the surface 

o:f deposits at Mount Rainier that are younger than the 

pumice. 

Although most o:f the recognizable py•·oclastic deposits in the park originated at Mount Rainier, :few are 

widespread, distinctive, or preserved well e.nough to be 

o:f use in elating other deposits except in limited areas. 

The most useful pumice :from Mount Rainie.r is layer C, 

which is mostly of lapilli size and which is widely distributed over most o:f the park east o:f the volcano. It is 

generally one to several inches thick and is between 

2,150 and 2,500 years old. For convenience c:f reference, 

it will be assumed to have an age o:f about 2,300 years. 

The following description o:f lahars and some other 

unconsolidated deposits at Mount Raini,~r contains 

many references to the stratigraphic relations o:f these 

deposits to certain pumice layers. The reac ~r is urged 

to take special note o:f the :following pyroclastic deposits 

and to remember their approximate age: lay3r W, about 

450 years old; layer C, about 2,300 years old; layer Y, 

about 3,600 years old; and layer 0, about 6,600 years 

old. 

The reader may wonder why the pyroclas+ic deposits 

were not given letter designations in alphah~tical order 

by age. Letters were arbitrarily assigned to the deposits 

at an early stage of the study, when only five layers 

were recognized (Crandell and others, 1962), to allow 

for the possible later addition o:f other layers. More 

than 15 pyroclastic deposits have now h~en distinguished and given letter designations. 

ORIGIN OF THE CLAY IN SOME LAHARS 

Many lahars at Mount Rainier contain substantial 

amounts of montmorillonite or kaolinite, or both, as 

well as lesser amounts o:f some other clay 1ninerals. The 

source o:f these clays is a critical problem because most 

other unconsolidated deposits at Mount Rainier are 

typically poor in clay minerals. The magnitude o:f the 

problem can be illustrated by some very crud~ estimates 

o:f the volume o:f clay in the Electron and Osceola Mudflows, which, respectively, are about 600 and 5,700 

years old and which originated on the wes+. and east 

sides o:f the volcano. The Electron Mudflow has a volunle o:f at least 200 million cubic yards in the Puget 

Sound lowland alone, where it has a clay-size :fraction 

o:f about 9 percent; the clay-mineral conte.nt o:f this 

:fraction is about 60 percent. The total clay-mineral content of the mudflow, therefore, probably is at least 10 

million cubic yards. The estimated volume of the 

Osceola Mudflow is at least 2.6 billion cubic yards. The 

clay-sized :fraction of nine analyzed sample;;- averages 

about 9 percent, o:f which clay minerals make up an 

average of 75 percent. The mudflow, thereJore, may 

contain ~as much as 150 million cubic yards of clay 

minerals. 
INTRODUCTION 13 

The large a1nount of clay in some la1hars seems to have 

a direct bearing on their n1anner and place of origin. 

The two 1nost obvious possible origins of the clay minerals are through weathering processes and by hydrothermal alteration of rock in the volcano.2 

MontmoriUonite and kaolinite are known to be products of weathering processes and are commonly found 

together, although in different proportions, in many 

soils (Grim, 1953, p. 340-341). At Mount Rainier, I 

found no extensive area of rock or surficial deposits altered to clay by surface weathering processes on the 

lower slopes of the volcano. This lack of weathered 

material is readily explained by the predominance of 

mechanical weathering processe~s near and above tiJnberline. Furthermore, in the unlikely event that clayey profiles of weathering ever existed on the flanks of the volcano, they surely would have been stripped a way during 

the Fraser Glaciation. No such profiles have been for1ned 

in Holocene time at Mount Rainier. 

Nevertheless, Fiske, Hopson, and Waters ( 1963, p. 

85) suggested that weathered material provided the 

primary source of the largest Holocene lahar from 

Mount Rainier----the Osceol,a Mudflow. Crandell and 

Waldron ( 1956, p. 353) reported abundant montlnorillonite in the matrix of the mudflow, which was accompanied by a kaolin mineral. They thought both of these 

1ninerals were derived from hydrothern1ally altered 

rocks of the volcano. Fiske and his colleagues, however, 

concluded that the primary source of the montmorillonite was in "altered water-laid pun1iceous sediments 

and pmnice-slurry flood deposits interstratified in the 

valley fills along the headwaters of White River." Such 

a deposit on the south side of Inter Fork valley, which 

was first identified as the Osceola Mudflow by Crandell 

and Waldron ( 1956) , was described by Fiske and his 

coworkers as consisting of two parts-a lower part of 

chiefly "well-stratified sands and gravels" and an upper 

part of "water-laid pumiceous sediments and pumiceous 

mudflows now partly altered to a sticky clay." When I 

reexamined this outcrop during the present investigation, I found a lower lmit of glaciolacustrine sand and 

silt interbedded with thin layers of till, all part of the 

Evans Creek Drift, which was deposited during the 

Fraser Glaciation. Size-distribution analysis of a sample of the till indicated 8 percent clay-sized material. An 

X-ray examination of the clay fraction revealed feldspar, cristobalite, and quartz ; no clay minerals were 

identified. A sample of the fine-grained glaciolacustrine 

sediment also contained 8 percent clay-sized material, 

1nost of which consisted of feldspar and cristobalite but 

2 I am indebted to Professor Howard A. Coombs of the University of 

Washington for first suggesting to me, in 1953, that the abundant clay 

in the Osceola Mud:fiow might have been derived from hydrothermally 

altered rock at Mount Rainier. 

420-479 0 - 7l - 3 

included a small a1nount of an unidentified clay mineral. The overlying unit, which was described by Fis1

re, 

Hopson, and Waters (1963, p. 86) as ptuniceous seiiments and pumiceous mudflows, is the Osceola Mudfl.ow 

itself, which is as 1nuch as 100 feet thick here. I found 

no ptunice within the 1nuclflow, although several f,?1Bt 

of young, unweathered pumice ove,rlies it. This remnr.nt 

of the Osceola is indistinguishable from the mudflow 

farther upvalley, where it veneers the floor and sides of 

Glacier Basin, as well as the ridgetops bordering the 

basin. 

Remnants of sedimentary fills, such as those descrit(jd 

by Fiske and his coworkers, a.re present in some of the 

valleys that head at Mount Rainier; some of the fill 

remnants include clayey lahars, and some include layers 

of fresh, lmaltered pumice a few inches thick. The clay 

in such lahars was thought by Fiske and his associates 

to have been partly formed in place by weathering of 

pumice, and some of the clay was thought to have b€.en 

transported by slopewash and derived from a blanJ~et 

of weathered volcanic ash on the adjacent valley walls. 

As evidence of a widespread blanket of weathered ash, 

Fiske, Hopson, and Waters (1963, p. 80) described a 

layer "mostly altered to a greasy yellow clay containing abundant montmorillonite" at Mist Park and in the 

headwaters of Marmot Creek, both northwest of the 

volcano. The layer they noted at these two localities is 

pyroclastic layer 0, the Maza1na ash (table 5). Mechanical analyses of four samples of this ash, collected from 

outcrops at various places within Mount Rainier ~T ational Park, show that the ash contains only from 1 to 

7 percent of clay-sized material (D. R. Mullineaux, oral 

commun., 1969). In one sample, montmorillonite and 

a 1nixed-layered montmorillonite-mica mineral each 

made up one part in 10 and were accompanied by a 

trace of kaolinite. In the other three samples, clay minerals either were absent or were present in only tnr.ce 

amounts. According to D. R. Mullineaux (oral co"ll.-

mun., 1969), microscopic examination shows that de.licate shard points and filaments of glass from layer 0 

are intact, and the glass appears to be virtually unweathered. Thus, I do not believe that layer 0 could 

have provided an adequate source for the large volmne 

of clay in the Osceola Mudflow. 

Hopson, Waters, Bender, and Rubin (1962, p. 640) 

and Fiske, Hopson, and Waters ( 1963, p. 81) evidently 

considered the ash layer at Mist Park to be correlative 

with a layer of yellow clay (pyroclastic layer F) on the 

uplands northeast of the volcano (Crandell and W aldron, 1956, p. 355). That latter clay is, however, stratigraphically above layer 0, as is demonstrated in countless natural exposures and roadcuts. In contrast to the 

meager clay content of layer 0, the yellow clay in-
14 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Years 

ago 

1,000-

2,000-

3,000 -

4,000-

5,000-

6,000-

7,000-

8,000 -

Eruptions that produced summit 

cone of Mount Rainier and main 

pyroclastic deposits in Mount 

Rainier National Park 

Layer G erupted by Mount Rainier 

between 110 and 150 yr ago 

Layer W erupted by Mount St. 

Helens about 450 yr ago 

~"0 '+<"' .s § ... 

]~:§ 

e§~ :;§ 

lit ... 0 <8i::;1 

~ ~ ~ 

Layer C erupted by Mount Rainier 

about 2,300 yr ago 

Layer Y erupted by Mount St. 

Helens about 3,600 yr ago 

Layers B and H erupted by Mount 

Rainier between 3,600 ( Y) and 

5,800 ( N) yr ago 

Layer F erupted by Mount Rainier 

about 5,700 yr ago 

Layer S erupted by Mount Rainier 

between 5,700 (F) and 6,600 (0) 

yr ago 

Layers N, D, L, and A erupted by 

Mount Rainier between 5,800 and 

6,600 yr ago 

Layer 0 erupted by Mount Mazama 

at Crater Lake, Oreg., about 

6,600 yr ago 

9,000 _ Layer R erupted by Mount Rainier 

more than 8,750 yr ago 

West Fork of the 

White River valley 

Lahar extended at least 

18 miles beyond Winthrop Glacier between 

275 and 400 yr ago 

Lahar extended atleast 

18 miles beyond Winthrop Glacier between 

2,30 0 ( C ) and 3,600 

(Y) yr ago 

Two lahars extended ll to 

18 miles beyond Winthrop Glacier between 

3,600 (Y) and 5,700 

tF) yr ago 

Osceola Mudflow extended at least 70 

miles down valley 

from volcano about 

5,700 yr ago 

TABLE 6.-Postglaaial eruptions, lahars, avalan 

rnates based on the approximate ages of bracketing pyroclastic layer 

Inter Fork and White 

River valleys 

Avalanches of rock 

debris from Little 

Tahoma Peak in 1963 

extended as far as 

4.3 miles downvalley 

At least 4 lahars extended 

between 4 and 13 miles 

beyond Emmons Glacier between 1,000 and 

2,300 (C) yr ago 

Lahar extended at least 

15 miles beyond Emmons Glacier between 

2,300 (C) and 3,600 

!Y) yr ago 

Osceola Mudflow 

At least 5 lahars extended 

2.5 to 9 miles beyond 

Emmons Glacier between 5,700 and 6,600 

(0) yr ago 

Green water lahar extended at least 28 miles 

downvalley from volcano bet ween 5, 700 

and 6,600 (0) yr ago 

Ohanapecosh River valley 

Lahar extended at least 

6 miles beyond Ohanapecosh Glacier between 450 ( W) and 

3,600 ( Y) yr ago 

Lahar extended at least 

6 miles beyond Ohanapecosh Glacier bet ween 3,600 (Y) and 

6,600 ( 0) yr ago 

Lahar extended at least 

as far downvalley as 

Indian Bar more than 

6,600 ( 0) yr ago 

Muddy Fork of the 

Cowlitz River valley 

Lahar extended at least 

3.5 miles beyond Cowlitz Glacier between 

450 ( W) and 3,600 (Y) 

yr ago 

Nisqually River valley 

Lahar extended downvalley at least as far 

as Longmire in the 

1860's 

Lahar extended at least 

1 mile beyond Longmire about 400 yr ago 

At leas~ 7 lahars ex:-

tended 4.5 to 9 miles 

beyond Nisqually Glacier b~tween 800 and 

3,600 ( Y) yr ago 

Lahar extended at least 

25 mil ~s beyond Nisqually Glacier so metime after 3,600 ( Y) 

yr age 

At least 3 lahars extendec' more than 15 

miles beyond Nisquall;y Glacier between 3,600 (Y) and 

6,600 (0) yr ago 

Paradise lahar ex:tended 

at least 18 miles downvalley from volcano 

bet weQn 5,800 and 

6,600 (0) yr ago 

Avalancl es of clayey 

rock debris covered 

Paradb~ Park more 

than 5,f'l0 ( N) yr ago, 

and Va'l Trump Park 

more than 6,600 ( 0) 

yr ago 
INTRODUCTION 

ches, and bZock-amd-ash flows at Mount Rainier 

s are followed by the letter designation of that layer in parentheses] 

Kautz Creek valley 

Lahars extended downvalley to Nisqually 

River in 1947 

At least 2 lahars extended more than 4 

miles beyond Kautz 

Glacier within last 

450 yr 

At least 3 lahars extended more than 3 

miles beyond Kautz 

Glacier bet ween 450 

( W) and 3,600 ( Y) yr 

ago 

Lahar extended more 

than 4 miles beyond 

Kautz Glacier before 

3,600 ( Y) yr ago 

Tahoma Creek valley 

Lahar extended 3~ 

miles from South 

Tahoma Glacier in 

1967 

Lahar extended at least 

4.5 miles beyond 

South Tahoma Glacier about 440 yr ago 

Two lahars extended 

more than 2 miles 

beyond South Tahoma 

Glacier between 450 

( W) and 2,800 yr ago 

Round Pass Mudflow 

extended at least 7 

miles beyond South 

Tahoma Glacier about 

2,800 yr ago 

South Puyallup River 

"alley 

At least 4 lahars of unknown extent have 

occurred within last 

450 (W) yr 

Electron M t1dflow extended about 30 miles 

down valley from volcano about 600 yr ago 

Lahar extended at least 

14 miles beyond 

Tahoma Glacier about 

1,000 yr ago 

Block-and-ash flow extended at least 3 miles 

beyond Tahoma Glacier about 2,500 yr 

ago 

Lahar extended at least 

3 miles beyond Tahoma Glacier between 

2,500 and 2,800 yr ago 

Round Pass Mudflow 

extended at least 15 

miles beyond Tahoma 

Glacier about 2,800 yr 

ago 

Lahar of unknown extent occurred more 

than 3,600 ( Y) yr ago 

North Puyallup River 

valley 

At least 2 lahars of unknown extent occurred more than 400 

yr ago 

Round Pass Mudflow 

South Mowich River 

valley 

Lahar extended at least 

2.5 miles beyond 

South Mowich Glacier within last 450 

(W) yr 

Lahar extended at least 

3 miles beyond South 

Mowich Glacier between 450 ( W) and 

3,600 (Y) yr ago 

At least 1 lahar extended more than 7 

miles beyond South 

Mowich Glacier before 3,600 (Y) yr ago 

Carbon River valley 

Lahar extended at least 

5 miles beyond Carbon Glacier between 

3,600 ( Y) and 6,600 

(0) yr ago 

15 

Years ago 

- 1,000 

- 2,000 

r-- 3,000 

r-- 4,000 

r-- 5,000 

r-- 6,000 

,_ 7,000 

-8,000 

-9,000 
16 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

eludes from 50 to 90 percent clay-sized 1naterial, in 

'vhich clay minerals make up as much as eight parts 

in 10. Montmorillonite is the most common mineral; 

it is accompaliied by illite or kaolinite, or by both minerals in some samples. The stratigraphic relations and 

lithology of this layer of yellow clay suggest tha.t the 

clay was formed at the same time as the Osceola 

Mudflow. 

A possible source of clayey material is the masses of 

glacial drift that lie on the lower slopes of the volcano 

and in the adjacent valleys. This drift is not regarded, 

however, as a potential source of clayey lahars chiefly 

because it is typically poor both in clay-sized material 

and in clay minerals. The Evans Creek Drift, which is 

the most widespread glacial deposit in the park, is characterized by an immature soil profile with little or no 

clay in the thin B horizon. X-ray analyses of clay fractions of unweathered till from five localities in the park 

revealed clay minerals in only trace amounts in three 

samples and none in the other two (table 7). These data 

suggest that the drift is not an adequate source for 

clayey lahars. 

From these data I conclude that neither the pyroclastic deposits nor the glacial drift at Mount Rainier could 

have provided an adequate source for the clayey lahars 

of Holocene age. 

Clay minerals are well-known products of hydrothermal alteration of rock, as has been amply demonstrated by studies of hot-springs areas and of mining 

districts, where the clays are associated with metalliferous veins. Hydrothermal wallrock ~alteration at 

Butte, Mont., for example, has resulted in a zoned clayInineral distribution in which montmorillonite and 

chlorite are farthest from the source of the hydrothermal solutions, and kaolinite lies in a zone closer 

to that source (Sales and Meyer, 1948). Similarly, zones 

of hydrothermal alteration in wallrock in the Cochiti 

1nining district of New Mexico are represented by a 

kaolinite-group clay mineral (dickite), illite-kaolinite, 

vermiculite-halloysite, and chlorite-montmorillonite, 

successively, from the vein outward into the host rock 

of rhyolite and andesite flows (Bundy and Murray, 

1959, p. 365). In some mineralized districts, similar 

zones of alteration seen1 tto be superimposed (Bateman, 

1950, p. 104). 

Studies of hydrothermal alteration in andesite and 

granodiorite at Steamboat Springs, Nev., show that 

the principal hydrothermal clay minerals are illite, 

montmorillonite, and mixed -layered illite-montmorillonite ( Sigvaldason and White, 1962, p. D1~.5). Where 

these minerals have been leached by strongly acid solutions percolating downward :from the ground surface, 

kaolinite is found ( Sigvaldason ~and White, 1961, p. 

D117; 1962, p. D115). Similarly, alteration of basalt 

in Iceland by nearly neutral hot-spring waters has produced kaolinite, which is associated with montmorillonite in some areas (Barth, 1950, p. 53). 

Montmorillonite and kaolinite are also cksely associated in the hydrothermally altered rocks of some volcanoes (table 8). Altered andesite that is part of the 

solfatarized vent rocks of Brokeo:ff Volcano in Lassen 

Volcanic National Park has been described ry Williams 

( 1932) and Anderson ( 1935). I collected three samples 

of this rock from a roadcut in the NE14NVT14 sec. 15, 

T. 30 N., R. 4 E., within a lateral distance of 200 feet, 

which were analyzed for clay mineralogy. The samples 

contained 10, 21, and 70 percent of clay-sizrd material, 

~0-90 percent of which consisted of clay minerals. Kaolinite, illite, and chlorite, listed in order of abundance, 

:>ccurred in one sample; kaolinite and montmorillonite 

were identified in a second sample; and montmorillonite 

alone occurred in the third (table 8, sample~ ~5-7). The 

clay mineralogy of these three samples clear~y indicates 

that the presence or absence of a specific clay mineral 

in a single sample m.ay have little signifhance with 

respect to the overall clay mineralogy of roclrs that have 

been hydrothermally altered. 

Active fumaroles were recognized ·at ~the summit of 

Mount Rainier at the time of the first authenticated 

climb to the top of the volcano in 1870, and the lavas 

TABLE 7.-Mineralogy of clay fractions determined from X-ray analysis of five samples of Evans Creek till in Mount Rainier National Park 

[Values are estimated parts ln ten] 

Till sample Montmorillonite Chlorite Mica 

Montmorillonitechlorite mixedlayer mineral 

1 ___________________ ------------------------ Trace -------------- 2__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Trace < 1 _ _ _ _ _ _ _ _ _ _ Trace 

3 ___________________ ------------------------------------------------ 4__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Trace _______________ - _-------

5 ___________________ ------------------------------------------------

Feldspar 

5 

4+ 

6 

6 

6+ 

Quartz 

Trace 

1+ 

1 

1+ 

<1 

Amorphous sillca 

and (or) opaline sillca 

1 

<1 

--------------

--------------

--------------

Crlstoballte 

3 

1+ 

3 

2 

3 

1. From an outcrop a few hundred feet northwest of the visitor center at Paradise 

Park. 

4. From a roadcut in Stevens Canyon 0.3 mile west of a highway tTlnnel. . 5. From an outcrop on the south side of the valley of Inter Fork about 1%' miles 

2. From a roadcut opposite west of Whlte River campground. the Marine Memorial at Round Pass. 

3. From a roadcut 1 mile southeast of Box Canyon. 
DESCRIPTION OF LAHARS 17 

of the summit cone have locally been hydrothermally 

altered rto a loose, sandy, clay-bearing materia;}. A 

sample obltained by Jack H. Hyde from t'he ground surface at the norith rim of the eastern crater near Columbia Crest contained an estimaJted seven parts in 10 of 

montmorillonite lin ,the sillt and cJ.ay fraction, and the 

remainder of the frootion consisted of feldspar and 

cristobalite (!table 8, sample 4). 

An even larger a;rea of altered clayey rock at Mount 

Rainier is now exposed in the east wall of Sunset Amphitheater (fig. 5), where a mass of yellow altered rock 

forms the western part of a solbtarized plug in the 

eroded central conduit of the volcano (Fiske, Hopson, 

and Waters, 1963, p. 72, 75). A sample of this rock was 

reported by Fiske and his coworkers (p. 75) to be opalized and to contain "some kaolinite, tridymite, cristohalite, and also a little pyrite mostly altered to limonite." They pointed out that the sample "strikingly resembles the solfatarized vent rocks of the Brokeoff volcano, near Mount Lassen" in northern C3!lifornia. They 

(p. 85) also emphasized the absence of montomorillonite 

from their sample and concluded from this that hydrothermally montmorillonitized rock was not available in 

the volcano which would provide montmorillonite for 

the Osceola Mudflow. 

An avalanche of dehris from the altered plug in Sunset Amphitheater, which occurred some time between 

1910 and 1930, formed a deposit that now lies on and 

just beyond the end of Tahoma Glacier (fig. 5). In three 

samples collected from the avalanche deposit, clay-sized 

material made up from 17 to 31 percent of the plastic 

yellow matrix. Montmorillonite was identified in two 

of the samples and was accompanied by kaolinite in 

the third (table 8). 

The clay mineralogy of the three samples of the 

avalanche deposit, as well as that of the altered rock 

from the summit cone, clearly indicates that hydrothermal alteration of the rocks of Mount Rainier typically produ~es montmorillonite or kaolinite, or both clay 

minerals. Altered rocks like these obviously could have 

been available in the past to provide the clay component 

of mudflows. The single sample reported by Fiske, 

Hopson, and Waters ( 1963, p. 85), in which montmorillonite was not identified, may have come from a part 

of the plug that had been strongly leached by acid 

solutions, so that montmorillonite was altered to kaolinite. Or, clay minerals in the plug may be zonally 

distributed like those adjacent to some hydrothermal 

ore veins. If the clay minerals are zonally distributed, 

debris derived from a specific zone could contain only 

one clay mineral. 

In summary, montmorillonite and kaolinite, as well 

as some other clay minerals, are normal and expectable 

products of hydrothermal alteration within a volcano. 

Because of the inherent structural weakness of hydrothermally altered rock, the rock should be especially 

susceptible to large-scale failure and sliding. Moreover, 

if slides of altered rock were to occur in an active hydrothermal area, the slide material most likely would 

already be wet because of condensed steam and thus 

would readily become a lahar as the slide moved downslope. The evidence now available clearly indicates that 

all <the large clayey 'lahars at Mount Rainier were derived from areas of hydrothermally altered rock on the 

volcano. 

DESCRIPTION OF LAHARS 

LAHARS IN THE WHITE RIVER DRAINAGE BASIN 

A sequence of lahars and fluvi3!l deposits extends 

down the White River and West Fork valleys for many 

miles beyond the base of Mount Rainier. The most 

voluminous units in this sequence are the Osceola Mudflow, which extended far into the Puget Sound lowland, 

and the older Greenwater lahar, which moved downvalley at least as far as a point 2 miles beyond the community of Greenwater. 

The stratigraphic relation of these lahars to one another and to pyroclastic deposits is summarized in 

table 9. The term "lahar assemblage," used in this table 

and in the following discussion, refers to a succession 

of two or more lahars which may be interbedded with 

TABLE B.-Mineralogy of clay fractions determined by X-ray analysis of hydrothermally altered andesite 

[Values are estimated parts in ten] 

Sample Montmorillonite Kaolinite Chlorite Illite Feldspar Quartz Crlstoballte 

L _ _ _ _ _ __ _ __ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _ _ _ _ _ _ __ _ _ 6 Trace _ _ _ _ _ __ _ __ _ _ _ _ _ __ _ _ _ <I <I 2+ 

2------------------------------------------ 7 ------------------------------ I <I I+ 

3------------------------------------------ 4 2 -------------------- 1+ <1 2 

4------------------------------------------ 7 ------------------------------ 2 ---------- I 

5------------------------------------------------------ 6 I I ------------------------------ 6___________ _______________________________ 7+ ------------------------------ <I I+ <1 

7------------------------------------------ 2 3 ------------------------------ Trace 5 

1-3. From various parts of a clayey avalanche deposit at the terminus of Tahoma 

Glacier. 

4. From the ground surface on the rim o! Mount Rainier's summit cone near 

li-7. Fr~~~~a'g~u?:~~\assen Volcanic National Park, Call!. (See text.) 
18 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

FIGURE 5.-Avalanche deposlit at and on the oorminus of Tahoma Glacier. Parts of the avalanche debris are a sticky yellow 

clay, which is the product of hydrothermal alteration of rock within the volcano. The al!tera;tion evidently OCC'Urred 

in an old conduit of the voloano which is now exposed in cross section in the cliffs immediately left of the area where 

Tahoma Glacier spills down frOiill the summit snowfields. The ice face in the ceruter foreground is about 150 feet high. 

alluvium. Thus, in the White River valley, the preOsceola lahar assemblage is a group of deposits which 

includes at least four lahars interbedded with fluvial 

gravels, all of which are younger than the Greenwater 

lahar and older than the Osceola Mudflow. 

GREENWATER LAHAR 

A lahar whose surface is dotted with scores of mounds 

forms terraces at several places in the White River 

valley as far downstream as a point about 2 miles west 

of the community of Greenwater (fig. 6). The largest 

remnants of the deposit lie on the west side of the White 

River valley between the mouth of Silver Creek and 

Buck Creek, at the mouth of the Huckleberry Creek 

valley, and in an area near Greenwater. 

The lahar consists of gray to yellowish-brown sand 

to angular and subangular blocks several tens of feet 

in diameter. In some places abundant large rock fragments are embedded in a loose sandy matrix; elsewhere 

the lahar consists largely of sand- and pebble-sized 

material. Pebbles were picked at random from the 

matrix of the lahar in a shallow pit on the west side 

of the White River valley aibou't 0.8 mile southsoutheast of Greenwater and examined for rock types. 

Pebbles derived from rocks of Mount Rainier made 

up 73 percent of the sample, those of granodiorite made 

up 7 percent, and those of volcanic rocks derived from 

other formrutions of Tertiary ·age made up the remainder. These pe!bbles were mostly subrounded ·and 

subangular. 

The mounds on the lahar are its unique feature. They 

range in height from 4 to about 35 feet and are a few 

tens of feet to about 200 feet in diameter. Most have a 

roughly circular ground plan, but some are elongate in 

seemingly random directions. Although most mounds 

have a single peak, some have two or more crests. The 

mounds are separated by fiattish areas that generally 
DESCRIPTION OF LAHARS 19 

TABLE 9.- Sequence of lahar assemblages and their stratigraphic relation to pyroclastic deposits (layers W, C, Y, and 0) in the White 

River and West Fork valleys 

White River valley West Fork valley 

Layer W 

Several lahars interbedded with fluvial gravels. Layer C 

Lahar 

Layer Y }

Post-Osceola lahar 

assemblage. 

Lahar and fluvial gravel 

Layer W 

Layer C 

Lahar 

Layer Y 

Post-Osceola lahar 

assemblage. 

Lahar 

Lahar 

Osceola Mudflow about 5,700 years old. Osceola Mudflow 

Several lahars interbedded with fluvial gravels. 

Lahar 

Two bomb-bearing lahars 

Greenwater lahar 

} 

Pre-Osceola lahar 

assemblage. 

Layer 0 

47"00' 

121°4 5' 

~I I' ' ' \ \I 

Little 

Taho m a 

Peak 

0 

I 2 I 

121 °30' 

4 MILES 

I 

FIGuRE 6.-Distribution of remnants of Greenwater laha r northeast of Mount Rainier is shown by the heavy pattern; its 

inferred original extent is shown in a light pattern. The lahar 

probably originated in massive rockslides from the northeast 

flank of Mount Rainier between Steamboat Prow and Little 

Tahoma Peak. 

slope both toward the center of the valley and downvalley. 

Some mounds have been partly excavated, and their 

internal composition can lbe seen. They are mostly 

made up of very l·arge blocks of rock, or clusters of 

Layer 0 

blocks, incorporated in an unsorted matrix of sand and 

smaller rock fragments. The blocks consist mostly of 

breccias from Mount Rainier. Two mounds were noted, 

however, that consist entirely of fragments of granodiorite. One of these, near the mouth of Buck Creek, consists of angular and subangular fragments, which range 

in maximum dimension from less than an inch to at 

least 6 feet (fig. 7). A search of adjacent mounds within 

a radius of a hundred yards located only one small 

boulder of granodiorite; the adjacent mounds are made 

up almost exclusively of rock fragments from Mount 

Rainier volcano, a few are made up of breccia from the 

Tertiary bedrock. 

The core of one mound, which is a,bout 20 feet high 

and 100 feet in diameter, in the area near Greenwater 

is made up of a large mass of flow breccia from Mount 

Rainier (fig. 8). The breccia is extensively altered to 

a plastic yellow clay, and some parts of it closely 

resemble the matrix of the Osceola Mudflow. This core 

of altered rock is veneered with a mixture of sand and 

rock fragments as large as a foot in diameter. The 

veneer is as much as 4 feet thick, and faint bedding in 

it that dips about 25° parallels the slope of the mound. 

The core of a nearby mound, which is about 10 feet 

high and 50 feet in diameter, is also a block of flow 

breccia from the volcano, but it is not altered to clay. 

The core of a mound in the same general area, but a 

little farther downvalley, consists of a block of reddishbrown and gray breccia which was derived from Mount 

Rainier. Some zones in this breccia are entirely altered 

to clay. A nearby mound that is about 12 feet high 

and 60 feet in diameter has been cut through by a road 

on the west side of sec. 9, T. 19 N., R. 9 E., 1 mile west 

of Greenwater. The interior of this mound is a jumble 

of angular and subangular rock fragments, and there 

is little or no matrix of finer material. Most of the fragments are from Mount Rainier, but a few are granodiorite and breccia derived from the Tertiary bedrock. 
20 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

FIGURE 7.-Mounds on the Greenwater lahar in the Buck Creek area. The mound at the right center consists wholly of 

angular blocks oif granodiorite ; it is 'RJbout 25 feet high and 100 feet in diam~ter. Adjacent mounds conSiist mostly of 

material derived from Mount Rainier 

The distribution of mounds within remnants of the 

lahar seems to be random; however, two of the mound 

groups are elongate in a downvalley direction, and in 

each of them the area of mounds is separated from the 

adjacent valley wall by a broad shallow depression that 

also is underlain by the lahar. 

The remnant of the lahar at the mouth of Huckleberry Creek extends back into the creek valley for more 

than half a mile. The surface of the lahar at the upvalley end of this backfill is about 200 feet higher than 

the present floor of the White River valley. Likewise, 

the highest remnant of the lahar in the vicinity of Buck 

Creek is about 200 feet higher than the White River, 

Although a thickness of more than 10 feet is rarely exposed, the vertical height of the lahar above the present 

valley floor suggests that the White River valley was 

filled to a depth of at least 200 feet during movement. 

The present surface of the lahar therefore, in most 

places, does not represent its original upper surface 

while it was moving. At the mouth of Huckleberry 

Creek, mounds dot the surface of the lahar in places 

100 feet lower than its inferred top during movement 

(pl. 2). 

The blocks that form the mounds probably were 

!brought down valley by an initial rush of the }ahar, came 

to rest, and remained in place while much of the finegrained fluid matrix of the lahar drained away from 

them and moved more slowly down the valley. The flat 

areas between the mounds, and between groups of 

mounds and the valley wall, probably were produced 

during this downvalley flowage of the fine-grained 

material. 

The Greenwater lahar was not recognized within 

Mount Rainier National Park for certain, although 

three large mounds in the valley of Fryingpan Creek, 

about 1 mile upstream from the mouth of the valley 

may be part of it. Comparable mounds were not observed anywhere in the White River valley within the 
DESCRIPTION OF LAHARS 21 

FIGURE 8.-:M:ound on the Greenwater lahar cOIIlSiists Olf an andesite breccia which was derived from Mount Rainier and which 

has been extensively altered to a plastic yellow clay. 

park, but their absence there may be due to burial beneath the Osceola Mudflow. 

The area thought to have originally been covered by 

the Greenwater lahar north of the park boundary is 

about 8 square miles. If it is assumed that the lahar had 

a thickness of 100 feet throughout this area after coming to rest, its original volume would have been a little 

more tha.n 800 million cubic yards. 

Near the upper limit of the lahar in the Huckleberry 

Creek valley a roadcut exposes the deposit on top of pyroclastic layer 0, which is about 6,600 years old. Although the Osceola Mudflow, which is about 5,700 years 

old, was not seen on top of the lahar, the topographic 

relations of the two deposits indicate that the Osceola 

is younger; thus, the Greenwater lahar is between 5,700 

and 6,600 years old. 

Mounds are known on the surfaces of lahars in the 

vicinity of other volcanoes, but they are by no means 

common. Aramaki (1963, p. 290-292) described a prehistoric mounded lahar on the south side of Asama 

420-479 0 - 71 - 4 

volcano in Japan. This lahar resulted from a phreatic 

eruption that destroyed the eastern part of Kurofuyama, the oldest of three major volcanoes that make up 

Asama. The material shattered by the explosion formed 

lahars that spread northward and southwestward beyond the volcano. The surface of the lahar southwest 

of the volcano is dotted with mounds arranged in groups 

that trend toward the southwest, the inferred direction 

of flowage; individual mounds are elongate in the same 

direction. The mounds have basa·l diameters of as much 

as 330 feet and heights up to 50 feet. The cores of most 

consist of very large blocks of pyroxene andesite from 

the volcano, some of which are 100 feet in maximum 

dimension. 

Hills that rise above the surface of a large Pleistocene lahar at the south base of Y atsuga-dake volcano 

inJapanhave been studied by Mason and Foster (1956). 

Many of these hills are substantially larger than those 

reported on other lahars; some have heights of as much 

as 700 feet and basal diameters of nearly half a mile. 
22 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

These large hills do not seem to have rock cores, and 

Mason and Foster concluded that the material of the 

hills was extruded above the top of the mudflow by hydrostatic pressure while still fluid, through cracks in a 

dried, hardened crust. 

The length of the lahar described by Mason and 

Foster is a little less than 15 miles, but its inferred original volume is at least 9.5 billion cubic meters, or 

roughly 2.3 cubic miles. The largest lahar from Mount 

Rainier, the Osceola Mudflow, has an inferred volume 

of ·a rrittle more than haH a cubic mile ( p. 26), and ,the 

Greenwater lahar only about a third of that. Mason 

and Foster suggested that the lahar originated in an 

avalanche of loose ejecta on the side of Yatsuga-dake 

that possibly was triggered by an earthquake or a volcanic explosion. 

A lahar whose surface is characterized by many 

mounds originated during an eruption of Komaga-take 

volcano in Japan that caused a large avalanche (Ishikawa and Yokoyama, 1962). The mounds are about 30 

feet high, and their cores are formed by blocks of lava 

from the volcano. 

Grange (1931) described the conical hills, which number in the thousands, on the slopes of Mount Egmont 

and Mount Ruapehu volcanoes in New Zealand. The 

mounds range in height from a few feet to 100 feet, but 

most are 25-30 feet high. The cores of most mounds 

th!Lt Grange examined consist of large blocks of agglomerate. He suggested that the blocks and the deposits 

that enolase them are of laharic origin. 

A plain studded with several thousand mounds lies at 

the southeast foot of Galunggung (Galounggoung) 

volcano on Java. The mounds are as high as 230 feet, 

and large andesite blocks form their cores. The blocks 

are enclosed in a matrix of finer rock debris similar to 

that between the mounds. The entire deposit is as much 

as 70 feet thick and has an estimated volume of nearly 

190 million cubic yards. The deposit heads at the mouth 

of a very large alcove in the southeast flank of the 

volcano. Escher (1925) concluded that the mounded 

deposit is an exceptionally large prehistoric landslide 

or mudflow from Galunggung. He suggested that when 

the side of the volcano slid outward and flowed downslope to the southeast, large blocks included in it came 

to rest first; continued downslope flowage of fine material lowered the overall surface of the mudflow and 

caused the blocks to protrude. 

It is noteworthy that in several of the lahars just 

described, mound dimensions are similar to those of the 

White River valley, and cores of large blocks from the 

volcanoes are found in all of them. However, the Greenwater lahar may be unique in having some mound cores 

that consist of rock not derived from the volcano. 

The Greenwater lahar is also unique among the lahars 

from Mount Rainier in that it contains abundant large 

blocks. Although the surfaces of some others have a few 

scattered blocks of andesite derived from the volcano, 

these blocks number only one or two dozen on ·any individual deposit. In contrast, scores of mounds thought 

to have block cores can be seen on nearly every remnant 

of the Greenwater lahar, and these seemingly deserve 

some special explanation. Glacial drift like that in 

Holocene moraines in the White River valley probably 

would not have been a suitable source, because blocks of 

rock comparable with those in mound cores are sparse. 

In contrast, large blocks are abundant in the 1963 rockfall and avalanche deposits from Little Tahoma Peak. 

(See Crandell and Fahnestock, 1965, p. A5-A8.) 

The abundant blocks in the Greenwater lahar therefore probably originated in rockfalls and rockslides 

from the slopes of the volcano and from the walls of the 

White River valley. The blocks of ·granodiorite could 

have fallen from outcrops at the head of the Fryingpan 

Creek valley, or from the walls of the White River 

valley between Emmons Glacier and the mouth of Sunrise Creek. 

The rockslides or rockfalls on the volcano may have 

been triggered by a steam explosion or by a.n earthquake 

which also shook down masses of granodiorite from the 

sides of the White River valley or at the head of Fryingpan Creek valley. 

Evidence of a volcanic explosion some time between 

5,700 and 6,600 yea!IS ago is present in the form of pyroclastic layer S in the Yakima Park area and on top of 

Goat Island Mountain (Crandell and Mullineaux, 1967, 

p. 7). The layer consists of an unsorted mixture of sand, 

silt, and angular rock fragments as large as 1.5 feet 

across and is entirely derived from Mount Rainier. The 

lack of new pumice or scoria suggests that the rubble 

was formed by a steam explosion that blew out previously solidified rock in the northeast flank of the 

volcano. Although there is no known way to make a firm 

correlation between layer S and the Greenwater lahar, 

the explosion that created the pyroclastic deposit could 

also have triggered the rockslides that caused the lahar. 

The absence of clay from the matrix of the lahar 

points to relatively fresh rock as the chief source; however, the presence of blocks of clayey, altered rock suggests that some of the material came from areas of 

hydrothermal alteration. The main source area of the 

lahar probably lay between Little Tahoma Peak and 

Steamboat Prow. In fact, these two features may be the 

only surviving remnants of the northeast side of the 

volcano that was largely destroyed when the lahar was 

formed. 
DESCRIPTION OF LAHARS 23 

The great rockslides that created the Greenwater 

lahar may have stripped a mass of mostly unaltered 

rock from the northeast flank of the volcano, t:hereby 

not only exposing the underlying rocks that had been 

extensively altered by hydrothermal solutions but also 

removing the support from these altered rocks. Thus, 

the events that created the Greenwater lahar may have 

set the stage for the subsequent rockslides that produced 

the Osceola Mudflow. 

PRE-OSCEOLA LAHAR ASSEMBLAGE 

A sequence of lahars and fluvial deposits, hereafter 

referred to as the pre-Osceola lahar assemblage, is exposed at many places along the White River valley 

within the park. Farthest upvalley, this assemblage 

consists of two lahars that contain volcanic bombs and 

one that does not contain bombs. These three lahars are 

exposed in the south bank of the White River about 

half a mile upstream from the highway bridge over the 

river. Were it not for a few inches of stratified sand 

between them, the two bomb-bearing lahars probably 

could not be differentiated from one another. Both are 

gray, have a matrix consisting mostly of coarse friable 

sand, and contain abundant angular and subangular 

fra<Yments of dense flow rock from Mount Rainier as 0 

large as 10 feet in diameter. Bombs, which are sparsely 

scattered throughout the lahars, range in maximum 

dimension from 6 inches to several feet; all are strongly 

bread crusted, and none have been modified by erosion. 

Some masses of dense flow rock are also breadcrusted 

(fig. 9). The lower lahar is more than 20 feet thick and 

probably extends below the level of the White River. 

The upper lahar is about 12 feet thick and is successively 

overlain by a lahar about 20 feet thick in which bombs 

were not seen and by the Osceola Mudflow. The mudflow forms the top unit and caps a broad terrace about 

100 feet a;bove the river; owing to an erosional unconformity, the Osceola locally also lies below river level. 

The three lahars in the assemblage contain very little 

silt or clay. The two bomb-bearing lahars were seen 

nowhere else in the valley, and their original extent is 

not known. 

Remanent magnetism determinations made on oriented samples from three bombs in the upper lahar 

and from five in the lower show a random orientation 

of the direction of remanent magnetism; thus, the temperature of the bombs apparently was below the Curie 

point of the included ferromagnetic minerals when the 

lahar oame rt.o rest (p. 5). Although the material in 

the lahars could have had a temperature above the 

boiling point of water, it seems more likely that the 

masses were cooler and were moving as lahars when 

they came to rest, rather than as hot dry avalanches. 

FIGURE 9.-Large breadcrusted block of dense flow rock in a 

lahar exposed in south bank of the White River about half 

a mile downstream from White River campground. 

However, the lahars may have originated in such avalanches that descended Emmons Glacier and melted 

large amounts of snow and ice. 

A roadcut on the south side of the valley near the 

south end of the highway bridge over the White River 

exposes a lahar that has a sandy matrix and is about 

40 feet thick. The lahar rests on granodiorite and is overlain by the Osceola Mudflow. One or more pre-Osceola 

lahars also are exposed on the north side of the valley 

a few hundred feet northeast of the bridge. 

Farther downstream, the pre-Osceola lahar assemblage is exposed on the south side of the White River 

about half a mile below the highway bridge across the 

river. In this area the assemblage is at least 80 feet thick 

and consists of several lahars 3-30 feet thick that are 

interbedded with fluvial deposits. The assemblage crops 

out half a mile farther downstream in a high bank near 

the mouth of Fryingpan Creek, where the material is 

mostly stratified and consists largely, if not wholly, of 

fluvial deposits. The assemblage also is seen in cuts along 

the highway between Fryingpan Creek and the White 

River Ranger Station and in the face of a terrace on the 

west side of White River 1 mile downstream from the 

mouth of Crystal Creek. At this northernmost exposure, 

more than 50 feet of coarse bouldery lahars and pebbleto-boulder gravel of fluvial origin forms a terrace that 

is capped with a few feet of Osceola Mudflow. The base 

of the lahar assemblage also apparently lies below the 

level of White River here. 
24 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Although it is possible that some of the deposits just 

described are those of the Greenwater .Jahar, t;he absence of very large blocks suggests that they are not correlative. Furthermore, the Greenwater lahar forms a 

fill in the White River valley north of the park that is 

as much as 200 feet ·above the valley floor. The depositional top of the pre-Osceola lahar assemblage is nowhere known to extend to a height greater than about 

80 feet above the White River. Topographic relations 

imply that the lahar assemblage is younger than the 

Greenwater lahar and thus lesS than 6,600 years old, 

because the Green water lahar postdates pyroclastic 

layer 0 of that age. 

The lahar assemblage forms a valley fill that was dissected to a depth of 200-250 feet by the White River 

before the Osceola Mudflow occurred. The base of the 

lahar assemblage is ·below the White River at nearly 

every outcrop; at many of these outcrops the Osceola 

unconformably overlies the lahar assemblage, and its 

base is also below river level. The deposition of the 

assemblage, which was followed by downcutting, was 

probably not climatically controlled, as is valley aggradation in some regions. Instead, the presence. of 

breadcrust bombs in two of the lahars strongly suggests 

that the aggradation was the result of volcanism. 

The pre-Osceola lahar assemblage probably originated as a direct consequence of hot rock debris avalanching down Emmons Glacier during or shortly after 

eruptions at the summit of the volcano. The assemblage 

was probably formed by floods and lahars caused by the 

rapid melting of snow. The building up of the lahar 

assemblage in the valley thus is thought to have been 

caused by large quantities of rock debris added to the 

White River as a result of volcanic activity. With the 

cessation of eruptions and of lahar deposition in the 

White River valley, the river cut down into the valley 

fill. No significant unconformities were noted within 

the lahar assemblage, and all the deposits within it 

probably were formed within a relatively short time, 

perhaps not more than a few years. 

OSCEOLA MUDFLOW 

The Osceola Mudflow is by far the largest mudflow 

of postglacial age from Mount Rainier and is one of the 

largest known volcanic mudflows in the world. Many of 

the facts concerned with the distribution, age, and origin of the mudflow have been discussed previously 

(Crandell and Waldron, 1956; Crandell, 1963a, b). 

The Osceola was first described by Willis (1898, p. 

143) as "a sheet of till that covers the plateau between 

the Green and White Rivers and extends southwest beyond White River about the head of Fennel Creek" 

(pl. 3). He correctly recognized the Mount Rainier 

provenance. of the deposit, but thought that the Osceola 

had been formed by a piedmont glacier that issued into 

the lowland from the Cascade Range. Willis noted that 

knobs of Vashon till deposited during the last major 

glaciation are topogr31phically higher than the surface 

of the adjacent Osceola deposit, and he thought that this 

indicated that the Osceola was somewhat older than the. 

Vashon till. 

Investigation of the Osceola (Crandell and Waldron, 

1956; Crandell, 1963b; Mullineaux, 1961, 1965a, b) has 

shown that the mudflow overlies the Vashon Drift and 

that the upper part of the drift contains a soil profile. 

This soil was formed after the Puget glacier lobe withdrew from the southeastern part of the Puget Sound 

lowland, about 14,000 years ago, and before the mudflow occurred. Four radiocarbon dates obtained from 

wood incorporated in the mudflow range from 

4,700+250 (W -564) to 5,040+150 (University of 

Washington radiocarbon date No. 62; this report, table 

4) . When corrected for variations in atmospheric C" 

and for a C" half life of 5,730 years, these ages range 

from 5,550 to 5,800 years; a "true" age of about 5,700 

years is here arbitrarily assumed for the Osceola 

Mudflow. 

DISTRIBUTION AND VOLUME 

ithin Mount Rainier N·aJtional P·ark the Osceola 

Mudflow underlies terraces in the White River and West 

Fork valleys and veneers valley sides above the terraces. The mudflow is, however, not well preserved in 

these valleys near the volcano because of erosion by 

younger valley glaciers. The largest outcrops of the 

Osceola close to the volcano are in the valley of Inter 

Fork. Near the mouth of the valley the mudflow is 

banked against a lateral moraine of Evans Creek Drift, 

which constricted the valley and caused the mudflow 

to accumulate behind it to a thickness of as much as 100 

feet. Farther upvalley, the mudflow veneers bedrock 

and glacial drift on the floor of Glacier Basin and on 

the floor of a high cirque directly north of the basin. 

During the Winthrop Creek Glaciation, Inter Glacier 

reworked part of the mudflow deposit and formed a 

series of lateral moraines in the upper part of Glacier 

Basin. 

The mudflow is preserved at many places on the 

ridgetops at the head of Inter Fork valley; the highest outcrop is at the top of Steamboat Prow at an altitude of 9,700 feet. On the ridgetop between Glacier 

Basin and the unnamed cirque directly to the north, 

several feet of the mudflow veneers a lava flow. Iron 

oxide, apparently derived from the mudflow, has impregnated the flow rock, forming a resistant iron-rich 

crust at its surface. This crust was recognized by Fiske, 

Hopson, and Waters ( 1963, p. 85), but they thought 
DESCRIPTION OF LAHARS 25 

that it had formed beneath deeply weathered volcanic 

ash, whereas the crust in fact lies beneath a remnant of 

iJhemudflow. 

Downstream from Inter Fork, above White River 

campground, the Osceola blankets a lateral moraine on 

the north valley wall to a height about 500 feet above 

the present valley floor. Pits dug on the crest of the next 

higher lateral moraine, which is about 1,000 feet above 

the valley floor, revealed a clayey deposit in the stratigraphic position of the Osceola Mudflow. 'Dhe deposit is 

pale yellow and contains small rock fragments; it may 

be part of pyroclastic layer F (table 5; p. 12). The 

mudflow evidently did not reach this height on the val· 

ley wall. 

According to information provided by H. W. Ander· 

son of the U.S. Geological Survey (written commun., 

December 1964), the Osceola Mudflow was penetrated 

at a depth of about 50 feet during drilling for a water 

well at the Silver Creek Ranger Station, on the White 

River valley floor near the north boundary of the pa.rk. 

The well was still in the mudflow when drilling was 

stopped at a depth of about 200 feet. The mudflow 

veneers the sides of the valley to a height of about 125 

feet a few miles downstream from the Silver Creel\ 

Ranger Station. At Federation Forest State Park about . ' 14 m1les downstream from Silver Creek, a well was reported by Mr. Anderson to have entered the Osceola 

Mudflow at a depth of about 200 feet beneath the valley floor. In this area the top of the mudflow forms a 

terrace thatt is about 35 feet higher than ,tJhe White 

River (fig. 10). 

This information from drilling on the valley floor 

indicates that the valley was at least 200 foot deeper 

when the mudflow occurred than tt is today. The mudflow must have temporarily filled the valley near Silver 

Creek Ranger Station to a depth of more than 300 feet 

during movement. 

The Osceola Mudflow also coats valley sides and 

forms terraces in the West Fork valley. The highest 

outcrop of the mudflow in the West Fork drainao-e 

basin, other than the one on Steamboat Prow is at :n 

altitude of about 6,800 feet just west of Winthrop Gla· 

cier. 'Dhe mudflow crops out in streambanks along the 

West Fork and Winthrop Creek at many places. On 

the east bank of the river at the mouth of Winthrop 

Creek, the base of the mudflow is below river level and ' its eroded top is 25 feet above the river. Successively 

above the mudflow are a layer of organic matter that 

contains logs, a coarse gravel deposit, and another lahar. 

At a point about 2.5 miles upstream from the mouth 

of West Fork vaHey the Osceola veneers the northwest 

valley wall to a height of about 320 feet above the val· 

ley floor, and at the mouth of the valley the mudflow ex· 

FIGURE 10.-0sceola Mudflow exposed in the face of a terrace 2 

miles southeast of Greenwater. Drilling for a well a few 

miles downstream from this point revealed that the mudflow 

extends to a depth of about 200 feet beneath the valley floor. 

The largest boulder in the center of the photograph is about 

6 feet in diameter. The fluvial sand and gravel that underlies 

the mudflow in the foreground probably is an old terrace deposit that was mantled by the Osceola. 

tends below river level. If the pre-Osceola valley of 

West Fork was as deep as that of the White River (see 

above), the Osceola may have temporarily reached a 

depth of at least 500 feet in the lower part of the West 

Fork valley. 

Forty miles downvalley from Mount Rainier, just 

inside the Cascade mountain front, the White River 

passes through a bedrock gorge th!lit is now blocked by 

Mud Mountain Dam. The gorge lies at the south edge 

of the ·white River valley, which is about 3 miles wide 

in this vicinity. A J.ong, narrow, ftat-lt.opped ridge (Mud 

Mountain) several hundred feet high, which extends 

southward across the broad White River valley, is made 

up largely of unconsolidated deposits that range in age 

from early or middle Pleistocene to late Pleistocene. 

The Osceola Mudflow was temporarily at least 450 feet 

deep in this part of the valley and cascaded in a sheet 

nearly a hundred feet deep down the west slope of 

Mud Mountain to the floor of a glacial melt-water channeL The mudflow poured from the Mud Mountain area 

into the Puget Sound lowland along several different 

routes (pl. 3). 

West of the mountain front the Osceola spread widely 

on a plain of Vashon till and melt-water deposits. The 

mudflow is only a few feet thick on some topographic 

scarps and till drumlins; elsewhere it is as much as 

75 feet thick. A high degree of fluidity permitted the 

mudflow to flow long distances down narrow topographic depressions on the drift plain. As a result the 
26 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Osceola finally came to rest in the lowland as a lobe as 

much as 8 miles wide and 20 miles long with very uneven, or digitate, margins (pl. 3). 

The mudflow profoundly changed the lower course 

of the White River. Before the mudflow, the river 

turned southward where it debouched from the mountain front and followed the valley of South Prairie 

Creek to join the Puyallup River near Orting. When 

the mudflow rushed out onto the drift plain, one lobe 

_of it extended down the old White River valley, but 

the greatest share flowed northwesterly across the plain, 

inundating all but the highest relief features. As the 

mudflow became more dilute and approached the consistency of a muddy stream, it became the White River; 

this river began to cut a new valley along the axis of 

the broad lobe, trending northwestward toward Auburn 

(Crandell, 1963b). 

The mudflow crops out in banks of the Puyallup 

River and has been penetrated in wells drilled into the 

flood plain south of Sumner (Crandell, 1963b). The 

Osceola also has been identified at a depth of about 265 

feet below sea level, beneath the floor of the PuyallupDuwamish valley, 4 miles northwest of Auburn (Luzier, 

1969, p. 14). At the time of the mudflow the PuyallupDuwamish valley was an arm of Puget Sound between 

Orting and Renton. This arm was filled first by the mudflow and later by deposits of the White River (Mullineaux, 1961, p. 185; Crandell, 1963b, p. A68). 

At least 30 blocks of reddish-brown breccia derived 

from Mount Rainier are scattered on the surface of the 

mudflow. The largest measures 30 by 40 feet and stands 

20 feet above the mudflow surface; it is located about 4 

miles west of Enumclaw. Nearly all these blocks are 

situated along topographic breaks in the mudflow surface that coincide with scarps in the buried drift plain. 

More than half the blocks in the Buckley-Enumclaw 

area lie along a northwest-facing scarp 1 mile west of 

Enumclaw that represents a side of a buried melt-water 

channel; the opposite side was formed by the glacier 

itself (Crandell, 1963b, p. A66, pl. 2). Blocks are probably concentrated along this scarp beeause the mudflow 

thinned considerably while flowing over it, and the large 

blocks became grounded on the underlying surface much 

as icebergs become grounded in shallow water. The 

presence of lower ground immediately northwest of the 

scarp permitted the fine matrix of the mudflow to drain 

away and leave blocks standing above the surrounding 

surface. The concentration along this scarp, as well as a 

lack of blocks to the southeast, suggests that this was the 

first place in the lowland where the mudflow thinned 

sufficiently for the blocks to become grounded. 

The volume of the Osceola Mudflow can be estimated 

on the basis of the known area of distribution of the 

flow, if several assumptions are made concerning its 

total inferred area and thickness: The mudflow originally covered a total land area of at least 100 square 

miles, in addition to a submerged area in the Puyallup 

River valley where the mudflow extended into ·a former 

arm of Puget Sound (pl. 3). The mudflow probably 

extended as far south in the Puyallup River valley as 

the confluence of the Puyallup and Carbon Rivers, as 

far west as the town of Puyallup, and northward in the 

Green River valley to the outski~ts of Kent ·and covered 

a submerged area of at least 27 square miles. The mudflow has subsequently been removed from a considerable part of its former total area by stream erosion or 

has been buried by younger alluvium. The mudflow 

ranges in thickness from a few feet to at least 200 feet. 

It is a reasonable assumption that the Osceola had an 

original average thickness of 20 feet over the land areas 

it covered; if it did, the mudflow would have had a 

volume of about 2 billion cubic yards. If the Osceola 

had had a comparable average thickness in the submerged areas, there would have been an additional 

volume of about 660 million cubic yards, making a 

probable total volume of a little more than half a cubic 

mile. 

TEXTURE AND MINERALOGY 

Grain-size distribution studies were made of samples 

of the Osceola Mudflow taken from outcrops at nine 

localities in the Cascade Range (samples 29-37, table 

10), from a point near Auburn to Glacier Basin (pl. 

3). Most of the samples were collected from a 3-footwide vertical trench at a depth of 4-7 feet below the 

mudflow surface. Because boulders are sparse at this 

depth, the samples represent the average texture of 

the mudflow in this zone. At greater depths, the cobble 

and boulder content increases and coarse material makes 

up a large proportion of the lower third of the deposit. 

The texture of the samples at each locality is shown 

in ta.ble 10; the clay-sized fraction of the samples ranges 

from 6 to 12 percent, the silt·-sized fraction from 11 to 

16 percent, and the sand-sized fraction from 28 to 41 

percent. The sorting coefficients of these samples range 

from 9 to 16.34 and average 11.53. The cumulative 

curves prepared from the size-distribution data are 

presented in figure 11. 

The overall texture of the mudflow does not seem to 

change with increasing distance from its source. The 

sample having the highest proportion of material 

smaller than 2 mm, as well as the lowest sorting index 

(sample 35), came from the crest of Mud Mountain. 

The material sampled there is a veneer left after the 

main body of the mudflow spilled across the top of a 

:vidge (p. 25). 
DESCRIPTION OF LAHARS 27 

TABLE !D.-Size-distribution data from samples of postglacial lahars and a block-and-ash flow from Mount Rainier 

[Arranged by age from youngest at top to oldest at bottom) 

Size distribution (percentage) Sorting 

Sample Clay Silt Sand 

( <0.004 =l (0.()()4.-{).0625 (0.0625-2 mm) 

Median 

diameter <=l Sorting co- Phi standard Phi Qutntllo efficient (So) deviation deviation 

=> (v<f>) (OD<t>) 

} ___ ___ ___ ____________ _____ _______________ ___ 4 10 49 0. 8 8. 10 4. 35 3. 03 

2-------------------------------------------- 4 11 60 6 3. 41 2. 78 1. 78 

3-------------------------------------------- 2 10 35 2. 8 13. 40 4 4. 10 

4-------------------------------------------- 7 7 32 2. 9 5. 48 3. 95 2. 48 

5-------------------------------------------- 3 11 31 4 7. 75 3. 85 2. 98 

6--------------------------- ----------------- 11 25 58 1 3. 94 3. 15 1. 70 

1-------------------------------------------- 7 13 37 1 8. 83 4. 36 3. 15 

8-------------------------------------------- 9 18 45 3 7. 42 4. 74 2. 90 

9-------------------------------------------- 3 11 29 4. 2 8. 72 4. 2 3. 13 

10------------------------------------------- 6 ---------- 40 3. 6 8. 88 3. 94 3. 20 !! ______________________________ _______ ______ 12 17 40 4 9. 75 4. 95 3. 29 

12------------------------------------------- 5 13 33 1. 9 10. 60 4. 58 3. 42 

13----------------------------------------- -- 8 16 21 1. 1 14. 18 5. 13 3. 83 

14-------------------------- --------- -------- 5 17 36 8 11. 20 4. 76 3. 50 15 _________________________________ ___ _____ __ 7 13 33 1. 6 9. 56 4. 54 3. 28 16 _________________________ __________________ 9 13 45 5 6. 70 4. 16 2. 75 17 ___________________________________________ 7 ---------- 43 2 5. 48 3. 43 2. 72 

18------------------------------------------- 5 ---------- 38 3. 2 10. 82 3. 56 3. 44 19 ___________________________________ ____ ____ 1 5 46 1. 5 6. 63 3. 99 2. 74 

20--------------------------------- ---------- 1 5 51 1. 1 4. 64 3. 11 2. 21 21 _________________________________ ____ _____ _ 1 15 37 1. 5 9. 84 4. 80 3. 30 22 __ ___________________________ __ __________ __ 2 10 27 12. 5 13. 20 ---------- 3. 73 23 _______________ ____________________________ 1 13 31 4. 2 13. 60 4. 66 3. 77 24 _____ ___ ___________________________________ 5 28 44 2 7. 75 4. 35 2. 90 

25------------------------------------------- 1 7 16 13 9. 04 2. 90 1. 53 26 _______ __________ __________ _______ _________ 2 16 32 2 14. 56 4. 97 3. 88 27 ________ __ _________ ________ _________ ____ ___ 4 15 33 1. 4 15. 75 4. 91 3. 99 28 __________________________ __ ___________ ____ 3 14 27 4. 3 16. 25 4. 94 4. 03 29 _______ __________________________ ______ ____ 9 13 28 2 11. 53 5. 23 3. 54 

30------------------------------------------- 12 16 31 7 16. 34 5. 79 4. 10 31 _______________ ____ ___________ __ ___________ 8 15 35 8 11. 27 4. 82 3. 50 32 _______________ ______ _____________ ___ ______ 9 12 31 1. 6 12. 85 5. 25 3. 70 33 ___________________ __ ______ __ ______ ____ ____ 7 11 33 1. 8 14. 63 5. 12 3. 88 34 ________ __ _________ ________ ________ ____ ____ 8 15 35 9 11. 62 4. 90 3. 58 35 ____ _______ ____ ________ ________ ______ ______ 8 15 41 6 9 4. 58 3. 18 36 _________ ____ ____________ _______ _________ __ 7 13 35 1. 3 10. 02 4. 61 3. 18 37 _____________________________ ____ _____ ___ __ 6 14 36 1 11. 79 4. 95 3. 20 38 __ ___________ ____ _________________ _________ 2 12 36 2 10. 86 4. 38 2. 34 39 ___ __ ____________ ____ ____________ ____ ______ 9 ---------- 51 1 6. 25 3. 53 2. 70 40 __________________________________ ____ _____ 7 41 _______ ___ _________ ________ ________ ______ __ 3 

1. Kautz Creek lahars (}f 194>7 .. North bank of Nlsqually River '(, mile 

upstream from mouth of Kautz Creek. Sample of a fairly coarse lahar. 2. Kautz Creek lahars of 1947. Same location as s·ample 1. Sample of a relatively fine-grained lahar. 

3. Post-Osceola lahar in West Fork valley. Roadcut at the west side 

of sec. 26, T. 19 N., R. 9 E. Sample of unoxidized lahar that over- lies pyroclastic layer Y. 

4. Lahar in South Puyallup River valley. Exposure adjacent to Wonderland Trail near south abutment of footbridge over South 

Pupal! up River (fig. 25). Sample of unit 3 in measured section 10. 

5. Lahar in South Puyallup River valley. Same location as sample 4. 

Sample of unit 1 in measured section 10. 

G. Electron Mudflow. Streambank SJt confluence of Carbon and 

Puyallup Rivers near 1\IcMillin In the Puget Sound lowland. 

S•ample taken from top foot of mudflow. 

7. Electron Mudflow. Same location as sample 6. Sample taken from 

basal foot of mudflow. 

8. Electron Mudflow. North bank of Puyallup River about 1 mile 

downstream from the mouth of the Mowlch River, in the SWl~ 

sec. 34, T. 17 N., R. 6 E. (fig. 25). Sample of unit 4 in measured 

sootlon 7. 

9. Lahar in 'l1a.homa Creek valley. North bank of Tahoma Creek 1.25 

miles upstream from '!.'ahoma Creek campground (fig. 25). Sample of lahar that Is unit 9 In measured section 9. 

10. Lahar In Tahoma Creek valley. Same location a,s sample 9. Sample of lahar that Is unit 6 In measured section 9. 

11. Lahar in South Puyallup River valley. North bank of South 

Puyallu•p River at Wonderland Trail footbridge (fig. 25). Sample of 1,000-year-old lahar. 

12. Round Pass Mudflow. Same location as sample 9. Sample of untt 3 

In measured section 9. 

13. Round Pass Mudflow. Roadcut at Round Pass (fig. 25). Sample of 

brown facies of mudflow. 

14. Round Pass Mudflow. Roadcut at Round Pass. Sample of purplishgray facies of mudflow. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

23. 

24. 

25. 

26. 27. 

28. 

35 33 1 10. 20 5. 22 3. 76 

18 32 1. 3 17 5. 03 4. 10 

Round Pass Mudflow (fig. 25). North bank of Mowlch River at its 

mouth. Sampte of mudflow at a horizon about 20 feet above river 

level. 

Lahar in Puyallup River valley. SB.!lile location as sample 8. Sample of 1,000-year-old lahar that Is unit 2 in measured section 7. 

Lahar in Muddy Fork valley. Terrace on east side of Muddy Fork, 

and 6'5 feet higher than river level, about Y, mile upstream from 

highway bridge at &x Canyon. Sample of a pre-W, post-Y lahar 

that underlies the terrace. Labar In Nisqually River valley. Roadcut in terrace on east side of 

the Nisqual!y River near the mouth of the Paradise River. Sample of a post-Y, pre-W lahar that directly underlies the terrace. Block-and-ash flow deposit in South Puyallup River valley. Roadcut 

0.2 mile northwest of bridge over river (fig. 25). Sample of coarse facies of deposit that contains breadcrust bombs and is about 

2,500 years old. 

Block-and-ash flow deposit In South Puyallup River valley. Roadcut 

0.4 mile northwest ()f bridge over river. Sample of fine facies of 

rlepostt r epresented by sample 19. Lahar in Nisqually River valley. Roadcut 0.2 mile southwest of 

Longmire. Sample of unit 6 In measured section 4. 

Post-Osceola lahar in West Fork valley. Same location as sample 3. 

Sample of oxidized lahar that underlies pyroclastic layer Y. 

Paradise lahar. Bank adjacent to parking lot 200 feet northwest of 

visitor center at Paradise Park. 

Paradise lahar. Cut adjacent to trail to Paradise ice caves, near west base of Mazama Ridge. Paradise lahar. Bank along Paradise River about Y, mile northeast 

of Narada Falls. Paradise Iabar. Roadcut about lh mile east of Ricksecker Point. 

Paradise lahar. Same location as sample 21. Sample of unit 4 In 

measured section 4. 

Paradise lahar. Roadcut near the center of sec. 5, T. 14 N., R. 8 E., In 

the Nisqually River valley near the south edge of Mount Rainier 

National Park. 

Footnotes continued on following page. 
28 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Footnotes continued from previous puge, 

29. Osceola Mudflow. Bank of Inter Fork near old Storbo Camp In 

Glaclo;n- Basin. 

30. Osceola Mudflow. Roadcut about '"h mile north of highway bridge <Over Frylngpan Creek. 

31. Osceola Mudflow. Roadcut In the West Fork valley about '"h mile 

north of the mouth of Jim Creek. 

32. Osceola Mudflow. Roadcut In the White River valley along U.S. Highway 410 about 0.1 mile north of the mouth of Ranger Creek. 

33. Osceola Mudflow. Bank on east side of the White River In the NW'A sec. 14, 'I'. 19 N., .R. 9 E., 2 miles southeast of Greenwater. 34. Osceola Mudflow. Roadcut a long U.S. Highway 410 near the mouths 

of East and West Twin Creeks. 

35. Osceola Mudflow. Roadcut near the center of the south edge of sec. 8, 

T. 19 N., R. 7 E. (approach road to spll!way at Mud Mountain 

Dam). 

E 

E 

w 

N 

en 

0 

0 

100 

w 

f-5 90 

0 

z 

z 

<( 

I 

ffI 

(!) 

80 

70 

~ 60 

>-

!D 

50 

E 

E E 

E ~ 

q ~ 

0 ci 

A 

(sa 

0:: 

w 

z 

u:: 40 

T~~~~~e~~), 

en 

w 

-' 

~ 30 0:: 

<( 

0.. 

u. 20 0 

w 

(!) 

~ z 

w 

u 

0:: 

w 

0.. 

10 

0 

In fa,>; 

~ ::J 

.-;:~ ~ f-•.f.:; b0/ .... 1--' ~ 

....... f.-"~' ..... 

36. Osceola l\Iudflow. Exposure along the north wall of the White River 

valley near the center of the SE',4 sec. 29, T. 20 N., R. 6 E., about 

2.5 miles northwest of Buckley ln the Puget Sound lowland. 

37. Osceola l\fudfle>w. Exposure at top of blu1f overlooking the Green 

lliver valley, at the east edge of sec. 28, T. 21 N .. , R. 5 E., about 

2 miles southeast of the town of Auburn In the Puget Sound 

lowland. 38. Lahar ln Nlsqually River valley. Same lt>Cation as sample 21. Sample of unit 1 In measured section 4. 

39 . Lahar In White River valley. South bank of river about midway between White River campground and highway bridge across river. Sample of lowest bomb-bearing la!Iar. 

40. Lahar at Van Trump Park. Bank of shallow ravine about 800 feet 

northeast of trail sh elter. Sample from lahar that pre-dates pyr<r clastic layer 0 and that may have originated more than 11,000 

years ago. 41. Lahar at Paradise Park. Same location as sample 23. Sample of lahar 

that underlies the Paradise lahar. 

E E 

E E E 

E 0 0 0 q 0 0 ~ ~ 

IUbL :rn 

:npl H7: 

k~ v 

k< 

~ v 

CLAY SILT SAND GRANULES PEBBLES COBBLES 

FIGURE 11.-0umumtive curves of the Size distribution of samples of the OsceoLa Mudfi.ow. The shaded zone represents the 

area covered by the curves of samples from eight localities; three of these samples are represented by individual curves 

as labeled ; sample number refers to table 10. 

The samples obtained :from two different localities in 

the Puget Sound lowland (localities near Auburn and 

Buckley, samples 37 and 36) show about the same degree 

o:f sorting. FufltJhermore, the sorting coefficient o:f the 

sample obtained at the outcrop near Auburn (sample 37) 

is nearly the same as that of the sample :from Glacier 

Basin (sample 29), even though the two localities are 

nearly 70 miles apart. The only downvalley change in 

texture noted in the lowland is an apparent decrease in 

the maximum size of stones in the basal zone of the mudflow, but this observation was not quantitatively 

verified. 

The highest sorting coefficient, 16.34, was determined 

on a sample from the locality near Fryingpan Creek 

(sample 30). Although the sample came from near the 

top of the outcrop there, the actual top of the mudflow 

during flowage probably was 100-200 :feet higher than 

the sample horizon. The deposit :from which the sample 

was obtained is a veneer le:ft a:fter most o:f the mudflow 

passed downvalley. 

The Osceola Mudflow is unique among the lahars in 

the White River drainage basin because o:f its relatively 

high clay content. Clay minerals make up :from 60 to 80 

percent of the clay-sized :fraction of each sample. Montmorillonite and kaolinite predominate in various propoDtions in every sample of the deposit (table 11, 

samples 29 through 37), and other day minerals are 

present in some samples. The remainder o:fthe clay-sized 
DESCRIPTION OF LAHARS 29 

TABLE 11.-M in era logy determined by X -ray analysis of clay-sized fraction of lahars 

[Values are estimated parts In 10. Localities and ages of the samples are given in table 10. Leaders ( ... ) , not present; Tr., trace; n.d., not determined] 

., 

13 .21 0 

"§ .21 

·.: ., ~ 'E- :2e '2-e a-

~ of! ...,, 

a"' %"' ~~ §~ 5 Sample ~ §"§ '2~ -gs a.s &>a ::l ~ 0 a ... o,.. E~ ....... "' :!! ., 

~ :a~ ·~., .<:: 

~ ., .21 d;,~ cl» .8~ il ... 0 

13~ .21 O"' ~ Ool "' .<:: 

§ 

~ S"' a.,. -5~ 

~ "" !l e .g ::::a) ] +>a) il~ il~ "' 0 

~ "" § 0 c o,. c.., :; c 0 "'·~ .c a s ::rs Sf§ ~ Ql 0 .§ ::s ~ ~a u I%. CJ -< -------------

2 __ __ ____ ________ ---- -- - ----- -------- -- - - -- ------ -------- - ------- -------- ------ 9 n.d. 1 n.d. 

3_ __ ____ __ _______ 1 2 2+ ---- - - -------- ------ -------- -------- ------ 1+ ------ Tr. 1+ -1 

4____ ________ ____ 5 - ----- -- ------ ------ ------ -------- -------- -------- -- 2 ------ n.d. 3 n.d. 

5________________ 5 ----- - - - -- - --- ------ ------ -------- -------- ---- ---- - ----- 2+ n.d. 2+ n.d. 

6__________ ______ 6 Tr. __________ ___________ _____ ____ ___ ___ -------- -- ---- 2 n.d. 1 n.d. 

8_____ __________ _ 3 ------ ------- - 1 ------ -------- -------- -------- - - ---- 3 -1 n.d. 2+ n.d. 

9 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 + Tr. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. _ _ _ _ _ _ _ _ _ _____ - - -- - - -- 2 Tr. 2+ 1+ 

11___ ______ ____ __ 4 ------ - -- ----- ------ - ----- -------- -- ------ --- --- - - ------ 4 n.d. 2 n.d. 12-- ------ Tr. ______ ____ ___ _ 1+ -1 -1 __ ______ ______ __ -1 2+ ------ -1 1+ Tr. 

14_ ___________ ___ 3 - ----- ----- - -- ------ ------ 1 -------- -------- - ----- 3 Tr. -1 2 -1 

15___ ____________ 4 ------ -------- ------ - - ---- -------- -------- ----- --- -- - --- 3 n.d. 3 n.d. 16________ _______ 3 ------ - ------- ------ ------ - - ------ -------- -------- ------ 4 n.d. 3 n.d. 

18 _______ ________ - - ---- ------ -------- ----- - - ---- - -------- ------- - -------- ------ 3 1 6 n.d. 21___ ____________ Tr. ___ ______ ___ __ ____ ______________ _________ __ _____ __ ------ 5 -1 3 1 

23_____________ __ 3+ 2 - - ------ ------ ------ - - ------ -------- -- - ----- ---- -- 1+ Tr. - 1 1+ 1 

27 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 4 2 -1 2 -1 

29 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5 3 _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. __ ______ ______________ - _ ------ 1 1 n.d. 1 n.d. 3Q___________ ___ _ 6 1 ----- - ----------- --- - ------- ------------ -- - - ------ Tr. 3 n.d. 1+ n.d. 

31_______________ 3 2 - - ------ ------------ -------- -------- 3 - ----- 1 1 n.d. -1 n.d. 32 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6 2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. _ _ _ _ _ _ _ _ _ ____ _ 1 1 n.d. 1 n.d. 33 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5 2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. _ _ _ _ _ _ _ _ - ___ - - 3 Tr. n.d. 1+ n.d. 34_______________ 2 2 -------- ------ 2 2 -------- -------- ------ 1 1 n.d. -1 n.d. 35----- ---------- 1 2 -------- ------ 2 1 - ---- --- - ------- ---- -- 1 2 n.d. -1 n.d. 36 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 1 Tr. _ _ _ _ _ _ _ _ _ __ - - - 1 1 n.d. 1 n.d. 

37------ - ----- --- 3 2 ----- --- ------ 2 - ------- --- ----- 1 ------ 1 1 n.d. 1+ n.d. 

38_ __ ____ ____ ____ 2 ______ ________ __ ___ _ ______ Tr. _____ _____ __ ____ ------ 4+ Tr. -1 -2 Tr. 

40_ -- ------------ ------ ------ -------- ------ ------ ------- - -------- -------- ------ 1+ ------ 8 1 n.d. 

41_______ ___ ____ _ 3+ - 1 _______ _ ______ __ ___ _ Tr. ________ _____________ _ I+ ------ Tr. 2 1+ 

fraction in ·all samples consisted c:hri.efly O'f plagioclase, 

quavtz, and cristobalite. In !the sand-sized fractions, the 

heavy mineral suite is dominated by hypersthene, which 

makes up as much as 95 percent of the sample. The light 

fraction consis'ts mostly of rock fmgments, gl,ass, and 

feldspar. 

·ties. Before emplacement in the fill, it was necessary to 

pass the material through heated rotating drums to 

remove excess moisture and to erect a huge canvas 

tent over the core to shield it from precipitation. 

Atterberg limits were determined on the - 0.420-mm 

fraction of eight samples (samples 29-37) of the Osceola Mudflow from outcrops in the Cascade Range 

and Puget Sound lowland and are as follows: 

Plasticitv 

Plastic limit Liquid limit index 

Range_____ _______ ___ __ ____ 19- 28 28-42 2-15 

Average_____ ______ ________ 24. 6 33 8. 4 

A plasticity index of 2 was determined on mudflow 

samples 34 and 36. These, and other low plasticity indices, indicate a need to control moisture content carefully when the mudflow is used to construct a fill. The 

Osceola was used extensively in the impermeable core 

of Mud Mountain Dam, and some unusual construction problems were encountered because of its proper420- 47 9 0 - 71 - 5 

OluGIN 

The Osceola Mudflow apparently originated in 

avalanches of hydrothermally altered rock from the 

summit of Mount Rainier. The presence of the mudflow high on the flank of the volcano at Steamboat 

Prow indicates that the flow came from above that 

point, and its distribution in Glacier Basin and the 

cirque north of the basin suggests that debris that descended the volcano surmounted Steambo!Lt Prow and 

cascaded into Glacier Basin in a sheet or sheets many 

hundreds of feet thick. The clay mineralogy of the 

mudflow is most readily explained if the avalanches 

originated in an extensive mass of rock that had previously been hydrothermally altered in large part to 

clay. 
30 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

'.Dhe water component of the mudflow may have been 

as much as 800 million cubic yards during movement 

if it is assumed that the material required a water 

content of 33 percent in order to flmv. The rock debris probably was derived from an active hydrothermal area on the volcano; if so, the clayey material 

could have had a high moisture content from condensation of steam. Moreover, if the avalanches contained 

steam as well as hot rock debris, snow could have been 

melted to provide added moisture as the masses moved 

down 'the flank of the volcano. 

An adequate source of material was not known when 

the Osceola was first recognized as a mudflow. Crandell 

and Waldron (1956, p. 360) suggested that the mudflow 

was initiated !by a volcanic explosion that expelled 

masses of hydrothermally altered rock from the northeast flank of the volcano, but I (Crandell, 1963a) later 

suggested that the mudflow originated at the summit 

of the cone. The source area I postulated also accounted 

for a "missing summit" of the volcano that was first 

noted by Russell (1898). The present summit of Mount 

Rainier is at the top of a young lava cone constructed 

wi~hin a large depression about 1~ miles across; high 

pomts on the rim of this depression are at Point Success, Gibraltar Rock, and along the ridge between 

Liberty Cap and Russell Cliff. These high points indicate that the summit of the volcano was removed above 

an altitude of about 14,000 feet. Both Russell (1898) 

and Matthes (1914) suggested that the top of the volcano had been blown off by a mighty volcanic explosion, 

but Coombs (1936) proposed that the former summit 

was removed piecemeal during a series of eruptions. 

Fiske, Hopson, and Waters (1963) concluded that the 

summit was lowered by subsidence into magma, by outward slumping and flowage of solfatarized rock in the 

central part of the volcano, or by head ward glacial erosion into the weak core rock. I (Crandell, 1963a) proposed that the summit of the volcano slid off and formed 

very large rockslides and avalanches that descended 

the northeast side of the cone to form the Osceola Mudflow. 

The discovery by D. R. Mullineaux (oral commun .. 

1969) of newly erupted material in an airlaid deposit 

formed at the same time 'as !the Osceola Mudflow suggests that the rockslides and avalal).ches were caused 

by volcanism. The airlaid deposit is layer F (table 5), 

and its correlation with the mudflow is based on stratigraphic relations, on its resemblance :to the matrix of 

the mudflow, and on the similar radiocarbon ages of 

the two deposits. Layer F does not occur on top of the 

Osceola Mudflow and thus cannot be younger, and organic material beneath layer F at Cowlitz Park has 

an age of 5,800 years (table 4, sample W-2053). 

According to Mullineaux, layer F is made up of three 

units in the Yakima Park-Berkeley Park area. The 

basal unit, 1-3 inches thick, consists mostly of clay and 

fragments of dense rock, about half of which have been 

strongly altered. The clay is mostly montmorillonite. 

The middle unit, ~-1 inch thick, consists mostly of 

glass-encrusted mineral euhedra and pumice, and the 

top unit is 1-3 inches of clay that contains abundant 

altered and unaltered dense rock fragments as well as 

mineral euhedra and pumice. Mullineaux believes layer 

F to be primarily of pyroclastic origin. He concludes 

that the pumiceous ash and lapilli in layer F demonstrate an eruption of magma and visualizes that the following sequence of events occurred. A phreatic explosion threw dense rock fragments and clay onto areas 

northeast of the volcano; this explosion was closely followed by an explosive eruption of magma that formed 

the thin layer of pumiceous ash and lapilli. Still later, 

pumiceous material was erupted along with dense rock 

fragments and clay. The initial explosion probably 

caused the slides of altered rock that formed the Osceola Mudflow, but perhaps less likely, the rockslides 

could have been triggered by earthquakes accompanying the eruption. 

There is little evidence concerning the behavior in 

detail of the Osceola Mudflow, and one can only speculate about its characteristics during flowage. The mudflow probably moved downvalley in a series of large 

surges, each initiated by an avalanche of moist, clayey 

rock debris. The mudflow's tremendous volume resulted 

in hydraulic damming and ponding at valley constrictions in the Cascade Range and caused inundation of a 

broad area of the lowland. In the absence of any topographic or stratigraphic evidence to the contrary, it is 

assumed that the Os~eola's entire fluid mass came to rest 

before any part of it dried enough to solidify. The time 

involved in the formation, movement, and emplacement 

of the mudflow may have been several days, or as little 

as a few hours. 

POST-OSCEOLA LAHAR ASSEMBLAGE 

Deposits in the White River valley that are younger 

than the Osceola Mudflow include at least four lahars 

and as many or more fluvial deposits; these are referred 

to collectively as the post-Osceola lahar aseemblage. The 

assemblage is typically exposed in the face of a terrace 

near the mouth of Fryingpan Creek (measured section 

1). The basal five units in this section evidently were 

deposited in a swamp adjacent to the White River; they 

seem to record a stable flood plain following the Osceola 

Mudflow, when the valley floor was at a level similar to 

that of the present. Some time after 2,700 years ago (see 

unit 5, measured section 1), alluvium and a thin lahar 
DESCRIPTION OF LAHARS 31 

Measured section 1 

[South bank or White River near mouth or Fryingpan Creek, Mount Rainier 

National Park] 

Thickneu 

(ft.) (ln.) 

19. Sand, very fine____ ______ ______ __ ____ _____ ___ ____ ~ 

18. Pyroclastic layer W (about 450 years old)____ ______ 2 

17. Sand, very fine, pinkish-gray_______ __ ___ _____ __ __ ~ 

16. Sand, very fine, yellowish-brown._ ___ _______ __ ___ _ 1 

15. Sand and coarse bouldery gravel of fluvial origin, 

light-yellowish-brown__________ _________ ___ 19 0 

14. Lahar: rock fragments as large as 8 in. in yellowish-brown sand matrix; rock fragments are 

mostly angular and subangular Mount Rainier 

rock types, a few of granodiorite and breccia 

from Ohanapecosh Formation. Material in 

uppermost 27~ ft. grades up from granule 

gravel, which contains scattered pebbles and 

cobbles, to medium sand________________ ___ 3 0 

Minor erosional unconformity. 

13. Lahar: rock fragments as large as 12 in. in 

matrix of purplish-gray coarse sand; grades into 

uniform medium sand at top_____ _______ ____ 6 0 

12. Sand, fine, horizontally stratified, purplish-gray __ 2 0 

11. Lahar: grades from pebble-sized material in a 

purplish-gray sand matrix at base to coarse 

sand at top____________ ______ _____ ________ 2 0 

10. Sand and pebble to boulder gravel of fluvial origin, iron-strained ; contains lenses of openwork 

gravel_ _________ ________ ____ ____________ _ 3 0 

9. Sand, very fine, purplish-gray to light-yellowishbrown___________________ ___ _____ ______ __ 1 6 

8. Peat_______________________ __ ___ ________ ___ 1 6 

7. Lahar: grades from angular rock fragments of 

pebble size in a purplish-gray sand matrix at 

base to very coarse purplish-gray sand at top. 2 0 

6. Pebble-and-cobble gravel of fluvial origin, 

purplish-gray, lenticular; as thick as ____ __ ___ 1 3 

5. Sand and silt, purplish-gray; contain scattered 

rock fragments and logs; lenticular; sample of 

wood from this unit is 2, 700 years old (table 4, 

sample W- 930); as thick as_________ __ ______ 2 0 

4. Pyroclastic layer Y (about 3,600 years old): 

includes contorted layer of peat above fairly 

pure basal layer of pumice 8 in. thick__ ______ 1 6 

3. Clay, peaty, gray to light-yellowish-brown______ 2 

2. Volcanic ash(?), sand-sized, micaceous, lightbrownish-gray_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 

1. Clay, woody and peaty; contains logs ___ _______ >5 0· 

were deposited, but a continued-sta,oble flood plain is 

indicated by the ove;rlying peat (unit 8). Flood plain 

stability ended when lahars and fluvial deposits aggraded the valley by at least 35 feet. 

The lahars exposed in the section near the mouth of 

Fryingpan Creek consist mainly of sand and fine gravel 

(fig. 12) , but lahars of considerably coarser texture occur in the same assemblage both upstream and downstream. 

A series of terraces is cut into, or formed by, the lahar 

assemblage along the valley wall at several places between the mouth of Inter Fork and Fryingpan Creek. 

FIGURE 12.-Lahar exposed near the mouth of Fryingpan Creek 

grading from sand- and pebble-sized material in the lower 

two thirds to a well-sorted medium sand at the top. The 

lahar is unit 13 of measured section 1. The pick head is at the 

contact of the lahar with an underlying fluvial sand deposit. 

White River campground is situated on one of these 

terraces. The terrace is about 3,600 feet long and is about 

30 feet above White River at its upper end and about 

45 feet at the downstream end. Its gradient is about 280 

feet per mile, whereas that of the river is about 300 feet 

per mile in this segment of the valley. A cut in the face 

of the terrace at the campground exposes crudely stratified fluvial gravel overlain by a lahar that contains 

boulders as large as 4 feet in diameter. Pyroclastic layer 

W veneers the terrace, but layer Cis absent, even though 

present on the adjacent valley wall. 

On the south side of the valley, opposite from and just 

downstream from White River campground, a 40-foot 

terrace is formed by a lahar 15-30 feet thick that overlies the Osceola Mudflow. A higher terrace here lies 

about 80 feet above the river, but the material that 

forms it is not exposed. 

On the north side of the valley, just downstream from 

the highway bridge over the White River, post-Osceola 

terraces are found at heights of about 10, 15, and 30 feet. 

A quarter of a mile farther downstream, on the south 

side of the river, a lahar older than pyroclastic layer W 

forms a terrace about 30 feet above the flood plain. The 

lahar consists of angular rock fragments in a matrix of 

purplish-gray sand. A still-higher terrace in the same 

vicinity, which is formed by one or more lahars younger 

than pyroclastic layer C but older than layer W, is about 

45 feet above the river. 
32 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Near the north boundary of the park, at Silver Creek 

Ranger Station, U.S. Highway 410 is situated on a postC, pre-W terrace that is only a few feet above the surface of the flood plain and is probably underlain by a 

lahar. This terrace is littered with boulders as large as 

10 feet in diameter. A little farther downstream, in the 

vicinity of Silver Creek Lodge, a terrace that is about 60 

feet above the river is underlain by pre-W alluvium and 

a lahar. On the west side of the valley and still farther 

downstream, a terrace at a comparable height above the 

flood plain is underlain by a pre-C sandy lahar about 4 

feet thick, beneath which are pyroclastic layer Y and 

the Osceola Mudflow. A diagrammatic cross section of 

the valley floor in this area is shown on plate 2. 

POST-OSCEOLA LAHAR ASSEMBLAGE IN THE WEST 

FORK VALLEY 

At least four post-Osceola lahars have been recognized in the West Fork valley north of Mount Rainier 

National Park; two are older than pyroclastic layer Y, 

one is younger than Y and older than layer C, ·and one 

is younger than layer W. Only one post-Osceola lahar 

was recognized within the park. 

One pre-Y lahar crops out in a road cut near the mouth 

of the valley on the west side of sec. 26, T. 19 N., R. 9 E. 

(Greenwater quadrangle). It is at least 4 feet thick and 

consists of subangular to subrounded stones in a matrix 

of oxidized dark-yellowish-brown sand. The lahar overlies the Osceola Mudflow and underlies, in the same 

outcrop, pyroclastic layer Y, another lahar, and pyro· 

clastic layers C and W. Its top is about 50 feet higher 

than the West Fork of the White River. Grain-size analysis of a sample of the lahar indicated a median diameter of 12.5 mm and a sorting coefficient of 13.2 (table 

10, sample 22). An oxidized lahar 3-4 feet thick, which 

probably is correlative with the one just described, crops 

out in a roadcut 1.5 miles farther upvalley in the NE1,4 

sec. 33. 

A second pre-Y lahar is exposed 3.5 miles farther 

upvalley in a small borrow pit near the mouth of Jim 

Creek. It is more than 10 feet thick and contains boulders as much as 8 feet in diameter. The matrix of the 

upper part of the lahar grades upward from sand-andcobble gravel to medium and coarse gray sand. Some of 

the large boulders are of granodiorite, but all the smaller 

fragments and the matrix seem to have been derived 

from Mount Rainier. 

A post-Y, pre-C lahar that is about 6 feet thick is 

exposed near the mouth of West Fork valley at the 

roadcut in sec. 26 just mentioned. Size analysis of a 

sample from a zone 4-5 feet below the top of the lahar 

indicaJted a median diameter of 2.8 mm and a sorting 

coefficient of 13.40 (table 10, sample 3). 

A deposit that probably is part of the same lahar occurs in a streambank exposure on the north side of the 

valley about 1 mile away, near the center of sec. 23. 

There, the lahar is 20 feet thick and consists almost 

wholly of rock fragments derived from Mount Rainier. 

It overlies a succession of deposits that includes, from 

top to bottom, 3 feet of fluvial sand derived from Mount 

Rainier, a layer of humic material a few inches thick, 

pyroclastic layer Y, and the Osceola Mudflow, the ba&> 

of which is below river level. 

A broad area of the floor of theW est Fork valley near 

its mouth is underlain by the youngest post-Osceola 

lahar. The lahar and fluvial deposits associated with it 

form a terrace 25-30 feet higher than West Fork. The 

lahar is a lenticular, bouldery deposit as much as 8 feet 

thick where it is exposed in a gravel pit south of West 

Fork, near the center of sec. 33. Granodiorite boulders 

as large as 12 feet in diameter are scattered over the 

surface, and boulders as large as 7 feet in diameter can 

be seen in the walls of the gravel pit. The lahar's matrix 

is purplish-gray sand and granule gravel. The lahar 

overlies as much as 15 feet of stratified purplish-gray 

sand and fine gravel that rests on top of the Osceola 

Mudflow. The absence of pyroclastic layer W from the 

top of the lahar indicates that it is less than 450 years 

old, and ring counts of tree stumps on the lahar's surface 

indicate an age of more than 275 years. 

Within Mount Rainier National Park, a post-Y lahar 

is exposed at the mouth of Winthrop Creek in the West 

Fork valley. It consists of 16 feet of angular and subangular rock fragments, which range in size from granules to boulders, in a purplish-gray sand matrix. The 

lahar overlies a bed of silt, clay, >and sand 1 foot tthick 

that contains pumice derived from layer Y. This fine 

deposit overlies about 20 feet of poorly sorted pebble to 

boulder gravel, which rests on top of the Osceola Mudflow. 

LAHARS IN THE NISQUALLY RIVER VALLEY 

Postglacial deposits in the Nisqually River valley 

within Mount Rainier National Park include at least 12 

lahars, more than eight fluvial deposits, and three layers of volcanic ash. Their sequence is as follows : 

Several lahars and associated fluvial Lahar assemblage D. 

deposits. 

Pyroclastic layer W (about 450 years 

old) 

At least seven lahars and at least eight Lahar assemblage C. 

fluvial deposits. 

Peat 

Pyroclastic layer Y (about 3,600 years 

old) 

Peat and peaty silt 
DESCRIPTION OF LAHARS 33 

Paradise lahar Lahar assemblage B. 

Fluvial sand and gravel Do. 

Pyroclastic layer 0 (about 6,600 years 

old) 

Two lahars interbedded with fluvial Lahar assemblage A. 

deposits. 

Although many of the lahars are intermittently exposed 

in the valley from the vicinity of Christine Falls downstream beyond the park boundaries, their general similarity makes correlation difficult or impossible. This 

lar()'e ()'roup of lahars and alluvium is divided for con- b b 

venience of discussion into four lahar assemblages, each 

consisting of two or more lahars or alluvial deposits, 

which are separated by pyroclastic deposits. The most 

widespread deposit that is recognized within these assemblages is the Paradise lahar, which also mantles the 

Paradise Park area. This lahar, and a similar one at 

Van Trump Park, will be discussed first; this discussion will be followed by a description of the assemblages 

along the floor of the Nisqually River valley. 

PARADISE LAHAR 

Ridges and valleys between Panorama Point and 

Ricksecker Point are veneered with a yellowish-orange 

deposit of angular to subrounded rock fragments in a 

plastic matrix consisting of a mixture of sand, silt, and 

clay. Although originally the deposit was informally 

designated as :the Paradise debris flow (Crandell, 

1963a), its name is changed here to Paradise lahar because of the textural variability within it. The lahar is 

younger than pyroclastic layer 0 and predates layer 

D; it was formed some time between about 5,800 and 

6,600 years ago (table 5). 

Blocks as large as 8 feet in diameter are embedded in 

the lahar, and even larger masses are scattered on its 

surface. Iron oxide occurs within the deposit as thin 

layers and lenses, and as thin coatings on most rock fragments. The lahar is 1- 5 feet thick in most outcrops, although thicknesses of as much as 15 feet are not uncommon. Owing to its general thinness, the lahar does not 

have a constructional topography of its own in most 

pl'aces, bu:t mantles ridges, knobs, arrd depressions 

formed of bedrock and glacial drift. At Reflection 

Lakes, however, the surface of the lahar is hummocky, 

and the lakes occupy shallow basins in the deposit. In 

outcrops along the floor of the Nisqually River valley 

the lahar is 2-8% feet thick, but it veneers the valley 

sides to a height of more than 100 feet near the mouth 

of the Kautz Creek valley. 

Nearly everywhere that the base of the Paradise lahar 

is exposed along the Nisqually River valley it rests directly on pyroclastic layer 0, and there is little or no 

evidence of erosion along the contact. A layer of forest 

duff several inches thick lies on top of the lahar at 

several places and underlies pyroclastic layer Y and 

a younger lahar. . 

In the Paradise Park area 1the lahar underhes the 

surface south of Panorama Point and from Mazama 

Ridae westward to the young lateral moraines of Nisqually Glacier (pl. 3). According to D. R. Mullineaux 

(oral commun., 1969), the lahar is represented on Mazama Ridge by a deposit a few inches thick that underlies pyroclastic layer D and other layers just south of 

Sluiskin Falls. The maximum height of the lahar deposit in that area is about 600 feet above the floor of 

Paradise Valley. Farther south, a large lobe of the lahar 

under lies the Reflection Lakes area. 

Evidently the Paradise lahar entered the Reflection 

Lakes area through a saddle on Mazama Ridge that is 

about 200 feet higher than the floor of Paradise Valley. 

A thin remnant of the lahar that crops out along the 

highway at Reflection Lakes (measured section 2) indicates that the lahar initially filled that area to a level 

at least 20 feet higher than the present lake level. However, the surface of the lahar was subsequently lowered 

as the still-fluid material drained away to ,the west and 

rejoined the main mass of the lahar in the Parll!dise 

River valley ( pls. 1, 3) . The west end of the largest 

lake may be dammed by laharic material that flowed 

off Mazama Ridge. 

High remnants of the Paradise lahar both upstream 

and downstream from N arada Falls indicate that a very 

large mass of material moved down the !'aradise R~ver 

valley. The most conspicuous remnant 1s exposed m a 

road cut near Ricksecker Point (fig. 13). The lahar there 

is a few feet thick and directly overlies pyroclastic layer 

0 at a height of about 800 feet above the ~?Dr of the 

Paradise River valley. Because of the pos1t10n of the 

lahar on a south-facing slope overlooking the valley, 

there seems to be no other way to explain its presence 

except by the temporary filling of the valley with the 

lahar to a height of at least 800 feet. 

Measured section 2 

[Roadcut south of the center of the largest Jake at Reflection Lakes] 

Thickness 

(ft) (in.) 

9. Colluvium: reworked volcanic ash and forest duff __ 1-2 

8. Pyroclastic layer Y --- ------------- - - ------ ---

7. Colluvium: reworked pumice and forest duff ____ _ 2. 5 

6. Paradise lahar: unsorted mixture of angular to 

subrounded pebbles and cobbles in matrix of 

sand, silt, and clay- - ------ ----------------- 2-4 

5. Sand, gray ____ - - -------------------------- - -

4. Pyroclastic layer 0 __ _ - ------------------- - ---

3. Sand, gray- _- _- --------------------- - - ---- -- 2. Evans Creek till: gray, lenticular ________ ______ _ 

1. Granodiorite (bedrock)-----------------------

0 

4-6 

0 

0 

6 

1- 2 

0-5 

0-6 
34 POSTGLACIAL LAHARb FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Evans Creek till • 

. .. 

FIGURE 13.-Paradise lahar above pyroclastic layer 0 in roadcut half a mile east of Ricksecker Point. Beneath layer 0 

are Evans Creek till and a lava flow from Mount Rainier. This outcrop is about 800 feet higher than the floor of the 

adjacent Parad'ise River valley and indicates that the lahar was at least 800 feet deep here. 

Farther down the valley the Paradise lahar forms 

part of assemblage B. Its vertical extent indicates that 

the valley was at least as deep when the lahar was moving as it is today and that the lahar was temporarily 

several hundred feed deep at Longmire. The lahar was 

identified as far downvalley as a point near the mouth 

of Tahoma Creek, ·and it may be one of several lahars 

that crop out in the valley near National, 12 miles west 

of Longmire. 

Stones in the lahar are principally of Mount Rainier 

provenance. Identification of 100 pebbles in the deposit 

at Reflection Lakes and at Longmire showed 75 and 80 

percent, respectively, to be of Mount Rainier origin. At 

Reflection Lakes the deposit contains only 5 percent 

granodiorite in the pebble-sized fraction, but this rock 

type makes up 20 percent of the pebbles at Longmire. 

The greater proportion of granodiorite at Longmire 

may be due to incorporation of loose gravel from the 

Nisqually flood plain. 

Three samples of the lahars from the Paradise Park 

area contained 1- 5 percent clay, 7- 28 percent silt, and 

16-44 percent sand (table 10, samples 23, 24, 25). X -ray 

examination of a sample from an outcrop near the visitor center at Paradise Park indicated that montmorillonite and kaolinite are the predominant clay-sized 

minerals (table 11, sample 23). They are accompanied 

by small amounts of cristobalite, feldspar, iron oxide, 

and quartz. Amorphous silica constituted 6.4 percent of 

the clay-sized fraction. It is of interest to note that a 

sample of Evans Creek till (table 7, sample 1) from the 

same outcrop had mostly feldspar and cristobal'ite in the 

clay-sized fraction, and only a trace amount of clay mineral was found. Some samples of the lahar are among 

the most poorly sorted of those examined in this study 

(fig. 14). It is especially interesting to note the poor 

sorting of the lahar at Ricksecker Point (sample 26). 

The deposit there must represent a zone in the upper 
E 

E 

~ 

LLJ 8 N 0 <f) 100 

0 

LLJ 

1-

<( 

u 

Ci 

z 

z 

<( 

:c 

II-

:c 

(.!) 

90 

80 

70 

w 60 3:: 

>- Ill 

Cl: 

LLJ 

z 

50 

t---

1-----

Sample 

23 

26 

27 

41 

DESCRIPTION OF 

E 

E E 

E ~ 

0 ~ 

ci ci 

Sorting 

coefficient 

13.60 

14.56 

15.75 

17.00 

LAHARS 35 

E E 

E E E 

E 0 0 ci 0 ci 0 ~ ~ 

I/~ 

~~~ 

l,~ ~ v 

v 

~ v 

~ ~ ~ ~----~.--

~ v 

~ v v ~~ [....--

s ~Q b 

~v, 

~ 40 

<f) 

LLJ 

..J 

u 

i= 

a:: 

<( 

0.. 

... 

0 

lJ.J 

(.!) 

<( 

1-

z 

LLJ 

30 

20 

10 

~ . 0 

""" 

..... ~ 

f-l- ~ ::...-----

~ s~ '2-

~ / ,.,,e 

~ v ~<"'. 

II.'> Q,e s~~~ v 

~~v 

~ ----~--~'-------~~--------A-----------~----------~~r-A---------~--------~ 

CLAY SILT SAND GRANULES PEBBLES COBBLES 

lJ'IGURE 14.- 0u.mulative CUTVes of size distribution of the Paradise lahar (solid lines) at rt.hree localities and of an older lahar 

(dashed line) at Paradise Park. Sample 23 is from an outcrop near the visitor center at Paradise Park, 26 is from an 

outcrop near RidQrecker Poinil; and 27 is from measured section 4 at Longmire. Sample 41 i-s from the older lahar, at 

the same locality as sample 23. The S8.1ll1Ples rure those described in table 10. 

10-20 feet of a lahar that was momentarily at least 800 

feet deep in the Paradise River valley during flowage. 

Silt and clay mrude up about 19 percent of a sample 

(27) of the Paradise lahar that was taken from an outcrop near Longmire. (See measured section 4.) X-ray 

diffraction analysis of the clay-sized fraction of this 

sample showed a kaolinite-halloysite mixed-layer mineral, and cristobalite, feldspar ·and a small amount of 

iron oxide (table 11, sample 23). Amorphous silica made 

up 8.3 percent of the clay fraction. 

The distribution of the Paradise lahar in the area between Panorama Point and Ricksecker Point suggests 

that the lahar originated in one or more huge avalanches 

of moist rock debris that swept down the south flank 

of the volcano. The clay mineralogy of the deposit indicates that it was derived in part from hydrothermally 

altered rocks, perhaps at the summit of Mount Rainier. 

Although I once thought that the deposit at Paradise 

Bark was of the same age ·as the Osceola Mudflow 

(Crandell, 1963a, p. B139), I now know that the Paradise lahar is somewhat older because it is stratigraphically below pyroclastic layer D, which is older than the 

Osceola (D. R. Mullineaux, oral commun., 1969). It 

seems likely that counterparts of the slides that resulted 

in the Greenwater lahar in the White River valley 

caused the Paradise lahar and were triggered in the 

same way (p. 22). 

Although the distribution of the lahar in the Paradise 

Park area. ind'icates that the lahar originated in an 

avalanche down the south side of Mount Rainier, the 

area of transition from an avalanche to a lahar is not 

known. At Paradise Park, where the transition may 

have occurred, grain-size distribution in samples of the 

deposit indicate a rather wide variability in texture 

and a range in sorting coefficients of 7.75-13.6 (samples 

23-28, table 10). Median diameters range from 0.2 to 13 

mm in these samples. Samples obtained from two locations farther downvalley (samples 27, 28), where there 

is little doubt thrut movement was that of a lahar, have 

sorting coefficients of 15.75 and 16.25 and median diameters of 1.4 and 4.3 mm, respectively. One might expect that the deposit would be most poorly sorted where 

it was moving as a rapid avalanche and that it would 

show somewhat better sorting where it was moving as a 

lahar. However, the opposite seems to be true, if the 

samples described here are representative. 

The originrul volume of the Baradise lahar is difficult 

to determine because the deposit is highly variable in 
36 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

thickness, and nowhere does it form a broad thick fill in 

the Nisqually River valley. Beyond the community of 

N rutional, 6 miles west of the park, Evans Creek Drift 

directly underlies surfaces on both sides of the river; 

if the lahar reached this far downvalley, it must 

have been confined to a narrow channel, and its top 

could not have been appreciably higher than the present 

flood plain. The depth of the channel of the Nisqually 

River at that 'time is not known. 

The volume of the lahar was originally estimated to be 

400-500 million cubic yards on the basis of the heights 

to Which it reached on vaHey sides, the assumption that 

the Paradise and Nisqually River valleys were simultaneously filled with the lahar upstream from Rickseeker Point, and the probability that the lahar was 

draining from one area while its crest was passing 

points farther downvalley (Crandell, 1963a). Subsequent geologic mapping has shown that the total area 

covered by the lahar probably is no more than about 13 

square miles, and its original average thickness in this 

area after it came to rest and lost much of its water content probably was between 5 and 10 feet. The estimated 

volume is either 67 million or 134 million cubic yards, 

according to whether the smaller or larger average thickness value is used in the computation. 

The great depth of the Paradise lahar at some places, 

notably in the lower Paradise River valley, seems entirely out of proportion to such a relatively small volume, even if it is assumed that the lahar probably 

contained an additional volume of water of as much as 

one-third of the estimated volume of the deposit. The 

anamolous relations involved can be illustrated by considering the capacity of the lower Paradise River valley. 

Near Ricksecker Point, the valley has a cross-sectional 

area of about 130,000 square yards up to a height of 

about 800 feet above the valley floor. The 1-mile segment of the valley immediately east of Ricksecker Point 

has an estimated volume of at least 230 million cubic 

yards up to a similar height. Thus, it is apparent that 

even the total estimated volume of the lahar could 

not entirely fill this short valley segment at one time. 

The problem becomes even more acute when it is remembered that a considerable part of the estimated volume of the lahar remained in the area aJbove the lower 

Paradise River valley and in the Nisqually River valley 

above Ricksecker Point. Moreover, to explain the great 

depth of the lahar in the Paradise River valley by any 

conventional means, it is necessary not only to have this 

valley segment full of mud, but simultaneously to have 

mud of comparable thickness in the Nisqually River 

valley at the mouth of the Paradise River. 

On the basis of the assumption that the estimated volume of the lahar is not grossly in error, the most probable explanation of the contradictory relations just 

described is that the lahar moved across Paradise Park 

and down the Paradise River valley in a single massive 

transient wave with a height of as much as 800 feet. 

Such a wave must have been generated by a large avalanche of wet, clayey, rock debris from an area high 

on the south flank of the volcano, or perhaps at its summit. Because of momentum the avalanche-generated 

wave swept across Paradise Park, rather than moving 

directly down the Nisqually River valley. The valley 

swings from a southward course to a southwestward 

course just west of Panorama Point. Here the great 

momentum of the wave, created by a vertical drop of 

perhaps as much as 8,000 feet, carried it up over the 

east valley wall. The wave surmounted the ridge between Panorama Point and Alta Vista, surged across 

Pa11adise Park, and slopped up onto Mazama Ridge just 

south of Sluiskin Falls. The bulk of the material, however, was deflected by Mazama Ridge to the southwest 

and down the ParadJise River valley. 

The transient wave probably lost much of its height 

when it debouched from the Paradise River valley at 

Ricksecker Point. Its momentum must have carried it 

high on the flank of Rampart Ridge along the west 

side of the Nisqually River valley. At Longmire, a little more than 1 mile downvalley, the lahar was at least 

80 feet and probably several hundred feet deep. As the 

lahar wave progressed farther down the Nisqually 

River valley, it gradually lost height as the valley 

widened and as more and more volume was lost by 

material being left behind as a coating on the lower 

valley walls and valley floor. 

OLDER LAHAR AT PARADISE PARK 

An older lahar that underlies ~he Paradise lahar 

is exposed at severaJ places in the Paradise Park area. 

The oontact between tlhe two deposits is marked by 

a humic zone several inches thick that formed in and 

on t!he lower lahar (fig. 15; measured section 3). 

A grain-size distribution analysis of a sample of the 

lower lahar from the measured section indicates 21 pe.rMeasured section 3 

[Trench exposure temporarily open during construction of sidewalk and retaining wall at the northwest edge of the Paradise Visitor Center in September 1966 

(fig. 15)] 

Thickness 

(ft) (in) 

5. Pyroclastic layer W ___ _______ __ __ _______________ _ 

4. Pyroclastic layer y_____ ____ __________________ 1 

3. Paradise lahar: light-yellowish-brown (2.5Y 6/4) 

to brownish-yellow (10YR 6/6) mixture of 

rock fragments, sand, silt, and clay; humified 

in upper 4-6 in__________________ __ ___ _____ 1 

2. Older lahar: light-yellowish-brown (2.5Y 6/4) 

mixture of rock fragments, sand, silt, and clay; 

humified in upper 1-3 in ____ _______________ _ 2-3 

1. Evans Creek till: gray (2.5Y 4/0) _______________ >5 

1 

3 

8 

0 

0 
DESCRIPTION OF LAHARS 37 

FIGURE 15.- 0utcrop of the Paradise lahar and an older lahar in a trench excavated for a retaining wall at the north edge of 

the visitor renter at Paradise Park (measured section 3). 

cent clay and sil1t and 32 percent sand (table 10, sample 

41; fig. 14). The sample had a median diameter of 1.25 

mm and a sorting coefficient of 17. 

The clay minerals in a sample of the older la.har 

were cihiefly montmorillonite and a small amount of 

kaolinite. The remainder of the clay-sized fraction 

was cristobalite, feldspar, and iron oxide (table 11, 

sample 41). 

The older lahar at Paradise Park probably originated 

in a slide of hydrothermally altered rock from the summit or south flank of the volcano. It may be correlative 

with the lahar that is older than layer 0 at Van Trump 

Park. (See below.) 

LAHARS AT VAN TRUMP PARK 

At Van Trump Park, the ridge between Van Trump 

and Comet Creeks is veneered with a yellowish-orange 

lahar, which is older tihan pyroclastic layer 0 and which 

consists of stones up to 11;2 feet in diameter in an unsorted matrix of sand, silt, and clay. On the ridgetop 

the deposit ranges in thickness from a few inches to as 

much as 4 feet, but the lahar is as much as 6 feet thick 

on the east slope of the ridge, where it overlies Evans 

Creek till and a lava flow from Mount Rainier. It extends down the east side of the ridge to the floor of Van 

Trump Creek, but it was not seen on Cushman Crest or 

the ridge at the west edge of Van Trump Park. 

The lahar's distribution suggests that it was formed 

by an avalanche of rock debris on the south flank of the 

volcano. Although the lahar was not identified in the 

Van Trump Creek valley below Van Trump Park, it 

may be represented in the Nisqually River valley by one 

of the lahars of assemblage A. 

The lahar is not present on top of a lateral moraine of 

Van Trump Glacier. The lateral moraine probably is of 

Sumas age (table 3). However, the lahar does overlie 

Evans Creek Drift in areas just beyond the moraine. 

This relation suggests lthll!t the mudflow occurred during the Everson Interstade. 

A sample of the lahar :from an outcrop about 800 

feet northeast of the V'an Trump trail shelter contained 42 percent clay and silt and 33 percent sand 
38 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

(table 10, sample 40). The sample had a median diameter of 0.1 mm and a sorting coefficient of 10.2. X-ray 

analysis of the clay-sized fraction of the lahar resulted 

in the identification of glass (probably amorphous silica) , feldspar, and cristobalite. 

A series of younger lahars is exposed in the valleys 

of Van Trump and Comet Creeks. The basal lahar of 

this series in the Van Trump Cre~k valley is a purplishgray ibouldery deposit 1-2 feet thick that underlies 

pyroclastic layer 0 and unconformably overlies a gray 

fluvial gravel as much as 10 feet thick. Above layer 

0 is a bouldery reddish-brown lahar at least 3 feet thick. 

It is overlain by pyroclastic layer Y, above which is 

another reddish-brown lahar, only about 1 foot thick, 

in which the coarsest material is of pebble size. This 

deposit is overlain by pyroclastic layer Wand a ·post-W 

gray lahar 1.5~6 feet thick that is oxidized to a depth 

of about 1 foot. The gray lahar is overlain by scattered 

boulders and coarse, unsorted, lenticular deposits that 

were formed by a still younger lahar or flood. These 

deposits form low bouldery ridges that trend downvalley. 

At least two bouldery lahars form low terraces in the 

Comet Creek valley upstream from Comet Falls. The 

lower terrace is about 5 feet above Comet Creek and is 

underlain by a lahar and fluvial gravel; the upper 

terrace is about 12 feet higher and is underlain by a 

lahar. 

The lahars in the Van Trump drainage basin occur in 

the same stratigraphic position with respect to pyroclastic deposits as some of those in the Nisqually River 

valley. Lahars having ·a reddish-brown matrix, similar 

to that of some deposits in the Van Trump Creek valley, 

were not recognized alons; the Nisqually River. 

LAHAR ASSEMBLAGE A 

Lahar assemblage A contains the oldest postglacial 

deposits recognized in the Nisqually River valley. These 

deposits consist of two lahars and interbedded fluvial 

sand that overlie Evans Creek Drift and predate pyroclastic layer 0. The assemblage is intermittently exposed in streambank outcrops between Longmire and 

a point about P/2 miles downstream, where the Nisqually River turns westward. Sporadic exposures as 

far west as the mouth of the Tahoma Creek valley suggest that the deposits originally extended downstream 

beyond the park boundary. 

In exposures Yz-lYz miles downstream from Longmire, the lahars in assemblage A are composed of angular to subrounded pebbles, cobbles, and boulders as 

large as 12 feet in diameter in a friable, purplish-gray, 

silty sand matrix (fig. 16). The matrix contains voids, 

and some small lenses of pebbles within the lahars have 

openwork texture. The top 2-3 feet of the upper lahar 

is oxidized to a light yellowish brown, and films of iron 

oxides coat the surfaces of most stones. At one locality, 

a layer of humus occurs at the top of the upper lahar 

immediately beneath pyroclastic layer 0, but no wood 

was seen in either lahar. In most outcrops, the two 

lahars rest directly on one another, but at one locality 

they are separated by 1-2 feet of stratified sand and 

pebble gravel. 

The maximum thicknesses of these lahars are difficult 

to determine because their base and top are rarely seen 

in the same outcrop. At an exposure adjacent to the 

Nisqually flood plain in the NW¥4 sec. 5, the lower lahar 

is 8 feet thick, but its base is not exposed. The greatest 

exposed thickness o£ the upper lahar is only 4-5 feet, 

but the vertical distance between its base and top is 37 

feet at a locality 1Yz miles downstream from Longmire. 

Although the lahar must thus have been at least 37 feet 

deep during movement, nowhere are the veneers that 

were left on valley sides after its passage known to 

reach a comparable thickness. 

A sample of the oldest lahar of assemblage A at 

Longmire (unit 1, measured section 4) was analyzed 

for size distribution and clay mineralogy (tables 10, 

11, sample 38; fig. 17). The sample was taken from a 

zone about 4Yz feet below the top of the deposit in the 

outcrop. X-ray analysis of the fine fraction of the 

sample resulted in the identification of montmorillonite 

Measured section 4 

[Riverbank outcrop on the west side of the N!squa\ly River In center of the NEJ.i sec. 32, T. 15 N., R. 8 E., at Longmire) 

Thlckne&8 

(ft) (in) 

8. Duff; thickness variable, as thick as-- ---- -- - ------ - 6 

7. Pyroclastic layer W ___ __ ____ ____ - - - _- _- -- - - --- - - - 1-2 

6. Lahar: subangular to subrounded pebbles, 

cobbles, and boulders in matrix of sand and 

silt, unsorted and unstratified, mottled light 

yellowish brown and purplish gray ___ ____ --- 2 0 

5. Pyroclastic layer Y: contains scattered fragments of charcoal in upper 2 in_ _____ ____ __ 1 1 

4. Paradise lahar: subangular to subrounded 

pebbles, cobbles, and boulders in matrix of 

silt and sand, slightly plastic, unsorted and 

unstratified; matrix purplish gray, but stones 

coated with yellowish-brown iron oxides____ _ 8 6 

3. Sand, coarse to fine, lenticular; contains 

scattered pebbles; as thick as_ ________ _____ 4 0 

2. Pyroclastic layer 0 _____ ________ ---- -------- -- - -- - 1- 3 

1. Lahar: angular to subrounded pebbles, cobbles, 

and boulders in matrix of silt and sand; has 

some zones that show faint planar structures 

that suggest bedding; has some layers of 

openwork gravel a few inches thick; purplish 

gray, oxidized to light yellowish brown in 

upper 2-3 feet ___ ___ _______ __ ___ ____ _____ >10 0 

The base of unit 1 is below the level of the adjacent flood plain. 
DESCRIPTION OF LAHARS 39 

FIGURE 16.-Lahar in sil:reambank on west Sii.de of Ni:squally River flood plain at meaSillred section 4, about a quarter of a mile 

southwest od' Longmire. The lahar shown here, which is older than pyroclastic layer 0, js unit 1 in the measrured. section. 

(2 parts in 10). The rest of the clay-sized fraction consisted chiefly of feldspar and cristobalite. 

The lahars in assemblage A could be the downvalley 

correlatives of the older lahar at Paradise Park or of 

the lahar at Van Trump Park that is older than py.roclastic layer 0. 

LAHAR ASSEMBLAGE B 

Lahar assemblage B is overlain by more recent deposits at most places along the valley floor and is best 

exposed in the faces of terraces along the Nisqually 

River. The most extensive lahar in assemblage B is the 

Paradise lahar, which has already been described. The 

basal part of the assemblage is a deposit of sand and 

gravel that was noted at three localities. One is in a 

road cut at a switehback near the mouth of Van Trump 

Creek, where pebble to boulder gravel underlies pyro· 

clastic layer Y. The Paradise lahar was not seen here, 

and units beneath the gravel are not exposed. The top 

of the gravel deposit is about 70 feet higher than the 

Nisqually River. 

Fluvial gravel and the Paradise lahar are also exposed 

in a series of outcrops about 1,000 feet upstream from 

the bridge to Longmire campground (measured sect-ion 

5) . The gravel is a crudely stratified deposit of cobbles 

and bouldevs more than 15 feet thick. Its base locally 

lies below river level. In one streambank outcrop the 

gravel overlies 4 feet of fine sand, which is underlain 

by talus. In another outcrop the Paradise lahar is 3 

feet thick and overlies the fluvial gravel at a height of 

about 15 feet above the flood plain. A short distance upstream, however, the base of the lahar is below the level 

of the flood plain; there, the lahar is overlain by fluvial 

gravel younger than pyroclastic layer Y. 
40 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Measured section 5 

[East bank of Nisqually River about 1,000 ft upstream from bridge at Longmire] 

Thickne88 

(jt) (in) 

12. Pyroclastic layer W: .white pumiceous ash__________ 2 

11. Lahar: angular to subrounded pebbles, cobbles, 

and boulders in matrix of purplish-gray sand _ 10 0 

10. Sand and pebble to boulder gravel; boulders as 

large as 5 ft across; dark yellowish brown___ _ 12 0 

Erosional unconformity. 

9. Lahar: angular to subrounded pebbles, cobbles, 

and boulders, as much as 4 ft across, in matrix 

of purplish-gray sand __ _____ ___ _____ _______ 6 0 

8. Pebble to boulder gravel ; both crossbedding and 

horizontal bedding locally present; purplish 

gray, but iron stained along some bedding 

surfaces_______________________________ ___ 3 0 

7. Lahar: angular to subrounded boulders, as much 

as 4ft across, in matrix of purplish-gray sand ; 

as thick as___ ________________ ______ ____ __ 13 0 

6. Sand and pebble to boulder gravel, dark-yellowish-brown; boulders are as large as 3 ft in diam- eter _____ __ __ __________ ____ _________ _____ 6 0 

5. Peat interbedded with medium to coarse sand ; 

individual beds of each are lenticular; as thick as _______ _______ _______ ___ ___ ____________ 2 0 

4. Pyroclastic layer Y : yellow pumiceous ash, 

lenticular; as much as______________________ 1 3 

3. Peat and peaty silt; contains fragments of wood; as thick as_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6 

2. Paradise lahar: angular to subrounded boulders 

in plastic clay and sand matrix ; purplish gray 

where unoxidized, light yellowish brown where 

locally oxidized; as thick as______________ ___ 15 0 

Erosional unconformity. 

1. Pebble to boulder gravel, crudely stratified, 

purplish-gray; extends beneat h level of adjacent flood plain; more than_______________ 15 0 

A third exposure in which fluvial deposits underlie 

the Paradise lahar is at measured sootion 4, a short distance downstream from Longmire. Here the rtop of .the 

fluvial deposit is about 15 feet above flood-plain level. 

After the formation of lahar assemblage A, ·and for 

some time after deposition of pyroclastic layer 0 about 

6,600 years ago, the Nisqually River evidently was flowing on a surface lower t han the present flood plain. 

Later, but before the Paradise lahar was formed, the 

river aggraded to a profile that was at least 15 feet 

higher than it is now in the vicinity of Longmire, only 

to cut down again to a lower profile before the Paradise 

lahar occurred. The causes of this aggradation and 

downcutting are not known. The Nisqually River flood 

plain seems to have been nearly stable between the time 

the Paradise lahar occurred and deposition of pyroclastic layer Y about 3,600 years ago. 

LAHAR ASSEMBLAGE C 

Lahar assemblage C consists of fluvial gravels and 

lahars which are stratigraphically between pyroclastic 

J·ayers Y ·and W (p. 32). The fluvial deposits are best 

exposed in banks along the west side of the Nisqually 

River between Van Trump Creek and Longmire. Just 

south of Van Trump Creek tthe lahar assemblage is represented by poorly sorled fluvial gravel (fig. 18) about 

25 feet thick, locally capped by two lahars that are 3 

and 5 feet thick. In this area and farther downvalley 

tJhe lahar assemblage forms terraces that are from 20 to 

80 feet above the adj acent Nisqually River flood plain. 

The terrace on which the entrance road is situated has 

a gradient of about 250 feet per mile. 

At the mouth of the Paradise River valley a terrace 

underlain by the assemblage extends a few hundred 

yards back into the valley, and the river flows along 

the south edge of the terrace's southward-sloping surface. An outcrop in the face of the terrace a quarter of 

a mile north of the Paradise River reveals a series of 

four lahars separated by beds of fluvial sand and granule gr avel 1-2 feet thick. The lowest lahar exposed is 

more than 15 feet thick and consists of an unsorted rubble that cont ains angular and subangular blocks as 

large as 7 feet in maximum dimension in a matrix of 

purplish-gray sand. Blocks in the rubble consist of andesite that was derived from the volcano and granodiorite. The three overlying lahars are texturally similar 

and re from 1 to 4 feet thick. The clay-sized fraction of the uppermost, lahar consists of cristobalite, 

feldspar, and glass (probably amorphous or opaline silica, or both); no clay minerals were identified by X-ray 

examination (table 11, sample 18). This lahar probably 

is correlative with the one that caps the terrace at 

Cougar Rock campground on the opposite side of the 

valley. The lahar at the campground is rut least 5 feet 

thick, and blocks on its surface are as large as 14 feet 

in maximum dimension. 

The stratigraphic complexity of lahar assemblage C 

is well illustrated by outcrops on both sides of the Nisqually River about a quarter of a mile north of Longmire (measured section 5) . There are six terraces within the va1ley in this area, at heights ranging from 20 

to about 80 feet above the river. The stratigraphic succession of the deposits and the relation of the deposits 

to the terraces are shown diagrammatically on plate 

2. The sequence of events that can be inferred from 

this cross section follows. The sequence depends on an 

uncertain correlation of individual gravel deposits and 

lruhars. If the correlations are incorrect, the sequence 

would be differenlt lin detail but not in overall complex 

character. 

18. Downcutting to level of present flood plain. 

17. Aggradation of fluvial deposit J. 

16. Downcutting probably of at least 20 feet. 
DESCRIPTION OF LAHARS 41 

w 

N 

(ii 100 

0 

w 

f-5 90 

0 

z 

z 

<( 

I 

80 

f- 70 fI 

Cl 

iii 60 ~ 

>-

co 

0:: 

w 

z 

50 

ii: 40 (/) 

w 

_J 

~ 30 

0:: 

~ 

"- 20 0 

w 

~ 10 fz 

w 

u 0 0:: 

w 

()_ 

E 

E 

~ 

0 

0 

0 

r----

r----

CLAY 

Sample 

21 

38 

E 

E 

~ 

0 

0 

Sorting 

coefficient 

9.84 

10.86 

~ 

SILT 

!-' 

/ !--" 

v-v 

E 

E 

0 

v1---/ 

~ r/ 

SAND 

v 

E 

E 

C> 

~ 

./ 

v___... ..... v 

"' 

v v v v 

-v 

GRANULES 

~ 0) I=' :a- v 

E 

E 

0 

0 

~ 

,L 

ft~/ 

/ 

/ 

PEBBLES 

/ 

/ 

/ 

v 

v~ f1 

E 

E 

0 

0 

0 

~ 

COBBLES 

FIGURE 17.-0umul.lltive curves of grain-size distribution of lahars near Longmire. Sample 38 is unit 1 of meaSJUred section 4, 

and sample 21 is unit 6. 

15. Deposition of pyroclastic layer W about 450 years 

ago. 

14. Deposition of lahar I. 

13. Downcutting of about 20 feet. 

12. Aggradation of about 30 feet by fluvial deposit H. 

11. Downcutting of about 35 feet. 

10. Deposition of lahar G. 

9. Aggradation of at least 20 feet by fluvial deposit F. 

8. Downcutting of at least 20 feet. 

7. Aggradation of about 40 feet by fluvial deposit E. 

6. Downcutting of unknown amount. 

5. Deposition of lahar D. 

4. Deposition of fluvial gravel C. 

3. Deposition of lahar B. 

2. Channel of Nisqually River represented by fluvial 

deposit A. 

1. Deposition of peat and pyroclastic layer Y on top 

of Paradise lahar. 

In reconstructing these events, I assumed that the 

presence of a lahar at a certain height does not necessarily imply tJhat the valley was filled by solidified lahar 

to that height. This is because lahars typically attain a 

"high-water mark" formed by a transient crest and ma:y 

only leave veneers on preexisting terraces of various 

heights as the bulk of the flow drains on down the 

valley. 

ORIGIN OF LAHAR ASSEMBLAGES IN THE NISQUALLY 

AND WHITE RIVER VALLEYS 

The histories of the White and Nisqually River valleys are strikingly similar during the period between 

deposition of pyroclastic layers Y and W. When layer 

Y was formed about 3,600 years ago, both valley floors 

were at or near their present altitudes, and peat was being deposited in both valleys, probably in back swamps 

adjacent to the flood plains or on low swampy terraces. 

At this time flood plains in both valleys probably were 

relatively stable and Mount Rainier volcano had long 

been dormant, or nearly so. A radiocarbon date on wood 

from a bed of clay in the White River valley indicates 

that the White River flood plain was still relatively 

stitble until some time 'after 2,700 years ago (p. 30). 

Some time later, however, both valley floors changed 

drastically as the rivers began alternately to aggrade 

and erode. 

Possible explanations for the drastic change in the 

habit of the White and Nisqually Rivers, as well as that 

of some other rivers that head on the volcano, include 

the following three factors : tectonic movement of the 

land, climatic change, or most likely, an episode of 

volcanism. The relatively short time during which the 

valley floors were repeatedly aggraded and eroded suggests that recurring vertical movements of the land were 
42 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

FIGURE 18.----0rudely sltratified poorly sorted fluvial gravel in lahar assemblage C, exposed in west bank of Nisqoolly River 

near the mouth of Van Trump C'reek. The large granodiorite boulder at the upper right is about 11 feet long; handle o.f 

pick beneath boulder is about 17 inches long. 

not the cause. Nor is it likely that the climate could have 

changed sufficiently and often enough in this interval to 

account for the recurring cutting and filling. Climate 

changes generally alter the discharge-load ratio of 

streams and cause them to erode or aggrade. Aggradation of a valley floor in a basin occupied by valley 

glaciers typically occurs during a glacial episode, and 

downcutting follows during late glacial and early interglacial time; in such an environment most of the remainder of the interglacial interval is normally characterized by relative stability of the flood plain 

(Schumm, 1965, and references therein). At Mount 

Rainier the valleys in question contain glaciers today 

at their heads, and there is little question that these 

glaciers have been present, though variable in size, 

throughout Holocene time. 

The lahar assemblages must predate trees growing on 

them. In the White River valley a tree more than 700 

years old was found on a terrace underlain by the lahar 

assemblage just downvalley from the terminal moraine 

of Emmons Glacier. Sigafoos and Hendricks (1961, p. 

A16) thought that the forested surface of this terrace 

is at least 1,000 years old. In the Nisqually River valley 

I found a living tree ·at least 790 years old on the surface 

of lahar assemblage C near Cougar Rock campground. 

The lahar assemblages in both valleys probably were 

formed prior to 1,000 years ago. 

The interval during which the White and Nisqually 

Rivers repeatedly aggraded and eroded coincides generally with the Winthrop Creek Glaciation (table 3). 

During the Burroughs Mountain Stade of that glaciation, which probably occurred between 3,000 and 2,500 
DESCRIPTION OF LAHARS 43 

years ago, most glaciers in the park were no larger than 

they were at the beginning of the present century, and 

En1mons and Nisqually Glaciers were smnewhat s1naller 

(Crandell and Miller, 1964). Most of the lahar assemblage in the White River postdates pyroclastic layer C, 

which was erupted about 2,300 years ago, and thus its 

origin seemingly cannot be related to climatic or glacial events of Burroughs Mountain time. The stratigraphic relation of lahar assmnblage C in the Nisqually 

River valley to pyrodastic layer C cannot be directly 

determined. 

The oldest known moraines of the Garda Stade of the 

Winthrop Creek Glaciation were formed about 750 years 

ago (Crandell and Miller, 19·64). Inas1nuch as the lahar 

assemblages in the Nisqually and White River valleys 

evidently are more than 1,000 years old, both predate the 

oldest known glaci'al advance of the Garda Stade. Thl' 

assemblages in both valleys probably were fonned during the interval between the two glacial stade.s of the 

Winthrop Creek Glaciation and thus have no genetic 

relation to glaciation. It is pertinent to note that in no 

valley heading on Mount Rainier is there a depositional 

record of large-scale aggradation and downcutting during the Garda Stade con1parable to that represented by 

lahar assemblage C in the White and Nisqually River 

valleys. 

Aggradatinn of the complex lruhar assemblages in 

the two valleys and t:he periods of downcutting recorded within ·the assmnblages probably were caused 

by inter1nittent eruptive activity of the voleano at the 

time the present sum1nit cone was formed. Eruptions 

of the lava flows that fonn the cone could ha.ve caused 

a succession of floods down the flanks of the voleano 

by me1lting extensive fields of snow and ice at the sunlInit. Smne floods may have been transformed into lahars as the,y picked up l'oose n1:a,teria:l from taluses, glacial drift, and alluviun1 on the valley floors. Temporary aggrada:tion :farther down valley, resulting from 

a series of lahars and debris-laden floods, probably was 

quickly followed by downcutting between eruptions, 

when the discharge of rive.rs approacil1ed or returned to 

normal. Subsequent floods and lahars, separated by periods of downcutting, formed the deposits that underlie the terraces. 

The lahars of these assemblages in valleys on the 

east and south sides of the volcano see:n1 to be nearly 

or wholly lacking in clay minerals. This lack is attributed to the derivation of the roek debris in the 

lahars chiefly from talus, glacial drift, alluvium, and 

newly erupted detritus, rather than :from hydrothermally altered rocks of the volcano. 

The proposed c:ause-and-e:ffect relation between 

building of the summit cone and the formation of the 

lahar assemblages cannot be proved, but it is eonsistent 

with all the known :faets. The oone-building erupti0ns 

are not dated, but tihey are thought to have oceur:--ed 

dlu~ing a late part of an extended episode of voleani~m, 

early parts of which are represented by the :formation 

of a bomb-bearing block-and-ash flow deposit in the 

South Puyallup River valley that is about 2,500 ~~a.rs 

old and by the eruption of pyroelastie layer C. 

If this c-ause-and-effect relation is valid, the relative 

abundance of lahars and fluvial deposits in the White 

Riv·er valley may be due to the :faet that tllie sumnrit 

eone was built on the east side of the depression forr'led 

at the top of the volcano by the landslides that lec1

. to 

the Osceola Mudflow. Floods caused by melting srryw 

and ice at the summit deseended Emn1ons, Winthrf}p, 

Nisqually, and l(autz Glaciers. Lahars of post-Y, preW age in each of the valleys below these glaciers prob-

·ably originated during the building of the summit cone. 

Comparable lahar assemblages of the same age are 

lacking in t:he Ohanapecosh, Mowich, and Carbon J>iver valleys, probably because none of these valleys drain 

the summit cone of the voleano. 

LAHAR ASSEMBLAGE D 

Assemblage D in the Nisqually River valley consists 

of alluvium and lahars, younger than the 450-year-old 

pyroclastic layer W, that form low, tree-covered terraees adja.eent to the modern flood plain. The park headquarters building, museum building, many of the r-=-sidences, and maintenance buildings at Longmire are c:Dnstrueted on a eoarse bouldery lahar that is part of this 

unit. The oldest tree I :found on this deposit started to 

grow in the 1860's. The lahar evidently topped the· VTest 

riverbank immediately downstream from the site of the 

bridge over the river at Longmire and :formed a hbe 

that spread westward into the Long~nire meadow. The 

presenee of old trees around the lobe's south margin indieates that it did not rejoin the lahar along the center 

of the valley. A similar but older lahar forms the terrace on the opposite side of the valley at Longmire 

eampground. The terrace is 5-10 feet higher than the 

sur:faee of the adjacent ehanneled and unvegetated fl')Od 

plain of the Nisqually River. The oldest tree I founc1

. on 

the l'a:h1ar at the eampground started to grow about 400 

years ago, and the absence of pyroclastic layer W ii'ilieates that the lahar eannot be older than about 450 ye~.rs. 

The surface of the lahar is crossed by south-trend~ng 

gullies 1-5 feet deep and is strewn with boulderf as 

large as 4 feet in diameter. 

Small lahars have occurred in the upper reacher of 

the Nisqually River valley several times within the last 

:few decades. Descriptions of some of these lahars am in 
44 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASIDNGTON 

the files of the National Park Service, and they have 

recently been discussed by Richardson ( 1968). 

On October 14, 1932, a lahar destroyed a highway 

bridge across the Nisqually River just below Nisqually 

Glacier. Eyewitnesses told of a mixture of rock debris, 

mud, and water which had a front 25 feet high and 150 

feet wide and which advanced rapidly downvalley toward the bridge. The impact of the flowing mass carried away the center span of the reinforced concrete 

bridge, which was 27 feet wide, 55 feet long, ·and 

weighed an estimated 40 tons. The bridge was carried 

more than half a mile downstream. The observers reported that the moving mass resembled wet concrete 

except :for being darker in color, and they stated that 

large boulders in it were thrown 10-30 feet into the air 

as the mass moved forward. The lahar evidently terminated on the flood plain between the highway bridge 

and Longmire. 

Two years later, on October 24 and 25, 1934, a series 

of four floods or lalhars again carried masses of debris 

down the Nisqually River valley. This time rock debris 

was dumped to a depth of 15 feet on top of a new highway bridge. Richardson (1968) described other "glacier 

outburst floods" that occurred in October 1947 and October 1955. At the same time as the 1947 flood, lahars 

moved down the Kautz Creek ¥alley (p. 46). 

LAHARS IN THE NISQUALLY RIVER VALLEY DOWNSTREAM FROM THE PARK 

Lahars o:f Holocene age are present in the Nisqually 

River valley at least as :far downstream as Elbe. Although they have not been seen in the valley below 

Alder Da1n, it seems likely that remnants also underlie 

the part o:f the valley inundated by Alder Reservoir. 

Upstream :from the reservoir, the deposits are divided 

into two groups by their stratigraphic relation to pyroclastic layer Y; thus, the pre-Y lahar assemblages A 

and B of the upper part of the valley are grouped here, 

as are the post-Y assemblages C and D. 

The deposits older .than layer Y ~nclude uJt least rtwo 

~ahars as well as fluvial gravel. These deposits crop out 

In. streambank exposures on both sides of the Nisqually 

River downstream from the Kernahan Road, which is 

a north-south road that crosses the river 3 miles west 

of the park. On the south side they form a terrace about 

40 feet above the flood plain, which abuts a hill of driftveneered bedrock. An exposure in the :face of this terrace 0.6 mile downstream from the Kernahan Road 

reveals 15-20 :feet of fluvial gravel, overlain by a pre-Y 

lahar about 20 feet thick. The sand and gravel may be 

outwash of Evans Creek age. A similar sequence occurs 

on the north side o:f the valley only a few hundred yards 

downstream, where two lenticular lahars, with a total 

thickness o:f about 12 :feet, overlie 30 feet of fluvial 

gravel. 

Another lahar older than layer Y was n 'lted near 

stream level in the face of a 20-foot terrace ir. the same 

area. An outcrop at the upstream end of the terrace 

exposes a compact lahar, whose base is below river level; 

this lahar is overlain by lenticular fluvial gravel and 

sand. The fluvial deposit is unconformably overlain 

by layer Y, above which is another fluvial g:'.'Rvel. 

Near the mouth of Big Creek, 2% miles dcwnstream 

:from Kernahan Road, outcrops in the :face o:f a terrace 

that is older than pyroclastic layer Y show in descending order a lahar 18 inches thick, lenticular sand 20 

inches thick, and a lenticular lahar as much as 10 feet 

thick. The lower lahar lies in a channel cut into fluvial 

boulder gravel12-20· feet thick. The terrace i? about 25 

feet above the Nisqually flood plain. 

Fluvial gravels and lahars along the Nisqually River 

valley that are younger than layer Y form lew terraces 

adjacent to the flood plain. The most extens~ve depoffit 

floors a channel south of the flood plain :for a distance of 

5 miles between the park and Ashford. The channel, 

which marks a :former course of the Nisqually River, 

is separated :from the modern flood plain by ridges and 

knobs of drift-veneered bedrock. The gradient of the 

channel is less steep than that of the flood plain, so the 

relative height o:f the channel increases downstream. At 

its upstream end, the channel's floor is only about 5 feet 

above the present Nisqually flood plain, but at its west 

end it is 35 feet above the flood plain. Exposures of the 

deposits beneath the channel are poor and for the most 

part reveal only a few :feet of poorly sortecl sand and 

gravel. In some shallow exposures the text·1re of this 

material resembles that of coarse lahars with a sand 

matrix. 

Near the east end of the channel there is ·a gap in the 

bedrock ridge that separates the channel :frc~ the Nisqually River flood plain. In a shallow cut in the floor 

o:f the gap can be seen a compact sandy lahar 3 feet 

thick which overlies a 20-inch layer of Y pumice. A 

shallow excavution in the floor of the channel near a mill 

pond (SW%, sec. 36, T. 15 N., R. 6 E.) 0.4 mile west 

of Kernahan Road shows 6 feet o:f boulder gravel. Most 

o:f the boulders are less than 11h feet in dianeter, but a 

:few are as large as 8 :feet. Farther west, d 'lwncutting 

by Catt Creek into the channel deposit has exposed 

lahars interbedded with fluvial sand. 

From the mouth o:f Mineral Creek to Elhe, deposits 

younger than layer Y consist principally o:f fluvial sand 

and fine gravel. However, a lenticular lahar crops out 

in the north bank o:f the Nisqually River (SW1,4 sec. 

26, T. 15 N., R. 5 E.) 0.2 mile downstrean from the 

railroad bridge south of Park Junction. The deposit 
DESCRIPTION OF LAHARS 45 

is as 1nuch as 12 feet thick and lies in a channel about 

125 feet wide which is floored by pebble to boulder 

gravel and sand. Farther downstre.am, 1nost exposures 

on the valley floor are of deposits of medium to very 

coarse gray sand and granule gravel. Such a deposit 

. was exposed in 1962 in the sides of a trench used as a 

trash dmnp by the residents of Elbe, in the NEl!t sec. 

29, T. 15 N., R. 5 E. There the sand and gravel deposit 

is about 5 feet thick and contains granule-sized pumiee 

derived frmn layer Y; it overlies a sandy lahar more 

than 2 feet thick in which there are a few scattered 

cobbles. 

The gene.ralizecl sequence of postglacial events in the 

valley downstrea1n f1~om the park, reconstructed from 

the deposits preserved in terraces, is as follows (event 

1 is the oldest) : 

1. Aggradation by fluvial gravel fron1 a surface below 

the present flood plain to one at least 20 feet 

higher. 

2. Deposition of lahar, locally as 1nuch as 20 feet thick, 

to forn1 a surface 40 feet higher than the present 

flood plain. 

3. Downcutting of valley floor to a level below present 

flood plain. 

4. Deposition of lahar on valley floor. 

5. Deposition of thin fluvial gravel on valley floor. 

6. Deposition of pyroclastic layer Y. 

7. Aggradation of valley floor by fluvial gravel to surface 10-15 feet higher than present. 

8. Deposition of lahar as 1nuch as 12 feet thick on valley floor. 

9. Downcutting of at least 20 feet to level of present 

valley floor. 

The cmnplex sequence of aggradation and clowncutting that. is recorded by the deposits, terraces, and 

unconfonnities within lahar assemblage C upvalley 

frmn Longmire is only poorly represented in the valley 

west of the park. However, both the channel south of 

the flood plain and that followed by the Nisqually River 

today were aggraded during the deposition of that assemblage. It seen1s likely that the effects of the recurring episodes of aggradation and downcutting diminished progressively downvalley and that they may not 

have extended as far as tlw Puget Sound lowland. 

KAUTZ CREEK VALLEY LAHAR ASSEMBLAGE 

The floor of l{autz Creek valley is underlain by an assemblage of lahars and fluvial deposits into which the 

creek has cut a trench about 31-h miles long, 100-200 

feet wide, and as much as 75 feet deep; the south end 

of the trench is about 11;2 1niles u pstrea1n from the 1nouth 

of the creek. Exposures in the sides of the trench reveal 

a succession of unweathered gray fluvial deposits and 

lahars interbedded with horizons of forest duff and 

tree stlunps (fig. 19) and pyroclastic layers Y and W. 

Beyond the edges of the trench the surface of the as~ 

smnblage is interrupted by old channels of Kautz C-:-eek 

that are separated by ridges and terraces. Parts of the 

surface are forested (fig. 20) and some of these forested areas are older than pyroclastic layer W. Because 

of the convex surface of the assemblage (pl. 2), Pyramid 

Creek flows along its west margin for about 31;2 n1iles 

before joining l{autz Creek. 

Pyroclastic layer Y and deposits beneath it were seen 

at only three places along the valley floor, although the 

pumice mantles the valley walls above the surfac·'3 of 

the lahar assemblage. A buried pumice deposit was first 

noted by Hopson, Waters, Bender, and Rubin (1Pfl2) 

in the east wall of the trench about three-fourths mile 

upstream from the Wonderland Trail bridge across 

Kautz Creek, and my associates and I (Crandell and 

others, 1962) subsequently also examined the sequence 

of deposits exposed there. In that outcrop, pyroclr .;;tic 

layer Y ov·erlies cobble-and-boulder gravel and is overlain by interbedded fluvial gravels and lahars (mo.asured section 6). Layer Y'also crops out in the east bank 

of the creek about 11;2 rmiles upstrea1n from Hs 

mouth. At a third outcrop the pumice over lies a lr.har 

more than 12 feet thick. This locality is about 100 yards 

downstream fr01n the south end of the "box canyon" of 

the Kautz, which is ·a bedrock-walled constricltion in 

the valley southeast of Pearl Falls and 5 miles northeast of the Entrance Road. The "box canyon" is alv·mt 

a quarter of a 1nile long and 250-300 feet wide. 

The lower pyroclastic deposit at measured section 6 

was referred to by Hopson, Waters, Bender, and Rubin 

(1962, p. 641) as "the main ash fall of sand- to granulesized pumice, which constitutes the 1najor part of the 

youngest ash hlanket from Mount Rainier." They found 

stumps of two trees in the bed of l{autz Creek 25 feet 

from the wall of the trench, which they thought ~ere 

rooted in the deposit beneath the pumice. Radiocarbon 

age detennination of their sample of wood from one 

of these stumps indicated an uncorrected age of 3!10 ± 

250 years (W -925). However, microscopic examination 

of pum'ice taken from the outcrop led D. R. Mullineaux 

(in Crandell and others, 1962) to conclude that it is 

pyroclastic layer Y. Layer Y has been hracketed by 

uncorrected radiocarbon dates of 3,500 ± 250 (W -11 15) 

and 2,980-+-250 years (W-1118) (table 4; Crandell and 

others, 1962) . The marked increase in grain size and 

thickness of the pumice layer toward Mount St. Helens 

indicates that this volcano was its source. 

The relations at the Kautz Creek locality and the 

addition of a "correction fa0tor" to the radiocarbon date 

led Hopson and his associates to conclude that the 
46 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Measured section 6 

[East bank of Kautz Creek about 3,000 ft upstream from Wonderland Trail 

footbridge across creek] 

Thickne&B 

(Jt) (in) 

21. Lahar: boulders and cobbles in medium- to 

fine-sand matrix. Deposited in October 

1947_________________________________ 2-8 

20. Duff, silty, dark-grayish-brown; contains 

roots and wood fragments ___________________ _ 

19. Boulders; 1-4 ft in diameter, in matrix of 

stratified coarse sand__________________ 3 

18. Sand, fine to medium, gray; horizontally 

stratified and interbedded with layers of 

yellowish-gray silt_____________________ 2 

17. Duff; contains fragments of carbonized wood _____________________________________ _ 

16. Silt and fine sand, yellowish-gray, horizontally bedded; contains pebbles and granules near top_________________________ 1 

15. Duff and roots (radiocarbon sample W1120, uncorrected age: 290± 200 years, see table 4) ________________________________ _ 

14. Sand, fine, gray ______________________________ _ 

13. Pyroclastic layer W: white pumiceous ash _____ _ 12. Sand, fine, gray ______________________________ _ 

11. Duff, wood, and carbonized wood fragments 

(radiocarbon sample W -1119, uncorrected 

age: 320± 200 years) ________________________ _ 

10. Sand, fine to medium, gray; contains scal,-

tered cobbles ______________________________ _ 

9. Lahar: pebbles and cobbles in compact sand 

and granule matrix; gray_______________ 2 

8. Sand, medium; mostly horizontally stratified but has some faint crossbedding; 

contains reworked pumice of layer Y 

and wood fragments___________________ 5 

7. Lahar: boulders and cobbles in fine- to 

medium-sand and granule matrix_______ 2 

6. Duff mixed with gray fine sand; contains 

fragments of charcoaL ______________________ _ 

5. Sand, fine, gray; contains reworked pumice 

of layer Y and wood fragments _________ ~-2 

4. Lahar: boulders as large as 4ft in diameter 

in gray sand and granule matrix________ 15 

3. Sand, fine to mediunt, stratified, lenticular__ 1-3 

2. Pyroclastic layer Y: yellow pumiceous ash _______ _ 

1. Pebble-to-boulder gravel and sand_________ 1+ 

0 

6 

0 

0 

2 

0 

u-~ 

U-Y2 

~-2 

~ 

Y:l-1 ~ 

6 

0 

0 

6 

~-2 

0 

0 

0 

8 

0 

latest eruptions o:f Mount Rainier occurred about 500 

years ago. However, the pumice deposit on which they 

based this conclusion is not an eruptive product o:f 

Mount Rainier. A prob8Jble explanation :for the relatively young radiocarbon date they cited is that the 

stump from which they took their sample was at a 

horizon stratigraphically above the pumice deposit, instead o:f below it, as they thought. 

Most o:f the lahars and fluvial deposits exposed in 

the walls o:f the Kautz Creek trench are younger than 

layer Y, but some are older and some younger than 

layer W. The lahars range :from layers less than 1 :foot 

thick to unstratified, unsorted beds 20 :feet thick that 

contain boulders as much as 10 :feet across. Des"lite their 

unconsolidated nature, the alluvium and lahars stand 

in very steep and locally vertical banks along tl ~trench. 

Although the lahars are not cemented, the fine material in them makes them somewhat more coherent than 

fluvial gravels in which the fine componert is less 

abundant. The layers o:f fluvial gravel are distinguished 

chiefly by the presence o:f bedding and by Eomewhat 

better sorting. However, the overall range in texture in 

a thick lahar and some comparably thick fluvial deposits does not appear to be appreciably differ~nt. 

Layers o:f :forest litter in the lahar assemblF.~e range 

:from beds o:f duff less than an inch thick to accumulations o:f logs and organic trash that may reprn.sent log 

jams in stream channels that were subsequently buried 

by }ahars or alluvium. The only horizon o:f drff t:haJt is 

easily traceable along the trench walls is that a8Sociated 

with layer W. Stumps are commonly rooted in materia] 

just beneath layer W (fig.19). 

The youngest deposits o:f the lahar assembla ,ge in the 

Kautz Creek valley were :formed during the night o:f 

October 2-3, 1947, and during the early morning hours 

o:f October 3. Details of the events that prec~ded and 

accompanied the lahars are largely taken :fron reports 

by R. K. Grater (1948; unpub. data, Oct. 28., 1947, in 

files o:f the National Park ~ervice) and :from an unpuhlished, undated report by C. E. Erdmanr1 and Arthur 

Johnson o:f the U.S. Geological Survey, also in the files 

o:f the National Park Service. 

According to Erdmann and Johnson, rain Ftarted to 

:fall a few hours after midnight on October 1 and 

reached its greatest intensity between 5 and 9 a.m. on 

October 2. A total o:f 5.85 inches :fell at the Ranger Station at Paradise Park between 4: 30 p.m. Oc;tol:ler 1 and 

the same time the next day, but very little :fell d·1ringthe 

~arly hours o:f October 3. During the downpour, a cloudburst evidently occurred in the upper part o:f the Kautz 

Creek drainage basin, and an additional anount of 

water n1ay have boon contributed by a "glacier outburst 

flood" :from Kautz Glacier (Richardson, 1968, p. D83). 

The discharge o:f Kautz Creek ntcnw~d gre,atly during 

the daylight hours o:f Octdber 2, and ~tweer. 7 and 8 

p.m., high water washed out the entran~ ror"l bridge 

over the creek. The first 1ahar occurred between 10 and 

11 p.m. and was heralded by a dull roar and vibration 

o:f the ground as it advanced down the valley. A succession o:f lahars flowed downvalley during the night, and 

the last occurred 1at 8 ·a.m. the next morning. The lahars 

were described by eyewitnesses as having tl,~ consistency o:f wet concrete, carrying along vegeta Jtion and 

boulde·rs as large ·as 13 :feet in diameter. 

After the lahars ceased, Kautz Creek was fl f)Wing in 

a trench 30-75 :feet deep and 100-200 :feet wide south 
DESCRIPTION OF LAHARS 47 

FIGURE 19.-Deposits in west bank af Kautz Creek, about 0.35 mile downstream from the Wonderland Trail. The cobbleand-<boulder gravel (A) at the base is probably a fluvial deposit. It is overlain by a layer of dufl' and roots (B), above 

which is a lenticular lahar (C) a few feet thick. Above the l-ahar, at the right sdtle Olf the photogmph, is a layer of 

roots and dufl' (D) which includes pyroclastic layer W. Above this are other lahars and fluvial deposits. 

of the "box canyon." How much of this trench existed 

before the lahars occurred is not clear; Grater ( 1948, 

p. 279) stated that "an entirely new stream channel was 

out, with the old bed of Kautz Creek left high on the 

side of the canyon." The topography of the valley floor 

suggests, however, that the present trench could have 

been localized along a preexisting channel (pl. 2.) Remnants of the 1947 lahars form discontinuous narrow 

strips along the edges of the trench, and although they 

locally extend beyond. the trench in lobes, they do not 

veneer wide areas in the upper part of the valley. Their 

distribution suggests that the lahars were largely confined to the trench and that the trench either predates 

them or was formed contemporaneously. The narrow 

strips of laharic deposits are generally less than 10 feet 

thick, but near the south end of the trench they a.re as 

much as 18 feet thick. 

Even though the present trench may have been localized along a former course of Kautz Creek, that stream 

course undoubtedly was cut down and wiG.ened at some 

time on October 2 or 3. Evidence from the lahar assemblages exposed in the Kautz Creek valley and in other 

valleys at Mount Rainier indicates that lahars themselves are not effective erosional processes at the gradients found on most valley floors below the glaciers. If 

this is true, downcutting of the trench probably was 

accomplished not by the lahars themselves, but by floodwaters. 

During the morning of October 3, according to the 

report of Erdmann and Johnson, the valley floor downstream from the trench aggraded about 28 feet where 

it is crossed by the entrance road. The area of aggradation forms a fan whose base, along the Nisqually River, 

has a breadth of about 2,500 feet. The area narrows 

northward to 500 feet or less and apexes at the mouth 

of the trench. Although the fan in the lower part of the 

valley probably contains most of the coarse debris transported on October 2 and 3, much of the fine material 

was carried downstream by the Nisqually River and 

was deposited on :the floor of Alder Reservoir. Grater 

( 1948) estimated the total volume of the lahars and flood 

deposits to be at least 50 million cubic yards. 

During a subsequent investigation of the upper Kautz 

Creek valley, R. K. Grater (unpub. data, 1947; 1948) 

found that the lower 1-mile segment of Kautz Gla.cier 

had largely disappeared, and a gorge 300 feet deep and 

as much as 900 feet wide had been cut into the ice. Grater 

inferred that the gorge had been cut by excessively high 
48 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

FIGURE 20.-Bouldery surface of a pre-W l11har assemblage that 

underlies ·the floor of tlhe Kautz Creek valley about 1 mil(' 

north of the Wonderland Trail crossing of Kautz Creek. 

runoff, aided by toppling of ice masses as the glacier was 

undercut. Blocks of ice, accompanied by masses of glacial drift that slid from the precipitous canyon walls, 

created temporary dams in the "box canyon," the failure 

of which caused floods of water and masses of saturated 

debris to flow down the valley. Repetition of sliding and 

daJmming caused successive lahars •and floods to surge 

down the valley. The trench of Kautz Creek probably 

was cut by the floods, and this erosion itself may have 

created lahars as the undercut sides of the trench toppled into the floodwaters. 

Samples of some of the fluvial gravels and lahars deposited on October 3, 1947, were obtained from an outcrop in the bank of the Nisqually River along the south 

edge of the fan (fig. 21). The size distribution of four 

samples, and other data, are shown in table 12 and figure 22. X-ray analysis of a sample of one of the lahars 

(sample 2, table 11) indicated that the silt and clay 

fractions consist almost wholly of plagioclase feldspar. 

TABLE 12.-Grain-size distribution data on deposits formed by 

floods and lahars in October 1947 in the Kautz Creek valley 

Unit Thick- Clay S!lt Sand Median Sorting (fig. Description ness (per- (per- (per- diameter coeffi21) (ft) cent) cent) cent) (mm) clent 

4 Sand and pebble graveL ________ 3--4 1 5 53 1.6 2. 32 

3 2 Lahar ___ ---- ---- 3.5 4 11 48 .8 8.10 _____ do ___________ 1. 5 3 11 51 .63 3.41 1 Sand and 

granule graveL >2 3 40 2. 75 3.38 

FIGURE 21.-Lahars and fluvial sand and gravel deposited near 

the moutb of Kautz Creek in October 1947. Units 2 and 3 

are fine and coarse lahars, respectively; units 1 and 4 are 

probably both fluvial deposits. 

On August 23, 1961, a short-lived flood was observed 

in Kautz Creek at the entrance road bridge by Park 

Service personnel (fig. 23). This flood occurred during 

a dry spell and thus apparently originated from the release of unusual amounts of melt water by Kautz Glacier. Photographs of the flood and eyewitness accounts 

suggest that the flood was heavily laden with both fine 

and coarse rock debris, but not so extensively as to form 

a viscous mudflow. In its proportion of water to rock 

debris, the flood may have been a "hyperconcentrated 

flow" (Beverage and Culbe11tson, 1964; p. 4, !this report). 

Photographs taken of various parts of the Kautz 

Creek trench in the vicinity of Wonderland Trail before and after the flood indicate that the increased discharge caused aggradation in some parts of the trench, 

removed loose debris along ·the sides, and in some places 

resulted in sideways erosion into the lower parts of the 

trench walls (fig. 24). If the increased discharge had 

been appreciably greater and of longer duration, wholesale sloughing of the trench walls probably would have 
DESCRIPTION OF LAHARS 49 

E 

E 

~ 

w 8 N 0 

Ui 100 

0 

w 

~ u 

Ci 

z 

z 

< 

I 

ffI 

(!) 

90 

80 

70 

w 

:;:: 60 r--

>-

m 

0:: 

w 

z 

u: 

en 

w 

..J 

u 

f= 

0:: 

< 0.. 

u.. 

0 

w 

(!) 

~ z 

w 

u 

0:: 

w 

0.. 

50 

40 

30 

20 

10 

0 

r----

CLAY 

Sample 

1 

2 

A 

B 

--

E E E E 

0 

0 0 

Sorting 

coefficient 

8.10 

3.41 

3.38 

2.32 ~/ ~ 

/ l/ 

/ I 

/ 

-~ ~ ~/ 

~ 

--- -;;::::. -::::-~ 

-- c:::::: :::::: ::: 

SILT SAND 

E E 

E E 

E E 0 

~ 0 ~ 0 0 ~ ~ ~ 

:---/' // 

/ '// I v 

/ / v 

/ I ~ rv/ 

~ f --- Q / [/ Q\";) II 't?:'b / ~; _,/ 

~I-_ '?- 0/ 1>~1' I"';' 

ll I 

I 

GRANULES PEBBLES COBBLES 

FIGURE 22.- Cumulative curves of size distribution of deposits formed by :floods and lahars in the Kautz Creek valley in 

October 1947. Samples 1 and 2 are both from lahars; samples A and B are probably both :fluvial deposits and are 

frOI!ll units 1 and 4, respectively, in figure 21. 

resulted from undercutting, and lahars might have been 

formed. 

I traversed the Kautz Creek valley from Wonderland Trial to the entrance road on September 13, 1961, 

and found that the flood had been at least 6 feet deep and 

perhaps as much as 12 feet deep in places because it had 

overflowed the stream channel where the banks are that 

high. Part of this channel depth, however, may have 

been caused by stream downcutting following the flood's 

passage. At the entrance road, the flood was confined 

to the channel of Kautz Creek (fig. 23). 

This flood formed bouldery ridges in some places on 

the flood plain. Boulders and trees in its path were 

coated up to a height of 4 feet with a cementlike slurry 

of coarse sand in places where the flow was not confined to a well-defined channel. The slurry had been 

subsequently washed off the lower 1% feet of these 

boulders and trees; thus, the p3S'lage of the flood evidently was followed by high discharge of relatively 

clear water before Kautz Creek returned to normal. 

LAHARS IN THE VALLEYS OF TAHOMA CREEK AND THE 

NORTH AND SOUTH PUYALLUP RIVERS 

Nine lahars were recognized in the valleys of Tahoma 

Creek and the two branches of the Puyallup River; 

their age and stratigraphic relation to some other Holocene deposits present on the west side of the volcano are 

as follows: 

Two or more lahars of unknown age. 

Lahar about 4M) years old. 

Pyroclastic layer W (about 450 years old). 

IDle0tron Mudfiow about 600 years old. 

Lahar about 1,000 years old. 

One or more lahars of unknown age. 

Bomb-bearing block-and-ash flow about 2,500 years old. 

One or more lahars of unknown age. 

Round Pass Mudfiow about 2,800 years old. 

Pyroclastic layer Y (about 3,600 years old). 

Lahar of unknown age. 

The Round Pass Mudflow, the 1,000-year-old lahar, 

and the Electron Mudflow occur in more than one vallay and are described first; others, which are not known 

in more than one valley, are discussed subsequently, 

according to the valley in which they are found. 

ROUND PASS MUDFLOW 

Roadcuts at Round Pass (fig. 25) expose a mudflow 

as much as 25 feet thick, which overlies pyroclastic 

layer Y and underlies layer W. The color of the mudflow is purplish to pinkish gray where seen in the roadcuts. The deposit is here named the Round Pass Mud-
50 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

FIGURE 23.-Flood. in Kautz Orleek channel at entrance rood on August 23, 1961. The character of the water surface 

and the muddiiness of the water suggest that the flood was a "hypeooonoentrated flow." The dead tvees in the background were killed by the 1947 lahrurs and floods in the Kautz Creek valley. National Park Service phot<Jgraph. 

flow ; its type locality is at Round Pass. Roadcuts on 

the north side of the Tahoma Creek valley between the 

valley floor and Round Pass show a veneer of mudflow 

a few inches to as much as 6 feet thick on top of layer 

Y and Evans Creek Drift. In one exposure, reworked 

pumice from layer Y forms irregular masses within 

the mudflow. The Round Pass Mudflow crops out along 

the trail to Lake George (fig. 25) up to an altitude of 

about 4,350 feet, which is about 350 feet higher than 

the pass and a little more than 1,000 feet above the floor 

of the Tahoma Creek valley. 

The Round Pass Mudflow also underlies parts of 

Indian Henrys Hunting Ground, which is on the divide 

between Tahoma Creek and Kautz Creek. The southwest margin of the mudflow ends there in an abrupt 

front about 17 feet high (fig. 26) where it is crossed by 

the Wondedand Trail about 300 yards south of a patrdl 

cabin (pl. 1). The boundary between the mudflow and 

the adjacent Evans Creek Drift is conspicously marked 

by the absence or presence of pyroclastic layer Y. At 

Indian Henrys Hunting Ground the mudflow extends 

to a maximum altitude of about 5,350 feet, which is 

nearly 1,000 feet higher than the floor of the Tahoma 

Creek valley directly to the north. 

The Round Pass Mudflow crops out at several places 

along the Tahoma Creek valley. One of these outcrops 

is a streambank exposure about 1 mile upvalley from 

Tahoma Creek campground (measured section 9). 

There the mudflow unconformably overlies coarse fluvial gravel, from which it is separated by pyroclasti<~ 

layer Y, and is as much as 20 feet thick. The mudflow 

contains boulders as large as 6 feet in maximum dimen-
FIGURE 24.-Banks of Kautz Creek about half a mile upstream from theW onder land Trail shortly after the flood of Augu9t 23, 1961. The high discharge steeoened and looally undercut 9treambanks. The sparsely vegetated areas on the terraces on both sides of the creek were covered by 

the lahars and floods of October 1947. National Park Service photograph. 

t1 

trl 

\11 

() 

::0 

...... 

'"C 

>-3 

...... 

0 

z 

0 

"::: 

::0 

~ \11 

Cl 

....... 
52 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

122" 

0 

0 

0 

• Ashford 

• National 

1 'h 0 2 3 4 MI LES 

Mo'Wich /,ake 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

/,./) 

I I I U I 

/f I 

11 J 

(/~~! --

FIGURE 25.-Inferred original extent of Round Pass Mudflow. The west edge of the Oaooade Range lies about 4 miles 

beyond the northwest corner of the ma p. Numbers show localities of samples (table 10) of the Round Pass Mudflow 

and other lahars west of the volcano. 

sion and logs as large as 4 feet in diameter. The mudflow 

was identified downvalley to a point about 1 mile north 

of the Nisqually River. At that point it caps a terrace 

which is about 60 feet higher than the Tahoma Creek 

flood plain. 

In the North and South Puyallup River valleys I 

recognized the mudflow as far downstream as a point 10 

miles beyond the park boundary, and it may have extended even farther. Remnants of the mudflow veneer 

the valley walls of the North Puyallup River up to a 
DESCRIPTION OF LAHARS 53 

FIGURE 26.-South edge of Round Pass Mudfiow along the Wonderland Trail at Indian Hoorys Hunting Ground. The front 

af the mudfiow is abo111t 17 feet high; surface to the right is underlain by thin IDv·ans Oreek Drift and bedrock and veneered 

with pyroclastic layer Y. The pumice is absent from the mudfiow. 

maximum height of about 350 feet above the valley floor 

directly north of Klapatche Park. Farther downstream, 

a quarter of a mile west of Mount Rainier N a;tional 

Park, the mudflow coats the valley walls to a maximum 

height of about 240 feet. The mudflow, exposed there in 

cuts along logging roads, lies on top of layer Y (fig. 

27) and talus. In these exposures, the base of the pumice 

layer contains many small pieces of charcoal, but none 

were noted either at the top of the layer or in the overlying mudflow. About three-quarters of a mile farther 

downvalley, near the mouth of the North Puyallup 

River, cuts along another logging road expose the 

Round Pass Mudflow up to a height of a little more than 

200 feet above the river. 

In the South Puyallup River valley, remnants of the 

mudflow coat the valley wa:lls to a height 'Of about 1,000 

feet above the river at a point 1.7 miles north of Round 

Pass, about 350 feet at the mouth of St. Andrews Crook 

just west of the park, and about 250 feet at the northwest end of Kl,apatche Ridge (fig. 25). Near the mouth 

of the Mowich River, 51;2 miles farther downstream, the 

highest remnants are 160 feet higher than the Puyallup 

River, and the base of the mudflow is below river level. 

An imaginary line connecting these high remnants of 

the mudflow has a downvalley slope of about 550 feet 

per mile between Round Pass and the mouth of St. 

Andrews Creek, whereas the valley floor now has a 

gradient of about 300 feet per mile between these points. 

However, this line might not represent the' sloping upper surface of a continuous, deep, flowing stream of 

mud, but instead could record the maximum height 

reached by one or more transient waves of the mudflow. 

Below St. Andrews Creek, where the valley widens 

appreciably, the slope, as reconstructed from high 

mudflow remnants, decreases and becomes more nearly 

parallel to the present slope of the valley floor. 
54 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

FIGURE 27.- Round Pass Mudfiow on top of pyroclastic layer Y at a poirut 24() foot above the floor of North PuyW!lup River 

valley a quarter of a mile west of the park. 

The Round Pass Mudflow underlies a broad area in 

the Puyallup River valley :from the mouth o:£ Deer 

Creek downstream to the mouth of LeDoux Creek. The 

Puyallup River has cut a trench as much as 100 :feet 

deep into this mudflow fill. Although the Round Pass 

Mudflow may underlie the floor of the Puyallup River 

valley beyond the mountain :front, I did not recognize 

it in outcrops while mllipping the valley nor did I identify it in logs o:£ wells beneath the valley floor. 

Two samples of the mudflow at Round Pass were examined for grain-size distribution, and one was examined for clay mineralogy. The samples contained 24 

and 22 percent silt- and clay-sized material, respectively, 

and had sorting coefficients o:£ 14.18 and 11.2 (table 10, 

samples 13 and 14). Montmorillonite is the predominant 

clay mineral; it is accompanied by feldspar and cristohalite in the clay-sized fraction (table 11, sample 14). 

A sample of the Round Pass Mudflow from an outcrop 

near the mouth o:£ the Mowich River contained 20 percent silt and clay; montmorillonite made up about four 

parts in 10 of the clay (tables 10 and 11, sample 16). 

Cumulative curves o:£ grain-size distribution o:£ samples 

o:£ the mudflow :from two localities are shown in figt1re 

28. 

A sample taken :from 1-2 feet below the top o:£ the 

mudflow at measured section 9 in the Tahoma Creek 

valley oon'ta.:ined 18 percent clay and silt and had a 

sorting coefficient of 10.6 (table 10, sample 12). The 

clay-sized :fraction of tJhe sample consisted mostly o:£ 

:feldspar and cristobalite and contained small amounts 

o:£ several clay mineraJs (table 11, sample 12). 

At~terberg limits were determined for one sample o:£ 

the Round Pass Mudflow from the outcrops at Round 

Pass. The plastic limit o:£ the sample was 20, and the 

liquid limit 25; thus, it had a plasticity index o:£ 5. 

Because remnants o:£ the Round Pass Mudflow can 

be found on tJhe slopes o:£ the volcano at least as :far 

as the east end o:£ Emerald Ridge and to an altitude 

o:£ nearly 7,000 :feet on the ridge that extends :from St. 

Andrews Park to Puyallup Cleaver, I presume thrut 

the mudflow originated somewhere on the flank o:£ the 

volcano upslope from these points. The mudflow's clay 
DESCRIPTION OF LAHARS 

E 

E 

..... 

0 LLJ 0 

~ c.i 

(/) 100 

0 

LLJ 

!;;: 90 ~ 

0 

z 

z 

<( 

J: 

80 

f- 70 fJ: 

(!) 

w 60 ~ 

>-

(0 50 0:: 

~ 

'----

Sample 

6 

7 

9 

11 

12 

E 

E 

..... 

0 

c.i 

Sorting 

coefficient 

3.94 

8.83 

7.42 

9.75 

10.60 

E 

E 

// 

/ 

/I 

/ 

/ 

// 

~ 

~~~·" 1><f:' 

~/ 

"/ 

~ 

v·v ~/ 

E 

E 

~ ..... 

,."' 

,. ...... ... -1- ·- .......... 

_,Y 

E 

E 

0 

s 1----

// 

~/ 

... ~ / 

/ 

// 

.......... , /A \.~/./ l))"' ~ 9\e 3 ~A . s•"'/ 1~ ~/ v/ (<' 9\e / ..!/ 

~1> ~'Q (<:' ~~~~e/ IS.~.· ·::;;;.,..v c;,~~ •• ,;v v~ ;. ... ~vv ... ·· 

~;:::>"'" 

~·/ / 

/ I 

~A ~· 

~/ 

.--:::p 

;.-:~ 

~ 

;;~~"' 

E 

E 

0 

c.i 

8 

LLJ 

z 13 14.18 / 

/" v· 

/"" .... .v 

I"' jill v ____ ,. 

~,.. .·· ~ _..I' .. Li: 40 ~· ...... ~ .,-·· (/) 

LLJ 

...J 

/ 

/ .. 

v· 

I'~ 

// ~ ~/ v ~ ,. .. •" . v . ~-

~ 30 

I' ,.,..... .. 0:: 

0: 

LL. 20 

0 

LLJ 

~ 10 fz 

LLJ 

~ 0 

_.:.--::::-.:: 

----

----·----

f'-

-- ....... 

_ ..... 

~-::-;:: .:;::: ~~~ ~~ --- = 1::-: ':'::.- . . . =:-:::-:: .... .. -: . 

,. ... / ,.I--I'~ ..... .. · v· v ,....,..... ~/ ,,-" ,; 

k~ v 1-- 1-' ••• 

v I-' 

~ ~~~ .,..,.·· 

p __ ... ~ -·· 

~ ----C,L~AY--~~-------S,ILrT--------~~----------S-A~N-0----------~G~R~ANULES PEBBLES COBBLE~ 

FIGURE 28.-0umulative curves of size distribution Olf ·samples of •the E'lectron Mud:flow (samples 6 and 7), lahar that is unit~ 

in measured section 9 in the Tahoma Cr-ook vaUe.y (sample 9), 1.000-year-ol!d lahar in the South Puyallup River V'alley 

(sample 11), and the Round Pass Mud:flow (samples 12 and 13). 

mineralogy suggests derivation from 1nasses of alt€red 

and partly altered rock similar to those now present 

in !the east wall of Sunset Amphithea.ter (p. 17). The 

mudflow probably originated as a massive avalanche 

or series of avalanches of this kind of rock. The distribution of the mudflow as a veneer on older deposits 

in the valleys dose to ~fount Rainier indicates that the 

mud was very fluid and that almost al'l of it drained 

away afte·r the crest of the mudflow passed downvalley. 

The heights reached by the mudflow suggest that the 

flow had enough volume to fill temporarily the upper 

South Puyallup and Tahoma Creek valleys to a depth 

of at least 1,000 feet, either as a flowing stream of mud or 

as one or more large waves. The mass of the mudflow 

needed to form a deep flowing stream of mud probably is adequately represented in the Puyallup River 

drainage by extensive deposits which probably have a 

volume of at least 200 million cubic yards in the area 

west of the park. Because of its water content, the lahar 

must have had a substantially greater volume while 

moving. Deposits of comparable volume have not been 

found in the Tahoma Creek valley, and the mudflow .apparently had a depth of only a few tens of feet at a point 

just 4 miles downvalley from Round Pass. These relations may have resulted from movement of the mudflow 

down Tahoma Creek valley as a single huge transient 

wave, which progressively decreased in height, similar 

to that inferred for the P.aradise lahar ( p. 36) . Substantial amounts of the mudflow were left only in are:r.s 

where a low slope did not permit it to drain away; 

elsewhere veneers only a few thick were left on the 

sides and floor of the valley. Different volumes oft]'~ 

mudflow in the three valleys may have resulted fro"ll 

slightly different directions of initial downslope movement of successive avalanches from Sunset Ampl1 itheater, which caused unequal amounts of debris to move 

into the respective valleys. Or, the different volum~s 

could have been caused by unequal lateral distribution of 

rock debris within a single enormous avalanche. 

Three radiocarbon dates have been determined on 

wood from logs contained in the Round Pass Mudflow. 

One of these was from a streambank exposure in the 

Tahoma Creek Valley (measured section 9) ; it had a 

radiocarbon age of 2,610±350 years (W-2114). Tvro 

other samples were from streambank outcrops near the 

mouth of the Mowich River. One sample, from the north 

bank 500 feet upstream from the river's mouth, had a 

radiocarbon age of 2,170+200 ye·ars (W-566). Th~ 
56 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

other, from the south bank 500 feet further upstream, 

had an age of 2,710+250 years (W-1972). When corrected, these three dates are about 2,800, 2,200, and 

2,900 years, respectively (table 4). The reason for the 

substantial age difference is not known because there is 

no stratigraphic evidence in the outcrops near the mouth 

of the Mowich River of two n1udflows. I assume that the 

Round Pass Mudflow is about 2,800 years old. 

1,000-YEAR-OLD LAHAR 

A clayey lahar initially recognized at a streambank 

outcrop in the South Puyallup River valley near the 

Wonder land Trail bridge was first thought to be the 

Round Pass Mudflow, but a radiocarbon date of 1,100± 

250 years (W-1971) on a log from the outcrop showed 

it to be younger. The lahar also was subsequently identified 10 miles farther downstream by a radiocarbon date 

of 1,050+350 years (W-2113) on a log from a preElectron lahar at measured section 7. When corrected, 

t~ese two dates are about 1,050 and 1,000 years, respectively (table 4). 

At the Wonderland Trail outcrop in the South Puyallup River valley, the lahar is more than 10 feet thick; 

its base is below the river, but bedrock probably is not 

far below river level there. On top of the lahar is a 

bouldery lahar about 6 foot thick that may be only a 

few decades old. The 1,000-year-old lahar is compact, 

clayey, and yellowish brown. It contains about 29 percent silt and clay (table 10, sample 11) in which the 

clay-sized fraction consists of montmorillonite, cristohalite, and feldspar (table 11, sample 11). 

Atterberg limits. determined on a single sample of the 

mudflow obtained from the Wonderland Trail outcrop 

are as follows: plastic limit 21, liquid limit 25 and 

plasticity index 4. ' 

The 1,000-year-old lahar may have a correlative in the 

Tahoma Creek valley, where, at measured section 9, 

there are two l·ahars younger than the Round Pass Mudflow but older than pyroclastic layer W. 

ELECTRON MUDFLOW 

The Electron Mudflow was named from Electron, 

a small community beside the Puyallup River at the 

west margin of the Cascade Range (Crandell, 1963b, 

p. A50). Remnants of the mudflow underlie much of 

the valley floor from Electron northward to the outskirts of Sumner (pl. 3). The mudflow is ·an unsorted 

mixture of subangular to subrounded rock fragments 

in a purplish-gray matrix of sand, silt, and clay. It 

generally exhibits a size gradation upward from coarse 

material at the base to rne material at the top. Samples 

of the bottom foot and top fOdt of the mudflow from 

a seetion 6·¥2 foot thick near McMillin were examined 

for grain-size distribution. The bottom and top samples 

had median diameters of about 1 and 0.1 mr1 and a silt 

and olay content of 20 and 36 percent, respectjvely (table 

10, samples 7 and 6). The cumulative curvo.s of these 

samples are shown in figure 28. In the clay-sized fraction o£ sample 6, montmorillonite made up an estimated 

six part in 10, plagioclase feldspar two parts, and cristohalite one part. 

A sample of the Electron Mudflow from t.he outcrop 

at measured section 6 contained about 27 percent silt 

and clay, in which montmorillonite and chlor.te together 

made up -about four parts in 10, with the former clay 

mineral predominating (tables 10 and 11, sample 8). 

The rem·ainder of the silt and clay fractio:'l consisted 

of feldspars and quartz. 

Rocks from Mount Rainier volcano made up an aver~ 

age of 41 percent and older rocks of the Cascade Range 

59 percent of samples of pebbles collected fro:-n the mudflow at five different localities in the lowland (Crandell, 

1963b). The most distinctive rock in the muaflow in the 

low land is a scoriaceous, black, hypersthene andesite, 

which occurs as boulders as large as 5 feet in diameter. 

These are mostly found lying on the surface of the mudflow. The largest boulders, however, are of a reddish~ 

brown breccia derived from the volcano, some of which 

are at least 35 feet in maximum observable dimension. 

These large boulders were seen mostly in an area extend~ 

ing from Orting southward for a distance of a:bout 2 

miles. This distribution proba:bly is a result. of a more 

gentle gradient in this area than along the valley farther 

upstream. The gradient of the mudflow is al'0Ut 68 feet 

per mile just downstream from the mountain front at 

Electron; however, at a point '2 miles south of Orting 

the valley widens, and the gradient decreas':\,8 to about 

34 feet per mile. The very large masses of breccia probably lodged on the old valley floor in this area as the 

mudflow spread laterally, thinned, and d£'-0reased in 

velocity. 

Hand angering and power angering, in addition to 

natural exposures, show the mudflow to ovr.rlie fluvial 

sand and gravel deposited by the Puyallup F.nd Carbon 

Rivers; the mudflow itself is overlain by f·1vial sand 

and silt deposited by overbank floods. A wooi fragment 

obtained from the mudflow near Electron had a radiocarbon age of 530+200 years (W-565; Cran~ell, 1963b, 

p. A51). When corrected, this age is about 600 years 

(tabJe4). 

The Electron Mudflow has been tentatively identified 

at many places along the Puyallup River valley between 

Electron and the lower slopes of Mount Rainier. The 

following units crop out in a streambank on the north 

side of the river about 1 mile downstream :from the 

mouth of the Mowich River (measured section 7). 
DES·CRIPTION OF LAHARS 57 

Measured section 7 

[Streambank on north side Puyallup River in the SW~ sec. 34, T. 17 N., R. 6 E.] 

Thickness 

(ft) 

4. Electron Mudflow: subrounded to subangular pebbles, 

cobbles, and boulders as large as 7 ft across in 

plastic matrix of purplish-gray clayey sand________ 9 

Erosional unconformity. 

~. Sand and pebble to boulder gravel, lenticular; contains 

some layers of openwork pebble gravel, oxidized to 

yellowish brown; as thick as_____________________ 3 

2. Lahar: subrounded to subangular pebbles, cobbles, and 

boulders as large as 3 ft across in plastic matrix of 

purplish-gray clayey sand, mottled with yellowishbrown iron oxide; lenticular; contains logs and wood 

fragments, one of which was dated as about 1,000 

years old (table 4, sample W-2113); as thick as____ 5 

1. Sand and pebble to boulder graveL_________________ > 1 

Covered, to river leveL______________________________ 4 

Unit 2 in measured section 7 is the 1,000-year-old 

lahar described previously ; this lahar and the Electron 

Mudflow lie within a valley eroded into the Round Pass 

Mudflow by the Puyallup River. The top of the lahars 

and alluvimn within this valley is only a little more than 

20 feet above river level, whereas the top of the Round 

Pass Mudflow in this area is about 100 feet above the 

river. 

Near the mouth of St. Andrews Creek, just west of 

the park boundary, the Electron l\fudflow is about 6 feet 

thick and overlies a sandy lahar more than 15 feet thick. 

The two deposits form a terrace in the South Puyallup 

River valley whose top is about 50 feet above river 

level. Ring counts of recently cut stumps indicate that 

some trees on the terrace were at least 435 years old. 

Inside the park two clayey lahars, one of which may be 

the Electron, overlie the bomb-bearing block-and-ash 

flow; the three deposits are superposed in a cut ( measured section 7) along theW est Side Road near the South 

Puyallup River bridge. 

Measured section 8 

[Cut along the West Side Road about~ mile northwest of the South Puyallup River 

bridge] 

4. Lahar: subangular to subrounded pebbles, cobbles, 

and boulders as large as 2 ft across in a plastic 

Thickness 

(ft.) (in.) 

clayey yellowish-brown sand matrix__________ 4 6 

3. Lahar: angular to subangular rock fragments as 

large as 4 in. across in a purplish-gray sand 

matrix; lenticular. Locally, only fine sand occurs 

at this horizon, which contains scattered grains 

of pumice W and bits of carbonized wood_ _ _ _ _ 6 

2. Electron(?) Mudflow: subangular to sub rounded 

pebbles, cobbles, and boulders as large as 2 ft in 

diameter in a plastic clayey yellowish-brown 

sand matrix_______________________________ 7 0 

1. Bomb-bearing block-and-ash flow______________ > 10 0 

The Electron Mudflow underlies about 14 square 

miles of the Puyallup River valley in the Puget Sound 

low land. In this area its thickness ranges frmn a few 

inches to more than 26 feet; it is generally about 15 

feet thick from McMillin southward to a point 2 miles 

south of Orting. If an average thickness of 15 fee~ is 

assumed for the area beyond the n1ountain front, the 

deposit has a volume of a little more than 200 million 

cubic yards. An additional amount of unknown area 

and volume lies between the lowland and its source, 

22 miles away, on the west flank of Mount Rainier. 

The clay-mineral content of the Electron Mudflow 

suggests an origin like that proposed for the other 

clayey mudflows from Mount Rainier; thus, the Electron probably was caused by massive slides of mcist, 

hydrothermally altered rock. These slides may have 

been triggered by an earthquake or by a volC'z.nic 

explosion. 

The Electron Mudflow may have occurred at a t~me 

when the volcano was dormant, for we have found no 

deposits that indicate an eruption about 600 years ago. 

LAHAR ASSEMBLAGE IN THE TAHOMA CREEK VALLEY 

Four lahars have been recognized in the valley of 

Tahoma Creek ; three are older than pyroclastic layer 

W, and one is younger. All are younger than layer Y. 

The sequence is as follows: 

Several small lahars and :floods in 1967, 1968, and 1970. 

Lahar about 440 years old. 

Pyroclastic Layer W (about 450 years old). 

Two or more laha;rs of unkoown age. 

Round Pass Mudflow about 2,800 years old. 

Pyroclastic layer Y (about 3,600 years old). 

Coarse fl.uvia'l gravel. 

Seldom can more than one post-Round Pass lahar 

be recognized in a single outcrop, but stream bank exposures ahout 1 mile upvalley from the Tahomta Cr~k 

picnic area reveal an unusually complete section ( me,asured section 9). In these outcrops, lithologically similar 

lahars in the assemblage can readily be differentiated 

because of the presence of interbeds of alluvium, volcanic ash, and forest duff. Especially striking in the 

1neasured section is the reddish .-brown zone at the top 

of one lahar (unit 5). The association of this zone with 

abundant carbonized wood indicates that its color is the 

result of a forest fire. One can speculate that the forest 

fire was caused by the hot, bomb-carrying block-andash flow in the South Tahoma Creek valley about 2,500 

years ago (p. 64). When some of the l'ahars are t:vaced 

along the outcrop beyond the limit of a lenticular interbed, the contact between them disappears, and they are 

so similar that they cannot be differentiated. 

The youngest lahar in measured section 9 also undo.rlies low terraces at Tahoma Creek picnic area and 

veneers terraces between the picnic area and recent IJ10-
58 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

Measured section 9 

[North bank of Tahoma Creek 1~ miles upstream from Tahoma Creek picnic area] 

ThickneBs 

(ft) (fn) 

9. Lahar: subangular to subrounded cobbles and boulders as large as 2 ft in diameter in matrix of silt 

and sand; no apparent sorting or stratification; 

oxidized throughout to brownish yellow (10YR 

6/8) ; contains wood fragments and logs as large as 3 ft in diameter_ - _____ - _____ - _ - ___ - ______ - - __ 

8. Pyroclastic layer W: lenticular; as thick as _______ _ 

7. Duff; contains bits of carbonized wood; stumps 

rooted in unit 6 extend up through 7 and 8 and are 

truncated by unit 9. Horizontally bedded, medium 

to coarse fluvial sand 2-3 in. thick locally underlies the duff ______________________ - _______ - _ -

6. Lahar: lithologically similar to unit 9; lenticular; as thick as ____________________________________ _ 

5. Lahar: lithologically similar to unit 9; uppermost 

1-4 in. is reddish brown (5 YR 5/4); at top is a 

lenticular layer of carbonized wood 1-4 in. thick. 

6 0 

~ 

1-6 

3 0 

Lahar is lenticular; as thick as_________________ 3 0 

4. Sand, fine to medium, and granule gravel, horizontally bedded, lenticular; as thick as_____________ 1 0 

3. Round Pass Mudflow: subangular to subrounded 

cobbles and boulders in a purplish-gray matrix 

of sand, silt, and clay; contains scattered wood 

fragments throughout and in a concentration 

near the base; sample of wood from log had an 

age of 2,800 years (sample W-2114, table 4); 

lenticular; as thick as _________________________ 20 0 

2. Pyroclastic layer Y: lenticular; as thick as ____ -------- 8 

1. Fluvial gravel: cobbles and boulders as large as 

5 ft across in purplish-gray coarse sand matrix; 

crudely stratified; thickness more than _________ - 20 0 

raines of South Tahoma Glacier. The lahar is exposed 

south of the creek in the banks of a small tributary that 

is crossed by the Wonder land Trail; the highest remnants of the deposit in this vicinity are a little more than 

200 feet higher than the valley floor of Tahoma Creek. 

The oldest trees growing on the lahar are at least 435 

years old. Inasmuch as the lahar is younger than pyroclastic layer W (fig. 29), it probably is ·about 440 years 

old. 

Grain-size analysis of a sample taken from the lower 

2 feet of the lahar at measured section 9 showed a median diameter of 4.2 mm and a sorting coefficient of 8.72 

(table 10, sample 9) ; the cumulative ourve of its size 

distribution is shown in figure 28. The sample contained 

14 percent clay- and silt-sized material. The clay fraction consisted of about three parts in 10 of clay minerals, 

almost wholly montmorillonite, although traces of kaolinite and a montmorillonite-chlorite mixed-layered clay 

were also identified. The remainder of the clay fraction 

consisted mostly of cristobalite, feldspar, and iron oxide 

(table 11, sample 9). 

Each of the lahars in the Tahoma Creek valley originated in avalanches of clay and partly altered rock on 

the west flank of Mount Rainier. These avalanches probably were caused by rockfalls in Sunset Amphitheater, 

which moved southward across Tahoma Glacier and 

into the head of the Tahoma Creek valley. 

Lahars and floods occurred in the Tahoma Creek 

valley in late August and September of 1967. Their 

formation was heralded on August 29 by a short-lived 

flood on Tahoma Creek. On the afternoon C'f the 29th, 

probably between 1 and 1 :30 p.m., the Wonderland 

Trail footbridge across the creek was wash('d out, and 

shortly thereafter the stream rose between 1 and 2 feet 

at Tahoma Creek picnic area (then a campg:-:-ound). At 

the footbridge, the creek flows through a c}' ~tnnel constricted by a low bedrock cliff on the south r.nd a ridge 

of very large boulders on the north, and the. channel Is 

only about 30 feet wide. The flood had a crest in this 

channel about 15 feet above the normal stream level. On 

the morning of August 30, the creek was still unusually 

high and muddy. 

The flood occurred on a clear day aft:er a. long spell 

of warm dry weather and probably was caused by the 

sudden release of a oonsiderable volume of water that 

had been impounded within South Tahon1a Glacier. 

According to David L. Fluha.rty (ora] commun., September 19·67), Fire Control kid at the Gobblers Knob 

Fire Lookout, the water that caused the flood seemed 

to emerge at an icefall on South Tahoma G~acier at an 

altitude of about 7,500 foot. Gobblers Knob is about 

llh miles west of Tahoma Creek picnic area and is 

2,500 feet higher in elevation (pl. 1.) 

Two days after the flood, at about 8:40 p,m. on .._1\.ugust 31, Mr. Fluharty reported hearing a loud roar 

coming from the Tahoma Creek valley. P~.rk Ranger 

James D. Erskine (oral oommun., September 1967), 

who arrived at the Tahoma Creek campground between 9 and 9 :30 p.m., found that the part of tlhe campground that is only 5 feet above the river was being 

buried by a slurry of mud and boulders that resembled 

wet concrete.3 By means of a powerful flr.shlight he 

was able to see la.rge boulders being morred by the 

slurry along the main clhannel of Tahoma Creek, and 

he also noted that many small stones 'vere being 

thrown, with a forward projection, above the surface 

of the moving mass. Erskine reported that there was 

a deafening roar, and the ground was vihr11ting very 

strongly under his feet at the west edge of the campground. He left the area because of concern for his 

safety; when he returned about an hour later, relatively 

clear water was flowing in the main channel, and 

shallow water was also flowing across the 1 ':'IW part of 

the campground. Richardson ( 1968) infern-rl that the 

3 The campground had been closed by the National Park Service on August 30 because of an extremely high danger from forest fires. 
DESCRIPTION OF LAHARS 59 

FIGURE 29.-Lahar resting on top Oif fluvial cobble-and-boulder gravel at measured Sleetion 9 in the Tahoma Creek valley. 

Separating the two deposits is :14-% inch of duff and PY'roclastic layer W. Three more lahars occur in the stratigraphic 

interval between layer W and the fluvial gravel in outcrops out of view to the right. 

rapidly moving mass seen by Erskine was a "hyperconcentrat ed flow" (p. 4), hut booause of a lack of data 

on the sediment-to-water ratio, it will be referred to 

here as a lahar. 

The deposit in the campground area now is no more 

than about 3 feet thick and consists of boulders as large 

as 2 by 3 by 4 feet in a matrix of medium to coarse sand 

(fig. 30). The lahar evidently terminated a short distance from the campground, for I could not identify 

deposits formed by it on the valley floor at a point about 

1 mile downstream. 

At the Wonder land Trail footbridge over Tahoma 

Creek, the lahar banked up on the south channel wall 

to a maximum height of about 25 feet. Two hundred 

yards downstream, on the outside of a bend, the lahar 

banked up to a maximum height of 35 feet, whereas on 

the inside of the bend on the opposite bank, 150 feet 

away, it only reached a height of 15 feet. The lahar 

left a coating of sand and granule-sized material on the 

tops and sides of boulders and tree trunks, but this 

material had been washed off by the creek up to a height 

of 6 feet after the lahar passed downvalley. 

The lahar of August 31 was caused by a flood similar 

to, but evidently of greater volume than, the one of 

August 29. The second flood issued from the glacier at 

the icefall and carved a deep channel down the glacier's 

surface (fig. 31). Upon reaching the valley floor, the 

floodwaters picked up large amounts of loose glacial 

drift and alluvium and were transformed into a lahar. 

The peak discharge of Tahoma Creek at the campground was estimated by Richardson (1968) to be about 

24,000 cfs, of which perhaps half consisted of sediment. 
60 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

FIGURE 30.-Bouldery deposit left in Tahoma O'reek picnic area (then a campgronnd) on evellli.ng of August 31, 1967. The 

photograph was taken on the following day. The unvegetated part of the Tahoma Crook flood pluin is faintly visible in the 

background. 

A flood crest was reached about 10: 30 p.m. at the highway bridge across Tahoma Creek, 4.3 miles below the 

campground. From high-water marks left by the flood 

crest, Richardson estimated a peak discharge there of 

only about 100 cfs and inferred that the higher discharge farther upstream had been dissipated by channel 

storage and infiltration downstream from the campground. 

Evidently the conditions that led to the lahar and 

floods continued for some time, because a small lahar 

moved downvalley as far as the campground on September 15, 1967 (N. A. Bishop, Chief Park Naturalist, 

oral commun., 1968). Floods not associated with rainfall also moved down the valley from time to time during the summer of 1968, and one again inundated Tahoma Creek picnic area on August 21, 1970. 

The cause for large volumes of water to be released 

suddenly and repeatedly by South Tahoma Glacier is 

not known, but there is a possibility that the floods were 

related to thermal activity of volcanic origin. On the 

afternoon of September 23, 1967, Miss Marilyn Siehl 

(oral commun., September 1967) of Tacoma, Wash., 

was in the vicinity of the Wonderland Trail footbridge 

across Tahoma Creek with a companion when she heard 

what she described as a loud explosion from the direction of Mount Rainier. The explosion was followed 

by a rumbling noise and a vibration of the ground underfoot. She quickly moved to a vantage point from 

which she could see the volcano and observed clouds of 

what she believed to be brown dust and white water 

vapor ("steam") billowing from a west-facing cliff at 

the head of South Tahoma Glacier. Miss Siehl observed 
DESCRIPTION OF LAHARS 61 

FIGURE 31.-Aerial view Qf the debris-covered surface Qf South Tahoma Glacier (at right). The channel down the middle Olf 

the glacier was carveld by floods in late Auguslt and early September 1967 that issued from the icefall at the right center. 

Cirele indicates the area in wh'ich a rock fall occurred in February 1969. The glacier is about 500 ~eet wide ~ar its 

terminus. Photograph taken Beptember 18, 1967, by Austin S. Post, U.S. Geological Survey. 
62 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

the clouds the rest of the afternoon and evening from 

the point where the Wonderland Trail crosses Emerald 

Ridge and noted that clouds were still being formed the 

next morning when she left the area. She described 

the weather both days as hot, dry, and clear. 

Hikers and climbers reported seeing an unusual number of dust clouds rising from the area near the head of 

South Tahoma Glacier earlier in the summer, and some 

days these could also be seeen from Longmire. It seems 

likely that the clouds were caused by recurring rockfalls. Small rockfalls continued at the same general 

locality at least until mid-October (N. A. Bishop, oral 

commun., 1968) (fig. 32). 

While at Longmire one evening in August 1008, D. C. 

Thompson and Duane Nelson of the National Park 

Service observed four or five clouds of what seemed to 

be water vapor which rose at intervals above the cliffs 

at the head of South Tahoma Glacier. They noted that 

each of these white clouds was followed by a cloud which 

was brown and apparently consisted of rock dust. Another observer witnessed a similar succession of clouds 

at the same place a few days later (D. C. Thompson, oral 

commun., 1969). The recurrence of clouds of what 

seemed to be water vapor and of dust could have resulted from a succession of small steam explosions which 

caused repeated rockfalls. 

On February 16, 1969, still another event occurred on 

the west side of Mount Rainier which may bear on the 

origin of the recent floods and lahars in the South 

Tahoma Creek valley. Local newspapers in western 

Washington reported that on the afternoon of that day 

Mr. and Mrs. Oliver Edmonds of Seattle had seen 

"steam and smoke" rising from the west side of the volcano for about 45 minutes. Their viewpoint was in the 

vicinity of Buckley, which is about 25 miles northwest of 

Mount Rainier. On February 20, . Jack H. Hyde of 

Tacoma Community College, and Stewart Lowther of 

the University of Puget Sound, flew over the west flank 

of the volcano in an attempt to find the cause of the reported "steam and smoke." They found an area of newly 

deposited rock debris lying on the snow-covered surface 

of South Tahoma Glacier at an altitude of between 6,WO 

and 7,000 feet near the point in the icefall at which 

floods emerged in late August 1967 (fig. 31). 

The clouds observed on the west side of Mount Rainier 

on February 16 may have been caused by water vapor 

rising from a short-lived steam vent and by dust originating in a small rockfall that resulted from a steam 

explosion. Thus, there has been a repetition of events in 

the area of South Tahoma Glacier whioh may have been 

caused by some kind of thermal phenomena. It seems 

likely that the repeated floods in Tahoma Creek were 

caused by abnormal melting of South Tahoma Glacier 

around steam vents. 

LAHAR ASSEMBLAGE IN THE SOUTH PUYALLUP RIVER 

VALLEY 

At least eight lahars are present in the valley of the 

South Puyallup River, only one of which is older than 

pyroclastic layer Y. The sequence is as follows: 

Four lahars younger than layer W. 

Pyroclastic layer W (about 450 years old). 

Lahar about 1,010 years old. 

Bomb-bearing block-and-ash flow about 2,500 years old. 

Lahar and fluvial deposits. 

Round Pass Mudflow about 2,800 years old. 

Pyroclastic layer Y (about 3,600 years old) . 

The pre-Y lahar is dark brown and has a clayey plastic 

matrix. It is a foot or less thick and was observed in a 

roadcut at Round Pass. It occurs between layer Y and 

the underlying Evans Creek till in an outcrop 100 feet 

southwest of the Marine Memorial there, and the lahar 

is texturally similar to the Round Pass Mudflow which 

is above layer Y in the same exposure. Layer Y and the 

lahar are separated by a mixed layer about 10 inches 

thick, which probably is colluvium derived from both 

units. Perhaps downslope movement of the pumice and 

the lahar occurred after part of the pumice had been 

deposited, but before the upper, clean pumice was laid 

down. The pre-Y lahar was not recognized elsewhere, 

and the significance of this single outcrop is not known. 

However, it may record a lahar that was temporarily 

at least 600 feet deep in the South Puyallup River 

valley. 

An inexplicable section that may be due partly to 

local downslope creep or flowage is exposed in ·a cut 

along the West Side Road on the valley wall about 500 

feet directly north of Round Pass. Here a very compact, 

greenish-gray deposit 14 feet thick which texturally resembles a mudflow is overlain by a purplish-gray mudflow 2 feet thick. The contact between the two units is 

indistinct, and the units may be facies of the same deposit. Above them is a layer a few inches thick of duff 

and carbonized wood mixed with gray sand. The duff 

and sand layer is conformably overlain by a third mudflow which is lenticular and as much as 32 inches thick 

and which has a layer of duff and wood fragments. The 

upper duff layer contains a few pumice grains of layer 

W. Conformably above the duff is a fourth mudflow, as 

much as 5 fee.t thick, which is unconforma.bly overlain 

by still another layer of duff and carbonized wood 

mixed with gray sand, and by a fifth mudflow, also 5 

feet thick. Some of these deposits probably are of colluvial origin and were derived from other mudflows on 

the side of the South Puyallup River valley, but it is not 
DESCRIPTION OF LAHARS 63 

FIGURE 32 . - Straight slanting area of dirty snow, formed by rockfall debris below PO'int Success, heads alt a cliff where a 

steam vent wa·s witnessed on September 23--24, 1967. The rockfall debris reaches down to the head of South Tahoma 

Glacier. Photograph taken with a telephoto lens at Round Pass October 8, 1967, by N. A. Bishop, National Park Service. 

known which deposits represent the original mudflows 

in the valley and which ones might be colluvium. 

Several lahars are exposed in a trail cut in the front 

of a terrace at the Wonderland Trail footbridge across 

the South Puyallup River (measured section 10). The 

terrace is about 42 feet above river level. The basal lahar 

of this section contains about 14 percent silt and clay~ 

Montmorillonite makes up about half of this size fraction, and feldspar and cristobalite the other half (table 

11, sample 5). The lahar that is designated as unit 3 in 

the measured section contains about 14 percent silt and 

clay (table 10, sample 4) about half of which consists of 

montmorillonite; the remainder is mostly feldspar and 

cristobalite (table 11, sample 4). 

A lahar is exposed in a cutbank on the north side of 

the river to a height of about 10 feet directly opposite 

Measured section 10 

[In south bank of the South Puyallup River at Wonderland Trail bridge] 

Thicknus 

(ft) (in.) 

5. Lahar: boulders as large as 6 ft in diameter in a 

purplish-gray matrix of silt and sand_ _ _ _ _ _ _ _ _ _ _ 4-8 0 

4. Fluvial deposit: sand and pebble-to-cobble gravel, 

poorly sorted______ __ __ ____ __ ____ ___ _________ 5 0 

3. Lahar: cobbles and boulders in a yellowish-brown 

sand, silt, and clay matrix __________ __ __ - ____ __ 7 6 

2. Lahar: cobbles and boulders in a purplish-gray matrix of medium to coarse sand__ ________ ____ ____ 6 0 

1. Lahar: boulders and cobbles in a yellowish-brown 

matrix of sand, silt, and clay _____ __ __________ _ >6 0 

Covered interval of 10 feet to river level. 

the measured section. It is very compact, yellowish 

brown, and does not resemble any of the lahars in the 

measured section nearby, all of which probably are 
64 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

younger. A log taken from the lahar in the north bank 

was reported to have a radiocarbon age of 1,110+250 

years (W- 1971). The lahar is overlain by a bouldery 

lahar about 6 feet thick that is younger than any of the 

deposits in rthe measured section. Bedrock crops out in 

the riverbed a :few hundred :feet upstream :from the measured section. 

Size analysis of a sample of the 1,100-year-old lahar 

indicated that it contains about 37 percent silt and clay 

(table 10, sample 11). X-ray examination of this size 

fraction indicated the presence of montmorillonite, cristobalite, and :feldspar (table 11, sample 11). 

BLOCK-AND-ASH FLOW IN THE SOUTH PUYALLUP 

RIVER VALLEY 

One of the most interesting deposits on the west side 

of Mount Rainier contains innumerable light-olivegray breadcrust bombs. The deposit resembles some 

lahars in its coarse, unsoJ'Ited texture and distribution, 

but the presence of charcoal suggests that the deposit 

was formed by a hot dry flow of rock debris. The results of a remanent magnetism study of rock :fragments 

in the deposit indicated emplacement of the debris at 

a high temperature. 

The block-and-ash flow deposit is well exposed in 

c~ts along the West Side Road in the South Puyallup 

River valley (figs. 33, 34). From a distance it resembles 

glacial drift, and a succession of sharp-crested ridges 

cut through by the road could easily be mistaken :for 

lateral moraines . .. dowever, when each ridge is :follo:wed a short distance upvalley, it is :found to merge 

with a terrace that represents the flattish top of the 

deposit. The ridges ate simply narrow interfluves between adjacent small valleys cut into the deposit. The 

top of the block-and-ash flow is about 135 feet above 

the river near the highway bridge and about 200 :feet a 

mile further upvalley. 

Bombs in the deposit have black glassy interiors 

range ·in diameter from 6 inches to 4 :feet, and hav; 

bread crusted exteriors (fig. 35). Most are highly vesicular, and many have large voids in their interiors, adjacent to which the rock is locally iridescent. Some bombs 

are nearly spherical, but most are flat on one or more 

sides. The bombs are very abundant and are randomly 

distributed throughout a loose matrix of purplish-gray 

sand and small angular to subangular :fragments of 

dark-gray to black glassy rock. Only a :few bombs are 

present in the northwesternmost outcrop of the blockand-ash flow along West Side Road, and the deposit 

there consists mostly of material smaller than 4 inches 

in diameter. 

Where the base of the block-and-ash flow is exposed, 

it is flat and lies on a lenticular fluvial gravel a :few feet 

FIGU RE 33.-Bomb-bearing block-and-ash flow deposit in outcrop along the West Side Road near the South Puyallup 

River overlies a coarse lahar that does not contain any 

bombs. The contact is marked by a thin horizontal layer 

of light-gray sand. 

thick or on a very coarse lahar that lacks bombs and is 

more than 15 feet thick. 

The bomb-bearing deposit was not identified in the 

South Puyallup River valley outside of the park, although a lahar that forms a terrace 50 feet higher than 

the river west of the park contains much scoriaceous 

black andesite. This lahar, which was seen in cuts along 

a logging roa.d near the mouth of St. Andrews Creek, 

may have been derived from the block-and-ash flow. 

Grain-size distribution was determined on samples 

of the coarse-grained and the fine-grained facies of 

the block-and-ash flow; no bombs were included in 

either sample. The sample of the coarse-grained :facies 

contained 6 percent silt and clay and had a median diameter of 1.5 mm (table 10, sample 19); its sorting coefficient was 6.63, and the cumulative curve of the size 

distribution is polymodal (fig. 36). The sample of the 

relatively fine-grained facies is texturally similar. It 

contained 6 percent silt and clay ·and had a median diameter of 1.1 mm (table 10, sample 20) ; its sorting index 

was 4.64, and its cumulative curve also was polymodal. 

A log completely converted to charcoal, about 6 

inches in diameter and 4 feet long, was found 1 foot 

above the base of the bomb-bearing deposit, resting on 

and against bombs. The log had no bark and was surrounded by a layer of white sand, silt, and clay a fraction of an inch thick. The charcoal was relatively fragile, 
DESCRIPTION OF LAHARS 

FIGURE 34.-0utcrop of a relatively fine grained facies of the bomb-bearing blV!Ck-ffild-ash flow along the West Side Rood 

near the South Puyallup River. A large breadcrust bomb is just left of the pick, but most other rock fragment!> are of 

dense rock. 

and probably could not have been transported without 

being broken into small fragments. The wood probably 

was fresh when incorporated by the block-and-ash flow 

and was converted to charcoal by heat retained in the 

adjacent bombs and rock fragments after the flow came 

to rest. The radiocarbon age of a sample of the log was 

2,350+250 years (W-1587), and the corrected age is 

about 2,500 years (table 4) . 

65 

Samples oriented with respect to magnetic north 

and the horizontal were taken from eight bombs and 

five dense rock fragments in the deposit exposed along 

the West Side Road. Examination of cores taken from 

these samples indicated that the north-seeking poles in 

all but four have northward dips o:f 50°-72° and that 

their azimuths lie within 20° of magnetic north (fig. 

37). This strong preferred orientation of thermoremanent magnetism suggests that most of the bombs and 

many of the dense rock fragments were above the Curie 

FIGURE 35.-Breadcrust bombs from the block-and-ash flow in 

the South Puyallup River valley. The bomb on the right has 

been broken open to show the highly vesicular interior. 
66 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

w 

N 

Ui 100 

0 

w 

I-

<( 90 ~ 

0 

z 

z 

<( 

I 

80 

I- 70 II 

(!) 

w 60 3: 

>-

CD 

Cl: 50 

w 

z 

Li: 40 (f) 

w 

-' 

~ 30 Cl: 

ct. 

"- 20 0 

w 

(!) 

~ 10 

z 

w 

u 

Cl: 

w 

0.. 

0 

E 

E 

-

0 

C! 

0 

E 

E 

0 

'--""~--"" 

E 

E 

-

c::i 

~"' y ; 

/ 

vv 

E 

E 

0 

Q• Qv 9J~ 

v 

/ 

/ 

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C! 

0 

-

v 

/ 

v 

v"" 

v 

E 

E 

0 

c::i 

0 

-

CLAY SILT SAND GRANULES PEBBLES COBBLES 

FIGURE 36.--0umulative curve of the size distribution of the relatively coarse facies of the bomb-bearing block-and-ash flow 

in the South Puyallup River valley. So, sorting coefficient. 

point of the magnetite in the rock when the block-andash flow came to rest. The few samples that do not have 

this orientation presumably had cooled below the Curie 

point during movement of the flow. 

The Curie temperature of a sample of dense rock 

from the block-and-ash flow was experimentally determined to be 517°C during both heating and cooling of 

the sample (Richard R. Doell, unpub. commun., 1968). 

The Cur,ie temperature of a sample of a breadcrust bomb 

was found to be 485°C during heating and 332°C during cooling. Both samples were taken from rocks in the 

deposit whose remanent magnetism was oriented towardmagneticnorth (fig. 37). 

These Curie-point determinations indicate that rock 

fragments were still several hundred degrees centigrade 

above the boiling point of water after movement of the 

rock debris had stopped. In view of these high temperatures, it seems unlikely that any incorporated water 

could have remained in the liquid state long enough to 

have provided mobility to the debris. Thus, I conclude 

that the debris was moving not as a lahar but as a blockand-ash flow which owed its mobility to entrained hot 

air, steam, and perhaps other gases. 

The close similarity in age of the bomb-bearing blockand-ash flow (about 2,500 years) and pyroclastic layer 

C (between 2,150 and 2,500 years) suggests that both 

originated during the same episode of volcanism. 

LAHARS IN THE NORTH PUYALLUP RIVER VALLEY 

Three lahars were recognized in the North Puyallup 

River valley, the oldest of which is probably correlative 

with the Round Pass Mudflow. In exposures near the 

north end of the West Side Road this lahar consists 

of a mixture of angular and subangular rock fragments as large as 8 feet in maximum dimension in a 

plastic matrix of yellowish-brown silty and clayey sand 

Along the Wonderland Trail on the south side of the 

North Puyallup River valley, the Round Pass Mudflow 

is present up to an altitude of about 3,920 feet-a height 

of about 400 feet above river level. 

Younger lahars form two terraces on the north side 

of the valley downstream from the end of the West Side 

Road, 55 and 90 feet higher than the North Puyallup 

River. A boulder about 20 feet in diameter was seen 

near river level in the lahar that makes up the lower 

terrace, and living trees 3-4 feet in diameter and as 

much as 400 years old are growing on the terrace. Boulders as large as 8 feet across lie on the upper terrace, and 

although no trees were cored, the largest are of com·· 

parable diameter with, or a little larger than, the largest 
DESCRIPTION OF LAHARS 67 

w 60 E 

• 

s 

l!~IGURE 37.-Point diagram of azimuth and dip of north-seeking poles in dense rock fragments (squares) and bombs 

(circles) from block-and-ash flow in the South Puyallup 

River valley. A l-inch core from each sample was split into 

two pieces for determination of the direction of remanent 

magnetism ; open circles or squares tied .together represent 

the results of determination on the two pieces, and the solid 

circles and squares represent determinations on two pieces 

that coincided o•r nearly coincided in azimuth and dip. The 

two samples on which Curie temperatures were determined 

are indica ted by arrows. 

trees on the lower terrace. An exposure of the 1naterial 

making up the upper terrace was not seen, but the size 

of boulders on the terrace suggests that it is underlain 

by a lahar. Pyroclastic deposits were seen on neither 

terrace. 

LAHARS IN THE MOWICH RIVER VALLEY 

Inside Mount Rainier National Park the South 

Mowich River valley contains at least one lahar that 

is older than pyroclastic layer Y, one younger than 

layer Y but older than layer W, and one that is younger 

than layer W. The pre-Y lahar crops out in the streambank on the north side of the river about a mile upstream from its mouth. There it forms a terrace whose 

top is about 30 feet above the adjacent flood plain. 

Farther upstrea1n, two post-Y lahars can be seen in scattered outcrops in the face of a terrace whose height 

above the flood plain ranges from a few feet to as much 

as 25 feet. This difference in height seems to be due to 

variations in slope of the flood-plain surface. The 

post-W lahar at the surface of the terrace is yellow to 

yellowish brown and contains abundant angular to subangular fragments of altered rock. It ranges in thickness from 3 to at least 15 feet and closely resembles so"'lle 

post-Y lahars in the Puyallup River and South Taho:na 

Creek valleys. 

The post-W lahar was seen as far downstream as a 

point about 1.5 miles above the mouth of the South 

Mowich River. In some outcrops the lahar is on top 

of fluvial sand and gravel, and in others it overlies a 

coarse gray lahar which contains pumice reworked from 

layer Y and which includes angular and subangular 

boulders as large as 4 feet in diameter. The maximnm 

thickness of the gray lahar is at least 20 feet. 

One or more lahars that are older than pyrocla~tic 

layer Y are present in the Mowich River valley dovrnstream from the park. In the SW% sec. 30, T. 17 N., R. 

7 E., a lahar that contains boulders as large as 5 feet 

forms a terrace that is about 25 feet above the Mow~~h 

River flood plain. Farther upstream, in the Slh sec. 29, 

outcrops reveal a lahar that consists of angular and subangular rock fragments as large as 3 feet in a mat:rix 

of purplish-gray silt and sand. This deposit extends to a 

height of at least 40 feet above the flood plain. At one 

place, in ~the SWlh sec. 29, a compact lahar that contains boulders as large as 7 feet n1ay be a facies of t.he 

lahars previously described or it may be an entirely dif· 

ferent deposit. The stratigraphic relation of these l•ahars 

to those of the Puyallup River valley is not known. 

LAHAR IN THE CARBON RIVER VALLEY 

The only lahar observed in the Ca~bon River valley 

is on the south side of the valley opposite Chenuis Falls. 

It is as much as 10 feet thick and consists of angular 

and subangular rock fragments as large as 6 feet across 

in a matrix of purplish-gray medium to coarse sand. 

The lahar lies on top of bedrock and is overlain by 

pyroclastic layer Y. 

The scarcity of lahars in this valley may be due in 

part to the configuration of the volcano above the he~.d 

of Carbon Glacier. At the top of Willis Wall a ridge 

extends eastward from Liberty Cap to Russell Cliff. I 

believe this ridge to be the north rim of a depression in 

the volcano that was left when massive slides to the 

northeast created the Osceola Mudflow. Because of the 

ridge, a flood originating at or near the summit of the 

volcano would be diverted away from the head of Carbon Glacier. This ridge is the largest remnant of the old 

crater rim, and its preservation may be due to a lack of 

hydrothennal alteration or to less intense alteration in 

these rocks than in those elsewhere on the volcano. 
68 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON 

LAHARS IN THE MUDDY FORK OF THE COWLITZ RIVER 

AND OHANAPECOSH RIVER VALLEYS 

A single lahar was found in the Muddy Fork valley 

above Canyon Bridge (pl. 1), but none downstream 

from it. About half a mile north of the highway bridge 

over the Muddy Fork, terraces on both sides of the valley -are 50 or 60 feet higher than the flood plain. The 

terrace on the west side is formed by ~a coarse fluvi,al 

deposit of sand and pebble-to-boulder gravel in which 

there are boulders as large as 5 feet in diameter. The 

terrace deposit on the east side of the valley is capped 

by a lahar 13 feet thick. It is made up of angular to 

subrounded rock fragments as much as 5 feet in diam~er in a dark-yellowish-brown matrix of silt and 

sand. X-ray analysis of the clay-sized fraction of the 

lahar indicated the presence of feldspar, cristobalite, 

and glass, and a lack of clay minerals. The only pyroclastic deposit on top of it is layer W, and it seems 

likely that the lahar as well as the underlying fluvial 

deposits are the same age as lahar assemblage C in the 

Nisqually River valley 'and !that they originated lin the 

same manner ( p. 43). 

Lahars were noted in the Ohanapecosh River valley 

at Indian Bar and near the mouth of Chinook Creek. 

~he part of the valley that lies between these two places 

was not examined because accessibility is relatively difficult. Stream bank outcrops in the meadow at Indian Bar 

reveal a lahar that consists of subangular to subrounded 

rock fragments in a purplish-gray matrix of silty sand. 

The lahar is more than 5 feet thick and extends beneath 

the base of the outcrops. It is overlain by a fluvial sand 

and p~bble-to-boulder gravel deposit 2-3 feet thick and 

by layer 0 and younger pyroclastic deposits. A short 

distance upstream from the mouth of Chinook Creek a 

compact lahar is exposed where the East Side Trail 

crosses the Ohanapecosh River. The lahar is between 5 

and 10 feet thick, and it overlies sand and pebble-toboulder gravel about 5 feet thick that is mantled with 

pyroclastic layers Y and W. 

THE ASSOCIATION OF LAHARS WIT}I 

VOLCANISM 

The possible relation of lahars at Mount Rainier to 

volcanism was of paramount concern in this g.tudy. The 

possibility of lahar formation would undoubtedly be increased by the phenomena that are typically associated 

with eruptions. There are a num:ber of indications, or 

lines of indirect evidence, that link the formation of 

some lahars to contemporary volcanism. The presence of 

fresh volcanic bombs in a lahar suggests that the lahar 

was caused in some way by an eruption. The eruption 

of pyroclastic material at the same time a lahar is 

formed carries a strong implication that the lruhar was 

caused by volcanism. The occurrence of lahar~ within a 

general period during which pyroclastic de:r'lsits were 

erupted is another, but less satisfactory, basiF for inferring a causal relation. Still another line of reasoning 

to support the association of lahar formation with volcanism is the presence of complex assemblage:;- of fluvial 

deposits and laha.rs whose aggradation is best. explained 

by repeated floods from the volcano. These floods, in 

turn, are most readily explained by repeated eruptions 

of hot pyroclastic debris or lava onto sno~ and ice. 

Finally, because of their size and composition, some 

lahars could only have been caused by tremendous slides 

from the volcano. The most probable cause<;'\ of these 

slides are volcanic explosions, earthquakes associated 

with volcanism, and possibly lateral spreading or tilting 

of parts of the volcano caused by the rise of magma; 

however, nonvolcanic earthquakes cannot be ruled out 

as possible triggering mechanisms. 

The lahars discussed below seem to have been triggered by eruptions or to have occurred during known 

periods of eruptive activity; lahars for which there is 

no independent evidence of contemporaneous volcanism 

are not mentioned here. 

Evidence of the age of lahars and eruptions before 

6,600 years ago is too fragmentary to relate them with 

confidence. The oldest eruptions recorded by ryroclastic 

deposits are those that produced layer R more than 8,750 

years ago (tables 5, 6). Lahars older than layer 0 have 

been found in the valleys of Van Trump Creek and 

the Nisqually River, but their age with respect to layer 

R is not known. 

The Paradise lahar is between 5,800 and 6,600 years 

old and thus was formed sometime during an interval 

of repeated pumice eruptions (table 6) . F,:roclastic 

layer N, formed during this interval, is younger than 

the Paradise lahar, but any one of the erupfions that 

produced layers A, L, D, or S could have triggered the 

avalanche that caused the lahar. The Greenwater lahar, 

also formed by avalanches of rock debris, may ha-ve been 

caused by the same volanic explosion that produced 

pyrodaStic layer S. (p. 22). Most of the pre-Osceola 

lahar assemblage in :the White River valley probrubly 

was formed after the Green water lahar occurred. The 

two bomb-bearing lahars in the assemblage evidently 

were caused by eruptions of hot rock debris and bombs. 

A detailed study of airlaid deposits contemporaneous 

with the Osceola Mudflow indicates that an ertption led 

to the formation of the Osceola ( p. 30) . 

The last major episode of volcanic activity l:~gan with 

the formation of the block-and-ash flow in the South 

Puyallup River valley about 2,500 years ago. The evidence that it was hot clearly shows that thE flow was 

associated with an eruption. A lahar older than pyro-
HAZARDS FROM FUTURE LAHARS 69 

clastic layer C in the White River valley may have been 

formed at about the same time. Pyroclastic layer C was 

erupted next in sequence, after which the summit lava 

cone of the volcano was built :and accompanied by aggradation of lahar assemblages in the valleys of the 

White River, Nisqually River, and Kautz Creek. Lahars 

probably also moved down the Muddy Fork, West 

Fork, and Van Trump Creek valleys at the same time. 

This attempt to assign individual lahars or lahar 

assemblages to certain eruptive episodes leads to the 

speculation that there is a genetic relation between kinds 

of volcanic activity and eertain types of lahars. Lahars 

at Mount Rainier that lack a considerable content of 

clay and clay minerals probably resulted from eruptions 

that produced large quantities of blocks and lithic ash 

or from eruptions during which much ice and snow 

was melted by hot pyroclastic debris or lava flows. 

Lahars that contain a significant amount of clay (per~ 

haps 5 percent or more) seem to be derived from old, 

hydrothermally altered parts of the volcano, and some 

may have been started by phreatic explosions. Such explosions n1:ay not necessarily have been accompanied by 

the eruption of new magma. 

HAZARDS FROM FUTURE LAHARS 

A recent evaluation of volcanic hazards at Mount 

Rainier (Crandell and Mullineaux, 1967) was based on 

an examination of the events that have occurred there 

during the last 10,000 years, as inferred from a study 

of the surficial deposits of the park. We concluded that 

if future phenmnena of the sa1ne type and magnitude 

occur with the san1e frequency as in the past, the direct 

danger fron1lahars greatly exceeds that from lava flows 

and pumice eruptions. La:hars are especially dangerous 

because of their possible very large size and ability to 

n1ove long distances, and also the speed with which they 

can 1nove. In areas downstream fron1 the lower slopes 

of the volcano, their effects would be mostly confined to 

valley floors and the lower parts of valley walls. 

The scale of the hazard presented by lahars might be 

illustrated by a brief review of their number and frequency in Holocene time. The deposits of at least 55 different lahars, representing a vast range in size, have 

been recognized in the various valleys that head on 

Mount Rainier (table 6), and many 1nore probably occurred whose deposits were not seen or recognized during this study, or had been removed by erosion. Some 

areas have been affected by lahars 1nore often than 

others; the valleys of the White and Nisqually Rivers 

and Tahoma Creek have been devastated freqtiently 

during ce:vtain intervals of postglacial time. Large 

lahars have moved down the White River valley at least 

10 times within the last 6,600 years; thus, the average 

frequency of large lahars in that valley has been at least 

one per 660 years. In the Nisqually River valley the 

average frequency indicated by 12lahars in the last 10,-

000 years is at least one per 830 years, and in the Tahmna Creek valley, four lahars in about the last 3,2>00 

years indicate an average frequency of at least one per 

825 years. Even though they are roughly sin1ilar, these 

indieated1ninimium average frequencies do not signify 

repetition of lahars at regularly spaced intervals. During a long interval when the volcano is dormant, f€w, 

if any, large lahars might occur. However, conditicns 

that lead to lahar formation are substantially increaf~d 

during relatively brief intervals of volcanic activity. 

It has been noted elsewhere in this report that at least 

seven lahars occurred in the Nisqually River valley during a relatively brief interval. In fact, lahars caused in 

various ways could occur again and again in1nore than 

one valley within a space of only a few weeks, as they 

did during the eruption of Mount Peh~e in May and 

June of 1902 (Hovey, 1902, p. 346-347) and during the 

e.ruption of Irazu Volcano (Waldron, 1967, p. I 1-I 17). 

In regard to the speed of lahars, Kemmerling (1921) 

noted that during the 1919 eruption of l{elut in Java, 

the passage of lahars down valleys lasted only 45 minutes, and some lahars had an average speed of 45 miles 

per hour. A velocity of about 56 miles per hour was 

reported by Iida (1938, p. 681) for a 1nudflow at Mount 

Bandai in Japan in 1938. Waldron (1967, p. I 24) found 

velocities of as much as about 22 miles per hour in debris 

flows that resulted indirectly from eruptions of Irazu 

Volcano in Costa Rica. He reported that the flows h::J.ving the highest velocities had sediment concentratic ns 

between 60 and 7 4 percent. These were "hyperconc£"1-

trated flows," according to the terminology of Beverage 

and Culbertson ( 1964; th[s report, p. 4). 

One conclusion reached from the present study is that 

the largest lahars of postglacial time originated in massive slides and avalanches of hydrothermally altered 

rock. Presumably, therefore, future slides and lahr.rs 

may originate in those parts of the volcano that have 

been affected by hydrothermal alteration. The only large 

outcrops of altered rock known today are at the head of 

Sunset Amphitheater, but smaller areas are also presr"'lt 

high on the west side of the volcano at the heads of 

North and South Mowich Glaciers. 

Although the visible outcrop area of altered rock is 

small today, there may be large masses of such rock 

tens or hundreds of feet below the surface at many 

places within the volcano. Because of the possibility 

that such zones exist at depth, we cannot be certain that 

a massive rock slide comparable to those that produc~d 

the Greenwater and Paradise lahars, or the Osceola, 

Round Pass, and EleCtron Mudflows, will not occur 
70 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASIDNGTON 

again, triggered perhaps by a severe earthquake or by 

a volcanic explosion. 

The chance that a destructive lahar will affect a given 

segment of a valley ·decreases with distance from the 

volcano. Thus, on the basis of the events of the last 10,-

000 years, a devastating lahar might cover the floor of 

the Nisqually River valley within or close to the park on 

an average of at least once in 800 years, and in the White 

River valley at least once in 600 years. In oontrast, beyond the Cascade mountain front, the White River valley has been affected by only one lahar within the last 

10,000 years, and the Nisqually River valley apparently 

by none. 

Ways of reducing the hazard of future lahars include 

the evacuation of valley floors and zoning the valley 

floors to prevent construction of permanent residences 

and other installrutions within areas that -are rela..tJively 

hazardous. In addition, existing dams could be utilized 

to trap all or part of a lahar and prevent it from reaching populous areas. 

One of the greatest difficulties to overcome in the 

evacuation of critical areas probably will be the inability of people to comprehend the nature of the threat 

facing thmn in the event of ·a future eruption. For this 

reason, ex,tensive publicity should be given, at the first 

sign of renewed volcanism, of the possible consequences 

of an eruption. In this way the residents of areas that 

might be affected by lahars and floods could be forewarned that rapid evacuation might become necessary. 

To be most effective, evacuation of people from 

valley floors would require foreknowledge of which 

valley or valleys might be affected. This information 

might be available if an eruptive vent appeared low on 

a flank of the volcano, because lahars would then most 

likely be restricted to the drainage basin heading on 

that slope of the cone. However, an eruption at the present summit crater could affect valleys on almost any side 

of rthe volcano. Furthermore, inasmuch as the subsurface distribution of possible large masses of hydro·· 

therm·ally altered rock is nolt known, it should be assumed that a large clayey lahar also could originate on 

any side of the volcano. 

The valley floors adjacent to the park that have been 

inundated most frequently by lahars are not yet densely 

populated. From the standpoint of the lahar hazard 

alone it seems appropriate to recommend thrut permanent 

residences should not be constructed on the floor of the 

Nisqually River valley, downstream from the park, on 

surfaces that are less than 20 feet above river level. 

Construction is also inadvisable on the floors of the 

White River and West Fork valleys between the park 

and Greenwater (pl. 3). In addition, new campgrounds 

and other recreational facilities within and adjacent to 

the park could be constructed, and existing fr.cilities relocated, in areas of low or nonexistent hazf,rds. A related consideration should be the design and location of 

new bridges and highways to accommodate or avoid 

floods and lahars of small to moderate dim ~nsions, so 

that routes will remain usable for safe evacuation if an 

eruption should result in these phenomena. 

Within the mountains, the topographic se~ting is especially significant in areas that are on or closely adjacent to valley floors, for the degree of hazard decreases 

with greater height. Sites less than 10 feet above present 

rivers are susceptible to inundation by floods and lahars 

of modest size, whatever their origin. Sites 30 feet or 

higher above the rivers probably would be ai:~cted only 

by major floods or lahars resulting from volcanism of 

some kind. In the Nisqually River valley vrest of the 

park, for example, the terrace along the no:':'th side of 

the river for about 4 miles west of Ashford is less hazardous with respect to lahars and floods because of its 

height than is the valley floor farther west. The crosssection area and configuration of the valley below and 

adjacent to a terrace also is important because it will 

affect the capacity of that part of the valley to accommodate a flood or lahar without inundating the terrace. 

Large dams in valleys downstream from Mount 

Rainier could trap all or part of a lahar if reservoirs 

behind the dams were empty. Such a trap new exists in 

the White River valley in the form of Mud Mountain 

Dam, which would substantially reduce the l'azard of a 

lahar no larger than the Electron Mudflow. The floodcontrol reservoir created by the dam is designed to store 

106,000 acre-feet of water, which is the equivalent of 

about 170 million cubic yards and roughly comparable 

to the inferred volume of the Electron Mud1ow in the 

Puget Sound lowland. The dam is an earthfill structure 

that has an impervious core m·ade up chiefly of material 

derived from the Osceola Mudfl.ow. If th~ reservoir 

could not accommodate the entire volume of a lahar, 

mud would initially discharge through tl ~ concrete 

spillway and then might overtop the dam itself. Spillover would proceed down the White River valley, but 

probably would not be a threat unless it were deep 

enough to overtop the valley wall near Buckley or of 

sufficient volume to reach the Auburn urban area. 

Similarly, Alder Dam could trap a lahar in the Nisqually River valley, but only if the reservoir had previously been drained. Otherwise a lahar would displace 

the lake very rapidly and would cause it to srill over the 

concrete-arch dam and flood the valley bel(]W. Thecapacity of the reservoir is 232,000 acre feet, o~ about 375 

million cubic yards. The only areas of relatively dense 

population along the Nisqually River bety;een Alder 

Dam and Puget Sound are at the small communities of 
REFERENCES CITED 71 

Yeln1 and McKenna. Yelm is situated 50-75 feet higher 

than the river, but parts of McKenna are close to the 

flood plain. 

Lahars were not recognized in tJhe Cowlitz River valley outside the park during this study, although the 

valley has been inundated by floods within historic tin1e. 

A future lahar that would have the volume of the Electron Mudflow would bury the valley floor at Packwood 

and .perhaps also at Randle. A lahar no larger than the 

Electron might not extend much beyond Randle because of the loss 'Of volume and velocity as it spread 

across the broad, gently sloping floor of the valley west 

of Packwood. 

I recmnmend that responsible authorities establish 

procedures to be followed if Mount Rainier should 

again become active. These procedures should include 

the following : 

1. The development and installation of a detection system in certain critical valleys, whereby a large flood 

or lahar could be detected at an early stage. 

2. The development of a warning system, whereby residents of valley floors could be warned, either 

night or day, of a need for in1mediate evacuation. 

3. The establishment of an evacuation plan for areas 

likely to be threatened by floods or lahars. 

4. A plan for lowering the level of Alder Reservoir in 

the event of a major eruption. 

5. Plans for restricting travel in hazardous areas. 

There is a strong likelihood that a lahar could travel 

with such speed that a warning system for individual 

lahars would provide little benefit except for areas many 

miles from the volcano. For the purpose of planning, 

it should be assumed that a lahar n1ight travel at a speed 

of as much as 50 miles per hour. For this reason, especially, valley floors within a radius of at least 25 miles 

from the center of the volcano should be evacuated as 

soon as possible after an eruption actually began. 

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Page 

Age oflahars __ -------------- ____ ------ ______ _ 11 

AgeofMount RainierVolcano______________ 10 

Alder Dam----------------------------------- 70 _, Alder Reservoir ______________________________ 44,47 

Alderton Interglaciation ________ ------------- _ 10 

Alta Vista _________ --------------- ___ --------_ 36 

Avalanche deposits _________________ 5, 9, 11, 22, 30,58 

Block-and-ash flows __________________ 5, 11, 43,57,64 

Bombs_----------- ___ ---------- 5, 11, 23, 43, 57, 64,68 

Buck Creek_-----------------------------· ___ 18,19 

Burroughs Mountain Stade ___________________ 10,42 

Carbon Glacier_______________________________ 67 

Carbon River_-------------------------- 2, 26, 43,56 

Carbon River valley, lahars __________ -------- 67 

Catt Creek----------------------------------- 44 

Chinook Creek------------------------------- 68 

Christine Falls_______________________________ 33 

Clay, origin in some lahars___________________ 12 

Climate ___ -----------________________________ 3 

Columbia Crest______________________________ 17 

Comet Creek _______________ ------------- _____ 37,38 

Cowlitz River ________________________________ 2, 71 

Cowlitz River valley, lahars__________________ 68 

Crystal Creek________________________________ 23 

Cushman Crest______________________________ 37 

Dating oflahars _______ --------------------- __ 11 

Description oflahars __________ --------------- l7 

Echo Rock----------------------------------- 11 Electron Mudflow __________________ 4,8, 12,66, 70,71 

Emerald Ridge ______ ------------------------- 54,62 

Emmons Glacier ____________________ 22, 23, 24, 42,43 

Evans Creek Drift _______________ 13, 16, 24, 36, 38,50 

Evans Creek till ___________________________ 34, 37,62 

Everson Interstade _____ ---------- ____________ 10,37 

Features oflahars ___ ----------------------- __ 3 

Fluvial deposits ________ 4, 5, 23, 32,39, 40, 44, 45, 48,68 

Fraser Glaciation _________________ ------------ 11, 13 

Fryingpan Creek ____ ------------- 20, 22, 23, 28, 30,31 

Fumaroles ___________ -----------------------__ 1

6 

Garda Stade ______ ---------------------------- 10,43 

Geographic setting, volcano and lahars_______ 2 

Gibraltar Rock_______________________________ 30 

Glacier Basin __________________ --------- 10, 13, 24,29 

Goat Island Mountain________________________ 22 

Gobblers Knob_______________________________ 58 

Green RiverValley__________________________ 26 

Greenwater lahar ______________ ------ 17, 18, 24, 68,69 

Hazards from lahars__________________________ 69 

Huckleberry Creek ____________ ------------ 18, 20,21 

Hydrothermal alteration______ 16, 22, 29, 37, 43, 57, 69 

Indian Bar _______ -----------------------_____ 68 

Inter Fork ________ ---------------------- 13, 24, 25,31 

Introduction ______ ------_____________________ 1 

INDEX 

[Italic page numbers indicate major references] 

Page 

Kautz Creek ______________________________ 33,44,50 

Kautz Creek valley, lahar assemblage________ 46 

Kautz Glacier ____ ------------------------- 43, 46,48 

Klapatche Ridge_____________________________ 53 

Lake George_________________________________ 50 

LeDoux Creek_______________________________ 54 

Liberty CaP---------------------------------- 30,67 

Lithology of Mount Rainier Volcano__________ 10 

Little Tahoma Peak ______________ ------------ 5, 22 

Marmot Creek ______ c_________________________ 13 

Mazama Ridge _______________________________ 33, 36 

Mineral Creek._______________________________ 44 

Mist Park_-------- ___ ---------·______________ 13 

Mounds on lahars _____________________________ 18,19 

Mowich River _______________________ 43, 53, 54, 55,56 

Mowich River valley, lahars__________________ 67 

Mud Mountain __ ----------------------------- 25,26 

Mud Mountain Dam ___ ------------------- 25, 29,70 

Muddy Fork_________________________________ 69 

Narada Falls.-------------------------------- 33 

Nisqually Glacier ______ ----------------- 4, 33, 43,44 

Nisqually River __________ 2, 36, 37, 38, 39, 47, 52, 69,70 

Nisqually River valley, lahar assemblage, 

origin ___________ --------- ___ ----__ 41 

lahars ___ ----------- ____ ---------_-------- 44 

North Mowich Glacier________________________ 69 

North Puyallup River _______________________ 2,52 

North Puyallup River valley, lahars _________ 49, 66 

Observation Rock____________________________ 11 

Ohauapecosh River _______ -------____________ 43 

Ohanapecosh River valley, lahars____________ 68 

1,000-year-old lahar ____________________ ------_ 66 

Origin of lahars_______________________________ 8 

Osceola Mudflow ----------------------------- 7, 

8, 12, 13, 17, 19, 21, 22, 23, 24, 30, 32, 35, 43, 

67,68, 70 

Panorama Point __________________ --------- 33,35, 36 

Paradise lahar _____________________ 7, 33, 39, 40, 55,69 

Paradise Park ____________________ ---------_ 3, 33,34 

older lahar _________ ---------------_______ 96 

Paradise River _________ ---------------------- 36,40 

Pearl Falls_------------ __________ ------------ 45 

Phi quartile deviation ____________ ------------ 4 

Phi standard deviation_______________________ 4 

Point Success __ -----------------_____________ 30 

Post-Osceola lahar assemblage________________ 90 

Pre-Osceola lahar assemblage_________________ !3 

Puget Sound lowland _________ 1,4, 8, 10, 17, 25,43, 70 

Pumice deposits _____ ------------- ___ 12, 22,45,46, 62 

Puyallup River ______________________ 2, 26, 54, 56,67 

Pyroclastic deposits _______________ 3, 11, 12, 22, 45,68 

Pyroclastic layer A-- _____________ ------------ 40,68 

c _________________________ 12, a1, 32,40, 43, oo, 68 

D.-----------------------_------------ 33, 35,68 

F ____ --------------------- _ --------- ___ 13, 25,30 

L _______ ------- ______ --------- _ ----------- 68 

P~~e 

Pyroclastic layer N___________________________ 68 

o ________________ 12, 1a, 21, 24, 33, 37, 38, 39,41, 68 

R. ____ --- ___ ------ ____ ----- ___ ---- __ ----- 68 

s ________________ ---------------- _________ 22, 68 

w-.12, 31, 32, 38, 40, 41, 43, 45, 46, 49, 57, 58, 62, 6"1', 68 

y---------------------------------------- 12, 

31, 32, 33, 38, 39, 40, 41, 44, 45, 46, 49 ,50, 

52, 53, 57, 62, 67, 68 

Rampart Ridge______________________________ 36 

Reflection Lakes _____________________________ 31,34 

Remanent magnetism ___________________ 5, 23,64,66 

Ricksecker Point __________________________ 33,3"( 36 

Round Pass Mudflow ------------ 49, 55, 57, 62,61. 69 

Russell Cliff __________________________________ 31, 67 

St. Andrews Creek ___________________________ 5~ 57 

St. Andrews Park____________________________ 54 

Silver Creek _________ -- ______ ----------_______ 18 

Size-distribution analyses ____ 6, 26, 32, 35, 37, 54,51 64 

Sluiskin Falls ______ ----- ____ ------ ________ --- 31.36 

Sorting coefficient ________ 4, 26, 28, 32, 35, 37, 54, 5"' 64 

South Mowich Glacier________________________ 69 

South Prarie Creek _____________ -------------- 26 

South Puyallup River ____ ------------ 2, 43, 53, 51.68 

South Puyallup River valley, block-and-ash 

flow ___ ------ ________ ----_________ 64 

lahar assemblage ________ -----------______ 6! 

lahars __ ----------- __ -- __ ----------------- 49 

South Tahoma Glacier __________________ 4,58,61,62 

Steamboat Prow ___ ----------------- ___ 22, 24, 2:; 29 

Sunrise Creek________________________________ 22 

Sunset Amphitheater ___________________ 17, 55,51 69 

Tahoma Creek. __________ 2, 34, 38, 50, 54, 55, 58, 61. 69 

Tahoma Creek valley, lahar assemblage______ 67 

lahars_----------- ___ --------------------- 49 

Tahoma Glacier ________ ---------------------- 17,58 

Terminology oflahars________________________ S 

Thermoremanent magnetism _________________ 5,65 

Till __________ ---- ___________________________ 5,1~, 16 

Van Trump Creek ___________________ --------- 3"~'.38 

Van Trump Park_____________________________ 33 

lahars____________________________________ 97 

Vashon Drift ____ ----------------------------- 24 

Vashon till.----------- ____ ------------------- 2~ 25 

Volcanic ash _____ ----------------------------- 1 ~- 32 

Volcanism, associated with lahars_____________ flll 

West Fork _________________________________ 17,2.5, 70 

West Fork valley, Post-Osceola lahar assemblage ____________ ----------------_ as 

White River _________________ 2, 20, 22, 23, 24, 26, 69,70 

White River drainage basin, lahars___________ 17 

Willis Wall____________________________________ 2, 67 

Winthrop Creek______________________________ 32 

Winthrop Creek Glaciation ________________ 24,42,43 

Winthrop Glacier _____________________________ 2.5, 43 

Yakima Park________________________________ 22 

75 

-u.S. GOYERNMtNT PRINTING OFFICI;:: 1!171