U.S. Department of the Interior 

U.S. Geological Survey

Debris Flows from Failures of NeoglacialAge Moraine Dams in the Three Sisters and 

Mount Jefferson Wilderness Areas, Oregon

Professional Paper 1606

science 

uses

for a changing world
Cover photograph: View northwest of Broken Top volcano and moraine-dammed lake. South, 

Middle, and North Sisters in background. Photograph by Austin Post, USGS, September 22,1966.
Debris Flows from Failures of NeoglacialAge Moraine Dams in the Three Sisters and 

Mount Jefferson Wilderness Areas, Oregon

By Jim E. O'Connor, Jasper H. Hardison III, and John E. Costa

A study of the recent debris flows from moraine-dammed 

lake releases at central Oregon Cascade Range volcanoes— 

Mt. Jefferson, Three Fingered Jack, and the 

Three Sisters/Broken Top

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1606
U.S. DEPARTMENT OF THE INTERIOR 

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director

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

and does not imply endorsement by the U.S. Government.

Reston, Virginia, 2001

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center 

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

O'Connor, Jim E., 1959-

Debris flows from failures of Neoglacial-age moraine dams in the Three Sisters 

and Mount Jefferson wilderness areas, Oregon / by J.E. O'Connor, J.H. Hardison III, and J.E. Costa, 

p. cm.-- (U.S. Geological Survey professional paper; 1606) 

Includes bibliographical references and index. 

1. Debris avalanches-Oregon-Three Sisters Wilderness. 2. Debris 

avalanches-Oregon-Mount Jefferson Wilderness. 3. Moraines-Oregon-Three Sisters 

Wilderness. 4. Moraines-Oregon-Mount Jefferson Wilderness. I. Hardison, J.H. 

(Jasper H.), 1965- II. Costa, John E. III. Title. IV. Series

QE599.U5 026 2001

551,3'07-dc21 2001023270

ISBN 0-607-96719-6
CONTENTS

Abstract.......................................................................................................................................... 1

Introduction................................................................................................................................... 2

Background............................................................................................................................ 2

Purpose and Scope ................................................................................................................. 2

Acknowledgments.................................................................................................................. 2

The Central Oregon Cascade Range.............................................................................................. 2

Physiography.......................................................................................................................... 2

Geologic and Topographic Setting................................................................................. 2

Climate and Vegetation .................................................................................................. 4

Glaciers........................................................................................................................... 4

Previous Work........................................................................................................................ 4

Neoglaciation in the Central Oregon Cascade Range ................................................................... 5

Neoglaciation and Little Ice Age Chronology and Deposits ................................................. 5

Chronology..................................................................................................................... 5

Neoglacial Deposits........................................................................................................ 6

19th-and 20th-century Glacier Behavior.............................................................................. 9

Glacier Activity .............................................................................................................. 9

Climatic Forcing............................................................................................................. 13

Moraine-Dammed Lakes............................................................................................................... 15

Distribution ............................................................................................................................ 15

Chronology............................................................................................................................. 24

Lake Basin Bathymetry and Topography .............................................................................. 26

Formation and Preservation of Moraine-Dammed Lakes...................................................... 26

Debris Flows from Lakes Dammed by Neoglacial Moraines ....................................................... 26

General Features .................................................................................................................... 26

Indirect Discharge Estimation Methods................................................................................. 27

Velocity-Area Discharge Estimates................................................................................ 27

Critical-Flow Discharge Estimates................................................................................. 39

Case Studies in the Central Oregon Cascade Range.............................................................. 41

Mount Jefferson Wilderness Area.................................................................................. 41

East Jefferson Park.................................................................................................. 42

West Jefferson Park ................................................................................................ 43

Waldo Glacier......................................................................................................... 44

Jack Glacier............................................................................................................. 45

Three Sisters Wilderness Area ....................................................................................... 46

Collier Glacier......................................................................................................... 46

Diller Glacier........................................................................................................... 53

Eugene Glacier........................................................................................................ 60

East Bend Glacier.................................................................................................... 65

Contents ill
Processes................................................................................................................................ 69

Breaching of Moraine Dams................................!.......................................................... 70

Downstream Flow Characteristics.................................................................................. 73

Evaluation of Hazards from Moraine-Dammed Lake Breakouts.................................................. 76

Assessing Potential Failure of Moraine Dams....................................................................... 76

Topographic Setting ....................................................................................................... 76

Likelihood of Future Breaches in the Central Oregon Cascade Range.......................... 77

Assessing Downstream Flow Hazards................................................................................... 79

The Outflow Hydrograph at the Breach ......................................................................... 79

Downstream Flow Behavior........................................................................................... 81

Conclusions ................................................................................................................................. 85

References Cited............................................................................................................................ 87

PLATES

I. Maps of the Neoglacial moraines and glacial positions since the culmination of the

Little Ice Age for Mount Jefferson, Three Fingered Jack, and the Three Sisters Wilderness Area— 

In pocket

II. Maps of debris flow paths for flows originating from moraine-dammed lakes in the 

Three Sisters Wilderness Area—In pocket

FIGURES

1. Regional map of central Oregon Cascade Range and surrounding area ......................................... 3

2. Graph of equilibrium line altitudes for present and reconstructed late Quaternary glaciers

at Mount Jefferson and Three Sisters.............................................................................................. 5

3. Photograph of Neoglacial lateral moraines of Collier Glacier........................................................ 7

4. Oblique aerial photograph of Carver Lake and terminus of northern lobe of Prouty Glacier ........ 8

5. Matched photographs of ablation area of Diller Glacier................................................................. 10

6. Matched photographs of the right lateral moraine and terminus of Hayden Glacier...................... 11

7. Matched photographs of Collier Glacier......................................................................................... 12

8. Graph of changes in the glacier areas of Three Sisters and Mount Jefferson since the

culmination of the Little Ice Age .................................................................................................... 13

9. Oblique aerial photograph of Collier Glacier.................................................................................. 13

10. Map showing extent of Collier Glacier at several times during the 20th century........................... 14

11. Graph of equilibrium line altitude and glaciated area at Collier Glacier since the culmination

of the Little Ice Age ........................................................................................................................ 15

12. Sequence of photographs by R.H. Keen from Collier Glacier viewpoint....................................... 16

13. Graphs of measured mean annual temperatures from northern hemisphere land data and

Corvallis, Oregon............................................................................................................................ 17

14. Graphs of annual climate data for Crater Lake, Oregon ................................................................. 18

15. Photographs of moraine-dammed lakes in the Three Sisters and Mount Jefferson Wilderness

Areas, Oregon.................................................................................................................................. 23

IV Contents
16. Graphs of moraine-dammed lake chronologies for lakes in the Three Sisters and Mount

Jefferson Wilderness Areas, Oregon............................................................................................... 25

17. Maps of bathymetry and topography of lakes and lake basins dammed by Neoglacial moraines

in the Three Sisters and Mount Jefferson Wilderness Areas .......................................................... 28

18. Graph of area-volume relations for moraine-dammed lakes and lake basins in the study area...... 30

19. Definition diagram for flow transforming from a state of subcritical to supercritical through a

control section of critical flow ........................................................................................................ 39

20. Schematic plan and profile illustrations of an ideal field situation for a critical flow discharge

measurement.................................................................................................................................... 40

21. Critical depth and specific energy curves for a surveyed cross section .......................................... 41

22. Aerial photograph of Mount Jefferson and the northern lobes of White water Glacier................... 41

23. Composite of oblique aerial photographs of the debris flow at the terminus of a lobe of

Whitewater Glacier, Mount Jefferson ............................................................................................. 42

24. Graphs of longitudinal profiles along the flow routes of debris flows from moraine-dammed

lakes at terminal lobes of Whitewater Glacier, Mount Jefferson.................................................... 43

25. Oblique aerial photograph of Waldo Glacier, Mount Jefferson...................................................... 44

26. Photograph of moraine and outwash fan from Jack Glacier on Three Fingered Jack .................... 46

27. Photograph of outlet from the basin that formerly contained the lake at the terminus

of Collier Glacier, North Sister ....................................................................................................... 47

28. Graph of surveyed cross section of outlets to the former lake at the terminus of

Collier Glacier................................................................................................................................. 48

29. Oblique aerial photograph of remnant lake, breached moraine, and downstream

deposits left after the 1942 flow from the lake at Collier Glacier................................................... 48

30. Graph of stage-discharge relation for critical flow through the left breach at the

outlet to the lake at Collier Glacier ................................................................................................. 49

31. Photograph of Sawyer Bar covered by bouldery deposits from the 1942 breach and debris

flow from the lake at the terminus of Collier Glacier ..................................................................... 49

32. Graph of longitudinal profile of White Branch, showing indirect discharge estimates and 

reaches of erosion and deposition during the 1942 debris flow from the breach of the lake 

at the terminus of Collier Glacier.................................................................................................... 50

33. Photograph of a single sinuous ridge of bouldery gravel along the 1942 flow path down

White Branch................................................................................................................................... 51

34. Photograph of deposits from the 1942 debris flow down White Branch........................................ 52

35. Graph of indirect estimates of peak discharge for the 1942 debris flow down White Branch ....... 53

36. Graph of range of cumulative curves for 13 samples of matrix material from the 1942

White Branch debris-flow deposits ................................................................................................. 53

37. Graphs of downstream variation in particle-size distribution characteristics of matrix

materials for the 1942 White Branch flow...................................................................................... 54

38. Stereophotograph pairs of Diller Glacier before and after the September 7, 1970,

breach of the moraine-dammed lake ............................................................................................... 55

39. Graph of longitudinal profile of North Fork Squaw Creek, showing indirect discharge 

estimates and reaches of erosion and deposition during the September 7, 1970, 

debris flow and flood from the breach of the lake at the terminus of Diller Glacier...................... 56

40. Photograph of distal end of the large fan deposited below the September 7, 1970,

breach in the Diller Glacier moraine ............................................................................................... 57

Contents
41. Photograph of a debris flow levee or boulder berm deposited by the 1970 North

Fork Squaw Creek flow................................................................................................................... 58

42. Photograph of boulders trapped by trees in an overbank area during the 1970 North

Fork Squaw Creek flow................................................................................................................... 58

43. Photograph of buried trees in depositional area of the 1970 North Fork Squaw Creek debris

flow ............................................................................................................................................. 59

44. Hydrograph for September 7, 1970 on Squaw Creek, 24 km from the breach............................... 60

45. Graph of range of cumulative curves for 13 samples of matrix material from the 1970

North Fork Squaw Creek debris flow deposits ............................................................................... 60

46. Graphs of downstream variation in particle-size distribution characteristics of matrix

materials for the 1970 North Fork Squaw Creek debris flow ......................................................... 61

47. Graph of rock-type counts downstream from the breach of the moraine at Diller Glacier............. 61

48. Matched photographs of the north slope of South Sister from the summit of Middle Sister.......... 62

49. Map of topographic setting of August 12, 1933, and 1946(?) moraine-dammed lake

releases at Eugene Glacier, South Sister......................................................................................... 63

50. Oblique aerial photograph of the August 12, 1933, lake breach and debris flow from

Eugene Glacier................................................................................................................................ 64

51. Graph of longitudinal profile of Separation Creek, showing indirect discharge

estimates and reaches of erosion and deposition during the August 12, 1933, debris

flow and flood from the breach of the lake at the terminus of Eugene Glacier .............................. 64

52. Graph of longitudinal profile of the drainage from East Bend Glacier, Broken Top, 

into Sparks Lake, showing indirect discharge estimates and reaches of erosion and 

deposition during the October 7, 1966 debris flow and flood from the breach of the 

lake at the terminus of the glacier ................................................................................................... 66

53. Photograph of the October 7, 1966, breach in the Neoglacial moraine impounding the

lake at the terminus of East Bend Glacier, Broken Top.................................................................. 66

54. Photograph of valley-bottom bedrock erosion about 1.6 km downstream from breach

of the East Bend glacial lake........................................................................................................... 67

55. Photograph downstream of deposits left by the October 7, 1966, debris flow from the

lake at the terminus of East Bend Glacier....................................................................................... 67

56. Photograph of a boulder and timber fan deposited by the October 7, 1966, debris flow from

the lake at the terminus of East Bend Glacier, Broken Top............................................................ 68

57. Graph of range of cumulative curves for four samples of matrix material and fine gravel

from the 1966 debris flow from East Bend Glacier, Broken Top ................................................... 69

58. Graphs of cumulative curves of particle sizes for three Neoglacial moraines in the

Three Sisters Wilderness Area ........................................................................................................ 70

59. Graphs of breach cross sections and previous lake levels at four sites of morainedammed lake releases in the Three Sisters and Mount Jefferson Wilderness Areas ...................... 72

60. Hydrographs and debris flow characteristics during the September 12, 1991, experiment

at the Chemolgan Debris Flow Testing Ground, Kazakhstan......................................................... 74

61. Graph of channel slopes associated with reaches of deposition, erosion, and

conveyance for the debris flows on White Branch, Squaw Creek, Separation Creek,

and Soda Creek................................................................................................................................ 75

62. Topographic-setting criteria for qualitative assessment of the potential of a moraine-dam

breach ............................................................................................................................................. 78

VI Contents
63. Graphs of topographic profiles for the five largest moraine-dammed lakes in the 

Three Sisters and Mount Jefferson Wilderness Areas, and for Collier Glacier and 

adjacent basin.................................................................................................................................. 79

64. Graph of decadal incidence of formation and breaching of Neoglacial moraine-dammed lakes

in the Three Sisters and Mount Jefferson Wilderness Areas .......................................................... 80

65. Hydrographs of effects of breach shape, erosion rate, and lake hypsometry on

calculated erosion rates ................................................................................................................... 81

66. Calculated hypothetical hydrographs for sis existing and potential moraine-dammed

lakes in the Three Sisters and Mount Jefferson Wilderness Areas ................................................. 82

67. Graph of downstream variation in peak discharges for debris flows from morainedammed lake releases in the Three Sisters Wilderness Area, Oregon, and other alpine 

areas. ............................................................................................................................................. 84

TABLES

1. Lakes dammed by Neoglacial moraines in the Cascade Range, Oregon and Washington............. 19

2. Failed moraine dams in various mountainous areas worldwide ..................................................... 31

3. Hypothetical peak discharges from moraine-dammed lakes in the Three Sisters and

Mount Jefferson Wilderness Areas for various breach erosion rates.............................................. 79

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

International system units to inch-pound units

millimeter (mm) 0.0397 inch (in)

meter (m) 3.281 feet (ft)

square kilometer (km2 ) 0.3861 square mile (mi2 )

cubic meter (m3 ) 35.31 cubic foot (ft3 )

cubic meters per second (m3/s) 35.31 cubic feet per second (fWs)

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 

(NGVD of 1929) — a geodetic datum derived from a general adjustment of the first-order 

level nets of both the United States and Canada, formerly called "Sea Level Datum of 1929."

Contents VII

Debris Flows from Failures of Neoglacial-Age 

Moraine Dams in the Three Sisters and 

Mount Jefferson Wilderness Areas, Oregon

By Jim E. O'Connor, Jasper H. Hardison III, and John E. Costa

Abstract

Cascade Range alpine glaciers have shrunk 

substantially as average annual temperature has risen 

0.5 to 2 degrees Celsius since culmination of the 

Little Ice Age in the mid- to late 1800's. In recently 

deglaciated areas in the Cascade Range, hundreds of 

lakes have formed. Most of these newly formed lakes 

are partly or entirely bound by bedrock rims and are 

stable, but at least 30 are dammed by unconsolidated 

moraines that are susceptible to breaching.

The highest concentration of lakes dammed by 

Neoglacial moraines in the conterminous United 

States is in the Mount Jefferson and Three Sisters 

Wilderness Areas in central Oregon, where there are 

currently eight moraine-dammed lakes. The largest 

lake, Carver Lake on South Sister, has a volume of 

almost 1 million cubic meters. Most of these lakes 

formed between 1920 and 1940 during a period of 

substantial warming and glacier retreat. In the Mount 

Jefferson and Three Sisters Wilderness Areas, there 

have been 11 debris flows from 4 complete and 7 

partial emptyings of moraine-dammed lakes. Most of 

these breaches occurred between 1930 and 1950, but 

some were as recent as the 1970's.

All moraine-dam breaches in the Three Sisters 

and Mount Jefferson Wilderness Areas occurred 

during the melt season (July-October), usually during 

periods of warm or rainy weather. Many breaches 

were probably a result of erosion of the steep outlet 

channels, triggered by unusually large discharges 

caused by (1) waves generated by rockfalls or ice 

avalanches into the lake or (2) increased lake outflow 

caused by precipitation and melting snow and ice. 

Water flows from breached moraine dams rapidly 

evolved into debris flows that traveled as far as 9

kilometers before stopping or evolving into sedimentladen water flows. Peak discharges of at least four of 

the flows exceeded 300 cubic meters per second. 

Flows from breached morainal dams transformed 

from clear water at the outlet into debris flows within 

500 meters of the breaches by incorporating large 

volumes of loose Neoglacial till and outwash from 

the moraines and proglacial outwash. For the two 

largest lake releases, the volume of sediment eroded 

near the outlet exceeded 25 percent of the total 

volume of water released. Morphological evidence 

indicates that sediment was introduced into flows by 

bank collapse and channel incision. Indirect discharge 

estimates (primarily by a critical-depth procedure) 

show that peak discharges increased in erosional 

reaches; in one instance by more than a factor of four. 

Erosion and sediment entrainment was restricted to 

reaches with slopes that exceeded 8°, and deposition 

occurred in reaches with slopes less than 18°.

Several moraine-dammed lakes still exist, and 

some pose downstream hazards. Two of the lakes are 

remnants of previously larger lakes that have partially 

breached their moraine dams. Five lakes in the Three 

Sisters and Mount Jefferson Wilderness Areas are 

impounded by Neoglacial moraines that have not 

been breached. Qualitative assessments of 

downstream hazards from moraine-dammed lakes are 

possible on the basis of the topographic setting of the 

lake and downstream channel conditions. 

Quantitative assessment of the likelihood of 

breaching or the magnitude of downstream flows is 

difficult because of the variety of mechanisms that 

trigger breaches, the sensitivity of outflow 

hydrographs to breach shape and erosion rate, and the 

large uncertainty of downstream flow characteristics.

Abstract
INTRODUCTION 

Background

Recent floods and debris flows1 resulting from 

moraine-dam failures are one of several 

geomorphic consequences of substantial 19th and 

20th century alpine glacier retreat at the end of the 

Neoglacial period2 (Clague and Evans, 1993; 

Evans and Clague, 1993; O'Connor and Costa, 

1993). Worldwide retreat and thinning of glaciers 

from advanced late Neoglacial positions has 

resulted in the exposure of a large volume of 

unconsolidated, unvegetated, and locally ice-cored 

sediment. These deposits include moraines, 

outwash, and ice-stagnation drift and are 

commonly composed of a heterogenous mixture of 

particle sizes emplaced on steep slopes. This 

sediment is readily mobilized, transported, and 

deposited by a variety of processes, including mass 

wasting, moraine-dammed lake failures, glacial 

outburst floods, rapid snow and ice melting, and 

precipitation-induced flooding. Although 

deglaciation has triggered these processes in all 

temperate glacierized environments, recent 

geomorphic activity on Cascade Range volcanoes 

has been notable because these volcanoes are steep, 

extensively glacierized, and composed of jointed 

and locally highly altered loose rock and 

fragmental material (Osterkamp and others, 1986; 

Walder and Driedger, 1994).

Purpose and Scope

This report focuses on central Oregon Cascade 

Range stratovolcanoes of Mount Jefferson, Three

Debris flows are slurries of rock debris, organic material, 

and water that have sufficient yield strength and 

viscosity to support gravel-sized particles in suspension 

(Pierson and Costa, 1992).

The Neoglacial period was defined by Porter and Denton 

(1976) as encompassing the last 5,000 to 6,000 14C yr, 

when alpine glaciers reformed and advanced. The "Little 

Ice Age" (Matthes, 1939) is generally regarded as the 

culmination of the Neoglacial period, and is a term used 

by climatologists, geologists, and glaciologists to 

describe a period of worldwide lower temperatures and 

advanced glacier positions from the 16th century through 

the late 19th century (Grove, 1988, p. 3-5).

Fingered Jack, and the Three Sisters/Broken Top 

area because of the unique concentration of recent 

debris flows that have resulted from morainedammed lake releases. We evaluate the relevant 

late Holocene glacier and climate history of the 

Three Sisters and Mount Jefferson Wilderness 

Areas between Mount Jefferson and Crater Lake, 

Oregon (fig. 1) and describe conditions that led to 

formation and failure of Neoglacial moraine dams. 

We mapped, described, sampled deposits from, and 

calculated multiple indirect discharge 

measurements for four debris flows that resulted 

from breaching of moraine dams to determine and 

track aspects of flow characteristics as each debris 

flow moved downstream. The report concludes 

with a discussion of hazard assessment for existing 

moraine-dammed lakes in the Three Sisters and 

Mount Jefferson Wilderness Areas.

Acknowledgments

Field assistance was provided by Janet Curran, 

Ross Hartlieb, Gerardo Benito, and Chris Surville 

(U.S. Geological Survey volunteers). David 

Wieprecht (U.S. Geological Survey) assisted with 

matching of historic photographs. William Scott, 

Kevin Scott, Joseph Walder, and Thomas Pierson, 

all of the U.S. Geological Survey, provided ideas, 

guidance, and unpublished data for use in this 

report. Previous versions of this report were 

reviewed by C. Waythomas, A. Laenen, 

W Osterkamp, J. Major, J. Walder, R. Iverson, 

W Scott, and K.M. Nolan, all of the U.S. 

Geological Survey. Editorial assistance, manuscript 

preparation, and graphics by Christine Janda.

THE CENTRAL OREGON 

CASCADE RANGE

Physiography

Geologic and Topographic Setting

In the United States, the Cascade Range 

extends from northern California to northern 

Washington. In Oregon, south of Mount Hood, the 

Cascade Range is 50 to 120 km wide, and is 

composed primarily of upper Eocene to Quaternary 

volcanic, volcaniclastic, sedimentary, and igneous

Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Mt. Jefferson LINN 

COUNTY

\ MT, JEFFERSON ^ - 

] WILDERNESS,. O 

AREA

JEFFERSON 

COUNTY Mt. Baker i - _^ ,

^.'Glacier Peak ' '

WASHINGTON

' •N.J.L.--'' '-, ii —-i|- r..

Mt. Rainier f. j

j Three Fingered Jack

MT. WASHINGTON i

:. Mt. Washin

WILDERNESS 

AREA

Middle Sister 

South Sister

Broken Top

LANE | \ THREE

COUNTY ^SISTERS

WILDERNESS

Mt. Bachelor

DESCHUTES 

COUNTY

Figure 1. Central Oregon Cascade Range and surrounding area.
intrusive rocks. The crest of the Cascade Range is 

generally at an altitude of 1,500 to 2,000 m, with 

several of the high volcanoes exceeding 3,000 m 

(Callaghan and Buddington, 1938; Sherrod, 1986). 

The high stratovolcanoes and volcano remnants of 

the central Oregon Cascade Range include Mount 

Jefferson, Three Fingered Jack, Mount Washington, the three volcanoes of the Three Sisters, 

Broken Top, Mount Bachelor, Diamond Peak, 

Mount Thielsen, and Crater Lake Caldera (Mount 

Mazama)(fig. 1). These are all Pleistocene 

stratovolcanoes of rhyolitic to basaltic composition and are formed mostly of interlayered thin 

lava flows and pyroclastic deposits overlying 

cinder cone cores. Of the large stratovolcanoes, 

there has been Holocene volcanic activity on the 

summit and flanks of South Sister and at Mount 

Bachelor as well as the caldera-forming eruptions 

of Mount Mazama (Taylor, 1981; Taylor and 

others, 1987; Scott, 1989). The general conical 

morphology is best preserved on the volcanoes of 

Middle Sister, South Sister, and Mount Bachelor; 

the rest have been deeply eroded by Pleistocene 

glaciation.

Climate and Vegetation

Western Oregon has a temperate maritime 

climate that is dominated by winter Pacific frontal 

systems moving eastward across the State. The 

Cascade Range is a major orographic barrier that 

intercepts much of the eastward-flowing moisture. 

Generally warm and dry summers result from 

northward expansion of the eastern Pacific high 

pressure system and diversion of the prevailing 

westerlies to the north. Consequently, precipitation 

generally occurs during the winter and is greatest 

at high altitudes. Annual precipitation is about 

3,500 to 4,000 mm at the highest elevations within 

the Three Sisters and Mount Jefferson Wilderness 

Areas (Taylor, 1993) and falls mostly as snow. At 

Crater Lake (fig. 1), 90 percent of the 1,620 mm of 

annual precipitation falls between October 1 and 

May 31. Annual precipitation decreases eastward 

across the Oregon Cascade Range, diminishing 

from more than 2,500 mm on the western slopes to 

less than 400 mm within 30 km east of the range 

crest (Taylor, 1993).

The highest peaks of the cenl ral Oregon 

Cascade Range rise above treeline, which is about

2,200 m above sea level on the north side of 

Mount Jefferson, about 2,300 m on the north side 

of South Sister, and 2,500 m on the south side of 

Broken Top. The tallest trees of the subalpine 

forests and parks near timberline are mountain 

hemlock (Tsuga mertensiana) and whitebark pine 

(Pinus albicaulis).

Glaciers

The central Oregon Cascade Range peaks that 

presently sustain glaciers or permanent ice masses 

are, from north to south, Mount Jefferson, Three 

Fingered Jack, North Sister, Middle Sister, South 

Sister, and Broken Top. In addition, 

Mount Bachelor, Diamond Peak, and Mount 

Thielsen all had small glaciers that persisted until 

the end of the Little Ice Age in the early 20th 

century. The Three Sisters Wilderness Area is the 

most extensively glacierized region of the central 

Oregon Cascade Range, with 17 named glaciers 

that presently cover about 7.5 km2 (pi. 1). In the 

Three Sisters and Mount Jefferson Wilderness 

Areas, name assignments to some glaciers have 

varied over the years. In this report, we use the 

names on the current U.S. Geological Survey 

(USGS) topographic quadrangles (1988 

provisional editions) and informally use the names 

"Jack Glacier" and "East Bend Glacier" for the 

unmapped glaciers or perennial ice masses in the 

northeast-facing cirques of Three Fingered Jack 

and Broken Top.

Previous Work

Previous studies of debris flows and floods in 

other recently deglaciated alpine areas complement 

this analysis of debris flows that resulted from 

moraine-dammed lake releases in the Mount 

Jefferson and Three Sisters Wilderness Areas. 

Jackson (1979), Jackson and others (1989), and 

Leonard (1985) described the role of recent glacier 

retreat in promoting the incidence of debris flows 

and increased sediment flux in the Canadian 

Rockii'V Walder and Driedger (1994) studied the 

formation of debris flows by incorporation of 

Neoglacial sediment at Tahoma Creek, Mount 

Rainier. Lundstrom (1992) analyzed the alpine 

geomorphology of Eliot Glacier and surrounding 

moraines on Mount Hood. Osterkamp and others

Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
(1986) and Hupp and others (1987) evaluated the 

frequency and magnitude of debris flows from 

glacierized basins on Mount Shasta.

Floods and debris flows originating 

specifically from moraine-dammed lakes have 

been reported in Peru (Lliboutry and others, 1977; 

Reynolds, 1990), Canada (Blown and Church, 

1985; Evans, 1987; Clague, 1987; Clague and 

Evans, 1994), Great Britain (Carling and Glaister, 

1987), the Himalayas (Ives, 1986; Vuichard and 

Zimmermann, 1987; Ding andLiu, 1992), the 

European Alps (Haeberli, 1983; Eisbacher and 

Clague, 1984), and the former Soviet Union 

(Yesenov and Degovets, 1979). For the central 

Oregon Cascade Range, Laenen and others (1987, 

1992) provided a summary of known debris flows 

from moraine-dammed lakes in the Three Sisters 

Wilderness Area in their analysis of the hazard 

posed by failure of the moraine dam impounding 

Carver Lake. A 1966 debris flow from a morainedammed lake on Broken Top was described by 

Nolf(1966).

NEOGLACIATION IN THE 

CENTRAL OREGON CASCADE 

RANGE

Except for areas subject to recent volcanism, 

glacial processes and deposits of the last few 

millennia are the dominant influences on the 

landforms and deposits of glaciated alpine areas in 

the Cascade Range. Recent reviews of Holocene 

glacier fluctuations in the North American 

Cordillera are provided by Osborn and Luckman 

(1988), Davis (1988), Grove (1988), Ryder (1989), 

and Luckman and others (1993).

Neoglaciation and Little Ice Age 

Chronology and Deposits

In the central Oregon Cascade Range, sharpcrested, largely unvegetated Neoglacial moraines 

stand within 2 km of the present glacier termini, 

contrasting with older, more densely vegetated 

moraines that are blanketed by Mazama tephra 

(6,845 ± 50 14C yr BP; Bacon, 1983) and on the 

south flank of Broken Top, scoria from Cayuse 

Crater (>9,520 + 100 14C yr BP; Scott and

Gardner, 1992). Altitudes of Neoglacial terminal 

moraines indicate that equilibrium line altitudes 

(ELA) varied widely but were as much as 200 m 

below present (fig. 2) (Scott, 1977; Dethier, 1980). 

The wide variation in their ELA's probably reflects 

topographic controls on accumulation, insolation, 

and debris cover of these small glaciers.

Chronology

In the absence of historical records, periods of 

glacier retreat and advance are difficult to date 

accurately. According to the summary of Davis

2800

LJJ 

LJJ

£J 2600

LJJ

O

CO

to 2400 

cc

LU

- 2200

LU

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=>

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LU

5= 1800 

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o

LJJ

1600

THREE SISTERS MT. JEFFERSON

PRESENT 

GLACIERS

\

J

NEOGLACIAL 

MAXIMUM

\

\

\

\

\

\

\

LATE

PLEISTOCENE 

VALLEY-HEAD 

J_ GLACIERS

LATE

PLEISTOCENE 

SUTTLE LAKE 

ADVANCE

Figure 2. Equilibrium line altitudes (ELA) for present 

and reconstructed late Quaternary glaciers at 

Mount Jefferson and Three Sisters, Oregon. ELA 

calculations were based on an accumulation area ration 

of 0.6. Data for the later Pleistocene Suttle Lake 

advance and the valley-head (Canyon Creek) glaciers 

are from Scott (1989, p. 14) and are for glaciers east of 

the Cascade Range crest. Data for present and 

Neoglacial ELA's are from this study, (Scott, 1974, 

p. 68; 1977, fig. 11; 1989, p. 14), and Dethier (1980).

Neoglaciation in the Central Oregon Cascade Range
(1988), however, there were at least three periods 

of advanced ice positions during late Holocene 

time in the North American Cordillera: (1) a poorly 

dated early Neoglacial phase believed to date 

between 5 and 2.5 ka3; (2) a middle Neoglacial 

phase, which is recognized only in the Rocky 

Mountains of Colorado and Wyoming, where 

moraines date between 2 and 1 ka; and (3) a late 

Neoglacial, or Little Ice Age readvance (Davis, 

1988). Ages of early Neoglacial and Little Ice Age 

moraines in the Cascade Range have been 

determined by tephrochronology, radiometric 

dating, dendrochronology, and lichenometry. Early 

Neoglacial advances, all dated by radiocarbon 

dating of stratigraphically linked deposits, 

occurred between 5.5 and 3.0 ka at Glacier Peak 

(Beget, 1984); between 4.0 and 2.0 ka at 

Mount Rainier (Crandell and Miller, 1964); 

younger than 4 ka at Mount Adams (Hopkins, 

1976); older than 1.5 to 1.8 ka at Mount Hood 

(Lundstrom, 1992, p. 143); and between 6.8 and 

2.1 ka at Broken Top and Mount Bachelor (Scott, 

1989). These dates are consistent with results of 

recent studies in the Canadian Rockies that 

indicate a period of glacier advance between 3.1 to 

2.5 ka (Luckman and others, 1993).

In the Three Sisters and Mount Jefferson 

Wilderness Areas, most early Neoglacial deposits 

were removed or buried by Little Ice Age glacier 

advances during the last few centuries. This is 

consistent with many observations throughout the 

world that the Little Ice Age was, in general, the 

period of most advanced glacier positions of the 

Holocene (Grove, 1988). Evidence from 

lichenometric and dendrochronologic studies in 

Oregon and Washington indicates that glaciers 

reached maximum downvalley positions during the 

17th, 18th, and 19th centuries. At Mount Rainier, 

which has had the most thoroughly developed 

Little Ice Age chronology, the outermost terminal 

moraines of most major glaciers stabilized between 

1750 and 1850 AD, and there was general and 

substantial retreat between 1830 AD and 1950 AD 

(Crandell and Miller, 1964; Sigafoos and

"ka" is an abbreviation for "kilo-annum," referring to 103 

years. In this report, dates reported in this format are on 

the basis of radiocarbon dates that have not been 

calibrated to a calendar year reference.

Hendricks, 1972; Burbank, 1981, 1982). The 

maximum advance of Eliot Glacier on Mount 

Hood culminated about 1740 AD (Lawrence, 1948; 

Lundstrom, 1992, p. 118-126).

Late Neoglacial moraines formed by the 

glaciers of the central Oregon Cascade Range may 

have stabilized somewhat later than those 

constructed by the larger glaciers at Mount Rainier 

and Mount Hood. On Three Fingered Jack, the 

oldest tree cored on the Neoglacial moraine crest 

germinated about 1884 (Scott, 1974, p. 81). 

Similarly, the oldest trees growing on the left 

lateral moraine of Skinner Glacier, on the north 

flank of South Sister, germinated about 1865. This 

evidence indicates that the maximum late 

Neoglacial advance in the Central Oregon Cascade 

Range probably culminated in the 1850's and 

1860's. A substantially older moraine, however, 

was formed by a post- 2.3-ka advance of Lewis 

Glacier. The moraine was not covered by a tephra 

erupted 2.3 to 2.0 ka (Scott and Gardner, 1992) but 

does have large mountain hemlocks and whitebark 

pines growing on it, including one that germinated 

more than 500 years ago. Although they had 

thinned substantially, most glaciers in the Three 

Sisters area remained in contact with Neoglacialage moraines through the first two decades of the 

20th century.

Neoglacial Deposits

Late Holocene glaciers have effectively 

eroded and transported a large volume of sediment 

to proglacial positions. Massive lateral and end 

moraines, and downstream outwash fans were left 

as glaciers retreated from early 20th century 

positions. The lateral and end moraines are large 

constructional forms with crests rising to at least 

120 m above the adjacent terrain (fig. 3). The 

volume of Neoglacial lateral and end moraines on 

North, South, and Middle Sisters, determined by 

using the methods outlined by Lundstrom (1992, 

p. 137-139), is about 40 million m3 , equivalent to 

about 30 percent of the present ice volume 

(Driedger and Kennard, 1986).

Neoglacial moraines in the study area are 

composed of poorly sorted bouldery, gravelly, silty 

sand. The large lateral and end moraines appear to 

be abandoned "dump moraines" (Small, 1983)

Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
formed by supraglacial debris sliding onto the 

moraine surface from glacier margins that sloped 

above the moraine crest. Moraine stratigraphy is 

consistent with this interpretation. Fresh exposures 

reveal crude layering, defined by strata of varying 

boulder concentration, dipping orthogonally from 

the moraine crest at angles of 30° to 40°.

Some of these moraines are possibly icecored. Excavations into the moraine impounding 

Carver Lake exposed glacier ice at depths less than 

a meter (Rector, 1988). Dense ice was observed in 

a landslide scar on the proximal face of the end 

moraine of Thayer Glacier (L.D. Sorensen and 

M.A. Groesch, Oregon State University, unpub. 

data, 1982). Scott (1977) inferred that the moraine 

impounding the proglacial lake on Three Fingered 

Jack may be ice-cored because of its steepness and 

wet landslide scars on its proximal face. We 

observed stagnant glacier ice in the ground

moraine left by Collier Glacier near Collier Cone 

and near the termini of Skinner and Diller 

Glaciers.

Many of the proglacial areas are covered with 

morainal material, stagnant ice, and outwash 

sediment deposited during the maximum advance 

of the Little Ice Age and during subsequent retreat, 

masking most deposits of earlier Neoglacial 

advances (pi. 1). Little Ice Age moraines are 

sharp-crested and steep, with side slopes 

commonly 40° to 45°. Only a few plants are found 

growing in windblown accumulations of sand and 

silt on the moraine slopes, and protected boulder 

surfaces have less than 20 percent lichen cover.

Distinct Neoglacial moraines that predate the 

Little Ice Age are scarce. Older lateral moraines 

locally flank Little Ice Age moraines, and, in a few 

locations, older Neoglacial terminal moraines 

protrude up to a few hundred meters downvalley

Figure 3. View northeast of Neoglacial lateral moraines of Collier Glacier, Oregon, September 8, 1993. Note people 

on left lateral moraine.

Neoglaciation in the Central Oregon Cascade Range
from Little Ice Age moraines (pi. 1, fig. 4). Such 

pre-Little Ice Age moraines are not mantled with 

Mazama tephra, readily distinguishing them from 

late Pleistocene moraines that are found 

immediately downvalley (Scott, 1989). Pre-Little 

Ice Age moraines have slightly more rounded 

crests than do Little Ice Age moraines, and are 

commonly vegetated with krummholz-forrn 

whitebark pines on lee surfaces. Protected boulder 

surfaces are 50 to 100 percent lichen-covered, and 

within boulder interstices, there are accumulations 

of locally oxidized sand and silt several 

centimeters thick.

For most of these pre-Little Ice Age moraines, 

it is unclear if they represent advances during the

early Neoglacial (5 to 2 ka), or perhaps later 

Neoglacial advances. In the southern part of the 

Three Sisters Wilderness Area, early Neoglacial 

moraines are distinguished from Little Ice Age and 

Pleistocene moraines by a 2.3 to 2.0 ka tephra that 

is found only on these deposits (Dethier, 1980; 

Scott, 1987). On the basis of tephra relations, 

moraines that are clearly early Neoglacial (5 to 

2 ka) have been mapped beyond the southern 

portion of Prouty Glacier on South Sister, Bend 

Glacier on Broken Top (Dethier, 1980), and on 

Mount Bachelor (Scott, 1987; Scott and Gardner, 

1992). Outside the southern part of the Three 

Sisters Wilderness Area, the 2.3 to 2.0 ka tephra is 

thin or absent and cannot be used to date pre-Little

Prouty Glacier , ^

EXPLANATION

———— Little Ice Age moraine crests

-•••-• Pre-Little Ice Age, Neoglacial moraine crests

...... |_ate Pleistocene or early Holocene valley-head moraine crests

Figure 4. View southwest of Carver Lake and terminus of northern lobe of Prouty Glacier, October 

1956. Moraine crests of Little Ice Age, pre-Little Ice Age, and late Pleistocene valley-head glaciers 

are indicated. Photo reproduced with permission of Ackroyd Photography (neg. 7145-65).

Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Ice Age moraines. Older Neoglacial moraines are 

possibly correlative with the early Neoglacial 

moraines described above, or perhaps resulted 

from a later advance, similar to the 0.5 to 2 ka 

moraines of Lewis Glacier.

19th- and 20th-century 

Glacier Behavior

Glacier Activity

The remarkable shrinkage of Cascade Range 

glaciers since the late 1800's has set the stage for 

current geomorphic activity in glacierized basins 

of the Cascade Range (figs. 5, 6, and 7). 

Dendrochronologic evidence described above 

indicates that late Neoglacial moraines in the 

central Oregon Cascade Range did not stabilize 

until the mid-1800's. Historical 19th-century 

records of glacier positions in the central Oregon 

Cascade Range are restricted to anecdotal accounts 

by early mountaineers and explorers. 

J.S. Newberry, geologist for the Pacific Railroad 

Survey of 1855, viewed glaciers on the volcanoes 

of the Cascade Range in Oregon, but made no 

detailed observations. J.S. Diller, of the USGS, 

reconnoitered the central Oregon Cascade Range 

in 1883, ascending Mount Thielsen and Diamond 

Peak. Russell (1885) stated that Diller observed 

"glaciers of considerable magnitude on 

Mount Jefferson, Diamond Peak, and the Three 

Sisters," and that "the group of peaks known as the 

Three Sisters is considered by Mr. Diller as 

probably affording the most interesting field for 

glacial studies in the United States, with the 

exception of Alaska."

Twentieth-century records of central Oregon 

glaciers begin with the 1903 observations of USGS 

geologist I.C. Russell (1905). His photographs of 

several glaciers on the east side of Middle and 

South Sister (figs. 5A and 6A) show that glaciers 

abutted against their Neoglacial moraines but had 

thinned somewhat. Russell (1905, p. 126) 

recognized this "recent shrinkage," noting that the 

margin of Hayden Glacier was 12 to 20 m lower 

than the moraine crests. Photographs of the north 

side of Mount Jefferson (Oregon Historical Society 

neg. 73427) and of Collier Glacier (fig. 7A), taken 

in the first decade of the 20th century, also reveal

similar relations: by 1910, all glaciers had thinned 

considerably, but remained in contact with 

Neoglacial lateral and terminal moraines.

Glacier activity in central Oregon during the 

first half of the 20th century has been recorded by 

the Mazamas, an alpine club based in Portland, 

Oregon. Articles, photographs, and aerial surveys 

sponsored and published by the Mazamas 

(Williams, 1916; Hatch, 1917; Research 

Committee of the Mazamas, 1938; Phillips, 1938; 

unpub. aerial photographs taken in October, 1956 

[available for inspection at the Mazama library, 

Portland, Oregon]; and Hopson, 1960) document 

substantial and rapid glacier retreat. These records, 

combined with photographs from the archives of 

the Oregon Historical Society and U.S. Forest 

Service vertical aerial photographs taken in 1949, 

1967, 1974, and 1990, provided sufficient 

information for us to map glacier termini and 

compute glacier area at various times this century 

(pi. 1; fig. 8).

The most complete record of historic glacier 

retreat is for Collier Glacier, which has its source 

on the northwest flank of Middle Sister (figs. 7 

and 9). Collier Glacier is the largest glacier in the 

central Oregon Cascade Range, presently covering 

about 0.85 km2. At its maximum advance during 

the Little Ice Age, Collier Glacier covered nearly 

2.4 km2 and had an ELA about 195 m lower than 

present. The pattern of shrinkage of Collier Glacier, 

illustrated in figures 10 and 11, was apparently 

common to most central Oregon Cascade Range 

glaciers. Substantial reduction in glacier mass 

during the period between the late Neoglacial 

maximum (assumed to be about 1850 locally) and 

about 1910 was accommodated by glacier thinning, 

whereas termini positions did not retreat 

substantially from Little Ice Age moraines until 

early in the 20th century. The response lag 

probably was due to the large volume of ice stored 

behind the tall terminal and lateral moraines. 

Between 1910 and 1950 there was rapid retreat of 

the Collier Glacier terminus and reduction of 

glacierized area and ice volume (Hopson, 1960; 

McDonald, 1995) (fig. 12).

Beginning about 1950, glacier retreat slowed 

or reversed worldwide (Haeberli and others, 1989). 

This reversal was also observed in the Cascade 

Range and Olympic Mountains of Washington,

Neoglaciation in the Central Oregon Cascade Range 9
where, by 1955, most glaciers were advancing 

(Hubley, 1956; Meier and Post, 1962). Glaciers in 

the Cascade Range of northern Washington and on 

Mount Baker and Mount Rainier continued to 

advance until the late 1970's and early 1980's 

(Heikkinen, 1984; Driedger, 1986, 1993). Ground 

and aerial photographs show that most glaciers in 

the Three Sisters Wilderness Area stabilized at or 

near positions shown on 1949 photographs (pi. 1; 

fig. 8), and small lateral and terminal moraines a 

few meters high formed during the 1960's and 

1970's at the margins of many glaciers.

Since the early 1980's, and through the mid1990's, there has been renewed retreat of glaciers

in the Cascade Range. This recent retreat has been 

noted in the more extensively glacierized northern 

Cascades (Pelto, 1993) and on the glacierized 

volcanoes in Washington State. About 75 percent 

of northern Cascades glaciers were retreating in 

1988 and all glaciers on Mount Baker retreated 

between 7 and 75 m from 1979 through 1990 

(Pelto, 1993). Most termini of glaciers on 

Mount Rainier have been retreating since the mid 

1980's (Driedger, 1993). Termini of many glaciers 

in the Three Sisters Wilderness Area have retreated 

several meters from the small terminal moraines 

formed in the I960's and 1970's. Glacier retreat 

between 1967 and 1990 has been more substantial

Figure 5. Approximately matched views southeast toward the ablation area of Diller Glacier from near the left lateral 

moraine at altitude 2,620 m. A, Composite of August 16, 1903 (USGS Photographs by I.C. Russell; negs. 815 and 

816). These photographs probably were taken from the glacier surface. B, Composite of September 12, 1993, 

photographs taken several meters east (left) of the original photograph. The icefalls and bergschrund are at 

approximately the same locations, although the glacier has thinned and shrunk substantially. The breached moraine 

(from September 7, 1970, lake release) is visible near the glacier terminus. (Photographs by David E. Wieprecht, 

USGS).

10 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Figure 6. Approximately matched views northeast toward the terminus of Hayden Glacier from near the right 

lateral moraine at altitude 2,560 m. A, Photograph by I.C. Russell, USGS (neg. 812) taken August 16, 1903; 

B, Photograph by David E. Wieprecht, USGS, taken from the same location on September 12, 1993, shows 

substantial thinning and shrinkage of Hayden Glacier. There also has been several meters of erosion and lowering 

of the crest and inner slope of the right lateral moraine between photograph dates, eliminating the double crest noted 

by Russell (1905, p. 126) and probably contributing to the rubble at the base of the slope.

Neoglaciation in the Central Oregon Cascade Range 11
Figure 7. Approximately matched views southeast toward Collier Glacier from near the right lateral moraine at 

elevation 7,600 m. A, Photograph by Kiser Photo Co. appears in the 1912 Mazama Annual and is reproduced with 

permission of the Oregon Historical Society (Photograph 4799, album 663). Based on Mazama Club records, the 

photograph was probably taken during the 1910 annual summer outing. The glacier surface was several meters below 

the moraine crest, but still occupied the entire area bound by the moraines. B, September 8, 1993 photograph showing 

present terminus of Collier Glacier and illustrating the remarkable shrinkage during the last 80 years. A large mass 

movement removed much of the moraine crest visible in the foreground of the 1910 view. (Photograph by David E. 

Weiprecht, USGS.)

12 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
in the Mount Jefferson Wilderness Area where 

termini of several glaciers have retreated several 

tens of meters (pi. 1).

Climatic Forcing

The observed 19th- and 20th-century glacier 

activity in the central Oregon Cascade Range is 

likely the result of regional and worldwide 

warming since the late 19th century. Alpine 

glaciers respond sensitively to climate, adjusting to 

periods of positive or negative mass balance by 

thickening and advancing or thinning and 

retreating. For Cascade Range glaciers, the 

changes in temperature or precipitation required to 

cause a terminus response are quite small. 

Tangborn (1980) demonstrated that a decrease in 

mean summer temperature of 0.5°C or an increase 

in winter snow accumulation by 10 percent is 

sufficient to overcome the mass balance deficit that 

accompanied the extreme retreat of northern 

Cascade glaciers during the first half of this 

century. Furthermore, the time between climatic 

perturbation and the consequent terminus response

for Cascade Range glaciers is short—on the order 

of 1 to 5 years (Hubley, 1956; Burbank, 1982).

Historical temperature changes clearly had a 

large effect on glacier behavior in the Cascade 

Range. The profound retreat of glaciers worldwide 

from late Neoglacial positions accompanies a 

0.45±0.15 C° increase in global (combined land 

and ocean) air temperature since the late 19th 

century (Folland and others, 1990). On the decadal 

scale, temperature change has not been monotonic, 

but irregular, with periods of rapid temperature 

increase separated by periods of steady or declining 

temperature. Surface air temperatures measured 

over land increased in the northern hemisphere by 

about 0.4°C between 1920 and 1940 (fig. 13). This 

corresponds to the period of greatest glacier retreat 

in the central Oregon Cascade Range. 

Temperatures then decreased by about 0.2°C 

between 1940 and 1970, resulting in renewed 

advance of many Cascade Range glaciers, 

especially in the northern Cascades and at 

Mount Rainier, and stabilization of the central 

Oregon Cascade Range glaciers. Temperatures 

have increased again by about 0.3°C since 1970

LU 

DC

Three Sisters 

Wilderness Area

Mt. Jefferson 

Wilderness Area

1840 1860 1880 1900 1920 1940 1960 1980 2000 

YEAR

Figure 8. Glacier areas of the Three Sisters and 

Mount Jefferson Wilderness Areas since the culmination 

of the Little Ice Age (assumed locally to be about 1850). 

Neoglacial glacier areas measured from planimetry of 

moraine crests. Glacier areas in the Three Sisters 

Wilderness Area in 1925 and 1981 are measurements 

reported in Hodge (1925) and Driedger and Kennard 

(1986). All other glacier areas were measured from 

dated vertical aerial photographs.

Figure 9. Oblique aerial photograph of Collier Glacier 

flowing northwest from the saddle between Middle and 

North Sisters. Photograph by Austin Post, USGS 

(September 1, 1965, photograph F655-119).

Neoglaciation in the Central Oregon Cascade Range 13
12r48' 121°47' 121°46'

44°10'

,,

\ \ "N ^Collier Cone

N '"^-^ '. ^^; . •'

; * « \ 7,534 /

EXPLANATION

Moraine crest 

Neoglacial moraine

GLACIER POSITION— 

queried where uncertain

North

* Sister

-|4 .10,085

uM 5 - --J n^

I I 

0 0.25 0.5 MILES

CONTOUR INTERVAL 200 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF I929

Base modified from U.S. Geological Survey 

1:24000, North Sister, Oreg., 1988

Figure 10. The extent of Collier Glacier at several times during the 20th century. The moraine crest approximates 

the maximum Neoglacial extent in the late 19th century. Limits shown for years 1910 and 1931 are very 

approximate because they are based on single photographs (fig. 7 and Oregon Historical Society [neg. DB1568]) 

and inferences from descriptions. Limits for 1934, 1938, and 1943 are from vertical aerial photographs. 

McDonald (1995) presents a similar, but more detailed analysis of Collier Glacier mass balance and geometry 

changes since the Little Ice Age.

14 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
(Folland and others, 1990). During the 1980's, 

globally averaged land temperatures have been 

higher than during any other decade since the 

middle of the 19th century (Jones, 1988; Hansen 

andLebedeff, 1988) (fig. 13).

The latter part of this northern-hemisphere 

temperature record accords with records from 

weather stations in Oregon, although regional 

temperature fluctuations have been greater than 

those for the entire northern hemisphere (fig. 13). 

At Corvallis, L15 km west of Mount Jefferson, the 

average annual temperature rose about 2°C 

between 1890 and 1940, the period of most rapid 

historical glacier retreat. The most complete 

higher-elevation data set that we have found is for 

Crater Lake National Park (altitude 1,975 m), 

about 100 km south of the Three Sisters 

Wilderness Area (fig. 14). Records starting in 1932 

indicate an approximate 1°C decline in average 

daily temperature between 1940 and 1970. Over 

the same time period, the average daily June, July, 

and August temperature dropped almost 2°C. In 

the central Oregon Cascade Range, this 

temperature decline corresponds to cessation of 

terminus retreat and formation of small moraines. 

From 1980 through 1992, average annual 

temperatures at Crater Lake rose, recouping most 

of the 1940-1970 drop (fig. 14).

2.4 

2.2 

2.0

O 

=d 1.8

LU

CC ! K

< 1-6

a

w 1.4

z

< 1 9

LU 

OC

1.0

0.8

2,500

2,450 Q >

2,400

R <

-J LLI

< CO

LLJ LLJ

z >

=i O

2,350

CC CC 

CO LLJ

2,300 =>

a

1840 1880 1920 

YEAR

1960 2000

2,250

Figure 11. Equilibrium line altitude (ELA) (based on an 

accumulation area ratio of 0.6) and glaciated area at 

Collier Glacier since the culmination of Neoglacial time.

Cascade Range glaciers respond to the 

combined influence of winter snowfall 

accumulation and summer ablation (Tangborn, 

1980). At Crater Lake, there has been no apparent 

relation between precipitation and temperature 

patterns over the last 60 years (fig. 14). There were 

two periods, however, when precipitation and 

temperature anomalies apparently combined to 

change regional glacier behavior substantially. The 

halt of rapid glacier retreat and readvance of many 

glaciers in the 1940's and 1950's corresponds with 

the temperature decline noted above and a period 

of higher than average precipitation and winter 

snowpack (fig. 14). Between 1982 and 1992, there 

was a substantial decline in precipitation in 

conjunction with higher average temperatures, 

which corresponds to the substantial glacier retreat 

of the late 1980's and early 1990's. During water 

year 1992, when the warmest average daily 

temperatures since 1934 combined with one of the 

driest years of record, the result was substantial 

glacial mass-balance deficit.

The terminus positions of most central Oregon 

Cascade Range glaciers have fluctuated in tandem 

with temperature and precipitation patterns. Some 

glaciers, however, have responded to nonclimatic 

influences. For example, the terminus of the 

southern lobe of Prouty Glacier advanced 450 m 

between 1949 and 1974 (pi. 1), probably because 

the glacier was partially insulated by a debris 

avalanche from Hodge Crest that occurred during 

that time period. Similar debris avalanches appear 

to have affected the mass balances and termini 

behavior of Lost Creek Glacier and the northern 

Lobe of Diller Glacier. The termini of Thayer 

Glacier on the east flank of North Sister and East 

Bend Glacier on Broken Top calve into morainedammed lakes. Consequently, their positions have 

not changed substantially since the formation of the 

lakes in the 1920's.

MORAINE-DAMMED LAKES 

Distribution

In the wake of rapid glacier retreat during the 

first part of the 20th century, lakes dammed by 

Neoglacial moraines have formed in most 

glacierized regions of the world. Thirty-five

Moraine-Dammed Lakes 15
1934 1938

1940 1942

1949 1960

Figure 12. Sequence of photographs from Collier Glacier viewpoint (fig. 10), reproduced with permission of 

R.H. Keen. Photographs show the retreat and thinning of Collier Glacier and the growth and demise of the proglacial 

moraine-dammed lake. The lake breached the moraine dam and partially emptied in July 1942 at the site of the former 

outlet through the left lateral moraine (on the right edge of the photographs).

16 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
moraine-dammed lakes have been documented in 

the Cordillera Blanca of the Peruvian Andes 

(Lliboutry and others, 1977). At least 29 of these 

lakes formed prior to 1950, and at least 9 more 

formed between 1932 and 1950. About 130 lakes 

dammed by Neoglacial moraines have been 

identified in the Himalaya of Nepal and Tibet 

(Fushimi and others, 1985; Vuichard and 

Zimmermann, 1987; Liu and Sharma, 1988; Ding 

and Liu, 1992). Moraine-dammed lakes also exist 

in mountain ranges in Kazakhstan, Asia (Yesenov 

and Degovets, 1979; Popov, 1990), the European 

Alps (Eisbacher and Clague, 1984; Haeberli, 

1983; Dutto and Mortara, 1992), and the Canadian 

Cordillera (Clague and others, 1985; Blown and 

Church, 1985; Evans, 1987; Clague and Evans, 

1992, 1994).

Several dozen proglacial lakes formed this 

century in the Cascade Range in areas abandoned 

by Neoglacial-age glaciers. Basins of most of these 

lakes are partly rimmed by resistant bedrock 

barriers, but several are completely bounded by 

Neoglacial lateral and terminal moraines (table 1). 

The highest concentration of past and present 

Neoglacial moraine-dammed lakes in the 

conterminous United States is in the central Oregon 

Cascade Range. There are seven moraine-dammed 

lakes in the Three Sisters Wilderness Area and one 

in the Mount Jefferson Wilderness Area that have 

surface areas larger than 5,000 m2 (table 1; figs. 15, 

16, and 17). In addition, there were five other 

moraine-dammed lakes with surface areas as great 

as 105 m2 that existed as long as 40 years before 

breaching their morainal dams. This high

0.8

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w 0.2 

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I'""""! 1 " 11 ""!""" 1 "!""" 111 !"" 111 "!" 11 ""

_ A. Northern hemisphere land data

LLJ 

DC

nDC

- B. Corvallis, Oregon, data

1850 1860 1870 1880 1890 1900 1910 1920 

YEAR

1930 1940 1950 1960 1970 1980 1990

Figure 13. Measured mean annual temperature, portrayed as anomalies from 1951-1970 averages. Curves are 7-year 

moving averages. A, Average northern hemisphere land data from Jones and Bradley (1992); B, Average annual 

temperature at Corvallis, Oregon (data from Western Regional Climate Center, Reno, Nevada).

Moraine-Dammed Lakes 17
O LJJ 

Z CC 

< CD

00

2

LJJ 00

ID LU LJJ 

< D_ DC 

^> ^ CD

Z

O

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<

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A Annual average temperature

B. June, July, August average temperature

i , , , , i , , , , i . , , , i , , , , i , , , , i . . . . i , , , , i

1000

800

600

400

200

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-200

-400

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1 | 1 1 1 . | 1 1 1 ! | 1 1 1 1 | 1 1 1 1 | 1

~ C. Annual precipitation

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i i . , , i , , , , i , , , , i , , ,

i | i i i i | i i

Till [J-l!"J [ 1 •ui 1 , , , , 1 , ,

i | i . i i | i i i ,

Ib n ^-mj.

,!,,,,!,

V L

\

1 '

yy

\l

:

Dnn -

' H|;

1 , , , , 1 , , , , 1 , ,

1930 1935 1940 1945 1950 1955 1960 1965

WATER YEAR

1970 1975 1980 1985 1990

Figure 14. Annual climate data for Crater Lake, Oregon (elevation 1,975 m). Data are plotted as anomalies from 

1951-1970 average. Curves are 7-year moving averages. All data are plotted for water years (October 1 to 

September 30). A, Annual average temperature; B, June, July, and August average temperature; C, Annual 

precipitation. Dashed line indicates incomplete or missing records. Data from Western Regional Climatic Center, 

Reno, Nevada. D, Maximum annual snowpack at Annie Springs, Crater Lake, Oregon (1,835 m). Data from Natural 

Resources Conservation Service, Portland, Oregon.

18 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Table 1. Lakes dammed by Neoglacial Moraines in the Cascade Range, Oregon and Washington

[This list of lakes is based on inspections of aerial photographs maintained in U.S. Forest Service, National Park Service, and U

collections. Dates of photographs range from 1970 to 1992. Areasof present glaciers and lakes measured from aerial photogr

Survey topographic maps. Maximum Neoglacial glacier areas based on photointerpretation. The indicated release potential 

and is based on qualitative assessment of the topography of the lake setting (fig. 62). For areas outside the Mount Jefferson a

this assessment is based solely on photograph inspection, km2, square kilometers; m2, square meters; m, meters; —, unnamed

MoraineD 

0>

3

CDm

uses

7.5 min. 

quadrangle

Forbidden Peak, 

Washington

Mount Shuksan, 

Washington

Mount Baker, 

Washington

Mount Challenger, 

Washington

Mount Challenger, 

Washington

Mount Triumph, 

Washington

Maximum 

Neoglacial 

glacier 

area 

Glacier (km2)

— 0.4

Price Glacier 2.9

Sholes Glacier 2.5

— 2.6

(2 km west-south- .7 

west of Luna 

Peak)

(1 km north of .3 

Triumph Pass)

Present 

glacier Lake 

area area 

(km2) Lake name (m2)

0.1 — 40,000

1.5 Price Lake 180,000

1.1 — 20,000

1.2 — 27,000

.3 Luna Lake 51,000

.1 — 34,000

Lake 

altitude

(m)

1,570

1,190

1,600

1,110

1,490

1,460

Latitude 

(decimal 

degrees 

north)

48.587

48.863

48.803

47.540

48.823

48.715

Longitude 

(decimal 

degrees 

west)

121.125

121.600

121.759

121.425

121.295

121.367
= Table 1. Lakes dammed by Neoglacial Moraines in the Cascade Range, Oregon and Washington—Continued

Debris Flowfro

3 

O9

F

re

U)

2

o

33*

re

O 

09

3

I3"

re

re

CO

re"

09

3

a.

3

o

c_

re

=ft

re

o

§

a. 

re

3

re 

e/9

CD

09

O

uses

7.5 min. 

quadrangle

Damnation Peak, WA

Downey Mtn.,

Washington

Snowking Mtn.,

Washington

Snowking Mtn.,

Washington

Big Snow Mtn.,

Washington

Maximum 

Neoglacial Present 

glacier glacier Lake 

area area area 

Glacier (km2) (km2) Lake name (m2 )

(5 km southwest 0.2 0.1 — 19,000

of Mount Despair)

(5 km north of .8 .4 15,000

Bench Lake)

(2 km south of .8 .4 — 60,000

Snowking Mtn.)

(2 km southeast 1.0 .3 — 45,000

of Snowking

Mtn.)

(1 km northwest .4 0 Overcoat Lake 45,000

of Overcoat Peak)

Latitude Longitude 

Lake (decimal (decimal 

altitude degrees degrees 

(m) north) west) 

1,335 48.709 121.438 

1,690 48.368 121.133 

1,770 48.395 121.283 

1,540 48.400 121.257 

1,755 47.517 121.302 

re

U3

o

3
Table 1. Lakes dammed by Neoglacial Moraines in the Cascade Range, Oregon and Washington—Continued

Moraine-Dammed Lal

^ 

CD 

V>

uses

7.5 min. 

quadrangle

Blanca Lake, 

Washington

Glacier Peak West,

Washington

Lime Mountain, 

Washington

Walupt Lake, 

Washington

Mount Adams East, 

Washington

Mount Adams West, 

Washington

Maximum

Neoglacial 

glacier 

area 

Glacier (km2 )

(2 km east-south- 0.4 

east of Monte 

Cristo Peak)

White Chuck 4.8

Glacier

Milk Lake .9

Conrad Glacier 1 .2

Gotchen .6

Adams Glacier .8 

(north lobe)

Present 

glacier Lake 

area area 

(km2 ) Lake name (m2 )

0.1 Goblin Lake 11,000

2.8 — 36,000

.5 Milk Lake 100,000

.6 — 35,000

.3 — 10,000

.6 — 18,000

Lake 

altitude

(m)

1,265

1,960

1,835

1,955

2,180

2,290

Latitude 

(decimal 

degrees 

north)

47.965

48.058

48.153

46.498

46.160

46.235

Longitude 

(decimal 

degrees 

west)

121.313

121.132

121.150

121.402

122.575

121.511

Mount Jefferson and Three Sisters Wilderness Areas

Three Fingered Jack, 

Oregon

North Sister, 

Oregon

Jack Glacier . 1

Thayer Glacier .29

.01 — 6,000

.1 _ 40,000

2,180

2,330

44.483

44.163

121.838

121.758
Table 1 . Lakes dammed by Neoglacial Moraines in the Cascade Range, Oregon and Washington—Continued

n

lebris Flowfrm Failur

00

o

3

CD

D 

OS

!

ree Sisters andMount Jef

^h

CD

O 

3

s7

CD

3 

CD

00

3

O3 

00

O

3

<a

o

USGS 

7.5 min. 

quadrangle

South Sister, 

Oregon

South Sister,

Oregon

South Sister, 

Oregon

South Sister, 

Oregon

South Sister, 

Oregon

Broken Top, 

Oregon

Maximum

Neoglacial Present 

glacier glacier Lake 

area area area 

Glacier (km2) (km2 ) Lake name (m2 )

Carver Glacier 1.4 0.2 Chambers 26,000 

Lakel

Carver Glacier 1.4 .2 Chambers 9,000

Lake 2

Carver Glacier 1.4 .02 Chambers 13,000 

Lake 3

Prouty Glacier 1.9 1.1 Carver Lake 70,000

Lewis Glacier 1.3 .3 — 5,000 

East Bend Glacier .2 .05 — 30,000

Latitude Longitude 

Lake (decimal (decimal 

altitude degrees degrees 

(m) north) west) 

2,190 44.125 121.85 

2,200 44.125 121.833 

2,210 44.123 121.85 

2,385 44.115 121.755 

2,695 44.092 121.768 

2,440 44.082 121.687 
A, Jack Glacier is mostly shaded by the serrated ridge 

of Three Fingered Jack in this westward view. The 

26,500 m3 lake with its steep outlet probably formed 

after 1930 as the glacier retreated from the sharp-crested 

moraine that now dams the lake. Photograph by Austin 

Post (R21-51), September 21, 1960.

C, Aerial view of Diller Glacier, Middle Sister, showing 

the glacier calving into the moraine-dammed lake that 

breached September 7, 1970. Photograph by Austin 

Post (R21-74), September 21, 1960.

B, View north-northeast of the lake at terminus of 

Thayer Glacier, North Sister. At the time of this 

photograph, September 14, 1991, the lake surface was 

7.5 m below the level of the surface outlet through the 

notch in the moraine. The lake presently drains through 

the moraine, with water exiting from several springs 

100-110 m below the lake surface on the outer moraine 

slope. At the present lake level, the impounded volume 

is 360,000 m3, but the lake would contain twice this 

volume if it filled to the level of the surface outlet.

Figure 15. Moraine-dammed lakes in the Three Sisters and Mount Jefferson Wilderness Areas, Oregon.

Moraine-Dammed Lakes 23
-T-JU*.*

i*^%4.

D, View north of Chambers Lakes No. 1 and No. 2. At 

the time of September 10, 1991, surveys of the basins, 

Chambers Lake No. 1 had a volume of 260,000 m3 and 

26 m of freeboard; Chambers Lake No. 2 had a volume 

of 70,000 m3 and 0.2 m of freeboard. Photograph by 

Robert L. Schuster, USGS.

f

£", Oblique aerial view of Carver Lake impounded by 

Neoglacial moraines at the terminus of Prouty Glacier 

on South Sister. Carver Lake is the largest of the 

moraine-dammed lakes in the Oregon Cascade Range, 

with a surface area of 700,000 m3 and a volume of 

900,000 m3 . Photograph courtesy of U.S. Department 

of Agriculture, Forest Service, September 3, 1986.

F, Oblique aerial view of lake at the terminus of East 

Bend Glacier on Broken Top. Prominent notch at outlet 

was cut October 7, 1966, when 140,000 m3 of water 

escaped in conjunction with 4.4 m of lake-level 

lowering.

Figure 15—Continued. Moraine-dammed lakes in the Three Sisters and Mount Jefferson Wilderness Areas, Oregon.

concentration of moraine-dammed lakes is unique 

in respect to the rest of the Cascade Range. On 

other Cascade Range volcanoes, we have identified 

only nine other lakes that are partly impounded by 

Neoglacial moraines; two are on Mount Adams, 

one is in the Goat Rocks Wilderness Area (between 

Mount Adams and Mount Rainier), two are near 

Glacier Peak, and one is on Mount Baker. There

are, however, at least 10 other moraine-dammed 

lakes on nonvolcanic peaks in the Cascade Range 

(table 1).

Chronology

Historical maps, climbers' accounts, 

newspaper reports, and photographs document that

24 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
most lakes dammed by Neoglacial moraines in the 

central Oregon Cascade Range formed in the 

1920's and 1930's during rapid glacier retreat 

(fig. 16). The best documented is the lake bounded 

by moraines of Collier Glacier. Hopson (1960) 

documented the growth and demise of this lake in a 

series of photographs taken between 1934 and 

1960 (fig. 12), noting that the lake formed in 1934; 

photographs show that the lake had not yet formed 

in 1931 when the terminus of Collier Glacier still 

impinged on Collier Cone (Oregon Historical 

Society photograph, neg. DB-1568). Some 

moraine-dammed lakes existed for very short times 

before rupturing their bounding moraines. For 

example, two small lakes at the termini of lobes of

Whitewater Glacier on Mount Jefferson, and a 

small water body at the terminus of the central lobe 

of Eugene Glacier on South Sister, possibly formed 

the same summer as their release. Since about 

1940, all long-lived lakes, except Carver Lake and 

Chambers Lakes No. 1, No. 2, and No. 3 have 

become smaller (fig. 16). Carver Lake and 

Chambers Lakes No. 1 and No. 2 have remained 

the same size; Chambers Lake No. 3 grew between 

1931 and 1949 as Carver Glacier retreated. The 

remainder of the lakes have shrunk, either by 

eroding outlets into their morainal dams, or by 

establishing subsurface drainage that has caused 

lake levels to drop below outlet elevations.

7,000 p50,000 j—

0 F ,/

800,000 ,— 

(/) t 

^ t

uj n r , j

h- ° '

UJ 800,000 ro — n 1 / 7i

D 400,000,— ° r

? nF /

LAKEATEAST 

JEFFERSONPARK ^KEATWEST 

I JEFFERSON PARK i i H i i i ——— 1

LAKE AT JACK GLACIER "*"*

i i i i . 1

AI LAKE AT COLLIER GLACIER

/ , , "^ , , |

/^^^LAKEAT THAYER GLACIER

iii i 1

'LAKEATDILLER GLACIER

iii i 1

LLJ

300,000 CHAMBERS LAKES LAKE1

o F L-

<

0

30,000

0

1,000,000

0

LAKE 2

•— i •*-

LAKES AT EUGENE GLACIER 

West

I r

CARVER LAKE

400,000,— LAKE AT EAST BEND GLACIER

1920 1930 1940 1950 1960 1970 1980 1990 

YEAR

Figure 16. Moraine-dammed lake 

chronologies for lakes in the Three Sisters 

and Mount Jefferson Wilderness Areas, 

Oregon. Lake volumes are from surveys 

of the lake basins at Jack Glacier, Collier 

Glacier, Thayer Glacier, Diller Glacier, 

East Bend Glacier, Chambers Lakes No. 1 

and No. 2, and Carver Lake. Volumes of 

the lakes at the termini of Eugene and 

Whitewater Glaciers and Chambers Lake 

No. 3 were determined on the basis of 

estimates of lake area (from aerial 

photographs and field measurements) and a 

generalized area-volume relation for 

moraine-dammed lakes (see fig. 18). Data 

points are dates of information regarding 

lake presence and size. This information is 

primarily from historic photographs, 

climbers' accounts, newspaper reports, 

dated topographic maps, and aerial 

photographs. Dashed lines show 

magnitudes of lake releases where the date 

of the breach is only known to the 

constraints indicated by the adjacent solid 

circles. Vertical lines between solid circles 

indicate lake releases at known or inferred 

dates by partial or complete breach of the 

moraine dam. Because of insufficient 

information, this diagram does not include 

the small lake at the terminus of Waldo 

Glacier on Mount Jefferson.

Moraine-Dammed Lakes 25
Lake Basin Bathymetry and 

Topography

We surveyed bathymetry and topography of 

five of the moraine-dammed lakes and lake basins 

in the Three Sisters Wilderness Area. Laenen and 

others (1992 and unpub. data) surveyed two 

additional lakes. The results of these surveys are 

shown in figure 17 and lake-basin hypsometric 

relations are shown in figure 18. Measured areas of 

existing lakes range from 6,000 to 30,000 m2. At 

its maximum extent, however, the lake at the 

terminus of Collier Glacier covered 100,000 m2. 

Past and present volumes range from 30,000 m3 to 

Carver Lake's 900,000 m3 . The lakes at the termini 

of Thayer and Collier Glaciers had, at their 

maximum extent, volumes of approximately 

700,000 m3 .

Because all the lakes, except for the lake at the 

terminus of Collier Glacier, were dammed by tall 

Neoglacial moraines emplaced on steep slopes, 

they have relatively large depths for their areas. 

The maximum depth of Carver Lake is about 33m. 

Likewise, the lakes bounded by the termini of 

Thayer, Diller, and East Bend Glaciers had 

maximum depths of at least 20 m. The basin in 

front of Collier Glacier is broader and more 

shallow than the other proglacial lake basins at 

their maximum extent (fig. 18). Consequently, the 

lak e at the terminus of Collier Glacier had a 

maximum depth of only 10m, but a volume of 

700,000 m3 .

Formation and Preservation of 

Moraine-Dammed Lakes

Moraine-dammed lakes form where glaciers 

have retreated from moraines sufficiently high and 

impervious to impound drainage from the glacial 

basin. This process requires conditions similar to 

those of the last few centuries, including (1) a 

prolonged period of relatively stable glacier 

terminus positions resulting in large lateral and 

terminal moraines and (2) a subsequent period of 

substantial and rapid glacier retreat. In the Cascade 

Range, moraine-dammed lakes are associated with 

small cirque and valley glaciers that had maximum 

Neoglacial areas of 0.13 to 2.9 km2 (table 1). 

Larger glaciers in the Cascade Range probably

generated meltwater discharges great enough to 

maintain a graded profile through the morainal 

sediment. The largest glaciers to have morainedammed lakes form, such as Collier Glacier in the 

Three Sisters Wilderness Area and Price Glacier in 

the North Cascades, Washington, terminate on low-- 

gradient valley floors where competence of 

meltwater streams was low. Here, terminal and 

lateral moraines impounded large, shallow lakes. 

Glaciers with Neoglacial areas less than about 

0.15 km2 apparently did not deposit terminal and 

lateral moraines large enough to impound 

proglacial lakes.

DEBRIS FLOWS FROM LAKES 

DAMMED BY NEOGLACIAL 

MORAINES

General Features

Lakes that formed behind Neoglacial moraines 

have been known to pose significant hazards for 

several decades. Most of the attention to these 

hazards has been outside the United States, where 

there have been accounts of about 60 floods and 

debris flows from rapid lake releases (table 2). 

Most reported incidents have been in glacierized 

areas of the European Alps (Eisbacher and Clague, 

1984), the Andes and Cordillera Blanca of Peru 

(Lliboutry and others, 1977; Reynolds, 1992), and 

the Himalayas of Nepal and Tibet (Ives, 1986; 

Vuichard and Zimmerman, 1987; Xu, 1988; Ding 

and Liu, 1992). These alpine areas are more 

intensely developed than those in North America; 

consequently, alpine floods and debris flows 

triggered by various processes, including morainedam failures, have caused substantial property 

damage (Eisbacher and Clague, 1984; Evans, 

1987). Because of the generally higher population 

densities in these areas, several outburst floods 

from moraine-dammed lakes have been lethal. For 

example, 6,000 people perished after rapid 

breaching of the moraine impounding Laguna 

Cohup in the Cordillera Blanca of Peru (Ericksen 

and others, 1970; Lliboutry and others, 1977). 

After the Laguna Cohup disaster, a program was 

established in Peru to lower levels of several 

moraine-dammed lakes that were perceived to be 

dangerous (Lliboutry and others, 1977). Likewise,

26 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
inventories of potentially hazardous glacial lakes 

have been completed in the Himalayas (Ives, 1986; 

Liu and Sharma, 1988) where debris flows and 

floods from moraine-dammed lake releases and 

glacial outburst floods pose risks to potential and 

developed sites of hydroelectric facilities.

The absence of intense development in alpine 

areas of North America generally restricts the 

hazards of moraine-dammed lakes to recreationists 

and their associated facilities. In this regard, the 

U.S. Department of Agriculture, Forest Service, 

has issued a "hazard alert" for moraine-dammed 

Carver Lake in the Three Sisters Wilderness Area. 

In British Columbia, the potential of floods and 

debris flows from moraine-dammed lakes has 

received interest because of potential hazards to 

hydroelectric facilities (Blown and Church, 1985).

Indirect Discharge Estimation 

Methods

A key aspect of analysis of debris flows in the 

central Oregon Cascade Range was the use of 

indirect discharge estimation methods to determine 

peak discharges resulting from moraine-dammed 

lake releases. Two primary discharge-estimation 

methods were used and they are described in this 

report as the "velocity-area" and "critical- flow" 

methods. These methods are modified for the 

purposes of this study from those described by 

Barnes and Davidian (1978). These methods of 

calculating debris-flow discharges are approximate 

and are not intended to yield discharge estimates 

that are as accurate as those normally published for 

water flows by the USGS.

Velocity-Area Discharge Estimates

Velocity-area discharge estimates were 

obtained simply by computing the product of the 

channel cross-sectional area at peak stage and an 

estimate of flow velocity. For this study, cross 

sectional areas were surveyed in the field, either by 

electronic distance meter or by tape and Abney 

level. Maximum flow stage was determined by 

surveying the highest evidence of inundation at the 

cross section. Such evidence included flow 

deposits, tops of boulder levees or berms, organic 

debris accumulations, and tree scars. Debris-flow

velocity was assumed to be between 3 and 6 m/s 

and results were presented as a discharge range on 

the basis of this range of velocity values.

The assumed velocity range of 3 to 6 m/s is 

based on observed velocities of rubbly debris flows 

in other alpine environments. Examples from 

moraine-dammed lakes and glacial outburst floods 

include measurements and estimates of 5.5 to 7 m/s 

in the Swiss Alps (Haeberli, 1983), 5 to 6 m/s for 

the flow from the moraine-dammed lake release of 

Midui Lake, Tibet (Li and You, 1992), 4 to 5 m/s 

velocity for the flood wave from the release of 

moraine-dammed Dig Tsho, Nepal (Vuichard and 

Zimmerman, 1987), 3.8 m/s velocity for the flood 

wave resulting from the 1977 moraine breach on 

the Dudh Kosi River, Nepal (Buchroithner and 

others, 1982), and 4 to 8 m/s at the Chemolgan 

Debris Flow Testing Ground, Kazakhstan (Khegai 

and others, 1992). Higher velocities have also been 

measured for the largest flows from morainedammed lakes. Notable examples include (1) the 

alluvions in the Cordillera Blanca that resulted 

from releases of Lago Ayhuinyarahu and Laguna 

Jancarurish and apparently had velocities of about 

9 m/s judging from Lliboutry and others (1977) 

account of flood wave arrival times, and (2) the 

debris flow resulting from the breach of Moraine 

Lake number 13 in Kazakhstan for which Yesenov 

and Degovets (1979) reported velocities of 12 to 

15 m/s.

Velocities measured for rubbly alpine debris 

flows triggered by mechanisms other than natural 

dam failures include 2.5 m/s at Mayflower Gulch, 

Colorado (Curry, 1966), 5.5 m/s in the Cathedral 

Mountains, Canada (Jackson and others, 1989), 

5 m/s at Bullock Creek, New Zealand (Pierson, 

1980), 1.2 to 4.4 m/s at Wrightwood Canyon, 

California (Sharp and Nobles, 1953), 7 m/s at 

Charles Creek, Canada (VanDine, 1985), and 3.4 to 

4 m/s at Monument Creek, Arizona (Webb and 

others, 1988).

The 3 to 6 m/s velocity range assumed for the 

debris flows in the Three Sisters and Mount 

Jefferson Wilderness Areas encompasses most of 

the reported velocities of rubbly debris flows in a 

variety of environments. It is possible, however, 

that at some cross sections debris-flow velocities 

were outside of the 3 to 6 m/s velocity range, and 

in these locations the reported discharge range

Debris Flows from Lakes Dammed by Neoglacial Moraines 27
LAKE AT THAYER GLACIER, 

NORTH SISTER, 1991

::^::::-^

i 50 100 150 FEET

CONTOUR INTERVAL 5 METERS

(16 405 FEET)

LAKE AT JACK GLACIER, THREE 

FINGERED JACK, 1993

0 25 50 FEET

CONTOUR INTERVAL 5 METERS

(16105 FEET)

CHAMBERS LAKES, 1991

50 100 150 FEET 

CONTOUR INTERVAL 5 METERS 

(16 405 FEET)

LAKE AT EAST BEND 

GLACIER, BROKEN TOP, 

1988 _^

\

1966 

shoreline

50 100 150 METERS

0 50 100 150 FEET

CONTOUR INTERVAL 5 METERS

(16.405 FEET)

EXPLANATION

Shoreline surrounding pond

-- Shoreline

— Moraine crest

•—• Stream

• Survey point

Figure 17. Bathymetry and topography of seven lakes and lake basins dammed by Neoglacial moraines in the Three 

Sisters and Mount Jefferson Wilderness Areas. Datum is present lake surface except for the basin at the terminus of 

Diller Glacier, Middle Sister, where the datum is arbitrary, but near the bottom of the former lake. Bathymetry for 

Carver Lake and the lake at the terminus of East Bend Glacier is from Laenen and others (1992 and unpub. data).

28 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
LAKE AT COLLIER GLACIER, MIDDLE SISTER, 1991

// * / shoreline

CARVER LAKE, 1986

LAKE AT DILLER GLACIER, 

MIDDLE SISTER, 1991

EXPLANATION *-^~*ggg&?j//!-:'

50 100 150 FEET 

CONTOUR INTERVAL 5 METERS 

(16 405 FEET)

Shoreline surrounding

— - - — Shoreline

— — Moraine crest

— ••— • Stream 

• Survey point

pond

Figure 17—continued. Bathymetry and topography of seven lakes and lake basins dammed by Neoglacial moraines 

in the Three Sisters and Mount Jefferson Wilderness Areas. Datum is present lake surface except for the basin at the 

terminus of Diller Glacier, Middle Sister, where the datum is arbitrary, but near the bottom of the former lake. 

Bathymetry for Carver Lake and the lake at the terminus of East Bend Glacier is from Laenen and others (1992 and 

unpub. data).

Debris Flows from Lakes Dammed by Neoglacial Moraines 29
O)

en

LLJ

LU 

2 

g

DO 

D 

O 

LL

O

co 

a

CO

D

O

I

LU

2

=)

§LU

1,400

1,300

1,200

1,100

1,000

900

800

700

600

500

400

300

200

100

0

• 1992 Lake Level

v Past Lake Level

D 1992 Outlet Level

—— Best Fit Curve

Chambers 

Lakes No. 1 /

0 10 20 30 40 50 60 70 80 90 100 110 

LAKE AREA, IN THOUSANDS OF SQUARE METERS

200

100 -

• 1992 Lake Level

v Past Lake Level

D 1992 Outlet Level

CO

en LUiLLJ

g

CD 

D 

O 

LL

O 

CO 

Q

CO=) O

i

LU

2

=)

§

LU

LAKE AREA, IN THOUSANDS OF SQUARE METERS

Figure 18. Area-volume relations for moraine-dammed lakes and lake basins in the study area, calculated on the basis 

of the surveys shown in figure 17. A second-order polynomial (V=3.114 A + 0.0001685 A2 , where V is lake volume in 

cubic meters, and A is lake area in square meters) was fit to the data in figure 18, excluding Collier Glacier Lake, to 

predict volumes for the unsurveyed lakes at the termini of Eugene and Whitewater Glaciers, and Chambers Lake 

No. 3.

30 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Table 2. Failed moraine dams in various mountainous areas worldwide

[This list is based on published accounts of moraine dams that have failed and our unpublished observations. Queries indicate 

value or failure mechanism. Discharge values are peak discharges as reported by authors. Many of the discharge estimates a

uncertain accuracy. Discharge values calculated at the breach are, in most cases, maximum values based on breach geomet

developing relations between breach geometry and peak discharge. Reported discharge values known to us to be based on e

discharge and dam or lake geometry have not been included, m, meters; m3, cubic meters; rrf/s, cubic meters per second; km, 

Lake or site name Location Date

Change 

in lake 

level 

(m)

North American

Debris F

0

M

|

g

CD

o

09 

CD

aZ

CD

O

ca

09 

0

g

0

i.

CD

Tats Creek

Tide Lake

Nostetuko Lake

South Macoun

Lake

North Macoun

Lake

Patience Mountain

Klattasine Lake

Bridge Glacier

Snowking Mountain

St. Elias Mountains,

British Columbia, Canada

Coast Mountains,

British Columbia, Canada

Coast Mountains, 

British Columbia, Canada

Columbia Mountains,

British Columbia, Canada

Columbia Mountains,

British Columbia, Canada

Columbia Mountains, 

British Columbia, Canada

Coast Mountains, 

British Columbia, Canada

Coast Mountains,

British Columbia, Canada

Cascade Range, 

Washington, USA

June 28, 1990

1927-1930

July 19, 1983

Before 1949

July 1983

1951-1966

1971-1973

1964-1970

Before 1955

0.4

—

38.4

7

—

8

13

11

5-8

Volume 

discharged Maximum 

(thousands of discharge

(m3) (m3/s)

Cordillera

4.0 —

— —

6,500 570 at 67 km1 

340 at 112 km1

400 —

— —

300 —

1,700 —

1,200 —

200 —

Fail

mec

— 

— 

Ice 

Ice 

Pipi

— 

Pipi

Ice 

— 

— 
ro Table 2. Failed moraine dams in various mountainous areas worldwide—Continued

Debris Flows frmFai

iCO

o

Moraine

Dams — 1

^^

3 

n

CO

isters anc

o

c

Jefferso

3

s

n

n

>

O)

y» 

0

CO

O

Lake or site name

Jefferson Park (east)

Jefferson Park (west)

Waldo Glacier

Waldo Glacier

Three Fingered Jack

Three Fingered Jack

Eugene Glacier (east)

Eugene Glacier (west)

Collier Glacier

Location

Cascade Range, 

Oregon, USA

Cascade Range,

Oregon, USA

Cascade Range, 

Oregon, USA

Cascade Range, 

Oregon, USA

Cascade Range, 

Oregon, USA

Cascade Range, 

Oregon, USA

Cascade Range,

Oregon, USA

Cascade Range,

Oregon, USA

Cascade Range,

Oregon, USA

Change Volume 

in lake discharged Maximum 

level (thousands of discharge 

Date (m) (m3) (m3/s)

Aug. 21, 1934 — 10 300-600 at 1.2 km

1957? <5 2.5 150-300 at

0.5km

Before 1937 — — —

July 1951 — — —

Before, I960 0.8? 5.7? —

1979-1988 1.8 11.7 —

Augl2, 1933 — — 175-350 at 1km

185 at 2.5 km

20 at 4.5 km 

1933-1949 — — —

July 1942 5.4 460 <140 at breach

245-490 at 0.5 km

530 at 1.4 km

545 at 1.8 km 

215 at 3-0 km 

260 at 3.7 km

160 at 4.2 km

150 at 4.6 km

120 at 5.4 km

100 at 5.7 km

Fail

mec

Rap

— 

— 

— 

— 

— 

— 

— 

Rap
Table 2. Failed moraine dams in various mountainous areas worldwide—Continued

Lake or site name

Diller Glacier

a

<D

S1 Broken Top

31

o

M

if

ET

a

0)

f Conness Glacier

o.

Z

<D

O

tn_

2.

— Lagunajancarurish

3_ SafunaAlta 5'

<DM LagunaArtesa

Change Volume

in lake discharged Maximum

level (thousands of discharge Fai

Location Date (m) (m3 ) (m3/s) me

225-450 at 5.8 km

130 at 6.3 km

43 at 6.8 km

Oat8 km

Cascade Range, Sept. 7, 1970 22.4 320 280 at 0.8 km Pre

Oregon, USA 450 at 2.8 km

490 at 4.6 km

65 at 6.7 km

50-100 at 8 km

50-100 at 9 km

36 at 11.5 km

35 at 24 km

Cascade Range, Oct. 7, 1966 4.4 320 <80 at breach Ice 

Oregon, USA 190-380 at 0.5 km Nol

150 at 1.7 km

180 at 2.4 km 

50 at 4.0 km 

20-40 at 6.0 km

170 at 7.0 km

Sierra Nevada, California, USA Summer, 1939 — — — —

South American Cordillera

Cordillera Blanca, Peru Oct. 20, 1950 21 600-1,000 7,000-8,0002 Ice 

Cordillera Blanca, Peru June 1970 38 — — Pip

Cordillera Blanca, Peru Jan. 20, 1938 10-15 250-500 — Ice 
Table 2. Failed moraine dams in various mountainous areas worldwide—Continued

Debris Flowsfrm Failui

CD 

V)

O

i

o

S. 3"

CD

O 

09

I

CD 

CD

COa"

CD

09

3 

O.

O

c

3

e_

CD

O 

3

|

derness t

*^

CD 

09 

tfi

0

CD 

(O

O 

3

Lake or site name

Palcacocha

Artesoncocha

LagunaAyhuinarju

Quebrada Huachesca

Allicocha

Huascaran

Quebrada Shantoc

Chacrucocha

Laguna Soltera

Ulta Quebrada

Quebrada Santa Cruz

Allicocha

Location

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Cordilleray Huayhuash, Perus

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Cordillera Blanca, Peru

Date

Dec. 13, 1941

July 16, 1951

Jan. 17, 1945

Before 1950

—

—

Before 1950

March 14, 1932

April 1939

1932-1951

Before 1970

Change Volume 

in lake discharged Maximum 

level (thousands of discharge Failu

(m) (m3 ) (m3/s) mech

— 1,850 — Ice fa

7 1,130 — Ice fa

14,000 at 17 km Rock 

— — — — 

— — — — 

— — — — 

— — — — 

— — — — 

— — — — 

— — — — 

— — — — 

— — — — 

Tempanos Patagonian Andes, Argentina 1942-1953 Rapi
Table 2. Failed moraine dams in various mountainous areas worldwide—Continued

o

CD

•is Flowsfrm Lakes1

Dammed b]

•^

2

CD

0

oT 

o

S

o

22. 5'

Lake or site name

Roseggletcher,Vadr 

et da Roseg

Steingletscher

Galruttferner

Madatchferner Glacier

Miage

Miage

Miage 

Miage 

Miage 

Miage

Miage 

Miage

Miage

Miage

Settentrionale delle Locce 

Settentrionale delle Locce

Settentrionale delle Locce

Location

Switzerland

Switzerland

Austria

Austria

Italy

Italy

Italy 

Italy 

Italy 

Italy

Italy 

Italy

Italy

Italy

Italy 

Italy

Italy

Change Volume 

in lake discharged Maximum 

level (thousands of discharge 

Date (m) (m3 ) (m3/s)

European Alps

Aug. 21-22,1954 0.85 120 —

1956 — — —

1890 — — —

Aug. 5, 1874 — — —

Aug. 9, 1990 — — —

July 8, 1986 — — —

1964 — — — 

August 1963 — — — 

1962 — — — 

1961 — — —

June 1956 — — — 

July 20, 1955 — — —

Aug. 10, 1950 — 180 —

Aug. 1930 — — —

July 17, 1979 — 300 — 

August 2, 1978 — — —

July 7, 1970 — — —

Failu

mec

Prec

— 

Ice f

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

Rap

— 

— 
« Table 2. Failed moraine dams in various mountainous areas worldwide—Continued

o

CD

35'

eT

S

(A

3

3

a>

3

(A

a

o 

35'

CD

o 

a>

3

I

3

CD

c/» a"

CD

a>

n.

o 

c

3

1

5

o

3

&

CD

3 

CD

>

3

a>

O

3

ca

o

3

Change Volume 

in lake discharged Maximum

level (thousands of discharge

Lake or site name

Gemelli di Ban

Scersen

Scerscen

Midui

Boqu River

Boqu River

Jinco

Taraco

Qubixiama

Gelhapuco

Damenlahai Glacier,

Tangbulang Gully

Zhanlonba

Hailuogou

Location

Italy

Italy

Italy

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Date (m) (m3)

Oct. 1971 — —

Aug. 10, 1927 — 500

Aug. 6-7, 1924 — —

Himalayas

July 15, 1988 17 5,400

July 11, 1981 32 19,000

July 1964 — —

Aug. 27, 1982 — —

Aug. 28, 1935 — —

June 10, 1940 — —

Sept. 21, 1964 41 23,400

Sept. 26, 1964 17 3,700

1902 — —

July 1955 — —

(m3/s)

—

—

—

1,250 at 1.8 km1

9,165 at 6 km

6,430 at 20 km

4,099 at 26 km

2,865 at 3 1km

2,619 at 40 km

2,316 at 52 km

1,296 at 56 km1

—

—

—

—

—

<2,0 10 at breach

2,812 at 14km

—

—

Failu

mec

—

—

—

Rap

Ove

afte

(fre

sub

—

Rap

Pipi

Ice 

Ice 

Roc

—

—
Table 2. Failed moraine dams in various mountainous areas worldwide—Continued

D 

CD

w'

T]

O 

M— h

rom Lakes

Dammed

«<

2

CD

O

5T 

o

2L

2

o 

a>

Lake or site name

Hailuogou

Hailuogou

Longda

Ayaco

Ayaco

Ayaco

Bugyai

Zari

JZirema

Gule

Sangwang

Dig Tsho

Dudh Kosi River 

others,

Location

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Tibet

Nepal

Nepal

Nepal

Change Volume 

in lake discharged Maximum 

level (thousands of discharge 

Date (m) (m3) (mVs)

July 1966 — — —

Aug. 30, 1976 — — —

Aug. 25, 1964 — — —

August 15, 1965 — — —

August 17, 1969 — — —

August 18, 1970 — — —

July 23, 1972 — — —

June 24, 1981 — — —

July 11, 1981 — — —

July 15, 1988 — — —

July 16, 1954 — — —

Aug. 4, 1985 18 5,100-6,750 1,600 at 3 km

Sept. 2, 1977 30 4,900 1,1 00 at 9 km 

830 at 80 km1

Failu

mec

—

—

Ice 

Ice 

Ice 

Ice 

—

Ice 

Ice 

Ice 

—

Ice 

Me

ice 
w Table 2. Failed moraine dams in various mountainous areas worldwide—Continued

0

0

-tw'

5s Lake or site name Location

^

M

3

3

Tl ——————————————————————————————————————————————————————— 

09

jf Moraine Lake No. 13 Kazakhstan

I

a

0

35'

0

a

09

V Akkul Kazakhstan

5" Austre Okstindbreen Norway

Change Volume

in lake discharged

level (thousands of

Date (m) (m3 )

Other Locations

Aug. 3, 1977 5.2 0.86

JulyS, 1963 — —

Aug. 5, 1977 — —

Maximum

discharge Failu

(m3/s) mec

2 1 0 at breach Pipi

1,000 at 3 km

3,400-3,900 at 7 km

7,000- 11, 000 at 15km

76 at 27 km1

46 at 30 km1

— —

— —

Glacier 

Keppel Cove Tarn Great Britain Oct. 29, 1927 8-12 124 108 at 0.1 km Pre

90 at 4.35 km 

\ 

o

o

I

*Gaged discharge measurement. 

2Average discharge.

3

09 

V)
would be inaccurate. Because most velocity-area 

measurements were in or immediately downstream 

from confined reaches on steep slopes, it is most 

likely that if velocities were outside the 3 to 6 m/s 

range, they were higher, and the reported discharge 

values may err by being too low. Nevertheless, 

where velocity-area discharge estimates are near 

locations of critical-depth estimates, there is 

general agreement, lending support to the 

supposition that debris-flow velocities in the study 

area were generally between 3 and 6 m/s.

Critical-Flow Discharge Estimates

Critical-flow discharge estimates were 

calculated where there were suspected transformations from subcritical flow to supercritical 

flow (fig. 19). This type of transformation can take 

place at free outflows from lakes, at severe width 

constrictions, and at increases in channel slope 

(Henderson, 1966). The procedure used in this 

study is a simplified version of the critical-flow 

method described by Barnes and Davidian (1978, 

p. 189-190). The method is premised on the 

occurrence of critical flow at control sections along

HSection of 

critical flow

Figure 19. Definition diagram for flow transforming 

from subcritical flow to supercritical flow through a 

control section of critical flow. In calculating criticaldepth discharge measurements, (1) flow velocity at//j

2

is assumed to be negligible ( — = o), and (2) energy

2£

loss between the subcritical and critical sections is 

negligible (H^ =H2 ).H is the specific energy of the 

flow, v is the mean flow velocity, g is the acceleration 

of gravity, and dc is the flow depth at the section of 

critical flow.

the flow path so that there is a fixed relation 

between the specific energy of flow and discharge. 

Flow is critical when the Froude number (F), 

which is the dimensionless ratio of inertial forces 

(expressed as velocity) to gravitational forces 

(expressed as flow depth and gravitational 

acceleration), is unity:

F = a = 1

(1)

where a is the energy coefficient accounting for 

nonuniform velocity distribution (typically varies 

between 1.0 [uniform velocity distribution] and 

2.0), v is the mean cross-section velocity, g is the 

acceleration of gravity, and d is the mean flow 

depth for any consistent set of units.

Because the Froude number is a dimensionless 

ratio based only on conservation of energy, the 

critical-flow concept is valid for all types of 

gravitationally driven free-surface flows, regardless 

of density and rheology. For debris flows in steep 

channels, which travel at velocities and depths 

comparable to water flows (Costa, 1984; Pierson 

and Costa, 1987), flow is likely to pass through 

states of subcritical, critical, and supercritical flow. 

Critical flow is the basis for discharge estimates at 

weirs and sluice gates, although these devices are 

generally calibrated. The chief advantages of 

critical-flow estimates are that (1) estimates of 

friction slopes and energy-loss coefficients are not 

required, and (2) critical flow is the maximum 

possible flow for a given specific energy (H = 

d + v2/2g), thus allowing confident statements 

about the maximum possible discharge at a site if 

field conditions are appropriate.

To obtain the debris-flow discharge estimates 

for this study, we chose reaches of resistant channel 

boundaries where there were severe channel 

constrictions or where there were abrupt increases 

in channel slope, such as near brinks of waterfalls. 

A single cross section was surveyed at these 

locations, and evidence of maximum flow stage 

was related to the elevation datum of the surveyed 

cross section (fig. 19). Highwater marks were 

surveyed to estimate the specific energy of the flow 

entering the control section. Consequently, the best 

field situation was where flow ponded upstream of 

the cross section and left deposits in backwater

Debris Flows from Lakes Dammed by Neoglacial Moraines 39
areas. Deposits in areas of flow runup immediately 

upstream of the control cross section (fig. 20) also 

provided a minimum indication of the energy 

surface. Because the channels in the Three Sisters 

Wilderness Area are irregular, with abundant 

channel steps, changes in gradient, and changes in 

width, several suitable sites for critical-flow 

estimates were found on each debris flow path. The 

search for highwater marks was generally confined 

to within 20 m upstream of the control cross 

section.

For the general case considered onedimensionally at critical flow,

where A is the channel cross-sectional area. 

Continuity also requires that

= Av.

(2)

(3)

For a measured cross section at a suspected 

site of critical flow, we calculated curves of 

specific energy (H = d + v2/2g) vs. discharge using 

equations 1, 2, and 3. The field evidence for the 

local specific energy (maximum flow stage a few 

channel widths upstream of the cross section) was

compared to this curve to obtain a discharge 

estimate for the cross section (fig. 21).

Hydraulic assumptions fundamental to the 

critical- flow discharge estimates are (1) fluid 

density is constant, (2) flow is steady, (3) flow is 

hydrostatic, and (4) flow is critical at or near the 

measured cross section. These assumptions are not 

required to be valid for the entire flow hydrograph, 

but simply for the brief span of time during which 

the evidence for the maximum energy surface is 

emplaced and the flow peak passes through the 

control section within a few meters downstream. 

The steadiness assumption is most susceptible to 

violation. If there are dynamic (energy) waves 

pulsing down the channel, the elevation of the 

deposits left by the dynamic waves may be higher 

than the energy surface actually associated with the 

maximum discharge; hence, leading to discharge 

overestimation (Iverson and others, 1994). 

Although, theoretically, dynamic waves should not 

pass through reaches of critical flow. Short 

wavelength kinematic waves will not result in 

erroneous estimates of peak instantaneous 

discharge, but the resulting discharge estimate will 

be that of the wave itself and may not be 

representative of the entire debris flow. Notably,

PLAN VIEW PROFILE

Sediment

Debris

Critical flow 

section

Critical flow 

section

Figure 20. Schematic plan and profile illustrations of an ideal field situation for a critical-flow discharge 

estimate at a flow constriction where debris or sediment give an accurate indication of the specific energy of 

the flow entering the constriction (//2 of figure 19).

40 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
violations of these assumptions, except for flow 

steadiness, result in discharge overestimation. In 

hydraulically complex areas, the maximum error 

may be as large as a factor of 0.5, but more likely is 

within a factor of 0.25 considering a reasonable 

range in hydraulic uncertainties at suitable field 

sites.

Field conditions in which the observed 

evidence of maximum flow stages fail to accurately 

represent the specific energy of the incoming flow 

can lead to discharge underestimation. The two 

most plausible scenarios of error introduction are 

situations where (1) observable evidence of 

maximum upstream ponding stages was not 

preserved to highest ponding levels, and (2) flow 

through the ponded reach had substantial velocity. 

For most plausible situations where field settings 

are appropriate for critical-flow discharge 

estimates, these errors will lead to discharge 

underestimation by a factor less than 0.5. 

Consequently, the critical-flow procedure used in 

this study is assumed to have an accuracy of ± 50 

percent.

LLJ

O 

DQ

LLJ •— '

uj cr:

^ <

C/3

105

104

103

102

101

100

99

98

97

96

95

I I I \ \ \ \ \ I 

o Energy surface 

v Water surface

Upstream

high watermark

I Q = 490 m3/s~1

I

I

I I I I i| I i I I

0 100 200 300 400 500 600 700 800 900 1,000

DISCHARGE, IN CUBIC METERS 

PER SECOND

Figure 21. Example of critical depth (V; d of figure 19) 

and specific energy (O; H2 of figure 19) plotted for a 

hypothetical surveyed cross section of critical flow. A 

peak discharge is estimated for the critical-flow section 

by relating the elevation of the upstream high-water 

evidence to the calculated specific energy curve for the 

critical-flow section.

Case Studies in the Central 

Oregon Cascade Range

In the Mount Jefferson and Three Sisters 

Wilderness Areas, deposits and source areas were 

studied at nine sites where debris flows resulted 

from rapid emptying or partial release of morainedammed lakes (pi. 2). Two small flows from a 

small lake at the terminus of Waldo Glacier, 

Mount Jefferson, also have been reported in 

newspaper accounts and are evident on aerial 

photographs. Although all debris flows affected 

popular recreational areas, and many occurred 

during the recreation season, the only adverse 

effects were damage to trails and campsites and the 

temporary burial of a county highway. The largest 

debris flows, nevertheless, substantially affected 

downstream valleys, locally eroding and depositing 

sediment on surfaces covered with Mazama tephra, 

indicating that these flows affected surfaces that 

had been previously unmodified for at least the last 

7,000 years.

The sections that follow describe debris flows 

at the individual locations. Although information 

was collected on flows in both the Mount Jefferson 

and Three Sisters Wilderness Areas, the most 

complete observations were compiled for the four 

largest flows that resulted from releases of 

moraine-dammed lakes at the termini of Collier, 

Diller, Eugene, and East Bend Glaciers in the 

Three Sisters Wilderness Area. Deposits left by the 

flows in the Mount Jefferson Wilderness Area are 

indicated on plate 1; deposits left by flows in the 

Three Sisters Wilderness Area are shown on 

plate 2.

Mount Jefferson Wilderness Area

Two debris flows originated on the north flank 

of Mount Jefferson from rapid emptying of shortlived proglacial lakes that formed at the margins of 

northern lobes of Whitewater Glacier (fig. 22). 

Another large debris flow in 1955 apparently was 

triggered by mass movement of Neoglacial till 

downvalley from Russell Glacier (Scott, 1974, 

p. 57). A small lake in front of Waldo Glacier, on 

the southeast side of Mount Jefferson, apparently 

partially breached its morainal dam at least twice. 

Three Fingered Jack, a separate volcanic center

Debris Flows from Lakes Dammed by Neoglacial Moraines 41
within the Mount Jefferson Wilderness Area, has 

had at least two small flows from the lake at the 

terminus of Jack Glacier.

East Jefferson Park

Whitewater Glacier is the largest glacier on 

Mount Jefferson, covering most of the eastern and 

northern flanks of the volcano (pi. 2; fig. 22). 

There have been two debrisflows from small and 

short-lived moraine-dammed lakes that formed at 

northern lobes of the glacier (fig. 22). The largest 

flow, on August 21, 1934, deposited silt, sand, 

gravel, and boulders over much of the broad, lakedotted alpine meadows of Jefferson Park before 

entering the drainage of Whitewater River (pi. 2, 

fig. 23). Downstream from Jefferson Park, the flow 

continued as sediment-laden streamflow.

The east Jefferson Park debris flow was 

described in newspaper articles reporting aerial 

surveys and ground expeditions that examined the 

debris-flow deposit in the weeks after the event 

(The Oregonian, Aug. 27, 1934; The Oregon Daily 

Journal, Oct. 19, 1934). According to these reports, 

the debris flow resulted from the emptying of a 

small, 4,000 m2 moraine-dammed lake at 2,660 m 

that had formed that same summer. The lake 

breached the moraine, eroding an outlet about 15m 

deep through the moraine. The resulting flow 

eroded a new channel up to 10m deep as it 

continued down the steep distal slope of the 

Neoglacial moraine and over older till, outwash, 

and colluvium composing the steep slopes below 

(fig. 23). Deposition began at 1,860 m on a steep 

forested outwash fan at the base of the 

Mount Jefferson edifice and covered 320,000 m2 of

Figure 22. Aerial view south of Mount Jefferson and the northern lobes of Whitewater Glacier. 

Moraine-dammed lake releases came from the indicated locations. Photograph by Austin Post 

(R21-32), September 21, 1960.

42 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
eastern Jefferson Park, where two established 

forest camps were buried by flow deposits (pi. 2; 

figs. 22 and 23). U.S. Department of Agriculture, 

Forest Service personnel, at the site within weeks, 

reported that the park was covered with "boulders, 

sand, and tree trunks to a depth of from 1 to 6 or 

8 feet" (The Oregon Daily Journal, Oct. 19, 1934). 

At the fan apex, debris flow levees on the margins 

of an incised channel define a cross-section area of 

100 m2. An assumed flow velocity of 3 to 6 m/s 

yields a peak discharge estimate of 300 to 

600 m3/s.

West Jefferson Park

In west Jefferson Park, one debris flow from a 

Neoglacial-dammed lake is documented at a site 

0.5 km west of the 1934 breach. No historical

Figure 23. Composite oblique aerial 

photographs of the debris flow that resulted 

from the August 21, 1934, release of the 

short-lived moraine-dammed lake (location 

indicated by arrow) at the terminus of a lobe 

of Whitewater Glacier, Mount Jefferson 

(fig. 22). Photograph courtesy of 

The Oregonian.

records of this lake, or resulting debris flows, are 

known except for Scott's description (1974, p. 57) 

of a "very recent flood deposit, perhaps no more 

than 5 years old." This lake formed at an elevation 

of 2,150 m behind a low Neoglacial moraine at the 

terminus of the northernmost lobe of Whitewater 

Glacier (pi. 2, fig. 22) sometime following the east 

Jefferson Park debris flow. The absence of records 

of this lake indicates that it was short-lived, 

perhaps forming the same year as the debris flow. 

The size of the lake is not known. However, the 

topography of the outlet area indicates that the 

maximum possible lake area was about 15,000 m2, 

with a maximum depth of 5 m. The flow resulting 

from the lake breakout travelled down the 27° 

slope of the moraine, incorporated Neoglacial and 

older till, and deposited sediment over 170,000 m2 

of Jefferson Park (pi. 2; fig. 24). At the fan apex,

Debris Flows from Lakes Dammed by Neoglacial Moraines 43
0.5 km from the breach, bouldery levee crests 5 m 

above the 17° channel thalweg define a cross 

section area of 50 m2. An assumed average flow 

velocity of 3 to 6 m/s yields a peak discharge 

estimate of 150 to 300 m3/s.

Aerial photographs (fig. 22) show that this 

flow occurred prior to 1960. A mountain hemlock 

in the path of the debris flow had its 15-cm-thick 

parent stem sheared off at a height of 1.5 m; this 

resulted in eccentric growth of a former branch that 

became the tree's main stem. A core through this 

stem shows a change in growth pattern that was 

detected by ring counting to 1957, providing a 

tentative date for the damage-causing event. A

false ring produced during the same year further 

indicates that the damage occurred during the 

spring and summer growing season.

Waldo Glacier

Waldo Glacier is a small, 0.3-km2 glacier that 

flows down the south flank of Mount Jefferson 

within the Warm Springs Indian Reservation (fig. 

25). During maximum Neoglacial advances, the 

glacier was about twice its present areal extent and 

built large lateral and terminal moraines that later 

impounded a lake with a maximum surface area of 

about 26,000 m2 at an elevation of 2,180 m. Freshappearing scars in the terminal moraine are visible

2,300

2,200

2,100

_j 

LLJ

> 2,000

UJ 1,900

C/D

LU

> 1,800

O

CO

< 1,700 

[Jj 2,300

LLJ

Breach

i I r | i 

EAST JEFFERSON PARK

— — Erosion

--------- Deposition

Peak discharge 

300-600 m3/s

Jefferson Park

_ A

2,200

uJ 2,100 

Q

j- 2,000

b

< 1,900 

1,800 

1,700

WEST JEFFERSON PARK

Peak discharge 

150-300 m3/s

Jefferson Park

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

DISTANCE, IN KILOMETERS

VERTICAL EXAGGERATION 2X

Figure 24. Longitudinal profiles along the flow routes of debris flows from moraine-dammed lakes at terminal 

lobes of Whitewater Glacier, Mount Jefferson. A, 1934 debris flow into east Jefferson Park; B, (1957(?) debris flow 

into west Jefferson Park.

44 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
on 1937 aerial photographs (Research Committee 

of the Mazamas, 1938), indicating that a previously 

larger lake had partially breached the moraine. A 

subsequent breach was noted by The Oregon Daily 

Journal (August 9, 1951, p. 5), which reported that 

a Mazamas climbing party had traced recent (late 

July, 1951) "mud-dying" (presumably meaning the 

mud-coloration) of the Metolius and Deschutes 

Rivers to an emptying of the lake behind the 

terminal moraine of Waldo Glacier. Aerial 

photographs taken in 1990 show there to be little 

water impounded behind the moraine.

Waldo Glacier was not visited; however, on 

the basis of inspection of aerial photographs taken 

before and after the 1951 lake breakout, the 1951 

debris flow followed the same outlet channel as the

Figure 25. Oblique aerial view northwest toward 

Mount Jefferson. A small moraine-dammed lake at the 

terminus of Waldo Glacier has breached its morainal 

dam at least twice, generating small debris flows. 

Photograph September 1987.

pre-1937 one. The 1951 flow slightly enlarged the 

breach and deposited bouldery debris over 

100,000 m2 on an outwash fan at an elevation 

between 2,070 m and 1,890 m. The debris flow 

apparently continued down an unnamed tributary 

of Jefferson Creek for at least another kilometer

(pl. I)-

Jack Glacier

Jack Glacier (an informal name proposed by 

Phillips [1938]) is a small, probably stagnant, ice 

body not shown on USGS topographic maps. The 

ice is in a deep and shaded cirque on the northeast 

side of the serrated ridge that forms Three 

Fingered Jack (pl. 1). The present extent of ice 

covers about 0.01 km2. During maximum 

Neoglacial advances, however, Jack glacier 

covered 0.13 km2 and formed 50-m-high moraines 

on its periphery. Jack Glacier is protected from 

insolation by high ridges to the south and west and 

is one of the lowest Oregon Cascade Range 

glaciers, lying between 2,000 and 1,860 m 

elevation.

The Neoglacial moraine dams a lake with a 

1993 surface area of 6,120 m2, a maximum depth 

of 8.0 m, and a volume of 26,500 m3 (figs. 15A and 

17). This lake was present in 1937 (Phillips, 1938), 

but is not shown on USGS topographic maps that 

were surveyed in 1928 and 1929, nor is it noted in 

a 1929 description of the scenery from the top of 

Three Fingered Jack (Lynch, 1929, p. 114). The 

lake overflows through a narrow, boulder-paved 

outlet and down a steep channel incised in the 30° 

distal moraine slope. This lake has one of the 

steepest outlets of the remaining moraine-dammed 

lakes and its seemingly precarious stability is 

apparently due to a few boulders, less than 1 m in 

diameter, that pave the channel thalweg at the 

outlet.

Debris-flow deposits on the fan below the lake 

were left by at least two partial breaches of the 

moraine dam (pl. 2). The first breach was prior to 

September 1960 and left anastomosing splays of 

bouldery debris-flow deposits over 12,000 m2 of 

the outwash fan at the base of the moraine. The 

second release further incised the upper part of the 

moraine and left a fan-shaped deposit on the 

outwash fan (fig. 26). Comparison of dated aerial 

photographs indicates that the second flow

Debris Flows from Lakes Dammed by Neoglacial Moraines 45
occurred between August 1979 and September 

1987. Neither debris-flow deposit extended past 

the outwash fan at the base of the Neoglacial 

moraine, 0.4 km from the outlet.

Two shorelines 2.6 + 0.1 m and 1.8 + 0.1 m 

above the present lake level are preserved on the 

west margin of the lake. Abandonment of these two 

shorelines possibly corresponds to the two sets of 

deposits on the outwash fan. If true, the first lake 

level lowering resulted in release of 5,700 m3 , and 

the second release was about 1 1,700 m3 . 

Considering the present topography of the outlet, 

the maximum possible water discharge at the 

breach during the second event was about 25 m3/s.

Three Sisters Wilderness Area

At least five debris flows caused by breaches 

of moraine-dammed lakes have occurred within the 

Three Sisters Wilderness Area since 1933. The 

largest were the debris flows from lakes at the 

termini of Collier, Diller, and East Bend Glaciers

on North and Middle Sisters and Broken Top, 

respectively. These debris flows traveled for 7.5 to 

9 km, and had peak discharges between 200 and 

500 m3/s in their upper reaches. Two smaller flows 

were caused by releases from two small, shortlived lakes at the terminus of Eugene Glacier on the 

north flank of South Sister.

Collier Glacier

A large Neoglacial moraine-dammed lake 

formed behind the Neoglacial moraine of Collier 

Glacier (fig. 9). Ruth Hopson Keen observed, 

photographed (fig. 12), and described conditions 

near the glacier terminus between 1933 and 1973 

(Hopson, 1960, 1961, 1962, 1963, 1965; Keen 

1969, 1978, 1981). According to her observations, 

the lake first formed between August 1933 and 

September 1934, and grew until 1940 as Collier 

Glacier retreated. At its maximum extent, the lake 

covered 100,000 m2 and had a volume of 

670,000 m3 (figs. 16, 17, and 18). The lake spilled 

over the low point in the lateral moraine, forming

Figure 26. Moraine and outwash fan from Jack Glacier on Three Fingered Jack. The outer slope of the 

moraine has been eroded and debris deposited on the fan by two partial releases from the lake impounded 

by the moraine. Photograph taken September 1987.

46 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
the primary source of White Branch. According to 

Hopson (1960, p. 4):

"At the northwest, White Branch has 

always breached the terminal moraine. 

This stream formerly flowed from under 

the ice where it now flows from the lake. 

Before 1940, the lake merely spilled over 

at this point, and spread out among the 

rocks leaving a few stepping stones 

above water. By 1941, the overflowing 

water had eroded to a depth of 1 or 2 feet. 

Pressure from increased meltwater, 

following a hot spell in July 1942, caused 

a sudden outbreak [prior to July 23, 

1942]. This cut a gorge several feet deep 

at the outlet, and as much as 30 feet deep 

a few hundred yards down stream. 

Farther along, White Branch changed its 

course in a few places. As much as a mile 

and a half below the glacier, it spread 

boulders over outwash plains. It covered 

the lowest outwash plain with fine

sediment, and generally changed the 

picture of upper White Branch Valley."

Our survey of the lake basin indicated that 

during the July 1942 flow there was 5.4 ± 0.5 m of 

incision at the outlet (fig. 27), resulting in release 

of about 460,000 m3 of water. The lake remained at 

this level until sometime between September 1954 

and October 1956, when a second breach in the 

lateral moraine formed 15 m to the north of the 

first breach (figs. 27 and 28). The 1942 flow 

resulted from the south breach and caused most of 

the visible incision in the moraine and the 

downstream deposition at Sawyer Bar. The 

sequence of events that led to development of the 

second breach is not clear. Its net effect, however, 

was 0.8 m of lake-level lowering and release of as 

much as 50,000 m3 of water. A 1956 aerial 

photograph shows the lake draining through the 

second breach (fig. 29). According to Hopson 

(1961), between July 1960 and August 1961 the 

lake almost completely drained, and meltwater 

from Collier Glacier no longer flowed into White

Figure 27. View west toward outlet from the basin that formerly contained the lake at the terminus of Collier 

Glacier, North Sister. The marked shorelines (note people for scale) indicate two former lake levels before and 

after the 1942 breach in the lateral moraine. A second breach formed about 15 m to the north (right) between 

1954 and 1956 and resulted in a further 0.8 m of lake-level lowering. Photograph taken August 12, 1987.

Debris Flows from Lakes Dammed by Neoglacial Moraines 47
W

2 < 6

£ cc -t

O m 4

CO

0 10 20 30 40 50 

DISTANCE, IN METERS

Figure 28. Surveyed cross section of outlets to the 

former lake at the terminus of Collier Glacier. At the 

time of the survey in 1991, the 1942 breach was 

partially filled with snow, so the dimensions have been 

reconstructed (point indicated by open circle) with the 

aid of figure 27 and August 1987 measurements when 

the breach was free of snow.

Branch, but entered what Hopson called the "melt 

hole," a subsurface outlet through ground moraine 

and stagnant ice near the northeast margin of the 

former lake. Glacial meltwater still drained into the 

"melt hole" from a seasonal pond in the former 

lake basin when we surveyed the site in August 

1991.

The 1942 outbreak transformed into a 

bouldery debris flow that traveled 7.5 km before 

ending where White Branch flows onto and drains 

into the surface of a late Holocene basalt flow 

from Collier Cone (pi. 2). Inspection of aerial 

photographs taken in 1949 and 1977 shows that the 

1942 debris flow was much larger than any flow 

that possibly resulted from the 1954-1956 breach. 

The only apparent effect of the second episode of 

lake lowering was about 3 m of incision of 

outwash and till at the breach and within 300 m

Figure 29. Oblique aerial view southeast toward remnant lake, breached moraine, and downstream deposits left 

after the 1942 flow from the lake at Collier Glacier. The 1942 flow resulted from the south breach and caused 

most of the visible incision in the moraine and the downstream deposition at Sawyer Bar. In this view, the lake 

drains through a second breach to the north that formed between 1954 and 1956. Photograph by Ackroyd 

Photography, October 1956.

48 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
downstream. Cobbles and boulders along the White 

Branch channel bottom, shown in unpublished 

1942 photographs by Ruth Hobson Keen, were 

apparently unmoved in 1995, indicating that any 

post-1942 event has had minimal effect on the 

channel.

The maximum possible discharge at the lake 

outlet during the 1942 breach was 140 ±30 m3/s. 

This discharge was calculated assuming critical 

flow and a 1942 water surface 5.4 ± 0.5 m above 

the thalweg of the first breach (fig. 30). Based on 

our basin survey, the water volume released was 

460,000 m3 , requiring at least 45 to 70 minutes of 

flow at peak discharge to lower the lake to the level 

of the breach thalweg. Our surveys of the outlet 

area downstream of the breach, and evaluation of 

photographic and geomorphic evidence of the preflow topography, indicate that about 120,000 m3 of 

till and outwash were eroded from the steep outlet 

area within 300 m of the breach, increasing the 

flow volume by about 25 percent. As discussed 

later, most of this material must have entered the 

flow within a few minutes. Large scallop-shaped 

reentrants along the channel margins (fig. 29) are 

interpreted as evidence that a large portion of the 

material was incorporated by mass movements into 

the deepening channel during the course of the 

flow.

C/D

cc

LLJ 

LLJ

CJ

£

C/D

— - Energy surface

—— Water surface

0 100 200 300 

DISCHARGE, IN CUBIC METERS PER SECOND

Figure 30. Stage-discharge relation for critical flow 

through the left breach at the outlet to the lake at Collier 

Glacier.

At the apex of Sawyer Bar (pi. 2), bouldery 

levees mantled with 1- to 2-meter diameter 

boulders 6 m above the present channel thalweg 

indicate that the flow transformed to a debris flow 

within the intervening 600 m from the breach. The 

debris flow inundated Sawyer Bar, a Neoglacial 

outwash surface, and deposited bouldery lobes over 

its 50,000-m2 surface (figs. 29 and 31). 

Downstream, the flow deposited sediment over 

wider and lower gradient reaches and passed 

through and eroded sediment from narrower and 

steeper reaches (pi. 2; fig. 32). In some 

depositional reaches, bouldery digitate lobes were 

deposited in mid-valley areas and resemble a single 

debris flow levee with the largest clasts on the 

edges (fig. 33). We cannot confidently interpret 

these features, but they may be the result of 

deposition on snow-covered surfaces. After the 

snow melted, the former flow channel that was 

eroded through the snow cover was preserved as a

Figure 31. View east toward Sawyer Bar, which was 

covered by bouldery deposits from the 1942 breach and 

debris flow from the lake at the terminus of Collier 

Glacier.

Debris Flows from Lakes Dammed by Neoglacial Moraines 49
sinuous ridge of coarse gravel and boulders located 

in the middle of the valley. In most locations, 

however, the entire valley was inundated and the 

flow margins and maximum stage of the debris 

flow are well defined by a cohesive silty sand that 

appears to have been the fluid, but viscous, matrix 

of the flow (fig. 34).

Using this evidence of maximum flow stage, 

we calculated estimates of instantaneous peak 

discharge for the largest flow wave at 13 sites 

along the debris flow path (figs. 32 and 35). Most 

measurements were made at flow constrictions and 

at brinks of channel steps where we used the 

critical-depth procedure. In addition, two velocityarea estimates based on the cross-sectional areas of 

the flow are included. All reported critical-depth 

estimates are estimated to be accurate within ±50 

percent. The velocity-area discharge estimates are 

generally presented as a range, resulting from an 

assumed average cross-sectional velocity of 3 and 

6 m/s.

The resulting discharge estimates correspond 

with the overall patterns of erosion and deposition. 

Two critical-flow estimates between 1.3 and 

1.5 km from the breach yield discharge estimates

of 530 and 545 m3/s (fig. 32). These values are 

similar to a 490 m3/s upper limit of a velocity-area 

estimate at the upstream end of Sawyer Bar, but 

slightly larger than a superelevation measurement 

of 360 m3/s made by Laenen and others (1987) at 

the downstream end of Sawyer Bar. Recent work 

in a large experimental flume indicates that when 

total channel width is used in superelevation 

calculations, debris-flow wave speed is 

consistently underestimated (Iverson and others, 

1994); thus, discharge is underestimated. The 

reported value of 360 m3/s (Laenen and others, 

1987) is considered a minimum value of discharge 

at this site.

Taken together, the peak discharge results and 

the estimates of sediment and flow volumes 

indicate that the peak flow rate increased from a 

maximum possible clear-water discharge of 

140 ±30 m3/s at the breach to a debris flow of 

about 500 m3/s at Sawyer Bar. This increase 

resulted from incorporation of 120,000 m3 of till 

and outwash eroded in the 300 m downstream from 

the breach, producing a peak discharge debris flow 

that was 65 to 80 percent by volume of entrained 

till and outwash. Such an entrainment rate could be

_

LiJ uj 

L±J UJ

2,200

2,100

2,000

1,900

1,800

1,700

1,600

1,500

1,400

I I I I I I I I I I I 

<110-170m3/s-1 at breach 

245-490 m3/^1

. 530 m3/^1

. 545 m3/^1

I i i i | , i i | i i i | i i i | i i i 

WHITE BRANCH LONGITUDINAL PROFILE

— - Erosion

•••••••• Deposition

225-

130m3/s- 1 

30 m3/s-1

40 m3/^1

•Om3/^1

10

DISTANCE, IN KILOMETERS

5X VERTICAL EXAGGERATION

Figure 32. Longitudinal profile of White Branch, showing indirect discharge estimates (in cubic meters per 

second) and reaches of erosion and deposition during the 1942 debris flow from the breach of the lake at the 

terminus of Collier Glacier. The critical-flow estimates are given as single values and inferred to be accurate to 

within ±50 percent. The velocity-area estimates are given as ranges based on assuming a mean flow velocity of 

3 to 6 meters per second.

50 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
sustained only for about 6 minutes, considering our 

estimate of the total volume eroded from below the 

breach. Because of the large volume of water in the 

lake, however, most of the released flow must have 

had a volumetric sediment concentration 

substantially less than 65 percent.

The discharge estimates for sites farther 

downstream indicate substantial decrease in the 

peak discharge—from greater than 500 m3/s near 

Sawyer Bar, 1 km from the outlet, to about 

150 m3/s, 4 km downstream (fig. 35). This 

decrease in discharge was over a 4 km reach of 

declining gradient and substantial deposition (pi. 2; 

figs. 32 and 35), indicating that the peak flow 

decreased primarily because of deposition rather 

than attenuation. Peak discharge may have 

increased from 225 to 450 m3/s within a steep, 

narrow reach near Obsidian Cliffs, perhaps due to

temporary blockage by wood or large clasts. 

Farther downstream, three critical-flow estimates 

indicate a downstream decrease of peak discharge 

due to continued deposition until the debris flow 

ended 8 km downstream from the breached 

moraine in a series of ponded embayments on the 

surface of a lava flow from Collier Cone (pi. 2).

Most of the material in the debris flow was 

derived from the moraine and outwash within 

600 m from the breach. Some additional sediment, 

however, apparently was incorporated into the flow 

from erosion of channel banks in constricted 

reaches. Cobbles and boulders from talus that 

flanks constricted valley segments were eroded and 

entrained. Most of the constrictions are at least 

partly bounded by lava from Collier Cone or the 

rhyodacite that forms Obsidian Cliffs (pi. 2). 

Downstream from the constrictions, these rock

Figure 33. Photograph of a single sinuous ridge of bouldery gravel deposited near the center of a wide 

depositional reach along the 1942 debris flow pathdown White Branch, perhaps the result of deposition onto 

snow (note person for scale). The maximum stage of the flow is indicated by the prominent light-colored 

deposits on the talus from the lava flow from Collier Cone, a result of fine sediment filling interstices.

Debris Flows from Lakes Dammed by Neoglacial Moraines 51
Figure 34. View east (upstream) of deposits from the 1942 debris flow down White Branch. The nowinundurated matrix was dense enough to support boulders up to a meter in diameter. Many of the larger clasts 

in this reach were entrained from talus of the lava flow from Collier Cone (partially visible on the left side of 

the photograph). Note person for scale.

types constitute most of the larger clasts in 

depositional areas.

Size distributions of the <32-mm sediment 

deposited by the flow are consistent with some of 

the flow aspects described above. The samples 

were collected by K.M. Scott (written commun., 

1991) and analyzed by wet sieve and pipette 

analysis. Cumulative frequency curves of 13 

deposit samples and a sample from the moraine 

show that most deposits have similar sediment-size 

distributions and are similar to the moraine 

material at the outlet. Similarity among deposits is 

most pronounced for the fine sand, silt, and clay 

factions, which is consistent with the field 

observation that the character of the now-indurated 

flow matrix changed little downstream.

Deposits of the White Branch flow had the 

highest clay content (1 to 6 percent) of all the 

measured debris flows (figs. 36 and 37). Debris 

flows with clay content greater than 3 percent have

a degree of cohesion that allows them to travel for 

relatively long distances without transforming into 

streamflow (Scott, 1988, p. 70-71; Scott and others, 

1992, p. 12-15). The White Branch flow was the 

only studied debris flow in the Three Sisters and 

Mount Jefferson Wilderness Areas that did not 

transform into sediment-laden streamflow.

The content of coarser clasts (greater than 

2 mm) in samples of the deposits was more varied 

than that of the matrix material and ranged from 

0 to 54 percent (fig. 37). The actual gravel content 

of the deposits is greater than the sample analyses 

indicate because the collected samples 

systematically excluded clasts larger than 32 mm. 

Part of this variation probably is due to difficulty in 

collecting samples from similar depositional 

environments along the flow course. Nevertheless, 

there was a general decrease in gravel content and 

mean particle size within deposits along the first 

4.5 km of White Branch, corresponding to the long

52 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
reach of declining gradient and diminishing peak 

discharge (pi. 2; fig. 32). Downstream fining of the 

deposits is inferred to be at least partly the result of 

size-selective deposition (Scott, 1967, 1988) by the 

debris flow. About 5 km from the outlet, White 

Branch descends through a steep and narrow reach 

that is constricted by rhyodacite bluffs and talus 

from the Obsidian Cliffs and by the lava flow from 

Collier Cone. There, gravel-content variation 

increased markedly (fig. 37) due to local 

incorporation and deposition of talus and bank 

material.

Other sediment-sample statistics, such as mean 

particle size and sorting, show no clear trend 

(fig. 37). This lack of trend is probably because of 

the overall cohesiveness of the flow; consequently, 

the flow matrix changed little over the length the 

flow. Also, large site-to-site variation in particlesize characteristics because of variations in local 

depositional environment probably masks 

downstream trends.

Diller Glacier

During maximum Neoglacial advances, Diller 

Glacier covered 1.03 km2 on the eastern slope of 

Middle Sister and formed high lateral and terminal 

moraines before retreating to a present area less 

than half its former size. Photographs by

u Q 

5 i

D O 

U O

800

600

400

200

Deposition/attenuation 

Entrainmentor

temporary T Deposition j 

blockage^ I /

012345678 

DISTANCE FROM BREACH, IN KILOMETERS

Figure 35. Indirect estimates of peak discharge for the 

1942 debris flow on White Branch. Data portrayed as 

points and error bars are critical-flow estimates; data 

portrayed only as ranges are velocity-area estimates. 

Solid curve is an interpretation of how peak discharge 

varied downstream, annotated with inferences of the 

processes controlling the changes in peak discharge. 

Compare with figure 32.

0.01 

H 0.,

B '

cc.

LU 10

LU 30

> 50

^ 70

=D 90

CJ

99

99.9

99.99

| | Range of sample values

—— Collier Neoglacial 

moraine sample

-4-2 0 2 4 6 8 phi 

16 4 1 0.25 0.0625 0.016 0.004 mm

PARTICLE SIZE

Figure 36. Range of cumulative curves for 13 samples 

of matrix material (less than 32 mm) from the 1942 

White Branch debris-flow deposits. Also shown is the 

cumulative curve for a sample from Collier Glacier 

Neoglacial moraine. Data provided by K.M. Scott 

(USGS, written commun., 1991).

I.C. Russell in 1903 (fig. 5) and a 1929 Oregon 

Historical Society photograph (neg. LOT 311-260) 

show the glacier in contact with Neoglacial 

terminal and lateral moraines, but with an ice 

surface substantially lower than the moraine crests. 

Between 1929 and 1937, a lake formed at an 

altitude of 2,300 m between the glacier terminus 

and the terminal moraine (pi. 2; figs. 15C and 16). 

On the basis of our survey of the basin (figs. 17 

and 18), the lake contained 3.2 x 105 m3 of water 

and had a maximum depth of 22.4 m.

Aerial photographs taken September 19, 1967, 

(fig. 15C) and July 17, 1973, (USFS photograph 

1672-96) show the moraine dam was breached 

between these dates, resulting in a debris flow that 

traveled 9 km down the North Fork of Squaw 

Creek before transforming into sediment-laden 

streamflow near the confluence of the North and 

South Forks (pi. 2; figs. 38 and 39). Sandy deposits 

from this flow are traceable for another 7 km 

downstream. Discharge records from a stream gage 

24 km from the breach (Squaw Creek near Sisters, 

Oregon) show a flow pulse of 35 m3/s on 

September 7, 1970, that almost certainly 

corresponds to this flow. By the time the flood 

wave reached the town of Sisters, 31 km from the 

breach, the flow was described as a muddy, 30-cmhigh surge (Laenen and others, 1992, p. 153).

Debris Flows from Lakes Dammed by Neoglacial Moraines 53
The lake completely emptied when the 

moraine dam failed, releasing 320,000 m3 of water 

and entraining about 130,000 m3 of till and 

outwash from the impounding moraine and steep 

outwash surface below the moraine (fig. 38). Three 

hundred meters from the breach, the flow dropped 

over a steep reach, eroded the channel to bedrock, 

and formed a set of falls. On the outwash surface at 

the base of the falls, the flow deposited a debris fan 

covering an area of 40,000 m2 . Near the fan apex, 

the largest clasts have intermediate diameters as

large as 3 m. Bouldery lobes on the fan surface are 

cut by lower and less bouldery surfaces (fig. 38), 

indicating that later phases of the flow were erosive 

and carried finer sediment. At the distal end of the 

fan, the debris flow inundated a meadow, covering 

it with 2 m of 1- to 2-m-diameter boulders within a 

gravelly sand matrix. Later, the distal fan deposits 

and the underlying fine-grained fluvial deposits of 

the meadow were entrenched as much as 4 m, 

apparently by a final, watery phase of the flow 

(fig. 40).

LU

cc

LU 

O 

CC 

LU 

D_

LU 

N

C/D

LU

_l 

O

cc

70 

60 

50 

40 

30 

20 

10 

0 

-6

• Percent gravel 

o Percent clay

n

0 • M7, with one standard

1234567 

DISTANCE FROM BREACH, IN KILOMETERS

Figure 37. Downstream variation in particle-size distribution characteristics of 

matrix materials (less than 32 mm) for the 1942 White Branch flow. A, Clay and 

gravel content variation. B, Graphic mean particle size (Mz) and standard deviations 

as defined by Folk (1980, p. 40-46). Data provided by K.M. Scott (USGS, written 

commun., 1991).

54 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
0.5 1 KILOMETERS

Figure 38. Stereophotograph pairs of Diller Glacier before and after the September 7, 1970, breach 

of the moraine-dammed lake at the glacier terminus. Arrows on the left pair show location of the 

lake. A, September 4, 1963; photographs by Austin Post. B, September 6, 1974; photographs by 

U.S. Department of Agriculture, Forest Service.

Debris Flows from Lakes Dammed by Neoglacial Moraines 55
The debris flow continued down North Fork 

Squaw Creek, eroding colluvium, till, and outwash 

from narrow and steep reaches, and deposited 

levees and boulder berms in wide reaches (fig. 41). 

At an elevation of 2,000 m, 1.5 km from the 

breach, the flow bifurcated, with a portion spilling 

over the left bank and into the drainage from 

Hayden Glacier before rejoining the main thread of 

flow 700 m downstream (pi. 2). From this point 

downstream, interactions between standing timber 

and logs and wood debris in the flow exerted 

substantial control on patterns of deposition. Large 

woody debris incorporated in the flow was lodged 

in overbank areas and caused large boulder and 

debris accumulations. Closely spaced standing 

timber in overbank areas trapped boulders and 

caused upstream deposition (fig. 42).

At an altitude of 1,840 m, the flow entered a 

4-km reach of gradually decreasing gradient 

(fig. 39, pi. 2). Within this reach, there was 

substantial deposition, especially in wide, forested, 

overbank areas. The area covered by debris-flow 

deposits within this reach was about 130,000 m2. 

Exposures near fan apices indicate deposit 

thicknesses greater than 4 m (fig. 43). At the

downstream end of this reach, near the confluence 

with Soap Creek, the flow descended a steep reach 

of narrow gorges and falls over and within several 

lava flows that outcrop along the channel. Evidence 

of the 1970 debris flow within this reach is sparse 

and includes small levees in locally wide reaches 

and small deposits of coarse gray sand along 

channel margins.

At the confluence of the North Fork and South 

Fork of Squaw Creek, bouldery bars, woody debris, 

and sand were deposited at the abrupt decrease in 

gradient (pi. 2; fig. 39). Downstream from the 

confluence, there are no bouldery levees or other 

features indicative of continued debris flow. 

Abundant gravel bars and gray sand deposited on 

the channel banks over the next 7 km do indicate, 

however, that a substantial discharge of water and 

sediment continued down Squaw Creek.

Indirect discharge estimates along the flow 

route are consistent with mapped patterns of 

deposition and erosion (pi. 2). We calculated 13 

indirect discharge estimates from measured cross 

sections and highwater marks along the flow path. 

Highwater evidence consisted of organic flotsam 

and deposits of gray sand in overbank areas, and

UJ LU

ui ffl

2,400

2,300

2,200

2,100

2,000

1,900

1,800

1,700

1,600

1,500

1,400

1,300

1,200

0

I ' [ ' I 

Moraine breach

I ^ I n \ ' I ' I ' I ' I 

NORTH FORK SQUAW CREEK PROFILE

— - Erosion

Deposition

500 m3/s-1

450 nV/s-

/ 330 m^s'1

'

490 m3/s- 1

145m3/s-'

/ 65

Transformation to water flow 

i I i I . I i I

10 12 13 14

Figure 39. Longitudinal profile of North Fork Squaw Creek showing indirect discharge estimates and reaches of 

erosion and deposition during the September 7, 1970, debris flow and flood from the breach of the lake at the 

terminus of Diller Glacier.

56 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
scars on trees near the channel. Five of these 

estimates were critical-flow cross sections, seven 

were velocity-area estimates, and one was a 

Manning Equation estimate.

Because the lake was deep (22.4 m) and the 

breach was large, the maximum possible discharge 

at the outlet, assuming critical flow from 

maximum lake level through a fully formed 

breach, is large—about 6,000 m3/s. The actual 

minimum discharge at the breach was probably 

substantially less because the lake level in this 

small, but deep, lake would have likely dropped

significantly as the breach developed. The first 

reliable discharge estimate below the breach is a 

critical-flow estimate 800 m downstream from the 

outlet where the maximum discharge was about 

280 m3/s. Downstream, as the flow eroded outwash 

and till from the channel banks, peak discharge 

apparently increased to about 450 m3/s, based on a 

critical-flow estimate at the beginning of the long 

depositional reach at 1,850 m altitude (pi. 2; 

fig. 39). Four kilometers downstream, after a large 

volume of the flow had been deposited, the peak 

discharge had diminished to about 65 m3/s. This

Diller Glacier

moraine

breach

Figure 40. Photograph of distal end of the large bouldery fan deposited below the September 7, 1970, 

breach in the Diller Glacier moraine. Photograph taken September 11, 1993.

Debris Flows from Lakes Dammed by Neoglacial Moraines 57
Figure 41. View upstream of a debris flow levee or boulder berm (Costa, 1984, p. 292-293) deposited by 

the 1970 North Fork Squaw Creek debris flow from Diller Glacier. Note people for scale. Photograph 

taken August 11, 1986.

Figure 42. View downstream of boulders trapped by trees in an overbank area during the 1970 North Fork 

Squaw Creek flow. Photograph taken September 19, 1992.

58 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
estimate is consistent with three additional 

velocity-area estimates over the next 2 km (fig. 39). 

Downstream from the transformation of the debris 

flow to water flow, a Manning Equation estimate 

and a critical-depth estimate yielded discharge 

estimates of 36 and 32 m3/s, respectively. These 

values are similar to the September 7, 1970, gaged 

discharge of 35 m3/s measured 12 km downstream.

The shape of the recorded hydrograph for 

September 7, 1970, is typical of floods resulting 

from dams that fail rapidly (Costa, 1988) (fig. 44). 

Measured stage rose 0.75 m in less than 10 

minutes, corresponding to discharge rising from 

5 to 35 m3/s. The duration of the flow pulse was 

less than I hour, and the volume of the surge 

passing the gaging station was 110,000 m3 , about a 

third of the lake volume. The remainder of the 

water from the lake probably was temporarily 

stored within the debris-flow deposits and 

underlying sediment along the floodplain and 

channel of Squaw Creek.

Overall, deposits from the Squaw Creek debris 

flow are coarser than deposits left by the flow 

down White Branch, especially in the finer size 

factions (figs. 45 and 46). Whereas samples from 

the White Branch flow deposits vary between 6.0 

and 33.7 percent silt-sized particles (0.0625 mm) 

and finer, samples from the Squaw Creek debris 

flow deposits contain only 1.2 to 7.7 percent siltsized and finer particles. Likewise, clay content of 

the Squaw Creek flow deposit is less than 0.5 

percent compared with clay contents of 1 to 6 

percent for deposits left by the White Branch flow. 

This resulted in a distinct difference in the 

character of the preserved deposits. The finer 

matrix of the White Branch flow hardened upon 

drying, leaving the deposits from the 1942 flow 

indurated and well-preserved. The matrix of the 

1970 Squaw Creek flow was primarily gray sand, 

resulting in comparatively loose, but distinctive, 

deposits in overbank areas and along flow margins 

for the entire flow route.

Figure 43. The buried trees in this September 20, 1992, view indicate that there was locally as much as 

4 meters of aggradation in depositional areas during the 1970 North Fork Squaw Creek debris flow from 

Diller Glacier. Note people for scale.

Debris Flows from Lakes Dammed by Neoglacial Moraines 59
The wide site-to-site variation in sediment 

texture shown by analyses of deposit samples 

(fig. 46) is apparent in the field and appears to have 

resulted from different channel geometries that 

controlled local patterns of deposition and to facies 

variations within the deposits. Nevertheless, there 

is an overall downstream decrease in mean particle 

size, size variation, and gravel content. Beyond the 

transformation of the debris flow to sediment-laden 

streamflow at 9 km from the breach, gravel content 

of the flow deposits diminished to less than 2 

percent. Nevertheless, the gray sand, deposited 

along the flow margins, is traceable for at least 

7 km farther downstream.

Analysis of the boulder and cobble rock types 

deposited by the flow indicates that there was 

substantial entrainment and deposition of large 

clasts along the flow path. Lithology of 50 clasts 

with diameters larger than 20 cm was noted at each 

of 3 sites (fig. 47): (1) at the distal end of the large 

fan 600 m from the breach, (2) in a deposit 2.1 km 

from the breach, and (3) at the North and South 

Fork Squaw Creek confluence, 9 km from the 

breach. Of the boulders deposited at the second 

site, less than half were of similar rock types to 

those at the fan immediately downstream of the 

breach, indicating that most of the larger particles

were entrained in the intervening reach. About 20 

percent of the clasts at the second site were of rock 

types exposed in the channel between the two sites, 

the others probably came from the till and outwash 

that composes the channel banks along the 

remainder of the intervening reach. At the small fan 

at the North and South Fork confluence, 9 km from 

the breach, less than 10 percent of the sampled 

clasts larger than 20 cm are similar to those 

deposited at either of the upstream sites. Greater 

than 60 percent of the clasts larger than 20 cm and 

21 of the 22 clasts larger than 50 cm appear to have 

come from basaltic andesite flows exposed in the 

steep canyon upstream from the fan.

Eugene Glacier

The first recorded debris flow from a morainedammed lake in the Cascade Range was from the 

failure of a Neoglacial moraine dam near the 

terminus of Eugene Glacier, a small ice body 

clinging to the steep, 600-m-high north-northwest 

facing slope on the north side of South Sister 

(pi. 2). During maximum Neoglacial advances and 

until the early 1930's, Eugene Glacier covered 

0.21 km2 and terminated in three separate lobes 

against large moraines at an altitude of about 

2,475 m (figs. 48 and 49). The present ice-covered

(/>

DC

LLJ

CJ Q

CO Z

=> O

DC 

O

Squaw Creek near Sisters, 

Oregon, September?, 1970

Volume = 110,000 cubic meters

35

30

25

20

15

10

5

0 

6:00 am 8:00 10:00 12:00 pm 2:00 4:00 6:00 8:00 pm

PACIFIC DAYLIGHT TIME

Figure 44. Hydrograph for the period 6:00 am to 6:00 

pm for September 7, 1970, on Squaw Creek, 24 

kilometers from breach (Squaw Creek near Sisters, 

Oregon: station 14075000). The 1 1,000 m3 volume of 

the flood at the stream gage (indicated by shaded area) 

was estimated by subtracting an estimate of the 

baseflow component from the total hydrograph volume.

LJJ 

O 

DC 

LU 

D_

=> 

O

0.01 

0.1

1

10

30

50

70

90

99.99

—— Range of deposit 

samples

—— Diller Glacier

Neoglacial moraine 

sample

-4 

16

-2

4

2

0.25

4

0.0625

6

0.016

8 phi 

0.004 mm

PARTICLE SIZE

Figure 45. Range of cumulative curves for 13 samples 

of matrix material (less than 32 mm) from the 1970 

North Fork Squaw Creek flow debris-flow deposits. 

Also shown is the cumulative curve for a sample from 

the Diller Glacier Neoglacial moraine. Data provided 

by K.M. Scott (USGS, written commun., 1991).

60 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
area is about 0.09 km2. Two debris flows resulted 

from moraine-dammed-lake releases at Eugene 

Glacier. The first, in 1933, was the largest, and 

involved the central and eastern lobes of ice. The 

second resulted from a small release between 1933 

and 1949 from a lake dammed behind the terminal 

moraine formed by the western ice lobe.

According to newspaper accounts (The 

Oregonian, Aug. 14, 17, 20, and 22, 1933), a large 

volume of water and ice escaped Eugene Glacier 

on August 12, 1933. The resulting debris flow 

inundated 250,000 m2 and traveled 6.3 km (pi. 2) 

before evolving into sediment-laden water flow. 

The Oregonian (Aug. 20, 1933) reported that the 

McKenzie River was "brick red" as far as 100 km 

downstream at Blue River, and suspended "lava 

dust" had to be filtered out of Eugene's water 

supply.

100

90

80

70

60

50

40

30

20

10

n

•

-

•

•

.

.

•

-

•

CA

LLJ

o_^>

tco

o

£

CO

I

•

V)

LLJ

D.

V)

o

LLJ

(7) 5rfW

UJ

"Ei

:•"

:§

tM

|5

*?

SITE 1 SITE 2 SITES

Figure 47. Results of rock-type counts of greater than 

20-cm diameter clasts (n = 50) at sites 1-3 (0.6, 2.1, and 

9 km, respectively, downstream from the breach of the 

moraine at Diller Glacier).

Debris flow

Sediment-laden 

water flow

• Mz, with one standard deviation 

error bars

o

DC

CO 

DC

0.016

M 

C/3

LLJ

O 

DC 

D_ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 

DISTANCE FROM BREACH, IN KILOMETERS

Figure 46. Downstream variation in particle-size 

distribution characteristics of matrix materials (less than 

32 mm) for the 1970 North Fork Squaw Creek debris 

flow. Definitions of graphic mean (Mz) and standard 

deviation are from Folk (1980, p. 40-46). A, Clay and 

gravel content variation. B, Graphic mean particle size 

and standard deviation. Data provided by K.M. Scott 

(USGS, written commun., 1991).

Photographs and reports published by The 

Oregonian (Aug. 17 and 20, 1933) (fig. 50) provide 

clues to the sequence of events (note that the 

glacier is referred to as Skinner Glacier in the 

newspaper reports). Apparently a body of possibly 

subglacial water had formed at the central terminal 

ice lobe. A 1929 photograph (fig. 48) does not 

show a lake at the location, although this was a 

period of rapid glacier recession and it is possible 

that the lake formed in the intervening 3 years. The 

water body breached a moraine between the central 

and eastern ice lobes, and escaped eastward, 

eroding through the eastern ice lobe and the 

moraine at the end of the lobe. A week after the 

flow, in the basin formerly occupied by the central 

ice lobe, there was a subaerial remnant of the lake 

held by the partially breached moraine, and most of 

the eastern lobe of ice had been removed (fig. 50).

The outburst apparently transformed into a 

debris flow within 500 m of the breached moraine 

and deposited gravelly sand with abundant and 

distinctive 10- to 20-cm-diameter red cinders over 

wide and low-gradient parts of the Separation 

Creek valley (pi. 2). A small portion of the flow 

spilled into the westernmost Chambers Lakes 

basins. Most of the material entrained in the flow 

was derived from Neoglacial and older till and 

outwash that composes the steep slopes in the 

proglacial area north of Eugene Glacier. In

Debris Flows from Lakes Dammed by Neoglacial Moraines 61
Figure 48. Approximately matched views of the north slope of South Sister from the summit of Middle Sister. 

A, 1929 photograph reproduced with permission of the Oregon Historical Society (neg. 311-70). 

B, September 13, 1993, photograph by David E. Wieprecht (USGS).

62 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
narrower reaches, bouldery levees define the flow 

margins.

Deposits from this flow are traceable to 

Separation Creek Meadow, 6 km from the source 

(pi. 2; fig. 51), where a thin fan of gravelly sand 

containing cobbles and boulders was deposited 

over 20,000 m2 of the meadow surface. Several 

channels at the downstream end of the meadow 

were incised as deeply as 1.5 m, probably by the 

watery remainder of the flow as it continued across 

the meadow. According to observations published 

in The Oregonian (Aug. 20, 1933), the flow was 3 

to 4 m deep across the meadow, and entrained 

"tons of the soft red silt from the meadows." No

evidence of debris flow was observed downstream 

of Separation Creek Meadow, but a sizeable, 

sediment-laden flow must have continued far 

downstream to form the basis of the newspaper 

accounts of downstream sediment concentrations in 

the MacKenzie River.

An estimate for the maximum discharge at the 

breach is 230 m3/s, assuming critical flow through 

the present breach, and assuming flow stage did not 

reach the level of the uneroded moraine crest. 

Because the breach was deepening as the flow 

exited, the actual peak discharge at the outlet was 

probably much less than 230 m3/s. A measured 

cross section 1 km from the outlet gives a velocityN

EXPLANATION

Neoglacial moraine 

(Dashed line indicates crest)

1981 Glacier

150 METERS

CONTOUR INTERVAL 40 FEET

To convert feet to meters multiply by 0.3049

Figure 49. Topographic setting of August 12, 

1933 and 1946(?) moraine-dammed lake 

releases at Eugene Glacier, South Sister. "A" 

is the basin, formerly occupied by a central 

lobe of ice from Eugene Glacier, which was 

the source of water in the August 12, 1933, 

flow. A second and much smaller flow, 

perhaps in 1946, resulted from partial 

breaching of the moraine impounding the 

small western basin "/?."

Topography from US Geological Survey 

North Sister, Oreg., 1988

Debris Flows from Lakes Dammed by Neoglacial Moraines 63
Figure 50. Oblique aerial view west toward the August 12, 1993, lake breach and debris flow from Eugene 

Glacier. This photograph (reproduced with permission of The Oregonian) was taken about one week after 

the flow. "A" is the middle basin, from which water escaped by breaching a morainal ridge to the 

southeast. "/?" is the eastern glacial lobe where escaping water eroded through the ice, depositing a track 

of dark-colored deposits on the ice and downslope on snow and moraines.

2,500

2,400

_ 

UJ LU 2,300

Z <

— LU

2,200

2,100

Q

t § 2,000

< 1,900 

1,800 

1,700

i ' r 

Breach 

<230 m3/s-]

SEPARATION CREEK PROFILE

— - Erosion

•••••••• Deposition

Pacific Crest Trail

20 mS/s- 1

Separation Creek 

Meadow

0

DISTANCE, IN KILOMETERS

VERTICAL EXAGGERATION 5X

Figure 51. Longitudinal profile of Separation Creek, showing indirect discharge estimates and 

reaches of erosion and deposition during the August 12, 1933, debris flow and flood from the 

breach of the lake at the terminus of Eugene Glacier. The critical depth measurements are 

given as single values and inferred to be accurate to within ±50 percent. The velocity-area 

measurements are given as ranges.

64 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
area estimate of 175 to 350 m3/s. This is consistent 

with a critical-flow estimate of 185 m3/s an 

additional 1.5 km downstream (pi. 2; fig. 51). 

Farther downstream, the peak discharge apparently 

attenuated rapidly, decreasing to about 20 m3/s at 

4.5 km from the breach before transforming to 

sediment-laden flood flow at Separation Creek 

Meadow.

A second and much smaller debris flow from 

Eugene Glacier apparently resulted from rapid 

release of a small lake impounded by the moraine 

formed around the western lobe (fig. 49). The date 

of this flow is not known. On the basis of 

inspection of oblique and vertical aerial 

photographs, however, the breach occurred after 

August 1933, when the lake had not yet formed 

between the ice margin and the moraine, and 

before August 25, 1949, when the lake had formed 

and already partially emptied. A tree in the path of 

the release was partly knocked over in 1946, 

providing a tentative date for the release. August 

1949 aerial photographs show a small lake with a 

surface area of about 2,500 m2 draining from the 

breached outlet. The flow exiting the lake carved a 

channel down the 20° moraine slope and deposited 

a small fan of bouldery gravel and sand on top of 

deposits from the 1933 debris flow. Deposits from 

the second flow are traceable only to about 1.2 km 

from the breach.

East Bend Glacier

During maximum Neoglacial advances, East 

Bend Glacier4 covered about 0.24 km2 and was 

contiguous with Bend Glacier before diminishing 

to a separate ice mass of 0.07 km2 by 1990 (pi. 1). 

During retreat, a lake formed between the 

Neoglacial moraine and the calving glacier 

(fig. 15) at an altitude of 2,500 m. The date of lake 

formation is not known precisely. The lake

On early topographic maps, this small glacier in an east-facing 

cirque on Broken Top was labeled "Crook Glacier" (Hodge, 

1925; USGS 1932, Three Sisters, 30-min. Quadrangle). The 

name Crook Glacier, however, is now assigned on current 

USGS maps (USGS, 1959, Broken Top, 15-min. and USGS, 

1988, Broken Top, 7-1/2-min. Quadrangles) to a small glacier 

on the south side of Broken Top; the previous Crook Glacier is 

unnamed. In this report, this unnamed glacier is referred to as 

"East Bend Glacier."

apparently existed prior to 1928 (Phillips, 1938), 

and possibly formed after 1924 (no lake is 

mentioned in Hodge's [1925] report and 

topographic map of the Three Sisters/Broken Top 

region). At its largest, the lake contained 

340,000 m3 of water, had a maximum depth of 

18m (figs. 15, 16, and 17), and spilled over an 

outlet and down the steep distal slope of the 

moraine.

On October 7, 1966, 140,000 m3 of water was 

released and the lake-level lowered 4.4 m in 

conjunction with partial breaching of the moraine 

dam. The resulting debris flow flowed down an 

unnamed tributary, joining Crater Creek 6 km 

downstream from the breach. The debris flow 

continued down Crater Creek until it entered Soda 

Creek 1 km farther downstream. The debris flow 

followed Soda Creek for another 3 km until it 

spread out over the broad meadows near Sparks 

Lake (pi. 2; fig. 52). The flow was described in the 

Bend Bulletin (Oct. 10 and 11, 1966) and by Nolf 

(1966), both of whom summarized observations of 

reconnaissance trips to the source within a week 

after the event. The writers of these reports each 

speculated that erosion of the outlet was triggered 

by a wave caused by calving of a large block of ice 

into the lake. A photograph (Austin Post, U.S. 

Geological Survey photograph, 6615-47) taken a 

week before the release shows a large ice cornice 

overhanging the west edge of the lake. The lake did 

not completely empty; 200,000 m3 of water 

remains with a maximum depth of 13.7 m (figs. 15 

and 17). Downcutting at the outlet possibly was 

halted by several 0.5- to 2-m-diameter boulders 

that presently compose the outlet thalweg and 

margins.

Flow at the outlet evolved into a debris flow 

by entraining bouldery gravel from the Neoglacial 

moraine impounding the lake (fig. 53). The debris 

flow locally eroded bedrock in steeper reaches 

(fig. 54), whereas small fans and levees were 

deposited in wide and low-gradient reaches (pi. 2; 

figs. 52 and 55). Much of the initial debris flow 

was deposited upstream from the Crater Creek 

confluence, leaving little evidence of a large 

discharge along the channel between altitudes of 

1,950 and 1,830 m. The flow increased 

substantially, however, within the steep reach 

between the Crater Creek and Soda Creek

Debris Flows from Lakes Dammed by Neoglacial Moraines 65
-i 2,600

LU

LLI 2,500

LLJ 2,400

^ 2,300 

ffl 2,200

cc

LLJ

ILLJ

ti 

<

2,100

2,000

1,900

1,800

1,700

1,600

1,500

1 ' T 

'Breach 

<120m3/s-1

190-380

180m3/s

1 ' I ' I ' I ' I ' I r 

EAST BEND GLACIER DRAINAGE PROFILE

— - Erosion

-•--•-•- Deposition

20-40

170 mW Sparks Lake 

Meadow

0 10 11

DISTANCE, IN KILOMETERS

VERTICLE EXAGERRATION 5X

Figure 52. Longitudinal profile of the drainage from East Bend Glacier, Broken Top, into Sparks Lake, showing 

indirect discharge estimates obtained in this study and locations of mapped reaches of erosion and deposition during 

the October 7, 1966, debris flow and flood from the breach of the lake at the terminus of the glacier. The indirect 

discharge estimates are by the velocity-area and critical-flow methods. Critical-flow estimates are given as single 

values and inferred to be accurate to within ±50 percent. The velocity-area measurements are given as ranges.

W«^, i"';^':

^?€s ,^'

•Pfe^". ':*vX4?3j

•P^AVi ' e v - /•" ' . , v ^;3 «^

a*-. --': ,'. /^^-";x;^, "^C%1

%>•; ' / x " '^ " ^^^ •:;"

^^'SS^^I^^^Ai;,^*;:^

k~«**~aP -i^»' "-.*'*v >.' 1."' TV ^>,,* *: »-• '3 tt5" ^ ^'-i'^Yv'^4!*".;,* -•.- r-.-m*-*". ..,«- ,^,- . — • ^«"" 3fci' 5X £; B 'V^-^^^*"¥'***^S'

Figure 53. View of the October 7, 1966, breach in the Neoglacial moraine impounding the lake at the 

terminus of East Bend Glacier, Broken Top. The view is from near the base of the moraine, taken 

October 3, 1991. Note person standing on one of several large boulders at the present lake outlet.

66 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Figure 54. View of valley-bottom bedrock erosion about 1.6 kilometers downstream from breach of the 

East Bend glacial lake. Flow was left to right. Many of the 1- to 2-m clasts eroded from the jointed 

basaltic andesite flows along the channel bottom were deposited in the next several hundred meters 

downstream. Photograph taken August 15, 1988.

Figure 55. View downstream (southwest) of deposits left by the October 7, 1966, debris flow from the lake 

at the terminus of East Bend Glacier. The debris fan is about 500 m downstream of the eroded reach shown 

in figure 54. Part of the flow left the main channel, spilled over the divide to the west (to the right as 

viewed on this October 3, 1991 photograph), and rejoined the main channel 0.5 km downstream.

Debris Flows from Lakes Dammed by Neoglacial Moraines 67
confluences by incorporating trees, outwash, and 

colluvium from the steep valley slopes. Much of 

this debris was apparently provided by a mass 

movement of glaciofluvial sediment (about 

200,000 m3 ) triggered by undercutting of the valley 

side at an altitude of about 1,830 m.

At the Soda Creek confluence, the valley 

widens and the rejuvenated debris flow deposited 

levees and a large fan of woody debris and 

bouldery gravel, including boulders with diameters 

of at least 2 m (fig. 56). Downstream from the fan, 

flow transformed into sediment and wood-laden 

streamflow until debouching onto the meadow near 

the State Highway 46 crossing, burying the road 

and covering about 250,000 m2 of the meadow 

with sand and silt.

Seven indirect estimates of peak discharge 

along the flow route are consistent with the flow 

behavior outlined above (fig. 52). A maximum

possible discharge of 80 ±40 m3/s at the breach 

results from calculating the discharge associated 

with critical flow for conditions of a fully formed 

breach and maximum lake level. As with other lake 

releases, the actual maximum discharge at the 

breach probably was less. A velocity-area estimate 

of 190 to 380 m3/s at a cross-section 700 m from 

the outlet indicates that peak discharge had 

increased by a factor of at least 2, owing to 

entrainment of debris from the distal slope of the 

moraine. Two critical-flow estimates (150 and 

180 m3/s) calculated at cross sections measured 

within 2 km downstream from the 190 to 380 m3/s 

measurement are consistent with the low end of the 

velocity-area estimate.

Downstream, peak discharge greatly 

diminished below reaches of substantial deposition 

(pi. 2). A critical-flow estimate 4 km from the 

breach indicates a maximum discharge of 50 m3/s,

Figure 56. View upstream of a boulder and timber fan deposited by the October 7, 1966, debris flow from the 

lake at the terminus of East Bend Glacier, Broken Top. This site is 150 m downstream from the confluence of 

Soda and Crater Creeks. Photograph taken August 16, 1988.

68 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
and a velocity-area estimate at 6 km from the 

breach gives a peak-discharge estimate of 20 to 

40 m3/s. Farther downstream, after entraining 

substantial debris between the Crater Creek and 

Soda Creek confluences, peak discharge of the 

debris flow increased to close to its maximum 

value of 170 m3/s before ending on the Sparks 

Lake meadows 10 km from the breach (pi. 2; 

fig- 52).

The discharge values obtained in this study are 

consistent with two of three indirect estimates 

made by Laenen and others (1987) by 

superelevation and slope-area procedures. One 

superelevation measurement obtained by Laenen 

and others (1987) of 210 m3/s is substantially 

higher than adjacent estimates of 50 m3/s (criticalflow) and 20-40 m3/s (velocity-area) obtained by 

us. We found no field evidence for such changes in 

flow conditions between measurement sites. 

Therefore, we think the discharge attained was less 

than that estimated by Laenen and others (1987), 

but are uncertain as to the reasons for the 

discrepancy.

Sediment samples of the moraine, the original 

source of debris, and of four downstream deposits 

all have less than 1 percent clay (fig. 57) and have

o DC

LLJ 

D_

LU

=> 

O

0.01 

0.1

99.9

99.99

I I Range of deposit samples

- - - East Bend Neoglacial 

moraine sample

-4 

16

-2

4

2 4 6 8 phi 

0.25 0.0625 0.016 0.004mm

PARTICLE SIZE

Figure 57. Range of cumulative curves for four samples 

of matrix material and fine gravel (less than 32 mm) 

from the 1966 debris flow from East Bend Glacier, 

Broken Top. Also shown is the cumulative curve for a 

sample from the Neoglacial moraine that impounds the 

remnant lake. Data provided by K.M. Scott (USGS, 

written commun., 1991).

distributions similar to samples from the 1970 

Squaw Creek debris flow (fig. 36). In part, due to 

the small amount of silt- and clay-sized particles, 

the flow from East Bend Glacier behaved similarly 

to the Squaw Creek flow, transforming from a 

debris flow to sediment-laden streamflow where 

most of the coarse fraction was deposited at the 

pronounced gradient decrease 7.5 km from the 

breach.

Processes

Analysis of moraine dam failures and resulting 

debris flows in the Three Sisters and Mount 

Jefferson Wilderness Areas provides a basis for 

interpretation of some natural-dam-failure and 

debris-flow processes. Only limited conclusions 

can be gleaned from study of deposits as old as 50 

years, and indirect measurements and interpretation 

of stratigraphy and sedimentology do not fully 

replace direct observation and measurement. 

Nevertheless, observations of moraine-dam failures 

and large debris flows, reconstructed from geologic 

evidence, provide new information about many 

aspects of natural-dam failures and resulting flow 

behavior.

Magnitudes of 20th-century debris flows in 

the Three Sisters and Mount Jefferson Wilderness 

Areas varied widely. The largest debris flows 

traveled as far as 9 km, had peak discharges as 

great as 500 m3/s, and involved up to 1 million m3 

of debris and water. These flows were substantially 

larger and travelled farther than did the less than 

3-km-long debris flows typical of the densely 

forested Cascade Range and Coast Range 

watersheds in Washington and Oregon (Benda and 

Cundy, 1990). The size of the debris flows in the 

Three Sisters and Mount Jefferson Wilderness 

Areas is not unusual relative to other alpine debris 

flows in the Cascade Range (Gallino and Pierson, 

1985; Osterkamp and others, 1986; Walder and 

Driedger, 1994), and other alpine areas (Pierson, 

1980; Eisbacher and Clague, 1984; Jackson and 

others, 1989). The resulting debris flows from 

breached moraine dams are small, however, 

compared to Holocene Cascade Range debris flows 

caused by large volcano sector collapses and 

volcanic eruptions (Crandell, 1971; Pierson, 1985; 

Scott, 1988; Scott and others, 1992).

Debris Flows from Lakes Dammed by Neoglacial Moraines 69
Nonvolcanic debris flows in glacierized alpine 

environments are generated primarily by three 

mechanisms: (1) mass movement of debris into 

stream courses and consequent fluidization and 

downstream flow, (2) outburst floods of subglacial 

water accumulations, and (3) rapid release of 

moraine- and ice-dammed lakes. During the 19th 

and 20th centuries, incorporation of Neoglacial till 

and outwash has been a key factor in allowing 

water flows to evolve into debris flows in 

proglacial areas (Haeberli, 1983; Evans and 

Clague, 1993; Zimmerman and Mani, 1993; 

O'Connor and Costa, 1993; Walder and Driedger, 

1994). On steep Cascade Range volcanoes, the 

abundance of unconsolidated volcaniclastic 

deposits, locally reworked by glacial processes and 

then exposed by glacier retreat, further fosters 

debris-flow activity (Osterkamp and others, 1986). 

Incorporation of Neoglacial till and outwash 

appears to have been an important factor for 

formation of all the alpine debris flows studied in 

the Three Sisters and Mount Jefferson Wilderness 

Areas.

Breaching of Moraine Dams

Moraine dams are especially susceptible to 

rapid failure because (1) they are composed of 

loose silt, sand, and gravel, and contain less than 

3 percent clay (fig. 58), (2) deep lakes can form 

behind moraine dams and exert significant 

hydrostatic forces, (3) width-to-height ratios of 

moraine dams are usually small, and (4) outlet 

slopes are generally steep, on the order of 10° to 

30° (Costa and Schuster, 1988; Clague and Evans, 

1994). Some moraines contain ice cores and 

melting of these cores possibly contributes to 

failure (Costa and Schuster, 1988; Reynolds, 1992). 

Moraine dams, similar to other types of natural and 

constructed dams, generally fail either by 

overtopping, piping, or gravitational collapse 

(Costa and Schuster, 1988; Reynolds, 1992). There 

are few direct observations of moraine dam 

failures; consequently, most conclusions regarding 

initiation mechanisms are inferences from field 

observations after the event.

0.001

0.01

0.1

5 i

CJ 

DC 

LLJ 

Q_

01 10

< 30

^ 50

0 70

90

99

— — Diller Glacier

———— East Bend Glacier

———. Collier Glacier

Boulders .Cobbles

-10 

1024 256

-6 

64

-4 

16

-2

4

2

0.25

4

0.063

6

0.016

CJ 

CC

1Z

8

4 

0

12

8

4 

0

12

8

4 

0 ——————————

- -

if

j-.

-

T"

— -

T

"-i Diller

Glacier

TMtk_ ,

-, I-,

-

East Bend

._, Glacier

TlmT^ ,

Collier

- Glacier

Ifl Trm ,

-10 -50 5 10 phi

1024 32 1 0.031 0.001 mm

PARTICLE SIZE

8 phi 

0.004 mm

PARTICLE SIZE

Figure 58. Cumulative curves of particle sizes for three Neoglacial moraines in the Three Sisters Wilderness Area. 

Following the procedure described by Scott (1988, p. 22), particle-size distributions were determined by field 

measurements of clasts greater than 2 mm combined with laboratory measurements of the sand, silt, and clay 

fractions.

70 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Overtopping is by far the most common 

mechanism cited for breaching of moraine dams 

(Evans, 1987; Costa and Schuster, 1988). Ice falls, 

rockfalls, and avalanches into the lake frequently 

are cited as causing large displacement waves that 

exit the outlet, temporarily increasing the 

discharge, and eroding the outlet channel 

(Lliboutry and others, 1977; Blown and Church, 

1985; Evans, 1987; Ding andLiu, 1992; Reynolds, 

1992). Piping was a factor in only a few failures 

(Yesenov and Degovets, 1979). In the Cordillera 

Blanca of Peru, a 1970 breach was triggered by 

piping following an earthquake (Lliboutry and 

others, 1977).

Several models exist to help evaluate wave 

heights as the consequence of avalanches of 

material into lakes (Noda, 1970; Slingerland and 

Voight, 1979). Unfortunately, these models require 

estimates of avalanche volume and velocity in 

addition to lake geometry. Estimates of avalanche 

dimensions and velocities prior to a failure are 

difficult to obtain, and it is uncertain that wave 

height alone is responsible for initiating failure of 

Neoglacial moraine dams. Temporary increases in 

the outlet discharge by other means, such as rapid 

snowmelt, rainfall (Lliboutry and others, 1977), or 

sudden releases of subglacial water, also possibly 

lead to erosion of the outlet and initiation of failure 

(Blown and Church, 1985; Evans, 1987; Costa and 

Schuster, 1988; Reynolds, 1992).

It is uncertain what triggered the moraine-dam 

failures in the central Oregon Cascade Range; no 

single mechanism is likely to have produced all the 

failures. The August 12, 1933, and August 21, 

1934, debris flows from lakes at the termini of 

Eugene Glacier on South Sister and Whitewater 

Glacier on Mount Jefferson resulted from release 

of short-lived lakes during a several-year period of 

exceptionally warm temperatures (fig. 13) and 

rapid glacier retreat (fig. 8). Such dynamic 

conditions, involving rapidly melting glaciers and 

associated calving and avalanching, probably lead 

to increased runoff and/or large wave formation 

that can cause moraine-dam failures. This sequence 

may also be true for the July 1942 flow down 

White Branch Creek from the lake at the terminus 

of Collier Glacier, Middle Sister. The lake had 

grown rapidly from its inception in 1934 and 

reached its maximum size in 1940 (fig. 12).

In contrast, lakes at the termini of Jack, Diller, 

and East Bend Glaciers drained after several 

decades of stable termini and lake levels (fig. 16), 

indicating that these failures may have been 

unrelated to general changes in lake or glacier 

conditions. Glaciers terminated at the margins of 

all three lakes at the time of failure, suggesting the 

possibility that large blocks of ice calved into the 

lake, forming waves that triggered erosion of the 

outlet. Nolf (1966) speculated that glacier calving 

was the cause of the October 7, 1966, debris flow 

from the lake at the terminus of East Bend Glacier. 

Another possible triggering mechanism for the 

drainage of lakes is rockfall or icefall. Like many 

Neoglacial-age moraine-dammed lakes, the lakes at 

the termini of East Bend and Jack Glaciers lie at 

the base of steep cirque headwalls composed of 

weathered and hydrothermally altered volcanic 

breccia and thin lava flows. Mass movements of 

ice or rock from these slopes could have caused 

waves that led to partial releases of these lakes.

Dam failures may also be caused by rainfall. 

Failure of the moraine impounding the lake at the 

terminus of Diller Glacier on September 7, 1970, 

was probably triggered by precipi-tation. 

According to records at Santiam Pass, 30 km north 

of Middle Sister, 33 mm of rain fell on 

September 7, culminating a 5-day total of 80 mm. 

Similar precipitation over the 1.2 km2 contributing 

area for the lake at the terminus of Diller Glacier 

would equal about 30 percent of the maximum lake 

volume. Consequently, flow through the lake outlet 

was undoubtedly greater than normal and perhaps 

triggered erosion of the steep outlet channel.

Only one observation of a moraine-dam failure 

and resulting dam-break flood has been reported. 

At Laguna Jancarurish in the Cordillera Blanca of 

Peru, engineers were attempting to lower the lake 

level in 1949 when part of an ice apron flanking 

the lake calved, creating large waves that 

overflowed and destroyed the temporary gate at the 

outlet. According to Lliboutry and others (1977, 

p. 250), "there was fast regressive erosion of the 

moraine,... a waterfall formed, which widened 

while moving towards the lake. Finally the moraine 

around the gate failed and the big alluvion ... took 

place." Similarly, for all the lake releases in the 

Three Sisters and Mount Jefferson Wilderness 

areas, initial erosion during a moraine-dam failure

Debris Flows from Lakes Dammed by Neoglacial Moraines 71
probably began on the steep outer moraine slopes. 

Retrograde erosion is probably an important 

mechanism for breach enlargement. A knickpoint 

or series of knickpoints proceeds up the channel, 

ultimately deepening the outlet at the lake, which 

in turn further increases flow and accelerates 

erosion. Breaches enlarge, usually forming a 

parabolic or triangular cross section (fig. 59), until

either the lake drains completely (for example the 

1970 Diller Glacier/Squaw Creek release) or 

erosion of the outlet ceases and the lake stabilizes 

at a lower level. A photograph (Nolf, 1966), taken 

days after the partial emptying of the lake at the 

terminus of East Bend Glacier, Broken Top, helps 

illustrate the process. The photograph shows that 

within a few meters of the lake outlet, a 3- to 5-mcc

LLJ 

ILJJ

!_- 15 

5 10

LU

10 20 30 40

r i i i i r i i

Collier 

Glacier

i i

10

I I I I

20 30 40 50

I I I I I I I

20

10

cc

LU\-

LJJ

East Bend Glacier

I I i i i i i i i i i

i i i i i i i i i i i i

— 30

K

I 

(D 

LJJ 20

I

10

Diller Glacier

i i i i i

10 20 30 40 50 60 70

DISTANCE, IN METERS

80 90 100

Figure 59. Breach cross sections and previous lake levels (indicated by dashed lines) at four sites of morainedammed lake releases in the Three Sisters and Mount Jefferson Wilderness Areas. Most breaches have parabolic 

or triangular shapes, generally with side slopes of 25° to 45°. No vertical exaggeration; datums are arbitrary.

72 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
high waterfall tumbles down the outlet channel, 

apparently the last in a series of knickpoints that 

migrated up-channel during the lake release. This 

knickpoint halted just meters from the lake outlet, 

probably preventing complete emptying of the 

lake. Subsequently, slumping and hillslope debris 

from the banks of the outlet filled the channel 

downstream from the waterfall, increasing the 

present stability of the outlet. Similar knickpoints 

were observed in the channel of White Branch 

Creek after the 1942 breach (Ruth Hobson Keen, 

oralcommun., 1995).

Similar to the 1966 Broken Top release from 

the lake at East Bend Glacier, other moraine-dam 

failures in the central Oregon Cascade Range did 

not result in complete lake drainage, for example 

the 1942 flow down White Branch Creek, and two 

releases from the lake at the terminus of Jack 

Glacier. The thalwegs of the present lake outlets at 

Broken Top and Three Fingered Jack are paved 

with cobbles and boulders, many with diameters 

about 1 m, indicating that armoring of the breach 

thalweg inhibited erosion of the outlet during 

previous releases.

As noted in the eyewitness account of the 

moraine-dam failure in Peru, moraine dams can fail 

very rapidly. Hydraulic reconstruction of the 1970 

Squaw Creek (Diller Glacier) debris flow led 

Laenen and others (1992) to conclude that the 

22.4-m-deep breach was fully formed in about 

5 minutes. A similar analysis for a moraine-dam 

failure in Great Britain resulted in an estimate of 

24 minutes for erosion of a 10-m-deep breach 

(Carling and Glaister, 1987). As described above, 

the 1942 lake release down White Branch must 

have entrained a large volume of debris in only a 

few minutes, implying that the 5.4 m breach eroded 

quite rapidly. These rates are broadly similar and 

perhaps greater than the vertical erosion rates of 

0.03 to 1.34 m/min documented during earthendam failures (Froehlich, 1987; Walder and 

O'Connor, 1997).

The peak discharge and duration of flow 

exiting a breaching dam depends on the erosion 

rate, size and shape of the breach, and the 

hypsometry of the lake behind the dam. In general, 

erosion of natural dams, once started, proceeds 

rapidly and hydrographs of most types of natural 

dam failures are quite peaked (Costa, 1988). This

was true for the 1970 flow down Squaw Creek, 

where peak discharge was attained 10 minutes after 

flow onset (fig. 44). Because critical flow over a 

weir, analogous to flow exiting a lake through a 

steep outlet, is a power function of the elevation 

difference between the lake surface and outlet 

thalweg (discharge is proportional to the depth at 

the outlet to the 1.5 power), minor differences in 

the interplay between the vertical erosion rate at 

the outlet and lake hypsometry can substantially 

affect the peak discharge and shape of the outflow 

hydrograph (Walder and O'Connor, 1997).

Downstream Flow Characteristics

The presence of channels flanked by bouldery 

levees and fans of poorly sorted mud and debris is 

compelling evidence that the lake releases evolved 

from clear water streamflow at the outlets into 

rubbly debris flows within a few hundred meters. 

Flow bulking (Scott, 1988, p. A6) was apparently 

due to incorporation of till and outwash from the 

outer moraine slopes and enlargement of outlet 

channels. Scallop-shaped reentrants into moraines 

that flank the present outlet channels of lakes that 

have emptied (fig. 31) are evidence that mass 

movement of till into the flow was an important 

mechanism of introducing debris into the flow. 

David Rasmussen (U.S. Forest Service, oral 

commun., 1994) visited the site of the 1966 release 

of the lake at the terminus of East Bend Glacier, 

Broken Top, and recalls that the moraine slopes 

above the eroded channel were extremely unstable, 

and continual mass wasting of debris into the 

channel near the outlet prevented him from 

proceeding up the channel. Although difficult to 

prove, mass movements from the channel margins 

and channel knickpoint retreat likely were the 

primary mechanisms of introducing debris into all 

these flows.

For the larger flows in the Three Sisters 

Wilderness Area, addition of sediment resulted in 

debris flows with substantially larger volumes and 

peak discharges than could be provided solely by 

the water in the impounded lakes. The 1942 release 

of the lake at the terminus of Collier Glacier 

incorporated 120,000 m3 of till and outwash within 

the first kilometer from the outlet, increasing the 

total flow volume by 25 percent and increasing the

Debris Flows from Lakes Dammed by Neoglacial Moraines 73
peak discharge from 140 m3/s to about 500 m3/s 

(figs. 32 and 35). Similar magnitudes of flow 

bulking probably occurred during partial drainage 

of the lake at East Bend Glacier, Broken Top, 

where outflow increased from less than 80 m3/s at 

the outlet to at least 190 m3/s 0.5 km downstream, 

and at Diller Glacier, Middle Sister, where 

130,000 m3 of the impounding moraine was eroded 

during drainage of the 320,000 m3 lake.

Direct measurements and observations of 

debris flows started by controlled releases from a 

moraine-dammed lake at the Chemolgan DebrisFlow Testing Ground, Kazakhstan, provide support 

to the indirect observations in the Three Sisters 

Wilderness Area (Khegai and others, 1992). 

Release of 400,000 m3 of clear water at a peak 

discharge of 22 m3/s resulted in a downstream 

debris flow of substantially larger volume and a 

peak discharge of 150 to 200 m3/s. The measured 

debris flow hydrograph (fig. 60) portrays an almost 

instantaneous rise to a peak discharge of 150 to 

200 m3/s, followed by a series of about seven 

surges of gradually decreasing peak discharge. The 

flow front travelled downstream at 4 to 8 m/s. Like 

flows in the Three Sisters and Mount Jefferson 

Wilderness Areas, the source of debris is

250

in 

cc

LU 200 -

^

O Q

§ O 150 - 

U O

Z a)

(D o. 

CC

<

IE 

U

100 -

50 -

Maximum outlet (water)

discharge: 22 m3/s 

Maximum debris flow

discharge:

150-200 m3/s 

Velocity of debris flow

front: 4-8 m/s 

Mean density of debris .

flow:1970kg/m3

1,000 2,000 

TIME, IN SECONDS

3,000

Figure 60. Hydrographs and debris flow characteristics 

at the Chenolgan Debris Flow Testing Ground, 

Kazakhstan, during a September 12, 1991, experiment. 

"A" is the hydrograph at the outlet. "/?" is the debris 

flow hydrograph measured approximately 1 km 

downstream. Modified from Khegai and others (1992).

Quaternary glacial deposits introduced into the 

flow from the margins of the eroding outlet 

channel.

Similar conclusions were reached from 

analysis of debris flows that have been triggered by 

water flows in other environments. The 

commonality is an abundance of loose debris on 

steep slopes. Examples are primarily from 

mountainous environments and include flows 

started by natural dam failures (Yesenov and 

Degovets, 1979; Haeberli, 1983; Blown and 

Church, 1985; Scott, 1988), high rainfall or 

cascading streamflow on weak, sheared rock 

(Fryxell and Horberg, 1943; Pierson, 1980; Webb, 

1993), glacial outburst floods (Jackson and others, 

1989; Haeberli, 1983; Walder and Driedger, 1994), 

and debris flows started by meltwater from 

volcanic eruptions on snow-covered volcanoes 

(Waitt and others, 1983; Pierson and Scott, 1985).

The largest debris flows in the Three Sisters 

and Mount Jefferson Wilderness Areas continued 

several kilometers downstream from outlet areas, 

eroded channel margins along steep and narrow 

reaches, and deposited sediment in wider and 

lower-gradient reaches. Erosion and flow bulking, 

judging from scoured channel banks and thalwegs, 

was dominantly in reaches where channel thalweg 

gradient exceeded 8° (fig. 61). Reaches of net 

erosion are generally near the release points where 

gradient is high, the channels are bounded by 

unconsolidated till and outwash, and hillslopes are 

sparsely forested. Flows, such as the 1966 Soda 

Creek debris flow, were locally enlarged by mass 

movements entering at sites of channel 

undercutting.

Deposition occurred primarily in reaches of 

gradients less than 8°, but also occurred locally in 

channel expansions and on fans with slopes as 

great as 18° (fig. 61). In lower reaches, where 

woody debris was abundant in the flow and in 

overbank areas, extensive overbank deposition was 

aided by log and boulder jams formed behind 

standing trees. Similar gradient values for erosional 

and depositional slopes have been measured for 

rubbly debris flows in New Zealand 

(Pierson, 1980), Japan (Ikeya, 1981), Canada 

(VanDine, 1985; Jackson and others, 1989; Clague 

and Evans, 1994), the Rocky Mountains in 

Colorado (Curry, 1966), and in the Cascade and

74 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Coast Ranges of Washington and Oregon (Benda, 

1990; Walder and Driedger, 1994).

On sustained gradients of 4° or less, cobbles 

and boulders were rapidly deposited and all flows 

ceased behaving like debris flows. Nevertheless, 

flow records, newspaper reports, and deposit 

sedimentology of the 1933 Separation Creek and 

1970 Squaw Creek flows indicate that substantial 

sediment-laden streamflow continued downstream 

from the debris flows, probably as 

hyperconcentrated streamflow (Pierson and Scott, 

1985). As described above, the gaged volume of 

the Squaw Creek flood wave downstream of the 

transformation from debris flow to streamflow was 

about a third of the water released by the lake, 

indicating that a substantial volume of water was 

temporarily retained with the deposits left by the 

debris flow or percolated into fan and channel 

bottoms.

Deposits of the Squaw Creek and Soda Creek 

debris flows have clay contents of less than 

1 percent (figs. 45 and 57) indicating that these 

flows were noncohesive; hence, they were 

susceptible to rapid flow transformations (Scott, 

1988, p. 71). Accordingly, both of these flows 

evolved from debris flow to sediment- and debrisladen streamflow at pronounced gradient decreases 

about 7 to 9 km from the lake outlets. Qualitative 

observations of the deposits from the debris flows 

on the north flank of Mount Jefferson, on Three 

Fingered Jack, and the 1933 Separation Creek flow 

indicate that these flows were noncohesive and 

transformed rapidly to sediment-laden streamflow 

at locations of substantial gradient decrease. In 

contrast, the 1942 White Branch flow deposits 

have clay contents as high as 6 percent (fig. 37), 

indicating a more cohesive flow.

40

35

30

25

20

LU 

o

LU

D 

O

O 15 

O

10

5

0

Erosional reaches 

Conveyance reaches 

Depositional reaches

ll

10 12 14 

SLOPE, IN DEGREES

16 18 20

Figure 61. Histogram of channel slopes associated with reaches of deposition, erosion, and conveyance (no obvious 

evidence of erosion or deposition) for the debris flows on White Branch (Collier Glacier), Squaw Creek (Diller 

Glacier), Separation Creek (Eugene Glacier), and Soda Creek (East Bend Glacier). Channel slopes were measured for 

the entire length of each debris flow and were compiled on the basis of channel subdivisions defined by 40-foot 

contour intervals on topographic maps. Reaches of erosion and deposition were mapped in the field. Slopes were 

determined from l:24,000-scale topographic maps and field measurements.

Debris Flows from Lakes Dammed by Neoglacial Moraines 75
Downstream patterns in discharge, 

sedimentology, and clast lithology indicate that 

there were substantial interactions between the 

debris flows and the valley floors and channel 

substrates, and that these interactions were largely 

controlled by behavior of the coarse clasts within 

the debris flows. The noncohesive debris flows 

transformed into sediment-laden streamflow only 

after deposition of the coarse faction of the 

sediment load. Deposition of large clasts in 

channel reaches of less than 8° (fig. 61) indicates 

that continued downstream flow in the form of a 

debris flow in these channels requires either a 

channel slope consistently greater than about 8° in 

order to maintain coarse clast transport or local 

introduction of large clasts along the flow route. 

The varied abundance and lithology of coarse 

clasts along the flow routes indicate that 

introduction of large clasts was indeed an 

important process. The coarse phase of the flow 

also influenced deposition. Bouldery dams fostered 

deposition, especially in forested overbank areas, 

and completely plugged smaller channels with 

lobate deposits. In contrast, the fine-grained 

component of the debris flows apparently 

remained constant for the lengths of the flows.

These conclusions regarding flow behavior 

are consistent with flow processes observed during 

alpine debris flows. Pierson (1980) witnessed 

several rubbly debris flows at Mount Thomas, 

New Zealand, noting that large boulders were 

suspended in a slurry with a consistency of "wet 

concrete." According to Pierson (1980), cobbles 

and boulders were concentrated at the flow fronts 

during flow pulses, and were forced laterally by 

internal flow sorting processes to form levees, 

thereby narrowing the channel. Channel 

downcutting was accomplished by headward 

migration of knickpoints, and channel widening 

resulted from undercutting and slumping of the 

channel banks into the flow.

EVALUATION OF HAZARDS 

FROM MORAINE-DAMMED LAKE 

BREAKOUTS

At many locations, floods and debris flows 

from moraine-dammed lakes pose a serious hazard 

(Lliboutry and others, 1977; Evans, 1987; Laenen

and others, 1992; Ding and Liu, 1992). Assessing 

this hazard is difficult because formation of 

moraine-dammed lakes can depend on interacting 

and temporally changing factors such as century- to 

daily-scale changes in climate and weather, glacier 

behavior, and local topographic setting. Rapid 

release of lakes, once formed, can be caused by 

changes in the above factors or triggered by quasirandom events such as weather, rock and ice 

avalanches, and earthquakes. The downstream flow 

from a moraine-dam failure is influenced by the 

volume and rate of water released, downstream 

channel morphology, and interaction of the flow 

with the channel and adjacent banks. These varied 

factors conspire against accurate and precise 

statements of the likelihood and magnitude of 

downstream hazards from moraine-dammed lakes.

Nevertheless, qualitative assessments of 

hazards from moraine-dammed lake releases are 

possible. Worldwide, there have been several 

preliminary assessments of hazards from morainedammed lakes, mostly in regions such as the 

Himalayas and the Andes, where there has been 

interest in developing hydroelectric facilities in 

glacierized basins and where past floods from 

moraine-dammed lakes have been lethal. As a first 

step, most of these assessments are an inventory of 

moraine-dammed lakes (Lliboutry and others, 

1977; Ives, L986, p. 34-34; Liu and Sharma, 1988; 

Ding and Liu, 1992). For the Cascade Range of 

Oregon and Washington, we have compiled a 

similar inventory, primarily on the basis of aerialphotograph reconnaissance of lakes that are at least 

partly dammed by Neoglacial moraines (table I).

Assessing Potential Failure of 

Moraine Dams

Topographic Setting

An evaluation of topographic setting of a 

moraine-dammed lake can provide a preliminary 

assessment of the potential for rapid release 

(Lliboutry and others, 1977; Ding and Liu, 1992; 

Clague and Evans, 1994). Dams with lakes that 

have surficial outlets on steep moraine slopes are 

more likely than other types to fail because of the 

high potential for overtopping and retrograde 

erosion of the outer moraine slope. The amount of

76 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
freeboard and the slope of the moraine 

impoundment also are critical and easily assessed 

factors. Many overtopping failures are triggered by 

waves generated by mass movements into the lake 

(Blown and Church, 1985; Reynolds, 1992). The 

types of triggering mass movements likely include 

rockfall, ice avalanches, and ice calving. 

Consequently, moraine-dammed lakes that are 

located at the base of steep cirques, or have steep 

glaciers above or calving into the lake, are 

susceptible to rapid release (fig. 62).

In the Three Sisters and Mount Jefferson 

Wilderness Areas, seven lakes presently have 

surface areas greater than 5,000 m2 (table 1). The 

lakes at the termini of Jack, Prouty (Carver Lake), 

and East Bend Glaciers have steep surface outlets 

and sit below steep, unstable edifices (figs. 15 and 

63). The Chambers Lakes (pi. 1; fig. 15) and the 

lake at the terminus of Thayer Glacier (fig. 15) have 

low-gradient or subsurface outlets with up to 25 m 

of freeboard (fig. 63). Additionally, although the 

present drainage of Collier Glacier is through the 

"melthole," a closed basin still could contain 

160,000 m3 of water if subsurface drainage ceased 

and the lake filled to the outlet. Considering the 

present conditions, the moraines impounding 

Carver Lake and the lakes at the termini of East 

Bend and Jack Glaciers appear most susceptible to 

failure owing to steep outlet channels and high 

potential for rock or icefall into the lakes. If 

hydrologic/glaciologic conditions change, it is 

possible that Chambers Lake No. 1 and the basins 

at the termini of Thayer and Collier Glaciers could 

fill with water, increasing the potential for rapid 

release. This assessment considers only the 

potential for failure by overtopping. Any of these 

lakes, whether they have freeboard or not, could 

empty rapidly as a result of piping or mass wasting 

of the moraine dams.

Quantitatively assessing the likelihood and 

timing of potential moraine-dam failure is difficult. 

Accurate geotechnical assessment of moraine dams 

depends on knowledge of the internal moraine 

structure and sedimentology—details that are 

difficult to determine (Reynolds, 1992). 

Furthermore, triggering mechanisms, such as 

rockfall, icefall, and rainstorms, are unpredictable 

and occur in the background of climatologic, 

glaciologic, and hydrologic changes. Nevertheless,

all 50 northern hemisphere moraine-dam failures 

with known dates occurred during the July through 

October melt season, and 39 of 49 were during July 

and August (table 2). In the central Oregon 

Cascade Range, the frequency of moraine-dam 

failures is decreasing. Most moraine-dam failures 

occurred in the 1930's and 1940's, soon after the 

period of rapid glacier retreat and lake formation 

(fig. 64). The presence of lakes dammed by late 

Pleistocene moraines (for example Camp Lake and 

Moraine Lake in the Three Sisters Wilderness 

Area) indicates that lakes can remain stable for 

thousands of years, especially if they are in settings 

removed from failure-triggering processes such as 

rockfall or icefall.

Likelihood of Future Breaches in the 

Central Oregon Cascade Range

If climatologic, glaciologic, and hydrologic 

conditions do not change substantially, the rate of 

moraine-dam failure in the Three Sisters and 

Mount Jefferson Wilderness Areas likely will 

continue to decrease. If, however, conditions 

change rapidly, the potential for failure could 

increase. More specifically, if glaciers retreat 

rapidly, ice avalanches or rockfall could become 

more common (Evans and Clague, 1993; 

O'Connor and Costa, 1993), increasing the 

frequency of processes that trigger lake releases. 

Given these conditions, the moraine dams 

impounding Carver Lake and the lakes at the 

termini of Jack and East Bend Glaciers appear to 

be highly susceptible to failure. If climate 

conditions change to foster glacier advance, and 

especially if glaciers reenter lakes, the potential for 

calving ice to trigger moraine failures will increase. 

Also, the increased hydrologic flux associated with 

larger glaciers could lead to (1) erosion of outlets 

and (2) increasing lake volumes and decreasing 

freeboard for lake basins not presently draining 

subaerially. In particular, increased lake volume 

would substantially increase the hazard posed by 

the lake at the terminus of Thayer Glacier because 

of its steep outlet (fig. 63). Considering longerterm possibilities, if glaciers advance to the extent 

that late-Neoglacial moraines are reoccupied, the 

present lake bodies will be displaced, and the stage 

would be set for a new round of moraine-dammed 

lake formation and failure upon glacier retreat.

Evaluation of Hazards from Moraine-Dammed Lake Breakouts 77
A. Most dangerous (release potential 1)

Mountain

Moraine

B. Less dangerous (release potential 2)

C. Least dangerous {release potential 3)

Figure 62. Schematic illustration of topographic-setting criteria for qualitative assessment of the potential of a 

moraine-dam breach. A, Most dangerous situation of a steep glacier calving into a brimful moraine-dammed 

lake (similar to the present setting at Carver Lake and the settings at East Bend Glacier and Diller Glacier 

before breaching). B, Less dangerous settings of (1) a presently unglacierized, but steep, cirque above a 

brimful moraine-dammed lake (similar to present situation at "Jack" Glacier), or (2) a glacierized cirque above 

a moraine-dammed lake that does not drain over the moraine crest (similar to present setting at the terminus of 

Thayer Glacier). C, Least dangerous situation of a presently unglacierized valley above a moraine-dammed 

lake that does not drain over the moraine crest (similar to present setting of Chambers Lake No. 1).

78 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Assessing Downstream Flow 

Hazards

Beyond questions of "if and "when" a 

particular moraine dam might fail is the issue of 

determining the downstream hazards from a 

resulting flow. Assessing downstream hazards from 

dam failures has been a subject of substantial 

research and model development, especially for 

constructed dams (Land, 1980; Ponce and 

Tsivoglou, 1981; Hunt, 1984; Singh and Quiroga, 

1987; Quiroga and Singh, 1987; Fread, 1988; 

Macchione and Sirangelo, 1990), but also for

natural dams (see Costa, 1988; Costa and Schuster, 

1988; Clague and Evans, 1994, for summaries). 

Most quantitative hazard assessments of dam-break 

floods consist of two aspects: (1) determining of 

the outflow hydrograph at the breach and 

(2) routing floods downstream.

The Outflow Hydrograph at the Breach

The rate of outflow from a failing dam 

ultimately depends on the rate and extent of breach 

growth, breach shape, and basin hypsometry 

(Walder and O'Connor, 1997). Breach growth and

2,500

2,250

2,000

1,750 

4,000 

3,500 

3,000 

2,500 

2,000

P 4,000 

3,500 

3,000 

2,500 

2,000

HI 

HI

HI (/)

HI

O

CD

DC 

HI

HI

JACK GLACIER PROFILE

J"hree Fingered

Jack 2,390 meters

•— 1993 lake level and

outlet 

~~ Glacier basal profile

Lake

250 500 750 1,000 1,250 1,500

CHAMBERS LAKES PROFILE

South Sister 

3,157 meters 1992 lake level

Carver Glacier

* Neoglacial moraines

Lake #3 

/ /Lake #1

0 1,000 2,000 3,000 4,000

- North Sister 

3,074 meters

COLLIER GLACIER PROFILE

..... Dry outlet

— — Glacier basal profile

-— North Sister profile above

the east side of Collier Glacier

1,000 2,000 3,000 

DISTANCE IN METERS

4,000

3,100

2,900

2,700

2,500

2,300

2,100

3,500

3,250

3,000

2,750

2,500

2,250

2,000

3,000

2,750

2,500

2,250

North Sister THAYER GLACIER PROFILE

.3,073 meters

-. 19?? lake 

level an

— Glacier basal profile

, Lake 

level and outlet ^-==->t.J-r»v^ springs

0 500 1,000 1,500 2,000

South Sister 

3,157 meters

PROUTY GLACIER PROFILE

1993 lake and outlet profile 

Glacier basal profile

0 500 1,000 1,500 2,000 2,500 3,000

EAST BEND GLACIER PROFILE

Broken Top, east peak

2,730 meters

— ••• 1993 lake level and outlet

— — Glacier basal profile

Lake

250 500 750 1,000 1,250 1,500 

DISTANCE IN METERS

Figure 63. Present topographic profiles for the five largest moraine-dammed lakes in the Three Sisters and 

Mount Jefferson Wilderness Areas, and for Collier Glacier and adjacent basin, where there is potential for a morainedammed lake. Datum for horizontal scale is arbitrary.

Evaluation of Hazards from Moraine-Dammed Lake Breakouts 79
shape are difficult to predict accurately, but are 

usually the most important factors in determining 

the outflow hydrograph for moraine-dam failures. 

Because most moraine-dammed lakes are on steep 

slopes, their volumes are relatively small compared 

to depths; consequently, lake levels lower rapidly 

as outflow increases. Discharge from the lake, 

assuming critical flow at the breach and ignoring 

negative waves propagating from the outlet, 

depends on the elevation difference between the 

lowering lake surface and the breach thalweg at the 

outlet. Depending on breach shape, discharge 

increases at a rate that exceeds the 1.5 power of the 

elevation difference between the lake surface and 

breach bottom (Walder and O'Connor, 1997). 

Consequently, for outlets that erode slowly, the 

elevation difference between lake surface and 

breach thalweg remains small and peak discharge 

is small. In contrast, if the outlet erodes quickly, a 

large elevation difference will form between the 

water surface and breach thalweg, and a much 

larger peak discharge will result. For large lakes, 

breaches are likely to form completely prior to 

significant drawdown. In this situation, the peak

U

z

LLJ

D

o

LLJ 

DC

Lake formation 

Lake breakout

1920's 1930's 1940's 1950's 1960's 1970's 1980's 1990's 

DECADE

Figure 64. Decadal incidence of formation and 

breaching of Neoglacial moraine-dammed lakes in the 

Three Sisters and Mount Jefferson Wilderness Areas. 

For lake formation times and for breaches of that could 

not be constrained to particular decades (formation of 

Chambers Lake No. 2 and the lakes at the termini of 

Thayer and Waldo Glaciers, and the first releases from 

the lakes at the termini of Waldo and Jack Glaciers), 

occurrence is plotted by assuming formation or breach 

to have been within the decade deemed most likely on 

basis of available information. Plot based on data 

portrayed in figure 16 and additional information for 

Waldo Glacier on Mount Jefferson (described in text).

discharge is more a function of breach shape than 

rate of growth. Using a simplified formulation of 

this process developed by Walder and O'Connor 

(1997), we have developed hypothetical 

hydrographs illustrating the sensitivity of breach 

hydrographs to breach geometry and breach 

erosion rate for several lake basins in the Three 

Sisters and Mount Jefferson Wilderness Areas 

(figs. 65 and 66).

More-complex physically based mathematical 

models of breach erosion have been developed 

recently by Ponce and Tsivoglou (1981) and Fread 

(1987). The models are similar in that they predict 

breach size, shape, and rate of growth by coupling 

lake inflow, outflow, and sediment transport 

associated with a growing outlet channel. The 

models use variations of the Meyer-Peter and 

Muller (1948) sediment-transport relation to 

calculate the sediment eroded by the breach 

channel and resulting rate of growth. The 

BREACH model (Fread, 1987) further considers 

mass wasting of the outlet sides as a mechanism of 

breach enlargement. It is not clear, however, if 

bedload-transport relations of the model simulate 

conditions in a growing breach more accurately 

than simple parameterization of an overall erosion 

rate on the basis of empirical data (Walder and 

O'Connor, 1997). The Meyer-Peter and Muller 

bedload-transport relation is based on 

measurements of sand and gravel (the largest clast 

size analyzed was 28.6 mm) transport in a flume 

under conditions of steady or gradually varied 

flow. Conditions at an eroding outlet, however, are 

much more complex. Flow is nonuniform and 

rapidly varying, slopes are steeper, and ranges of 

particle sizes are larger. Field observations of the 

overtopping of landslide dams (Costa and Schuster, 

1988) suggest that the assumption of the physical 

process of lowering the outlet thalweg from grainby-grain entrainment in a vertical fashion may be 

incorrect. Retrogressive erosion of knickpoints by 

headcut retreat from the toe of the dam toward the 

dam crest appears to be an important process, and 

one that is likely to be more difficult to reliably 

model.

A further complicating factor for prediction of 

potential downstream flow conditions and hazard 

analysis is that breach growth commonly ceases 

prior to complete evacuation of the impounded

80 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Breach side slope = 26.6 -

4m/min ——— Breach side slope = 11.3 =

1,500 3,000 4,500 6,000 7,500 9,000 

TIME, IN SECONDS

Figure 65. Effects of breach shape, erosion rate, and 

lake hypsometry on calculated hydrographs. 

Hydrographs are calculated on the basis of formulation 

in Walder and O'Connor (1997). In all cases, lake 

volume is assumed to be linearly related to the third 

power of lake depth, and the entire lake volume is 

released during the breach. A, Effects of breach shape 

and erosion rate for a lake with a volume and geometry 

similar to Carver Lake (volume 933,000 m3 ; maximum 

depth 36 m). Solid lines represent hydrographs for a 

triangular-shaped breach cross section with side slopes 

of 26.6° and vertical erosion rates of 4.0, 1.0, and 

0.25 m/min. Dashed lines are hydrogiaphs for the same 

lake volume and erosion rates, but with breach side 

slopes of 11.3°. B, Effects of lake hypsometry and 

erosion rate for a 1,000,000 m3 lake with a triangularshaped breach cross section with side slopes of 26.6° 

and vertical erosion rates of 4.0, 1.0, and 0.25 m/min. 

Solid lines are hydrographs for a lake with a maximum 

depth of 36.8 m (similar to Carver Lake); dashed lines 

are hydrographs for a lake with a maximum depth of 8.7 

m (similar to the lake that breached the moraine dam at 

the terminus of Collier Glacier).

lake. Breach erosion is commonly arrested by 

processes that are largely unpredictable in 

numerical models. Most moraine-dam failures in 

the Three Sisters and Mount Jefferson Wilderness 

Areas resulted in only partial emptying of the 

impounded lakes. For most of these partial 

releases, large boulders contained in the moraine 

accumulated in the breach thalwegs, inhibiting 

downcutting and stabilizing the outlet channels. 

Likewise, icebergs could accumulate at the outlet, 

reducing outflow and ending downcutting.

A simpler approach to study downstream 

hazards from moraine-dammed lakes is to postulate 

a breach shape, rate of erosion, and ultimate depth 

on the basis of intuition and data from previous 

moraine-dam failures. This approach was used by 

Laenen and others (1987) to evaluate the hazard 

from Carver Lake, for which it was suggested that 

a "worst case event is the most appropriate design 

analysis for planning possible mitigating 

measures." Possible outflow hydrographs for lakes 

in the Three Sisters and Mount Jefferson 

Wilderness Areas, based on a similar procedure for 

various failure scenarios, are shown in figure 66 

and are summarized in table 3.

Downstream Flow Behavior

Developed areas near the central Oregon 

Cascade Range that may be subject to hazards from 

moraine-dammed lakes are generally many 

kilometers downstream from the moraine dams. 

Consequently, evaluating hazards depends on how 

flow evolves as it moves downstream. This aspect 

of hazards analysis is also difficult. In addition to 

the numerical complexity of routing highly 

unsteady flows down steep channels, lake releases 

generally evolve into debris flows, which have 

distinctly different rheologic properties than those 

of streamflow (Laenen and others, 1987).

All the dam-failure flows in the Three Sisters 

and Mount Jefferson Wilderness Areas gained and 

lost volume as they moved downstream. For the 

debris flows studied, reaches of increasing and 

decreasing peak discharge largely coincided with 

channel reaches of erosion and deposition, 

indicating that exchange of mass with the channel 

and adjacent banks exerts large control on peak 

discharge and volume as the flow moves

Evaluation of Hazards from Moraine-Dammed Lake Breakouts 81
LAKE AT THREE FINGERED JACK 4 m/min LAKE AT COLLIER GLACIER

0.25 m/min

Maximum Volume: 165,000 m3 

Maximum Depth: 4.8 m

Maximum Volume: 38,250 m3 

Maximum Depth: 9.7 m

0 2,000 4,000 6,000 8,000 10,000

LAKE AT THAYER GLACIER CHAMBERS LAKE 1

Maximum Volume: 1,360,250 m3 

Maximum Depth: 38.4 m

Maximum Volume: 666,000 m3 

Maximum Depth: 26.4m

1,000 2,000 3,000 4,000 5,000 6,000 7,000

Maximum Volume: 925,000 m3 

Maximum Depth: 36.6 m

0 1,500 3,000 4,500 6,000 7,500 9,000

,500 3,000 4,500 6,000 7,500 9,000

TIME, IN

1,000

800

600

400

200

0

LAKE AT EAST BEND GLACIER

4 m/min

1 m/min

Maximum Volume: 201,000 m3 

Maximum Depth: 13.7 m

0.25 m/min

0 1,000 

SECONDS

2,000 3,000 4,000

Figure 66. Calculated hypothetical hydrographs for six existing and potential moraine-dammed lakes in the Three 

Sisters and Mount Jefferson Wilderness Areas. Basis and numerical methods of calculating hydrographs are described 

in Walder and O'Connor (1997). For each lake, the calculated hydrographs are based on the following: (1) complete 

emptying of the lake, (2) triangular-shaped breach cross sections with side slopes of 26.6°, and (3) uniform erosion 

rates of 4.0, 1.0, and 0.25 m/min. For Chambers Lake No. 1 and lakes dammed or potentially dammed by moraines at 

Thayer and Collier Glaciers, the hydrographs are based on assuming that the lake level rises to the low point of the 

moraine crest before the moraine breaches. For other cases, where lakes now drain over the moraine crests, the 

calculated hydrographs are for the present lake geometry.

82 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
Table 3. Hypothetical peak discharges for moraine-dammed lakes in the Three Sisters and Mount Jefferson 

Wilderness Areas for various breach erosion rates.

[These hypothetical peak discharges are calculated on the basis of the following conditions: (1) Complete 

emptying of the lake; (2) Triangular-shaped breach cross section with constant side slopes of26.0P; (3) the 

breach enlarges at a constant vertical erosion rate until the bottom of the breach reaches the altitude of the lake 

bottom, at which time vertical erosion ceases and the breach geometry remains constant. Numerical methods 

for calculating hydrographs are described in Walder and O'Connor (1997). m3, cubic meters; m, meters; m/min, 

meters per minute; rrf/s, cubic meters per second]

Vertical erosion rate (m/min)

Lake name or 

glacier terminus

Carver Lake

Chambers Lake No. 1

Chambers Lake No.2

Collier Glacier

East Bend Glacier

Jack Glacier

Thayer Glacier

Volume

(m3 )

925,000

l,360,300i

76,300

165,080i

200,930

38,270

666,1001

Depth

(m)

36.6

38.4i

12.8

4.8i

13.7

9.7

26.4i

v.e.j U.UU I.U e..v t.u

Peak discharge (m3/s)

240

335

50

80

120

35

35

455

630

95

85

225

65

65

850

1,175

175

85

415

120

120

1,590

2,190

320

90

710

220

220

2,940

4,030

565

90

945

340

340

1 Volume and depth values (and calculated discharges) are for maximum potential lakes that would be achieved only if lake levels 

rose so that they were draining over the moraine crest. The present depths and volumes and much smaller.

downstream. Similar observations of peak 

discharges increasing several-fold have been made 

for flows resulting from rapid release of morainedammed lakes in other parts of the world (fig. 67). 

This aspect of debris-flow hazard assessment is 

important because most research in debris-flow 

modeling has been focused on rheology and the 

effect of flow rheology on flow behavior 

(Takahashi, 1978, 1981; Iverson and Denlinger, 

1987; O'Brien and others, 1993). Postulated 

rheologic models of debris flow are usually 

incorporated into fixed-bed streamflow-routing 

models to determine downstream propagation of 

debris-flow hydrographs (Laenen and Hansen, 

1986; Fread, 1988; O'Brien and others, 1993; 

Costa, 1997). For some of the rubbly debris flows 

from moraine-dammed-lake releases in the central 

Oregon Cascade Range, material from the bed and 

banks increased the flow volume by more than 25 

percent and increased peak discharge by 100 

percent or more (fig. 67). Likewise, deposition 

resulted in substantial reductions of flow volume 

and peak discharge over short distances. During the

1970 Squaw Creek flow, about 65 percent of the 

lake volume was temporarily retained within the 

flow deposits or elsewhere along the flow route 

and was not part of the measured flow pulse 24 km 

downstream. At least for these types of debris 

flows, depositional and erosional effects on the 

flow hydrograph potentially overwhelm routing 

effects that might result from choices of rheologic 

model and routing scheme.

Crude predictions of flow bulking and 

debulking are possible on the basis of gradient 

criteria as described above. The magnitude and 

locations of erosion and deposition, however, 

depend on flow size and rheology, channel and 

overbank substrate, channel geometry, and 

hillslope stability. All are factors difficult to 

parameterize accurately in a predictive model. An 

attempt to construct a model postdictively for the 

1970 Squaw Creek flow (Laenen and others, 1987) 

using only channel friction to attenuate the peak, 

resulted in peak discharges that failed to match 

most of the field-based indirect discharge estimates 

within a factor of two. Combined with the

Evaluation of Hazards from Moraine-Dammed Lake Breakouts 83
o (J

LLJ 

(/)

DC 

LLJ 

Q_

CC 

LU

ILU

CJ 

GO

D 

CJ

LU 

d 

DC 

<

CJ 

GO 

Q

LU 

Q_

10,000

8,000 -

6,000 -

-•— Separation Creek

-T-- White Branch

-••- Squaw Creek

+••• Soda Creek

4,000 -

2,000

B

Boqu River, Tibet 

Demenlahi Glacier, Tibet 

Nostetuko Lake, Canada 

Dudh Kosi River, Nepal 

Moraine Lake No. 13, Kazakhstan

20 40 60 80 100 

DISTANCE FROM BREACH, IN KILOMETERS

120

Figure 67. Downstream variation in peak discharges for (A) four debris flows from moraine-dammed lake releases 

in the Three Sisters Wilderness Area and (B ) five debris flows and floods from moraine-dammed lake releases in 

other alpine areas. Sources for data are given in table 2.

84 Debris Flows from Failures of Moraine Dams — Three Sisters and Mount Jefferson Wilderness Areas, Oregon
considerable uncertainty in the hydrograph at the 

breach, precisely and accurately assessing the 

magnitude of downstream debris hazards from 

rapid release of moraine-dammed lakes is fraught 

with uncertainty. This uncertainty, however, does 

not diminish the importance of identifying 

drainages subject to flows from moraine-dam 

breakout floods, and increasing our understanding 

of the processes and conditions that contribute to 

flow hazards in the Three Sisters and 

Mount Jefferson Wilderness areas of Oregon.

CONCLUSIONS

In the wake of regional warming and 

substantial 20th-century glacier retreat, numerous 

proglacial lakes have formed in recently 

deglaciated alpine valleys and cirques in the 

Cascade Range of Oregon and Washington. In the 

Three Sisters and Mount Jefferson Wilderness 

Areas of the central Oregon Cascade Range, at 

least 14 lakes impounded by late Neoglacial 

terminal and lateral moraines, have formed since 

the early 1920's. Six of these lakes had maximum 

volumes of at least 200,000 m3 . Many of these 

moraine dams proved to be unstable, and at least 11 

rapid releases of lake water resulted from total or 

partial breaching of moraine dams. Evaluation of 

the geologic evidence left by these flows helps to 

understand aspects of flows caused by natural dam 

failures in glacierized volcanic terrains.

All of the moraine-dam failures resulted in 

debris flows, the largest ones attaining peak 

discharges of about 500 m3/s and travelling almost 

10 km downstream. Farther downstream, many of 

the debris flows transformed into sediment-laden 

streamflow, affecting discharge and water quality 

for up to 100 km downstream. Water releases at the 

breaches evolved into debris flows by 

incorporation of Neoglacial-age morainal and 

outwash sediment near the outlet channel; in all 

cases they transformed into debris flows within 

500 m. The quantity of debris introduced into the 

flows was large, in some cases exceeding 25 

percent of the volume of water released, and 

resulted in downstream peak discharges 

substantially greater than those at the outlet. 

Morphological evidence indicates that most debris

entered the flows by mass wasting of outlet 

channel banks and knickpoint migration up the 

steep outlet channels.

As these debris flows travelled downstream, 

they eroded material from steeper parts of the 

channels and deposited sediment in wider, lowergradient reaches. Most flows ceased continuing as 

debris flows at channel gradients less than 4°. 

Erosion and deposition by these debris flows had 

large effects on the peak discharge as the flow 

moved downstream. Peak discharges locally 

doubled in reaches of substantial entrainment.

Several moraine-dammed lakes remain in the 

Washington and Oregon Cascades, posing 

downstream hazards to communities and 

recreationists. Because of the large uncertainties in 

the present conditions of moraine dams and 

possible future glaciologic and hydrologic 

conditions, quantitatively assessing the potential 

for failure is difficult. Nevertheless, topographic 

setting provides at least a qualitative indication of 

the potential of moraine-dam failure, especially by 

overtopping. If climate and glacier-termini 

positions remain stable, the likelihood of sudden 

lake releases will probably continue to diminish. 

If, however, climate or glaciologic conditions 

change, causing either substantial glacier retreat or 

advance, the potential for moraine-dam failures 

may increase.

The downstream consequences of possible 

failures of moraine dams are also uncertain and 

largely unquantifiable. Worst-case scenarios can be 

defined and could be useful for planning mitigative 

measures, but the likelihood of such worst-case 

events may be vanishingly small. Uncertainties in 

the volume and rate of water release make 

predicting more likely outflow rates and 

downstream behavior difficult. Transformation to 

debris flow, and subsequently to sediment-laden 

streamflow, plays a large role in the downstream 

behavior of the flow. Incorporation and deposition 

of material substantially changes the rheology, 

volume, and peak discharge of the flow as it 

travels downstream. These factors, plus the 

numerical complexity of routing peaked 

hydrographs down steep channels, conspire against 

robust quantitative assessment of downstream 

hazards presented by moraine-dammed lakes.

Conclusions 85
View west of Broken Top volcano and moraine-dammed lake, Three Sisters Wilderness Area. 

Photograph by Austin Post, USGS, September 22, 1966.
REFERENCES CITED

Baraes, H.H., and Davidian, J., 1978, Indirect

methods, in Hershey, R.W., ed., Hydrometry: John 

Wiley and Sons, p. 49-204.

Beget, I.E., 1984, Tephrochronology of late 

Wisconsin deglaciation and Holocene glacier 

fluctuations near Glacier Peak, North Cascade 

Range, Washington: Quaternary Research, v. 21, 

p. 304-316.

Benda, Lee, 1990, The influence of debris flows on 

channels and valley floors in the Oregon Coast 

Range, U.S.A.: Earth Surface Processes and 

Landforms, v. 15, p. 457^66.

Benda, L.E., and Cundy, T.W., 1990, Predicting 

deposition of debris flows in mountain channels: 

Canadian Geotechnical Journal, v. 27, p. 409^17.

Blown, lain, and Church, Michael, 1985, Catastrophic 

lake drainage within the Homathko River Basin, 

British Columbia: Canadian Geotechnical Journal, 

v. 22, p. 551-563.

Bodenlos, A.J., and Ericksen, G.E., 1955, Lead-zinc 

deposits of the Cordillera Blanca and Northern 

Cordillera Huayhuash, Peru: U.S. Geological 

Survey Bulletin 1017, 166 p.

Buchroithner, M.F., Jentsch, G., and Wanivenhaus, B., 

1982, Monitoring of recent geological events in the 

Khumbu area (Himalaya, Nepal) by digital 

processing of Landsat MSS data: Rock Mechanics, 

v. 15, p. 181-197.

Burbank, D.W, 1981, A chronology of late Holocene 

glacier fluctuations on Mt. Rainier, Washington: 

Arctic and Alpine Research, v. 13, p. 369-386.

————, 1982, Correlations of climate, mass balances, 

and glacial fluctuations at Mount Rainier, 

Washington, U.S.A., since 1850: Arctic and Alpine 

Research, v. 14, p. 137-148.

Callaghan, E., and Buddington, A.F., 1938, 

Metalliferous mineral deposits of the Cascade 

Range in Oregon: U.S. Geological Survey Bulletin 

893, 141 p.

Carling, P.A. and Glaister, M.S., 1987, Reconstruction 

of a flood resulting from a moraine-dam failure 

using geomorphological evidence and dam-break 

modeling, in Mayer, L. and Nash, D., Catastrophic 

flooding: Winchester, Mass., Alien and Unwin, 

p. 181-200.

Clague, J.J., 1987, Catastrophic outburst floods: 

GEOS, v. 16, no. 2, p. 18-21.

Clague, J.J., and Evans, S.G., 1992, A self-arresting 

moraine dam failure, St. Elias Mountains, British 

Columbia—Current Research, Part A: Geological 

Survey of Canada, Paper 92-1 A, p. 185-188.

————, 1993, Historic retreat of Grand Pacific and 

Melbern Glaciers, Saint Elias Mountains, 

Canada—An analogue for decay of the 

Cordilleran ice sheet at the end of the 

Pleistocene?: Journal of Glaciology, v. 39, no. 133, 

p. 619-624.

—————, 1994, Formation and failure of natural

dams in the Canadian Cordillera: Geological 

Survey of Canada Bulletin 464, 35 p.

Clague J.J., Evans, S.G., and Blown, I.G., 1985, A 

debris flow triggered by the breaching of a 

moraine-dammed lake, Klattasine Creek, British 

Columbia: Canadian Journal of Earth Sciences, 

v. 22, p. 1492-1502.

Conrey, R.M., 1991, Geology and petrology of the 

Mount Jefferson area, High Cascade Range, 

Oregon: Pullman, Washington State University, 

Ph.D. dissertation, 357 p., 2 pis., 94 figs.

Costa, J.E., 1984, Physical geomorphology of debris 

flows, in Costa, J.E., and Fleisher, P.J., eds., 

Developments and applications of 

geomorphology: Berlin, Springer-Verlag, 

p. 268-317.

————, 1988, Floods from dam failures, in Baker, 

V.R., Kochel, R.C., and Patton, PC., eds., Flood 

geomorphology: John Wiley and Sons, 

p. 439-463.

————., 1997, Hydraulic modeling for lahar hazards

at Cascade volcanoes: Environmental and 

Engineering Geoscience, v. Ill, p. 21-30.

Costa, J.E., and Schuster, R.L., 1988, The formation 

and failure of natural dams: Geological Society of 

America Bulletin, v. 100, p. 1054-1068.

Crandell, D.R., 1965, The glacial history of western 

Washington and Oregon, in Wright, H.E., Jr., and 

Frey, D.G., eds., The Quaternary of the United 

States: Princeton, N.J., Princeton University Press, 

p. 341-353.

Crandell, D.R., 1971, Postglacial lahars from Mount 

Rainier Volcano, Washington: U.S. Geological 

Survey Professional Paper 677, 73 p.

Crandell, D.R., and Miller, R.D., 1974, Quaternary 

stratigraphy and extent of glaciation in the Mount 

Rainier region, Washington: U.S. Geological 

Survey Professional Paper 847, 59 p.

References Cited 87
Curry, R.R., 1966, Observation of alpine mudflows in 

the Tenmile Range, central Colorado: Geological 

Society of America Bulletin, v. 77, p. 771-776.

Davis, P.T., 1988, Holocene glacier fluctuations in the 

American Cordillera: Quaternary Science 

Reviews, v. 7, p. 127-157.

Dethier, D.P., 1980, Reconnaissance study of 

Holocene glacier fluctuations in the Broken Top 

area, Oregon [abs.]: Geological Society of 

America Abstracts with Programs, v. 11, p. 104.

Ding Yongjian, and Liu Jingshi, 1992, Glacier lake 

outburst flood disasters in China: Annals of 

Glaciology, v. 16, p. 180-184.

Driedger, C.L., 1986, A visitor's guide to Mount 

Rainier glaciers: Longmire, Washington, Pacific 

Northwest National Parks and Forests Association, 

80 p.

————, 1993, Glaciers on Mount Rainier: Water Fact 

Sheet, U.S. Geological Survey Open-File Report

92-474, 2 p.

Driedger, C.L., and Kennard, P.M., 1986, Ice volumes 

on Cascade volcanoes—Mount Rainier, Mount 

Hood, Three Sisters, and Mount Shasta: U.S. 

Geological Survey Professional Paper 1365, 28 p.

Dutto, Furio, and Mortar, Giovanni, 1992, Rischi 

connessi con la dinamica glaciale nelle Alpi 

italiane [Glacial hazards in the Italian Alps]: 

Geografica Fisica Dinamica Quat., v. 15, p. 85-99. 

[In Italian, English summary and figure captions.]

Eisbacher, G.H., 1982, Mountain torrents and debris 

flows: Episodes, v. 1982, no. 4. p. 12-17.

Eisbacher, G.H., and Clague, J.J., 1984, Destructive 

mass movements in high mountains—Hazard and 

management: Geological Survey of Canada Paper 

84-16, 230 p.

Ericksen, G.E., Plafker, George, and Conch, J.F., 

1970, Preliminary report on the geologic events 

associated with the May 31, 1970, Peru 

earthquake: U.S. Geological Survey Circular 639,

25 p.

Evans, S.G., 1987, The breaching of morainedammed lakes in the southern Canadian 

Cordillera, in International Symposium on 

Engineering Geological Environment in 

Mountainous Areas, Beijing, 1987, Proceedings: 

v. 2, p. 141-150.

Evans, S.G., and Clague, J.J., 1993, Glacier-related 

hazards and climatic change, in Bras, Rafael, ed.,

Conference on The World at Risk—Natural 

Hazards and Climate Change, Cambridge, Mass., 

1992: New York, American Institute of Physics, 

p. 48-60.

Folk, R.L., 1980, Petrology of sedimentary rocks: 

Austin, Texas, Hemphill Publishing, 184 p.

Folland, C.K., Karl, T.R., and Vinnikov, K.Y.A., 

1990, Observed climate variations and change, in 

Houghton, J.T., Jenkins, G.J., and Ephraums, J.J., 

eds., Climate Change—The IPCC Scientific 

Assessment: Cambridge, Mass., Cambridge 

University Press, p. 195-238.

Fread, D.L., 1987, BREACH—An erosion model for 

earthen dam failures: Silver Spring, Maryland, 

Hydrologic Research Laboratory, National 

Weather Service, 34 p.

Fread, D.L., 1988, The NWS DAMBRK modelTheoretical background/user documentation: 

Silver Spring, Maryland, Hydrologic Research 

Laboratory, National Weather Service, 120 p.

Froehlich, D.C., 1987, Embankment-dam breach 

parameters, in Ragan, R.M., ed, Hydraulic 

Engineering, Proceedings of the 1987 National 

Conference on Hydraulic Engineering: New York, 

American Society of Civil Engineers, p. 570-575.

Fryxell, KM., and Horberg, L, 1943, Alpine 

mudflows in Grand Teton National Park, 

Wyoming: Geological Society of America 

Bulletin, v. 54, p. 457^72.

Fushimi, H., Ikegami, K., Higuchi, K., and Shankar, 

K., 1985, Nepal case study: catastrophic floods, in 

Young. GJ, ed., Techniques for prediction of 

runoff from glacierized areas: International 

Association of Hydrological Sciences (IAHSAISH) Publication No. 149, p. 125-130.

Galay, V.J., 1985, Hindu Kush-Himalayan erosion 

and sedimentation in relation to dams, in 

International Workshop on Water Management in 

the Hindu Kush-Himalaya region, Chengu China, 

1985: Kathmanddu, Nepal, International Centre 

for Integrated Mountain Development (ICIMOD), 

24 p.

Gallino, G.L., and Pierson, T.C., 1985, Polallie Creek 

debris flow and subsequent dam-break flood of 

1980, East Fork Hood River basin, Oregon: U.S. 

Geological Survey Water Supply Paper 2273, 

22 p.

Gerasimov, V.A., 1965, Issykskaia katastrofa 1963 g. 

i otrazhenie ee in geomorfoogii doliny r. Issyk 

[The Issyk catastrophe in 1963 and its effect on

88 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
geomorphology of the Issyk River valley]: 

Akademiia Nauk SSSR, Izvestiia Vsesoiuznogo, 

Geograficheskogo Obshchestva, v. 97, p. 6, 

p. 541-547. [In Russian.]

Grove, J.M., 1988, The Little Ice Age: London, 

Methuen, 498 p. [Reprinted 1990, New York, 

Routledge.]

Haeberli, Wilfried, 1983, Frequency and characteristics of glacier floods in the Swiss Alps: Annals 

of Glaciology, v. 4, p. 95-90.

Haeberli, W., Alean, J.-C., Muller, P., and Funk, M., 

1989, Assessing risks from glacier hazards in high 

mountain regions: some experiences in the Swiss 

Alps: Annals of Glaciology, v. 13, p. 96-102.

Hansen, J., and Lebedeff, S., 1988, Global surface 

temperatures—Update through 1987: Geophysical 

Research Letters, v. 15, p. 323-326.

Hatch, Laura, 1917, The glaciers of Mount Jefferson: 

Mazama, v. 5, no. 2 (December, 1917), 

p. 136-139.

Heikkinen, O.O., 1984, Dendrochronological

evidence of variations of Coleman Glacier, Mount 

Baker, Washington, U.S.A.: Arctic and Alpine 

Reserach, v. 16, p. 53-64.

Henderson, P.M., 1966, Open-channel flow: 

MacMillan, N.Y, 522 p.

Hodge, E.T., 1925, Mount Multnomah—Ancient 

ancestor of the Three Sisters: Eugene, Oregon, 

University of Oregon, 158 p., 1 pi.

Hopkins, D.M., 1975, Geology of the south and east 

slope of Mount Adams volcano, Cascade Range, 

Washington: Seattle, Washington, University of 

Washington, Ph.D. dissertation, 79 p.

Hopson, R.E., 1960, Collier Glacier—A photographic 

record: Mazama, v. 42, no. 13, p. 15-26.

————, Collier Glacier, 1961: Mazama, v. 43, 

no. 13, p. 37-39.

————, 1962, Collier Glacier, 1962: Mazama, v. 44,

no. 13, p. 44-47. 

——, 1963, Collier Glacier, 1963: Mazama, v. 45,

no. 13, p. 48^9. 

——, 1965, Collier Glacier, 1963: Mazama, v. 47,

no. 13, p. 54-56.

Hubley, R.C., 1956, Glaciers of the Washington 

Cascade and Olympic Mountains; their present 

activity and its relation to local climatic trends: 

Journal of Glaciology, v. 2, p. 669-674.

Hunt, Bruce, 1984, Dam-break solution: Journal of 

Hydraulic Engineering, v. 110, no. 6, p. 675-686.

Hupp, C.R., Osterkamp, W.R., and Thornton, J.L., 

1987, Dendrogeomorphic evidence and dating of 

recent debris flows on Mount Shasta, Northern 

California: U.S. Geological Survey Professional 

Paper 1396-B, 39 p.

Ikeya, H., 1981, A method for designation for area in 

danger of debris flow, in Davies, T.R.H., and 

Pearce, A.J., eds., Proceedings of the Christchurch 

Symposium, January 1981, Erosion and Sediment 

Transport in Pacific Rim Steeplands: International 

Association of Hydrological Sciences (IAHSAISH) Publication No. 132, p. 576-588.

Indacochea, A.J., and Iberico Mariano, 1947, 

Aluvionamiento de Chavin de Huantar el 17 de 

enero de 1945: Boletin de la Sociedad Geologica 

del Peru, v. 20, p. 21-28. [In Spanish.]

Iverson, R.M., and Denlinger, R.P., 1987, The physics 

of debris flows—A conceptual approach, in 

Beschta, R.L., Blinn, T., Grant, G.E., Ice, G.G., 

and Swanson, F.J., eds., Erosion and 

Sedimentation in the Pacific Rim: International 

Association of Hydrological Sciences (IAHSAISH) Publication No. 165, p. 155-165.

Iverson, R.M., LaHusen, R.G., Major, J.J., and 

Zimmerman, C.L., 1994, Debris flow against 

obstacles and bends—Dynamics and deposits: 

EOS, American Geophysical Union, v. 75, no. 44,

p. 274.

Ives, J.D., Glacial lake outburst floods and risk 

engineering in the Himalaya: Kathmandu, Nepal, 

International Centre for Integrated Mountain 

Development (ICIMOD) Occasional Paper No. 5, 

42 p.

Jackson, L.E., Jr., 1979, A catastrophic glacial

outburst flood (jokulhlaup) mechanism for debris 

flow generation at the Spiral Tunnels, Kicking 

Horse River basin, British Columbia: Canadian 

Geotechnical Journal, v. 16, p. 806-813.

Jackson, L.E., Jr., Hungr, O., Gardber, J.S., and 

Mackay, C., 1989, Cathedral Mountain debris 

flows, Canada: International Association of 

Engineering Geology Bulletin, no. 40, p. 35-54.

Johnson, A.M., 1970, Physical processes in geology: 

San Francisco, Freeman and Cooper, 577 p.

Jones, P.D., 1988, Hemispheric surface air

temperature variations—Recent trends and an 

update to 1987: Journal of Climatology, v. 1, 

p. 654-660.

Jones, P.O., and Bradley, R.S., 1992, Climatic 

variations in the longest instrumental records, in

References Cited 89
Bradley, R.S., and Jones, P.D., eds., Climate since 

A.D. 1500: London, Routledge, p. 246-268.

Keen, R.H., 1969, Collier Glacier report: 1966-1969: 

Mazama, v. 51, p. 42-46.

————, 1978, Collier Glacier: 1970-1978: Mazama, 

v. 60, p. 22-35.

————, 1981, Collier Glacier: 1979, 1980, 1981:

Mazama, v. 63 , p. 59-62.

Khegai, A.Y., Popov, N.V., Plekhanov, P.A., and 

Keremkulov, V.A., 1992, Experiments at the 

Chemolgan debris-flow testing ground, 

Kazakhstan: Landslide News, no. 6 (August 

1992), p. 27-28.

Kinzl, H., 1940, La ruptura del lago glacial en la 

quebrada de Ulta an el afio 1938: Boletin del 

Meseo de Historia Natural "Javier Prado" [Lima, 

Peru], v. 4, no. 13, p. 152-167. [In Spanish.]

Laenen, Antonius, and Hansen, R.P., 1986,

Simulation of three lahars in the Mount St. Helens, 

Washington area, using a one-dimensional, 

unsteady-state streamflow model: U.S. Geological 

Survey Water-Resources Investigations Report 

88-4004, 20 p.

Laenen, Antonius, Scott, K.M., Costa, J.E., and 

Orzol, L.L., 1987, Hydrologic hazards along 

Squaw Creek from a hypothetical failure of the 

glacial moraine impounding Carver Lake near 

Sisters, Oregon: U.S. Geological Survey OpenFile Report 87-41, 48 p.

Laenen, Antonius, Scott, K.M., Costa, J.E., and 

Orzol, L.L., 1992, Modeling flood flows from a 

hypothetical failure of the glacial moraine 

impounding Carver Lake near Sisters, Oregon, in 

Subitzky, Seymour, ed., Selected papers in the 

hydrologic sciences, 1988-92: U.S. Geological 

Survey Water Supply Paper 2340, p. 151-164.

Land, L.F., 1980, Evaluation of selected dam-break 

floodway models by using field data: U.S. 

Geological Survey Water-Resources Investigations 

Report 80-44, 54 p.

Lawrence, D.B., 1948, Mount Hood's latest eruption 

and glacier advances: Mazama, v. 30, p. 22-29.

Leonard, E.M., 1985, Glaciological and climatic 

controls on lake sedimentation, Canadian Rocky 

Mountains: Zeitscrift fur gletscherkunde und 

Glacialgeologie, v. 21, p. 35-42.

Liu Chaohai, and Sharmal, C.K. (eds.), 1988, Report 

on first expedition to glaciers and glacier lakes in 

the Pumqu (Arun) and Poiqu (Bhote-Sun Kosi)

River basins, Xizang (Tibet), China: Beijing, 

China, Science Press, 192 p.

Lliboutry, Louis, Arnao, B.M., Pautre, Andre, and 

Schneider, Bernard, 1977, Glaciological problems 

set by the control of dangerous lakes in Cordillera 

Blanca, Peru. I. Historical failures of morainic 

dams, their causes and prevention: Journal of 

Glaciology, v. 18, p. 239-254.

Li Deji, and You Yong, 1992, Bursting of the Midui 

Moraine Lake in Bomi, Xizang: Mountain 

Research [China], v. 10, no 4. p. 219-224. [In 

Chinese, English summary.]

Lu Ruren, and Li Dehi, 1986, Debris flow induced by 

ice lake burst in the Tangbulang gully, 

Gongbujiangda, Xizang (Tibet): Journal of 

Glaciology and Geocryology, v. 8, p. 61-71. [In 

Chinese, English summary.]

Luckman, B.H., Holds worth, Gerald, and Osborn, 

G.D., 1993, Neoglacial glacier fluctuations in the 

Canadian Rockies: Quaternary Reserach, v. 39, 

p. 144-153.

Lundstrom, S.C., 1992, The budget and effect of 

superglacial debris on Eliot Glacier, Mount Hood, 

Oregon: Boulder, Colo., University of Colorado, 

Ph.D. dissertation, 193 p., 61 figs.

Lii Ruren, and Li Deji, 1986, Debris flow induced by 

ice lake burst in the Tangbulang Gully, 

Gonbujiangda, Xizang (Tibet): Journal of 

Glaciology and Geocryonlogy [China], v. 8, no. 1, 

p. 61-70. [In Chinese, English summary.]

Lynch, Margaret, 1929, An ascent of Three Finger 

Jack: Mazama, v. 11, no. 12, p. 110-114.

Macchinoe, F., and Sirangelo, B., Floods resulting 

from progressively breached dams, in Proceedings 

of Lausanne Symposia, August 1990, Hydrology 

in Mountainous Regions: International 

Association of Hydrological Sciences (IAHSAISH) Publication No. 194, p. 325-332.

McDonald, Gregory, D., Changes in mass of Collier 

Glacier, Oregon, 1910-1994: Corvallis, Oregon, 

Oregon State University, M.S. thesis, 183 p.

Meier, M.F., and Post, Austin, 1962, Recent

variations in mass budgets of glaciers in Western 

North America, in Symposium of Obergurgl: 

International Association of Hydrologic Sciences 

(IAHS-AISH) Publication No. 58, p. 63-77.

Noda, Edward, 1970, Water waves generated by 

landslides: Journal of the Waterways, Harbors,

90 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
and Coastal Engineering Division, American 

Society of Civil Engineers, v. WW4, p. 835-855.

Nolf, Bruce, 1966, Broken Top breaks—Flood 

released by erosion of glacial moraine: Ore Bin, 

v. 28, no. 10, p. 182-188.

O'Brien, J.S., Julien, P.Y., and Fullerton, W.T., 1993, 

Two-dimensional water flood and mudflow 

simulation: Journal of Hydraulic Engineering, 

v. 119, no. 2, p. 244-261.

O'Connor, J.E., and Costa, J.E., 1993, Geologic and 

hydrologic hazards in glacierized basins in North 

America resulting from 19th and 20th century 

global warming: Natural Hazards v. 8, 

p. 121-140.

Oppenheim, Victor, 1946, Sobre las lagunas de 

Huaraz: Boletin de la Sociedad Geologica del 

Peru, v. 19, p. 68-80. [In Spanish.]

Osborn, G.D., and Luckman, B.H., 1988, Holocene 

glacier fluctuations in the Canadian Cordillera 

(Alberta and British Columbia): Quaternary 

Science Reviews, v. 7, p. 115-128.

Osterkamp, W.R., Hupp, C.R., and Blodgett, J.C., 

1986, Magnitude and frequency of debris flows, 

and areas of hazard on Mount Shasta, Northern 

California: U.S. Geological Survey Professional 

Paper 1396-C, 21 p.

Pelto, M.S., 1993, Current behavior of glaciers in the 

North Cascades and effect on regional water 

supplies: Washington Geology, v. 21, no. 2, 

p. 3-10.

Phillips, K.N., 1938, Our vanishing glaciers: 

Mazama, v. 20, no. 12, p. 24-^1.

Pierson, T.C., 1980, Erosion and deposition by debris 

flows at Mount Thomas, North Canterbury, New 

Zealand: Earth Surface Processes, v. 5,

p. 227-247.

———————., 1985, Initiation and flow behavior of 

the 1980 Pine Creek and Muddy River lahars, 

Mount St. Helens, Washington: Geological 

Society of America Bulletin, v. 96, p. 1,056- 

1,069.

Pierson, T.C. and Costa, J.E., 1987, A Theological 

classification of subaerial sediment-water flows: 

in Costa, I.E. and Wieczorek, G.F., eds., Debris 

flows/avalanches: process, recognition, and 

mitigation: Geological Society of America 

Reviews in Engineering Geology, v. 7, p. 1-12.

Pierson, T.C., and Scott, K.M., 1985, Downstream 

dilution of a lahar—Transition from debris flow to

hyperconcentrated streamflow: Water Resources 

Research, v. 21, p. 1511-1524.

Porter, S.C., and Denton, G.H., 1967, Chronology of 

Neoglaciation in the North American Cordillera: 

American Journal of Science, v. 265, p. 177-210.

Ponce, V.M., and Tsivoglou, A.M., 1981, Modeling 

gradual dam breaches: Journal of the Hydraulics 

Division, Proceedings of the American Society of 

Civil Engineers, v. 107, no. HY7, p. 829-838.

Popov, N., 1990, Debris flows and their control in 

Alma-Ata, Kazakh SSR, USSR: Landslide News, 

no. 4 (July 1990), p. 25-27.

Quiroga, C.A., and Singh, V.P., 1987, A dam-breach 

erosion model—II. Application: Water Resources 

Management, v. 1, p. 199-221.

Rabassa, Gorge; Rubulis, Sigfrido; and Suarezm 

Jorge, 1979, Rate of formation and sedimentology 

of (1976-1978) push-moraines, Frias Glacier, 

Mount Tronador (41°10'S; 71°53'W), Argentina, in 

Schliichter, C., ed., Moraines and varves: 

Rotterdam, A.A. Balkema, p. 65-79.

Rector, M.L., 1988, An analysis of suspected

Neoglacial ice-cored moraines impounding Carver 

Lake, South Sister region, High Cascades, 

Oregon: Corvallis, Oregon State University, 

Research paper in partial fulfillment of the 

requirement for the degree of Master of Science, 

29 p.

Research Committee of The Mazamas, 1938, An 

aerial photographic survey of the glaciers of 

Mount Hood, Mount Jefferson and The Three 

Sisters, Oregon: 47 p. [Copy available for 

inspection at Mazama Clubhouse, Portland, Ore.]

Reynolds, J.J., 1990, Geological hazards in the 

Cordillera Blanca, Peru: AGIO News, no. 61/62, 

p. 31-33.

————, 1992, The identification and mitigation of 

glacier-related hazards—Examples from the 

Cordillera Blanca, Peru, in McCall, G.J.H., 

Laming, D.J.C., and Scott, S.C., eds., 

Geohazards—Natural and man-made: London, 

Chapman and Hall, p. 143-157.

Russell, I.C., 1885, Existing glaciers of the United 

States: U.S. Geological Survey Fifth Annual 

Report (1883-1884), p. 303-355.

————, 1905, Preliminary report on the geology and 

water resources of central Oregon: U.S. 

Geological Survey Bulletin 252, 138 p.

References Cited 91
Ryder, J.M., 1989, Holocene glacier fluctuations, in 

Fulton, R.J., ed., Chapter 1 of Quaternary Geology 

of Canada and Greenland: Geological Survey of 

Canada, Geology of Canada, no. 1, p. 74-75. [also 

Geological Society of America, The Geology of 

North America, v. K-l.]

————, 1991, Geomorphological processes 

associated with an ice-marginal lake at Bridge 

Glacier, British Columbia: Geographic physique et 

Quaternaire, v. 45, p. 34-44.

Scott, K.M., 1967, Downstream changes in

sedimentological parameters illustrated by particle 

distribution from a breached rockfill dam, in 

Symposium on river morphology, General 

Assembly of Bern, 1967: International Association 

of Scientific Hydrology, International Union 

Geodesy and Geophysics, Publication No. 75, 

p. 309-318.

————, 1988, Lahars and lahar-runout flows in the 

Toutle-Cowlitz River system, Mount St. Helens, 

Washington—Origins, behavior, and 

sedimentology: U.S. Geological Survey 

Professional Paper 1447-A, 74 p.

Scott, K.M., Pringle, P.T., and Vallance, J.W., 1992, 

Sedimentology, behavior, and hazards of debris 

flows at Mount Rainier, Washington: U.S. 

Geological Survey Open-File Report 90-385, 

105 p.

Scott, W.E., 1974, Quaternary glacial and volcanic 

environments, Metolius River area, Oregon: 

Seattle, Washington, University of Washington, 

Ph.D. dissertation, 95 p., 23 figs., 1 plate 

(1:62,500).

————, 1977, Quaternary glaciation and volcanism, 

Metolius River area, Oregon: Geological Society 

of America Bulletin, v. 88, p. 113-124.

————, 1987, Holocene rhyodacite eruptions on the

flanks of South Sister volcano, Oregon, in Fink, 

J.H., ed., The emplacement of silicic domes and 

lava flows: Geological Society of America Special 

Paper 212, p. 35-53.

-, 1989, Temporal relations between eruptions

of the Mount Bachelor volcanic chain and 

fluctuations of late Quaternary glaciers, in Scott, 

WE., Gardner, C.A., and Sarna-Wojcicki, A.M., 

Guidebook for field trip to the Mount BachelorSouth Sister-Bend area, Central Oregon High 

Cascades: U.S. Geological Survey Open-File 

Report 89-645, p. 10-18.

Scott, WE., and Gardner, C.A., 1992, Geologic map

of the Mount Bachelor volcanic chain and 

surrounding area, Cascade Range, Oregon: U.S. 

Geological Survey Miscellaneous Investigations 

Map 1-1967, scale 1:50,000.

Sharp, R.P., and Nobles, L.H., 1953, Mudflow of 

1941 at Wrightwood, Southern California: 

Geological Society of America Bulletin, v. 64, 

p. 547-560.

Sherrod, D.R., 1986, Geology, petrology, and

volcanic history of a portion of the Cascade Range 

between latitudes 43°-46° N, central Oregon, 

U.S.A.: Santa Barbara, University of California, 

Ph.D. dissertation, 320 p., 4 pis., 33 figs.

Sherrod, D.R., and Smith, J.G., 1989, Preliminary 

map of upper Eocene to Holocene volcanic and 

related rocks of the Cascade Range, Oregon: U.S. 

Geological Survey Open-File Report 81-14, 

scale 1:500,000.

Sigafoos, R.S., and Hendricks, E.L., 1972, Recent 

activity of glaciers of Mount Rainier, Washington: 

U.S. Geological Survey Professional Paper 387-B, 

24 p.

Singh, V.P., and Quiroga, C.A., 1987, A dam-breach 

erosion model—I. formulation: Water Resources 

Management, v. l,p. 177-197.

Slingerland, R.L. and Voight, B., 1979, Occurrences, 

properties, and predictive models of landslidegenerated water waves, in Voight, B., ed., 

Rockslides and avalanches, Vol. 2: Amsterdam, 

Elsevier, p. 317-397.

Small, R.J., 1983, Lateral moraines of glacier de 

Tsidojiore Nouve—Form, development, and 

implications: Journal of Glaciology, v. 29, 

p. 250-259.

Takahashi, Tamotsu, 1978, Mechanical characteristics 

of debris flow: Journal of the Hydraulics Division, 

American Society of Civil Engineers, v. 104, 

p. 1153-1169.

Takahashi, Tamotsu, 1981, Debris flow: Annual 

Reviews of Fluid Mechanics, v. 13, p. 57-77.

Tangborn, WV, 1980, Two models for estimating 

climate-glacier relationships in the North 

Cascades, Washington, U.S.A.: Journal of 

Glaciology, v. 25, p. 3-21.

Taylor, E.M., 1978, Field geology of the S.W Broken 

Top Quadrangle, Oregon: Oregon Department of 

Geology and Mineral Industries Special Paper 2, 

50 p., 1 plate.

92 Debris Flows from Failures of Moraine Dams—Three Sisters and Mount Jefferson Wilderness Areas, Oregon
—— 1981, Central High Cascade roadside 

geology, Bend, Sisters, McKenzie Pass, and 

Santiam Pass, Oregon, in Johnston, D.A., and 

Donnelly-Nolan, J., eds., Guides to some volcanic 

terranes in Washington, Idaho, Oregon, and 

Northern California: U.S. Geological Survey 

Circular 838, p. 55-83.

-, 1987, Field geology of the northwest quarter

of the Broken Top 15' quadrangle, Deschutes 

County, Oregon: Oregon Department of Geology 

and Mineral Industries Special Paper 21, 20 p., 

1 plate.

Taylor, E.M., MacLeod, N.S., Sherrod, D.R., and 

Walker, G.W, 1987, Geologic map of the Three 

Sisters Wilderness, Deschutes, Lane, and Linn 

Counties, Oregon: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1952, scale 

1:62,500.

Taylor, G.H., 1993, Normal annual precipitation, 

State of Oregon: Corvallis, Oregon, Oregon 

Climate Service. [Isohyetal map and explanatory 

text, scale approximately 1:1,000,000.]

VanDine, D.F., 1985, Debris flows and debris torrents 

in the southern Canadian Cordillera: Canadian 

Geotechnical Journal, v. 22, p. 44-68.

Vuichard, Daniel, and Zimmermann, Markus, 1987, 

The 1985 catastrophic drainage of a morainedammed lake, Khumbu Himal—Cause and 

consequences: Mountain Research and 

Development, v. 7, p. 91-110.

Waitt, R.B., Pierson, T.C., McLeod, N.S., Janda, R.J., 

Voight, B., and Holcomb, R.T., 1983, Eruptiontriggered avalanche, flood, and lahar at Mount St. 

Helens—Effects of winter snowpack: Science, 

v. 221, p. 1394-1397.

Walder, J.S., and Driedger, C.L., 1994, Geomorphic 

change caused by outburst floods and debris flows 

at Mount Rainier, Washington, with emphasis on 

Tahoma Creek valley: U.S. Geological Survey 

Water-Resources Investigations Report 93-4093, 

93 p.

Walder, J.S., and O'Connor, I.E., 1997, Methods for 

predicting peak discharge of floods caused by 

failure of natural and constructed earthen dams: 

Water Resources Research, v. 33, no. 10,

p. 2337-2348.

Webb, R.H., 1993, Initiation and frequency of debris 

flows in Grand Canyon [abs.]: Geological Society 

of America Abstracts with Programs, v. 25, no. 7, 

p. A-395.

Williams, LA., 1916, Glaciers of the Three Sisters: 

Mazama, v. 5, no. 1 (December, 1916), p. 14-23.

Xu Daoming, 1988, Characteristics of debris flow 

caused by outburst of glacial lakes on the Boqu 

River in Xizang, Ching: Geojournal, v. 17, 

p. 569-580.

Yesenov, U.Y., and Degovets, A.S., 1979,

Catastrophic mudflow on the Bol'shaya Almatinka 

River in 1977: Soviet Hydrology, Selected Papers, 

v. 18, p. 158-160.

Zimmermann, Markus, and Mani, Peter, 1993, The 

effect of global warming on debris flow activity in 

the Swiss Alps: A challenge for the 21st century 

[abs.]: Programme with Abstracts, Third 

International Geomorphology Conference, 

Hamilton, Ontario, p. 282.

References Cited 93
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• Menlo Park, California—Rm. 3128, Bldg. 3, 

345 Middlefield Rd.

• Reston, Virginia—Rm. 1C402, USGS National Center, 

12201 Sunrise Valley Dr.

• Salt Lake City, Utah—2222 West, 2300 South

• Spokane, Washington—Rm. 135, U.S. Post Office 

Building, 904 West Riverside Ave.

• Washington, D.C.—Rm. 2650, Main Interior Bldg., 

18th and CSts.,NW.

Maps only may be purchased over the counter at the 

following USGS office:

• Rolla, Missouri—1400 Independence Rd.

Electronically

Some USGS publications, including the catalog New 

Publications of the U.S. Geological Survey are also 

available electronically on the USGS's World Wide Web 

home page at http://www.usgs.gov

Preliminary Determination of Epicenters

Subscriptions to the periodical Preliminary Determination of 

Epicenters can be obtained only from the Superintendent of 

Documents. Check or money order must be payable to the 

Superintendent of Documents. Order by mail from

Superintendent of Documents 

Government Printing Office 

Washington, DC 20402

Information Periodicals

Many Information Periodicals products are available through 

the systems or formats listed below:

Printed Products

Printed copies of the Minerals Yearbook and the Mineral 

Commodity Summaries can be ordered from the 

Superintendent of Documents, Government Printing Office 

(address above). Printed copies of Metal Industry Indicators 

and Mineral Industry Surveys can be ordered from the 

Center for Disease Control and Prevention, National Institute 

for Occupational Safety and Health, Pittsburgh Research 

Center, P.O. Box 18070, Pittsburgh, PA 15236—0070.

Mines FaxBack: Return fax service

1. Use the touch-tone handset attached to your fax

machine's telephone jack. (ISDN [digital] telephones 

cannot be used with fax machines.)

2. Dial (703) 648-4999.

3. Listen to the menu options and punch in the number of 

your selection, using the touch-tone telephone.

4. After completing your selection, press the start button 

on your fax machine.

CD-ROM

A disc containing chapters of the Minerals Yearbook 

(1993-95), the Mineral Commodity Summaries (1995-97), 

statistical compendium (1970-90), and other publications is 

updated three times a year and sold by the Superintendent of 

Documents, Government Printing Office (address above).

World Wide Web

Minerals information is available electronically at 

http://minerals.er.usgs.gov/minerals/

Subscription to the catalog New Publications of the U.S. 

Geological Survey

Those wishing to be placed on a free subscription list for the 

catalog New Publications of the U.S. Geological Survey 

should write to

U.S. Geological Survey 

903 National Center 

Reston, VA 20192
Selected Series of U.S. Geological Survey Publications

Books and Other Publications

Professional Papers report scientific data and interpretations 

of lasting scientific interest that cover all facets of USGS 

investigations and research.

Bulletins contain significant data and interpretations that are 

of lasting scientific interest but are generally more limited in 

scope or geographic coverage than Professional Papers.

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations of 

wide interest to professional geologists, hydrologists, and 

engineers. The series covers investigations in all phases of 

hydrology, including hydrogeology, availability of water, 

quality of water, and use of water.

Circulars are reports of programmatic or scientific 

information of an ephemeral nature; many present important 

scientific information of wide popular interest. Circulars are 

distributed at no cost to the public.

Fact Sheets communicate a wide variety of timely 

information on USGS programs, projects, and research. They 

commonly address issues of public interest. Fact Sheets 

generally are two or four pages long and are distributed at no 

cost to the public.

Digital Data Series (DOS) distribute large amounts of data 

through digital media, including compact disc-read-only 

memory (CD-ROM). They are high-quality, interpretive 

publications designed as self-contained packages for viewing 

and interpreting data and typically contain data sets, software 

to view the data, and explanatory text.

Water-Resources Investigations Reports are papers of an 

interpretive nature made available to the public outside the 

formal USGS publications series. Copies are produced on 

request (unlike formal USGS publications) and are also 

available for public inspection at depositories indicated in 

USGS catalogs.

Open-File Reports can consist of basic data, preliminary 

reports, and a wide range of scientific documents on USGS 

investigations. Open-File Reports are designed for fast release 

and are available for public consultation at depositories.

Maps

Geologic Quadrangle Maps (GQ's) are multicolor geologic 

maps on topographic bases in 7.5- or 15-minute quadrangle 

formats (scales mainly 1:24,000 or 1:62,500) showing 

bedrock, surficial, or engineering geology. Maps generally 

include brief texts; some maps include structure and columnar 

sections only.

Geophysical Investigations Maps (GP's) are on topographic 

or planimetric bases at various scales. They show results of 

geophysical investigations using gravity, magnetic, seismic, or 

radioactivity surveys, which provide data on subsurface structures that are of economic or geologic significance.

Miscellaneous Investigations Series Maps or Geologic 

Investigations Series (I's) are on planimetric or topographic 

bases at various scales; they present a wide variety of format 

and subject matter. The series also incudes 7.5-minute 

quadrangle photogeologic maps on planimetric bases and 

planetary maps.

Information Periodicals Metal Industry Indicators (Mil's)

is a free monthly newsletter that analyzes and forecasts the 

economic health of five metal industries with composite 

leading and coincident indexes: primary metals, steel, copper, 

primary and secondary aluminum, and aluminum mill 

products.

Mineral Industry Surveys (MIS's) are free periodic 

statistical and economic reports designed to provide timely 

statistical data on production, distribution, stocks, and 

consumption of significant mineral commodities. The 

surveys are issued monthly, quarterly, annually, or at other 

regular intervals, depending on the need for current data. The 

MIS's are published by commodity as well as by State. A 

series of international MIS's is also available.

Published annually, Mineral Commodity Summaries is the

earliest Government publication to furnish estimates covering 

nonfuel mineral industry data. Data sheets contain information 

on the domestic industry structure, Government programs, 

tariffs, and 5-year salient statistics for more than 90 individual 

minerals and materials.

The Minerals Yearbook discusses the performance of the 

worldwide minerals and materials industry during a calendar 

year, and it provides background information to assist in interpreting that performance. The Minerals Yearbook consists of 

three volumes. Volume I, Metals and Minerals, contains chapters about virtually all metallic and industrial mineral 

commodities important to the U.S. economy. Volume II, 

Area Reports: Domestic, contains a chapter on the minerals 

industry of each of the 50 States and Puerto Rico and the 

Administered Islands. Volume III, Area Reports: 

International, is published as four separate reports. These 

reports collectively contain the latest available mineral data on 

more than 190 foreign countries and discuss the importance of 

minerals to the economies of these nations and the United 

States.

Permanent Catalogs

"Publications of the U.S. Geological Survey, 1879-1961" 

and "Publications of the U.S. Geological Survey, 

1962-1970" are available in paperback book form and as a set 

of microfiche.

"Publications of the U.S. Geological Survey, 1971-1981" is

available in paperback book form (two volumes, publications 

listing and index) and as a set of microfiche.

Annual supplements for 1982, 1983, 1984, 1985, 1986, and 

subsequent years are available in paperback book form.