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Road Guide to 

Volcanic Deposits of 

Mount St. Helens and 

Vicinity, Washington 

By MICHAEL P. DOUKAS 

U.S. GEOLOGICAL SURVEY BULLETIN 1859 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, 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 .5. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE 1990 

For sale by the 

Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, 

Box 25425, Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Doukas, Michael P. 

Road guide to volcanic deposits of Mount St. Helens and vicinity, 

Washington I by Michael P. Doukas. 

p. cm.-(U.S. Geological Survey bulletin ; 1859) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:1859 

1. Volcanic ash, tuff, etc.-Washington (State)-Saint Helens, Mount, 

Region-Guide-books. 2. Saint Helens, Mount, Region (Wash.)-Description 

and travel-Guide-books. f. Title. fl. Series. 

QE75.B9 no. 1859 557.3 s-dc20 89-600384 

[QE461] [552.20979755] CIP 
CONTENTS 

Abstract 1 

Introduction 1 

The eruption of 1980-86 3 

Road guide 7 

Leg I. Vancouver to Spirit Lake 7 

Vancouver to the Swift Reservoir 7 

Side trip Ia. Yale Dam and Volcanic Monument headquarters 8 

Side trip lb. Swift Reservoir to Ape Cave lava tube, Pine CreekMuddy River fan, and Smith Creek-Muddy River 12 

Swift Reservoir to Spirit Lake 20 

Side trip Ic. Kalama River valley and the South Fork Toutle 

River 35 

Side trip Id. Randle to Meta Lake 38 

Leg II. Vancouver to Coldwater Lake via the North Fork Toutle River 40 

References cited 52 

FIGURES 

1. Map of southwestern Washington and northwestern Oregon, showing location 

of Mount St. Helens 1 

2. Generalized geologic north-south cross sections through Mount St. Helens 3 

3. Map of southwestern Washington, showing general distribution of volcanic 

deposits derived from Mount St. Helens 4 

4. Map of southwestern Washington, showing field-trip routes to Mount St. 

Helens 6 

5. Map of field-trip route along the Lewis River near Lake Merwin and Yale 

Lake 8 

6. Map of field-trip route near south side of Mount St. Helens in the Swift 

Creek area 10 

7. Oblique aerial photograph of south side of Mount St. Helens 11 

8. Photograph of interior of Ape Cave lava tube 12 

9. Map of field-trip route near southeast side of Mount St. Helens in the Pine 

Creek, Muddy River, and Smith Creek areas 13 

10. Oblique aerial photograph of southeast side of Mount St. Helens 14 

11. Generalized geologic map of upper Muddy River-Pine Creek fan 16 

12. Photograph of outcrop at stop 3 17 

13. Generalized stratigraphic section of outcrop at stop 4 18 

14. Generalized geologic map of area near confluence of Smith Creek and the 

Muddy River 19 

15. Photograph showing exposed section of fan at confluence of Smith Creek and 

the Muddy River 20 

16. Generalized geologic map of area near confluence of Smith Creek and Ape 

Canyon 21 

17. Map of field-trip route along the Swift Reservoir to confluence of the Lewis 

River, Muddy River, and Pine Creek 22 

18. Map of field-trip route near devastated-zone boundary 24 

19. Photograph showing air-fall tephra covering U.S. Forest Service Road 25 in 

July 1980 25 

20. Photograph showing section along axis of May 18, 1980, tephra 26 

21. Map of field-trip route near northeast side of Mount St. Helens 27 

Contents Ill 
IV Contents 

22. Photograph of volcanic deposits exposed in road cut along U.S. Forest Service 

Road 99 28 

23. Schematic stratigraphic column of pyroclastic deposits from Mount St. Helens 

along U.S. Forest Service Roads 94 and 99 in the devastated zone 29 

24. Sketch of Windy Ridge overlook of the crater and Pumice Plain 30 

25. Oblique aerial photograph of northeast side of Mount St. Helens 30 

26. Generalized geologic map of the area north of Mount St. Helens near Spirit 

Lake and Windy Ridge 31 

27. Schematic west-east geologic section and cross section at Timberline Road at 

stop 20 33 

28. Generalized geologic map and cross section of eastern part of Toutle River 

blockage near stop 22 34 

29. Photograph showing North Fork Toutle River blockage at stop 22 36 

30. Map of field-trip route near southwest side of Mount St. Helens 37 

31. Map of field-trip route near northeast side of Mount St. Helens 39 

32. Map of field-trip route near the Cowlitz and Toutle Rivers in the KelsoCastle Rock -Silver Lake area 42 

33. Map of field-trip route in area of confluence of the North and South Forks 

Toutle River 43 

34. Schematic stratigraphic section in Harry Gardner Park at stop 4 44 

35. Map of field-trip route on the North Fork Toutle River in the Pullen-Alder 

Creek-Elk Rock area 46 

36. Map of field-trip route on the North Fork Toutle River in the Elk RockColdwater Lake area 47 

37. Oblique aerial photograph of Mount St. Helens from the Elk Rock area 48 

38. Simplified geologic map of the Coldwater Lake blockage near stop 11 49 

39. Oblique aerial photograph of the Coldwater Creek-Castle Creek area, showing rockslide/debris avalanche near Coldwater Lake 51 

TABLES 

1. Summary of pre-1980 volcanic history of Mount St. Helens 2 

2. Eruptive activity at Mount St. Helens during 1980-86 5 

3. Traveling times from the Cascades Volcano Observatory to points near 

Mount St. Helens 7 

FIELD-TRIP STOPS 

Leg I 

1. Swift Reservoir overlook (deposits of the Cougar eruptive stage) 9 

2. Ape Cave (deposits of the Castle Creek eruptive period) 12 

3. USFS "Lahar Viewpoint" (1980 deposits) 15 

4. Stratigraphy (deposits of the Swift Creek eruptive stage to 1980) 15 

5. Lower Muddy River fan (deposits of the Kalama eruptive period to 1980) 16 

6. Beavertail slide (deposits of the Ape Canyon eruptive stage to 1980) 17 

7. Cougar pyroclastic flow (deposits of the Cougar eruptive stage) 20 

8. Pine Creek bridge (1980 deposits) 22 

9. Pine Creek assemblage lahars (deposits of the Pine Creek eruptive period 22 

10. Muddy River bridge (1980 deposits) 22 

11. Elk Pass (deposits of the Kalama eruptive period to 1980) 23 

12. Bear Meadows (1980 deposits) 23 

13. Northeast edge of sear zone (1980 deposits) 25 

14. Norway Pass trailhead (1980 deposits) 25 
15. Miners' car and Meta Lake (deposits of the Smith Creek eruptive period to 

1980) 25 

16. Snack stand (deposits of the Smith Creek eruptive period to 1980) 26 

17. Independence Pass trail (deposits of the Smith Creek eruptive period to 

1980) 26 

18. Harmony Falls overlook (1980 deposits) 27 

19. Windy Ridge (1980 deposits) 28 

20. Timberline Road (deposits of the Kalama eruptive period to 1980) 32 

21. Pumice Plain (1980-84 deposits) 32 

22. Avalanche blockage (1980 deposits) 32 

23. Kalama Quarry (deposits of the Kalama eruptive period) 35 

24. Goat Marsh Quarry (deposits of the Kalama eruptive period to Fraser 

glaciation) 35 

25. South Fork Toutle River overlook (deposits of the Cougar eruptive stage to 

1980) 35 

26. Crockett quarry (deposits of the Swift Creek eruptive stage to 1980) 36 

27. Macbride Lake (deposits of the Swift Creek to Cougar eruptive stages) 38 

28. Hyde stop (deposits of the Swift Creek eruptive stage to Fraser glaciation) 38 

29. Quartz Creek (1980 deposits) 38 

30. Ryan Lake (1980 deposits) 40 

Leg II 

1. U.S. Interstate Highway 5 bridge from the west bank of the Cowlitz River 

(1980 deposits) 41 

2. Washington Highway 99 bridge (1980 deposits) 41 

3. U.S. Forest Service Visitor Center 43 

4. Harry Gardner Park (deposits of the Smith Creek eruptive period to 1980) 44 

5. Toutle River bridge (deposits of the Smith Creek eruptiv~ period to 1980) 45 

6. Camp Baker-Hoffstadt Creek (1980 deposits) 45 

7. Sediment-retention structure N-1 (1980 deposits) 46 

8. North Fork Toutle River debris avalanche (1980-84 deposits) 46 

9. North Fork Toutle River overlook (1980 deposits) 47 

10. Elk Rock (1980 deposits) 48 

11. Coldwater Lake blockage, North Fork Toutle River debris avalanche (1980 

deposits) 48 

Contents V 

Road Guide to Volcanic Deposits of 

Mount St. Helens and Vicinity, Washington 

By Michael P. Doukas 

Abstract 

Mount St. Helens, the most recently active and most 

intensively studied Cascades volcano, is in southwestern 

Washington. The volcano is a superb outdoor laboratory for 

studying volcanic processes, deposits of observed events, 

and deposits whose origins are inferred by classic geologic 

techniques, including analogy to recent deposits. During the 

past 4,500 years, Mount St. Helens has been more active and 

more explosive than any other volcano in the conterminous 

United States. 

Mount St. Helens became active in mid-March 1980, 

and eruptive activity began on March 27. Since the climactic 

eruption of May 18, 1980, the volcano has continued to be 

active at least until 1988. The 1980 activity of Mount St. 

Helens is summarized in U.S. Geological Survey Professional 

Papers 1249 and 1250. 

This road guide is a tour of Mount St. Helens volcano 

and vicinity, with emphasis on the effects and deposits of the 

1980 eruption. The road log starts from the U.S. Geological 

Survey's David A. Johnston Cascades Volcano Observatory, 

Vancouver, Wash. The guide is organized around two primary routes. Leg I is on paved and gravel roads from 

Vancouver to areas east of Mount St. Helens, including 

Windy Ridge Overlook near Spirit Lake. This is possibly the 

most scenic route described in the guide, including a 

transect of the devastated zone of May 18, 1980, Spirit Lake, 

and numerous vistas of the volcano. Leg II leads to areas 

west of the volcano from Vancouver via U.S. Interstate 

Highway 5,.then on a paved and gravel road along the Toutle 

River. Highlights include the spectacular effects of mudflows 

and a view of the huge debris-avalanche deposit that was 

formed on May 18, 1980. 

INTRODUCTION 

Mount St. Helens, the most recently active and most 

intensively studied Cascade volcano, is in southwestern 

Washington (fig. 1). The volcano is a superb outdoor 

laboratory for studying volcanic processes, deposits of 

observed events, and deposits whose origins are inferred 

by classic geologic techniques, including analogy to recent deposits (fig. 1 ). Most of the visible cone has been 

formed within the past 1,000 yr, capping an older volcanic 

center active more than 40,000 to 2,500 yr B.P. (Hoblitt 

and others, 1980; Mullineaux and Crandell, 1981; HopManuscript approved for publication, June 7, 1988. 

son, 1971). Before 2,500 yr B.P., the repeated emplacement of dacite domes was accompanied by eruption of 

pyroclastic materials of similar composition (table 1 ). 

Since th~n, more mafic magma has also been erupted 

(fig. 2). Lava flows from Mount St. Helens are found 10 

mi (16 km) away from the volcano, pyroclastic-flow 

deposits 12 mi (19 km) and lahar (mudflow) deposits 35 

mi (56 km) away (fig. 3). Air-fall tephra from Mount St. 

Helens has been widespread; the Y tephra, for example, 

is found more than 600 mi (965 km) away in Alberta, 

Canada. 

0 

0 

WASHINGTON 

OREGON 

MOUNT 

.&RAINIER 

MOUNT 

.&HOOD 

50 KILOMETERS 

25 MILES 

Figure 1. Southwestern Washington and northwestern Oregon, showing location of Mount St. Helens relative to nearby 

Mounts Rainier, Adams, and Hood volcanoes. 

Introduction 
Table 1. Summary of pre-1980 volcanic history of Mount St. Helens 

[Eruptive stages and periods are separated by dormant intervals for which no unequivocal volcanic products 

have been recognized. Years before 1980 are based on tree-ring dates (Yamaguchi, 1983), 14c ages, and (or) 

historical records. A.D. dates during the Goat Rocks and Kalama eruptive periods from Yamaguchi (1983, 

1985). All tephras consist of multiple layers not subdivided further here; only the thickest layers of W, B, 

and Y tephras are distinguished. Locations are of outcrops that illustrate the various deposits during each 

eruptive period. Do., ditto. After Crandell and others (1981), Mullineaux and Crandell (1981), and Crandell 

( 1988) 1 

Eruptive stages and periods 

Spirit Lake eruptive stage: 

Modern eruptive period 

( 1980-88). 

Goat Rocks eruptive period 

Eruptive products Location (leg and stop) 

Avalanche--------------------------------- (See table 2). 

Lateral blast---------------------------------------------------------

Lahar-----------------------------------------------------------------

Pyroclastic flows-----------------------------------------------------

Tephra----------------------------------------------------------------

Domes (dacitic)-------------------------------------------------------

(150-100 yr B.P.)-------------- Dome (dacitic)---------------------------- (Destroyed May 18, 1980). 

Lava flows (andesitic)-------------------- North flank of volcano. 

(A.D. 1800)-------------------- T tephra (dacitic)------------------------ I-15, I-16, I-17, I-30. 

Kalama eruptive period 

(500-338 yr B.P.)-------------- Pyroclastic flows (dacitic, andesitic)---- Ic-22, I-23. 

(A.D. 1647?)------------------- Summit dome (dacitic)--------------------- (Destroyed May 1980). 

Lahars from summit------------------------ Muddy River fan, Ib-5. 

Lava flows (andesitic)-------------------- Southeast flank. 

X tephra (andesitic)---------------------- I-4, I-6, I-16, I-17. 

(A.D. 1482)-------------------- We tephra (dacitic)----------------------- I-4, I-6. 

(A.D. 1480)-------------------- Wn tephra (dacitic)----------------------- I-16, I-17, I-20, I-30. 

Sugar Bowl eruptive period 

( 1 , 200 yr B. P. ) • 

Castle Creek eruptive period 

(2,500-1,600 yr B.P.). 

Pine Creek eruptive period 

(3,000-2,500 yr B.P.). 

Smith Creek eruptive period 

(4,000-3,,300 yr B.P.). 

Swift Creek eruptive stage 

(13,700-9,200 yr B.P.). 

Fraser Glaciation (ended approx 

13,000 yr B.P.). 

Cougar eruptive stage 

(20,400-19,200 yr B.P.). 

Ape Canyon eruptive stage 

(approx 40,000?-35,000 yr B.P.). 

Dome (dacitic)---------------------------- Northeast flank of volcano. 

Pyroclastic flows (dacitic)--------------- Do. 

Deposits of lateral blast (dacitic)------- I-17, I-20. 

Bu tephra (basaltic)---------------------- I-4, I-16, I-17. 

Bi tephra (dacitic)----------------------- Do. 

Bo tephra (andesitic)--------------------- Do. 

Bh tephra (andesitic)--------------------- Do. 

Lava flows (basaltic)--------------------- I-2, I-4, I-20. 

Pyroclastic flows (dacitic, andesitic)--------------------------------

P tephra (dacitic)------------------------ I-4, I-16, I-17. 

Pyroclastic flows (dacitic)--------------- canyon of Pine Creek. 

Domes (dacitic)--------------------------- Crater. 

Lahars------------------------------------ I-9, II-4. 

Ye tephra (dacitic)----------------------- I-4. 

Pyroclastic flows (dacitic)-------------------------------------------

Yn tephra (dacitic)----------------------- I-16, I-17. 

J tephra (dacitic)------------------------ I-4, Ic-23. 

Pyroclastic flows (dacitic)--------------- West Fork Swift Creek. 

Lahars------------------------------------ rc-26. 

Domes (dacitic)-------------------------------------------------------

s tephra (dacitic)------------------------ I-4. 

K tephra (dacitic)------------------------ I-l. 

Pyroclastic flows (dacitic)--------------- I-7, I-25. 

Domes (dacitic)-------------------------------------------------------

Avalanche--------------------------------- Ic-27. 

Lava flows (andesitic)-------------------- West Fork Swift Creek. 

M tephra (dacitic)------------------------ I-1. 

C tephra (dacitic)------------------------ I-6. 

Pyroclastic flows (dacitic)--------------- Do. 

Lahars------------------------------------ I, Lewis River. 

2 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
In comparison with its several-hundred-thousandyear-old neighbors, Mounts Rainier and Adams, Mount 

St. Helens is a young volcano. During the past 4,500 yr, 

Mount St. Helens has been more frequently and explosively active than any other volcano in the conterminous 

United States (Crandell and Mullineaux, 1978). Many 

dated deposits (Mullineaux and Crandell, 1962; Greeley 

and Hyde, 1972; Crandell and Mullineaux, 1973; Hyde, 

1975; Crandell and others, 1981; Mullineaux, 1986) show 

the high frequency of eruptions. Before the current 

activity began, Crandell and others (1975) and Crandell 

and Mullineaux (1978) had suggested that the volcano 

could erupt soon, possibly before the end of the 20th 

century. 

THE ERUPTION OF 198Q-86 

The 1980 activity of Mount St. Helens is summarized 

in U.S. Geological Survey (USGS) Professional Papers 

1-

w 

w 

l.L 

l.L 

10 

9 

8 

7 

0 5 

(/) 

0 

A 

Older dacite 

1249 (Foxworthy and Hill, 1982) and 1250 (Lipman and 

Mullineaux, 1981). The activity began on March 15 with 

an increasing number of earthquakes beneath the volcano. The first phreatic eruption occurred on March 27, 

coincident with a high level of seismic activity. A summit 

crater formed and continued to enlarge for 2 months as 

phreatic activity continued. Tephra erupted during this 

time was composed of pulverized old rock, not new 

magma; however, viscous magma was intruding high into 

the cone, forming a cryptodome whose surface manifestation was the famous "bulge" on the north flank. This 

bulge grew outward at a maximum rate of 8.2 ft/d (2.5 

m/d) with no acceleration or other significant change 

until the climactic eruption. 

The eruption at 8:32a.m. p.d.t. May 18 was apparently triggered by a magnitude 5.1 earthquake that 

caused the unstable north flank to fail as three great 

retrogressive landslide blocks. The landslides developed 

into a complex debris avalanche that sped down the valley 

Goat Rocks dome 

~ 4 L_ ________________________________ ~-L--------------------------------------~~~~ 

(/) 

::::> 

0 

I 

1-

~ 

8 1: [ B 

:; I ~ 8 w 

7 

6 

5 

4 L-----------------------------------~--------------------------------------------~ 

0 

0 

Figure 2. Generalized north-south geologic cross sections 

through Mount St. Helens. A, Young summit dome (dacite) 

and surface flows (stippled areas) overlie older (more than 

2,500 yr) dacitic pyroclastic flows, lavas flows, and domes. 

Geology generalized from C.A. Hopson (written commun., 

1983) and Glicken (1986). Dashed line, approximate outline 

1 KILOMETER 

1 MILE 

of 1980 crater floor. 8, Preeruptive summit dome. Roman 

numerals denote main-slide blocks of avalanche; arrows 

indicate direction of failure. Dotted line, pre-1980 surface; 

long-dashed line, presumed outline of intruding magma in 

1980; short-dashed line, approximate outline of 1980 crater 

floor. 

The Eruption of 1980-86 3 
of the North Fork Toutle River, reaching its termination 

16 mi west of the volcano in about 10 minutes. Unloading 

of the volcano by these landslides relieved pressure on 

the cryptodome and its associated hydrothermal system; 

the depressurized gases violently expanded and generated a northward-directed lateral explosion or blast. A 

pyroclastic surge (Moore and Sisson, 1981) or flow 

(Walker and McBroome, 1983) developed from the blast 

and fanned outward from the volcano, felling trees and 

killing most wildlife in a 212-mi2 (550 km2 ) area. Two 

columns convectively rose from the devastated zone and 

joined to reach a maximum height of 16 mi (25 km) by 

9:00a.m. 

The landslides and blast removed the upper 1,312 ft 

(400 m) of the cone and left a crater 2,050 ft (625 m) 

deep, 1.7 mi (2.7 km) long, and 1.3 mi (2.0 km) wide. 

About 30 min after the blast, debris falling from the 

unstable crater wall and lesser vesiculating dacitic magma from the roots of the cryptodome were explosively 

ejected in an eruption column that ranged from 9 to 10 

mi (14-16 km) in height throughout the morning. Darkgray ash, consisting largely of lithic debris from this 

Figure 3. Southwestern Washington, showing general distribution of volcanic deposits derived from Mount St. Helens. 

Shaded areas, lava flows, pyroclastic flows, lahars, and 

avalanches from Mount St. Helens; contact dashed were 

appFoximately located. Heavy-dashed line, 20-cm isopach 

(equal-thickness contour) of major ash falls younger than 

column, fell more than 930 mi (1,500 km) away. The 

eruption column lightened in color and became more 

energetic at about noon, possibly as a fresh supply of 

gas-rich magma reached the surface; pumiceous pyroclastic flows spilled northward from the crater and covered part of the debris avalanche, forming the Pumice 

Plain. Light-gray magmatic ash from this 9 to 12 mi 

(14-19 km) column fell on earlier, dark-gray lithic ash in 

eastern Washington and northern Idaho. The eruptive 

activity declined and ended that night. 

Many mudflows formed on May 18, mostly by melting of snow and glacial ice. The largest mudflow, down 

the North Fork Toutle River, formed as the debris 

avalanche dewatered (Janda and others, 1981; Voight 

and others, 1981, 1983). This flow destroyed or heavily 

damaged 200 homes and deposited more than 95 million 

yd3 (72 million m3

) of sediment in the Cowlitz and 

Columbia Rivers, where clogged shipping channels required costly dredging (Schuster, 1981 ). 

Five explosive eruptions between May 25 and October 18, 1980 (table 2), generated pyroclastic flows and 

tephra falls, and three eruptions ended with emplace 

+ 

0 

I 

0 

5 

I 

/ 

, 

; 

, 

, 

+ 

10 KILOMETERS 

I 

5 MILES 

/ 

, 

, 

" ' \ 

I 

I 

2,500 yr (T, Wn, We, Yn, Ye tephras of Crandell and Mullineaux, 1978). CR, Castle Rock; KLV, Kelso-Longview; MSH, 

Mount St. Helens; NFL, North Fork Lewis River; NFT, North 

Fork Toutle River; SFT, South Fork Toutle River; SL, Spirit 

Lake; W, Woodland. 

4 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
Table 2. Eruptive activity at Mount St. Helens during 198G-86 

[Dome growth occurred both by endogenous and exogenous processes. Tephra and pyroclastic-flow 

pumice erupted during 1980-83 contain Fe-Mg phenocryst-assemblage hypersthene-hornblende-augite 

(Kuntz and others, 1981; Cashman and Taggart, 1983); augite is reported at less than 0.5 volume 

percent. Locations are of outcrops that illustrate the various types of eruptive processes 

during each period. Do., ditto] 

Date 

1980 Mar. 27 

Apr. 

May 18 

May 25 

June 12 

July 22 

Aug. 

Oct. 17 

Dec. 28 

1981 Feb. 

Apr. 22 

June 19 

Sept. 6 

Oct. 31 

1982 Mar. 19 

Mar. 21 

Apr. 4, 5 

May 14 

Aug. 18 

1983 Feb. 2, 3 

Feb. -Dec. 

1984 Jan. 

Feb. 10 

Mar. 29 

May 14, 26 

June 17 

Sept. 1 2 

1985 May 30 

1986 May 9 

Oct. 21 

Dominant activity Other products Location (leg and stop) 

Explosive-------------- Lithic ash-------------- Minor amounts around volcano. 

do------------------- do-------------------- Do. 

do------------------- Avalanche--------------- I-22, II-11, II-13. 

Lateral blast----------- 1-11, I-12, I-13, I-14, I-15, 

I-17, I-20. 

Blast deposit 1---------- II-1 2, II-13. 

Lahar------------------- I-3, I-4, I-5, I-6, I-8. 

Pyroclastic flow-------- I-20, I-22. 

May 18 tephra----------- I-11, 1-12, I-17. 

do------------------- Pyroclastic flow; 

May 25 tephra. 

I-22; minor air-fall lobe 

northwest of volcano. 

Explosive, dome 

growth. 

Pyroclastic flow; 

June 1 2 tephra. 

I-22; minor air-fall lobe 

southwest of volcano. 

Explosive-------------- Pyroclastic flow; 

July 22 tephra. 

I-11, I-22; air-fall lobe 

northeast of volcano. 

Explosive, dome 

growth. 

Pyroclastic flow; 

August 7 tephra. 

Minor air-fall lobe north 

of volcano. 

do------------------- Pyroclastic flow; Minor air-fall lobe southOctober 17 tephra. west of volcano. 

Dome growth, minor Crater. 

explosive. 

Dome growth------------------------------------- Do. 

do-------------------------------------------- Do. 

do-------------------------------------------- Do. 

do-------------------------------------------- Do. 

do-------------------------------------------- Do. 

Minor explosive-------- Lahar------------------- I-21. 

Dome growth------------ Ice and ash ava- Do. 

lanche. 

March 19 tephra--------- Minor air-fall lobe southeast of volcano. 

Minor explosive--------------------------------- Crater. 

Dome growth------------------------------------- Do. 

do-------------------------------------------- Do. 

Minor explosive-------- Lahar------------------- North flank. 

Dome growth 

(continuous). 

Dome growth (end of 

continuous). 

Crater. 

Do. 

Dome growth------------------------------------- Do. 

do-------------------------------------------- Do. 

Minor explosive-------- Lahar------------------- North flank. 

Dome growth------------------------------------- Crater. 

do-------------------------------------------- Do. 

do-------------------------------------------- Do. 

do------------------- Rockfall---------------- Do. 

do-------------------------------------------- Do. 

1'l'he term "blast deposit" is here used to designate a deposit resulting from any process 

initiated by the lateral explosion. Precise transport and deposition mechanisms are controversial (Walker and McBroome, 1983; Hoblitt and Miller, 1984; Waitt, 1984a; Walker and Morgan, 

1984). 

The Eruption of 198o-86 5 
ment of a small dacitic lava dome. From October 18 until 

at least June 1985, a composite dome grew in the new 

crater in an episodic but predictable way (table 2; Swanson and others, 1983 and in press). 

Natural events continue to affect Mount St. Helens. 

Eruptions periodically add dacitic lava to the dome 

within the crater and deposit minor amounts of ash 

downwind from the volcano. Streams erode and rework 

the debris-avalanche and mudflow deposits in the valleys 

and slopes surrounding the volcano. 

Man has also affected the landscape around Mount 

St. Helens. Construction of a sediment-retention dam 

has altered the appearance of the avalanche deposit. 

"-Lewis & Clark 

Visitor Center 

OREGON 

Figure 4. Southwestern Washington, showing field-trip 

routes to Mount St. Helens. Leg I consists of routes to areas 

south, east and northeast of the volcano. Leg II leads to areas 

west of the volcano. Radiating lines, inner devastated zone 

where virtually every large tree was uprooted or broken off, 

Spillways have been constructed at three lakes impounded by the avalanche, and in 1982-84 the level of Spirit 

Lake was controlled by a major pumping operation. 

Salvage of downed timber has removed much evidence of 

the lateral blast in many areas. The natural state is being 

preserved insofar as possible within the newly created 

Mount St. Helens National Volcanic Monument. 

This road guide to Mount St. Helens volcano, emphasizes the effects and deposits of the 1980 eruption. 

The road log starts from the USGS, David A. Johnston 

Cascades Volcano Observatory, 5400 MacArthur Boulevard, Vancouver, Wash.; travelers can also join the route 

at other locations (fig. 4). This road guide is intended 

~Mount St. Helens 

National Monument 

Headquarters 

0 

I 

0 

5 KILOMETERS 

I 

~MILES 

branches stripped, and the trunk abraded and left aligned in 

the direction of local blast motion. Patterned areas, sear zone 

at fringe of devastated zone where vegetation was left 

standing but killed by heat. A, avalanche; P, pyroclastic 

flows. Long-dashed line, area of 1980 tephra fall. 

6 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
mainly for use by individuals with a background in 

geology, although parts of it may be useful to the layman. 

The guide is organized around two primary routes. Leg I 

(fig. 4) leads on paved and gravel roads from Vancouver 

to the Windy Ridge overlook near Spirit Lake via Cougar 

(legs I, Ib ). This is possibly the most scenic route 

described in the guide, yielding a transect of the devastated zone of May 18, 1980, Spirit Lake, and numerous 

vistas of the volcano. The trip requires at least a full day 

from Vancouver. Be advised that gas, food, and other 

services are available only in Cougar, at the Eagle Cliff 

store (east end of the Swift Reservoir), and in Randle. 

Leg II (fig. 4) leads to the volcano from Vancouver 

via U.S. Interstate Highway 5, then on a paved and gravel 

road along the Toutle River. Highlights include the 

spectacular effects of mudflows and a view of the huge 

debris-avalanche deposit that was formed on May 18, 

1980. This trip also requires a full day from Vancouver; 

it is not now possible to connect legs I and II north of the 

volcano to make a convenient loop. For those who wish to 

see other geologic features not on the main routes, 

several side trips are described to points of special 

interest (legs Ia, Ib, Ic, Id). Because visitors may have 

various amounts of time and varied interests while visiting Mount St. Helens, tables have been provided so that 

the visitor may decide what stops to make (tables 1, 2). 

Each table contains a list cross-referencing the periods of 

volcanic activity at Mount St. Helens with outcrops that 

illustrate the various types of processes and products 

from that period; outcrops are located by leg and stop 

number. Included within the road log are mileages 

between points of interest. Parts of leg I from the Swift 

Reservoir and leg Id from Randle have mileages that can 

be read either north or southbound. 

Access to some of these sites requires a four-wheeldrive vehicle; a few areas also require special permits. 

We recommend that you discuss your itinerary with U.S. 

Forest Service (USPS) or USGS personnel who are 

familiar with current conditions. 

Weather and road conditions can change access to 

the volcano, so check with the Gifford Pinchot National 

Forest (Vancouver, Wash.) or Mount St. Helens National Volcanic Monument Headquarters (Amboy, Wash.). 

The traveling times between the Cascades Volcano Observatory and localities near the volcano are listed in 

table 3. 

The most valuable references for this road guide are 

USGS Professional Paper 1250, "The 1980 Eruptions of 

Mount St. Helens, Washington," and the USPS-USGSWashington Department of Natural Resources 

1:100,000-scale map "Mount St. Helens and Vicinity." 

Other useful material is listed in the section below 

entitled "References." 

Table 3. Traveltimes from the Cascades Volcano Observatory to points near Mount St. Helens 

[CVO, Cascades Volcano Observatory; USFS, u.s. Forest Service] 

Route Distance 

(mi) 

Time 

(h) 

vancouver (CVO) to Woodland via 

u.s. Interstate Highway 5. 

vancouver (CVO) to Castle Rock via 

u.s. Interstate Highway 5. 

vancouver (CVO) to Randle via 

22.1 

50 

118.8 

1+ 

2 

u.s. Interstate Highway 5 and 

u.s. Highway 12. 

vancouver (CVO) to Cougar via 

washington Highway 503 and 

USFS Road 90. 

50.3 1+ 

Cougar to Windy Ridge parking lot 

via USFS Roads 90, 25, and 100. 

54 2+ 

ROAD GUIDE 

CAUTION: SOME OF THE ROADS IN THIS 

GUIDE ARE SUITABLE ONLY FOR FOURWHEEL-DRIVE VEHICLES AND ARE IMPASSABLE IN THE WINTER AND SPRING. CHECK 

WITH LOCAL AUTHORITIES BEFORE ATTEMPTING ROADS OFF THE MAIN HIGHWAYS. 

Leg I. Vancouver to Spirit Lake 

Cumulative 

mileage 

0.0 

15.6 

19.8 

Vancouver to the Swift Reservoir 

(mileage 

between 

points) 

0.0 

(15.6) 

(4.2) 

Leave Cascades Volcano Observatory. Travel west on Mill Plain 

Blvd. to junction with U.S. Interstate Highway 5. Head north on 

U.S. Interstate Highway 5. Surface is underlain by gravel and 

sand of the sreat Pleistocene glacial Lake Mtssoula floods. 

Pass Ridgefield exit to Washington 

Highway 501. View of Mount St. 

Helens to the northeast. 

Cross the East Fork Lewis River. 

Outcrops in roadcut on east side 

of road are lava flows of the upper 

Eocene or lower Oligocene Goble 

Volcanics Series of Lowry and 

Baldwin (1946), interbedded with 

sandstone and siltstone of the 

Cowlitz Formation (in part equivalent to the Hatchet Mountain 

Formation (Roberts, 1958), consisting of porphyritic andesite, olivine basalt, basalt, and breccia, 

with interbedded sedimentary 

rocks). 

Road Guide 7 
21.5 (1.7) Cross the North Fork Lewis River. 44.5 (2.4) Valley glaciers occupied the Lewis 

River valley during the local Am22.1 (0.6) Take exit 21 to Woodland; head boy glaciation (Mundorff, 1984). 

east along Washington Highway Here, glaciers reached a thickness 

503 along north side of the Lewis of 1,950 ft (600 m). The Amboy 

River. drift deposited from these glaciers 

23.4 (1.3) Concrete retaining walls for flood 

was found to be overlain by the C 

tephra from Mount St. Helens 

protection. ~35,000--40,000 yr old). Mundorff 

29.8 (6.4) Lewis River fish hatchery. 1984) suggested that the Amboy 

rift is correlative with the Hay31.8 (2.0) Outcrops of interbedded Tertiary den Creek drift C4 C dating 

showed wood found in Canyon lava flows and breccia of the Creek east of Lake Merwin to be Hatchet Mountain(?)Formation older than 60,000 yr) and repre- (Roberts, 1958), eqmvalent of the sents a geologic event of early Goble Volcanic Series of Lowry Wisconsin age. and Baldwin (1946). 45.2 (0.7) Junction of Lewis River Road and 

32.5 (0.7) Junction with road to the Merwin Washington Highway 503. 

Dam and Lelooska Indian exhibit. 

SIDE TRIP Ia. Yale Dam and Volcanic Monument headquarters 

33.5 (1.0) Outcrops of Tertiary lava flows and 

other volcanic rocks along road (mileage 

for several miles. Entering area of Cumulative between 

figure 5. mileage points) 

37.8 (4.3) Junction with Wilkinson Road. 0.0 (0.0) Road to headquarters of Mount St. 

Helens National Volcanic Monu42.1 (4.3) Red-baked sedimentary 

beneath lava flow. 

deposits ment. Head south on Washington 

Highway 503. 

0 2 KILOMETERS 

I I I I 

0 1 2 MILES 

Figure 5. Field-trip route along the Lewis River near Lake Merwin and Yale Lake, showing part of leg I and starting point of legs 

Ia and lc. Triangles, viewpoints; circled numbers, U.S. Forest Service roads; USFS, U.S. Forest Service station. 

8 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
1.4 (1.4) 

2.9 (1.5) 

3.4 (0.5) 

5.7 (2.3) 

VIEWPOINT. Speelyai viewpoint, 

17 mi (27 km) SW. of Mount St. 

Helens. Southwest flank of Mount 

St. Helens is visible from here. 

Yale Dam turnoff. About 300 ft 

(100 m) beyond the intersection 

are laharic overbank deposits of 

the Swift Creek erui?tive stage 

(13,000-8,000 yr B.P.) overlying 

brown silt (loess?). Near the base 

of the brown silt is a bed of air-fall 

lapilli, probably part of the M 

tephra (early Cougar eruptive 

stage, 20,000-18,000 yr B.P.). 

Two fine-grained lahars exposed 

in a small borrow pit several hundred yards farther down the road 

are separated by about 0.4 in. (1 

em) of S tephra (early Swift Creek 

eruptive stage, 13,000 yr B.P.). 

Bridge over east end of the Merwin 

Reservoir. 

Chelatchie, USPS Mount St. Helens 

Volcanic Monument headquarters. Check in here if you have a 

gate key to pick up, passes to sign, 

and so on. 

END OF SIDE TRIP Ia 

Return north on Washington Highway 503; rejoin leg I. 

(mileage 

Cumulative between 

mileage points) 

0.0 

1.3 

2.5 

3.1 

3.3 

4.4 

4.7 

5.1 

5.4 

(0.0) 

(1.3) 

(1.2) 

(0.6) 

(0.2) 

(1.1) 

(0.3) 

(0.4) 

(0.3) 

Turn right and head east on Lewis 

River road to the town of Cougar. 

Terrace surface and valley fill contain deposits of the Cougar eruptive stage. 

Cross Speelyai Creek. Terrace surface is underlain by lahars of the 

Cougar eruptive stage. 

Yale Reservoir to the right. 

Across lake to the east are deposits 

of the Cougar eruptive stage. 

Visitor-information station to 

Mount St. Helens National Volcanic Monument. 

Junction with USPS Road 81 and 

side trip to Merrill Lake (leg Ic). 

Bridge over Dog Creek. Entering 

area of figure 6. 

Road to borrow pit and outcrop of 

lahar of the Swift Creek eruptive 

stage. Deposits predating the S 

tephra (ca. 13,000 yr B.P.) 

Enter the town of Cougar, where 

gas and food are available (may be 

7.3 (1.9) 

7.8 (0.5) 

8.2 (0.4) 

9.5 (1.3) 

9.9 (0.4) 

10.8 (0.9) 

11.6 (0.8) 

last gas for 160-mi [260 km] round 

trip). Travel east from Cougar on 

Lewis River road, which becomes 

USPS Road 90. 

Ahead, the surface unit is the Cave 

Basalt, formed durin~ the Castle 

Creek eruptive penod (2,200-

1,700 yr B.P.), a high-alumma basalt, uncon formably overlying deposits of the Cougar eruptive 

stage. 

Hydroelectric-power house on 

right. Rip-rap of hydroelectricpower canal on left is composed of 

Cave Basalt. 

On both sides of the road are tumuli, a feature common in tube-fed 

pahoehoe basalt flows. During 

Castle Creek time, the Cave Basalt flowed down a broad fan from 

the south flank of Mount St. 

Helens and poured over the cliff 

north of the road, covering the 

floor of the Lewis River valley. 

In north bank and bed of the Lewis 

River ahead on the right is a lahar 

of the Ape Canyon eruptive stage 

(40,000-35,000 yr B.P.) that contains wood dated at 36,000±2,100 

yr (Crandell and others, 1981). 

The wood here is slightly charred 

or uncharred, but the presence of 

larger biotite-bearing dacite clasts 

showing consistent paleomagnetic 

vectors suggests that the clasts 

were hot upon emplacement 

(C.G. Newhall, oral commun., 

1983l. To visit this spot, you 

shou d pull off the road before it 

rises up to cross the hydroelectricpower canal. 

Power canal bridge; Swift Dam up 

valley. OutcroJ?S of deposits of the 

Cougar eruptive stage on north 

side of road. 

North side of road. Lower 30ft (9 

m) consists of lahar and stream 

deposits of the Cougar eruptive 

stage, above which is exposed 

reddish-pink outcrops of a debrisavalanche deposit (coarse flowage 

deposit of Hyde, 1975) and pyroclastic flows of the Cougar eruptive stage. 

STOP 1 AND VIEWPOINT. Swift 

Reservoir overlook. 

The road between the power canal bridge and the 

Swift Reservoir overlook climbs through a dissected fan 

of deposits of the Cougar eruptive stage that blocked the 

Lewis River valley here and extended as far downstream 

Road Guide 9 
•\ 

,.: ......... _ 

·~ / '·. 

, ,. ·-~-~)A ·- . ' ( 

' ~~/---''·~:. 

c,;*N< N ; 

... -........ 

0 2 3 KILOMETERS 

0 2 MILES 

Figure 6. Field-trip route near the south side of the volcano in the Swift Creek area, showing part of leg 

I. Circled numbers, U.S. Forest Service roads; triangles, viewpoints; long-dashed line, devastated-zone 

boundary. 

10 Road Guide to Volcanic Deposits of Mount St. Helens and VIcinity, Washington 
as the Merwin Reservoir (side trip Ia). You are standing 

on the upper surface of a fan that once extended across 

the Lewis River valley (fig. 7). Southwest of the overlook, 

across the Lewis River valley at this altitude, is a remnant 

of the fan surface. In a borrow pit in this remnant are 

stratified sand and gravel, lahar deposits, pyroclastic-flow 

material, and tephra of the Cougar eruptive stage (Crandell, 1987). An 18,560-yr age was obtained on charcoal 

from a 6-ft (2 m)-thick pyroclastic-flow deposit overlying 

M tephra and a 20,350-yr age was obtained on charcoal 

from a pumiceous pyroclastic-flow deposit underlying M 

tephra (Crandell and others, 1981 ). During an earlier 

part of the Cougar eruptive stage, an avalanche similar to 

that of 1980 may have occurred on the south flank of 

Mount St. Helens (Hyde, 1975; Newhall, 1982). These 

deposits can be seen as reddish-pink outcrops on the 

north side of the road as you travel up the hill. The 

deposits once had a volume of at least 0.4 me (1 km3), 

and extended at least 9 mi (15 km) from the volcano 

(Newhall, 1982). A lake apparently formed behind the 

avalanche. Breaching of the blockage by the lake generated a large lahar. This and a similar 2,800-yr-old deposit 

of the Pine Creek eruptive period (seen on leg II, stop 5) 

may represent the type of phenomena that could result if 

the large lakes dammed by the 1980 eruptions of Mount 

St. Helens were to breach their barriers. 

Figure 7. South side of Mount St. Helens. Qc, Cave Basalt (Holocene); dashed lines indicate approximate boundaries. 

Numbers, U.S. Forest Service roads. Photograph by Austin Post, taken June 30, 1980. 

Road Guide 11 
GO TO PAGE 20 FOR CONTINUATION OF SWIFT RESERVOIR 

ROUTE LEG I. 

SIDE TRIP lb. Swift Reservoir to Ape Cave lava tube, Pine 

Creek-Muddy River fan, and Smith Creek-Muddy River 

(mileage 

Cumulative between 

mileage points) 

0.0 (0.0) STOP 1 AND VIEWPOINT. Swift 

Reservoir dam overlook. Continue on USFS Road 90. 

0.9 (0.9) 

2.6 (1.7) 

2.8 (0.2) 

Junction of USFS Roads 83 and 90. 

Leg I continues to right (route to 

Spirit Lake). Turn left onto USPS 

Road 83 for side trip Ib to the Ape 

Cave lava tube and east slopes of 

Mount St. Helens. 

Junction of USFS Roads 83 and 

8303. Turn left to Ape Cave. 

Lava Cast picnic grounds. Exposed 

in basalt 300 ft (100 m) south of 

the parking lot are molds of trees 

that were mundated by the Cave 

Basalt flow. 

3.8 (1.0) STOP 2. Parking lot of lower entrance to Ape Cave. 

Warm clothing and flashlight or lantern are needed if 

you plan to explore the cave. Ape Cave is one of 

numerous lava tubes formed in the Cave Basalt (fig. 8). 

The basalt consists of pahoehoe flows that originated on 

the southwest flank of Mount St. Helens and flowed 

down the surface of older pyroclastic-flow deposits. 

Charcoal samples from two localities under the lava 

tubes yielded 14C ages of 1,860±250 and 1,925±95 yr 

(Greeley and Hyde, 1972). 

Return to junction of USPS Roads 83 and 8303 to 

continue leg Ib. 

Cumulative 

mileage 

0.0 

(mileage 

between 

points) 

(0.0) Turn left on USPS Road 83 and 

head north. Road follows the surface of pyroclastic-flow deposits 

and lahars of the Cougar eruptive 

stage. 

Figure 8. Interior of Ape Cave lava tube within the Cave Basalt; tube here is approximately 30ft (9 m) wide. Photograph by Ken 

Cameron. 

12 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
1.3 (1.3) Junction of USPS Roads 83 and 81. 

Road to left (USPS Road 81) 

leads to Red Rock Pass, Merrill 

Lake, the Kalama River basin, 

and leg Ic. 

Bear right and continue on USPS Road 83. For the next 

half-mile (0.8 km) are exposed deposits of the Swift 

Creek and Cougar eruptive stages. Pyroclastic flows and 

lahars of the Swift Creek eruptive stage are interbedded 

with S tephra (13,000-18,000 yr old) and overlie till of 

the Fraser glaciation. This till consists predominantly of 

rock debris derived from the volcano (Hyde, 1975). 

1.8 (0.5) Cross the West Fork Swift Creek. 

The oldest and longest andesite 

flow from Mount St. Helens is 

exposed for the next half-mile (0.8 

km) along the southwest-facing 

slope. The flow is overlain here by 

a pumiceous pyroclastic-flow deposit of the Cougar eruptive stage. 

These deposits are, in turn, overlain in the roadcut by pyroclasticflow deposits and lahars of the 

Swift Creek eruptive stage. 

0 

0 

Figure 9. Field-trip route near southeast side of the volcano 

in the Pine Creek, Muddy River, and Smith Creek areas, 

showing part of leg lb. Triangles, viewpoints; circled numbers, U.S. Forest Service roads; long-dashed line, 

The best drinking water on the mountain is from a spring 

on the north side of road, a short distance east of the 

creek crossing. 

3.8 

4.2 

4.8 

5.7 

6.2 

6.8 

2 KILOMETERS 

2 MILES 

(2.0) 

(0.4) 

(0.6) 

(0.9) 

(0.5) 

(0.6) 

Cross the East Fork Swift Creek. 

Exposed in the creek bed is a 

basalt flow of the Castle Creek 

eruptive period overlain by lahar 

deposits of the same age. 

Junction of USPS Roads 83 and 

8312. Bear left (for road to Marble Mountain, turn right on USPS 

Road 8312). 

Outcrops of the Ohanapecosh Formation on left, north of road. 

Junction of USPS Roads 83 and 

N825; bear right. Entering area of 

figure 9. 

Junction of USPS Road 83 and unmarked road; bear left. 

Tephra deposits, ranging in age 

back to the Swift Creek eruptive 

stage (table 1 ), are exposed in 

outcrop just past unnamed creek. 

These deposits include dark scoria 

devastated-zone boundary; short-dashed lines and shading, areas covered by pyroclastic flows and lahars on east 

side of volcano; stippling, areas covered by pyroclastic 

flows and avalanche on north side of volcano. 

Road Guide 13 
7.1 (0.3) 

of the X tephra and white pumice 

lapilli of the We tephra from the 

Kalama eruptive period, basaltic 

and dacitic ash of the B tephra 

from the Castle Creek eruptive 

period, the P tephra from the Pine 

Creek eruptive period, yellow 

pumice of the Y e tephra from the 

Smith Creek eruptive stage, and 

orange pumice of the J tephra 

from the Swift Creek eruptive 

stage. 

Road crosses over a spur composed 

of Ohanapecosh Formation that 

underlies Marble Mountain volcanic rocks south of road; enter the 

Pine Creek-Muddy River fan 

complex. 

Information concerning events that occurred at the following stops in the Lewis River-Pine Creek-Muddy 

River-Smith Creek drainage basin (fig. 10) on May 18, 

1980, was reported by Janda and others (1981). 

8.2 (1.1) 

8.6 (0.4) 

VIEWPOINT. Cross Pine Creek. A 

previous bridge survived the May 

18, 1980, eruption but was destroyed the following winter by 

high water. 

Leave forested area that was little 

affected by mudflows and enter 

onto mudflow-swept fan surface. 

Figure 10. Southeast side of Mount St. Helens. Numbers, U.S. Forest Service roads. Photograph by Austin Post, taken June 

30, 1980. 

14 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
8.7 (0.1) STOP 3. USPS "Lahar Viewpoint." 

A short walk to the east brings you to a small hill and 

the viewpoint. This area was swept by a lahar within 15 

minutes after the onset of the May 18 eruption (fig. 11 ). 

At this point, the speed of the lahar was estimated at 

about 44 mi!h (20 m/s). Conspicuous notch in east rim of 

Mount St. Helens is truncated valley cut by the Shoestring Glacier. This glacier formerly was fed by an ice and 

snow field at the summit of Mount St. Helens. The 

eruption of May 18 decapitated the glacier and removed 

approximately three-quarters of its original volume 

(Brugman and Meier, 1981). 

Depending on road conditions and vehicle restrictions, 

you may have to walk to the next stop. Travel on road that 

leads to northeast from the parking area. 

9.2 (0.5) STOP 4. Outstanding outcrofs of 

pyroclastic-flow and air-fal deposits, and the lahar-impact area. 

Here is one of a few exposed sections that show an 

extensive stratigraphic record of Mount St. Helens eruptive history (figs. 12, 13). S tephra underlies an erosional 

surface (early Swift Creek eruptive stage). Two conspicuous orange layers of J tephra (late Swift Creek eruptive 

stage) are overlain by Y tephra (Smith Creek eruptive 

stage), which is interbedded with pyroclastic-surge deposits. Overlying the deposits of the Smith Creek eruptive period is P tephra (a mixture of reworked tephra and 

possible surge deposits of the Pine Creek eruptive period); B tephra (basaltic and basaltic andesite scoria and 

dacite of the Castle Creek eruptive period, older than the 

Cave Basalt); W tephra (layer We, white pumice lapilli 

and ash of the Kalama eruptive period, erupted A.D. 

1482); X tephra (andesitic ash of the Kalama eruptive 

period, in part contemporaneous with andesitic flows on 

the south flank of the mountain); and 1980 lahar deposits 

and 1982 tephra deposits. 

Head downstream from the tephra exposure, cross 

the road washout, and walk up USPS Road 83 into the 

stand of trees. A lahar on the morning of May 18, 1980 

(approx 8:45a.m. P.d.t.), traveled over the small ridge on 

the northeast banks of the Muddy River and moved 

through here. Examples of battering as the flow traveled 

through the trees are evident: The bark has been removed from the lower trunks of trees, laharic debris 

remains trapped on the upslope side of standing trees, 

and cobble-size rocks can be found embedded in tree 

trunks. Large boulders carried by the flow were left 

behind. Bayonet trees (sharpened by the abrasive action 

of the flow) point downstream. 

Downstream from the washed-out USPS Road 83 

are outcrops of columnar-jointed basalt from the Castle 

Creek eruptive period. 

END OF SIDE TRIP lb 

Return to parking lot and head south down the Pine 

Creek fan (fig. 11 ). This part of the guide describes the 

route down into the Muddy River-Smith Creek, drainage 

along USPS Road 83. The trip will return to the junction 

of USPS Roads 2588 and 83, continue southeast, and 

connect with leg I. 

0.5 (0.5) Junction of USPS Roads 83 and 

2588 on surface of the Pine 

Creek-Muddy River fan. Note relation between lahar-swept surface and unaffected areas. This 

area was clear cut before the 1980 

eruption, and the lahar that 

passed here battered cut stumps. 

Just east of the road, the position 

of the edge of the lahar can be 

detected by the presence of unbattered stumps. 

Continue straight on USPS Road 2588 to the Muddy 

River, Pine Creek, Lewis River, and USPS Roads 25 and 

90, or turn left on USPS Road 83. 

0.7 (0.2) You are now at top of grade leading 

to the Muddy Rtver. In the next ¥4 

mi {1.2 km), note effects of the 

May 18, 1980, mudflow that 

spilled into the Hoo Hoo Creek 

drainage from the Pine CreekMuddy River fan. X through B 

tephras crop out for the next 3 mi. 

Entering area of figure 14. 

4.7 (4.0) 

5.1 (0.4) 

Tephra layers of the Cougar eruptive stage are exposed on the 

south bank of Hoo Hoo Creek 

just west of USPS Road 83. 

Bridge over the Muddy River at 

south edge of lower Muddy River 

fan. Here is a view upstream of 

part of the dissected fan. The bulk 

of the Muddy River fan consists of 

dacite debns from the summit 

dome of Mount St. Helens dating 

from the Kalama eruptive period 

(370 yr B.P.). 

On the east bank of the Muddy River in a borrow pit 

is an almost complete set of representative air-fall tephras from Mount St. Helens, as defined by Mullineaux 

(1986; see table 1). 14C ages of 37,600±1,300 and 

36,000±2,500 yr (Crandell and others, 1981) were obtained on charcoal from two horizons within the C tephra 

exposed in the slope above the quarry. Locate temporary 

footbridge or wade the river to visit the locality. 

5.2 (0.1) Enter onto lower Muddy River fan 

surface, swept by lahars on the 

morning of May 18, 1980. 

Road Guide 15 
5.5 

. . !·.· · .. ' _.· ,.,, 

N 

\ '\. 

(0.3) STOP 5. North end of fan (fig. 15). 

Erosion by Smith Creek has exposed materials of the Kalama 

. -- . ~ .... ~ ·. \ .. 

0 300 

0 1000 

600 METERS 

2000 FEET 

eruptive period, which make up 

the bulk of the fan, and May 18 

deposits at the top. The 1980 

) 

; 

) 

) 

/ 

figu_re 11. Generalized geologic map of upper Muddy River-Pine Creek fan, showing extent of lahar that swept this area 

(shading). Arrows indicate direction of lahar's path. Circled numbers, U.S. Forest Service roads; short-long-dashed lines, 

streamcourses; short-dashed line, path to stop 3. Contour interval, 200ft. 

16 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
materials, which are about 3ft (1 

m) thick here, overlie preeruption 

roots and woody debris. 

On the morning of May 18, two floods converged on 

this locality; one from the Muddy River probably reached 

here about 8:40 a.m. P.d.t. (traveling at 65 to 105 ft/s 

[20-32 m/s] over a distance of 6 mi [10 km ]). The Smith 

Creek flood, combined with the lahar that came down 

Ape Canyon, appears to have become impounded for. a 

short time before continuing downstream to the Swift 

Reservoir. 

A stand of trees that probably date from the period 

during emplacement of the old summit dome has been 

exhumed on the east bank of Smith Creek upstream from 

the main part of the lower Muddy River fan. 

Continue upvalley on USPS Road 83. (THIS ROAD IS 

CLOSED TO PUBLIC ACCESS, AND A VEHICLE 

PERMIT IS REQUIRED; CHECK WITH THE 

USPS.) Entering area of figure 16. 

7.2 (1.7) STOP 6. Smith Creek bridge site 

and the Beavertail landslide. 

An outcrop containing C tephra and pyroclastic 

flows of the Ape Canyon eruptive stage can be reached 

by walking upstream on the west bank or climbing u~h~ll 

and heading north, depending on how much water IS m 

creek- outcrop is highest, light -colored cutbank south of 

the ~outh of Ape Canyon. A 14C age of older than 

42,000 yr (Crandell and others, 1981} was obtain~d on 

charcoal from a pumiceous pyroclastic-flow deposit exposed in an old roadcut (now a high bank) about 650ft 

(200 m) south of the mouth of Ape Canyon. In this 

roadcut are three pyroclastic flows, with pumice of the C 

tephra lying between the top two. 

The lahar that coursed down Ape Canyon on the 

morning of May 18 flowed 260ft (80 m) up the east valle! 

wall of Smith Creek onto the toe of the Beavertail 

landslide; this runup distance requires a flow velocity 

exceeding 85 mi!h (135 km/h). Ape Canyon marks the 

south edge of the blast zone; vegetation on the south side 

of the canyon was ·little affected, whereas trees to the 

north were singed or downed by the hot lateral blast. The 

1980 tephra deposited here consists of the A11ayer from 

the blast air-fall pumice from the morning of May 18, 

and lapiili from the July 22, 1980, eruption (whiteand-gray pumice and dark lithic material). 

Figure 12. Outcrop at stop 4. Letters denote air-fall-tephra layers (see fig. 13; table 1). 

Road Guide 17 
TEPHRA 

- X -

- We 

-

B 

p 

- Ye 

-

Jb 

Js 

-

- -

~-- s 

DEPOSIT 

TYPE 

Lahar 

Lahar 

Lahar 

Lahar 

Surge 

Surge 

Lahar 

Lahar 

ERUPTIVE PERIOD 

OF MULLINEAUX 

(1986) 

Modern 

Kalama 

Castle Creek 

Pine Creek 

Smith Creek 

Swift Creek stage 

(Crandall, 1988) 

EXPLANATION 

Figure 13. Generalized stratigraphic section of outcrop at 

stop 4. Layers include deposits from lahars and surges (ash 

clouds), alternating with pyroclastic-flow deposits, air-fall 

tephra, and lava flows that traveled down the Muddy RiverLapilli 

0 1 METER 

3 FEET 

Ash 

Pine Creek fan. One lava flow of Castle Creek age lies 

buried beneath the active stream channel. Deposit type 

indicates presumed style of deposition of flowage 

material. 

18 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
Return to Pine Creek-Muddy River fan surface and 

junction of USFS Roads 83 and 2588, and turn left. 

14.5 (0.5) VIEWPOINT. Overlook of Pine 

Creek-Muddy River fan and 

Mount St. Helens. View of laharswept Pine Creek-Muddy River 

fan surface. On the morning of 

May 18, 1980, the lahar moved 

j oo 

', I 

j. 

I I I / 

0 300 

0 1000 

21.2 (6.7) 

600 METERS 

2000 FEET 

down the fan and then poured into 

deeper canyons of the Pine Creek 

drainage (fig. 11). 

Junction of USFS Roads 25 and 

2588 with leg I. Turn right to 

return to Cougar; turn left to go to 

Spirit Lake and Randle. 

........... . _. 

\ 

:- ~~~~~(]- . ·. @ ->;, .. ,·. 

Figure 14. Generalized geologic map of area near confluence of Smith Creek and Muddy River, showing 

extent of lahar generated on May 18, 1980 (shading). Solid arrows, direction of Muddy River lahar's path; 

open arrow, direction of Smith Creek lahar's path. Circled number, U.S. Forest Service road; shortlong-dashed lines, streamcourses; dashed line, edge of channel cut into fan deposits. Contour interval, 

200 feet. 

Road Guide 19 
Swift Reservoir to Spirit Lake 

Swift Reservoir dam overlook to Elk Pass and road to 

Spirit Lake via USFS Road 25. (Route can be followed by 

reading southbound along USFS Road 25 from USFS 

Road 99 junction or northbound from the Swift Reservoir dam overlook.) 

Northbound 

0.0 

(0.0) 

0.9 

(0.9) 

1.5 

(0.6) 

1.8 

(0.3) 

Southbound 

40.1 

(0.9) 

39.2 

(0.6) 

38.6 

(0.3) 

38.3 

(3.0) 

Swift Reservoir dam overlook, 

heading north on USFS Road 90 

(leg I, fig. 17). 

Junction of USFS Roads 83 and 

90. Stay on USFS Road 90. 

STOP 7. Park on right side of 

road. Pyroclastic-flow deposits of 

the Cougar eruptive stage are exposed on north side of road. BEWARE OF TRAFFIC. Note 

large breadcrust bombs within finer grained matrix of a pyroclastic 

flow, 64ft (20m) thick. 

Bridge over Swift Creek. 

2.1 

(0.3) 

3.2 

(1.1) 

4.3 

(1.1) 

5.0 

(0.7) 

5.3 

(0.3) 

6.0 

(0.7) 

8.5 

(2.5) 

9.9 

(1.4) 

11.0 

(1.1) 

38.0 

(1.1) 

36.9 

(1.1) 

35.8 

(0.7) 

35.1 

(0.3) 

34.8 

(0.7) 

34.1 

(2.5) 

31.6 

(1.4) 

30.2 

(1.1) 

29.1 

(1.6) 

USFS Road 7900 to Marble 

Mountain, a Pleistocene shield 

volcano. 

Porphyritic basalt from Marble 

Mountain. 

Andesite flow from Marble 

Mountain. 

On left side of road, lava flow 

from Marble Mountain overlies 

sedimentary rocks of the Ohanapecosh Formation (Oligocene). 

Good example of a baked contact. 

Turnout to examine baked contact. WATCH OUT FOR LOGGING TRUCKS! 

Cross Diamond Creek. 

Cross Marble Creek. 

Partially welded rhyodacitic tuff 

of Oligocene or early Miocene 

age. 

Well-bedded volcaniclastic rocks 

of the Ohanapecosh Formation 

Figure 15. Exposed section of fan at confluence of Smith Creek and Muddy River at stop 5. Section consists of summit-dome 

material of the Kalama eruptive period of Mullineaux (1986) overlain by 5 ft (1.5 m) of May 1980 deposit. 

20 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
12.6 

(1.6) 

14.6 

(2.0) 

, .. ...-... \ ___ _ _.,,..,. ~· 

_.-'··-----···- ___ __ ... -· 

0 

0 

7.5 

(2.0) 

25.5 

(0.7) 

-~-· . 

are exposed in a large clearcut 

area. 

Camp Creek inlet overlook. On 

north side of road is till deposited 

by glaciers that descended the 

Lewis River valley. 

OPTIONAL SIDE TRIP. Turn 

right at Forest Caml? sign. Here, 

at east end of the Sw1ft Reservoir, 

is an alluvial fan formed by debris 

N 

300 600 METERS 

1000 2000 FEET 

Figure 16. Generalized geologic map of area near confluence of Smith Creek and Ape Canyon showing extent of 

lahars generated on May 18, 1980 (shading). Solid arrow, 

direction of Ape Canyon lahar's path; open arrow, direction 

of Smith Creek lahar's path; circled number, U.S. Forest 

from the Mount St. Helens eruption of May 18, 1980. 

Return to USFS Road 90; turn right. 

15.3 

(0.7) 

24.8 

(0.2) 

INFORMATION STOP. USFS 

Information center; preeruption 

Mount St. Helens District Ranger 

Station. 

Service road; triangles, viewpoints; solid-dashed line, boundary of tree blowdown; open-dashed line, boundary of singe 

zone; dotted line, boundary of Beavertail landslide. Contour 

interval, 200ft. 

Road Guide 21 
15.5 

(0.2) 

16.2 

(0.7) 

24.6 

(0.7) 

23.9 

(0.1) 

Junction of USPS Roads 25 and 

90; continue straight on USPS 

Road 25. 

STOP 8. The Pine Creek bridge 

crosses Pine Creek just upstream 

of its confluence With the Lewis 

River. 

Pine Creek drains an area of about 24 me (62 km2 ) 

and heads on the south flank of Mount St. Helens. 

Voluminous lahars associated with the 1980 eruption 

flowed down the creek. It took approximately 28 minutes 

for the flow, averaging 34 ft/s (10 m/s) in velocity, to 

traverse the 14.8 mi (24 km) from the cone. Lahars 32ft 

(10 m) deep flowed past the bridge (Janda and others, 

1981, p. 465); mudlines are still visible on trees upstream. 

A boulder estimated to weigh about 60 tons was found 

resting on the road surface, only the bottom meter buried 

in lahar deposits. The boulder has been moved a few 

meters to permit work on the road and bridge. At the 

bridge, more bank erosion occurred from storm runoff in 

late 1980-83 than from the May 18, 1980, lahars. 

16.3 

(0.1) 

23.8 

(1.8) 

STOP 9. Turn right into borrow 

pit on east side of road. Good 

0 

0 

18.1 

(1.8) 

19.4 

(1.3) 

19.8 

(0.4) 

22.0 

(1.3) 

20.7 

(0.4) 

20.3 

(1.2) 

exposures of lahars and associated 

fluvial materials of the Pine Creek 

eruptive period (Crandell and 

Mullineaux, 1973). 

Junction of USPS Roads 25 and 

2588. If you were to turn left, in 

7.3 mi (12 km) you would join up 

with leg I at the upper part of the 

Muddy River fan. Continue 

straight. 

Junction of USPS Roads 25 and 

2586. Continue straight. 

STOP 10. Muddy River bridge 

and viewpoint. 

Shifting channels and fluvial processes have reworked much of the lahar deposits from May 18, 1980, 

but areas up stream and downstream from the bridge still 

show effects of the lahars: mudlines on trees, large 

boulders, and downstream-pointing "bayonet" trees. As 

on Pine Creek, subsequent storms have deeply eroded 

and broadened channels in the lahar deposits. 

2 KILOMETERS 

2 MILES 

Figure 17. Field-trip route along the Swift Reservoir to confluence of the Lewis River, Muddy River, and Pine Creek, showing 

part of leg I. Triangles, viewpoints; circled numbers, U.S. Forest Service roads; dashed lines and shading, extent of lahar 

inundation. 

22 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
Continue on USFS Road 25. For the next 20 mi (32 km) 

are many good exposures of tephra, in order of increasing 

age: 1980, X, We, B, P, Ye, J, and S. 

21.0 

(1.2) 

19.1 

(3.7) 

Junction of USPS Roads 25 and 

93. 

Bear left on USFS Road 25. You are approaching the 

south edge of the tephra deposit from the July 22, 1980, 

eruption and 20-cm isopachs of the We (ca. A.D. 1482) 

and Ye (ca. 4,000-3,300 yr B.P.) tephras (fig. 18). 

24.7 15.4 Now crossing the south edge of 

(3.7) (0.5) the tephra deposit from the plini25.2 

(0.5) 

29.4 

(4.2) 

14.9 

(4.2) 

10.7 

(0.2) 

an eruption column of May 18, 

1980. Most of this deposit has 

been removed by erosion or covered by vegetation, but farther 

north the deposit thickens. Along 

USFS Road 25, the deposit is 

about 22 mi (35 km) wide. 

Junction of USPS Roads 25 and 

2573. Continue on USFS Road 

25. A view of this road in July 

1980 before it was cleared of airfall tephra is shown in figure 19. 

VIEWPOINT. (No turnout here; 

be careful of traffic.) Overlook 

into the Clearwater Creek drainage. 

To the north is part of the zone devastated by the 

May 18, 1980, blast. On the east wall of Clearwater Creek 

valley is the east edge of the devastated zone, about 10 mi 

(16 km) from the summit. Most of the fallen or damaged 

timber has been salvaged. 

29.6 

(0.2) 

30.0 

(0.4) 

36.2 

(6.2) 

40.1 

(3.9) 

Northbound 

Westbound 

0.0 

(0.0) 

10.5 

(0.4) 

10.1 

(6.2) 

3.9 

(1.7) 

0.0 

(4.6) 

Southbound 

Eastbound 

9.0 

(4.6) 

Junction of USFS Roads 25 and 

2565. 

On the south side of road is a 

Quaternary basalt flow erupted 

from a vent at the top of the ridge 

to the south (Hammond, 1980). 

STOP 11. Elk Pass. You are 

now at the approximate· axis of the 

May 18, 1980, tephra fall, here 

about 6 in. (15 em) thick. The 

stratigraphy of the deposit is visible in and around a borrow pit just 

to the west (fig. 20). 

Junction of USFS Roads 25 and 

99. Turn left onto USPS Road 99 

to Spirit Lake. 

Junction of USFS Roads 25 and 

99. Eastbound traffic: Turn right 

for Cougar and left for Randle. 

4.6 

(4.6) 

4.4 

(2.1) 

STOP 12. Bear Meadows. Here, 

Gary Rosenquist and Keith Ronholm each took a remarkable set 

of photographs of the early stages 

of the eruption on the morning of 

May 18, 1980 (Lipman and Mullineaux, 1981, f1g. 38). 

Eyewitness reports (Rosenbaum and Waitt, 1981) 

stated: One observer watching the mountain through 

binoculars saw the north side of the volcano start to get 

"fuzzy, like there was dust being thrown down the side." 

Several seconds later, the north face began to slide. The 

lower part of the north side seemed to slide away more 

quickly than the upper. The first dark-colored cloud 

appeared near the middle of the north slope in an area 

vacated by the slide, and a light-colored cloud formed 

near the summit. A short time later, a very black cloud 

emerged from the summit area. The upper part of the 

north flank moved downward, and the flank eruption 

seemed to explode through the moving material. The 

flank eruption grew rapidly, especially to the north. 

The "bulge was moving-the whole north side was 

sliding down." The first cloud appeared to form at the 

bottom of a cirque-like wall from which the bulge had 

moved. Within about 20 seconds the landslide was out of 

view behind a ridge. At this time, there were two distinct 

clouds which seemed to be emanating from separate 

vents: an extremely dark one rising vertically from the 

summit, and a lighter one from the north flank. 

The dark cloud grew vertically from the summit. The 

lighter cloud, which seemed to come from the area 

vacated by the landslide, grew more. or less spherically, 

except that a large "arm" shot out to the north in the 

direction of the avalanche. The spherical cloud seemed to 

approach from the mountain-not as part of the northward arm-and reached the ridge closest to the mountain 25-30 seconds after the start of the landslide. When 

the cloud hit the ridge, it rose and boiled upward. 

Shortly after the vertical eruption began, a large horizontal blast occurred. Just before the top of the mountain 

became obscured, the south side of the summit crumbled 

into the hole formed by the landslide. As the cloud grew, 

what appeared to be a shock wave similar to that associated with a nuclear explosion moved ahead of the cloud. 

About 1 Y2 minutes after the blast, a noise like a clap of 

thunder accompanied some sort of pressure change. The 

initial noise was followed by a continuous rumbling "like 

a freight train." 

A rumbling noise began within 7-8 seconds of the start 

of the landslide. One member of the group sensed a 

pressure decrease at about the same time. A "shock 

wave," which looked like heat waves, formed ahead of the 

blast cloud. The witness had driven 2 or 3 miles to the 

northeast. Seven or eight minutes after the eruption's 

start, rocks began falling from the part of the cloud that 

had passed overhead. He collected two "golfball size" 

Road Guide 23 
rocks (determined later to be dacite) from the fall. The 

rock fall continued for roughly 30 seconds and was then 

replaced by material that splattered on the windshield. 

------ ......_ __ _ 

As he drove, this material was replaced by "mud drops," 

which would flatten, not splatter. The maximum diameter of a mudball observed after flattening was about% in. 

North edge of July 22, 1980, tephra 

/ ; North edge of May 18, 1980, tephfa 

North edge ofT tephra, 

20-cm isopach 

-South edge ofT tephra, 

20-cm isopach 

--Approximate axis of May 18, 1980, 

tephra; USFS Road 25 crosses 

at 15-cm isopach 

-North edge of We tephra, 

20-cm isopach 

- North edge of Ye tephra, 

20-cm isopach 

- South edge of We tephra, 20-cm isopach 

- South edge of Ye tephra, 20-cm isopach 

--South edge of July 22, 1980, tephra 

Figure 18. Field-trip route near 

devastated-zone boundary (dashed 

line), showing limits and isopachs of 

plumes of the We, Ye, May 18, 1980, 

and July 22, 1980, tephras crossed by 

leg I. Mount St. Helens is 4.5 mi (7.2 

km) from the west edge of the area. 

Data for We and Ye tephras from Crandell and Mullineaux (1978); data for 

May 18, 1980, from Waitt and Dzurisin 

(1981); data for July 22, 1980, from 

Wood and others (in press). Triangle, 

viewpoint; circled numbers, U.S. Forest 

Service roads. 

0 2 4 6 KILOMETERS ~----~--r-~----~ 

0 2 4 MILES 

24 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
Gradually, the mud fall abated, and the ash fall became 

heavier. The ash was finer than sand. For a short time he 

encountered a second fall of mud drops, similar to but 

heavier than the first. This was quickly replaced by 

intense ash fall. Soon the ash fall became so intense that 

he could no longer see to drive. The ash fall eventually 

abated very gradually. 

Continue east on USPS Road 99. 

6.7 

(2.1) 

2.3 

(2.3) 

STOP 13. Northeast edge of 

sear zone and headwaters of 

Clearwater Creek. A good place 

to contrast unaffected forest with 

the blast-devastated landscape 

(try to find the 1980 blast deposit 

here). 

Westbound, entering area of figure 21. 

Eastbound, leaving map in figure 21. 

9.0 

(2.3) 

0.0 

(0.0) 

Junction of USPS Roads 26 and 

99. Westbound, turn right to go to 

the Norway Pass trailhead. 

This is the start of the eastbound (read up) exit from the 

devastated zone. Westbound traffic only from here down. 

9.5 (0.5) STOP 14. Norway Pass trailhead. 

Spectacular view in upper Green 

River of timber blowdown. In this 

area, timber will not be salvaged 

but left untouched. 

You may continue north on USPS Road 26 (leg Id) 

toward Randle (see fig. 31) or return to Meta Lake (stop 

15). 

10.0 (0.5) STOP 15 AND VIEWPOINT. 

Junction of USPS Roads 26 and 

99. 

A car damaged by the blast belonged to a family 

killed at tl?.eir small mine, on the ridge 1¥2 miles (2.4 km) 

to the west. Thick tephra layers are exposed along USPS 

road 99 from here to the Windy Ridge parking lot (figs. 

22, 23). 

Another good exposure is ahead at the Independence 

trailhead. The 1980 air-fall tephra and 1980 blast deposit 

overlie forest duff, T tephra (dacite pumice), Z tephra 

(pink dacite ash from old summit dome, ca. A.D. 1600), 

X tephra (thin, andesite ash), and Wn tephra (dacite 

pumice). A blast deposit from Sugar Bowl dome on the 

northeast flank of the volcano is patchy and difficult to 

define here but thickens toward the volcano. B tephra 

(andesite and basalt ash, with one thin dacite layer) 

Figure 19. Air-fall tephra covers part of U.S. Forest Service Road 25 in July 1980. 

Road Guide 25 
overlies P tephra (dacite ash layers), which, in turn, 

overlies Yn tephra (yellow-brown dacite pumice) and 

layers of the J tephra (table 1). 

10.2 (0.2) STOP 15. Trail to Meta Lake. 

This site within the blast zone is about 8.5 mi (14 km) 

from the volcano; to the northeast, the blast swept out to 

a distance of 13 mi (21 km). A short trail leads from the 

road to Meta Lake, an interesting path through downed 

timber, to a lake that was only moderately disturbed by 

the blast. Small trees on the shore and fish in the lake 

survived because they were under the snowpack. One 

blown-down tree near the start of the trail shows tightly 

clustered rings for a few years after A.D. 1800 (the year 

when pumice of the T tephra was erupted from Mount 

St. Helens). 

11.8 (1.6) STOP 16. Snack stand. Junction of 

USPS Roads 94 and 99, 8 mi (13 

km) from the summit of Mount 

St. Helens. Headwaters of Bean 

Creek to the south have exposures 

of the Ohanapecosh(?) Formation 

(conspicuous outcrops of greenish.:brown tuft) and the andesite 

13.3 (1.5) 

of Smith Creek Butte (Hammond, 

1980). 

STOP 17. Independence Pass trail 

parking lot: ¥4-mi (0.4 km) hike 

through downed timber. 

In the parking turnaround here is an excellent exposure of the Windy Ridge tephra sequence. At the end of 

the trail is an excellent view of Mount St. Helens and 

Spirit Lake. In good weather you can see part of the 

growing lava dome within the crater (1986 height, 918ft 

[280 m]). Along this trail is a cut tree trunk that shows 

tightly clustered growth rings corresponding to the years 

A.D. 1801-5 (effects of eruption of pumice of the T 

tephra in A.D. 1800; Yamaguchi, 1983). Along the trail 

the blast deposit can be recognized by its gray color. It 

contains gravel- to sand-size rock fragments from the 

edifice of Mount St. Helens, pieces of slightly vesicular 

gray dacite from the cryptodome, and fragments of 

shredded wood. The hike is an opportunity to explore the 

diverse effects of the blast on both large and small trees. 

Small trees buried under the winter snow remained 

untouched. Very few large trees were transported or 

reoriented after they fell. Standing trunks on and behind 

Figure 20. Section along axis of May 18, 1980, tephra deposit. Below the knife is ~~veral i~ches (c.entimeters) ?f material 

deposited by the lateral blast; above the knife is more than 6 in (15 em) of ash and lapllh depo~1ted dunng the morn1ng of May 

18, ·1980 (see fig. 22). Overlying these layers are coarse lapilli from the July 22, 1980, erupt1on. 

26 Road Guide to Volcanic Deposits of Mount St. Helens and VIcinity, Washington 
the ridge to the north indicated that the flow was diffuse 

enough to loft over them but still snapped off their 

crowns. 

14.7 (1.4) STOP 18. Harmony Basin 

viewpoint. 

The first gap in the ridge to the west (fig. 21) 

provides a view of the north end of Spirit Lake and the 

Harmony Falls basin. Here, you can see evidence that the 

avalanche displaced water from the Spirit Lake basin: 

Logs are sparse in a zone extending far above lake level, 

and the few logs in this zone commonly point downslope, 

in contrast to those higher up that were felled by the blast 

and point uniformly away from Mount St. Helens. Many 

of the logs washed from the slope are now floating in the 

lake. In 1980, the surface of the lake was almost entirely 

covered by a matte of floating logs and debris. 

Waitt (1984) inferred the following sequence of 

events: 

1. The surge rushed northeastward, leveling the forest 

and depositing layer A1 (fig. 23). Patterns of downed 

0 2 

0 

timber indicate that topography partly channeled 

movement. Most of the Spirit Lake basin was swept 

by a northeast-moving density current, whereas the 

head of the Harmony Falls basin was engulfed by a 

current rushing northward out of Smith Creek and 

over the divide. 

2. The first landslide, moving more than 160 mi!h (250 

km!h), entered Spirit Lake. It created a catastrophic 

wave that surged up the Harmony Falls basin and 

rinsed the slopes clean of timber and layer A1 to a 

level marked by the sharp trimline on the north side 

of the valley. 

3. Losing momentum, this water descended to the basin 

floor and poured back into the lake, carrying most of 

the logs with it but leaving some grounded in "rafts." 

4. The gradually waning pyroclastic current continued, 

depositing layer A2. 

5. Layer A3 (blast fallout) and later air falls accumulated. 

15.1 

3 KILOMETERS 

2 MILES 

(0.4) VIEWPOINT. Cedar Creek viewpoint, 2d gap. 

Figure 21. Field-trip rout~ near northeast side of Mount St. Helens, showing part of leg I. Triangles, viewpoints; circled 

number, ~.S . Forest Serv1ce road; short-dashed lines and shading, limits of lahar inundation; stippling, areas covered by 

pyroclastiC flows and avalanche on north side of volcano; long-dashed line, devastated-zone boundary. 

Road Guide 27 
15.9 (0.8) VIEWPOINT. A panorama of Spirit Lake. 

16.5 (0.6) VIEWPOINT. Good view and exposed tephra stratigraphy. 

16.8 (0.3) VIEWPOINT. Into headwaters of 

Smith Creek and the northeast 

slopes of Mount St. Helens. 

17.6 (0.8) STOP 19. Windy Rid~e parkin~ lot 

is at end of the public road, a out 

4 mi ( 6.5 km) from the summit. 

The blast deposit here is about 3 ft (1 m) thick, 

veneered by 1980 air-fall deposits. The best viewpoint is 

reached by a short climb to the top of the hill just north 

of the parking lot (figs. 24-26). All of Spirit Lake, 

including the floating logs, the swash zone from the water 

wave generated by the avalanche, and much of the crater, 

is visible. The debris-avalanche deposit dams Spirit Lake 

and forms the hummocky topography in the distance. On 

the south end of Harrys Ridge, (the first ridge west of 

Spirit Lake) all trees and soil were removed down to 

bedrock by the avalanche and blast. Light-gray pyroclastic-flow and ash-cloud deposits, mainly from May 18 

but also from June 12 and July 22, 1980, cover and lap 

against the debris avalanche south of Spirit Lake. Many 

of these deposits have been stripped· or buried by lahars 

generated by rapid snowmelt during explosions in the 

lava dome. Several fumaroles apparently rooted in the 

pyroclastic flows still steam in 1986, visible best on humid 

days. Much of the northern part of the crater is visible 

from here, but in October 1986 only the very top of the 

dome, 918ft (280m) high, 2,600 ft (800 m) wide, and 

located in the southern part of the crater, shows over the 

shoulder of Sugar Bowl dome. The water level in Spirit 

lake is maintained by a gravity-fed tunnel cut through 

Harrys Ridge to South Coldwater Creek, which drains 

into the North Fork Toutle River. The portal is visible 

about halfway along the west shore of the lake. The 

spillway prevents overtopping and possible catastrophic 

erosion of the unstable debris-avalanche blockage. Between November 1982 and April1985, U.S. Army Corps 

of Engineers contractors maintained lake level by using 

barge-mounted pumps that withdrew water and sent it 

down a channel on the pumice plain. The progressive 

shorelines of Spirit Lake are mapped in figure 26. The 

altitude of the lake before the eruption was 3,198 ft (975 

m); in fall 1980, it was 3,408 ft (1,039 m), and the level 

controlled by pumping was 3,463 ft (1,056 m ), a total 

increase since May 17, 1980, of 265 ft (80 m). Current 

lake level is 3,438 ft (1,048 m). A tiny shed high on 

Harrys Ridge houses surveying and radio equipment 

used by USGS volcanologists to monitor volcanic activity; 

Fig·ure 22. Volcanic deposits exposed in roadcut along U.S. Forest Service Road 99 (see fig. 23). 

28 Road Guide to Volcanic Deposits of Mount St. Helens and VIcinity, Washington 
B1 

A2 

A1 

1980 deposits 

EXPLANATION 

July 22, 1980 

Scattered ash and lapilli 

Plinian air fall of May 18, 1980 

D Fine ash from waning eruption column- Silty, 

medium to fine sand, about 2 em thick 

C Fine ash from ash cloud produced by pyroclastic flows 

B4 Upper pumice-rich layer 

B3 Upper lithic-rich layer -Finer grained than B2 

B2 Lower pumice-rich layer- Pumice/lithic-pebble gravel 

B 1 Basal lithic-rich layer - Pumice/lithic-granule gravel 

Blast deposit of May 18, 1980 

A3 Sand-silt facies - Massive, dark-olive-gray sandy silt 

less than 2 em thick; contains pisolites 

A2 Sand facies - Normally graded, fine to coarse sand 

A 1 Basal gravel facies- Contains light-gray to gray, 

vesicular, juvenile dacite clasts; lithic granules, 

and macerated-wood fragments; poorly sorted, 

weakly stratified to nonstratified gravel of angular 

clasts 

---) Air-fall 

blast 

Forest floor 

] T 

) X 

J Wn 

Sugar Bowl 

~ B 

p 

Yn 

/ 

0 1 METER L....--.--1 

Tephra sets along Windy Ridge 

Eruptive 

period 1 of 

Mullineaux (1986) 

Approximate 

age (yr) 

T (A.D. 1800) tephra, 

Goat Rocks. 

180-123 

X tephra, 500-350 

Wn (A.D. 1482) tephra, 

Kalama. 

Sugar Bowl tephra, 

Sugar Bowl. 

B tephra, 

Castle Creek. 

P tephra, 

Pine Creek. 

Yn tephra, 

Smith Creek. 

1,150 

2,200-1,700 

3,000-2,500 

4,000-3,300 

Figure 23. Schematic stratigraphic column of pyroclastic deposits from Mount St. Helens along U.S. 

Forest Service Roads 94 and 99 in devastated zone. Deposits include mainly tephra consisting of 

pumice lapilli; two layers not consisting of typical air-fall material are the Sugar Bowl and 1980 blast 

deposits, which consist of slightly vesicular to nonvesicular lithic fragments in a poorly sorted matrix. 

Description of air-fall and blast deposits of 1980 from Waitt and Dzurisin (1981) and Waitt (1984). 

Road Guide 29 
Mount St. Helens 

Figure 24. Windy Ridge overlook, about 4.6 mi (7.8 km) from 

crater. View westward, down valley of North Fork Toutle 

River, with Spirit Lake (SL) in foreground. Volcanic gas and 

steam continuously rise from dome; during humid weather, 

water vapor condenses to form visible plumes from dome 

and from fumaroles in pyroclastic flows of the Pumice Plain 

(PP). A, debris avalanche (Spirit Lake blockage); H, Harrys 

Ridge; J, Johnston Ridge; P, Windy Ridge parking lot; S, 

Sugar Bowl dome; T, Spirit Lake outlet tunnel. Drawing by 

Bobbie Myers. 

MOUNT ST. HELENS 

Figure 25. Northeast side of Mount St. Helens. NFTRV, North Fork Toutle River valley. Dashed line, U.S. Forest Service Road 

99. Photograph by Bob Krimmel, taken September 10, 1980. 

30 Road Guide to Volcanic Deposits of Mount St Helens and Vicinity, Washington 
- ,_N 

~<~ ~~' ; iJ%-f~ . .~ · ... 

\ ' 

Figure 26. Generalized geologic map of area north of Mount St. Helens near Spirit Lake and Windy Ridge, 

showing 198Q--o82 deposits and progressive shorelines of Spirit Lake, pre-1980, 1980, and 1983; irregular 

closed outlines in lake are debris-avalanche islands. A, debris avalanche; H, Harrys Ridge; J, Johnston 

Ridge; SB, Sugar Bowl dome;. T, Spirit Lake Tunnel; WR, Windy Ridge overlook; triangles, 1980 pumiceous 

pyroclastic flow (Rowley and others, 1981); stippling, path and deposits of March 19, 1982, lahar (Waitt and 

others, 1983); numbered dots, field-trip stops; circled number, U.S. Forest Service road. 

Road Guide 31 
most current monitoring is conducted within the crater 

and on the dome. The USGS notifies the USPS and other 

Government agencies when monitoring indicates significant changes in activity. All decisions regarding access 

and land use in Mount St. Helens National Monument 

are made by the USPS. 

ENTRY BEYOND THE WINDY RIDGE PARKING 

LOT TOWARD SPIRIT LAKE REQUIRES SPECIAL USPS PERMITS, A GATE KEY, RADIOS, 

AND SO ON. ARRANGEMENTS FOR ENTRY 

MUST BE MADE WITH THE USPS. THE ROAD TO 

SPIRIT LAKE IS NOT MAINTAINED. 

Cumulative 

mileage 

(mileage 

between 

points) 

0.0 (0.0) From Windy Ridge parking lot, enter restricted zone through locked 

gate at south end of parking lot. 

1.8 (1.8) Saddle View to west overlooks junction of road to Spirit Lake with old 

road to preeruption Timberline 

parking lot and northeast slope of 

Mount St. Helens. 

Deposits of the Pine Creek eruptive period through 

1980 are exposed east of the crest of this saddle. The 

Sugar Bowl blast deposit, tephra of the Kalama eruptive 

period, and 1980 deposits are exposed in cuts along the 

east side of the road beyond the saddle. During the 

formation of Sugar Bowl, a dome of porphyritic dacite, a 

directed blast carried rock fragments laterally northeastward more than 15 mi (24 km). Here, the Sugar Bowl 

deposit is characterized by distinct dark-gray ash, lapilli, 

and breadcrusted bombs. 

2.1 (0.3) STOP 20. First creek crossing near 

junction with Timberline Road. 

Stop off on right side of road. 

This drainage was swept by a blast dacite-bearing 

pyroclastic flow on the morning of May 18. The surface 

of the flow is littered with vesicular as well as dense, 

glassy, breadcrust blast dacite. Explore northeastward 

along the gully. At the base of the south-facing ridge, 

streamcuts expose deposits ranging in age from 2,200 yr 

B.P. to A.D. 1980 (fig. 27). 

2.5 (0.4) Outcrops of basalt flows of the Castle Creek eruptive period south of 

the road. 

3.8 (1.3) STOP 21. Road crosses outer edge 

of deposits of the March 19, 1982, 

snow avalanche and lahar (Waitt 

and others, 1983) (fig. 26). During 

summer 1986, a revegetation 

study plot was located here. 

4.0 (0.2) STOP 22. Here, the 1982 lahar 

deeply scoured the pyroclastic 

flows of May 18, 1980. Walking 

south upchannel will bring you to 

exposures of 1982 lahar deposits 

in the bed of the channel and of 

1980 p~roclastic-flow deposits in 

the big banks. 

4.3 (0.3) STOP 22. Parking area. Road rises 

uE onto hummocky surface of ava anche deposit. Stok here and 

explore the Spirit La e blockage 

(figs. 28, 29). 

Six major events occurred on the morning of May 18, 

1980: (1) a magnitude 5.1 earthquake, (2) a huge 

rockfall/debris avalanche, (3) a lateral explosion (the 

blast), (4) a heavy ash fall, (5) pyroclastic flows, and (6) 

lahars (mudflows). Near the shores of Spirit Lake can be 

seen examples of all these phenomena except the earthquake itself. 

The deposits exposed in the outcrop shown in figure 

29 tell a story about the events that morning. Here, the 

blast deposit overlies a fractured block of red basalt in 

the avalanche. Explosions within the chaotic mixture of 

hot debris deposited ash in draping layers over the 

outcrops. Illutriate from pyroclastic flows drifted over the 

pile of rubble and laid down a blanket of fine ash. 

Pyroclastic flows on May 18, 1980, reached this area, 

smoothing the rough topography of the avalanche deposit east of stop 22. By midday, tephra from the main 

plinian eruption mixed with the locally produced phreatic 

ash, further masking the underlying deposits. By the 

afternoon of May 18, this area was a drab-gray landscape. 

Pyroclastic flows from the June 12, 1980, eruption 

reached here; they are distinguishable by a pink coating 

Figure 27. Schematic west-east geologic section at Timberline Road at stop 20, showing position of pyroclastic flow 

(dotted where missing or eroded) containing abundant clasts 

of blast dacite. Heavy line, present land surface; gullies filled 

with reworked pyroclastic material. Prismatic jointing indicates that clasts were hot during transport. In inset, 1980 

tephra overlies blast deposit (modern). Pyroclastic flow is 

from the Sugar Bowl eruptive period. B, tephra layers from 

the Castle Creek eruptive period; Wn, tephra set from A.D. 

1482 eruption of the Kalama eruptive period; X, andesitic ash 

layer of the Kalama eruptive period; Z, late ash of the Kalama 

eruptive period; T, tephra set from A.D. 1800 eruption of the 

Goat Rocks eruptive period. 

32 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
of ash on the surface of pumice blocks. Tephra from the 

fifth eruption on August 7, 1980, was also deposited here. 

The last major natural impact was a lahar on March 19, 

1982. A slurry of rock, water, and ice generated by an 

eruption in the crater swept down the north flank of the 

volcano and entered Spirit Lake. 

TEPHRA 

T 

z 

X 

Wn 

8 

Road to 

Spirit Lake 

: ; 

DEPOSIT 

TYPE 

Air fall 

Density 

current 

Air fall 

Air fall 

Air fall 

Air fall 

Pyroclastic 

flow 

Air fall 

=o .. ·. . . . ·.Pyroclastic 

Lava of • ·-- · • 

Castle Creek 

eruptive period 

"" v 

ERUPTIVE PERIOD 

OF MULLINEAUX 

(1986) 

MODERN 

............. 

GOAT ROCKS 

KALAMA 

"o:o:o :? ~~-- ~- ~--.: 

o_t?o p o

0 ·

0 o 

•;oo'o o 0 · o:J'\ ·. l>o o: ·-~o o Oo ·~( 

b ·o·o Q bO C> ot'\o 00 o·O ~· "ltrc'o 

ov 0 oo oO.· o'O 0 

;oOOoo'o.sl 

. . 0 .0 . 1>"" : _,..o oOo o • o vo& o 0 0 o•o o 0 ~ C? ; Q ........ .. 

. . • . ·S·U·G.AR .. 80. W. L.. • . • • . ~#,~:~0~·•'··~·;· 

• 

·?AP~: ·~A . A . ·o 

0· ~'!" ... tv-: Q .. . 1 1 . 1 I I 1 I I I I I . I I . I f 1 ........ ···············I . -. · .... ~·. : . : .·. · .... . ~-· . :. : ::. ·. ~ 

CASTLE CREEK -~~//)i=i~·/~:.:{~~:}:~~-: .· .•. :. !: :: · ... ::. · .. . . . . .. - . . . . . . . . . . . ' . . . . ........................ .. 

Pre -1980 deposits 

\ 

I 

I 

=- ('t)E • U) CX) • 

..... ~ 

E 

Road Guide 33 
As Spirit Lake began to fill with water during the 

following years, a potential disaster was in the making. 

Steps taken by the U.S. Army Corps of Engineers to 

\ 

... 

::,:·.·. ,-'· .. 

. . . . 

.... 

::: : .. ... 

prevent breaching of Spirit Lake included pumping of 

lake water over the avalanche blockage and filling in of 

critical low spots (figs. 28, 29) in the avalanche. 

Bedrock 

SPIRIT 

LAKE 

200METERS 

I 

400 FEET 

A 

_,.,.,.,.,""""'~ r- Area covered by March 19, 1982 lahar 

A' 

EXPLANATION 

E:J Avalanche deposit 

(:?.=.:':] Blast deposit 

D Ash-doud deposit 

f77l7777A Artifidal fill for 

~ critical low spot 

~ Phreadc ash deposit 

r-:-::l Lahar deposit of 

L....:.....;J March 19, 1982 (t) 

34 Road Guide to Volcanic Deposits of Mount St. Helens and VIcinity, Washington 

en 

3510 

a: 

w 

.,_ 

w 

::E 

3500 ~ 

z 

0 

3490 

w 

~ ..J 

3480 w 
SIDE TRIP lc. Kalama River valley and the South Fork Toutle River 

(fig. 30} 

(mileage 

Cumulative between 

mileage points) 

0.0 (0.0) Turn left (north) from Lewis River 

2.1 

3.6 

4.8 

6.0 

6.9 

7.4 

8.2 

(2.1) 

(1.5) 

(1.2) 

(1.2) 

(0.9) 

(0.5) 

(0.8) 

Road toward Merrill Lake (USPS 

Road 81). 

Outcrops of Tertiary intrusive 

rocks. 

Junction of Weyerhaeuser Roads 

7200 and 7600. 

Junction with road to Merrill Lake 

and Washington Natural Resources campground. Continue 

straight ahead. 

Entering upper Kalama River valley. Outcrops are of the Cave Basalt (formed during the Castle 

Creek eruptive period, 2,200-

1,700 yr B.P.); tumuli dot the surface of lava flows. 

Junction of Weyerhaeuser Roads 

7200, 7500 and 7600. Continue 

straight ahead on USPS Road 81. 

Entering Gifford Pinchot National 

Forest. 

STOP 23. Turn right into quarry. 

Outcrops of lithic pyroclastic flows of the Kalama 

eruptive period overlie the Cave Basalt. Charcoal from 

the lowermost pyroclastic-flow deposit yielded a radiocarbon age of 610±200 yr (Crandell and others, 1981). 

Paleomagnetic study of this unit indicates that it was 

emplaced over a range of temperatures (Hoblitt and 

Kellogg, 1979; R.P. Hoblitt, oral commun., 1985). Charcoal from the uppermost pumiceous pyroclastic-flow 

deposit yielded a radiocarbon age of 290±70 yr. The 

deposit, which contains abundant hypersthene-hornblende pumice similar to that in the W tephra, probably 

originated during explosive eruptions of the W tephra. 

Figure 28. Generalized geologic map and cross section of 

eastern part of Toutle River blockage near stop 22. North half 

of area is covered by veneer of ash-cloud deposits. t, 

terraced lahar deposits of March 19, 1982; 12pf, June 12, 

1980, pyroclastic-flow deposit; 18pf, May 18, 1980, pyroclastic-flow deposit. Dot-dashed lines, latest streamcourses. 

Solid arrows indicate directions of pyroclastic flow; open 

arrows indicate direction of avalanche runup over Johnston 

Ridge (see fig. 29). Heavy line in cross section denotes 

present land surface. 

Across the road from the quarry, the Kalama River has 

eroded through the pyroclastic flows and exposed the 

Cave Basalt. 

8.7 

11.1 

11.7 

12.3 

(0.5) 

(2.5) 

(0.6) 

(0.6) 

Junction of USPS Roads 81 and 

8117. You are driving up the 

Kalama River valley on a surface 

underlain by lithic pyroclastic 

flows erupted during the Kalama 

eruptive period. 

Junction of USPS Roads 81 and 

8122; continue straight ahead on 

USPS Road 81. 

Junction of USPS Roads 81 and 

8123; continue straight ahead on 

USPS Road 8123. 

STOP 24. Junction of USPS Roads 

70 and 8123. Park and walk west 

(5 min). A quarry exposes 

pyroclastic-flow deposits of the 

early Kalama eruptive period 

from Mount St. Helens (table 1). 

The flows overlie an ash-cloud 

deposit, oxidized J tephra, colluvium, till, and bedrock. 

Return to USPS Road 8123 and continue northeast. 

13.4 (1.1) Junction of USPS Roads 8123 and 

8123170. USPS Road 8123 was 

inundated by lahars on May 18, 

1980, and washed out the following winter. 

Continue along USPS Road 8123170. Good water is 

available just past the intersection at Coldspring Creek. 

Along the road for the next mile (1.6 km) are outcrops of 

a pyroclastic flow of the Kalama eruptive period that 

topped the ridge to the north and flowed down into Clear 

Creek. Genetically associated ash-cloud deposits overlie 

the pyroclastic-flow deposit. 

14.4 

15.0 

15.8 

16.0 

(1.0) 

(0.6) 

(0.8) 

(0.2) 

Junction of USPS Roads 4192 and 

8123170; bear right. 

Along the road are deposits of pre1980 eruptions, most of which are 

probably ash-cloud deposits of the 

Kalama eruptive period; no 

coarse pumice layers are evident. 

Junction of USPS Road 8123170 

and Weyerhaeuser Road 4100. 

Turn left. 

STOP 25. Overlook into headwaters 

of the South Fork Toutle River, 

which was swept by two lahars on 

May 18, 1980. 

Less than 10 minutes after the start of the eruption 

(Rosenbaum and Waitt, 1981): "* * * a huge mass of 

Road Guide 35 
water, mud, and trees crashed down a small tributary 

within the South Fork Toutle valley. It snapped off trees 

and 'exploded' when it hit lows, bursting as much as 60ft 

when it hit obstacles * * * ." The river returned to and 

stayed within its deep channel until about 2:00p.m. P.d.t., 

when there occurred a second smaller flood deep enough 

to spill out of the channel. 

In the 6 years since the eruption, the surface of the 

riverbed has been reworked, so that little, if any, of the 

1980 surface remains. Across the river valley to the north 

is timber that was seared and downed by the laterally 

directed blast. In the roadcut on the south side of the 

road is till of the Fraser glaciation overlying lithic 

pyroclastic-flow deposits containing blocks with prismatic 

jointing. These pyroclastic-flow deposits are of the Cougar eruptive stage. 

16.5 (0.5) 

17.0 (0.5) 

Junction of Weyerhaeuser Roads 

4100 and 4195; bear left, staying 

on Weyerhaeuser Road 4100. 

First 0.2 mi (0.3 km) is on a poorly 

maintained gravel road along 

which are excellent outcrops of 

Figure 29. North Fork Toutle River blockage at stop 22. Here, 

red fractured rock of avalanche deposit underlies blast deposit and pumiceous surge deposit from secondary phreatic 

~xplosions on the Pumice Plain. In foreground are pumiceous pyroclastic-flow deposits of June 12, 1980; in surrounding middle ground is artificial fill at one of the critical 

17.4 (0.4) 

18.1 (0.7) 

18.2 (0.1) 

18.4 (0.2) 

19.0 (0.6) 

19.1 (0.1) 

prismatically jointed blocks in 

pyroclastic-flow deposits of the 

Cougar eruptive stage. 

Weyerhaeuser Road 4100 leaves 

the hill and enters onto the flood 

plain of the South Fork Toutle 

River, heading west. 

Junction of Weyerhaeuser Roads 

4100 and 5700; bear right on Weyerhaeuser Road 4100. 

Junction of Weyerhaeuser Roads 

4100 and 5710; turn left on Weyerhaeuser Road 5710. 

Cross bridge: bear right, leaving 

Weyerhaeuser Road 5710, and 

head west. 

Turn left, road continues 500 ft (150 

m). 

STOP 26. Bear left to borrow pit. 

Here are ~ood exposures of lahars 

of the Swift Creek eruptive stage. 

Charcoal from sand at the top of 

the lahars has a 14 C age of 

HARRYS RIDGE 

points in the Spirit Lake blockage; in background are 

light-colored ash-cloud deposits overlying the avalanche 

runup, where the avalanche crossed over Johnston Ridge 

into South Coldwater Creek drainage basin. Dashed and 

dotted lines indicate approximate boundaries. View 

northward. 

36 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
0 2 

0 

3 KILOMETERS 

2 MILES 

Figure 30. Field-trip route near southwest side of volcano in the Kalama and South Fork 

Toutle River areas, showing leg lc. Triangles, viewpoints; circled numbers, U.S. Forest 

Service and Weyerhaeuser roads; long-dashed line, devastated-zone boundary; shortdashed lines and shading, limits of lahar inundation; stippling, area covered by pyroclastic 

flows and avalanche on north side of volcano. 

Road Guide 37 
12,270±90 yr (Crandell and others, 1981). 

Just south of here is the former location of the 

KOMO TV car where David Crockett was trapped by 

lahars on May 18, 1980. Lahars carried away the bridge 

south of here and covered the road behind him. 

20.0 (0.9) Return to junction of Weyerhaeuser 

Roads 4100 and 5710 at bridge. 

20.1 (0.1) Turn right on Weyerhaeuser Road 

4100. 

20.8 (0.7) Junction of Weyerhaeuser Roads 

4100 and 5700; bear left on Weyerhaeuser Road 4100. 

21.2 (0.4) Weyerhaeuser Road 4100 leaves 

the flood plain and climbs the hill. 

Return to junction of USFS Roads 81 and 8123 in the 

Kalama River valley and turn left. 

27.9 (0.0) A pyroclastic flow containing dacitic 

clasts is exposed for the next 330 ft 

(100m). 

For the next half-mile (0.8 km) the surface is littered 

with breadcrust bombs. The deposit consists of a loose, 

reddish-gray, unsorted and unstratified mixture of sand 

and angular andesite fragments. The deposit was formed 

by a pyroclastic flow during the Kalama eruptive period. 

Hoblitt (1979) reported that these deposits were emplaced at temperatures above 550° C. 

28.3 (0.4) 

28.4 (0.1) 

28.5 (0.1) 

28.9 (0.4) 

29.0 (0.1) 

30.2 (1.2) 

32.1 (1.9) 

Junction of USFS Roads 81 and 

81610. Here, the Kalama Springs 

campground was inundated by a 

mudflow on May 18, 1980. Burial 

of the root burl of these trees was 

deep enough to kill them. 

The Kalama River and McBride 

Lake. McBride Lake was probably created by impoundment from 

pyroclastic flows of the Kalama 

eruptive period. 

STOP 27. Outcrops of pyroclastic 

flows and avalanche deposits, 

probably of the Cougar eruptive 

stage (Hyde, 1975; Newhall, 

1982). 

The Cave Basalt, underlain by an 

andesite flow of the Castle Creek 

eruptive period ( C.A. Hopson, 

written commun., 1984 ). 

Andesite of the Kalama Springs 

area and Red Rock Pass. 

Junction of USFS Roads 81 and 

8100830. 

STOP 28. Deposits north of the 

road are described by Hyde 

(1975; stop 1) as parts of the Swift 

32.7 (0.6) 

Creek assemblage. These outcrops consist of till of the Fraser 

glaciation overlain by pyroclasticflow deposits and S tephra from 

the Swift Creek eruptive stage. 

Junction of USPS Roads 81 and 83. 

Turn left to join up with leg Ib 

(fig. 6) to the Muddy River fan; 

turn right to Ape Cave and the 

town of Cougar. 

END OF SIDE TRIP lc 

SIDE TRIP ld. Randle to Meta Lake 

Route can be followed by reading southbound from 

Randle or northbound from Meta Lake and the junction 

of USFS Roads 26 and 99. Stop numbers run north to 

south. 

North- Southbound bound 

25.5 

(0.9) 

0.0 

(0.0) 

From Randle, head south. Here 

you are about 25 mi ( 40 km) from 

Mount St. Helens; burnt branches 

and ash fell here on May 18, 1980. 

24.6 0.9 Bear right on Woods Creek 

(1.2) (0.9) Road. 

23.4 

(6.6) 

16.8 

(3.6) 

13.2 

(4.5) 

8.7 

(1.0) 

7.7 

(0.2) 

7.5 

(0.5) 

2.1 

(1.2) 

8.7 

(6.6) 

12.3 

(3.6) 

16.8 

(4.5) 

7.8 

(1.0) 

8.0 

(3.2) 

Bear right onto Spear Road and 

the entrance to Gifford Pinchot 

National Forest; stay on paved 

road. Entering north end of area 

of figure 31. 

Cross the Cispus River. J unction of USFS Roads 25 and 26; 

bear right onto USFS Road 26. 

About 1 mi (1.6 km) south on 

USFS Road 25 is the northern 

portal to the monument. 

Strawberry Mountain trail. 

Junction of USFS Roads 26 and 

2608; bear left on USFS Road 26. 

Outcrop of the T, Wn, and Yn 

tephras in roadcut. Now crossing 

the north ed~e of tephra deposit 

from the pliman eruption of May 

18, 1980. Most of the deposit has 

been removed by erosion or covered by vegetation, but farther 

south the deposit thickens. 

STOP 29. Quartz Creek. Stop 

just within sear zone that borders 

the blast zone of May 18, 1980. 

This locality is 14 mi (23 km) from 

the summit. 

Continue on USFS Road 26. 

38 Road Guide to Volcanic Deposits of Mount St. Helens and VIcinity, Washington 
0 

0 

Figure 31. Field-trip route near northeast side of volcano in the Green River and Quartz 

Creek areas, showlr1g leg-ld and part of leg I. Triangles, viewpoints; circled numbers, U.S. 

Forest Service roads; dashed line, devastated-zone boundary; stippling, area of debris 

avalanche. 

Road Guide 39 
4.3 

(0.5) 

21.2 

(3.2) 

STOP 30. Junction of USPS 

Roads 26 and 2612. Hike 150 ft 

(50 m) to Ryan Lake and e~osures of tephra stratigraphy (see 

fig. 22). One person died here 

from asphyxiatiOn caused by the 

ingestion of fine ash. 

Witnesses approximately 6 mi (9.6 km) west of here 

reported noises like three rifle shots in the distance and 

then an apparent pressure change that seemed to force 

them to the ground. A black cloud shot overhead 10 to 15 

seconds after the noises. "Golfball size" and smaller 

pieces of rock dropped from this cloud (some of which 

were collected and are a glassy dacite). The cloud moved 

some distance north and then pulled back to the south 

(so that blue sky appeared overhead) in a span of about 

5 seconds, although it did not completely disappear from 

sight. Then, the cloud reapproached with a "roaring 

noise." As it passed overhead, a cedar tree began to fall, 

and within seconds "there were no trees left." Seconds 

later, it was totally dark, and ash was falling so heavily 

that visibility, with a flashlight, was no more than a foot. 

Although thousands of trees fell, the witnesses did not 

hear them, nor did they feel a blast or wind at that time: 

"Whatever happened, it happened over our heads." The 

first material to fall ''was cold and was like mud," and 

may have contained some ice. The particles seemed to be 

somewhat larger than sand size and appeared to fall 

vertically. A minute or two after the trees blew down, it 

became uncomfortably hot, as if a forest fire was nearby. 

The heat did not last long (excerpted from Rosenbaum 

and Waitt, 1981). 

3.7 

(2.8) 

21.7 

(0.5) 

VIEWPOINT. To the west lies 

the Green River. You have 

crossed the drainage divide between Quartz Creek, which flows 

north into the Cispus and Cowlitz 

Rivers, and the Green River, 

which flows west into the Toutle 

and Cowlitz Rivers. 

For the next 3 mi (4.8 km) are excellent views of downed 

timber. This area had a mature old-growth forest of 

Douglas-fir (and other species); some trees were more 

than 500 yr old. 

0.9 

(0.3) 

0.6 

(0.6) 

24.5 

(2.8) 

24.8 

(0.3) 

STOP 14 (of leg I). Norway Pass 

trailhead. Spectacular view in upper Green River of timber blowdown. The blowdown here will not 

be salvaged but left untouched 

and allowed to decay naturally. 

Meta Lake on south side of 

road. Good examples of downed 

timber and pre-1980 air-fall tephra exposed on north side of road. 

0.0 

(0.0) 

25.4 

(0.6) 

Junction of USPS Roads 26 and 

99 and leg I. Continue right to 

Spirit Lake, or left to Randle or 

Cougar. 

END OF SIDE TRIP ld 

END OF LEG I 

Leg 11. Vancouver to Coldwater Lake via the 

North Fork Toutle River (see fig. 4). 

Events that occurred on May 18, 1980, in the Toutle 

River drainage basin were discussed by Janda and others 

(1981). 

CAUTION: SOME OF THE ROADS IN THIS 

GUIDE ARE SUITABLE ONLY FOR FOURWHEEL-DRIVE VEHICLES AND ARE IMPASSABLE IN THE WINTER AND SPRING. BE SURE 

TO CHECK WITH LOCAL AUTHORITIES BEFORE ATTEMPTING ROADS OFF THE MAIN 

HIGHWAY. TRAVEL EAST OF GREEN RIVER 

SEDIMENT RETENTION DAM (STOP 7) MAY BE 

CLOSED TO PUBLIC ACCESS AND A VEHICLE 

PERMIT REQUIRED TO TRAVEL ON. CHECK 

WITH THE USPS. 

(mileage 

Cumulative between 

mileage points) 

0.0 

15.6 

19.8 

21.5 

22.5 

(0.0) 

(15.6) 

(4.2) 

(1.7) 

(1.0) 

Leave Cascades Volcano Observatory. Travel west on Mill Plain 

Boulevard to junction with U.S. 

Interstate Highway 5. Drive north 

on U.S. Interstate Highway 5. 

Surface is underlain by gravel and 

sand of the great Pleistocene Missoula floods. 

Junction with Ridgefield exit. View 

northeastward of Mount St. 

Helens. 

Cross the East Fork Lewis River. 

Outcrops in roadcut on east side 

of road are lava flows of the upper 

Eocene or lower Oligocene Goble 

Volcanic Series of Lowry and 

Baldwin (1946) interbedded with 

the Eocene Cowlitz Formation (in 

part equivalent to the Hatchet 

Mountain Formation), composed 

of porphyritic andesite, olivine basalt, basalt, and breccia, with interbedded sedimentary rocks. 

Cross the Lewis River. 

Junction with Woodland exit. Continue north on U.S. Interstate 

Highway 5. 

40 Road Guide to Volcanic Deposits of Mount St. Helens and VIcinity, Washington 
33.5 (11.0) Cross the Kalama River. 

The Trojan Nuclear Power Plant is located directly 

west of here on the west bank of the Columbia River, 5 

mi (8 km) upstream from the mouth of the Cowlitz 

River. Soundings by the U.S. Corps of Engineers on May 

24, 1980, showed that the river channel in front of the 

plant, which originally had a depth of 120 ft (36 m ), had 

partially filled to a maximum depth of 40ft (12m). This 

deposition of material was confined to the deeper parts of 

the river channel and did not affect the plant's waterintake structure, which is at a depth of 10 ft (3 m) 

(Schuster, 1981). 

38.5 (4.7) Junction with Longview exit. Continue north on U.S. Interstate 

Highway 5. 

41.2 (3.0) Passing Kelso exit. 

During the May 18, 1980, eruption and subsequent 

flooding, high flow was recorded at Kelso at 4:00 a.m. 

P.d.t. May 19, nearly 19¥2 hours after the eruption 

began; peak water temperature was 90 °F (32 °C). A 

smaller peak was recorded here at 5:00p.m. May 18, with 

a high-water temperature of 51 °F (10.5 °C) from a flood 

that traveled down the South Fork Toutle River. West of 

the freeway, what was once a golf course has now become 

a repository for dredge spoils and the site of a shopping 

mall. 

Entering area of figure 32; continue north on U.S. 

Interstate Highway 5. 

47.9 

51.6 

Cumulative 

mileage 

0.0 

0.3 

0.8 

1.3 

(6.7) West of U.S. Interstate Highway 5 

are areas inundated by lahars 

from the May 18, 1980, eruption 

and spoil piles of debris dredged 

from the Cowlitz River. 

(3.7) Leave freeway at Castle Rock, exit 

49. 

(mileage 

between 

points) 

(0.0) Turn left and cross freeway, heading 

west. 

(0.3) Dredging operations on right. 

(0.5) Turn right onto A street. 

(0.5) VIEWPOINT. Cross Castle Rock 

bridge over the Cowlitz River. 

During the May 18, 1980, eruption and subsequent 

flooding, the effects of the South Fork Toutle River lahar 

were scarcely noticed here. At 1:30 p.m. P.d.t. the stage 

had risen to 13.15 ft (4 m), but by 2:15 p.m. it had 

returned to the preflood condition of 10 ft (3 m). The 

high flow from the North Fork Toutle River lahar was 

recorded at the Castle Rock bridge at midnight, nearly 

15¥2 hours after the 8:32 a.m. eruption. High-water 

temperature here was 85 °F (29 °C). To your left as you 

leave the bridge is the Cowlitz County Fairgrounds. 

From 3 to 5 ft (0.9-1.5 m) of sediment was deposited 

over the entire fairgrounds by the flood on May 18-19, 

1980 (Lombard and others, 1981 ). 

1.6 (0.3) 

2.0 (0.4) 

Right turn at next intersection onto 

Washington Highway 411. 

Lahar deposits of the Cougar eruptive period in upper terrace and of 

the Pine Creek eruptive period in 

lower terrace surface. 

3.0 (1.0) Bear right onto Chapman Road. 

3.7 (0.7) STOP 1 AND VIEWPOINT. View 

eastward to U.S. Interstate Highway 5 bridge and confluence of 

the Cowlitz and Toutle Rivers. 

Here, the lahar from the South Fork Toutle entered 

the Cowlitz River at 1:00 p.m. P.d.t. on May 18, 1980. 

The lahar from the North Fork Toutle River arrived at 

the mouth of the Toutle River at about 8:30 p.m., where 

it was described as having a homogeneous, mortarlike 

consistency from bank to bank. The early part of the 

lahar past this point was seen to carry logs, buildings, and 

a pickup truck. As the lahar entered the Cowlitz River, 

the main mass moved downstream, but part moved 

upstream for 2.5 mi (4 km) (Cummans, 1981). Logs from 

the flow were deposited onto the Burlington Northern 

Railroad bridge, and U.S. Interstate Highway 5 was 

closed to traffic. 

Return to U.S. Interstate Highway 5 overpass. Travel 

east on Washington Highway 504 from overpass, past on 

ramp to next left. 

Cumulative 

mileage 

0.0 

2.5 

(mileage 

between 

points) 

(0.0) Turn left onto Old Pacific Highway. 

(2.5) STOP 2. Washington Highway 99 

bridge across the Toutle River. 

Bridge survived the May 18, 1980, 

lahar. 

Here, the front of the mudflow from the South Fork 

Toutle River passed by at about 1:00 p.m. P.d.t. on May 

18; the mudflow from the North Fork Toutle River 

arrived at about 8:30p.m. High-mudflow marks may still 

be visible on nearby trees. Houses rafted on the lahar 

Road Guide 41 
\ ,-,-.---

0 2 KILOMETERS 

0 2 MILES 

Figure 32. Field-trip route on the Cowlitz and Toutle Rivers in the Kelso-Castle Rock-Silver 

Lake area, showing part of leg II. Triangle, viewpoint; circled number, U.S. Forest Service 

road; dashed lines and shading, limits of lahar inundation. 

42 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
surface crashed into the bridge superstructure. Water 

temperature here was 91 °F (33 °C) at 9:45a.m. May 19. 

Peak floods probably arrived here around 10:00 p.m. 

May 18, 14 hours after the 8:32a.m. eruption. 

Return to Washington Highway 504. 

Cumulative 

mileage 

0.0 

1.9 

2.5 

5.4 

(mileage 

between 

points) 

(0.0) 

(1.9) 

(0.6) 

(2.9) 

Turn left onto Washington Highway 

504 and travel east. 

Junction with Tower Road; continue straight. 

Outcrops of the upper Eocene or 

lower Oligocene Goble Volcanic 

Series of Lowry and Baldwin 

(1946) (equivalent to the Hatchet 

Mountam Formation). 

STOP 3. Seaquest State Park and 

Mount St. Helens National Volcanic Monument Visitor Center. 

( ·, j 

------- - -/-:.~- - _j_ 

0 

0 

A stop at the visitor center is highly recommended. 

Silver Lake was formed when a tributary valley of the 

North Fork Toutle River was dammed by prehistoric 

lahars from Mount St. Helens that moved down the 

Toutle River drainage. Entering area of figure 33. 

8.9 

10.5 

(3.5) 

(1.6) 

Junction with a campground turnoff. 

Junction of Washington Highway 

504 and South Fork Toutle River 

Road. 

Take road that bears right, past store, to South Fork 

Toutle River Road. 

10.8 

2 KILOMETERS 

2 MILES 

(0.3) Cross over Outlet Creek draining 

Silver Lake. Exposed in streambank are outcrops of lahars of the 

Pine Creek eruptive period (part 

of the Silver Lake lahar assemblage of Crandell and Mullineaux, 

1962). Wood fragments from sand 

beneath this sequence of lahars 

Figure 33. Field-trip route in area of confluence of the North and South Forks Toutle River, showing part of leg II. Triangle, 

viewpoint; circled number, U.S. Forest Service road; dashed lines and shading, limits of lahar inundation. 

Road Guide 43 
11.7 (0.9) 

13.0 (1.3) 

. () .... 

'.\···· 

:I o, : 

0 

give a radiocarbon age of about 

2,810 yr. Alluvium and a lahar 

deposit beneath the sand contain 

pumice derived from the Y tephra 

of the Smith Creek eruptive period (4,000-3,300 yr B.P.) (Crandell and others, 1981). 

Enter area inundated by May 18, 

1980, lahars from the South Fork 

and North Fork Toutle Rivers. 

STOP 4. Cross South Fork Toutle 

River bridge and pull off on north 

side of road. Walk about 600 ft 

(182m) north, to high bank. 

Here, the outcrops, more than 20 ft (7 m) high, 

consist of lahars of the Pine Creek eruptive period (fig. 

34). One lahar here contains unusually well rounded 

clasts and monolithic megaclasts of silt-size material. 

This lahar has been interpreted as a breakout lahar, 

formed by sudden breaching of an ancient Spirit Lake 

(K.M. Scott, oral commun., 1985). A lahar would have 

been able to carry the fragile megaclasts of silt, whereas 

a stream would have destroyed the clasts. 

To the right of the high cliff are deposits from the 

May 18, 1980, mudflows that overlie asphalt paving of the 

Harry Gardner Park parking lot. The lower, lithic-rich 

layer represents the first and largest lahar that came 

down the South Fork Toutle River, arriving here at 10:13 

a.m. P.d.t. on May 18. The upper, pumice-rich layer 

Lahars of the Pine Creek 

-:·_ 4-. 

. ·0 -:-:·~_.:~ . . -

Figure 34. Schematic stratigraphic section in Harry Gardner Park at stop 4. L, lithic-rich layer; P, pumice-rich layer. 

44 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
represents deposits from a second lahar in the South 

Fork Toutle River. This pumice-rich lahar reached here 

in the evening of May 18 and was dammed by thick 

deposits of the lahar from the North Fork; the pumice 

came from the plinian eruption that began around noon. 

David Crockett, 6 mi (9.6 km) west of the volcano, 

reported a second mudflow originating in the South Fork 

Toutle River around 2:00p.m. May 18 (Rosenbaum and 

Waitt, 1981). 

Return to junction of Washington Highway 504 and 

South Fork Toutle River Road. 

(mileage 

Cumulative between 

mileage points) 

0.0 (0.0) 

0.6 (0.6) 

Turn right onto Washington Highway 504 and proceed east. 

STOP 5. Pull off just before bridge 

across the Toutle River. View 

from here, with bridge at 12 

o'clock. 

Downstream (at 10 o'clock) is the location of the 

gaging station where mudflow marks were as high as 53 

ft (16m) above the gage datum, about 39ft (12m) higher 

than the South Fork Toutle River lahar. About 0.8 mi 

(1.3 km) downstream is a constriction in the Toutle River 

valley, probably the cause of blockage and subsequent 

ponding of the North Fork Toutle River. Peak flow 

probably occurred at 7:00 p.m. P.d.t. May 18. Just 

downstream of Washington Highway 504 is Outlet 

Creek, which drains Silver Lake. Upstream (1:00 

o'clock), to the left, is the North Fork Toutle River, and 

to the right (2:30 o'clock) is the South Fork Toutle River. 

In the far distance (2:30 o'clock) is Mount St. Helens, 

and in the middle ground is Harry Gardner Park (2:30 

o'clock). Upstream in the high west bank are lahars and 

fluvial deposits of the Pine Creek eruptive period overlying deposits of the Smith Creek, Swift Creek, and Ape 

Canyon eruptive periods. Both bridges, here and about 1 

mi (1.6 km) SE. over the South Fork Toutle River, 

survived the South Fork Toutle River lahar. Later, at 

6:10 p.m., the North Fork Toutle River lahar destroyed 

the Washington Highway 504 bridge. 

Cross over Washington Highway 503 bridge and continue cast on Washington Highway 504. 

3.9 (3.3) Junction with Tower Road; continue straight. 

4.9 (1.0) Junction with Washington Highway 

505; continue straight ahead on 

Washington Highway 504. 

For the next 12 mi (19 km), many sections of the road 

cross river terraces inundated by May 18 lahars. Inundated areas are readily identifiable by the thick growths 

of young alder. 

9.2 

10.5 

(4.3) 

(1.3) 

Maple Flats turnout. Observations 

between 3:00 to 4:30p.m. P.d.t. on 

May 18, 1980, indicate that the 

lahar kept rising and had the consistency of fresh mortar. Peak flow 

here occurred shortly before 5:00 

p.m. May 18. Near here, the 

Goble Volcanic Series has been 

dated at 32.2 to 35.9 m.y. (Oligocene). 

Entering area of figure 35. Travel 

along new roadbed. Lahars of the 

Pine Creek eruptive period are 

exposed in cutbank across river. 

A new sediment-retention dam will be constructed near 

the mouth of the Green River to prevent sediment from 

being washed down the North Fork Toutle River. Farther 

travel up the North Fork depends on road conditions and 

degree of completion of dam. Check with the USFS for 

new routing of road. 

13.6 (3.1) 

13.9 (0.3) 

14.2 (0.25) 

16.4 (2.2) 

16.5 (0.1) 

18.0 (1.5) 

Alder Creek. Exposed on south side 

of road are deposits of the Pine 

Creek and Smtth Creek eruptive 

period. The May 18, 1980, flow on 

the North Fork Toutle River arrived here at about 2:40p.m. P.d.t. 

Buried bridge on left. This bridge 

was carried 0.25 mi (0.4 km) 

downstream by the lahar of May 

18, 1980. 

Cross the North Fork Toutle River. 

Here is the original position of the 

bridge, destroyed at 3:01 p.m. 

P.d.t. May 18, 1980. 

Camp Baker, a sorting yard for the 

Weyerhaeuser Corp., was swept 

by lahars starting at 1:57 r.m. 

P.d.t. May 18, 1980. Many o the 

damaged buildings and equipment have been removed by salvage operations. 

STOP 6. Bridge just east of the 

Camp Baker sorting yard, over 

Hoffstadt Creek. East streambank 

shows lithic lahar deposits of May 

18, 1980, similar to the deposit at 

Harry Gardner Park, underlain by 

road asphalt and deposits of the 

Pine Creek eruptive period and at 

least one lat~r eruptive period. 

Turn off for N-1 Visitor Site. 

Road Guide 45 
Farther travel up the North Fork Toutle River depends 

on road conditions. 

18.5 (0.5) STOP 7. Site of abandoned U.S. 

Army Corps of Engineers 

sediment-retention structure N-1. 

This rock-fill dam was designed and constructed as a 

temporary sediment-control measure in July-September 

1980; it was originally more than 6,100 ft (1,860 m) long 

and 43ft (13m) high. In two stilling basins, sediment was 

deposited and water allowed to continue downstream. 

During its effective life-time the structure was breached 

three times (February, March, and December 1982). The 

structure gave planners 2 years to develop a more 

permanent sediment-management strategy (Meyer, 

1986b). 

STRUCTURE N-1 MARKS THE RESTRICTEDZONE BOUNDARY IN 1986. ENTRY REQUIRES 

SPECIAL PERMITS, RADIOS, GATE KEY, AND SO 

ON. ARRANGEMENTS FOR ENTRY MUST BE 

MADE WITH THE USFS. 

20.0 (1.5) Approximate location of toe of 1980 

debris avalanche. Original logladen toe was removed during 

construction of structure N-1. 

The mounds and hummocks you 

see upstream are parts of the avalanche. Grass and clover were 

planted in an attempt to stabilize 

the surface here. 

Junction of Weyerhaeuser Roads 3100 and 3500; continue on Weyerhaeuser Road 3500 (to right). 

21.7 (1.7) 

22.4 (0.7) 

22.9 (0.5) 

Bridge over Bear Creek. Note exposures of dissected hummocks. 

Junction of Weyerhaeuser Roads 

3300 and 3500; continue on Weyerhaeuser Road 3300. 

STOP 8. Park at bottom of hill and 

hike about 0.5 mi (0.8 km) up the 

North Fork Toutle River on the 

avalanche. At this locality are excellent examples of avalanche topography (hummocks, entrapped 

lakes, mudflows), erosion, deposi0 2 KILOMETERS 

0 2 MILES 

Figure 35. Field-trip route on the North Fork Toutle River in 

the Pullen-Aider Creek-Elk Rock areas, showing part of leg II. 

Triangles, viewpoints; circled numbers, Weyerhaeuser 

roads; short-dashed lines and shading, limits of lahar inundation; long-dashed line, devastated-zone boundary; stippling, area of debris avalanche; dotted line, settlement 

pond of sediment-retention structure N-1. 

46 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
23.1 

tion, and revegetation (manmade 

or natural). 

(0.2) STOP 9. View of the North Fork 

Toutle River debris avalanche. 

Note the contrast between replanted avalanche surface (west of Elk Rock) and undisturbed avalanche, 

avalanche levees, lakes, and hummocks below and east of 

Elk Rock. Note also deposits and effects of the March 19, 

1982, lahar, as well as fluvial deposits and downed timber 

that has not been salvaged. Reworked blast deposit is 

locally present in this area. Tephra from the May 25, 

1980, eruption deposited here has been almost completely removed by erosion. 

Continue on Weyerhaeuser Road 3300. Pay careful 

attention to the road numbers-it's easy to get lost in the 

maze of roads here. 

24.6 

26.6 

28.0 

28.3 

28.9 

(2.0) 

(1.4) 

(0.3) 

(0.6) 

the event of an outbreak from 

Spirit Lake. A lahar traveling 

downstream from here would take 

4 to 6 hours to reach the Cowlitz 

River and Castle Rock. 

Junction of Weyerhaeuser Roads 

3300, 3380, and 3381; turn right 

onto Weyerhaeuser Road 3381 

(follow stgns leading to Weyerhaeuser Road 3540). 

Junction of Weyerhaeuser Roads 

3340, 3344, and 3381; bear left on 

Weyerhaeuser 3340 (follow signs 

leading to Weyerhaeuser 3540). 

Junction with Weyerhaeuser Roads 

3340 and 3346; turn right onto 

Weyerhaeuser 3346 road (follow 

signs leading to Weyerhaeuser 

3540). 

Junction with Weyerhaeuser Road 

3540; turn right onto Weyerhaeuser Road 3540. 

(1.5) Junction with Weyerhaeuser Road 

3310 to the Cowlitz County riverwatch station. This outpost was 

used by Cowlitz County as a backup to the USGS warning system in Entering area of figure 36. 

0 2 KILOMETERS 

0 2 MILES 

Figure 36. Field-trip route on the North Fork Toutle River in the Elk Rock-Coldwater Lake area, showing part of leg 11. 

Triangles, viewpoints; circled numbers, Weyerhaeuser roads; short-dashed lines and shading, limits of lahar inundation; 

long-dashed line, devastated-zone boundary; stippling, area of debris avalanche. 

Road Guide 47 
29.5 (0.6) STOP 10. Right turn to a dead end 

on the east slope of Elk Rock. 

Here is an excellent view of Mount St. Helens, the 

debris avalanche, and the spillway draining Coldwater 

Lake (fig. 37). The crater of Mount St. Helens is 10 mi 

(16 km) away. The blast deposit was thin here (5 in. [13 

em]), and is being eroded further. 

Return to Weyerhaeuser Road 3540; continue to right. 

30.9 (1.4) Bear left on Weyerhaeuser Road 

3540. 

32.4 (1.5) Junction of Weyerhaeuser Roads 

3540 and 3545. Road to north 

(Weyerhaeuser Road 3545) leads 

to Morton and the Green River 

drainage basin. Turn right for the 

Coldwater Lake blockage on 

Weyerhaeuser Road 3540 (main 

construction road to South Coldwater Creek). 

Entering area of figure 38. 

36.4 ( 4.0) STOP 11. Coldwater Lake blockage. 

Figure 37. Mount St. Helens from the Elk Rock area. A, area of debris avalanche; J, Johnston Ridge; SL, Spirit Lake. Dashed 

line, Weyerhaeuser Road 3540. View southeastward; photograph by Bob Krimmel, taken June 16, 1982. 

48 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
0 1 KILOMETER 

0 1 MILE 

Figure 38. Simplified geologic map of Coldwater Lake blockage near stop 11. A, area of rockfall-debris 

avalanche that filled the North Fork Toutle River valley; CC, Castle Creek; CW, Coldwater Creek; MC, Marada 

Creek; R, runup of debris avalanche on valley walls; long-short-dashed lines, streamcourses; dashed lines, 

location of avalanche scarps; stippling, source area of May 18, 1980, North Fork Toutle River lahars. Arrows 

indicate direction of lahar flow. 

Road Guide 49 
The view from the Coldwater exit affords an excellent view of the debris-avalanche deposit and its diverse 

parts. The following description comes from reports by 

Glicken (1986) and Meyer (1986a, b). 

The eruption on May 18, 1980, was initiated by a 

magnitude 5.1 earthquake, which triggered a large landslide off the volcano; the landslide was quickly hidden by 

the advancing cloud of steam and hot rocks of the lateral 

"blast." Beneath this maelstrom came the 2.7-km3 (0.7 

mi3 )-volume debris avalanche. 

The failure of the avalanche took place as huge slices 

or slide blocks (Giicken, 1986). Slide block I consisted of 

the north face of Mount St. Helens, mostly young rocks 

less than 2,500 years old (dacite, andesite, and basalt). 

The block remained relatively intact, depositing material 

on and adjacent to Johnston Ridge as it passed over the 

ridge; part of it went into Spirit Lake, and part of it 

flowed downvalley to form the material on the margins of 

the debris-avalanche deposit. Slide block I unroofed the 

magma chamber ( cryptodome) that had been growing 

inside the mountain for 6 weeks. The explosions that 

resulted from depressurization of the cryptodome burst 

through slide block II and created a pyroclastic density 

current (the "blast") that devastated 212 mi2 (550 km2

) 

of the surrounding landscape. 

Most of the volume of slide block II, as well as all of 

slide block III, made a 90° turn to the west at Harrys 

Ridge and Johnston Ridge and became a flowing-debris 

avalanche. Slide block II contained fragments of ancestral dacite from the core of the volcano; slide block III 

contained fragments of ancestral dacite and "blast" dacite of the cryptodome. 

The debris avalanche moved in part as a flow of 

blocks that traveled 10 mi (16 km). Much of slide block 

III moved as an explosively motivated flow that traveled 

over the debris-avalanche blocks of slide block II and 

moved 17.6 mi (28 km) from the crater. The avalanche 

reached its present length in 3 to 10 minutes. 

Water contained within and under the avalanche and 

from melted ice was squeezed up through the debris and 

coalesced into a lahar that moved down the valley of the 

North Fork Toutle River. 

The debris-avalanche deposit is characterized by 

extremely irregular topography. Hummocks of many 

shapes and sizes are interspersed with irregular and 

circular depressions, creating a surface with as much as 

246ft (75 m) of relief. Surface expression on the debrisavalanche deposits results from (1) lateral spreading 

during primary deposition; (2) differential compaction of 

the deposit after deposition; (3) phreatic explosions 

resulting from hot debris coming in contact with water 

(ice melt or preexisting streams); (4) postlahar bank 

failures; and (5) melting of buried ice. 

One of the most striking features of the post-1980 

geomorphology of the North Fork Toutle River debrisavalanche deposit is the development of major stream 

channels. Here, near the Coldwater Creek blockage area, 

the channels are those of Coldwater Creek and the upper 

North Fork Toutle River (figs. 38, 39). 

Coldwater Creek, downstream from Coldwater 

Lake, formed during the controlled release of Coldwater 

Lake July 1981. In May 1985, outflow from Spirit Lake 

was diverted into the South Fork Coldwater Creek 

through a tunnel under Harrys Ridge. In response to the 

additional flow, the channel widened 65 ft (20 m) and 

incised about 13 ft ( 4 m). 

The upper North Fork Toutle River developed along 

a 2-mi (3 km)-long, aligned group of closed depressions. 

Individual depressions had 20 to 100 ft ( 6-30 m) of local 

relief. Some lahars formed in this area on May 18, 1980, 

but the throughflowing channel was created by the November 7, 1980, breaching of Carbonate Lake, a temporary lake on the debris avalanche. Subsequent channel 

modification has resulted from (1) breakout of small 

lakes on the surface of the debris-avalanche deposit; (2) 

storm flow; (3) lahars, primarily those of March 19, 1982, 

and May 14, 1984; and (4) pumping from Spirit Lake 

during 1982-84. 

Across the outlet channel to the south are hummocks that consist of semicoherent blocks of volcanic 

rock (fig. 39). The closer ones, within the deposits of slide 

block I, are chiefly composed of andesite and basalt. 

Beyond the sharp escarpment, which marks a marginal 

avalanche levee, are deposits mainly of block II, composed of dacite from ancestral domes within the volcano. 

The marginal levees can be found throughout the middle 

part of the debris-avalanche deposit; they formed along 

valley walls or across the mouths of tributary valleys, as 

the debris-avalanche flowed downvalley. Coldwater, Castle, and Jackson Lakes and numerous unnamed ponds 

were impounded by this facies of the debris-avalanche 

deposit (Voight and others, 1981). To the south, east of 

Castle Lake, the surface of the debris-avalanche deposit 

is mantled with blast deposit, creating a relatively flat 

surface (fig. 38). Along the north margin of the flat, 

landslide scarps mark the left bank of the North Fork 

Toutle River. This bank is highly unstable because of a 

high water table and ground-water outflow. Brown 

"bathtub rings" from the May 18, 1980, lahar are present 

throughout most low-lying areas of the Coldwater Creek 

blockage. The lahar was formed on the surface of the 

debris-avalanche deposit by slumping and flowing of 

water-saturated debris, and by dewatering of the deposit 

through numerous springs (Meyer, 1986a). 

END OF LEG II 

50 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
Figure 39. Coldwater Creek-Castle Creek area, showing rockslide/debris avalanche (A) near Coldwater Lake. Manmade outlet 

channel cuts diagonally across bedrock spur south of stop 11, draining Coldwater Lake into Coldwater Creek. Scarps (dotted 

lines) designate avalanche levees; arrow indicates direction of debris flow. Dashed line, field-trip route. H, hummocks. View 

northeastward. 

Road Guide 51 
REFERENCES CITED 

Armstrong, J.E., Crandell, D.R., Easterbrook, D.J., and Noble, 

J.B., 1965, Late Pleistocene stratigraphy and chronology in 

southwestern British Columbia and northwestern Washington: Geological Society of America Bulletin, v. 76, no. 

3, p. 321-330. 

Brugman, M.M., and Meier, M.F., 1981, Response of glaciers 

to the eruptions of Mount St. Helens, in Lipman, P.W., and 

Mullineaux, D.R., eds., The 1980 eruptions of Mount St. 

Helens, Washington: U.S. Geological Suxvey Professional 

Paper 1250,p. 743-754. 

Cashman, K.V., and Taggart, J.E., 1983, Petrologic monitoring 

of 1981 and 1982 eruptive products from Mount St. 

Helens: Science, v. 221, no. 4618, p. 1385-1387. 

Crandell, D.R., 1988, Deposits of pre-1980 pyroclastic flows 

and lahars from Mount St. Helens Volcano, Washington: 

U.S. Geological Suxvey Professional Paper 1444, 91 p. 

Crandell, D.R., and Mullineaux, D.R., 1973, Pine Creek volcanic assemblage at Mount St. Helens, Washington: U.S. 

Geological Suxvey Bulletin 1383-A, p. A1-A23. 

--- 1978, Potential hazards from future eruptions of 

Mount St. Helens Volcano, Washington: U.S. Geological 

Suxvey Bulletin 1383-C, p. C1-C26. 

Crandell, D.R., Mullineaux, D.R., and Rubin, Meyer, 1975, 

Mount St. Helens Volcano: Recent and future behavior: 

Science, v. 187, no. 4175, p. 438-441. 

Crandell, D.R., Mullineaux, D.R., Rubin, Meyer, Spiker, Elliot, 

and Kelley, M.L., 1981, Radiocarbon dates from volcanic 

deposits at Mount St. Helens, Washington: U.S. Geological Suxvey Open-File Report 81-844, 15 p. 

Cummans, John, 1981a, Mudflows resulting from the May 18, 

1980, eruption of Mount St. Helens, Washington: U.S. 

Geological Suxvey Circular 850-B, p. B1-B16. 

--- 1981b, Chronology of mudflows in the South Fork and 

North Fork Toutle River following the May 18 eruption, in 

Lipman, P.W., and Mullineaux, D.R., eds., The 1980 

Eruptions of Mount St. Helens, Washington: U.S. Geological Suxvey Professional Paper 1250, p. 479-486. 

Doukas, M.P., and Swanson, D.A., 1987, Mount St. Helens, 

with emphasis on 1980-85 eruptive activity as viewed from 

Windy Ridge, in Hill, M.L., ed., Decade of North American Geology Project centennial field guide 1: Boulder, 

Colo., Geological Society of America, Cordilleran Section, 

p. 333-338. 

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

Mount Rainier National Park, Washington: U.S. Geological Suxvey Professional Paper 444, 93 p. 

Foxworthy, B.L., and Hill, Mary, 1982, Volcanic eruptions of 

1980 at Mount St. Helens-the first 100 days: U.S. Geological Suxvey Professional Paper 1249, 125 p. 

Glicken, Harry, 1986, Rockslide-debris avalanche of May 18, 

1980, Mount St. Helens Volcano: Santa Barbara, University of California, Ph.D. thesis, 303 p. 

Greeley, Ronald, and Hyde, J.H., 1972, Lava tubes of the Cave 

Basalt, Mount St. Helens, Washington: Geological Society 

of America Bulletin, v. 83, no. 8, p. 2397-2418. 

Hammond, P.E., 1980, Reconnaissance geologic map of the 

southern Washington Cascade Range: Portland, Oreg., 

Portland State University, Department of Earth Sciences, 

scale: 1:125,000. 

Hildreth, Wes, and Fierstein, Judy, 1983, Mount Adams and its 

30 "parasites" [abs.]: Geological Society of America Abstracts with Programs, v. 15, no. 5, p. 331. 

Hoblitt, R.P., Crandell, D.R., and Mullineaux, D.R., 1980, 

Mount St. Helens eruptive behavior during the past 1;500 

yr: Geology, v. 8, no. 11, p. 555-559. 

Hoblitt, R.P. and Kellogg, K.S., 1979, Emplacement temperatures of unsorted and unstratified deposits of volcanic rock 

debris as determined by paleomagnetic techniques: Geological Society of America Bulletin, v. 90, pt. 1, no. 7, p. 

633-642. 

Hopson, C.A., 1971, Eruptive sequence at Mount St. Helens, 

Washington: Geological Society of America Abstracts with 

Programs, v. 3, p. 138. 

--- 1983, Stratigraphy of Mount St. Helens 1980 crater 

walls [abs.]: Eos (American Geophysical Union Transactions), v. 65, no. 45, p. 1144. 

Hyde, J.H., 1975, Upper Pleistocene pyroclastic-flow deposits 

and lahars from Mount St. Helens, Washington: U.S. 

Geological Suxvey Bulletin 1383-B, p. B1-B20. 

Hyde, J.H., Greeley, R., 1973, Geological field trip guide, 

Mount St. Helens lava tubes, Washington, in Beaulieu, 

J.D., compiler, 1973, Geologic field trips in northern 

Oregon and southern Washington: Oregon Department of 

Geology and Mineral Industries Bulletin 77, p. 183-206. 

Janda, R.J., Scott, K.M., Nolan, K.M., and Martinson, H.A., 

1981, Lahar movement, effects, and deposits, in Lipman, 

P.W., and Mullineaux, D.R., eds., The 1980 eruptions of 

Mount St. Helens, Washington: U.S. Geological Suxvey 

Professional Paper 1250, p. 461~78. 

Kuntz, M.A, Rowley, P.D., Macleod, N.S., Reynolds, R.L., 

Mcbroome, L.A., Kaplan, A.M., and Lidke, D.J., 1981, 

Petrography and particle-size distribution of pyroclasticflow, ash-cloud, and surge deposits, in Lipman, P.W., and 

Mullineaux, D.R., eds., The 1980 eruptions of Mount St. 

Helens, Washington: U.S. Geological Survey Professional 

Paper 1250, p. 525-539. 

Lipman, P.W., and Mullineaux, D.R., eds., 1981, The 1980 

eruptions of Mount St. Helens, Washington: U.S. Geological Suxvey Professional Paper 1250, 844 p. 

Lombard, R.E., Miles, M.B., Nelson, L.M., Kresch, D.L., and 

Carpenter, P.J., 1981, Channel conditions in the lower 

Toutle and Cowlitz Rivers resulting from the mudflows of 

May 18, 1980: U.S. Geological Suxvey Circular 850-C, p. 

C1-C16. 

Lowry, W.D., and Baldwin, E.M., 1946, Late Cenozoic geology 

of the lower Columbia River Valley, Oregon and Washington: Geological Society of America Bulletin, v. 63, no. 

1, p. 1-24. 

Meyer, D.F., 1986a, Channel formation and modification under 

various water and sediment discharges, South Fork Coldwater Creek, Washington, in Iverson, R.M., and Martinson, H.A., eds., Mount St. Helens; American 

Geomorphological Field Group, Field Trip Guidebook 

and Abstracts, 178 p. 

--- 1986b, Surficial processes and deposits at the Coldwater Drainage, in Iverson, R.M. and Martinson, H.A., eds., 

Mount St. Helens: American Geomorphological Field 

52 Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington 
Group field trip guidebook and abstracts, 178 p. 

Moore, J.G., and Sisson, T.W., 1981, deposits and effects of the 

May 18 pyroclastic surge, in Lipman, P.W. and Mullineaux, 

D.R., eds., The 1980 eruptions of Mount St. Helens, 

Washington: U.S. Geological Sutvey Professional Paper 

1250, p. 421-438. 

Mullineaux, D.R., 1986, Summary of pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington State, 

USA: Bulletin Volcanologique, v. 48, no. 1, p. 17-26. 

Mullineaux, D.R., and Crandell, D.R., 1962, Recent lahars 

from Mount St. Helens, Washington: Geological Society of 

America Bulletin, v. 73, no. 7, p. 855-869. 

--- 1981, The eruptive history of Mount St. Helens, Washington, in Lipman, P.W., and Mullineaux, D.R., eds., The 

1980 eruptions of Mount St. Helens, Washington: U.S. 

Geological Survey Professional Paper 1250, p. 3-15. 

Mullineaux, D.R., Hyde, J.H., and Rubin, Meyer, 1975, Widespread late-glacial and post-glacial tephra deposits from 

Mount St. Helens volcano, Washington: U.S. Geological 

Survey Journal of Research, v. 3, no. 3, p. 329-335. 

Mundorff, M.J., 1964, Geology and ground-water conditions of 

Clark County, Washington, with a description of a major 

alluvial aquifer along the Columbia River: U.S. Geological 

Survey Water-Supply Paper 1600, 268 p. 

--- 1984, Glaciation in the lower Lewis River basin, southwestern Cascade Range, Washington: Northwest Science, 

v.58, no. 4,p. 269-281. 

Newhall, C.G., 1982, A prehistoric debris avalanche from 

Mount St. Helens [abs.]: Eos (American Geophysical 

Union Transactions), v. 63, no. 45, p. 1141. 

Roberts, A.E., 1958, Geology and coal resources of the ToledoCastle Rock district, Cowlitz and Lewis Counties, Washington: U.S. Geological Survey Bulletin 1062, 71 p. 

Rosenbaum, J.G., and Waitt, R.B., Jr., 1981, Summary of 

eyewitness accounts of the May 18 eruption, in Lipman, 

P.W., and Mullineaux, D.R., eds., The 1980 eruptions of 

Mount St. Helens, Washington: U.S. Geological Survey 

Professional Paper 1250, p. 53-67. 

Rowley, P.D., Kuntz, M.A., and Macleod, N.S., 1981, 

Pyroclastic-flow deposits, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 eruptions of Mount St. Helens, 

Washington: U.S. Geological Survey Professional Paper 

1250, p. 489-512. 

Schuster, R.L., 1981, Effects of the eruptions on civil works and 

operations in the Pacific Northwest, in Lipman, P.W., and 

Mullineaux, D.R., eds., The 1980 eruptions of Mount St. 

Helens, Washington: U.S. Geological Survey Professional 

Paper 1250, p. 701-718. 

Swanson, D.A., Casadevall, T.J., Dzurisin, Daniel, Malone, 

S.D., Newhall, C.G., and Weaver, C.S., 1983, Predicting 

eruptions at Mount St. Helens, June 1980 through December 1982: Science, v. 221, no. 4618, p. 1369-1376. 

Swanson, D.A., Dzurisin; Daniel, Holcomb, R.T., Iwatsubo, 

E.Y., Chadwick, W.W., Jr., Casadevall, T.J., Ewert, J.W., 

and Heliker, C.C., in press, Growth of the lava dome at 

Mount St. Helens, Washington (USA), 1981-83, in Fink, 

Jonathan, ed., The growth of silicic domes: Geological 

Society of America Special Paper. 

Voight, Barry, Glicken, Harry, Janda, R.J., and Douglass, P.M., 

1981, Catastrophic rockslide avalanche of May 18, in 

Lipman, P.W., and Mullineaux, D.R., eds., The 1980 

eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 347-377. 

Voight, Barry, Janda, R.J., Glicken, Harry, and Douglass, P.M., 

1983, Nature and mechanics of the Mount St Helens 

rockslide-avalanche of 18 May 1980: Geotechnique, v. 33, 

no. 3, p. 243-273. 

Waitt, R.B., 1984, Deposits and effects of devastating lithic 

pyroclastic density current from Mount St. Helens on 18 

May 1980-field guide for northeast radial: U.S. Geological Survey Open-File Report 84-839, 10 p. 

Waitt, R.B., and Dzurisin, Daniel, 1981, Proximal air-fall 

deposits from May 18 eruption-stratigraphy and field 

sedimentology, in Lipman, P.W., and Mullineaux, D.R., 

eds., The 1980 eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 

601-616. 

Waitt, R.B., Pierson, T.C., MacLeod, N.S., Janda, R.J., Voight, 

Barry, and Holcomb, R.T., 1983, Eruption-triggered avalanche, flood, and lahar at Mount St. Helens-effects of 

winter snowpack: Science, v. 221, no. 4618, p. 1394-1397. 

Walker, G.P.L., and McBroome, L.A., 1983, Mount St. Helens 

1980 and Mount Pelee 1902-flow or surge?: Geology, v. 

11,no. 10,p.571-574. 

Wilkinson, W.D., Lowry, W.D., and Baldwin, E.M., 1946, 

Geology of the St. Helens quadrangle, Oregon: Oregon 

Department of Geology and Mineral Industries Bulletin 

31, 39 p. 

Wood, S.H., Doukas, M.P., Shipley, S., Waitt, R.B., Vallance, J., 

Eggers, A., and Sarna-Wojcicki, A.M., in press, The July 

22, 1980, eruption of Mount St. Helens: Characteristics of 

the eruption and airfall tephra, in U.S. Geological Survey 

Professional Paper 1251. 

Yamaguchi, D.K., 1983, New tree-ring dates for recent eruptions of Mount St. Helens: Quaternary Research, v. 20, no. 

2, p. 246-250. 

References Cited 53 

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