U.S. Department of the Interior

U.S. Geological Survey

Professional Paper 1762

Volcanic Processes and Geology 

of Augustine Volcano, Alaska
Front Cover: Photograph of en plein air painting by Josephine Crumrine from West Hills 

above Homer, Alaska, in June 1986 while viewing Augustine Volcano erupting 71 miles 

(113 km) away. Original oil on canvas hangs at Pratt Museum, Homer, Alaska. Image 

used by permission.
Volcanic Processes and Geology 

of Augustine Volcano, Alaska

By Richard B. Waitt and James E. Begét 

Debris avalanches, pyroclastic flows and surges, and ashfalls of the 

past few millennia at Augustine Volcano in lower Cook Inlet, Alaska, 

illuminated by historical photographs and a new topographic and 

geologic map

Professional Paper 1762

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation:

Waitt, R.B., and Begét, J.E., 2009, Volcanic processes and geology of Augustine Volcano, Alaska: 

U.S. Geological Survey Professional Paper 1762, 78 p., 2 plates, scale 1:25,000.

Cataloging-in-publication data are on file with the Library of Congress (http://www.loc.gov/).
Contents

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

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

Landslide ................................................................................................................................................4

Lava-Dome Effusion Rates ..................................................................................................................6

Rock Type, Grain Size, Grain Shape............................................................................................................6

Chronology......................................................................................................................................................8

Radiocarbon Ages ................................................................................................................................8

Tephra and Tephrochronology............................................................................................................8

Geomorphology...................................................................................................................................14

Distinguishing Lithic Pyroclastic Flows from Lahars in Proximal Areas ..........................15

On Map “Units”...................................................................................................................................15

Synopsis of Geologic History.....................................................................................................................17

Pre-Augustine Mesozoic Rocks................................................................................................................18

Pleistocene to Late Holocene Materials .................................................................................................19

Pleistocene Deposits..........................................................................................................................19

Landslide Block..........................................................................................................................20

Glacial Deposits .........................................................................................................................20

Basaltic and Rhyolitic Deposits...............................................................................................21

Pleistocene and Holocene Pumiceous Fall and Pyroclastic-Flow Deposits ............................22

Lava Domes of Uncertain Late Holocene Age...............................................................................23

Kamishak Dome (Dome K)........................................................................................................23

Domes F and P............................................................................................................................23

Prehistoric Summit Domes.......................................................................................................23

Lava Flows...................................................................................................................................24

Prehistoric Deposits of Late Holocene Age ...........................................................................................24

Deposits Older Than Tephra G (about 2,500–2,100 14C yr B.P.).....................................................25

East Point Debris-Avalanche Deposit(s)................................................................................25

Deposits Between Tephras G and I (about 2,100–1,800 14C yr B.P.)............................................25

Yellow Cliffs Debris-Avalanche Deposit.................................................................................25

Southeast Point Debris-Avalanche Deposit..........................................................................25

Deposits Between Tephas I and H (about 1,700–1,400 14C yr B.P.)..............................................25

Northeast Point Debris-Avalanche Deposit..........................................................................25

Northeast Bench Debris-Avalanche or Lahar Deposit........................................................28

Diamict atop Landslide Block ..................................................................................................28

Deposits Between Tephras H and C (about 1,450–1,100 14C yr B.P.)...........................................29

South Point Debris-Avalanche Deposit..................................................................................29

Long Beach Debris-Avalanche Deposit.................................................................................29

Southwest Pyroclastic Fan ......................................................................................................30

Southeast Pyroclastic Fan .......................................................................................................31

North Bench Debris-Avalanche Deposit ...............................................................................31

Deposits Between Tephras C and M (about 1,000–750 14C yr B.P.).............................................32

Lagoon Debris-Avalanche Deposit.........................................................................................32

Pumiceous Pyroclastic-Flow Deposit ....................................................................................34

 iii
Lithic Pyroclastic-Flow (or Lahar?) Deposit ..........................................................................34

Deposits Between Tephras M and B (about 750–400 14C yr B.P.)................................................34

Pyroclastic-Flow and Lahar Deposits ....................................................................................34

Southeast Beach Debris-Avalanche Deposit .......................................................................34

Deposits Younger than Tephra B (younger than about 400 14C yr B.P.)......................................34

West Island Debris-Avalanche Deposit.................................................................................34

Rocky Point Debris-Avalanche Deposit.................................................................................39

Unassigned Debris-Avalanche Deposits ...............................................................................39

North Slope Lava Flow..............................................................................................................40

Beach and Eolian Deposits ...............................................................................................................40

Historical Deposits.......................................................................................................................................40

1812 Eruption........................................................................................................................................42

1883 Eruption........................................................................................................................................42

Burr Point Debris-Avalanche Deposit....................................................................................44

Pyroclastic-Flow and Surge Deposits....................................................................................47

Lava Dome...................................................................................................................................48

Discussion...................................................................................................................................48

1935 Eruption........................................................................................................................................49

Lava Dome...................................................................................................................................49

Flank Deposits ............................................................................................................................49

1963–64 Eruption .................................................................................................................................49

Lava Dome...................................................................................................................................49

Pyroclastic-Flow and Lahar Deposits ....................................................................................49

Ballistics......................................................................................................................................50

1976 Eruption........................................................................................................................................50

Pyroclastic-Flow, Surge, and Lahar Deposits.......................................................................50

1986 Eruption........................................................................................................................................52

Lava Dome and Agglutinate.....................................................................................................52

Pyroclastic-Flow and Lahar Deposits ....................................................................................52

Occasional Small Events ...................................................................................................................55

2006 Eruption........................................................................................................................................56

Nonvolcanic Deposits........................................................................................................................56

Talus and Stream Deposits.......................................................................................................56

Eolian Deposits...........................................................................................................................56

Beach Deposits..........................................................................................................................56

Tidal-Flat Deposits and Marsh Deposits................................................................................57

Comparison to Previous Geologic Map ...................................................................................................57

Précis of Eruptions.......................................................................................................................................57

High-Energy Flows From Insular Setting .................................................................................................58

Pyroclastic Density Currents ............................................................................................................58

Debris Avalanche and Surge (“Blast”) ...........................................................................................58

Augustine’s Debris Avalanches...............................................................................................58

Mobility and Speed of Volcanic Debris Avalanches............................................................59

Tsunami.................................................................................................................................................62

Augustine Island, 6 October 1883............................................................................................62

Analysis of 6 October 1883 Records .......................................................................................63

iv
Evidence on Augustine Island for Augustine Tsunami........................................................66

Evidence on Mainland for Augustine Tsunami .....................................................................66

Sparseness of Mainland Evidence for Augustine Tsunami................................................67

Numerical Simulation of Augustine Tsunami........................................................................68

Can Augustine Generate Large Tsunami? .............................................................................68

Hazards .........................................................................................................................................................69

Acknowledgments.......................................................................................................................................70

References Cited..........................................................................................................................................70

Plates [in pocket]

 1. Map showing the geology of Augustine Island, Alaska.

 2. Map showing measured sections on Augustine Island and Shuyak Island, Alaska.

Figures

1. Index maps of Cook Inlet area, Alaska and Augustine Island .......................................................2

2. Photo looking south-southwest of Augustine Volcano....................................................................4

3. Oblique aerial photo looking northeast of Augustine Island and Augustine Volcano................6

4. Plot of chemical composition analyses of volcanic rocks (whole-rock analyses) and

tephra (glass-separate analyses) from Augustine Island...............................................................7

5. Summary of mean annual wind directions 1949–62 .......................................................................12

6. Tephra stratigraphy overlying flowage deposits on Augustine Island just north of

southeast gully .....................................................................................................................................13

7. Isopach maps of coarse pumiceous tephra-layers on Augustine Island .................................... 14

8. Graph showing thickness of some sheets of tephra erupted from volcanoes in western

United States plotted against distance downwind........................................................................15

9. Summary of eruptive history of Augustine Volcano based on data in this report.....................16

10. Sketch showing in profile development of arrested sea cliffs at Augustine Island..................16

11. Map showing offshore distribution of debris avalanches off Augustine Volcano

based on seaward extent of conspicuously hummocky submarine topography......................18

12. Oblique aerial photo looking north-northwest of Augustine Volcano...............................................19

13. Photo showing Naknek Formation (Jurassic) on south side of Augustine Island.....................20

14. Photo showing great landslide block capped by layered Augustine-volcanic debris,

south coast Augustine Island.............................................................................................................21

15. Photo showing view north of glacial till containing striated exotic stones and

associated glacial drift (g) overlain by dacitic fall pumice of Augustine Volcano....................21

16. Photo looking eastward showing bedded olivine-basalt hyaloclastite at or near

base of discontinuously exposed volcanic materials of Augustine Volcano.............................22

17. Photo showing basaltic hyaloclastite overlain by dacite pumice on

south flank of Augustine Island .........................................................................................................22

18. Photo showing pumice-fall deposit from Augustine interbedded with

distal thin beds of Pleistocene glacial outwash, south-southwest flank of volcano................23

19. Oblique aerial photo looking toward east-southeast of Augustine Volcano summit

area including landslide-truncated prehistoric summit-dome complex.....................................24

 v
20. Photos showing details within East Point debris-avalanche deposit..........................................26

21. Photo showing view of sea cliff along Augustine Island east shore...........................................27

22. Photo showing Southeast Point and Northeast Point debris-avalanche deposit.....................27

23. Schematic sketch of coastal cliffs along east side of Augustine Island showing

stratigraphic relations of four oldest debris-avalanche deposits................................................27

24. Photo showing view west of hummocky surface of Northeast Point

debris-avalanche deposit...................................................................................................................28

25. Oblique aerial photo looking west-southwestward of prominent huge-boulder “mound” 

area of hummocky Northeast Point debris-avalanche deposit, Augustine Island ...................28

26. Oblique aerial photo looking west-northwestward of Augustine’s Northeast Point

debris-avalanche deposit and apparently overridden sea cliff ...................................................29

27. Photo showing nine-meter megaclast of summit-dome porphyritic andesite forming

a single hummock of Long Beach debris-avalanche deposit on lower southwest

flank of Augustine Island ....................................................................................................................30

28. Photo looking northwest of boulders on southeast pyroclastic fan of Augustine Island ........31

29. Vertical aerial photo of Augustine’s north flank showing dome complex, North

Slope lava flow and the debris-avalanche deposits .....................................................................32

30. Oblique aerial photo looking south-southeast showing North Slope lava flow, arrested 

sea cliff cut in North Bench debris-avalanche deposit, Rocky Point debris-avalanche deposit, 

and 1883 debris-avalanche levee across and below the lava flow..................................................33

31. Photo looking west-northwest from high on cone of Augustine Volcano showing

West Island, one of the largest of Augustine’s debris-avalanche deposits...............................34

32. Photo showing oblique aerial view southwestward of Augustine Volcano and its

offshore West Island ...........................................................................................................................35

33. Photo showing coastal sea cliff exposing interior of debris-avalanche hummock on

West Island, just off Augustine Island..............................................................................................35

34. Photo looking southeastward of southwest side of central core of high conical

hummocks of West Island debris-avalanche deposit....................................................................36

35. Stratigraphic section showing succession atop debris-avalanche hummock on

southwest coast of West Island ........................................................................................................36

36. Sketch map showing details of Grouse Point area, Augustine Island ........................................37

37. Oblique aerial photos of oddly planed-off hummocks on southwest part of West

Island, at Augustine Island.................................................................................................................38

38. Photo looking northeast of southwestmost part of Augustine’s West Island showing

oddly flattened hummocks..................................................................................................................38

39. Photo showing Bouldery diamict of debris-avalanche levee resting atop North Slope

lava flow, north flank of Augustine Volcano..........................................................................................39

40. Photos and a sketch of Augustine Volcano showing large-scale effects to summit

area by 1883 eruption ..........................................................................................................................41

41. Photographic portraits of George Davidson ....................................................................................42

42. Oblique aerial photo of Augustine Volcano from the north showing hummocky

deposit about Burr Point deposited by landslide of 6 October 1883............................................44

43. Photos showing eastern cluster of hummocks of 1883 Burr Point debris avalanche,

Augustine Island...................................................................................................................................45

vi
44. Schematic sketch of stratigraphic relations at seaside hummocks east of Burr Point...........46

45. Oblique aerial photos of Augustine Volcano showing 1935, 1883 and 1935 domes...................47

46. Photo of Augustine Volcano from southwest showing large steaming dome and

below it a light-colored fan of debris................................................................................................48

47. Photo looking south-southeast of summit-dome complex showing 1976 dome

nested below summit...........................................................................................................................49

48. Photos looking westward of Augustine Volcano summit area .....................................................50

49. David A. Johnston’s “isodroop” curve from an experiment of melting plastic 

like that at Burr Point hut in the 1976 eruption................................................................................51

50. Photo looking southward in then-new 1986 dome and lava-flow tongue at its base ...............52

51. Photo looking north-northeast of Augustine’s 1935 and 1986 domes, from 1964 dome............53

52. Photo showing lithic-fall beds at summit domes of Augustine Volcano that bury the

former rough-surfaced crescent of the 1976 dome........................................................................53

53. Photo looking southwest of moving 1986 pyroclastic flow that issued from

collapsing lava dome flowing down lower Augustine’s north flank near Burr Point................54

54. Photo looking east on lower north flank of Augustine Island showing imbricated

boulders stacked by 1986 flood..........................................................................................................55

55. Sketch map of largest deposits of the January-April 2006 eruption............................................55

56. Plot of fall versus runout for volcanic debris avalanches from around the world ....................59

57. Profiles of large landslides..................................................................................................................60

58. Schematic sketch illustrating how the stilling well in tide gauges causes a

decrease in recorded wave height and a delay in recorded peak height from the

actual wave...........................................................................................................................................62

59. Tide-gauge marigram from St. Paul (Kodiak), Alaska on 6 October 1883 showing

arrivals of wave train of air wave and of tsunami from Augustine..............................................62

60. Map showing tsunami travel times from north flank of Augustine Island ..................................63

61. Timing of contemporary records of initial events in morning 6 October 1883 eruption

of Augustine Volcano...........................................................................................................................64

62. Plot of variation in tidal ranges at Kodiak, Seldovia, and English Bay, Alaska ..........................65

63. Photo showing 1883 tsumani and ashfall deposits near Nanwalek.............................................66

64. Photo of core from Beluga Lagoon near Homer with sand-gravel bed of 1883

Augustine tsunami ...............................................................................................................................67

Tables

1. Summary of previous geologic work bearing on description of rocks and deposits

at Augustine Volcano............................................................................................................................5

2. Radiocarbon ages and stratigraphy of tephra layers at Augustine Volcano...............................9

3. Stratigraphy of coarse pumiceous “marker-bed” tephra layers and

debris-avalanche deposits at Augustine Volcano .........................................................................12

4. Some historical tsunami caused by nonvolcanic landslides and by volcanic debris

avalanches............................................................................................................................................61

 vii
Image of an original pastel on canvas by artist Josephine Crumrine painted en 

plein air at Homer, Alaska, while viewing Augustine Volcano at about 13:30 on 

9 June 1986. Small eruption clouds occurred late in the 1986 Augustine eruption 

when parts of the still-growing summit dome repeatedly collapsed into small 

pyroclastic flows (see fig. 53). Used by permission.
Volcanic Processes and Geology 

of Augustine Volcano, Alaska

By Richard B. Waitt and James E. Begét

Abstract

Augustine Island (volcano) in lower Cook Inlet, Alaska, 

has erupted repeatedly in late-Holocene and historical times. 

Eruptions typically beget high-energy volcanic processes. 

Most notable are bouldery debris avalanches containing 

immense angular clasts shed from summit domes. Coarse 

deposits of these avalanches form much of Augustine’s lower 

flanks. A new geologic map at 1:25,000 scale depicts these 

deposits, these processes. We correlate deposits by tephra layers calibrated by many radiocarbon dates.

Augustine Volcano began erupting on the flank of a small 

island of Jurassic clastic-sedimentary rock before the late Wisconsin glaciation (late Pleistocene). The oldest known effusions 

ranged from olivine basalt explosively propelled by steam, to 

highly explosive magmatic eruptions of dacite or rhyodacite shed 

as pumice flows. Late Wisconsin piedmont glaciers issuing from 

the mountainous western mainland surrounded the island while 

dacitic eruptive debris swept down the south volcano flank.

Evidence is scant for eruptions between the late Wisconsin and about 2,200 yr B.P. On a few south-flank inliers, 

thick stratigraphically low pumiceous pyroclastic-flow and fall 

deposits probably represent this period from which we have no 

radiocarbon dates on Augustine Island. Eruptions between about 

5,350 and 2,200 yr B.P. we know with certainty by distal tephras. 

On Shuyak Island 100 km southeast of Augustine, two distal fall 

ashes of Augustinian chemical provenance (microprobe analysis 

of glass) date respectively between about 5,330 and 5,020yrB.P. 

and between about 3,620 and 3,360 yr B.P. An Augustine ash 

along Kamishak Creek 70 km southwest of Augustine dates 

between about 3,850 and 3,660 yr B.P. A probably Augustinian 

ash lying within peat near Homer dates to about 2,275 yr B.P.

From before 2,200 yr B.P. to the present, Augustine eruptive products abundantly mantle the island. During this period, 

numerous coarse debris avalanches swept beyond Augustine’s 

coast, most recently in A.D. 1883. The decapitated summit after 

the 1883 eruption, replaced by andesite domes of six eruptions 

since, shows a general process: collapse of steep summit domes, 

then the summit regrown by later dome eruptions. The island’s 

stratigraphy is based on six or seven coarse-pumice tephra 

“marker beds.” In upward succession they are layers G (2,100 

yr B.P.), I (1,700 yr B.P.), H (1,400 yr B.P.), C (1,200–1,000 yr 

B.P.), M (750 yr B.P.), and B (390 yr B.P.).

A coarse, hummocky debris-avalanche deposit older than 

about 2,100 yr B.P.—or perhaps a stack of three of them—

lies along the east coast, the oldest exposed such bouldery 

diamicts on Augustine Island. Two large debris avalanches 

swept east and southeast into the sea between about 2,100 and 

1,800yrB.P. A large debris avalanche shed east and eastnortheast into the sea between 1,700 and 14,00 yr B.P.

Between about 1,400 and 1,100 yr B.P. debris avalanches 

swept into the sea on the volcano’s south, southwest, and 

north-northwest. Pumiceous pyroclastic fans spread to the 

southeast and southwest, lithic pyroclastic flows and lahars(?) 

to the south and southeast. Pyroclastic flows, pyroclastic 

surges, and lahars swept down the west and south flanks 

between about 1,000 and 750 yr B.P.

A debris avalanche swept into the sea on the west, and a 

small one on the south-southeast, between about 750 and 

400yrB.P. Large lithic pyroclastic flows shed to the southeast; 

smaller ones descended existing swales on the southwest and 

south.

Between about 400 yr B.P. and historical time (late 

1770s), three debris avalanches swept into the sea on the 

west-northwest, north-northwest, and north flanks. One of 

them (West Island) was large and fast: most of it rode to sea 

far beyond a former sea cliff, and its surface includes geomorphic evidence of having initiating a tsunami. Augustine’s only 

conspicuous lava flow erupted on the north flank.

During this prehistoric period numerous domes grew 

at the volcano’s summit, remnants of which form the east 

and south sides of the present summit-dome complex. Three 

domes grew below the summit area on the upper south and 

northwest flanks. In between large eruptions that deposited 

coarse pumiceous fall beds, many smaller eruptions emplaced 

beds of sand-sized ash on the volcano flanks.

During the past 750 years, beach and back-beach eolian 

dunes accreted at the southwest coast, forming a ribbed coastwise topography. Lesser dunes grew at the backs of beaches in 

coves on other flanks.

An eruption in 1883 shed a debris avalanche swiftly into 

the sea on the north-northeast, followed by pyroclastic flows 

and surges. Eruptions in 1935 and 1963–64 grew summit 

domes that spilled over the southwest and south flanks and 

shed coarse rubbly lithic pyroclastic flows down those flanks. 

Eruptions and 1976 and 1986 grew domes that draped down 
Bristol

Bay

Cook Inlet

Shelik of Strait

Anchorage

Kodiak

Augustine

Island

Barren Islands

Shuyak Island

Homer

KATMAI

ALEUTIAN RANGE

Chigmit Mountains

Augustine

KENAI

PENINSULA

ALASKA

PENINSULA

Kamishak

River

(English Bay)

Naknek King Salmon

Iliamna

Tyonek

Kenai

Soldatna

Ninilchik

Anchor

Point

Nanwalek Seldovia

Port Graham

Ukinrek

Kejulik

Novarupta Katmai

Douglas

Iliamna

Spurr

Hayes

Redoubt

Fourpeaked

Kaguyak

155°

61o

60°

154° 153° 152° 151° 150°

158° 157° 156° 59°

58°

A

Study

Area

2 Volcanic Processes and Geology of Augustine Volcano, Alaska

the north flank and shed voluminous pyroclastic flows to the 

northeast through north-northwest flanks, when smaller pyroclastic flows and (or) lahars swept down other flanks. A small 

dome-building eruption in January-March 2006 after this 

report was all but complete we treat only fleetingly.

The largest debris avalanches sweep into the sea at 

Augustine’s coast at speeds inferred between 60 and 80 m/s. 

Augustine is capable of initiating damaging tsunami to lower 

Cook Inlet, but geologic evidence for them on the mainland is 

sporadic and sparse.

Introduction

A very remarkable mountain, rising with a uniform 

ascent from the shores to its lofty summit, which is nearly 

perpendicular to the centre of the island . . . . Towards 

the seaside it is very low, from whence it rises . . . with a 

rather steep ascent, and forms a lofty, uniform, and conical 

mountain, presenting nearly the same appearance from 

every point of view, and clothed with snow and ice, through 

which neither tree nor shrub were seen to protrude . . . .

—Peter Puget, Chatham, May 1st, 1794 

(Vancouver’s “Voyage of Discovery”) (Lamb, 1984)

Augustine Island lies in southwestern Cook Inlet, southcentral coastal Alaska, 280 km southwest of Anchorage (fig. 

1A).The nearly circular island of about 90 km2 is 12 km wide 

east-west, 10 km north-south. A nearly symmetrical central summit—Augustine Volcano—peaks at altitude 1,254 m (figs.1B, 2, 

and 3).1 The volcano lies along an active segment of the eastern 

1

 “Discovered” during Capt. James Cook’s 3rd Voyage of Discovery on 

26 May 1778. In England this being St. Augustine’s Day, the name became 

Mount St. Augustín (Beaglehole, 1967). (Outside Britain, St. Augustine’s 

feast day is the 28th not 26th of May.) The saint commemorated is the British 

Augustine—the late 6th-c. and early 7th-c. Augustine of Cantebury—not the 

famous literary early 5th-c. doctor of Christianity, Augustine of Hippo. Within 

a few days Cook distinguished Mount St. Augustine as also an island, not a 

peninsula, and charted it “St. Augustín Island.”

The next British voyage, a commercial one by Portlock and Dixon (two of 

Cook’s 1778 officers) called the mountain by Cook’s name “Mount St. Augustine” in July and August 1786. Dixon’s 24 December 1788 chart labels the 

peak “Mt. St. Augustine.” Cook’s name is also accepted in Vancouver’s 1794 

narrative (“Mount St. Augustin” and “the island of St. Augustin”). Meanwhile 

in late 18th and early 19th centuries the Russian explorers and traders had 

called it “Chernoburoy” (=black-brown mountain), a name abandoned once 

Alaska became United States territory in 1867.

Dall (1884) called it Augustin Island; Davidson (1884) called it Mount St. 

Augustine; Becker (1898) called it Mount St. Augustine and St. Augustine 

Volcano; Coats (1950, p. 44) simplified it to Augustine Volcano, but Forbes 

and Kienle (1971) and Jürgen Kienle’s many papers in the 1970s and 1980s 

Figure 1. Index maps. A, Cook Inlet area, Alaska; 

volcanoes shown by triangles, towns by dots; 

Augustine Volcano constitutes most of Augustine 

Island. B, Augustine Island; surveyed benchmarks 

shown by solid circles; four of them—Grouse, 

Burr, Mound, Kamishak—define now-common 

place names.
Introduction 3

Aleutian arc and 90–140 km above a seismic Benioff zone 

(Kienle and Forbes, 1976, fig. 6; Kienle and Swanson, 1983a, 

fig. 8). Augustine is the region’s most explosive and frequently 

erupting volcano. It has erupted countless times since the end 

of the last ice age (since about 15,000 radiocarbon years ago 

[Hamilton and Thorson, 1983]) including six historical eruptions: 1812, 1883, 1935, 1963–64, 1976, and 1986—and now a 

small 7th eruption in 2006.

In the 1940s–1950s there had been a small pumicemining operation on the lower west flanks and a barge-loading 

ramp on West Lagoon. The ramp and bulldozer tracks, parts 

of which still exist, are plotted on plate 1 from airphotos and 

extracted from Detterman’s (1973) map.

From 1990 aerial photographs, the U.S. Geological 

Survey (USGS) National Mapping Division scribed a new 

topographic map of Augustine Island at 1:25,000 scale with 

a 10-m contour interval. On this new base we plot a new 

clung to the earlier version: “Mount St. Augustine.” To this day it’s sometimes 

written and spoken as “Mount St. Augustine”—even if not on USGS maps, 

which print only Augustine Island and Augustine Volcano. Today the mountain—the whole edifice—is usually called Augustine Volcano or just plain 

“Augustine.” “Mount Augustine,” though still sometimes used, has not been 

formalized by the U.S. Board of Geographic Names (see Orth, 1967).

geologic map (plate 1). We mapped rocks and deposits of 

Augustine Island during eight brief field sessions between 

1988 and 1997, plotting field data on vertical 9-by-9-inch 

aerial photographs taken in August 1990. We distinguish 

some look-alike deposits of the 1976 and 1986 eruptions 

having similar distributions by comparing the 1986 and 1990 

aerial photographs with others of August 1976. Some deposits of 1963–64 eruption are distinguished from those of 1935 

by aerial photographs of July 1957. With an analog Kern 

PG-2 stereoplotter outfitted with an automatic plotting table, 

Waitt in 1995–96 compiled the field-mapped geology from 

the aerial photographs to the topographic map. A provisional 

version of this topographic and geologic map is published 

uncolored (Waitt and Beget, 1996).

In 1998 the topographic and revised geologic sheets 

were scanned into GIS (Arc/Info) format by Jacqueline 

McIntire and Steve Schilling, proofed and corrected by 

Waitt and McIntire. The digital map can be readily altered 

in the future—for instance in areas affected by the 2006 

eruption and any future ones—without having to redo the 

entire map.

Figure 1.—Continued 

Trilateration benchmark

S. AUGUSTINE

W. AUGUSTINE

MOUND

BURR

GROUSE

Long Beach

NOTE: All places names associated with Augustine are informal with the exception of Burr Point, Augustine Creek, Augustine Island, and Augustine Volcano.

South Point

Southeast Beach

Southeast Point

East Point

Yellow Cliffs

Northeast Point

Northeast Beach

Burr Point

Rocky Point

Grouse Point

Augustine Creek

West K

ma ishakCr.

West-southwest Swale

Summit

dome

Lava flow

Northeast Bench

North Bench

Pinnacles

COOK

INLET

A U G U S T I N E I S L A N D

West

Island

West Lagoon

Northwest Lagoon

 59°

25’ 

59°

20’ 

KAMISHAK

153°35’ 30’ 25’ 153°20’

0 2 4 Kilometers

B

East Kamishak Cr.

Middle Kamishak Cr.
4 Volcanic Processes and Geology of Augustine Volcano, Alaska

Landslide

Augustine’s summit consists of several overlapping 

domes and marginal breccias emplaced during many prehistoric and historical eruptions. Most fragmental debris in 

coastal exposures are coarse diamicts comprising angular 

blocks of dome-rock andesite typically of cobble to boulder 

size but carrying clasts as large as 4 to 8 m, rarely as large as 

30m—all set in a sandy matrix full of finer very angular fragments. The surface of such deposits is hummocky, a field of 

steep conical mounds and intervening depressions with many 

meters of local relief.

During a brief 1913 visit, Robert Griggs inferred landslide (debris avalanche)2

 as the origin of Augustine’s hummocky coastal topography about Burr Point (fig. 2), which 

he later thought analogous with the hummocky and blocky 

deposit of the 1912 Mageik landslide at nearby Katmai 

(Griggs, 1920, p. 341). Several other reports noted hum2

 Large landslides off volcanoes are commonly called “debris avalanches,” 

like that which started the cataclysmic Mount St. Helens eruption on 18 May 

1980 (Voight and others, 1981). Similar processes and their deposits in nonvolcanic terrain are usually called “landslides.” At Augustine, we distinguish 

“slide,” which describes the beginning of the process on the upper slopes of 

a volcano when the detached block is still intact, from “avalanche,” which 

describes the process once the block has broken up and its fragments are complexly sliding and tumbling down the lower slopes of the volcano. The final 

deposit is thus called a “debris-avalanche deposit.”

mocky, coarse deposits on the flanks of several Pacific volcanoes: Bandai-san and Yatsugatake in Japan, Galunggung and 

Raung in Indonesia, and Ruapehu, Egmont, and White Island 

in New Zealand. Such deposits had been inferred to originate 

suddenly by landslide or “lahar” and were summarized and 

discussed in textbooks (Cotton, 1944, p. 247–253; Macdonald, 1972, p. 180). Catastrophic nonvolcanic landslides in 

mountain valleys—at Elm, Switzerland, in 1881; at Frank, 

Alberta, in 1903; at Gros Ventre valley, Wyoming, in 1925—

had also formed coarse blocky deposits with similarly hummocky topography. A gigantic (20 km3

) prehistoric endmember at Saidmarreh valley, Iran, became known and discussed 

(Harrison and Falcon, 1937, 1938; Oberlander, 1965, p. 

61–62, 155–156). These phenomena figured in syntheses and 

in geomorphology textbooks (Sharpe, 1938, plates 1 and 8; 

Thornbury, 1954, p. 90–93). But unaware of Griggs’s (1920) 

obscure paragraph and unattuned to geomorphic literature, 

students of Augustine in the 1960s–1970s did not include 

large landslide among the volcano’s seminal processes (Detterman, 1973; Johnston, 1978; Kienle and Swanson, 1980).

The hummocky deposits on Augustine’s lower flanks 

mimic topographically and lithologically those of the great 

landslide or debris avalanche that initiated the spectacular 

18 May 1980 eruption of Mount St. Helens in Washington 

(Voight, 1981; Voight and others, 1981, 1983; Glicken, 1991, 

1996, 1998). The deposit of that landslide revealed to all 

the origin of coarse diamicts with hummocky topography at 

Figure 2. View south-southwest of Augustine Volcano, Alaska. Hummocky coastal debris in foreground is deposit of debris avalanche 

that removed summit of volcano at start of 1883 eruption, overrode a coastal cliff (arrows), and flowed into the sea. Five subsequent 

dome-building eruptions (1883, 1935, 1963–64, 1976, 1986) have restored summit to its pre-1883 height and steepness. (USGS photograph 

by Richard Waitt, July 1990.)
Introduction 5

Table 1. Summary of previous geologic work bearing on description of rocks and deposits at Augustine Volcano.

[Note: Table excludes recent reports, such as those on geophysical monitoring and petrology, especially after 2003]

Reference Topic

Dall, 1884 Brief summary of observed effects of 6 October 1883 Augustine eruption

Davidson, 1884 Summary of observed effects of 6 October 1883 Augustine eruption

G.E., Davidson, (unpub. letter 6 

Nov. 1884)

Relates direct observation in June 1884 by a Capt. Cullie that N. flank Augustine slid as cataclysmic landslide into sea on 6 Oct. 1883

Becker, 1898 Direct observations of flanks and crater in 1895, after 1883 eruption

Dall, 1918 Includes brief reminiscence of 1895 Augustine visit with Becker

Griggs, 1920 Brief stop at Augustine, interprets Burr Point deposit as landslide

Coats, 1950 Listing of Aleutian-arc volcanoes and summary of historical eruptions

Detterman and Reed, 1964 Geologic map at 1:250,000 including Augustine Island (generalized)

Detterman, 1968 Summary of observed effects of 1963–64 Augustine eruption

Forbes and Kienle, 1971 Popular summary of historical observations from Cook’s voyage to 1964 eruption

Detterman, 1973 Geologic map at 1:63,360 of Augustine Island

Kienle and Forbes, 1976 Summary of observed effects of 1976 Augustine eruption

Buffler, 1976 Map and stratigraphy of Mesozoic rocks, south flank Augustine Island

Johnston, 1978 Summary of historical eruptions; 1976 eruption chronology, processes, and petrology of erupted materials

D. Johnston, J. Kienle, J. Whitney, 

~1978

“Hazards of Augustine Volcano, Alaska” (90 p. 32 figs.)—a detailed report, unpublished, but a major 

resource for Kienle and Swanson, 1980 [1985]

Johnston, 1979 Evidence that Augustine volcanism began during the late Pleistocene

Johnston and Detterman, 1979 Summary of historical eruptions; deletion of spurious “1902 eruption”

Kienle and Swanson, 1980 

 [reprinted 1985] History of Augustine Volcano; volcano hazards (mostly pyroclastic flow, lahar, and dome growth)

Kienle and Swanson, 1983a Plate-tectonic setting and petrology, including Augustine

Kienle and Swanson, 1983b Revised (from Kienle and Swanson, 1980) hazard assessment of Augustine; adds concept that Mount-St.-

Helens-like debris avalanches repeatedly reached the sea

Siebert, 1984 Documentation of Mount-St.-Helens-type debris avalanches off many volcanoes, including Augustine

Kienle, Davies, Miller, Yount, 1986 Summary of chronology and observed effects of 1986 Augustine eruption

Daley, 1986 Petrology, petrography, geochemistry of Augustine domes and lava flows

Reeder and Lahr, 1987 Seismic evidence for behavior and timing of Augustine 1976 eruption

Yount, Miller, and Gamble, 1987 Summary processes and effects of 1986 eruption

Siebert, Glicken, Ui, 1987 Debris avalanches and consequent lateral blasts and tsunami at many volcanoes, including Augustine

Kienle, Kowalik, and Murty, 1987 Numerical simulation of 1883 Augustine tsunami

Swanson and Kienle, 1988 Comparison of 1986 Augustine eruption of pyroclasitc flows and dome growth with hazards report of Kienle 

and Swanson (1980); occurrence of a debris avalanche, though unlikely, a concern during 1986 eruption

Siebert, Glicken, and Kienle, 1989 Concept of debris avalanche forming flanks of Augustine Volcano; details on prehistoric West Island and 

1883 Burr Point debris avalanches

Kamata, Johnston, and Waitt, 1991 1976 eruption chronology, effects, deposits, and stratigraphy of north flank

Begét and Kienle, 1992 Tephra- and 14C-dated 12 Augustine debris avalanches in last 2,000 yr; early deposits >40,000 yrs

Siebert, Begét, and Glicken, 1995 Details of debris-avalanche deposits on north flank

Waitt and Begét, 1996 Provisional version of present report; map uncolored; revisions to Begét and Kienle (1992) and to Siebert 

and others (1995)

Waythomas and Waitt, 1998 Provisional assessment of hazards from Augustine Volcano

Power and others, 2006 Summary of 2006 eruption

Begét and others, 2008 Evidence of Augustine tsunami on mainland coasts
6 Volcanic Processes and Geology of Augustine Volcano, Alaska

the bases of other stratovolcanoes. And so since 1980 many 

hummocky, coarsely fragmental deposits on Augustine’s 

lower flanks have been reinterpreted as deposits of numerous 

great landslides and debris avalanches (Kienle and Swanson, 

1983b; Siebert and others, 1989; Begét and Kienle, 1992; 

Waitt and Begét, 1996).

Table 1 summarizes themes of geologic reports about 

Augustine Island volcano that precede this report and map.

Lava-Dome Effusion Rates

Estimating cumulative volumes of historical domes 

and of Augustine’s prehistoric debris-avalanche deposits, 

Begét and Kienle (1992) calculated a long-term lava-dome 

effusion rate of 1–3 million m3

/yr. Such rates are 10 to 100 

times greater than typical effusion rates for calc-alkaline 

volcanoes in subduction zones (Crisp, 1984). The present report elaborates summaries such as Begét and Kienle 

(1992), but our current list and analysis of radiocarbon dates 

do not much alter the earlier generality. During the late 

Holocene, Augustine Volcano has sustained one of the highest rates of magma effusion from a subduction zone. This is 

probably why Augustine’s summit area is unusually prone to 

fail by landslide.

Rock Type, Grain Size, Grain Shape

In hand specimen and thin section, the dome and lavaflow rocks of Augustine Volcano are plagioclase-porphyritic 

andesite (rarely dacite) ranging from dark gray to light gray 

to reddish (oxidized). Deposits of debris avalanches, debris 

flows, and pyroclastic flows consist of or contain boulders and 

smaller fragments of gray to reddish porphyritic andesite. To 

the eye the lithic fragmental deposits are all more or less alike, 

all more or less identical to summit-dome rocks. Some of the 

pyroclastic flows and all the coarse fall layers are rich in white 

to cream to pale-gray pumice. On the south volcano flank are 

rare inliers of fragmental olivine basalt.

In hand specimen and thin section the “lithic” clasts of 

andesite contain 20 to 50 percent phenocrysts, mostly plagioclase but including hypersthene, augite, iron-titanium oxides, 

and traces of olivine, apatite, and opaque minerals. Johnston 

(1978) describes microscopic details of 1976 eruption products. Daley (1986, appendix II) describes petrographic details 

of various domes, lava flows, and rubble flows.

Chemically analyzed Augustine rocks scatter across the 

SiO2 field of andesite of LeBas and Streckeisen (1991, fig. 5) 

(fig. 4). A few analyzed whole-rock samples range down into 

the basaltic-andesite field or up to the dacite field. The glass 

fraction of pumice fragments ranges from dacite to rhyolite. 

For each of six coarse pumice layers of the past 2,000 years 

Figure 3. View northeast of Augustine Island and Augustine Volcano. Much of vegetated (dark-toned) area of lower flanks is debrisavalanche deposits: BP, Burr Point; WI, West Island; L, West Lagoon; SP, South Point; LB, Long Beach; SEP, Southeast Point. Light-toned 

areas are deposits of pyroclastic flows of 1963–64, 1976, and 1986 eruptions. (USGS photograph by Austin Post, 25 August 1987.)
50 55 60 65 70 75 80

2

3

4

5

6

7

8

9

x x

x xxx

x

xx

xxx

x

x

x

x

x

x

SiO2, in weight percent

K O + Na 2 O, in weight percent 2

BASALT

RHYOLITE

Pleistocene hyaloclastite

ANDESITE DACITE BASALTIC

ANDESITE

Daley, 1986, wholerock

Johnston, 1978, glass

Swanson and Kienle, 1988, wholerock

Kienle and Forbes, 1976, wholerock

Swanson and Kienle, 1988,

 and Siebert and others, 1995, glass

J.R. Riehle and C.E. Meyers, unpub. data, 

 1995, glass

x J.E. Beget, unpub data, 1989, glass

EXPLANATION

Rock Type, Grain Size, Grain Shape 7

as well as for some older layers, the most silicic of the glass 

analyses are well into the rhyolite range (above 72 percent 

SiO2). Most of the glass-separate data from various tephrapumice layers (SiO2 above 65 percent) are unpublished. 

Begét in 1989 analyzed 20 tephra samples with a microprobe 

at Washington State University, and James R. Riehle and 

Charles E. Meyer analyzed 68 samples with the microprobe 

at the USGS in Menlo Park in 1995 (for example, Riehle and 

others, 1998).

Petrologic studies show that neither mineralogically 

nor chemically have Augustine rocks varied much through 

thousands of years including successive historical eruptions 

(Kienle and Swanson, 1980, p. 69–72; Daley, 1986). Each 

eruption seems to emit a similar suite of porphyritic andesite, 

some ranging up to dacite. By far the most intensely studied 

suite of deposits is of the 1976 eruption: Johnston (1978) 

makes the case for intrusion of basalt into a dacite magma 

chamber, where the two were partly mixed before erupting. 

Clasts of variegated “mixed-magma” pumice lie among the 

pumicous deposits of several eruptions.

Many deposits at Augustine Volcano are to some degree 

pyroclastic in origin, but also they are sediments. As in 

field studies of other volcanoes (for example, Waitt, 1981; 

Waitt and others, 1994), at Augustine one needs a grain-size 

designation for each phi (grain-size) interval between silt 

and cobble size to apply commonly to various pyroclastic, 

landslide, laharic, waterlaid, beach, and eolian deposits and 

to some deposits of ambiguous origin. Pyroclastic size terms 

like ash, lapilli, blocks (Schmid, 1981) are far too-little 

subdivided for these purposes. For instance, “coarse ash” 

comprises fully five size intervals that are routinely distinguished by hand-lens in the field (−1 through +4 phi, very 

coarse sand through very fine sand). Standard sedimentologic 

(Wentworth, 1922) size terms are usefully divided. The universally used “Wentworth” terms for nonpyroclastic sediments are unambiguous and avoid our inventing an ad hoc 

and strange modification of pyroclastic size terms—say “fine 

coarse ash” for a pyroclastic-fall deposit of median grain size 

2 to 3 phi (0.5 to 0.125 mm).

Grain sizes are determined in the field by comparing 

a sample to Wentworth size standards, and named as by 

Folk (1954; 1974, 1980). Thus a designation such as “pebbly sand” denotes grain size solely, raw description with no 

implication whatever to genesis or emplacement process. 

Though provincial pyroclastic grainsize terms like “ash” and 

“lapilli” deserve to be abandoned, for old-times’ sake we in 

places substitute a pyroclastic noun for the sedimentologic 

one where it seems appropriate and is not confusing. Thus to 

avoid the term “gravel” in defining a pumiceous fall deposit, 

we say “medium-pebble pumice” instead of “medium-pebble 

Figure 4. Plot of chemical composition analyses of volcanic rocks (whole-rock analyses) and tephra (glass-separate 

analyses) from Augustine Island, Alaska. The glass analyses are from the six coarse coastal pumice-tephra layers, 

from older tephras on nunatak-like inliers, and from historical eruptions in 1963, 1976, and 1986. Glass analyses done 

by microprobe, each point representing the mean of values counted for 10–18 shards. Fields named according to 

LeBas and Streckeisen (1991, fig. 5).
8 Volcanic Processes and Geology of Augustine Volcano, Alaska

gravel”; to avoid calling as simply descriptive “silt” what is 

clearly a fall ash, we say “silt ash.”

Clast roundness, designated in terms like “very angular” 

and “subrounded” we estimate in the field from the visual 

standards of Powers (1953).

Chronology

Radiocarbon Ages

We obtained a few dozen radiocarbon ages from organic 

materials interbedded with tephra deposits on Augustine 

Island or with Augustine tephras at a few distal sites (table 2). 

In a layered sequence, a dated organic sample from just 

above a tephra gives a minimum-limiting age of that tephra; 

one from just below gives its maximum-limiting age. Most 

radiocarbon ages directly limit the age of tephra layers. Once 

age-bracketed by radiocarbon dates, a distinguishable tephra 

layer becomes a useful date by proxy. Table 3 depicts a generalized composite stratigraphy of Augustine’s debris-avalanche 

deposits relative to the main tephra deposits.

The radiocarbon timescale is unsteady because 14C activity 

in atmospheric CO2 has varied through time. High-precision 

calibrating, as by dating a single tree ring of known age, accord 

radiocarbon time closely with calendar time (Stuiver, 1982; 

Stuiver and Pearson, 1993). Such analyses with improvements 

over the years allows routine high-precision calibration of radiocarbon dates by using computer programs “CALIB” (Stuiver 

and Reimer, 1993; Stuiver and others, 1998) and “OxCal” 

(Bronk Ramsey 1998, 2000, 2001). The 53 Augustine radiocarbon dates are calibrated (col. 3 of table 2) by OxCal (v. 4, 2006), 

which can be run online at http://c14.arch.ox.ac.uk/. Similar 

results had been obtained from CALIB (v. 4.2, 2000) currently 

available (v. 5, 2005) at http://calib.qub.ac.uk/calib/ (Stuiver, 

Reimer, and Reimer, 2005).

The stratigraphy and geologic history in this report of 

Augustine Volcano is timed by the raw radiocarbon scale 

(uncalibrated). An expression like “about 1,700 years ago” 

implies radiocarbon (14C) time (table 2, col. 1). But the calibrated ages for each date allow one to tell more precisely how 

long between one event and another. Raw radiocarbon ages 

between about 300 and 2,500 yr B.P. are generally “older” than 

in calibrated (calendar) time. Raw 14C ages older than about 

2,500 yr B.P. are generally “younger” than their calibrated 

times. Thus a raw radiocarbon age of about 6,500 yr B.P. is 

roughly 7,400 yr B.P. in calibrated (calendar) time.

Tephra and Tephrochronology

Tephra blankets parts of Augustine’s flanks and veneers 

mainland areas far downwind. Wind data for a 14-year period 

(fig. 5) show that in lower Cook Inlet average annual wind 

is eastward about 80 percent of the time, westward about 20 

percent. Only about 10 percent of the time is wind toward the 

90-degree arc between northwest and southwest. The prevailing winds govern directions toward which tephra tends to drift 

from Augustine. Indeed during Augustine’s 1986 explosive 

phase of eruption, ash blew to the northeast, east, southeast, 

and south (Yount and others, 1987, fig. 8).

Tephra sequences 1- to 3.5-m thick are fairly continuous along the east, southeast, and south coasts of Augustine 

Island, which are the generally downwind azimuths where 

tephra should tend to accumulate. But also these lower flanks 

are where many flowage deposits are older than on other flanks, 

and thus older tephras are preserved here more than elsewhere. 

Upper Holocene stratigraphy established in these most complete 

sections shows six coarse pumiceous layers stratigraphically 

superposed, separated by peat, fine (sand or silt) tephra layers 

and in places eolian sand. In upward stratigraphic order (fig. 6; 

tables 2 and 3) the coarse tephra layers we designate as tephras 

G (2,100 yr B.P.), I (1,700 yr B.P.), H (1,500–1,400 yr B.P.), 

C (1,200–1,000 yr B.P.), M (750 yr B.P.), and B (390 yr B.P.). 

Between tephras C and M a seventh tephra O—rare and in most 

places missing, its origin and significance obscure—we eventually dropped as a reliable marker bed but it shows in certain 

measured sections (plate2). These coarse tephra layers also contain 10 to 40 volume percent lithic andesite fragments smaller 

than pumice fragments. Isopach maps, drawn from thickness 

measured mostly at coastal exposures, show the azimuths to 

which five of the coarse layers drifted (fig. 7).

The lowest five coarse-pumice beds at the coast—tephras 

G, I, H, C, and O—drifted east and southeast. Tephra G and 

ambiguous tephra O are known only from a few sites each on 

the east and southeast, neither with enough data points to warrant a map. Drawn from data at many stratigraphic exposures, 

isopach maps clearly show tephras I, H, and C drifted eastsoutheast and southeast. Of the two youngest coarse tephras, 

M drifted south and B strongly northeast (fig. 7). All these 

azimuths—northeast, east, southeast, south—are among the 

common directions of modern winds (fig. 5).

Between the coarse pumiceous layers are numerous layers 

of sand and silt ash, volumetrically much of any one fall section 

but not useful for correlating between sites. Within a few scattered inlier sections of older debris lie several additional coarse 

tephra layers that are not readily correlated from place to place. 

Some are surely older than coastal tephra G.

In 1989 Begét, and in 1995 James R. Riehle and Charles 

E. Meyer (written commun., 1995), analyzed by microprobe for 

eight major elements in glass from many samples of Augustine 

proximal pumiceous tephra. These data support many of the 

correlations within 1 km of the coast based on field stratigraphy, 

and they suggest correlations with upper parts of some of the 

inlier sections farther inland. But they also show that several 

superimposed tephras are chemically heterogeneous and that 

some of their compositional ranges overlap. Glass separates 

of tephras C and M are chemically nearly identical—as close 

as replicate microprobe analyses of either tephra C or tephra 

M alone. Correlation of tephras between separated localities 

is thus mainly by field stratigraphy, in some places strengthened or augmented by the microprobe data.
Table 2. Radiocarbon ages and stratigraphy of tephra layers at Augustine Volcano.

Ages (tephra)

(14C yr B.P.)1 Lab. No.

Calibrated 

Ages1

(Calendar yr 

B.P.)

Material Overlain by Underlain by 

50±503 

(modern) B–117198 269–13 Wood (log) Lies within Augustine-tsunami? gravelly sand (distal, at Red River delta) Lies within Augustine-tsunami? g

sand (distal site) 

80±803 

(modern) B–117199 283– −4 Wood (log) Lies within Augustine-tsunami? gravelly sand (distal, at Red River delta) Lies within Augustine-tsunami? g

sand (distal site) 

101.7 ±0.7%

(modern) B–55672 254–32 Peat Katmai-1912 ash and two older ashes Grouse Point debris-avalanche de

±185 (modern) I–14992 ± 285– −3 Peat Pyroclastic ash unknown age 1883 debris-avalanche hummock 

±285 (modern) I–14923 ±422–301 Soil Pyroclastic ash unknown age Peat of previous date 

140±60 B–24773 285– −1 Willow branch Fan deposit Fan deposit 170±70 B–24779 418– −4 Soil Silt below modern soil Hummock of Rocky Point debris-

lanche deposit 

195±115 ? 416– −4 Soil Ash (pre-1883?) 30 cm below Katmai 1912 ash Tephra B, 10 cm downsection 205±90 I–14924 455– −4 Organic layer Sand ash below Katmai 1912 ash Sand over West Island debris-ava

deposit 

280±100 B–24781 511– −3 Organic layer 40 cm ash below Katmai 1912 ash Tephra B lapilli pumice 330±145 ? 623– −3 Soil Soil of 195 yr B.P. age Tephra B 367±55 ? 505–310 Uncharred alder bark “Blast” deposit atop West Island debris-avalanche deposit West Island debris-avalanche dep380±20 QL–4808 504–328 Bulk peat Lahar deposit and ash below Katmai 1912 ash Tephra B 

Tephra B

400±50 B–55673 522–316 Dense organic layer Tephra B(?) Eolian sand 410±50 B–24777 530–316 Soil layer Pumice layer B(?) Pumice layer (M?) 450±80 B–28536 635–309 Soil between pumice layers Pumice layer (B?) 19 cm higher Pumice layer (M?) directly below

down Tephra C 

470±140 ? 694– −2 Soil Tephra B directly Tephra M directly 490±70 B–24776 654–325 Soil Tephra B 15 cm up Tephra M? directly below 710±50 B–55667 732–558 Organic layer Pumice layer (B?) Pumice bed (M?) 730±60 B–28537 779–557 Soil 41 cm of ash and soil capped by lithic ash (1883?) Tephra B? or M? 

Tephra M

760±60 B–55662 891–561 Peat Tephra M directly Tephra C, 1.5 m downsection 770±50 ? 790–653 Peat Tephra M directly Tephra C, 1 m downsection 800±60 B–55664 905–657 Top 8 cm of organic layer Tephra M directly Lithic pyroclastic-flow deposit 800±120 ? (beget) 936–548 Soil Tephra M directly Tephra C, 10 cm downsection 
Table 2. Radiocarbon ages and stratigraphy of tephra layers at Augustine Volcano—Continued. Ages (tephra) (14C yr B.P.)1 Lab. No. Calibrated Ages1 (Calendar yr B.P.) Material Overlain by Underlain by 

860±80 B–24780 925–675 Willow wood uncharred Rockfall \ pumiceous pyroclastic flow \ Tephra M Pumiceous pyroclastic flow \ rock

1,000±100 B–24780 1,169–725 Soil Silt beneath tephra M Alluvium atop tephra C 1,110±70 B–-58976 1,063–745 charcoal and soil Debris flow Tephra C? 1,200±140 ? 1,373–798 Peat Lithic pyroclastic-flow deposit Tephra C (top) directly 

Tephra C 1,020±50 B–55666 1,055–796 Soil Lahar deposit beneath Tephra C Lahar 

1,130±50 B–28535 1,173–938 Burned wood Pyroclastic-flow deposit beneath Tephra C Pyroclastic flow overlying South 

debris-avalanche deposit 

1,195±120 ? 1,340–835 Peat Tephra C Tephra C 1,280±80 ? 1,336–1,005 Buried branch Pyroclastic-flow deposit and diamict beneath Tephra C Debris-avalanche deposit 1,290±80 B–28539 1,345–1,009 Buried branch Pyroclastic-flow deposit and diamict beneath Tephra C Debris-avalanche deposit 1,400±50 B–28534 1,402–1,188 Burned log Pyroclastic-flow deposit Pyroclastic-flow deposit (near bas1,420±60 B–28538 1,508–1,185 Soil 18 cm of pumice (Tephra C?) Silt and soil overlying tephra (H?

(Tephra H) 1,190±80 B–57901 1,279–962 Peaty soil Ash beneath Tephra I(?) (Date is anomalously “young”) Northeast Point debris-avalanche 

1,470±160 ? 1,733–1,013 Unknown Unknown 1,500±155 ? 1,774–1,072 Unknown Unknown 1,580±206 QL–4811 1,525–1,411 Peat Peat Tephra I (distal) 1,610±708 ETH 3826 1,692–1,354 Soil Tephra H Northeast Point debris-avalanche 

Tephra I

1,725±256 QL–4812 1,703–1,562 Peat Tephra I (distal) Peat 1,830±80 B–24775 1,930–1,560 Soil Silt beneath Tephra I Silt over debris-avalanche deposit 

Tephra G4

2,160±60 B–55674 2,324–2,002 Peat Unidentified tephra (Tephra G?) Pumiceous pyroclastic-flow depo2,275±25 QL-4810 2,348–2,163 Peat (As below, peat sampled just above & below ash) Distal Augustine tephra (near Hom

Distal tephra5

2,275±25 QL-4810 2,348–2,163 Distal Augustine tephra (near Homer) (As above, peat sampled just abov

below ash) 

3,360±256 QL–4813 3,688–3,486 Peat Peat Distal Augustine tephra 

Distal tephra6

3,620±256 QL–4814 4,061–3,849 Peat Distal Augustine tephra (Shuyak Is.) Peat 3,660±1007 I–16120 4,289–3,700 Peat Distal Augustine tephra (Kamisha
Ages (tephra)

(14C yr B.P.)1 Lab. No.

Calibrated 

Ages1

(Calendar yr 

B.P.)

Material Overlain by Underlain by 

Distal tephra7

3,850±1007 1–16121 4,225–3,676 Peat Distal Augustine tephra (Kamishak Cr.) 

5,020±306 QL–4815 5,892–5,659 Peat Peat Distal Augustine tephra (on Shuy

Distal tephra6

5,330±306 QL–4816 6,206–5,997 Peat Distal Augustine tephra (Shuyak Is.) Distal Augustine tephra (Shuyak I

Distal tephra6

6,460±306 QL–4817 7,430–7,316 Peat Distal Augustine tephra (Shuyak Is.) Peat 6,210±70 B–55676 7,270–6,938 Marine shells Allochthonous bay-mud clast Allochthonous bay-mud clast 7,170±60 B–55675 8,161–7,868 Marine shells Allochthonous bay-mud clast Allochthonous bay-mud clast 

≥39,8908 ETH 7166 Charcoal Waterlaid pumice beneath glacial outwash Waterlaid pumice ≥40,4408 ETH 7167 Charcoal Waterlaid pumice beneath glacial outwash Waterlaid pumice 

1 Raw radiocarbon ages and calibrated (calendar) ages are both in years before A.D. 1950 (= yr B.P.). Samples analyzed by University of Washington Quaternary Isotope Lab 

direct method and have very low lab-counting standard deviations. Samples analyzed by commercial labs such as Beta Analytic (B) and Isotopes (I) were counted by liquid-sci

Calibrated ages by Oxford University “OxCal.” Ranges in calendar years B.P. (before 1950). Calculated to 2σ (95.4%) confidence level. For some very young samples, negativ

younger that the A.D. 1950 datum; −4 thus = A.D. 1954. Radiocarbon ages older than 20,265 yr B.P are beyond range for calibration. (Bronk Ramsey, 1998, 2000, 2001). Age

sity of Washington radiocarbon-age calibration program “CALIB REV ver. 4.2” (2000) to generally similar results.

2A99, Anders (1999); BK92, Begét and Kienle (1992); SGK89, Siebert and others (1989); SK88, Swanson and Kienle (1988); RWMC98, Riehle and others (1998).3These dates from Red River delta 85 km NE of Augustine in sandy gravel seemingly of 1883 Augustine tsunami (Anders, 1999; Anders and Begét, 1999).4Stratigraphic relation of tephra G to the date listed just below it is uncertain.5One peat sample, taken immediately above and below the ash at Homer, to closely date this Augustine medium-sand ash.6These seven radiocarbon dates and the four bracketed tephra samples are from section RBW 93Ko.09 on Shuyak Island 110 km SSE of Augustine (plate 2). Tephra identifie

fraction by J.R. Riehle and C.E. Meyer, partly discussed by Riehle and others (1998, fig. 8, site 6).

7These two radiocarbon dates bracketing a tephra sample are from J.R. Riehle’s section along Kamishak Creek on mainland about 70 km SW of Augustine. Tephra identified 

fraction by J.R. Riehle and C.E. Meyer, partly discussed by Riehle and others (1998, fig. 8, site 4).

8Accelerator Mass Spectrometry (AMS) date.

Table 2. Radiocarbon ages and stratigraphy of tephra layers at Augustine Volcano—Continued.
2 

2 

2 

3 6 9 

14 

2 

3 4 5 

8 

10 

14 

14 

8

11

37

43

2

SSE SSE SSE

SSE

WSW

SE

ESE

E

ENE

NE

NNE N NNW

NW

WNW

W

12 Volcanic Processes and Geology of Augustine Volcano, Alaska

Limitations to correlating with tephra-index beds 

are several. Proper identification of the lowest tephra in a 

sequence is critical to deciphering the age of an underlying 

deposit. Parts of the tephra sequence are readily distinguishable in the field. Tephra C in places comprises three coarse 

horizons and commonly is a couplet of coarser beds separated by finer material. Several decimeters of thin beds of 

fine sand to silt (ash) separate tephra layers I and H (fig. 6). 

On the south and west, tephra M seems everywhere much 

thicker than tephra B. In sections along the south and east 

coasts that contain several superposed tephra layers, field 

characters are usually enough to identify many tephra layers with certainty. But where only one or two tephra layers 

appear in section, identity can be ambiguous. A tephra may 

be “missing” at exposed or unstable sites like the crests of 

levees and hummocks, in areas above the level of vegetation, 

and on slopes steeper than 15°. Stratigraphic discontinuities caused by erosion soon after emplacement, for instance, 

are overcome only by exploring numerous sites on any one 

deposit, including in swales and vegetated areas where a 

deposited tephra is likely to remain uneroded.

The thickness and particle size of a tephra deposit 

generally decrease exponentially away from the vent (fig. 8). 

Numerous Augustine eruptions in the last few millennia have 

deposited thick and (or) coarse layers of pumiceous tephra on 

the volcano flanks (tables 2, 3; fig. 6), most recently about 390 

years ago. The largest fragments in the coarse tephra layers 

on Augustine’s flanks are many centimeters in diameter. The 

thickest such deposits are toward the northeast, east, southeast, 

and south (fig. 7). But between the coarse pumice beds are 

many finer tephra layers of only sand-size material recording 

numerous lesser eruptions, including the six historical ones 

1812–1986 (figs. 6, 9).

Figure 8 shows the downwind decrease in thicknesses 

of two coarse Augustine tephras and of several tephras from 

eruptions from three volcanoes in the Washington and Oregon 

Cascade Range that typically erupt tephra. The seven curves 

depict downwind thicknesses for fall for eruptions whose 

erupted volumes range between about 35 km3

 and 0.01 km3. 

The two major Augustine proximal tephras that are also identified in distal locations are tephra B (about 390 yr B.P.) and 

tephra I (about 1,700 yr B.P.). Tephra I is about 3 cm thick at 

a distance of 110 km, and B is about 7 mm thick at a distance 

of 200 km (fig. 8). Ash from even a large Augustine eruption 

would be thinner than 5 cm on habited areas of Cook Inlet.3

 During the 1976 pumiceous tephra fall, angular rock 

fragments as large as 10 cm punctured a corrugated-steel 

roof of a hut on Augustine’s north-northeast coast 6 km from 

the vent (Kienle and Swanson, 1983b, p. 30; Kamata and 

others, 1991, fig. 4). The moderate eruptions of ash in 1976 

3

Davidson (1884) reports second-hand that 4 to 5 inches (10–13 cm) of ash 

fell at Kodiak (distance to Augustine 175 km) during the 1883 eruption. But 

stratigraphic sections on Shuyak Island (similar SSE azimuth, at distance 110 

km) show no large fall just beneath the 1912 Katmai ash (plate 2, sections 

RBW 93Ko.06 and .09). Casual observers during the 1980 eruptions of Mount 

St. Helens overestimated ashfall thickness (precompacted) by 2 to 5 times.

Figure 5. Summary of mean annual wind directions 1949–62

(in percent of mean-annual) from 200 millibar level (about 13 km 

altitude) from recording station at Kodiak 180 km south-southeast 

of Augustine Island, Alaska (fig. 1). Wind directions for King Salmon 

195 km west-southwest from Augustine and for Anchorage 240 km 

northeast are similar. Data from National Weather Service (NOAA) 

compiled by J. Madore and Tina Neal, USGS.

Debris-Avalanche Deposit Tephra

Layer

Approx. Age

(

14C yr B.P.)

Burr Point (A.D. 1883)

Rocky Point

West Island (incl. Grouse Pt.)

B 390

Southeast Beach

M 750

Lagoon

C 1,000–1,200

Long Beach

South Point

North Bench (perhaps older?)

H 1,400–1,500

Northeast Point

I 1,700

Southeast Point

Yellow Cliffs

G 2,100

East Point (perhaps comprises 

3 separate avalanches

Table 3. Stratigraphy of coarse pumiceous “marker-bed” tephra 

layers and debris-avalanche deposits at Augustine Volcano.
Pebble- gravel pumice

Organic layer

White silt ash

Brown fine sand ash

Brown fine sand ash; organic layers between

Granular pumice

Very fine sand ash

Pebble gravel pumice

Pebble gravel pumice

Pebble-gravel pumice

Silt ash

Silt ash

Two sand ashes

Many thin beds of fine-sand to silt ash

Sand ash

G

I

H

C

M

B

1976 ?

1963 ?

1883 ?

Katmai 1912

Flowage deposit

Flowage deposit

Pebble-gravel (lapilli) pumice

Sand ash

Granule pumice

Sand-silt ash

AGE

14C B.P.

Organic duff and vegetation

Very fine sand silt ash

370

750

1,000

1,400

1,700

2,200

METERS LITHOLOGY DESCRIPTION TEPHRA

LAYER

0

1

2

3

4

Chronology 13

Figure 6. Tephra stratigraphy overlying flowage deposits on Augustine Island just north of Southeast Gully

about 0.9 km coastwise north-northeast from Southeast Point. The flowage deposits are each several meters 

thick. On plate 2, section RBW 91A.74 (CAG 910804-1) is similar.
13

10

9

2

40

30

Tephra I

8 12

21

17

15

25

Tephra H

12 29

12

17

7 8

25 15

5

30 50 75

35 36 39

60

40

80

28

50

10

35

>23

65 75

40

20

22

40

25

Tephra M

30

>19

15

21

3

10

10

0

7

8 18

5

5

5 5

11 5

11

4

4

6

3 1

13

5

Tephra B

Tephra C

12

5

32

30

20

29

35

78

40

35

31

45

25

50

55

28

30

60 10 50

29

60

Summit

Augustine Volcano

11

34

25

?

?

15

90

27

10

10

5

20

2

5

0

10

8

59°25’

59°20’

59°25’

59°20’

0 1 2 3 Kilometers

0 1 2 Miles

153°35’ 30’ 25’ 153°20’

59°25’

59°20’

153°35’ 30’ 25’ 153°20’

59°25’

59°20’

59°25’

59°20’

14 Volcanic Processes and Geology of Augustine Volcano, Alaska

Figure 7. Isopach maps of coarse pumiceous tephra-layers 

B, M, C, H, and I on Augustine Island, Alaska; values in 

centimeters. The older tephras, especially H and I, are confined 

to the east and southeast where the older deposits lie. Any 

former exposures to other azimuths have been buried beneath 

ubiquitous younger deposits.

and 1986 were hazardous to air traffic and airports (Kienle 

and Shaw, 1979).

Tephra layers are much too thin and discontinuous to distinguish as separate map units. A tephra at the surface is thus 

mapped with the underlying flowage deposit.

Geomorphology

Many map units are distinguished from neighboring 

deposits partly by geomorphic relations. Sharp levees define 

the margins of some debris-avalanche deposits. A deposit fanning gently seaward must be much younger than a neighbor of 

like material cut back to a straight and high sea cliff. A unit far 

more vegetated than its lithologically similar neighbor at the 

same altitude must be much older.

Sea waves over time erode back any unconsolidated 

debris shed to the coast. Augustine’s coastal cliffs rise as 

high as 40 m, cut far back into ancient deposits. A sea cliff 

(fig. 10A) ceases to develop when a flowage from a new eruption overrides and spreads beyond the cliff, shifting the coast 

seaward (fig. 10A,B). Or a sea cliff can be surrounded by a 

flowage down an adjacent gully that then spreads along the 

coast, isolating the cliff from the sea (fig. 10C). Many such 

sea cliffs lying back from Augustine’s present coasts tell of 
35 km3

1.0 km3

0.3 km3

0.2 km3

0.01 km3

0.4? km3

0.1 km3

D

E

G

A

B

F

Kodiak

Homer Anchorage Valdez Fairbanks

0.1

Thickness, in centimeters

1.0

10

100

0 100 200 300 400 500 600 700

Distance from vent, in kilometers

Augustine limit

C

Chronology 15

gradual wave erosion suddently arrested when new eruption 

deposits arrive (plate 1).

Details of topography help to identify emplacement 

mechanisms. Debris-avalanche deposits are distinguished from 

other types of flowage deposits by their composition of coarse 

angular diamict freighted with huge angular dome-andesite 

boulders and by their topography of high conical hummocks 

and intervening closed depressions. Hummocky topography also shows in bathymetric contours offshore of most of 

Augustine’s debris-avalanche deposits (fig. 11), pointed out 

by previous authors (Kienle and Swanson, 1983b; Begét and 

Kienle, 1992; Siebert and others, 1995). Below wave base and 

isolated from pyroclastic and other flows that have smoothed 

onshore topography, the characteristic hummocky form of the 

offshore deposits is preserved. This bathymetry is evidence 

that several of these debris avalanches extend as far as 1–4 km 

and to depths of 25–45 m beyond present coasts. Where two or 

more debris-avalanche deposits lie atop one another, as along 

the east and southeast coastal cliffs, the offshore deposit may 

correlate with one or both or several avalanches.

Lithic pyroclastic-flow deposits comprise gravelly sand 

or sandy gravel of angular clasts. One or several pairs of 

levees lead down to intricately multilobate termini. These 

flowage deposits are not characteristically hummocky, yet 

between levees and adjacent channels there can be several 

meters of local relief. This geomorphic character helps distinguish them from the hummocky debris-avalanche deposits.

Distinguishing Lithic Pyroclastic Flows from 

Lahars in Proximal Areas

Bouldery lithic pyroclastic flows (hot dry flows) and 

debris-flow lahars (cool wet flows) may leave similar deposits 

that are lithologically and geomorphically difficult to distinguish from each other. In a hot pyroclastic flow, any contained 

wood is baked or turned to charcoal, but in a cooler debris 

flow wood remains fresh though perhaps abraded. Yet on 

weakly vegetated and shallow-gullied Augustine Volcano, 

deposits are all but devoid of wood fragments.

Actively extruding dacite domes on Mount St. Helens, 

as observed by R.B. Waitt in April 1982, repeatedly slough 

hot-rock avalanches. While cascading and flowing to lower 

slopes this thermally stressed rock continuously and profusely 

breaks into very angular gravel fragments that exude roiling 

clouds of sand-sized fragments. A lithic pyroclastic flow from 

such a dome failure is monolithologic, the clasts very angular, 

commonly unabraded; on cooling a few may be radially prismatically jointed, indicating a hot-rock source. The matrix of a 

pyroclastic-flow deposit tends to be loose.

More adept at eroding its bed, a moving debris flow 

or lahar incorporates a mixture of clast types, some of them 

becoming abraded. The water in a debris flow concentrates 

finer particles, which adhere to each other, drying to a tough 

matrix. A debris flow that has traveled many kilometers may 

be thus distinguished from a far-traveled lithic pyroclastic 

flow. But on Augustine’s fairly steep slopes and only 2 to 4 km 

from summit source, such textural distinctions can be subtle. 

Because Augustine lacks glaciers and by late summer harbors 

only a few snowfields, its eruptions generate lahars by swift 

melting only in winter-spring. Even the winter eruptions of 

1976 and 1986 caused only small lahars down gullies, while 

pyroclastic flows (pumiceous and lithic) were far broader and 

more voluminous. Pierson and others (in press) discuss in 

some detail these and other criteria by which such look-alike 

flowage deposits of unlike origins may be distinguished.

On Map “Units”

The various Augustine deposits, lava domes, and old 

rocks described in this report are physical realities. The large 

ones, as exposed at the surface, are depicted on the geologic 

map (plate 1) as “units.” Unlike the materials themselves, map 

“units” stem considerably from a cartographer’s imagination.

Figure 8. Thickness of some sheets of tephra erupted from 

volcanoes in western United States plotted against distance 

downwind. A, Mount Mazama (Crater Lake) (35 km3

); B, Mount 

St. Helens layer Yn (1 km3

) C, Mount St. Helens layer T (0.1 km3); 

D, Mount St. Helens 18 May 1980 (0.2 km3

); E, Glacier Peak 

layer D (0.01 km3

); F, Augustine layer B (0.3 km3); G, Augustine 

tephra I (0.4? km3

). Data from Williams and Goles, 1968; Crandell 

and Mullineaux, 1978; Sarna-Wojcicki and others, 1981; Begét 

and others, 1994 (for Augustine tephra B); and R.B. Waitt (for 

Augustine tephra I). Dashed line depicts inferred maximum 

tephra accumulation downwind from Augustine Volcano. 

Alaskan cities at bottom are plotted at distance from Augustine’s 

summit vent.
New flowage

Wave erosion

New sea cliff

Buried sea cliff

B

Flowage

Deposit

Wave

erosion Sea level

A

Arrested sea cliff

New coastwise deposit

Wave erosion

C

0 500 1,000 1,500 2,000

2000 1900 1800

Dome

Debris avalanche

Tephra

Lava flow (tiny)

Debris avalanche

Tephra

A

B Radiocarbon years ago (before 1950)

Year A.D.

?

16 Volcanic Processes and Geology of Augustine Volcano, Alaska

Figure 9. Summary of eruptive history of Augustine Volcano based on data in this report. A, past ~2,200 radiocarbon 

years; as calculated on conventional radiocarbon timescale, “ago” means before 1950. Thus the symbols 

representing eruptions between 1963 and 2006 plot in the future (on radiocarbon timescale). B, historical eruptions 

(last two centuries). A depicts mostly large eruptions, B mostly smaller ones.

Figure 10. Sketch showing in profile development of arrested sea cliffs at Augustine Island. A, High sea 

cliff cut into flowage (such as debris-avalanche) deposit. Wave erosion of this cliff can be arrested by 

either B or C. B, Initial sea cliff is overridden by new flowage deposit, which isolates initial cliff by moving 

coast seaward; into this deposit a new sea cliff is cut. C, Initial sea cliff is isolated from sea by a coastwise 

flow delivered through an adjacent side gully; into this deposit a new sea cliff is cut.
Synopsis of Geologic History 17

A heading may be “Lagoon debris-avalanche deposit 

(unit CMal).” The deposit is natural reality, but the “unit” is 

invented to portray on a map and to organize discussion. A 

deposit may extend beneath younger deposits well beyond its 

expression as a map unit, or it may be subdivided into smaller 

“units.” For instance, profuse, large boulders just offshore 

of Augustine Island are clearly relics of the onshore debris 

avalanches. But there may be no objective way to link them to 

a particular avalanche, nor by cartographic convention does a 

map unit show if it’s below water. So these offshore elements 

are designated as a separate map unit (unit ob) though they are 

but a continuation of an onshore deposit. Future investigators 

may define and portray units differently, as our map differs 

from earlier maps. But it is the same materials that constitute 

Augustine Island.

Synopsis of Geologic History

Augustine Volcano began erupting before the late Wisconsin glaciation (late Pleistocene) on the flank of a small 

island of upper Jurassic to upper Cretaceous sedimentary 

rock in lower Cook Inlet, Alaska. The oldest known effusions 

ranged from explosive eruptions of olivine basalt interacting 

with water to dacitic or rhyodacitic pumiceous pyroclastic 

flows. Late Wisconsin piedmont glaciers issuing from the 

mountainous western mainland surrounded the island at a 

time when dacitic eruptive debris swept down the south volcano flank.

Augustine erupted between the late Wisconsin and about 

2,200 14C yr B.P.,4 but the evidence on Augustine Island is 

scant. On a few south-flank inliers, pumiceous pyroclasticflow and several pumiceous-fall deposits below a peat dated 

to about 2,160 yr B.P. (table 2) reveal at least several early 

to middle Holocene silicic eruptions of Augustine. Between 

about 6,460 and 2,275 yr B.P., several Augustine silicic tephras reached sites 25 km northwest, 70 km southwest, 110

km 

southeast, and (or) 110 km northeast of Augustine Island 

(table 2) (see below).

From somewhat before 2,200 yr B.P. to the present, 

numerous debris avalanches have swept to Augustine’s coast 

and beyond, most recently in A.D. 1883 (fig. 9). The decapitated summit after the 1883 landslide and replacement by 

andesite domes of six eruptions since then suggest common 

processes: collapse of the steep summit dome flowing as an 

avalanche to the sea, then regrowth of the summit by later 

dome eruptions—this pattern repeated again and again.

The volcano shed several large debris avalanches 

before 1,400 yr B.P. Beneath tephra G (probably older than 

2,100yrB.P.) along the east coast lies a coarse, hummocky 

debris-avalanche deposit—or a stack of 2 or 3 of them—the 

oldest exposed such deposit(s) on Augustine Island. Between 

4

 Such dates throughout report and on explanation to the map are in raw 

(uncalibrated) radiocarbon time. See discussion under heading “Radiocarbon 

Ages” and in table 2.

about 2,100 and 1,800 yr B.P. (between tephras G and I) two 

large debris avalanches swept east and southeast into the sea. 

Between 1,700 and 1,400 yr B.P. (between tephras I and H) a 

large debris avalanche shed east and east-northeast into the sea.

Since 1,400 yr B.P. Augustine Volcano has repeatedly 

shed debris avalanches and other flows. Between about 1,400 

and 1,100 yr B.P. (between tephras H and C) one debris 

avalanche swept into the sea on the south, another on the 

southwest, and a third on the north-northwest. Pumiceous 

pyroclastic fans spread to the southeast and southwest, lithic 

pyroclastic flows and perhaps lahars to the south and southeast. Between about 1,000 and 750 yr B.P. (between tephras 

C and M) a debris avalanche swept to the sea on the west, 

and pyroclastic flows, pyroclastic surges, and lahars swept 

down the west and south flanks. Between about 750 and 400 

yr B.P. (between tephras M and B) a small debris avalanche 

swept into the sea on the south-southeast. Lithic pyroclastic 

flows shed to the southeast; smaller ones descended existing 

swales on the southwest and south. Between about 400 yr 

B.P. (after tephra B) and the 1770s, three debris avalanches 

swept into the sea on the west-northwest, north-northwest, 

and north flanks. One of them (West Island) was large and 

fast, most of it having ridden to sea far beyond a sea cliff cut 

back into older deposits. Augustine’s only conspicuous lava 

flow erupted on the north flank.

During this prehistoric period numerous domes must 

have grown at the summit, renewing material repeatedly 

shed off as catastrophic debris avalanches. Remnants of 

these older domes form the east and south sides of the present summit-dome complex. Below the summit area at least 

three domes grew on the upper flanks, one on the south 

(Kamishak), and soon after 390 yr B.P. two on the northwest. Another undated and nearly buried dome or lava flow 

lies on the middle south flank. Intermittently throughout the 

late Holocene period many smaller eruptions emplaced beds 

of sand-sized ash on the volcano flanks, in between larger 

eruptions that deposited the conspicuous coarsely pumiceous 

fall beds. During at least the past 750 years, beach and backbeach eolian dunes accreted at the southwest coast, forming 

faintly ribbed coastal topography there. Lesser dunes grew 

at the backs of beaches in several coves on the northwest, 

north, and northeast flanks.

In historical times an eruption in 1883 shed a debris 

avalanche into the sea on the north-northeast, followed by 

pyroclastic flows and surge. Eruptions in 1935 and 1963–64 

grew summit domes that spilled respectively over the southwest and south rim and shed coarse rubbly lithic pyroclastic 

flows down those flanks. Eruptions in 1976 and 1986 grew 

domes that draped down the north flank and shed voluminous pyroclastic flows to the northeast, north, and northwest 

flanks. During these last two eruptions but especially in 1976, 

smaller pyroclastic flows and (or) lahars swept down valleys on other flanks. In early 2006 came a new eruption that 

emplaced a dome and stubby lava-flow extensions on the 

upper north-northeast flank. Only one large lithic fragmental 

flow reached the lower north flank.
0 5 10 Kilometers

CONTOUR INTERVAL 200 METERS

 BATHYMETRIC CONTOURS IN METERS BELOW SEA LEVEL

59°

15’ 

59°

 25’ 

153°45 153°30’ 153°15’

25

25

20

25

25

25

15

 5

5

 5

 5

15

15

10

10

10

30

30

30

40

50

50

40

30

20

20

20

25

15

45

45

45

45

45

35

35

35

20

20

20

5

15

10

Augustine Volcano

1000

H/L = 0.18

18 Volcanic Processes and Geology of Augustine Volcano, Alaska

Pre-Augustine Mesozoic Rocks

Sedimentary bedrock constituted Augustine Island before 

the volcano existed (fig. 12). This rock reaches from below sea 

level at the south coast to as high as altitude 400 m, the lower 

300 m mapped by Buffler (1976). Constituent invertebrate 

fossils (especially pelecypods) identify most of these rocks 

with the Upper Jurassic Naknek Formation (Detterman and 

Jones, 1974). The typically gently dipping Naknek in its type 

area crops out thickly and broadly on the Alaskan Peninsula 

along tectonic strike 50–180 km south-southwest of Augustine 

(Keller and Reiser, 1961, plate 29), and on the nearest points 

of the Peninsula, 15–20 km southwest, west, northwest, and 

north of Augustine (Detterman and Reed, 1964; Detterman 

and Hartsock, 1966; Magoon and others, 1976, mapsheet2).

On Augustine Island the Naknek Formation comprises a 

lower member of thin-bedded dark-gray siltstone to very fine 

sandstone (unit Jnsh, plate 1) (fig. 13A) and an upper member 

of cliff-forming thick-bedded, medium to fine sandstone in 

places showing trough-type fluvial crossbeds 10 to 20 cm tall 

(unit Jns) (fig. 13B). Though deposited in a marine environment, the sandstone contains flattened fossil logs and pods 

of lignite. These suggest a nearshore environment of deposition, perhaps a protected bay. The bedrock block dips southeast, south, and south-southeast variably at 5 to 36°, mostly 

8to20°. The south dips are despite the subsequent overgrowth 

of the volcanic edifice that must have isostatically depressed 

the bedrock northward, flattening these dips. The cliff-forming 

upper sandstone is exposed almost continuously for more than 

2 km along strike below altitude 280 m.

Figure 11. Offshore distribution of debris avalanches off Augustine Island based on seaward extent of conspicuously hummocky 

submarine topography. The 200-ft contours on Augustine Island and the 5-m contours of bathymetry are traced from U.S. Geological 

Survey 1:250,000 Iliamna quadrangle. The hummocky topography extends to depth of 45 m and as far as 3.8 km off east coast; it extends 

to depth 25 m as far as 2.8 km off north coast. Significance of circle—H/L ratio = 0.18—explained in section on “Mobility and Speed of 

Volcanic Debris Avalanches.”
dk

64d

Pg Pvr

Pg

Pg

Pvr

Pvr

Pvr

Pvb Pvb

64p

64p

Jn

Jn

Pleistocene to Late Holocene Materials 19

Below Kamishak dome at the head of West Kamishak 

Creek (fig. 1B) lies a patch of highly oxidized and soft-weathered greenish sandstone and sandy pebble conglomerate at 

altitudes 350 to 400 m, poorly exposed in a gully head and 

poking up sparsely and discontinuously through overlying coarse 

andesitic rubble for 350 m to the southwest. The gully exposure 

(unit Kk) is one of three outcrops in which Detterman and Jones 

(1974) identify fossils including Inoceramus pelecypod (clam) 

of late Campanian to early Maestrichtian (upper Cretaceous) 

age (Jones and Clark, 1973). They correlate these rocks with the 

fossiliferous Kaguyak Formation in the uplands of Cape Douglas 

on the Alaskan Peninsula 65 km south-southwest of Augustine 

(Jones and Detterman, 1966) and the coastal type section along 

Kaguyak Bay 90 km south-southwest of Augustine (Keller and 

Reiser, 1961, p. 275–277 and plate 29; Jones, 1963).

The western two outcrops bearing upper Cretaceous fossils examined in 1972 and 1974 (Detterman and Jones, 1974; 

Buffler, 1976) along Augustine Creek at altitudes 150 to 250 m 

seem no longer to exist, evidently buried by thick pyroclasticflow and laharic deposits of the 1976 Augustine eruption now 

mapped in that area.

The conspicuously smooth slopes broadly between sea 

level and about 550 m and between azimuths south-southeast 

and south-southwest, including an inlier to the west along 

Augustine Creek are fundamentally of this bedrock but thickly 

mantled by Augustine pumicous flow and fall deposits. The 

Mesozoic rock must have existed as an island before Augustine Volcano began to erupt. Slopes of 20 to 30° projected 

north from today’s outcrops suggest that the buried north part 

of this island lies beneath the Augustine central vent (see cross 

section on plate 1).

Along the south coast of Augustine Island, angular boulders of fossiliferous sandstone are common within the Long 

Beach debris-avalanche deposit (map unit HCal) and among 

the beach boulders eroded from it by waves. These sandstone 

boulders extend as far as 2 km west of the westmost gully that 

today can convey such blocks from existing outcrops to the 

coast. This distribution indicates that the Jurassic-Cretaceous 

bedrock lies buried beneath Augustine debris at least 0.4 km 

northwest of the present limit of outcrop.

Springs emerge at the contact of the Naknek sandstone 

with the underlying shale, water that by sapping contributes 

to retreat and maintenance of the prominent upper cliff. A 

wet layered sequence sloping toward a steeply incised cliff is 

conducive to landsliding. Such a landslide seems the cause of 

a highly fractured block of the sandstone member lying at the 

south coast (unit Pl).

Pleistocene to Late Holocene Materials

Pleistocene Deposits

Pleistocene materials crop out sporadically on Augustine’s south flank—a landslide block, glacial deposits, and 

volcanic materials.

Figure 12. Oblique aerial view north-northwest of Augustine Volcano. Most geomorphically smooth topography of south flank is block of 

Jurassic Naknek Formation (Jn) that is being gradually buried by the growing Augustine cone and is capped by many meters of Augustine 

fall deposit. Also shown are locations of Kamishak dome (dk) and Pleistocene deposits: basaltic hyaloclastite (Pvb), rhyolitic fall and flow 

deposits (Pvr), and glacial deposit (Pg). Photo taken just after end of growth of 1964 dome (64d), from which are extensive coarse deposits of 

1963–64 pyroclastic flows (64p). Map-unit symbols (parentheses) from plate 1. (USGS photograph by Austin Post, 3 September 1966.)
20 Volcanic Processes and Geology of Augustine Volcano, Alaska

Landslide Block

A block along the south coast east of the mouth of West 

Kamishak Creek is 500 m long and 60 m high of nearly intact 

sandstone of the upper member of the Naknek Formation, 

which crops out 200 m higher. By its size this rock at first 

appears in situ (fig. 14), and Detterman (1973) so mapped it. 

But unlike unambiguously in-situ rock, the coastal block (unit 

Pl, plate 1) is riddled with small faults and joints, some of 

them open fissures. Bedding is highly variable, dips as steep 

as 43°, and even some anomalous north dips as steep as 35°. 

These properties suggest many subblocks that have jostled and 

rotated with respect to each other. The block is cut back into 

a 50-m-high sea cliff, and wave-beveled sandstone is exposed 

at low tide as much as 100 m seaward of the cliff. Despite its 

enormous size and the near continuity of rock, the exposure 

seems clearly to be a block landslide, as Buffler (1976) tentatively suggested. Probably the sandstone block slid gradually, 

on a wet sole of the underlying shale.

Glacial Deposits

Scattered surface exotic stones or diamicts containing 

exotic stones, some of them glacially striated, crop out at several places on the south flank (unit Pg, plate 1). These stones 

range from angular to rounded and from pebbles to boulders 

as large as 1.6 m (fig. 15). Among the diverse rock types are 

granite, granodiorite, diorite, quartz diorite, gabbro, diabase, 

porphyritic dike rocks, granite-gneiss, hornfels, greenstone, 

amphibolite, vein quartz, banded limestone and chert, and 

argillite. All these rocks are exotic to Augustine Island. They 

seem derived from the nearby glaciated, mountainous terrain (Detterman and Reed, 1964; Detterman and Hartsock, 

1966) along the west side of lower Cook Inlet. The coarse 

and striated stones appear to be ice-deposited till, not deposits within a glacial lake as Johnston (1979) inferred. Most of 

the glacial deposits contain locally derived rounded pumice; 

some of them also contain clasts of nearby Naknek Formation 

sandstone.

 All the exotic stones are unweathered and hard, probably of the last (late Wisconsin) glaciation. Radiocarbon dates 

show that the late Wisconsin glaciation in Cook Inlet region 

occurred between about 30,000 and 12,000 14C yr B.P. (Karlstrom, 1964; Hamilton and Thorson, 1983, p. 46–47). The 

scattered debris on Augustine Island that contain exotic stones 

lie between altitudes 120 and 290 m but apparently no higher. 

This altitude may register the height to which coalesced late 

Wisconsin piedmont glaciers descending from western mountains had filled lower Cook Inlet (during lowered global sealevels) and banked against Augustine Volcano, perhaps about 

15,000 years ago (Hamilton and Thorson, 1983, fig. 2.4). On 

a spur 1 km north of South Point, Johnston (1979) reported 

exotic stones as high as 320 m. But the range of unarguably 

glacial exotic stones in that area is 230 to 275 m, like that on a 

spur 1.6 km farther west (250 to 290 m). The exotics Johnston 

reported higher are much smaller and far more rounded, apparently weathered from congomerate beds within the Jurassic 

Naknek Formation.

As Johnston (1979) reported, glacial debris on spots 

seems to overlie the Mesozoic bedrock, no Augustinian 

volcanic debris in between. He inferred that Augustine began 

erupting just after the late Wisconsin. But pumice within some 

glacial deposits and the some “old” dates (see below) suggest 

that Augustine had erupted earlier or that some of the glacial 

deposits are older than late Wisconsin.

A section at 10 to 30 m altitude overlying the southcoastal landslide block (unit Pl) includes exotic-bearing outwash of chiefly volcanic debris (unit Po) and an interbedded 

primary pumiceous fall deposit from Augustine Volcano. The 

pumiceous-gravel outwash dips as steeply as 38° north and 

northeast, onshore dips implying glacier ice banked against 

Augustine Island. Adjacent or underlying glacier ice that had 

supported the deposits melted and caused the beds to settle and 

rotate to dips steeper than repose angle.

At altitude about 290 m along Augustine Creek (westmost of the Pleistocene sections), one of the lowest beds of a 

Figure 13. View of Naknek Formation (Jurassic) on south side of 

Augustine Island. A, shale facies (map unit Jnsh). B, sandstone 

facies (map unit Jns). (USGS photographs by Richard Waitt.)
Pleistocene to Late Holocene Materials 21

section of alternating tephra and pumiceous pyroclastic-flow 

deposit is waterlaid pumice whose wood and charcoal fragments by two radiocarbon AMS dates precede 39,000 yr B.P. 

(table 2). This bed is overlain by several thin beds apparently 

of glacial outwash (containing exotic stones) intercalated with 

beds of waterlaid(?) pumice sand and gravel, beds overlain in 

turn by angular pumice gravel (Augustine fall) (fig. 15). Thus 

some Pleistocene glacial and volcanic materials may predate 

the late Wisconsin glaciation of Cook Inlet.

Numerous varieties of exotic pebbles, essentially the list 

above, lie among beach gravel on most shores—northwest, 

north, east, southeast, and southwest—azimuths no longer 

with glacial deposits exposed upslope. Constituting no more 

than 0.2 percent of beach stones, they must have arrived at 

the coast in debris-avalanche or pyroclastic-flow deposits. 

The nearly universal distribution of exotic pebbles in modern beach gravel around the island suggests glacial deposits 

mantled all flanks of Augustine Volcano but postglacial eruptions have since buried all but a few south-flank remnants.

Basaltic and Rhyolitic Deposits

Several small inliers on Augustine Volcano’s south flank 

(fig. 12) expose dark, basaltic fragmental material bedded 

in layers 1 to 30 cm thick (unit Pvb, plate 1) (fig. 16). These 

beds alternate between medium sand and granule gravel, most 

of them poorly sorted. Some beds contain much mud-sized 

material, are yellowish (palagonitic) and tightly cemented. 

Fragments of porphyritic olivine basalt as large as 20 cm are 

scattered through the sections. Most fragments are very angular, but a few are subangular to subround, distinctly abraded. 

These beds also contain sparse rounded pebbles of sandstone 

and angular chips of shale, both derived from the Naknek Formation. The basaltic vent is buried but probably lies nearby; 

the sandstone clasts suggest that the Naknek Formation must 

at depth extend east of its exposed limits.

A few beds have low-angle cross beds; some laminae 

contain mud balls (accretionary lapilli) 3 to 8 mm in diameter, 

and some beds contain angular bombs as large as 20 cm whose 

impact sagged the underlying beds as much as 25 cm. These 

characteristics, the blocky shape of apparently juvenile clasts, 

and retention of fine sand and silt in many beds are evidence 

that external (meteoric) water-vapor was the main propellant in the explosions, and are evidence that at least some of 

the beds were wet when emplaced. Such deposits are called 

“hyaloclastite.”

Basaltic-hyaloclastite beds at altitude 270 m on the south 

flank are underlain by several beds 0.5 to 1 m thick of nonsorted andesitic sandy pebble-cobble diamict rich in clasts of 

Naknek sandstone, probably thin pyroclastic flows. The basalt Figure 14. Great landslide block capped by layered Augustine 

volcanic debris, south coast Augustine Island. (USGS photograph 

by Richard Waitt.)

Figure 15. View north of glacial till containing striated exotic 

stones and associated glacial drift overlain by dacitic fall pumice 

of Augustine Volcano. Figure 18 photograph shows pit opened just 

beyond boulder in left-center. (USGS photograph by Richard Waitt.)
R

B

Rhyolite Interbedded Basaltic

hyaloclastite

22 Volcanic Processes and Geology of Augustine Volcano, Alaska

eruptions are a brief, extraordinary episode in a volcano erupting andesite before and long afterward. The uppermost 20 cm 

of the basaltic hyaloclastite is interlayered with the base of 

dacitic-rhyolite fall pumice (unit Pvr).

At altitude 310 m on the south flank, 10 m of white 

pumiceous beds (unit Pvr, plate 1) range from openwork, 

angular pumice pebbles (fall bed) to pebbly sand with subangular pumice clasts (pyroclastic-flow deposit). The lowest 

pumiceous beds of very coarse sand are interlaminated with 

the upper 20 cm of the Pleistocene basaltic-hyaloclastite beds 

(fig. 17). Thus rhyolitic white pumice erupted from the summit 

vent more or less simultaneously with olivine basalt from a 

separate south-flank vent.

In the lowest parts of the westmost inlier sections 

(azimuth south-southwest, altitude 280 m), pumiceous beds 

overlie and are interbedded with the top of glacial and glaciofluvial deposits that bear exotic stones and from whose 

base come the radiocarbon dates exceeding 39,000 yr B.P. 

(fig. 18). Overlying the glacial horizon is 17 m of sandy flow 

deposits punctuated by four major pumice-fall beds (unit 

PHfp; see just below).

Pleistocene and Holocene Pumiceous Fall and 

Pyroclastic-Flow Deposits

Exposed on the steeply eroded sides of four south-side 

nunatak-like inliers at altitudes 250 to 700 m are sections 8 to 

17 m high comprising several beds of pumiceous and lithic 

pyroclastic-flow deposits interbedded with many beds of 

loose, sorted pumiceous fall deposit (unit PHfp, plate 1).

The upper pumiceous fall beds of all these sections 

probably correlate with tephras C and M, and perhaps with 

other tephra beds of the coastal sections. But ambiguous field 

character and chemical data make such correlation tenuous. At 

altitude 370 m on the south-southeast azimuth, an east-facing 

17-m section contains seven pumiceous-fall beds, at least five 

intervening lithic-fall beds, two pumiceous pyroclastic-flow 

beds, and several sand-ash beds. At 9 m above base, a peat layer 

dates by radiocarbon to about 2,160 yr B.P. (table 2). Above it 

lie five coarse pumiceous tephra layers, which must correlate 

with the late Holocene coastal tephras. A less complete east-facing section of interlayered thick pumiceous fall and pyroclasticflow beds lies at altitude 460 to 550 m on the south azimuth.

Augustine erupted at least several times between the 

late Wisconsin and about 2,200 14C yr B.P., but the evidence on Augustine Island is scant. On a few south-flank 

inliers, pumiceous pyroclastic-flow and several pumiceousfall deposits underlying peat dated to about 2,160 yr B.P. 

(table2) represent this broad period. On Shuyak Island 

Figure 17. Basaltic hyaloclastite (B) overlain by rhyolitic pumice 

(R), on south flank of Augustine Island. Top of hyaloclastite is 

interlayered with thin beds of base of rhyolite. (USGS photograph 

by Richard Waitt.)

Figure 16. View eastward showing bedded olivine-basalt 

hyaloclastite at or near base of discontinuously exposed volcanic 

materials of Augustine Volcano, probably of very late Pleistocene 

age. (USGS photograph by Richard Waitt.)
F

O

O

F

T

F

Pleistocene to Late Holocene Materials 23

110 km southeast of Augustine (fig. 1A), two fall tephras 

of Augustine chemical provenance (probe analysis of glass 

by J.R. Riehle and C.E. Meyer) date between about 6,460 

and 5,020 yr B.P.; a higher Augustine tephra there dates 

between 3,620 and 3,360 yr B.P. (table 2; plate 2, section 

RBW 93Ko.09) (tephras identified in Riehle and others, 

1998). Along Kamishak Creek 70 km southwest of Augustine (fig. 1A), a fall tephra of Augustine provenance dates 

between about 3,850 and 3,660 yr B.P. (table2) (Riehle 

and others, 1998, fig. 8). A probably Augustinian ash dated 

to about 2,275 yr B.P. lies near Homer 110km northeast 

of Augustine. Several Augustine tephras probably also of 

early to middle Holocene age lie on Fortification Bluff 22 

km west-northwest of Augustine (J.R. Riehle, written commun., 1996; Riehle and others, 1998). Undoubtedly early 

and middle Holocene eruptions laid deposits on Augustine 

Island, but except for the south-flank kipukas—where 

details of age remain undeciphered—such deposits lie buried beneath voluminous younger eruptive deposits.

Lava Domes of Uncertain Late Holocene Age

Kamishak Dome (Dome K)

Kamishak dome, a massive light-gray porphyritic andesite (unit dk, plate 1) forms a conspicuous bump on Augustine 

Volcano’s south flank (figs. 3, 12) at altitude 513m. It is 

thickly blanketed by fall and ballistic debris, the only exposure being its steep south (downslope) face. Because even the 

upper part of the dome seems to be overlain by far less than 

the 10 to 20 m of fragmental deposits that lie downslope, it 

seems to be late Holocene in age.

The cross section (on plate 1) shows its imagined feeder 

vent at depth 515 m (sea level) a pipe separate from central 

pipe. But Kamishak domerock is essentially identical to 

the cluster of summit domes, its feeder must at depth must 

flare from the central pipe, implied on the cross section by 

Kamishak’s north plunge with depth.

Domes F and P

Two domes of porphyritic gray andesite form bumps at 

altitudes 1,025 (dome F, unit df, plate 1)5 and 910 m (dome P, 

unit dp) on the upper northwest flank, some 400 to 800 m northwest of the central summit-dome complex (fig. 19). The large 

West Island debris avalanche (table 3) must have left a large crater scar including this area, so the domes must be younger than 

about 390 yr B.P. (table 2) but precede historical eruptions.

Prehistoric Summit Domes

Probably several overlapping domes make up the east 

and south sides of the summit cone. Three are distinguished 

by variations in overall color separated by shallow moats. 

Map units ds1 through ds3 (plate 1) suggest relative ages (ds3

youngest as geomorphically it seems to cover the others), but 

this is rather speculative. Part of the east side is deeply eroded 

into the “pinnacles,” which on a 1909 photograph (Kienle and 

Swanson, 1980, fig. 10; Swanson and Kienle, 1988, fig. 5) is 

old rock remaining after a summit collapse during the 1883 

eruption. This old dome rock is overlapped by the several historical domes: the south side by the 1964 dome and the west 

side by 1883 (buried), 1935, and 1964 domes.

5

 These domes had been informally called domes “I” and “H” after seismic 

stations (AUI and AUH) installed on them long ago. But “tephra I” and 

“tephra H” in the coastal Holocene stratigraphy, also in long and published 

use and continued here, are in source and time unrelated to the two domes. To 

avoid confusion the continued dual use of I and H would cause, the domes are 

here renamed to dome F (upper one) and dome P (lower).

Figure 18. Pumice-fall deposit from Augustine interbedded with 

distal thin beds of Pleistocene glacial outwash, south-southwest 

flank of volcano at altitude 155 m. View shows top, layered part 

of thick bed of coarse till (and outwash?). O, glacial outwash; T, 

glacial till; F, Augustine pumiceous fall deposit. For context see 

figure 15. (USGS photograph by Richard Waitt.)
64

35 35

F

P

S

R

K

L

83a

24 Volcanic Processes and Geology of Augustine Volcano, Alaska

Lava Flows

Massive porphyritic andesite crops out far below the level 

of summit and subsummit domes at five sites on the volcano’s 

south and north flanks (unit ld, plate 1). Largely buried by 

younger fragmental debris, these inliers crop out only in small 

patches that have diminished even in recent decades. They are 

far enough downslope to be lava flows and in form they seem 

not to be large mounds, though the porphyritic andesite is 

lithologically like that of the domes.

Prehistoric Deposits of 

Late Holocene Age

In writing, “describe” means to tell of a thing; in geometry it means to draw an outline of a thing. Here you get 

both: text and map. Most of Augustine’s exposed apron of 

coarse debris is younger than 2,500 years. Radiocarbon-dated 

overlying and intercalated pumiceous fall deposits limit the 

timing and correlation of many coarse deposits (table 2). 

Most of the volume of flank deposits is bouldery diamicts of 

angular clasts, and each diamict is an unsorted, unstratified 

mixture of angular clasts of all sizes from sand to enormous 

boulders. Almost all clasts are of sparsely vesicular porphyritic andesite similar to rock of the present dome complex. 

Many of the coastal diamicts contain rare clasts derived from 

the middle-lower slopes—from Mesozoic rocks that underlie the south mountain flank, and from Pleistocene glacial 

deposits.

The dominant eruption style seems to be growth of summit domes followed by collapse as a debris avalanche. Table

3 

suggests a significant debris avalanche every 180–200 years 

average. Similar arithmetic suggests eruptions of coarse pumiceous tephra are spaces about 31⁄2 centuries average, and eruptions yielding significant ashflows every 31⁄4 centuries or less.

The “Description of Map Units” on plate 1 explains 

labeling. Unit IHa, for instance, overlies tephra I and underlies 

tephra H.

Figure 19. Oblique aerial view toward east-southeast of Augustine summit area including landslide-truncated prehistoric summit-dome 

complex (S). Off summit area on west-northwest are prehistoric lava domes F and P, and below dome P a rubble flow (R). On south flank 

lies Kamishak dome (K). North flank lava flow (L) overlain by 1883 debris-avalanche levee (83a). Visible in summit area are parts of 1935 

lava dome (35) and the newly emplaced 1964 lava dome (64). (USGS photograph by Austin Post, 3 September 1966.)
Prehistoric Deposits of Late Holocene Age 25

Deposits Older Than Tephra G 

(about 2,500–2,100 14C yr B.P.)

East Point6 Debris-Avalanche Deposit(s)

A continuous high sea cliff between Southeast Point and 

Northeast Point7 (fig. 1B) exposes bouldery diamicts (unit Ga, 

plate 1) that by color and relation to tephra layers we separate 

into four units, all apparently deposits of debris avalanche, the 

youngest overlain by the H tephra. All are clearly fragmental 

but contain angular boulders as large as 8 m and rare shattered 

megablocks much larger.

A diamict forming the lowest part of this coastal sea 

cliff for 3 km along the east coast and named for East Point is 

at least 13 m thick, its base not exposed. It contains angular 

andesite fragments as large as 5 m; on the beach below the 

sea cliff are wave-winnowed lag boulders as large as 7 m. 

Large clasts in the sea cliff are set in a gravelly sand matrix 

of shattered andesite (fig. 20A), generally gray but in places 

oxidized reddish. Most of the boulder-sized andesite clasts are 

gray, some are reddish, and a few are highly altered to yellow 

or white. A few delicate, prismatically jointed clasts must have 

been hot juvenile dome-rock clasts that cooled after emplacement (fig. 20B).

The lower two-fifths of the bluff near East Point is too 

covered to assess internal stratigraphy reliably. Within the 

17-m section of debris avalanche is one definite break 4 m 

above the base of exposure (base of deposit not exposed) and a 

possible break at 121⁄4 m above base (see plate 2, section RBW 

91A.102). Thus this thick bouldery diamict may actually comprise the deposits of two or more debris avalanches. Some of 

the substantial field of mostly submerged large boulders (unit 

ob, plate 1) offshore of the east coast is probably part of these 

older avalanches.

East Point diamict is capped by the sparsely exposed G 

tephra, and that overlain by oxidized Yellow Cliffs bouldery 

diamict (part of unit Glays).

Deposits Between Tephras G and I 

(about 2,100–1,800 14C yr B.P.)

Yellow Cliffs Debris-Avalanche Deposit

Overlying the sparsely exposed G tephra that caps the 

East Point debris-avalanche deposit is a highly altered and 

oxidized massive diamict containing angular andesite boulders 

commonly 1 to 2 m in diameter, some as large as 3.5 m (lower 

part of unit Glays, plate 1). This distinctively yellowish unit 

6

 Begét and Kienle (1992, table 1, bottom) inadvertently transposed the 

names East Point and Yellow Cliffs debris avalanches. East Point deposit 

indeed lies below tephra G, Yellow Cliffs deposit above tephra G.

7

 Local place names in this section—East Point, Yellow Cliffs, Southeast 

Point, and Northeast Point—are all informal. See figure 1B for the distinction 

of formal and informal place names. This paper prints informal names, like 

the formal ones, with capitals for clarity in reading.

5 to 9 m thick forms the middle to upper part of the sea cliff 

for at least 2.5 km along the east coast (fig. 21). The matrix 

and large clasts alike are strongly altered to soft zeolite (?) 

and clay. But the unit also contains sporadic pods meters in 

diameter of gray to reddish coarse diamict of scarcely altered 

andesite. Midway between East Point and Northeast Point its 

surface shows sharp local relief of 3 to 4 m where directly 

buried by the Northeast Point debris-avalanche deposit. At and 

south of Southeast Point, the Yellow Cliffs diamict is overlain 

by the gray Southeast Point debris-avalanche deposit, which is 

capped by tephra I.

The hummocky surface topography and the massive and 

coarse texture clearly identify the Yellow Cliffs diamict as a 

debris-avalanche deposit. The enclosed pods of unoxidized 

diamict and the fact that the unit is both overlain and underlain 

by unoxidized to weakly oxidized similar diamicts show that 

the strong alteration had occurred in the source area, before 

the avalanche. Apparently most of the avalanche is of summit 

dome rock that had become strongly altered by hydrothermal 

fluids before the avalanche occurred.

Southeast Point Debris-Avalanche Deposit

Overlying the Yellow Cliffs diamict and beneath tephra 

I along the coastal cliff 350 m west of Southeast Point lies 

a diamict at least 8 m thick with in-situ boulders as large as 

3.5 m (fig. 22) (upper part of unit Glays, plate 1), winnowed 

boulders on the beach below reach 7.5 m. The angular clasts 

and most of the matrix are gray to reddish and scarcely altered, 

contrasting with the underlying Yellow Cliffs diamict. The 

Southeast Point debris-avalanche deposit extends at least 2.5 

km northeast along the coastal cliffs to Northeast Point, where 

it is also overlain by the I tephra. The I tephra is overlain in 

turn by the Northeast Point debris-avalanche deposit (unit 

IHa). Surface slope atop the sea cliff, if projected seaward, 

indicates that the Southeast Point debris-avalanche deposit 

has been wave eroded back at least 0.5 to 1.0 km. Figure 23 

schematically shows relations among four debris-avalanche 

deposits—two of this map unit, one of the underlying unit, one 

of the overlying unit.

The south part of the offshore belt of mostly submerged 

large boulders (unit ob, plate 1) is of this eroded-back 

avalanche.

Deposits Between Tephas I and H 

(about 1,700–1,400 14C yr B.P.)

Northeast Point Debris-Avalanche Deposit

Beneath the H tephra and 1.5 to 3 m of underlying sand 

ash, a coarse and massive diamict extends along the coast 

for more than 4 km from north of Northeast Point to south 

of East Point (unit IHa, plate 1). The deposit contains very 

angular boulders of gray andesite typically as large as 5–7 m 

in intermediate diameter but the largest 12 m, some of them 
26 Volcanic Processes and Geology of Augustine Volcano, Alaska

are internally shattered, set in a gravelly sand diamictic matrix 

with smaller clasts of identical composition and angularity. At 

East Point the deposit is at least 20 m thick (base not exposed); 

it tapers 1 km south of East Point to 10 m thick and in another 

0.5 km to 7 m thick, where it overlies a thin pyroclastic-flow 

deposit. Within a few hundred meters farther south it pinches 

out altogether. Its south part overlies three (or more) older 

debris-avalanche deposits (fig. 23). Coarse, rubbly diamict 

with boulders as large as 4 m crops out upslope in the walls of 

incised gullies, traceable apparently up to the base of the summit dome complex at altitude 700 m.

 Within a kilometer of the coast the surface is broadly 

hummocky, having a relief generally of 3 m but much higher 

over distances of 50 m (figs. 24, 25). A straight levee 3–8 m 

high delineates the north side of the main body of deposit. 

But similarly hummocky, bouldery deposit also lies north of 

(outside) this levee. This too may be part of the Northeast 

Point debris avalanche, emplaced just before the leveeforming phase. Mantling tephra and peat, 3 m and more thick, 

have considerably smoothed this topography. But beneath this 

mantle in coastal exposure its sharp local relief is at least 6 m 

over distances of 20 m. A few boulders larger than 2.5 m in 

the top of the deposit protrude through the tephra-peat blanket. 

The upslope margin of the debris-avalanche deposit is widely 

buried by 1976 (and prehistoric?) pyroclastic-flow deposits at 

least 80 cm thick.

About 0.8 km south of Northeast Point the upper part of 

this diamict is strikingly monolithologic. Every fragment is 

very angular, most of them pebble size and coarser. Here the 

deposit appears to be a single dome block at least 30 m long; 

it is more disaggregated than so-called “jig-saw” blocks in 

the 1980 Mount St. Helens avalanche deposit described by 

Glicken (1996), yet it did not dilate and disaggregate enough 

to form or admit “matrix.” This more-or-less-intact block, far 

too large to have been moved by pyroclastic flow or lahar, 

could only have piggybacked atop a moving avalanche.

At Northeast Point the deposit crosses a straight eastfacing coastwise scarp 650 m long and 30 m high that lies 

about 450 m back from the sea (fig. 26, plate 1). This scarp 

apparently is a sea cliff cut back into the Yellow Cliffs (and 

older?) debris-avalanche deposits. Seemingly identical 

hummocky coarse debris lies both behind and in front of the 

scarp, and the overlying tephra section (lowest pumiceous 

tephra is H) is the same both sides of the scarp. The Northeast Point debris avalanche must have overridden and buried 

the scarp, though not so thickly to obliterate (fig. 10B). The 

material atop the buried sea cliff is delicately hummocky 

(fig. 26), apparently stranded. This material could not itself 

be older and overridden by the seaward debris forming 

Northeast Point, for that would have smoothed and fluted the 

scarp—like the scarp behind West Island debris-avalanche 

deposit (see below).

Nearly continuous boulders, some as large as 5 m, extend 

at least 600 m offshore of Northeast Point (unit ob, plate 1). 

Storm waved have eroded the original subaerial deposit back 

at least that far, to its present sea cliff.

Figure 20. Details within East Point debris-avalanche deposit. A, 

Close view of shattered-andesite matrix of debris avalanche. B, 

Radially, prismatically jointed porphyritic andesite block. Radial 

joints signify that block was hot when emplaced, evidence of 

eruption in progress or of eruption triggered by the developing 

landslide. (USGS photographs by Richard Waitt.)
N

Y

E

N

Y

E

Sea

level

45

6 kilometers 6 kilometers

Elevation, in meters

S N

G tephra

I tephra

H and I tephras H tephra

Southeast Point debris avalanche

(GIays)

Northeast Point debris avalanche

(IHa)

Yellow Cliffs debris avalanche

(GIays)

East Point debris avalanche

(Ga)

N

Tephra and soil Tephra

and soil

N

S

Tephra I Tephra I

N

S

Prehistoric Deposits of Late Holocene Age 27

Figure 21. View of sea cliff 

along Augustine Island east 

shore showing Yellow Cliffs 

debris-avalanche deposit (Y) 

overlain by Northeast Point 

debris-avalanche deposit (N). 

Colluvium covers East Point 

debris-avalanche deposit (E). 

(USGS photograph by Richard 

Waitt.)

Figure 22. Southeast Point debrisavalanche deposit (S) overlain by 

tephra I (at man), in turn overlain by 

Northeast Point debris-avalanche 

deposit (N). East coast of Augustine 

Island. (USGS photograph by 

Richard Waitt.)

Figure 23. Schematic sketch of coastal cliffs along east side of Augustine Island showing stratigraphic relations of four oldest debrisavalanche deposits (d.a.) and the three oldest of the coarse pumiceous-tephra marker beds (G, I, H). Map-unit labels (of plate 1) in 

parentheses.
28 Volcanic Processes and Geology of Augustine Volcano, Alaska

Northeast Bench Debris-Avalanche or 

Lahar Deposit

A bouldery gravel diamict (unit IHl, plate 1) containing 

angular porphyritic andesite stones as large as 4 m lies outside 

(north of) the levee that delineates the north side of main body 

of Northeast Point debris-avalanche deposit (unit IHa). The 

seaward part of this seemingly continuous unit north of the 

levee is relatively nonhummocky and called here Northeast 

Bench. By this morphology the unit underlying the bench 

would seem to be a lahar deposit (unit IHl). But more than 

200m back from the sea cliff the area outside the levee is 

nearly as hummocky as that inside (south of) the levee; thus 

we map that area with unit IHa. Both map units IHl and IHa are 

overlain by a tephra sequence having tephra H near its base.

Sandy gravel lacking large blocks underlies tephra H 

(tephra I absent) at several places on southeast and south 

coast. Besides the debris avalanche, this eruption thus seems 

to have generated voluminous south-side lahars, since cut back 

to sea cliffs.

Diamict atop Landslide Block

A massive diamict as thick as 20 meters containing angular clasts as large as 4 meters (unit IHla, plate 1) overlies the 

west end of the big south-coastal landslide block (unit Pl) and 

overlying Pleistocene glacial till and outwash interfingered with 

eruptive products (units Pg and Po). The diamict’s massive, 

unstratfied matrix rich in smaller angular clasts and the coarse 

size of the largest ones suggest its origin by debris avalanche. 

But in the central and east part of the 800-meter-long exposure, 

the matrix is in places slightly bedded and the enclosed stones 

smaller, more like lahar. This whole deposit underlies tephra C 

and in places tephra H (see plate 2, section RBW 91A.20). By 

its tephra-bracketed age, this flow could be a small west tongue 

Figure 24. View west of hummocky 

surface of Northeast Point debrisavalanche deposit. Hummock in 

right middle distance is about 18 m 

high. Its top holds the benchmark 

“mound.” In distance, cone of 

Augustine Volcano, its top in clouds. 

(USGS photograph by Richard Waitt.)

Figure 25. Oblique aerial view, Augustine Island. This point is 

0.8 km south of bold Northeast Point; sea cliff is 35 m high. Hill in 

lower center is “mound” shown from ground in figure 24. (USGS 

photograph by Richard Waitt.)
Prehistoric Deposits of Late Holocene Age 29

of the huge Northeast Point debris avalanche that mostly flowed 

east of the south-flank’s high of Jurassic sandstone.

Deposits Between Tephras H and C 

(about 1,450–1,100 14C yr B.P.)

Several bodies of coarse bouldery diamict lie along the 

lower slopes and in coastal exposures at azimuths southwest, 

south, and southeast from Augustine’s summit. They are all 

capped by tephra C but seemingly not by tephra H. Two are 

hummocky, evidently debris-avalanche deposits. Another, also 

very coarse, is nonhummocky and microlobate and evidently 

not a great avalanche (southeast fan). These separated deposits 

all may be close in age, but by the bracketing tephra layers they 

are dated only within a range spanning about four centuries.

South Point Debris-Avalanche Deposit

South Point, jutting 600 m seaward from the south coast, 

consists of a diamict of angular clasts of porphyritic andesite 

as much as 9 m in intermediate diameter (unit HCas, plate1). 

Its hummocky surface has local relief of 10 m. Clearly a 

debris-avalanche deposit, it has no evident levees upslope, 

where it has been deeply buried by younger eruption deposits, 

especially in 1963–64.

Like the geomorphic relation at Northeast Point, the surface of South Point debris avalanche seems to be a depostional 

feature rather than an erosional one. A conspicuous seaward 

step across the surface lies 200 m back from South Point. The 

hummocky surface topography in front of this step seems 

identical to that behind. Geomorphically the step resembles an 

overridden, partly buried a sea cliff at at Northeast Point. But 

unlike Northeast Point, it doesn’t align with a demonstrably 

old sea cliff, nor is there older deposit exposed either east or 

west of South Point. The step may be primary topography of 

emplacement. The 1980 debris avalanche at Mount St. Helens 

has two large steps along its length.

South Point debris-avalanche deposit is at least 30 m 

thick, the height of the modern sea cliff. That South Point is 

much broader and projects farther seaward than Northeast 

Point geomorphically suggests its relative youth, consistent 

with the tephra H lacking in the overlying stratigraphy.

The tephra-and-peat sequence that overlies the debrisavalanche deposit ranges from nil to 8 m thick, typically 1 to 

2m thick, having the C tephra near its base. This is the youngest of the large debris avalanches forming Augustine’s south 

and east coast. Yet it too is eroded back into a high cliff, and 

thus is geomorphically older than any of the weakly cliffed 

and uncliffed debris-avalanche deposits on the northwest and 

north coasts.

Long Beach Debris-Avalanche Deposit

A hummocky diamict is sparsely exposed in the distal 

southwest quarter of Augustine Island (unit HCal, plate 1). It 

protrudes as irregular rocky mounds through 1976 and older 

pumiceous lahar deposit and as a belt of hummocks just beyond 

the limit of 1976 deposits. The hummocks are as much as 9 m 

high and 20 m in diameter. One of the largest consists mostly 

of one 9-m andesite boulder (fig. 27). Numerous large boulders 

protruding through swampy terrain near the southwest coast 

probably are of this deposit. A lithic diamict exposed along 

Long Beach also includes hummocks exposing boulders as large 

as 6 m, capped by tephras C and M. Large boulders lie in matrix 

of smaller angular material of identical composition, most lithic 

clasts being porphyritic andesite. But a few clasts are sandstone: 

this avalanche must have flowed down across now-buried Jurassic sandstone west of current outcrops.

In the southwest quarter 0.6 to 1.0 km back from the 

south coast, a swamp nearly at sea level is devoid of large 

hummocks but interrupted by large boulders. This low area 

suggests that the debris avalanche had enough momentum that 

most of it swept to sea. This low, swampy area is not unlike 

a low area behind hummocks of the 1883 debris avalanche 

now largely filled by younger flows (see below). Both of these 

are analogous to Northwest Lagoon behind West Island (see 

below). Younger pyroclastic and laharic deposits, including 

from 1935, 1964, and 1976 eruptions, have largely filled the 

former southwest low.

At low tide and on aerial photographs, large-boulder lag 

can be seen as far as 0.5 km off the south-southwest shore 

(unit ob, plate 1); maps show convoluted bathymetric contours 

extending to a depth of 10 m as far as 2 km offshore, some 

8.5km from the summit. Similar submarine hummocky topography extends generally 2 to 4 km outboard of demonstrable 

debris-avalanche deposits on other azimuths and must record 

the seaward extent of debris avalanches (fig 11). The muchburied Long Beach debris-avalanche deposit thus seems to 

extend a similar distance from the summit cone as the younger 

and well-preserved West Island debris-avalanche deposit.

Figure 26. Oblique aerial view west-northwestward of Augustine’s 

Northeast Point debris-avalanche deposit and apparently 

overridden sea cliff (arrows). Hummocky diamict mantles both 

sides of scarp. (USGS photograph by Richard Waitt.)
30 Volcanic Processes and Geology of Augustine Volcano, Alaska

Long Beach debris-avalanche deposit (unit HCal) is perhaps only slightly older than the overlying pumiceous deposit 

(southwest pyroclastic fan, unit HCpwp), for along the eastern 

part of Long Beach the pumiceous deposit directly overlies the 

diamict, whose top lacks evidence of weathering or soil.

Long Beach debris avalanche, like South Point debris 

avalanche, is overlain by tephra C but evidently not tephra H. 

These two avalanches could be arms of one large avalanche 

or may instead be two separate avalanches during the four centuries between the fall of the two marker tephras. Only further 

refinements of stratigraphy and dating will tell.

Southwest Pyroclastic Fan

Lithic Pyroclastic-Flow Deposit

A steep fan of angular-boulder gravel of flow-banded 

andesite on Augustine’s southwest flank heads at altitude 

390m and extends downslope 2.5 km to altitude 25 m (unit 

HCpwl, plate 1). The boulders are commonly as large as 4 m 

in intermediate diameter, rarely to 6 and even 9 m. (Perhaps 

these largest are of underling Long Beach avalanche and 

merely surrounded by this gravel fan.) Matrix-bearing debris, 

or in places 1- to 3-m boulders piled atop one another upslope 

of huge boulders. Therefore small-bouldery flow continued 

after the huge clasts had grounded. Many close-spaced levees 

and numerous intricately lobate margins embellish the surface 

of the deposit. 

The huge boulders suggest an origin by debris avalanche 

like other deposits lower on all flanks of the volcano. But the 

steeper surface of this deposit, its intricately leveed surface on 

aerial photographs, and its lack of conical high-relief hummocks all show it to be a pyroclastic-flow deposit, though 

lithic. This unit is similar to similarly aged unit HClp on the 

southeast flank, which contains a few prismatically jointed 

blocks showing that deposit was shed from a hot-dome source. 

This deposit (and unit HClp) also has many characteristics 

of laharic debris flow, though their sheer areal extents and 

volumes argue against lahar (see discussion under heading 

“Geomorphology”).

This fan is capped very sparsely by tephra C and semicontinuously by tephra M as thick as 75 cm. The fact that 

tephra C is so thin and spotty atop this deposit but is as thick 

as 29 cm at the nearby coast suggests this lithic fan was 

emplaced late during the accumulation of tephra C.

The toe of this lithic deposit is partly buried by much 

gentler sloping pumiceous pyroclastic-flow deposit (unit 

HCpwp), which flowed down a deep swale just east and spread 

clockwise along the coast. Along the steep coastal exposures, 

lithic gravel—probably distal unit HCpwl (in vertical projection outcrop is too narrow to map on plate 1)—widely underlies the pumiceous pyroclastic-flow deposit.

To the east a lithic gravel diamict prominently capped by 

tephra C lies at the coast about the mouths of East Kamishak 

and Augustine Creeks. This deposit is not hummocky but 

contains large boulders, its emplacement mode debatable. Possibly it is a thin west tongue of South Point debris avalanche. 

This flow, mapped with unit HCpwl, had momentum to ride 

25m up over a coastal landslide block. This relation suggests 

that flow velocity just before runup was at least 20 m/s. Such 

speed suggests debris avalanche more than pyroclastic flow.

Pumiceous Pyroclastic-Flow Deposit

In coastal cliffs of the southwest volcano flank a massive 

sandy pumiceous pyroclastic-flow deposit (unit HCpwp, plate

1) 

as thick as 16 m overlies the Long Beach debris-avalanche 

deposit and an associated lahar deposit (units HCal and HCl), 

and it directly underlies tephra C. The pumiceous pyroclastic 

deposit is about 80 percent sand matrix; among the coarser clasts 

three-quarters are pumice and one quarter lithics as large as 5 cm 

Figure 27. Nine-meter megaclast of 

summit-dome porphyritic andesite 

forming a single hummock of Long 

Beach debris-avalanche deposit on 

lower southwest flank of Augustine 

Island. (USGS photograph by 

Richard Waitt.)
Prehistoric Deposits of Late Holocene Age 31

(rarely 30 cm). The deposit is graded by density: pumice clasts 

are concentrated in the upper 3 m of deposit, lithic clasts in the 

lower 10 m, though lithics lie sparsely throughout the deposit. 

The upper 3 m of the deposit is pale red, oxidized by high 

temperature. One site reveals two massive deposits—a lower 

one 13m thick with openwork gas-escape pipes and an upper 

one 4m thick—separated by 20 cm of apparently fluvial deposit 

lacking a paleosol. These two flows probably followed Augustine Creek and spilled through a western swale.

This sand-ash (unit HCpwp) is the largest and thickest 

pumiceous pyroclastic-flow deposit known on Augustine Island. 

Thinner pumiceous and lithic pyroclastic-flow deposits locally 

underlie it. This pumiceous deposit apparently partly buries the 

toe of the upslope lithic-pyroclastic deposit (unit HCpwl).

Southeast Pyroclastic Fan

On Augustine Island’s south-southeast coast a set of 

pumiceous pyroclastic-flow deposits (unit HCpe, plate 1) is 

exposed only in section in lower parts of the sea cliff. Farther 

east at Southeast Point a lithic pyroclastic-flow deposit (unit 

HClc) consists of cobble gravel to sandy cobble gravel that is 

vaguely stratified and lacking in large boulders, suggesting a 

pyroclastic-flow or perhaps laharic deposit. Correlated with 

this is similar lithic debris capped by tephra C at and east of 

the mouth of Middle Kamishak Creek 3 km farther west.

Upslope from Southeast Point, a proximal facies (unit 

HClp) contains numerous angular lithic (dense) porphyriticandesite boulders 4 to 6 m across, a few as large as 9 m 

(fig.28). Some smaller dense blocks are prismatically jointed, 

showing that the flow originated from hot dome rock. Several 

close-paired levees trend downslope, and from them extend 

small, multilobate convex-downslope ridges. The deposit is 

unhummocky, its local relief only 2.5 m and less. This is the 

morphology of lithic pyroclastic flow, not of debris avalanche. 

The short distance (2.2–3.2 km) and steep slope (24°) between 

the summit and the deposit accounts for the unusually large 

blocks (for a pyroclastic-flow deposit). The deposit is almost 

continuously vegetated, much of it by alder. Distal tatters of 

1976 pumiceous pyroclastic flows overlap the head of deposit.

This coarse lithic deposit resembles lithic unit HCpwl

on the southwest flank. Emplaced at about the same time, the 

two probably originated similarly. Both the coastal and the 

proximal facies are overlain by tephra C, the coastal facies 

underlain by tephra H.

North Bench Debris-Avalanche Deposit

North Bench diamict, at least as thick as 15 m, comprises 

angular fragments as large as 5 m and bears a mildly hummocky topography with sparse local relief of 6 m. The diamict 

is surely a debris-avalanche deposit (unit IMan, plate 1) but 

its surface relief vastly subdued by pyroclastic-flow deposit, 

and possibly by overwash by tsunami, that have filled lows 

between hummocks.

The deposit is truncated by a gently convex-seaward sea 

cliff as high as 23 m, the highest topographic feature along 

Augustine’s northwest coast (figs. 29, 30). This cliff is now 

isolated 340 to 460 m from the sea by younger deposits that 

descended intervening gullies, built seaward-sloping fans, 

and spread along the coast—burying the former lower third 

of the sea cliff (fig. 10C; plate 1). And so geomorphically 

North Bench diamict is much older than neighboring debrisavalanche deposits (described below) that nearly surround the 

arrested sea cliff that had cut back into North Bench.

If we compare North Bench to debris-avalanche deposits on the east and south coasts, the gently arcuate sea cliff 

of moderate height well back from the present coast shows 

the North Bench deposit to be geomorphically as old as the 

interval between tephras H and C (like South Point avalanche), 

between tephras I and H (like Northeast Point avalanche), or 

even older (like Southeast Point avalanche).

Unfortunately for stratigraphy, this northwest flank is 

statistically upwind, the least likely direction to accumulate 

tephra ejected from Augustine’s summit (fig. 5), and there’s 

no evidence that tephra M or any of the older tephras reached 

this far northwest (fig. 7). Most of the area being underlain by 

Figure 28. View northwest of boulders on southeast pyroclastic 

fan of Augustine Island, apparently a lithic pyroclastic-flow deposit 

formed from partial collapse of prehistoric hot dome (modern dome 

forms skyline). (USGS photograph by Richard Waitt.)
Do

0 1

1

2 KM

La

B

L

W

W

W

N

N G

R

R

S2

S2

S3

S1

S11

S11

32 Volcanic Processes and Geology of Augustine Volcano, Alaska

young deposits, any old tephra that may have fallen here is 

buried. Only tephra B demonstrably fell this far north. In gullies upslope and back from the sea cliff, North Bench debrisavalanche deposit is discontinuously overlain by as much as 

1.5 m of deposits including a pyroclastic-flow deposit (not 

distinguished on plate 1), pumiceous tephra B, three younger 

sand ashes, and the Katmai 1912 silt ash. This stratigraphy 

includes tephras older than atop the nearby West Island debrisavalanche deposits (including Grouse Point).

Yet atop North Bench near the prominent arrested sea 

cliff, overlying strata are oddly thin and young, only 1 or 

2 sand-ashes beneath the Katmai 1912 white-silt ash. The 

strata here seem incomplete. This could be related to why 

stratigraphy of the seaward part of Lagoon avalanche deposit 

(described below) is incomplete: later overwash by tsunami as 

big West Island avalanche crashed into the sea.

Deposits Between Tephras C and M 

(about 1,000–750 14C yr B.P.)

Lagoon Debris-Avalanche Deposit

Lagoon debris-avalanche deposit (unit CMal, plate 1) 

is hummocky with local relief of 10 m and contains angular 

andesite boulders at least as large as 3 m. In the highest two 

coastal exposures and in high places inland, it is overlain by 

about 60 cm of peat and tephra, at whose base is discontinuous pumice lapilli locally as thick as 20 cm. A pumice deposit 

this thick is far more characteristic of tephra M than tephra 

B. Indeed on the highest coastal hummock, a thin discontinuous pumice (tephra B) distinctly overlies the thick pumice 

(tephra M). Trace-element chemistry also suggests the thick 

layer is tephra M (Begét, unpub. data).

Figure 29. Vertical aerial photo of Augustine’s north flank showing dome complex (Do), North Slope 

lava flow (La) and the debris-avalanche deposits named North Bench (N), Lagoon (L), West Island (W), 

Rocky Point (R), Burr Point (B), and the Grouse Point arm (G) of West Island avalanche. The arrested 

sea cliff cut into North Bench deposit (S1) may continue southwest as the scarp that bounds Northwest 

Lagoon (S2), which is then crossed by the strange scarp (S3) bounding Lagoon debris-avalanche 

deposit. (USGS photograph by Richard Waitt.)
64

35

P

83a

83a

RP

RP

1964?

NB

UD

L

35

83a

83a

RP

RP

1964?

NB

UD

L

Prehistoric Deposits of Late Holocene Age 33

Lagoon deposit has a conspicuous left-lateral levee partly 

buried by a lithic pyroclastic-flow deposit (unit MBplo) to the 

south, which downslope at the coast is capped by tephra B and 

underlain by tephra M. Like Northeast Point debris-avalanche 

deposit, part of the hummocky Lagoon debris-avalanche 

deposit lies outside (south of) this levee, which suggests that 

the avalanche arrived in at least two closely spaced pulses.

Lagoon debris-avalanche deposit apparently buried 

and rode beyond a northeast-trending sea cliff cut into 

older deposits, perhaps a southwest continuation of the sea 

cliff bounding North Bench 4 km to the northeast. Lagoon 

debris-avalanche deposit projects 700 m seaward of this old 

cliff but is itself only moderately cut back and thus geomorphically is fairly young.

Yet the north side of Lagoon debris-avalanche deposit is 

truncated by a strange, sharp and continuous scarp (scarp S3 on 

fig. 29) bounded by a patch of the younger West Island debrisavalanche deposit (see below). The orientation and straightness 

of this scarp and the fact that landward it starts above the older 

wave-cut scarp, are all wrong for it to have been cut back into 

Lagoon debris-avalanche deposit by sea waves. Its form suggests that the huge, fast-moving West Island debris-avalanche 

Figure 30. Oblique aerial photo toward south-southeast showing North Slope lava flow (L), arrested 

sea cliff cut in North Bench debris-avalanche deposit (NB), Rocky Point debris-avalanche deposit

(RP), and 1883 debris-avalanche levee (83a) across and below the lava flow. Most recent domes 

are 1935 (35) and 1964 (64, in clouds). Pinnacles (P) is part of prehistoric summit-dome complex 

beheaded by 1883 landslide. Conspicuous debris-flow levees on midslope (UD) are likely historical 

but cannot be dated. Light-colored, fresh-looking pyroclastic flows and lahars(?) (1964?) are probably 

of 1964 eruption. They have since been buried by similar deposits of 1976 and 1986 eruptions. (USGS 

photograph by Austin Post, 3 September 1966.)
34 Volcanic Processes and Geology of Augustine Volcano, Alaska

remobilized and incorporated the north edge of Lagoon debris, 

the scarp a result of this shearing off.

Almost all of the 400-m-long coastal cliff cut into 

Lagoon deposit is devoid of the M and B tephras. Only the top 

of the highest two hummocks, above altitude 8 m, contain the 

tephras. Something seems to have washed over these coastal 

hummocks and removed the once-present tephras (see below).

Pumiceous Pyroclastic-Flow Deposit

In a coastal gully 300 m west of Augustine Creek, a 

sandy pumiceous pyroclastic-flow deposit (unit CMp, plate1) 

0–3m thick underlies tephra M(?) and overlies the thick, oxidized pumiceous pyroclastic-flow deposit of Southwest pyroclastic fan (unit HCpwp). This younger unit, scarcely eroded, 

pinches out about 0.5 km west of the creek: its overbank spillage was thus limited to the vicinity of the present creek.

The top of a pumiceous, faintly bedded fine sand to silt 

deposit (ash-cloud surge?) crops out sparsely—it is mostly 

covered—just beneath the M tephra along West Lagoon 

(unit CMp). This is perhaps a pyroclastic flow that descended 

a westward gully the same time as the southward flow down 

Augustine Creek.

Lithic Pyroclastic-Flow (or Lahar?) Deposit

A lithic small-bouldery diamict—perhaps a pyroclastic 

flow of lahar (unit CMl, plate 1)—as thick as 2.5 m poured 

down a broad paleoswale west of Southeast Point and lies atop 

the coastal bluff there. Similar flows poured across the Jurassic 

bedrock block and channeled down Middle and East Kamishak 

Creeks to overtop part of South Point debris-avalanche deposit. 

At the mouth of Middle Kamishak Creek the deposit is eroded 

back into a sea cliff that descends east from 50 to 30 m high with 

the slope of the fan surface. These easily eroded south-coast 

deposits must have been extensive before they were cut back into 

sea cliff remnants. They must be a source that longshore drift 

distributed into the older of the extensive beach deposits accreted 

to southwest corner of Augustine Island (unit bedo).

Deposits Between Tephras M and B 

(about 750–400 14C yr B.P.)

Pyroclastic-Flow and Lahar Deposits

Atop a sea cliff now isolated from the sea along the inner 

margin of West Lagoon is a 4-m bed of massive cobbly sand, 

apparently lithic pyroclastic-flow (or lahar?) deposit (unit 

MBplo, plate 1). It is capped by tephra B(?) and at one site 

underlain by tephra M(?). This deposit formerly extended at 

least 300 m seaward, its legacy a lag of numerous boulders in 

West Lagoon as large as 2.5 m. Waves must have eroded the 

deposit back during the M-B period, and then a north-growing 

sand spit enclosed the lagoon and isolated the sea cliff from 

ocean waves.

Upslope at altitudes 40 to 90 m the deposit (unit MBpli) 

is marked by intricately lobate termini, where it is bouldery 

with angular clasts as large as 1.7 m, some reddish, some 

gray, in a granular-sand matrix. High (proximal) parts of this 

deposit are marked by numerous sharp levees containing 

boulders as large as 3.3 m, some of them with smaller boulders piled behind (upslope). The bouldery levees superficially 

resemble the occasional tall ones along the margins of some 

debris-avalanche deposits, but here they are much lower and 

are many. The levees associate with scores of separate small, 

delicate flow lobes, clearly a lithic pyroclastic-flow deposit. 

The deposit adjacent to the levees lacks a hummocky topography even though it’s scarcely infilled by tephra and soil. The 

granular-sand matrix has developed a brown nonclayey soil 

and is capped by Katmai 1912 ash. This coarse inboard facies 

is overlapped from upslope by coarse debris shed during the 

later growth of dome P.

Southeast Beach Debris-Avalanche Deposit

A bouldery diamict exposed in upper part of bluff along 

Southeast Beach (unit MBas, plate 1) is studded with angular 

blocks as large as 2.5 m; lag boulders on the beach are as large as 

6 m, and in the surf zone are as large as 7 m. The diamict is overlain by tephra B and underlain by tephras M and C. These tephras overlie unit HCpe that forms most of bluff. Adjacent lahar or 

pyroclastic-flow deposits (units MBlp and MBp) are smoother 

and contain angular lithic andesite clasts no larger than 2 m.

Deposits Younger than Tephra B 

(younger than about 400 14C yr B.P.)

West Island Debris-Avalanche Deposit

Main Deposit

A diamict of brecciated andesite forms West Island, 

separated from the northwest coast of Augustine Island by 

Northwest Lagoon, 1⁄2 km wide (figs. 29, 31, 32). (Most local 

Figure 31. View west-northwest from high on cone of Augustine 

Volcano showing West Island, one of the largest of Augustine’s 

debris-avalanche deposits. Arrows point to an old sea cliff the 

avalanche overrode. (USGS photograph by Richard Waitt.)
F

P

C

Prehistoric Deposits of Late Holocene Age 35

names in this section are informal. See figure 2 and note7.) 

The deposit is a mixture of angular to very angular reddish to 

gray porphyritic andesite boulders commonly as large as 2–3 m, 

rarely to 5 m, set in a nonsorted brown matrix of finer diamict 

of mixed andesite rock types (fig. 33). This matrix surrounds 

rare irregular convoluted pods of loose, gray, monolithologic 

andesite, apparently highly disaggregated single blocks.

The West Island deposit comprises a central core of 

unmodified conical hummocks as high as 30 m with slopes as 

steep as 40° (fig. 34), surrounded on seaward sides by a wide 

zone of lower hummocks (all unit Bawo, plate 1). A patch of 

this hummocky deposit also lies south of the lagoon, lodged 

against the older Lagoon debris-avalanche deposit (unit CMal), 

whose north side seems sheared by the West Island avalanche 

and incorporated into its deposit there (see above). A second 

hummocky patch lies east of the lagoon, southeast of West 

Island. Indeed the hummocky topography of the mainland 

parts of unit Bawo is indistinguishable from that on West 

Island. Much of the area is thickly furred by alder and scrub 

spruce, far more than any historical deposit.

On the seaward (north) side of West Island a discontinuous sea cliff cut into sporadic hummocks (fig. 33) is fairly 

straight. A continuous field of boulders ranging up to 5 m in 

diameter extends at least as far as 11⁄3 km offshore (unit ob, 

Figure 32. Oblique aerial view southwestward of Augustine Volcano and its offshore West Island. The 

back of Northwest Lagoon is an overridden former coastal sea cliff (C). Most of West Island debris 

avalanche had enough momentum to ride well beyond former shore. Two domes (F and P) below 

summit-dome complex probably fill a former crater scar that must have been evacuated by the great 

West Island landslide (avalanche). (USGS photograph by Richard Waitt.)

plate 1), much of it visible at lowest spring tides and discernible on aerial photographs. Hummocky topography extends 

21⁄2km offshore (fig. 11)—5 km beyond the sea cliff.

The hummocks and intervening lows are overlain by 0 

to 30 cm of humic soil and peat interrupted by five sand ashes 

of which three underlie the Katmai 1912 ash (fig. 35). Coarse 

tephra B is absent from West Island, and thus the hummocky 

Figure 33. Coastal sea cliff exposing interior of debris-avalanche 

hummock on West Island, just off Augustine Island, Alaska. For 

scale note person on the left. (USGS photograph by Richard Waitt.)
Sandy boulder diamict

White very fine sand ash 

with pumice granules

Humus

Humus

Gray silt ash

Humus

Gray ash (very fine sand to silt),

well sorted

Humus

Yellowish-white silt ash

Granular medium sand

Surge

(”blast”)

deposit?

Prehistoric

ashfall

West Island

debris

avalanche

1883

Katmai 1912

1986

1976

Gray ash (very fine sand to silt)

Lithic ash (very coarse sand

to coarse sand)

0

10

20

30

40

DEPTH

(cm)

LITHOLOGY DESCRIPTION AGE

(interpretation)

36 Volcanic Processes and Geology of Augustine Volcano, Alaska

diamict is younger than about 390 yr B.P. (table 2). A radiocarbon age from alder bark at about 370 yr B.P. (table 2) probably 

closely dates the avalanche (Siebert and others, 1995, p. 383).

A broad part of the lower northwest volcano flank upslope 

of Northwest Lagoon is veneered by the coarse West Island 

debris-avalanche deposit (unit Bawi), a nonsorted angular 

coarse rubble containing angular boulders as large as 4 meters. 

This inland facies is distinguished by a separate map symbol 

(plate 1) only because it veneers older topography rather than 

being a thick new deposit. The area of the inland facies is 

mostly covered by dense scrub spruce. In a gully 1.2 km back 

from the lagoon at altitude 85 m, the deposit is underlain by 

35 cm of tephra M (or B?). Lower in same gully a meager soil 

developed on the diamict is capped only by 1883(?) pyroclasticflow deposit and by several layers of sand-sized fall ash.

This inland rubble overlies similar but ambiguously 

exposed bouldery rubble of an older deposit (a west arm of 

North Bench avalanche? or east part of Lagoon avalanche?). 

Into this older diamict a sea cliff had been cut 8 to 18 m high. 

It demarked the northwest coast of Augustine Island just 

before the West Island avalanche and now forms the southeast coast of Northwest lagoon. The overriding West Island 

avalanche fluted the surface of this deposit, especially the sea 

cliff. This erosional fluting normal to the coastwise cliff, and 

the veneer of unit Bawi, smooths the cliff face to a slope 30° 

and less. And the cliff’s top is broadly upwardly convex in 

place of the usual sharp angle. Most of West Island avalanche 

swept more than half a kilometer beyond this old cliff, a gap 

behind now occupied by Northwest Lagoon.

At several sites the tough diamict is immediately overlain 

by a much looser poorly sorted gravelly sand typically 10 to 

30cm thick containing angular clasts of juvenile-looking andesite (fig. 35). Siebert and others (1989) interpret this material 

deposit as the residue of a Mount-St.-Helens-type lithic pyroclastic-surge (some call it “blast”)8

 deposit (for example, Waitt, 

1981)—which the Augustine deposit indeed resembles. It is 

widely but sporadically distributed—on both sides of Northwest 

Lagoon but only rarely on hummocks on the west and north of 

8

 Term “blast” is much misunderstood at Mount St. Helens and could be here. 

“Blast” is in sense of a fierce blast of wind, not an explosion. Thus in the Oxford 

English Dictionary (1971 edition) definition 1, not definition 8 (explosion).

Figure 34. View southeastward of 

southwest side of central core of high 

conical hummocks of West Island 

debris-avalanche deposit. Compare 

with Burr Point hummocks (fig. 43B). 

(USGS photograph by Richard Waitt.)

Figure 35. Stratigraphic section (at field station RBW 88A.110) 

showing succession atop debris-avalanche hummock on 

southwest coast of West Island, an area of strangely flat-topped 

hummocks, evidently eroded by tsunami.
Figure 36. Sketch map showing details of Grouse Point area, 

Augustine Island. N, North Bench debris-avalanche deposit cut back 

into sea cliff, since arrested; Nw, western whaleback part of North 

Bench deposit that divided later West Island flow: G, Grouse Point 

tongue down east swale; and W, lump of West Island flow down 

west swale (both of them apparently sweeping beyond sea cliff cut 

into headlands). B, gullies just upslope from whaleback exposing 

tephra B, thus minimum-limiting age for the North Bench diamict 

but not for the Grouse Point tongue. White area, Augustine deposits 

mostly younger than the units specially depicted (see plate 1).

Grouse Point tongue

Lump of West Island flow

North Beach debris-

 avalanche deposit

Whaleback part of North

 Beach deposit

Gullies exposing tephra B

Former sea cliff

Approximate location of

 covered former sea cliff

EXPLANATION

G

Augustine

volcano

0 1 KM

B

1

N

W

G

B

Nw

N

W

Nw

Cook Inlet

Prehistoric Deposits of Late Holocene Age 37

West Island. This deposit suggests that the large West Island 

landslide(s) unleashed a series of summit explosions—as did the 

Mount St. Helens landslides on 18 May 1980—that swept over 

the new avalanche as a pyroclastic surge.

Grouse Point Tongue

A diamict about Grouse Point (unit Bag, plate 1) needs 

discussion because of earlier interpretations. The deposit is 

hummocky with local relief as high as 7 m and is composed 

of gray to reddish porphyritic andesite whose angular boulders 

are at least as large as 2.5 m. One hummock 9 by 15 m in plan 

seems to consist largely of a single highly shattered andesite 

block. On the beach just seaward, wave-winnowed boulders 

reach 7 m. Clearly this is a debris-avalanche deposit. Overlying 

deposits in upward stratigraphic succession are pyroclastic-flow 

or waterlaid sand, two or three ash layers, and the distinctive 

white Katmai 1912 ash—not unlike stratigraphy overlying the 

outboard main phase (unit Bawo) of West Island.

At lowest tides a field of boulders extends nearly a kilometer seaward of the present beach, and bathymetric contours 

suggest it extends another 0.5 km offshore. This is the area of 

Peter Puget’s boulder-obstructed landing in 1794 (see below). 

The deposit has been eroded back into a nearly continuous, 

sharply curving sea cliff 4 to 7 m high. This geomorphic 

character is similar to that of the coarse and hummocky West 

Island deposit but much less eroded back. Thus it is much 

younger than the South Point and other debris-avalanche 

deposits on the south and east coasts.

Grouse Point deposit crosses part of the sea cliff cut into 

North Bench debris-avalanche deposit (figs. 29, 36). By this 

and its far more hummocky surface texture, Grouse Point 

deposit is geomorphically distinct from North Bench deposit. 

Also contrasting the arrested high sea cliff bounding North 

Bench, Grouse Point is low and juts into the sea. Grouse Point 

deposit thus considerably postdates the North Bench deposit.

Tephra B does not overlie the Grouse Point deposit, but 

it is exposed in several gullies upslope from North Bench 

diamict (unit IMan) (fig. 29). Earlier reports (Begét and 

Kienle, 1992; Siebert and others, 1995) lumped the west part 

of North Bench deposit and the Grouse Point deposit together. 

Because of the tephra in the upslope gullies, they inferred 

(incorrectly) that Grouse Point deposit predates tephra B.

The Grouse Point rubble flowed to the coast down a 

swale east of a broadly whalebacked west part of North Bench 

deposit (figs. 29, 36); a similar flow descended a gully west 

of the whaleback. This western deposit is continuous with the 

West Island debris-avalanche deposit (plate 1). These deposits 

about Grouse Point seem to be a thin east edge of West Island 

debris avalanche. Descending the cone, this east edge struck 

the upslope end of the North Bench whaleback, bifurcated, 

and flowed down the swales on both sides.

Beveled West Island Hummocks

Hummocks on the southwest side of West Island are 

oddly flat topped, apparently beveled down as much as 10m 

and more (fig. 37) and are steeply incised by a network of 

steep-sided channels etched along adjacent lows. Some of the 

hummocks are capped by a coarse winnowed lag of openwork boulders as large as 4 m (fig. 38). Separating some some 

of these boulders are gaping voids as deep as 1.5 m. These 

modified hummocks are evidence of a great rush of water over 

them—probably as West Island debris avalanche plowed at 

high momentum into the sea. And so here is field evidence of 

of a great sea wave (tsunami) being initiated by the speeding 

avalanche. An 1883 tsunami originating from Burr Point could 

not have caused the modification, for the low-level hummocky 

north part of West Island closer to and facing Burr Point is not 

also modified. And at least one of the modified hummocks is 

overlain by three layers of sand ash beneath the 1912 Katmai 

ash as on northern West Island and on Grouse Point (fig. 35). 

Therefore the wave modification occurred about the time of 

emplacement of West Island, not much later.

The two coauthors favor different origins of the hydraulic 

planing. Waitt thinks its cause was the initially stationary sea 
38 Volcanic Processes and Geology of Augustine Volcano, Alaska

catastrophic washing of the underlying surface by sea wave 

was brief—the surface soon again became subaerial to receive 

the surge deposit. A weak brown soil in the pebbly sand is 

8cm thick, atop which lie two or three sand ashes beneath the 

distinctive white-silt Katmai 1912 ash.

Modified Hummocks of Lagoon Avalanche (and North 

Bench Avalanche?)

Tephras M and B clearly overlie Lagoon avalanche back 

from the coast and also the highest two hummocks (above 

8m) at the coast. But just south of West Island avalanche, 

most of the nearly continuous 420-m-long coast exposure of 

Lagoon avalanche that lies below altitude 8 m is devoid of 

the M and B tephras. This absence over so large an area is 

striking. Parts of these low coastal parts of Lagoon debrisavalanche deposit are also strangely capped by many large 

boulders, as if a coarse lag from an episode of erosion. These 

low parts of Lagoon avalanche thus resemble in some ways 

the beveled hummocks on the southwest coast of West Island 

but are far less modified. They too seem to have been swept 

over by some great wash of water at about the time the nearby 

southwestern West Island hummocks were modified. From this 

evidence at Lagoon avalanche—independent of relations on 

West Island—we infer that as the West Island debris avalanche 

plowed into the sea, it raised a great wave of water. Briefly 

it swept energetically up onto the older Lagoon deposit to at 

least 8 meters above tide.

This same wave may have washed over North Bench to 

the east, and thus explain the seemingly truncated overlying 

stratigraphy for a deposit old geomorphically by its straight 

sea cliff evidently eroded far back.

riding back over the top of the swift-flowing debris avalanche 

as it plowed into the sea. This act suddenly displaced water, 

generating the initial tsunami wave, most of the displacement having been by the huge undersea portion of the deposit 

(unit ob offshore of West Island, plate 1). Begét thinks that 

two debris avalanches may compose West Island, the second 

avalanche represented by the central core of high steep hummocks. Thus a less-extensive second catastrophic displacement of seawater washed over and planed off hummocks 

of the first. Both hypotheses imply violent displacement of 

seawater—and initiation of a tsunami.

A few of the beveled hummocks 4 to 5 m above high-tide 

level retain a capping of poorly sorted pebbly sand 5 to 25 cm 

thick, apparently a distal phase of a lithic pyroclastic-surge 

(“blast”) facies9

 (see above). This deposit implies that any 

9

 By its stratigraphic position directly atop the apparently wave-beveled 

eroded hummocks, we contemplated this as a tsunami deposit. But all its 

gravel clasts are angular andesite, and two samples submitted for diatom 

analysis revealed not one marine diatom (Eileen Hemphill-Haley, written 

commun., 1995). We discarded the tsunami-deposit idea.

Figure 37. Oblique aerial photos of oddly planed-off hummocks on 

southwest part of West Island, at Augustine Island, Alaska. The 

modified hummocks and scabland-like channels between them 

are inferred to be erosional beveling by tsunami across this part of 

the West Island debris-avalanche deposit. A, Distant view east. B, 

Near view north. (USGS photographs by Richard Waitt.)

Figure 38. View northeast of southwestmost part of Augustine’s 

West Island showing oddly flattened hummocks cut by scablandlike channels and surficial matrix-free lag of large boulders. View 

is from one flattened hummock across to others. On horizon are 

Chigmit Mountains of the Alaska (or Aleutian) Range exposing 

mostly Mesozoic sedimentary, volcanic, and plutonic rocks. 

(USGS photograph by Richard Waitt.)
Prehistoric Deposits of Late Holocene Age 39

Rocky Point Debris-Avalanche Deposit

East of Grouse Point and west of Burr Point, a coarse 

diamict (unit Bar, plate 1) forms a broad point of land, Rocky 

Point (figs. 29, 30). The deposit contains angular andesite boulders at least as large as 5 m. Its sharply hummocky 

topography has relief of 5–15 m and slopes as steep as 35°. 

At low tide this debris also forms bouldery islands and shoals 

(unit ob) as far as 1.5 km offshore that waves have winnowed 

and beveled. The Rocky Point deposit is about 80 percent covered by scrub alder but lacks the spruce covering parts of West 

Island and Lagoon debris-avalanche deposits and thus seems 

younger than West Island. Upslope from the main deposit 

about Rocky Point are vegetated debris levees as high as 15 m 

that apparently define the two sides of this debris avalanche.

Capping the coarse diamict in upward succession is 

weakly oxidized soil 20 cm thick, an organic layer, a graysilt ash (1883 eruption?), and the white-silt ash from the 

1912 Katmai eruption. The sharp morphology of the hummocks and the irregular, curving sea cliff line are similar to 

that at West Island. But a single sand-ash layer beneath the 

Katmai ash makes this deposit considerably younger than the 

West Island debris-avalanche yet the soil and peat atop the 

avalanche show it to be distinctly older than the Burr Point 

avalanche (see below).

Hummocks on the east side of the Rocky Point diamict 

are coated by ash-cloud deposits of 1976 and 1986 eruptions. 

Airphotos of July 1957 show parts of the deposit also scorched 

and mantled by ash clouds that swept beyond 1883 pyroclastic flows. Because these east-side alder thickets having been 

burned off repeatedly, the hummocks appear as if unvegetated 

youth like the adjacent Burr Point hummocks. This blurred 

vegetative distinction between the Rocky Point and Burr Point 

deposits in the 1980s and early 1990s had been somewhat 

repaired by 2002—by when the alder thicket on the eastmost 

Rocky Point deposit had partly regrown.

The coarse boulders and shoals jut 600 to 1,500 m 

seaward from both the Rocky Point and Burr Point deposits. 

We draw the boundary between the Rocky Point and Burr 

Point avalanches at a sharp reentrant in this offshore bouldery 

debris, where instead lies only sand. Within this reentrant the 

offshore debris is much finer, lacks boulders, and even at lowest spring tide is exposed no more than 200 m offshore (unit 

os, plate 1).

Before the October 1883 landslide that formed the 

present-day rocky, island-studded Burr Point, there had been 

a small harbor on the north flank used by seafaring natives 

in their kayaklike “baidarkas.” Capt. Cullie of the Alaska 

Commercial Company called it the “rocky” boat harbor. Dall 

(1918) wrote: “Formerly there was a boat harbor where the 

Aleut otter-hunters left their kayaks while they watched for 

their prey from the cliffs, but . . . years [before our 1895] visit 

. . . part of the wall of the crater filled the harbor with fragments of lava and masses of ashes.” The pre-1883 coastal 

cliffs on the north-northeast and north were fairly straight but 

bowed inland in the form of a bay (plate 1) suggesting erodedback soft deposits such as pyroclastic flows. The “rocky” area 

with seaward arms protecting a harbor probably was the east 

edge of the Rocky Point debris-avalanche deposit, perhaps in 

the vicinity of the recent shallow pond (plate 1). This pond 

that existed at least since the 1976 eruption was in late January 2006 filled by the one large flow during that eruption (see 

below).

Unassigned Debris-Avalanche Deposits

Several small-volume (less than 0.1 km3) lobes of coarse 

diamict (unit Bau, plate 1) containing boulders commonly as 

large as 6 m, rarely to 15 m, lie on the north flank between 

altitudes 100 and 800 m and between the azimuths of Rocky 

Point and West Island debris-avalanche deposits. They have 

the pristine geomorphic form and lithologic character of 

debris-avalanche deposits but were small and did not reach the 

coast (fig. 30). They lack distinctive overlying stratigraphy but 

Figure 39. Photo showing Bouldery diamict of debris-avalanche 

levee, a deposit of mixed andesite rock types, resting atop 

North Slope lava flow, north flank of Augustine Volcano. (USGS 

photograph by Richard Waitt.)
40 Volcanic Processes and Geology of Augustine Volcano, Alaska

are geomorphically unmodified, clearly younger than deposits 

like North Bench and Lagoon debris-avalanche deposits. They 

may be small, late arms of the Rocky Point and West Island 

deposits, or they may be younger.

North Slope Lava Flow

A lava flow forming a prominent broad spur on the 

middle north flank of Augustine Island (figs. 29, 30) consists 

of massive porphyritic andesite (unit Bln, plate 1). The apex 

of the landform at altitude 650 m apparently marks the flank 

vent 600 m below the present summit—indeed below the base 

of the entire summit-dome complex. The lava flow terminates 

450 m lower at a distance of 1.75 km. The lava flow is usually considered the last part of the 1883 eruption (Kienle and 

Forbes, 1976; Siebert and others, 1987, 1989, 1995; Swanson 

and Kienle, 1988). Kienle and Swanson (1980) had called it 

prehistoric but gave no evidence.

Overlying the upper east side of the lava flow is a sharpcrested ridge at least 640 m long and as thick as 15 m consisting of diamict including many angular fragments as large as 

6 m of dome-rock porphyritic andesite (fig. 39). In any one 

small area of this deposit the andesite boulders are diversely 

black, reddish, and gray, and they are of varying degrees of 

vesicularity. This clearly mixed deposit is a debris-avalanche 

levee, which can be traced downslope to altitude 450 m and 

discontinuously below that. It aligns with a sharp levee well 

defined below altitude 200 m, the west edge of the Burr Point 

debris-avalanche deposit (see below). Thus the 1883 debrisavalanche deposit overlies the lava flow and clearly postdates it.

The Burr Point debris avalanche occurred at or near the 

beginning of the 1883 eruption, and so the lava flow is of a 

pre-1883 eruption. The lava flow apparently is overlain by 

just one coarse diamict and so must postdate the Rocky Point 

debris avalanche, which would have swept over the lava flow 

had it then existed. The lava flow seems to show on Augustine 

Volcano’s north flank in Doroshin’s 1870 sketch (fig. 40A)—

though Siebert and others (1989, 1995) claim it doesn’t show. 

Its azimuth aligned with Rocky Point and its stratigraphic 

level beneath the Burr Point diamict together suggest that the 

lava flow occurred late during an eruption that began with the 

Rocky Point debris avalanche.

Beach and Eolian Deposits

An area of about 1.5 km2 lying 3 to 7 m above sea level on 

the southwest corner of Augustine Island comprises dozens of 

subparallel ridges, a succession of accreted beach and overlying 

eolian deposits (fig. 3, plate 1). The shape of spits—even the 

innermost (oldest) curl landward—tell that longshore currents 

have for more than a millennium been clockwise around the 

south and west of Augustine Island. From geomorphic position alone the landward ridges are much older than seaward 

ones, and to reflect this we divide the whole sequence into 

older, intermediate and younger phases (units bedo, bedi, bedy, 

plate1) separated only by indefinite (wash) contacts. Small 

wave-cut cliffs into this deposit along the south coast and along 

West Lagoon and several pits dug into it show that the ridges 

are mostly of well-sorted medium sand, apparently eolian.

Pits dug into the landward half of these ridges (unit bedo

and part of unit bedi) show tephra M to be 30 cm and more 

thick (plate 2, section RBW 92A.26). These landward ridges 

thus predate 750 yr B.P.; they are mantled by 25 to 70 cm and 

more of younger eolian sand containing reworked tephra M. 

The cut in West Lagoon (exposing unit bedi) shows that overlying tephra M is 3 m of eolian sand capped by Katmai 1912 

ash. The landmost ridges (unit bedo) may well contain tephra 

C beneath tephra M, but when examined even in late summer 

the deposit has been frozen—unexcavatable—below 70 cm.

On the southwestern beach-ridge deposit, the sand ridges 

seaward of a small north-draining estuary seem devoid of 

tephra M and thus accreted since about 750 yr B.P (unit bedy). 

All but several of the most seaward of these eolian ridges 

enclose one or more sand ashes beneath the Katmai 1912 ash 

and thus are prehistoric in age.

The seaward two ridges (west part of unit bedy) have less 

than 40 cm of eolian sand overlying beach deposit of coarse 

sand to pebble gravel. Probably all the ridges originated as 

pebbly-sand beach strand. With time they become more and 

more mantled by eolian sand.

This sandy platform probably reflects a sudden delivery 

of voluminus sand-sized material to the south coast. By far 

the largest such additions from the volcano were “Southwest pyroclastic fan” and “Southeast pyroclastic fan” (units 

HCpwp and HCpe)—both emplaced between 1,400 and 1,000 

years ago (in uncalibrated radiocarbon time). The pumiceous 

pyroclastic-flow deposit exposed as thick as 16 meters along 

the beach cliff west of Augustine Creek (unit HCpwp) is 

fairly loose and easily attacked by coastal surf, and it must 

have at first extended more than a hundred meters into the 

sea. It was an abundant and easy source of sand. Similar 

pyroclastic-flow deposits at Southeast fan (unit HCpe) would 

have been a ready source too, but smaller. Another loose 

pumiceous flow swept into the sea at Augustine Creek (unit 

CMp) later, between about 1,000 and 750 years ago. All 

together, these loose flows gave the south coast—especially 

south-southwest—a large source of sand far more erodible than the coarse and rocky South Point and Long Beach 

debris-avalanche deposits (units HCas and HCal). No new 

large and loose deposit accumulated on the south coast after 

the M tephra fell (about 750 yr B.P.) And so the abundant 

older deposits still being eroded back by storm waves must 

be the main sand source for the whole beach platform on the 

southwest of the island.

Historical Deposits

By “historical” we mean the period since journalkeeping European explorers seeking a Northwest Passage and 
A

1870

Northeast view

B

1909

Northeast view

C

1895

West view

P F

K

1883 D

1904

West view

P F

Historical Deposits 41

Figure 40. Augustine Volcano, Alaska, showing large-scale effects to summit area by 1883 eruption. A, 

Sketch by Doroshin (1870) showing spine, view from northeast. Bump on right horizon seems to be North 

Slope lava flow (unit Bln, plate 1). Compared to later photographs, the northeast shoreline of Augustine 

shown here is less extended: Burr Point deposit does not yet exist. B, Photograph taken 1909 from the 

northeast by John Thwaites. Since 1870 the former spine and part of upper north flank disappeared, 

replaced by a large lava dome. View like Doroshin’s from northeast (Bln, North Slope lava flow). Compared 

to Doroshin’s sketch, the Burr Point deposit now exists. C, Photograph taken July 1895 by C.W. Purington 

from a few miles west of Augustine shows crater scar left by 1883 landslide (debris avalanche) (see 

Becker, 1898, p. 28–30 and plate X). Subsequent 1883 dome is small, wholly within crater and below crater 

rim. F, dome F; P, dome P; K, dome K (Kamishak). D, Photograph taken from west in 1904 by T.W. Stanton 

from just inside West Lagoon. Domes: P, F, 1883. Spine of 1883 dome barely visible.
42 Volcanic Processes and Geology of Augustine Volcano, Alaska

competing for land and fur and trading rights began visiting 

Alaska in 1741—the beginning of written records. First came 

Vitus Bering’s 1741–42 voyage, then other Russian explorers 

such as Grigori Shelikhov entered Cook Inlet by 1785. The 

first such English-language report of Augustine Island was by 

Capt. James Cook on 26 May 1778, who penned: “This Mountain is of a conical figure and of a very considerable height” 

(Beaglehole, 1967). An English voyage under Capt. Nathaniel Porlock and Capt. George Dixon (both had sailed with 

Cook in 1778) explored Cook Inlet between 19 July and 13 

August 1786 and found “smoke” issuing mildly from Iliamna 

(Beresford, 1968 [1789]). French ships came later in 1786, 

Spanish in 1792. George Vancouver (also with Cook in 1778) 

explored between 14 April and 12 May 1794 (Lamb, 1984) 

and found “whitish smoke” (steam) issuing from Iliamna. In 

Vancouver’s lesser ship, Peter Puget sailed around Augustine’s 

south and west on 1 May (“a lofty, uniform, conical mountain 

. . . the same from every point of view”) and next day in the 

launch threaded past hundreds of huge offshore rocks to the 

north-northwest coast. There were many other coastal-Alaska 

explorations besides these though few of them pertinent to 

Cook Inlet (see, for example, Cook and Norris, 1998, chap. 3). 

These various reports are very brief, each covering a few days 

to a couple weeks during which Augustine neither erupted 

nor otherwise evinced recent activity. Iliamna is the only lofty 

peak any of the early explorers call “volcano.”

In the 1790s to 1860s, traders such as Aleksandr Baranov 

tended a few small and intermittent fur-trapping and trading 

posts in Cook inlet. In 1849 Mikhail Teben’kov initiated a 

map of Cook Inlet and coastal provinces eastward. Russians 

probed the coasts and Cook Inlet for gold and coal in the 

1850s and 1860s. After Russia sold Alaska to the United States 

in 1867, George Davidson (fig. 41A) began coastal mapping 

for the U.S. Coast and Geodetic Survey (USCGS). Since then 

explorations and settlement grew gradually more continuous. 

In all these early historical reports, the only reported Augustine eruption was 1812.

1812 Eruption

An obscure report by Russian geologist and mining engineer Petr Doroshin (1870) says that Chernobory (Augustine 

Volcano) “burned” in 1812, and native villagers from across 

the water couldn’t reach the island because flows had entered 

the sea and could rend the skin of the baidarkas (sealskin-clad 

kayaks). This sparse and cryptic information suggests pyroclastic flows carrying boulder-sized pumice swept down the north 

and northeast flanks and into the sea. Such flows could voluminously reach down the short and steep run to water before debris 

avalanche added land to that coast in 1883 (plate1).

Yet we identify on Augustine Island no mappable deposit 

definitely of 1812. At the likely focus of pyroclastic flows, 

north and northeast, five later eruptions also focused debris— 

voluminously so in 1883, 1976, and 1986. The 1883 debris 

avalanche deeply buried that lower volcano flank in coarse 

Figure 41. Photographic portraits of George Davidson. A, in 1850s 

(Bancroft Library, University of California, used by permission). B, 

about 1884 by photographer named “Miley,” from B.A. Colonna 

Album, National Oceanographic and Aeronautics Administration 

(NOAA).

rubble and established a new coast more than 2 km beyond the 

old one. There’s no seeing what lies below these deposits. But 

in our interpretation of some measured sections (plate 2) we 

speculate that a thin ash below the ash layer we identify with 

1883 to be 1812 ash.

1883 Eruption

1883 is the first Augustine eruption documented to some 

extent by contemporaneous written accounts: an unpublished 

logbook of the Alaska Commercial Company post situated 

atop the spit at English Bay, published summaries by Dall 

(1884), Davidson (1884), and Becker (1898), an unpublished 

letter and an unpublished mission report both of 1884, and 

field notes by J.E. Spurr in 1898.

On the 6th of October 1883, Augustine Volcano—or Chernoburoy (variously spelt) as the Russians knew it—generated a 

tsunami and an ash plume experienced from English Bay 85km 

away on the east mainland. The record book of the Alaska 

Commercial Company (1883) at Alexandrovsk (English Bay) 

records various routine data for 6 October 1883. Then this entry:

At this Morning at 8.15 o’clock 4 Tidal Waves flowed 

with a westerly current, one following the other at a 

rate of 30 miles p. hour into the shore, the sea rising 

20 feet above the usual Level. At the same time the 

air became black and foggy, and it began to thunder. 

With this at the same time it began to rain a finely 

Powdered Brimstone Ashes, which lasted for about 10 

Minutes, and which covered all the parts of Land and 

everything to a depth of over 1⁄4 of a inch, clearing up 

at 9 o’clock A.M. Cause of occurrence: Eruption of the 
Historical Deposits 43

active Volcano at the Island of Chonoborough. Rain 

of Ashes commencing again at 11. o’clock A.M. and 

lasting all day.

And for 7 October:

Volcano ejecting fire and heavy black Clouds of 

Smoke all day long.

The geographer William Dall (1884) rushed into print 

summary information derived from George Davidson 

(USCGS) (fig. 41B) and from a Capt. Sands and a Capt. 

Cullie (Alaska Commercial Company) observed from English Bay and then the sea:

Smoke first arose from the peak in August. On the 

morning of Oct. 6 the inhabitants heard a heavy 

report, and saw smoke and flames issuing from the 

summit of the island. The sky became obscured, and 

a few hours later there was a shower of pumice-dust. 

About half-past eight o’clock the same day an earthquake wave, estimated at thirty feet height, rolled in 

upon the shore, deluging the houses on the lowland, 

and washing the boats and canoes from the beach. It 

was followed by others of less height. The ash fell to a 

depth of several inches, and darkness required lamps 

to be lighted. At night flames were seen issuing from 

the summit. After the first disturbances were over, it 

was found that the northern slope of the summit had 

fallen to the level of the . . . shore, and the mountain 

appeared as if split in two. . . . The cleft . . . crosses the 

island from east to west.

George Davidson, who for the USCGS mapped much of 

the Washington-Oregon-California coast in 1850–53 (fig.41A) 

and the Alaska coast in 1867–69, was experienced with 

coastal ship captains and eyewitness reporting. Having been 

partly scooped of his own story by Dall, Davidson (1884) 

gives a more detailed account of Augustine’s effects partly 

derived from “settlers and fishing-parties” at English Bay:

About eight o’clock on the morning of Oct. 6, 1883, 

the weather being beautifully clear, the wind light 

from the south-westward, and the tide at dead low 

water, the settlers and fishing-parties at English 

Harbor heard a heavy report to windward (Augustin bearing south-west by west three-fourths west 

by compass). So clear was the atmosphere that the 

opposite of north-western coast of the inlet was in 

clear view at a distance of more than 60 miles.

When the heavy explosion was heard, vast 

and dense volumes of smoke were seen rolling out 

of the summit of St. Augustin, and moving to the 

north-eastward; and at the same time (according 

to a hunting-party in Kamishak Bay), a column 

of white vapor arose from the sea near the island, 

slowly ascending, and blending with the clouds. 

The sea was also greatly agitated and boiling, making it impossible for boats to land upon or to leave 

the island.

From English Harbor . . . it was noticed that columns of smoke, as they gradually rose, spread over 

the visible heavens, and obscured the sky, doubtless 

under the influence of a higher current (probably 

north or northeast). Fine pumice-dust soon began to 

fall, but gently, some of it very fine, some very soft, 

without grit.

At about twenty‐five minutes past eight A.M., or 

twenty-five minutes after the great eruption, a great 

‘earthquake wave,’ estimated as from twenty‐five to 

thirty feet high, came upon Port Graham [English Bay] like a wall of water. It carried off all 

the fishing‐boats from the point, and deluged the 

houses. This was followed, at intervals of about 

five minutes, by two other large waves, estimated 

at eighteen and fifteen feet; and during the day 

several large and irregular waves came into the 

harbor. The first wave took all the boats into the 

harbor, the receding wave swept them back again 

to the inlet, and they were finally stranded. Fortunately it was low water, or all of the people at the 

settlement must inevitably have been lost. The tides 

rise and fall about fourteen feet.

These earthquake waves were felt at Kadiak 

[Kodiak], where they are doubtless on the register of 

the coast-survey tide-gauge at that place.

An indirect but independent record of the sea waves 

striking the Kenai Peninsula mainland exists in a report of the 

Russian Orthodox priest heading the Kenai mission, Heiromonk Nikita, who after a visit of his southern parishes wrote 

on 28 May 1884:

Influenza Kenai, Ninilchik, Seldovia, Alexandrovsky [English Bay], nearly all children up to 

2 years of age were swept away. At the same time 

this region suffered from innundation caused by the 

eruption of Chernabura volcano, which is about 60 

miles across the straight from Alexandrovsky. The 

innundation so frightened natives of Alexandrovsky 

that they moved their huts to higher ground in one 

night.10

This report is consistent with Davidson’s and Dall’s that 

the largest sea wave was high enough to “deluge the houses” 

at English Bay.

The volcano evidently continued in eruption at least intermittently for weeks or months. Some time after 10 November 

1883 (when in schooner Kodiak Captains Cullie and Sands 

approached Augustine Island), Davidson (1884) includes in 

his account:

The condition of the Island of Augustin or Chenaboura, according to the latest accounts, is this: —

At night, from a distance of fifty or sixty miles, 

flames can be seen issuing from the summit of the 

volcano; and in the day-time vast volumes of smoke 

roll from it.

10 Russian Orthodox church records, Diocese of Alaska, Library of Congress (microfilm copy of Reel 1, Box 400, University of Alaska Anchorage 

Archives).
CS

BP BP

RP

CS CS CS

44 Volcanic Processes and Geology of Mount Augustine, Alaska

Another entry in the Kenai Mission record by Heiromonk 

Nikita on 27 May 1885 reads:

Earthquakes still quite frequent here [at Kenai?] and 

Chernabura is still smoking.

Davidson’s (1884) account includes several obvious 

errors of observation or interpretation, including a Capt. Cullie 

description rendered into a fanciful figure (Davidson, 1884, p. 

188). A chagrined Davidson later tried to rectify this in a letter 

(unpublished) dated 5 November 1884 addressed to Prof. J.E. 

Hilgard, Superintendent of the USCGS. One of Davidson’s 

late-1883 sources, Capt. Cullie of the Alaska Commercial 

Company at English Bay, had sailed past Augustine Island in 

June 1884. As reported in Davidson’s November letter, Capt. 

Cullie saw from the north that:

. . . from the summit a great slide of the mountain 

over half a mile broad had taken place towards the 

rocky boat harbor on the northnorthwestward.11

It appeared as if there had been a great sinking of 

the rocks under the summit leaving a face of wall 

overlooking the slide. Down this had poured the 

lava [sic] and erupted material to the base of the 

mountain and had pushed into the boat harbor and 

filled it up. In the upper part of lava [sic] outflow 

was issuing great volumes of white smoke . . . 

A later record about Augustine’s preeruption “boat 

harbor” exists in the field notes of USGS geologist J.A. Spurr 

(USGS archives):

Oct. 17 (1898)

Trader says here at Katmai that eighteen years ago 

[sic] three families from Kodiak went with families 

and baidarkas to St. Augustine Island to spend the 

winter. Built barabaras on the shore of a bay. The 

11 True azimuth to Burr Point is north to north-northeast. Capt. Cullie probably reports (correctly) magnetic azimuth, 22° west of true azimuth.

mountain began to shake continually and finally they 

took their families off, while they stayed on themselves. Finally the mountain began to shake so violently that they put all their effects in their bairdarkas and started on a stormy day. Scarcely were they 

at the mouth of the bay when an explosion occurred, 

ashes, boulders, and pumice began pouring down 

and the barabaras were buried and the bay filled up 

with debris. At the same time there were many tidal 

waves, so the natives nearly perished with fright, yet 

finally escaped.12

Becker’s (1898) published account mostly reiterates 

information in Davidson (1884) and Dall (1884) about events 

of 6–7 October 1883 but includes a few details from a climb in 

1895 by Becker and his assistant Purington nearly to the summit and to the new dome (Becker, 1898, p. 29):

. . . steam escaped from countless crevices, most 

of them on the inner cone [that is, a new dome] . . . . 

masses were from time to time detached, rolling down 

to the bottom of the deep moat which separates the 

outer crater from the inner cone . . . . The inner cone 

[is] nearly as high as the outer rim.

Burr Point Debris-Avalanche Deposit

The landscape at the north-northeast shore of Augustine 

Island changed dramatically and suddenly on 6 October 1883. 

The deposit about Burr Point is fragmental diamict capped 

by pyroclastic flows (unit 83a, plate 1)—not exactly “lava” 

of Capt. Cullie’s description. The intricately lumpy topography about Burr Point and the almost random distribution of 

12 Native-Alaskan barabaras are temporary plank huts. Baidarkas are woodframed sealskin-clad kayaks for hunting. Historical photographs of them can 

be seen in Cook and Norris (1998, chap. 2).

Figure 42. View of Augustine Volcano from the north showing hummocky deposit about Burr Point (BP) deposited by landslide (debris 

avalanche) of 6 October 1883. Cliffed shoreline (CS) that the 1883 avalanche overrode as it entered the sea. Debris-avalanche deposit is 

in turn overlain by light-colored pyroclastic-flow debris of 1883 (and 1935?). Smaller late-prehistoric Rocky Point avalanche (RP) lies just 

west. Summit point is the then-new 1964 dome. (USGS photograph by Austin Post, 3 September 1966.)
Historical Deposits 45

hummocks with relief as much as 30 m and steep (20–35°) 

sides (figs. 2, 29, 42, 43A, 43B)—the freshest such deposit on 

Augustine Island—resemble the deposit of the great debris 

avalanche off Mount St. Helens on 18 May 1980. In the 

central coastal part, hummocks align in seaward-convex arms 

embracing the sea. This part of the moving flow thus evidently 

organized into discrete lobes just before movement ceased. 

Most of this hummocky debris lies seaward of a preeruption 

sea cliff: most of the avalanche swept into the sea.

Brecciated andesite fragments compose the Burr Point 

hummocks. Individual blocks are commonly as large as 5 m; 

a few intact blocks are as large as 10 m; one coastal slab is 

25m long and 9 m thick. Many of these large blocks are intact 

though much fractured, what Glicken (1996) calls “jig-saw” 

texture. The matrix between large blocks is pulverized andesite, an unsorted cobbly and pebbly sand diamict entirely of 

very angular clasts identical to the large blocks.

Several varieties of porphyritic andesite compose the 

blocks, in many places randomly thrown together—the gray 

with the reddish, the irregularly broken with the columnarly 

jointed. A few blocks as large as 4 m are of sintered vent spatter. A few hummocks incorporate fragile clasts of fall pumice, beds that must have mantled part of the north flank just 

before the 1883 eruption. Though carried to the coast within 

the avalanche, these loose materials were scarcely disrupted. 

Thus the flow was nonturbulent enough to raft some fragile 

blocks without disintegrating and assimilating them. Several 

hummocks 8 to 15 m high near the coast and 1 to 1.5 km back 

from it contain shattered, soft, yellow to brown andesite that 

apparently had been hydrothermally altered within the former 

cone.

A continuous, high sea cliff had been cut back into old 

fragmental debris on the north-northeast of Augustine Island 

(figs. 2 and 42, and plate 1). The cliff was probably cut into 

1812 deposits, but in the seven decades after that eruption 

the sea may well have cut back to a pre-1812 sea cliff carved 

in underlying older deposits. This cliff was overridden and 

smoothed by the 1883 debris avalanche. 

Figure 43. A, Close aerial photograph toward west-northwest showing eastern cluster of 

hummocks of 1883 Burr Point debris avalanche, Augustine Island. Northeast Beach on left. 

B, View northward along eastmost hummocks, Mount Iliamna volcano in distance on skyline; 

compare with West Island hummocks (fig. 34). (USGS photograph by Richard Waitt.)
Katmai 1912 ash capped by peat

and younger sand ash

Deformed mud slabs with exotic pebbles and marine shells

Debris-avalanche deposit

Pyroclastic flow deposit

46 Volcanic Processes and Geology of Augustine Volcano, Alaska

For at least a couple months after the eruption there may 

have been a lagoon between the old sea cliff and the new 

hummocky deposit seaward, and this the origin of Davidson’s 

(1884) and Dall’s (1884) secondhand account (quoted above) 

from Capt. Cullie that the mountain “appeared as if split in 

two,” the new island being separated from the main island by 

an east-west waterway,13 an area filled to above sea level by 

pyroclastic-flow deposits later in the eruption (see below).

The pre-1883 sea cliff remains unmistakable on aerial 

photographs of 1957. It becomes less conspicuous and less 

continuous on post-1976 and especially post-1986 aerial 

photographs as the scarp got more and more buried by the 

thick pyroclastic-flow deposits of these recent eruptions. The 

1976 and 1986 pyroclastic deposits (see below) all but fill the 

former low area that had existed behind the Burr Point debrisavalanche hummocks since the 1883 eruption—a low analogous to Northwest Lagoon behind the West Island hummocky 

avalanche. The present coast of Burr Point is 11⁄4 to 21⁄8 km 

beyond the 1883 sea cliff (plate 1). Offshore islands extend to 

22⁄3 km beyond the sea cliff and submarine hummocky topography (fig. 11) extends 4 km beyond.

A conspicuous straight, sharp-crested lateral levee 3 to 

10m high containing blocks of porphyritic-andesite dome 

rock as large as 6 m marks the west margin of the debrisavalanche path. The most upslope part of the levee overlies 

the North Slope lava flow at altitudes 700 to 450 m (figs. 30, 

39). At altitude 80 m a slightly older levee sticks beyond the 

outside edge of the main levee. This relation suggests the 1883 

debris avalanche had two pulses: a lesser one just before the 

main one. Below altitude 200 m, the east side of the levee is 

partly buried and in low reaches overtopped by pumiceous 

pyroclastic flows of the 1976 and 1986 eruptions.

In contrast to the West Island debris-avalanche deposit, the 

Burr Point deposit is nearly devoid of vegetation, has numerous 

13 Directions in the historical accounts are magnetic rather than true. (At 

one point Davidson [1884] specifies “compass” direction.) To obtain azimuth 

with respect to true meridian, rotate the compass directions and azimuths 

about 22° clockwise.

offshore islands not yet consumed by the sea, and is only locally 

and discontinuously carved back into sea cliffs. Burr Point is 

thus geomorphically much younger than West Island. The hummocky topography about Burr Point is only slightly sharper than 

that at adjacent Rocky Point, but overlying soil on the Rocky 

Point deposit shows it to be older than the Burr Point diamict. 

Both deposits have offshore remnants, but those at Rocky Point 

are wave beveled to rocky shoals rather than remaining as island 

hummocks—further evidence of Rocky Point’s relative antiquity. Many of the central and western hummocks of the Burr 

Point deposit were partly or wholly overtopped by pumiceous 

pyroclastic flows of 1883, 1976, and 1986. Deposits of these 

flows partly bury the southern (upslope) hummocks.

Some of the Burr Point hummocks are overlain by an 

organic soil, which contains the distinctive 1–3 cm white-silt 

ash of the 1912 Katmai eruption. In distal (seaward) places 

this Katmai ash is underlain by a thin organic horizon that 

overlies a gray silt ash, apparently of the 1883 eruption. In 

proximal low areas between hummocks this gray ash is in 

places overlain by 30 to 200 cm and more of massive sand, 

apparently pyroclastic-flow deposit (Kamata and others, 

1991, figs. 4, 5). This fall ash and the overlying pyroclasticflow deposit, both of them overlying and among Burr Point 

hummocks, are evidence that the debris avalanche came early 

and perhaps inaugurated the 1883 Augustine eruption—as the 

Mount St. Helens landslide (debris avalanche) inaugurated that 

18 May 1980 eruption.

When measured in 1988–92 on large coastal boulders of 

the 1883 debris avalanche, the largest thalli of a black-dotted 

pale-yellow-green lichen (Rhizocarpon geographicum?) were 

15–17 mm in intermediate diameter. Fast-growing rugose yellow lichen meanwhile had radiated out 8 to 21 cm in diameter.

Bay-Mud Clasts

Atop the coarse diamict but beneath the gray ashfall 

deposit, the north sides and tops of several coastal avalanche 

hummocks are draped by exotic rounded pebbles of argillite, 

granite, diorite, gabbro, amphibolite, hornfels, vein quartz, 

Figure 44. Schematic sketch of stratigraphic relations at seaside hummocks east of Burr Point. 

Bouldery debris-avalanche deposit is overlain by pyroclastic-flow deposit (light stipple in lows) 

and by Katmai 1912 ash and younger sand ashes interlayered with peat (heavy line). Deformed 

slabs (bedding lines and light stipple) of compact, fissile mud containing marine shells and 

rounded small pebbles of diverse exotic lithology are draped over some hummocks. Marine shells 

(see explanation in text) from these slabs are radiocarbon dated at 6,210 and 7,170 yr B.P. (table 2).
P

F

1935 S

S

P S 1883

1935

1935

K

A

B

Historical Deposits 47

and others. These stones affiliate with discontinuous slabs of 

deformed mud 1⁄2 to 2 m thick and as long as 15 m that locally 

overlie these seaward slopes of coastal hummocks (fig. 44). 

One pebbly-mud clast lies atop a hummock 320 m back from 

the coast. Most of the mud clasts are rich in broken shells 

of several marine species. Radiocarbon analyses of shells 

from two different coastal hummocks yield ages of 6,210 and 

7,170 yr B.P. (table 2). The mud clasts lie as much as 10 to 

13 m above storm high water registered by the upper limit of 

stranded driftwood and fishing floats.

The mud clasts are slabs of bay mud scraped up by the 

debris avalanche as it plowed into offshore sediments. Picture 

a carpenter’s plane shaving off a layer of wood, leaving more 

wood below. Repeated planings bite into deeper and deeper 

wood. The shaved-off strip laid over the foreface of the blade is 

analogous to the bay-mud slabs laid over the foreface of coastal 

hummocks. Leading parts of the debris avalanche, deposited 

below sea level and forming the farthest-offshore islands, must 

have scraped off the surfacemost mud, allowing trailing parts 

of the avalanche to bite into middle and early Holocene mud. 

Modern rocky snow avalanches illustrate that an avalanche 

moving down across snowpack can in this manner scrape off 

the upper layers of snow and lay it atop the moving debris but 

leave most of the snowpack beneath the avalanche (Waitt and 

others, 1994, fig. 14). The shelly mud slabs atop hummocks 

are evidence that the Burr Point avalanche entered the sea fast 

and energetically. The inland hummock capped by shelly mud 

shows that before October 1883 the bay and its Holocene mud 

reached more than 1⁄3 km inland of the present shore.

Evidence of High Water

Davidson (1884) tells of a Native party at Augustine 

when the eruption started: “the sea was greatly agitated and 

boiling, making it impossible for boats to land on or leave the 

island.” In his 1898 fieldnotes Spurr says of a Native party at 

Augustine when the bay on the north-northeast suddenly filled 

with debris “there were many tidal waves.” These minimal 

second- and third-hand accounts show that Augustine’s sudden 

debris generated sea waves, but it’s hard to know their height.

The shelly megaclasts overlying several Burr Point hummocks imply that sea waves reached at least that high—10 to 

13 meters above normal spring-high tide. (Or up to 12 m if we 

subtract from this a 1-m rise of the island above sea level during the 1964 earthquake [Plafker, 1969])

Besides the deformed shelly clasts of mud atop central 

hummocks about Burr Point are discontinuous sand bodies 

containing marine shells on some outer Burr Point hummocks as much as 3 m above spring-high tide (Keskinen and 

Begét, 2006).14 On some outer hummocks isolated driftwood, 

some of it mostly buried by 1883 pyroclastic-flow deposit, 

is stranded 3–5 m above highest modern tides. And some 

hummocks seems oddly planed off by water well above high 

tide. Though only recently and incompletely explored, these 

14 These results are from occasional brief fieldwork in 2002, 2004, 2006, 

and still in progress.

deposits and effects near Burr Point give new evidence of the 

tsunami impelled by the 1883 landslide as it slammed into the 

sea (see below).

Pyroclastic-Flow and Surge Deposits

Overlying and partly filling a moat landward of the Burr 

Point debris-avalanche deposit are a few centimeters of laminated silt ash, overlain by nonsorted and massive pebbly sand 

0 to 2 m and more thick, in turn grading up to a reddish-brown 

granular medium sand 5 to 10 cm thick (unit 83p, plate1). 

Near Burr Point the pebbly-sand phase is cut by vertical pipes 

2 to 30 cm in diameter of intensely oxidized openwork lithic 

pebble gravel with clasts as large as 8 cm. The oxidation is 

orange to brown to yellow coatings on clasts, which suggests 

these structures were hot fumaroles though rootless. The 

source of gas (steam) would have been underlying water or 

wet sediment of a shallow bay that the 1883 avalanche and 

Figure 45. Oblique aerial photos of Augustine Volcano. A, 

toward northeast, showing 1935 dome draped over west rim of 

1883 crater; P, F, S, K identify domes P, F, summit, and Kamishak. 

USGS photograph by Bruce L. Reed, August 1959. B, toward 

east-southeast, showing 1883 and 1935 domes. Arcuate scarp 

behind 1883 dome is scar left by 1883 landslide, which beheaded 

composite summit dome (S) including pinnacles area (P). (USGS 

photograph by Austin Post, 24 August 1960.)
Figure 46. View of Augustine Volcano from southwest showing large steaming dome and 

below it a light-colored fan of debris shed down into “west-southwest swale.” P, F, and S 

identify domes P, F, and compound summit done; 1935, growing 1935 dome. At midflank, K, 

Kamishak dome. On coast, A, Augustine Creek; WK, West Kamishak Creek, Pl, Pleistocene(?) 

landslide block. (Photograph by Kenai Peninsula resident Steve Zawistowski, 9 July 1935.)

P

F

1935

K

S

WK

Pl

A

48 Volcanic Processes and Geology of Augustine Volcano, Alaska

pyroclastic flows had filled. The fumaroles were vigorous 

enough to eject upward the original sand-granule matrix. 

This massive-sand deposit, which overlies the rocky debrisavalanche deposit with no intervening soil, is of a pyroclastic 

flow or surge. The lack of a soil shows that it occurred soon 

after the debris avalanche.

The pyroclastic deposit in places ponded at least a few 

meters deep against the upslope sides of hummocks and 

even large boulders. The deposit thins to nil over the debrisavalanche hummocks. Thus it smooths the original relief of 

the debris-avalanche deposit by irregularly filling lows. The 

sand deposit is thickest in the western and southern part of the 

hummock field and thins to a few centimeters at the eastmost 

coastal hummocks.

Our excavations by small hand shovel are no deeper than 

2 m. In deepest areas inland from Burr Point this material could 

be 6 m or more thick. Judging from the scanty hints in contemporaneous accounts such as Davidson’s (1884 [quoted above]), 

eruptive incandescence and ashclouds on Augustine’s northeast 

flank lasted many weeks and perhaps months. These may have 

included voluminous pyroclastic flows that eventually filled 

a lagoon seaward of the preeruption sea cliff landward of the 

debris-avalanche deposit—a lagoon like that still behind West 

Island. Before it was filled, this lagoon could have been Capt. 

Cullie’s east-west waterway behind a new island (see above).

Rare lithic bouldery deposits on Augustine’s other flanks, as 

on the south shore at the mouth of Augustine Creek, are immediately overlain by—thus shortly predate—the Katmai 1912 ash. 

Perhaps some of these too are 1883 pyroclastic-flow deposit.

Lava Dome

A sizable, broad lava dome grew in the newly evacuated crater near the summit, shown on several photographs of 

Augustine Volcano taken between 1895 and 1960 (figs. 40B,C, 

and D and 45). Becker (1898) called it the “inner cone” of the 

crater. He reported that in 1895 it still emitted steam profusely 

while rocks copiously rolled from its surface. The large gap in 

the pre-1883 rim showing on photos from the west was later 

filled by the 1935 dome. The 1883 dome was incorporated into 

and built over by a succession of later domes—1935, 1964, 

and especially 1976 and 1986 and now 2006. None of the 

primary 1883 dome remains.

Discussion

In the wake of Augustine’s 6 October 1883 eruption, 

Dall (1884) and Davidson (1884 and unpub. 1884 letter) 

reported second-hand information on dramatic changes to 

the volcano, including a collapse of the summit area northward (quoted above). Three decades later (in 1913) Robert F. 

Griggs briefly stopped by the north side of Augustine Island 

and inferred that the Burr Point deposit was a great recent 

landslide. After visiting Katmai 2 years later, he noted how 

similar was the hummocky deposit about Burr Point to that of 

the 1912 Mageik landslide at Katmai (Griggs, 1920, p. 341). 

The slide that formed Burr Point was doubtless the cause of 

the series of extraordinary waves (tsunami) that, according to 

the log of Alaska Commercial Company (1883) and according 

to Davidson (1884) and Dall (1884), swept at least 6 m high 

into English Bay harbor on Kenai Peninsula on the morning of 

6October 1883.

In Davidson’s November 1884 letter, Capt. Cullie’s 

“white smoke” evidently issues from the top of pyroclastic 

flows, not lava, and it reminds of the first images of Katmai 

after the 1912 eruption that inspired the name “Valley of 

Ten Thousand Smokes” (Griggs, 1922). The vertical openwork pipes we note in the shallow subsurface of the 1883 
Figure 47. View south-southeast of summit-dome complex showing 

1976 dome nested below summit. (Photograph by Jürgen Kienle, 27 

July 1984.)

Historical Deposits 49

pyroclastic-flow deposit are consistent with Capt. Cullie’s 

description 8months after the Augustine eruption.

1935 Eruption

Lava Dome

Remnant of a 1935 dome of gray porphyritic andesite 

forms a prominent point on the north-northwest of the summit 

dome complex (unit 35d, plate 1; fig. 16) and a broad dome 

lobe that descends the west-southwest summit cone. The 1935 

dome is identified by several sources: (1) contemporaneous 

shipboard photographs taken by Kenai Peninsula resident 

Steve Zawistowski in July 1935 showing the steaming westsouthwest lobe (fig. 46); (2) USGS oblique aerial photographs 

taken in 1944 by John Reed, in 1959 by Bruce L. Reed, and in 

1960 by Austin Post—all before large changes to the summit 

area during the 1963–64 and 1976 eruptions; and (3) Detterman (1968, 1973), who in 1967 in the field distinguished the 

then-new 1963–64 dome from remnants of older domes. The 

1944, 1959, and 1960 photographs actually show two domes: 

one (1883) inside the 1883 crater, the other (1935) on and 

outside the west rim (fig. 45).

Flank Deposits

High on the southwest flank downslope of the 1935 

dome heads a fan of rubble whose angular andesite dome-rock 

boulders are as large as 6 m (unit 35b, plate 1). This material is 

similar to coarse lithic pyroclastic-flow deposits on the south 

flank of the 1963–64 eruption. Because the southwest fan lies 

directly downslope from the 1935 dome, we interpret it to 

have been emplaced then.

Zawistowski’s July 1935 photographs from a boat off the 

southwest coast show light-colored fresh deposits in westsouthwest swale, clearly recently shed downslope from a 

steaming, active dome (fig. 46). Some of the pyroclastic-flow 

deposits in this broad swale that we map with the 1964 eruption 

may include indistinguishable similar coarse debris from 1935.

1963–64 Eruption

The timing and behavior of an eruption between October 

1963 and August 1964 is described by Detterman (1968), who 

mapped on Augustine Island in 1967 when those effects were 

fresh and unambiguous. The dome and south-flank deposits 

remain well exposed.

Lava Dome

The 1964 eruption built a porphyritic-andesite dome (unit 

64d, plate 1) that crowns an old summit-dome complex that 

had been decapitated to form the 1883 debris avalanche (figs. 

12, 19). The 1963–64 dome flowed only 100 to 150 m down 

the south slope.

Pyroclastic-Flow and Lahar Deposits

The south-southeast flank bears several broad swaths of 

coarse rubble, the largest 2 km long and as wide as 1 km. The 

rubble is nonsorted and angular, generally boulder gravel. 

Clasts are as large as 7 m but generally smaller than 3 m, 

comprising largely dome-rock debris but also 2 to 15 percent 

pumice. The debris displays an intricate series of downslopetrending paired levees as high as 4 m, evidence of emplacement by several pyroclastic flows. All these coarse-rubble 

patches (unit 64p, plate 1) lie within the area of fresh 1964 

deposits mapped by Detterman (1968, fig. 1; 1973).

The 1964 rubble is now heavily but discontinuously 

coated by moss; by 1990 there were well-established groundcreeping blueberry with stems as thick as 0.7 cm and a few 

starts of alder. The deposit is readily distinguishable from 

adjacent 1976 deposits by the coarseness of the 1964 deposit 
50 Volcanic Processes and Geology of Augustine Volcano, Alaska

and its greater vegetation. East of the eastmost inlier exposing 

Pleistocene deposits, remnants of the coarse lithic 1964 flows 

are surrounded and veneered by finer and far more pumiceous 

1976 flows. Because the 1976 flows feather out downslope 

into discontinuous patches, the map boundary (plate 1) 

between 1964 and 1976 deposits is in places arbitrary.

Ballistics

Large angular blocks of gray, slightly vesicular, porphyritic andesite lie scattered about upland surfaces of the middle 

and lower south and southeast volcano flanks, an area of 1964 

ballistic fall denoted by Detterman (1968, fig. 1). At a distance 

of 2.2 km south of the 1964 dome summit, these blocks are 

30cm in diameter.

Computed using variable but low drag coefficients 

developed by Waitt and others (1995) for the 1992 eruptions 

of Mount Spurr volcano, since revised into online program 

“Eject!” by Mastin (2001), minimum ejection velocities for 

the southside Augustine ballistic blocks are between 150 and 

170 m/s. Such velocities are well within the range generated 

by shallow but powerful Vulcanian-type explosions from 

historical eruptions of several other volcanoes.

1976 Eruption

Augustine’s 1976 eruption is better chronicled than earlier ones—in summary by Kienle and Forbes (1976), in detail 

by Johnston (1978, p. 16–28), and the sequence of airborne 

plumes by Kienle and Shaw (1979). Augustine erupted explosively from 22 to 25 January and from 6 to 8 February. During 

the explosive phase, pumiceous pyroclastic flows descended 

several flanks, though most voluminously the north. In middle 

to late February and especially in middle April, the volcano 

built a large summit dome (figs. 47, 48A), which truncated 

and incorporated the 1883 dome and part of the 1935 dome. 

During episodes of dome growth, the steep north edge of the 

dome repeatedly sloughed, descending the north flank as lithic 

pyroclastic flows. The 1976 dome was in turn incorporated by 

the 1986 dome and buried by very coarse 1986 proximal fall.

Johnston (1978, p. 29–35) documented stratigraphy of the 

main north-flank pyroclastic deposits, but before publishing it he 

perished in the Mount St. Helens 1980 eruption. More complete 

stratigraphy in 1988–89 (Kamata and Waitt, 1989; Kamata and 

others, 1991) incorporates the earlier studies as well as material 

culled from Johnston’s unpublished field notes and manuscript 

fragments. The north-flank stratigraphy is known in far more 

detail than can be portrayed by the geologic map (plate 1).

Pyroclastic-Flow, Surge, and Lahar Deposits

During field mapping in 1988–93, degree of vegetation 

readily distinguished pyroclastic-flow deposits of the 1976 eruption low on the volcano flanks from adjacent ones of 1986. The 

1986 flows were scarcely vegetated, only a few grass sprigs and 

Figure 48. Views westward of Augustine Volcano summit area. 

A, showing 1976 dome with scarp and moat separating it from 

1964 and prehistoric dome complex to south. (Photograph by 

Jürgen Kienle, 27 August 1985.) B, Similar view of new 1986 dome 

and smooth-topped fill after 1986 eruption. (Photograph by Betsy 

Yount, 24 August 1987.)

only the smallest blueberry starts. The similar 1976 flows were 

covered as much as 15 percent by grass and contained groundhugging blueberry plants with stems as thick as 0.5 cm. Aerial 

photographs at 1:24,000 scale taken in August 1976 show the 

distribution of pyroclastic flows just after the 1976 eruption. 

Comparing these airphotos to those taken in 1986 and 1990 

further aided our distinguishing 1976 from 1986 flows.

North-flank 1976 pyroclastic flows project beyond the 

north and northeast margins of the covering 1986 pyroclastic 

flows. They comprise two lithologic varieties: pumiceous flows 

that on the northeast were mobile enough to approach and reach 

the sea (unit 76p, plate 1); and overlapping lithic flows later 

shed from the growing dome that spread not quite as far (unit 

76l). Both varieties contain banded (brown to white) pumice, 

especially conspicuous in the pumiceous flows. The pumiceous 

flows have intricately lobate marginal scarps 1.5 to 3 m high. On 

the north-northeast are two sets of overlapping pumiceous flows. 

They contain pumice blocks as large as 1 m but typically 10 to 

50 cm, and they also include many breadcrusted bombs, some 

of them well banded. These pumiceous flows were emplaced in 
0

200

400

600

800

1

5 15 25 seconds

0 2

Time, minutes

Temperature, in degrees Celsius

3

Historical Deposits 51

the early, most explosive phases of the eruption—in late January 

and early February 1976 (Johnston, 1978; Kienle and Forbes, 

1976; Kamata and others, 1991). Airphotos of 1976 show that 

on the north-northwest flank between Burr Point and west of 

Grouse Point, 1976 pyroclastic flows are distributed similarly to 

those that in 1986 spread down these same shallow vales.

Of a once-continuous lithic fan from the 1976 dome, only 

a toe on the north-northeast is unburied by 1986 flows. Details 

of the lithic flows are thus lost. In the main patch of 1976 

flows on the lower north-northeast flank (plate 1), the toes of 

lithic pyroclastic-flow deposits (unit 76l) overlap more-extensive pumiceous ones (unit 76p). These lithic flows contain 

blocks rarely as large as 6 m, commonly as large as 1 m, and 

contain almost no pumice. Most or all of them must have been 

emplaced during growth of the dome beginning in late February but mostly in April 1976, when the rapidly growing hot 

dome repeatedly sloughed flows down the north flank (Kienle 

and Forbes, 1976; Johnston, 1978).

Near Burr Point a very fine sand to silt ash apparently of 

a 1976 pyroclastic surge (Kamata and others, 1991) extends as 

much as 11⁄2 km beyond the limits of 1976 pyroclastic flows. It 

is stratigraphically separated from underlying 1883 pyroclastic-flow deposit by as much as 18 cm of peat that locally contains the Katmai 1912 ash. According to David Johnston’s field 

notes taken at Burr Point in August 1976, Hans-U.Schmincke 

found that window glass of the corrugated-steel research hut 

had been broken outward. Thus this surge, which apparently 

occurred at 02:17 local time on 24 January (Kamata and 

others, 1991, fig. 10), first lofted over a protecting ridge just 

southwest to create a negative pressure outside the hut in its 

lee, popping the windows outward. Then an arm of the surge 

skirting the ridge on the south (Kamata and others, 1991, 

fig.2) ripped off part of the south wall of the hut and scorched 

and burned mattresses inside. An outhouse overturned northward had its bottom burned; the undersides of upturned alder 

roots too were scorched.15 Plastic just inside the research hut’s 

broken-out east window partly melted, but plastic farther back 

in the hut had not. This led Johnston to surmise the heat had 

been unidirectional (through the window) and brief—seconds 

rather than minutes. In a lab oven he melted a plastic papertowel holder to approximately the condition of “droop” of 

the towel holder that had hung just below the window in the 

Burr Point hut (fig. 49). Temperature would have been around 

700°C for 5 seconds, or 500°C for 15 seconds. Heating at 600 

to 500°C for 5 seconds fails to yield the required “droop” in 

the plastic. In 1988 the deposit of this surge still lay a few 

centimeters thick in protected, unswept corners inside the hut. 

It is largely eroded from the surrounding rocky landscape but 

in low areas extends as a discontinuous lamina to the curving 

coast of the bay and thus to an unknown distance offshore.

In a few northside swales the pumiceous pyroclastic 

flows emplaced during the early part of the 1976 eruption mixed with the winter snowpack enough to transform 

15 Some information here culled from David A. Johnston’s 1976–79 field 

notes and manuscript fragments apparently of 1978–79.

downslope into hybrid flows or lahars (included in unit 76p). 

Similarly on the east flank above altitude 120 m in the gully 

that enters the coast at East Point, the pumiceous 1976 deposits 

look like those of normal pyroclastic flows with pumice-rich 

broadly lobate termini 1 to 2 m high, feathering out on vegetated adjacent highs. But where the gully is narrow and sinuous 

in its last 900 m, the flow(s) had momentum to flow nearly 

straight, running 3 m up on sharp bends. The deposit in this 

lower reach contains uncharred wood and apparently no charcoal, evidence that it was cool. The apparently hot flows are 

nearly identical lithologically to the apparently cool ones, and 

the transition one to the other is gradational. The two cannot be 

distinguished systematically, so they are mapped as one unit.

The 1976 pumiceous pyroclastic flows descended swales 

and gullies on other flanks, overriding older fragmental debris 

nearly to the coast. These deposits are similar to the more 

extensive ones on the north flank and are similarly rich in 

banded (brown to white) pumice but generally contain lithic 

blocks only as large as about 2 m. On the southeast flank, 

alder sticks imbedded in the tops of flows are only browned, 

not blackened to charcoal—evidence that while descending 

the cone, the flows cooled by incorporating snow. Some of the 

distal reaches of south-flank 1976 pumiceous pyroclastic-flow 

deposits, as in Augustine Creek, blend downgully into more 

compact, apparently waterlaid deposit. Near the mouth of a 

gully 0.8 km northeast of Southeast Point, such a 1976 lahar 

rode up 8 m high on an outside bend. By routine superelevation methodology (Chow, 1959; Waitt, 1989), this runup 

suggests a flow velocity of at least 12 m/s. Experiments in a 

large flume suggest actual velocity in this circumstance could 

Figure 49. David A. Johnston’s “isodroop” curve illustrating time 

and temperature conditions in a laboratory furnace to reproduce 

the degree of drooping of a plastic paper-towel holder just inside 

a window of the Burr Point research hut that had partly melted 

in a hot blast on 24 January 1976. Open circles depict conditions 

of tests in which degree of melting was less than observed. Data 

imply that temperature was very high if the duration of heat wave 

was short. (Redrawn from illustration for talk [Johnston, 1977] and 

in unpublished manuscript by Johnston of vintage 1978–79.)
Prehistoric

Prehistoric

Prehistoric

Prehistoric

1886 dome

1935

dome

1986 lava flow

1986 fan

1986 fan

Prehistoric

Prehistoric

Prehistoric

Prehistoric

1886 dome

1935

dome

1986 lava flow

1986 fan

1986 fan

52 Volcanic Processes and Geology of Augustine Volcano, Alaska

be slightly higher than by the superelevation equation around a 

bend (Iverson and others, 1994).

1986 Eruption

Augustine Volcano erupted between 27 March and 31 

August 1986. It sent scores of pyroclastic flows down its north 

and northeast flanks while also erupting a new dome in the 

summit area (Yount and others, 1987; Swanson and Kienle, 

1988). The pyroclastic flows ranged from highly pumiceous 

to entirely lithic (disintegrated hot dome rock). As Johnston 

(1978) had inferred of the 1976 eruption, Roman and others (2006) argue on petrologic evidence that mafic magma 

injected from below induced the 1986 eruption.

Lava Dome and Agglutinate

The 1986 dome andesite (unit 86d, plate 1) forms the 

prominent part of summit area viewed from the north (figs.2, 

50, 51).16 As the dome grew it incorporated the large dome 

that had been emplaced there in 1976, which had incorporated 

part of the 1935 dome and all of the 1883 dome. The 1986 

dome thus embodies four successive domes emplaced across 

a century. As the dome grew in 1986, it shed numerous lithic 

16 This discussion written between 1992 and 2003. In January-March 2006 

a new eruption blew out part of the 1986 dome and emplaced a new dome, 

filling the former moat south of 1986 dome and otherwise changing summitarea topography.

pyroclastic flows down the north and northeast flanks. Map 

unit 86d includes a lava tongue that flowed from the north base 

of the dome late in the 1986 eruption. The composite summit 

dome is larger than was the summit just before the 1883 eruption shown by Doroshin’s (1870) sketch (fig. 40A).

A crescent-shaped bench south of 1986 dome is underlain by spatter and blocky, very angular cobble and boulder 

fragments of dome rock laid in numerous beds 1 to 3 m 

thick (figs.48B and 52). They apparently are agglutinate and 

proximal-fall beds (unit 86g). By its morphology the feature 

could be (and has been) mistaken for a truncated remnant of 

1976 dome debris, but Jürgen Kienle’s successive photographs 

of the area show that neither this smooth-surfaced bench nor 

the fragmental deposits composing it existed before 1986. 

They can only have accumulated during that eruption.

Pyroclastic-Flow and Lahar Deposits

The largest pyroclastic flows of 1986 lost at least 1 km in 

altitude (from summit) while extending 4 km to the sea along 

the northeast and north margins of the 1883 debris-avalanche 

deposit. At least three flows reached the sea on the northeast 

in late March (Swanson and Kienle, 1988). These deposits are 

1–3 m thick, lobate, rich in pumice, and contain breadcrust 

bombs. Upslope, they are overlapped by a late-April to lateAugust sequence of less extensive lithic (dome rock) pyroclastic flows.

These voluminous flows, like the similar underlying ones 

of 1976, further infilled a broad low that had existed between 

Figure 50. View southward in then-new 1986 dome and lava-flow tongue at its base. (Photograph 

by Jürgen Kienle, 14 July 1986.)
Historical Deposits 53

into the 1986 pyroclastic-flow deposit, the deposit is punctured 

by vertical fines-free gas-escape pipes. Atop these deposits 

incorporated tree trunks and branches 15 cm through are 

heavily charred, many of them entirely (contrast with twigs 

atop “hybrid flows” below). Between Rocky Point and west of 

Grouse Point, several 1986 pumiceous pyroclastic flows and 

lahars reached the sea or nearly did, overlapping and veneering similarly distributed 1976 pumiceous deposits.

Lithic Pyroclastic Flows

While the dome was growing during the latter part of the 

1986 eruption, parts it repeatedly collapsed to form smallvolume pyroclastic flows of porphyritic andesite (dome rock), 

including blocks as large as 3 to 4 m, some of them compositionally banded as Johnston (1978) described of the similar 

1976 deposits. Lateral levees of some individual flows are 1 

to 3 m high and traceable hundreds of meters upslope. Some 

lithic flows contain as much as 20 percent surface pumice. A 

few of these flows were filmed in progress by Maurice Krafft 

Figure 52. Lithic-fall beds at summit domes of Augustine Volcano 

that bury the former rough-surfaced crescent of the 1976 dome. View 

south from 1986 dome showing bedded debris shed and thrown by 

growing 1986 dome. Background, composite summit dome capped 

by 1964 dome. (Photograph by Jürgen Kienle, 1 July 1988.)

Figure 51. View north-northeast of Augustine’s 1935 (left) and 1986 

domes, from 1964 dome (foreground). Iliamna volcano in distance. 

(USGS photograph by R.B. Waitt, 9 July 1989.)

an old sea cliff and the mass of 1883 debris-avalanche 

hummocks.

Pumiceous Flows

Some 1986 pumiceous pyroclasic flows (unit 86p, 

plate1) on the north flank reached the sea, but others stopped 

well short of the coast with steep margins 1 to 3 m high and 

unchanneled surfaces. These discrete flow fronts show that 

the pumiceous pyroclastic flows numbered at least several. 

Pumice clasts, including some to 1 m and smaller breadcrust 

clasts, concentrate around flow margins and at the surface. At 

depth they are sparse. Burned small logs also mark the termini 

of a few lobes on the north. The flow matrix is brownish 

granular medium sand, poorly sorted. Even the pumiceous 

flows contain in distal reaches lithic clasts as large as 1.5 m; 

where swept from adjacent 1883 debris-avalanche hummocks 

the clasts are as large as 3 m. A few such clasts from these 

hummocks are hydrothermally altered andesite. Along the 

back of Northeast Beach (fig. 2B) where storm waves have cut 
54 Volcanic Processes and Geology of Augustine Volcano, Alaska

(fig. 53) and may be seen in the IAVCEI volcanic-hazards 

video (Krafft, 1991). These numerous flow deposits (unit 86l, 

plate 1) constitute a broad fan leading down from the 1986 

dome. This fan buries most of a similar 1976 fan.

Hybrid Flows and Lahars

Along a lower north-flank swale (4.8 to 5.2 km north of 

Augustine’s summit on azimuth 004), a March 1986 pumiceous pyroclastic-flow deposit merges downslope into an 

area where an underlying 1976 pumiceous flow deposit is 

beveled and channeled 1 to 3 m deep. Numerous large lithic 

boulders are stranded or stacked against each other, in places 

small boulders stacked upslope of a large one (fig. 54). The 

surface is clearly water scoured, and the deposit is winnowed, 

matrix-free large boulders and boulder gravel. The lack of 

matrix between and atop boulders contrasts with recent laharic 

deposits that include abundant sand and fine-gravel matrix—at 

Mount St. Helens (1980–86) in Washington, and at Redoubt 

volcano (1990) and Mount Spurr (1992) in Alaska (Waitt 

and others, 1983; Pierson and Janda, 1994; Waitt and others, 

1994; Waitt, 1995; Pierson and Waitt, 1999). Thus some early 

pumiceous pyroclastic flows at Augustine in 1986 must have 

swiftly melted snow to transform into water-rich floods. These 

Figure 53. View southwest of moving 1986 pyroclastic flow that issued from collapsing lava dome 

(out of view upslope left) flowing down lower Augustine’s north flank near Burr Point. Center figure 

is Jürgen Kienle. On left Maurice Krafft films the show. (Photograph by Katia Krafft, 29 August 1986.) 

The Kraffts—French volcanologists, husband and wife—died in a fierce fiery flow of this type that 

swept off Fugendake (Unzen) volcano, Japan, on 3 June 1991.

floods scoured the 1976 deposits and left small bars of gravel 

and lags of boulders. One of these 1986 scour-and-bar areas 

is overlapped from upslope by a pumiceous steep-margined 

pyroclastic-flow deposit. And so these slightly younger 1986 

pumiceous flows, sweeping mainly over recently emplaced 

pyroclastic-flow deposit, could not entrain and melt much 

snow or cause floods. All these deposits are lumped with unit 

86p (plate 1).

On the east side of the north-flank swale, an extensive 

early 1986 pumiceous flow that nearly reached the sea has 

properties hybrid between pumiceous pyroclastic flow and 

pumiceous lahar. This pumiceous flow (also mapped with unit 

86p) has only centimeters-high margins, low surface slope and 

relief. Discontinuous narrow and shallow channels decorate its 

surface, on which perch delicate willow twigs charred only at 

their resting points. Several broad areas are marked by many 

shallow but wide explosion pits and (or) collapse topography. 

At the center of many of these pits, only 0.3 to 1 m deep, lie 

openwork cobbles, apparently the tops of (rootless) fumarolic 

pipes. Some of these pits are surrounded by a small rim of 

ejected ash. Some of them align north-south along an infilled 

gully. In one sharp gully the pumice is concentrated in small 

waterlaid bars. Such features show that this pyroclastic flow 
Lithic rubble

Dome and lava flows

Lithic pyroclastic flow

Benchmark

153°35’ 153°20’

 59°

 25’ 

59°

20’ 

KAMISHAK

MOUND

Burr Point

Summit dome

Lava flow

COOK

INLET

AUGUSTINE

ISLAND

West

Island L

P

D

P

D

L

EXPLANATION

0 2 4 6 Kilometers

Historical Deposits 55

was relatively thin and cool yet highly mobile, that it collapsed 

and vented by melting of underlying snow, and that free surface water locally rilled and redeposited it. This flow deposit 

terminates atop one of the flood-scoured surfaces described 

just above. Thus the hybrid flow followed and was separate 

from the water flood.

Pyroclastic flows in 1986 also melted snow on other 

flanks of the volcano. Small-volume pumiceous pyroclastic 

flows, some grading into lahars, descended gullies on the 

northwest and east flanks. Distinguishing the deposit of small 

pyroclastic flows from hybrid flows from lahars is difficult. 

Thus these deposits also are mapped with unit 86p.

Occasional Small Events

Besides the definite historical eruptions since 1812, several brief, small events have been reported in newspapers or 

occasional notes (Becker, 1898; The Alaskan (newspaper) 21 

June 1902; The Seward Daily Gateway (newspaper) v. 4, no. 

1, 1908; Cordeiro, 1910; Russell, 1910). None of them suffice 

to qualify as a separate eruption. Several minor events were 

reported in the 15 years after the 1883 eruption. Thus in 1885 

“steam from shore to summit” was a likely symptom of rain or 

snowmelt infiltrating still-hot 1883 pyroclastic-flow deposits that covered the north-northeast flank. And “smoke” or 

“steam” from the summit in 1893 and 1895 were likely lingering effects of the still-hot 1883 dome within the summit crater. 

This is especially clear in Becker’s (1898) brief remarks of his 

1895 climb to the dome. In 1902 there may have been a small 

summit intrusion into the 1883 dome, for increased fumarolic 

exhalations inspired a report of unusual levels of “smoke 

and steam for several months.” A minor burst of molten lava 

occurred in March 1908.

In September-October 1971 billowing fumaroles and a 

report of incandescence followed an earthquake swarm within 

the volcanic cone in late August and early September (Kienle 

and Swanson, 1980, 1985, p. 25–28). And after the 1986 

eruption, a minor burst may have occurred in July 1988. On 

10July 1998 part of the still-warm 1986 dome spine collapsed, melted snow below, and formed small mudflows one 

of which reached the sea (McGimsey and others, 2003).

None of these events were closely observed nor individually lasted long. They are likely persisting effects (in 1885–95 

and 1988–98) of an earlier eruption, or (in 1971) a failed 

eruption yet gaseous herald to the next one. They are analogous to closely monitored behavior at Mount St. Helens after 

the intermittent dome-building eruptions for six years after 

the explosive 1980 eruptions. The last gaseous dome eruption 

came in May 1985 and then small gas-poor dome eruptions in 

May and October 1986. Between December 1989 and February 1992 came at least 17 small but spectacular gas bursts 

from the still-hot dome, several of them spewing ballistics and 

small lithic flows out 1⁄2 kilometer or so, but no new magma 

came to the surface (USGS, Mount St. Helens monthly reports 

[unpublished]). The next true eruption of Mount St. Helens 

began in late September 2004 (Dzurisin and others, 2005).

Figure 55. Sketch map of largest deposits of the January-April 

2006 eruption of Augustine Volcano. P, pyroclastic flow of dense 

pumice on 28 January 2006 that filled former shallow pond at 

lower west edge of 1986 pumiceous pyroclastic flows (plate 1); 

D, new dome and short, steep lava flows from it; L, lithic coarserubble flows that cascaded from growing dome and lava-flow 

fronts. Highly simplified from map compiled by Michelle Coombs. 

Our plate 1 no longer accurately portrays either surface deposits 

or topography in these now-buried areas. See provisional map 

detailing all 2006 deposits by Michelle Coombs in Power and 

others (2006).

Figure 54. View east on lower north flank of Augustine Island 

showing imbricated boulders stacked by 1986 flood. Lack of sandy 

matrix indicates flow was water flood rather than debris flow 

(compare Waitt, 2002, fig. 10). USGS photograph by R.B. Waitt, 23 

June 1988.)
56 Volcanic Processes and Geology of Augustine Volcano, Alaska

Augustine’s occasional small events probably reflect 

similar behavior in the wake of significant eruptions. After 

1986, Augustine’s next true eruption began in January 2006.

2006 Eruption

Small earthquakes increased beneath Augustine Volcano 

through fall 2005, and by mid-December the moat south of the 

1986 dome and a fumarole on the upper south flank steamed 

heavily. From 11 to 17 January 2006 several explosions 

burst from the moat just south of the 1986 dome. The largest 

spewed small flows onto the snowclad upper flanks to several 

azimuths (Power and others, 2006). On 28 January 2006 the 

largest pyroclastic flow, of dense pumice, swept down down to 

the lower north flank to the west edge of the 1986 pyroclastic 

fan and filled the shallow pond there. The flow was hot: as in 

the previous two eruptions, clouds rolling beyond the flow’s 

edge burned off surrounding scrub alder. In winter 2006, a 

dome grew at the summit, filling the subsummit moat north of 

the 1986 dome and covering that dome and draping new stiff 

lava flows down the upper north and northeast flank. These 

and small lithic pyroclastic flows spalling from the lava flows 

expanded until the end of March 2006.

The 2006 pyroclastic flows and lahars were far less 

extensive than during the previous three eruptions. Mapping 

the new deposits is beyond the scope of this report that was 

essentially complete, edited, and revised by fall 2003. Our 

topographic and geologic map (plate 1) remains as earlier 

plotted. On this map, geographic details such as of the summit and of the north-flank pond are as they existed before the 

2006 eruption. A small figure generally outlines deposits on 

the north flank large enough to be future map units (fig. 55). In 

these areas our map (plate 1) shows surface deposits that have 

since been more or less buried by 2006 materials. For details 

and more accurate outlines of all 2006 deposits, see map compiled by Michelle Coombs (Power and others, 2006, fig. 2).

Nonvolcanic Deposits

Talus and Stream Deposits

Once emplaced, volcanic domes cool from the outside, 

leaving abundant very angular fragments of all caliber on 

their steep sides. Especially during thaw and snowmelt in 

late spring to midsummer, this material frequently spalls 

and cascades. And so a talus apron formed around the steep 

base of the 1986 dome, lapping downslope onto the top of 

the 1986 pyroclastic fan. The material is trifling in volume, 

is lithologically identical to the dome-collapse debris during 

eruption, and cannot be distinguished on plate 1. Sometimes 

a relatively large collapse occurs, for instance a piece of the 

1986 dome spine fell on 12 July 1998. As of summer 2003 

the 1986 dome spine remained warm, fumaroles steaming at 

its base. In descending the head of the 1986 fan, collapsing 

dome debris sometimes melts some snowpack there to form a 

small debris-and-water flow down the lower northeast flank. 

From the newly hot 2006 dome and its steep lava flows, such 

processes are likely to continue for years.

Most gullies on Augustine contain small streams that 

flow especially during snowmelt April to July. All but a few 

like southside Augustine Creek dry up by midsummer. Each 

season these streams rework eruptive material and deliver 

some of it to the coast, expanding small fans seaward that are 

then attacked and beaten back by sea waves. These streamcourse tracks are too narrow to distinguish at 1:25,000 scale 

on plate 1.

Eolian Deposits

At the back of most sandy beaches exposed directly to the 

sea and above high-tide level are one or more coastwise ridges 

of loose, well-sorted medium sand, material wind-winnowed 

from the adjacent beach. These eolian deposits (unit e, plate 1) 

ranges from a discontinuous skim only a few decimeters thick 

to ridges a kilometer and more long and as high as 8 m.

Where the seaward side of a tall dune is opened by storm 

waves, internal stratigraphy shows several strata emplaced 

over decades and centuries—made clear by interbeds 1 to 

5cm thick of ash or peat. Thus at Rocky Point (second youngest debris-avalanche deposit) a 113-cm section in back-beach 

dune sand lies atop rounded beach cobbles that in turn overlie 

the wave-beveled top of Rocky Point diamict. The eolian wellsorted medium sand is interrupted by at least seven gray-sand 

ash layers, three peaty layers, and near section’s top the unmistakable Katmai 1912 white-silt ash.

On the southwest coast a dune ridge 8 m high exposes 

tephra M (750 14C yr B.P.) at depth 4 m (section RBW 

91A.138, plate 2). But generally the capping veneer of eolian 

sand thickens gradually inland from the southwest coast from 

a few centimeters to a meter and more atop older and older 

beach ridges. Atop the oldest mapped band (unit bedo, plate

1) 

a pit excavated down into eolian sand reveals tephra B at 

depth 80 cm, that underlain by a lithic ash, and beneath which 

is peat yielding a radiocarbon age of 400±50 yrs BP (table 2) 

(sections RBW 92A.26 and 27, plate 2).

And so the lower, older parts of many eolian deposits are 

clearly prehistoric, but except atop the broad southwest beach 

ridges (units bed) they are far too small and spottily exposed 

to distinguish cartographically.

Beach Deposits

The coast of Augustine Island is a nearly continuous 

beach ranging from bouldery headlands to sandy coves to a 

long sand spit on the southwest part of the island. The geologic map (plate 1) classifies beaches as either rocky or sandy. 

At and above the level of beach deposits at the back of many 

beaches are jams of logs and diverse manmade flotsam. In 

exposed reaches (northeast, east, southeast) storm surf has 

thrust flotsam as much as 2 m above spring-high tide.
Précis of Eruptions 57

The rocky beach deposits (unit br, plate 1) consist mostly 

of cobbles to boulders. Some boulders are as large as 7 m, 

a lag winnowed from adjacent bluffs of debris-avalanche 

deposit. But generally the beach stones are 1⁄4 to 2 m in 

intermediate diameter, most of them submerged at high tide. 

Almost all gravel clasts are of porphyritic andesite and subordinate pumice, but southside beaches also have sandstone 

and shale fragments derived from the nearby Jurassic Naknek 

Formation. Because the boulders and in many places stranded 

large logs defend the sea cliffs against normal waves, erosion 

of the cliffs and new contributions to the beaches occur mainly 

during exceptional winter storms.

Exotic pebbles (granite, granodiorite, quartz diorite, 

gabbro, porphyritic dikerocks, hornfels, quartzite, argillite, 

gneiss, greenstone, vein quartz) are a minor component of fine 

gravel on south beaches downslope from Pleistocene drift. 

Some small exotic stones derive from conglomerate beds 

within Jurassic sandstone. Exotic pebbles lie more sparsely on 

beaches on the east, north, and west sides of the island, though 

only on the south lies an apparent upslope source. The exotic 

pebbles must derive from glacial drift that formerly blanketed all slopes of the volcano. Most of this material has been 

brought down to the shore in Holocene debris avalanches, and 

then over time winnowed out by waves.

The sandy beach deposits (unit bs, plate 1) are loose 

medium sand to pebbly sand, locally pebble and cobble gravel. 

In many places the sandy deposits surround numerous large 

boulders, a lag deposit from storm waves over time attacking 

debris-avalanche, pyroclastic-flow, and laharic deposits. Most 

beach faces slope less than 10°. But where 1986 pyroclastic 

flows are being rapidly eroded back and the local supply of 

sand large as at Northeast beach, the material is very coarse 

sand to granule gravel and beach faces reach 12 to 14°. Those 

like Northeast Beach most exposed to storm waves vary in 

width and steepness from time to time.

Tidal-Flat Deposits and Marsh Deposits

Extensive low-lying irregular flats of muddy sand in 

areas open to tidal inundation but protected from coastal 

surf are floored by gravelly muddy sand (unit t, plate 1) that 

overlies debris-avalanche and other coarse deposits especially 

on Augustine’s west and north shores. Most of these deposits 

have been very gradually winnowed by fairly gentle currents 

and waves—probably especially storm waves during springhigh tides—from adjacent debris-avalanche hummocks and 

pyroclastic-flow deposits.

Among these deposits are pancake-like slabs as large as 

4m diameter and 30 cm thick of gravelly sand that sporadically overlie even last-season’s marsh grasses and sedges. 

These odd bodies can only have been imported by winter’s 

shorefast neap-tide ice that higher spring tides later float and 

raft inland.

Gravelly muddy sand also underlies several freshwater 

marshy areas back from the shoreline, the largest near southeast coast (unit am).

Comparison to Previous Geologic Map

This geologic map of Augustine Island (plate 1)—supported by stratigraphy, chronology, geomorphology, and field 

sedimentology—differs from the previous geologic map 

(Detterman, 1973). That map depicts most surficial deposits, 

except for the clearly late historical, as “Pleistocene” or “Pleistocene and Holocene” in age. Our new map and report show 

that all but a few inliers are late Holocene, younger than about 

2,200 radiocarbon years. The 1973 map also labels extensive 

areas on east, south, and northwest coasts as in-situ “lava 

flows;” our descriptions and map show these to be instead 

large-bouldery debris-avalanche deposits. The one clear lava 

flow on Augustine Island—North Slope lava flow—the 1973 

map calls “volcanic mud.”

The largest changes in implied processes are the number 

and extent of the newly mapped hummocky boulder diamicts 

that we infer to be deposits of catastrophic debris avalanches 

from the summit. By stratigraphy and geomorphology, at 

least 12 late-Holocene debris-avalanche deposits are discernible. The youngest three lie on north coast: Rocky Point is of 

moderate volume, Burr Point and especially West Island rather 

large.

All the large debris-avalanche deposits identified on 

Augustine Island lie at the present coast and most of them 

extend seaward some distance, perhaps kilometers according 

to hummocky topography shown on bathymetric charts. The 

older avalanche deposits have been wave eroded back hundreds of meters into tall sea cliffs.

Précis of Eruptions

Augustine began erupting during the late Pleistocene. 

Late Wisconsin (>20,000 to 15,000 years ago) glacial debris 

directly overlie Mesozoic rocks (Johnston, 1979). But two of 

our radiocarbon dates older than 39,000 years (table 2) suggest 

that some of Augustine’s obscure glacial history predates the 

late Wisconsin.

Several south-flank exposures reveal a sporadic history 

from the Late Wisconsin to the late Holocene (2,500 B.P.), 

occasional explosive eruptions of pumiceous flows and coarse 

pumiceous tephra. Through the late Holocene from 2,200 to 

390 B.P., six eruptions deposited coarse-pumice tephra, averaging one every 300 to 360 years.

Whether most of debris avalanches occurred during or 

between eruptions is unclear. Most stratigraphy of the coarse 

prehistoric tephras lies in spots away from a contemporaneous debris avalanche. Yet tephra G overlies nearly directly 

the uppermost of the East Point avalanches, tephra C immediately overlies the South Point avalanche, and tephra I overlies 

Southeast Point avalanche (fig. 22).

The seven historical eruptions between 1812 and 2006 

have yielded no tephra bed comparable to the six thick and 

coarse prehistoric ones. Yet on Augustine’s north flank, the 
58 Volcanic Processes and Geology of Augustine Volcano, Alaska

1976 and 1986 eruptions built pumiceous-flow fans as thick as 

some of those in prehistoric eruptions on other flanks.

High-Energy Flows From Insular Setting

Pyroclastic Density Currents

Hot pyroclastic density currents (pyroclastic flows and 

pyroclastic surges) move at speeds generally between 10 and 

50 m/s but sometimes exceed 100 m/s. Krafft (1991) shows 

images of moving pyroclastic flows, some from Augustine 

(fig. 53). Pyroclastic surges can move across water. During 

the 1883 Krakatau eruption in Indonesia, large hot pyroclastic 

surges moved as far as 80 km across the sea to coastal Sumatra 

(Verbeek in Simkin and Fiske, 1983; Sigurdsson and others, 

1991; Carey and others, 1996). Smaller pyroclastic surges 

moved several kilometers across water during the eruptions 

in 1902 at Mont Pelée in Martinique and of La Soufrière in 

St. Vincent, and in 1911 and 1965 at Taäl in the Philippines 

(Anderson and Flett, 1903; Moore and others, 1966; Bullard, 

1976; Blong, 1984; Scarth, 2002). A much-shown video of a 

1997 eruption of Montserrat, West Indies, shows a pyroclastic flow or surge moving vigorously from the coast 2 km out 

across the sea surface.

Such a flow beyond the present coast is possible from 

Augustine Volcano, whose numerous eruptions in the past 

2,500 years have included pyroclastic flows and surges. Thick 

pyroclastic-flow deposits about 1,100 years old extend to the 

coast on the southwest and south-southeast, 4 to 7 km from the 

summit (plate 1), now eroded back into sea cliffs. Pyroclasticflow and -surge deposits of the 1883, 1976, and 1986 eruptions 

on the north volcano flank extend to the coast 5.7 km from the 

summit.

Debris Avalanche and Surge (“Blast”)

The landing upon this island was effected with 

some difficulty on the ebbing tide, in consequence of 

the shore being bounded at the distance of a quarter 

of a mile by innumerable large detached rocks, 

through which a passage was found with much labor 

for the boat. Fragments of [such] rock . . . appeared 

to lie off most parts of the island, but no where at so 

great a distance as from its northern shore.

—Peter Puget, Chatham, May 2, 1794 (Vancouver’s 

“Voyage of Discovery”) (Lamb, 1984)

Augustine’s Debris Avalanches

Augustine has shed far more coarse, hummocky avalanches in late Holocene time than have been reported from 

any other of the world’s volcanoes. Augustine’s abundant 

coastal hummocky, boulder diamicts originated by debris 

avalanche from the summit-dome complex (table 3, plate 1). 

These deposits lie at nearly all azimuths, seaward from which 

are wave-winnowed lags of huge boulders exposed at low tide, 

like those on the north-northwest that encumbered Puget’s 

1794 landing.

The volumes of most Augustine debris avalanches are 

difficult to measure because of uncertainties in their extent 

offshore and especially in mean thickness. Siebert and others (1995, p. 387 and fig. 18) estimate that bulk volume 

of Augustine’s debris avalanches would be no larger than 

about 0.5km3, judged from an empirical relation among 

eight volcanoes that debris avalanches tend to be no larger 

than about 10 percent the volume of a cone. The Burr Point 

avalanche deposit is about 1,800 m wide and 3,500 to 4,000 

m long. Its thickness at the former coast is 70 m and less. If 

its average thickness is 40 m, bulk volume of the Burr Point 

debris avalanche beyond the former coast is 0.25 to 0.3 km3. 

The avalanche that formed West Island some 350 years ago 

is about 2,900 m wide and 4,100 m long beyond the former 

coast. If its average thickness is 40 m, the volume of the West 

Island avalanche deposit lying beyond the former coast is 

about 0.5km3. Thus a typical large avalanche might be 0.3 to 

0.4 km3, the largest perhaps 0.5 to 0.6 km3.

Most of the Burr Point avalanche deposit, perhaps 0.25 

km3, lies beyond a preexisting sea cliff (plate 1) marking the 

former coast, conspicuous on aerial photographs before the 

1976 and 1986 eruptions (fig. 42). The part of West Island 

debris avalanche beyond that former coast is perhaps 0.4km3

or more, 11⁄2 to 2 times the volume of the Burr Point debris 

avalanche. And most of West Island avalanche rode far 

seaward of the cliff, indicating its higher speed. The southsouthwestmost hummocks of West Island are planed off 3 to 

12 m above highest spring-tide level and capped by a lag of 

huge boulders (figs. 37, 38), some of the mounds separated 

from each other by scabland-like gashes. These effects seem 

to record a great wave that swept over this area, removing the 

fines and cutting the gashes—probably the seawater being 

displaced as the avalanche surged into and beneath it.

The dimensions and volumes of the many older debrisavalanche deposits are more speculative. At least five of them 

are 4 km or so wide at the coast (plate 1). At least two of them 

overrode sea cliffs and ran seaward. All these coarse deposits 

are themselves now eroded back hundreds of meters into tall 

sea cliffs. Submarine hummocky topography extending far 

offshore (fig. 11) indicates at least some of the thick deposits 

of the east-coastal cliffs had plowed 4 km through seawater. 

Off Augustine’s other coasts such submarine hummocky 

topography extends 1 to 3 km. Thus several of the older 

debris-avalanche deposits must have been as large as the Burr 

Point or West Island avalanches.

A fissure-riddled moving landslide removing a volcano’s 

summit will suddenly depressurize below it any intruding 

magma body and the surrounding hot groundwater system. 

These can explode as at Mount St. Helens in May 1980. This 

ejected gas-rock mixture collapses into a gravitational groundhugging swift-flowing pyroclastic surge—at Mount St. Helens 
5.0

2.0

1.0

0.5

2 5 10

L, horizontal runout, in kilometers

H, vertical drop, in kilometers

50 100 200

H/L 0.18

H/L 0.13

H/L 0.09

H/L 0.04

<1 km3

Augustine West Island

 and Burr Point

≥1 km3

High-Energy Flows From Insular Setting 59

it swept as far as 25 km across the surrounding landscape 

(Waitt, 1981; Moore and Sisson, 1981; Druitt, 1992). The 

1956 landslide off Bezymianny in Kamchatka also released 

such a lateral hot surge (so-called “blast”) (Gorshkov, 1959; 

Bogoyavlenskaya, 1962); the 1888 landslide off Bandai-san 

in Japan may have. Of the 12 eruptions of Augustine in the 

last 2,200 years or so that include a debris avalanche, only one 

(West Island, about 370 yr B.P.) shows evidence of an attending ground surge (figs. 9A, 35).

Debris avalanches are rare events in the history of any 

volcano. Augustine has many ordinary eruptions between 

those that slough a large avalanche. Only one of seven historical eruptions of Augustine included a debris avalanche 

(fig.9B). Attendant lateral surges (“blasts”) are rarer yet.

Mobility and Speed of Volcanic Debris 

Avalanches

Large debris avalanches, whether from volcanic or alpine 

sources, are much noted for their huge runouts from source—

Hsü (1975) called it “excessive travel distance.” Compilations by Siebert and others (1987; 1995, fig. 17) on dozens of 

volcanic debris avalanches show that the ratio of maximum 

vertical fall to maximum horizontal runout (H/L ratio) of 

avalanches smaller than 1 km3 ranges from 0.09 to 0.18 with 

a mean at 0.13 (fig. 56). That is, the toe of a debris avalanche 

typically flows downvalley five to ten times the height lost. 

At Augustine Island, even the steepest bounding H/L ratio 

0.18 puts an avalanche at the coast, and at most azimuths 1 to 

3 km beyond (fig. 11). All of the 11 largest debris-avalanche 

deposits mapped at Augustine (plate 1) extend beyond the 

coast, those older than a millennium having been wave eroded 

far back into sea cliffs. Because in the past 750 years deposits have been most voluminous on the north and west flanks, 

those coasts are built out farther from the summit than are the 

island’s wave-receded east and south coasts.

The mean and limiting H/L ratios for data of debris avalanches of volumes 0.1 to 1.0 km3

 plotted on figure 56 show 

that the limits of Augustine’s avalanches indicated by bathymetry are somewhat short of the mean runout for avalanches 

less than 1 km3 in volume. But this relation is logical: Augustine’s avalanches should decelerate when the bulk density of 

the surrounding medium being displaced jumps three orders of 

magnitude—from air to water—as an avalanche sweeps into 

the sea.

Several of the hummocks about Burr Point draped by 

great slabs of mud containing marine shells (fig. 44) shows 

that the 1883 avalanche entered the sea swiftly and violently. 

But just how fast might this and older debris avalanches have 

been flowing when they struck the sea?

In an early simulation of the Mount St. Helens debris 

avalanche, Voight and others (1983) suggest speeds of 60 

to 80m/s at the base of the cone; a more recent simulation 

suggests speeds as high as 100 to 110 m/s (Sousa and Voight, 

1995, fig. 10). Dynamic simulations of two debris avalanches 

in Japan by Ui and others (1986) indicate speeds as high as 

100 to 150 m/s at the bases of volcanic cones. A dynamic 

simulation for Augustine’s 1883 avalanche suggests speeds 

exceeding 100 m/s at the coast (Siebert and others, 1989, table 

4). But are such high speeds “reasonable” for an Augustine 

debris avalanche at the seacoast?

A few North American debris avalanches have a simple 

geographic means for estimating speed. Where an avalanche 

runs up onto an opposite valley side and converts its kinetic 

energy to altitudinal energy, one measure of its velocity just 

before runup is the conservation-of-energy relation v = 2gh, 

where v is velocity of flow, g is gravitational acceleration, and 

h is height or runup.

At a distance of 7.3 km from the former summit of Mount 

St. Helens, a toe of the 1980 debris avalanche, having crossed 

a valley floor, rode 390 m up over ridgecrests (fig. 57A). If this 

debris were flowing entirely by its own momentum, a frictionless flow converting kinetic energy to altitudinal energy 

would be moving at least 87 m/s to achieve this runup. A small 

tongue of this flow struck Spirit Lake at a distance of 8.6 km 

from the summit. It entered the lake with enough speed and 

volume to raise a tsunami wave as high as 275 m on opposite 

shores (Waitt and Pierson, 1994).

From Plinth Peak at Mount Meager volcano in British 

Columbia near the end of an eruption about 2,400 years ago 

(Stasiuk and others, 1996), a landslide slid into and across the 

Lillooet valley and ran up as much as 458 m on the opposite 

side (fig. 57B) (Evans, 1992; R.B. Waitt and C.J. Hickson, 

1996, unpub. data). By the energy equation above, a frictionless flow entirely under its own momentum needs a velocity as 

high as 95 m/s to achieve this runup. An older landslide ran as 

high as 503 m up the open Salal Creek valley; by the same calculation, it needs a velocity of 99 m/s. Actual velocities would 

be higher, for the calculation ignores energy (thus velocity) 

lost to friction during the runup.

Figure 56. Plot of fall (H) versus runout (L) for volcanic debris 

avalanches (circles) from around the world (Siebert and others, 

1995, fig. 17). Augustine’s West Island avalanche (H/L = 0.148) and 

Burr Point avalanche (H/L = 0.157) plot above (are less mobile 

than) average H/L = 0.13 for their volume class (0.1–1.0 km3

).
45° 2,100 ft

4,000 ft

3.46 Kilometers

Detachment surface

Headscarp

30°

Sea level

1,000

2,000

3,000

Elevation, in feet4,000

Burr Point — NNE

West Island — WNW

Landslide source

0 1 2 3 KM

Maximum

runups

2,000

3,000

4,000

5,000

Elevation, in feet

Landslide 2 Landslide 1

6,000

7,000

Landslide source

0 1 2 3 KM

Path to

Spirit Lake

Maximum

runup

Johnston

Ridge

Spirit Lake

tsunami

Path to

Johnston Ridge

Spirit Lake

Posteruption

Pre-eruption

9,677 ft

8,000

Elevation, in feet

6,000

4,000

2,000

10,000

0 1 2 3 KM

C. Avalanche Lake

D. Augustine

B. Plinth Peak

A. Mount St. Helens

Landslide sources

60 Volcanic Processes and Geology of Augustine Volcano, Alaska

Avalanche Lake (Northwest Territories, Canada) rock 

avalanche, in a fairly uncomplicated field situation, achieved 

an astonishing runup of 640 m (fig. 57C). The simple conservation-of-energy calculation above requires a minimum velocity of 112 m/s just before runup. But because the run-up toe of 

this slide—just 2.5 percent of the whole volume of the slide—

began its journey 500 m below the level it came to rest (Evans 

and others, 1994, fig. 11), this situation shows clearly the runup mass could not have flowed solely by its own momentum. 

It had to have been shoved from behind by higher parts of the 

slide mass that could achieve higher momentum.

So. If a debris avalanche can transfer momentum from 

its head to its toe, the simple relation v = 2gh can yield a 

calculated velocity too high—rather than being a minimum 

velocity as often imagined. The shove-from-behind idea is 

implicit in several dynamic models (Savage and Hutter, 1989, 

Figure 57. Profiles (A, B, C) of large 

landslides from whose runup heights the 

“minimum” velocity (excluding friction) 

at start of runup is calculated [in square 

brackets below] by simple conservationof-energy relation of Chow (1959). These 

values, which do not consider longitudinal 

forces, are almost surely too high (see text). 

D, Profiles of two of Augustine’s youngest 

debris avalanches. For B and C, run-down 

altitude and volumes of landslides (debris 

avalanches) are comparable to D. Rundown altitude and avalanche volume of A

much exceed Augustine’s. A, Two profiles 

of Mount St. Helens, Washington, 18 May 

1980 landslide paths—to South Coldwater 

Creek runup (311 km/hr) and into Spirit Lake 

(dashed line tsunami). B, Profile of two 

Plinth Peak avalanches near Mt. Meager, 

British Columbia: (II) is about 2,360 yr B.P. 

(342 km/hr); (I) is older (356 km/hr). C, Profile 

of nonvolcanic avalanche at Avalanche 

Lake, North West Territories (Evans and 

others, 1994, fig. 6) (403 km/hr). D, Profiles 

of Augustine: summit north-northeastward 

through Burr Point, and summit westnorthwestward through West Island.

1991; Iverson and Denlinger, 2001; Denlinger and Iverson, 

2001; McDougall and Hungr, 2003). To the Avalanche Lake 

slide, Hungr applied dynamic simulations that include longitudinal forces, a push from behind (Evans and others, 1994, 

fig. 17). Calculations from centers of mass before and after 

the slide yield maximum velocity of 80 m/s—or 71 percent 

of the “minimum” velocity from the relation v = 2gh. The 

exercise for Avalanche Lake provides an arithmetic means 

to down-scale the high velocities for the volcanic avalanches 

cited above. Thus a velocity for the Mount St. Helens slide 

just before runup—if assisted by a push from behind—reduces 

from 87 m/s to about 61 to 65 m/s. The two Plinth Peak 

avalanches thus reduce to about 67 and 70 m/s. By analogy to 

these examples, speeds at which Augustine debris avalanche 

(fig. 57D) enters seawater scales back to between 60 and 80 

m/s (215 to 290 km/hr). Whatever the velocity a slide enters 
Mountain, volcano, 

or bay Region Year Slide volume (km3

)

Wave runup 

height (m)

Distance 

away (km) Fatalities Reference 

Nonvolcanic

Mayuyama Japan 1741 0.54 22 14,524 Aida (1975), Ui and others (1986), Bryant (2001) Off Mayuy

erupting as a volc

Goldau Switzerland 1806 .02 5–15 1–4 many Eisbacher and Clague (1984, p. 156–159) Large slide 

Fjords Norway 1660– 1967 .001–.015 20 5–50 240 Jørstad (1968) Confined b

10 as ro

Loen Lake Norway 1905 1936 .00035 .001 1–40.5 3–74 1–7 1–7 6173 Bjerrum and Jørstad (1968); Slingerland and Voight (1979); Fritz (2002)

Scotch Cap Alaska 1946 ? 35 100+? 5 Lander (1996); Walter Dudley, oral commun., 2000 Earthquak

submarilarge tsu

Lituya Bay Alaska 1958 10–525 0 Miller (1960) Steep fall t

of sever

Vaiont Italy 1963 35 Kiersch (1964) Steep slide 

Prince William Sound 

area (many separate slides) Alaska 1964 various 20–52 Plafker and others (1969) Many earth

slides; t

Kenai Lake Alaska 1964 .000004 2–22 1–4 0 McCullough (1966) Earthquak

fronts in 

Yanahuin Lake Peru 1971 .0001 5–30 0.5 600 Fritz (2002)

Skagway Alaska 1994 11 1.5 Kulikov and others (1996); Plafker and others (2000)

Bismark Sea Papua New Guinea 1998 3–15 20–30 >2,200 Tappin and others (1999) Earthquak

slide, wh

Volcanic

Komagatake Japan 1640 0.3 8.5 35–50 700 Nishimura and Satake (1993)

Oshima-Oshima Japan 1741 0.4 60–100 1,475 Ui and others (1986)Mayuyama Japan 1792 (See aboveRuang Indonesia 1871 25 Padang (1959), Blong (1984)Krakatau Indonesia 1883 5–36 36–120 35,500 (tsunami) Verbeek in Simkin and Fiske (1983), Latter (1981), Francis (1985); Carey and others (1996); Winchester (2003) Huge pyro

and coll

Augustine Alaska 1883 0.35 6 90 None? Alaska Commercial Co. (1883); Davidson (1884) Harbor wa

ably exa

Ritter Island Melanesia 1888 5 7–15 25–330 Many Cooke (1981), Johnson (1987), Ward and Day (2003), Silver and others (2005)Palaweh Indonesia 1928 <0.1 5–10 ~200 Latter (1981)

Harimkotan Kurile Is. 1933 <0.4 20 30 2 Belousov and Belousova (1996); A. Belousov, oral commun. (2007)

Ili Werung Indonesia 1979 0.05 9 540 Blong (1984)Mount St. Helens Washington, USA 1980 >250 2 0 Waitt and Pierson (1994) Large land

Vulcano Italy 1988 .0002 1–2 0.5–2 0 Tinti and others (1999) Very small 

Stromboli Italy 2002 .02 .006 6–10 2–6 0 Tinti and others (2005, 2006) Small land

coastal d

Table 4. Some historical tsunami caused by nonvolcanic landslides and by volcanic debris avalanches.
St. Paul, Kodiak Island

October 6, 1883

Local time (152°25’W)

+10:10 for GMT

Tsunami arrival

11:00

Air wave arrival

8:31

Pressure front

0

0.4

0.8

1.2

Height, in meters1.6

2.0

2.4

7 8 9 10 11 12

Time, in hours

13 14 15 16 17

T0 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11

Time

Wave height

Sea

level

Tide

gage

Actual

wave

Recorded

wave

62 Volcanic Processes and Geology of Augustine Volcano, Alaska

water, it slows to nil as it flows another 2 km or more against 

the resisting sea.

Tsunami

At least twelve debris avalanches off Augustine Volcano 

during the past about 2,200 years entered the sea (table 3, 

plate1); that in 1883 (Burr Point) did so swiftly enough to 

generate a witnessed tsunami. Many other historical debris 

avalanches off alpine mountains or volcanoes have run into 

lakes or the sea fast enough to generate damaging waves along 

distant shorelines (table 4).

Augustine Island, 6 October 1883

Contemporary accounts (reproduced above in section 

“1883 Eruption”) document that Augustine Volcano generated 

a tsunami experienced at English Bay. The unpublished later 

letter of November 1884 from Davidson to the Superintendent 

of U.S. Coast and Geodetic Survey includes a verbal picture 

from Capt. Cullie of Alaska Commercial Company as he 

sailed close around Augustine Island in June 1884. Thus the 

1883 landslide off Augustine left a semicircular summit crater 

and a hummocky deposit spread about Augustine’s north 

shore—new Burr Point (figs. 40, 42, 43).

An instrumental record of the 6 October 1883 tsunami 

exists: a tide-gauge drum record (marigram) from St. Paul 

(Kodiak) harbor on Kodiak Island. To understand characteristics of such records, reader is referred to general discussions 

of tide-gauge records of tsunami (Lander and Lockridge, 

1989, p. 1–15; Lander and others, 1993, p. 1–9; Lander, 1996, 

p.1–9 and 143). Thus for tide gauges to perform their primary function of precisely recording very low-frequency tidal 

fluctuations, they have but a small inlet hole into a stilling well, 

a design that filters from the record high-frequency “noise” 

like wind waves and boat wakes—and so also tsunami. These 

stilling effects cause a slight time lag between the actual arrival 

of a wave at the gauge and its registry by the pen recorder 

(fig.58). Also the recorded range may be far smaller than 

actual range for a tsunami wave, owing to these same damping 

of high-frequency effects by the tide gauge. Once a tsunami 

enters a confined harbor like Kodiak, the gauge may record 

standing waves (seiches) sloshing about inside the harbor—

aside from further waves of a tsunami train still invading the 

harbor. And for tsunami initiated by volcanic eruption, explosions broadcast pressure waves that may couple with the water 

surface to produce small “air-wave” pseudotsunami long ahead 

of true tsunami traveling as water waves. Such air-wave excitation and slower moving true tsunami are much analyzed for the 

Krakatau eruption in Indonesia in late August 1883 (Ewing and 

Press, 1955; Harkrider and Press, 1967; Yokoyama, 1981; Latter, 1981; Francis, 1985; Winchester, 2003).

The Kodiak marigram of 6 October 1883 shows a tidal 

oscillation of amplitude 1.8 m. Superimposed on it are two 

high-frequency signals, interpreted by Lander (1996, p. 49) as 

air-wave arrival followed by tsunami arrival (fig. 59). The gauge 

registers the air wave at 08:31, the sea wave (tsunami) at 11:00. 

A 21⁄2-hour travel time of sea wave from Augustine to Kodiak 

harbor is consistent with an approximately 2-hour travel time 

of a prediction model run in 1995 for a north-Augustine source 

Figure 58. Schematic sketch illustrating how the stilling well in 

tide gauges causes (1) a decrease in recorded wave height and 

(2) a delay in recorded peak height from the actual wave. Redrawn 

from Lander and Lockridge (1989, fig. 6), Lander and others (1993, 

fig. 31), and Lander (1996, fig. 47).

Figure 59. Tide-gauge marigram from St. Paul (Kodiak), Alaska 

on 6 October 1883 showing arrivals of wave train of air wave and 

of tsunami from Augustine, both superimposed on a tidal cycle of 

1.8-m amplitude. Marigram retrieved from U.S. Coast and Geodetic 

Survey archives by James F. Lander (see Lander, 1996, p. 49 and 

fig. 16) (see text for explanation). The 1883 tide gauge probably was 

at town pier at Kodiak (St. Paul Harbor at about longitude 152°25’ 

W). Time is local sun time, before advent of global time zones in 

1884. For GMT add about 10:10 hours. First motion in tide gauge for 

air-pressure wave (that depresses sea surface) is logically negative 

but for tsunami (that raises sea surface) is positive.
202.7 204.7 206.7 208.7 210.7

60.4

59.4

58.4

57.4

56.4

Homer

Kodiak

North Latitude

East Longitude

2

2

2.5

1

0.5

Augustine Island

High-Energy Flows From Insular Setting 63

by Paul Whitmore of Alaska Tsunami Warning Center (fig. 60) 

(Lander, 1996, fig. 15). The apparent first arrival of the Augustine air wave at Kodiak harbor is negative (fig. 59), as expected 

of a pressure wave depressing the sea surface. The apparent first 

arrival of the true tsunami wave is positive, as expected of a 

wave initiated by landslide raising the sea surface. The regular 

wave train after this first arrival may be partly seiching of that 

wave within Kodiak harbor. The maximum range of the sea 

wave scaled from the marigram is 19 to 20 cm. The actual range 

may well have been higher, the record damped by the gauge’s 

small intake hole and its stilling well. A similar pattern of air 

waves far ahead of tsunami is shown by tide-gauge records of 

1883 Krakatau effects (Latter, 1981, fig. 3).

Analysis of 6 October 1883 Records

The air wave of the Kodiak marigram must record an 

explosive eruption. Traveling at sound speed (about 331m/s), 

the air wave covers the 185 km air distance in about 9.3 minutes. Its recorded arrival at 08:31 local time implies initiation 

at Augustine at about 08:22 (fig. 61)—or perhaps a bit earlier 

if one assumes a short delay for the wave to transmit through 

the gauge’s aperture and stilling well to the recorder. In this 

era before the adoption in 1884 of global time zones, local 

time is “sun time” (Lander, and Lockridge, 1989, p. 8; see 

popular discussion by Sobel, 1995, p. 5 and 167–168). Maintained by the U.S. Coast and Geodetic Survey, the St. Paul tide 

gauge’s sun-time clock probably was accurately set. English 

Bay lies 30 minutes of longitude east of St. Paul (Kodiak) 

harbor: English Bay sun time is 2 minutes ahead of Kodiak 

sun time.

Initiation of the marigram’s primary air wave by explosion at Augustine at 08:22 or slightly earlier is crudely 

consistent with Davidson’s report of eyewitnesses at English 

Bay that the first heavy report from Augustine was at about 

08:00. Traveling at sound speed, an air wave covers the 85 km 

Figure 60. Tsunami travel times (in hours) from north flank of Augustine Island plotted 

in 1995 by Paul Whitmore of West Coast/Alaska Tsunami Warning Center in Palmer, 

Alaska. Contour interval, 6 minutes; index contours (heavy solid lines) labeled in hours. 

The fractional values for North Latitude and East Longitide are artifacts of the plotting 

routine. (Retraced from figure 15 in Lander [1996] but cropped on east and south; used by 

permission of Paul Whitmore).
×

×

×

× ×

Local time, 6 October 1883

Distance from Augustine summit vent, in kilometers

Air wave,

Kodiak marigram

A: “Rain of ashes commencing again,”

 “Lasts all day.’

Sound speed

(331 m/s)

English Bay, 85 km from Augustine

Kodiak, 185 km from Augustine

5:00 5:15 5:30 5:45 6:00 7:15 7:30 7:45 8:00 8:15 8:30 8:45 10:45 11:00

0

100

200

Tsunami originates

north of vent

D: “Heavy report to windward”

A: “Tidal wave and thunder”

D: “Earthquake wave”

D: Davidson (1884)

A: Alaska Commercial Company log

English Bay suntime

Kodiak time

Inferred eruption time

for ash to fall at

English Bay at 8:15

Ash-plume speed

 85 km/3 hrs = 7.9 m/s

Mean tsunami

speed (24.3 m/s)

Ash plume (7.9 m/s)

64 Volcanic Processes and Geology of Augustine Volcano, Alaska

to English Bay in about 4.3 minutes. Subtracting this and the 

2-minute difference in sun time, Davidson’s “heavy report to 

windward” would begin about 07:53 Kodiak time, about 29 

minutes before the airwave recorded by the marigram (figs. 

60, 61)—if Davidson’s times are correct. By the same arithmetic the 08:15 of the Alaska Commercial Company (A.C.C.) log 

when “it began to thunder” would have initiated at Augustine 

about 08:08 Kodiak time, or about 15 minutes ahead of the 

air wave of the Kodiak marigram. Perhaps there were a few 

Augustine explosions, variously remembered and reported at 

English Bay.

Time between the first explosion of 6 October 1883 

reportedly seen and heard at English Bay at about 08:00 and 

then tsunami at about 08:15 (by A.C.C. log) or about 08:25 

(by Davidson’s account) is far too short for the visual event 

to have occurred at the time the tsunami originated (tsunami 

travel time discussed below). Figure 61 shows that a tsunami 

would have been initiated at about 07:17 or 07:27 (Kodiak 

time) to have arrived at English Bay at the 08:15 or 08:25 

(English Bay time). Yet the May 1980 Mount St. Helens eruption suggests an explanation. After its initial landslides (in 

that case triggering a spectacular surge cloud and thus also an 

immense upward mushroom cloud), emission from the Mount 

St. Helens vent was feeble for half an hour. Only gradually 

did it form a vigorous high jet visible from far away (Criswell, 

1987). Stratigraphy on Augustine Island shows that the 1883 

Burr Point landslide did not trigger a directed surge (“blast”) 

that would be visible from the mainland. The landslide must 

have occurred unseen half an hour to an hour before the beginning of observed venting. During Augustine’s 1986 eruption, 

explosive activity visible from a distance too waxed only 

gradually (Power, 1988).

During an explosive eruption at Augustine, an ashcloud 

takes far longer to drift the 85 km to English Bay than it takes 

a sound wave to travel the same distance. Davidson’s (1884) 

“heavy report to windward” and “vast and dense volumes of 

Figure 61. Timing of contemporary records of initial events in morning 6 October 1883 eruption of Augustine Volcano. By longitudecalculated sun time (before global time zones established in 1884), English Bay time (•) is 2 minutes ahead of Kodiak time (x). The plotted 

points (• and x) are three eyewitness observations at English Bay and the first arrival of the air wave of the Kodiak marigram (fig. 59). 

English Bay time (•) is also plotted in Kodiak time (x). Sound speed (331 m/s) and mean tsunami speed through an average 60 m water 

depth (24.3 m/s) are projected from these points back in time to Augustine Island to discover approximate initiation times.

Explosion-like sounds reported at English Bay 85 km away would have originated at Augustine between 07:55 and 08:11 by English 

Bay time—or between 07:53 and 08:09 by Kodiak time. The tsunami observed at English Bay would have been underway from Augustine 

earlier, between 07:15 and 07:26—it had initiated at Augustine’s north shore some 2 to 1 hour before the explosion(s) from Augustine’s 

vent were heard at English Bay.

The ashfall reported at 11:00 (by Alaska Commercial Company [A.C.C.] log, 1883) seemingly results from the sound and sight of 

eruption at about 08:00 (by Davidson, 1884)—a very plausible time interval for ash to drift the 85 km from volcano to English Bay. And so 

this same 3-hour time interval is projected back from the approximate 08:15 start of ashfall at English Bay (by A.C.C. log) to infer time of 

first 6 October 1883 eruption of Augustine at about 05:00 a.m.
Neap high

High 6 October 1883

Spring high

Mean low water

14

12

10

8

6

4

2

0 0

5

10

15

20

25

30

35

40

45

HAZARD

KODIAK

(tide tables)

SELDOVIA

(tide tables)

ENGLISH BAY

(reports of 6 October 1883)

A.C.C.

post

30’

25’

20’

20’

20’

18’

15’

Height above sea level (mean low), in feet

Height above sea level (mean low), in meters

High-Energy Flows From Insular Setting 65

smoke . . . rolling out of the summit of St. Augustin . . . northeastward” at about 08:00 must be the cause of the A.C.C. 

logbook entry: “Rain of Ashes commencing again at 11. 

o’clock A.M. . . .”—thus about 3 hours for the eruption cloud 

to drift 85 km east-northeast to English Bay (fig. 60).17 The 

10-minute ashfall at English Bay at 08:15 a.m. or so (A.C.C. 

account) suggests an earlier eruption from Augustine at 

roughly 05:15—two hours or so before the landslide initiates 

the tsunami (fig. 60).

The small amplitude of the 6 October 1883 tsunami 

disturbance to the tidal cycle at St. Paul (Kodiak) is consistent 

with the sea distance of at least 250 km from Burr Point to 

Kodiak, the tsunami waves arriving via refracted and reflected 

paths into a bay on Kodiak Island’s far side and the tide gauge 

17 Ash plumes ejected during Augustine’s 2006 eruptions typically took 2 to 

4 hours to reach inhabited areas of Kenai Peninsula to the east and northeast 

(Alaska Volcano Observatory at website http://www.avo.alaska.edu; Power 

and others, 2006; Begét and others, 2007).

itself wave-damped. The arrival of an air wave far ahead of 

water waves at Kodiak on 6 October 1883 resembles patterns 

of the far more dramatic sea-surface effects from the eruption 

of Krakatau in Indonesia six weeks earlier as recorded by tide 

gauges in the southwest Pacific (Latter, 1981, fig. 3).

By 1995 tide tables, tides at Seldovia 14 km north of English Bay rise and fall as much as 23.8 ft (7.3 m) for spring tide 

and as little as 5.3 ft (1.6 m) for neap tide. The average monthly 

rise and fall is thus about 14.5 ft (4.4 m), approximately the 

figure stated by Davidson (1884) for tidal range (fig. 62). At 

Kodiak the tidal range varies between 3.0 and 0.9m. The 1.8-m 

tidal range of the Kodiak marigram indicates an intermediate 

tidal range for 6 October 1883. Thus Davidson’s “fourteen feet” 

(4.3 m) for tidal range approximately applies to English Bay for 

the intermediate-range tide of 6 October 1883. A 6-m tsunami 

(“20 feet” of A.C.C. log) occurring at low tide (according to 

Davidson, 1884) would have risen about to the limit of 1883 

spring high tides at English Bay (fig. 62). A 7-m tsunami would 

have risen a little above spring high tide. That would account 

for the “deluging the houses” and “moving the huts” in the 

contemporary accounts by Dall (1884), Davidson (1884), and 

Heiromonk Nikita (see “1883 Eruption”).

The Alaska Commercial Company’s post was on the 

spit at English Bay—renamed in 1991 to Nanwalek, meaning 

“place by lagoon.” Since 1955 the site of the former post has 

been an airport runway. It sits about 6 m above mean lower 

low water. But this area subsided about 1.1 m with respect to 

sea level in the 1964 earthquake (Plafker, 1969). So in 1883 

the Alaska Commercial Company post stood 7 m or so above 

low water, a little above the limit of spring high tide. The 

post’s log entries for 6 October 1883 and succeeding days do 

not suggest that the post and its trading goods were at all inundated by sea waves—damage that would have been important 

enough to the post’s commerce to show in its meticulous 

logbook. The absence of reported damage accords with the 

estimate in the Company log of a “20 feet above usual level” 

for tsunami height. Dall’s (1884) “thirty feet height” and 

Davidson’s (1884) wave heights of “25 to 30 feet” (8 to 9 m) 

probably would have reached the trading post enough to cause 

damage, and therefore these values seem a little too high. But 

the four contemporaneous accounts (including Nikita’s) are 

entirely consistent with a tsunami rise of 20 to 23 ft (6 to 7 m).

Might a great earthquake have independently generated 

the 1883 tsunami? Instrumental detection of earthquakes in 

Alaska did not begin until 1898, but Davies and others (1981) 

list earlier historical events reported in newspapers, diaries, 

and other local sources for the Kodiak-Shumagin region. The 

years of largest shocks are 1788, 1792, 1844, 1847, 1854, 

1868, 1880, 1899, 1900, and 1903. Other detailed research of 

written records (Soloviev and Go, 1984; Lander and others, 

1993; Lander, 1996) reveals no earthquake or tsunami originating in the Pacific basin on 6 October 1883. Apparently no 

large regional or distant earthquake caused the 1883 tsunami 

in lower Cook Inlet. The waves could only have come from 

the observed eruption of nearby Augustine Volcano as contemporaneous accounts infer.

Figure 62. Plot of variation in tidal ranges at Kodiak, Seldovia, 

and English Bay (Nanwalek), Alaska. Cluster of ranges at Kodiak 

and Seldovia are typical tides from 1995 predictive tide tables for 

Kodiak and Seldovia. Included are the 6 October 1883 marigram 

range (for Kodiak) and Davidson’s (1884) 14 ft at English Bay (for 

Seldovia). Dashed line is height of maximum (spring) high tide 

for Seldovia. English Bay shows the five tsunami-height figures 

reported by the 6 October 1883 eyewitness accounts. Mean low 

water is the approximate tidelevel at the time of tsunami on 6 

October 1883. A.C.C., Alaska Commercial Company.
Katmai 1912 ash

Augustine 1883 ash

Augustine 1883

tsunami pebble

Pre-1883

sand with soil

66 Volcanic Processes and Geology of Augustine Volcano, Alaska

Evidence on Augustine Island for Augustine 

Tsunami

Augustine Island contains some direct evidence of 

1883 tsunami. Burr Point debris avalanche ran as much as 

4km beyond the preeruption sea cliff on the north-northeast 

coast (fig. 11), and atop some avalanche hummocks lie thick 

clasts of deformed mud containing exotic stones and early 

Holocene marine shells scraped from the former bay. These 

relations show that the 1883 avalanche slammed into the 

bay at high speed and momentum. The shelly clasts of mud 

show that central parts of the Burr Point avalanche violently 

raised seawater at least 13 m above modern spring-high tide 

line. And atop outer Burr Point hummocks, pockets of shellcontaining sand, isolated driftwood, and water-erodeded 

hummocks reaching 3 to 5 m above spring-high tide seem to 

be tsunami effects.

The larger West Island debris avalanche of age about 

370 yr B.P. overrode and strongly fluted the sea cliff that 

marked the former northwest coast. Almost all the avalanche 

mass rode well beyond the cliff into the sea—as much as 

5km beyond—evidence that this bouldery mass plowed into 

the sea at very high speed and momentum. In the planed-off 

southern hummocks, West Island contains direct evidence of a 

tsunami caused by this mass. Lagoon avalanche just south of 

West Island avalanche too has been washed up to 8 m above 

sea level and possibly also North Bench avalanche just east of 

West Island avalanche.

Evidence on Mainland for Augustine Tsunami

A sand layer containing fine gravel, rounded large beach 

cobbles, abundant driftwood, and fallen local trees overlies 

about 300 yr B.P. Iliamna volcaniclastic deposits at Red 

River delta on the west coast of Cook Inlet (fig. 1A) 67 km 

north-northeast of Augustine’s Burr Point (Anders and Begét, 

1999). The deposit lies about 1.5 to 2 m about current high 

tide. Radiocarbon dates on the driftwood are about 90 to 

100yr B.P. (with large statistical errors); dendrochronology of 

trees rooted below the gravelly-sand layer shows a tree-ring 

perturbation (a few years of wider rings) dates to A.D. 1883 

(Anders, 1999). The most likely cause of this deposit is the 

1883 tsunami from Augustine that eyewitnesses reported at 

English Bay on the east side of Cook Inlet. The deposit on Red 

River delta lies on a point where computer models (see below) 

predict tsunami wave height should be high.

An apparent 1883 tsunami deposit crops out on the 

south and east of the sand spit that guards the harbor of 

the village of Nanwalek (English Bay). About 12 meters 

above spring high-tide level, the deposit consists of sand 

and rounded pebbles to small cobbles that overlie a brown 

soil developed on older silt (fig. 63). The pebbles and sand 

evidently washed upslope in the tsunami observed between 

8:15 and 8:25 a.m. on 6 October 1883. Directly overlying 

the pebbles are several centimeters of gray fine-sand ash 

(fig.63), surely the ashfall from Augustine on 6 and 7 October 1883 reported in the contemporary accounts (A.C.C., 

1883; Dall, 1884; Davidson, 1884). The gray-sand ash is in 

turn overlain by the distinctive regional white-silt ash from 

Katmai eruption of 1912 (see also Begét and Kowalik, 2006; 

Begét and others, 2007).

An 1883 tsunami deposit may be preserved in sediment 

in Beluga Lagoon near Homer. Several shallow cores from the 

lagoon recovered sequences of mud interrupted by two beds of 

sand and gravel each 1 to 2 cm thick (fig. 64). Historical observations suggest the upper layer was deposited by tsunami during 

the 1964 earthquake. The lower sand and gravel bed at depth 

20 to 50 cm is directly overlain by a thin organic horizon mixed 

with volcanic ash that chemically fingerprints as Katmai 1912 

eruption and Augustine 1883 eruption (J.E. Begét, unpub. data). 

Thus the coarse sand-and-gravel bed just below these ashes 

must record an 1883 Augustine tsunami. These cores at the limit 

of spring-high tide to a half meter below don’t reveal if the 1883 

tsunami at Homer rose above highest tides.

Figure 63. View of 1883 tsumani and 

ashfall deposits near Nanwalek (in 1883 

called English Bay). Overlying a brown soil 

developed over time on sand are beach 

pebbles transported up to 12 meters above 

high-tide level, evidently by tsunami in 

early morning 6 October 1883. Immediately 

above the pebbles lies 12 cm of fine-sand 

ash evidently of 1883 ashfall deposited 6–7 

Oct 1883; overlying that is the unmistakable 

Katmai 1912 white-silt ash. A different view 

of identical stratigraphy 10 meters away 

appears in Begét and Kowalik (2006, fig. 5). 

(Photograph by J.E.Begét.)
1883

tsunami

gravel

1964

tsunami

sand

Mud

and

organics

Sand,

mud,

and 

organics

High-Energy Flows From Insular Setting 67

Prehistoric possible tsunami deposits—beds of sand and 

water-rounded cobbles as thick as 5 to 7 cm—lie within thick 

peat beds near Nanwalek and Seldovia as much as 5 m above 

high tide (Begét and Gardner, 2004; Begét and others, 2008). 

These deposits overlie peat dated to about 1,620–1,650 14C 

yr B.P. They are thus close in age to the voluminous Northeast Point debris-avalanche deposit that overrode a sea cliff 

and crashed into deep water off Augustine Island’s east coast 

(plate1; tables 2 and 3).

Another likely prehistoric tsunamigenic deposit (discovered by C.F. Waythomas in 1995) lies at the bedrock 

headland of Point Bede on lower Kenai Peninsula about 

5 km south of Nanwalek (fig 1A). The deposit is of very 

angular boulders as large as 1.3 m thrown as much as 10m 

back from a 3-m sea cliff and 1 to 2 m above high tide. 

Three blocks a meter or so in diameter and dozens of smaller 

ones, all very angular, derive from an outcrop in the hightide surf zone just seaward. Overlying some of the boulders 

is a peaty accumulation containing two to four laminae of 

sand-silt ash beneath the distinctive Katmai 1912 ash. These 

ashes—resembling the ash stratigraphy overlying the West 

Island debris avalanche (fig.35 and plate 2)—show that the 

boulders were cast onto Point Bede at least a few centuries 

before 1883.

Sparseness of Mainland Evidence 

for Augustine Tsunami

Besides the deposits at Red River delta, Nanwalek 

(English Bay), and Homer studied by Begét and colleagues, 

no other definitive evidence of a 1883 tsunami has yet been 

deciphered along the shores of lower Cook Inlet. In 1991 Waitt 

and B.F. Atwater examined several likely sites on the east and 

west sides of lower Cook Inlet in search of 1883 and older tsunami deposits, and Waitt further explored coasts near Homer 

in 1992–95. We found two candidate deposits, both clearly 

older than 1883, both later rejected as tsunami deposits. C.F. 

Waythomas and others repeated this field exercise in 1995 

along these coasts and again found no evidence of an 1883 

tsunami (Waythomas, 1997). But the 1883 tsunami is directly 

recorded by historical accounts like the five cited above.

Many students of tsunami elsewhere have commented on 

a typical sparseness of lasting geologic evidence of historical 

tsunami, even along erodable sandy coasts. Papua New Guinea 

was struck in July 1998 by tsunami as high as 10 to 15m. 

Along a sand-spit reach of the coast, the field-survey team 

“had to act quickly . . . because water marks and other indicators are highly ephemeral and can be lost after even a single 

heavy storm” (Kawata and others, 1999, p. 104).

Much of the tsunami-deposit literature dwells on such sand 

sheets spread inland from broadly low-lying sandy coasts. But 

most coastlines of Cook Inlet consist of rocky cliffs and it is 

coarse material that abounds. Several local tsunami caused by 

submarine landslips during the great 1964 Alaska earthquake 

left mainly ephemeral effects like smashed trees and diverse 

wooden and marine-organic flotsam (Plafker and Kachadoorian, 

1966; Plafker and others, 1969). As permanent deposit they 

typically left not sand but boulders (Plafker and others, 1969). 

Sparsely distributed boulder deposits and water-stripped headlands are the main or only evidence for powerful prehistoric 

tsunami that have swept many coasts in Australia, Caribbean 

and Pacific islands, Portugal, and Japan (Andrade, 1992; Jones 

and Hunter, 1992; Kawana and Nakata, 1994; Bryant and 

Young, 1996; Young and others, 1996; Nott, 1997, 2000, 2003; 

Bryant, 2001, 2008; Bryant and Nott, 2001; Nott and Bryant, 

2003; Scheffers, 2002; Frolich and others, 2009). The only 

physical evidence for a tsunami (or arguably large storm surge) 

that on 30 January 1607 swept up Bristol Channel and Severn 

Estuary between southwest England and south Wales is eroded 

salt marsh, wave-stripped headlands, and deposits of boulders 

(Haslett and Bryant, 2005; Bryant and Haslett, 2007).

Unlike flowage processes such as glaciers, streamflood, 

and debris flow that inherently move and deposit sediment, a 

tsunami is clear water devoid of sediment. It entrains sediment 

only as the current crashes ashore in its last moments. Prerequisites to a permanent deposit are abundant, loose sediment 

just seaward, and a deposit-retaining environment just landward. Few such sites exist in lower Cook Inlet. Most coasts 

are rocky or cliffy; beaches are few and most of them gravel. 

Small wonder the record in deposits is sparse.

Figure 64. Photo of core from Beluga Lagoon near Homer with 

sand-gravel bed of 1883 Augustine tsunami. Inset photo shows 

core being obtained. (Photographs by J.E.Begét.)
68 Volcanic Processes and Geology of Augustine Volcano, Alaska

Numerical Simulation of Augustine Tsunami

Generation and propagation of tsunami involve various phenomena of initiation, propagation, and runup. Some 

processes, like propagation through deep water, are regular, 

understood, and reduced to linear equations. Time for a tsunami 

to propagate from Augustine Island to a mainland coast is estimated by the relation V dg = , where V is velocity of propagation, d is depth of water, and g is acceleration of the force of 

gravity (Lander and Lockridge, 1989, p. 3). From northside 

Augustine to Nanwalek (English Bay), 84 km across water of 

average depth about 60 m, travel time is thus roughly 58 minutes. In Troshina’s (1996) detailed model, propagation velocity 

is computed incrementally through cells of a grid; travel time is 

computed by summing the times to pass through each increment of distance at each instantaneous velocity. From Augustine 

Island to Nanwakek on lower Kenai Peninsula, this time varies 

among the model runs from 50 to 60 minutes.

Simulations by Troshina (1996), Kowalik and Murty 

(1989), Kienle and others (1987), and Begét and Kowalik 

(2006) show that an Augustine tsunami strikes coasts across 

Cook Inlet with greatest energy on broad headlands—between 

Homer and Anchor Point, and between Seldovia and Port Chatham (fig. 1A). Wave energy concentrates upon peninsulas as 

waves slow and refract when they cross from deep to shallow 

water. And three sites bearing geologic evidence of the 1883 

tsunami (Red delta, English Bay, Homer) are areas numerical 

modeling suggests a tsunami generated by a northside Augustine landslide should concentrate (Begét and Kowalik, 2006). 

For Homer and English Bay, Troshina (1996) much improves 

resolution of bathymetry calculations and includes runup routines. For a landslide off Augustine’s north side at low tide, her 

models “generate” wave runups at Nanwalek (English Bay) as 

high as 3 m, compared with a value of 6 m or so reported there 

in 1883. For other patterns of Augustine landslides, Troshina’s 

runups in lower Cook Inlet range 1 to 6 m.

All numerical simulations of tsunami are limited in 

depicting nature: unproven assumptions enter the equations; 

the equations greatly simplify actual natural phenomena; they 

contain constants to be manipulated; bathymetry is insufficient, especially in near-coastal shallows; diverse processes in 

the shoals both at initiation site and in runup areas are physically complex and the simulating equations nonlinear; many 

complicating processes are ignored (Troshina, 1996, p. 11–28, 

and written and oral commun., 1995 and 1997; Elena Suleimani [formerly Troshina], oral commun., 2000, 2002, 2006). 

Tsunami models typically “underpredict” observed local maximum runup height by factors of 2 to 10 (Satake and Tanioka, 

1994; Myers and Baptista, 1995; Synolakis and others, 1995; 

J. Bourgeois, oral commun., 1995; Tappin and others, 1999), 

while along a coast observed runup heights vary locally by 

factors of 2 to 5. A recent numerical model of tsunami generated by Augustine landslides (Waythomas and others, 2006) 

reconfirms the limitations inherent in all numerical simulations. Of the initiation mechanism at Burr in 1883 they note: 

“Wave phenomena in the splash zone are complex and difficult 

to evaluate quantitatively, especially in nature, where it is typically impractical to obtain data on water behavior.”

The numerical models of the 1883 Augustine northside 

tsunami “postdict” runups on Kenai Peninsula of 3 m or less 

where the observed height of the largest wave in 1883 was 

6–7 m. Yet numerical simulations typically yield tsunami 

runups only a half to a tenth observed maximum runups. Elena 

Troshina (oral commun., 1997, 2002) reflects that with all the 

assumptions and numerical simplifications that such models 

embody, an output runup of half an observed runup is the best 

one should expect.

Can Augustine Generate Large Tsunami?

Subaqueous landslides, and subaerial landslides entering 

water, have caused numerous tsunami in historical times (table 

4). Some very large prehistoric landslides in or into deep water 

have caused tsunami that have run up 20 meters and more on 

nearby coasts and sometimes hundreds of kilometers away (for 

instance, Moore and Moore, 1984; Moore and others, 1994; 

Bondevik and others, 1997, 2003; Bryant, 2001; Whelan and 

Kelletat, 2003). Scores of moderate others have sent tsunami 

across the sea to run up 5 to 10 meters on shores tens of kilometers away. The numerous tsunami deposits discovered since 

the early 1990s far above sea level around the world’s oceans 

evoke Ted Bryant’s apropos book title: Tsunami, the underrated hazard. A slide off Mayuyama into the adjacent shallow 

bay in 1792 took almost 15,000 lives (table 4). It was only a 

little larger than a large Augustine landslide into its adjacent 

sea.

Whether a northside debris avalanche from Augustine 

Volcano can generate a tsunami damaging to mainland coasts 

of lower Cook Inlet is an enduring question (Waythomas and 

Waitt, 1998). Several reports over the years argue “aye” (Johnston, 1977; Keinle and Swanson, 1983b; Kienle, 1986; Kienle 

and others, 1987; Siebert and others, 1989, 1995; Begét and 

Kienle, 1992; Siebert, 1992; Troshina, 1996). But others—

misunderstanding Augustine’s field records and downplaying 

the contemporary accounts—argue “nay” on more theoretical 

grounds (Waythomas, 1996, 1997, 2000; Waythomas and others, 2006).

Population and development in lower Cook Inlet were trifling in the 1880s—Homer and Halibut Cove for instance lay 

in the future. Seldovia’s 1880 population was only 74, mostly 

natives (Klein, 1981), and with the fur industry declining even 

that much reduced by May 1883 (Jacobsen, 1977, p. 197). 

Native villages like Seldovia having until recently preserved 

their history orally, they left no permanent written records 

about the 1883 Augustine eruption and tsunami.

The train of tsunami waves as high as 6 or 7 m witnessed 

at English Bay on 6 October 1883 apparently originated 

when an avalanche of moderate volume swept into the shallow sea on Augustine’s north shore. Judged by comparing 

the volcano’s current summit with Doroshin’s 1870 sketch 

(fig. 40A), Augustine’s dome summit has grown back wider 

and taller during the 1883, 1935, 1964, 1976, 1986, and now 
Hazards 69

2006 eruptions than it was just before the 1883 eruption. The 

volcano’s summit seems as primed for landslide now as just 

before the 1883 eruption.

Because Augustine’s 1883 avalanche occurred by chance 

during a falling low tide in a sparsely populated region, the 

effects of its tsunami on people were small. Even so, Davidson 

(1884) wrote of the first and largest wave at English Bay on 

6 October 1883: “Fortunately it was low water, or all of the 

people at the settlement must inevitably have been lost.” Were 

a large Augustinian debris avalanche—say the volume of West 

Island—to enter the sea during a rising high tide, a consequent 

tsunami to the modern populations in coastal areas of lower 

Cook Inlet would likely be larger and far more damaging than 

were the tsunami on 6 October 1883. Tsunami are not just one 

inundation but typically a series. Three 1883 accounts mention several waves, even the lesser ones 4 to 6 m high. Were an 

Augustine-caused tsunami to occur in the future at high tide, 

a succession of tsunami waves along with a relentless current 

could sweep shorelines in lower Cook Inlet 4 m and more 

above normal high water.

Hazards 

Hazards from Augustine Volcano to people about lower 

Cook Inlet have been a concern since the 1976 eruption began. 

A detailed draft hazards report in 1978 by David A. Johnston 

and others went unpublished after Johnston’s death at Mount 

St. Helens in 1980—though parts were incorporated into a 

hazards report by Kienle and Swanson (1980, 1985). A later 

nontechnical update summarizes possible hazards from Augustine Volcano (Waythomas and Waitt, 1998).

Most potentially lethal processes like falling cobble-sized 

particles, scorching pyroclastic flow or surge, or lahar are 

confined to the uninhabited island. The brief 700°C heat blast 

(as David Johnston inferred) at Burr Point hut during the 24 

January 1976 surge would have maimed or killed there and to 

some distance offshore. During the 1968 eruption of Mayon 

volcano in the Philippines, a wind blast uprooted trees, then a 

heat surge torched upturned roots into charcoal and killed many 

animals and one human but left little or no deposit (Moore and 

Melson, 1969; J.G. Moore, written commun., 1977 [to D.A. 

Johnston] and 2000 [to R.B. Waitt]). And people died near the 

outer edge of the 18 May 1980 surge at Mount St. Helens where 

today more than a quarter century later little deposit remains to 

record the event. From Krakatau in 1883, scorching flows and 

surges swept lethally across the sea as far as 80 km (Carey and 

others, 1996; Winchester, 2003) where today there remains little 

or no deposit. At Mont Pelée, Martinique in 1902 such surges 

swept offshore across a few kilometers with enough energy and 

heat to ravage and capsize ships and to kill crew and passengers 

(Anderson and Flett, 1903; Macdonald, 1972; Scarth, 2002). 

At Monserrat in 1996 to 1998, surges ran down valleys to the 

coast and then more than a kilometer over the sea (Cole and 

others, 2002). Clearly the zone of safety from hot surge off an 

island volcano must be drawn some distance beyond the coastal 

limit of deposits from past events. At Augustine Island it should 

be some kilometers offshore of the north and northeast flanks 

where recent eruptions have focused activity.

The potentially most hazardous processes at greater 

distances from Augustine Island are airborne volcanic ash, and 

tsunami generated by debris avalanche. During the 1976 pumiceous tephra fall, angular rock fragments as large as 10cm 

punctured a corrugated-steel roof on Augustine’s coast 6km 

from the vent. Falling lithic clasts could affect boats some distance offshore. But tephra both thins and fines sharply downwind (fig. 8). Ash from even a large Augustine eruption would 

be thinner than 5 cm on habited areas of Cook Inlet. Even wet 

it would be heavy enough to collapse only the flimsiest roofs.

 The moderate eruptions of ash from Augustine in 1976 

and 1986 were hazardous to aircraft and airports. At least five 

jet aircraft (two military, three commercial) encountered and 

were damaged by airborne ash of two separate plumes during the 1976 Augustine eruptions (Kienle and Shaw, 1979). 

During eruptions of Redoubt volcano (80 miles north of 

Augustine) in 1989–1990, five aircraft encountered airborne 

ash, including a large passenger airliner that for a time lost 

its engines (Casadevall, 1991, 1994b). Airborne ash has since 

become a recognized hazard to jet aircraft (Casadevall, 1992, 

1994a; Casadevall and Krohn, 1995).

Effects and hazards by tsunami from Augustine are much 

debated. Some infer likely damage, others deny even the 

observed harbor waves of 6 October 1883, suggesting that future 

hazards from an Augustinian tsunami are no greater than by 

severe coastal storms. Tsunami researchers of NOAA’s Alaska 

Tsunami Warning Center argue against this last notion (Thomas 

Sokolowski and Paul Whitmore, written commun., 1997):

. . . The danger from a 12–25 m wind wave cannot be compared directly to the danger of a 6-m tsunami, [owing] to their different periods. The runup 

or inundation from even large storm waves like these 

is minimal, [owing] to their breaking nature. [But] a 

6-m tsunami is a 6 m inundation along with a dangerous current. As an example, 6-m wind-generated 

waves along the southern California coast are not 

uncommon and are typically not damaging. The 

0.8-m 1960 Chile tsunami, though, produced over $1 

million damage in L.A. harbor alone.

Indeed Nott (1997, 2000) calculates that for coastal 

boulder deposits, a storm wave would have to be 4 times 

the height of a tsunami to transport a given boulder—thus 

a boulder moved by a 6-m tsunami would requires a 24-m 

storm wave. The provisional hazard report for Augustine 

Volcano (Waythomas and Waitt, 1998) argues that because 

the debris avalanches enter shallow water they can’t develop 

large, fast-moving sea waves. The logic is only theoretical. In 

practice, numerous shallow-water displacements have produced observed tsunami waves. A trifling landslide into shallow water off Vulcano in Italy in 1988 induced a small local 

tsunami, and a small landslide into shallow water on coastal 

Fatu Hiva in French Polynesia in 1999 spread a tsunami that 
70 Volcanic Processes and Geology of Augustine Volcano, Alaska

ran up 3 to 7 m high into a nearby bay (Tinti and others, 1999; 

Okal and others, 2002). Larger historical examples are numerous (parts of table 4). By the field relations on Augustine 

Island and on distant coasts, by the tsunami observed in 1883, 

and by the fact that along rocky coasts tsunami can leave 

only small and sporadic records, we looking outward from 

Augustine Island think that tsunami generated by future debris 

avalanches into the sea threaten distant mainland shores.

Acknowledgments

Jürgen Kienle introduced us to Augustine in 1986–1988, 

when our fieldwork began on this project. In the late 1960s 

through 1970s, Robert B. Forbes and Jürgen Kienle had collected many historical photographs and written accounts of 

past eruptions, materials that contribute to our understanding of historical eruptions and aid in illustrating this report. 

Begét’s stratigraphic work on coastal exposures was mostly 

1986–1988. Waitt’s fieldwork for this report and map occurred 

1988–1993, 1995, 1997, and 2002 (minor). We two coauthors had several days of joint fieldwork scattered over the 

period 1988–2002. Collaborating with or assisting Waitt in 

the field at various times were Jürgen Kienle, Hiroki Kamata, 

Robert G. McGimsey, Michael P. Doukas, Cynthia A. Gardner, and Christina A. Neal. Kienle contributed directly to the 

provisional version of this report and map (Waitt and Begét, 

1996). Several colleagues aided our knowledge of Augustine 

or shared in field logistics: Michael Doukas, Jack Kleinman, 

Thomas L. Murray, John A. Power, Christopher J. Nye, and 

Samuel E. Swanson. Lee Siebert kindly sent a copy of George 

Davidson’s official letter of 1884 that he found in the archives 

of the U.S. Coast and Geodetic Survey at Washington, D.C. 

Wes Hildreth supplied David Johnston’s unpublished Augustine manuscript fragments of 1978–79 and copies of some of 

his Augustine fieldnotes.

After his Ph.D. thesis on Augustine’s 1976 eruption, David 

A. Johnston began in summer 1978 investigating deposits of 

Augustine’s historical eruptions, picking up where Detterman 

(1973) had left off. His 1978–79 fieldnotes and preliminary airphoto maps show deposits especially of 1976 that we remapped 

in 1988–94. Though we examined Johnston’s materials mostly 

after our fieldwork ended, his careful notes and annotated 

airphotos from when 1976 deposits were still fresh and distinct—before the north flank considerably changed in the 1986 

eruption—helped us distinguish between certain deposits of 

Augustine’s 1935, 1963–64, and 1976 eruptions.

On the administrative front, the concept of a comprehensive Augustine map and report and early needs like fieldwork, 

new aerial photographs, and new topographic maps were 

encouraged and supported by Thomas P. Miller, Scientist-InCharge of Alaska Volcano Observatory. And so the project 

flourished in 1988–1993.

Since our fieldwork began on Augustine, nearly two 

decades have passed as we put finishing touches to this report 

in 2007–08. One by one, four of Augustine’s earlier geologists have disappeared. Dave Johnston, who studied the 

petrology of Augustine’s 1976 eruption, died far too young 

in Mount St. Helens’ eruption on 18 May 1980. Bob Detterman of the USGS, maker of the island’s first geologic maps, 

is gone. Jürgen Kienle, who began the modern instrumental 

investigations of Augustine is gone too. So is his University 

of Alaska mentor and former Alaskan State Geologist, Bob 

Forbes—some of whose early collected historical photographs of Augustine adorn this report. Three of these men 

shared a frightening experience on erupting Augustine in 

early February 1976. A helicopter crash and windstorm had 

stranded Forbes, Kienle, Johnston, and four others at Burr 

Point. They huddled by the shore for three days in a corrugated-steel research hut that Kienle and Forbes had recently 

built, but which in late January 1976 a hot Augustine surge 

had ripped into and scorched. When the storm abated the men 

were finally plucked off the island. Twelve hours later the 

volcano sent another hot flow down to the sea. In June 2002 

we authors (Waitt and Begét) were leading an international 

field trip to Augustine Island when at Burr Point we found 

that winter’s wind had at last toppled the rotting old hut. A 

couple hours later a Cessna flew oddly low and slow over 

the north coast. It was family mingling Bob Forbes’s ashes 

among Augustine’s bone-white pumice.

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Produced in the Western Region, Menlo Park, California

Manuscript approved for publication, February 13, 2009

Layout and graphics by David R. Jones and Christine G. Janda

Back Cover: View east-southeastward of Augustine Volcano from seaward 

side of hummocky West Island avalanche shed from the volcano about 370 

years ago. (USGS photograph by Richard B. Waitt, 19 July 1993.)
Waitt and Begét—Volcanic Processes and Geology of Augustine Volcano, Alaska—Professional Paper 1762