50

50

50

100

150

200

250

300

350

400

450

500

600

700

800

900

150

100

250

200

450

500

600

700

800

900

1000

1100

1200

1200

400

350

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UPPER

JURASSIC PLEISTOCENE

UPPER

JURASSIC

HOLOCENE

25,000

10,000

2,500

1,600

1,200

800

400

200

25,000

10,000

2,500

1,600

1,200

800

400

200

Unconformity

1

Pleistocene and Holocene ages in uncalibrated radiocarbon time

B

M

C

H

I

G

UPPER

CRETACEOUS

UPPER

CRETACEOUS

bedy

bedi

bedo

ld IMan

Pl

PHfp

ds

Pg

Jns

Kk

Jnsh

Po

Bln Bpl

MBpli MBp MBlp MBl MBas

CMal

IHa

GIays

Ga

Bar Bau

CMp

HClp HClc HCpwp HCpwl HCpe HCl

IHla

CMl

IHl

HCas HCal

Pvr

Pvb

MBplo

83a

Bawi Bawo Bag

bed

dp

dk

df

hpus

PLEISTOCENE HOLOCENE

Dome agglutinate and proximal-fall deposit—Rampart composed of weakly 

welded clasts of porphyritic andesite, not present in photographs before 1986 

eruption. A possible remnant (unmapped) of underlying 1976 dome consists of 

microvesicular gray (N 6/0) highly porphyritic andesite containing about 30 

percent plagioclase phenocrysts as large as 4 mm (in 2006, covered and 

adsorbed within new 2006 dome)

Deposits of lithic pyroclastic flow—Lithic pyroclastic-flow deposits of large 

fan on north flank heading at dome (86d). Consist mostly of fragments of 

porphyritic andesite dome rock but can have 0–30 percent pumice. Some large 

lithic blocks exceed 4 m in diameter. Overlaps pumiceous pyroclastic-flow 

deposit downslope

Deposits of pumiceous pyroclastic flow, mixed flow, and lahar—Gravelly 

sand in which pumice clasts, as large as 1 m but typically 10–25 cm, range 

from white to gray to brownish gray and contain 5–10 percent inconspicuous 

plagioclase phenocrysts and some pumice clasts conspicuously banded; some 

have “breadcrust” surface texture. Contains as much as one-third angular lithic 

clasts generally smaller than 80 cm but in places including rare boulders as 

large as 2–4 m. Pumiceous flows have local surface relief as much as 1 m and 

steep margins 0.1 to 3 m high in digitate lobes, some as small as 3–10 m 

across; some flows have lateral levees 0.5–3 m high. Overlapped upslope by 

lithic pyroclastic-flow deposits. Deposits are mostly gravelly sand; pumice 

boulders are concentrated at surface. In years 1988–1993 vegetated only by a 

few sprigs of grass, blueberry, and moss.

 Gravel lahar deposits grade downslope from pumiceous pyroclastic-flow 

deposit; range from matrix supported (debris-flow deposit) to openwork (flood 

deposit)

Products of 1976 eruption—Divided into:

Deposits of lithic pyroclastic flow—Patch on lower north-northeast flank 

similar to unit 76p but shed from 1976 dome and so contains little or no 

pumice. Nearly buried by units 86p and 86l

Deposits of pyroclastic flow and lahar—Similar to such flows of 1986 (see 

above) but are especially rich (as much as 40 percent) in banded 

brown-gray-white pumice clasts. Comprises several separate flows; internal 

contacts indicate flow fronts. Lithic clasts of andesite (and locally of 

sandstone) as large as 1.4 m. In 1988–1993 had many clumps of grass, 

blueberry, and moss, 1 to 2 orders of magnitude more vegetation than on 

similar 1986 deposits but still very sparse (less than 5 percent of surface 

covered). In places such as lower west-southwest swale, braided deposit 

veneers similar deposit of 1964 (and 1935?) more intricately than can be 

shown on map

Products of 1963–64 eruption—Divided into:

Lava dome—Gray (N 5/0) to reddish porphyritic andesite containing about 15 

percent plagioclase phenocrysts as large as 3 mm. It is slightly microvesicular. 

Forms geomorphically distinct south rim (including summit) of summit-dome 

complex

Deposits of pyroclastic flow and lahar—Similar to pumiceous 

pyroclastic-flow deposit of 1986 and 1976 but much richer in lithic component 

and carrying larger lithic boulders. In places angular lithic boulders 0.5 to 2 m 

in diameter form much of surface, rare boulders are as large as 4 m. Internal 

lateral levees are common, some as high as 4 m. Deposits form broad paths 

leading nearly from base of dome to within 0.2 to 1.3 km of the coast. In 

contrast to younger (1986 and 1976) deposits, these (in 1991–1995) are caked 

with moss and a few alder are established. Deposits in west-southwest swale 

may be partly of 1935 eruption

Products of 1935 eruption—Divided into:

Lava dome—Gray (N 5/0) to reddish porphyritic andesite with 15 percent 

plagioclase phenocrysts as large as 4 mm and a few dark rounded, finely 

crystalline xenoliths. Forms geomorphically distinct northwest part of summit 

dome complex and a western lobe

Blocky rubble—Coarse bouldery rubble in form of fan shed from summit 

dome. Perhaps partly of 1964 dome collapses

Products of 1883 eruption—Divided into:

Pyroclastic-flow and pyroclastic-surge deposits—Massive poorly sorted 

lithic granular medium sand 0.3 to 2 m thick containing pebbles to 3 cm. 

Locally cut by upward-tapering fines-poor (gas-escape) pipes of small-pebble 

gravel. Capped by 10–20 cm of massive moderately sorted very fine sand to 

silt ash. Smooth surfaced, this deposit overlies debris-avalanche deposit back 

from Burr Point, partly filling lows between hummocks. Overlapped in many 

places by 1976 and 1986 pyroclastic-flow deposits, which where thin and 

discontinuous have arbitrary contacts with unit 83p. Internal contact on 

northeast indicates a flow front

Debris-avalanche deposit—Bouldery diamict including nearly intact but 

highly fractured blocks as large as 8 m in intermediate diameter (one is 25 m 

long!) and unfractured ones as large as 4 m. Matrix is sandy gravel of identical 

but finer-grained angular material. Jointing patterns are diversely irregular, 

platy, and columnar; rare blocks are of sintered spatter. Rare hummocks 

contain lenses of rounded pumice, apparently smeared-out clasts of 

pre-eruption pyroclastic-flow deposit. Rare hummocks contain yellow to 

brown blocks of soft and clayey, highly altered andesite. Whole deposit is 

hummocky: individual hummocks as high as 30 m and with basal diameter as 

much as 200 m, but typically 3–15 m high with basal diameters 20–80 m; some 

hummocks are arranged in curving arms. West side of deposit is marked by 

conspicuous nearly straight levee descending from 650 to 40 m altitude. 

Hummocky deposit is locally overlain by as much as 10 cm of eolian sand and 

peat containing distinctive white-silt fall ash as thick as 3 cm of Katmai 1912 

eruption. Near the outer margins of overlapping 1976 and 1986 

pyroclastic-flow deposits, ash-cloud silt overlies hummocky deposit

Topography by photogrammetric methods from aerial

photographs taken 14 August 1990. Topography and

hydrology scribed in 1991 on Kern PG-1 stereoplotter and

automatic table by Dan Turkington, USGS National Mapping 

Division, Cascades Volcano Observatory, Vancouver, Washington

1927 North American Datum 

DESCRIPTION OF MAP UNITS

Most map units are divided by age, which in prehistoric deposits is determined largely 

by presence of overlying marker beds in the form of coarse pumiceous tephra layers (fall 

deposits). These tephra layers are designated in ascending stratigraphic order: G, I, H, C, 

M, and B. All are late Holocene age by radiocarbon dating (table 2). Prehistoric volcanic 

deposits are designated in time by the tephra layers they lie between. Thus, unit HCas

lies above tephra layer H and below tephra layer C. Prehistoric units that are older than 

tephra G or younger than tephra B are designated by the one tephra symbol, such as units 

Ga and Bar.

Age of historic deposits is inferred from the absence of any of these beds and from 

various historic records, especially aerial photographs. Historic deposits are designated 

by the last two digits of the eruption year, thus unit 83a belongs to the 1883 eruption and 

unit 76p to the 1976 eruption.

Informal names: On Augustine Island most geographic names—like West Island, 

Southeast Point, and North Bench—are informal and most properly written in lower 

case. They are capitalized only for clarity in the reading. To distinguish formal from 

informal names, please see figure 1B.

Radiocarbon dates in titles and on correlation chart, as in main text and the tables, are in 

raw (uncalibrated) radiocarbon time.

Centered headings do not appear on correlation chart.

Grouped pyroclastic and laharic deposits—Divided into:

Deposits of historic eruptions—Muddy fall deposits (and pyroclastic-flow 

deposits?) of historic eruptions, nestled among 1935 and 1964 domes in 

summit area

Pyroclastic-flow and lahar deposits of historic and prehistoric(?) 

eruptions—Pumiceous to lithic coarse rubble on steep (18–25?) upper- to 

middle-level slopes descending from base of summit-dome complex. Variable 

surface and indefinite stratigraphy but apparently swept repeatedly. Insufficient 

evidence (capping tephra, vegetative cover, morphology) to differentiate 

systematically by age. Includes a few patches of flowage and fall deposits of 

indeterminate age on lower flanks

Smooth slopes—Smooth-surfaced slopes on south covered by prehistoric 

pumiceous falls and perhaps flows but not by coarse rubble flows 

characteristic of most areas mapped as hpu swept by flows from summit during 

historic eruptions. Probably essentially Jurassic-Cretaceous bedrock but 

thickly veneered by Augustine debris 

PREHISTORIC HOLOCENE DEPOSITS AND FLOWS

Beach and eolian deposits—Area of about 1.5 km2 on southwest coast of 

well-sorted, loose, medium to coarse sand arranged in long, linear, subparallel, 

coastwise ridges. In deepest and most coastal excavations, sand overlies 

cobble gravel of subrounded to rounded stones of porphyritic andesite. Central 

and eastern (farthest inland) sand ridges enclose B(?) and M(?) tephras 

variously at depths of 0.4 to 5 m; western (near-coast) ridges are thinner and 

contain neither B nor M tephra. Cartographically divided into older, 

intermediate, and younger phases (units bedo, bedi, and bedy, respectively). 

Near present coasts passes upward into unit e

Deposits younger than B tephra (<370 14C yr B.P.)

North Slope lava flow—Massive porphyritic andesite ranging from light gray 

(10YR 7/1) to oxidized light reddish brown (5YR 6/3); about 10 percent 

plagioclase phenocrysts as long as 4 mm. East side overlain by coarse 

debris-avalanche levee (unit 83a) as thick as 15 m

Rocky Point debris-avalanche deposit—Bouldery nonsorted diamict including 

blocks as large as 5 m. Matrix is sandy gravel of identical angular, 

finer-grained material. Upper 1 m of a few hummocks shows schlieren of 

highly altered andesite. Whole deposit is hummocky like nearby Burr Point 

deposit (unit 83a). On east and southeast parts, hummocks overlain by as much 

as 30 cm of pyroclastic debris from 1883?, 1976, and 1986 eruptions. On north 

side against beach, some hummocks are overlain by eolian sand capped by the 

Katmai 1912 ash and at least one (1883?) older ash

Lithic pyroclastic-flow deposit (or lahar deposit?)—Bouldery diamict 

including blocks as large as 2 m. Matrix is sandy gravel of identical but 

finer-grained angular material. Has leveed, lobate form but heavily vegetated. 

Overlaps unit Bawi downslope

Undifferentiated small debris-avalanche deposits—Bouldery diamict of 

porphyritic andesite including blocks commonly as large as 6 m, rarely as 

large as 15 m. Matrix is finer-grained nonsorted diamict of angular clasts. 

Forms several small lobes on north slope that did not reach below altitude 60 m. 

Most likely affiliated with events that formed west-island or rocky-point 

deposits

West Island debris-avalanche deposit—Divided into:

Inboard facies—Bouldery diamict similar to unit Bawo but with less local 

relief, thus much smaller, less distinct, and continuous hummocks. Apparently 

an irregular, thick veneer over older deposits that had been cut back into 

coastal sea cliff. Upslope locally underlain by M(?) tephra

Outboard facies—Bouldery diamict including blocks as large as 4 m. Matrix is 

sandy gravel of identical finer-grained angular material. Whole deposit is 

hummocky, the hummocks as high as 30 m with irregular basal diameter as 

much as 200 m, but typically 3–15 m high with basal diameters 20–80 m. In 

places directly overlain by gravelly sand pyroclastic-surge(?) deposit. 

Southwestmost hummocks (hachured area) have flattened tops overlain by 

patchy poorly sorted sand and capped by lag of 0.5- to 4-m boulders

Grouse Point tongue—Bouldery diamict of angular blocks as large as 2.5 m. 

Matrix is sandy gravel of identical but finer-grained angular material, a 

nonsorted diamict of andesite clasts. Deposit is hummocky with relief as high 

as 5 m. Overlain by gravelly sand containing angular andesite cobbles and at 

least six fine-ash layers including two below Katmai 1912 ash. Unit could be 

an independent small debris avalanche similar in age to Bawo

Deposits between M and B tephras (about 750–370 14C yr B.P.)

Lithic pyroclastic-flow or lahar? deposit—Divided into:

Inboard facies—Bouldery diamict of angular andesite, finely lobate and 

leveed. Consists of angular gray to reddish andesite clasts as large as 3.3 m but 

mostly smaller than 1 m. Capped by pinkish incipient soil, and the soil 

discontinuously topped by rare pumiceous B tephra and by Katmai 1912 silt 

ash. Below altitude 180 m, heavily vegetated; above altitude 180 m, only 

sparsely so but more than 1976 and 1964 deposits

Outboard facies—Cobbly sand diamict as thick as 4.1 m atop sea cliff (now 

isolated from the sea) along inner margin of West Lagoon. Overlies soil 

developed on M? tephra and capped by pumiceous B? tephra. Upslope 

becomes intricately lobate and leveed and with many meters of local relief. 

Included are poorly exposed patches in adjacent southeast swale similarly 

vegetated in brush alder but veneered by tongues of unit 76p too thin and 

digitate to map at 1:25,000 scale 

171⁄2°

TRUE NORTH

MAGNETIC NORTH

APPROXIMATE MEAN

DECLINATION AT

CENTER OF MAP,

2009

Pyroclastic-flow deposit—Massive pebbly sand at least 1.2 m thick containing 

lithic clasts as large as 20 cm. Overlain by more than 1 m section of fluvial 

debris, ash layers, and organic layers capped by B? tephra

Southeast Beach debris-avalanche deposit—Bouldery diamict exposed in 

upper part of bluff along Southeast Beach. Deposit studded with angular 

blocks as large as 2.5 m in sand and as large as 6 m as lag on beach and as 

large as 7 m seaward. Matrix is sandy gravel of similar finer-grained 

material. Overlain by B tephra; underlain by M and C tephras, which overlie 

unit HCpe that forms most of bluff

Lahar or pyroclastic-flow deposit—Sandy gravel diamict containing angular 

lithic andesite clasts rarely as large as 2 m on southeast coast. Associated with 

unit MBas to west. Overlain by B tephra, underlain by M and C tephras. 

Apparently similar deposit mapped as unit MBplo in southwest swale

Lahar deposit—Diamict of granular medium sand capping terrace at mouth of 

West Kamishak Creek. Contains angular andesite clasts as large as 50 cm but 

no pumice. Overlies M tephra. Underlies laharic facies of unit 76p at mouth of 

creek

Deposits between C and M tephras (about 1,000–750 14C yr B.P.)

Lagoon debris-avalanche deposit—Bouldery diamict including blocks as large 

as 4 m. Matrix is sandy gravel of identical but finer-grained angular material. 

Whole deposit is hummocky, individual hummocks having relief as high as 

30 m and irregular basal diameters as much as 200 m, but typically 3–15 m 

high with basal diameters 20–80 m. Overlain by B tephra

Pyroclastic-flow and pyroclastic-surge deposits—Along northwest margin of 

West Lagoon, vaguely bedded very fine sand to silt ash at least 30 cm thick 

(base not exposed); overlain by M(?) tephra. Also west of West Kamishak 

Creek at coast, small-volume nonoxidized massive gravelly sand 

(pyroclastic-flow deposit) overlying oxidized unit HCpw and sandwiched 

between tephra layers C and M

Lithic pyroclastic-flow (or lahar) deposits—Cobble gravel to poorly sorted 

gravelly sand; angular to subangular lithic clasts as large as 25 cm; includes 

pumice. Underlain by tephra layer C; overlain locally by an ill-defined tephra 

layer O and by tephra M

Deposits between H and C tephras (about 1,400–1,100 14C yr B.P.)

North Bench debris-avalanche deposit—Bouldery diamict including blocks 

as large as 3.5 m. Matrix is sandy gravel of identical but finer-grained 

angular material. Deposit is only moderately hummocky with local relief as 

high as 6 m. Cut into gently curving sea cliff as high as 35 m (since half 

buried), whose development was arrested by emplacement of Grouse Point 

deposit. This deposit with its high seacliff is geomorphically similar to 

several coarse deposits on east and south coast and must be older than 

indicated by local stratigraphy. Sparsely overlain by B or M tephra. May 

predate C tephra

Southeast lithic pyroclastic-flow (and lahar?) deposit—Divided into:

Proximal facies—Contains numerous angular surface boulders 4–6 m, a few 

as large as 9 m. Surface texture coarsely lobate and leveed with local relief as 

high as 2.5 m. Some smaller blocks prismatically jointed. Directly overlain by 

C tephra

Coastal facies—Cobble gravel to sandy cobble gravel containing subangular 

rather than very angular clasts, vaguely stratified and lacking in large boulders, 

suggestive of lahar deposit. Surface laced with many close-spaced levees. 

Directly overlain by C tephra and directly underlain by H tephra

Southeast pyroclastic fan—Massive pumiceous gravelly medium sand 

(pyroclastic-flow deposit) with interbedded gravelly zones as thick as 31 m. 

Overlain by C and M tephras

Southwest pyroclastic fan—Divided into:

Pumiceous pyroclastic-flow deposit—Massive pumiceous gravelly medium 

sand (pyroclastic-flow deposit) as thick as 5 m. About 80 percent of gravel 

clasts are pumice as large as 10 cm, the rest are angular lithic andesite as large 

as 5 cm. Upper 2 m oxidized reddish. Overlain by C and M tephras; underlain 

by massive sandy gravel more than 5 m thick, unit HClu. Surfaces inland are 

smooth and free of boulders

Lithic pyroclastic-flow deposit—Cobble to boulder gravel containing angular 

to subangular clasts of variously gray to reddish porphyritic andesite. Upslope, 

boulders commonly as large as 3 m, rarely as large as 9.5 m; in coastal 

exposures boulders smaller than 0.5 m. Surface of upslope portion embellished 

by numerous intricately lobate margins downslope from close-spaced levees. 

Upslope portion overlain erratically by tephra C and extensively by tephra M. 

Coastal portion overlain by pumiceous pyroclastic-flow deposit (unit HCpwp) 

capped by these tephras

Lahar—Massive sandy gravel more than 5 m thick, probably laharic

South Point debris-avalanche deposit—Bouldery diamict of angular 

porphyritic-andesite fragments. Similar to units Bar, MBag, and MBal, 

including surface boulders commonly as large as 2 m, many in 4–5 m range, 

rarely as large as 9 m. Hummocky surface with as much as 10 m of local relief 

but much subdued by overlying tephra and peat deposits. Overlain only by 

section containing C and M tephras. Cut back into sea cliff as high as 30 m 

that projects 600 m seaward as a broad, sharp salient

Long Beach debris-avalanche deposit—Bouldery diamict of angular 

fragments dominantly of porphyritic andesite but also containing smaller 

sandstone clasts. Hummocks as tall as 9 m, andesite boulders rarely as large as 

6–9 m. Poorly exposed 

RECENT TO PREHISTORIC DEPOSITS (HOLOCENE)

Beach deposits—Divided into:

Sandy—Beach deposits consisting mostly of moderately sorted loose medium 

sand to small-pebble gravel lying in tidal zone of about 7 m

Rocky—Beach deposits consisting mostly of boulders, generally smaller than 

2 m but in several places as large as 7 m in intermediate diameter and many 

also in cobble range. Most boulders and cobbles derive from debris-avalanche 

or pyroclastic deposits exposed in a seacliff at back of beach

Tidal-flat and salt-marsh deposits—Flat expanses of sand, gravelly sand, and 

sandy gravel winnowed from adjacent deposits and frequently covered at 

medium to high tide in areas that seaward deposits defend against surf

Marsh and pond alluvium—Flat expanses of mud and sand in and along 

marshes and ponds on southwest part of island behind coastal deposits

Eolian sand—Loose, well-sorted medium to coarse sand forming coastwise 

ridge at back of beach above high-tide level. In places includes interbedded 

ash layers or peaty layers. In places includes identical underlying prehistoric 

deposits. In a few places, especially on southwest coast, is continuous 

downsection into older eolian sand of unit bed and its subunits

Offshore deposits—Divided into:

Boulders—Fields of angular boulders of porphyritic andesite, some of them

 >4 m in diameter, extending variously 0.2 to 1.5 km offshore. Many visible at 

low tides, and on aerial photographs expressed as conspicuous dark areas 

beneath the sea. Derived from coarse fragmental deposits of various ages. 

Seaward “contacts” delineate only where these deposits become too deep 

below sea level to show on aerial photographs or at lowest tides 

Sand—Banks of sand lacking boulders

DEPOSITS AND FLOWS OF HISTORIC ERUPTIONS (HOLOCENE)

Products of 1986 eruption—Divided into:

Lava dome—Very dark gray (5YR 3/1)1

 to reddish porphyritic, 

microvescicular andesite containing about 20 percent plagioclase phenocrysts 

as large as 5 mm. Includes assimilated remnants of dome that had grown at 

same site in 1976. Geomorphically distinct north part of summit-dome 

complex (in 2006, covered and adsorbed within new 2006 dome)

__________

1 Munsell® colors and color names specified for a few units, estimated in field to 

nearest color chip of Munsell® Soil Color Charts (1975 version), Kollmorgen 

Corp., Baltimore, Maryland

y pg

seaward 400 m as a narrowed salient. Buries an older sea cliff

Lahar and debris-avalanche deposit—Deposit as thick as 20 m 

block 2.2 km west of South Point. Massive diamicts with angu

boulders as large as 4 m (debris-avalanche deposit?) overlie an

similar deposits but with smaller and fewer boulders and with v

(apparently lahar deposit). May be arms of units HCl and of uni

May underlie H tephra as well as C tephra

Lahar(?) deposit—Sandy gravel diamict containing angular porp

outside (north) of levee delineating north side of main part of N

diamict (unit IHa). Similar sandy gravel lies south of margin of 

Point debris-avalanche deposit and also beneath tephra H? atop 

landslide block on south side of island

Deposits between G and I tephras (about 2,100–1,800 14C y

Yellow Cliffs and Southeast Point debris-avalanche deposits, 

composite—Bouldery diamict of angular porphyritic-andesite 

Comprises two stratigraphically superposed similar deposits, th

overlain by Southeast Point diamict. Where not buried by unit 

hummocky surface of Southeast Point deposit has 5 to 8 m of l

albeit much subdued by thick capping tephra and peat deposits 

interhummock lows). Southeast Point deposit overlain by I and 

tephras. Unlike all other Augustine debris-avalanche deposits, 

Cliffs unit consists largely of andesite clasts that are yellowish 

altered to clay; its local surface relief seen in sea-cliff section i

Deposits older than G tephra (about 2,500–2,100 14C yr 

East Point debris-avalanche deposit—Bouldery diamict of angu

porphyritic-andesite fragments, a few prismatically jointed (juv

Underlies Yellow Cliffs diamict (lower diamict of unit GIysa) a

sparsely exposed G tephra. Similar to unit IHa, including angul

large as 4–8 m

Domes and lava flows of uncertain late(?) Holocene a

Pre-1883 summit-dome complex—Succession of porphyritic-an

forming east crater rim and steep upper east and south outer fla

little changed since 1883 eruption. Divided by surface color an

overlapping relations into three parts (oldest, 1; youngest, 3)

Flank features—Divided into:

Dome P—Topographic bump on the northwest volcano flank at 

consisting of gray (N 5/0) porphyritic andesite containing abou

plagioclase phenocrysts as long as 4 mm

Dome F—Topographic bump on the northwest volcano flank a

1,025 m consisting of pinkish gray (7.5R 6/2) porphyritic ande

about 15 percent plagioclase phenocrysts as long as 4 mm

Dome Kamishak—Topographic bump on the south volcano fla

513 m consisting of light gray (N 7/1 to 5YR 6/1) porphyritic a

containing about 15 percent plagioclase phenocrysts and about 

hornblende phenocrysts, both as long as 3 mm

Lava flow—Inliers on south flank of in-situ porphyritic andesite 

seaward slope: old dome and (or) lava flow nearly buried by yo

DEPOSITS OF LATE PLEISTOCENE (TO HOLOCENE ?) AG

Fall deposits and pyroclastic-flow deposits, undivided—Interbe

pumiceous pyroclastic-flow deposit, lithic pyroclastic-flow dep

beds of loose, sorted pumiceous fall deposits exposed on sides 

south-flank kipukas. Uppermost beds probably correlative with 

older tephra beds of coastal sequences. In places, lowest parts o

sequences overlain by Pleistocene glacial deposits

DEPOSITS OF LATE(?) PLEISTOCENE AGE

Glacial deposits—Sandy gravel or gravel veneer of diverse ang

large as 1.5 m of exotic lithology including black argillite, dio

granodiorite, granite, gneiss, porphyritic dike rocks, gabbro, g

banded limestone and chert. Probably discontinuous till; foun

south side of island

Outwash gravel—Water-laid pumiceous and lithic pebble to gra

locally rich in exotic, rounded pebbles. Found only on south s

Section contains bed of angular pumice, apparently tephra-fal

Volcanic materials—Divided into:

Rhyolitic pumiceous beds—Thickly bedded gravelly sand diam

angular to rounded pumice clasts (pyroclastic-flow beds), altern

of sorted angular pebble gravel of angular pumice clasts (fall b

contain as much as 40 percent lithic clasts

Basaltic hyaloclastite—Poorly bedded sandy pebble gravel con

clasts as large as 10 cm, rarely to 20 cm, of scoriaceous olivine 

overlain by bedded rhyolitic pumice (unit Pvr). Base exposed in 

shows 3 m of fragmental flow deposits containing lithic andesit

clasts (included in this map unit)

Block landslide—Sandstone and shale of Naknek Formation hi

and faulted, riddled with open fissures, apparently a displaced 

upslope from unit Jnsu

ROCKS PREDATING AUGUSTINE VOLCANO

Kaguyak Formation (Upper Cretaceous)—Poorly exposed, ox

weathered, greenish sandstone and sandy pebble conglomerat

containing Inoceramus and other upper Cretaceous fossils (D

Jones, 1974). Since 1976 Augustine eruption, exposed only in 

of West Kamishak Creek at altitude 350–400 m 

Naknek Formation (Upper Jurassic)—Shown only on cross se

Divided into:

Upper sandstone—Cliff-forming medium to fine thick-bedde

pale-brown sandstone with partings of very fine sandstone to 

Locally ripple marked and containing foreset beds as thick as 

west or southwest. Rich in marine shells and rare flattened log

Upsection becomes rich in granule to pebble conglomerate co

rounded stones of mixed crystalline rock types

Shale—Dark-gray shale, mostly siltstone with thin interbeds o

Includes at base lower sandstone of Buffler (1976); crops out 

high-tide line

Geology field-mapped 1988–1995 by Richard B. Waitt

Geologic map compiled 1994–1999 by Richard B. Waitt 

on Kern PG-2 stereoplotter

Analog topographic, hydrologic, and geologic maps 

converted to combined Arc/Info digital map by 

Jacqueline McIntire in 1999–2006 

Final map prepared in Adobe Illustrator by Christine G. 

Janda in 2007-2008

IHl

153°35’ 30’ 25’ 153°20’

24’

21’

22’

23’

59°20’

24’

21’

20’

59°19’

22’

23’

C o o k

I n l e t

Contact—No contact where boundary is gradational and arbitrary

Internal contact—Delineates boundaries of separate flow deposits 

obvious in the field, like steep outer margins of a pumiceous 

pyroclastic flow within units 76l and 86p

Levees at margins of debris avalanches

Linear south edge to central core of high hummocks on West 

Island

Beach ridges—Except near coast, thickly mantled by eolian sand 

and tephra

Partially buried shoreline—Old, mostly prehistoric shorelines. 

Dashed where thoroughly covered by younger deposits

Tsunami-flattened hummock

Isolated large boulders—In West Lagoon, a lag

Strike and dip of bedrock—Value is dip of bedding in degrees

Bulldozer tracks—Made in 1950s

Pumice pit—Made in 1950s; mostly covered by 1976 flows

EXPLANATION 

25

P A C I F I C O C 

GEOLOGIC MAP OF AUGUSTINE ISLAND, ALASKA

By

Richard B. Waitt and James E. Begét

2009

35

12

25 25

10

36

15

13

8

15

A

SCALE 1:25,000

1/2 0 1 MILE

1000 0 1000 2000 3000 4000 5000 FEET

1 .5 0 1 2 KILOMETERS

CONTOUR INTERVAL 10 METERS

National Geodetic Vertical Datum of 1929

Shoreline is arbitrary, sea level at time air photos were taken. Shoreline

represents an intermediate level below mean high water and

above mean low water, probably closer to the latter.

0 1 2 3 4 KILOMETERS

?

?

VERTICAL EXAGGERATION ABOUT 11⁄4

SEA LEVEL

200

400

600

800

1,200

1,400

1,000

METERS

SEA LEVEL

200

400

600

800

1,000

1,200

1,400

A A’

SSW

METERS

NNE

Naknek Formation, undifferentiated—Includes units Jns and Jnsh

? Unknown but probably from Augustine

Jn

hpus

hpus

Jns

Jnsh

HCpwl

Pl

83a 83a 83a 83a 83a 83a

83a

br

IHla

64p

hpu

ds3

64d

86g

86d

83a 76l 76l 83a 76p 83a 83a 83a

86l

83a

83a

86l

Jn

dk

ds3

ds2

Jnsh

Jn

Kk

Kk

Jn

Buried shoreline

Burr Point

Buried fragmental debris

Bay mud and sand

Buried fragmental debris

153°35’

Map

Area

Photograph by Richard B. Waitt, 29 June 1988

bed

bs

br

t

am

e

ob

os

86g

86l

86p

76p

76l

64d

64p

35d

35b

83p

83a

hu

MBp

MBas

MBlp

IHl

ds

dp

df

dk

ld

PHfp

Pg

Po

Pvb

Pl

Jnsh

Glays

MBl

CMal

CMp

IMan

CMl

HClp

HClc

HCpwl

HCpwp

hpu

hpus

bedy

bedi

bedo

Bln

Bpl

Bau

Bawo

Bag

MBpli

MBplo

Bawi

Bar

HCpe

HCas

HCal

HCl

Pvr

Kk

Jns

IHla

Ga

86d

bs

br

t 83a

83a

83a

br

t

br

83p

86p

83a

83a

br

e

bs

86p

e

br

86p

86p

76p 76p

76p

e

e

Bar

Bar

Bar

83a 83a

e

76p e

76l

76p

76p

76p

76p

76l

bs

br

br

83p

86p

83p

83p 86p e

e

83p

86l

86p

86p

86p 86p

76l

bs

bedy

e IMan br

e IMan

IMan

Bag

Bag

Bag

Bag

Bag

br e

e

bs

Bawo

bs

bs

e

e

e

am

IMan

76p

hpu

Bawi

Bawi

t

hpu

e

br

br

br

br

br

br

Bawo

am

hpu

Bau

Bau

Bau

Bau

Bau

Bau

IHl

IHl

IHl

IHl

86p

hpu

bs hpu

bed

Bln

Bln

Bln

hpu

hpu

hpu

hpu bs

bs

bs

e

t

86p

Bawi

IHa

IHa

IHa

IHa

IHa

GIays IMan

IMan

hpu

hpu

76p

Bawo 76p

76p

76p

83a

76p

ld

ld

br

76p

GIays

GIays

ld

Bawo

Bawo

86d ds2

Ga

t

Bpl

bed

bs

bs

76p

76p

86l

t 76p

76p

86p

86p

76p

35d

86p

76p

dp

CMal

76p

df hpu

hpu

hpu

hpu

76p

86g

t

ds3

e

hu 76p

bs t 64d

MBpli

e

MBplo

MBplo

76p

e

bedy

CMp

64 p

64p

35b

76p

76p

ds1

76 p

76p 76p 76p

76 p

Bpl

64 p

76p

76p 64p

HClp

64 p

64 p

ld

bedy

76p

PHfp

HCpwl

HClc

MBlp MBplo

PHfp hpu 64p ld 76p

PHfp

HCpwl 76p PHfp

hpu 76p

MBplo MBplo

76p dk

76p

Bpl

bedo

MBplo

64p MBplo PHfp 76p

Pg

hpus

hpu

hpu

hpu

hpu

HClp

64p

Pvr

Pvb

Pvb

Pvb

hpu

MBplo

Pg

64p

64p

64p

MBplo

hpus

Jns

Jns

Kk

bedo

64p

MBplo

e

e

76p

am

am

am

MBlp

Jnsh

Jnsh

hpus

HCpwp

MBas

MBas

Pg

HCpwl

64p Pg

MBp

am

HCpe

CMp

bs

HCas

bedo

CMl

CMl

CMl

64p

HClc

HClc

MBl

am

am

HClc

br

IHla

Po

Pl bs

br

HCl HCl

bs

HCal

HCal

bedo

83a

83a

83a

83a

83a

83a

83a

83a

83a

83a

76p

76p 76p

76p

HClp

HCal

HCal

HCal

HCal

HCal HCal

HCal

GIays

Ga

e

bs

bs

br

bs

76p

bedy

bedi

Bar

IHa

IHa

Bawi

MBl

MBl

ob

ob

ob

ob

ob

ob

ob

os

os

83p

HCal

HCal

Bawo

76p

bs

br

HCl

Any use of trade, product, or 

publication is for descriptive 

not imply endorsement by the 

For sale by U.S. Geological Su

Services, Box 25286, Federal 

1-888-ASK-USGS

GIS files and a PDF file for thi

http://pubs.usgs.gov/pp/pp176

Waitt, R.B., and Begét, J.E., 2009, Volcanic processes and 

geology of Augustine Volcano, Alaska: U.S. Geological Survey

Professional Paper 1762.