s i

1 Geologic Reconnaissance 

of Frosty Peak Volcano 

and Vicinity, Alaska

-' By HOWARD H. WALDRON

INVESTIGATIONS OF ALASKAN VOLCANOES

i.

^ GEOLOGICAL SURVEY BULLETIN 1028-T

~>

Prepared in cooperation with the Office, 

^ Chief of Engineers, U.S. Army

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY

Thomas B. Nolan, Director

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

Washington 25, D.C.
PREFACE

In October 1945 the War Department (now Department of the Army) requested the Geological Survey to undertake a program of volcano investigations 

in the Aleutian Islands-Alaska Peninsula area. The first field studies, under 

general direction of G. D. Robinson, were begun as soon as weather permitted 

in the spring of 1946. The results of the first year's field, laboratory, and 

library work were assembled hastily as two administrative reports. Part of 

the data was published in 1950 in Geological Survey Bulletin 974-B, "Volcanic 

Activity in the Aleutian Arc," by Robert R. Coats. The remainder of the 

data have been revised for publication in Bulletin 1028.

The investigations of 1946 were supported almost entirely by the Military 

Intelligence Division of the Office, Chief of Engineers, U.S. Army. The Geological Survey is indebted to the Office, Chief of Engineers, for its early recognition 

of the value of geologic studies in the Aleutian region, which made this report 

possible, and for its continuing support.

ni

CONTENTS

	Page 

Abstract____-------_---_-_-_--.__.______________._. 677

Introduction. -_-_-____--_-______-__-_________-___________-_.___-_- 678

Previous investigation________________________________________ 678

-v Fieldwork..___________________________________._ 679

Acknowledgments- _-_-___-_-__-____-_____________-_-__--__---- 679

** Geography__ _ __________________________________________________ 679

Location and accessibility.__---___-___-_--____________---__--__ 679

Topography and drainage.-_--__-_-___-_-_-_____-___-_---_--___ 681

Climate-_-__-_--____--__---_-_----__-_----__----------_.----- 682

Vegetation__________--____-___--__-____.-___-_--__-_-__ 683

v Animal life.---______-____---____-_____-_-_-_-___-_--____--__- 683

Geology...___-----_-__-__--_-_____-_-_-_---_-_-_-___-_--_.-_-_- 684

^ General features__-_______-_____-_-_-__--___.___-_-_-_____--- 684

Tertiary rocks______________________-__-_._____-_-_--__-___- 684

Belkofski tuff....._.____.._._____.___..__-_.._._____ 684

Tachilni formation____________.__-__-_______-_-_-_-___--- 686

^ Volcanic rocks of Thinpoint Lagoon________________________ 688

Tertiary and Quaternary rocks.____-_______-___-_-______-_-__-__ 688

Morzhovoi volcanics-___---__-______-_-_____-_-_-_----__-_- 688

,4 Basalt flows of Mount Simeon._____________________________ 690

Intrusive rocks___-_____--____-___-_-_-___---_-_-__--_--_-_ 691

+ Quaternary rocks ___-___-_--____-----_-_-_.___-_-_--_--_-__-- 692

Frosty Peak volcanics____.___-______-_-_______-__----____ 692

Glacial deposits._-_______-_--_______-________-_-_____-_-_- 695

Recent deposits..____-___-_______-__--_-_-_._____-___-_--- 698

Ash and lapilli_____._._...___-_._..__._._._.._.__... 698

Sanddunes________-_-_____-_______._-_-_-___--_ 698

f Alluvium________-____-______-_.___-____ ____.___ 699

v Beach deposits.-______________________________________ 699

Colluvium_________________-___-_-._____________ 700

Structure_______-__--____-____-__--___._______---___-_-__ 700

Geomorphology _ ______________________________________________ 701

Geologic history_______________________________________________ 703

References cited.._________________________________________________ 705

Index____________________________________________________ 707

~)

ILLUSTKATIONS

PLATE 79. Geologic reconnaissance map and section of Frosty Peak

volcano and vicinity.__--______--.___--._-_-__-___ In pocket

FIGURE 104. Map of Alaska Peninsula and Aleutian Islands.___________ 680

INVESTIGATIONS OF ALASKAN VOLCANOES

GEOLOGIC RECONNAISSANCE OF FROSTY PEAK 

VOLCANO AND VICINITY, ALASKA

By HOWARD H. WALDRON

ABSTRACT

Frosty Peak is a nested summit cone of a prominent Quaternary volcano 

on the western end of the Alaska Peninsula, between Cold Bay on the east 

and Morzhovoi Bay on the west. This part of the peninsula comprises two 

major physiographic provinces a deeply glaciated and eroded mountainous 

area bordering the Pacific Ocean and a tundra-covered coastal lowland bordering the Bering Sea.

The oldest rock unit recognized in the area is the Belkofski tuff, a thick 

sequence of well-bedded volcanic sedimentary rocks, tuff, agglomerate, and 

some interbedded flows, principally of basaltic composition, that crop out along 

the Pacific coast east of Cold Bay. The rocks have been moderately deformed 

and intruded by quartz diorite stocks and by dikes, sills, and plugs of basalt and 

andesite. These rocks have been deeply eroded and are believed to be middle 

Tertiary in age. A sequence of poorly consolidated and slightly deformed 

marine sedimentary rocks, here named the Tachilni formation, which are 

probably derived from the Belkofski tuff and associated intrusive rocks, crop 

out along the Pacific coast west of Cold Bay. The age of these rocks is believed 

to be late Tertiary. Volcanic rocks in isolated knobs and hills in the vicinity 

of Thinpoint Lagoon are of unknown age, but are also believed to be Tertiary.

In very late Tertiary or early Quaternary time, volcanic activity southeast of Morzhovoi Bay built up a large stratovolcano, here called Morzhovoi 

volcano, on the eroded remnants of the older rocks. The rocks of this ancient 

volcano are light-gray porphyritic olivine basaltic lava flows and interbedded 

pyroclastic rocks, and some reworked volcanic material, and are here named 

the Morzhovoi volcanics. Eruption of this volcano, in early to middle Pleistocene, culminated in collapse of the central part, leaving a great caldera. 

Later, a large double-coned volcano, here called Frosty volcano, was built up on 

the northern flanks of the eroded remains of Morzhovoi volcano. Frosty 

volcano was partly destroyed by caldera-forming activity, and subsequent renewal of eruption built a prominent volcanic cone, Frosty Peak cone, in the 

southern part of the caldera. The rocks of the ancestral Frosty volcano and of 

the younger Frosty Peak cone are basaltic lava flows and some associated 

pyrdclastic rocks, here named the Frosty Peak volcanics. Since the last eruptions at Frosty Peak, probably very late in Pleistocene or in Recent time, 

glaciers, streams, and frost action have been rapidly dissecting its upper slope. 

The area was glaciated extensively during the Pleistocene. Glaciers drain677
678 INVESTIGATIONS OF ALASKAN VOLCANOES

ing to the north formed large piedmont glaciers, from which was deposited 

thick drift on the lowlands; glaciers draining to the south, however, calved 

off directly into the Pacific Ocean, and left little or no glacial drift along the 

Pacific coast. A large icefield, now occupying the northern part of the caldera 

of old Frosty volcano, spills over low cols in the caldera rim and pushes a 

large tongue of ice down toward Morzhovoi Bay.

INTRODUCTION

Frosty Peak, a prominent Quaternary volcano on the western end 

of the Alaska Peninsula (fig. 104), is one of more than 75 major 

volcanoes known in the Aleutian volcanic arc (Coats, 1950). This 

great arc, which is dominated nearly throughout by volcanoes and 

the products derived from them, extends for more than 1,500 miles 

south westward and westward from the Alaskan mainland, and is 

one of the earth's major structural features in the north Pacific 

Ocean. The potential threat of destruction by these volcanoes to 

major military and civil installations in the area, led to a request 

by the War Department, in 1945, for the Geological Survey to undertake a program of volcano research in the Aleutian arc. The 

investigation of Frosty Peak and surrounding area, as described in 

this report, is a part of the program of research designed by the 

Geological Survey to provide basic information on the general geology 

of the Aleutian arc, and on its past and probable future volcanic 

activity with respect to the various military and civilian establishments.

PREVIOUS INVESTIGATION

Very little geographic or geologic investigation has been done on 

the western end of the Alaska Peninsula. Although the Alaska 

Peninsula was discovered and visited by Russian and English explorers as early as 1741 (Baker, 1906), the first significant examination of the peninsula was not made until the summer of 1828, when 

Capt. M. N". Staniukovich surveyed the north shore of the Alaska 

Peninsula. Lieutenant Woronkofski surveyed the southern shore 

of the peninsula in 1836. Ilia G. Wosnenski collected minerals and 

fossils from the peninsula in 1842-43 for the Imperial Academy of 

Science of St. Petersburg. In 1848, Grewingk (1850) compiled a 

summary of all previous work of a geographic and geologic nature 

and assembled the facts in a single convenient volume. Dall (1896, 

p. 842-847) briefly discussed areas reported to contain upper Miocene 

fossiliferous marine strata on the western end of the peninsula. Atwood (1911) mapped parts of the Alaska Peninsula, including the 

Balboa-Herendeen Bay and Unga Island regions, in 1908. Jaggar 

(1929, 1945) visited the area in 1927 and 1928 while making a reconnaissance investigation of the Alaska Peninsula and Aleutian
Islands, but the scientific results of his investigations were not published. Capps (1934) briefly examined some coastal parts of the 

area in 1932. Hubbard (1935) visited the area in 1934. Kennedy 

and Waldron (1955) mapped the geology of Pavlof Volcano and 

vicinity, immediately east of the Frosty Peak area, in 1946. A very 

interesting and useful summary account of the people and natural 

history of the Aleutian Islands and Alaska Peninsula, including 

keys for the identification of birds and plants of the area, was prepared by the Smithsonian Institution as a War Background Study 

(Collins and others, 1945).

FIELDWOBK

The fieldwork on which this report is based was done by the 

writer, assisted by D. K. Nichols, during the summer of 1947. As 

no base maps were available at the time of the investigation, field 

data were compiled on trimetrogon aerial photographs. Subsequent 

to the field investigations, single-lens vertical aerial photographs 

of parts of the area were made available and examined. The base 

map (pi. 79) is a 1:100,000 composite of parts of the False Pass and 

Fort Kandall 1:250,000 quadrangles.

The geologic information presented in this report is of reconnaissance nature. Accessibility of much of the area is difficult even 

under the most ideal conditions. During the 1947 field season the 

work was severely hampered by exceptionally stormy weather that 

prevailed throughout the summer and by the serious loss of a boat 

and other field equipment, including notes, cameras, and aerial photographs. Consequently, for some parts of the area, the data and interpretations presented here are based only on fragmentary information.

ACKNOWLEDGMENTS

Grateful acknowledgment is made of the friendly cooperation of 

the many officers and men stationed at the Thornborough Air Force 

Base at the time of the investigation, especially Majors F. J. "Wesson, 

Jr., and E. S. Hinchliff, commanding officers; Capt. E. R. Hoover, 

ordnance officer, W. A. Brooks, post engineer, and Lt. D. B. Hartung, 

air installation officer. The cooperation and assistance given to the 

Survey party by the officials and employees of the Pacific American 

Fisheries, Inc., King Cove, are also gratefully acknowledged.

GEOGRAPHY

LOCATION AND ACCESSIBILITY

The area mapped geologically and called the Frosty Peak area in 

this report comprises a part of the western end of the Alaska Peninsula 

(fig. 104) that extends from the Bering Sea on the north to the

580554 61 2
680 INVESTIGATIONS OF ALASKAN VOLCANOES

S-
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 681

Pacific Ocean on the south and from Morzhovoi Bay on the west to 

the western shore of King Cove on the east. Cold Bay Airport,1 the 

only village in the mapped area, is on the northwest shores of Cold 

Bay, about 425 airline miles southwest .of Kodiak and about 175 

airline miles northeast of Dutch Harbor on Unalaska Island. King 

Cove, the site of a Pacific American Fisheries salmon cannery, lies 

at the eastern edge of the area mapped. Many trappers' huts and 

barabaras (native Aleut sod huts) are found-throughout the. area, 

principally along the shores of the bays and coves; they provide some 

emergency shelter and protection from storms.

At the time of the investigation, the' area was accessible only by 

military air or sea transport and by scheduled airline flights of the 

Reeve Aleutian Airways, Inc., from Anchorage. Because there are 

no roads or manmade trails, except in the vicinity .of the airbase, 

movement in most of the area is restricted to travel by foot or by 

water. Good anchorages are scarce, but small boats can obtain some 

shelter in the many lagoons and small bays.

TOPOGRAPHY AND DRAINAGE

The Alaska Peninsula, of which the Frosty Peak area is a part, 

consists of a chain of mountains known as the Aleutian Eange. This 

range is bordered on the north by the extensive Bering Sea coastal 

lowland, and separated in some places nearly isolated by large 

northward-trending partly flooded lowlands. Several large islands 

and numerous islets and rocks lie offshore. In general the islands 

in the Pacific Ocean south of the peninsula are rugged and mountainous with rockbound and cliffed shores, whereas those to the north 

in the Bering Sea are low sandy bars.

The Aleutian Kange in the Frosty Peak area is relatively low, 

averaging less than 1,000 feet in altitude. Large stratovolcanoes rise 

above the general level to an altitude of about 3,000 to 7,000 feet. The 

range has been deeply eroded by streams, glaciers, and frost action 

to produce many steep slopes, scarps, cliffs, and bare rock. Icefields 

and small glaciers occur on the higher peaks, especially on the north 

and northeast slopes. The mountains rise abruptly from the Pacific 

Ocean; steep-walled, fiordlike bays indent the rugged coastline, and 

with the exception of the lowlands partly encircling the larger bays, 

only a few broad, flat valleys interrupt the persistent cliffs and steep 

slopes. Narrow boulder beaches lie at the foot of the rocky cliffs, 

and sand beaches are found along the coastal lowlands and at the

1 Known as Fort Randall during World War II and In the early postwar years, and as 

Thornborough Air Force Base from about 1947 until about 1954 or 1955, and now operated by Civil Aeronautics Administration.
682 INVESTIGATIONS OF ALASKAN VOLCANOES

heads of some bays and coves. Sand and gravel spits and bars are 

common in the bays and coves, whereas reefs and offshore rocks, 

abundantly fringed with kelp, commonly flank the rocky headlands.

The Bering Sea lowland constitutes a gently sloping plain that 

rises gradually from the sea to merge either imperceptibly with the 

mountain slopes, or in places, to intersect them sharply. The Bering 

Sea lowland is continuous throughout the area mapped, and is from 

less than 2 miles to more than 10 miles in width. The surface of this 

lowland is generally less than 200 feet above sea level; it is characterized by a dense growth of vegetation, many rounded hills, and 

numerous lakes, streams, and swamps. The shores are commonly 

sandy and backed by low bluffs cut into the grass-covered f oredunes.

Eivers and streams abound in the area. Those draining into the 

Pacific Ocean generally flow in steep-walled valleys and are both 

shorter and of steeper gradient than those draining into the Bering 

Sea. The valleys are principally U-shaped glacial troughs with relatively flat floors; many of the streams head in glacial cirques. Permanent ice fills the coalescing craters of Frosty Peak volcano and 

spills over several low cols, where it forms either hanging glaciers or 

short cascading glaciers. The main ice drainage is westward into 

Morzhovoi Bay through a breach in the caldera rim north of the 

summit cone of Frosty Peak volcano. Here a large tongue of ice, 

heavily laden with rock debris, extends for nearly a mile downvalley.

CLIMATE

The Frosty Peak area is in one of the stormiest regions of the 

world. The frequent cyclonic storms crossing the North Pacific 

Ocean and the Bering Sea are the dominant factors influencing the 

weather of the area and account for the frequent occurrences of high 

winds, low clouds, and fog. The climate is basically maritime, and 

temperatures, though cold, are not normally severe, principally due 

to the moderating effect of warm water transported into the area by 

the Japan Current system. The mean annual temperature is about 

37.5° F, but the mean annual maximum and minimum temperatures 

differ less than 10°. Temperature extremes range from 78° to 9° F, 

but temperatures below zero are extremely rare. Winter lasts 7 to 9 

months, and frosts have been recorded for every month of the year 

except July and August.

The total precipitation is low, only about 33-34 inches per year, 

but it is fairly evenly distributed throughout the year. Total snowfall also is low, averaging about 40-45 inches, but it may accumulate 

to considerable thicknesses in drifts. Cloudiness averages about eight-
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 683

tenths (80 percent) sky cover the year around; fog occurs most frequently during spring and summer months.

Winds of high velocities are common in the region; average 

monthly wind speeds of 20 miles per hour or more throughout the 

year are recorded at Cold Bay. In winter the winds are most frequently northwesterlies; in summer the prevailing winds are southsoutheast. Kapid variations in wind direction occur throughout the 

year, however, and strong winds of gale force may come from any 

direction during any time of the year. Williwaws, violent katabatic 

winds of local extent, frequently occur on the leeward side of the 

mountains. The williwaw is an especially dangerous wind for small 

boats, owing to the suddenness of its occurrence as well as to its 

violence and extreme gustiness.

VEGETATION

Arctic-type vegetation prevails in the area. The dominant and 

most conspicuous forms are the grasses, sedges, and mosses constituting the tundra plants that grow so profusely in the lowland areas 

and blanket the lower mountain slopes. Alder bushes and stunted 

willows, several varieties of shrubs and berry bushes, ferns, water 

plants, and many varieties of flowering plants also thrive on the lowland. Alder bushes generally are limited to the lower 400-500 feet 

of the mountain slopes and occur in irregularly scattered thickets on 

the lowlands. In places willows and alder bushes are as high as 20 

feet, but generally they are only 4r-6 feet high and grow as a maze of 

low, creeping branches. The upper limit of vegetation ranges from 

1,000 to 1,500 feet in altitude.

ANIMAL LIFE

Animal life is abundant in the area. North America's largest 

omnivorous animal, the great brown bear, is both common and unpredictably dangerous enough that a traveler in the area must be 

armed and constantly alert. The caribou, which were once plentiful 

on the peninsula, were rapidly disappearing at the time of the investigation, mainly because of the ravages of wolves. The waters of the 

area, both salt and fresh, also abound in wildlife. Salmon, halibut, 

trout, and shellfish are especially abundant, and sea mammals, such 

as whales, dolphins, porpoises, seals, and sea lions are frequently 

seen. Land birds, although common, are small in number compared 

to the great numbers and varieties of sea birds. The most frequently 

seen land birds are the song sparrows, ravens, Alaskan longspurs, 

ptarmigans, hawks, and eagles. Ducks, geese, gulls, terns, puffins, 

murres, and cormorants abound along the coasts.
684 INVESTIGATIONS OF ALASKAN VOLCANOES

GEOLOGY 

GENERAL FEATURES

The general geologic features of the Frosty Peak area are shown 

on plate 79. The area is readily divisible into three general geologic 

units: a group of moderately deformed, probably middle to late 

Tertiary volcanic and marine sedimentary rocks that crop out along 

the Pacific coast; a series of younger, probably late Tertiary and early 

Quaternary volcanic rocks that make up the composite stratovolcanoes 

built up on the northern flanks of the older rocks; and the Pleistocene 

and Recent unconsolidated deposits that comprise the Bering Sea 

coastal lowlands and the lowlands adjacent to the larger bays. 

Frosty Peak volcano dominates the area; its history is virtually the 

history of the building and development of successive composite 

volcanic cones, their waning and partial destruction by eruption, collapse, and erosion; and finally, the building and development of the 

present Frosty Peak volcano summit cone within the caldera of the 

ancestral volcano.

TERTIARY ROCKS

Tertiary units of the area consist of both sedimentary and igneous 

rocks. The sedimentary rocks include marine graywacke, poorly 

consolidated marine sandstone and fine conglomerate, and volcanic 

sandstone and conglomerate. The igneous rocks are predominantly 

extrusive rocks of basaltic composition tuffs, flows, breccias, and 

agglomerates but some are of andesitic composition, and some are 

mafic and felsic intrusive rocks. In general, these igneous rocks appear to belong to the calc-alkalic circum-Pacific suite (Coats, 1952; 

Gates and others, 1954).

BELKOFSKI TUFF

A thick series of well-bedded tuffs and agglomerates and some 

interbedded flows, named the Belkof ski tuff by Kennedy and Waldron 

(1955, p. 6), crop out principally east of Cold Bay and are believed 

to be the oldest rocks in the Frosty Peak area. The Belkofski tuff 

occurs along the Pacific coast from King Cove to Kaslokan Point, 

and although not observed, probably also underlies most.of the mountainous area immediately surrounding Lenard Harbor. Only one 

isolated.outcrop, too small to map, was observed west of Cold Bay. 

This outcrop is exposed for about 10 feet vertically and for less than 

200 yards along the base of the south wall of the large valley that 

trends westward from Thinpoint Lagoon. Fragments and pebbles 

of tuff that lithologically resemble the Belkofski tuff occur in many 

beach and stream deposits.
685

The Belkofski tuff is composed largely of fine- to coarse-grained 

lithic tuff, ranging from green to purple to gray. In many places 

the tuff has been reworked by water, so that the originally angular 

fragments are now subrounded to rounded, and the rocks may be 

classed as volcanic sandstone and volcanic conglomerate (Wentworth 

and Williams, 1932, p. 50). The tuff is made up chiefly of a microcrystalline aggregate of feldspar microlites and chlorite, but includes 

crystals and angular fragments of oligoclase feldspar. Interbeddecl 

flows or sills of basalt and andesite are common and, because of their 

greater resistance to erosion, form benches on the steeper slopes in 

many places. Locally, tuff has been silicified and sericitized; introduced metallic minerals are not abundant, and the chief one is pyrite. 

The total thickness was not ascertained, but it is at least several thousand feet.

The age of the Belkofski tuff is believed to be middle Tertiary, 

but evidence for the age determination is not conclusive. The only 

pyroclastic deposits on the peninsula known to be of early Tertiary 

age are the "lower" beds of Palache's (1904, p. 74-77) Stepovak 

series. These rocks seem to occur only locally, however, and are 

not comparable to later pyroclastic deposits that occur extensively 

throughout the peninsula^ and are assigned a post-Eocene age by 

Atwood (1911, p. 48-52), Smith and Baker (1924, p. 185-187), and 

Knappen (1929, p. 198-201). No fossils were found in Frosty Peak 

area, but many plant fossils were found in better exposures of the 

tuff in the Pavlof area (Kennedy and Waldron, 1955, p. 6). The 

principal fossils are silicified and carbonized plants and trunks of 

both deciduous and evergreen trees; in places, impressions of conifer 

needles also occur. Partly on the evidence of the fossil trees and 

partly by analogy with nearby areas, a post-Eocene and pre-Pleistocene age for the Belkofski tuff in the Pavlof area was indicated, 

and the rocks were tentatively assigned an age of late Tertiary 

(Kennedy and Waldron, 1955, p. 7), principally because younger 

sediments of known Tertiary age did not crop out in the area. Atwood (1911, p. 59-62), however, describes a sequence of pyroclastic 

deposits, intruded by dacite (?) and diorite porphyrite, that occur 

in the Herendeen Bay-Unga Island area to the east. He considered 

these volcanic rocks to be late Eocene to, early Miocene in age because 

they overlie the Kenai formation (Eocene) and.underlie the Unga 

formation (Miocene). The occurrence in the Frosty Peak area of 

younger Tertiary marine sedimentary rocks (Tachilni formation) 

suggests that the Belkofski tuff is most nearly correlative with 

Atwood's late Eocene or early Miocene volcanic rocks and that the 

most probable age for the Belkofski tuff, therefore, is middle Tertiary 

rather than late Tertiary.
686

TACHILNI FORMATION

The name Tachilni formation is here given to a sequence of 

predominantly marine sedimentary rocks that crop out discontinuously along the Pacific coast from the west side of Thinpoint Cove 

at least as far west as Cape Tachilni. Owing to hazardous landing 

conditions along the Pacific coast and to the difficult accessibility of 

the area, except by boat, these rocks were examined only cursorily 

in a few localities along the beach. Consequently, neither their extent inland nor the details of their stratigraphy are known. The 

formation contains a series of very dark brown to light-greenishgray fine- to coarse-grained fossillferous sandstone, graywacke, grit 

and fine-grained conglomerate, and some black shale. Stratification 

and sorting differs and grades abruptly, both laterally and vertically. 

Crossbedding occurs in places. The material is mostly only semiconsolidated; locally near intrusive bodies, the rocks are well 

indurated.

Near Cape Tachilni, the type locality, more than 200 feet of poorly 

consolidated sedimentary rocks, rich in marine fossils, is well exposed in a small ravine. Here the beds dip gently northward and 

are unconformably overlain by lava flows. They include crossbedded 

coarse-grained gray to brown sandstone alternating with fine-grained 

conglomerate, pebbly sandstone, and some thin black shale. Some 

beds are cemented with iron oxides; others contain many concretionary masses. Locally, thin-bedded shale and sandstone are crumpled, contorted, and cut by many small faults; this suggests slumping 

during or shortly after deposition.

A typical sandstone in the vicinity of Thinpoint Cove consists of 

about 30-35 percent angular to subrounded quartz grains 10-15 percent euhedral feldspar grains, including some microcline, 5 percent 

pyroxene and amphibole grains, 30 percent angular to rounded fragments of volcanic rock, and 20 percent matrix mainly composed of 

a mixture of chlorite and some calcite, mica, and sericite. The rock 

may be classed as a medium-grained subgraywacke (Pettijohn, 1949, 

p. 255). It occurs in a sequence of light-greenish-gray sandstone 

that weathers to light brown and ranges in grain size from fine to 

coarse. These beds also contain pelecypods and many lenses and 

scattered pebbles of volcanic rock.

A typical fine-grained conglomerate or granule sandstone of this 

formation consists predominantly of well-rounded granule-sized 

fragments of altered volcanic rocks and pumice and contains a few 

scattered small grains of quartz. The matrix is composed of an 

intimate mixture of chlorite, calcite, serpentine, and an unidentified 

cryptocrystalline material which appears to be a mixture of clay
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 687

minerals and chalcedony, but part of which may be devitrified ash. 

Pelecypods and gastropods occur in this unit.

The total thickness of the formation is not known, but at least 

several hundred feet of the material is exposed along the coast. The 

base of the formation was not seen.

In the eastern part of the area, the Tachilni formation is unconformably overlain by lava flows; westward, however, it appears to 

pass upward conformably into a basal sequence of nonfossiliferous 

volcanic sedimentary rocks succeeded by interbedded pyroclastic rocks 

and lava flows. Presumably all the overlying rocks are part of the 

Morzhovoi volcanics, but the true relation between these two formations in that area is not known.

Some collections of marine invertebrate fossils were made from 

rocks of the Tachilni formation, but unfortunately they were lost in 

transit. Fossils most common seen were echinoids, gastropods, and 

pelecypods, apparently shallow-water types similar to the presentday forms found on the beaches, and hence probably not too diagnostic, 

except to indicate that the rocks are not older than Tertiary in age. 

Some fragments of carbonaceous plant material also occur in parts 

of the formation, but none suitable for identification were obtained. 

The author believes that the formation is younger than the Belkofski 

tuff, but the contact between the two was not seen. Farther east on 

the peninsula, Atwood (1911) describes marine sedimentary rocks 

of both Eocene and Miocene ages, the Kenai and Unga formations, 

respectively, which are separated by a considerable thickness of 

volcanic rocks. The rocks of the Kenai formation are more deformed 

and better consolidated than those of the Unga formation; in addition, 

the Kenai formation has been intruded by silicic intrusive rocks, but 

the Unga formation has not. Lithologic, stratigraphic, and structural 

similarities that seem to exist between the Unga and Tachilni formations suggest that they may be correlative in time of deposition. 

Therefore, pending future paleontological determinations, the Tachilni 

formation is tentatively assigned to the late Tertiary.

The fauna and lithology of the rocks suggest that they were deposited in a shallow-water nearshore shelf environment on a slowly 

subsiding coast. The invertebrate fossils, although occurring 

throughout the formation, appear to be most concentrated in finegrained conglomerate, suggesting either rapid burial during times of 

more vigorous alluviation, or niore likely, accumulations by wave 

action along interstream strandlines. Likely sources of the clastic 

material in the Tachilni formation are the volcanic sedimentary rocks 

of the Belkofski tuff and the related stocks of quartz diorite of the 

Frosty Peak area and of the Pavlof area to the east.

580554 61 3
688 INVESTIGATIONS OF ALASKAN VOLCANOES 

VOX.CANIC ROCKS OF THINPOINT JLAGOON

Isolated knobs and hills of volcanic rocks of unknown age, which 

appear to be lithologically similar, occur in the vicinity of Thinpoint 

Lagoon. The material consists predominantly of basaltic lapilli tuffs 

and includes some basaltic lava flows and very coarse grained breccias 

and agglomerates. Some of the breccia and agglomerate fragments 

are as large as 20-30 feet in diameter; most fragments, however, are 

coarse lapilli, and range from 1 to 3 inches in diameter. The very 

coarse breccias and agglomerates are probably throat or vent breccia 

remnants of old volcanoes. Olive-drab colors, largely the result of 

oxidation and palagonitization, predominate in the rocks, but some 

included fragments are black. The lavas and pyroclastic fragments 

are predominantly porphyritic basalts with intersertal textures and are 

composed chiefly of tabular- and lath-shaped phenocrysts of labradorite in a matrix of brown glass and palagonite. Some of the rocks 

have a hyalopilitic texture, and the groundmass is composed of microcrystalline laths of feldspar interwoven with glass and grains of 

magnetite. Commonly, only a small amount of pyroxene is present, 

either augite or hypersthene, or both. Other minor constituents 

include magnetite, other iron oxides, zeolites, calcite, cristobalite, 

tridymite, and chlorites. Olivine, where present, is commonly replaced by iddingsite and magnetite.

The age and stratigraphic relationships of these volcanic rocks to 

other rocks in the area are not definitely known; they appear to be 

definitely older than the stratovolcanoes and possibly as old as the 

Belkofski tuff. They are arbitrarily assigned a Tertiary age.

MORZHOVOI VOIXDANICS

.The name Morzhovoi volcanics is here given to a sequence of lara 

flows and interbedded pyroclastic rocks, and some associated volcanic 

sedimentary rocks, that overlie the Belkofski tuff and Tachilni formation. This mass of volcanic rocks comprises the eroded remnants 

of an ancient large composite volcanic cone, here called Morzhovoi 

volcano, in the area south of Frosty Peak. The two Walrus Peaks 

and other higher peaks in the area are believed to be remnants of the 

caldera rim of this ancient volcano.

Volcanic sedimentary rocks constitute the base of the formation 

and crop out along the Pacific coast south and east of Keynolds Head, 

here designated as the type locality. These rocks consist of poorly 

consolidated dark sandy shale, sandstone, and fine- to coarse-grained 

conglomerate composed of subrounded to rounded fragments of 

volcanic debris. They are conformably overlain by interbedded lava 

flows, coarse agglomerates, and volcanic breccias.
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 689

The lava flows of Morzhovoi volcano are light- to pinkish-gray 

porphyritic basalts; an intersertal texture is most common, but in 

some of the flows textures are intergranular or hyalopilitic. The 

principal phenocrysts are plagioclase (30-40 percent), augite (3-10 

percent), hypersthene (2-15 percent), and olivine (0-5 percent). Accessory minerals are principally magnetite and apatite. Secondary or 

alteration products are magnetite, limonite, iddingsite, serpentine, 

chlorite, tridymite, cristobalite, biotite, antigorite, and zeolites. The 

plagioclase phenocrysts are mostly subhedral labradorite, but some 

are bytownite; they range in size from 0.1 to 3.0 mm. The composition ranges from An60 to An75 and averages about An63 . Most 

of the feldspars are unaltered, but many have inclusions of glass, 

apatite, and unidentified cryptocrystalline materials; commonly they 

have progressive zoning and polysynthetic twinning. Hypersthene 

phenocrysts are euhedral to subhedral, weakly pleochroic, commonly 

unaltered, and range in size from 0.1 to 2.8 mm. Augite phenocrysts 

are euhedral to subhedral, commonly twinned, unaltered, and range 

in size from 0.1 to 0.8 mm. Olivine occurs in small amounts in nearly 

all the rocks examined. Where olivine is present, the hypersthene 

content is low; where olivine is absent, the hypersthene content is 

higher. Most of the olivine is subhedral and rarely larger than 0.2 

mm in diameter; commonly it is altered to iddingsite along joints and 

fractures, and less commonly it is partly or completely replaced by 

serpentine. Magnetite pseudomorphs of hornblende were seen in a 

few of these rocks; generally they are associated with minor amounts 

of chlorite and limonite, and only rarely with biotite.

Most of the interbedded pyroclastic rocks of Morzhovoi volcano 

are coarse-grained agglomerates and breccias. In the field the rocks 

appeared to be composed of fragments of light- to pinkish-gray porphyritic lava, similar to the flows just described, set in a tuffaceous 

matrix. The rocks were not examined microscopically.

The Morzhovoi volcanics do not appear to have been deformed. 

The low dips observed are believed to be all primary or initial .outward dips of a quaquaversal nature, which originated by eruption 

from either a central vent or from fissures on the flanks of the cone. 

The total thickness of the Morzhovoi volcanics is not known, but ,at 

least 3,000 feet.of the formation is exposed.

The lack of fossils in the Morzhovoi volcanics precludes, any precise 

determination of their age. The relative age, however, can be determined with some degree of confidence. Lithologically and mineralogically they are distinct from the older Belkofski tuff and Tachilni 

formation, and to a lesser degree from the rocks comprising the 

younger stratovolcanoes. The older rocks are better consolidated and
690 INVESTIGATIONS OF ALASKAN VOLCANOES

more altered than the Morzhovoi volcanics. Olivine, which is common in the Morzhovoi volcanics, is a rare component of the postMorzhovoi volcanic rocks. Structural differences are not diagnostic 

because the amount of deformation of the older Tertiary formations 

in many places is no greater than the initial dips of the Morzhovoi 

volcanics. The Morzhovoi volcanics, although believed largely to 

postdate the deformation of the older rocks, may be in part contemporaneous with some of the deformation. If the older rocks are late 

Tertiary in age, as postulated, then the Morzhovoi volcanics cannot 

be older than latest Tertiary in age. Late Tertiary and early 

Quaternary (?) volcanism has been described in the western Aleutians 

by Simons and Mathewson (1955, p. 28-29) and by Coats (1956a, p. 

50; 1956b, p. 72; 1956c, p. 91), and farther east on the Alaska Peninsula by Atwood (1911, p. 69-71), and by Kennedy and Waldron 

(1955, p. 11).

. By comparing the intensity and degree of glacial erosion of Morzhovoi volcano with that of Frosty Peak volcano, it is readily apparent 

that Morzhovoi volcano either is much older than Frosty Peak volcano, or that the latter has been active for a much longer span of time. 

Morzhovoi volcano has been deeply eroded into serrated peaks and 

knifelike ridges, separated by broad flat U-shaped valleys, some of 

which have completely breached what must have been the old caldera 

wall. Consequently, the original shape of the volcano has been almost 

completely destroyed, and all that can be seen now is the skeletal 

remains of what was once a major volcano. Frosty Peak volcano, in 

comparison, has been less severely eroded by glaciers, so that it retains much of its original symmetry. It is the author's opinion, 

therefore, that Morzhovoi volcano is not younger than middle Pleistocene in age.

BASAJLT FLOWS OF MOUNT SIMEON

A sequence of olivine basalt flows makes up a low isolated mountain mass, 942 feet high, 3 miles west of the airfield. The mass occurs 

as an asymmetric island of rock with steep northeast slopes and gentle 

southwest slopes surrounded by glacial drift. Because of the glacialdrift cover, exposures are poor, but four separate flows could be seen 

in the steeper northeast side. All flows have an apparent gentle dip 

southwestward toward Frosty Peak. These lavas are light-gray 

porphyritic rocks with an intergranular texture. The principal 

phenocrysts are plagioclase (35-40 percent), olivine (5 percent), pyroxenes (10-15 percent), and amphibole (5 percent). Accessory 

minerals are magnetite, apatite, crystobalite, and zeolites. The 

plagioclase is euhedral labradorite with an average composition of 

about An68 . The phenocrysts range in size from a few tenths of a millimeter to about 2 mm and are commonly zoned and polysynthetically
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 691

twinned. The pyroxene phenocrysts consist of both euhedral and subhedral augite crystals as large as 1 mm and hypersthene crystals as 

large as 2 mm; the hypersthene is only weakly pleochroic. The amphibole is brown basaltic hornblende that occurs as phenocrysts as large 

as 0.8 mm. Invariably the hornblende is partly replaced by magnetite 

and chlorite, and the magnetite commonly forms dark corroded rims 

around the crystals of hornblende. The olivine phenocrysts are subhedral, unaltered, and as large as 0.5 millimeter in maximum diameter. 

The extreme dissection and the composition of the lavas, which are 

similar to those of Morzhovoi volcano, suggest that the basalt flows of 

Mount Simeon were extruded sometime during late Tertiary to middle 

Quaternary time.

INTRUSIVE BOCKS

Intrusive rocks of the area include Tertiary stocks of quartz diorite, 

and Tertiary and Quaternary plugs, sills, and dikes of basalt and 

andesite. The two stocks in the mapped area are intruded into the 

Belkofski tuff: one is at the head of Lenard Harbor, and the other 

near the head of the large valley that trends westward from Thinpoint 

Lagoon. At Thinpoint Lagoon the stock is unconformably overlain by younger volcanic rocks. The stocks are made up of a medium 

to coarsely crystalline quartz diorite that contains about 5-10 percent quartz, 70-75 percent feldspar, and about 20 percent mafic minerals. Accessory minerals are apatite, biotite, and magnetite; the only 

alteration product is uralite. The quartz is anhedral and commonly 

forms granophyric intergrowths with orthoclase. Potassium feldspars 

are principally orthoclase and some microcline; plagioclase feldspars 

are principally andesine with an average composition of about An48, 

and a range in composition of from about An30 to An60 . The mafic 

minerals are largely augite and hypersthene; twinning is common 

in the augite but absent in hypersthene, and normally both are partly 

altered to uralite. The adjacent tuff beds have been locally sericitized, 

silicified, and bleached for a considerable distance from the stocks, so 

that the original composition of the rocks in these altered areas is 

difficult to determine.

Twin intrusive plugs of porphyritic hornblende andesite of an unknown age constitute Amagat Island. A landing was not feasible 

at Egg Island, but observed from a boat close inshore, it appeared 

to be a single plug similar to Amagat, and possibly contemporaneous 

with it in age. The Amagat Island plugs consist of approximately 

25 percent andesine phenocrysts, 0.1 to 5.5 mm long, and 5 percent 

green hornblende euhedra, 0.1 to 4.0 mm long, in a microgranular 

groundmass of stubby, tabular feldspar crystals and some carbonate 

minerals." Most of the feldspar phenocrysts are strongly zoned and 

resorbed. The hornblende phenocrysts are strongly pleochroic but
692 INVESTIGATIONS OF ALASKAN VOLCANOES

rarely twinned; some of them are rimmed by calcite and magnetite. 

Other minor accessory minerals are apatite, antigorite, chlorite, and 

limonite.

Several other plugs of a porphyritic dark-gray to black augite 

and olivine basalt intrude the Tertiary formations. At the margins 

of the plugs, the adjacent strata have been locally tilted and deformed. Numerous sills and dikes of dark-gray andesite and darkgray to black basalt also intrude the Tertiary formations, and some 

basalt dikes intrude the younger stratovolcanoes. Most of the 'dikes 

are small, ranging in thickness from 6 inches to 15 feet; only a few 

are more than 20 feet thick. As they can be traced for only short 

distances, they were not mapped.

QUATERNARY ROCKS

Quaternary rocks of the area include volcanic rocks of the composite cone of Frosty Peak volcano and the Pleistocene and Recent 

unconsolidated sediments of glacial, fluvial, marine, eolian, and volcanic origin.

FBOSTY PEAK VOI/CANICS

The dominant topographic and geologic feature in the area is the 

composite volcanic structure whose most prominent cone is Frosty 

Peak; the composite volcano is here called Frosty volcano. Although 

the earliest history of this volcano is obscured, activity presumably 

began from a single central vent somewhere near the present craters, 

and additional vents and fissures on its flanks probably contributed 

to its growth at various times. A shifting of the principal vent 

during the later stages of its development is indicated by the remnants of the two coalescing craters which now form the present 

summit caldera. Although explosive activity occurred at intervals 

throughout the growth of the main cone, it was subordinate to effusive activity. The explosions that did occur must have originated 

mainly from a magma at a low temperature, as most of the ejecta 

was blown out in a solid state and came to rest on the slopes as 

angular blocks in an ashy matrix. Because true scoria and rounded 

bombs are rare, the explosions were probably not of the Strombolian 

type of eruption, in which the ejecta would be sufficiently viscous 

to have their forms modified in flight.

The lava flows and pyroclastic rocks erupted from Frosty volcano, 

here named the Frosty Peak volcanics, are mostly augite basalts or 

hypersthene-augite basalts; a few are hornblende basalts. The type 

locality is Frosty Peak. The rocks are predominantly light gray, 

where unoxidized or unaltered, and are porphyritic. Most of the 

rocks have a felted or pilotaxitic texture; some have an intersertal 

texture; and only a few have an intergranular texture. The prin-
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 693

cipal phenpcrysts are plagioclase (25-40 percent), hypersthene (trace 

to 6 percent), and augite (3-8 percent); hornblende (0-8 percent) 

and olivine (0-2 percent) were seen in some thin sections.

The plagioclase phenocrysts are mostly subhedral labradorite, 

ranging in size from 0.1 to 3.5 mm and in composition from An60 to 

An65 . Generally the crystals are euhedral and unaltered and rarely 

do they show any resorption; commonly, however, they are progressively zoned, and many of the crystals show inclusions, principally of 

glass and apatite. The hypersthene phenocrysts are euhedral or subhedral and weakly pleochroic and range in size from 0.2 to 1.6 mm. 

In a few flows some of the hypersthene and augite crystals are intergrown; in others, augite occurs as thin reaction rims around some 

of the hypersthene crystals. The augite phenocrysts are euhedral 

or subhedral and commonly twinned and range in size from 0.3 to 

 1.0 mm. Both green hornblende and basaltic hornblende occur in 

these rocks. The latter predominates, and nearly all the crystals 

are rimmed witli secondary magnetite, or are partly to almost completely replaced with magnetite. Olivine occurs sporadically and 

rarely, generally as anhedral crystals altered to antigorite, iddingsite, 

and magnetite. Accessory minerals are magnetite, apatite, and 

pyroxene and feldspar in laths and microlites; also included is volcanic glass. The most common secondary or alteration products are 

palagonite or chlorophaeite, magnetite, and calcite; others include 

hematite, limonite, antigorite, Iddingsite, and zoisite. Tridymite, 

calcite, and zeolites occur as vesicle filling.

Separation and measurement of individual flows is impossible at 

most localities, but it is estimated that the individual flows average 

less than 40 feet in thickness, and in only a few places does the 

thickness of any .one flow appear to exceed 100 feet. Columnar 

structures in the flows are rarely well developed, but platy or slabby 

jointing is well developed in some places. Most of the rocks have 

little or no flow structure, and inclusions are uncommon. Local unconformities, which separate agglomerate beds from overlying lava 

flows, were seen in the large valley on the west flank of the mountain. 

Here small valleys 10 to 30 feet deep were eroded in some of the 

softer pyroclastic material prior to burial by later flows.

The maximum diameter of the two coalescing summit craters, which 

together constitute the caldera of Frosty volcano, is approximately 

31/2 miles in a northerly direction. The southern crater, which is 

the.largest, is now nearly filled by the younger volcanic rocks of 

Frosty Peak; the northern crater, and the remainder of the southern 

crater, are almost completely filled with ice. Because of intensive 

ice action, probably no part of the original crater walls now exists;
694 INVESTIGATIONS OF ALASKAN VOLCANOES

nevertheless, the present walls show the effects of extensive fumarolic 

action, and the normally somber colors of the lavas give way to more 

colorful hues of yellow, buff, brown, and orange. Where the lavas 

and pyroclastic materials have been attacked by rising gases and solutions they have been reduced to soft, friable masses of a brown earthy 

material, or they have been bleached to white kaolinic masses with 

films of sulfur and other minerals, chiefly iron oxides, lining the 

joints and fracture planes.

The compound nature and the scalloped margin of the caldera are 

probably related to concentric fracturing and collapse of separate 

cones, or the caldera may have been determined, in part, by collapse 

of the roofs of two semidetached magma chambers. Scalloped margins of the Santorin caldera in Greece (Williams, 1941, p. 268) and 

the Aso caldera in Kyushu in Japan (Williams, 1941, p. 278) have 

been ascribed to such processes, although both of these calderas are 

much larger in diameter than the caldera of Frosty volcano.

North of Frosty Peak, a rounded pluglike nunatak projects a few 

tens of feet above the icefield. Gaping bergschrunds, which surrounded it, prevented a detailed examination of the rock mass; it 

appeared, however, to be similar in megascopic character to the Frosty 

Peak lavas. Because of its position, the mass has been mapped with 

the Frosty Peak volcanics, but it could have been formed later than 

the formation of the caldera and contemporaneously with the volcanic 

rocks of the summit cone.

The age of Frosty volcano is not known, but it is presumed to be 

not older than Pleistocene. The amount of erosion by glaciers on the 

flanks of the volcano indicates that the volcano was probably largely 

completed before late glacial (Wisconsin) time, although the preservation of the symmetry of the cone suggests that the cone is probably not older than middle Pleistocene. The age of the Frosty Peak 

volcanics is therefore considered to be Pleistocene.

Because a permanent icefield obscures the configuration of the surface of the floor of the caldera, the summit cone of Frosty Peak is 

the only recognizable feature formed by volcanic activity after the 

development of the caldera. That some minor fumarolic activity 

still persists in the caldera, however, is apparent from a very mild 

odor of sulfur dioxide noted by the author while crossing the caldera 

icefield. The fumes presumably came from the eastern wall of the 

caldera, which was not examined at the time because of inclement 

weather. The presence of fumarolic activity in the caldera, however, does not necessarily mean that any violent eruptive activity 

has occurred within the caldera recently.

Volcanic rocks of the summit cone. The summit cone of Frosty 

Peak volcano is a fairly symmetrical composite volcanic cone built
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 695

up mainly within the southern crater, but partly overlapping the 

western rim of the caldera of its ancestral cone. The cone is approximately 11/2 miles in maximum basal diameter; perennial snow 

and ice mantle the slopes of the cone, and only relatively narrow, 

knifelike ridges project above the frozen cover. Instead of the usual 

bowl-shaped crater, the summit is a precipitous spineltke mass. The 

summit of the spine stands 1,000 feet or more above the caldera icefield at the base of the cone. The altitude of the summit is not 

definitely known. On plate 79 it is shown as approximately 6,700 

feet; on other maps and charts the altitude is shown as 5,784 and 

5,820 feet. The rocks of the cone are very similar to the lavas of the 

main volcano and consist of light-gray hypersthene and augite porphyritic basalts and minor amounts of pyroclastic material. Phenocrysts. of labradorite and subordinate augite and hypersthene are the 

most conspicuous minerals. Magnetite and apatite are common accessory minerals. The groundmass consists of plagioclase laths, 

augite grains, magnetite dust and grains, and brown glass.

Because erosion by ice and frost action has been most intensive on 

the eastern and northern slopes, where it has produced sheer cliffs, 

the summit is accessible only from the western side. The spine and 

parts of the cone exposed above the glacier on the north flank consist of lavas altered by solfataric action, producing colorful hues 

of brown, red, purple, yellow, and orange. The rocks are characteristically banded, containing considerable whitish material, probably from kaolinization of the feldspars. One thin section of relatively fresh rock from the summit spine resembles other lavas of 

the cone, but it is much more glassy. Zoned and twinned labradorite 

and pyroxene phenocrysts occur in a fine-grained matrix of stubby 

plagioclase laths, magnetite and hematite dust, glass, and some tridymite or cristobalite. Magnetite and hematite, and in places limonite, 

rim the pyroxenes; resorption and intergrowths of orthopyroxenes 

and clinopyroxenes are common. The specimen differs from others 

examined in thin section, however, in that unaltered glass occurs both 

as central cores and as concentric bands included within the plagioclase phenocrysts; this suggests that the lava was subjected to repeated and abrupt changes in temperature or pressure during 

extrusion and solidification.

The age of the summit cone, Frosty Peak, is not definitely known; 

considering the amount of glacial erosion, it probably has not been 

active for several hundreds or perhaps thousand of years.

GLACIAL DEPOSITS

Evidence of glaciation is abundant throughout the area: in the 

highlands, erosional features predominate; in the lowland, deposi-
696 INVESTIGATIONS OF ALASKAN VOLCANOES

tional features are largely dominant. Both till and stratified drift 

occur, but stratified drift in the form of glaciofluvial deposits greatly 

exceeds all others.

Only small patches of thin glacial drift occur in the mountainous 

areas or in the areas bordering the Pacific Ocean. Most of the 

Bering Sea coastal lowland and the lowlands encircling the larger 

bays, however, are mantled to an unknown depth by glacial drift. 

The drift extends well into some of the valleys and to the heads of 

some of those now occupied by active glaciers. Eskers and moraines 

form prominent local topographic features on the lowlands, but the 

dominant surface expression of the lowlands is that of a pitted outwash plain with innumerable low hills and depressions, which commonly contain lakes, swamps, or mud playas. This pitted outwash 

surface is in turn mantled by a dense vegetal cover of tundra, grasses, 

flowering ferns, shrubs, and thickets of alders and willows. Consequently, except in the bluffs along the shores, exposures are extremely poor, and a separation of the drift into individual units 

was not made.

Glaciofluvial deposits of sand and gravel predominate in the exposures afforded by the sea bluffs. Varved clays are exposed at the 

bases of the bluffs at a few localities. Capps (1934, p. 152) noted 

glaciolacustrine deposits on the west shores of Cold Bay during 

his reconnaissance of parts of the Alaska Peninsula. Thin beds of 

ash and lapilli, 2-5 inches thick, occur near the surface of the proglacial deposits in many places. Lateral and vertical gradations 

in the glacial sediments are rapid, and both foreset bedding and 

local unconformities occur commonly. Generally, the quantity, size, 

and angularity of included cobbles and boulders increases progressively from the coast to the mountain slopes, along with a similar 

increase in the size and angularity of the particles constituting the 

matrix.

Typical sections exposed in the beach cliffs are as follows:

Section on sea bluff near foot of dock at Cold Bay

Feet

8. Soil, silty, ashy; capped by tundra and grass________________ 2-3 

7. Ash, silty, poorly stratified__ ______ ___ ___ _______ 4

6. Sand, pumiceous, coarse; thin clay strata less than .5 in. thick_____ 1-1. 5 

5. Lapilli, fine, light-tan; in thin beds alternating with fine black lapilli,

and light-tan plastic clay; 6 in. of silty sand at base_ _____ 1-1.5 

4. Silt, sandy, brown____________________ . 2

3. Sand, poorly sorted and poorly stratified __ __ __ _ 6 

2. Gravel, sandy________________________ _ ' 2

1. Gravel, pebbly, sandy; base not exposed, lower 12 ft covered with

slopewash_______________ 25

Total thickness of section_____________________ 45±
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 697

Section on sea bluff in tack of old hangar at Cold Bay

Feet

6. Tundra and soil, dark-brown, ashy____________________ 1-2 

5. Silt, sandy, dark-brown, massive_:____________________ 11 

4. Sand and pebble gravel alternating in thin beds__________;_ 16 

3. Sand, stratified, coarse________:___________________ 3 

2. Sand, silty, fine; with lenses of clay fragments______________ 18 

1. Clay, massive at top; grading into thinly laminated varved clay at 

base; dark layers % in. thick, light layers 2-3 in. thick; base covered with slopewash_____________________________ 25

Total thickness of section_______________________ 75±

Nearly all fragments in the glacial deposits are volcanic rock types ; 

the only erratics observed were pebbles of vein quartz or granitic 

rock. Both types are believed to be chiefly of local derivation, but 

their source is not definitely known. The granitic rocks are probably 

derived from local small intrusive bodies, such as the diorite stocks 

in Thinpoint Valley and at the head of Lenard Harbor; or they may 

be, in part, of accidental ejecta origin. Some small quartz stringers 

and veins are in mineralized zones bordering dioritic intrusive masses, 

and these could account for the erratic pebbles of vein quartz. 

Striated boulders are rare in the glacial drift; striated bedrock, however, is common.

The exact thickness of the glacial drift is unknown. Bedrock 

underlying drift in the lowland area is not exposed. During the 

Army's occupation of the present airport site during World War II 

approximately 35 wells were dug or drilled for water supply. Unfortunately, no logs of these wells were kept at the time, but several 

of the dug wells were deep (maximum of 71 ft), and many more 

were drilled to depths of 100 feet or more (maximum of 119 ft); none 

is believed to have penetrated bedrock below the drift.

The glacial drift mapped on the lowlands is probably nearly all 

late Pleistocene, presumably late Wisconsin in age (Capps, 1931, p. 4; 

Pewe, and others, 1953, p. 12). Although Atwood (1911, p. 87, 90) 

found no evidence of older glaciations in his reconnaissance of much 

of the southwestern part of the Alaska Peninsula, recent workers in 

many other parts of Alaska, including the northern part of the 

peninsula, have recognized the existence of several major glaciations 

Pewe and others, 1953, p. 12). Although Atwood (1911, p. 87, 90) 

occurs in the Frosty Peak area, but if so, it was not recognized in this 

study. The ice certainly melted from the lowlands prior to the 

last crustal movement, which elevated the peninsula at least 100 feet 

in respect to sea level, as indicated by elevated stream and marine 

terraces along the Pacific coast, by entrenched-stream channels in
698 INVESTIGATIONS OF ALASKAN VOLCANOES

major valleys, both in alluvium and in bedrock, and by wave-cut 

cliffs and caves situated behind elevated beach ridges. Glaciers 

lingered in the mountains, however, long after ice had retreated from 

the lowlands; in the higher mountains, active glaciers are now contributing minor amounts of glacial drift to the upper reaches of the 

major valleys.

RECENT DEPOSITS

ASH AND LAFILLI

Thin layers of ash and lapilli, 2-5 inches thick, are widespread 

in the area both overlying the glacial drift and within the upper 

part of the drift. The material is generally coarse and falls in the 

upper and lower limits, respectively, of ash and lapilli. The material is commonly black and cindery or scoriaceous and includes 

some thin interbedded layers of pale-colored plastic, clayey very fine 

ash. The ash beds are overlain by a mantle, from 1 to 3 feet thick, 

consisting of a fairly homogeneous mixture of volcanic ash, silt, fine 

sand and plant remains, presumably mostly eolian in origin. Soil 

tests by the U.S. Army Corps of Engineers, Seattle District, Seattle, 

Wash., for the Civil Aeronautics Administration, reveal the material 

to consist of approximately 50 percent clay mineral aggregates, 20 percent volcanic ash, 10 percent quartz grains, 10 percent feldspar grains, 

and 10 percent organic material. The clay aggregates were probably 

formed from weathering of the feldspars and volcanic ash. Prevailing wind directions are such that only rarely could ash from Pavlof 

volcano or any of its satellites ever reach the western shores of Cold 

Bay. Most ash in the Cold Bay area was presumably derived from 

the volcanoes of Frosty Peak, or Amak Island to the north, which has 

been active more recently than Frosty Peak cone (Coats, 1950).

SAND DUNES

Large areas of well-sorted sand occur in dunes along the coasts; 

on the geologic map (pi. 79) only a few of the larger dune areas 

are shown. Onshore winds from the Bering Sea have blown sand 

from the wide beaches to form large foredunes which parallel the 

shoreline and cap the low bluffs. Large sand dunes parallel the 

shoreline and cap older beach ridges along the Pacific coast and in 

some of the larger bays, especially in the vicinity of the mouths of 

large streams and at the heads of shallow bays where abundant 

source material is available. Most of the dunes are fixed at present 

by a rank growth of beach grass; this suggests that most were formed 

during a much drier or colder climate than exists today.
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 699 

ALLUVIUM

Eecent alluvial deposits of unconsolidated gravel, sand, silt, and 

clay mantle the valley bottoms and flood plains. Terraces are rare, 

mostly because the overdeepening and widening of the valleys by 

glaciers has promoted the accumulation rather than removal of alluvium since glaciers filled the valleys. Detritus, contributed by steep, 

swift tributaries and by talus and soil creep, overloads the main 

streams, which then form braided channels on the flat valley floors 

of the streams draining into the Bering Sea and some of the larger 

bays. Streams draining into the Pacific Ocean, however, have been 

able to transport this detritus because they have steeper gradients 

and shorter courses. Consequently some valleys contain only a thin 

alluvial cover, 10 feet or less in thickness, and some of the streams 

are now incising their channels into bedrock.

Coarse gravel and sand predominate in the alluvium, but large 

amounts of silt and clay are mixed with the coarser fractions in the 

lower stretches of the larger streams; this fine material is contributed 

as rock flour from active glaciers and permanent icefields. In some 

of the larger valleys which still retain active cirque glaciers at their 

heads, outwash as it moves downstream is gradually diluted by nonglacial alluvium until eventually the outwash is lost in this alluvium. 

The distinction between glacial outwash and valley alluvium on the 

geologic map (pi. 79), therefore, is arbitrarily shown in most places.

BEACH DEPOSITS

A variety of beach deposits occur in the area, ranging from 

lagoonal muck and muds to coarse cobble and boulder deposits in 

beaches, spits, and bars. On the Pacific coast the Tertiary sedimentary and volcanic rocks and the glacial drift are being eroded 

rapidly by the vigorous action of waves and currents. The sand 

and gravel thus produced is deposited nearby as spits and bars, 

or as broad sandy beaches in the more sheltered heads of bays and 

coves. Spits at the mouths of lagoons are commonly composed of 

cobbles, indicating strong longshore currents; and prominent cobble 

spits nearly enclose Littlejohn Lagoon in Morzhovoi Bay and the 

two lagoons on the west shores of Cold Bay opposite Kaslakan Point. 

Large sand spits similarly almost enclose Thinpoint Lagoon and also 

produce the large lagoons at the heads of Morzhovoi and Cold Bays. 

Successive beach ridges are conspicuous behind the sand spits on 

the seaward side of Thinpoint Lagoon. The beach ridges are composed of either sand or gravel, whereas the swales commonly contain lakes or are swampy and filled with muck. Black sand, consisting chiefly of magnetite and pyroxenes, occurs locally along some 

of the beaches. Boulders, principally erratics derived from the glacial
700 INVESTIGATIONS OF ALASKAN VOLCANOES

drift, occur in many places along the beach and offshore. Most of 

these boulders are small, but some exceed 6 feet in diameter and are a 

hazard to small boats.

On the Bering Sea coast, where no bedrock is exposed to direct wave 

action, the erosion of the low bluffs of glacial drift and alluvium 

has produced extensive sand beaches. Large offshore sandbars, from 

a few feet to several tens of feet high, have been built upon the gently 

shelving floor of the Bering Sea. In places these sandbars are as 

much as 3 miles from the mainland shore. .

COLLUVIUM

Unconsolidated talus and other waste rock, ranging from coarse 

blocky lava rubble to fine sand and silt, mantles the lower slopes of 

the valley walls and beach cliffs. Composition of the material mainly 

reflects the type or types of rocks that crop out in the walls of the 

cliffs and valleys. In many places some finer eolian material included 

in these deposits is principally intermingled ash and silt. Most of 

the valley colluvium is relatively stable, except' at those points where 

the stream is actively cutting into a slope. However, colluvium along 

the coast tends to be less stable because of continued wave erosion, 

unless the slopes are protected by beach ridges.

STRUCTURE

The inferred structure of the area is shown in the geologic cross 

section shown on plate 79. The major structural feature is the north 

limb of a broad anticline that forms the Aleutian Range farther east 

on the Alaska Peninsula. Superimposed on the eroded remnants and 

northern flank of this anticline are the great masses of late Tertiary 

and Quaternary stratovolcanoes with their individually developed 

structures. The oldest rocks in the area, the Tertiary marine and 

volcanic sedimentary rocks, in general, have northerly and northwesterly dips of 10°-20°, locally as steep as 35°; dips as steep as 

75°-80° were noted only in the vicinity of intrusive masses. Although 

these older rocks are faulted to some extent, there appears to be very 

little contortion of individual beds. Only at one locality, where thinbedded shale, sandstone, and lenses of fine conglomerate were cut by 

many faults of small displacement, was crumpling and contortion of 

the shale beds observed. The abrupt termination of the Belkofski 

tuff at the eastern shores of Cold Bay suggests the existence of a 

major transverse fault in the vicinity of the bay, which probably accounts for the existence of the bay. No major linear faults were 

recognized in the younger volcanic rocks, but it is inferred that arcuate faults border the calderas.
GEOMOEPHOLOQY

Before the geomorphology of the Frosty Peak area can be completely understood, much more detailed local and regional studies 

of the western extremity of the Alaska Peninsula are needed. It 

is proposed here to point out some of the events that have occurred 

in the evolution of the major topographic features of the area, and 

to present some of the problems.that must await future studies.

A major lowland of varied width extends northwest from the 

mountain slopes to the shores of Bristol Bay. It is nearly continuous for the entire length of the peninsula, with a greatest width 

of about 25 miles. This tundra-covered lowland plain rises gradually 

from the Bering. Sea to intersect sharply with the mountain slopes 

at an altitude of about 200 feet; in some places the plain merges 

imperceptibly with the mountain slopes. The surf ace of this plain 

is now underlain to an unknown depth with glacial drift and alluvium. 

With the exception of a few isolated volcanic knobs projecting above 

the plain, bedrock was not observed anywhere on the lowland in the 

Frosty Peak or Pavlof areas. Exposures are very poor, however, 

and much of the lowland was not examined in detail, so that bedrock may be at or very near the surface in several places. The total 

areal extent of this plain, which certainly is much greater than 

that now exposed, is difficult to determine because of the lack of 

detailed hydrographic surveys of the adjoining Bering Sea.

How the plain was formed is not known, but it is presumed to be 

a broad coastal plain, formed before Pleistocene time, apparently the 

result of subaerial and marine erosion of a gradually rising coast 

which was subsequently modified by glacial action and the deposition of drift, and by changes of sea level during the Pleistocene. 

That part of the plain now exposed is almost entirely constructional 

and has been formed by the deposition of till and proglacial outwash 

which, in part, have been reworked and redeposited by streams and 

waves.

The age of this coastal plain is similarly unknown, but it may have 

been in the process of forming since middle Tertiary time, comparable to major erosion surfaces noted farther west (Gates and 

others, 1954, p. 447; Gates and others, 1956, p. 130; and Coats, 1956c, 

p. 91).

Little else is known of the earlier erosional history of the area 

because of the subsequent modification by intensive glaciation throughout the Pleistocene. At some time, and perhaps several times during 

the Pleistocene epoch, the mountainous areas accumulated extensive 

icefields. Valley glaciers from these icefields coalesced on the Bering 

Sea lowland to form large piedmont glaciers several hundreds of
V 

702 INVESTIGATIONS OF ALASKAN VOLCANOES >~

feet thick. Valley glaciers that discharged southward, however, were 

much shorter and apparently calved off directly into the Pacific Ocean 

without forming piedmont glaciers.

A local icecap may have existed in the area during glacial times. <"' 

Although the present-day climate is cool and comparatively mild 

and the precipitation is relatively low, this climate together with the 

topography are such that a much greater accumulation of snow and 

ice could very easily occur with any prolonged lowering of temperatures. If it is assumed, as has just been suggested, that the Bering 

Sea surface was completely frozen during glacial times, then the air 

overlying the frozen surface of the Bering Sea could take on continental characteristics, and much lower temperatures would occur 

than under present conditions. Then, if the Pacific Ocean remained 

as an open body of water, the peninsula would be the confluence of 

very cold and dry northern continental air masses with moister and 

warmer maritime air masses an ideal situation for large accumula- W 

tions of snow and ice. Also, with progressively lowered normal tern- f, 

peratures, a perennially frozen Bering Sea would tend to produce even 

lower temperatures than normal, thus the persistence of snow would be 

increased throughout the summer months. The volume of ice produced from both increased snowfall and reduced melting might very 

easily grow to local ice-sheet proportions.

Because of the comparative warmth of the north Pacific Ocean, it yseems unlikely that much sea ice developed along the Pacific coast, 

even during the glacial epochs. Because of the comparative coldness 

of the Bering Sea, however, it seems probable that sea ice very likely 

completely filled the Bering Sea during those parts of glacial times 

when sea level was high. During the winter of 1955-56, Cold Bay 

froze over for the first time on record, forming an ice layer about ^ 

4 inches thick and indicating that the Bering Sea surface to the 

northward was also completely ice covered (U.S. Dept. Commerce, 

1956). Therefore it seems reasonable to expect that during times 

of glaciation, which were also times of prolonged minimum temperatures, the Bering Sea, and probably many of the smaller bays, were 

solidly packed with sea ice. Flint (1947, p. 223) arrived at a similar *i 

conclusion concerning the conditions that probably existed during 

glacial episodes in the Bering Sea and north Pacific Ocean. ^

Eustatic changes in sea level must have occurred in the area both 

during and after Pleistocene time, but to what extent is not known. 

The latest change in the Frosty Peak area has been an elevation of 

the land relative to sea level of a maximum of about 100 feet. Evi- ^ 

dences of this change, however, were not studied in detail. A maximum sea-level reduction of about 45 to 150 meters (about 150-500 ft)
GEOLOGIC RECONNAISSANCE OF FROSTY PEAK VOLCANO 703

probably occurred during the most extensive glaciation (Tmmbull 

and others, 1958, p. 10). A lowering of sea level of this magnitude 

would expose nearly all of the Bering Sea shelf. Buffington and 

others (1950), believed that a rather continuous slope break at about 

85 fathoms (510 ft) on this conspicuously flat shelf marked an old 

shoreline cut at a time of lowered sea level. How much of this depth 

can be attributed to an overall lowering of sea level and how much 

to crustal deformation is not known. Barth (1956, p. 154) believed 

that the Pribilof area in the Bering Sea was subject to large vertical 

crustal movements during the Pleistocene. His evidence, however, 

is based on the singular belief that the erosion surface developed on 

the basement peridotite could be due only to normal ice erosion. It 

seems more likely that the erosion surface was actually formed before 

Pleistocene time by wave action and that the evidence for glacial 

erosion is superimposed on a preexisting wave-cut platform. However, the erosion surface may have been formed principally by pack 

ice, as were the "strand flats" in the Frobisher Bay area on Baffin 

Island, Canada (Wengerd, 1951, p. 631). Either of these possibilities precludes the necessity for large crustal movement in the area.

GEOLOGIC HISTORY

The geologic history of the Frosty Peak area records recurrent and 

prolonged periods of volcanism separated by periods of relative quiescence. The latter are characterized by weathering, erosion, and 

normal stream alluviation and marine deposition.

The earliest event that can be inferred from the visible geologic 

records is a relatively long period of explosive volcanism, presumably 

in middle Tertiary time, when the beds of Belkofski tuft accumulated 

to a thickness of several thousand feet. Locally, the eruptive materials were extensively reworked by streams, and volcanic sands 

and gravels were deposited in lowland areas. Active volcanism was 

interrupted periodically, and forests of conifers flourished, only to be 

subsequently destroyed by burial from renewed volcanic activity. 

Later, volcanism ceased and a period of orogeny ensued, during which 

time the beds of the Belkofski tuff were intruded and altered by 

diorite.

Later in Tertiary time, when the land masses had been lowered by 

erosion, sea level fluctuated and sandstone, graywacke, fine conglomerate, and some shale the Tachilni formation accumulated on the 

bottoms of the shallow seas of the Pacific Ocean and the adjoining 

low-lying landmasses. These sedimentary processes were then interrupted, presumably near the close of Tertiary time, and the Tachilni formation and older rocks were compressed into gentle folds, 

and faulted. During this deformation, igneous activity was renewed,
704 INVESTIGATIONS OF ALASKAN VOLCANOES

and basalt and andesite were intruded along zones of weakness developed in these older rocks.

Volcanism was again resumed in very late Tertiary or in early 

Quaternary time, and the large stratovolcano of Morzhovoi was built 

on the older Tertiary sediments and volcanic rocks, probably along 

rifts that developed in the older rocks; the basalt flows of Mount 

Simeon were also probably extruded at this time. At first the eruptions of Morzhovoi volcano must have been mostly explosive, as the 

initial products are predominantly pyroclastic and volcanic sedimentary rocks. Later, however, quiet flows of basaltic lava predominated. Formation of the summit caldera indicates that late in 

the history of this volcano active volcanism culminated in a series of 

eruptions, probably of gas-rich magma. The initial explosions were 

probably weak; later, however, the size and volume of ejecta increased 

until the energy had spent itself and the magma chamber had been 

depleted. When the magma chamber became exhausted, or nearly so, 

the crater walls began to collapse, until the entire summit of the cone 

had collapsed to form a large caldera, similar to the formation of other 

large calderas, such as Krakatoa, Santorin, and Crater Lake 

(Williams, 1941, 1942). Apparently after the collapse, in early or 

middle Pleistocene time, the volcano became inactive. Subsequent 

erosion by streams, glaciers, and frost action has removed much of 

the original volcano.

Later in the Pleistocene, while Morzhovoi volcano was still being 

dissected, volcanism was again renewed in Frosty volcano to the 

north. Whether this renewed activity stemmed wholly from an 

entirely new vent, or whether it represents renewed activity of .a 

parasitic cone on the north flanks of the older volcano is not known. 

Late in the history of this volcano, active volcanism also culminated 

in a series of eruptions similar to that postulated for Morzhovoi 

volcano, and the summit of the cone collapsed to form a small compound caldera.

Late in Pleistocene time, after another period of quiescence, volcanism was again renewed this time in the southern crater of the Frosty 

caldera and the composite summit cone of Frosty Peak was built. 

After volcanism ceased, probably in late Pleistocene or Eecent time, 

erosion by wind, waves, ice, and water greatly modified these volcanoes and their surrounding lowlands.

Some eustatic changes of sea level have occurred in the Frosty Peak 

area, probably both during and since the Pleistocene. The most 

recent change is a relative lowering of sea level, recorded by elevated 

stream and marine terraces near the Pacific coast, by entrenchedstream channels in major valleys, both in alluvium and in bedrock, 

and by wave-cut cliffs and caves behind elevated beach ridges.
705

REFERENCES CITED

Atwood, W. W., 1911, Geology and mineral resources of parts of the Alaska

Peninsula: U.S. Geol. Survey Bull. 467, 137 p. 

Baker, Marcus, 1906, Geographic dictionary of Alaska: U.S. Geol. Survey Bull.

299 (2d ed.), 690 p. 

Barth, T. F. W., 1956, Geology and petrology of the Pribilof Islands, Alaska :

U.S. Geol. Survey Bull. 1028-F, p. 101-160. 

Buffington, E. C., Carsola, A. J., and Dietz, R. S., 1950, Oceanographic cruise to

the Bering and Chukchi Seas, summer 1949: Navy Electronics Lab. Rept.

204, pt. 1, Sea floor studies. 

Capps, S. R., 1931, Glaciation in Alaska: U.S. Geol. Survey Prof. Paper 170-A,

p. 1-8.

 1934, Notes on the geology of the Alaska Peninsula and Aleutian

Islands: U.S. Geol. Survey Bull. 857-D, p. 141-153. 

Coats, R. R., 1950. Volcanic activity in the Aleutian Arc: U.S. Geol. Survey

Bull. 974-B, p. 35-^9.

 1952, Magmatic differentiation in Tertiary and Quaternary volcanic 

rocks from Adak and Kanaga Islands, Aleutian Islands, Alaska: Geol. Soc. 

America Bull., v. 63, p. 485-514.

 1956a, Geology of northern Adak Island, Alaska: U.S. Geol. Survey 

Bull. 1028-C, p. 45-67.

 1956b, Geology of northern Kanaga Island, Alaska: U.S. Geol. Survey 

Bull. 1028-D, p. 69-81.

 1956c, Reconnaissance geology of some western Aleutian Islands, Alaska:

U.S. Geol. Survey Bull. 1028-E, p. 83-100. . Collins, H. B., Jr., Clark, A. H., and Walker, E. H., 1945, The Aleutian Islands:

Their people and natural history: Washington, Smithsonian Institution,

War Background Studies 21. 

Ball, W. H., 1896, Report on coal and lignite of Alaska: U.S. Geol. Survey 17th

Ann. Rept., pt. 1, p. 763-875. 

Flint, R. F., 1947, Glacial geology and the Pleistocene epoch: New York, John

Wiley and Sons, 589 p. 

Gates, Olcott, Fraser, G. D., and Snyder, G. L., 1954, Preliminary report on the

geology of the Aleutian Islands: Science, v. 119, no. 3092, p. 446-447. 

Gates, Olcott, Fraser, G. D., Snyder, G. L., and Gibson, William, 1956, Interpretation of the configuration of the Aleutian Ridge: Geol. Soc. America

Bull., v. 67, p. 127-146. 

Grewingk, Constantin, 1850, Beitrag zur Kenntniss der orographischen und

geognostischen Beschaffenheit der Nordwest Kuste Amerikas, mit den

anliegenden Inseln: Russ. K. min. Gesell. Verh., St. Petersburg, 1848-49,

p. 76-342. 

Hubbard, B. R., 1935, Cradle of the storms: New York, Dodd, Mead, and Co.,

285 p. 

Jaggar, T. A., 1929, Mapping the home of the great brown bear: Natl. Geog.

Mag., v. 55, p. 109-134. 

 1945, Volcanoes declare war; logistics and strategy of Pacific volcano

science: Honolulu, Hawaii, Paradise of the Pacific, Ltd., 166 p. 

Kennedy, G. C., and Waldron, H. H., 1955, Geology of Pavlof Volcano and

vicinity, Alaska: U.S. Geol. Survey Bull. 1028-A, p. 1-19. 

Knappen, R. S., 1929, Geology and mineral resources of the Aniakchak district,

Alaska: U.S. Geol. Survey Bull. 797, p. 161-227.
706 INVESTIGATIONS OF ALASKAN VOLCANOES

Palache, Charles, 1904, Geology about Chichagof Cove, Stepovak Bay; with 

notes on Popof and Unga Islands [Alaska]: Harriman Alaska Expedition, 

v. 4, p. 69-88.

Pettijohn, F. J., 1949, Sedimentary rocks: New York, Harper and Brothers, 

526 p.

P6w6, T. L., and others, 1953, Multiple glaciation in Alaska, a progress report: 

U.S. Geol. Survey Circ. 289,13 p.

Simons, F. S., and Mathewson, D. E., 1955, Geology of Great Sitkin Island, 

Alaska: U.S. Geol. Survey Bull. 1028-B, p. 21-43.

Smith, W. R., and Baker, A. A., 1924, The Cold Bay-Chignik district, Alaska: 

U.S. Geol. Survey Bull. 755, p. 151-222.

Trumbull, James, and others, 1958, An introduction to the geology and mineral 

resources of the continental shelves of the Americas: U.S. Geol. Survey 

Bull. 1067, 92 p.

U.S. Dept. of Commerce, Weather Bureau, 1956, Local climatological data with 

comparative data, 1956, Cold Bay, Alaska.

Wengerd, S. A., 1951, Elevated strandlines of Frobisher Bay, Baffin Island, 

Canadian Arctic: Geol. Rev., v. 41, p. 622-637.

Wentworth, C. K., and Williams, Howel, 1932, The classification and terminology 

of the pyroclastic rocks: Natl. Research Council Bull. 89, Rept. Comm. Sedimentation 1930-32, p. 19-53.

Williams, Howel, 1941, Calderas and their origin: California Univ. Pub., Dept. 

Geol. Sci. Bull., v. 25, no. 6, p. 239-346.

 1942, The geology of Crater Lake National Park, Oregon, with a reconnaissance of the Cascade Range southward to Mount Shasta: Carnegie 

Inst. Washington Pub. 540,162 p.
INDEX

Page

Abstract-_.________________ 677-678 

Accessibility--... 079-683 

Acknowledgments____.___.___._ 679 

Alaska Peninsula..._...__._.... . 681

Aleutian Range. _._____________ 681 

Aleutian volcanic arc___________-_ 678 

Alluvium.... 699

Amagat Island plug.._.___-___-_ 691 

Amak Island_...._____... ... 698

Animal life 683

Anticline___._._____. _._.. 700 

Antigorlte 692,693

Apatite 689,692,693

Ash.... 698

Aso caldera, Japan...______...._ 694

Augite ..... 688,693

Barabaras (native Aleut sod huts)____._ 681 

Basalt flows. 690-691,692,693 

Beach deposits... . 699-700

Belkofskituff..... ............ 684-685,703

Bergschrunds_ .... ... ... ... 694

Bering Sea lowland .... ....... 682

Calcite . ...... 688,692,693

Ohlorite ..................... ....... 692

Chlorophaeite___________._...... 693

Climate.- 682-683

Cold Bay Airport... 681

Colluvium__.________._._._ 700 

Cristoballte.... ........... ....... 688,689

Dikes........ 692

Drainage... 681-682

Echinoids.. ....................... ... 687

Egg Island plug.._ . . .. 691 

Erosion____ 694,700,703

Erratics.. 697

Eustatic changes in sea level_... . 702-703,704

Fieldwork ............................ 679

Fossils.-... 685,687 

Frosty Peak volcanics ... 692-695

Gastropods________________._ 687 

Geography..__________... .. 679-683 

Geologic history_____._...__ . 703-704 

Geomorphology.._... .. ....... 701-703

Glacial deposits__ -__.___ . ... 695-698 

Glacial drift ... ....... 697

Glaciers.. 698,699,701

Hematite___.__....__ ._..__ 693 

History, geologic_______________ 703-704 

Hornblende_____..___.__... . 693 

Hypersthene_ __.___ 688

Page 

Iddingsite-. ............. ..... 688,689,693

Introduction._________________ 678 

Investigations, previous.. _________ 678-679

Kenai formation..._____________.. 687

Labrador! te...___--...______.... 

Lapilli ... ...... 698

Lavas.. .. 688,689,690,694 

Lenard Harbor____________ _____. 684 

Llmonite___________________ 692 

Littlejohn Lagoon...._____________ 699

Location_ 679-681

Lowland....._________________ 701

Magnetite 688,689,692,693 

Morzhovoi volcano_________ 688,689,690,704 

Mount Simeon, basalt flows of_______ 690-691

Nunatak__....._______________ 694 

Ollvlne... ... ........ 688,689,693

Palagonite._____...._.__... 693

Pa vlof volcano ..___.________ 679 

Pelecypods. ........... ... .... 686,687

Phenocrysts .............. 689,690,691,693,696

Plugs.... . 691-692

Precipitation ................. _... 682

Pumice. . ________ ... 686 

Pyrite ......... ...... .... ... 685

Pyroxene____________________ 688

Quartz. . ..__.. ..._.... 686 

Quartz diorite________________ 691 

Quaternary rocks .___............... 692-700

Recent deposits.... ............ 698-700

References cited......___....._...... 705-706

Reynolds Head. 688

Sand dunes__________________ 698 

Sandstone- ....____._....... 686

Santorin caldera, Greece. . . . 694 

Sills. 692

Soil, tests of.. - 698

Solfataric action. __........__..._ 695

Stocks. 691,697

Storms, in report area____________ 682 

Strand flats. ._____ .. .... . 703

Stratovolcanoes ..___._.__. 692,700,704 

Streams...--- 699

Structure-_._.__..._____..... 700

Tachilni formation....---...___.__ 686-687 

Tertiary rocks.... ... .. 684-688

Tertiary and Quaternary rocks. ______ 6S8-692 

Thlnpolnt Lagoon, volcanic rocks of____ 688,691

707
708 INDEX

Page

Topography____.._____.__...__ 681-682 

Transportation facilities, in report area... __ 681 

Tridymite 688,689,693

Tundra plants__________________ 683

Unga formation ___ 687 

Uralite.- 691

Vegetation...___ ......___ _.. 683

Page

Volcanic rocks.__._____.._______ 688 

Volcanoes, potential danger to civil and military installations from______ 678

Williwaws.. ....... ......... 683

Winds.... 683, 698

Zeolites-... 688,689,693

Zoisite - . 693

o