U.S. Geological Survey Bulletin 2072 
Frontispiece. Mount Wrangell from near Tonsina (about no, and a prominent steam plume rises from one of the 

20 mi south of Copper Center), probably during summer summit craters. Mount Zanetti, a large cinder cone on 

1902. Dark ash, apparently from phreatic eruptions, the north flank of Mount Wrangell, is at left. Photograph 

blankets the ice- and snow-covered surface of the volca- by W.C. Mendenhall, U.S. Geological Survey. 
Guide to the Volcanoes of the 

Western Wrangell Mountains, 

Alaska-Wrangell-St. Elias 

National Park and Preserve 

By Donald H. Richter, Danny S. Rosenkrans, and Margaret J. Steigerwald 

U.S. GEOLOGICAL SURVEY BULLETIN 2072 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director 

For sale by 

U.S. Geological Survey, Information Services 

Box 25286, Federal Center 

Denver, CO 80225 

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

not imply endorsement by the U.S. Government. 

Text and illustrations edited by George A. Havach 

Graphics prepared by Michele Coveau 

Book design and layout by Linnea Larsen 

Library of Congress Cataloging-In-Publication Data 

Richter, Donald H. 

Guide to the volcanoes of the western Wrangell Mountains, Alaska : Wrangell-St. Elias National Park and Preserve / by 

Donald H. Richter, Danny S. Rosenkrans, and Margaret J. Steigerwald 

p. cm. - (U.S. Geological Survey bulletin ; 2072) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:2072 

1. Volcanoes-Alaska-Wrangell Mountains. I. Rosenkrans, Danny S. II. Steigerwald, Margaret J. III. Title. IV. Series. 

QE75.89 no. 2072 

[QE524] 

557.3 s-dc20 94-32571 

[551.2'1 '097983] CIP 

Cover. The massive, ice-covered face of Mount Sanford. View westward across West Glacier. Photograph by 

D. Rosenkrans, 1984. 
CONTENTS 

Introduction ................................................................................................................ . 

Early history and geologic exploration....................................................................... 1 

A national park in the Wrangells ............ .................................................................... 3 

Geologic background ... . . .... . . ...... .... .. . ... . . . ..... . .. . . ..... . . . ... . . .... . ..... ... . ... .. ............... . . .. ... .... 3 

Volcanoes and plate tectonics ....... .. .. .... .. .... ............. .................. ..... ...... ............ ... ... . ... 3 

The Wrangell volcanoes.............................................................................................. 7 

How did they form?............................................................................................ 7 

How old are they?............................................................................................... 8 

How tall are they?............................................................................................... 10 

How do they compare with other mountains?..................................................... 10 

Descriptions ofindivictual volcanoes ......... ............... ... . ....... ..... . ........... ..... . ....... 10 

Mount Wrangell....................................................................................... 10 

Mount Drum............................................................................................. 13 

Mount Sanford......................................................................................... 16 

Capital Mountain...................................................................................... 18 

Tanada Peak ..... ....... ... . . ..... ... ....... ...... .... . . .. ...... . . . . ... . . . ... . . . ........ ... .. ...... ...... 20 

Mount Jarvis............................................................................................. 21 

Skookum Creek Volcano.......................................................................... 22 

Mount Blackburn ................. ........................... ........................... .............. 24 

Boomerang Volcano ...... .... . . . ... ........... ..... ...... .. ... . ...... ...... ........ ... . . ..... ... ... . 25 

Mount Gordon.......................................................................................... 25 

White River Ash.......................................................................................................... 27 

Mud volcanoes ... . . .... .. .. .. . . .... .. ..... ..... ..... .. ......... ....... ............... ... . .. ... . . ......... ... . . ... ... . . .. .. 29 

Ackno\vledgments ... . .... . . . . .. . . ....... ..... .. .. . . . ......... .................. ... . ...... .... ........ ........ ........... 29 

Selected references...................................................................................................... 30 

FIGURES 

1. South-central Alaska and part of the Yukon Territory, Canada, showing early exploration routes of Allen 

in 1885 and Schwatka and Hayes in 1891 and route of the Cordova-Kennicott Railroad that was used from 

191ltol938 ......................................................................................................................................................... 2 

2. South-central Alaska and part of the Yukon Territory, Canada, showing Wrangell volcanic field and some 

major geologic features......................................................................................................................................... 4 

3. Western North America, showing present position of Wrangellia composite tcrrane and its probable 

position 250 million years ago, before it moved northward as part of an ancient Pacific plate ........................ 5 

4. Major crustal plates of the world ..... .... .... .. .. ... ..... ....... ... ... .... ....... ... .... .... ................... .... . ...... ...... .. ..... .. ... ... .......... 5 

5. Diagrammatic cross section through the Earth's crust and upper mantle, showing plate-tectonic features 

discussed in text.................................................................................................................................................... 6 

6. Diagrammatic north-south cross sections through south-central Alaska and the northern Pacific Ocean, 

showing development of Wrangell volcanic field through subduction of the Pacific plate................................ 7 

7. Wrangell Mountains and part of the St. Elias Mountains.................................................................................... 8 

8. Diagrammatic cross section model illustrating development of a Wrangell volcano......................................... 9 

9. Known periods of eruptive activity for radiometrically dated western Wrangell volcanoes.............................. IO 

10. Comparative profiles of some Pacific-rim volcanoes........................................................................................... 11 

11. Topographic and generalized geologic map of Mount Wrangell......................................................................... 12 

12. Mount Wrangell from Willow Lake at mile 87 on the Richardson Highway..................................................... 12 

V 
VI CONTENTS 

13. Topographic and generalized geologic map of Mount Drum.............................................................................. 14 

14. Mount Drum from mile 1 on the Tok Cutoff of the Glenn Highway................................................................. 14 

15. Mount Drum at sunset from Willow Lake at mile 87 on the Richardson Highway........................................... 15 

16. Generalized geologic cross section through Mount Drum .................................................................................. 16 

17. Approximate extent of volcanic avalanche and mudflow deposits probably generated by late cataclysmic 

eruptions of Mount Drum..................................................................................................................................... 16 

18. Topographic and generalized geologic map of Mount Sanford........................................................................... 17 

19. Mount Sanford from the Gulkana Airport on the Richardson Highway............................................................. 18 

20. Topographic and generalized geologic map of Capital Mountain....................................................................... 19 

21. Capital Mountain and Mount Sanford from mile 58 on the Tok Cutoff of the Glenn Highway........................ 19 

22. Topographic and generalized geologic map of Tanada Peak............................................................................... 20 

23. Tanada Peak from mile 26.5 on the Nabesna Road............................................................................................. 21 

24. Topographic and generalized geologic map of Mount Jarvis.............................................................................. 22 

25. Mount Jarvis from southeast slopes of Skookum Creek volcano........................................................................ 23 

26. Topographic and generalized geologic map of Skookum Creek volcano........................................................... 23 

27. Cross section through Skookum Creek volcano, showing some hypothetical subsurface features.................... 24 

28. A pair of 6-foot-thick andesite dikes intrude poorly consolidated rhyolite pyroclastic deposits of 

Skookum Creek volcano....................................................................................................................................... 25 

29. Topographic and generalized geologic map of Mount Blackburn....................................................................... 26 

30. Mount Blackbum, highest of western Wrangell volcanoes, from east of Nabesna Glacier............................... 27 

31. Topographic and generalized geologic map of Boomerang volcano................................................................... 27 

32. Topographic and generalized geologic map of Mount Gordon ......... ......... ............ .............. ................ ............ ... 28 

33. Mount Gordon from southeast slopes of Skookum Creek volcano..................................................................... 28 

34. Distribution of the White River Ash Bed in Alaska and Canada........................................................................ 29 

35. Lower Klawasi mud volcano................................................................................................................................ 30 

TABLES 

1. Highest peaks of the Wrangell Mountains........................................................................................................... 10 

2. Highest mountains of North America................................................................................................................... 1I 

GLOSSARY OF GEOLOGIC TERMS 

This glossary defines some geologic words and terms that are used frequently throughout this guide and that may be 

unfamiliar to the reader. Definitions are mostly modified from the third edition (1987) of the Glossary of Geology, 

published by the American Geological Institute, Alexandria, Va. 

Accreted- The attachment, or welding, of an exotic terrane to another terrane. 

Agglutinate- A lava flow consisting chiefly of remobilized, generally welded cinder, spatter, and volcanic bombs. 

Andesite- See basalt. 

Asthenosphere- The part of the upper mantle that is we·ak and behaves more like a fluid than a solid. 

Basalt- Basalt and the other rock names- andesite, dacite, and rhyolite-used frequently in this guide refer to a series of 

common volcanic rocks that are distinguished primarily by their silica (SiO2) content. Basalt contains the least silica 

(less than about 52 weight percent) and rhyolite the most silica (more than about 70 weight percent); andesite and 

dacite contain intermediate amounts. The silica content of a volcanic rock is determined by that of its parent magma, 

which, in turn, affects a magma's physical properties and allows insight into its mode of eruption. For example, lowsilica rocks (basalts) tend to crystallize from hot (>l ,000°C [2,040°F]), fluid, nonexplosive magmas, whereas highsilica rocks (rhyolites) tend to crystallize from "cool" (<900°C [1,675°F]), viscous, sometimes-explosive magmas. 

Caldera-A large, generally circular volcanic depression whose diameter is many times larger than that of the included 

central vent. 
VII CONTENTS 

Chalcocite-A heavy, blackish-gray mineral containing approximately 80 weight percent copper and 20 weight percent 

sulfur. 

Cinder cone-Small, steep~sided conical hill built mainly of cinder, spatter, and volcanic bombs 

Cirque-A crescentic or horseshoe-shaped basin at the head of a glacial valley, formed by the plucking action of ice 

when the valley was filled by a glacier. 

Dacite-See basalt. 

Dike swami-A group of dikes (tabular injections of magma along crustal fractures), either radial outward from a single 

source or in parallel arrangement. 

Exotic terrane-A sequence of rocks that formed at some distance from where it is now found that was transported to its 

present position by crustal-plate motion. 

Fumarole-A vent that discharges hot volcanic gases and steam. 

Granite-A coarsely crystalline igneous rock that results from solidification of a magma at depth in the Earth's crust. Its 

chemical composition is nearly equivalent to that of rhyolite. 

lntracaldera-Referring to lava flows and other volcanic features that are confined to a caldera. 

Litlwsphere-Th,:, sulil.l parl of Lhe Earth (as opposed to the atmosphere and hydrosphere) that includes the crust and 

upper mantle and rides on the underlying asthenosphere. 

Magma-Molten rock generated within the asthenosphere; the parent of all volcanic and plutonic rocks. 

Mantle-The zone of the Earth below the crust and above the core. 

Metamorphic rock-A rock derived from preexisting rocks by chemical, mineralogic, or structural changes at depth in the 

Earth's crust. 

Meteoric-Referring to water of recent atmospheric origin, such as rain or snow. 

Paci.fie "rim offire"-Part of the continental margin of the Pacific Ocean, so named because of the active volcanoes that 

occur along much of it. 

Phreatic activity-An explosive steam and rock-fragment eruption caused by the sudden heating of ground water as it 

comes in contact with hot volcanic rock or magma. 

Pluton-A body of igneous rock that solidified in the Earth's crust. 

Pyroclastic-A general term referring to all volcanic material that is produced by explosive eruptive activity, such as ash, 

cinder, spatter, and bombs. 

Radiocarbon dating-Calculating the age of organic material by measuring the relative amount of the radioactive isotope 

of carbon (

14C) remaining in the sample. 

Radiometric K-Ar dating-Calculating the geologic age of a rock by measuring the relative amounts of the radioactive 

isotope of potassium (K) and its decay product argon (Ar) within the rock. 

Rhyolite-See basalt. 

Rift zone-A system of fractures on the flank of a volcano that generally originate in the summit area and along which 

eruptions may occur. 

Ring fracture-A circular fault pattern generally associated with caldera subsidence. 

Shield volcano-A broad dome built mainly of fluid lava flows. 

Spreading ridge-A suboceanic zone where magma rises between two crustal plates and forces them apart. 

Stratovolcano-A large, steep-sided conical mountain built mainly of pasty lava flows, cinder, and pyroclastic deposits. 

Strike-slip fault-A major vertical erustal break along which movement has been generally horizontal and parallel to the 

trace of the fault. 

Subduction-A zone were one crustal plate overrides another along a convergent margin. 

Volcanic arc-A curved belt of volcanoes above a subduction zone area where crustal plates converge. 
Guide to the Volcanoes of the Western Wrangell Mountains, 

Alaska-Wrangell-St. Elias National Park and Preserve 

By Donald H. Richter, Danny S. Rosenkrans,1 and Margaret J. Steigerwald1 

INTRODUCTION 

Magnificent, breathtaking views of the snow-covered 

Wrangell Mountains in Wrangell-St. Elias National Park 

and Preserve (see back cover) await every visitor to this 

part of Alaska on a clear day. Mount Wrangell itself, a 

massive shield-shaped volcano and namesake of the range, 

still occasionally signals its active presence with steam 

plumes, while nearby, Mounts Sanford, Drum, and Blackburn lie dormant, the eroded peaks of older, once larger 

volcanoes. Knowing that these spectacular mountains are 

volcanic remnants provokes many intriguing questions: 

When did they last erupt? How tall were they? How do 

they compare with other volcanoes of the world? Will they 

erupt again? These are some of the questions addressed in 

this guidebook. 

Designed for both the geologist and the lay reader, 

this guide describes the geologic history of various landscapes viewed from major roadways in and around 

Wrangell-St. Elias National Park and Preserve. It identifies 

places where visitors can touch a mudflow, view the chronologic development of a Wrangell volcano, and even hike 

into the core of an ancient volcano. In addition, it summarizes current studies on the eruptive history of the 

Wrangell volcanoes and interprets their significance and 

origin in light of modern geologic theory. 

A "Glossary" is included at the front of this guide, 

and a listing of "Selected References" are included at the 

end. The glossary briefly defines many of the geologic 

terms that are used throughout the guide and that may be 

unfamiliar to the general reader; a term defined in the 

glossary is italicized the first time it appears in the text. 

The references enable the reader to pursue in more detail 

such areas of interest as early exploration, general geology, volcanology, and geologic maps. 

1

Wrangell-St. Elias National Park and Preserve, U.S. National Park 

Service, Glennallen, Alaska. 

Manuscript approved for publication September 27, 1993. 

EARLY HISTORY AND 

GEOLOGIC EXPLORATION 

Ahtna Athabaskan natives traveled the river corridors, foothills, and passes of the Wrangell Mountains for 

several hundred years prior to European arrival in the area. 

They Lived in semipermanent camps, leaving for weeks at 

a time to hunt and to gather berries, birch wood, and other 

resources. Trade routes with other native peoples were 

well established. Copper, found near the present-day town 

of McCarthy, was used for tools and for trade with other 

native groups. Rumors of the copper deposits, as well as 

the lure of fur animals, attracted Russians into the Copper 

River Basin from the 1760's to 1867. Many encountered 

considerable hostility from the Ahtna, who resisted the 

Russian domination of their villages. 

The first recorded geographic observations ofthe western Wrangell Mountains were made by Lt. Henry T. Allen of 

the U.S. Army in 1885. In March ofthat year, Allen and three 

companions landed at the mouth of the Copper River and 

began one of the most remarkable journeys in the history of 

Alaskan exploration (fig. l). Mapping as they went, the party 

ascended the Copper River around the west end of the 

Wrangell Mountains, crossed the Alaska Range through SusIota Pass, and then proceeded down the Tok, Tanana, 

Koyukuk, and Yukon Rivers to the Bering Seajust in time to 

catch the last boat to leave the Alaska coast before freezeup in 

early September. Allen's party was the first scientific expedition to cross the Alaska Range from the GulfofAlaska to the 

Yukon River. 

Before going north over the Alaska Range divide into 

the Tanana River Valley, Allen explored the upper Copper 

River Basin, theChitinaRiver Valley, and the western Wrangell 

Mountains. He named the Chitina and the Chitistone Rivers 

(both names incorporating theAthabaskan word "chiti," meaning "copper") and established friendly relations with Chief 

Nicolai and his Copper River group of Ahtna Indians. He 

measured the heights and named many of the high Wrangell 

peaks, including Mount Blackburn, Mount Drum, and Mount 

Sanford, during his long summer sojourn in the area. 
2 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

After Allen's exploration, several scientific parties explored the Wrangell Mountains area. The team ofLt. Frederick Schwatka ofthe U.S. Army and geologist C.W. Hayes of 

the U.S. Geological Survey reached the Cbitina River Valley 

by way of the White River and Skolai Pass (fig. 1) in 1891. 

Spurred by these early explorations and the influx of 

prospectors during the Klondike gold discoveries in Canada, 

the U.S. Geological Survey and the War Department notably 

increased their efforts to make topographic and geologic 

maps of the country. U.S. Geological Survey geologist F.C. 

Schrader accompanied the 1898 U.S. Army survey led by 

Capt. William Abercrombie up the Copper River and into the 

sa0 

Wrangell Mountains. That same year, U.S. Geological Survey geologist WC. Mendenhall joined U.S. Army Capt. 

Edwin Glenn's expedition from Cook Inlet up the Matanuska 

River into the Copper River Basin. Alfred Brooks and William Peters of the U.S. Geological Survey and Oscar Rohn 

and A.H. McNeer ofthe War Department conducted separate 

expeditions to the Nabesna and Chisana areas on the north 

side of the Wrangell Mountains in 1899. 

These journeys eventually led to mineral development 

of the Wrangell Mountains. The first gold discovery in the 

northern Wrangell Mountains was on Jacksina Creek near the 

headwaters of the Nabesna River in 1899. In that same year, 

148° 

Copper River 

Basin 

River 

Pacific 

136° 

144° 140° 

Ocean 

0 50 100 MILES 

0 50 100 KILOMETERS 

Figure 1. South-central Alaska and part of the Yukon Territory, Canada, showing early exploration routes of Allen in 1885 (red 

dashed line) and Schwatka and Hayes in 1891 (red dotted line) and route of the Cordova-Kennicott Railroad (barred line) that was 

used from 1911 to 1938. 
GEOLOGIC BACKGROUND 3 

Oscar Rohn, on his exploration of the upper Chitina VaJley, 

found rich pieces of chalcocite ore in the glacial moraine of 

Kennicott Glacier1 and pointed out similarities to the rich 

copper deposits ofMichigan's Lake Superior District. Rohn 

also named the ChitistoneLimestone and the Nikolai Greenstone, geologic formations that proved to be important hosts 

for mineral deposits. A year later, prospectors traced the 

chalcocite to deposits on Bonanza Ridge, which eventually 

became the incredibly rich Bonanza Mine, one offive mines 

that supplied copper and silver ore to the now-historic Kennecott Mill. 

The Kennecott mines did not go into full production 

until 1911, when the completion of a 196-mi-long railroad 

from Cordova, near the mouth of the Copper River, to the 

Kennicott mining town allowed transport of the rich copper 

concentrate (fig. 1). In 27 years of operation, over a billion 

pounds of ore valued at $100 to 300 million was hauled on 

the railroad. 

The mine and the railroad were abandoned in 1938, 

when the rich ore was exhausted. The railroad bed now 

provides the base for most of the Chitina-McCarthy Road 

along the south flank of the Wrangell Mountains in the heart 

ofWrangell-St. Elias National Park and Preserve. 

Gold discoveries in the Nabesna area led to construction ofthe NabesnaRoad, which was built in the early 1930's 

and used to haul gold ore from the now-closed NabesnaMine. 

Today, the Nabesna Road provides vehicle access along the 

north side ofthe Wrangell Mountains into Wrangell-St. Elias 

National Park and Preserve. 

A NATIONAL PARK 

IN THE WRANGELLS 

After the Kennecott mines closed, several efforts were 

made to revive interestin the area. Ernest Gruening, Director 

of U.S. Territories and later Alaska's governor and a U.S. 

Senator, was the first to recommend the area as a national park 

or monument. After a flight overthe area in 1938, he wrote a 

memorandum to the Secretary ofthe Interior: 

* * *the region is superlative in its scenic beauty and * * * measures up fully and beyond the requirements for its establishment as a National Monument and later as a National Park. 

It is my personal view that from the standpoint of scenic 

beauty, it is the finest region in Alaska * * *. I have travelled 

through Switzerland extensively, have flown over the Andes, 

1

Kennicott Glacier was named by Oscar Rohn ofthe U.S. War Depanment in 1899 for Roben Kennicott, a pioneer Alaska explorer and 

director of the scientific corps of the Western Union Telegraph Expedition 

in 1865. The Kennecott Mines Co., which developed and mined the rich 

copper deposits, took its name from the glacier but misspelled it with an 

"e0 instead of an "i". 

and am familiar with the Valley of Mexico and with other 

parts ofAlaska. It is my unqualified view that this is the finest 

scenery that I have ever been privileged to see. 

Passage of the Alaska Native Claims Settlement Act 

in 1971 authorized the Federal government to withdraw and 

study Federal lands in Alaska for future uses. In 1978, President Jimmy Carter declared the area a National Monument 

becauseofits scientific and cultural significance. When Congress passed theAlaska National InterestI.:ands Conservation 

Act in 1980, the Wrangell Mountains became part of the 

13.2 million acre Wrangell-St. Elias National Park and Preserve, the largest unit in the U.S. National Park system. 

Wrangell-St. Elias is one of four contiguous conservation units spanning some 24 million acres that have been 

recognized by the United Nations as an international World 

Heritage Site. The original 1978 designation included 

Wrangell-St. Elias and Kluane National Park in the Yukon 

Territory ofCanada. In 1993, both GlacierBay National Park 

and Preserve and a new park, the Alsek-Tatshenshini Provincial Park in British Columbia were added to that designation. Altogether, it is the largest internationally protected 

area in the world. 

GEOLOGIC BACKGROUND 

The Wrangell Mountains, ·which form much of 

Wrangell-St. Elias National Park and Preserve, are made up 

largely of thousands of lava flows that have been erupted 

mostly from large broad volcanoes during the past 26 million 

years. This extensive volcanic terrain, which is called the 

Wrangell volcanic field (fig. 2), covers about 4,000 mi2 

(10,400 krn2)--an area a little smaller than the State of 

Connecticut-and extends eastward from the Copper River 

Basin through the Wrangell Mountains, into the St. Elias 

Mountains of Alaska and the Yukon Territory of Canada. 

The principal basement rocks on which the Wrangell 

volcanoes erupted their great outpourings oflava are much 

older rocks and have had a complex geologic history. These 

rocks belong to what is referred to in the geologic literature 

as the Wrangellia terrane, which is part of an even larger 

group of exotic terranes-the Wrangellia composite terrane-that have been accreted toAlaska and the North American Continent during the past few hundred million years. 

On the basis ofgeophysical and fossil evidence, rocks of the 

Wrangellia terrane were formed in a tropical environment 

thousands ofmiles south ofits present position.TheWrangel1ia terrane began as a volcanic arc about 300 million years 

ago, probably along themargin of an ancient NorthAmerican 

Continent. As arc-related volcanic activity waned, a rift developed between the arc and continent, allowing the eruption 

ofthousands of cubic miles ofbasalt lava flows that flooded 

and filled the rift-formed basin. Subsequently, shallow warm 

seas inundated the land, depositing layers of marine limestone and other sediment on the volcanic rocks. 
--

4 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

During the next 200 million years, the Wrangellia 

terrane was gradually transported northward, where it was 

welded to other terranes and eventually docked against western North America about 100 million years ago (fig. 3). It 

now forms a belt extending from southern Alaska to southern 

British Columbia. Subsequently, other terranes, such as those 

composing the Southern Margin composite terrane, have 

been carried northward and accreted to continental Alaska. 

The last terrane to arrive-the Yakutat terrane-docked 

about 26 million years ago, concurrent with and partly responsible for the development ofthe Wrangell volcanic field. 

148° 

Pacific Ocean 

sa· 

VOLCANOES AND PLATE TECTONICS 

The preceding section briefly discussed how the rocks 

on which the Wrangell volcanoes are built were not formed 

where they are found today but were transported a great 

distance from their place of origin. The tremendous forces 

capable of moving terranes and even entire continents are 

principally the result of the motion and interaction of the 

many semi rigid plates that compose the crust ofthe Earth (fig. 

4). This concept of a dynamic Earth's crust, called plate 

tectonics, has developed since the 1950's and revolutionized 

136° 

144° 140° 

Area shown 

in figure 7 

rnPos· --............. lfe -....._ 

terr. 

---- I q

Yakut;---------

te ,. 

Line of section ~>.~.... in figure 6 -s.: . - <.<'~ ....,, 

0 50 100 MILES 

I I I I 

0 50 100 KILOMETERS 

Figure 2. South-central Alaska and part of the Yukon Territory, Canada, showing Wrangell volcanic field (red stippled) and some 

major geologic features. Lines of faults dotted where concealed by water; dashed lines, terrane boundaries, where not depicted as 

faults. 
VOLCANOES AND PLATE TECTONICS 5 

A B 

ximate shore line 

ient North America 

r-/ 

Figure 3. Western North America, showing (A) present position of Wrangellia composite terrane (red stippled area) and (B) its 

probable position 250 million years ago, before it moved northward as part of an ancient Pacific plate. 

EURASIAN PLATE 

Plate boundaries 

--...,_ Subduction zone 

..J""'-../ Spreading ridge 

Fault, fracture zone 

PACIFIC 

PLATE 

ANTARCTIC 

Figure 4. Major crustal plates of the world. Arrows indicate directions of relative plate motion. 
6 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

our understanding of the processes that build mountains and 

cause earthquakes and volcanic eruptions. 

The speeds at which these crustal plates move across 

the surface of the Earth range from less than 1 to as much 

as 5 in/yr (2- 12 cm/yr). Seemingly slow, these rates, over 

the course of millions of years, however, can move crustal 

plates hundreds, even thousands, of miles. 

Although the ultimate causeofthe motion ofthe plates 

is not well understood, geologists surmise that the immediate 

driving force is magma welling up from the asthenosphere 

along zones referred to as spreading ridges or rift zones (fig. 

5). Most of these spreading ridges occur in the Earth's midoceanic areas, where they mark the boundaries between 

oceanic crustal plates. As new magma is periodically or 

continuously erupted along an oceanic spreading ridge, it 

forces older crust outward. The new magma cools, welding 

itselfto the older crust, and then is followed by another batch 

of new magma, repeating the process. In contrast to new 

crust being added to a plate along a oceanic spreading ridge, 

old crust can also be consumed alc?ng crustal plate boundaries 

through a process called subduction. Here, one plate, generally a heavier oceanic plate, plunges under a lighter continental plate, where it eventually is assimilated back into the 

asthenospbere. 

More importantly, however, in terms of the hazard to 

life and property, these subduction zones underlie most of 

the world's destructive volcanoes and are the ultimate cause 

oftheir volcanic activity. At depths of about 65 mi (100 km), 

heating ofthe subducting slab oflight oceanic plate produces 

a magma (different chemically from the magma produced at 

a spreading ridge) by processes that are not well understood. 

This magma may form by partial melting of the crustal slab, 

by partial melting ofthe overlying mantle wedge as hot fluids 

stream up from the slab, or by combinations of these and 

other processes. Whatever its origin, the newly generated, 

light magma rises through the dense lithosphere, where it 

may undergo further chemical, changes. It may eventually be 

erupted at the surface as a.Java flow, dome, or as volcanic 

ash in a volcano. If the magma fails to reach the surface, it 

cools and crystallizes underground to form a body ofigneous 

rock, generally referred to as a pluton. 

In addition to plate subduction and ridge spreading, 

another important type of plate boundary occurs where two 

adjacent plates, traveling in different (but parallel) directions 

ASTHENOSPHERE 

Magma 

EXPLANATION OF TERMS 

Mantle-The zone of the Earth below the crust and above the core. 

Lithosphere-The solid part of the Earth (as opposed to atmosphere and 

'--------------1 hydrosphere). It includes the crust and part of the upper mantle and rides on the1--- - ---' 

underlying asthenosphere. 

Asthenosphere-The part of the upper mantle that is weak and behaves more 

like a fluid than a solid. 

Subduction zone-Zone where one crustal plate overrides another along a 

convergent margin. 

Spreading ridge-Suboceanic zone where magma rises between two crustal 

plates and spreads them apart. 

Magma-Molten rock generated within the asthenosphere; the parent of all 

volcanic and plutonic rocks. 

Volcanic arc-A curved belt of volcanoes above a subduction zone where 

crustal plates converge. 

Figure 5. Diagrammatic cross section through the Earth's crust and upper mantle, showing plate-tectonic features discussed in text. 

Arrows indicate directions of relative plate motion. 
+ + + COMPOSITE TERRA ~ 

+ + ERRANE T + + + + +'_J~+_.-......_____ 

Rising PACIFIC PLATE 

B 

Wrangell volcanic field 

Ocean 

Asthenosph29 subduction 

7 THE WRANGELL VOLCANOES 

and at different speeds, slip past each other, forming a strikeslipfault zone. These plate boundaries, like subduction zones, 

are the sites of some of the world's largest earthquakes. 

The San Andreas fault system in California is an example 

of a plate-contact strike-slip fault. In Alaska, the DenaliTotschunda fault system, north of the Wrangell Mountains, 

and the Fairweather fault, south of the Wrangell Mountains, 

are strike-slip faults that presently form a principal boundary 

between the Pacific and North American crustal plates (fig. 2). 

THE WRANGELL VOLCANOES 

HOW DID THEY FORM? 

The first Wrangell volcanoes formed about 26 million years ago, when the northwestward-moving Pacific 

plate, with its piggyback load of the Yakutat terrane, began 

to be subducted beneath the continental North American 

plate (fig. 6). Strong subduction and voluminous magma 

production, which have continued until relatively recently, 

A 

NORTH AMERICAN PLATE 

North -----

+ + +++++ 

have been responsible for the growth of the volcanoes and 

the development of the Wrangell volcanic field. 

Since about 200,000 years ago, strike-slip movement 

along the Fairweather and Denali-Totschunda faults has accommodated some of the stress imposed by the northwestward motion of the Pacific plate. Thus, both the rate of 

subduction of the Pacific plate under the North American 

plate and the production of magma under the western 

Wrangell volcanoes have decreased. Although some eruptive 

activity will undoubtedly continue here in the future, voluminous outpourings oflava, like those that built the large shields 

ofMount Sanford and Mount Wrangell, seem unlikely. 

The volcanoes oftbe western Wrangell mountains (fig. 

7) are unlike most other volcanoes erupted above subduction 

zones and, indeed, may be unique around the entire Pacific 

rim. Rather than erupting explosive lavas forming steepsided cones, they have been built by the accumulation of 

hundreds of relatively fluid lava flows to form broad mountains with gentle slopes, typical of shield volcanoes (fig. 8). 

Now, however, only youthful Mount Wrangell still displays 

a shieldlike form; the other, generally older volcanoes have 

South 

++ + 

+ + WRANGELLIA COMPOSITE .. SOUTHERN MARGIN t+ + 

Figure 6. Diagrammatic north-south cross sections through south-central Alaska and the northern Pacific Ocean (see 

fig. 2), showing development of Wrangell volcanic field through subduction of the Pacific plate beneath the North American plate 25 million years ago (A) and at present (B). 
8 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

had much of their superstructure removed by glacial and 

other erosional processes. 

Moreover, all of the known Wrangell shield volcanoes, except Boomerang, are characterized by large summit 

collapse areas or calderas, I to more than 6 mi (1-10 km) 

in diameter, that have been filled with great thicknesses of 

flat-lying lava flows (fig. 8). Unlike most volcanoes along 

convergent plate margins, however, these calderas have 

formed relatively passively, possibly like the volcanoes of 

Hawaii. There, caldera collapse has occurred in response to 

the subvolcanic withdrawal of magma from beneath the 

summit, which, in effect, removes support for the summit 

area and causes it to subside or collapse. There is no known 

field evidence in the Wrangell Mountains to suggest that 

any of the calderas formed as a result of explosive volcanic 

activity, like what occurred at Mount Pinatubo in the Philippines in 1991. In the St. Elias Mountains, however, a 

small caldera on Mount Churchill probably formed as a 

145° 144° 

result of large explosive eruptions that produced the White 

River Ash Bed (described later in this guide). 

In addition to the large shield volcanoes, many smaller 

cinder cones are scattered, apparently randomly, throughout 

theWrangell volcanic field. These cones, typically of basaltic 

or andesitic composition, represent eruption from a single, 

small volcanic vent and generally were fonned after the 

growth of their host shield volcano. The largest of these 

cones, Mount Gordon, is descr ibed later in this guide. 

HOW OLD ARE THEY? 

All the volcanoes of the western WrangelJ Mountains 

are less than 5 million years old. Their ages record a progression in volcanic activity from Mount Blackburn (3-4.5 

million years old) in the southeast to Mount Drum (0.2-0.5 

million years old) in the northwest (fig. 9). Mount Wrangell, 

143° 142° 

a 

Chistoc · 

~ 

00-<._0f 

.\ 

&~ ·--· ------- Boomerang , ~1\14 · "'--'\ 

1 . 

et 

62° 

0 

I 

10 

Volcano~ '--..._Ro,._,0

Capital Mountain ?@',, ... 

10 

I 

20 KILOMETERS 

~ Skookum \ ~ Creek .&. 

Volcano Nabesna /. and Preserve 

.&. 1-G .,~ 

Tanada .· 

u 

····..: 

.... 

"---·--

1 

~ 

~ 

I 

I 

~ 

I 

I 

White River . 

.-... .._~,fr ./·V · · .._ -· -1 Mo . ,..... ·..·· ·, lJft/fR' .. _._ ·.·-~(~s- ... 

Figure 7. Wrangell Mountains and part of the St. Elias Mountains (see fig. 2), showing locations of volcanoes and other geologic 

features discussed in text. Stippled lines, areas of icefields and glaciers. Arrows indicate accessible viewing areas discussed in text; 

circled numbers refer to figures showing photographs of volcanoes. 
THE WRANGELL VOLCANOES 9 

Dikes (eruption 

A. Shield growth 

feeders) 

sn\eld 

----------- Pre-volcano -- basement rocks 

B. Caldera formation 

lntracaldera lavas 

-

C. Caldera fill 

Present-day 

land surface 

/ 

D. Topography after erosion 

Figure 8. Diagrammatic cross section model illustrating development of a Wrangell volcano. A, Growth of 

shield by outpourings of voluminous lava flows from summit and rift vents. B, Collapse of summit caldera due 

to withdrawal of magma from a high-level magma reservoir. C, Filling of caldera by lava flows erupted from 

intracaldera vents. D, Present topography after erosion. Profile is that ofTanada volcano from mile 26 on the 

Nabesna Road. Growth of shield and collapse and filling of caldera probably occur partly concurrently. 
10 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

I BLACKBURN I 

SKOOKUM CREEK I 

r TANAOA 

~ l 

6 CAPITAL 

I SANFORD I 

I ORUM I 

I WRANGELL I 

I 

2 3 4 5 

TIME, IN MILLIONS OF YEARS BEFORE PRESENT 

0 

Figure 9. Known periods of eruptive activity for radiometrically dated western Wrangell volcanoes. 

Ends of bars correspond to known beginning and end of eruptive activity. 

which bas fumaroles on its summit and is considered an 

active volcano, may have erupted lava flows as recently as 

50,000 years ago, but reliable data to fully verify this young 

age are unavailable. Farther to the southeast, in the eastern 

Wrangell Mountains and the St. Elias Mountains (beyond 

the general area of this guide), the volcanoes are progressively older. The earliest known volcanic activity in the 

Wrangell volcanic field occurred about 26 million years ago 

near the Alaska-Yukon Territory boundary. 

HOW TALL ARE THEY? 

The Wrangell volcanoes range in elevation from a few 

thousand feet above sea level (Boomerang, 3,949 ft [1,204 

ml) to a maximum of 16,390 ft (4,996 m) at Mount Blackburn. Many have impressive summits, higher than 10,000 ft 

(3,050 m); others, especially some of th.e older volcanoes, 

are more subdued and generally have had large parts oftheir 

structures removed by erosion. The JO highest named peaks 

in the Wrangell Mountains are listed in table 1. All of these 

peaks are volcanic in origin, and most mark the general area 

of central-vent eruptive activity. In addition to these peaks, 

a few unnamed peaks, all of volcanic origin and all higher 

than 13,000 ft (4,000 m) occur in the general vicinity of 

Mount Blackburn and Mount Jarvis. 

HOW DO THEY COMPARE 

WITH OTHER MOUNTAINS? 

Table 1. Highest peaks of the Wrangell Mountains. 

[Peaks are listed in descending order by height; those in boldface are described in 

text) 

Height 

Rank Name 

(ft) (m) 

I Mount Blackburn-------­ 16,390 4,996 

2 Mount Sanford----------­ 16,237 4,949 

3 Mount Wrangcll---------­ 14,163 4,317 

4 Atna Peaks ---------------­ 13,600-13,860 4,145-4,225 

5 

6 

Regal Mountain-----------­ Mount Jarvis-----------­

13,845 

13,421 

4,220 

4,091 

7 Parka Peak---------------·­ 13,200 4,023 

8 Mount Zanetti -----------­ 13,009 3,965 

9 Rime Peak----------------­ 12,741 3,883 

10 Mount Drum-------------- 12,010 3,661 

volume) in the world. As )jsted in table 2, Mount Blackburn and Mount Sanford are the 12th and 13th tallest 

mountains, respectively, in North America; Mount Bona, a 

Wrangell volcano to the east in the St. Elias Mountains, 

ranks 11th. 

In comparison with most stratovolcanoes associated 

with convergent plate margins, such as along the Pacific 

"rim offire," the Wrangell shield volcanoes are much more 

voluminous (fig. 10). Mount Wrangell and Mount Sanford, 

for example, each consist of about 250 mj3 (1,000 km3

) of 

lava in comparison with about 8 mi3 (32 km3) for Mount 

St. Helens, Wash., which ernpted in 1980, and about 45 mi3 

(190 km3) for Mount Rainier, Wash. Fujiyama, in Japan, 

The Wrangell volcanoes are among the highest one of the world's largest stratovolcanoes, has a volume of 

mountains in North America and some of the largest (by about 185 mi3 (740 km3

). 
THE WRANGELL VOLCANOES 11 

Table 2. Highest mountains of North America. 

[Mountains are listed in descending order by height; those in boldface are in the Wrangell 

Mountains) 

Height 

Rank Name Location 

(fl) (m) 

I Mount McKinley------ Alaska ----------- 20,320 6,194 

2 Mount Logan---------- Canada------------ 19,850 6,050 

3 Pico de Orizaba------- Mexico------------ 18,700 5,700 

4 Mount St. Elias-------- Alaska-Canada -- 18,008 5,489 

5 Popocatepetl ----------- Mexico------------ 17,887 5,452 

6 Mount Foraker -------- Alaska ------------ 17,400 5,304 

7 lztaccfhuatl------------- Mexico------------ 17,343 5,286 

8 Mount Lucania -------- Canada------------ 17,147 5,226 

9 King Peak-------------- Canada------------ 16,971 5,172 

10 Mount Steele ---------- Canada------------ 16,440 5,011 

II Mount Bona ----------- Alaska ------------ 16,421 5,005 

12 Mount Blackburn --- Alaska ------------ 16,390 4,996 

13 Mount Sanford------- Alaska ------------ 16,237 4,949 

14 Mount Wood----------- Canada------------ 15,880 4,840 

15 Mount Vancouver----· Alaska-Canada -- 15,700 4,785 

KM MILES 

.-C",., : 

4 b 5 MILES Mount Gordon 

(Cinder cone) 1 3 5 KILOMETERS 

Mount St. Helens Mount Rainier 

(Stratovolcano) (Stratovolcano) 

Fujiyama 

(Stratovolcano) 

s

n

p

p

Mount Wrangell 

(Shield volcano) 

Figure 10. Comparative profiles of some Pacific-rim volcanoes. 

Mount Gordon, a cinder cone, and Mount Wrangell, a shield volcano, are described in text; Mount St. Helens, Mount Rainier, 

and Fujiyama are well-known stratovolcanoes. 

DESCRIPTIONS OF INDIVIDUAL VOLCANOES 

MOUNT WRANGELL 

Mount Wrangell, the youngest volcano in the western Wrangell Mountains (figs. 11, 12), is a large, broad, 

ice-covered shield of tremendous bulk. Although no lavaproducing eruptions have been documented in historical 

time, geologists consider the volcano to be active . 

Name.-Reported in 1885 by Lt. Henry T. Allen of 

the U.S. Army as named by the Russians after Baron von 

Wrangell, Russian explorer, admiral ofthe Imperial Russian 

Navy, and Governor ofRussian America from I830 to 1836. 

Mount Zanetti, a large cinder cone on the Mount Wrangell 

hield, is a local name reported by W.C. Mendenhall, U.S. 

Geological Survey geologist, in 1903_ Ahtna name: K'elt'aei ("the one who controls the weather"); when erupting: 

Uk'eledi ("the one with smoke on it"). It is interesting to 

note that Allen named another mountain in the western 

Wrangell Mountains, Mount Tillman, after Samuel L. 

Tillman, a professor at the U.S. Military Academy. In a 

anoramic sketch of the volcanoes as seen from about the 

resent Tonsina townsite, Mount Sanford was called Mount 

Tillman; and on a plan map ofthe volcanoes, Mount Wrangell 

was called Mount Tillman_ Although we will probably never 

know what lay behind this "extra" volcano, the confusion 

possibly stemmed from observations at widely separated 

viewpoints during times of inclement weather. The name 

"Tillman" was dropped from all maps after about 1900. 

Type and /orm.-Shield volcano containing an icefilled summit caldera, 3.5 mi (6 km) long by 2.5 mi (4 km) 

wide, that is breached on its south side. Three small craters, 

containing active fumaroles, are situated along the rim of 

lhe summit caldera: Nurlh and West craters lie directly on 

the rim, and East Crater sits on top of a small cone on the 

rim. North Crater, the largest, consists of two overlapping 

craters, about 0.6 mi (1 km) in total diameter; West and East 

craters are somewhat smaller, less than 0.5 mi (0.8 km) in 

diameter. Mount Zanetti, a large cinder cone, occurs high on 

the northwest flank of the Mount Wrangell shield. 
12 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

0 

0 5 KILOMETERS 

Figure 11. Topographic and generalized geologic map of Mount Wrangell. Heavy lines, approximate present limit 

of Mount Wrangell lavas, dotted where concealed by ice. Arrow indicates direction of view in figure 12. Base 

from U.S. Geological Survey Gulkana, Nabesna, Valdez, and McCarthy quadrangle maps. 

Mount 

Slopes of Mount Sanford Zanetti _.,.,,- Mount Wrangell 

/

\ 
THE WRANGELL VOLCANOES 13 

Location.- 50 mj (80 km) east of Glennallen, Alaska, at lat 62°00' N., long 144°00' W. Shown on U.S. Geological Survey Gulkana A-1, Nabesna A-6, Valdez D-1, 

and McCarthy D-8 quadrangle maps. 

Height.- 14,163 ft (4,317 m). First ascent, 1908. 

Mount Zanetti is 13,009 ft (3,965 m) hlgh. 

l.Atest eruptive activity.-Since the late l 700's, there 

have been at least three reports (1784, 1884-85, and 1900) 

of violent eruptive activity, including sightings of actjve 

lava flows, on Mount Wrangell. Although the reports of 

flowing lava have never been confirmed, Mount Wrangell 

is still considered an active volcano. The three summit 

postcaldera craters contain active fumaroles, and on calm 

days a steam plume can sometimes be seen rising from the 

summit. In addition, at least two craters (West and North 

Craters) have been the sites of sporadic phreatic activity 

throughout historical time, and occasionally the summit 

area is blanketed by a thin layer of dark ash (see frontispiece). On the basis of radiometric dating K-Ar dating, the 

lava flows most recently erupted from Mount Wrangell 

may be 50,000 to 100,000 years old. Some recent research 

indicates that summit fumarolic and phreatic activity may 

wax and wane in response to changes in the summit heat 

flux, whlch, in turn, may increase after major earthquakes 

in southern Alaska. For example, after the I899 Yakataga, 

Alaska, earthquake, ash falls on the summit icefield were 

apparently common; and after the great 1964 Alaska earthquake, thermal activity increased markedly at the summit. 

Apparently, seisrruc activity can open clogged parts of 

water-convection channels beneath the craters to allow 

more efficient heat transfer. Before the 1964 earthquake, 

visible plumes at the summit of Mount Wrangell were 

from West Crater, whereas after the earthquake, fumarolic 

activity increased markedly in North Crater. Through the 

early l980's, the heat flux increased again and melt rates 

were so high that lakes formed intermittently in North 

Crater for several years. Since 1986, however, after the 

melting of more than 130 million yd3 (100 million m3) of 

ice, the ice volume has been slowly building up again. 

Volcanic history.-The main bulk of the Mount 

Wrangell shield was built chiefly by the accumulation of 

hundreds of voluminous andesitic lava flows from 600,000 

to 200,000 years ago. The summit caldera probably collapsed 

within the past 200,000 years, possibly as recently as 50,000 

years ago. The cone of Mount Zanetti and a few flows on 

the south flank ofMount Wrangell are probably the youngest 

products of the volcano. Mount Zanetti probably erupted 

during the waning stage of the latest major glaciation, possibly less than 25,000 years ago, and a large, young andesite 

◄ Figure 12. Mount Wrangell from Willow Lake (in foreground) at mile 87 on the Richardson Highway. View northeastward; photograph by U.S. National Park Service. 

flow that originated in the summit area and traveled more 

than 40 mi (64 km) south and west into the ancestral Copper 

River Basin may be only 50,000 years old. 

G/aciers.-Perennial ice and snow cover more than 

90 percent of the Mount Wrangell shield. This large icefield is the source of many alpine glaciers that feed into 

both the Copper River and Yukon River drainages. Nabesna Glacier, the largest and longest of these glaciers, has 

its origin high on the southeast slopes of Mount Wrangell 

and flows more than 50 mi (80 km) east and then north, 

where it forms the Sot!rce of the Nabesna River, a major 

tributary of the Tanana River. 

Best viewing.- Mount Wrangell is readily visible 

along the Richardson Highway from Tonsina north to 

Glennallen and along most of the Edgerton Highway to 

Chltina. North of Glennallen, views are mostly blocked by 

Mount Drum; however, it comes into view again between 

Gakona and Chistochina on the Tok Cutoff of the Glenn 

Highway. Two excellent viewpoints are at Willow Lake 

(mile 87) (fig. 12) on the Richardson Highway and at mile 

20 on the Tok Cutoff of the Glenn Highway. 

Mount Wrangell, the first of the higher volcanoes of the Wrangell Mountains to be climbed, 

has also been the site of numerous scientific expeditions and investigations. The relative ease of access to the volcano and its high northern-latitude 

elevation combine to provide an ideal natural laboratory. rn I9'i3, Terris Moore, then president of the 

University of Alaska, landed a ski-equipped small 

plane in the ice-filled summit caldera to begin a 

cosmic-ray-research program in cooperation with 

New York University. Since then, more than JOO 

ski-plane landings have been made on the summit 

in support of various scientific investigations. In 

1961, Carl Benson of the University of Alaska's 

Geophysical Institute began glaciovolcanic studies 

on Mount Wrangell's summit, a program that continues to the present. 

MOUNT DRUM 

Mount Drum is the westernmost Wrangell volcano. 

Though more than 4,000 ft lower in elevation than its 

neighbor, Mount Sanford, this volcano dominates the local 

landscape as it rises above the adjacent Copper River 

Basin lowlands (figs. 13-15). 

Name.-Named in 1885 by Lt. Henry T. Allen, of 

the U.S. Army after Adj. Gen. llichard C. Drum (1825-

1909), who served in the Mexican and Civil Wars and 

later attained the rank of brigadier general. Ahtna name: 

Hwdaandi ("downriver")-K'elt'aeni ("the one who controls the weather"). 

Type and f orm.-Stratovolcano or shleld volcano 

whose original morphology has been severely modified by 
14 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

Figure 13. Topographic and generalized 

geologic map of Mount Drum. Heavy 

line, approximate present limit of Mount 

Drum lavas; stippled areas, cycle I domes; 

crossed areas, cycle 2 domes. Arrows indicate directions of view in figure 14 (from 

northwest) and figure 15 (from southwest). 

A- A', line of cross section in figure 16. 

Base from U.S. Geological Survey Gulkana and Valdez quadrangle maps. 

0 5 KILOMETERS 

Figure 14. Mount Drum from mile 1 on the Tok Cutoff of the Glenn Highway. The Copper River is in foreground. 

View southeastward; photograph by U.S. Geological Survey. Copper River in foreground. 
THE WRANGELL VOLCANOES 15 

violently explosive eruptive acuv1ty and subsequent glacial erosion. Several small peaks, each formed by an individual late-stage volcanic dome, ring the main structure 

along about 270° of arc on the south and east sides of the 

volcano. 

Locatio11.-29 mi (47 km) due east of Glennallen, 

Alaska, at lat 62°07' N., long 144°38' W. Shown on U.S. 

Geological Survey Gulkana A-2 quadrangle map. 

Height.-12,010 ft (3,661 m). First ascent, 1954; 

Heinrich Harrer, Keith Hart, and George Schaller. 

Latest eruptive activity.-Violently explosive volcanic activity destroyed the top and much of the south 

face of Mount Drum, probably between 250,000 and 

150,000 years ago. The last documented eruptive activity, 

based on radiometric K-Ar dating techniques, occurred at 

Snider Peak about 240,000 years ago (fig. 16). 

Volcanic history.-Mount Dr1,_1m was constructed between about 700,000 and 240,QO0 years ago during two 

major cycles of eruptive activity. The first cycle (700,000-

500,000 years ago) included the development of an early 

stratovolcano or, possibly, shield volcano, consisting largely of andesitic lava flows and breccias. A series of early 

rhyolite domes formed toward the end of the first cycle of 

activity; their distribution suggests that they were erupted 

along a short arcuate fracture system on the new volcano's 

southeast flank. The second cycle of activity (500,000-

240,000 years ago) apparently followed the emplacement 

of the rhyolite domes without a significant time break. 

Again, large volumes of mostly andesitic lava were erupted, building a volcanic pile that may have been as high as 

14,000 to 16,000 ft (4,300-4,900 m). Toward the end of 

this period of constructional activity, as many as 10 dacite 

domes were erupted along at least two major arcuate fracture systems that almost completely encircled the volcano 

at distances as far as 5 mi (8 km) from the central vent. 

Snider Peak dome and its associated lava flows, which 

were erupted about 240,000 years ago, probably represent 

the last products of constructional volcanic activity on 

Mount Drum. After the eruptions at Snider Peak and, possibly, as recently as 1.QQ,000 years ago, cataclysmic eruptions destroyed much of the volcano. These explosive 

eruptions, which apparently originated on the south flank 

of the volcano, possibly near Snider Peak, produced a series of hot and cold volcanic avalanches and mudflows 

containing as much as 1.5 mi3 (7 km3

) of material and 

covering an area of about 80 mi2 (207 km2). The mudflows (fig. 17) produced during the destruction of part of 

Mount Drum were extremely fluid because of the addition 

of large volumes of water from melted ice and snow at 

and near the eruption site. Cascading down the lower 

south flank of the volcano, these mudflows, carrying along 

house-size and larger masses of cohesive volcanic rocks, 

I 

Mount 

Drum"- Amphitheater Snider Peak 

Figure 15. Mount Drum at sunset from Willow Lake (in foreground) at mile 87 on the Richardson 

Highway. Great amphitheater, resulting from late cataclysmic explosive activity, is partly hidden by 

clouds. View northeastward; photograph by U.S. National Park Service. 
_

16 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

A 0 2 3 MILES A' 

North 1 South I I 1 I 

0 2 3 4 KILOMETERS _..-······... _ / Possible shape of Mount Drum 

_..-········ ··-.._ before explosive activity 

Cycle 2 dome 

I 

Pre-Mount Drum rocks 

Figure 16. Generalized geologic cross section through Mount Drum (see fig. 13 for location). 

~ . 

Ri"er 

0 

0 10 20 KILOMETERS 

Figure 17. Approximate extent of volcanic avalanche and mudflow deposits (red stippled areas) probably generated by late cataclysmic eruptions of Mount Drum (flow direction shown by 

long arrows). Short arrows denote areas along the Edgerton 

Highway and the McCarthy Road where mudflows are well exposed. Stippled lines, extent of glaciers and icefields. 

Avalanche 

deposits 

poured into the Copper River Basin and coursed down the 

Copper River Valley to at least the location of the present 

village of Chitina, a distance of more than 52 mi (84 km) 

from their source. The mudflow deposits are weJI exposed 

in the cliffs of the Kotsina River where it joins the Copper 

River near Chitina and in roadcuts along the McCarthy 

Road just east of the Copper River Bridge. The mudflows 

also crop out a t mile 17.9 on the Edgerton Highway to 

Chitina at the top of the bluff where the highway drops 

down into the Tonsina River Valley. 

Glaciers.-At least 11 alpine glaciers extend outward from the perennial icefield that mantles most of 

Mount Drum above elevations of about 8,000 ft (2,400 m). 

The largest, Nadina Glacier, flows southwest more than 

9 mi (14 km) from the large amphitheater on the volcano's 

south flank. Scattered spruce trees and shrubs cover the 

lower, stagnant end of the glacier below about 3,500 ft 

(1,070 m) elevation. 

Bestviewing.-MountDrum is the first oftheWrangell 

volcanoes to come into view when driving east from Anchorage toward Glennallen on the Glenn Highway. It is 

readily visible from the Glenn Highway as far east as Chistochina and all along the Richardson Highway from Tonsina 

north to Sourdough. Excellent viewpoints are at mile 1 on 

the Tok Cutoff of the Glenn Highway and at Willow Lake 

(mile 87) on the Richardson Highway (fig. 15). 

MOUNT SANFORD 

Mount Sanford is the highest and probably least understood of the three major volcanoes in the extreme western Wrangell Mountains (figs. 18, 19). Its imposing height 

makes it the first of the Wrangell volcanoes that visitors 

may see when driving to Anchorage from Tok and the 

Alaska Highway. The spectacular south face of the volcano, at the head of Sanford Glacier, rises 8,000 ft (2,400 rn) 

in 1 mi (1.61 km)-one of the steepest gradients in North 

America. 
THE WRANGELL VOLCANOES 17 

Name.-Narned in 1885 by Lt. Henry T. Allen of 

the U.S. Army after the Sanford family (Allen was a descendant of Reuben Sanford). Ahtna name: Hwniindi ("upriver") K'elt'aeni ("the one who controls the weather"). 

Type and form.-Complex shield(?) volcano whose 

present massive structure apparently was built on coalescing 

flows from at least three o]der volcanic centers referred to 

as the north, west, and south Sanford eruptive centers. 

Location.-30 m.i (48 km) southeast of Chistochina, 

Alaska, at lat 62° 13' N., long 144°08' W. Shown on U.S. 

Geological Survey Gulkana A-1 and B-1 quadrangle maps. 

Height.- 16,237 ft (4,949 m). First ascent, 1938; 

Terris Moore and Bradford Washburn. 

Latest eruptive activity.-The flows, domes, and 

subvolcanic intrusive rocks that constitute some of the 

main bulk of Mount Sanford may be as young as 100,000 

years on the basis of morphology and the apparent absence of extensive glacial erosion. The latest radiometrically dated activity, however, was the eruption of a series 

of basaltic lava flows from a rift zone on the northeast 

flank of the mountain about 320,000 years ago. 

Volca,iic history.-Tbe Mount Sanford volcanic 

complex began to fonn about 900,000 years ago, when 

eruptive activity was initiated from at least three centers, 

outboard of the present main structure. Andesitic eruptions 

from these centers probably continued for a few hundred 

thousand years and formed a group of low, coalescing 

shield(?) volcanoes. Volcanic activity then apparently 

shifted to a central vent, superimposing the large andesitic 

structure we see today on flows from the earlier outboard 

centers. Visual examination from aircraft of the south face 

of Mount Sanford, the principal window through the volcano's ice cover, suggests that the upper 2,000 ft (610 m) 

of the volcano is a broad, thick dome or lava flow filling a 

summit crater. A feature of the Mount Sanford complex 

that may be unique in the Wrangell volcanic field is a 

large rhyolite flow that probably was erupted from the 

north Sanford center about 600,000 to 500,000 years ago. 

This ap~arently single flow has a volume of about 5 mi3 

(20 km ) and is locally more than 1,000 ft (305 m) thick; 

it flowed more than ll mi (18 km) off the volcano's northeast flank (fig. 18). 

0 5 KILOMETERS 

Figure 18. Topographic and generalized geologic map of Mount Sanford (flow direction shown by 

heavy arrow). Heavy lines, approximate present limit of Mount Sanford lavas, dotted where concealed by ice or young surficial deposits; triangles, approximate vent areas of subsidiary eruptive 

centers. Arrows indicate directions of view in figure 19 (from west) and figure 21 (from north). 

Base from U.S. Geological Survey Gulkana and Nabesna quadrangle maps. 
18 VOLCANOES OFTHE WESTERN WRANGELL MOUNTAfNS, ALASKA 

Glaciers.-Above 8,000 ft (2,400 m), most of 

Mount Sanford is covered by a perennial icefield. On the 

south flank of the volcano, this icefield merges with the 

great expanse of ice that covers its neighbor, Mount 

Wrangell. Elsewhere, the icefield is the source of several 

large alpine glaciers. One of these glaciers, Sanford Glacier, whjch originates in the great cirque at the base of the 

spectacular south face of Mount Sanford, carries a tremendous load of debris from almost-continuous rockfall and 

avalanching off the 8,000-ft (2,400 rn)-high face. 

Best viewing.-As travelers drive south on the Tok 

Cutoff of the Glenn Highway, Mount Sanford is first visible at about mile 70, a few miles south of Mentasta Summit, and remains in view most of the way to Gakona and 

south to Glennallen on the Richardson Highway. Some of 

the best viewpoints are from the Gulkana Airport (fig. 19), 

a few miles north of Glennallen, and at miles 1, 20, and 

58 along the Tok Cutoff. 

CAPITAL MOUNTAIN 

Capital Mountain is a relatively small, dissected volcano north of Mount Sanford (fig. 20). Though extremely 

rugged. with spectacular scenery, the mountain is dwarfed 

by its younger and loftier neighbors (fig. 21). 

Name.- Reported as a local name in 1902 by 

Thomas G. Gerdine, U.S. Geological Survey topographer. 

Ahtna name: Tsedghaazi Dzel' ("rough-rock mountain") 

Type and form.-Shield volcano containing a small 

summit caldera. A dike swarm, which may be unique in 

the Wrangell volcanic field, radiates outward from a plug 

within the caldera (fig. 20). Much of the original shield 

has been removed by erosion, leaving the intracaldera 

lava flows as present topographic high points. 

Location.-20 mi (32 km) southeast of Chistochina, 

Alaska, at lat 62°25' N., long 144°07' W. Shown on U.S. 

Geological Survey Gulkana B-1 quadrangle map. 

Height.-7,731 ft (2,356 m). High point is on an 

erosional rib of intracaldera lavas. 

Latest eruptive activity.-The emplacement of a rhyolite dike, about 5 mi (8 km) long, across the summit of 

the volcano about 1 million years ago is the latest known 

activity on the volcano. 

Volcanic history.-Capital volcano was probably constructed within a period of less than 100,000 years about 1 

million years ago. It evidently began as a small andesitic 

volcano and rapidly built a shield about 10 mi (16 km) in 

diameter and probably no more than 8,000 ft (2,400 m) high. 

During the end phases of shield building, withdrawal of 

magma from beneath the central vent area allowed the summit to collapse and form a 2.5-mi (4 km)-diameter summit 

center\ 

North center 

I 

/ South center 

Dome 

/ 

Mount Drum 

"" 

Mount Sanford West I Slopes of 

Figure 19. Mount Sanford from the Gulkana Airport on the Richardson Highway. View southeastward; photograph by U.S. Geological 

Survey. 
THE WRANGELL VOLCANOES 19 

0 5 KILOMETERS 

Figure 20. Topographic and generalized geologic 

map of Capital Mountain. Heavy line, approximate 

present limit of Capital Mountain lavas, dotted 

where concealed by young surficial deposits; dashed 

(rhyolite dike) and dotted (andesite dikes) lines, radial dike swarm; dot, intracaldera plug. Arrow indicates direction of view in figure 21. Base from U.S. 

Geological Survey Gulkana and Nabesna quadrangle maps. 

Mount Sanford-- /Capital Mountain 

Figure 21. Capital Mountain (in midground) and Mount Sanford (in background) from 

mile 58 on the Tok Cutoff of the Glenn Highway. The Copper River is in foreground. 

View southward; photograph by U.S. Geological Survey. 
20 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

caldera. During and after caldera collapse, eruptive activity 

resumed, filling the caldera with more than 1,500 ft ( 450 m) 

of thick, flat-lying andesite flows. Final activity was the 

intrusion of a spectacular radial dike swarm, consisting of 

hundreds of andesite dikes and a few dacite and rhyolite 

dikes, as much as 4 mi (6 km) long, whose locus is a 

prominent andesitic plug near the center of the caldera that 

probably marks the volcano's central vent. 

Glaciers.-No glaciers exist on Capital Mountain 

today. However, young moraines in two deep valleys extending outward from the summit area were deposited by 

alpine glaciers that were present as recently as 10,000 

years ago. Also, the extent of deep erosion exhibited by 

Capital Mountain and the presence of old glacial deposits 

high on the volcano's flanks are evidence that it was virtually covered by ice during a major period of glaciation 

which followed the end of eruptive activity about 900,000 

years ago. 

Best viewing.-Viewed from a distance along the 

highways around the western Wrangell Mountains, Capital 

Mountain is nearly lost in the foothills of its much taller 

neighbor, Mount Sanford (fig. 21). The best viewpoints are 

between miles 20 and 70 on the Tok Cutoff of the Glenn 

Highway and along the first 25 mi of the Nabesna Road. 

TANADAPEAK 

Tanada Peak is the erosional remnant of an andesitic 

volcano that is mostly older and considerably larger than 

its neighbor to the west, Capital volcano (fig. 20). The 

peak is the high point on a prominent, ice-free, serrated 

ridge that rises precipitously above a series of more gently 

sloping foothills (figs. 22, 23). 

Name.-Named in 1902 by D.C. Witherspoon, U.S. 

Geological Survey topographer, after nearby Tanada Lake. 

Ahtna name: Tanaadi Dzel' ("moving-water lake"~ 

Type and /orm.-Shield volcano containing a 4-mi 

(6 km)-wide by 5-mi (8 km)-long summit caldera. Most of 

the shield has been removed by erosion, leaving the intracaldera lava flows as present topographic high points. 

Location.-17 mi (27 km) southwest of the old 

Nabesna Mine at the end of the Nabesna Road at lat 

62°18' N., long 143°31' W. Shown on U.S. Geological 

Survey Nabesna B-6 quadrangle map. 

Height.-9,358 ft (2,852 m). 

IA.test eruptive activity.-An elongate cluster of 

andesite cones on the north flank of the Tanada shield that 

erupted about 970,000 years ago probably represent the 

latest activity of the volcano (fig. 22). 

0 

0 5 KILOMETERS 

Figure 22. Topographic and generalized geologic map of Tanada Peak. 

Heavy hne, approximate present limit of Tanada Peak lavas, dotted where 

concealed by young surficial deposits. Arrow indicates direction of view in 

figure 23. Base from U.S. Geological Survey Nabesna quadrangle map. 
THE WRANGELL VOLCANOES 21 

Volcanic history.-Tanada volcano is built on a series 

of lava flows, most of which are older than 1.8 million 

years, indicating that the volcano had its beginning sometime later, probably about 1.5 million years ago. During the 

next few hundred thousand years, thousands of eruptions 

built a large andesitic shield that may have reached an elevation of more than 10,000 ft (3,000 m). Before about I 

million years ago, the top of the shield collapsed, forming a 

large summit caldera. Subsequent intracaldera eruptions 

filled the caldera with more than 4,000 ft (1,200 m) of 

andesite lavas before central-vent activity ceased. A few 

dikes that cut both the shield and intracaldera lavas may be 

related to the eruptive activity responsible for the late cinder cones on the volcano's north flank. 

Glaciers.-A few small glaciers that occupy some 

of the deep valleys in Tanada Peak's summit area are remnants of much larger alpine glaciers that 100,000 years 

ago covered most of the volcano and were responsible for 

carving away much of the volcano's shield. 

Best viewing.-Tanada Peak can best be seen along 

the first 30 mi of the Nabesna Road, which extends eastward off the Tok Cutoff of the Glenn Highway at the village of Siana. An excellent viewpoint is at Long Lake 

(mile 23.5) on the Nabesna Road. 

MOUNT JARVIS 

Mount Jarvis is the high point of a 5-mi (8 km)­

long, north-trending, ice-covered ridge largely hidden behind Mount Sanford and Tanada Peak (figs. 24, 25). 

Name.-Named by F.C. Schrader, U.S. Geological 

Survey geologist, in 1903 after Lt. Daniel H. Jarvis of the 

U.S. Revenue Cutter Service, who led an overland relief 

expedition to aid a whaling fleet trapped in Arctic Ocean 

ice off Point Barrow in 1897-98. Ahtna name: Tsic' 

etggodi Dzel' ("rock is chipping mountain") 

Type and form.-Shield volcano containing summit 

caldera. The summit caldera is poorly defined and may be 

a group of two or more nested calderas, as much as 6 mi 

(9.6 km) long. 

Location.-31 mi (50 km) southwest of the community of Nabesna, at lat 62°01' N., long 143°3-7' W. Shown 

on U.S. Geological Survey Nabesna A-6 quadrangle map. 

Height.-13,421 ft (4,091 m). High point at unnamed north end of ridge, 13,025 ft (3,970 m). 

Latest eruptive activity.-A large dacite dome-flow 

complex at the extreme north end of Jarvis volcano, which 

has been dated at 1.0 million years old, may be the latest 

activity of the volcano (fig. 24). 

Volcanic history.-Development of the Mount 

Jarvis volcano began about 1.7 million years ago with the 

eruption of extensive andesite flows. Andesite volcanism 

continued until about 1.0 million years ago, probably 

contemporaneously with the formation of a summit 

caldera or group of calderas. By 1.0 million years ago, 

the Jarvis magmas became more silicic in composition 

and produced the satellitic dacite domes and flows at the 

north end of the volcanic complex. An interesting product 

of a dacite cinder cone on the southeast flank of the volcano (fig. 24) is an extensive agglutinate flow that exhibits spectacular columnar joints. This flow resulted from 

Tanada Peak 

./. 

Caldera wall 

Flat-lying intracaldera 

lavas 

Figure 23. Tanada Peak from mile 26.5 on the Nabesna Road. View southward; photograph by U.S. Geological Survey. 
22 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

collapse of the cone wall and mobilization of the wall 

materials (cinders, spatter, and bombs) while they were 

still hot and fluid enough to flow. 

Glaciers.-Most of Mount Jarvis and the Jarvis 

ridge are covered by icefields and glaciers. Jacksina Glacier, the largest glacier associated with Mount Jarvis, has 

its origin low on the east flank of the massif, where ice 

tongues from the two high points of the Jarvis ridge 

coalesce. 

Best viewing.-Mount Jarvis can best be seen along 

the Nabesna Road between miles 13 and 20. 

SKOOKUM CREEK VOLCANO 

Skookum Creek volcano is the only volcano in the 

western Wrangell Mountains that is accessible by road 

(fig. 26). It is one of the oldest volcanoes described in this 

guide, and because it has been intensely modified by erosion, it offers opportunities to examine subsurface volcanic 

processes through its spectacular exposures of domes, 

vents, dikes, and other geologic features. 

Name.-Informal, after Skookum Creek, which has 

its source below the central high point of the volcano. 

0 5 KILOMETERS 

Figure 24. Topographic and generalized geologic map of Mount Jarvis. 

Heavy line, approximate limit of Mount Jarvis lavas, dotted where concealed by ice; red crossed area, young dacite dome and associated flows; 

red stippled area, young dacite cone. Arrow indicates direction of view in 

figure 25. From U.S. Geological Survey Nabesna and McCarthy quadrangle maps. 
THE WRANGELL VOLCANOES 23 

Figure 25. Mount Jarvis from southeast slopes of Skookum Creek volcano. View southwestward; photograph by U.S. Geological 

Survey. 

5 KILOMETERS 

Figure 26. Topographic and generalized geologic map 

of Skookum Creek volcano. Heavy line, approximate 

limit of Skookum Creek lavas, dotted where concealed 

by young surficial deposits; red crossed areas, rbyolite 

and dacite domes. Peak at 7 ,I 25 ft, at head of Skookum and Canyon Creeks, was apparent center of principal eruptive activity. X, area of dikes shown in figure 

28. Cross section through volcano along line A-A' is 

shown in figure 27. Base from U.S. Geological Survey 

Nabesna quadrangle map. 
24 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

Type and /orm.-Possibly a shield volcano with a 

large caldera that is outlined by a ring of domes. 

Location.-Central high point is 5 mi (8 km) northwest of the old gold-mining camp of Nabesna at lat 62°24' 

N., long 143°08' W. Shown on U.S. Geological Survey 

Nabesna B-5 quadrangle map. 

Height.-Central high point, 7,125 ft (2,172 m). A 

4-mi (6.5 km)-long, high ridge attains a height of 7,265 ft 

(2,214 m) 2.5 mi (4 km) southeast of this central high 

point. 

Volcanic history.-The earliest known eruptive activity of Skookum Creek volcano was the production of a 

series of basalt flows about 3.2 million years ago, followed by voluminous andesite flows that continued until 

about 2 million years ago, when most eruptive activity 

ceased. During the early period (3 million years ago) of 

andesitic volcanism, several dacite and rhyolite domes 

were emplaced around the periphery of the volcano (figs. 

26, 27). These domes, which form an approximate circle 

about 9 mi (14.5 km) in diameter, may reflect the leakage 

of magma along the walls of a subsiding caldera. If a 

caldera did form, then the younger (2-2. 7 million years 

old) andesite flows, which form an extensive flat-lying sequence throughout most of the central part of the volcanic 

edifice, may represent intracaldera fill. A few small basalt 

cinder cones that still show original morphology lie scattered over the eroded volcanic surface. These relatively 

young cones, which postdate Skookum Creek eruptive activity by at least 1 million years, probably are not part of 

the volcanic system responsible for the formation of Skookum Creek volcano. 

Best viewing.-The last 10 mi (16 km) of the Nabesna Road (about miles 32-42) follows a 2-mi (3 km)-wide 

valley that cuts through the northeastern part of the volcano. The road skirts two large domes on the volcano's flank 

and affords spectacular views of various volcanic rocks. 

Also, hikers can take short (less than 3 mi [5 km]) treks 

into side valleys, where the rocks and their structures can 

be observed in detail (fig. 28). 

MOUNT BLACKBURN 

Mount Blackburn, the highest peak in the Wrangell 

Mountains, is the erosional remnant of a large volcano 

(fig. 29). Although it is the oldest volcano described in this 

guide, its extreme height and ice cover largely preclude 

any detailed study of its internal structure (fig. 30). 

Name.-Named by Lt. Henry T. Allen of the U.S. 

Army in 1885 after Joseph Clay Stiles Blackburn (1838-

1918), State and U.S. Congressman and U.S. Senator from 

Kentucky. Ahtna name: K'als'i Tl'aadi ("the one at cold 

waters"). 

Type and form.-Probably a large shield volcano 

containing a large summit caldera. The original structure 

has been severely modified by erosion. 

Location.-Main peak, 36.5 mi (58.5 km) northeast 

of the village of Chitina at lat 61 °44' N., long 143°26' W. 

Shown on U.S. Geological Survey McCarthy C-7 quadrangle map. 

Height.-Main peak, 16,390 ft (4,996 m); unnamed 

subsidiary peak 1.5 mi (2.5 km) to the southeast, 16,286 ft 

(4,964 m). First ascent, 1912; Dora Keen and G.W. Handy. 

Volcanic history.-The oldest dated rock from 

Mount Blackburn (4.2 million years old) is a granite that 

intrudes Blackburn lavas along an arcuate ring fracture 

which is interpreted as a caldera margin (fig. 29). These 

older lavas, which probably represent the early products of 

a shield volcano, may be as old as 5 million years. Most 

of the Mount Blackbum massif, however, is composed of 

younger granite (3.4 million years old) that intrudes a 

thick sequence of fairly flat lying andesite flows, suggesting that a filled caldera collapsed into a large, shallow granitic magma reservoir between 4.2 and 3.4 million years 

ago. There is no evidence of any volcanic activity after the 

collapse and fill of this caldera. 

Glaciers.-The Mount Blackburn massif is almost entirely covered by icefields and glaciers. It is a principal source 

ofice for Kennicott Glacier, which flows south and terminates 

near the small town of McCarthy. The mountain also conA A' 

South North 

Dome or intrusive body 

me d Valley-fill

oa d 

-- Figure 27. Cross section (see fig. 26) through Skookum Creek volcano, showing some hypothetical subsurface 

features. 
THE WRANGELL VOLCANOES 25 

tributes a considerable volume of ice to large, north-flowing 

Nabesna Glacier and the Kuskulana Glacier system. 

Best viewing.-The best views of Mount Blackbum 

are from Glennallen south to beyond Willow Lake on the 

Richardson Highway. Additional excellent vantage points 

are at mile 24 (Chokosna Lake) and mile 49.2 along the 

Chitina-McCarthy Road, which skirts the south edge of 

the Wrangell Mountains, and from Kennicott, the historic 

millsite, 4 mi (6.5 km) north of McCarthy. 

BOOMERANG VOLCANO 

Boomerang volcano, which forms a low broad hill 

northeast of Capital volcano, is a conspicuous topographic 

feature, rising 1,000 ft (300 m) above the relative flatlands 

of the upper Copper River Basin (fig. 31 ). 

Name.-Informal, after nearby Lake Boomerang. 

Type a,zd form.-Small shield volcano with summit 

crater. 

,; 

. 

'--=- ,._.;.U~~..._-

Locatio,z.-13 mi (21 km) south of the village of 

Slana, Alaska, at lat 62°31' N., long 143°55' W. Shown on 

U.S. Geological Survey Nabesna C-6 quadrangle map. 

Height.-3,949 ft (1,204 m). 

Volcanic history.-Very little is known about the 

age and eruptive history of Boomerang volcano. It is a 

small shield volcano, composed principally of andesite 

flows, that was active before the construction of Capital 

volcano (l million years old), because Capital lavas appear to overlie the southwest flank of Boomerang volcano. 

Best viewing.-Boomerang volcano is visible from 

about mile 50 to Siana on the Tok Cutoff of the Glenn 

Highway and from Siana to about mile 20 on the Nabesna 

Road. 

MOUNT GORDON 

Mount Gordon is a largely ice covered cinder cone 

that was constructed on a broad volcanic plateau west of 

Figure 28. A pair of 6-foot-thick andesite dikes intrude poorly consolidated rhyolite pyroclastic deposits of Skookum Creek volcano. 

Where dikes are closer than about 3 ft (I m), the intervening rhyolite has been fused to a dense gray glass by heat from dikes. 

Photograph by U.S. Geological Survey. 
26 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

Nabesna Glacier (figs. 32, 33). Though not visible from any 

road in the area, it is included in this guide because it is 

typical-and one of the largest-of the many young cinder 

cones scattered throughout the Wrangell volcanic field. 

Name.-Named by F.C. Schrader, U.S. Geological 

Survey geologist, in 1903 after a prospector who was exploring in the area in 1899. 

Type and form.-Basaltic cinder cone with summit 

crater and associated lava flows. The cinder cone still exhibits most of its original volcanic form but has a significant ice mantle. 

Location.-16.8 mi (27 km) south of the community 

of Nabesna at lat 62°08' N., long 143°05' W. Shown on 

U.S. Geological Survey Nabesna A-5 quadrangle map. 

Height.-9,040 ft (2,755 m) 

Volca11ic history.-The Mount Gordon cinder cone 

is probably less than I mrnion years old, on the basis of 

freshness of form. A series of fluid basaltic lava flows that 

flowed mostly to the north preceded the construction of 

the cinder cone (fig. 32). Where not covered by ice. the 

cone consists largely of cinder, spatter, and spindle-shaped 

volcanic bombs. Coarse air-fall deposits that fell from ash 

plumes during Mount Gordon's eruptions blanket the area 

as far as 8 mi ( 13 km) from the cone. 

Best viewing.-Though not visible from any road, 

Mount Gordon is viewable from short climbs into the easily accessible mountains northwest of the small community 

of Nabesna. 

0 5 KILOMETERS 

Figure 29. Topographic and generalized geologic map of Mount Blackburn. AU remaining Mount Blackburn lavas are confined to an inferred caldera whose walls are mostly 

ice covered. Red stippled areas, granitic rocks of a postulated exhumed magma chamber 

in caldera; red crossed area, older syncaldera granites. Arrow indicates direction of view 

in figure 30. Base from U.S. Geological Survey McCarthy quadrangle map. 
WHITE RIVER ASH 27 

Unnamed 16,286-ft peak 

P~rka Peak Atna Peaks I

I 

Rime 

Peak 

"- ,..,,Mount Blackbum 

Figure 30. Mount Blackbum, highest of western Wrangell volcanoes, from east of Nabesna Glacier (in foreground). View southwestward; photograph by U.S. Geological Survey. 

WIDTE RIVER ASH 

Though not a product of any of the western 

Wrangell volcanoes, the White River Ash Bed is an important Wrangell volcanic deposit that is readily visible along 

the Alaska Highway near the Alaska-Yukon Territory 

boundary (fig. 34). The ash is briefly described here so 

that travelers along the highway may recognize it and understand its significance and origin. 

The White River Ash Bed is exposed in many roadcuts along the Alaska Highway between the village of 

Tok, Alaska, and the city of Whitehorse, Yukon Territory, 

Canada. It is present as a conspicuous light-gray layer, as 

much as 2 ft (0.6 m) thick, within a few inches (centimeters) of the surface, just under the organic-soil layer. The 

ash occurs in two distinct lobes, each the product of one 

of the most voluminous pyroclastic eruptions in North 

America in the past 2,000 yeaI"s. Radiocarbon dating of 

wood and other organic material buried by the ash indicates that the northern lobe was deposited from an eruption cloud about 1,900 years ago, and the eastern, larger 

lobe about 1,250 years ago. Together, these two lobes 

cover more than 130,000 mi3 (335,000 k.m3) in the Yukon 

and Northwest Territories of Canada and adjoining eastern 

Alaska and consist of a total of at least 12 mi3 (50 k.m3) of 

volcanic ash. 

0 

0 5 KILOMETER 

Figure 31. Topographic and generalized geologic 

map of Boomerang volcano. Heavy line, approximate 

present limit of Boomerang lavas. Peak at 3,949 ft is 

on small crater that was site of central-vent activity. 

Base from U.S. Geological Survey Nabesna quadrangle map. 
28 VOLCANOES OFTHE WESTERN WRANGELL MOUNTAINS, ALASKA 

0 

0 5 KILOMETERS 

Figure 32. Topographic and generalized geologic map of Mount 

Gordon. Heavy Line, approximate limit of Mount Gordon cinder 

and lavas, dotted where concealed by ice or young surficial deposits; red stippled areas, areas known to be underlain by lapilli 

tuff derived from Mount Gordon. Short arrow indicates direclion 

of lava flow from Mount Gordon; long arrow indicates direction 

of view in figure 33. Base from U.S. Geological Survey Nabesna 

quadrangle map. 

Figure 33. Mount Gordon from south of Skookum Creek volcano. View south; photograph by D.H. Richter, 1994. 
__ 

29 

Mount Churchill&~ ,-. · · · ' '-'4~ 

I ,S1⁄4 

/ 

0 

<'.t-?tq/ Haines 

0 , -?.s Junction 

50 MILES 1 L i ..........,.., r--/ _J_ _L ::___~~.L----

ACKNOWLEDGMENTS 

62 

60° L:::::==:::___-~__J__j_ __ 

The source of the White River Ash is Mount 

Churchill (15,638 ft [4,766 m]), a volcano in the eastern 

part of the Wrangell volcanic field in the St. Elias Mountains of Alaska (fig. 7). A small ice-filled caldera that 

formed as a result of the explosive eruptions occupies the 

summit area of Mount Churchill. . 

Mount Churchill is 40 mi (64 km) east of the town 

of McCarthy but is not visible from any road system. At 

the community of Koidern, Yukon Territory, Canada (fig. 

34), where the ash deposit is thickest (2 ft [0.6 m]) along 

the Alaska Highway, Mount Churchill lies 55 mi (88 km) 

to the southwest. 

MUD VOLCANOES 

The mud volcanoes of the Copper River Basin are 

another geologic feature that is visible from the highway 

and commonly asked about by visitors. They are not volcanoes like those we have described in the preceding part 

of this guide but instead are mud-rich springs that have 

built up mounds of mud, as much as 300 ft (91 m) high 

and 8,000 ft (2,440 m) in diameter, resembling small 

shield volcanoes (fig. 35). 

The largest of these mud volcanoes, referred to as 

Shrub, Upper Klawasi, and Lower Klawasi, occur within 

the boundary of Wrangell-St. Elias National Park and Preserve about 18 mi (29 km) west of Mount Drum (fig. 7). 

They are visible from the Richardson Highway between 

Glennallen and the Edgerton Highway, where they appear 

as low mounds rising above the forested floor of the Copper River Basin. The mud-rich waters are charged with 

carbon dioxide (CO2) and contain anomalously high concentrations of sodium (Na+), chloride (Cr-), and bicarbonate (HCO3_). Water temperatures range from about 54°F 

(12°C) at Shrub to about 85°F (29°C) at the Upper Klawasi springs. The chemistry of the waters suggests that the 

springs are discharging a mixture of ancient seawater and 

meteoric water, containing CO2 derived from both a magmatic source-possibly the cooling Mount Drum magma 

reservoir-and a metamorphic-rock source that might be 

deeply buried limestone in the underlying Wrangellia composite terrane which is being metamorphosed by the enormous pressures caused by deep burial and by the heat of 

the adjacent volcanic systems. 

ACKNOWLEDGMENTS 

We take this opportunity to acknowledge the work 

of the pioneer geologists of the U.S. Geological Survey, 

namely, C.W. Hayes, W.C. Mendenhall, F.C. Schrader, Alfred Brooks, Oscar Rohn, S.R. Capps, and F.H. Moffit, 

whose early studies in the Wrangell Mountains, have been 

invaluable to those of us who followed. We also express 

our heartfelt appreciation to Robert L. Smith of the U.S. 

Geological Survey, a more recent investigator, who many 

years ago not only started the first author thinking about 

Figure 34. Distribution of the White River Ash Bed in Alaska and Canada. Lines denote outer limits of 1 in (2.5 

cm) and I ft (0.3 m) accumulations of ash. Red stippled area, Wrangell volcanic field. 
30 VOLCANOES OF THE WESTERN WRANGELL MOUNTAINS, ALASKA 

Figure 3S. Lower Klawasi mud volcano. Light areas are mud covered and do not support any vegetation. Mud-rich springs discharge 

into a small mud-rich lake just visible at top of mound. Oblique aerial photograph by Bradford Washburn, taken in 1938. 

Wrangell volcanism but also aided in the first field studies 

of the Wrangell volcanoes. Tina Neal of the U.S. Geological Survey, Kitty Reed of the Washington Department of 

Natural Resources, and Carl Benson of the University of 

Alaska, Fairbanks, reviewed the manuscript and made 

major improvements in its contents and readability. 

The authors are very thankful for the support and 

cooperation of the staff of Wrangell-St. Elias National 

Park and Preserve, particularly Russell Galipeau, Chief of 

Resources Management, who early on encouraged us to 

prepare an interpretive guide for the general public. 

SELECTED REFERENCES 

Listed below are published reports, articles, and maps that 

the reader may refer to for additional information. The old exploration reports are out of print but are available for reading at ()) 

Alaska Resources Library, U.S. Department of the Interior, 222 W. 

7th Ave., Anchorage, AK 99513 and (2) Z.J. Loussac Library, 3600 

Denali Street, Anchorage, AK 99503. The geologic maps and topographic-quadrangle maps (listed under "Location" in the descriptions ofthe Wrangell volcanoes) are available for study and purchase 

at (I) U.S. Geological Survey, Public Inquiries Office, 4230 University Drive, Anchorage, AK 99508 and (2) Wrangell-St. Elias 

National Park and Preserve, Visitors Center, Olennallen, AK 99568. 

Alaskan history and names 

Orth, D.J., 1971, Dictionary of Alaska place names: U.S. Geological Survey Professional Paper 567. 1,084 p. 

Ricks, M.B., 1977, Alaska bibliography; an introductory guide to 

Alaskan historical literature: Portland, Oreg., Binford and 

Mort. 
SELECTED REFERENCES 31 

Early exploration 

Allen, H.T., 1887, Report of an expedition to the Copper, 

Tanana, and Koyukuk Rivers, in the Territory of Alaska, in 

the year 1885: Washington, D.C., U.S. Government Printing 

Office, 172 p. [reprinted 1985 by Northwest Publishing Co., 

Anchorage). 

Brooks, A.H., 1900, A reconnaissance from Pyramid Harbor lo 

Eagle City, Alaska, including a deScriptiort of the copper deposits of the upper White and Tanana Rivers: U.S. Geological Survey Annual Report 21, pt. 2, p. 331-391. 

Hayes, C.W., 1892, An expedition through the Yukon district: 

National Geographic Magazine, v. 4, p. I 17-162. 

Mendenhall, W.C., 1905, Geology of the central Copper River 

region, Alaska: U.S. Geological Survey Professional Paper 

41, 133 p. 

Mendenhall, W.C., and Schrader, F.C., 1903, Copper deposits of 

the Mount Wrangell region, Alaska, in Contributions to economic geology, 1902: U.S. Geological Survey Bulletin 213, 

p. 141-148. 

--1903, The mineral resources of the Mount Wrangell district, Alaska: U.S. Geological Survey Professional Paper 15, 

71 p. 

Rohn, Oscar, 1900, A reconnaissance of the Chitina River and 

the Skolai Mountains, Alaska: U.S. Geological Survey Annual Report 21, pt. 2, p. 393-440. 

Schrader. F.C., 1900, A reconnaissance of a part of Prince William Sound and the Copper River district, Alaska, in 1898: 

U.S. Geological Survey Annual Report 20, pt. 7, p. 341-

423. 

Kennecou copper t~ines and railroad 

Alaska Geographic, 1989, The copper trail: v. 16, no. 4, 77 p. 

Douglas. W.C., 1964, A history of the Kennecott mines, Kennecott, Alaska: published by the author, 141 l 26th Ave. East, 

Seattle, WA 98102, 12 p. 

Hunt, W.R., 1991, Mountain wilderness; historic resource study 

for Wrangell-St. Elias National Park and Preserve: Washington, D.C., U.S. Government Printing Office, 222 p. 

Janson, L.E., 1975, The copper spike: Anchorage, Northwest 

Publishing Co., 175 p. 

Kirchhoff, M.J., 1993, Historic McCarthy-The town that copper 

built: Juneau, Alaska Cedar Press, 137 p. 

Spude, Robert, and Faulkner, Sandra, 1988, Cordova to Kennecott: Cordova Historical Society, 51 p. 

Tower, E.A., 1990, Ghosts of Kennecott-the story of Stephen 

Birch: published by the author, 6761 Roundtree, Anchorage, 

Alaska, 88 p. 

Native culture 

de Laguna, Frederica, and McClellan, Catharine, 1981, Ahtna, in 

Helm, J., ed., Subarctic, v. 6 of Handbook of North American Indians: Washington, D.C., Smithsonian Institution, 

p. 641-663. 

Kari, James, transcriber, 1985, Tatl'ahwt'aenn' Nenn'; the headwaters people's country: Fairbanks, University of Alaska, 

Alaska Native Language Center, 219 p. 

General volcanology 

Bullard, F.M., 1976, Volcanoes of the earth: Austin, University of 

Texas Press, 579 p. 

Williams, Howe!, and McBimey, A.R., 1979, Volcanology: San 

Francisco, Freeman, Cooper & Co., 397 p. 

Regional geology 

MacKevett, E.M., Jr., 1978, Geologic map of the McCarthy 

quadrangle, Alaska: U.S. -Geological Survey Miscellaneous 

Investigations Series Map 1-1032, scale I:250,000. 

Plafker, George, I990, Regional geology and tectonic evolution 

of Alaska and adjacent parts of the northeast Pacific Ocean 

margin: Australasian Institute of Mining and Metallurgy Pacific Rim Congress 90, Queensland, Australia, 1990, Proceedings, p. 841-853. 

Richter, D.H., 1976, Geologic map of the Nabesna quadrangle, 

Alaska: U.S. Geological Survey Miscellaneous investigations Series Map 1-932, scale I:250,000. 

Richter, D.H, Smith, J.G., Lanphere, M.A., Dalrymple, G.B., 

Reed, B.L., and Shew, Nora, 1990, Age and progression of 

volcanism, Wrangell volcanic field, Alaska: Bulletin of Volcanology, v. 53, no. l, p. 29-44. 

Geologic maps ofthe Wrangell volcanoes 

Lowe, P.C., Richter, D.H., Smith, R.L., and Schmoll, H.R., 1982, 

Geologic map of the Nabesna B-5 quadrangle, Alaska: U.S. 

Geological Survey Geologic Quadrangle Map GQ-1566, 

scale I:63,360 (Skookum Creek volcano). 

Richter, D.H., Ratt6, J.C., Schmoll, H.R., Leeman, W.P., Smith, 

J.G., and Yehle, L.A., 1989, Geologic map of the Gulkana 

B-1 quadrangle, south-central Alaska: U.S. Geological Survey Geologic Quadrangle Map GQ-1655, scale 1:63,360 

(Capital Mountain). 

Richter, D.H., Smith, J.G., Schmoll, H.R., and Smith, R.L., 1992, 

Geologic map of the Nabesna B-6 quadrangle, Alaska: U.S. 

Geological Survey Geologic Quadrangle Map GQ-1688, 

scale I;63,360 (Tanada Peak). 

Richter, D.H., and Smith, R.L., I 976, Geologic map of the Nabesna 

A-5 quadrangle, Alaska: U.S. Geological Survey Geologic 

Quadrangle Map GQ-1292, scale I :63,360 (Mount Gordon). 

Richter, D.H., Smith, R.L., Yehle, L.A., and Miller, T.P., 1979, 

Geologic map of the Gulkana A-2 quadrangle, Alaska: U.S. 

Geological Survey Geologic Quadrangle Map GQ-1520, 

scale I :63,360 (Mount Drum). 

Winkler, G. R., and MacKeven, E.M., Jr., 1981, Geologic map of 

the McCarthy C-7 quadrangle, Alaska: U.S. Geological Survey Geologic Quadrangle Map GQ-1533., scale I :63,360 

(Mount Blackburn). 

U.S.G.P.O.:199~052