Alaska

Aleutian Islands

Kiska
Aleutian Islands
Volcano types:
Stratovolcano
Pyroclastic cones
Summit Elev: 1220 m
Latitude: 52.103°N
Longitude: 177.602°E
Conical Kiska volcano is the westernmost historically active volcano of the 2500-km-long Aleutian arc. The volcano lies at the northern tip of the elongated Kiska Island, across a low isthmus containing East Kiska and West Kiska lakes. A 400-m-wide elliptical crater, breached to the north, caps the 1220-m-high stratovolcano. The volcano is surrounded on three sides by sea cliffs up to 450 m high and overlies an older volcanic center exposed to the south. A massive submarine debris-avalanche deposit extends 40 km to the NNW. The southern part of the NE-SW-trending island, the westernmost of the Rat Island group, has been glaciated, but all lava flows on Kiska volcano post-date the last major glaciation. Young, steep-sided blocky lava flows, primarily on the northern and SW flanks, have originated from vents at locations ranging from the summit to near sea level. A flank cinder cone and associated lava flows were erupted in 1962 at Sirius Point on the northern coast. The island contains one of the best harbors in the Aleutian Islands, but is uninhabited.
About Volcano Data | Larger photo with caption and credit.
Smithsonian Volcano Information | Alaska Volcano Observatory

Segula
Aleutian Islands
Volcano types:
Stratovolcano
Caldera
Fissure vent
Summit Elev: 1160 m
Latitude: 52.015°N
Longitude: 178.136°E
The 6 x 7 km island of Segula east of Kiska volcano consists of a conical stratovolcano cut by a prominent NNW-SSE-trending fissure that extends to sea level at both ends of the island. The northern end of the fissure is flooded by the sea to produce a long, narrow cove. Segula was constructed above a 100-m-deep submarine platform that extends eastward to Khvostof and Davidof islands. A submarine debris-avalanche deposit extends up to 18 km offshore to the north. The summit of Segula contains a small, poorly defined caldera that is partly overtopped on the south by a cinder cone that forms the 1153 m high point of the island and on the north by extensive lava flows that reach the NE coast along a broad front. Another lava field on the SE coast originated from a cinder cone at 300 m altitude on the SE flank. No historical eruptions are known from Segula, but Nelson (1959) considered fresh lava flows on the north flank to possibly be only a few hundred years old.
About Volcano Data | Larger photo with caption and credit.
Smithsonian Volcano Information | Alaska Volcano Observatory

Little Sitkin
Volcano types:
Stratovolcano
Calderas
Summit Elev: 1174 m
Latitude: 51.95°N
Longitude: 178.543°E
Diamond-shaped Little Sitkin Island is bounded by steep cliffs on the east, north, and NE sides. Little Sitkin volcano contains two nested calderas. The older, nearly circular Pleistocene caldera is 4.8 km wide, may have once contained a caldera lake, and was partially filled by a younger cone formed mostly of andesitic and dacitic lava flows. The elliptical younger caldera is 2.7 x 4 km wide; it lies within the eastern part of the older caldera and shares its eastern and southern rim. The younger caldera partially destroyed the lava cone within the first caldera and is of possible early Holocene age. Young-looking dacitic lava flows, erupted in 1828 (Kay, in Wood and Kienle 1990), issued from the central cone within the younger caldera and from a vent on the west flank outside the older caldera. Fumarolic areas are found near the western coast, along the NW margin of the older caldera, and from the summit crater down the southern flank for a 1 km distance.
About Volcano Data | Larger photo with caption and credit.
Smithsonian Volcano Information | Alaska Volcano Observatory

Semisopochnoi
Caldera
Cones
Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is 1221-m-high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked 774-m-high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855-m-high Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

Gareloi
Fissure vents
Longitude: 178.794°W
The 8 x 10 km diameter Gareloi Island, the northernmost volcano of the Delarof Group at the western end of the Andreanof Islands, consists of a stratovolcano with two summits and a SE-trending fissure. This prominent fissure was formed during an eruption in 1929 and extends from the southern summit to the sea. Steep sea cliffs that are cut into rocks of an older, eroded center are found on the SW coast, and submarine deposits of three debris avalanches produced by edifice collapse are found offshore. Young lava flows cover the older volcano from the 1573-m-high summit of Gareloi to the coast along three broad axes trending NW, ENE, and south. The 1929 eruption originated from 13 craters along a 4-km-long fissure. Phreatic explosions were followed by the ejection of glassy pumice, lapilli, scoria, and older blocks, as well as by the emission of four short, steep lava flows, one of which reached the SE coast.

Tanaga
Andreanof Islands
Stratovolcanoes
Caldera
Longitude: 178.146°W
Tanaga volcano, the second largest volcanic center of the central Aleutians, is the central and highest of three youthful stratovolcanoes oriented along a roughly E-W line at the NW tip of Tanaga Island. Arcuate ridges to the east and south represent the rim of an arcuate caldera formed by collapse of an ancestral Tanaga volcano during the Pleistocene. Most Holocene eruptions originated from Tanaga volcano itself, which consists of two large cones, the western of which is the highest, constructed within a caldera whose 400-m-high rim is prominent to the SE. At the westernmost end of the Tanaga complex is conical Sajaka, a 1304-m-high double cone that may be the youngest of the three volcanoes. Sajaka One volcano collapsed during the late Holocene, producing a debris avalanche that swept into the sea, after which Sajaka Two cone was constructed within the collapse scarp.

Takawangha
Andreanof Islands
Pyroclastic cones
Longitude: 178.006°W
Takawangha is a 1449-m-high, youthful volcano with an ice-filled caldera on northern Tanaga Island, near the western end of the Andreanof Islands. Takawangha lies across a saddle from historically active Tanaga volcano to the west; older, deeply eroded volcanoes lie adjacent to Takawangha on the east. The summit of the dominantly basaltic to basaltic-andesite volcano is largely ice covered, with the exception of five Holocene craters that during the last few thousand years produced explosive eruptions and lava flows that reached the lower flanks of the volcano. No historical eruptions are known from Takawangha, although radiocarbon dating indicates explosive eruptions have occurred within the past several hundred years.

Kanaga
Andreanof Islands
Symmetrical Kanaga stratovolcano is situated within the Kanaton caldera at the northern tip of Kanaga Island. The rim of Kanaton caldera forms a 760-m-high arcuate ridge south and east of Kanaga; a lake occupies part of the SE caldera floor. The volume of subaerial dacitic tuff is smaller than would typically be associated with caldera collapse, and deposits of a massive submarine debris avalanche associated with edifice collapse extend nearly 30 km to the NNW. Several fresh lava flows from historical or late prehistorical time descend the flanks of Kanaga, in some cases to the sea. Historical eruptions, most of which are poorly documented, have been recorded since 1763. Kanaga is also noted petrologically for ultramafic inclusions within an outcrop of alkaline basalt SW of the volcano. Fumarolic activity occurs in a circular, 200-m-wide, 60-m-deep summit crater and produces vapor plumes sometimes seen on clear days from Adak, 50 km to the east.

Great Sitkin
Lava dome
Summit Elev: 1740+ m
Constructed within the caldera of an older shield volcano forming the northern half of Great Sitkin Island, 1740-m-high Great Sitkin volcano contains a small, 0.8 x 1.2 km ice-filled summit caldera. Deep glacial valleys radiate from the summit, which lies at the eastern rim of the caldera, which was formed by massive edifice failure that produced a submarine debris avalanche that traveled more than 40 km to the north. The entire island is blanketed with a light-brown to black pumice layer up to 6 m thick. This deposit is overlain over much of the NW side of the island by ash deposits from a subsidiary vent NW of the caldera. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century. In 1945, a 400-600 m wide, flat-topped lava dome was emplaced through a glacier filling the steep-sided, 180-m-deep summit caldera.

Kasatochi
Lava dome
Located at the northern end of a shallow submarine ridge trending perpendicular to the Aleutian arc, Kasatochi is small 2.7 x 3.3 km wide island volcano with a dramatic 750-m-wide summit crater lake. The summit of Kasatochi reaches only 314 m above sea level, and the lake surface lies less than about 60 m above the sea. A lava dome is located on the NW flank at about 150 m elevation. The asymmetrical island is steeper on the northern side than the southern, and the volcano's crater lies north of the center of the island. Reports of activity from the heavily eroded Koniuji volcano to the east probably refer to eruptions from Kasatochi. A lava flow may have been emplaced during the first historical eruption in 1760.

Atka
Stratovolcanoes
Lava dome
The largest volcanic center in the central Aleutians, Atka consists of a central shield and Pleistocene caldera with several post-caldera volcanoes. A major dacitic explosive eruption accompanied formation of the caldera about 500,000 to 300,000 years ago. The most prominent of the post-caldera stratovolcanoes are Kliuchef and Sarichef, both of which may have been active in historical time. Sarichef has a symmetrical profile, but the less eroded Kliuchef is the source of most if not all historical eruptions. Kliuchef may have been active on occasion simultaneously with Korovin volcano to the north. Hot springs and fumaroles are located on the flanks of Mount Kliuchef and in a glacial valley SW of Kliuchef.

Korovin
Atka I
Stratovolcanoes
Cinder cone
Korovin, the most frequently active volcano of the large volcanic complex at the NE tip of Atka Island, contains a 1533-m-high double summit with two craters located along a NW-SE line. The NW summit has a small crater, but the 1-km-wide crater of the SE cone has an unusual, open cylindrical vent of widely variable depth that sometimes contains a crater lake or a high magma column. A fresh-looking cinder cone lies on the flank of partially dissected Konia volcano, located on the SE flank of Korovin. The volcano is dominantly basaltic in composition, although some late-stage dacitic lava flows are present on both Korovin and Konia.
Smithsonian Volcano Information

Seguam
Calderas
The elliptical, 11.5 x 24 km island of Seguam, lying between Amlia and Amukta Islands in the central Aleutians, contains two calderas with Holocene post-caldera cones. Growth of the basaltic-to-rhyolitic Wilcox volcano on the east side of the island during the late Pleistocene was followed by edifice collapse and an associated ignimbrite eruption about 9000 years ago, leaving a horseshoe-shaped caldera open to the west, inside which a rhyolitic cone was constructed. The 3 x 4 km wide westernmost caldera has a central scoria cone, Pyre Peak, which rises above the caldera rim and is the source of most of the historical eruptions of Seguam volcano. A very young basaltic field surrounds Pyre Peak, and lava flows partially fill the caldera and reach the southern coast. Older Holocene lava flows were erupted from vents within the eastern caldera, and a monogenetic Holocene cone forms Moundhill volcano on the eastern tip of the island.

Amukta
Islands of the Four Mountains
Pyroclastic cone
The symmetrical Amukta stratovolcano lies in the central Aleutians SW of Chagulak Island and is the westernmost of the Islands of the Four Mountains group. Amukta was constructed at the northern side of an arcuate caldera-like feature that is open to the sea along the southern coast of the 8-km-wide Amukta Island. The 1066-m-high stratovolcano overlies a broad shield volcano and is topped by a 400-m-wide crater. A cinder cone is located near the NE coast. Amukta has had several eruptions in historical time from both summit and flank vents.

Chagulak
Islands of the Four Mountains
The 3-km-wide island of Chagulak in the Islands of the Four Mountains group is the summit of a small, unstudied stratovolcano NE of Amukta volcano. The two volcanoes coalesce at depth although they are separated by 7 km of ocean. Yunaska volcano lies about 20 km to the east. Sharp-topped Chagulak volcano rises steeply to 1142 m and is ruggedly dissected on the east side. No historical eruptions have been recorded from Chagulak volcano, and its age is not precisely known.

Yunaska
Islands of the Four Mountains
Shield volcano
Calderas
Pyroclastic cones
The elongated, 9 x 23 km island of Yunaska in the Islands of the Four Mountains group is comprised of two unnamed volcanic centers of greatly different morphology. The older, 950-m-high western center consists of the eroded remnants of four overlapping stratovolcanoes that form a linear, NNE-trending ridge. Cinder cones and fissure-fed lava flows extend from the western end of the complex. The younger, 550-m-high eastern complex consists of a shield volcano capped by two nested calderas. The 3.5-km-wide Coats caldera is located within an older 10 x 13 km caldera and contains cinder cones and a lava field. Two areas of particularly youthful lava flows extend down the flank through a gap in the SW caldera rim and blanket the upper northern flank of the caldera. Vents are found on the flanks of the caldera within a kilometer of its rim. A post-caldera cone is capped by a small summit crater. The eastern center is presumably the source of the island's historical eruptions, first recorded in 1817.

Herbert
The 10-km-wide Herbert Island, the SW-most of the Islands of the Four Mountains group, lies across a strait SW of Mount Cleveland. Herbert is a classic, symmetrical stratovolcano whose summit is broadly truncated by a 2-km-wide caldera that is breached to NW. No historical eruptions have been recorded from 1280-m-high Herbert volcano, which, like many other Aleutian volcanoes, has not been studied geologically.

Carlisle
Carlisle Island is a steep-sided, conical stratovolcano that rises to 1620 m across the Carlisle Pass strait from Mount Cleveland. Radar images suggest that this uninhabited, 7-km-wide island may contain two closely spaced volcanic cones (Myers, in Wood and Kienle 1990). Like nearby Herbert volcano, no geologic studies have been conducted on the volcano. Eruptions from Carlisle have been reported since the 18th century, but are very poorly documented. A variety of names was attached to Carlisle on early hydrographic maps, and Miller et al. (1998) noted that some 18th and 19th century eruptions reported at the closely spaced volcanoes of the "Islands of the Four Mountains" area could refer to Carlisle as well as Cleveland, Uliaga, or Kagamil volcanoes.

Cleveland
Chuginadak Island
Beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited, dumbbell-shaped Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Cleveland is joined to the rest of Chuginadak Island by a low isthmus. The 1730-m-high Mount Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name for Mount Cleveland, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks of the volcano. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions from Mount Cleveland have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

Tana
Chuginadak Island
Cinder cones
The Tana volcanic complex forming the eastern half of the dumbbell-shaped Chuginadak Island, opposite the dramatic conical Cleveland stratovolcano, is composed of two prominent E-W-trending volcanoes. The complex shows evidence of glacial erosion, but the observation on satellite imagery of highly irregular coastlines forming peninsulas west of Applegate Cove on the NW side of the complex and Concord Point on the south side imply lava flows of mid- to late-Holocene age (Nye 2007, pers. comm.). Prominent lava flow levees are visible near Concord Point, where a low-silica rhyolite sample was obtained. The undissected cone and youthful crater forming the western summit also imply a post-glacial age, and youthful cinder cones also lie east of the isthmus between Cleveland and Tana volcanoes.

Uliaga
The small, triangular, 3-km-wide island of Uliaga, located at the NE end of the Islands of the Four Mountains archipelago immediately NW of Kagamil Island, is composed of a small, eroded stratovolcano. Uliaga volcano rises to only 888 m and is the smallest of the Islands of the Four Mountains volcanoes. There are no reports of historical eruptions from Uliaga, but the volcano was considered to have been active during the Holocene (Nye et al., 1998).

Kagamil
Kagamil Island lies near the NE end of the Islands of the Four Mountains archipelago in the central Aleutians, between Chuginadak and Uliaga Islands. The southern half of 5 x 10 km Kagamil Island contains two undissected cones of postglacial age with small summit craters. The larger, 893-m-high cone is located at the SE end of the NNW-SSE-trending volcano. Arcuate ridges at the northern and southern ends of the island suggest a possible earlier caldera. Hot springs and fumaroles occur along a steaming beach at the SE coast. The early explorer Veniaminof (1840) indicated that Kagamil formerly "flamed and smoked," but the only eruptive report is of unspecified activity in 1929 (Coats 1950).

Vsevidof
Fox Islands
Fissure vents
The symmetrical Vsevidof stratovolcano, near the SW end of Umnak Island, is one of the most prominent volcanoes in the Aleutians. Vsevidof contains a 1.2-km-wide, ice-filled summit crater that is breached by glaciers on the east and north sides. An E-W-trending zone of scoria cones that extends from 1220 m down much of the western flank has been the source of historical eruptions. The bulk of the 2149-m-high cone of Vsevidof was constructed during the Holocene. Young andesitic and dacitic lava flows were extruded from vents on the north and south flanks and on the west-flank rift. The largest lava flow traveled down the west flank to the coast, forming Cape Kigushimkada.

Recheschnoi
Fox Islands
Cinder cones
Lava domes
The heavily glaciated, 1984-m-high Recheschnoi stratovolcano is located ENE of a roughly 900-m-high saddle across from Vsevidof volcano. Recheschnoi consists of an elongated, NE-SW-trending ridge that is dissected by deep glacier-filled valleys. Erosion is more extensive at the NE end. Holocene andesitic pyroclastic cones and rhyolitic lava domes, the latter west of the head of Russian Bay, are situated on the east and west flanks of the volcano. The Geyser Bight geothermal area on the NE flank of Recheschnoi is one of the hottest and most extensive thermal areas in Alaska. It consists of six zones of thermal springs and two fumarolic areas along upper Geyser Creek and contains the only known geysers in the state. Other thermal areas occur at Hot Springs Cove and Partov Cove on the rugged isthmus between Recheschnoi and Okmok volcanoes.

Okmok
Fox Islands
Shield volcano
The broad, basaltic Okmok shield volcano, which forms the NE end of Umnak Island, has a dramatically different profile than most other Aleutian volcanoes. The summit of the low, 35-km-wide volcano is cut by two overlapping 10-km-wide calderas formed during eruptions about 12,000 and 2050 years ago that produced dacitic pyroclastic flows that reached the coast. More than 60 tephra layers from Okmok have been found overlying the 12,000-year-old caldera-forming tephra layer. Numerous satellitic cones and lava domes dot the flanks of the volcano down to the coast, including 1253-m Mount Tulik on the SE flank, which is almost 200 m higher than the caldera rim. Some of the post-caldera cones show evidence of wave-cut lake terraces; the more recent cones, some of which have been active historically, were formed after the caldera lake, once 150 m deep, disappeared. Hot springs and fumaroles are found within the caldera. Historical eruptions have occurred since 1805 from cinder cones within the caldera.

Bogoslof
Submarine volcano
Lava domes
Bogoslof is the emergent summit of a submarine volcano that lies 40 km north of the main Aleutian arc. It rises 1500 m above the Bering Sea floor. Repeated construction and destruction of lava domes at different locations during historical time has greatly modified the appearance of this "Jack-in-the-Box" volcano and has introduced a confusing nomenclature applied during frequent visits of exploring expeditions. The present triangular-shaped, 0.75 x 2 km island consists of remnants of lava domes emplaced from 1796 to 1992. Castle Rock (Old Bogoslof) is a steep-sided pinnacle that is a remnant of a spine from the 1796 eruption. Fire Island (New Bogoslof), a small island located about 600 m NW of Bogoslof Island, is a remnant of a lava dome that was formed in 1883.

Makushin
The ice-covered, 1800-m-high Makushin volcano on northern Unalaska Island west of the town of Dutch Harbor is capped by a 2.5-km-wide caldera. The broad, domical structure of Makushin contrasts with the steep-sided profiles of most other Aleutian stratovolcanoes. Much of the volcano was formed during the Pleistocene, but the caldera (which formed about 8000 years ago), Sugarloaf cone on the ENE flank, and a cluster of about a dozen explosion pits and cinder cones at Point Kadin on the WNW flank, are of Holocene age. A broad band of NE-SW-trending satellitic vents cuts across the volcano. The composite Pakushin cone, with multiple summit craters, lies 8 km to the SW of Makushin. Frequent explosive eruptions have occurred during the past 4000 years, sometimes accompanied by pyroclastic flows and surges. Geothermal areas are found in the summit caldera of Makushin and on the SE and eastern flanks of the volcano. They represent the largest and most investigated high-temperature geothermal resources in Alaska. Small-to-moderate explosive eruptions have been recorded at Makushin since 1786.

Akutan
One of the most active volcanoes of the Aleutian arc, Akutan contains 2-km-wide caldera with an active intracaldera cone. An older, largely buried caldera was formed during the late Pleistocene or early Holocene. Two volcanic centers are located on the NW flank. Lava Peak is of Pleistocene age, and a cinder cone lower on the flank produced a lava flow in 1852 that extended the shoreline of the island and forms Lava Point. The 60-365 m deep younger caldera was formed during a major explosive eruption about 1600 years ago and contains at least three lakes. The currently active large cinder cone in the NE part of the caldera has been the source of frequent explosive eruptions with occasional lava effusion that blankets the caldera floor. A lava flow in 1978 traveled through a narrow breach in the north caldera rim almost to the coast. Fumaroles occur at the base of the caldera cinder cone, and hot springs are located NE of the caldera at the head of Hot Springs Bay valley and along the shores of Hot Springs Bay.

Westdahl
Stratovolcano ?
Westdahl is a broad, 1654-m-high glacier-covered volcano occupying the SW end of Unimak Island. Two peaks protrude from the summit plateau, and a new crater formed in 1978 cuts the summit icecap. The broad volcano has a somewhat of a shield-like morphology and forms one of the largest volcanoes of the Aleutian Islands. The sharp-topped, conical Pogromni stratovolcano lies 5 km north of Westdahl. Pogromni rises to 2002 m, several hundred meters higher than Westdahl, but is moderately glacially dissected and presumably older. Many satellitic cones of postglacial age are located along a NW-SE line cutting across the summit of Westdahl. Some of the historical eruptions attributed to the eroded Pogromni volcano may have originated instead from Westdahl (Miller et al. 1998). The first historical eruption of Westdahl occurred in 1795. An 8-km-long fissure extending east from the summit of Westdahl produced explosive eruptions and lava flows in 1991.

Fisher
Lava domes
The 11 x 18 km Fisher caldera on western Unimak Island NE of Westdahl volcano is one of the largest calderas in the Aleutian arc. The caldera, which is elongated in a NE direction, formed around 9400 years ago, accompanied by emission of large-volume, mobile pyroclastic flows that reached the Bering Sea and the Pacific Ocean. Two satellitic cones are located below the north rim, NE of its 1112-m high point at Eickelberg Peak, which rises more than 900 m above three lakes on the caldera floor, one of which drains through a notch in the southern caldera rim. A large composite cone, Mount Finch, is found at the center of the caldera, which also contains a small breached cinder cone. Historical eruptions have occurred in the 18th and 19th centuries. Low-temperature fumaroles are located at the western flank of Mount Finch, and Turquoise Lake, at the base of the cone, emits hydrogen sulfide gas.

Shishaldin
Maars
The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, Shishaldin is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 m elevation. Shishaldin contains over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Roundtop
The flat-topped, glacier-covered Roundtop volcano is the easternmost and lowest of an E-W-trending line of volcanoes on eastern Unimak Island. Roundtop lies 13 km SW of the village of False Pass. The snow and ice-covered edifice fills much of a 3-km-wide caldera that formed during the early Holocene. The caldera-forming eruption produced pyroclastic flows and a rhyolitic tephra layer that is widespread throughout the southwestern end of the Alaska Peninsula. A group of lava domes was constructed south of Roundtop volcano. No historical eruptions are known from the 1871-m-high stratovolcano. In the 1930s warm springs were found on its slopes.

Amak
Amak, the easternmost of the Aleutian Islands, is a small island stratovolcano that like Bogoslof, lies north of the main Aleutian volcanic front. Amak is located about 50 km NW of Frosty volcano on the western tip of the Alaska Peninsula. The summit of the small, roughly 1 cu km Amak volcano is only 488 m above sea level. Blocky lava flows with prominent levees were emplaced during historical eruptions from 1700-1710 and in 1796 (Marsh, in Wood and Kienle 1990). The flows radiate from a well-defined central crater and cover much of the central part of the island. Earlier volcanism perhaps 4000-5000 years ago consisted of the emission of thin, platy andesitic lava flows. A flat alluvial plain on the south flank contains a flat-bottomed crater that may be a maar.

Alaska Peninsula

Frosty
Alaska Peninsula
Frosty volcano, the youngest of two large volcanic structures of the Cold Bay volcanic complex, is the westernmost Holocene volcano of the Alaska Peninsula. The oldest products of the roughly 100 cu km Cold Bay complex, which lies SW of the village of Cold Bay, form the glacially dissected late-Pliocene to early Pleistocene Morzhovoi Volcanics at the southern end of the complex. Frosty Peak to the north is a symmetrical late-Pleistocene to Recent stratovolcano constructed within the southernmost of two coalescing craters. The western wall of the ice-filled northern crater is breached by a large valley glacier. The symmetrical summit cone rises about 600 m above the floor of the southern crater.

Dutton
Alaska Peninsula
The Mount Dutton volcanic center east of Cold Bay near the tip of the Alaska Peninsula consists of a glacier-covered, 1506-m-high central lava dome complex. Early andesitic lava flows and late-stage dacitic lava domes have been partially removed by one or more Holocene edifice collapses about 5100-6800 years ago. This created debris avalanches that traveled to the west and to the south, reaching Belkofski Bay. The important regional fishing center of King Cove lies less than 15 km from the volcano, and the village's airstrip is built on top of the southern avalanche deposit. A steep-sided complex of lava domes forms the summit of the volcano, and young block-and-ash flow deposits extend to the east. Two small unglaciated lava domes on the NE flank 3.5 km from the summit are also of Holocene age. Major earthquake swarms near the volcano were recorded in 1984-85 and 1988.

Emmons Lake
Cinder cones
The massive Emmons Lake stratovolcano, located north of Volcano Bay and SW of Pavlof volcano, is truncated by one of the largest calderas of the Aleutian arc. The 11 x 18 km caldera contains a narrow elongated lake at its SW end that drains through a breach in the SE caldera rim to the Pacific Ocean. The compound caldera was formed during six voluminous dacitic-to-rhyolitic eruptions between about 294,000 and 26,000 years ago that produced extensive ashflow tuffs. Mount Emmons, Mount Hague, and Double Crater are post-caldera cones of dominantly basaltic composition that were constructed along the SW-NE trend of the elongated caldera, which is up to 1150 m deep. Some young Holocene flows have moved through a gap in the southern caldera rim to within 3 km of the Pacific Ocean. A large fumarolic area is located on the south side of Mount Hague, and the only reported historical activity from Emmons Lake volcano was the emission of steam plumes from Hague in 1990 and 1991.

Pavlof
The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing strombolian to vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption of Pavlof took place in 1911, at the end of a 5-year-long eruptive episode. During this eruption a fissure opened on the northern flank of the volcano, ejecting large blocks and issuing lava flows.

Pavlof Sister
Located at the end of a chain of volcanoes trending NE from Emmons Lake caldera, the symmetrical Pavlof Sister stratovolcano is somewhat more eroded than its twin volcano to the SW, Pavlof. Pavlof Sister, along with Pavlof and Little Pavlof is a stratovolcano that formed outside of the Emmons Lake caldera; these and other volcanoes inside Emmons Lake caldera are not glaciated and thus would have formed since the area was last glaciated about 15-20,000 years ago. The 2142-m-high Pavlof Sister is almost 400 m lower than Pavlof and has a sharper-peaked summit. Some sources attributed a period of intermittent eruptive activity from 1762 to 1786 AD to Pavlof Sister, but other sources consider this event to have been from Pavlof volcano. The two symmetrical volcanoes form a dramatic backdrop to Pavlof Bay and Volcano Bay near the western end of the Alaska Peninsula.

Dana
Mount Dana is a small calc-alkaline volcano NE of Canoe Bay inlet at the head of Pavlof Bay consisting of an apron of volcaniclastic debris surrounding a central dome complex. The 1354-m high point is located at the north rim of a 1.5 x 2 km crater, whose SW rim exposes Mesozoic sedimentary rocks. Andesitic lava domes occur on the west crater rim and as a small mound east of Knutson Lake inside the crater. Mount Dana is the source of a mid-Holocene block-and-ash flow that reached the sea at Canoe Bay. No historical eruptions are known from Dana, but a 200-m-wide tufa mound and several cold springs are located on the SW flank of the volcano.

Stepovak Bay 2
Cinder cone
A group of four late-Pleistocene to Holocene volcanoes is located along a NE-trending line SW of Kupreanof volcano. The SW-most of the 4 volcanoes, located NW of Stepovak Bay and 24 km SW of Kupreanof, is of late-Pleistocene age. Stepovak Bay 2 is a 200-m-high cinder cone with a Holocene andesitic lava flow extending initially to the NE, then SE.

Kupreanof
Kupreanof is the largest and NE-most of a group of five relatively closely spaced Quaternary volcanic centers opposite Stepovak Bay. A debris flow or block-and-ash flow with possible juvenile fragments descended a late-Pleistocene valley south of the volcano. The 1895-m-high stratovolcano displays vigorous fumarolic activity. Its only known historical activity consisted of minor steam and ash emission that was reported from a SSW-flank solfatara field in 1987.

Veniaminof
Massive Veniaminof volcano, one of the highest and largest volcanoes on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which reaches an elevation of 2156 m and rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

Black Peak
The highly eroded stratovolcano and lava dome complex of Black Peak was constructed within an ice-free mid-Holocene caldera with two small caldera lakes on the northern and eastern sides. The pre-caldera volcano consists of andesitic-dacitic lava domes, lava flows, and volcaniclastic rocks that were constructed over a basement of Pliocene volcanogenic sedimentary rocks. Ash-flow tuffs and block-and-ash-flow deposits from the >10 cu km caldera-forming eruption, which occurred less than about 4000 years ago, fill the Ash Creek and Bluff Creek valleys to the west and north to depths of as much as 100 m. Most of the 3.5-km-wide caldera floor is occupied by a complex of nested dacitic lava domes and associated lava flows centered in the southern part of the caldera.

Aniakchak
One of the most dramatic calderas of the Aleutian arc, the 10-km-wide Aniakchak caldera was formed around 3400 years ago during a voluminous eruption in which pyroclastic flows traveled more than 50 km north to the Bering Sea and also reached the Pacific Ocean to the south. At least 40 explosive eruptions have been documented from Aniakchak during the past 10,000 years, making it the most active volcano of the eastern Aleutian arc. A dominantly andesitic pre-caldera volcano was constructed above basement Mesozoic and Tertiary sedimentary rocks that are exposed in the caldera walls to elevations of about 610 m. The ice-free caldera floor contains many pyroclastic cones, tuff cones, maars, and lava domes. Surprise Lake on the NE side drains through The Gates, a steep-walled breach on the east side of the 1-km-high caldera rim. Vent Mountain and Half Cone are two long-lived vents on the south-central and NW caldera floor, respectively. The first and only confirmed historical eruption took place in 1931 from vents on the west and SW caldera floor.

Yantarni
Yantarni is a small andesitic stratovolcano located between Aniakchak caldera and Chiginadak volcanoes that was not discovered until 1979. A large breached crater on the NE side, which was formed by collapse of the summit about 2000-3500 years ago, contains a lava dome that marks the volcano's 1345 m high point. This eruption, which resembled that of Mount St. Helens in 1980, began with a debris avalanche produced by the edifice collapse that was accompanied by a possible lateral blast and followed by the emplacement of 1 cu km of pyroclastic flows related to growth of the summit lava dome. No historical eruptions have been documented from Yantarni.

Chiginagak
The symmetrical, calc-alkaline Chiginagak stratovolcano located about 15 km NW of Chiginagak Bay contains a small summit crater, which is breached to the south, and one or more summit lava domes. Satellitic lava domes occur high on the NW and SE flanks of the glacier-mantled volcano. An unglaciated lava flow and an overlying pyroclastic-flow deposit extending east from the summit are the most recent products of Chiginagak. They most likely originated from a lava dome at 1687 m on the SE flank, 1 km from the summit of the volcano, which has variably been estimated to be from 2075 to 2221 m high. Brief ash eruptions were reported in July 1971 and August 1998. Fumarolic activity occurs at 1600 m elevation on the NE flank of the volcano, and two areas of hot-spring travertine deposition are located at the NW base of the volcano near Volcano Creek.

Kialagvik
Kialagvik is a small, poorly known glacier-mantled stratovolcano NE of Chiginagak volcano with a Holocene central lava dome and associated pyroclastic-flow deposits (Riehle, in Wood and Kienle 1990). The volcano draws its name from the Eskimo word for Wide Bay, which lies beyond the mouth of Kialagvik Creek, NE of the volcano. The central dome rises 350 m above an ice field that mantles the upper part of the volcano. Andesitic lava flows and overlying dacitic block-and-ash-flow deposits are exposed broadly on the SW flank and in a small area on the NE flank. No historical activity is known from Kialagvik.

Ugashik-Peulik
The Ugashik-Peulik volcanic complex lies south of Becharof Lake and east of Upper Ugashik Lake. Late-Pleistocene caldera formation at Ugashik volcano was followed by the emplacement of at least 5 Holocene lava domes within the 4.5-km-wide caldera. Most of the caldera walls consist of basement sandstones of Jurassic age. Following caldera formation the small, 3 cu km Peulik stratovolcano grew 2.5 km to the north to a height of 1474 m, more than 500 m above that of Ugashik. Lava flows from Peulik cover the caldera rim to the south and extend to Becharof Lake, 6 km to the north. A small lava dome at 1200 m elevation on the east flank of Peulik was the source of a small block-and-ash flow. The summit of Peulik volcano contains a 1.5-km-wide crater breached to the west that is partially filled by a lava dome. Debris-avalanche deposits cover a 75 sq km area to the NW. A single documented historical eruption took place from Peulik volcano in 1814.

Ukinrek Maars
Maars
Ukinrek Maars are two explosion craters that were created in an area without previous volcanic activity during a 10-day-long phreatomagmatic eruption March-April 1977. The basaltic maars were erupted through glacial deposits in the Bering Sea lowlands 1.5 km south of Becharof Lake and 12 km west of Peulik volcano; their location is related to the regional Bruin Bay fault. The elliptical West Maar, which was the first to form, is 105 x 170 m wide and 35 m deep. The other maar, 600 m to the east, is 300 m wide and 70 m deep. Both maars are now filled by crater lakes; the eastern lake encircles a 49-m-high lava dome that was emplaced at the end of the eruption. Base surges were directed primarily to the NW. Juvenile material from the Ukinrek eruptions was of mantle-derived olivine basaltic composition. The dacitic Gas Rocks lava domes, of Quaternary age, are located on the shores of Becharof Lake, 3 km north of Ukinrek maars and were the site of a phreatic eruption about 2300 years ago.

Unnamed
Summit Elev: 300? m
A small unnamed lava dome and an associated lava flow about 30 km east of Becharof Lake and 8 km NW of Alinchak Bay are not significantly modified by glacial erosion. Detterman et al. (1987) suggested a Holocene age for the small dome, whose summit lies only about 300 m above sea level. Lava flows traveled a short distance to the north.

Martin
The mostly ice-covered Mount Martin stratovolcano lies at the SW end of the Katmai volcano cluster in Katmai National Park. The volcano was named for George C. Martin, the first person to visit and describe the Katmai area after the 1912 eruption. Mount Martin is capped by a 300-m-wide summit crater, which is ice-free because of an almost-constant steam plume and contains a shallow acidic lake. The edifice of Martin volcano overlies glaciated lava flows of the adjacent mid- to late-Pleistocene Alagoshak volcano on the WSW and was constructed entirely during the Holocene. Mount Martin consists of a small fragmental cone that was the source of ten thick overlapping blocky dacitic lava flows, largely uneroded by glaciers, that descend 10 km to the NW, cover 31 sq km, and form about 95% of the eruptive volume of the volcano. Two reports of historical eruptions that originated from uncertain sources were attributed by Muller et al. (1954) to Martin.

Mageik
Summit Elev: 2165? m
Mount Mageik is a broad ice-capped stratovolcano at the head of the Valley of Ten Thousand Smokes across Katmai Pass from Trident volcano. Four small overlapping peaks form the broad summit, three of which lie along a NE-SW trend south of the northern peak. The central summit consists of a lava dome, while the east, SW, and north volcanoes are capped by fragmental cones with ice-filled craters. The three westernmost summits are glaciated and of primarily Pleistocene age, but the East Mageik summit cone was the source of at least six Holocene eruptive episodes and fed Holocene lava flows that descended toward Katmai Pass and blanket the NE-to-SE flanks of the volcano. A young, 300-m-wide explosion crater between the east and central summits that formed about 2400-2500 years ago contains a shallow, acidic lake and many superheated fumarole jets. Three Holocene debris avalanches from south-flank failures descended into the Martin Creek drainages, one perhaps reaching the coast. Reports of historical eruptions from Mageik were questioned by Miller et al. (1998) and Hildreth and Fierstein (2000).

Trident
The Trident stratovolcano cluster was named for the three prominent peaks that were the most visible features at the summit prior to 1953. The andesitic-dacitic Trident group consists of four overlapping stratovolcanoes and numerous flank lava domes, including Falling Mountain and Mt. Cerberus on the far west flank. The summit complex of Trident is located 3-5 km SE of Novarupta volcano, and merges along a ridge to the NE with Katmai volcano. The three oldest Trident volcanoes are glaciated and Pleistocene in age, while the youngest was formed during historical time. In 1953 a new lava dome began growing on the SW flank of Trident. A series of thick andesitic lava flows were erupted between 1953 and 1968, forming a cone with 400-800 m of local relief. Periodic explosions took place until 1974, and the current summit contains a 350-m-wide crater. Some of the distal lava flows from West Trident stratovolcano collapsed into the Novarupta vent during its 1912 eruption.

Katmai
Prior to 1912, Mount Katmai was a compound stratovolcano with four NE-SW-trending summits, most of which were truncated by caldera collapse in that year. Two or more large explosive eruptions took place from Mount Katmai during the late Pleistocene. Most of the two overlapping pre-1912 Katmai volcanoes are Pleistocene in age, but Holocene lava flows from a flank vent descend the SE flank of the SW stratovolcano into the Katmai River canyon. Katmai was initially considered to be the source of the Valley of Ten Thousand Smokes ash flow in 1912. However, the 3 x 4 km wide caldera of 1912 is now known to have formed as a result of the voluminous eruption at nearby Novarupta volcano. The steep walled young caldera has a jagged rim that rises 500-1000 m above the caldera floor and contains a 250-m-deep, still-rising lake. Lake waters have covered a small post-collapse lava dome (Horseshoe Island) that was seen on the caldera floor at the time of the initial ascent to the caldera rim in 1916. Post-1912 glaciers have formed on a bench within Katmai caldera.

Novarupta
Novarupta, the least topographically prominent volcano in the Katmai area, was formed during a major eruption in 1912. This eruption was the world's largest during the 20th century and produced a voluminous rhyolitic airfall tephra and the renowned Valley of Ten Thousand Smokes (VTTS) ash flow. At the end of the eruption a small, 65-m-high, 400-m-wide lava dome grew to an elevation of 841 m within the source vent of the VTTS ashflow, a 2-km-wide area of subsidence NW of Trident volcano. The NE side of the Falling Mountain lava dome of the Trident volcanic cluster, as well as Broken Mountain and Baked Mountain, was removed by collapse of the Novarupta depression, which is marked by radial and scalloped arcuate fractures. Much larger collapse took place at Katmai volcano, 10 km to the east, where a 3 x 4 km wide caldera formed in response to magma reservoir drainage toward Novarupta.

Griggs
The summit of Mount Griggs towers above Knife Creek on the NE side of the Valley of Ten Thousand Smokes. The volcano is uniquely offset west of the NE-trending alignment of volcanoes in the Katmai area. The broad, 2317-m-high stratovolcano, formerly known as Knife Peak, consists of a late-Pleistocene volcano with glacial valleys on the north that was truncated on its SW side by an early Holocene edifice collapse. A Holocene volcano was subsequently constructed within the 1.5-km-wide scarp left by the emplacement of a large SW-flank debris avalanche. Nested cones with three concentric craters mostly fill the scarp, and thick, blocky lava flows blanket the SW flanks of the volcano below the collapse scarp. In contrast to the more silicic centers of the Katmai area along the crest of the range, lava flows from Griggs are dominantly andesitic in composition, and dacitic lava flows are uncommon. No historical eruptions have occurred from Griggs, but noisy fumarolic jets near the summit can be heard from the valley floor, 1750 m below.

Snowy Mountain
Glacier-covered, 2161-m-high Snowy Mountain, located 15 km NE of Mount Katmai, is the SW-most of a chain of closely spaced volcanoes extending NE along the crest of the Alaska Range. More than 90% of the compound Snowy volcano is mantled by glacial ice, which prompted the naming of the volcano by members of the 1917 Katmai expedition. Two small andesitic-dacitic stratovolcanoes, SW Snowy and NE Snowy, originated about 200,000 years ago. Only NE Snowy has been active during the Holocene. Late-Holocene collapse of this volcano produced a large debris avalanche that traveled to the north and left a large breached crater inside which a blocky lava dome was constructed. Peat beneath an ash layer thought to be associated with the the lava dome was radiocarbon dated at about 250 +/- 70 years ago. No historical eruptive activity has been documented, but fumarolic activity has been observed at NE Snowy. A zone of persistent diffuse shallow seismicity is located on and NW of the volcano.

Steller
Mount Steller is part of a chain of closely spaced NE-SW-trending vents in Katmai National Park and lies between Mount Denision and Kukak volcanoes. Uncertainty surrounds the number and location of volcanic vents in this heavily glaciated area. The precise age of the most recent activity at Steller volcano is not known, but the volcano was considered to have been active during the Holocene (Nye et al., 1998).

Kukak
The almost completely ice-covered Kukak volcano lies west of Hallo Bay near the NE end of a glacier-mantled range extending from Mount Katmai. Kukak volcano contains a vigorous fumarole field at the southern base of the hydrothermally altered northern summit and is the only one of the Denison-Steller-Kukak chain of volcanoes to display geothermal activity. Two reports of historical eruptions at Kukak from Hantke (1959) appear to be erroneous. The report of a 1951 eruption is an apparent reference to a July 22, 1951 ashfall at Kukak Bay, which was attributed by Muller et al. (1954) to Martin volcano. A 1953 explosive "eruption" was single large puff of steam followed by steaming from caverns in Hook Glacier (Muller et al., 1954).

Kaguyak
The small, but spectacular 2.5-km-wide Kaguyak caldera in the NE part of Katmai National Park is filled by a >180-m-deep lake whose surface lies more than 550 m below the caldera rim. Kaguyak volcano is only 901 m high, but rises directly from lowland areas near sea level south of the Big River. Pre-caldera lava domes are located on the east rim and SE flank. Two post-caldera lava domes extend into the lake on the SW side and another dome forms a small island in the center of the lake. The youthful caldera is unglaciated, and distal tephras from the caldera-forming eruption have been radiocarbon dated at about 3600 years before present. Voluminous dacitic pyroclastic-flow deposits surround the caldera, which is one of four Holocene calderas in the Alaska Peninsula that formed within a few hundred years of each other about 3500-4000 years ago.

Fourpeaked
Poorly known Fourpeaked volcano in NE Katmai National Park consists of isolated outcrops surrounded by the Fourpeaked Glacier, which descends eastward almost to the Shelikof Strait. The orientation of andesitic lava flows and extensive hydrothermal alteration of rocks near the present 2105-m-high summit suggest that it probably marks the vent of Fourpeaked volcano. Eruptive activity during the Holocene had not been confirmed prior to the first historical eruption of Fourpeaked in September 2006. A N-trending fissure extending 1 km from the summit produced minor ashfall.

Douglas
Glacier-covered, dissected Mount Douglas stratovolcano is located at the northern end of the Alaska Peninsula south of Kamishak Bay. The volcano, the NE-most in Katmai National Park, contains a small, ice-free summit crater lake and an active fumarole field. The volcano was constructed above Cretaceous and Jurassic sedimentary rocks. A lake temperature of 25 degrees Centigrade and a pH of 1 were measured in 1982. The fumaroles, which are actively depositing sulfur, were all at the pressure boiling point in 1982 and heated up to 114-118 degrees in 1991. The fumaroles are located on the NE wall of the 160 x 200 m wide crater lake; some fumaroles are subaqueous and produce turbulence on the surface of the blue-green lake. Unglaciated and relatively uneroded lava flows are found on the NW flank of the volcano. The age of the most recent eruptions from Douglas is not known, but Nye et al. (1998) considered activity to have occurred during the Holocene.

Alaska (southwestern)

Augustine
Southwestern Alaska
Augustine volcano, rising above Kamishak Bay in the southern Cook Inlet about 290 km SW of Anchorage, is the most active volcano of the eastern Aleutian arc. It consists of a complex of overlapping summit lava domes surrounded by an apron of volcaniclastic debris that descends to the sea on all sides. Few lava flows are exposed; the flanks consist mainly of debris-avalanche and pyroclastic-flow deposits formed by repeated collapse and regrowth of the volcano's summit. The latest episode of edifice collapse occurred during Augustine's largest historical eruption in 1883; subsequent dome growth has restored the volcano to a height comparable to that prior to 1883. The oldest dated volcanic rocks on Augustine are more than 40,000 years old. At least 11 large debris avalanches have reached the sea during the past 1800-2000 years, and five major pumiceous tephras have been erupted during this interval. Historical eruptions have typically consisted of explosive activity with emplacement of pumiceous pyroclastic-flow deposits followed by lava dome extrusion with associated block-and-ash flows.

Iliamna
Southwestern Alaska
Iliamna is a prominent, 3053-m-high glacier-covered stratovolcano in Lake Clark National Park on the western side of Cook Inlet, about 225 km SW of Anchorage. Its flat-topped summit is flanked on the south, along a 5-km-long ridge, by the prominent North and South Twin Peaks, satellitic lava dome complexes. The Johnson Glacier dome complex lies on the NE flank. Steep headwalls on the southern and eastern flanks expose an inaccessible cross-section of the volcano. Major glaciers radiate from the summit, and valleys below the summit contain debris-avalanche and lahar deposits. Only a few major Holocene explosive eruptions have occurred from the deeply dissected volcano, which lacks a distinct crater. Most of the reports of historical eruptions may represent plumes from vigorous fumaroles east and SE of the summit, which are often mistaken for eruption columns (Miller et al., 1998). Eruptions producing pyroclastic flows have been dated at as recent as about 300 and 140 years ago (into the historical period), and elevated seismicity accompanying dike emplacement beneath the volcano was recorded in 1996.

Redoubt
Southwestern Alaska
Redoubt is a 3108-m-high glacier-covered stratovolcano with a breached summit crater in Lake Clark National Park about 170 km SW of Anchorage. Next to Mount Spurr, Redoubt has been the most active Holocene volcano in the upper Cook Inlet. The volcano was constructed beginning about 890,000 years ago over Mesozoic granitic rocks of the Alaska-Aleutian Range batholith. Collapse of the summit of Redoubt 10,500-13,000 years ago produced a major debris avalanche that reached Cook Inlet. Holocene activity has included the emplacement of a large debris avalanche and clay-rich lahars that dammed Lake Crescent on the south side and reached Cook Inlet about 3500 years ago. Eruptions during the past few centuries have affected only the Drift River drainage on the north. Historical eruptions have originated from a vent at the north end of the 1.8-km-wide breached summit crater. The 1989-90 eruption of Redoubt had severe economic impact on the Cook Inlet region and affected air traffic far beyond the volcano.

Spurr
The 3374-m-high summit of Mount Spurr, the highest volcano of the Aleutain arc, is a large lava dome constructed at the center of a roughly 5-km-wide horseshoe-shaped caldera that is open to the south. The volcano lies 130 km west of Anchorage and NE of Chakachamna Lake. The caldera was formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an ancestral Spurr volcano. The debris avalanche traveled more than 25 km to the SE, and the resulting deposit contains blocks as large as 100 m in diameter. Several ice-carved post-caldera cones or lava domes lie in the center of the caldera. The youngest vent, 2309-m-high Crater Peak, formed at the breached southern end of the caldera and has been the source of about 40 identified Holocene tephra layers. Spurr's two historical eruptions, from Crater Peak in 1953 and 1992, deposited ash on the city of Anchorage.

Hayes
Hayes volcano, located in a remote and rugged part of the Alaska Range NW of Anchorage and north of Mount Gerdine, was not discovered until 1975. It was named after nearby Hayes Glacier and consists of scattered remnants of a largely snow-and-ice covered volcano that has been destroyed by catastrophic eruptions. The most widespread Holocene eruptions in the Cook Inlet area originated from Hayes volcano between about 3800 and 3400 years ago and produced six regional tephra layers with an average volume of 2.4 cu km. The latest known eruption took place about 1000 years ago.

Alaska (western)

St. Paul Island
Western Alaska
Shield volcano
Tuff cone
The largest of the Pribilof Islands, St. Paul contains numerous young cinder cones. St. Paul Island consists of a 110 sq km area of coalescing small basaltic-to-trachybasaltic shield volcanoes capped by cinder cones, similar in style to the Snake Rive Plain volcanism in Idaho. The most widely exposed lava flows originated from E-W-trending vents in the Bogoslof Hill area in the center of the island and a NE-trending row of cinder cones in the Rush Hill area at the west side of the island. Subaerial activity at St. Paul began about 540,000 years ago and produced a basaltic lava platform. Later eruptions produced a series of monogenetic vents and two small shield volcanoes. Bogoslof Hill in the center of the island and Hutchinson Hill, forming isolated Northeast Point, which is connected by a low narrow isthmus to the rest of the island, were formed during the Pleistocene. The youngest vent is the Fox Hill cinder cone on the western side of the island that produced a lava flow about 3200 years ago that traveled into the sea at Southwest Point.

Nunivak Island
Western Alaska
Maars
Nunivak Island contains about 60 cinder cones and four maars; the surface of the island consists dominantly of thin pahoehoe lava flows that form a carapace over Cretaceous sedimentary rocks. The 110-km-wide permafrost-covered island lies about 30 km off the coast of SW Alaska. The widespread, thin pahoehoe lava flows originate from small shield volcanoes and cover much of the island, which is dotted throughout by cinder cones and other vents. Two of the maars have about 200 m of relief, with floors near sea level. Eruptions occurred during 5 broad periods of activity that began 6.1 million years ago and continued into the Holocene. The bulk of the >427 cu km volcanic field was formed during two Pleistocene eruptive periods that ended about 300,000 years ago. The most recent eruptions at Nunivak produced a series of alkalic basalt lava flows and ash deposits from cinder cones and maars along an E-W zone in the southern part of the island.

Ingakslugwat Hills
Western Alaska
The Ingakslugwat Hills consist of at least 32 small cinder cones and 8 larger craters covering an area of more than 500 sq km in the Yukon-Kuskokwin delta area of SW Alaska. Numerous small spatter cones and cinder cones of the Ingakslugwat Hills range from 8 to 190 m in height; many are concentrated in the NW side of the volcanic field. The latest activity was considered to have occurred during the Holocene (Moll-Stalcup, in Wood and Kienle 1990). One low cone containing a 400-m-wide lake may be a maar. This dominantly alkali olivine basaltic volcanic field also contains basanitic and nephelinitic rocks, some with inclusions of lherzolite and layered and granular gabbro.

St. Michael
Shield volcanoes
The St. Michael volcanic field, at the south end of Norton Sound, covers all of St. Michael and Stuart Islands with more than 55 cones and craters. Broad low shield volcanoes underlie the younger cones, and maar volcanoes are located at the SW part of the volcanic field, which covers >3000 sq km and extends inland along the Golsovia and Kogok rivers. The youngest activity is of Holocene age, and native tradition says that a village was submerged by lava three times.

Kookooligit Mountains
The Kookooligit Mountains are a 30 x 40 km wide shield volcano of Pleistocene-to-Holocene age in north-central St. Lawrence Island. The 673-m basaltic shield is composed of massive columnar-jointed lava flows that are overlain by more than 100 small cones (20-60 m high). Most of the cones are aligned E-W along the crest of the elongated shield volcano.

Imuruk Lake
Shield volcanoes
Summit Elev: 610+ m
The Oligocene-to-Holocene Imuruk monogenetic volcanic field in the central Seward Peninsula north of the Bendeleben Mountains contains around 75 small basaltic vents surrounded by voluminous lava flows. The largest and most recent vent is the Lost Jim cone, a 30-m-high cinder cone near Imuruk Lake that produced the only Holocene lava flow of the Imuruk field. The massive Lost Jim lava flow, erupted about 1655 years ago, extends 35 km west and 9 km north of the vent and covers about 230 sq km. The next youngest flow, the late-Pleistocene Camille lava flow, traveled 39 km from its vent.

Alaska (eastern)

Buzzard Creek
Eastern Alaska
Tuff rings
Two Holocene tuff rings form craters 300 and 66 m wide near the headwaters of Buzzard Creek at the northern foot of the central Alaska Range NE of the town of Healy along the Parks Highway. The total volume of ejecta, most of which is accessory material, probably does not exceed 0.001 cu km. The ejecta overlies young glacial terraces that correlate with a glacial stage that ended about 10,000 years ago, and radiocarbon dates give an age for the eruption that formed the tuff rings of about 3000 years. This minor volcanic feature lies along trend with the Aleutian arc, but is located 320 km NE of its nearest Holocene neighbor, Hayes volcano and lies directly over the northernmost corner of the subducting Pacific Plate.

Wrangell
Eastern Alaska
With a diameter of 30 km at 2000 m elevation, 900 cu km Mount Wrangell is one of the world's largest continental-margin volcanoes. The massive andesitic shield volcano has produced fluid lava flows as long as 58 km and contains an ice-filled 4-6 km diameter caldera located within a 15-km-wide ancestral caldera. Most of he massive shield volcano was constructed during eruptions between about 600,000 and 200,000 years ago. Formation of the summit caldera followed sometime between about 200,000 and 50,000 years ago. Three post-caldera craters are located at the broad 4317-m-high summit of the volcano, along the northern and western rims of the 1-km-deep, ice-filled caldera. A steep-sided flank cinder cone, Mount Zanetti, is located 6 km NW of the summit. The westernmost cone has been the source of infrequent historical eruptions beginning in the 18th century. Increased heat flux in recent years has melted large volumes of ice in the northern crater.

Churchill
Eastern Alaska
The Bona-Churchill massif in the St. Elias Mountains forms the highest Quaternary volcano in the United States. A 2.7 x 4.2 km wide caldera caps the summit of 4766-m-high Mount Churchill, which is now known to be the source of the White River Ash, produced during two of the largest explosive eruptions in North America during the past 2000 years (McGimsey et al. 1992). The 5005-m-high summit of Mount Bona lies 4 km across a high saddle from the younger Mount Churchill. The source vent of the widespread bilobate White River Ash deposit, which blankets more than 340,000 sq km of eastern Alaska and NW Canada, was initially thought to be a pumice mound that is mostly buried beneath the Klutlan Glacier NE of Churchill volcano. More recent work has revealed thick young pumice deposits mineralogically and chemically similar to the White River Ash deposits along the rim of the Mount Churchill caldera.

Edgecumbe
Southeastern Alaska
The Pleistocene-to-Holocene Mount Edgecumbe volcanic field covers about 260 sq km of Kruzov Island west of Sitka in the SE panhandle of Alaska. The basaltic-to-dacitic field is dominated by the large composite cones of Mount Edgecumbe, Crater Ridge, and Shell Mountain and has an unusual tectonic setting only 16 km east of the Queen Charlotte-Fairweather transform fault separating the North American and Pacific plates. Mount Edgecumbe, a 970-m-high stratovolcano with a well-defined crater, is the largest volcano of the Edgecumbe field. Crater Ridge is truncated by a 1.6-km-wide, 240-m-deep caldera. These and other vents of the volcanic field are oriented along a SW-NE line. Volcanic activity originated about 600,000 years ago along fissures cutting Kruzof Island. A series of major silicic explosive eruptions took place about 9000-13,000 radiocarbon years ago. The latest dated eruptions were phreatomagmatic explosions during the mid-Holocene, and all postglacial activity has been pyroclastic. Reports of historical eruptions of Mount Edgecumbe are unsubstantiated.

Duncan Canal
Southeastern Alaska
Volcanic field
Conspicuous fresh-looking pahoehoe and aa lava flows overlie glacial till at Kupreanof Island in the central panhandle of SE Alaska. Quaternary basaltic lava flows of Holocene and/or Pleistocene age up to 10 m thick form several broad flat-lying peninsulas and scattered outcrops on the shores of Sumner Strait at the southern end of Kupreanof Island (Brew et al. 1985). On a peninsula in Kah Sheets Bay a basaltic flow depositionally overlies till of the youngest glaciation, and youthful-looking flows are exposed along a broad 12-km-wide front westward toward Douglas Bay. Two probable vents are found to the north within Mesozoic and Paleozoic rocks at the northern end of the Castle Islands in the Duncan Canal fault zone, and at Indian Point the flows contain inclusions of picrite. At High Castle Island, the basaltic flows are columnar-jointed and overlie planar to cross-bedded coarse sandstone and poorly sorted volcaniclastic conglomerate. Basaltic flows in the Duncan Canal area are both subaerial and submarine.

Tlevak Strait-Suemez Is.
Southeastern Alaska
Volcanic field
Scattered flat-lying basaltic lava flows with fresh pahoehoe surfaces occur near Tlevak Strait and on the SW end of Suemez Island near the southern end of the panhandle of SE Alaska. Outcrops are located on western Prince of Wales Island, along Bobs Bay on the NW side of Dall Island, and at Trocadero Bay on Suemez Island. The flows overlie Paleozoic sedimentary rocks and are associated with Tertiary rhyolitic and dacitic lava flows on Suemez Island. The younger alkaline olivine basaltic flows were considered by Brew (in Wood and Kienle 1990) to be of probable postglacial age.