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Akutan Peak description and information

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Official Name: Akutan Peak
Type:Stratovolcano with caldera
Most Recent Activity:December 18, 1992
Seismically Monitored: Yes
Color Code:GREEN
Alert Level:NORMAL
Elevation: 4275 ft (1303 m)
Latitude: 54.13308° N
Longitude:165.98555° W
Quadrangle:Unimak Unalaska
CAVW Number:311320
Pronunciation: Sound file
Associated Features:Lava Peak
Lava Point
Half Peak
Flat Top Peak
Cascade Bight
Long Valley Center
Nearby towns:Akutan 9 mi (14 km) NE
Unalaska 29 mi (46 km) SW
False Pass 115 mi (185 km) NE
Pauloff Harbor 134 mi (216 km) NE
Anchorage 766 mi (1233 km) NE
DESCRIPTION
From Miller and others (1998): "Akutan volcano is a composite stratovolcano with a circular summit caldera about 2 km across and 60 to 365 m deep (Byers and Barth, 1953; Romick and others, 1990; Motyka and others, 1981) and an active intracaldera cinder cone. The caldera rim reaches a maximum altitude of 1303 m at Akutan Peak, the remnant of a pre-caldera cone now filled with a lava plug. The caldera is breached to the north. Caldera subsidence accompanied or followed eruptions from a series of rim vents. The vestige of a larger caldera, of probable late Pleistocene age and at least in part older than the cone of Akutan Peak, extends 1.5 km southwest of Akutan Peak and is terminated to the north by the younger caldera. Small glaciers fill the older crater and lie within the southwest and southeast margins of the younger caldera.

"The active intracaldera cinder cone is over 200 m high, about 1 km in diameter, and located in the northeast quarter of the caldera. Three small sulfur-lined craters occupy its summit and several fumarole zones are present along its south and southwest flank (Byers and Barth, 1953). A crescent-shaped lake along the inner southwest rim of the caldera and a hot and slightly acidic lake along the northern caldera wall were noted by Byers and Barth in 1948 but Motyka and others (1981) speculate that these lakes may have been obliterated by more recent activity. Both lakes drained to the north through a gap in the caldera wall.

"The lava flows and pyroclastic deposits of Akutan volcano are no older than Pleistocene as Romick and others (1990) report ages of 1.1 +/- 0.1 to 1.8 +/- 0.8 Ma for the oldest of these rocks. The caldera-forming eruption occurred about 5,200 yBP (Reeder, 1983) and was the source of small volume andesitic pyroclastic-flow deposits in valleys on the north, south, and east sides of the volcano (Miller and Smith, 1987; Romick and others, 1990). Young basaltic lava flows, some of which were erupted in 1929, cover the caldera floor south and north of the cinder cone and extend several hundred m downslope through the crater rim gap. Flows extruded in 1947 blanket the central portion of the northwest end of the island at Lava Point, where about 4 square kilometers of jagged aa basalt occurs adjacent to several cinder cones. The entire island is mantled by an ash layer that thickens toward Akutan Peak; landslide and mud flow deposits have concentrated this ejecta in the valleys north and northeast of the caldera and a maximum fill depth of 7 m occurs at Wooly Cove (Finch, 1935).

"Active hot springs occur northeast of the caldera at the head of Hot Springs Bay valley and along the shore of Hot Springs Bay; Byers and Barth (1953) and Motyka and others (1990) recorded temperatures between 67 and 84 degrees C and a pH range of 6.6 to 7. Surface waters of the hot caldera lake were 50 degrees C with a pH of 5.0 and steam issuing from fumaroles along the cinder cone base averaged 96 degrees C (Finch, 1935)."

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Page modified: June 12, 2014 07:20
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