Atka Volcano - John Seach


Aleutian Islands, Alaska

52.38 N, 174.15 W
summit elevation 1530 m

Atka volcano is located in the central Aleutian Islands, Alaska. It consists of a large shield volcano capped by small andesitic and
dacitic vents. Atka is located 184 km E of Adak island, 600 km W of Unimak island, and 1,760 km SW of Anchorage.

Northeastern Atka is formed of young volcanic rocks which have been transformed into rugged terrain by a combination of volcanic and glacial activity. This part of the island covers 360 sq km and an eruptive volume of 200 cubic km.

The oldest eruption products are a series of basaltic andesite to dacite flows, pyroclastic rocks and lahars found around the edge of Korovin Bay. A caldera-forming eruption occurred 300,000 to 500,000 years ago. After caldera collapse, four major volcanic cones grew around the edge of Atka caldera: Korovin, Kliuchef, Konia and Sarichef.

Korovin is the highest peak (1530 m) and located along the northern coast. It has a base of 7 km. The cone has not been modified by glaciers, and is currently glacier-free. Korovin is a double cone, with the two summits 0.6 km apart. The NW summit is the lower of the two. The SE summit contains a steep-walled crater about 1 km wide and several hundred meters deep. A geothermal field is located at the head of a glacial valley 6.5 km SW of Korovin. Most historic activity has occurred at Korovin. Korovin lava contain 1–12% clinopyroxene, 0.4–3.6% olivine, 25–32% plagioclase, and 0–2% oxides.

Kliuchef is the second highest peak 1450 m) and is located at the center of the volcanic field. It is ringed by a series of peaks with heights from 748 m to 1433 m. The peak has a double summit with two small lakes. The summit has been modified by glacial ice, and the lower southeastern flank is partly covered by an ice field. There are three hot springs and fumerolic areas occur on the southern and western flanks. Lavas from Mount Kliuchef contain from 0.4 to 4% clinopyroxene, 0–7.2% olivine, 21.6–36.4% plagioclase, and 0 to 0.6% oxides.

Konia is a small post-caldera cone, situated in a saddle between Korovin and Kliuchef. A fresh cinder cone is located on the western flank.

Sarichef is located on the eastern edge of the island and formed on the flanks of the ancestral Atka Volcano.

2006 Eruption
In November and December 2006, seismic levels were above background levels. In late November satellite images showed ash on the E flank of the main crater. On 21st December 2006, small amounts of ash were emitted.

2005 Eruption
On 23rd February 2005, a small ash emission occurred from Korovin. Ash emissions reached an altitude of 2.4 km and was followed by several smaller ash emissions.

1998 Eruption
On 30th June 1998 an eruption plume reached 9 km above sea level.

1986 Eruption
On 23 May 1986 a steam eruption occurred at Atka Volcano 15 days after a
magnitude 7.7 earthquake 100 km away.

Atka Volcano Eruptions

2006, 2005, 1998, 1996, 1998, 1995, 1987, 1986, 1812