Great Sitkin Volcano | John Seach


Aleutian Islands, Alaska

52.08 N, 176.13 W
summit elevation 1740 m

Great Sitkin is an eroded active stratovolcano in the central Aleutian Islands, 35 km NE of the community of Adak on
Adak Island.

Great Sitkin is a circular volcanic island 14 x 16 km in diameter. It contains a summit caldera 2.5 km x 1.5 km in diameter. Great Sitkin Island is part of the Alaska Maritime National Wildlife Refuge.

Geology of Great Sitkin Island
The volcano is composed of andesite and basaltic andesite lava flows, andesite lava domes, and pyroclastic-flow and lahar deposits. A series of lava flows and lava domes comprise the current volcano, which is located in NW of Great Sitkin Island.

Great Sitkin Edifice Collapse
The edifice of Great Sitkin contains a horseshoe-shaped amphitheatre open to the
northwest toward the Bering Sea, formed during edifice collapse. A Holocene cone has grown within the scarp, indicating that the collapse occurred in the late Pleistocene or early Holocene. North of the volcano there is a hummocky region between 13 and 42 km offshore, with a slide-disturbed area covering 900 sq km.

Fumarolic Activity
Fumaroles, hot springs, and bubbling hot mud are located on the south flank of the volcano at the head of Big Fox Creek. Small fumaroles are locate in the crater and on the crater rim.

2002 Earthquake Swarm
An earthquake swarm occurred at Great Sitkin volcano on 27-28 May 2002. Hundreds of small earthquakes were located 5-6 km SE of the crater at depths of 0-5 km.

1974 Eruption
An eruption in 1974 produced minor ash fall on the flanks of the volcano and created an 800-900 m diameter lava dome in the summit crater. A magnitude 2.6 earthquake accompanied the eruption, and a plume was ejected to a height of 10,000 ft. Most of the 1945 lava dome was destroyed or covered by the 1974 eruption. The 1974 lava dome remained hot for several years after the eruption.

1945 Eruption
In March 1945 a summit glow was visible from Adak Island for several weeks. Pilots reported steam rising from the crater. A circular lava dome, 600-800 meters in diameter, formed in the crater.

Great Sitkin Volcano Eruptions

1974, 1950, 1949-50, 1946?, 1945, 1933, 1904?, 1829?, 1828?, 1792, 1784?, 1760?