The Alaska Volcano Observatory reported a vapour plume rising 300 m about the summit of Great Sitkin, a volcanic island in the Andreanof Islands, part of the Aleutian Island chain, on Sunday 19 November 2017. This is the first observed eruptive activity on the volcano since February 1974, though it is not entirely unexpected, as there has been a steady increase in seismic activity beneath the island since July 2016. Seismic activity beneath volcanoes can be significant, as they are often
caused by the arrival of fresh magma, which may indicate that a volcano
is about to undergo an eruptive episode. A second small plume was spotted over the island by a satellite on Tuesday 21 November.
Small plume over Great Siskin Island on 19 November 2017. Alaska Volcano Observatory.
The volcanoes of the Alaskan Peninsula and Aleutian Islands are fed by
magma rising from the Pacific Plate, which is being subducted beneath
the North American Plate to the south along the Aleutian Trench. As the
subducting plate sinks into the Earth it is subjected to enormous heat
and pressure, causing more volatile minerals to melt. These then rise
through the overlying North American plate as magma, fuelling the Alaskan
volcanoes.
How the subduction of the Pacific Plate beneath the North American
Plate fuels the volcanoes of Alaska. Alaska Volcano Observatory.
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