The Kamtchatka Volcanic Eruption Response Team reported seeing an avalanche of incandescent ashy material on the southeast flank of the lava dome of Mount Bezymianny, a 2882 m stratovolcano (cone shaped volcano made up of layers of ash and lava) on the central part of the Kamchatka Peninsula, on Monday 18 December 2017. This was followed by a brief eruptive episode that started at about 3.55 pm local time on Wednesday 20 December, that produced a column of ash that rose to 10-15 km above sea level, and drifted about 85 km to the northeast.
Ash column over Mount Bezymianny on 20 December 2017. Yuri Demyanchuk/Institute of Volcanology and Seismology of the Far Eastern Branch of the Russian Academy of Sciences/KVERT.
Mount Bezymianny was thought to be extinct until 1955, when it began a volcanic cycle that ended in 1956 with an explosive eruption caused the summit to collapse and created a large horseshoe-shaped crater. This has subsequently been filled in by further eruptive episodes on Bezymianny. The current summit is 2882 m high, but it is overshadowed by the nearby Kamen and Kluchevskaya volcanoes at 4579 m and 4750 m respectively. Bezymianny is thought to have formed about 4700 years ago, on the remains on an older, Pleistocene, volcano active between 11 000 and 7000 years ago. It has undergone three periods of intense activity since its formation, but was apparently inactive for about a thousand years prior to its 1955 reactivation.
The approximate location of Mount Bezmianny. Google Maps.
Mount Bezymianny is part of the Klyuchevskoi Volcano Group in the Ust-Kamchatka (East Kamchatka) District, along with mounts Klyuchevskoi and Kamen. The Kamchatka Peninsula lies on the eastern edge of the Okhotsk Plate, close to its margin with the Pacific and North American Plates. The Pacific Plate is being subducted along the margin, and as it does so it passes under the southern part of the Kamchatka Peninsula, and as it does so is partially melted by the friction and the heat of the Earth's interior. Some of the melted material then rises through the overlying Okhotsk Plate as magma and fuelling the volcanoes of southern Kamchatka.
Simple diagram showing the subduction of the Pacific Plate beneath the Okhotsk Plate along the Kuril Kamchatka Trench. The Kamchatka Peninsula is at the top of the diagram. Auburn University.
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