Friday 24 August 2012

Eruption on Ivan Grozny.

On 16 August 2012 the Itar-Tass news agency reported an eruption on the Ivan Grozny (Ivan the Terrible) volcano on Iturup Island in the Kuril Archipelago to the northeast of Hokkaido, producing ash-falls up to 25 km from the caldera. Ivan Grozny forms a caldera 3 × 3.5 km, open to the south. Their are several Holocene (less than 10 000 year old) lava domes to the northeast of this caldera, and a single large dome to the south, which is called the Grozny Dome (Terrible Dome). To the east lies a second volcano, Tebenkov, and south of this the Machekh Crater, which frequently produces fumaroles (gas emissions).

The location of Ivan Grozny. Google Maps.

The first recorded eruption on Ivan Grozny occurred in February 1968, when a small explosive eruption occurred. Similar events happened in 1970, January 1973 and May 1973. In 1989 a series of small eruptions lasted from May to August, triggering several lahars (mud flows), since when the volcano has been quiet.

The Kuril Archipelago runs from the northwestern tip of Hokkaido to the southern tip of the Kamtchatka Peninsula. It marks the southern margin of the Okhotsk Plate, which underlies the Sea of Okhotsk, the Kamchatka Peninsula, Sakhalin Island and Tōhoku and Hokkaidō in Japan. Along this southern margin the Pacific Plate is being subducted beneath the Okhotsk Plate in the Kuril Trench. As the Pacific Plate sinks under the Okhotsk Plate it is partial melted by the resultant friction and the heat of the Earth's interior. Some of the melted material then rises up through the overlying Okhotsk Plate as magma, fueling the volcanoes of the Kuril Archipelago.

Simple diagram showing the subduction of the Pacific Plate beneath the Okhotsk Plate along the Kuril Trench. Auburn University.

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