Tuesday 20 August 2013

Japanese city covered in ash by eruption on Sakurajima Volcano.

An eruption on Sakurajima Volcano, situated on an island in Kagoshima Bay, Kyushu, has coated the city of Kagoshima in a layer of ash. The eruption, which occurred in the afternoon of Monday 19 March 2013, from the Showa vent on the side of the volcano rather than the main caldera, and produced a 5 km high column of ash and smoke. This is the tallest ash column ever produced by the vent, but is not being taken as cause for alarm locally, as the volcano frequently undergoes larger events. The ashfall covering the city has been blamed on a lack of wind, which usually blows such ash away from the city, rather than exceptional volcanic activity on Sakurajima, which is one of Japan's most active volcanoes. Local press are describing this as the 500th event this year, though with such frequent eruptions this is hard to evaluate since eruptions often merge or overlap and it is difficult to say where one ends and the next starts.

Ash column from Sakurajima over the city of Kagoshima on Kyushu Island on Monday 19 August 2013. AP/Reuters.

Japan has a complex tectonic environment with four plates underlying parts of the Islands; in addition to the Pacific in the east and the Othorsk in the North, there are the Philipine Plate to the south and the Eurasian Plate to the West. Kyushu Island lies at the northeast end of the Ryukyu Island Arc, which sits on top of the boundary between the Eurasian and Philippine Plates. The Philippine Plate is being subducted beneath the Eurasian Plate, in the Ryukyo Trench, to the Southeast of the Islands. As it is drawn into the interior of the Earth, the tectonic plate is partially melted by the heat of the Earth's interior, and liquid magma rises up through the overlying Eurasian Plate to form the volcanos of the Ryukyu Islands and Kyushu.

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