Saturday, 8 October 2016

Eruption on Mount Aso, Kyūshū Island, Japan.

The Japan Meteorological Agency has reported a major eruption on Aso (or Asosan) a volcanic caldera on central Kyūshū Island, Japan. The volcano erupted early on the morning of Saturday 6 October 2016, producing an ash column over 11 km in height, which drifted to the northeast, producing ashfalls as far as 16 km away from the caldera. This is the first eruption on Mount Aso since September last year.

Smoke emerging from Aso Caldera following an eruption on 8 October 2016. Kyodo News/Reuters.

The Aso Caldera is the largest in Japan, and one of the largest in the world, being approximately 25 km in diameter. The caldera is thought to be the result of a series of four massive eruptions, the first of which took place around 300 000 years ago, and the last around 90 000 years ago. The caldera contains five smaller summits in a complex at its center, the highest of which Mount Taka, rises 1592 m above sea-level. These are also a series of hot springs within the caldera, which is a popular tourist resort and part of the Japanese Geoparks Network. Despite the site's dramatic history modern eruptions tend to be quite small, and there are no records of any historical fatalities connected with the volcano.

 Cars covered by ash following the 8 October 2016 Aso eruption. 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. Kyūshū 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. This is not a smooth process, with the two plates continuously sticking together then breaking apart as the pressure builds up, leading to frequent Earthquakes in the region.

 The movement of the Pacific and Philippine Plates beneath eastern Honshu. Laurent Jolivet/Institut des Sciences de la Terre d'Orléans/Sciences de la Terre et de l'Environnement.

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