Monday 25 July 2022

Evacuations ordered after eruptions on Mount Sakurajima, on Kyūshū Island, Japan.

Authorities in Kagoshima Prefecture have issued an evacuation order to people living within 3 km of Mount Sakurajima, a 1117 m high stratovolcano (cone-shaped volcano made up of layers of ash and lava) on Kyūshū Island, Japan, following a series of large eruptions. The Japan Meteorological Agency (which is also responsible for monitoring volcanic and seismic threats in Japan) began detecting ground deformation around the volcano on 18 June 2022, but there were no major seismic events (Earthquakes) prior to the onset of eruptions. The volcano erupted four times on Saturday 23 and Sunday 24 July, producing columns of ash and gas up to 1.2 km high, and throwing rocks as far as 3 km from the Minimidake crater, mostly towards the south and southeast. A smaller eruption occurred at about 6.00 am local time on Monday 25 July, producing another ash column, this time about 2.2 km high, and the volcano shows no sign of ceasing activity.

Eruption on Sakurajima Volcano at 8.05 pm local time on Sunday 24 July 2022, from an unmanned, fixed point camera. Kyodo News.

Japan has a complex tectonic situation, with parts of the country on four different tectonic plates. 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. 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 volcanoes of the Ryukyu Islands and Kyūshū.

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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