The Sakurajima volcano on Kyūshū Island, Japan, underwent a major eruption slightly before 5.25 pm local time on Friday 8 November 2019, producing an ash column more than 5.5 km in height. This is the largest eruption on the volcano since July 2016, and more than the hundredth eruption this year (though with very active volcanoes it can be difficult to give an exact number of eruptions, as they tend to run into one-another). This high level of activity
is impressive, but prevents Sakurajima from becoming a major hazard,
partly because people tend not to build homes or other structures too
close to very active volcanoes, but also because the high levels of
activity tend to prevent pressure within the volcano from building up to
dangerous levels, which can lead to sudden very large and destructive
eruptions on less obviously active volcanoes.
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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