Sunday 15 September 2013

Thousands evacuated following eruption on Mount Sinabung.

Over three thousand villagers have been evacuated following an eruption on Mount Sinabung, a volcano in the Karo Regency, North Sumatra, early on Sunday 15 September 2013. Villagers within 3 km of the volcano have been evacuated, after the volcano began to rain ash and small rocks upon their homes. Sinabung is potentially a very dangerous volcano, as a large number of people live in its immediate vicinity. The last major eruption prior to the twenty-first century happened in about 1600, with small eruptions occurring in 1889 and 1912. However the volcano returned to life in late August 2010,   erupting throughout September and causing about 12 000 people to flee their homes.

Smoke and ash emitting from Mount Sinabung on Sunday 15 September 2013. Kharisma Tarigan/AFP.

The Indo-Australian Plate, which underlies the Indian Ocean to the west of Sumatra, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Sumatra and neighboring Java, along the Sunda Trench, passing under Sumatra, where friction between the two plates can cause Earthquakes. As the Indo-Australian Plate sinks further into the Earth it is partially melted and some of the melted material rises through the overlying Sunda Plate as magma, fueling the volcanoes of Sumatra.

This does not happen at a 90° angle, as occurs in the subduction zones along the western margins of North and South America, but at a steeply oblique angle. This means that as well as the subduction of the Indo-Australian plate beneath the Sunda, the two plates are also moving past one-another. This causes rifting within the plates, as parts of each plate become stuck to the other, and are dragged along in the opposing plate's direction. The most obvious example of this is the Sumatran Fault, which runs the length of Sumatra, with the two halves of the island moving independently of one-another. This fault is the cause of most of the quakes on the island, and most of the island's volcanoes lie on it.

The location of Mount Sinabung. Google Maps.

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