Sunday 21 April 2019

Eruption on Mount Agung, Bali.

Mount Agung, a 3000 m stratovolcano (cone shaped volcano made up of layers of ash and lava) on the eastern part of Bali, erupted suddenly at about 3.20 am local time on Sunday 21 April 2019, producing an ash column about 2 km high, and reports of ash falls in the Karangasem, Bangli and Klunglung districts of the island. Despite this there has been no change to the volcano's alert status, with the ash column dissipating to quickly to be considered a hazard to aviation, and the 4 km exclusion zone currently in place around the volcano thought to be sufficient, although there have been concerns about foreign tourists entering the exclusion zone to attempt to climb the mountain.

(Top) Explosions on Mount Agung at 3.22 am local time on 21 April 2019. (Middle) Ash coloum over the volcano at 3.25 am. (Bottom) Ash column at 3.30 am. Organisasi Daerah Bali/Youtube.

Mount Agung became active in September 2017, for the first time in over fifty years. This activity has caused considerable concern on the island, as when it last erupted in  1963-4, when it produced ash columns reaching 10 km above its 3 km high summit and lava flows that reached 7 km from the volcano, as well as triggering a series of lahars and pyroclastic flows that killed over 200 people, making people on the island very cautious about any future eruptions.

 The approximate location of Mount Agung. Google Maps.

The Indo-Australian Plate, which underlies the Indian Ocean to the south of Java, Bali and Lombok, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies the islands and neighbouring Sumatra, along the Sunda Trench, passing under the islands, 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, fuelling the volcanoes of Java and neighbouring islands.

 Subduction along the Sunda Trench beneath Java, Bali and Lombok. Earth Observatory of Singapore.

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