Authorities in Indonesia have been forced to close airports in Lombok and Bali following a series of eruptions on Mount Rinjani, an active volcano on Lombok. There are no reports of any damage or casualties associated with the eruptions, however volcanic ash is extremely hazardous to aircraft in a number of ways. At its most obvious it is opaque, both visually and to radar. Then it is abrasive, ash particles physically scour aircraft, damaging components and frosting windows. However the ash is most dangerous when it is sucked into jet engines, here the high temperatures can melt the tiny silica particles, forming volcanic glass which then clogs engine. When this happens the only hope the aircraft has is to dive sharply, in the hope that cold air passing through the engine during the descent will cause the glass to shatter, allowing the engine to be restarted.
Volcanic ash emerging from Mount Rinjani. Le Chaudron de Vulcain/Pusat Vulkanologi dan Mitigasi Bencana Geologi.
Mount Rinjani has been inactive since 2010, but on Sunday 25 October 2015 the Pusat Vulkanologi dan Mitigasi Bencana Geologi (which monitors volcanoes and other geohazards in Indonesia) reported a small eruption that produced a plume rising 200 m above the summit of the volcano and ashfalls on the southwestern flank. This was followed by much larger eruptions on 26, 28 and 31 October, which the Darwin Volcanic Ash Advisory Centre recorded as producing plumes 3-4 km high and drifting 45-75 km to the southwest. All flights from Lombok are currently cancelled until at least Tuesday 3 November, access to the volcano, a popular tourist attraction, has been suspended and local authorities are making contingency plans for an evacuation of nearby communities if the situation grows worse.
The approximate location of Mount Rinjani. 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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