Authorities in Indonesia have been forced to close several airports in East Java and Bali following a series of eruptions on Mount Raung, an active volcano in East Java. 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.
Ash issuing from the summit of Mount Raung on 10 July 2015. AP.
Raung is a 3332 m stratovolcano (cone shaped volcano made of layers of ash and lava in East Java. It is a highly active volcano, typically erupting two or three times per decade. The latest eruptive episode began on 24 July 2014, and as well as causing disruption to air travelers, has resulted in the production of a lava lake in the volcano's caldera; this is thought unlikely to overtop the caldera (which is roughly 2 km wide and 500 m deep) but a 3 km exclusion zone around the volcano has been put in place as a precaution.
The approximate location of Mount Raung. Google Maps.
The Indo-Australian Plate, which underlies the Indian Ocean to the south of Java, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Java and neighbouring Sumatra, along the Sunda Trench, passing under Java, 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 Sumatra.
Subduction along the Sunda Trench. Earth Observatory of Singapore.
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