Thursday 3 May 2012

Eruptions on Batu Tara.

Batu Tara is a small island volcano rising 748 m above the Flores Sea in Indonesia, about 50 km north of Lembata. It is the tip of a stratovolcano (cone-shaped volcano made up of layers of ash and lava) which rises from the seafloor 3000 m below. On 25-26 April 2012 the Darwin Volcanic Ash Advisory Centre reported an ash cloud rising 2.4 km above the island, which then drifted 37 km to the west. On 30 April-01 May a second ash cloud was observed, which followed roughly the same pattern as the first.

An eruption on Batu Tara in 2007. Global Volcanism Program.

Such eruptions have been frequent on Batu Tara since the onset of its current volcanic cycle in 2006; there were at least 15 such events in 2011, though the exact number is hard to tell since activity on the island is generally detected by satellite photography, making eruptions close together hard to differentiate. The eruptions are frequently accompanied by the ejection of incandescent ash and lava bombs, as well as flows of lava, but since the island is remote and uninhabited these are seldom recorded.

An eruption on Batu Tara seen from close up. Geonauten.

The nature and frequency of eruptions on Batu Tare, combined with its position directly between Jakarta and Sidney, means that it frequently causes problems for aircraft, which need to be diverted around any ash clouds. This can add significantly to flight times, and therefore costs.

Map showing the regular flight path between Jakarta and Sidney (Blue) and alternative routes that have to be taken due to eruptions on Batu Tara (Red and Black), dependent on wind direction. Global Volcanism Program.

Prior to the start of the current eruptive cycle Batu Tara had been quiet since its previous, and only other recorded, eruptive cycle, which lasted from 1847-52.

Batu Tara is located to the north of the Flores Thrust, where the Timor Microplate is being subducted beneath the Banda Sea Plate (part of the collisional area between the Australian and Eurasian Plates). As this happens the Timor Plate is forced down into the Earth's interior, where it is partially melted by the heat. Melted material then rises through the overlying Banda Sea Plate, fueling the volcanoes located upon it.

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