Friday 1 September 2017

Eruptions on Mount Ibu, Halmahera, Indonesia.

The Darwin Volcanic Ash Advisory Center has reported eruptions on Mount Ibu, a stratovolcano (cone-shaped volcano made up of layers of volcanic ash and lava) on the northwest coast of Halmahera Island, Indonesia, on Thursday 24 and Monday 28 August 2017. Both eruptions were identified from ash plumes that rose 1.5-1.8 km above the summit of the 1325 m volcano and drifted to the west.

The approximate location of Mount Ibu. Google Maps.

The Halmahera Islands arc a volcanic arc; formed where one tectonic plate is being subducted beneath another, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. However the Halmahera Islands are unusual in that they lie on a double subduction zone. The underlying plate, a northeaster extension of the Molucca Sea Plate, is being overridden form the Philippine Plate from the east and the Eurasian Plate from the west. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

 Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

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