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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