Thursday, 20 September 2012

Eruption on Gamalama.

Gamalama is a largely submerged volcano to the west of Halmahera in Indonesia. It's tip forms the island of Ternate, home to 145 000 people, and formerly the home of the Sultanate of Ternate, which at its height ruled much of what is now eastern Indonesia and the southern part of the Philippines. The island covers 76 km², and the summit of the volcano rises 1715 m above the sea. Gamalama is an active volcano, typically erupting several times a decade, it's last eruptive episode, in December 2011-January 2012, killed at least three people and produced a number of destructive lahars (mudflows triggered by volcanic activity) which destroyed several villages.

A lahar sweeps through a village on Ternate. Pusat Penanggulangan Krisis Kesehatan.

For the first two weeks of September 2012 the summit of Gamalama was obscured by cloud and fog, although what appeared to be a small plume could frequently be seen over the volcano. Then on the evening of 15 September an explosive eruption lead to ashfalls in the capitol (also Ternate). The next day rumbling was audible from the volcano, before a second eruption at about 2.15 pm, which produces a plume roughly 1 km high which drifted to the south and southeast, producing further ashfalls. The alert status on the island remains high, with people recommended to avoid going within 2.5 km of the summit.

Aerial photograph of a plume over Gamalama taken on Sunday 16 September 2012. Jakarta Post.

Halamahera and Ternate lie on the eastern edge of the Molluca Sea, which is underlain by the Molluca Sea Plate, a remnant plate being subducted from both sides. In the west the Molluca Sea Plate is being subducted beneath the Sangihe Plate, which underlies the northern part of Sulawesi, to the east it is being subducted beneath the Philippine Sea Plate, which underlies Halamahera and its surrounding islands. As it is subducted the Molluca Sea Plate is heated by friction with the overlying Sangihe and Philippine Sea Plates, and by the heat of the Earth's interior. Some of the melted material rises through the overlying plates, fueling the volcanoes of Halamahera and Sulawesi.

Map showing the location of Ternate at the eastern edge of the Molucca Sea. Google Maps.
Diagram showing the Molucca Sea Plate beneath the Molucca Sea. Hall & Wilson (2000).

See also Earthquake hits SulawesiEruptions from the Tompaluan Crater, Lokon-Empung, SulawesiVolcanic activity in the Halmahera Islands and Volcanoes on Sciency Thoughts YouTube.

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