Mount Karangetang (sometimes known as Api Siau) is a stratovolcano (a cone shaped volcano formed from successive layers of ash and lava) located on Siau Island, roughly 130 km to the north of Sulawesi, or a third of the way to the Philippine Island of Mindanao. It is one of the most active volcanoes in Indonesia and frequently erupts several times a year.
The location of Mount Karangetang.
The volcano started to spit gas and lava 600 m into the air towards the end of last week, then this morning (8 August 2011) a large explosion was followed by an ashfall on the volcano's slopes causing people to flee in panic. Early reports suggested that one person had been injured by the ashfall, and several more were missing, although local search and rescue authorities have now found the missing people and confirm the injured man only fell while fleeing, receiving cuts and bruises.
Local people were right to be concerned about the eruption, Mount Karangetang has a vicious reputation, having killed three people as recently as June 1997, when a pyroclastic flow entered a village. Another pyroclastic flow killed six people in May 1992. Siau Island is only 10 km × 5 km at its widest and is dominated by the Mount Karangetang, yet it is home to 22 000 people, 600 of whom live on the upper slopes of the volcano.
Siau Island is part of the Sangihe Islands, a group of volcanic islands running north from the northernmost point on Sulawesi to the southernmost point on Mindanao. Conventional geology places this in the eastern Sunda Plate, but geologist Colin Macpherson of the Department of Earth Sciences, University of Durham, has developed a new model of geology in the region. Under Macpherson's model the Sanghi Islands lie on the western margin of a northward extension of the Molucca Plate, which is being subducted beneath the Sangihe microplate to the west. To the east of this the Molucca Plate extension is being subducted beneath the Halmahera Plate. This is not yet universally accepted.
Macpherson's Model of the Sangihe Islands.
See also Magnitude 6.8 earthquake hits Bam Island, Papua New Guinea, Sumatra shaken by a series of earthquakes and Volcanoes on Sciency Thoughts YouTube.