Eruption on Mount Karangetang triggers pyroclasitc flow.

Authorities on the Indonesian island of Siau, in the Sangihe Archipelago to the north of Sulawesi, have extended an exclusion zone around Mount Karangetang, a 1784 m high stratovolcano (cone-shaped volcano) on the northern end of the island, following a pyroclastic flow (flow of heavy superheated gas containing large amounts of hot ash, rocks and debris) on Tuesday 5 February 2019, which blocked a road on the island. Mount Karangetang is one of Indonesia's most active volcanoes, typically erupting several times per year, with the current phase of eruptions having begun in November 2018, after several months of inactivity.

Pyroclastic flow blocking a road on Siau Island, Indonesia on 5 February 2019. 3 alacarta.

Siau Island is quite densely populated with around 22 000 permanent residents, and Mount Karangetang frequently causes problems for the islanders, having most recently caused fatalities in August 2010. The Sangihe Island Arc is a chain of volcanic islands running between the northern tip of Sulawesi and the southern tip of Mindanao. The chain marks the boundary between the Molucca Plate to the east and the Sangihe Plate to the west, with the Molucca Plate being subducted beneath the Sangihe Plate. As the Molucca Plate sinks into the Earth it is heated by the friction and the heat of the planet's interior, causing it to partially melt. Some of the melted material then rises through the overlying Sangihe Plate as magma, fuelling the volcanoes of the Sangihe Arc.

 The subduction zones beneath Sulawesi and the surrounding islands. Hall & Spakman (2015).

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Eruption on Mount Karangetang.

On 9 April 2013 the Darwin Volcanic Ash Advisory Centre in Australia reported a 4.3 km ash plume rising from Mount Karangetang, a volcano on Siau Island, one of the Sangihe Islands roughly 130 km north of Sulawesi and 260 km south of Mindanao in the Philippines. The plume drifted about 45 km to the northwest of the island. Karangetang, which is one of Indonesia's most active volcanoes, has been fairly quiet since December 2012, but began a new phase of volcanic activity on 4 April this year, with lava-flows on the flanks of the volcano and ash avalanches reaching as far as 2 km from the summit.

Lava flows on Karangetang on 4 April 2013. ROMY/European Pressphoto Agency/National Geographic.

Karangatang is a 1784 m high stratovolcano (cone-shaped volcano) on the northern end of Siua Island. It has erupted 41 times since written records began on the island in 1675. The island is quite densely populated with around 22 000 permanent residents, and the volcano frequently causes problems for the islanders, having most recently caused fatalities in August 2010.

The Sangihe Island Arc is a chain of volcanic islands running between the northern tip of Sulawesi and the southern tip of Mindanao. The chain marks the boundary between the Molucca Plate to the east and the Sangihe Plate to the west, with the Molucca Plate being subducted beneath the Sangihe Plate. As the Molucca Plate sinks into the Earth it is heated by the friction and the heat of the planet's interior, causing it to partially melt. Some of the melted material then rises through the overlying Sangihe Plate as magma, fueling the volcanoes of the Sangihe Arc.

See also Eruption on Mount Lokon, Sulawesi, Eruption on Gamalama, Volcanic activity in the Halmahera Islands, Fresh eruption on Mount Karangetang, Indonesia and Volcanoes on Sciency Thoughts YouTube.

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Fresh eruption on Mount Karangetang, Indonesia.

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.

Mount Karangetang.

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.