Eleven confirmed dead and twelve still missing following eruption on Mount Marapi, Sumatra.

Eleven people have been confirmed dead and another twelve are still missing following an eruption on Mount Marapi, a 2885 m high volcano in West Sumatra Province, Indonesia on Sunday 3 December 2023. The volcano erupted with little warning, producing a 3 km high column of ash as well as ash falls on villages more than 5 km from the summit of the volcano. Seventy five people, including a group of 18 students, were on the volcano at the time of the eruption. Forty nine people of the hikers were able to escape from the mountain promptly, leaving 26 unaccounted for. Over 160 rescue workers were deployed to the mountain, and were able to rescue three of the missing hikers alive, all of who were suffering from burns and one from a broken leg. They also recovered eleven bodies, but were eventually forced to break of the search before accounting for all of the missing persons, due to the ongoing eruption.

A survivor of the 3 December 2023 Mount Marapi eruption being carried off the mountain by rescue workers. Antara Foto/Reuters.

The Indo-Australian Plate, which underlies the Indian Ocean to the west of Sumatra, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Sumatra and neighbouring Java, along the Sunda Trench, passing under Sumatra, where friction between the two plates can cause Earthquakes. As the Indo-Australian Plate sinks further into the Earth it is partially melted and some of the melted material rises through the overlying Sunda Plate as magma, fuelling the volcanoes of Sumatra.

The Subduction zone beneath Sumatra. NASA/Earth Observatory.

The two plates are not directly impacting one-another, as occurs in the subduction zones along the western margins of North and South America, but at a steeply oblique angle. This means that as well as the subduction of the Indo-Australian plate beneath the Sunda, the two plates are also moving past one-another. This causes rifting within the plates, as parts of each plate become stuck to the other, and are dragged along in the opposing plate's direction. The most obvious example of this is the Sumatran Fault, which runs the length of Sumatra, with the two halves of the island moving independently of one-another. This fault is the cause of most of the quakes on the island, and most of the island's volcanoes lie on it.

The movement of the tectonic plates around Sumatra. NASA/Earth Observatory.

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Eruption on Mount Sinabung produces 5 km high ash column and leads to ash falls 20 km from its summit.

Mount Sinabung, a 2460 m stratovolcano (cone shaped volcano made up of layers of ash and lava) in North Sumatra, Indonesia, erupted on Monday 10 August 2020, producing an ash column that rose 5 km into the atmosphere, and producing ash falls up to 5 km deep in (previously evacuated) villages up to 20 km from the summit of the volcano. Nobody was injured in this incident, largely due o an existing evacuation order that prevents people from approaching the volcano, with nobidy allowed to approach within 5 km of the volcano, and villages evacuated over a wider zone. 

An ash column over Mount Sinabung, North Sumatra, on Monday 10 August 2020. Sugeng Nuryono/AP

Sinabung is considered to be a potentially very dangerous volcano, as a large number of people live in its immediate vicinity. The last major eruption prior to the twenty-first century happened in about 1600, with small eruptions occurring in 1889 and 1912. However the volcano returned to life in late August 2010, erupting throughout September and causing about 12 000 people to flee their homes, and has been erupting intermittently ever since.

 

The location of Mount Sinabung. Google Maps.

 

The Indo-Australian Plate, which underlies the Indian Ocean to the west of Sumatra, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Sumatra and neighbouring Java, along the Sunda Trench, passing under Sumatra, where friction between the two plates can cause Earthquakes. As the Indo-Australian Plate sinks further into the Earth it is partially melted and some of the melted material rises through the overlying Sunda Plate as magma, fuelling the volcanoes of Sumatra.

 

The Subduction zone beneath Sumatra. NASA/Earth Observatory.

 

The two plates are not directly impacting one-another, as occurs in the subduction zones along the western margins of North and South America, but at a steeply oblique angle. This means that as well as the subduction of the Indo-Australian plate beneath the Sunda, the two plates are also moving past one-another. This causes rifting within the plates, as parts of each plate become stuck to the other, and are dragged along in the opposing plate's direction. The most obvious example of this is the Sumatran Fault, which runs the length of Sumatra, with the two halves of the island moving independently of one-another. This fault is the cause of most of the quakes on the island, and most of the island's volcanoes lie on it.

 

The movement of the tectonic plates around Sumatra. NASA/Earth Observatory.

 

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