Monday 13 June 2022

Eruptions on Mount Balusan, Luzon Island, the Philippines.

Mount Balusan, a 1565 m high stratovolcano (cone shaped volcano made up of layers of ash and lava) on southern Luzon Island, the Philippines, erupted slightly after 10.35 am local time on Sunday 5 June 2022, producing an ash column that rose slightly over 1 km above its summit and drifted to the west. Ashfall was reported in several nearby villages, and following the event, the Philippine Institute of Volcanology and Seismology recorded gas emissions from both the volcano's main crater and a vent on its northwest summit.

An ash column produced by Mount Balusan on 5 June 2022. Rissa Bonita/AFP/Getty Images.

The volcano erupted again slightly after 3.35 am on Sunday 12 June, this time producing an ash column only 500 m high, but again leading to ash falls in several local communities. The eruptions are believed to have been phreatic in nature, i.e. caused by hot magma encountering liquid water somewhere within the volcano, causing the water to vaporise instantly and explosively. The ashfalls have affected about 16 000 people, covering homes and crops and polluting water sources, with 418 people living in the communities closest to the volcano being evacuated as a precaution against further, more violent action.

Ash covering villages and plantations near Mount Balusan following an eruption on Sunday 12 June 2022. Sorsogon Provincial Information Office.

The geology of the Philippines is complex, with the majority of the islands located on the east of the Sunda Plate. To the east of this lies the Philippine Sea plate, which is being subducted beneath the Sunda Plate (a breakaway part of the Eurasian Plate); further east, in the Mariana Islands, the Pacific Plate is being subducted beneath the Philippine Sea Plate. This is not a smooth process, and the rocks of the tectonic plates frequently stick together before eventually being broken apart by the rising pressure, leading to Earthquakes in the process. Material from the subducting Philippine Plate is heated by the temperature of the Earth's interior, causing lighter minerals to melt and the resultant magma to rise through the overlying Sunda Plate, fuelling the volcanoes of the Philippines.

Subduction beneath the Philippines. Yves Descatoire/Singapore Earth Observatory.

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