Friday 27 November 2020

Eruptions on Mount Sabancaya, southern Peru.

The Instituto Geofísico del Perú and Instituto Geológico Minero y Metalúrgico reported increases seismic activity beneath the Sabancaya volcano in southern Peru from Wednesday 11 November 2020 onwards. Over the next week several satellites detected thermal anomalies (hotspots) at the northeast end of the Volcano's crater, with a new lava dome being detected on the 16th, when the first of a series of explosive eruptions which lasted until the 22nd was observed. These eruptions produced ash columns that rose as high as 3.5 km above the volcano. The north and southeast flanks of the volcano are still reported to be inflated, and people are being warned not to come within 12 km of the summit.

An eruption on Mount Sambancaya on 20 November 2020. Instituto Geológico Minero y Metalúrgico.

Sabancaya is a 5967 m stratovolcano (cone shaped volcano) located on a saddle between the older, and larger Hualca Hualca and Ampato, neither of which has been active in historic times. The three volcanoes are located in the Andes of southern Peru. Eruptions were first recorded on Sabacnya by Europeans in 1595, and the volcano is likely to have been intermittently active prior to this. The volcano erupted a number of times in the eighteenth century, then remained quiet until 1986, since when it has undergone six bouts of explosive eruption.

The approximate location of Mount Sabancaya. Google Maps.

The volcanoes of the Peruvian Andes, and of South America in general, are fuelled by the subduction of the Nazca Plate beneath the South American Plate. The Nazca Plate underlies a large chunk of the eastern Pacific Ocean, and is being subducted along Peru-Chile Trench to the west of South America. As it sinks into the Earth, the Nazca Plate passes under South America, where it is heated by friction with the overlying South American Plate and by the heat of the planet's interior. This causes the Nazca Plate to partially melt, and some of this melted material then rises through the South American Plate as magma, fuelling the volcanoes of the Andes. The motion of one plate beneath another is not a smooth process, and the Nazca and South American Plates frequently stick together, then break apart as the pressure builds up, triggering frequent Earthquakes along the western coast of South America, and sometimes further inland.

The subduction of the Nazca Plate beneath the South American Plate, and how it causes Earthquakes and volcanoes. Pacific Earthquake Engineering Research Center.

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