Saturday 20 October 2018

Warnings issued to aviation after eruptions on Mount Sabancaya, Peru.

The Buenos Aires Volcanic Ash Advisory Center issued a warning to aviation after an eruption was seen by a webcam on the Sabancaya volcano in southern Peru by web cameras around the volcano. The webcam images showed an ash plume of uncertain size plus ongoing gaseous emissions. Volcanic ash is extremely hazardous to aircraft in a number of ways. At its most obvious it is opaque, both visually and to radar. Then it is abrasive, ash particles physically scour aircraft, damaging components and frosting windows. However the ash is most dangerous when it is sucked into jet engines, here the high temperatures can melt the tiny silica particles, forming volcanic glass which then clogs engine. When this happens the only hope the aircraft has is to dive sharply, in the hope that cold air passing through the engine during the descent will cause the glass to shatter, allowing the engine to be restarted.

The approximate location of Mount Sabancaya. Google Maps.

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 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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