Tuesday 8 August 2017

Aviation warning issued after eruption on Bogoslof Island, Alaska.

The Alasaka Volcano Observatory issued a warning to aviation following an eruption on Bogoslof Island in the Aluetian Chain on the morning of Monday 7 August 2017. The eruption produced an ash column which rose to over 9750 m above the uninhabited island. This is the latest in a series of eruptions that began in December last year, many of which have produced ash columns that rose to heights of over 6000 m, the trigger point for aviation warnings in the Aleutian Islands.

The approximate location of Bogoslof Island. Google Maps. 

Bogoslof Island is uninhabited, and the islands around is are home to at most sparse Human populations, however it still presents a serious threat to air-traffic, as the Aleutian Islands lie in the path of a number of commercial aircraft routes, connecting the US to East Asia. 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. Obviously this is a procedure that pilots try to avoid having to perform.

Bogoslof Island forms the tip of a submarine volcano that rises from the Bering Sea floor, 1.8 km below the surface. The island only rises 150 m above the surface, but is 1.76 km in length and 500 m wide, forming part of the rim of the caldera (crater) of the volcano; all eruptive activity occurs beneath the surface to the northeast of the island itself. The nature of the island means that it is frequently reshaped by eruptions.

The volcanoes of the Alaskan Peninsula and Aleutian Islands are fed by magma rising from the Pacific Plate, which is being subducted beneath the North American Plate to the south along the Aleutian Trench. As the subducting plate sinks into the Earth it is subjected to enormous heat and pressure, causing more volatile minerals to melt. These then rise through the overlying North American plate as magma, fuelling the Alaskan volcanoes.

 How the subduction of the Pacific Plate beneath the North American Plate fuels the volcanoes of Alaska. Alaska Volcano Observatory.

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