Thursday, 23 April 2015

Chilean authorities begin evacuations after eruptions on Mount Calbuco.

Authorities in Chile have began to evacuate homes within 20 km of Mount Calbuco, a volcano in the Los Lagos Region in the south of the country, after the volcano began to erupt at about 6.00 pm local time (about 9.00 pm GMT) on Wednesday 22 April 2015. The initial eruption produced an ash column 10 km high, according to the Buenos Aires Volcanic Ash Advisory Center, and drifted to the northeast, leading to the closure of Bariloche Airport in Argentina (volcanic ash is a particular hazard to aircraft, as it is easily melted, coating the engines in glassy material). A second large eruption has reportedly occurred since this event.

Column of volcanic ash over Mount Calbuco. The red colour is caused by the sunset rather than  the volcano. EPA.

The area around Mount Calbuco is sparsely populated, though a few small communities are supported by the local tourist community; it is thought that about 4000 people will be affected by the evacuation. The Chilean government has sent troops to the area to aid with getting people to safety, as well as supplies of fresh water, as it is uncertain how ashfalls will impact the local water supplies. At the current time nobody is thought to be missing or injured, and the evacuations have largely been carried out due to concern about the possibility of lahars (extremely dangerous ash laden flood events which can be triggered either by hot volcanic water impacting frozen ice or snow or by rainfall on fresh ash deposits).

As cloud over Mount Calbuco seen from Bariloche in Argentina. Andrés Manzanares/Misiones Online.

The last volcanic activity on Mount Clabuco was recorded in 1996, when the volcano underwent a brief bout of fumarole activity (gas emissions). Prior to this a small and short-lived (about four hours) eruption was recorded in  August 1972. In February 1961 an eruption produced ash columns 12-15 km high, which also drifted towards Bariloche, and two lava flows were sighted. An eruption in January 1929 also produced lava flows, as well as a pyroclastic flow (avalanche of hot gas and ash). An eruption in April 1917 led to the formation of a lava dome in the crater of the volcano, as well as a series of lahars, and an eruptive episode in 1893-4 resulted in lava bombs falling up to 8 km from the summit.

The approximate location of Mount Calbuco. Google Maps.

The volcanoes of Chile and the Andean region of South America in general are fed by the subduction of the Nazca Plate beneath the South American Plate along the Peru-Chile Trench, which lies offshore parallel to the west coast of South America. As the Nazca Plate sinks it is melted by the heat of the Earth's interior, and the lighter portions of it rise up through the overlying South American Plate to form volcanoes at the surface. These are dotted throughout the Andes Mountains; a range of mountains that is formed by a mixture of volcanism and crumpling of the South American Plate where is is forced against the Nazca Plate.

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

See also...

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