Monday, 31 December 2012

Eruption on Mount Copahue.

Mount Copahue is a composite volcano in central Chile, close to the border with Argentina. It comprises a chain of nine craters along a 2 km east-west line, with the most recent, still active, crater at the eastern end. This chain sits within the 400 000 to 600 000 year old, 6.5 by 8.5 km Trapa-Trapa Caldera, which in turn sits inside the older (more than 2.5 million years old), 15 by 20 km Caviahue Caldera. The active crater contains an acid lake, the Del Agrio, which is fed by acidic hot springs at its east end. The lake is noted for frequent fumerole (gas) emissions, and occasional explosive events.

The Del Agrio volcanic lake in the Copahue Crater. Mountain Forecast.com

On 22 December 2012 the Servicio Nacional de Geología y Minería recorded a sharp increase in seismic activity (tremors) around Copahue, followed by the production of an ash column rising 1.5 km above the summit and drifting to the southeast. On 23 December a number of explosions were observed, combined with incandescence (glowing) from the crater. This continued through 24 December, with a number of incandescent blocks being thrown out of the crater, then seemed to tail of on the 25th.

Ash coloulmn issuing from Copahue, seen from the Argentinian side of Lake Caviahue. AFP.

The volcanoes of Chile, and South America in general, are fuelled by the subduction of the Nazca Plate beneath the South American Plate, off the west coast of the continent. The subducting plate passes under South America as it sinks, and is partially melted by the friction and the heat of the Earth's interior. Some of the melted material then rises through the overlying South American Plate, fuelling the volcanoes dotted throughout the Andes.

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