Monday 23 April 2012

Eruption on Rincón de la Vieja, Costa Rica.

Rincón de la Vieja is a complex volcano in northwest Costa Rica. It takes the form of a ridge with a number of craters along a northwest-southeast axis, within an ancient volcanic caldera. Volcanic activity has been recorded on Rincón de la Vieja since 1765, during which time all significant eruptions have occurred from a lake filled crater known as 'The Active Crater' on the side of one of the higher summits, Von Seebach Peak.

Rincón de la Vieja. Blue River Resort & Hot Springs.

On 14 April 2012 villagers living to the north of the volcano reported seeing a phreatic eruption from the Active Crater (a phreatic eruption is an eruption in which lava emerges underwater, prompting an explosion of steam and rock fragments), according to the Observatorio Vulcanológico y Sismológico de Costa Rica. After this eruption volcanic material was found on the outer northern flank of the summit, and a plume of steam was seen over the crater for some time.

There were four similar eruptions in February this year, two on the 24th and one each on the 19th and 20th. A larger eruption occurred on 16 September 2012 this caused fish kills in streams and rivers up to 18 km away and ashfall deposits up to 15 cm thick within 2 km of the crater. Prior to this there had been intermittent Earthquake and fumarole (gas vent) activity around the crater since September 2006, but no actual eruptions.

Previous eruptive cycles have tended to follow a pattern of a long period of fumaroles and Earthquakes, followed by short bursts of phreatic eruptions, followed by more fumaroles and quakes, followed by a quiet period which may last several years, then the start of a new eruptive period. In the past some phreatic eruptions have been large enough to be heard over 25 km away, and have triggered lahars (floods of water and ash) that have swept down rivers and streams causing considerable damage.

The volcanoes of Costa Rica, and neighboring parts of Central America, are caused by the subduction of the Cocos Plate (which underlies the area of the Pacific immediately to the south of Central America) beneath the Caribbean Plate (upon which Central America sits). As the Cocos Plate passes under Central America it is partially melted by the heat of the Earth's interior and friction with the overlying plate. Some of the melted material then rises through the overlying Caribbean Plate as magma, fueling the volcanoes.

Diagrammatic representation of the Cocos Plate passing beneath the Central American Plate, showing how it fuels the volcanoes of Central America. VCS Mining.

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