Friday 2 November 2012

Eruption on Mount Poás, Costa Rica.

Mount Poás is a volcano in central Costa Rica. It rises to 2708 m above sea level, but has gently sloping, forested flanks making the summit easily accessible. The summit consists of two craters, each with a lake. To the south is the cool, clear, Lake Botos, which has not seen an eruption for 7500 years, and to the north is Laguna Caliente, which is thermally heated, extremely acidic (about pH 0), and prone to frequent eruptions. The volcano and its surrounding area form the Poás Volcano National Park.

Areal photograph of Mount Poás. Laguna Caliente in the foreground. Villa Rita Country Cottages.

According to the Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional the volcano underwent a series of phreatic eruptions (ejections of magma underwater, superheating the water and causing an explosion) on 27-28 October 2012. The first occurred at 11.20 am on the 27th, the second at 5.57 pm, this time throwing sulphur rich sediment and rock onto the south and southwest shores of the lake. A third eruption was heard by local residents at about 1.00 am on the 28th, this time throwing ash and steam 500 m into the air and causing ash falls several hundred meters from the lake.

Costa Rica, along with the rest of Central America, likes on the southwest margin of the Caribbean Plate. To the south the Cocos Plate is being subducted along the Middle American Trench, passing under Central America as it sinks into the Earth. As this happens it is heated by the friction and the warmth of the planet's interior, causing it to partially melt. Some of the melted material then rises through the overlying Caribbean Plate, fueling the volcanoes of Central America.

Diagrammatic representation of the passage of the Cocos Plate beneath Central America, and how this fuels the volcanoes of Central America. The Science Education Resource Center at Carton Collage.

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