Saturday, 25 February 2012

Eruptions on Mount Turrialba

On 11 January 2012 people living close to Mount Turrialba in central Costa Rica reported hearing rumbling from the mountain, according to the Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional. The next day there was a small eruption from a new vent on the southeast flank of the west crater, with an ash cloud rising 500 m into the atmosphere above the volcano, and the Turrialba Volcano National Park, which surrounds the volcano was closed as a precaution, and surrounding communities were out on a state of high alert. The ash cloud eventually reached a height of 4 km. Residents in the area reported seeing a dark plume from the fissure (probably a mixture of gas, steam and ash) accompanied by a white plume from the central crater (probably steam), and ash-fall was recorded in the town of Tres Rios, 27 km to the southwest of the volcano.

Archive photo of Mount Turrialba. From Monumental FM (Costa Rican radio station).

On 18 January scientists from Observatorio Vulcanológico y Sismológico recorded gas emissions, reddish flames and tephra (rocks and/or ash) being ejected from the new vent, an ash cloud over the volcano reached 6.1 km, and ash-fall was recorded in La Central, 4 km to the southwest. The scientists again visited the volcano on the 2nd and third of February, and reported incandescence (glowing) and temperatures of 600-700°C from the vent, and two other vents on the crater rim, that had opened in 2010 and 2011 respectively.

Turrialba is a stratovolcano located at the end of a volcanic ridge. It has a complex of three craters at its summit, of which most recent activity has been at the westernmost, the central crater having been inactive since a series of eruptive explosions in the 1860s.

Aerial photo of the summit of Mount Turrialba. Federico Chavarria Kopper (1999)

The volcanoes of Costa Rica, and Central America in general, are fed by the subduction of the Cocos Plate to the southeast beneath the Caribbean Plate, on which Central America sits. The Cocos Plate is subducted in the Middle American Trench, which runs offshore along the coast of Central America. As it sinks into the Earth it is is heated by the heat of the planet's interior and partially melts. Some of the melted material then rises up through the overlying Caribbean Plate as magma, forming the volcanoes of Central America.

In this sense Central America can be seen as an island arc, albeit one that has joined up completely. 50 million years ago the isthmus did not exist at all, and it only completed the join between North and South America about 3 million years ago, allowing the fauna's of North and South America to mix for the first time, and causing a cooling of the global climate as the warm current between the tropical Pacific and the tropical Atlantic was halted.

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