Friday 20 May 2016

Eruptions on Mount Turrialba

The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional reported a series of eruptions on Mount Turrialba, a stratovolcano (cone shaped volcano made up of layers of ash and lava) in the central part of the country, on Thursday 19 May 2016. The initial eruption occurred at about 2.05 pm local time, and produced a column of ash about a kilometer im height. This was followed by a second slightly after 3.45 and a third slightly before 4.10 pm. Ash from the volcano was blown to the southwest. 

Ash column over Mount Turrialba on 19 May 2016. Comisión Nacional de Emergencias.

The volcano has been undergoing continual of small eruptions since September 2014, although the last week has been particularly active, with a number of reports of ash accumulating in fields and rivers nearby. Ash deposits falling in or near waterways are considered to be particularly hazardous due to the danger of lahars, ash-laden flash floods associated with volcanoes. These are also common in areas of high seasonal rainfall, where ash deposits from a volcano can build up during the dry season, creating dams on seasonal waterways, which temporarily halt the flow of water, then give way rapidly leading to dramatic flash floods. However May marks the beggining of the riany season across much of Costa Rica, and the increased rainfall appears to be washing much of the ash away before it can form hazardous dams.

Ashfall on pasture and woodland near Mount Turriabla. Comisión Nacional de Emergencias.

Turrialba forms part of the Cordillera Central, a range of volcanic mountains running through central Costa Rica and forming part of the Central American Arc. These volcanoes are fueled by the subduction of the Cocos Plate, which underlies part of the east Pacific Ocean, beneath the Caribbean Plate, on which Central America lies, along the Middle American Trench, which lies off the south coast of the country. As the Cocos Plate is subducted it is gradually melted by the heat and pressure of the Earth's interior, with some more volatile minerals rising through the overlying Caribbean Plate as volcanic magma.

Diagram showing the passage of the Cocos Plate beneath Costa Rica (not to scale). Carleton College.

See also... zone established around Mount Turriabla after a series of eruptions on Sunday 1 May 2016.                                                 The Costa Rican Comisión Nacional de Emergencias has... on Rincón de la Vieja, Costa Rica. The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional reported a small eruption on Rincón de la Vieja, an active volcano in the northwest of the country, at about 4.20 pm local time on Tuesday 15 March... eruption on Mount Turrialba. The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional reported a short explosive eruption which lasted about ten minutes, beginning slightly after 1.10 pm local time on Monday 7 December 2015...

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