Tourist access to Mount Poás, a stratovolcano (cone-shaped volcano made up of layers of ash and lava) in central Costa Rica, has been closed off following a series of eruptions over the weekend of 15-16 April 2017. The two largest eruptions occurred between 8.40 and 9.00 am on Sunday 16 April, producing an ash column about a kilometre high and throwing rocks over a kilometre from the summit, some falling onto viewpoints from which tourists can observe the volcano.
Rock embedded into the concrete of a viewing point near Mount Poás following the 18 April 2017 eruption. Redy Conejo/Poás Volcano National Park.
Mount Poás 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.
Ash column over Mount Poás following an eruption on 14 April 2016. Observatorio Vulcanológico y Sismológico de Costa Rica.
Mount Poás 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 fuelled 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.
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