Eruption on Mount Poás, central Costa Rica.

Mount Poás, a 2708 m stratovolcano (volcano with a classic cone-shape, which is made from the build up of layers of ash and lava) in central Costa Rica, erupted at about 5.40 am local time on Monday 30 September 2019, producing a column of ash and debris about 2 km high. The volcano had been quiet since February this year, and Poás Volcano National Park, a popular tourist attraction centred on the volcano, had been re-opened to the public in August, but on Sunday 22 September underwent a significant degassing episode, which appears to have marked the onset of a new volcanic phase, and which prompted the closure of the national park until further notice.

Eruption on Mount Poás on 30 September 2019. Comisión Nacional de Emergencias.

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.

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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Access to Mount Poás, Costa Rica, closed off following eruptions.

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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Phreatic eruption on Mount Poás.

The  Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional in Costa Rica reported a large phreatic eruption on Mount Poás, a volcano in the central part of the country, slightly after noon local time (slightly after 6.00 pm GMT) on Tuesday 25 February 2014. Phreatic eruptions occur when magma or other very hot material is produced by a volcano in direct contact with water, in this case beneath the surface of a crater lake, causing a large volume of the water to convert immediately to vapor, resulting in an explosion. On this occasion the eruption resulted in a blast which through material over 300 m into the air.

Phreatic eruption on Mount Poás on Tuesday 25 February 2014. Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional.

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.

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, fuelling the volcanoes of Central America.
See also Magnitude 6.0 Earthquake off the coast of northwest Costa Rica, Eruption on Mount Turrialba, Costa Rica, Eruption on Mount Poás, Costa Rica and Substantial Earthquake in Costa Rica.  

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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.

See also Substantial Earthquake in Costa Rica, Eruption on Rincón de la Vieja, Costa Rica, Hydrothermaly heated active seeps from the continental shelf margin, south of Costa Rica, Eruptions on Mount Turrialba and Volcanoes on Sciency Thoughts YouTube.

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