Poás volcano crater
|Elevation||2,708 m (8,885 ft) 78|
|Parent range||Cordillera Central|
|Last eruption||2009 to 2014|
There are two crater lakes near the summit. The northern lake is known as the Laguna Caliente ("hot lagoon") and is located at a height of 2,300 m in a crater approximately 1.7 km wide and 290–300 m deep. It is one of the world's most acidic lakes. The acidity varies after rain and changes in volcanic activity, sometimes reaching a pH of almost 0; consequently, it supports little or no aquatic life. The bottom of this lake is covered with a layer of liquid sulphur. Acid gases create acid rain and acid fog, causing damage to surrounding ecosystems and often irritation of eyes and lungs.
Poás was near the epicenter of a 6.1-magnitude earthquake in January 2009 that killed at least forty people and affected Fraijanes, Vara Blanca, Cinchona (the most affected area), the capital San José, and the Central Valley region of Costa Rica.
On February 25, 2014, a webcam from the Volcanological and Seismological Observatory of Costa Rica (OVSICORI) captured the moment a dark cloud exploded about 1,000 feet in the air from a massive crater of the Poás Volcano. This volcano remains active today.  
Poás is one of 9 volcanoes currently monitored by the Deep Earth Carbon Degassing (DECADE) initiative. DECADE is collecting data on the carbon dioxide and sulphur dioxide emission rates from subaerial volcanoes.
- O.Vaselli, F.Tassi, A.Minissale, G.Montegrossi, E.Duarte, E.Fernandez, E.Bergamaschi (2003), Fumarole migration and fluid geochemistry at Poás Volcano (Costa Rica), The Geological Society of London.
- "DECADE Installations at Turrialba and Poás". Deep Carbon Observatory. Retrieved 26 September 2016.
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