Poás Volcano
Volcán Poás
Interesting facts
- When Laguna Caliente dried out completely in 1989, it left pools of bubbling yellow sulphur and gas-venting sulphur chimneys on the crater floor.
- Between 1984 and 1990 the crater lake's temperature swung between about 38 and 96 degrees Celsius as the volcano's activity changed.
- Poás often throws out geyser-like jets of crater-lake water during its eruptions.
- Acid gases from the crater produce acid rain and fog, and the resulting belt of dead vegetation downwind is visible from space.
- Scientists compare the toxic sulphur-and-iron chemistry of Laguna Caliente to conditions thought to have existed on the early Earth and on Mars.
- Poás was one of nine volcanoes monitored by the Deep Earth Carbon Degassing Project, which measured carbon dioxide and sulphur dioxide emissions worldwide.
- On 14 April 2017 two explosions eighteen minutes apart sent an ash and steam column more than three kilometres into the sky.
- The crater lake is about 30 metres deep, filling a pit within the much larger main crater of the volcano.
Why it is worth it
Poás is a stratovolcano in Costa Rica's Cordillera Central, rising to 2,697 metres, and it offers one of the rare chances to stand at the rim of a living crater and look straight into it. The main crater is a vast bowl, around a kilometre and a half across, and at its bottom, at about 2,300 metres, lies Laguna Caliente: a lake roughly 300 metres wide that ranks among the most acidic bodies of water on Earth, with a pH that has at times dropped to almost zero. A layer of molten sulphur has been found on its floor. Almost nothing lives in it apart from acid-loving bacteria.
The volcano has erupted dozens of times since records began in 1828, and its moods change the scene from year to year. A long eruptive phase began in 1953 and lasted until 1956; another strong eruption followed in April 2017. Between outbursts the lake can shrink, boil or vanish altogether, so no two visitors see quite the same crater. In 2022 Poás was named an IUGS Geological Heritage Site, a list of places of outstanding value for geoscience.
The contrast with the rest of the mountain is part of its beauty. Next to the active crater lies a second, long-extinct one, holding Laguna Botos, a cold, clear lake ringed by cloud forest; its crater has been quiet for some nine and a half thousand years. The whole summit area has been protected since 1971 as Poás Volcano National Park, so within a short walk you pass from a raw, steaming moonscape to dripping green montane forest.
Getting there
The volcano lies about 20 km from Alajuela, and Juan Santamaría International Airport (SJO), Costa Rica's main gateway, is about 23 km away, so it is one of the most easily reached volcanoes in Central America; most visitors drive up from Alajuela or San José.
On these lists
From the encyclopaedia
The Poás Volcano, is an active 2,697-metre (8,848 ft) stratovolcano in central Costa Rica located within Poas Volcano National Park. It has erupted 40 times since 1828, with a strong eruption in April 2017—causing the evacuation of visitors and residents. The volcano and surrounding park were closed for nearly 17 months, with a 2.5 kilometer safety perimeter established around the erupting crater. On September 1, 2018, the park was reopened to the public only with limited access to the crater observation area. They have started to require a reservation on the National Park Website before visitation. Adjacent trails to Lake Botos, and the museum at the visitor center remained closed. The volcano erupted briefly twice in September 2019.
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