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Global Volcanism Program | Image GVP-09197

Escaping fumarolic gases pour from the sulfur-lined wall of a lava dome at the bottom of the active crater of Poás.  The water filling the turquoise-colored crater lake is among the most acidic natural waters on Earth (pH = 0).  The hot (roughly 50 degrees Centigrade) lake has been the source of frequent phreatic eruptions that produce geyser-like plumes of steam, ash, and mud.  Pyroclastic sulfur has also been ejected. Photo by Guillermo Alvarado (Instituto Costarricense de Electricidad).

Escaping fumarolic gases pour from the sulfur-lined wall of a lava dome at the bottom of the active crater of Poás. The water filling the turquoise-colored crater lake is among the most acidic natural waters on Earth (pH = 0). The hot (roughly 50 degrees Centigrade) lake has been the source of frequent phreatic eruptions that produce geyser-like plumes of steam, ash, and mud. Pyroclastic sulfur has also been ejected.

Photo by Guillermo Alvarado (Instituto Costarricense de Electricidad).


Poás