Photo and caption by Yuray Morales

The Poás Volcano is an active stratovolcano in central Costa Rica. Poás has erupted 39 times since 1828. The lake shown is one of the world's most acidic lakes. Acidity changes after rain and volcanic activity. The bottom of the lake is covered with liquid sulphur. Acid gases create a phenomenon of acid rain and fog, causing damage to ecosystem. In January 2009 Poás erupted and killed 40 people. It also has had eruptive activity in 2009 involving minor phreatic eruptions and landslides. Poás eruptions often include geyser-like ejections of crater-lake water.

Location: Costa Rica