Copahue (]) is a stratovolcano in the Andes on the border of Bío Bío Region, Chile and Neuquén Province, Argentina. There are nine volcanic craters along a line, the easternmost of which is historically the most active, and contains a 300 m (1000 ft) wide crater lake with a pH ranging between 0.18 and 0.30. Eruptions from this crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments. Although the lake emptied during the 2000 eruption, it later returned to its previous levels. Copahue means sulphur waters in Mapuche.