The volcano has a warm and highly acidic crater lake approximately 160 m (525 ft) wide. In 1982, the lake had a temperature of 21 °C and a pH of 1, and temperatures of 114-118°C were measured in 1991. At the north flank of the volcano unglaciated and relatively uneroded lava flows are found. The last eruption is not known, but probably occurred during the Holocene.[1]