Copahue, active volcano, 9,688 ft (2,953 m) high, on the central Argentina-Chile border. A stratovolcano (see volcano) consisting of an elongated composite cone with nine craters extending along a 1.2-mi (2-km) line, it is within the Trapa-Trapa caldera, formed c. 500,000 years ago. Copahue's eastern summit contains an acidic crater lake that is c. 1,000 ft (300 m) wide. Eruptions at the volcano have been recorded since the mid-18th cent.; its most recent eruption occured in Dec., 2012.