The historically active Gunung Tandikat lies across the Bukittinggi plain from Marapi volcano in central Sumatra. The summit of Tandikat's twin volcano, Singgalang, is seen here from Bukittinggi city across the steep-walled Ngarai canyon north of the volcano. Gunung Tandikat contains a central cone and a small crater lake constructed within a larger 1.2-km-wide crater. Three small explosive eruptions, the last in 1924, have occurred in historical time. Photo by Tom Casadevall, 1987 (U.S. Geological Survey).