The Quaternary Singkut caldera is about 7 x 4 km with the S half of the rim topographically distinct. Post-caldera cones have filled much of the crater and the N rim, including Sibayak, Pintau, and Pratektekan. The 900-m-wide Sibayak crater is partially filled on the north by Pintau. A lava flow traveled through a gap in the western crater wall from the summit lava dome of Sibayak; the active geothermal field SE of the summit has abundant solfataras and fumaroles. Area residents record legends of eruptions. Neumann van Padang (1983) cited a report by Hoekstra of ash clouds emitted from the volcano in 1881. The town of Berastagi is within the caldera immediately SE of the younger cones.