Nemrut Dagi is the westernmost of a group of volcanoes near Lake Van in eastern Anatolia and the only one that has erupted in historical time. It contains a 9 x 5 km caldera partially filled on its western side by a caldera lake. Post-caldera volcanism, of basaltic to rhyolitic composition, initially occurred along the caldera rim and floor. Pyroclastic flows and the emission of glassy obsidian lava flows accompanied construction of lava domes within the caldera; later activity formed a series of cinder cones and lava domes erupted along N-S-trending fissures on the northern flank. The most recent activity has been concentrated along a NNW-trending fissure cutting the eastern caldera floor and extending beyond the north caldera rim; nearly two dozen cinder cones and lava domes were constructed on the caldera floor. Ash layers in Lake Van document numerous Holocene eruptions, and an eruption in 1441 CE from a N-flank fissure involved compositionally bimodal lava flows.