The stratovolcano, which is the only large central volcano in its part of Iceland, has many pyroclastic cones on its flanks. Upper-flank craters produced intermediate to felsic materials, while lower-flank craters produced basaltic lava flows. Several holocene eruptions have originated from the summit crater and have produced felsic material. The latest eruption took place 200 AD ± 150 years, and erupted approximately 0.11 cubic kilometres (0.026 cu mi) of volcanic material. The eruption was explosive and originated from the summit crater, and may have produced lava flows.