Tolmachev Dol (Tomachev Plateau) is broad volcanic highland NE of Opala volcano that includes numerous late-Pleistocene and Holocene cinder cones and associated lava flows. The cones and lava fields cover a broad area on both sides of Lake Tolmachev, which lies in large depression halfway between Opala and Gorely volcanoes. The Pleistocene Tolmachev stratovolcano lies on the SE side of the lake. A major explosive eruption took place about 4,600 years ago from Chasha crater in the northern part of the plateau, during which about 1 km3 of rhyolitic tephra was ejected. The latest dated eruption occurred from a cinder cone in the NW part of the plateau about 1,600-1,700 years ago.