The southern half of Onekotan Island in the northern Kuril Islands contains the 7.5-km-wide Tao-Rusyr caldera, which is mostly filled by Kal'tsevoe lake. The basaltic-to-andesitic caldera formed about 7,500 years ago, in which the large post-caldera Krenitsyn Peak grew, building a 4-km-wide island in the NW part of the lake that rises above the caldera rim. A 350-m-wide, 100-m-deep crater truncates the peak, and a large crater is located on the upper NE side. An eruption in 1952 formed a small lava dome in an explosion crater along the eastern shore of the island.