Rishirizan is a highly dissected andesitic stratovolcano that forms a 20-km-wide island west of the northern tip of Hokkaido. Extensive erosion has produced an extremely rugged topography, with a dramatic sharp-topped, summit flanked by steep-sided radial ridges. A stratovolcano and flank lava domes were constructed beginning less than 200,000 years ago. After about 37,000 years ago only flank vents were active. Late-stage eruptions took place from scoria cones and maars along a 15-km-long NW-SE trend that extends to the SE coast. Flank eruptions were dominantly basaltic, but also included andesitic and rhyolitic activity. Extensive lava flows during the late Pleistocene form much of the northern and western coasts and extend offshore. The latest eruptions took place a few thousand years ago.