Shikotsu is a caldera located near the southwestern end of the Kurile arc. About 30,000 years ago the volcano erupted 125 cubic km of compositionally zone (rhyolite to andesite) ashfall and pyroclastic flows. Most of the caldera is now filled with a lake. In the Holocene, Shikotsu has had three pre-historic and 34 historic eruptions. Nearly all of these eruptions have been from the Tarumai vent. The eruptions in 6950 BC and 800 BC were very large (VEI=5). There were two more very large historic eruptions in 1667 and 1739. Both of these historic eruptions produced pyroclastic flows. Most of the remaining historic eruptions have been small to moderate (VEI=1-2) in size. The most recent eruption, in 1982, was phreatic. This photo is across the Lake Shikotsu to the Fuppushi (dormant?, right) and Tarumai (active, left) stratovolcanoes. Photograph courtesy of and copyrighted by Mike Lyvers.
Shikotsu caldera and distribution of ash from 1739 (trending northeast) and 1667 (trending east) eruptions. Isopachs are in centimeters. Pumice fall deposits from the 1739 and 1667 eruptions are also shown. Map from Newhall and Dzurisin (1988).
Source of Information:
Newhall, C.G., and Dzurisin, D., 1988, Historical unrest at large calderas of the world: U.S. Geological Survey Bulletin 1855, 1108 p.
Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p.