緑湖カルデラ

The Zavaritzki volcano on Simushir Island in the central Kuril Islands contains three nested calderas 10, 8, and 3 km in diameter. The steep-walled youngest caldera was formed during the Holocene and includes several young cones and lava domes near the margins of Biryuzovoe Lake. The current lake surface is at ~40 m elevation with the bottom ~30 m below sea level, but lacustrine sediments overlying pumice deposits indicate that the surface of an earlier caldera lake lay at 200 m above sea level. A small 500-m-diameter scoria cone, sketched by Gorshkov (1958, CAVW) that reportedly grew between 1916 and 1931, formed a peninsula extending into the lake from the NE caldera wall. Explosive eruptions in 1957 removed the cone and filled much of the NW part of the lake, including emplacement of a 350-m-wide, 40-m-high dome. Hutchison et al. (2024) provided convincing evidence that Zavaritski Caldera was the source for a significant sulfur-rich eruption in 1831 CE, which was previously known only from ice core data and thought to have possibly originated from Babuyan Claro volcano.