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Mashu volcanoMashu volcano is a 7 km wide caldera in NE Hokkaido, Japan.
The caldera formed ca. 7000 years ago and truncates a stratovolcano which formed the ESE rim of the large Kutcharo caldera to the west. The steep-walled Mashu caldera contains Lake Mashu (摩周湖 Mashū-ko), known for its very clear water, and is one of the scenic highlights of Hokkaido.
Background:A small andesitic stratovolcano, Kamuinupuri, was constructed beginning about 4000 years ago in the SE part of of the deep caldera lake. The latest dated eruption of the volcano was a large explosive eruption about 1000 years ago, which created a 1.2 x 1.5 km crater at the summit of Kamuinupuri.
Kamuishu is a small island in the center of Lake Mashu. It is the tip of a mostly submerged dacitic lava dome.