Mount Kamui rose on the rim of 6 km-wide Mashū caldera, about four thousand years ago, after the collapse of Mashū volcano. Its last eruption took place about 1000 years ago.
Tourism
Hikers can follow a 7.2 km wooded trail to the peak of the mountain, walking along the ridge of the caldera, which is a 300-m vertical drop to the surface of the Lake Mashū.