Mount Kamui (Lake Mashū caldera)

Mount Kamui sits as the central cone within the Lake Mashu caldera in eastern Hokkaido and is part of the Akan-Mashu National Park complex. The lake is noted for exceptional water clarity and considerable depth, and the cone rises directly from the caldera basin.

Visitors use a series of designated observatories on the crater rim to view the caldera and the cone, since the shoreline is generally closed to protect the fragile environment. The rim viewpoints offer short walks and interpretive signs rather than long trails down into the caldera.

The cone and caldera were formed by volcanic activity; the steep caldera walls and isolated central peak are the result of explosive eruptions and subsequent collapse. The site is managed for conservation and controlled public access to preserve water quality and vegetation.

The feature lies within Akan-Mashu National Park on Hokkaido’s eastern side and is accessed by road to the rim viewpoints; it is a distinct volcanic caldera rather than a standalone mountain.

• Lake depth and clarity: The caldera lake is among Japan's deepest and clearest, with reported maximum depths on the order of 200 metres.
• Access restrictions: Access to the crater floor and shoreline is restricted; viewpoints on the rim are the primary places for viewing the lake and central cone.

What to See #

• Central cone: A prominent volcanic cone that rises from the center of the caldera and forms the island or central peak within the crater lake.
• Rim observatories: A set of roadside observatories and short walking paths on the crater rim that provide framed views into the caldera and across the lake surface.