Lake Mashū

A caldera lake in eastern Hokkaido, Japan, enclosed by steep volcanic walls. Its exceptionally clear water and frequent fog are defining features.

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Mashū Caldera: A volcanic depression formed when a volcano collapses after a major eruption. Lake Mashū occupies this steep-walled volcanic depression.
Mashū Volcano: A stratovolcano in eastern Hokkaido whose eruptions formed Mashū Caldera. Its eruptive history created the basin now occupied by the lake.
Akan-Mashu National Park: A national park in eastern Hokkaido that protects volcanic landscapes, forests, and lakes. Lake Mashū lies within this protected park.
Lake Akan: A caldera lake in eastern Hokkaido, known for its marimo algae. It offers a nearby contrast between Mashū's clear water and a lake famous for aquatic life.
Caldera: A large volcanic depression formed by collapse after magma is withdrawn during an eruption. Mashū Caldera is one example of this volcanic landform.
Kussharo Caldera: A large volcanic caldera in eastern Hokkaido containing Lake Kussharo. This neighboring caldera records the region's broader volcanic history.
Lake Mashū Observatory No. 1: A public observation point on the western rim of Lake Mashū. It provides a prominent viewpoint across the lake and its steep rim.
Lake Shikotsu: A deep caldera lake in southwestern Hokkaido, noted for clear water and limited seasonal freezing. It is another exceptionally clear Hokkaido caldera lake, but lies in a different volcanic region.
Water transparency: The degree to which light passes through water without being scattered or absorbed. Mashū's unusually transparent water is measured with Secchi-disk observations.
Lake Kussharo: A large caldera lake in eastern Hokkaido, northwest of Lake Mashū. It is another major volcanic lake in the same part of Hokkaido.