The Caldera Lake Mashu with a 7.5 km major axis and 5 km minor axis was formed less then 32'000 years ago and is surrounded by steep up to 200 metres high crater walls. It forms together with the Kussharo Caldera and Akan Caldera the Akan Nationalpark.
Two volcanoes have grown out of the Mashu caldera: The lava dome Kamuishu, which rises as an island from the middle of the lake, and the Mashu-dake, also known as Mt. Kamuinupuri or Mt. Kamui.
Japan 1950, Lake Mashu.
The Mashu caldera lake with the lave dome Kamuishu, which rises from the middle of the lake, and the Mashu-dake (857 metres) on the right.
Japan 2010, the frozen Mashu caldera lake with the Mashu-dake (857 metres) on the right.
Japan 2011, Mashu caldera lake with the Kamuishu Island and the Mashu-dake.
The stamp was issued in the sheet "Hokkaido Scenes from Autumn to Winter".