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Akan-Mashū NP, Hokkaido
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Lake Akan’s “frost flowers” grow on bare, newly formed ice in calm weather below −15°C. Their featherlike crystals are so delicate that even a breath can make them disappear.
At Lake Kussharo, cracks in the frozen lake can rise into ice ridges stretching as far as 10 km. Researchers recorded how overnight cooling opens cracks and daytime warming pushes the ice upward.
Wakasagi smelt are a Lake Akan winter-fishing favorite, but they weren’t native to the lake: their eggs were brought from Lakes Abashiri and Tofutsu. Today, the freshly caught fish can become hot tempura.
Near Akan’s bubbling mud volcanoes, geothermal warmth melts snow from the ground, and crickets sing even in winter. Unlike most Hokkaido crickets, this population can breed twice a year.
Akan’s winter lake is not always silent: a park ranger described high, chirping notes and sharp crackles echoing across the ice as it freezes and breaks.
From 1974 to 2021, Lake Mashu froze completely in 27 of 48 winters. Researchers found that the previous summer’s warmth also affects how much winter cold the lake needs to freeze over.
Under Lake Akan’s winter ice and snow, marimo live in water that stays near 2°C. After thaw, cold water and strong sunlight briefly suppress their photosynthesis, but research found they recover within 20–30 days.
Many swans leave Hokkaido for the winter, but geothermal warmth keeps patches of Lake Kussharo unfrozen. Those open-water spots give swans a place to rest and feed through the cold season.
Akan’s geothermally warmed mud-volcano areas can serve as winter resting places for Ezo deer. A ranger survey found many deer traces near the ski area, but almost none around a vent deeper in the snowy mountain forest.
On clear-ice days at Lake Akan, bubbles rising from below can be trapped in striking layers beneath the surface—a frozen snapshot of gas bubbling up from the lakebed.
Fresh snow at Akan’s south-shore Bokke forest can reveal squirrels digging up walnuts they buried in autumn. Rangers have also found fox tracks and feeding traces left by flying squirrels.
