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Akan-Mashū NP, Hokkaido
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At Oyakotsu Jigoku on Wakoto Peninsula, explorer Matsuura Takeshiro recorded in 1858 that volcanic fire reflected on Lake Kussharo so brightly at dusk, it seemed like daylight.
At Lake Akan’s Bokke, gray mud bubbles up with volcanic gas, and geothermal warmth keeps the ground snow-free. Its name comes from the Ainu word “pofuke,” meaning “boiling”; crickets chirp here even in winter.
At Mt. Io’s base, hot-spring-steamed eggs inspired an unusual local dessert: soft-serve topped with one. Introduced in 2022, it tastes like pudding when the egg and ice cream are mixed together.
In 1887, a 41-km railway carried Mt. Io sulfur to Shibecha, built in just 8 months as Hokkaido’s second railway. The boom relied on prison labor; sulfur gas and dust caused blindness and eye disease.
Satellite radar found an area more than 10 km across around Atosanupuri swell by over 20 cm around 1994, then slowly contract. No eruption was observed in that interval; the volcano was quietly changing underground.
Atosanupuri—“bare mountain” in Ainu—lives up to its name: more than 1,500 fumaroles send white steam from Mt. Io, with vivid yellow sulfur crystals among them.
At Mt. Io’s foothills, an alpine shrub called isotsutsuji forms a roughly 100-hectare community at only about 150 m elevation. In June and early July, its white blossoms carpet the volcanic landscape.
Wakoto Peninsula’s geothermal warmth keeps crickets active in winter. At nearby Kussharo Shrine, the Minmin cicada has a northern-range-limit population designated a National Natural Monument.
Mt. Io feeds Kawayu Onsen, whose hot spring water has a pH of 1.6–1.8. That unusually strong acidity is a striking reminder that the steaming volcano is still shaping everyday life nearby.
Long before sulfur became a regional industry, Ainu people used sulfur from Mt. Io as tinder. The mountain’s story begins not just with mining and railways, but with local knowledge of its volcanic materials.
