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Daisetsuzan NP, Hokkaido
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About 2,800 years ago, a powerful steam-driven explosion opened the horseshoe-shaped Jigokudani (“Hell Valley”) beside these vents. A debris avalanche and hot volcanic mudflow swept as far as the Asahidake Onsen area.
Sulfur from these vents once went into gunpowder. In the 1940s, miners even used a small horse-drawn railway to haul it down the slope; faint traces of the old tracks can still be spotted.
Active steam does not mean a recent eruption: research dates Asahidake’s latest known eruption to a small steam explosion about 700 years ago, and its last magma eruption to roughly 5,000 years ago.
The white plume is largely water: underground-heated water escapes as steam, then cools into tiny droplets. The vents are audible too—their roar has been compared to a jet engine.
The yellow fragments around the vents are native sulfur, not colored rock. Fumarole gases carry sulfur out, where it condenses on cooler surfaces into pieces that can look like ordinary yellow pebbles.
At Asahidake’s foot, the annual Nupurikoro Kamuinomi mountain-opening ceremony includes Ainu prayers for hikers’ safety. The highlands around this steaming peak are known as Kamuy Mintara, “the playground of the gods.”
