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Daisetsuzan NP, Hokkaido
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A gully about 10 minutes up Bogakudai’s trail exposes 3,300-year-old pyroclastic-flow deposits. Two layers touch directly, suggesting eruptions came in quick succession; charred wood records the scorching heat.
Marutani Onsen once stood at today’s viewpoint. At 12:11 p.m. on May 24, 1926, the first small mudflow destroyed it, killing owner Yoshinosuke Marutani and family members; relatives later built a lava-stone memorial here.
On December 25, 1988, a pyroclastic flow surged toward Bogakudai and came within 100 m of the mountain refuge hut. That hut is uphill—not the modern shelter beside the viewpoint.
A trail from the viewpoint reaches lava from about 500 years ago, Tokachidake’s youngest known lava flow. Its rough, knobbly fragments are clinker torn from the cooling crust as the molten rock moved.
Along the trail, the 1926 Taishō mudflow forms a thin cap over older volcanic deposits. Its pale fragments are rocks altered by hot water inside the volcano before the mudflow carried them downhill.
Bogakudai’s pikas hide among rocks and feed on Ezo isotsutsuji. After photographers strayed off-trail and trampled vegetation, local agencies extended guide ropes to help protect their habitat.
JMA lists a seismometer, ground-tilt meter, infrasound detector and GNSS equipment at Bogakudai. So while visitors watch the mountain, instruments here are measuring signals from beneath and around it.
Built to shield visitors from volcanic rocks, the viewpoint’s disaster shelter also displays volcano-monitoring footage and activity information. It stocks emergency supplies and has a generator for temporary refuge.
Novelist Ayako Miura named a bridge on the road from Shirogane Onsen to Bogakudai. Her novels about the 1926 eruption and the community’s recovery made this local history part of Hokkaido literature.
