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Chubu-Sangaku NP, Nagano
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An ice tunnel forms beneath the snow patch in the same place each year. Exposed sections measured 9–16 m high and 20–31 m wide; researchers found expanding cracks and small dips can precede a collapse.
One tributary, Sango Sekkei, preserves a mining clue: its name comes from the Hakuba copper mine’s No. 3 adit, not from a count of snowfields. The mine was prospected from 1901 and abandoned by 1907.
Melting snow can tip rocks that had been resting still, sending them sliding again. At Daisekkei, rock fragments have been reported traveling up to 1 km across the snow.
Hakuba Village describes the Daisekkei as 3.5 km long, with a 600 m elevation difference. This immense ribbon of snow persists through summer in the Northern Japanese Alps.
On Mt. Shirouma above the Daisekkei, a separate dark snowmelt pattern forms the “paddy-preparation horse.” Its spring appearance once signaled it was time to begin rice-field work—and is traditionally linked to the name Shirouma.
Ice Age glaciers carved this valley, but today’s Daisekkei is a perennial snow patch, not a glacier. Summer runoff melts it from below through a recurring tunnel, preventing thick glacier ice from developing.
Late-melting snowbeds around Mt. Shirouma support flowers such as Shinano kimbai and Hakusan fuuro. Across the massif, about 280 alpine plant species grow—roughly 74% of the species recorded in the Northern Alps.
In 1919, 25 residents of Hakuba’s Hosono district organized the Hakuba-dake mountaineering guides. The local guide association traces its history to that group and remains active today.
