↘ Tokachidake — Ansei Crater

[Check the restriction first] Tokachidake is an active volcano. JMA raised it to Volcanic Alert Level 3 (mountain access restriction) at 09:30 JST on 12 September 2026 (in force as of 2026-09-12) and warns of large ballistic rocks within roughly 3 km of the crater. The Ansei (Nukkakushi) crater valley's track comes within about 1.7 km of the 62-2 crater, which places it inside that range. The Tokachidake Onsen trailhead this route starts from is closed (Kamifurano Tokachidake Tourism Association, 12 September 2026). Both the valley and the trailhead lie inside that range, so this route is closed. 'Outside the published ring' and '1.5 km' below are records from the Level 2 period (June 2026 to 11 September 2026) and do not establish current access; the old boundary was recorded as running close to the valley head. The live JMA restriction always overrides any historical route line: confirm the current bulletin before you go.

[Route overview] The Ansei Crater (~1450 m) is a steaming, geothermally active gully at the head of the valley east of Ryounkaku Onsen in the Tokachidake Onsen area, beneath the crag-bound western wall of Kamihorokamettoku-yama (1920 m). A plowed public parking area at ~1270 m puts complex alpine terrain within a small day: roughly 500 m of cumulative climbing over ~5 km and ~4 hours. This is not a single line but an exploratory zone — compact, relatively protected, sometimes steep bowls and gullies on either side and at the head of the valley, lapped as conditions allow. Baked maximum slope is ~57° (short pitches along the rock walls), median ~27°. Given fresh snow and light wind it is a smorgasbord of steep, lappable skiing.

[Getting in] From the public carpark beside Ryounkaku Onsen head east, keeping high along the summer-trail line, to where it crosses the Nukkakushi-Furano River; from there follow the valley east to the 'crater' — in truth a steaming stretch of gully. Return the way you came.

[Hazards specific to this valley] (1) Volcanic gas: the Ansei crater is an active fumarole area; SO2/H2S is colourless, pools in hollows and the valley floor, and can reach dangerous concentrations on calm days — never enter steaming hollows, stay upwind. (2) Rockfall and cornice fall off the walls: the valley is ringed by walls steep enough to be a winter-climbing venue; rock, ice and avalanches off them run to the valley floor. (3) Terrain traps: the valley floor and gullies are deposition zones — even a small slide buries deep. In March 2026 a size-2 wind slab in this Ansei / Sandan-yama area fully buried a ski tourer. (4) The zone is entirely alpine and extremely condition-dependent.

[Navigation] Before the restriction this was recorded as a good-visibility valley. In gas cloud or ground blizzard it is a cul-de-sac walled by crags and fumaroles; the further east you push at the valley head, the closer you are to the craters. Verify with GPS and compass, and check both the live JMA volcano bulletin and the JAN Central Hokkaido avalanche bulletin before any tour. A description of terrain, not a recommendation.

[Restriction check — first] Tokachidake is at JMA Volcanic Alert Level 3 (mountain access restriction, raised 12 September 2026; in force as of 2026-09-12). JMA warns of large ballistic rocks within roughly 3 km of the crater; the Ansei valley (closest point about 1.7 km) lies inside that range, and the Tokachidake Onsen trailhead is closed — confirm the live JMA volcano bulletin before every tour. The live restriction always overrides the historical line.

[Start & parking] The large plowed public parking area beside Ryounkaku Onsen (Tokachidake Onsen, ~1270 m) — one of Hokkaido's highest trailheads, buying alpine terrain for little climbing.

[Getting there] Take the prefectural road from Kami-Furano up to Tokachidake Onsen road-end. Expect ice and snow; public transport is limited, so a car is the practical option.

[Snow & kit] Entirely alpine and highly condition-dependent. Beacon, shovel and probe are mandatory; treat every gully and the valley floor as a terrain trap. Check the JAN Central Hokkaido bulletin (3x weekly).

[After] Ryounkaku, Kamihoroso and Hakuginso are all nearby — some of the best onsen in Hokkaido. Confirm hours locally.