雷電山オサンナイ川
Distance
Time
Ascent
Highest point
Best season
We visited this route on Mar 29, 2022
Raiden-yama is the last major peak of the Niseko Range, before reaching the Japan Sea coast, in southwestern Hokkaido. Osannai Bowl is the expansive bowl due south of the broad Raiden-yama peak – it’s the catchment for the Osannai River オサンナイ川. This route up to the Raiden-yama peak (and then back down via the bowl) starts in the Kamisato 上里 area of Rankoshi Town, at the end of the snow clearing, here.
Raiden-yama is a gargantuan mountain with a plateau-like, very broad peak. Hence, ascent options and descent options abound, all very nice in their own right. Raiden can be a hard nut to crack, however, as it bears the unimpeded brunt of northwesterly winter storms, straight off the Japan Sea. Hence, it’s relatively unheard of to see reports of skiers tackling the peak in mid-winter. Generally, mid-winter only allows ascents to Raiden’s foothills, such as Sankokunai (route guide here). As the days grow longer, and the weather gets milder, however, March and April offer some excellent days for shooting for the summit, and hitting the attractive Osannai Bowl.
Being a south-facing bowl serves up its own challenges in spring, though. Surfaces can heat up quickly in fine weather, and suncrust is common. For all the potential this zone offers, it doesn’t give up the goods easily.
Park up at the end of the snow clearing on the minor road off Route 229, around here. Note that the road heading to the right is a private driveway, so make sure not to block this or park on that road. Skin north along the snowed-in road for about 500m before carrying on north for about 2km, along a forestry road at first, then through some pine plantations. You’ll need to cross Osannai-gawa river at some point, and this is best done around where a summer trail is marked on the topomap. It’s a relatively deep gorge, with open holes in the snowpack to the river below, so you’ll likely need to be creative in your route selection for this minor ‘crux’.
Once across Osannai-gawa, it’s just a matter of making your way up to the main ridge that you’ll follow for the remainder of the way to the summit. The ridge starts out very broad at first, but narrows considerably in the final 25% or so of the climb. This final 45 minutes or so of the climb can be challenging – think rimed and icy surfaces with exposure to inconvenient falls. Boot crampons may be required, and some form of self-arrest ability is highly recommended.
The broad summit plateau is featureless. If visibility is low, consider turning around before getting to the summit plateau. There is a summit marker, but this may be buried.
For the descent, it’s not usually possible to ski direct south off the summit, as the entire northern rim of the Osannai Bowl is usually outlined with very large cornices. Head back the way you came, and descend into the bowl about 100m vertical meters below the summit on the ridge you used to access the summit.
There are a couple of steep cliff-like features on the western side of the bowl, so descend with caution, avoiding these if necessary. The bowl will naturally funnel you into the Osannai-kawa valley proper. Follow this valley back to where you crossed the valley earlier in the trip, or, at around 580m in altitude, start making a long, high traverse to the skier’s left away from the river. This will take you to a mellow run through trees to your original uptrack along the forestry road.
This route is a very solid day out, so allowing 6-7 hours would be best.
Transport
There is no public transport to this route.
There is easy car access to the start of this route – the trailhead is at the end of the snowclearing on a minor gravel road off Route 229, here. There’s no dedicated parking, so make sure not to block access – consider clearing another 1m or so off the side of the road in order to get your car off the road as much as possible.
NOTE: The official 1/25000 topo map(s) above can be purchased for 350yen from Kinokuniya bookstore next to Sapporo Station or online (in Japanese).
Snow and
route safety
We’ve ranked this route as Advanced. There’s a relative technicality to the final ascent to the summit – exposure to falls. There’s very real exposure to avalanche in the bowl and in the tight gully. The gully in particular is one long terrain trap. Take utmost care. This is also a long route with skiers exposed to the elements for a long time in the alpine.
Category
Grade
Points
Strenuousness
Vertical Gain
40
Time ascending
6
Technicality
Altitude
6
Hazards
12
Navigation
12
Totals
76/100
Weather forecast
If you’re headed back towards the direction of Niseko, our natural choice of onsen is the down-to-earth and local Yusenkaku Onsen 幽泉閣温泉 (location, 500yen) next to Kombu JR Train station. They’ve got a decent selection of indoor baths, an outdoor bathing area, and a nice relaxation area. They often sell local vegetables in the foyer area, as well as other local crafts, foods, and of course the famous Rankoshi rice.
See a detailed write-up of this route (in Japanese) in 212 Backcountry Routes (Yama to Ski, 2018), p. 42.
Guide Options
If you’d like to ski this route and/or explore other Niseko areas together with a local certified guide, get in touch with Yasuko Kikuchi. Born and raised in Hokkaido, she’s a JMGA-certified guide now based in Sapporo. Her outdoor experience is broad and worldwide, having worked as a Canadian Ski Patrol member, and has sumitted a number of 6,000m+ peaks around the world. She speaks good English. In addition to Yasuko, also see a full list of English-speaking Hokkaido Mountain Guides Association (HMGA) guides on the HMGA website here.
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Not much to say about this route other than it’s a blast in fine spring weather. Starting early meant bulletproof crust for the climb up, but this warmed up nicely later in the morning. I was just quick enough to avoid the worst of the heating in the sauna that is the Osannai Bowl around midday. While I didn’t see any indication of instability, the snow was clearly warming up very quickly in the gully on the descent. I left the gully early in favour of a high traverse.
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Done this route to Raiden-yama Osannai Bowl, or others nearby? Thinking of doing it? Please post any feedback, reports, or queries here. Thanks!
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Category
Grade
Points
Strenuousness
Vertical Gain
40
Time ascending
6
Technicality
Altitude
6
Hazards
12
Navigation
12
Totals
76/100
GRADES range from A (very difficult) to D (easy). Hazards include exposure to avalanche and fall risk. More details here. Rating rubric adapted from Hokkaido Yukiyama Guidebook 北海道雪山ガイド.
