Mt. Onuma Backcountry Ski Touring (Jozankei, Hokkaido, Japan)


The route up Mt. Onuma (大沼山 – 1,111m) near the Toyoha Mine in Jozankei (southwestern Sapporo City) may become your next favorite Hokkaido backcountry ski touring route. It is close to Sapporo City. The climb up is short; only about 2 hours or so. The terrain is suitably varied. On a clear day it boasts some magnificent views. But the real cherry on the cake is its downhill slopes. The upper, mostly tree-free slope is worthy of a few exhilarating laps, while the second half of the route back down to the carpark is a glorious dodge-em ride through nicely spaced woods.

Route GPS File

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Essential details


4.8km
Distance


3.5 hours
Time


511m
Ascent


1,111m
Highest point


4.5/10
Difficulty?


Dec-May
Best Season?

Need-to-Know Details

  • Location: This route starts near the end of the public access road (Route 95) up to the Toyoha Mine in the upper Jozankei area, near the south-western border of Sapporo City. Mt. Onuma is just one of the many minor peaks along a ridge connecting Mt. Yoichi, Mt. Muine, Mt. Kimobetsu-dake and Nakayama Pass.
  • General notes: There are a number of fantastic backcountry ski routes accessible from the old Toyoha Mine access road in Jozankei. While the mine is now closed (since 2005), the road is still cleared in winter due to ongoing treatment of waste water from the mine, and research into possibilities related to geothermal power. While the Hokkaido Development Department keeps the road open in winter, it will continue to be a popular place for access to the backcountry. Mt. Onuma is not marked as such on maps, but the trig station is officially labelled Onuma, so that’s where the popular name comes from.
  • Route markers: There are sporadic, unofficial route markers in the form of pink tape on trees. There is no summer trail.
  • Transport: This route is not accessible by public transport. There are no official car parks, although there are a few snow clearing areas where people often park their cars. 
  • Paper topographical maps: For topographical maps, you can either print out what you want from the Geospacial Information Authority of Japan here (Mt. Onuma is in the cross-hairs), or buy the following 1/25000 paper topo map (for 350yen) from a bookstore in Sapporo (such as Kinokuniya next to Sapporo Station).
  • Snow and route safety: The main risk noted in the Hokkaido Yukiyama Guide (ISBN: 978-4894538047) is the risk of avalanche in unstable conditions on the last steep section approaching the summit. Also noted are cornices on the summit ridge. When descending, it is very important to make sure you’re headed in the right direction, particularly when visibility is low and up tracks are no longer visible. It is quite easy to drop down too far to the skier’s right from the summit, into the gully to the east of the ridge you came up on. This gully has high avalanche risk and there are multiple cliffs and bluffs.
  • Weather forecast (Google Translated): Tenkurapinpoint for Mt. Muine (close vicinity to Mt. Onuma)
  • Other resources
    • See the write-up (in Japanese) in the Yuki-yama Guide (ISBN: 978-4894538047) from page 132-135.
  • Onsen neaby: If you are headed back towards Sapporo City, you’ll be passing through Jozankei Onsen area. A favourite of ours is the down-to-earth Matsu-no-yu Onsen on the Sapporo City side of Jozankei Onsen. There’s another onsen right next door (Kogane-yu Onsen), but Matsu-no-Yu has a view of the river and hills. Both onsen have cheap and cheerful restaurants attached. If you have time, you might want to check out the Ainu Culture Center (location) just across the road from the onsen.
  • Date visited: 7th January, 2017

See my Hokkaido Ski Touring Resources page for more trips and tips
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Trip Report

This mountain is not named on topographical maps, but its name is borrowed from the Onuma trig station at the top. It is likely this name comes from a tarn named Onuma close by. There’s no hiking trail on Mt. Onuma, so it is not possible to climb the mountain in summer. It has fantastic views including that of Mt. Yotei, and its sparsely wooded ridge is a popular route suited to skiing. The closure of the Toyoha Mine raises concerns about the future of access to this area for mountaineering (Translated from the Hokkaido Yukiyama Guide, p. 132).

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

We hadn’t planned on skiing Mt. Onuma today. The original plan had been to head up Mt. Kokimobetsu-dake (tentative route here) on the western side of Nakayama Pass. When we arrived at the parking spot at the base of the hill, however, the weather was not looking promising. Strong westerly gusts along with some driving snow were quickly damping our resolve to head out onto Mt. Kokimobetsu’s exposed, relatively treeless southwestern ridge.

We’d come all this way with our skis and gear, however, so it seemed a waste to just go home. A quick group meeting resulted in the suggestion that we head back towards Sapporo, and take a look at conditions in the Toyoha Mine valley. Tucked into the hills near Jozankei, this valley ought to be more sheltered, and would offer the choice of either the Mt. Muine route up to Senjaku Plateau (route guide here), or a route up Mt. Onuma.

When we arrived at the mine, we decided on the Mt. Onuma route. Rick and Jeff had done the route in spring, and were keen to check out the early winter conditions. It ended up being most excellent choice, as the snow was glorious, and we mostly had the route to ourselves.

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Photo by Rick Siddle

We parked up along with the 10 or so other cars at the Mt. Muine trailhead. Everyone else seemed to have been heading up Mt. Muine, while we walked a few hundred meters up the road to the hairpin bend to start up the School Ridge (学校尾根 – gakkou one) of Mt. Onuma.

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

At around 790m, there is a relatively flat spot on the ridge. Further on from this, there are a couple of humps in the ridge. It should be possible to traverse around the side of the 875m hump around the contour line, such that there is no climbing involved, although the west side of the hump is heavily wooded, and the eastern side has some steep bluffs. This traversing is important if you want to avoid a bootpack or putting the skins back on on the way down.

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Once beyond the 875m hump, the climb up to the peak starts in earnest. Expect some wide open slopes at this point, which require some careful zigzagging. In unstable snow conditions, keep distances between people in your party large, to avoid multiple casualties in the event of an avalanche.

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

The final approach to the summit is through low-lying trees. Pick a safe gap between the cornices, and you’ll suddenly find yourself on the summit ridge with expansive views on a good day to Mt. Muine, Mt. Yoichi, and if you’re lucky, all the way to Mt. Yotei.

We summited in low cloud, so I look forward to better weather next time.

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Photo by Rick Siddle

We returned to just below the summit for a quick lunch, and then skied back down the way we had come. There was a good layer of at least 50cm of fresh, light powder, and this made for some fantastic runs.

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

Mt. Onuma backcountry ski touring (Jozankei, Hokkaido, Japan)

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