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.
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.
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.
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.
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.
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.