24-25

We saw many crowns of wind slab avalanches along Lionhead Ridge. Photo: GNFAC

Cornice collapse and small avalanche at the start of Lionhead Ridge. Photo: GNFAC

I rode into Lionhead head with Ryan, Aaron, and Omar on an avalanche warning day. We went straight to Ski Hill and dug a pit there. With better visibility than I anticipated we dropped down to Denny Creek, travelled up and around to the head of Targhee Creek before dropping down through Targhee and back to the vehicles. During the day ~6" of snow fell with moderate winds. Wind slabs were widespread as we rode, and the surface conditions had stiffened in many locations due to the effects of the strong to extreme winds. 

We saw many R1-R2 wind slab avalanches below the cornice line. Visibility was limited so I won't estimate the exact number, but nearly every time we had good views of the steep faces, we saw cornice collapses, debris, or small crown lines. There were two slides on east aspects that ran closer to full path and piled debris more deeply. I expect that most of these had run within the last 24 hours, but continuing snowfall and hurricane force winds made precisely dating these a challenge (many trees were blown down during the wind event, these too were already somewhat buried). None of the avalanches broke on persistent weak layers as far as I could tell. 

We dug at Ski Hill. Pit results were unremarkable with an extended column test breaking and propagating with an extracurricular ECTP32 on the January facets. The January weak layer was buried a meter deep and was 1 Finger Hardness and had gained strength. However, we wrapped around the corner on our decent and found a shallower slope (1m deep) where Fist Hard facets were capped by a dense wind slab. I did not perform an official ECT, we had undercut the slope with our sleds and were able to knock 5-foot-wide sections of slab off with an arm chop, triggering miniature avalanches that slid easily. This showed us what we needed to know--an avalanche on a steep slope with that structure was likely (see video). 

This small wind slab avalanche failed on Mt Blackmore on Sunday. Photo: C Rendeiro

Debris pile from a small wind slab avalanche on Mt Blackmore. Photo: C Rendeiro
 

Nature or cornice triggered slides in Arrowhead and Hardscrabble Bowls. Photo: I Freeland

Nature or cornice triggered slides in Arrowhead and Hardscrabble Bowls. Photo: I Freeland

Nature or cornice triggered slides in Arrowhead and Hardscrabble Bowls. Photo: I Freeland