Skier triggered deep slab avalanche on NE face of Hyalite Peak 3/4/23.
Ben Zavora of Beartooth Powder Guides and the GNFAC investigated a skier triggered avalanche near Daisy Pass (3/2). It was remotely triggered (they were not on the slope) and failed on a layer of feathery surface hoar crystals that formed in early January. The slab was 4 feet thick and very dense and termed a Deep Slab Avalanche. The recent snow and wind added weight and stressed this layer to its breaking point. In January we found surface hoar on all aspects, so it's a bit scary. Remotely triggering a 4' deep hard slab avalanche is dangerous. The slope angle at and near the crown was only 31-32 degrees; very shallow. Surface hoar is known to break on less steep slopes, which can catch us off-guard.
It's time to recalibrate our thinking because deep slab avalanches are deadly, yet not very widespread. It will become a low-probability, high consequence problem.
Walking along Henderson ridge, Doug Chabot touched a cornice with his ski pole and it broke 40 feet wide. Cornices are touchy and need t be given a wide berth. Photo: GNFAC
Ben Zavora (rocking his 80's style sunglasses), is standing next to the crown of a skier triggered avalanche near Daisy Pass. The avalanche broke 4 feet deep on a layer of surface hoar, indicated by the blue crystal card. Photo: GNFAC
The slope angle at the crown was shallow: 31-32 degrees. A weak layer of surface hoar is notorious for breaking on shallow-angled slopes. Photo: GNFAC
"Chunk of cornice fell off the top of Arden Peak. Notably the same aspect/elevation as the 2/27 observed natural slide on E face of Mt Bole but the cornice fall did not step down beyond the surface snow." Photo: M. Zia
We skied the Throne today, the windboard from thursdays wind was more widespead than we had hoped. It wasn't very well bonded, and didn't feel good, but it wouldn't move, either. I dug a pit on the north facing at the top, away from the windboard, and got no results. I tried to get down to the older weak layers and could spot them and get them to break, but I had to wrestle with it to get it to do it. Parking is still limited.
Chunk of cornice fell off the top of Arden Peak. Notably the same aspect/elevation as the 2/27 observed natural slide on E face of Mt Bole but the cornice fall did not step down beyond the surface snow.
Traveling into Blackmore Basin we assessed two potential lines from below that we had already planned to potentially ski. We gained the saddle between Blackmore and Elephant. We observed snow transport from SW winds and noted the zone we were heading to might have wind loading occurring at the top. We traversed on scoured slopes by foot over to the entrance of the line that we intended to ski. Upon our arrival we noted a convexity of wind loaded snow on the skiers left of the start zone and made note to avoid it. We transitioned to skis and made a plan for skier 1 to enter traversing to the skiers right. Once skier 1 started traversing to the right, approximately 40 feet from skier 2, a small collapse propagated at the ski tips of skier 1 across the entire entrance. Skier 1 yelled avalanche and was able to self arrest on the bed surface/ crown. After the slide occurred, we reassessed and felt comfortable descending on the bed surface to the toe of the debris, one at a time. We decided that was enough for one day and headed back to the trailhead. In retrospect, we underestimated the size of the potential wind slab and the danger of the high consequences terrain where a slide might not bury but potentially carry and kill a skier by taking them over cliffs.
SS-ASu-R2-D1.5-I
Vertical Fall: ~700'
Distance Traveled: ~1000'
Aspect: 15 N
Elevation of start zone: 9645'
