Northern Gallatin

Skier triggered deep slab avalanche on NE face of Hyalite Peak 3/4/23.

Skier triggered deep slab avalanche on NE face of Hyalite Peak 3/4/23.

"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

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'

(NE, HS, ASu, D3, R4)

We toured into Hyalite with the intention of skiing the North East Face of Hyalite Peak. Our primary concern was wind loading on leeward slopes. Before starting the day 6" of snow was reported in the Northern Gallatin range however we only found up to three inches of new snow. Approaching the saddle we found soft snow (2-3") on a pencil-hard crust. Once reaching the summit we descended carefully onto the NE face observing a shooting crack on a pocketed soft wind-slab after performing a ski cut. Noting this we descended further staying on the ridgeline. We then found a similar snowpack to the saddle with no cracking after a few more ski cuts and decided to ski one at a time down the duration of the face. Skier 1 skied a few turns down the face when a loud wumph was heard and the whole face started sliding. Skier 1 was caught, carried, and partially buried at the tail of the slide path. Skier 2 observed skier 1 and skied down to them after the avalanche stopped. Skier 1 was then fully dug out and both skiers left the avalanche path unharmed. The slide was thought to be (D3,R4) breaking all the way to the ground and spanning at least 500' wide. 

We skied to the east face in mostly calm conditions. Last night's 2" of new snow was not blown around. We could still see the crown of the natural avalanche that broke on Friday, 24 February. Skiing across wind drifts produced no cracking. We dug off the ridge on the east face near the first line down. HS was 215 and we got an ECTN 11 at 195 cm. With a load of new or windblown snow this layer could propagate, but not today. The snowpack consisted of multiple layers of wind slab which was not surprising given the location.

Fortunately the goal on Sunday was exercise more than skiing.  Ellis had been ravaged by the winds, at least the top 400-500 feet.  We rested at the top and skied out our relatively safe route through the trees.  There was a band of snow where the skiing was ok and then we hit the thaw elevation where snow skiing felt more like water skiing.  No signs of snow instability and I would not have tempted the wind slabs in the burn.