Aspen
AvalancheCBAC Public · Nov 15, 2024 · Aspen
Snowpack
At site of avalanche: Elevation: 11,535. HS: 100 cm. Small (1mm or less) but sugary facets in first 35 cm. Bed surface of avalanche height at approximately 75cm. We also observed cracking above the exit gullies of Halloween Bowl.
Avalanche
Group of three traversed out to NW facing Halloween Bowl. Strong downslope winds predominated on both the northern facing slopes along the traverse around to Halloween Bowl and within the bowl. Not sure if these winds were actually southeasterly or just strong downslope winds. Much snow was being transported, mostly downslope but strong gusts upslope as well. Midway through the bowl, regrouped at safe spot. No cracking, whumpfing, or other signs of instability presented. Snow surface was generally variable wind buff, with a thin wind crust on the north and east aspects of the bowl. But we had found no significant consolidation while poking around the snowpack. Skier 1 poked out into the second pitch, a wide gully, with the plan of dropping across the west-facing terrain to enter the gut of the gully. Almost immediately and with very little pressure, the skier triggered a windslab that ran ~200' to ~300' vertical feet. The skier had entered at about 29/30 degrees, but the slope rolled over within 4-5 feet downhill into 33-35 degrees, sustained for about 300 vertical feet. The slab ran most of this length, but the pitch lessened and the mass came to a stop. It did not propogate all the way across the gully, and did not entrain the more easterly facing side of the gully. Thankfully Skier 1 remained safely at the crown. Though a portion of slab cracked and broke a few feet above Skier 1, it was not steep enough to slide with the rest of the slab. Slab was about 25-30 cm. The bed surface below the crown was surprising, we hadn't found anything that would suggest the presence of this layer. We failed to reevaluate the subtle change in aspect, and given the significant wind loading we should have done so.