Indian Creek

We rode out to investigate a remotely triggered D2.5 R4 avalanche on a W/NW aspect at 8900' that fully buried two snowmobilers ~4 feet deep. The group performed excellent rescue efforts and both individuals survived. The avalanche was triggered remotely from directly below a very steep 35-40 degree slope. No recent avalanche activity, cracking, or collapsing was observed on the approach. The avalanche failed on persistent weak layers formed in Nov and early Dec. Crown depth ranged from 2-4 feet. These weak layers propagated both upslope to trigger the avalanche as well as cross slope connecting large pieces of terrain. The slope was characterized by overall thin snowpack that experiences wind scouring from predominant SW wind that funnels up canyon. The thin snowpack helps explain the high sensitivity and large propagation of the avalanche. Moving forward, this is the type of terrain where the persistent weak layers are most likely to trigger due to the thin overlying slab being easier to penetrate and trigger. 

We found an average snowpack depth of 5-6' in terrain sheltered from the wind. In these locations the persistent weak layers were buried ~3-4 feet deep. Light snowfall throughout the day with overcast skies becoming broken by departure at 14:00. 

We dug on the flank of the avalanche. The avalanche failed on 1-2mm dry facets directly above the bed surface of a melt freeze crust. We performed an extended column test which failed on the same persistent weak layer as the avalanche (ECTP13 down 80cm, 2.5'). The overlying slab was firm with 4F-1F hardness.

Larger 2-3mm dry facets existed below the melt freeze crust. The overall height of the avalanche crown ranged from 2-4' deep. The top of the slope was wind loaded with the largest crown depths. The rest of the crown and flanks were 2-3'. The debris pile was measured around 10' deep.