Valanga

Avalanche: Cascade

Zimmerman-Wall, Kelly, WoodyProvo
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Avalanche

Slab Width
61 m
Weak Layer
Facets
Trigger Type
Skier
Vertical Fall
686 m
Avalanche Type
Cornice Fall
Slab Thickness
107 cm
Trigger Detail
Unintentionally Triggered
Start Zone Aspect
East
Avalanche Problem
Persistent Weak Layer
Start Zone Elevation
3292 m

This avalanche was an unintentionally triggered cornice fall that then triggered the persistent weak layer (PWL) facets (dry snow) near the ground on a very steep (greater than 40 °) hanging snowfield. This was a repeater avalanche. What was interesting is that the hanging snowfield was all faceted snow that failed near the ground, but the runout zone and the rest of the bowl which had slid a number of times earlier this season only entrained the surface snow on it's way down slope. We had discussed cornice hazard as one of our problems for today, and had mentioned staying back from the ridge to be safe. While we were transitioning from skins to skiing, this avalanche was triggered by one of our party members putting the tail of their ski into the slope on the backside of the cornice. This is what triggered a massive collapse and the subsequent avalanche. Best guess on dimensions, 3'-4' deep x 200' wide running between 2,300' and 2,400' vertical feet.