The slide was on an east-facing slope wrapping northeast. SS-AM-R4-D3+-O, slope angle averaging 30 to over 40 degrees. At 9,500 feet it was rocky alpine terrain with some sub alpine fir scattered across the slope. 1,000ft wide, 2-3 foot deep fracture line, 400-500 vertical foot drop, debris 12-15 feet deep and covering an estimated 6 acres.
The 2-3 foot deep slab was fist hard snow at the surface, pencil hard at the base and consisted of newer snow that had fallen since mid March. The weak layer and underlying snowpack consisted primarily of weak, very developed facets due to an extremely dry snow year (50-60% of average) and very little snowfall since January 9th.
The avalanche advisory had been warning of deep slab instability and the risk of triggering large, destructive avalanches. Exactly a week earlier, a backcountry skier had been caught in a smaller but similar avalanche and had been evacuated and survived with a crushed pelvis, two broken femurs, a broken tib-fib and lower arm fracture. Only days earlier, on the Payette Forest north of Boise, a snowmobiler had survived without injuries, an 8 and1/2 foot burial in a massive slide.
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