Isolated instablity (cracking and whumpfing) on Silver Peak.

We went searching for the problematic slab over facets snowpack structure in the Silver Peak area today and found an isolated area of reactivity with skier triggered cracking and whumpfing. We put in around 20 hand pits on N-NE aspects at and below treeline between 7,500' and 8,200'. Facets were always observed less than 30 cm below the snow surface. Slab thickness was noted to range from 5 to 25 cm and the weak layer was noted to range from 3 to 15 cm. HS in this area ranged from approx 60 to 90 cm. Some hard slabs over facets were noted near treeline and soft slabs over facets were noted below treeline.

We found that while the weak faceted layer was widespread, the degree of facet development and overlying slab characteristics were quite variable. In some areas the facets were too poorly developed. In other areas the facets were very weak, loose, and dry, but the overlying slab was too soft. In isolated areas the right combination of well developed facets and a sufficiently stiff slab existed for propagation, cracking, etc.