Small Wind Slabs and Surface Hoar in Castle Peak Area

In near and below treeline terrain sheltered from the winds a mix of snow conditions existed. We found soft, cold, unconsolidated snow on northerly aspects and variable crusts on the sun-exposed southerly aspects. As we ascended into near and above treeline terrain, we started to see some evidence of wind-loading. Small wind slabs had formed on a few leeward test slopes. We stopped to check out, these wind loaded test slopes and found buried surface hoar resting under 2 to 4 inch deep wind slabs. When we reached the ridge between Castle and Basin Peak scoured surfaces, active blowing snow, and new cornices all indicated that the wind slabs at these higher elevations were likely larger so we chose a low angle path down. Midway down the slope in some near treeline terrain, we found more wind-loaded test slopes. We triggered shooting cracks up to 30 ft long on these slopes and found wind slabs up to 10 inches deep. They failed on the buried surface hoar layer. They did not extend very far downslope. We chose to avoid areas that might be wind loaded for the rest of the tour and stayed on more sheltered terrain where softer snow existed. In sheltered areas below treeline, large surface hoar existed on top of the snow surface. Tests simulating a slab forming on top of this surface hoar showed it to be very weak.

Photo 1: Wind slab failure on buried surface hoar on a wind-loaded test slope.

Photo 2 and 3: Shooting cracks triggered by a ski cut on a near treeline wind-loaded test slope. This slab failed on buried surface hoar.

Photo 4: Large surface hoar on the snow surface in a sheltered area

Video 1: Wind loading on the Castle-Basin ridgeline.

Video 2: Wind slab failing on surface hoar on a test slope.