Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

We toured around multiple aspects in the Mammoth Area looking at surfaces, wind slabs, and cornices.

• Not for lack of trying we found wind slabs and cornices unreactive on all aspects. We got isolated cracking in 10 cm thick, hard drifts near and above treeline on north and southwest-facing slopes. Strong northeast wind was eroding cornices hanging over typically leeward slopes and blowing the snow onto south and west-facing terrain. We even did a compression test on the freshest slabs at 10,300 feet on a southwest slope and got no results (CTN). Total snow depth at that location was 185 cm. We dug down 90 cm and found only very hard (P+) wind-packed grains. At the bottom of our pit we saw 4 finger hard rounds with a few rounding facets thrown in the mix.
• The dominant surface near and above treeline is hard sastrugi.
• Below treeline on sheltered slopes we found soft snow with boot penetration around 25 cm. The surface there a mix of decomposing-fragmented grains, 1.5-2 mm surface facets and 2mm surface hoar. We found a temperature gradient more than sufficient to drive faceting in the morning. In the afternoon the snow surface had warmed enough that there was only 1 degree C difference in the upper 20 cm of the snowpack.
• Sunny aspects near and below treeline had sun crusts.