Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

We went to the Mammoth Crest to look for recent avalanche activity and test wind slabs.

• We saw numerous natural avalanches from the past 48 hours in the Sherwins and Mammoth Lakes Basin. A few were small. A few were sluffs or storm slabs below treeline. Most were medium to very large avalanches that had run down from wind-loaded terrain above treeline. (See avalanche observations for more details.)
• We found wind and storm instabilities had become stubborn quickly. We stomped around on many a test slope with only isolated cracking. We managed to trigger a few wind slabs once the slopes had been undercut. These were between 4 and 12 inches thick and soft (4F). There were some harder wind crusts (1F) at ridgelines. Snowpack tests on nearby slopes highlighted the surface slab over softer, weaker snow below, but did not propagate.
• We traveled in a lot of sheltered terrain near and below treeline and found the surface snow settled or wind-stiffened in all but the most sheltered areas. There were lots of big settlement cones around trees. We investigated snow available for transport in an alpine fetch (upwind slope) and found only about 15cm of soft snow above firmer snow (Ski penetration was 15cm in F hard snow, Boot penetration was 35cm through layers of 4 finger hard and 1 finger hard snow). In that same fetch we found that the wind had moved most of the recent storm snow. Snow depth on the west-facing fetch was 114cm, but on the east-facing, wind-loaded slope, it was 260cm.