Natural avalanche below treeline on Andesite Peak and other obs.

Touring on Andesite Peak this morning we saw a size D2 storm slab avalanche that appeared to have failed around 6-7 am. We found the crown and debris at 11:30 am under 8 inches of storm snow. We estimated time of occurrence based on snowfall rates. We did not see evidence of nor did we trigger any other avalanches in the area.

The avalanche occurred in below treeline terrain with minimal wind loading. The aspect measured NE (034 deg) with a slope angle at the crown ranging from 32 to 44 degrees. Crown height ranged to 2 to 3 feet. The avalanche failed at the old/new snow interface on stellar snow crystals. Snowpit tests performed in the crown at 11:45 am scored CTH-BRK and ECTX on the failure layer of the avalanche (see photos).

While breaking trail both below and above treeline we experienced no snow surface cracking. This was in both wind protected and wind exposed areas. Moving above treeline we encountered the expected wind slabs and blowing snow. Ski kicks, intentional small cornice collapses, and ski cuts on two different areas of wind loading along the summit ridge did not produce any signs of unstable wind slabs. The maximum extent of wind slab cracking we observed was when cutting above our track. Even then cracking was short and you had to get close to the undercut area (see photo).

Returning to our skin track in wind protected terrain below treeline, we found 3" of new snow in the track after the 2 hours between 11am and 1pm. Storm snow accumulation in this area had reached 3 feet by midday.