Northern San Juan
AvalancheAmy Pertuz · Jan 4, 2023 · Northern San Juan
Weather
Light lingering snowfall at elevation cleared by afternoon, light transport at ridgetop level.
Snowpack
The height of settled storm snow in the RMP summit area averages around 90cm. New snow on the surface was low density-stellar particles and releasing in small dry-loose avalanches in some steep terrain. The layer of concern is a drizzle crust buried ~45cm deep, with associated facets above and below it, which was created by warm precipitation event on December 31st. This layer, which is 4cm thick and 1F hardness, has faceted since my last field observation in this location on January 1st, and tests were producing clean and easy shears on this interface. Recent natural activity in the area is of two varieties: large natural avalanches failing on a deep facet layer, and slides which ran on a mid-storm interface which was created since December 27th. A number of shallower slides which ran on a storm interface later in the storm appear to have run on this layer. On a S aspect at 11, 200ft, this layer produced clean failures with moderate taps (CT11) and propagating failures on an Extended Column Test. The 12/27 interface was unproductive in tests in this location. I did not experience cracking or collapsing, but expect this weak layer in the upper snowpack to become more reactive as the glove and 4F hardness surface snow consolidated into more of a slab.
Avalanche
Many large natural avalanches ran on RMP since 12/27. Northeast slopes ran early in the storm, west stopes ran later, east and south aspects ran during the middle and end. Fresh activity within the last 24 hrs was observed on E and W aspects