Southern San Juan
AvalancheChris Bilbrey · Mar 18, 2022 · Southern San Juan
Weather
Sunny day with steady west-northwest winds along ridgetops. The wind made it feel wintry at upper elevations, and light drifting onto leeward slopes did not create new problems or change to overall hazard.
Snowpack
Today's wind kept snow surfaces from getting too soft. Even wind-sheltered south aspects below treeline only softened enough to provide decent "fake corn" turns, but not soft enough to sluff downhill from a rider's weight. We found moist grains about 15 cm's below the surface on southerly-facing slopes near and below treeline. Less downward moistening on east and west-facing slopes at the same elevation - about 5 to 10 cm's below the surface. On west to north through east aspects at upper elevations, the snowpack remains dry and winter-like below moist surface grains. Digging on an east-facing slope near treeline, we found a very stout (Ice hard), previously wetted crust above the "drought layer" facets. The facets are still dry and starting to round - grains have both rounded and angled edges. The tensile strength of the crust appears to keep avalanche activity at bay without a big new load or major warmup. However, after cutting the crust to perform a Compression Test, we observed sudden collapse failures in weak facets with 18 taps. Probing across northwest, north, and northeast aspects we found the "drought" facets anywhere from 80 cm up to 150 cm's deep. Deepest depths to weaker snow below was on due north-facing slopes above treeline. Upon visual inspection, buried facets on northerly-facing slopes ranged from 4F to 1F and thickness of this layer continues to decrease as the overlying slab settles. No cracking or collapsing observed. Exposure to more warmth and lesser snow totals below treeline has helped reduce the sensitivity of buried weak layers. Triggering a slide that breaks in buried weak snow seems less likely and would be more isolated in the terrain where we traveled.
Avalanche
Lots of loose wet activity (size 1-2) on east to south through west aspects at all elevations that most likely occurred between 3/13-3/16. One large Persistent Slab avalanche on an east aspect above treeline that looks to run between 3/12-3/14.