Southern San Juan

Avalanche

Chris Bilbrey · Jan 24, 2023 · Southern San Juan

Weather

Chilly day with moments of sun and scattered clouds. Winds were strongest during the morning relaxing in the afternoon, but light snow transport was visible along ridgetops.

Snowpack

New snow depths ranged from 30 cm around 9,000 feet, around 40 cm about 10,000 feet, and 65 to 70 cm near the treeline. East-northeast winds during the storm drifted the snow into deeper drifts on atypical slopes. The snow surface looked textured and pressed on east and northeast-facing slopes in the alpine, but slopes that face southeast through south to northwest looked phat and loaded. In general, the new snow was F to 4F (top to bottom) but we encounter soft slabs of 8 to 12 inches thick as we moved up in elevation or traveled in open areas prone to drifting below the treeline. We noticed cracking along the skin track but no outward shooting cracks or audible collapses. Compression Tests produced mostly Q2 failures (sudden collapse, progressive collapse, or break) at the new/ old snow interface in snowpits on a northeast, east, and southwest aspect. The most notable test result was a CT14 SC in faceted, decomposing fragments below a 1 cm crust on a southwest-facing slope, and CT18 SC in a near-surface facet layer (4F-) on an east-facing slope. Probing across aspects to assess the depth of persistent weak layers, specifically the 11/29 FC drought layer, depths were generally deeper than about 2 meters. These weaker grains rest below a stout holiday slab that felt 1F to P- with our probe (but we did not physically dig down to this harder layer).

Avalanche

Looks like most of the east-facing avalanche paths off Star Peak ran sometime during the last two storms. There is evidence of fresher debris piles in gullies and shallow crowns visible in steeper northeast-facing slopes near the treeline. However, the most recent snowfall made it difficult to rate avalanche size and relativity to the path.