Southern San Juan
AvalancheKrista Beyer Chris Bilbrey · Jan 30, 2024 · Southern San Juan
Weather
Warm, clear, and a light breeze along ridges. Temperatures climbed into the low-40s above 11,000 feet following a solid overnight freeze.
Snowpack
A quick pit on a northerly aspect below treeline yielded less than a meter deep snowpack. We found a slightly inverted January slab (1F to 1F-) around 40 cm thick, and sitting above around 40 cm of F hard facets/ depth hoar. Near-surface faceting was around 10 to 12 cm deep and very cohesionless. Traveling on easterly and southerly slopes near and below treeline, boot penetration was easily to the ground. As we moved into the alpine, we dug on an east-southeast-facing slope around 11,800 ft. Height of snow ranged 130-150 cm. This area saw plenty of stronger winds, scouring preceding the MLK weekend storm. Snowfall from that storm has settled into a 20 cm 1F to P hard slab sitting above a thin layer of near-surface facets (1/4 interface about 3 to 5 cm thick) directly above a very stout pencil hard wind layer (likely formed during strong winds at the end of December). The top 10 to 15 cm of the snowpack is accumulated snow from last week, capped by a melt-freeze crust and moist grains. We observed weaknesses at two upper snowpack interfaces - one around 15 cm deep (1/21 interface) and the other around 35 cm deep (1/4 interface). Compression Tests (CT) produced easy progressive collapse failures at the upper interface, and moderate resistant planar failures at the lower interface. Extended Column Tests (ECT) produced a non-propagating failure at the 1/4 interface 35 cm deep after 23 taps - crack propagated half-way across the column before arresting. Pit location was in a deep area of the slope away from protruding rocks. As we moved across the slope the slab thinned and was floating above weaker facets near rock outcroppings where the snowpack was less than a meter deep - highlighting variability in snow depth and associated snow structure.
Avalanche
Lots of recent loose wet activity on solar aspects above treeling. Size ranged from small point releases to D1s locally, but D2 activity could be seen on mountains out towards Lizard Head Pass.