Southern San Juan

Avalanche

Chris Bilbrey · Jan 17, 2024 · Southern San Juan

Weather

Skies quickly transitioned from overcast to obscured. Light snowfall started around 8:30 AM. By 10:30, S2 snowfall continued throughout our tour, but only amounted to around an inch. Moderate westerly winds with an occasional stronger gust. Efficient snow transport near and above treeline.

Snowpack

We dug two snow profiles BTL. One on a due north aspect (10,800 feet) and the other on a north-northwest aspect (11,300 feet). Height of snow at both locations was greater than a meter deep. Settled depth of the January slab above the New Year facets is between 60 to 70 cm. The lower portion of the January slab ranged 1F to P hardness. There is a thin, 4F hardness near-surface facet layer that likely developed during a one to two day break in the storm action (probably around January 8). These grains are small but angular. We observed easy force, progressive collapse failures in Compression tests (CT) at storm layer changes close to the surface. We observed non-propagating results in Extended Column Tests (ECT) and CT sudden collapse failures at the January 8 NSF interface. ECTs did not produce failures at the NY FC interface, but CTs produced break failures in our north snowpit, and resistant planar failures in our north-northwest snowpit. We only observed cracking in the snow on steep, micro-drifted terrain features. We observed one loud collapse below treeline once we climbed above 11,000 feet. Probing on slopes above 11,000 feet, the PWL of concern below was softer and had more of a trap door feel. Despite a hardening upper slab, we still punched through into weaker snow below when stepping off our boards.

Avalanche

Debris from the Mine Shaft avalanche path is the first to hit the road grade this season. It left around 8 feet of debris and small trees on the road. Debris flow also crossed the road grade and hit the creek bottom.