Southern San Juan

Avalanche

Chris Bilbrey · Feb 1, 2024 · Southern San Juan

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Weather

Mild, humid day in the mountains. Mostly a grey, overcast day with short-lived snow showers. Snowfall didn't amount to measurable accumulations. Light southerly wind.

Snowpack

A stout, robust crust exists on sunny slopes. This was more breakable on east and southeast aspects above treeline. Boot penetration ranged 4 to 6 inches, and said crust was around an inch thick. Probing across slopes, we felt a weaker faceted crust around 30 to 40 cm deep, and this will be a concerning layer once slabs build on top. Northerly slopes saw the least affects from the recent warm-up, and surfaces remain soft. More recent snowfall quickly settled under the current weather regime and ski penetration was generally 4 inches. This surface layer houses small, near-surface facets. Probing on northerly alpine slopes, the upper snowpack is defined by harder layering void of discernable weak snow layers in the top 2 to 3 feet. We could feel a weaker interface below (likely the 1/4 interface), but it seems to need a big load to awaken. Digging on a north-northwest aspect near treeline, we identified a couple of persistent weak layers in the top 30 cm, and the 1/4 interface was around 65 cm deep. The upper part of the 1/4 interface was 1F and about 10 cm thick, but a 10 cm thick layer of 1F- facets lurk below. The portion of the slab above the PWL of concern is generally P-. Only ECTXs at the 1/4 interface. The most notable tests result occurred in an Extended Column Test after 22 taps. A crack propagated half-way across the column before arresting. This occurred in a 3 to 5 cm layer of 4F hard near-surface facets buried around January 10. There's also a shallower near-surface faceted layer buried around January 21 that produced progressive collapse failures with moderate force.

Avalanche

Saw numerous older Loose Wet avalanches from the January 28 warm-up/ cycle, and a few older Persistent Slab avalanches that ran at the end of the big January storm cycle.