Southern San Juan

Avalanche

Chris Bilbrey · Mar 14, 2024 · Southern San Juan

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Weather

Mix of broken and overcast skies with off and on light snowfall (S1) late-morning into early-afternoon. Around 2 PM, snowfall intensity ramped up and increased to S2 to S5 by 4 PM. Moderate easterly winds were moving snow near and above treeline.

Snowpack

Snowfall over the last 24 hours demonstrated decent bonding at the new-old interface (melt-freeze crusts and near-surface facets). We could peel off the new snow while skinning on slopes around 35 degrees with a firm crust below, but none progressed to loose snow sluffs. Around 11,500 feet, storm slab properties changed and we started to see cracking along our skis. We dug snowpits at multiple elevations and found a reactive storm density change in the lower third of the new snow. This interface easily broke in hand pits, and in Compression Tests (CTs) and Extended Column Tests (ECTs) with less than 10 taps. Digging deeper, the March 2 dust-faceted interface seems problematic with additional snow load. This interface was much more reactive than the 2/26 interface - and that dust layer was hardly visible in pit walls. CTs and ECTs produced sudden planar and non-propagating failures at the 3/2 interface around 40 to 50 cm deep with moderate force. With a little pry from the shovel behind the isolated column after completing an ECT, both the storm density change interface and the 3/2 FC interface broke clean across the column. This suggest that with additional snow load, these upper snowpack interfaces will likely become more reactive, and steeper slopes may produce natural activity. Crust on sunny slopes were 2 to 3 inches thick below treeline, getting thinner as we climbed higher - around 1 to 2 inches near treeline. Below said crusts in weak (4F to 1F-) moist grains. Where we could break through the crusts with our boots, we sunk around 8 to 10 inches below the crust.

Avalanche

We saw numerous small, loose snow sluffs that ran in the last 24 hours, and confined to recent storm snow on east to south aspects above treeline. None looked to break deeper than the upper crust, but were traveling long distances.