Southern San Juan
AvalancheChris Bilbrey · Apr 9, 2024 · Southern San Juan
Weather
Warm, sunny day. Only a light breeze at upper elevations. Cumulus clouds started building around midday offering a brief reprise from direct sunshine.
Snowpack
Extensive surface wetting below treeline. Despite this, the refrozen layer below the last storm snow (approx. 4 to 6 inches) was still stout and supportive to foot travel. This frozen mass was on average 4 to 6 inches thick. Digging on an east-northeast aspect around 11,000 feet, we found moist grains down 150 cm (we did not investigate deeper and total snow depth at this snowpit location averaged 230 to 240 cm. The deeper we dug, the harder and more uniform the snowpack structure was. We identified three weaker, refrozen melt-form layers in the top 60 to 80 cm from the surface. The upper two layers were 1F- hardness, while the lower one (third) was closer to 1F. The middle of the three is the most concerning, and surrounds the dust layer from early-March. This layer produced sudden collapse failures in Compression Tests with 21 taps, and propagating failure in Extended Column Tests with 22 taps. After the ECT, the lower layer failed and a crack propagated across the column with a shovel pry. The upper of the three layers only failed in CTs and not in ECTs. As we moved higher in elevation, the wetting front decreased to about half the depth of the last storm snow, with drier snow below and above the old, refrozen surface. This front decreased further to only an inch on east to south aspects above treeline. Descending a south-facing slope around 1:30 PM, we found a mixture of corn snow on the surface, with sticky moistening snow below. This made for tricky ski conditions. Once we descended through near treeline and into below treeline elevations, we were able to provoke small wet snow sluffs and set into motion big rollerballs. These were still slow moving but definitely gaining more mass while traveling downhill. We did not encounter trap-door conditions at point in our travels.
Avalanche
Two notable Loose Wet avalanches spotted on our travels (east and west-facing slopes). Lots of smaller slides and rollerballs on southeast and south aspects.