Southern San Juan
AvalancheChris Bilbrey · Jan 12, 2024 · Southern San Juan
Weather
COLD day in the mountains. Ferocious west-northwest wind prevented any sort of warmup. The wind also contributed to lots of snow transport at upper elevations and open/ exposed areas below treeline. Broken to overcast skies with an occasional light snow shower in the afternoon.
Snowpack
Prior to snowfall this month, our best guess is about 50 to 70 cm of snow existed in this area. The lower portion of the snowpack consist of faceted grains of varying size and hardness. There is a somewhat intact lower old-snow slab that sits above weaker basal facets and depth hoar. We did not observe snowpack tests failing at the ground, but larger slides could gouge into these lower layers in the right terrain/ scenario. By far the most concerning weak layer sits directly below January snowfall (4F- near-surface facets, 10 to 15 cm thick). Extended Column Test (ECT) produced propagating failures with 11 taps on a west-facing slope, and with 16 and 18 taps on a southeast-facing slope. Where it took more taps to produce a failure, the overlying slab was wind-stiffened and deeper. Propagation Saw Test (PST) produced a crack to the end of the column after cutting between 15 and 20 cm through the weak layer below a 100 cm column. These cut lengths did not vary based on overlying slab hardness or depth. Despite the stiff over soft snowpack, we did not experience cracking or collapsing in wind-sheltered areas below treeline. Once we got into near treeline elevations, the Gremlin's were vocal and almost any wind-drifted terrain feature we walked above produced rumbling collapses and shooting cracks. Easterly-facing terrain looked phat and spooky from ongoing wind loading.
Avalanche
We remotely triggered several avalanches on east and southeast-facing slopes while walking along the ridgeline above. We triggered them from around 50 to 100 feet away, and each one was accompanied by a loud, rumbling collapse with long shooting cracks. All the slides were size 1-1.5, but terrain constraints limited their size potential. A similar moment in bigger terrain would likely have produced an avalanche reaching size 2.