Southern San Juan
AvalancheChris Bilbrey · Mar 13, 2024 · Southern San Juan
Weather
Overcast and obscured skies with periods of squally snow showers. One minute it was S2 to S5, then the next, brief pokes of sun and broken skies. Wash and repeat. Moderate southerly wind along ridgelines, and light to moderate drifting.
Snowpack
New low-density snow was bonding well to various old snow layers below treeline. The old, crusted snow surface on east and southeast aspects below treeline was trap-door conditions with weak, re-frozen grains below. When stepping out of our skis, we easily punched through to our knees. This structure will be something to monitor with the new snow load in the coming days. In drifted areas at upper elevations, the new snow easily broke in shallow soft slabs with ski pressure on steeper parts of the slope. Digging on a north aspect around 11,800 feet, we found the 2/26 dust layer sitting above 1F- faceted grains around 50 cm deep. This layer was unreactive in Compression Tests (CTs). Above that, is two softer near-surface facet layers (0.5-1 mm and 4F) surrounding the 3/2 dust layer. CTs produced break failures with moderate force in these two shallower interfaces, and they seem suspect to support much of a new snow load. Despite no results in CTs at the faceted grains below the 2/26 dust, finding the shallow part of the slope where either these grains are weaker or the overlying slab is thinner is still a looming threat. No cracking or collapsing across multiple aspects/ elevation bands outside of where we triggered the larger avalanche.
Avalanche
Triggered two separate avalanches today. One broke in the new snow while walking out above a steep, drifted area (around 38 to 40 degrees) from a flat area/ slope apex. The second broke while descending around a rock outcropping (around 35 degrees) on an adjacent part of the slope. This slide was not confined to the new-drifted snow. It failed in faceted grains (1F- hardness) around 45 to 60 cm deep sitting below the February 26 dust layer. The slide initially broke at my skis and was confined to the narrow area between two rock outcroppings - one on my left and right. It then propagated wider once moving downhill and traveled over 900 feet into the flat bench below. This slide occurred on the same aspect, and adjacent to the slope where we dug a snowpit. There, we observed no results in snowpack tests in the same faceted grains below the dust.