Northern San Juan
AvalancheChris Bilbrey · Mar 5, 2024 · Northern San Juan
Weather
Mix of overcast and broken skies. Moderate winds and gusts in the 20s to 30s MPH contributed to light drifting, mainly above treeline. Temperatures felt normal for early-March.
Snowpack
We dug on easterly and northerly aspects near treeline. At present, weak layers of concern reside in the top 30 to 70 cm below the surface. Deeper weak snow layers (February and January interfaces) still linger below, but likely need a multi-day storm event or major spring melt to awaken. The most exciting tests results occurred on an east-southeast aspect NTL where facets surround multiple melt-freeze crust. Compression Tests (CTs) produced sudden planar failures with 15 taps down approx. 70 cm in facets (1F-) above a crust. In the same pit, Extended Column Tests (ECTs) propagated with 18 taps down approx. 35 cm in facets (4F) below a crust. Both crusts were 1 to 1.5 inches thick. It seems that while the crusts are frozen an intact, they are holding the snowpack together. Snowpack tests in our north-northwest pit, at almost the same elevation, had less excitement and demonstrated more friction between the slab and faceted grains. CTs produced resistant planar failures with 21/ 22 taps down approx. 35 cm in a thin layer of facets (1F-) below a P hard wind layer. ECTs produced non-propagating results at the same interface with the crack stopping halfway across the column. A shovel pry behind the column helped the crack to expand across the column. South, southwest, and west alpine slopes look worked over from recent winds and the sun. Probing on alpine slopes yielded generally harder layers and softer storm layers mixed within. Alpine snow surfaces are a mixed bag of soft, wind-pressed areas, hard and sometimes breakable wind-board, or slick crusted surfaces. Upper snowpack layers BTL felt fairly homogenous when probing, and void of discernable weak layers.
Avalanche
We observed one, loud rumbling collapse while traveling uphill across a wind-drifted, dish-shaped terrain features around 12,200 feet. This occurred on a north-facing part of the slope that gets heavily cross-loaded. Only minor surface cracking and our skis when the collapse occurred. We descended the slope adjacent to the collapse and returned up the same skin track a second time without another collapse.