Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2
Snowfall during February is incrementally stressing buried weak layers that developed during the January dry spell. The character and distribution of these weak layers vary between our Northern and Southern Mountains, and subtle differences even exist within the same range. The differences reflect variations in rain-snow elevations, storm totals, aspect, and periods of warm, sunny weather. With each passing storm, the overlying slabs have gained thickness and cohesion, steadily increasing the likelihood for both human triggering and naturally occurring avalanches. After two weeks, these layers now lurk between 1 and 3 feet below the surface. Whether or not avalanches span adjacent terrain features, the depth of weak layers will likely result in larger, more dangerous avalanches if provoked.
The best way to navigate this problem is to favor southerly-facing slopes and those that are about 30 degrees without steeper hazards directly above. Mild weather in early February wetted and softened upper snowpack layers then later refroze into thicker crust layers on southerly aspects making it more difficult to impact weaker layers below. On west through north to east-facing slopes where these problematic layers are still intact, the threat is elevated. The current structure is particularly problematic because the main evidence of instability we’ve observed is lingering propagating failures in tests, but other warning signs like recent avalanches, cracking, or collapsing have been less frequent.
(2/13/2026)
Multiple weak interfaces exist in the upper snowpack (35 to 40 cm deep) to fall apart with additional snow load. The lower one is a mix of faceted grains and decomposing surface hoar resting on a slick rain crust. The upper two layers are weaker layers where the surface slab is faceting. This pit was dug on an east aspect around 5,900 feet. Selkirk Mountains. February 13, 2026.
Photo: Chris Bilbrey
