Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
Slabs 1 to 2 feet thick sit above buried weak layers of surface hoar, faceted snow, and hard crusts. Light but steady snowfall over the last two weeks has gradually overloaded these weaknesses, creating a concerning snowpack structure. The character and distribution of these weak snow layers varies between our northern and southern areas, and subtle differences even exist within the same mountain ranges. The differences reflect variations in rain–snow elevations, storm totals, aspect, and periods of warm, sunny weather.
Knowing exactly what load is needed to break the camels back is challenging to pinpoint, but a practical benchmark is new snow amounts. Slopes where you find around 6 inches or more of new snow, it's time to reassess your plan and give avalanche terrain a wider margin. The current structure is particularly problematic because the main evidence of instability we’ve observed is ongoing propagating failures in tests, while obvious warning signs like recent avalanches, cracking, or collapsing have been less frequent. Travel with a conservative mindset and favor slopes around 30 degrees without steeper hazards above.
(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