Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
A 3 to 5-foot-thick cohesive slab overlies two buried surface hoar layers. Slab depths are increasing during this current storm. One surface hoar layer got buried at the end of January (1/28) and the other in mid-February around Valentine’s Day (2/14). The slab above has stiffened and settled due to wind, warmer temperatures, and natural settlement.
As the slab has strengthened, the likelihood of human-triggered or natural avalanches has decreased. Yet, uncertainty inherently exists around persistent weak layers, and these layers are being tested with the current rapid loading. Large to very large destructive avalanche potential and inherent consequences remain significant if one of these persistent weak layers is woken up and an avalanche occurs.
(3/9/2026)
Large surface hoar up to 8mm in size is visible to the naked eye at the January 28th interface. This layer is found 3 to 5 feet below the surface and was exposed here after the overlying slab failed and slid downslope during a propagation saw test
Photo: Jackson George