Deep Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
Weak snow near the ground exists at all elevations and is deeply buried in most locations. In many areas, weak faceted snow is now bridged by stronger, stiffer layers in the middle of the snowpack. As this problem gets deeper, it becomes harder to trigger and is unlikely to produce obvious red flags like cracking or collapsing. Expect a stubborn, unreactive deep slab in most locations—this is a low-likelihood but high-consequence setup.
The most likely trigger points are thinner areas of the snowpack, especially steep, rocky terrain where weak layers are closer to the surface. A rider may be able to stress the basal weak snow in these shallow spots, and a small trigger could step down or propagate into deeper, thicker parts of the pack, producing a large and destructive avalanche. The best way to manage this problem is to avoid steep, rocky features and other shallow-snow areas where the snowpack is thin and variable.
In the Continental zone, the hazard will remain Considerable, where the snowpack is thinner, weaker, and more easily affected by human triggers.
(1/23/2026)
Large connected natural hard slab avalanche associated with our deep persistent weak layer. Mt Dimond north face
Photo: Gareth Brown