Persistent Slabs
- Hochgebirge
- Waldgrenze
- Unterhalb der Waldgrenze
- Wahrscheinlichkeit
- Possible
- Größe
- 1.5–2.5
Although triggering an avalanche involving these layers has become less likely, it can still occur, especially above 8000 feet in terrain that is connected to very steep (>35°) slopes. You're most likely to trigger a large hard slab avalanche 2-4 feet deep on the north half of the compass - where snowpack depth is variable. These avalanches are easiest to trigger in spots where the snowpack is thin. Signs of a thin snowpack include wind-scoured snow near ridges, cliff bands, and rocks sticking out of the snow. Signs of instability, such as snowpack collapsing and cracking, probably won't be present before triggering one of these avalanches.
Larger triggers in the form of groups, snowmobiles, or falling cornices will increase the odds of impacting these weak layers. Snowpack evaluation and safe travel practices remain the best methods to avoid triggering an avalanche involving the old snow layers.
(1/16/2025)
An example of a steeper, wind-affected slope where trigger points for a hard slab avalanche could be close to the surface.
Photo: Bridger-Teton Avalanche Center