Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
Triggering a large, dense slab avalanche is becoming less likely but remains possible. Avalanches are easier to trigger in thin spots at the edges of slabs and wind-features. Watch for these proverbial land mines on the northern half of the compass, where the wind frequently blows, and the snowpack depth is variable. This zone has a lot of rocky alpine terrain that perfectly fits that description. Some visual clues to identify suspect slopes:
- Stiff or textured surfaces and wind-pillows, evidence the wind has moved snow
- Rocks sticking out of the snow, either near or well below ridgelines
- Terrain where some part of the slope is at least 35 degrees in steepness
If you do trigger an avalanche, you probably won't observe obvious signs of instability like snowpack collapsing or cracking beforehand. Any triggered avalanches have the potential to break above you.
Additional Discussion: You may encounter small, easy-to-trigger, wind slabs at middle and upper elevations, particularly in alpine terrain. Be on the lookout for wind-loaded features near ridgelines and along the sides of cross-loaded gullies. Shooting cracks are a clear indication of wind-transported snow.
(1/7/2025) This is the type of terrain we're talking about when we say "rocky, wind-swept slopes with variable snowpack depths." Note how the avalanche crown "connects the dots" between exposed and buried rocks.
Washington basin - White Clouds Mtns - NW, 9,600-10,200'.
Photo: Sawtooth Avalanche Center