Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Unlikely
- Size
- 1–2
Your best chance of triggering an avalanche on a buried weak layer will be on slopes where February's snowfall has settled into a cohesive slab above weak facets and surface hoar formed in January. Slopes with snow stiffened by recent winds are prime candidates. Slabs could break 1 to 2 feet deep, or deeper in wind-favored locations. Recent observations have featured buried surface hoar on shaded aspects, propagating pit tests on slopes facing south and east, and isolated collapsing on weak layers.
Use thoughtful terrain selection to lessen the chances (or the potential consequences) of getting surprised. Choose planar slopes, where an accidental slide will not sweep you over a cliff, through trees, or into a ditch. When in doubt, defer to low-angle terrain. Steep roll-overs or slopes that have variable snow depths due to wind scouring and drifting are likely places trigger points.
(2/6/2025)
Propagating pit test results suggest weak layers may be sensitive to human triggering. This extended column test failed on facets formed in January.
Photo: Flathead Avalanche Center