Deep Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Unlikely
- Size
- 1
Triggering a persistent slab avalanche has become unlikely in most areas. While this weak layer may still exist on some NW-N-NE aspects and maybe some E aspects in near and below treeline terrain, observations indicate that it seems to be gaining strength. In areas where it was wet it is slowly refreezing and in other areas where it remained dry, it is slowly adjusting to the current load above it. Just because persistent slabs have become unlikely in most areas does not mean that triggering a persistent slab avalanche is impossible. Unstable persistent slabs that the additional weight of a person could trigger could still exist on some isolated terrain features. Open slopes sheltered from this winter's NE winds represent the best places to find lingering instability. More complex terrain like sheltered, shady couloirs, steep rocky slopes, or slopes with steep convex roll-overs where the persistent weak layer remains weak could also be suspect.
Tools like quick snowpit tests, handpits, and probing can help identify those isolated areas where the persistent weak layer may still exist. Avoiding those isolated areas where instability may linger and slopes connected to those areas still remains a prudent choice. If one of these isolated areas were to release, it could release above the person who triggers it and it may not release until that trigger fully commits to the slope. This weak layer is more likely to exist in the mid to lower part of a slope and so evaluating the slope from the traditional start zone at the top of a slope may not provide a meaningful or accurate assessment.