Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 3
A slab of cohesive snow now exists above a persistent weak layer of faceted snow on all aspects and elevations. Collapsing and whumphing continue to be widespread. This red flag sign of instability demonstrates how easily the slab fails under a person's weight. On northerly facing slopes, thick hard slabs of wind-drifted snow rest on top of this weak layer, and they are hanging in the balance just waiting for a trigger. Once triggered, these avalanches will break deep and wide, and will be un-survivable. On southerly aspects stabilty tests also demonstrate slab failure with propagation. These avalanches are more stubborn to trigger, and won't be quite as large, but make no mistake, they are not to be trifled with. Avoidance of slopes steeper than 30 degrees is the only safe strategy right now.
The video below illustrates unstable conditions with a slab failing on a weak layer on a SE aspect. An extended column test produced results of ECTP23.