Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
You will find a fragile base to the snowpack on northerly and easterly aspects from the early seasonal snowfall that accumulated back in October. Storms during the second half of November deposited up to 2 feet of snow on top of these Persistent Weak Layers. Observations from last weekend included natural avalanches, collapses, shooting cracks, and remotely-triggered avalanches. Slopes near and above treeline are the most conerning for human-triggered avalanches as slabs are widespread above known weak layers. Elevations below around 10,500 feet have the same weak layers, but slabs are much less common thus making avalanches less likely. You can manage the problem by avoiding aspects highlighted above, by selecting lower angled terrain without steeps slopes directly above, or carefully assessing terrain at lower elevations for the abscence of a slab.
This persistent slab avalanche was remotely triggered from below on Purple Ridge. 11/26