Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2
A persistent weak layer of faceted snow that formed during the December dry spell is our primary avalanche concern. This layer can be found about a foot below the surface on slopes facing W-N-E-SE. Near and above treeline, slabs of wind drifted snow have formed over top of this weak layer and this is where you are most likely to find trouble. Above treeline, however, northerly winds have created an erratic distribution of over-riding slabs, stripping and eroding snow off of many north and east aspects that are usually loaded. Cross-loading, however, is still a factor. This means you can be traveling through terrain that looks scoured and benign, and then suddenly find yourself on top of a hard slab with facets underneath. Suspect this scenario when the texture changes from rough and thin, to smooth, hard, and fat. Be alert to likely deposition zones such as gullies, depressions, and the leeward sides of terrain features. In these same areas, an outside chance lingers for avalanches to fail on weak facets near the ground. Avoiding extreme, rocky, slopes with a thin snowpack is the best way to mitigate this problem.
The snowpit below illiustrates the location of our current weak layers:
In our travels on Friday, Dave and I investigated a SE aspect at 11,600' where we continued to find the December drought layer as well as facets at the base of the snowpack. Stability tests produced no results but the adage that "structure trumps test results" keeps me leary of this kind of terrain. See the snowpit below.