Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 3
The Valentine's Day storm has built a dense, cohesive slab on top of our weak, underlying snowpack. On northerly aspects, the entire snowpack is faceted through with varying degrees of hardness, but a layer of fist hard facets exist directly beneath the slab. Outward signs of instability such as collapsing and whumphing have decreased significantly but they are still being observed, and stability tests remain reactive. The bottom line is that human triggered avalanches up to 2 feet deep or more, failing on this weak layer remain possible to likely. The danger is most prevalent on northerly aspects near treeline but don't think you can outsmart it by changing elevation. For the foreseeable future, I'll be avoiding all slopes steeper than 30 degrees on all northerly aspects.
As you wrap around to west, the problem still exists and it's a fine line between shady and sunny. Many westerly aspects still present as northerly if there are trees to provide shade. West facing slopes slopes should also be considered guilty until proven innocent, and a slope by slope analysis is required.
Last weekend, a reactive layer of facets was also observed on a south facing slope. In my travels this week I have not found this problem to be widespread although facet crust combinations do exist with very weak snow near the ground.. If you approach a steep slope that has good coverage, it's worth digging down to have a look at the structure. If you can find a slab on top of facets you should reconsider your objective.
The bottom line is that our snowpack this season is tenuous and weak, and it still remains quite immature. This is the season to dial it back.
Photo illustrates weak, faceted layer underneath the most recent snow.
An extended column test produced results of ECTP17.