Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 2
We have a nasty persistent weak layer (PWL) of faceted grains near the bottom of the snowpack. (There is also another, more spotty, weak layer of facets and/or surface hoar within the upper foot of snow.). This bottom layer of weak, sugary faceted grains are - in many locations - sitting uneasily underneath last weekend's snow and wind...just waiting for a trigger. These are Landmines that are sure to kill you, or darn near close. Take another look at the avalanches above. The mechanics of this structure allow for these avalanches to be triggered remotely (at a distance) and are completely unmanageable. The most likely place to trigger one would be on steep westerly to northerly to easterly facing aspects on wind-loaded terrain of the upper elevations. There's no question that we're all hungry for powder, but you have to ask yourself, What will happen if it slides? Your beacon, helmet or airbag may not be enough.
A couple of excellent observations from yesterday:
McKinley Talty's report from the Park City ridgeline (see snow profile below: easy to see the slab over weak layer structure)
Will Ambler's report from White Pine of LCC; he writes, "Whumph whumph whumph all day as we broke trail off the main white pine road. Some with obvious shooting cracks."
Mark White's tutorial from No Name.