Persistent Slabs
- Hochgebirge
- Waldgrenze
- Unterhalb der Waldgrenze
- Wahrscheinlichkeit
- Likely
- Größe
- 3
Many large and dangerous human-triggered avalanches have occurred over the past several days, failing on a layer of faceted snow (a persistent weak layer) that formed during the January/February drought. Avalanches failing on this weak layer are 2-4' deep and well over 100' wide and can easily catch, carry, bury, and kill a human.
My recommendation: is to avoid being on or below slopes steeper than 30 degrees on the north side of the compass for the time being. I have zero confidence in the snowpack right now. A few things to remember when dealing with persistent weak layers:
- Persistent weak layers can be triggered remotely, from a distance, or from below. Look at the avalanche in Millcreek.
- Avalanches can happen on short steep slopes in "what we think is benign terrain." Remember, avalanche terrain is anything over 30° in steepness. Read Lucky Days & Silver Fork.
- This avalanche problem can produce very large avalanches that run long distances. Look at the slide in Mineral Fork.
- Signs of instability may not always be present: you may or may not see or experience shooting cracks or audible collapsing.
- Tracks on the slope offer zero signs of stability. Avalanches can take out multiple existing tracks.
Forecaster Confession: Yesterday, I was wrong. I wrote, " Avalanche professionals and people with years of experience are simply avoiding this type of terrain." By my count, we've had eight very close calls, and in fact, all of these close calls are by people that are either avalanche professionals or very experienced backcountry riders. This tells me that if the avalanche professionals are getting it wrong, we all need to take two steps back, and re-evaluate our decisions.
