Persistent Slabs
- Alta quota
- Limite del bosco
- Sotto il limite del bosco
- Probabilità
- Likely
- Dimensione
- 2–3
Triggering a 1.5-3' thick persistent slab avalanche is likely on many slopes. Persistent weak layers (sugary facets, surface hoar, or crusts) exist on most aspects and elevations. The weakest facets we've found are on shadier aspects.
Thick slabs are more common as you climb into terrain that's exposed to the wind. Recently wind-loaded slopes with stiffer snow in the top couple of feet of the snowpack are the most likely to produce large avalanches. You're less likely to trigger a large avalanche on lower-elevation slopes and those more sheltered from the wind.
Snowpack cracking and collapsing are clear symptoms of an unstable snowpack. Tilt that collapse onto a steep slope, and you're flirting with an avalanche. Collapses can travel large distances releasing avalanches above you or on nearby steep slopes. Wind-loaded areas feel stiffer under your skis or sled and are more supportable. Don't be fooled, the weak snow beneath the slab still exists (video).
Unfortunately, avoidance is the only way to effectively manage this problem. Skiing or riding steep terrain is a risky roll of the dice. Recent reports of skier-triggered avalanches, abundant cracking and collapsing, and a widespread poor snowpack structure (dense slab + weak layers) are all the reasons I need to continue to travel conservatively.
(12/5/2022) This very large natural avalanche on Eureka Peak near Smiley Creek likely occurred around Dec 2. The heavily wind-loaded slope likely failed on a persistent weak layer that was buried in late November.
