Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
Triggering a 1-3 foot thick slab avalanche on a buried weak layer remains possible. Three rider-triggered slides occurred on this layer in the Whitefish Range over the past few days.
The conditions for a Persistent Slab avalanche are not present on all slopes, and it's challenging to determine where they are or aren't. The safest bet is to assume that the troublesome slab/weak-layer/crust combination exists on all slopes. You may or may not experience obvious signs of instability—snowpack collapsing or cracks shooting out from your skis or sled—before triggering an avalanche. The resulting slides may propagate farther than expected, triggering a large avalanche.
Friday's avalanche was triggered remotely from the side of a steep slope. This could also occur from lower-angle terrain above or below a steep slope.
Reduce your chances of triggering one of these beasts by selecting low-angle slopes not connected to steeper terrain.
(1/10/2026)
This crown of this large skier-triggered avalanche was at least 250' wide and 2' deep. These side by side images show the crown from the same point looking in opposite directions. The crown continued out of view in both images, wrapping multiple terrain features and aspects.
Photo: Mark Dundas