Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
Triggering an avalanche on weak layers buried 2-3 feet deep is possible on very steep slopes over 35° in the upper elevations. Signs of instability such as cracking, collapsing, or recent avalanches may not be present before triggering a large, dangerous avalanche. These avalanches are capable of propagating widely across or up a slope. Multiple tracks on a slope do not indicate stability with this problem type. Large triggers such as cornice falls and groups increase the odds of impacting buried weak layers. Little warning has accompanied these avalanches prior to triggering other than visual signs of wind affected snow.
On Sunday, a large avalanche was triggered by a snowmobiler on Mount Leidy. This avalanche likely involved persistent weak layers and is evidence that riders still have the potential to impact these layers.
(2/27/2025)
Steep, rocky, and wind affected terrain above 10,000’ near Togwotee Pass. The boundary between wind scoured and wind loaded features are the most likely places to trigger a persistent slab avalanche.
Photo: Bridger-Teton Avalanche Center