Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
The March 20th interface is now buried 2-3 feet below a stout slab. Active loading of new snow with heavy wind transport will add stress and increase the chance of triggering a large avalanche. This layer is composed of facets/crusts on solar aspects and small preserved facets on northerly aspects protected by the sun. The sensitivity and distribution of this layer is hard to gauge due to the varying slab depths, recent temperature fluctuations, and differing characteristics across slope aspects. Remote triggering could occur from gentler slopes above, below, or adjacent to steep slopes. Wind loaded terrain will have the highest likelihood of finding reactivity. Long story short: persistent slab avalanches are unpredictable, so careful snowpack evaluation is required.
In areas with a weaker snowpack, such as the southern portion of the Wyoming Range, deeper weak layers still remain a concern. Triggering a wind slab or persistent slab on the March 20th interface could step down to these layers resulting in a large to very large avalanche.
(3/28/2023)
The third rider near or on slope triggered 1' thick soft slab from the diagonal track on the right. The slab slid on a slick crust with small facets on it that was buried March 20.
Photo: Frank Carus