Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–2.5
Old, hard slabs 1.5 to 3+ feet thick overlie buried weak layers but are typically difficult to trigger, and may be reactive in a few shallow areas. Without obvious warning signs, avalanches are most likely triggered where the slab is thinner and easier to impact the weak layer below. The most fragile layers are buried in the middle and lower portions of the snowpack on northerly aspects. Persistent slab avalanches are dangerous in size; they can propagate widely and be remotely triggered from adjacent low-angle terrain. The most reliable way to manage this problem is to choose conservative slope angles or travel on southerly aspects, where the snowpack structure has become stronger and more spring-like. On northerly aspects, avoid steep terrain with a thin or variable snowpack, such as rocky areas, rollovers, or places where winds have created uneven slab thickness.
A destructive persistent slab that ran naturally around March 6th above Conundrum Creek. This is north of Pearl Pass, outside the Southeast Mountains forecast boundary, but in an area with a similar snowpack.
Credit: CAIC