Deep Persistent Slabs
- Hochgebirge
- Waldgrenze
- Unterhalb der Waldgrenze
- Wahrscheinlichkeit
- Possible
- Größe
- 2
Human-triggered avalanches that fail on weak snow (facets) buried about 2ft deep in sheltered areas and much deeper where wind drifted snow exists above it (up to 8 ft) remain possible today. These avalanches would be large (D2-D3). They could have severe consequences including trauma from collisions with trees or terrain features. They could propagate farther than expected and break above or behind the person who triggers them. In some places, these persistent slab avalanches may become easier to trigger as the recent snow consolidates into more of a slab layer above the persistent weak layer.
Near and below treeline NW-N-NE-E facing slopes represent the most likely places to find this problem. However, observers have found it in a few isolated areas in more exposed upper elevation terrain. Predicting exactly which slopes these persistent slab avalanches will occur on is impossible. Some slopes may have numerous tracks on them and not release, others may release with the first person on the slope, and others may release after several people have already used the slope.
Recent avalanches, cracking, snowpack collapse or whumfing, or unstable snowpit test results, can indicate a persistent slab problem, but in many cases, triggering a persistent slab avalanche is the first sign of instability. If you have any uncertainty about whether or not this layer exists on a slope, it is best to just avoid it and pick something else.
Due to the uncertainty and severe consequeces associated with persistent slabs we still recommend avoidance by choosing lower angle terrain (maximum slope angles less than 30 degrees) without steeper terrain above or to the side. Low angle due N facing slopes still hold soft snow that provides excellent skiing, snowmobiling, and snowboarding experiences.
See the photos below for some of the recent avalanches triggered on this layer.
