Deep Persistent Slabs
Deep persistent slab problem involve old persistent weak layers, buried deeply in the snowpack. They are difficult to predict because avalanches occur only when the right trigger is applied at the perfect time or place on a slope. As a result, deep persistent slab avalanches are often intermittent. However, if an avalanche is triggered, it is often large and destructive.
A deep persistent slab can be triggered by large forces like a cornice fall or machine, a rapid rise in temperature, or even a person in shallow areas where the weak layer is closer to the surface.
Deep persistent slab problems are unpredictable and difficult to manage. You should make very conservative terrain choices when one is present. Heed the expert advice in the forecast and avoid slopes where it exists. Stay away from big avalanche paths where an avalanche can be extremely dangerous.