Slab failure is synonymous with the initiation of a slab avalanche. For a slab avalanche to start, there must be:
- A cohesive, relatively strong layer of snow (the slab) overlying a weak layer, or a weak bond between layers.
- A closely balanced stress-strength relationship between the weak layer and the overlying slab.
- A trigger that upsets this balance, initiating a failure in shear at the weak layer, followed by a tensile failure that fractures the slab along the upper extent of the shear failure.
- A slab that is sufficiently stiff for the initial failure to travel, or 'propagate'.