What is the most important bond/boundary in snow stability?

• A. Bond Between New Snow and Old Snow
• B. Bond Between Snow and Air
• C. Bond Between Grains
• D. Bond Between Slab and Bed Surface

Answer: (D)

When thinking about snow stability, the key factor is where the snowpack is most likely to fail under load. In a slab avalanche, a large, cohesive block (the slab) sits on a weaker layer (the bed). The critical boundary is the interface between the slab and the bed surface because that is where shear failure will occur as the weight of the snow above adds stress. If the bond at this slab–bed boundary is weak, the slab can shear off along that plane even if the bonds within the slab or at the snow’s surface are relatively strong. The strength of this base layer essentially governs whether the slab will stay put or slide. The other bonds—between new and old snow, between snow and air, or among grains—affect how weak a layer forms or how the surface behaves, but the actual stability of a slab avalanche hinges on the slab–bed boundary.