Which term describes the lower fracture of a slab where snow slides up and over a slab that didn’t fracture?

• A. Crown
• B. Bed surface
• C. Staunchwall
• D. Debris

Answer: (C)

When a slab avalanche releases, there are two fracture boundaries: the top edge where the slab separates from the overlying snow (the crown), and a lower boundary where the moving slab sits on a layer that didn’t fracture. The boundary described—where snow slides up and over a slab that remains intact beneath—is called the staunchwall. It marks the lower fracture plane of the moving slab as it shears over the unchanged slab. The other terms don’t fit that specific boundary: the crown is the top crack, the bed surface is the interface at the bottom of the overall snowpack, and debris is simply the accumulated material left after the avalanche.