What is the top fracture surface of a slab avalanche called?

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

Answer: (D)

The top fracture surface of a slab avalanche is called the crown. In a slab avalanche, a cohesive block of snow sits on a weaker layer. When it fails, the crack that forms at the upper boundary—where the slab separates from what’s beneath—creates the crown. You can picture it as the visible crack running along the slope’s upper edge, marking where the release began. The bottom surface, where the slab rests on the ground or the weaker layer, is the bed surface; debris refers to the snow that ends up in the runout; and flanks are the sides of the avalanche path. That crown terminology is why this option is correct.