Dry avalanches are triggered when

• A. Rapid thaw
• B. Stress overcomes strength of weak layer
• C. Weak layer loses strength
• D. Collapse of snowpack

Answer: (B)

Dry avalanches release when the load from overlying snow creates shear stress that exceeds the strength of a weak layer within the snowpack. This failure plane in the weak layer allows the overlying slab to fracture and slide downward, producing the avalanche. The weak layer provides a plane of weakness; when stress from gravity and added loading (new snow, wind slabs) pushes past its bonding, the slab separates. Rapid thaw would favor wet avalanches due to meltwater lubrication, and describing the weak layer losing strength or a vague “collapse” doesn’t capture the actual trigger mechanism as clearly as the stress exceeding the layer’s strength.