Wet avalanches are triggered when

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

Answer: (B)

Wet avalanches happen when the snow becomes wet enough that the bonds in a weak layer weaken and fail. Water entering the weak layer reduces friction and cohesion, so the layer can no longer support the weight above it. Once that strength is lost, gravity can drive a flow, producing a wet avalanche. Rapid thaw or rain contribute to this wetness, but the decisive factor is the weak layer losing strength due to water. The idea that a stress threshold is exceeded describes dry-snow slab triggering, not the wet-snow situation, and a vague “collapse of the snowpack” doesn’t pinpoint the key process of moisture-induced strength loss.