A sudden drop in the snowpack, often with a "whumpfing" sound. An obvious sign of instability.
A collapse or “whumpf” is a sudden drop in the upper snowpack caused by the fracture of a lower snow layer. It is usually accompanied by an audible sound (whumpfing) as air escapes from the collapsing weak layer. On a steep slope, collapses will often result in an avalanche. Low angle slopes may produce shooting cracks after they collapse. If you hear or feel the snowpack collapse under your feet or snowmachine, it is a clear indication that the snowpack is unstable. Some collapses produce a dramatic rumbling noise and you feel the snowpack fall under your feet. Other collapses are quieter and softer. Collapses that propagate into surrounding steeper terrain can result in remotely triggered avalanches. Be wary of your immediate surroundings if you trigger a collapse – if you are in an avalanche runout zone, an avalanche might be coming down from above you.