Debris cones, or molards, occur on the deposits of rockslide avalanches. They are a few metres high, conical in shape, and contain material finer than the surrounding debris. Previously proposed formation mechanisms of molards were tested against field evidence from the Frank slide and are found to be unsatisfactory.
Laboratory experiments indicate that when a mass of cohesion-less soil is vibrated, particle formed. Molards, therefore, may form by vibration of the ground under rockslide avalanches. This formation mechanism may bear on the problem of rockslide-avalanche mobility.