PATTERN-FORMATION IN GRANULAR AVALANCHES

Three new experiments are described which exhibit strong pattern forma tion in the deposits left by successive granular avalanches. At low fl ow rates continuous deposition, erosion or rotation gives rise to inte rmittent avalanche release. Once in motion kinetic sieving of a bi-dis perse granular mixture creates a two-layer shear band in which the lar ger particles overlie the smaller particles. When this is brought abru ptly to rest by the upslope propagation of a shock wave a pair of stri pes is ''frozen'' into the deposited material. Successive releases cre ate a large scale pattern, which strongly reflects the history of the granular flow. At faster deposition, erosion and rotation rates a new flow regime is entered in which intermittency and shock formation ceas es, and the associated patterns change.