Pattern formation in granular avalanches

Three new experiments are described which exhibit strong pattern formation in the deposits left by successive granular avalanches. At low flow rates continuous deposition, erosion or rotation gives rise to intermittent avalanche release. Once in motion kinetic sieving of a bi-disperse granular mixture creates a two-layer shear band in which the larger particles overlie the smaller particles. When this is brought abruptly to rest by the upslope propagation of a shock wave a pair of stripes is "frozen" into the deposited material. Successive releases create 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 ceases, and the associated patterns change.