The Avalanching of Granular Solids on Dune and Similar Slopes

Avalanching occurs on slopes underlain by loose granular solids, for example, the slip faces of dunes and deltas and mountain screes, in response to a particle deposition-rate gradient which steepens these slopes to states of instability. The frequency, size, and behavior of the avalanches thus released are shown theoretically to depend on the particle deposition-rate gradient, the particle concentration at the time of deposition, the particle size and density, and the avalanching medium. Experiments made under simplified conditions using natural sands, glass beads, and natural grains provide satisfactory confirmation of major features of the theory, though some unexplored problems remain. The results are significant for the interpretation of certain kinds of sedimentary structure and landscape form and, insofar as data are available, prove consistent with the properties of avalanches observed from experimental sand dunes and mountain screes.