Modelling avalanche flows

We present a lattice model that illustrates avalanche flow ina driven, disordered system. Structural disorder is associatedwith rectangular grains that have orientational degrees of freedom.Grain orientation transitions couple the evolving disorder withsurface instabilities. The simulated event size distributionhas features in common with observed surface granular flow and,in contrast to previous sandpile models, does not have a simplescaling behaviour. We have identified properties of the sandpilesurface that correlate with the internal structural disorder.The simulation results support a model of granular dynamicsin which surface flow and granular relaxation processes arestrongly coupled.