A mixture of crushing and segregation: The complexity of grainsize in natural granular flows

The interplay between grain crushing and segregation controls the dynamics of dense granular flows that underpin many natural hazards. We address this issue for the first time by developing a simple lattice model with three interacting rulesfor grain crushing, mixing, and segregation. In earthquake faults, particles are trapped, they crush and mix, but do not segregate. In this case the model produces power law distributions, consistent with previous models. When segregation by kinetic sieving is added to the model, we predict depth-dependent lognormal distributions as previously observed, but not explained, in pyroclastic flows, debris flows, rock avalanches, and dry snow avalanches.