The growth of grain avalanches

We bring out the salient characteristics displayed by grain avalanches in laboratory experiments. We devise then elementary mechanisms accounting for these main features and we derive a modeling capable of capturing the nonlocal processes relevant to the avalanche expansion. The growth patterns that we obtain closely fit experimental data. Moreover, we succeed in recovering the two distinct growth mechanisms encountered in experiments, and we evidence that the transition between the different regimes originates in a singularity in the dependence of the rear front velocity as a function of the slope