Micromechanical analyses of sturzstroms (rock avalanches) on earth and Mars

Sturzstroms are very fast landslides of very large initial volume and extreme run out, which display intensive fragmentation of blocks of rock due to inter-particle collisions within a collisional flow. An investigation of the behaviour and energy budget of such sturzstroms has been carried out using physical, analytical and numerical modelling techniques. Results from centrifuge model experiments, based on a guided experimental rock slide imposed by a dynamic acceleration field, provide strong arguments to allow the micro-mechanics and energy budget of sturzstroms to be described quantitatively by a fractal comminution model. This deterministic comminution model has been incorporated within a numerical distinct element (DEM) code allowing for the computationally efficient simulation of fragmenting rock masses at true scale. This DEM experiment indicates rock mass and boundary conditions, which allow an alternating fragmenting and dilating dispersive regime to evolve, and to be sustained for long enough to replicate the spreading and run out of sturzstroms. The fragmenting spreading model supported here is able to explain the run out of a granular flow, which is free of volatiles, beyond the travel distance predicted by a Coulomb frictional sliding model, without resorting to explanations by mechanics that can only be valid for certain, specific of the boundary conditions. This, and ist strong relation to internal fragmentation, suggests that a sturzstrom constitutes a landslide category of ist own. This study provides a novel framework for the understanding of the physics of such sturzstroms.