Self-Lubrication for Long Runout Landslides

This paper, by simple model studies, demonstrates that the low friction observed for long runout landslides can be explained in terms of simple particle dynamics, without the intervention of extraneous devices such as air-layers. The proposed mechanism assumes that the bulk of material rides on a thin layer of highly agitated particles at low concentration. By employing the technique of two-dimensional particle dynamic computer simulation, I demonstrate that (1) this is the state to which a granular material tends when sliding down an inclined plane and (2) it is sufficient to explain the friction reduction. Finally, I present a simple mathematical model that yields order of magnitude predictions of runout distance. The argument suggests that there may be nothing particularly special about long runout landslides (except, perhaps, in the way they are initiated) and that they behave as would be expected given the current state of knowledge of particle flows.