Prediction of the areas threatened by landslides and gravity-driven mass flows are a key part of hazard assessment in mountainous regions. Whatever the material transported (debris, snow, etc.), the granular flow process involves determining the initiation mechanisms, initial volume, physical transport, entrainment processes as well as deposition and phase-separation mechanisms. Because of the number of scientific disciplines needed to solve it, there is a substantial benefit from interdisciplinary research. Furthermore, the definition of a unified rheology that accounts for the different regimes characterizing granular-fluid mixture flows is still lacking. The co-existence of the
collisional regime and the dense regime that have a very different behavior, makes the definition of a proper rheology quite challenging. So is the transition from dilute to dense regimes in granular-fluid
mixture flows.

This session aims to bring together new research results from a variety of different approaches to understanding these kinds of processes. In particular, we encourage presentations on physical modelling, innovative laboratory research, theoretical studies on the physics of multiphase and multiscale phenomena and detailed field observations, which yield insight into the triggering mechanisms, the mass movement or mass flow process. Another important aspect, still unclear, that will be addressed in the session, is the mechanism and consequence of grain sorting and particle-fluid separation, entrainment and deposition in debris and hyperconcentrated flows. A proper description of the granular-fluid mixture flow phenomena is fundamental in order to properly define the design criteria of the protection structures and to have reliable risk maps. So, contributions related to the numerical modelling of landslides and granular geophysical flows, including torrential sediment transport, debris flows, rock and snow avalanches, and similar flows are expected.

Selected contributions will be considered for a special issue of a relevant international journal.