Insights on the role of fine particles on the mobility of geophysical flows from large-scale experiments

Geophysical flows, such as debris flows, debris avalanches, pyroclastic density currents, etc., represent one of the main sources of natural hazards. Some of these can be classified as dry granular flows, i.e., gravity-driven mixtures of discrete grains that are prevalent in a wide range of volcanological scenarios (e.g. pyroclastic density currents, block and ash flows, debris avalanches, etc.). These flows are characterized by a high degree of polydispersity in terms of grain size and density, which in turn affects the flow properties. Specifically, the presence of fine particles modifies the flow structure by segregating downwards  forming a fine-rich basal layer, which  controls basal dissipation. Here, the role of fine grains within granular flows is investigated on the  mobility of granular flows through large-scale laboratory experiments, in which dry, initially-homogeneous granular mixtures are released vertically onto a sloped channel. In this presentation, we show the preliminary results of this experimental campaign with an emphasis on the effect of fine particles in polydisperse mixtures and its interaction with the basal roughness on the flow runout. We reveal how important it is to consider fine particles in granular flows, and look ahead to the future prospects of this study.