Abstract

Geophysical granular flows occur at the surface of the Earth and other planets with reduced atmospheric pressure. In this paper, we investigate the run-out of dam-break flows of particle-air mixtures with fine (d=75μm) or coarse (d=150μm) grains in a flume with different bottom roughness (δ) and vacuum degrees (P∗). Our results reveal an increase of the flow run-out as d/δ decreases for fine d=75μm-particles, and run-out decreases with the dimensionless ambient pressure (P∗) for a given d/δ. In contrast, the run-out for coarser d=150μm-particles, is almost invariant respect to P∗ and d/δ. These results show that autofluidization of fine-grained flows demonstrated by earlier works at ambient pressure also occurs at reduced pressure though being less efficient. Hence, autofluidization is a mechanism, among others, to explain long run-out of geophysical flows in different environments.