Granular flows generated by instantaneous release of initially gas-fluidised material O. Roche1*, M.A. Gilbertson2, J.C. Phillips1, R.S.J. Sparks1 University of Bristol, UK. 1 Department of Earth Sciences, 2 Department of Mechanical Engineering. * firstname.lastname@example.org The emplacement of granular flows generated by instantaneous release of a bed of initially gas-fluidised material into a horizontal channel was studied experimentally. We used particles corresponding to groups A, B, and D of Geldart's classification. The flow regime depends (1) on the initial fluidisation and the flow motion which disrupt the inter-granular contacts network of the initial static bed and (2) on the time-scale needed to re-establish strong contacts, which decreases as the grain size increases. Initially non-fluidised and fluidised flows of coarse particles (groups B and D) and non-fluidised flows of fine particles (group A) propagate as a wedge at a decelerating velocity after the initial acceleration. In contrast, flows of fine particles generated from fluidised beds propagate at constant thickness and velocity, in a regime similar to the slumping phase of gravity currents of simple fluids driven by buoyancy. This implies that internal particles interactions can be neglected to describe these granular flows and we have determined a Froude number Fr~2.6. All types of flows are characterised by a final stopping phase whose time-scale gives an estimate of the kinetics required to convert the granular material back to the fully solid-like, static state.