Waves, channels and levees in geophysical mass flows - Prof. Nico Gray


Event details

Date 24.08.2022 11:1512:00  
Speaker Nico Gray is a Professor of Applied Mathematics in the Department of Mathematics at the University of Manchester, UK. He is an expert on granular flows and the particle segregation that takes place within them. This has applications to a wide range of industrial processes, as well as to geophysical flows such as snow avalanches and debris flows. Nico holds a BSc in Mathematics from the University of Manchester, a PhD in Sea Ice Dynamics from the University of Cambridge and a Habilitation in Continuum Mechanics and Geophysical Mechanics from the Technical University of Darmstadt in Germany.  
Category Conferences - Seminars
Event Language English
Waves, channels and levees in geophysical mass flows

Prof. Nico Gray, University of Manchester
Abstract: Geophysical mass flows often break down into large amplitude wave pulses and/or spontaneously form channels with static levees in the arrest zone, enhancing overall run-out. This talk reviews recent depth-averaged models that capture the formation of (i) rollwaves, (ii) erosion-deposition waves (which exchange mass with the underlying substrate) and (iii) channel and levee formation within a single framework. The key is the inclusion of frictional hysteresis, which allows static and moving zones to coexist, as well as depth-averaged viscous terms that incorporate further details of the granular rheology. As well as being able to compute time-dependent spatially evolving solutions numerically, the resulting model allows steady-state solutions to be constructed for the height, width and depth-averaged velocity profile across a leveed channel, which are in good quantitative agreement with small scale analogue experiments using monodisperse dry sand. Colour change experiments are also used to show that erosion-deposition waves really do propagate downslope as a wave, rather than a coherent body of grains, and that the presence of the substrate gives them surprising mobility over very long distances. Photos and videos of the similar effects at field scale will be shown to emphasize the importance of these ideas for a wide range of geophysical mass flows. There are, however, still many open challenges in how to generalize these results to multiphase mixtures with broad grain size distributions.

Note - The illustrative picture is taken from
Rocha, F.M., Johnson, C.G. & Gray, J.M.N.T. 2019 Self-channelisation and levee formation in monodisperse granular flows. J. Fluid Mech. 876, 591–641.

Practical information

  • General public
  • Free


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