A stream of ambient air flows uniformly through the bottom of a shallow granular layer. The flow oscillates and the periodic perturbation to the energy input into the granules transforms into a spatiotemporal pattern due to the energy dissipated through inelastic collisions. (Minor adjustments made to enhance brightness and contrast).
Gas-driven pattern formation in shallow granular layers —

A stream of ambient air flows uniformly through the bottom of a shallow granular layer. The flow oscillates and the periodic perturbation to the energy input into the granules transforms into a spatiotemporal pattern due to the energy dissipated through inelastic collisions. (Minor adjustments made to enhance brightness and contrast).

https://fluids.ac.uk/files/02_Photo.1513333721.png