The teams of E. Guazzelli and M. Wyart explain in PNAS that the erosion of a granular bed is analogous to the plastic depinning of vortices in superconductors.

Channeling patterns and erosion in fluid flow over granular beds

When fluid flows across a granular substrate, shearing forces detach material from the interface and transport it downstream. Although erosion-deposition constitutes a central geomorphological process that shapes Earth’s landforms, decades of research has failed to yield a complete description of these systems at the microscopic level. Utilizing a flume apparatus to simulate river flow over a gravel bed, Pascale Aussillous et al. examine the threshold stress beyond which solid flow spontaneously arises and characterize the spatial organization of the erosion flux. The authorS show that near the origin of erosion the flow of particles is spatially heterogeneous, carried by only a few concentrated channels in the bed whose distribution is strongly power-law correlated in the along-flow direction. Furthermore, the authors demonstrate that these results support a model in which erosion is ultimately governed by a give and take between channelization, which accelerates erosion, and interactions among particles which tend to interfere with channeling. The findings argue that erosion along a fluid-sheared granular bed effectively represents a dynamic phase transition, consistent with other systems such as type II superconductors.