Granular flows in split-bottom geometries

There is a simple and general experimental protocol to generate slow granular flows that exhibit wide shear zones, qualitatively different from the narrow shear bands that are usually observed in granular materials. The essence is to drive the granular medium not from the sidewalls, but to split the bottom of the container that supports the grains in two parts and slide these parts past each other. Here we review the main features of granular flows in such split-bottom geometries.