  Dense granular flows are often unstable and form inhomogeneous structures.
Although significant advances have been recently made in understanding simple
flows, instabilities of such flows are often not understood. We present
experimental and numerical results that show the formation of longitudinal
stripes that arise from instability of the uniform flowing state of granular
media on a rough inclined plane. The form of the stripes depends critically on
the mean density of the flow with a robust form of stripes at high density that
consists of fast sliding plug-like regions (stripes) on top of highly agitated
boiling material - a configuration reminiscent of the Leidenfrost effect when a
droplet of liquid lifted by its vapor is hovering above a hot surface.

Soft Condensed Matter