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Granular materials composed of particles with differing grain sizes, densities, shapes, or surface properties may experience unexpected segregation during flow. This review focuses on kinetic sieving and squeeze expulsion, whose combined effect produces the dominant gravity-driven segregation mechanism in dense sheared flows. Shallow granular avalanches that form at the surface of more complex industrial flows such as heaps, silos, and rotating drums provide ideal conditions for particles to separate, with large particles rising to the surface and small particles percolating down to the base. When this is combined with erosion and deposition, amazing patterns can form in the underlying substrate. Gravity-driven segregation and velocity shear induce differential lateral transport, which may be thought of as a secondary segregation mechanism. This allows larger particles to accumulate at flow fronts, and if they are more frictional than the fine grains, they can feedback on the bulk flow, causing flow fingering, levee formation, and longer runout of geophysical mass flows.
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Supplemental Video 1: Movie of Savage & Lun's (1988) chute flow experiment.
Supplemental Video 2: Movie through the sidewall of Golick & Daniels (2009) annular shear cell experiment.
Supplemental Video 3: Movie showing the segregation of large and small particles in van der Vaart et al.(2015) shear box experiments. The particle positions are reconstructed from index-matched laser scans across the cell when the sidewalls are in the vertical position.
Supplemental Video 4: Movie showing the rise of an opaque medium and a large particle in an index-matched body of small particles (van der Vaart et al. 2015). The images are captured each time the shear box walls are in the vertical position.
Supplemental Video 5: Movie of the USGS debris flow flume experiments (Johnson et al. 2012) showing the full flume and tracer particles been dropped onto the surface of the flow at the exit onto the tun-out pad.
Supplemental Video 6: Overhead movie of the advance of the leveed channel onto the run-out pad of the USGS debris-flow flume (Johnson et al. 2012).
Supplemental Video 7: Animation of high resolution images tracking with the front of the debris flow (Johnson et al. 2012) showing the advection of tracer particles towards the front, where they are either over-rolled or deposited in the levee walls.
Supplemental Video 8: Numerical simulation of the formation of fingers in a bi-disperse mixture of large rough grains and finer less frictional particles on an inclined plane. The downslope direction is from top to bottom (Baker et al. 2016).
Supplemental Video 9: Experiment shoing the formation of fingers on an inclined planes (Baker et al. 2016). The mixture is composed of 80% (75-150 micron) ballotini and 20% brown carborundum (305-355 micron). The turquoise base is made of 750-1000 micron ballotini.
Supplemental Video 10: Movie showing the formation of the Catherine wheel and radial segregation patterns in a thin rotating drum (Gray & Hutter 1997; Gray & Chugunov 2006). The drum is initially shaken horizontally so that all the large white sugar particles are on the front face and the small grey iron spheres are on the rear side.
Supplemental Video 11: Simulations of segregation in a square rotating drum in the continuously avalanching regime (courtesy D. Mounty) showing the formation of pattern with a series of arms. Note the periodic rise and fall of the position of the free-surface.
Supplemental Video 12: Experiment showing the formation of petals in a 50% full circular drum. Small perturbations to the initial radial distribution build up over a number of revolutions, until a wave develops that locks in petals of a given wavelength (Zuriguel et al 2006).
Supplemental Video 13: When the half full drum with the petals of a given frequency is speeded up, the pattern initially destroys itself, before locking into another state with fewer petals (Zuriguel et al 2006).