dry gravel
wet gravel
dry gravel and sand (guest appearance by brent)
moist gravel and sand: a locked mass
dry sand: almost fluid-like
wet sand: conveyor-belt-like motion
top (plan) views
dry gravel: a bunch of pixels with an energetic front
wet gravel: lateral side-wall-influenced convection
slurry (sand, gravel, clay, water): the blob