Ripples formed by waves are nearly symmetrical with a slight coarsening in the troughs. Waves cause symmetrical ripples unless waves are near breaking, then asymmetrical ripples form as if flow were in the same direction as waves are moving. As orbital vel. increases, ripples give way to plane parallel beds of upper flow regime. Ice-transport load consists of mostly mud and all available coarser sizes. A slope and thus gravity are necessary for all gravity flows.
Fluids play a secondary role of reducing friction between particles until the flow is well underway.
Rock Falls Free falling debris from cliffs. Over-steepened mud and sand begins to move by some disturbance and quickly mixes with overlying water. The mixture is buoyed by turbulence caused by the rapid initial movement. The turbulent flow keeps grains suspended and persists so long as the density of the flow exceeds that of the surrounding water. The flow mixes with this water and loses density.