lewkiwuk

You will probably want to combine a deforming model with a procedural sand shader on it with another simple particle system with “slide on surface” particles.

I would use point colours to drive the model deformation. That way you can spray particles onto your geo, turn that into point colours, then using a VEX SOP that uses Cd as a mix, blend between positions. Further non-linear looking blending could then be done by using Cd.r/g/b differently to blend at different times/speeds.

Sean