  The erosion of lunar soil by rocket exhaust plumes is investigated
experimentally. This has identified the diffusion-driven flow in the bulk of
the sand as an important but previously unrecognized mechanism for erosion
dynamics. It has also shown that slow regime cratering is governed by the
recirculation of sand in the widening geometry of the crater. Scaling
relationships and erosion mechanisms have been characterized in detail for the
slow regime. The diffusion-driven flow occurs in both slow and fast regime
cratering. Because diffusion-driven flow had been omitted from the lunar
erosion theory and from the pressure cratering theory of the Apollo and Viking
era, those theories cannot be entirely correct.
