Hey Midnightrider,
DUST, lots of them.
The simple way is, to use the Landscape Object and animate the grow the Y-size of it. Use a Particle Emitter to “rain” the dust on it. Perhaps with hair as shader/render option.
The Landscape needs an dusty shader/texture, which could be in its simplest form a Noise shader. As that would look rather static, I would connect the particles with an Proximal Shader as a layer Mask (in a layer Shader) to blend between two noise shaders, to get a little bit life into it. If the particles would slow down after reaching the surface, you might get a nice but simple impression. A animated texture, perhaps a filmed (practical) version of that sand clock effect is preferable.
Besides that, and more advanced version goes easily into the “direction” of fluid simulations, for that use Real-flow, if hi end quality is needed.
All in all, this is not a simple task, as each dust particle causes practically a calculation. So - I would invest some time in R&D if needed.
You might check out other options like displacement etc. Some stuff needs a lot of attention, and is not a ready made. Think about “Spiderman 3” the guy that was created out of sand, that was close to the limits of a complete studio. Perhaps the “Making Of” tells you a little bit about (Cinefex might help as well).
http://www.youtube.com/watch?v=rXOa5bWFRKw
Good luck
Sassi