Dr. Blackwell. First, I'd like to thank you for your posts. I always read them, and find them to be interesting and informative, a delightful counterpoint to my mindless drivel. Well, I'm too modest. Sometimes not mindless, always drivel.

Regarding the possibility of dry dust avalanches. I'm reminded of some waterfalls I've seen, which in certain low flow, high wind conditions have water falling and not hitting the ground.

What size dust particle could these things be in order for 90+% of them to be entrained in a thin atmosphere, even under low gravity?

Apparently they are quite small, with almost no cohesion, as even much less than a 10% accumulation at the (distal - love that word) end of the avalanche would result in the area levelling over time. Intuitively it seems odd that all of the dust would be scoured off even a hard surface. (Snow has the grace to melt or sublimate.)

Clearly, there is a size particle which settles under calmer conditions, and some which won't. However, I would imagine dust is always being created where there is some dust, some wind, and some rocks. All sizes of dust.

A last question. Are all of these suggested avalanche sites on the lee side of hills? Is the wind in the same direction the vast majority of the time? Would an upslope or wind more perpendicular to the slope remove light, slick dust drastically slowing the accumulation?

It would seem to argue against dust avalanches if there wasn't a very strongly prevailing wind. Alternatively, it's possible that in some seasons, when the wind was in the up- or cross-slope directions, the dust was frozen or somehow much more cohesive. That would account for the avalanches occuring after warmer temperatures.

And, they have to be talking about one dickens of a lot of dust.

This is a non-priority matter, the idle wonderings of someone trying to visualize the conditions described in you post. If it would be at all inconvenient, please don't take the time to respond.

Arf