and....
Pathfinder only caught one when the image was multicolor and processed at home. For these single B/W images, I wouldn't bank on catching one. Especially if this occurs at night.
The thing is, the atmosphere is more dense at night and perhaps turbulence associated with the rapid temperature change after sunset is when this happens. I don't know why a crater would be a site for more vigorous "wind".
It could ALSO have to do with electrostatic charge. UV may facilitate keeping particles charged and attractive during the day. Once they neutralize (at night?) then the coating is less sticky?
Who knows...