Rivers of water or 'rivers of very fine dust'? In some places of the world, there is a very fine dust that can flow like water. And fills up gaps and crevices.

Rivers of water or 'rivers of very fine dust'? In some places of the world, there is a very fine dust that can flow like water. And fills up gaps and crevices. I know, I hit a trench of the stuff while driving down a dirt road. I swear it splashed like water. I do know that I hit the roof of the truck very hard.