People have thought for so long that rivers must bring sand to beaches. You look at a river. The water moves many meters a second. You can watch the plume from it go out to the ocean. You see the plume slow down really, really fast. You think the sand must fall out. We never thought about gravity currents. It is one of those things, where we opened our eyes and said 'Wow.' We sort of have a hangover trying to understand it. |
We proved these flows exist. But we don't know how much sand is within them. I can guarantee that there is a lot of mud. We don't know about the sand. |