As the dirt/soil erodes from one place, it will move down hill or down stream from where it came. It is all stuck within our atmosphere, so it cannot leave the earth. It just goes down hill and deposits the soil and dirt at a lower elevation from where it started. Therefore it is "building up" in another location. A good example is the Mississippi River Delta.
Well, that's my guess. Hope it helps.
Well, that's my guess. Hope it helps.