Here's why:

* Erosion is the process of wearing away and transporting sediment from one location to another. Think of wind or water carrying sand away from a beach.

* Deposition is the process of laying down sediment in a new location. This happens when the forces that were carrying the sediment lose energy, such as when a river slows down and deposits silt at its mouth.

So, while erosion is involved in moving the sediment, it's deposition that actually places it in a new location.