Deposition is the geological process where material is added to a landform. This happens quite often. Some parts of a shoreline build up and grow out, whereas other parts of the shoreline erode and fall into the sea.
In deposition, wind and water lay down grains of material that has been eroded and transported from another place. Deposition happens when the forces which transport sediments are weaker than the forces of particle weight and friction. This causes a resistance to movement, and the particles drop down.
Deposition can also refer to the buildup of sediment from organically derived matter or chemical processes.