headward erosion

The backwards erosion of material at the source (start) of a river or stream. Broken rock and soil at the source are carried away by the river, causing the source of the river to move backwards as erosion takes place in the opposite direction to the river's flow. The resulting lowering of the land behind the source may, over time, cause the river to cut backwards into a neighbouring valley to ‘capture’ another river (see river capture).