During headward erosion, the distance from the mouth to the source of the stream increases as erosion causes the headwaters to extend further upstream.
During the process of headward erosion, which is the erosion at the origin of a stream that causes the stream to lengthen, the distance from the mouth to the source of the stream increases. This occurs because as erosion progresses upstream, it cuts away the soil and rock, effectively moving the starting point of the stream further from its mouth.
Headward erosion contributes to the expansion of drainage basins and stream networks over time. As the stream elongates at its headwaters, it can capture water from other watersheds, increasing its own size and complexity.