ZIMSEC O Level Geography Notes: River capture
- This is a process where one River captures the headwaters on a nearby stream.
- This can occur due to several reasons viz:
- Tectonic earth movements, where the slope of the land changes, and the stream is tipped out of its former course.
- Natural damming, such as by a landslide or ice sheet.
- Erosion, either:
- Headward erosion of one stream valley upwards into another,
- Lateral erosion of a meander through the higher ground dividing the adjacent streams.
- In an area of karst topography, where streams may sink, or flow underground (a sinking or losing stream) and then reappear in a nearby stream valley.
- The diagram above shows how river capture can occur.
- There are two consequent rivers: Stream A and B and Stream B has a tributary (subsequent A)
- Stream B has higher discharge and thus higher erosional activity than stream A.
- Stream B might also have a lower base level and thus increasing its ability to erode.
- Subsequent A migrates upstream (headward erosion) until it reaches Stream A’s channel.
- Through a process known as watershed migration Subsequent A enlarges its own drainage basin at the expense of Stream A.
- In time because Subsequent A and Stream B have a lower base level the headwaters of Stream A will be captured and diverted into Subsequent A.
- The point at which the headwaters of the minor river change direction is known as the elbow of capture.
- Below this point a wind gap marks the former course of the now beheaded stream or misfit stream.
- A misfit stream is a river whose headwaters were captured resulting in the stream flowing in a valley that is too large to be accounted for by the low discharge.
- A knickpoint and waterfall might form at the elbow of capture especially if the base level of the capturing river is far lower than that of the beheaded stream.
To access more topics go to the Geography Notes page.