(a) Using appropriate diagrams, explain the process of formation of a (i) river capture (ii) waterfall (b) Describe one way in which each of the two feature...

Answer Details

(a) Formation of the two features

(i) River capture (river piracy)

• Two rivers flow in roughly parallel valleys, but one (the captor) has a steeper gradient and greater erosive power than its weaker neighbour (the captured/victim).
• The more powerful stream cuts headward (backward) erosion up its valley faster.
• In time its head reaches and taps the channel of the weaker river, diverting the upper part of the victim's water into itself.
• The point of diversion is the elbow of capture; below it the now-dry, water-deprived section of the victim's valley is the wind gap, and the beheaded lower stream is the misfit stream.

Diagram required: two parallel rivers with the captor cutting back at right angles into the victim, marked with the elbow of capture, wind gap and misfit stream.

(ii) Waterfall

• A waterfall forms where a river flows over a band of hard (resistant) rock lying over softer rock, or over an edge such as a fault scarp or a plateau.
• The soft rock downstream is worn away faster than the hard rock, creating a vertical step over which the water plunges.
• At the foot the falling water and load erode a deep plunge pool, and undercut the soft rock, leaving the hard cap-rock overhanging.
• The overhang eventually collapses, and by repetition the fall retreats upstream, leaving a steep-sided gorge below it.

Diagram required: cross-section showing hard rock over soft rock, the vertical fall, plunge pool, overhang and receding gorge.

(b) Usefulness of each feature to man

• River capture: the diverted, increased volume of water in the captor river provides a larger, more reliable supply for water supply, irrigation and navigation, and the wind gap can serve as a routeway for roads and railways.
• Waterfall: the fall of water is harnessed for the generation of hydro-electric power and also serves as a scenic attraction for tourism/recreation.