(a) List three landforms found in the upper course of a river valley (b) With tha aid of diagram, describe the characteristics and mode of formation of an o...

Answer Details

(a) Three landforms found in the upper course of a river valley

1. V-shaped valley.
2. Waterfalls and rapids.
3. Interlocking spurs (also gorges and potholes).

(b) The ox-bow lake

Characteristics: An ox-bow lake is a curved, crescent- or horseshoe-shaped body of stagnant water found on the flood plain of a river in its lower course. It lies beside, but is cut off from, the main river channel and it gradually dries up or becomes a swamp because it no longer receives flowing water.

Mode of formation:

1. In the lower course the river flows slowly across a flat flood plain and develops large bends called meanders.
2. On the outer bank of each meander the current is fastest, so it undercuts and erodes the bank laterally; on the inner bank the current is slow, so it deposits material.
3. Continued erosion on the two outer bends brings the necks of the loop closer and closer together, narrowing the neck of land between them.
4. During a flood the river cuts through the narrow neck, taking a new straight and shorter course.
5. Deposition then seals off the ends of the abandoned loop, leaving a curved stretch of water separated from the main channel. This is the ox-bow lake (also called a cut-off or mortlake).

A labelled diagram should show the meander loop, the narrowing neck, the point of cut-off, the new straightened channel, and the detached crescent-shaped ox-bow lake with deposition (plugs) sealing its ends.