Consider the following pairs : Features River Stage1. Gorge - Youth2. ...
Upper, middle and lower are the three courses into which a river valley is divided. Young rivers ( (A) denotes the below picture for the formation of the Young river) close to their source tend to be fast-flowing, high-energy environments with rapid downward and headward erosion, despite the hardness of the rock over which they may flow. The land features carved by a river in its upper course are as follows:
- Gorges,
- Canyons,
- V' shaped valleys,
- Rapids,
- Cataracts, and
- Waterfalls A gorge is a narrow valley with steep, rocky walls between hills or mountains.
The term comes from the French word gorge, which means throat or neck. So, Pair 1 is correct.
Mature rivers or Middle ( (B) denotes the above picture for mature river formation ) are lower-energy systems. Erosion takes place outside bends, creating looping meanders in the soft alluvium of the river plain. Deposition occurs on the inside of the bends and the river bed. Some of the land features formed by a river in its middle course are alluvial fans and meanders. A meander is a bend in the course of a river channel. A meander is formed in the middle course of a river; when the river leaves the mountains, it encounters a sudden slope break and slows down. The plains are broad and gentle. So the river has more time to amble away down to the sea. So, Pair 2 is correct.
Oxbow lakes are formed when the neck of a looping meander is broken through, usually during times of flood. They are U-shaped or curved bends in a river that are cut off from the main river flow, forming a lake. In the lower course of the river, meanders become much more pronounced. The outer or concave bank is so rapidly eroded that the meander becomes almost a complete circle. A time comes when the river cuts through the narrow neck of the loop. The meander, now cut off from the mainstream, takes the form of an oxbow lake. In the lower course or the stage of old age, the land features produced by the river are meanders, flood plains, braided steam, oxbow lakes, deltas and estuaries. So, Pair 3 is correct.