Landforms made by rivers
Rivers are the most important agents of change which make a large variety of landforms due to their erosional and depositional works. A river is mainly active as an agent of erosion in its upper course where slope of the land is steep and velocity of water is high. It is engaged in depositional work in its lower course because the river was sluggishly due to gentle slope of land. Thus, a river forms erosional landforms in its upper course when it is in its youthful stage and depositional landforms in its lower course where the river is in its old stage. In between, the river goes through mature stage when it is mainly active as an agent of transportation.
In highlands when the river passes through a bed of hard rocks, the main action of the river is downcutting. This results in a narrow and steep-sided valley which is known as gorge. The Sutlej, the Indus, the Brahmaputra, the Gandak, and the Kosi rivers have cut deep gorges in the Himalayas.
A canyon is just a magnified form of a gorge. In areas of arid climate with little rainfall, the valley sides fail to be widened at all and the river cuts deeper and deeper. This results in the formation of canyons or deepest gorges like that of the Grand Canyon of river Colorado in the United States of America. This is the largest canyon of the world.
V-Shaped Valleys are normally formed in areas of rainfall where the rocks are not very hard. Down cutting and side or lateral cutting are done simultaneously by the river and a V-shaped valley is formed.
When the river water falls down almost vertically from a sufficient height along the course of the river, it forms a waterfall. Hard and so rocks are found at several places in the course of the river. e so rocks are eroded easily and quickly and the river bed is lower at the place of so rock. Thus, the water falls from a height and a waterfall is created.
World’s Great Waterfalls
|Name||Height in Metres||Country or State|
|(A) Highest Waterfalls|
|Yosemite||782||(in three cataracts)||California (U.S.A.)|
|Sutherland||580||(in three cataracts)||New Zealand|
|Kalambo||426||(in two sections)||South Africa|
|Takkakau||400||British Colombia (Canada)|
|(B) Falls with large volume of water|
|Niagra||52||U.S.A. and Canada|
|Lower Yellowstone||102||Wyoming (U.S.A.)|
Sometimes there is a band of a hard-rocks along the path of a river which makes it jump over or fall downwards. is leads to the formation of rapids at places where the hard valley bottom offers great resistance to the erosion than the strips above and below it. A series of rapids is called a cascade. Nile river in Africa forms several rapids and cascades between Aswan and Khartoum