Landforms Formed by River Erosion
(1) Waterfalls – If hard and soft rock layers lie alternately in a valley, rocky platforms are formed. If the hard folds are located along the soft folds and are slightly inclined towards the flow of the river, a series of waterfalls form. If vertical rock is found within the flat soft rocky layers, waterfalls are also formed. When hard rock layers lie transversely over soft rock layers, a waterfall is formed in the valley, but the soft rocks below the break, cause the upper hard rocks to break and the waterfall to move backward. Such waterfalls may end over time.
(2) Formation of depression trough – When hard rock layers remain transversely positioned above soft rock layers, the soft rocks are cut, forming a depression trough. The bouncing water soaks the soft rocks, causing them to fall and get washed away over time. As these rocks are washed away, upper rocks fall due to their weight, and the waterfall moves backward. Over time, the waterfall ends when the hard rocks are destroyed. When hard rocks stand upright, they do not break, and the waterfall becomes permanent.
(3) Stepped Falls – When water falls in many steps along the side of a terraced wall, they are called Stepped Falls. When a large body of water flows over hard rocks, the rocks may not be visible from above, creating a waterfall. Madhya Pradesh is full of waterfalls. There is a waterfall named ‘Kapildhara’ in Amarkantak, 266 km from Rewa in the Narmada River. Adjacent to this beautiful, mesmerizing fall was Kapil Muni’s penance. The second fall in Narmada is Dugdhdhara. It is formed on the plateau inside the Vindhya ledge.
(4) River valley plain – Rivers start cutting the lower part and sides of their bed and deposit transported material, forming large plains called river-valley plains. In this condition, deposition is greater than erosion in the valley. The depth of the valley gradually decreases, and floods become present in the river. It is called the slope of the river valley because such bends are found in the Mind River. In the initial stage, the valley of the Visarpo River is narrow and the slip occurs in an underdeveloped state. They have less complexity. Gradually the valley also widens, and the turns become complicated.
(5) Formation of the river bend and Chandan Lake – The water stream collides with the concave bank of the valley, causing the bank to get cut and obstructing the flow of the river. The flow tends to divert due to the obstruction. Erosion materials start accumulating on the north bank. The concave edge appears to be erect, and the convex edge is blunt. The depth of the river is also greater towards the concave bank and gradually decreases towards the convex bank. For this reason, the steep banks keep eroding, and less sand is deposited on the banks, increasing the bend in the flow of the river. In this way, the slip increases so much that the shape of the river becomes completely circular. In this condition, the rivers leave their course at the time of flood and start flowing by cutting the part near the bend. This straight flow path remains even after the flood. In such a condition, the curved part takes the form of a lake called a Chandan lake. Many such lakes are found in the plains of the Ganga River.
(6) The velocity of the river is high in the middle of the delta-river stream. Therefore, the water from that part enters the sea to a greater extent. This creates a depression in the shape of a district far away in the sea, but due to the slower water flow along the shore, it ends at the confluence of the sea and the depression accumulates there. Gradually, this sea plain emerges above the water, and the river water flows in many streams into the sea. Thus, the mouth of the river takes the shape of a triangular plain called a delta, and Greek letters are often used to describe them. The delta plain slopes towards the sea. The following conditions are necessary for delta formation:
(a) The lower valley of the river should be wider so that the river’s flow becomes completely relaxed while reaching the mouth.
(b) There should not be any lakes in the course of the river because sediments get collected in the lakes and there are no sediments left in the rivers for delta formation.
(c) The mouth of the river should be free from tides and sea currents, otherwise, the depression will be far away from the river mouth, and a delta will not form.
(d) The river should originate from high mountains, and its tributaries should also be high so that sufficient river load can be given, and a delta can be formed.
There are three stages in the formation of a delta. In the first stage, deposition leads to the formation of many water distributaries of the river. Bhujihva becomes Radhika and Anoop. In the second stage, the distributaries become depressed and form marshes. In the third stage, plants grow in the delta, and swamps disappear. The delta becomes higher, and part of it becomes dry land.
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