Landforms created by River - Formation Processes & Types

Landforms created by the river and depend on the channel gradient, velocity, and volume of water. The landforms formed due to the action of rivers are called Fluvial landforms. They are divided into two major groups, i.e., depositional and erosional. Depositional landforms are leeves, deltas, and plains, while erosional ones are waterfalls, potholes, and V-shaped Valleys. A river goes through three stages: youthful, mature, and old. The course of a river includes the upper stage, the middle stage, and the lower stage, and a kind of work dominates each stage of the River. Landforms such as rapids, waterfalls, and gorges are generally formed in the upper course of a river due to high energy flows and steep gradients. In the middle course, gentler gradients can lead to the formation of pools, riffles, natural levees, oxbow lakes, and floodplains in geographical locations as well as various other natural sources. Two landforms in the lower course of a river are the Delta and the estuary.

This topic of “Landforms created by River” is important from the perspective of the UPSC IAS Examination, which falls under General Studies Paper 1 (Mains) and General Studies Paper 1 (Prelims) and particularly in the Geography section. In this article, we shall discuss the Landforms created by rivers and the processes involved. We shall also have an insight into the depositional and erosional landforms formed due to the action of rivers.

Processes of Landform Formation by Rivers

Processes involved in landform formation by rivers are:

• Corrosion / Abrasion: It is the mechanical grinding of the traction load of a river against the River’s banks and bed. This process results in the hurling of the rock fragments against the sides of the River and their rolling against the bottom of the River. Corrosion takes place in two manners:
  • Lateral corrasion: This results in sideways erosion and the widening of the V-shaped valley.
  • Vertical corrasion: it is associated with the downward action of the River leading to the deepening of the river channel.
• Corrosion / Solution: this process involves the chemical action of the water on the soluble components of the rocks. It is most significant in carbonate rocks due to its easy solubility.
• Hydraulic action: It is associated with the mechanical loosening of the rocks due to the action of the River, which leads to the sweeping away of the rock materials. The continuous action of the river water on the rocks leads to the disintegration of the rock.
• Attrition: It is the wear and tear of transported materials while they roll and collide among themselves. The coarser boulders are broken down into smaller stones and then smoothened to form pebbles.

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Types of Landforms created by River

The landforms formed by river processes are discussed below.

Potholes

Fig: Potholes

• Potholes are kettle-shaped depressions in the rocky beds of river valleys.
• They are usually formed in coarse-grained rocks such as granites and sandstones.
• Formation:
  • Whenever a soft rock comes in the way of the River, it is eroded and scattered all around. This results in the formation of eddies, and water whirls around and produces depression by plucking the sediment. This makes the depression deep and cylindrical.
• Stone pieces also enter the potholes along with water and act as grinders enlarging the diameter and depth of the holes.
• The potholes have a diameter varying from a few centimeters to several meters.
•  The depth of a pothole is greater than its diameter.
• Potholes of much larger size are called Plunge pools.
• In India, they can be discovered at Bhadbhada near Jabalpur, Madhya Pradesh.

Waterfalls

Fig: Waterfalls

• When the river water falls down almost vertically from a sufficient height along the course of the River, it forms a waterfall.
• In the course of the River, there is the presence of hard and soft rocks at several places. The soft rocks are eroded easily and quickly, and the river bed is lower at the place of soft rock. Thus, the water falls from a height, and a waterfall is created.
• Waterfalls may be formed in several manners.
  • When a bar of resistant rock lies transverse across a river valley. E.g., Niagara Falls, USA.
  • When a fault line scrap caused by faulting lies across the River. E.g., Victoria Falls.
  • When water plunges down the edge of a plateau. E.g.: Livingstone Falls
  • When tributary streams reach the main U-shaped valley as waterfalls. E.g., Yosemite Falls.

Meanders

Fig: Meanders

•  The word “meanders” is derived from the name of a small winding river’s meanders in Turkey.
• Meanders the longitudinal bends of river courses.
• Every bend of the river course has two slopes:
  • A concave slope where the River strikes valley sides directly. This side is steeper and is referred to as the cliff slope side.
  • A convex side receives the deposition of sand and gravel. This site is characterized by a gentle slope and is referred to as a slip-off side.
    • Thus, Meanders are a result of both erosion and deposition.
• The shape of the meander is semi-circular though it may be circular.
• A river meanders almost in every terrain. However, the magnitude varies according to the slope of the terrain. It is most pronounced in an even and gentle slope.
• In India, the Gomti River is a typical example of a highly meandering stream.

Oxbow Lakes

Fig: Oxbow lakes

• They are also referred to as cut-offs or buyouts in the Mississippi basin.
• Oxbow lakes are formed in the lower course of the River when a meander becomes more pronounced. The concave side of the meander is rapidly eroded and results in a complete circle. The curvature becomes so sharp due to the lateral erosion that the rivers break through the meander and form a loop. This is known as the Oxbow Lakes.
• Like meanders, oxbow lakes owe their origin to both erosion and deposition.
• In addition to the Meander River of Turkey, the Mississippi of the USA, the Ganga of India, and the Po of Italy are famous for oxbow lakes.

 V Shaped Valley and Interlocking Spurs

Fig: Interlocking spurs and V-shaped valleys

• Most of the world’s rivers have formed V-shaped valleys. Such valleys are normally formed in areas of sufficient rainfall where the rocks are not very hard.
• Downcutting and side or lateral cutting are done simultaneously by the River, and a V-shaped valley is formed.
• The valleys are gradually widened due to lateral erosion with the advancement of the cycle of erosion, and they become broad with flat valley floors and rectilinear valley slopes in the mature stage.

Interlocking Spurs

• Interlocking spurs are ridges of hard rock that are resistant to the flow of the River.
• They are formed when a river is forced to swing side to side around the spurs of hard rock with an interlock.

Fan-Shaped Plains

Fig: Fan-shaped plains

• Fan-shaped plains are formed due to the accumulation of materials at the base of the foothills.
• At the foothills, the carrying capacity of the River is reduced enormously due to an increase in channel gradient and a decrease in the velocity of the River.
• Consequently, the river load is deposited with coarser material settling first and finer towards the mouth of the plains.
• The shapes of the alluvial fans are usually semi-circular, with the apex located at the mouth of the opening through which the stream flows out of the hills and the plains.
• They have a gentle slope.
• The diameter of the fans ranges from a few kilometers to several hundred kilometers.

Flood Plains

Fig: Floodplains

Rivers, in their lower course, carry large amounts of sediments. These sediments spread over the low-lying adjacent areas. These results in the formation of flood plains.

Leeves

Fig: Levees

• Leeves are narrow belts of ridges of low height formed by the deposition of sediments by the River on either bank.
• They are most often formed during flood periods when water overtops the river banks and spreads over adjoining plain areas.
• They limit the lateral spread of water except during events of floods.
• They are also used for agricultural purposes due to the fact that the water table here is generally high.
• They also help in checking floods; however, during events of the breach, it may result in catastrophic floods since water gushes out in the plain areas with high velocity.

Braided Channels

Fig: Braided Channels

• The lower River is characterized by an excess deposit of the load on the floor of the channel because of the reduction in carrying capacity due to the slow movement of water in the stream. The stream, which thus gets divided into a network of channels, forming bars of sand and islands, is known as a braided channel.

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Deltas

Fig: Deltas

• The Greek letter ‘∆’ was first used by the Greek historian Herodotus to resemble the triangular Delta of the River Nile. Small or large, every River forms a delta.
• When the rivers enter the sea or lake, it deposits all the load at their mouth, giving rise to the formation of the Delta.
• It is a triangular feature with its apex pointing and is marked as a fan-shaped area of fine alluvium.
• The size of the Delta varies from a few square kilometers to thousands of square kilometers.
• The suitable conditions for the formation of deltas are:
  • Shallow sea
  • Long river courses
  • Medium size sediments
  • Calm or sheltered areas at the mouth of the River.
  • Large sediment supply
  • Stable sea coast.
• Eg: Ganga Brahmaputra Delta, Mississippi Delta

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Significance of Landforms Created by Rivers to Humans

The significance of landforms created by rivers to humans are:

• The flood plains, with their rich sediments, have acted as cradles of human civilizations. Many of the large cities and dense populations are found along the river banks.
• They have also been hotspots of agricultural activities.
• In the upper course, rivers with steep gorges have acted as major tourist attractions.
• They have also acted as a major source of hydroelectric power, thus supporting industries like metallurgical industries, engineering, and aluminum industries.
• Wind gaps and River capture in the upper course of the River are sites for the construction of upland roads and railways and thus facilitate communication.

Courses of River flow

The course of river flow can be divided into three sections.

• Upper or mountain course
• Middle or youth course
• Lower or plain course

Upper or mountain course

It is termed the youth stage of the river flow. This stage begins near the source of the River, which is the crest of the mountain. In this stage, the River moves swiftly, and the predominant action of the River is vertical erosion with the absence of lateral erosion. The valley formed in this stage is deep, narrow, and V-shaped. There is the development of steep and narrow gorges where the rocks are resistant to the flow of the River. In arid regions, there is a development of canyons due to insufficient rainfall to widen the valley sides. E.g., Bryce Canyon.

Middle or youth course

The middle course of the River is characterized by lateral corrosion by replacement of vertical corrosion. In this stage, active erosion leads to further widening of the V-shaped valley. The volume of water at this stage increases due to the confluence of many tributaries which leads to an increase in the River’s load. The River, at this stage, focuses on transportation with little deposition. Also, the work of the River of Valley cutting, bed smoothing, and debris removal are carried out in a more tranquil manner than in the youth stage.

Lower or plain course

Under this stage, vertical corrasion is replaced by lateral corrasion. The volume of the water increases due to the confluence of many tributaries. The River mainly plays the role of a depositor building up the bed resulting in the formation of extensive flood plains. The heavier materials are deposited first, and the finer materials are deposited toward the mouth of the River. The swift movement of the River ceases, and the River moves more calmly.

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