Denudation

Denudation

Deposition

Weathering

Erosion

Mass movement

Both A and R are true and R is the correct explanation of A.

Explanation — The upper course of a river generally lies in a hilly area and the river flows a considerable distance over a steep slope. Along its course, it erodes its bed and banks; and carries large boulders of rock with it. Under the impact of rush of water and the load the river carries, erosion action is swift and effective.

Deposition

Tributaries

Distributaries

Both A and R are true and R is the correct explanation of A.

Explanation — Meanders are the result of both erosion and deposition work of rivers. Meanders generally form under conditions of a gentle slope and sufficient water in rivers. The river flow is diverted by an obstruction allowing the river to do lateral erosion work.

Erosion

Meanders

Barchans

Seifs

Denudation

Both A and R are true and R is the correct explanation of A.

Explanation — The load-transporting capacity is drastically reduced due to sluggish flow as well as division of a river into many distributaries. This is why deposition becomes dominant in the lower course of the river.

Quality of water

They cover all surfaces with thick layers of sand.

Both A and R are true but R does not explain A.

Explanation — Barchans are moon-shaped live dunes which advance steadily before winds that blow from a particular direction. The migration of the barchans is a threat to desert life as they sometimes encroach on an oasis, burying palm trees or houses.

Deflation Hallows

A

Some activities that could prevent and reverse desertification are:

1. The growth of vegetation on the wind-ward slopes can prevent erosion by wind. It can help stabilize soil, prevent erosion, and promote groundwater recharge.
2. Long-rooted trees and sand-holding grasses can be planted to halt the advance of the dunes in order to prevent the fertile land from being devastated.
3. Rainwater harvesting can help replenish groundwater reserves and improve soil moisture, reducing the risk of desertification.
4. Overgrazing by livestock can contribute to desertification, so measures such as rotational grazing, herd management, and fencing can help prevent this.
5. Measures such as contour plowing, terracing, and cover cropping can help prevent soil erosion and improve soil fertility, reducing the risk of desertification.
6. Effective policy and planning can help prevent desertification by promoting sustainable land use practices, protecting natural resources, and encouraging community participation.

Denudation is the process of breaking and removing the rocks from the surface of the earth. It includes weathering, erosion, mass movement and transportation.

The factors which affect work of a river are-

1. Velocity of water
2. Volume of water
3. Load

The main function of a river in its upper course is erosion. It erodes its bed and banks and carries large boulders of rock with it.

The landforms formed in the upper course of a river are V-shaped valley and waterfall.

A waterfall is generally formed due to large differences in the rate of erosion. The water that falls down the edge of a hard resistant rock may have at the bottom a soft rock. It is this soft rock that gets eroded fast and creates a hollow basin called plunge pool.

The two characteristics of a river in its middle course are-

1. The lateral cutting is more active than down cutting.
2. The volume of water in the river increases due to many tributaries joining it.

Meanders generally form under conditions of a gentle slope and sufficient water in rivers. The river flow is diverted by an obstruction allowing the river to do lateral erosion work.

The Ganga in India is famous for its meanders.

Two landforms in the lower course of a river are delta and estuary.

Wind erosion is most predominant in arid regions such as deserts.

Deflation results in the lowering of the land surface to create depressions called deflation hollows.

Two chief landforms of wind deposition are sand dunes and loess deposits.

Two chief types of sand dunes are-

1. Barchan
2. Longitudinal dunes or Seifs

Two characteristics of barchans are-

1. They occur transversely to the wind, so that their horns thin out and become lower in the direction of the wind.
2. The windward side is convex and gentle-sloping while the leeward side is concave and steep.

The various processes involved in denudation are-

1. Weathering
2. Erosion
3. Mass movement or mass wasting
4. Transportation
5. Deposition

The results of denudation are the formation of erosional or depositional landforms on the surface of the earth.

(i) Erosion is the dominant activity of a river in its upper course because at this stage, the river flows swiftly, for the gradients are steep. Under the impact of rush of water and the load the river carries, erosion action is swift and effective.

(ii) Landforms of deposition are more prominent in the middle course of a river because at this stage, the gradient is reduced and the river flows more slowly. The energy required to transport the materials is just enough to drag large particles and the lateral cutting is more active than down cutting.

(iii) All the rivers do not form deltas because there are certain conditions for the formation of deltas, which include nearly calm sheltered sea, large amount of sediment supply and a reasonable size of the river.

Wind picks up loose debris like sand and pebbles and transports as well as deposits them in another location. Wind can lift and carry sand grains away. When the speed of wind slows down, the sediments brought by the wind begin to drop on the ground. This process continues and forms various landforms on the surface of the earth.

Two important landforms of wind erosion are deflation hollows and sand dunes.

The factors which affect the work of a river are-

1. Velocity of water — Erosion and transportation are both maximum when the velocity of water is high. Deposition takes place when the velocity of water is low.

2. Volume of water — The larger the volume of water, the greater is the power of erosion and transportation. Deposition takes place better when there is reduced volume of water and when the load is greater.

3. Load — The load of the river does all the work of erosion and deposition. Mass wasting, deepening of river valleys and formation of landforms depend on the load a river carries.

The three stages of a river are-

1. Upper course — At this stage, the river flows swiftly, for the gradients are steep. This course generally lies in a hilly area and the river flows a considerable distance over a steep slope.
   Along its course, it erodes its bed and banks, and carries large boulders of rock with it. The erosion action is swift and effective. V-shaped valleys and waterfalls are formed in the upper course of the rivers.
2. Middle course — At this stage, the gradient is reduced, and the river flows more slowly. In the middle course of the river, the energy required to transport the materials is just enough to drag large particles.
   The lateral cutting is more active and the volume of water in the river increases due to many tributaries joining it. Meanders and oxbow lakes are formed in the middle course of the rivers.
3. Lower course — In this stage, the river flows sluggishly and makes many landforms. All the ideal conditions for depositional landforms exist but the load-transporting capacity is drastically reduced due to the sluggish flow as well as division of a river into many distributaries.
   Deltas are formed in the lower course of rivers.

(i) The effects of wind erosion are more pronounced in desert areas since there is little vegetation or moisture to bind the loose surface materials.

(ii) Migratory sand dunes are uncertain and dangerous because when they migrate with the wind, they damage towns and villages.

(iii) Long rooted trees and sand holding grasses are grown bordering fields near deserts to halt the advance of the dunes in order to prevent the fertile land from being devastated.

The factors on which the shape and size of dunes depend are:

1. The direction and force of wind.
2. The speed of wind, carrying the dust and sand particles.
3. The nature and amount of sand brought by the wind.
4. Water features like lakes, streams etc., in the close-by area.
5. The nature of vegetation on the land.
6. The nature of the surface, where the formation of a sand dune takes place.

The River Tamsa in Madhya Pradesh is in its youthful stage (also called the upper course). This is due to following reasons:

1. Presence of Waterfalls (like Purva Falls): Waterfalls are classic features of a youthful river stage, where the river flows over a steep slope or escarpment. The Purva Falls are formed as the River Tamsa descends over the Rewa Plateau, which is an elevated region.

2. Steep Gradient: In the upper course, rivers have a high gradient, causing rapid flow and vertical erosion, which leads to the formation of waterfalls and gorges.

3. Vertical Erosion Dominates: The river cuts downwards more than sideways, creating sharp features like rapids and waterfalls.

Therefore, the formation of Purva Falls by Tamsa river is a characteristic of its youthful stage, marked by steep gradients, vertical erosion, and the presence of waterfalls.

(b) Other landforms (apart from Waterfalls) formed during the youthful stage are —

1. Rapids
2. V-shaped valleys and I-shaped valleys
3. Gorges
4. Canyons

(c) River Tamsa would form the following landforms in the next stage, i.e., mature stage (or middle course) —

1. Meanders
2. Oxbow lakes
3. Floodplains
4. Wider V-shaped valleys

(d) Waterfalls are important sources of energy because the falling water possesses great potential and kinetic energy, which can be harnessed to generate hydroelectric power (HEP). When water falls from a height, it drives turbines connected to generators, producing clean and renewable electricity. This makes waterfalls valuable for sustainable energy production, especially in hilly and mountainous regions.

Denudation, weathering, and erosion are three processes that work together to shape the Earth's surface. Weathering refers to the disintegration of rocks by atmospheric agents at or near the surface of the earth. It prepares them for further erosion. For example, in mechanical weathering rocks are disintegrated into blocks, pieces or fragments which can be eroded easily.

Erosion is the displacement of rock and soil from one place to another by natural agents such as wind, water, and ice. For example, water erosion can create channels and gullies in the landscape, carrying sediment downstream and depositing it in new locations to form deltas.

Denudation is the process of breaking and removing the rocks from the surface of the earth, which includes both weathering and erosion. It can lead to the formation of new landscapes and landforms, such as canyons and valleys. For example, the Grand Canyon in the United States was formed over millions of years through the combined processes of weathering and erosion. Together, these processes shape the Earth's surface over time.

While travelling from Haridwar to Prayagraj, I followed the course of Ganga river.

The landform associated with Ganga river along the course I followed are meanders.