1st PUC Geography Question Bank Chapter 4 Landforms

Karnataka 1st PUC Geography Question Bank Chapter 4 Landforms

You can Download Chapter 4 Landforms Questions and Answers, Notes, 1st PUC Geography Question Bank with Answers Karnataka State Board Solutions help you to revise complete Syllabus and score more marks in your examinations.

1st PUC Geography Landforms One Mark Questions and Answers

Question 1.
What is geomorphic process? (T.B.Qn)
Answer:
The process carried out by Endogenic and Exogenic forces are called as geomorphic process.

Question 2.
Define Diastrophism? (T.B.Qn)
Answer:
All processes that move, elevate or build up portions of the earth’s crust are called diastrophism.

Question 3.
Mention the force responsible for mass movement? (T.B.Qn)
Answer:
Gravity is responsible for mass movement.

Question 4.
What is Endogenic Forces?
Answer:
The internal forces are also known as endogenic forces. These are mainly the land building forces.

Question 5.
What is Exogenic Forces?
Answer:
The external forces are also known as external forces. These are found on the surface of the Earth.

Question 6.
What is weathering? (T.B.Qn)
Answer:
The process of disintegration and decomposition of rocks is known as “Weathering”.

Question 7.
Name any two factors of Mechanical weathering? (T.B.Qn)
Answer:
Temperature, frost and wind are the factors of Mechanical weathering.

Question 8.
How does granular disintegration occur?( T.B.Qn)
Answer:
Rocks consist of different types of minerals. Some minerals get heated faster than others. As a result of differential expansion of minerals, the rocks break up into mineral grains. This is called granular disintegration.

Question 9.
What is the role of oxygen in Oxidation? (T.B.Qn)
Answer:
The rain water with oxygen, reacts on rocks containing iron and produce oxides. This chemical reaction is known as “oxidation”.

Question 10.
Which region is predominant in Carbonation? (T.B.Qn)
Answer:
Carbonation is very active in limestone regions.

Question 11.
What is mechanical weathering?
Answer:
Disintegration of rocks into smaller pieces by mechanical agents is known as mechanical weathering

Question 12.
What kind of weathering is predominant in the limestone regions?
Answer:
Chemical weathering

Question 13.
Why the process of rocks disintegration is called weathering?
Answer:
The process is carried various elements like carbon dioxide and also by various organisms.

Question 14.
What are the important types of weathering?
Answer:
There are three types of weathering

• Mechanical weathering
• Chemical weathering
• Biological weathering

Question 15.
Which zone is the sources of weathering?
Answer:
Lithospheres the zone of weathering.

Question 16.
Which type of weathering is mining?
Answer:
Mining is a type of Biological weathering.

Question 17.
Which type of weathering is oxidation?
Answer:
Oxidation is a type of chemical weathering

Question 18.
Mention the types of chemical process of weathering?
Answer:
Oxidation, Carbonization, Hydration and solution are the major types of chemical weathering.

Question 19.
Mention the types of Block disintegration of rocks?
Answer:
Block disintegration is a type of mechanical weathering.

Question 20.
What is River capture? (T.B.Qn)
Answer:
It is formed mainly due to head-ward erosion by the river near its source. When the source of a river is captured by another major and strong river it is called ‘River Capture’.

Question 21.
How are Ox-bow lakes formed? (T.B.Qn)
Answer:
The river which flows through the shorter route leaving the curve of the meander cut off and, crescent-shaped lake is formed known as‘Ox-bow lakes’.

Question 22.
What is denudation?
Answer:
The wearing away of the surface of the earth by natural agents is known as denudation.

Question 23.
What is Sculpturing of the earth?
Answer:
Large landmass is uplifted by various internal forces of the earth, the subaerial agents begin to wear and reshape it. It is known as Sculpturing of the earth’s surface.

Question 24.
What are the agents of denudation?
Answer:
River, glacier, underground water, winds, sea waves are the major agents of denudation.

Question 25.
Which denudation agent is formed V shaped valleys?
Answer:
River denudation is formed v shaped valleys.

Question 26.
Define the source of the river?
Answer:
The place of its origin of the river is called a source of the river

Question 27.
Define the Mouth of the river?
Answer:
The place where the river reaches its end or sea is called the mouth of the river.

Question 28.
Where the natural levees are found?
Answer:
Natural levees are found in lower course of the river.

Question 29.
What type of lakes is found in the flood plain?
Answer:
Ox-bow Lake is found in the flood plain.

Question 30.
What is Course of river?
Answer:
The path of the river in which it flows from its source to its mouth is called Course of the River.’

Question 31.
What is River Mouth?
Answer:
The place where the river meets or drains into a sea or an ocean is called River mouth.

Question 32.
What is River Basin?
Answer:
The area drained by a river, and its tributaries including distributaries form “River basin”.

Question 33.
What is Water divide?
Answer:
A ridge of high land which separate two river (stream) system is called ‘Water shed’.

Question 34.
What is confluence?
Answer:
The place where a tributary river joins the main river or another river is called confluence.

Question 35.
What is Erosion?
Answer:
The process of wearing and taking away the part of rock is known as ‘Erosion’.

Question 36.
What is Catchment Area?
Answer:
It is the region from which a river or stream receives water from different sources.

Question 37.
What are the three stages of a river course?
Answer:
Youth stage, mature stage and old stage are the three stages of a river course.

Question 38.
What are the three types of works of agents of denudation?
Answer:
Erosion, transportation and deposition are the three stages of denudation.

Question 39.
What is a drainage basin?
Answer:
The entire region through which a river flows with its tributaries is called the river basin.

Question 40.
What is limnology?
Answer:
The scientific study of lakes and ponds with respect to their physical, chemical and biological.

Question 41.
In which stage of the river waterfalls are found?
Answer:
In upper course or Youth stage waterfalls are formed.

Question 42.
Who used the term of Delta for the first time in the world?
Answer:
The term delta was first used by the Greek historian Herodotus.

Question 43.
What are the pot holes?
Answer:
The irregular river bed with boulders, the river water develops spirals and whirlpools. The rock pieces during circulation along with water grind out circular holes in the bed rocks. They are known as pot holes.

Question 44.
Which is the highest water fall in the world?
Answer:
Angel falls of Venezuela (Orinoco River) is the highest water fall in the world.

Question 45.
On which river is Niagara Falls found?
Answer:
The Niagara Falls, located on the Niagara River draining Lake Erie into lake Ontario in the North America.

Question 46.
Why denudation is also called degradation?
Answer:
The word denudation is used to denote the process of wearing away of the earth’s surface. It includes the process of degradation.

Question 47.
What is river confluence?
Answer:
The point where the river joins the other is called confluence.

Question 48.
Mention the types of delta?
Answer:
Accurate or triangular delta and Bird foot delta are the major type of delta

Question 49.
What is floatation?
Answer:
The light material like wood floats down the river. This is known as Floatation.

Question 50.
What is Siltation?
Answer:
Small fragments of rocks move downward by leaping and jumping along the bed of a river. This work is known siltation.

Question 51.
What is suspension?
Answer:
Fine powder like mud or salt is suspended in water and is carried away to a great distance. This work is known as suspension.

Question 52.
What is solution?
Answer:
Chemicals like lime are dissolved in waster and are carried in solution form. This work is known as solution.

Question 53.
What is Traction?
Answer:
Bigger rock pieces like gravels, pebbles and boulders are dragged or rolled along the bed by the force of running water and these rock prices also help in the work of erosion. This process is known as traction.

1st PUC Geography Landforms Two Marks Questions And Answers

Question 1.
State the difference between Endogenic and Exogenic forces? (T.B.Qn)
Answer:
These are mainly the land building forces. Diastrophisnr includes all these processes tat move, elevate or build portions of the earth’s crust. The internal forces are also known as endogenic forces.

These forces are found on the surface of the Earth, Which bring changes through degradation and aggradations process. River, glacier, wind, sea waves are the major sources of external forces.

Question 2.
What is Mass movement? (T.B.Qn)
Answer:
Mass movement includes a variety of gravity induced movements of slope material, but excludes transportation by running water, wind, and glacier. Transfer of one mass of rock debris down the slopes is the regular activity of mass movement. Rockfall, talus, Earth flows, landslides, are the major forms of mass movements.

Question 3.
Name any two types of weathering processes? (T.B.Qn)
Answer:
The process of disintegration and decomposition of rocks is known as “Weathering”. Temperature, pressure, rainfall, frost, wind, plants, animals, and human beings are responsible for weathering.

Question 4.
Distinguish between Oxidation and Hydration? (T.B.Qn)
Answer:

The rain water with oxygen reacts on rocks containing iron and produce oxides. This chemical reaction is known as Oxidation.

The rock minerals take up water, the increased volume creates physical stress within the rock. As a result certain minerals like feldspar and gypsum are reduced into powder. This process is called “Hydration”.

Question 5.
How does Biological weathering take place? (T.B.Qn)
Answer:
The roots of the plant grow through soil and in the cracks of rocks to find water and minerals. As the roots grow deep in the rock they widen and disintegrate the rocks, The burrowing animals like rats, rabbits, ants influence in the braking up of rocks. The human activities on the earth surface like mining, agriculture, quarrying, and deforestation rocks are disintegrated on a large scale.

Question 6.
Name any two types of weathering processes? (T.B.Qn)
Answer:
Physical weathering and chemical weathering are the major types of weathering.

Question 7.
Distinguish between Oxidation and Hydration? (T.B.Qn)
Answer:
The rain water with oxygen reacts on rocks containing iron and produce oxides. This chemical ‘ reaction is known as Oxidation.

The rock minerals take up water, the increased volume creates physical stress within the rock. As a result certain minerals like feldspar and gypsum are reduced into powder. This process is called “Hydration”.

Question 8.
How does Biological weathering take place? (T.B.Qn)
Answer:
The roots of the plant grow through soil and in the cracks of rocks to find water and minerals. As the roots grow deep in the rock they widen and disintegrate the rocks. The burrowing animals like rats, rabbits, ants influence in the braking up of rocks. The human activities on the earth surface like mining, agriculture, quarrying, and deforestation rocks are disintegrated on a large scale.

Question 9.
What is solution?
Answer:
Rain water is able to dissolve certain minerals in the soil, such as potash, rock salt and gypsum. Then, minerals are taken to the lower layers of the soil and the rock’s chemical composition changes. This process is called solution. This happens in very wet regions.

Question 10.
What is block disintegration?
Answer:
Due to temperature variation, there is continuous expansion and contraction in the rocks causing tension and stress. Later these rocks disintegrate into blocks known as ‘Block distintegration’.

Question 11.
What is granular disintegration?
Answer:
Rocks consist of different types of minerals. Some minerals get heated faster than others. As a result of differential expansion of minerals, the rocks break up into mineral grains. This is called granular disintegration.

Question 12.
What is chemical weathering?
Answer:
Chemical weathering causes decay and decomposition of rocks. It is carried out chiefly by rain water atmospheric gases as well as minerals of the rocks. Chemical weathering reduced the size of rocks and also results in decomposition.

Question 13.
What is Exfoliation?
Answer:
Due to the heat of the Sun, outer surface of rocks gets heated up, but inside it remains almost cool. This makes the rock to expand and crack. The think layer of rocks peeis off, like the peeling of an onion. This process is called “Exfoliation”.

Question 14.
What Hydration?
Answer:
The rock minerals take up water, the increased volume creates physical stress within the rock. As a result certain minerals like feldspar and gypsum are reduced into powder. This process is called “Hydration”.

Question 15.
Mention two agents of mechanical weathering.
Answer:
Temperature, frost, wind, gravitation and sea-waves are the agents of mechanical weathering.

Question 16.
Mention any two agents of denudation? (T.B.Qn)
Answer:
The natural agents which are responsible for the modeling and shaping of the Earth’s surface are called “Agents of Denudation”.

• River-Its activity is common in the drainage regions
• Glaciers- Its activity is widespread in the polar and high mountain regions.

Question 17.
What is Canyon? Give example? (T.B.Qn)
Answer:
It is a wide, deep and steep valley almost with vertical walls like feature found in the arid or semi arid regions is called ‘Canyon’ eg. Grand Canyon of River Colorado in USA.

Question 18.
Distinguish between Meanders and Ox-bow lakes? (T.B.Qn)
Answer:
In the plain section, the river flows slowly because of gentle slopes heavy load. In this course even with a little abstruction, the river takes a turn rather than eroding. Such ‘S’ shaped curves of the-river are called meanders.
The river which flows through the shorter route leaving the curve of the meander cut off and crescent shaped lake is formed known as Ox-bow lakes.

Question 19.
What is Delta? Name any two types of delta? (T.B.Qn)
Answer:
A triangular shaped alluvial deposition formed at the mouth of the river is called ‘Delta. Important types of deltas are a. Arcuate or common delta b. Bird-foot delta

Question 20.
Mention the difference between Tributaries and Distributaries? (T.B.Qn)
Answer:
A tributary is that river which joins the main river and increases the volume of water. It is generally found in the upper or the middle course of a river, eg. Yamuna is the main tributary of Ganga.

A distributary is that river which originates from a main river. It is formed near the river’s mouth before it falls into the sea. It is found in the lower course of the river. Eg. Hooghly is the main distributary of the Ganga.

Question 21.
What is Erosion? Mention the types of erosion.
Answer:
The process of wearing and taking away the part of rock is known as ‘Erosion’. There are two types of erosion, a. Mechanical erosion b. Chemical erosion.

Question 22.
What are Gorges?
Answer:
As a result of vertical down cutting of the river, particularly in the resistant rock beds, the valleys are deep with steep sided walls known as gorges. For example rivers like Indus, Brahmaputra has carved out deep gorges in the Himalayan Mountains while entering India.

Question 23.
What is triangular delta?
Answer:
These are most common in every continent of the world. The Nile delta is a best example. Most of the India Rivers draining into the Bay of Bengal have formed Arcuarate Delta.

Question 24.
What is Bird foot delta?
Answer:
It resembles the talons of a bird and is formed with the deposition of finer sediments carried down by the river in suspension. The delta of Missippi is a best example of this type.

Question 25.
What is Corrosion?
Answer:
The beds or sides of the river are scratched or cut with the help of the load that the river carries. Thus the valleys are depended or widened. This is called corrosion or abrasion.

Question 26.
What is Attrition?
Answer:
The rock pieces carried by the river dash against each other and break into smaller pieces, and are rounded to form pebbles. This is called attrition.

Question 27.
What are rapids?
Answer:
These features are formed as a result of unequal erosion of different rock beds of the river course. When soft and hard layers are arranges vertically one after the other, soft riverbeds are more eroded than the hard layers. So the water jumps over the hard layer. If the jumps are small they are known as rapids.

Question 28.
What is transportation?
Answer:
The rock pieces carried by the river form the load. Steep slopes and large volume of water help the transportation of the load. Lighter marital is carried further down the river than heavier material.

Question 29.
What are Alluvial fans?
Answer:
A fan-shaped land form, composed of alluvium deposits, formed where a river enters a main valley form a mountain area or a gently sloping plain is called alluvial fan.

Question 30.
What are ox-bow lakes?
Answer:
A small crescent-shaped lake in a flood plain of a river’is called ox-bow Lake.

Question 31.
What is Meanders?
Answer:
A curve or loop in the course of a river channel is called river meander. The bends in the river are called meanders.

Question 32.
What is a natural levee?
Answer:
Natural embankments built up by a river along the edge of its channels are known as natural levees. These are formed during floods.

Question 33.
What is the erosional work of the river as an agent of denudation?
Answer:
Erosion: Erosion is the wearing away of the land surface. It is faster, if the slope is steep, the volume of Water is more. The speed of the flow is great and the rocks are soft. The erosion work of river consists of four actions. Hydraulic, abrasion, attrition on and solution.

Question 34.
What is Hydraulic action?
Answer:
This is mechanical action done by running waster by wasting away the loose rock material which is disintegrated due to weathering. This process is called hydraulic action

Question 35.
What is Abrasion?
Answer:
The beds or sides of the river are scattered or cut with the help of the load that the river carries. Thus the valleys are deepened or widened. This is called abrasion.

Question 36.
What are the Iandforras formed in Erosion work of rivers:
Answer:
The erosion work of rivers forms certain kinds of landforms. They are V shaped valleys gorges, canyons, waterfalls, rapids, cascades and pot holes.
V = Shaped valley: A river with v cross section is called V shaped valley.
Gorgers: A very deep and narrow valley with very steep sides is known a s a gorge

Question 37.
What is Canyons?
Answer:
Deep valleys with step, almost vertical walls are called canyons
Waterfall: A vertical drop of water from a great height along the course of a river is called a waterfall.

Question 38.
What is potomology?
Answer:
The scientific study of rivers.

Question 39.
What is Cascades?
Answer:
A series.of rapids bit and small, are known as cascades.

Question 40.
What are the processes of Transportation by river?
Answer:
Rivers transport rock pieces form one placed to another. This is known as transportation. The rock materials carried by the river from the upper course to the lower course are called the load of the river. Steep slopes and larger volume of water help the transportation of the load. The river caries its load in four different ways. They are: flotation and siltation, suspension, solution and traction.

Question 41.
What is Flotation and saltation?
Answer:
The light material like wood floats owns the river. This is known as floatation. Some fragments of the rocks move downward by leaping and jumping along the bed of a river. This is known as saltation.

Question 42.
What is Suspension?
Answer:
Some particles like mud or salt is suspended in water and is carried away to a greater distance. This is known as suspension

Question 43.
What is load?
Answer:
The rock materials and eroded particles carried by a river is called load.

Question 44.
What is Traction
Answer:
Bigger rock pieces like gravel,-pebbles, boulders etc. are dragged and rolled along the bed by the force of running water. This process is called traction.

Question 45.
What is alluvial fan?
Answer:
A fan shaped land form, composed of alluvium deposits. Formed where a river enters a main valley from a mountain area or a gently sloping plain is called alluvial fan.

Question 46.
What is Flood plain?
Answer:
A low-lying land that borders a river which has been formed form the deposition of sediments carried down by the river is called “flood plain”.

Question 47.
What are potholes?
Answer:
These are the small depressions in the rocky beds of the river valley. They are formed by corrosion. Pebbles, sand and small rocks are carried by the river swirled around on the river bed.

1st PUC Geography Landforms Five Marks Questions And Answers

Question 1.
What is landform? Explain the different types of geomorphic processes. ?(T.B.Qn)
Answer:
A land form is any natural formation of rock and dirt, found on the earth. A landform can be as. large as a mountain range or as small as a hill. Landforms are natural features of the landscape, natural physical features of the earth’s surface eg. Valleys, plateaus, Mountains, plains, hills loess plains. The minor landforms include hills, ridges, valleys, basin etc. According to Geo-scientist the landforms are formed by the forces acting from the interior and on the surface of the Earth.

The processes carried out by Endogenic and Exogenic forces are called geomorphic processes. Endogenic forces: The internal forces are also known as endogenic forces. These are mainly the land building forces. Diastrophism includes all these processes; that move, elevate or build portions of the earth’s crust.

The internal forces are also known as endogenic forces. Exogenic Forces: The external forces are also known as Exogenic forces. These forces are found on the surface of the Earth, Which bring changes through degradation and aggradations process. River, glacier, wind, sea waves are the major sources of external forces.

Question 2.
Describe the factors affecting Physical weathering? (T.B.Qn)
Answer:
The disintegration of rocks without any chemical change in their compost in is known as mechanical or physical weathering. The disintegration of rocks occurs mainly due to the influence of temperature variation, frost action, wind action, rainwater, etc.

A. Surface are heated and expand. During the nights the rock surfaces are cooled due to , fall in temperature, rocks contact. The repetition of exemptions and contraction causes tension and stress which leads to cracks in the rocks. Then the rocks disintegrate into i blocks. This process is known as Block disintegration, Rocks are made of different types of minerals.

So the different parts of the same rock mass react differently to temperature. This leads to differential expansion and contraction inside the rocks. The rocks break up into smaller grains. This process of weathering is, called “Granular disintegration”. Due to variat Temperature in the upper and lower layers, the outer layers of rocks peel out into the uric shells. This process of weathering is known as “Exfoliation”.

B. Frost: Rocks are disintegrated due to freezing and thawing of water in the cracks or joints in the rocks. This frost action is more important in the temperate and cold regions. The water present in the cracks of rocks freezes during the night due to fall in temperature below freezing point. When water freezes it expands by 1/10 its volume. It thaws (melts) during the day, due to increase of temperature and it contracts in volume. This alternative freezing and melting of water widens other cracks in the rocks, splits and breaks then into blocks. This is known as frost shattering.

C. Rain: Sometimes, when rain falls suddenly on highly heated rocks in hot desert numerous cracks are developed. This is just like a heated chimney of a lamp, when a drop of water falls on it. The repetition of this mechanism causes disintegration of rocks. In humid region, when torrential rain occurs, the drops strike the rock surface and loosen the particles.

D. Wind: In the deserts the wind blows with greater speed carrying with it sand and rock materials, they collide with each other or strike against the loose rock and cause weathering. In deserts the wind cause this type of weathering on a large scale.

E. Sea waves: Sea waves strike the costal rocks. Repeated striking enlarges the incipient joints. Fractures and cause breaking of rocks into small blocks. Weathering also takes place due to hydraulic pressure, abrasion and attrition caused.

F. Slope: A steep slope helps in weathering. In mountainous and hilly area, sometimes, on account of gravity, blocks of rocks move down the slope while rolling down the slope, they strike against other block and break up into pieces.

G Gravitation: the gravity of Earth makes the huge rocks to roll towards the slope. Rolling rocks strike against each other and break up into pieces.

Question 3.
Explain chemical weathering with examples. (T.B.Qn)
Answer:
Disintegration and Decomposition of rocks by chemical processes is called “Chemical weathering”.
In this process secondary or new minerals are developed from the original minerals of the rocks. The rain water and atmospheric gases are the main agents of chemical weathering. It is vey common in humid regions.

There are four types of chemical weathering process. They are:

a. Oxidation: The rain water with oxygen reacts on rocks containing iron and produce oxides. This chemical reaction is known as “oxidation”. The common process of rusting of iron is an example of oxidation. .

b. Carbonation: The rain water with carbon-di-oxide becomes a weak carbonic acid and it reacts with calcium carbonate or limestone to form calcium bicarbonate, which dissolves easily. This process is called “Carbonation”. It is very active in limestone regions.

c. Hydration: The rock minerals take up water the increased volume creates physical stress within the rock. As a result certain minerals like feldspar and gypsum are reduced into powder. This process is called “Hydration”.

d. Solution: The rain water is able to dissolve some of the soluble minerals, such as rock- salt, gypsum, potash. This process is called “Solution”.

Question 4.
Explain Biological weathering with examples.
Answer:
The disintegration of rocks caused by plants, animals and human beings is called “Biological Weathering”.
(a) Plants: The roots of the plant grow through soil and in the cracks of rocks to find water and minerals. As the roots grow deep in the rock they widen and disintegrate the rocks. This process is rn’ost prominent in thick forests and vegetative regions.

(b) Animals: The burrowing animals like rats, rabbits, ants, earthworms and termites influence in the breaking up of rocks and make passages below the ground. The seepage of air and water through these passage results in rapid weathering of rocks.

(c) Human beings: Human beings play an important role weathering of rocks, through activities like agriculture, mining quarrying, oil drilling, deforestation etc.

Question 5.
Explain the process of Physical weathering with examples.
Answer:
The disintegration of rocks by mechanical way and without any chemical changes is called “Mechanical weathering”. It is also called “physical weathering”.
The process of Mechanical weathering is in various forms, depending the types of rock. They are:

a. Block disintegration: Due to temperature variation, there is continuous expansion and contraction in the rocks causing tension and stress. Later these rocks disintegrate into blocks known as “Block Disintegration”.

b. Granular disintegration: Rocks consist of several types of minerals and these minerals
react differently to heat. As a result, the rocks break into different mineral grain known as “Granular Disintegration”.

c. Exfoliation: Due to the heat of the Sun, outer surfaced of rocks gets heated up, but inside it remains almost cool. This makes the rockto expand and crack. The thin layer of rocks peels off, like the peeling of an onion. This process is called “Exfoliation”.

Question 6.
Explain the types of River Course.
Answer:
The entire path of the river from source to mouth is divided into three courses.

a. The upper course: It is near the source of a river and is normally found in mountainous areas. Here erosional work is dominant, because the river flows I steep slopes with great velocity. This stage of the river course is known as ‘Young Stage’.

b. The Middle course: The middle course begins when the river enters the plateau and plains from the mountains the dominant work of the river in this stage is transportation. This stage of the river course is called ‘Mature stage’.

c. The lower course: It is the plain course of a river neat its mouth. In the lower course the slope is very gentle, the valley is broad, the speed of the river is very slow, and hence deposition work is dominant. This stage f the river is known as ‘Old Stage’.

1st PUC Geography Landforms Ten Marks Questions And Answers

Question 1.
Describe the Landforms associated to work of river. (T.B.Qn)
Answer:
River is an important external agent of denudation on the ever-changing face of the Earth. The work of river is more or less common in all the drainage systems of the world.
The work of river consists of three closely interrelated activities.

1. Erosional work: The process of wearing and taking away the part of rock is known as ‘Erosion’. It depends upon the volume and velocity of water, nature of slope and the nature of rocks. The erosional work of the river is performed in two ways.
a. The Mechanical and b. The Chemical erosion.
There are various Iandforms associated to erosional work of river.

a. ’V’ Shaped valley: In the mountain course the speed of the river is greater and volume is less. As the water rushes down the steep slopes there is maximum vertical , or later erosion. The rapid down cutting or vertical erosion results in the formation of ‘V’shaped valley.

b. Gorge: A deep and narrow valley with steep rocky, sides in the river course is known as ‘Gorge’. They are formed by the regular vertical cutting by the rivers in the valleys eg. Narmada gorge.

c. I shape valley: Avey steep, deep river valley formed by the river, lookinglike T, is called ‘I’ Shaped valley. These are very deep compared to gorges.

d. Canyon: It is a wide, deep and steep valley almost with vertical walls like feature found in the arid or semi arid regions is called ‘Canyon’ eg. Grand Canyon of River Colorado in USA.

e. Potholes: These are the small depressions in the rocky beds of other river valley. They are formed by corrosion. Pebbles, sand and small rocks carried by the river swirled around on the river bed. This action erodes the rock on the river bed forming potholes.

f. Waterfalls: Huge volume of water falling from a great height along the course of a river is called “Waterfalls’. They are formed when the hard and soft rocks come in the way of flowing river. The soft rock gets eroded faster and hard rock does not erode easily. Therefore huge amount of water falls from great height and creates waterfalls. Eg. The Jog falls, The Angel falls, The Victoria falls.

g. River Capture: It is formed mainly due to head-ward erosion by the river near its source. When the source of a river is captured by another major and strong river it is called‘River Capture’.

2. Transportational work: The process of carrying away the eroded materials is known as ‘Transportation’. The rock materials and eroded particles carried by a river is called its Load. The transportation capacity of a river is based on velocity of water, volume of water, load, slope, smooth valley floor etc.

The major landforms associated with the transportational work of the river are:

a. Alluvial fans: The term alluvium refers to the debris transported and deposited by rivers. When the fast flowing river enters the plateau or plain region, it experience sudden decline in gradient and obstruction in its path. Due to obstruction of the river spreads and deposits many of its light materials in fan shape known as ‘alluvial fans’.

b. Alluvial cones: In the plateau and foot hill region when the river spreads out, the eroded materials carried by the river is deposited in conical shape called ‘Alluvial cones’.

3. Depositional work: The process of carrying and accumulating the eroded materials by the river at the lower course is called ‘deposition’. In the lower course due to gentle slope the river slows down and deposits most of its materials on the banks, course and the mouth.

The important landforms resulting from depositional work of the river are:

a. Meanders: In the lower course, river flows slowly in zig zag or curved manner due . to smaller obstruction in its path. A curve or loop formed by the river in its path is called ‘Meander’. When the river course formed by such crescent shaped loops due to continuous lateral deposition it is called meandering course.

b. Ox-bow Lakes: The ox-bow lakes are formed by depositional and erosional actions taking place simultaneously and they are a result of excessive meandering. The River which flows through the shorter route leaving the curve of the meander cut off and crescent shaped lake is formed known as‘Ox-bow lakes’.

c. Flood Plains: When the river is in floods the water overflows on its bank and spreads in the surrounding regions. The silt carried by the water gets deposited in these areas and creates flat plains on both the banks of the rive known as ‘Flood Plains’.

d. Delta: A triangular shaped alluvial deposition forced at the mouth of the river is called ‘Delta’. Important types of deltas are

a. Arcuate or Common delta
b. Bird-foot delta

e. Distributaries: As the river approaches the sea or Ocean, due to reduction in gradient, joining of tributaries, its volume increases, speed decreases hence, the rivet begins to break up into a number of branches from the main river called ‘Distributaries’.

f. Estuary: Estuaries are the tidal mouth of a river having a narrow, gradually widening lay at the mouth. In Estuary River water is mixed with seawater. Eg. The Narmada estuary, The Kali estuary.