WBBSE Solutions For Class 10 Geography And Environment Chapter 1 Exogenetic Processes And Resultant Land Forms

Chapter 1 Exogenetic Processes And Resultant Land Forms Topic 1 Exogenetic Process and the Works of Rivers Long Answer Type Questions

Question 1 Describe the various works of landforms formed due to erosional works of rivers.
Answer:

The river performs three activities in its course flow erosion, transportation and deposition.

The landforms formed due to erosional works of a river are—

1. Canyons: The canyons are formed in the mountainous regions of arid climatic regions. The rivers which flow through these valleys are generally snowed. They have high erosive powers due to great velocity. Downcutting of the valleys is prolonged while side cutting is negligible, as there is no rainfall in this region and no tributaries meet the main river. E.g- the Grand Canyon of river Colorado.

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WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land fors i shped valley

 

2. Gorges: In humid mountainous regions, the rivers flow with great velocity and have great erosive power. The downcutting of the rivers makes the valleys very deep. At the same time, side-cutting of the valleys occurs due to weathering, mass wasting and other activities. Thus, the valleys become wider and look like the letter ‘V’. Example-Valley of river Kali in Nepal.

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WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms v shaped valley

 

3. Waterfalls: In the course of the river, if hard and soft rock beds lie alternately, the soft rocks get eroded very fast and the hard rocks stand out. This leads the water of the river to fall from a considerable height over a steep slope. Thus, a waterfall is formed. Example—The Angel waterfalls in the course of river Churun in Venezuela is the highest waterfalls in the world.

4. Potholes: As the river flows, the rocks and boulders carried along with the water rub against the floor of the river bed and cause the formation of small depressions due to abrasion. These are known as potholes. Example—Numerous potholes are present on the bed of river Tista.

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WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms potholes

 

5. Plunge pools: As the water falls from a height with great velocity, the rock beds at the base of the waterfalls get eroded, and huge depressions are formed there. These are formed due to abrasion and the plunging of the water and hence they are called plunge pools. Plunge pools are potholes of bigger dimensions.

6. Interlocking spurs: In mountainous regions, the hard rocks or mountain ridges may lie in such a way that the river has to take frequent turns to avoid these obstructions while flowing. The river erodes the foothills of these mountains to carve out its own path of flow. A distant view of the landscape looks as if the mountains are interwoven or interlocked. Such mountains are known as interlocking spurs.

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Interlocking spurs

7. Truncated spur: A truncated spur is a blunt-ended, sloping ridge which descends towards a valley. Its abrupt termination is normally due to erosion by glaciers and rivers. Example—Truncated spurs are seen in the valleys of the rivers Tista, Torsa, Mahananda, etc.

WBBSE Class 10 Geography Chapter 1 Question Answer

Question 2 Describe with sketches three major landforms developed by the erosional work of rivers.
Answer:

Three major landforms developed by the erosional work of rivers

1. Canyons: The canyons are formed in the mountainous regions of arid climatic regions. The rivers which flow through these valleys are generally snowed. They have high erosive powers due to great velocity. Downcutting of the valleys is prolonged while side cutting is negligible, as there is no rainfall in this region and no tributaries meet the main river. E.g- the Grand Canyon of river Colorado.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land fors i shped valley

 

2. Gorges: In humid mountainous regions, the rivers flow with great velocity and have great erosive power. The downcutting of the rivers makes the valleys very deep. At the same time, side-cutting of the valleys occurs due to weathering, mass wasting and other activities. Thus, the valleys become wider and look like the letter ‘V’. Example-Valley of river Kali in Nepal.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms v shaped valley

 

3. Waterfalls: In the course of the river, if hard and soft rock beds lie alternately, the soft rocks get eroded very fast and the hard rocks stand out. This leads the water of the river to fall from a considerable height over a steep slope. Thus, a waterfall is formed. Example—The Angel waterfalls in the course of river Churun in Venezuela is the highest waterfalls of the world.

Question 3 Describe the various landforms formed due to the depositional works of rivers.
Answer:

The various landforms formed due to depositional works of rivers are—

1. Alluvial cone and alluvial fan: As the rivers emerge from the mountains, they erode heavily and flow with great speed. However, when they leave their mountainous course and enter the plains, they suddenly lose their speed. Thus, the carrying capacity of the river is reduced considerably.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms i shaped valley alluvial fan

 

Hence, it deposits huge amounts of rocks, pebbles, sand, silt, clay, etc. at the foothills of the mountains. These depositions look like a cone and are called alluvial cones. If the cones spread wider, they are called alluvial fans. Example—Such alluvial cones and fans are present at the foothills of the Himalayas in the course of different tributaries of river Ganga.

2. Sand bars and islands: In the middle course, the river is unable to flow with great velocity. Hence, it cannot carry the huge amount of load brought down from the mountains and starts depositing them on the river bed. These depositions accumulate day after day and form sand bars or river islands. The rivers thus bifurcate at regions when it encounters such a sand bar along the flow. Such bifurcated channels are known as braided channels. Example—The Majuli island in the Brahmaputra river is the largest river island in India.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms sand bars

 

3. Flood plains: In the middle course, the valleys of the river are wide but less deep. During the rainy season, when the water volume in the channel increases, the river floods the adjacent areas. The silt, clay and mud present in the river water also flow out and spread over the area. When the flood recedes, a part of the flood water flows back into the river and some percolates down to recharge the underground water table. However, the silt and clay remain spread over the region. These silt deposits accumulated over the years form flood plains.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms food plain

 

4. Natural levees: On the plains, the silt, clay and sand particles flowing out of the river channel during floods get accumulated and compact on the banks of the river. These naturally forming accumulations rise in height forming a narrow belt of ridges and these are known as natural levees. Natural levees act as natural embankments and help in checking floods

Delta: In the lower course of the river, the slope of the land becomes so negligible that the river cannot carry its load any further. It deposits the load gradually near the mouth. These continued depositions eventually form small islands, encountering which the river channel bifurcates into several distributaries before meeting the sea. The islands formed to resemble a triangle or the Greek alphabet ‘A’. Hence, the region is called a delta.

WBBSE Class 10 Geography Chapter 1 Question Answer

Question 4 Discuss the favourable conditions for delta formation.
Answer:

The conditions favourable for the formation of a delta are—

1. The rate of deposition of silt and other materials by the river and its distributaries must be more than the rate of removal of the deposition by the sea waves.

2. The rivers should have a long course and should have a number of tributaries so that the eroded materials brought down altogether are sufficient for the development of a delta.

3. The river should not be turbulent and speedy near the mouth so that silt can easily deposit there.

4. The continental shelf where the river meets the sea should be wide and gentle in slope so that the sediments brought down can easily deposit there. A steep slope of the continental shelf will wash down the sediments into the deep sea and hinder delta formation.

5. Deltas are easily formed if the prevailing wind direction in the region is opposite to that the direction of the river.

6. Deltas are formed easily in regions where the sea is a little enclosed with the land rather than in regions with open seas.

7. Almost stable conditions (not subject to any rejuvenation or submergence) of the sea coast and oceanic bottom will allow the deposits to settle down.

8. Finer sediments will get carried away in suspension deeper into the sea. Very coarse and large size sediments would settle at the river bed. So, medium-sized sediments are the most suited for delta formation.

Question 5 Compare the works of a river in its three courses.
Answer:

A river performs different actions in its different courses. The actions of the river in its three different courses are—

 

Points of comparison  Upper course  Middle course   Lower Course
Location Extends from the source of the river in the mountains up to the foothills where the river enters the plains. Extends from the foothills of the mountains through the plains up to the beginning of the delta region. Extends from the beginning of the delta region up to the mouth of the river near the sea.
Work The main work is erosion due to the high velocity of the river. The river carries out downcutting of valleys in the upper mountains and side cutting along with downcutting in lower altitudes. The huge rocks and boulders eroded by the river are transported. The main work is transportation. Some amount of erosion and deposition is also noticed. Valleys become very wide and their depth reduces in this course. Mam’s work is deposited as the slope of the land becomes negligible and the river cannot carry the huge amount of bed load any further.
River velocity Very high velocity due to steep slope. Lower velocity due to the gentle slope of the land. Very low velocity due to the negligible slope of the land.
The shape of the Valleys T or ‘V’-shaped valleys are commonly seen due to more downcutting than side-cutting by rivers. Wide ‘U’-shaped valleys are commonly seen due to more side-cutting than downcutting by rivers. Very wide and flat-bottomed valleys are seen.
Landforms created ‘1’ and ‘V’-shaped valleys, waterfalls, plunge pools, potholes, interlocking spurs, truncated spurs, etc. Alluvial cones and fans, flood pains, natural levees, etc. Oxbow lakes deltas of various types.

 

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Shape of river valley

 

Question 6 How has the change in climate influenced the islands of Lohachara, New Moore and Ghoramara?
Answer:

The change in climate influenced the islands of Lohachara, New Moore and Ghoramara

Climatic changes have endangered the existence of the islands of the Sundarbans to a great extent. Global warming has caused the melting of ice caps and glaciers to such an extent that, the sea level has risen considerably. This has led to the submergence of numerous small islands. The large islands of Lohachara, New Moore and Ghoramara have also faced submergence and have been named Vanishing islands’. Numerous villages and agricultural fields have submerged, and thousands of people have become ‘climatic refugees’.

1. Lohachara island: The Lohachara island existed in the Sundarban region near the mouth of the river Hooghly. In 2006, the island was submerged completely. In 2009, it started re-appeared, but presently it lies submerged.

2. New Moore island: New Moore island lies 2 km from the mouth of the river Hariyabhanga. It is a part of the Ganga- Brahmaputra delta region. In 1970, the island was submerged as an aftermath of the super cyclone ‘Bhola’. In 1974, the size of the island was 2500 sq.m according to satellite images. However, at present, it lies completely underwater as a submerged bar or bank.

3. Ghoramara island: The Ghoramara island lies 92 km south of Kolkata, north of the Sagar Islands at the mouth of river Hooghly and east of the mouth of river Haldi in the Bay of Bengal. This is an island in the Sundarban region. In 1951, the size of the island was 38.23sq. km, but by 2011, the size reduced to a mere 4.37sq.km. Experts predict that the island will totally disappear due to submergence in the near future.

WBBSE Class 10 Geography Chapter 1 Question Answer

Chapter 1 Exogenetic Processes And Resultant Land Forms Short Explanatory Answer Type Questions

Question 1 Mention the extent of the different courses of river Ganga.
Answer:

The extent of the three courses of river Ganga is—

Course of river Extent
Upper course From Gomukh in Gangotri glacier in Uttarakhand to Haridwar in Uttarakhand.
Middle course From Haridwar in Uttarakhand to Rajmahal hills in Jharkhand.
Lower course  From Rajmahal hills in Jharkhand to the mouth of the river in the Bay of Bengal.

 

Question 2 Discuss the various types of erosion.
Answer:

Erosion by rivers can be divided into two types—

chemical erosion and mechanical erosion, which further involves various methods.

1. Chemical Erosion

1. Solution: This process involves the dissolution of soluble materials. The soluble materials are removed from their parent rocks by the processes of disintegration and decomposition.

2. Mechanical Erosion

1. Force of water: themayErosionrunningThefallIn the off removed water. river the wall valleys, materials of the valleys due to continuous hitting of water, and may get carried away to distant places with the flowing water.

2. Attrition: The rock fragments are already broken away from the valley walls or river bed strike against each other and break into smaller fragments in this process. These fragments are carried with the water in suspension and transported down the channel.

3. Abrasion: This process involves the removal of loosened rock materials from the valley walls and floors with the help of the tools of erosion. The rock fragments carried by the river collide and scratch against the river valley and erode materials from there, thus deepening and widening the valley.

4. Hydraulic action: The bubbles created in the river water in the course of flow may burst together and produce sound waves, which can gradually break down the rock fragments into smaller parts.

Question 3 On which factors does the carrying capacity of a river depend?
Answer:

The carrying capacity of a river depends upon the following factors-

Factor controlling carrying capacity Description
Volume of water Carrying capacity increases if the volume of water present in the river increases.
The velocity of the river Carrying capacity is mostly dependent on the velocity of the river and the slope of the land. According to the Sixth Power Law, if the velocity of the river is doubled, its carrying capacity is increased by 2G = 64 times.
Size and volume of load Carrying capacity depends on the size and volume of the load being carried. If the size of the materials is small and the volume is less the carrying capacity increases and vice versa.

 


Question 4 By which methods does the river carry its load?
Answer:

The river carries its load by the following four methods—

 

Methods  Description 
Solution  Rocks made of limestone and other soluble materials are dissolved in the river water and carried away  to distant places
Suspension  The sand, silt and clay particles remain suspended in water as the river flows along the slope about 70 % of the bed load is carried by the suspension
Saltation The particles that are big enough to be transported by suspension move forward by jumping and colliding with the valley walls.
Traction  The large rocks and boulders that cannot be lifted by the river bed and transported

 

Question 5 Under which conditions does the river deposit its load?
Answer:

A river deposits its load under the following situations—

1. Volume of water: Depositions occur when the volume of water in the river reduces.

The volume of water reduces in the following situations—

1. When the river enters a region of low rainfall.
2. During periods of droughts.
3. In dry seasons
4. In limestone or sandstone regions where water percolates down.

2. Reduced slope: The velocity of the river reduces if it flows over land with a gentle slope and thus the reduced velocity enhances the deposition process.

3. Bed load: If the amount of sediment carried by the river increases, as in the case of the middle and lower course of the river, the flow of the river becomes sluggish and thus it deposits much of its bed load to reduce the amount of sediment being carried.

Question 7 Mention the effects of the global climatic change on the active part of the Ganga-Padma-Meghna delta.
Answer:

The effects of the global climatic change on the active part of the Ganga-Padma-Meghna delta are—

1. Rise in temperature: During the period from 1980 to 2017, the temperature of water of the rivers of the Sundarbans region has risen by 0.5°C per decade. This rise in temperature has caused great harm to the mangrove ecosystem.

2. Cyclones and monsoon wind: The global climatic change has increased the frequency of the cyclones occurring in and hitting the Sundarbans. Clearing the mangrove forests to make way for human settlement has magnified the impact of the cyclones in this region.

3. Rise in sea level: The global rise in temperature is causing the ice caps to melt at the poles. This, in turn, is leading to the rise in sea level, posing a great threat to many islands and island nations of the world. Several islands of the Sunderbans are facing a similar danger. Example— Lohachara, South Talpatti.

4. Increase in salinity: The rise in sea level is causing the water and soil of the Sundarbans to become saline. This is affecting agriculture, the drinking water of the region, etc.

Question 8 How are waterfalls formed in the course of a river?
Answer:

Waterfalls formed in the course of a river:

When the water of a river plunges from a higher elevation to a lower elevation, it is known as a waterfall. In the course of a river, if hard and soft rock beds lie alternately horizontally one above the other, or diagonally, the harder rocks are less eroded and softer rocks are highly eroded by the river. This gradually gives rise to a steep slope over which the river plunges downwards. A waterfall may also be formed at a knick point along the course of the river where there is a sudden change of elevation in the longitudinal course.

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms waterfalls soft rocks

 

Example-The famous Niagara falls lies along the course of the Niagara river in the USA.

Question 9 Classify waterfalls.
Answer:

Waterfalls

Waterfalls can be classified into three types according to the slope of the land and the volume of water in the waterfalls—

 

Type Definition Example
Rapid If the slope of the mountain is gentle, the waterfall formed is rapid. The height of such falls is just a few metres. Rapids are waterfalls of smaller dimensions. Numerous falls in Chotanagpur Plateau.
Cascade If the waterfalls come down in numerous streams, step by step, over a large area, it is called a cascade. Jonha waterfalls in Ranchi.
Cataract The cliffs formed due to the presence of hard and soft rocks in the river course form large waterfalls called cataracts. Six cataracts are present between Khartoum and Aswan along the course of the river Nile.

 

Question 10 Explain why the river’s main work in the lower course is deposition.
Answer:

The river’s main work in the lower course is deposition:

In the lower course of the river, the slope of the land over which the river flows is negligible. As a result, the flow becomes sluggish. Also, the amount of bed load carried in this course is huge. The river loses all its erosional and transportation capacities. Thus, the huge amounts of load brought down from the upper and middle courses, get deposited along the lower course of the river. depositional features seen here are flood plains, natural levees, deltas, etc.

Question 11 Why do in their the mountainous rivers mainly course?
Answer:

The rivers mainly cause erosion in their mountainous course because—

1. The mountainous regions have rugged terrain and steep slope, which increases the velocity of the flowing water.

2. The valley walls and floors get highly eroded by the methods of hydraulic action, abrasion and attrition.

3. The amount of sediment transported by the river in this course is much less and thus the erosive power of the rivers is more.

Question 12 How is a delta formed in the lower course of a river? Or, Explain why a delta is formed at the mouth of a river.
Answer:

The deltas can be classified into four types according to their shapes—

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms ganga delta

 

loses its velocity and carrying capacity. The huge amount of sand, silt, clay, etc., brought down from the mountains is deposited in this region. The saline water at the mouth of the river where it meets the sea helps these deposited materials to get compacted. Thus, new islands are formed in the lower course of the river over a vast region from these deposited sediments. These islands are known as deltas.

It must be noted that the rate of deposition of sediments must exceed its removal rate by the sea waves as one of the factors affecting delta formation. E.g.— The largest delta in the world has formed at the mouth of the rivers Ganga-Brahmaputra.

WBBSE Class 10 Geography Chapter 1 Question Answer

Question 13 Classify deltas.
Answer:

The deltas can be classified into four types according to their shapes—

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forsdelta flow chart

1. The deltas that look like an arc of a circle or a bow at the region or side that meets the sea, are known as arcuate deltas. E.g.-The deltas formed by the river Ganga, Nile, Po, Rhine, Hwang Ho, etc. are arcuate deltas.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms delta

 

2. The deltas that resemble the foot of a bird pointing towards the sea i.e., finer materials

3. The deltas that are vaguely V-shaped with curved sides are known as cuspate deltas. E.g.-The delta formed by the river Ebro.

4. The deltas formed due to the filling of the estuaries of the rivers are known as estuarine deltas. E.g.-The delta formed by the river Rhine.

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Question 14 How are oxbow lakes formed?
Answer:

Oxbow lakes are Formed as follows:

Oxbow lakes are formed mostly at the end of the middle course and the beginning of the lower course of a river. The curvatures of the meander loops of the river are enhanced due to continued lateral erosion by the rivers in their middle course.

Thus, the two ends of the individual meander loops gradually come closer and their mouth is clogged by the sediments deposited by the river. The meander loop is eventually abandoned as the river straightens its course. Thus, the water in the abandoned loop forms an oxbow lake. Numerous oxbow lakes are seen along the course of river Ganga and its tributaries.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms oxbow lake

 

Question 15 Why are ‘V-shaped valleys formed in the upper course of a river?
Answer:

‘V-shaped valleys formed in the upper course of a river

The section of the river flowing through the mountainous region is known as the upper course of a river. The shape of the river valley formed in this region due to downcutting is like a V. The causes of the formation of the ‘V-shaped valleys are—

1. Slope of land: The slope of the land is steep in mountainous regions. This causes the river to flow with great velocity. The high velocity of the river and the rock fragments carried with it collide with the river bed and cause more downcutting than side cutting of the valleys. This makes the river valley narrow but deep.

2. Heavy rainfall and weathering: In mountainous regions that receive heavy rainfall, the rate of weathering by mechanical and chemical processes is high. The dissolving of certain minerals (like limestone) and mass wasting removes huge amounts of rock debris from the region. This makes the river valleys deep ‘And V-shaped and gradually the valleys start becoming wide due to lateral erosion also.

3. Others: Sometimes, landslides in river valleys are very steep, causing them to widen and become ‘V-shaped. The meeting of tributaries with the main river also makes the valleys ‘V-shaped.

Question 16 How are flood plains formed?

Answer: Flood plains are formed in the middle course of the river due to the deposition of silt. In the middle course of the river, when the volume of water suddenly increases due to heavy rainfall or due to snow-melt water draining into the river in the upper course, the excess water flows out of the river channel towards the adjacent plains on both sides of the river banks. Huge amounts of sand, silt and clay flow out with this water and spread all over the area during times of flood.

When the flood water recedes, some of the water flows back into the river, while some percolates underground. The silt and clay spread over the area form a thin layer of soil over the area. When this process continues year after year, the region develops into a new landform called a floodplain. Large flood plains are seen on both the banks of river Ganga and river Brahmaputra.

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Question 17 How do waterfalls move backwards?
Answer:

Waterfalls move backwards:

The plunging of water of a river from a height downwards, forms a waterfall. Such difference in height within the river course occurs due to the presence of hard rock beds alternated with soft rock beds. As the water plunges from a height, it creates a plunge pool at the foot of the waterfall. This plunge pool increases in dimension over time and the rocks of the wall seem to hang over a hollow. After a period of time this hanging wall collapses, thus the waterfall seems to move backwards, towards its source.

Example—The backward movement of the Chitrakoot waterfalls on river Indravati can be clearly understood.

Question 18 How are the Sundarbans being affected by climatic changes?
Answer:
The climatic changes all over the world are also affecting the Sundarbans in the following ways—

1. Due to the increased rate of global warming, the temperature of the earth will increase by 2-4“C by 2050. The amount of ice that will be melted due to this rise in temperature will increase the level of seawater. If the sea level rises by lm, most of the islands in the Sundarbans would submerge. A few already have.

2. The rise in sea level, is also turning the rivers of this region saline. This, in turn, is affecting the plants and animals of the region.

3. Saline soil is affecting the agriculture of the region and causing a shortage of food.

4. Increase in temperature is causing frequent cyclonic storms in this region.

Question 19 What is the role of a river as a part of the water cycle?
Answer:

The role of a river as a part of the water cycle

The rivers help in the circulation of rainwater from one place to another. The rivers help to prevent the rainwater from remaining arrested in a particular region.

The water present on the earth’s surface and in the atmosphere circulates through the hydrological cycle. The sun evaporates huge amounts of water from rivers, lakes, oceans and other water bodies. The water vapour thus created, concentrates and forms clouds.

These clouds cause snowfall and rainfall. The water coming from the rain or melting of snow accumulates and flows down the slope of the mountains as rivers. The water in the rivers once again evaporates and forms vapour.

A part of it also percolates down and recharges the underground water table. The rest of the water flows into the ocean. This is how the river plays an important role in the water or the hydrological cycle.

Question 20 Why are oxbow lakes formed in deltaic regions?
Answer:

The oxbow lakes are formed in deltaic regions due to the following reasons—

1. Meandering rivers: The slope of the land becomes negligible in the deltaic region. Thus, the river cannot flow with great velocity and takes a turn wherever it is obstructed.

2. Erosion at the curves of meanders: As the river starts meandering, erosion occurs at the concave side and deposition occurs at the convex side.

3. Increase in the curve of the meanders: As the processes of erosion and deposition occur simultaneously in a meander, the curvature increases, and the two ends of the curve come very close to each other.

As the ends of a curve of a meander come very close to each other, the curved part is cut off due to deposition from the main flow and the river continues to flow in a straight path. The enclosed body of stagnant water thus left behind becomes an oxbow lake.

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Question 21 What are constructive deltas and destructive deltas?
Answer:

Constructive deltas: The rivers bring down huge amounts of sand, silt and clay from the upper course and deposit them over vast areas to form a delta at its mouth. The size of the delta goes on increasing as more and more deposits are brought in. This is called a constructive delta. Constructive deltas can be of two types—

1. Tongue-shaped (e.g.—delta of river Nile).
2. Bird foot shaped (e.g.—delta of river Mississippi).

Destructive deltas: The deltas which go on changing their shapes and sizes due to the action of waves and tides, are called destructive deltas. E.g.—Delta formed by river Rhone is highly a wave-dominated delta.

Question 22 Why do floods occur frequently in the lower course of the river?
Answer:

The lower course of the river is frequently flooded due to the following reasons—

1. The river contains a huge volume of water in this course. However, the slope of the land is so negligible that the water cannot flow with great velocity towards the sea.

2. The maximum of the load brought down by the river is deposited in this region. Thus, the depth of the river channel gradually decreases. During the rainy season, as the volume of water in the channel in the upper course increases the lower course cannot hold the huge volume of water, hence the banks on either side get flooded.

Question 23 Why is the degradation process called a destructive process?
Answer:

Degradation is the process by which the higher landforms are lowered by erosion, mass wasting and denudation so as to attain an equilibrium position or a graded profile. Since the original landforms are eroded and lowered by the process of degradation, it is considered a destructive process.

Question 24 Why is vertical erosion or downcutting of river valleys in the upper course more prominent compared to lateral erosion or side cutting?
Answer:

The level of downcutting or vertical erosion of river valleys in the upper course is more prominent compared to side cutting or lateral erosion because the river flows over a steep slope in the upper course, hence having high velocity. Also, the river carries a huge amount of rocks and pebbles in this stage, which act as tools of erosion. Thus, the valleys are deepened due to abrasion by the tools of erosion and the force of the flowing water.

Question 25 Why are islands and sand bars created in the middle and lower course of a river?
Answer:

Islands and sand bars are formed in the middle and lower course of the river because of the following reasons—

1. The speed of the river reduces in the middle course as it leaves the mountainous region and enters the plains. Owing to the gentle slope of the land and increased bed load the carrying capacity of the river reduces considerably.
2. Depositions start occurring on the river bed. As more and more depositions occur, the sand bars grow bigger in size and rise out of the water as islands.

Question 26 Why have numerous islands and sand bars formed on the river Brahmaputra?
Answer:

Numerous islands and sandbars have formed on the river Brahmaputra because—

1. The course of river Brahmaputra flowing through Assam is the middle course. Hence, the river flows with less velocity.

2. The load brought down by the river gets deposited on the river bed and creates sand bars.

3. Numerous tributaries join the river Brahmaputra and contribute a huge amount of water as well as eroded materials. Thus, more sand bars are formed and each of them grows larger in size. Example—Majuli island has been formed in a similar way.

Class 10 Geography Chapter 1 WBBSE

Question 27 What are the different exogenetic processes?
Answer:

The exogenetic processes can be broadly divided into three parts—

1. Degradation: Through this process, the existing landforms are lowered in height. E.g.— residual hills.

2. Aggradation: By this process, the height of the existing landforms is increased by the deposition of materials brought down by rivers, glaciers and winds due to erosion. E.g.— flood plains, loess plains, deltas, etc.

3. Biotic activities: Sometimes, changes in landforms occur due to biotic activities. E.g.— Ponds, wetlands or depressions may get filled up with mosses, plants bushes, fruits, flowers, etc. People may cut down mountains to construct roads, railway lines, etc. Shallow seas or gulfs may be dammed to reclaim land from the water.

Question 28 How is landform levelled by the process of graduation?
Answer:

Gradation is the process of levelling rugged and uneven land into a smooth and even landform. It is the combined outcome of the process of degradation and aggradation. A graded profile is one in which no further erosion or deposition takes place.

Gradation is the combination of both degradation and aggradation. The high hills and rugged topography are lowered and levelled due to erosion by wind, water, snow, etc. This is known as degradation.

Through the process of aggradation, the low-lying regions, the depressions and gaps are filled up by the deposition of eroded materials brought down by rivers, glaciers or wind. Degradation and aggradation processes go on continue unless the graded profile is attained.

Question 29 Differentiate between gorges and canyons
Answer:

Gorges and canyons both are deep valleys created due to river erosion. However, there are some minor differences between the two.

The differences between them are—

Point of difference   Gorges  Canyons 
Shape  Deep, narrow valleys, resembling the letter ‘v’ Deep and narrow valleys, resembling the letter ‘I’
Location  Gorgrs are created in the upper course of the river in the mountainous regions, where heavy rainfall occurs Canyons  are created in the upper course of the river in the mountainous regions, where heavy rainfall occurs arid climate prevails
Rate of downcutting and side cutting  Georges are v-shaped because the rate of downcutting is greater than side cutting Canyons are i-shaped due to prolonged cutting and side-cutting is negligible

 

Question 30 Differentiate between alluvial cones and deltas.
Answer:

The differences between alluvial cones and deltas are as follows—

Class 10 Geography Chapter 1 WBBSE

Point of difference    Alluvial cones  Deltas
Course of river Alluvial cones are formed in the middle course of the river, where the river leaves the mountains and enters the plains. Deltas are formed in the lower course of the river where the river meets the sea.
Component Pebbles, sand, clay, silt, etc. Silt and clay.
Shape Triangular in shape and looks like a fan. Triangular in shape, depending on the action of the waves and tides they may look like an arc, cusp or bird’s foot.

 

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Short Answer Type Questions

Question 1 What do you mean by a river?
Answer:

River:

A naturally flowing body of water from the uplands to the lowlands under the gravitational force following the slope is known as a river. It originates in the mountains, hills or plateaus and drains into seas, lakes or other water bodies. A river may be both snow-fed and rain-fed. E.g. rivers Ganga, Brahmaputra, Yamuna, etc.

Class 10 Geography Chapter 1 West Bengal Board

Question 2 What do you mean by tributaries and distributaries? Give examples.
Answer:
Tributaries: The smaller streams of water from the nearby areas that join the main river are called tributaries. Tributaries contribute their water as well as eroded materials to the main flow. E.g. Yamuna is the most important tributary of the river Ganga.

Distributaries: The small streams branching out from the main river near its mouth in order to distribute its excessive bedload are called distributaries. The load deposited by the distributaries over a vast region from the delta, e.g. Bhagirathi-Hooghli is an important distributary of the river Ganga.

Question 3 What is an ideal river? Give example.
Answer:

Ideal river:

The river which exhibits all three courses, i.e., the upper, middle, and lower courses prominently is called an ideal river. The river generally erodes in the upper or mountain course, transports in the middle course and deposits in the lower or delta course. The middle and the lower courses are spread over vast areas. An ideal river doesn’t change its course frequently. For example—River Ganga is an ideal river.

Question 4 How can the course of a river be divided based on the work done?
Answer:

A river performs three activities right from its source to its mouth. The river course can be divided into three parts based on its work. They are as follows—

1. Upper course, marked mostly by the erosional work of the river.
2. Middle course, marked mostly by the transportation work of the river.
3. Lower course, marked mostly by the depositional work of the river.

Class 10 Geography Chapter 1 West Bengal Board

Question 5 What is the sixth power law?
Answer:

Sixth power law:

The velocity of the stream(river) is one of the major factors on which its carrying or transportation capacity depends. A law to establish their relationship is known as the sixth power law, propounded by G.K. Gilbert. It states that the transportation power of the streams is proportional to the sixth power of its velocity. In other words, if the stream velocity is doubled, the transportation power of the stream increases 64 times. This law can be expressed in the following manner— Transportation power a (stream velocity)

Question 6 What is a water divide?
Answer:

Water divide:

The elevated land acting as a boundary between two river systems is known as a water divide. The water flowing from each side of the water divide flows into each separate body of water. The height of the water divide ranges from a slight elevation on plain land to a crest on a mountain range.

Question 7 What is a catchment area?
Answer:

Catchment area:

A catchment area or a drainage basin is an entire area that collects rainwater and contributes it to a channel. The shape of a drainage basin determines how rapidly will the run-off reach the main river and the outlet. In the case of circular basins, the run-off reaches quickly as compared to the elongated basins.

Question 8 What is a river valley?
Answer:

River valley:

The valley carved out by the river due to excessive downcutting and side-cutting along its course is known as a river valley. The shape and dimension of such valleys vary in each course of the river. V-shaped valleys are formed by the river in its youth stage or upper course while flat valleys are formed when the river reaches its mature stage in its middle course.

Question 9 What are gorges?
Answer:

Gorges:

The narrow steep-sided valleys formed in the mountainous regions due to heavy downcutting by the rivers are known as gorges. These valleys are V-shaped valleys. Here, vertical erosion by the rivers is more prevalent than lateral erosion. Example-Kali Gandaki gorge is a famous gorge in the Himalayas.

Question 10 What are potholes?
Answer:

Potholes:

In the upper course of the river, holes and depressions formed in the beds of the river valleys by the rock fragments and boulders brought down by the rivers are called potholes. Potholes are formed when the rocks get caught in the whirling water, moving in a circular manner and drilling the rocky beds of the valleys to form small holes. These holes gradually become bigger by the repetition of the same mechanism.

Class 10 Geography Chapter 1 West Bengal Board

Question 11 What are meanders?
Answer:

Meanders:

The bends in the longitudinal course of the river are called meanders. Meanders have been named after the River Meander in Turkey because it flows through several bends. Once the river emerges onto the plains it loses speed due to the gentle slope of the land.

The slightest obstruction in the course forces the river to flow through various bends. Each of these bends has two types of slope. The side where the river strikes have a concave slope and are subjected to severe erosion. The other side is characterised by a convex slope where all the eroded materials are deposited. Thus, meanders are a result of both erosion and deposition.

Question 12 What are interlocking spurs?
Answer:

Interlocking spurs:

In a mountainous region, the mountain ridges obstruct the flow of the river in such a way that the river has to erode the foothills and take frequent turns in order to avoid the ridges. From a distance, it appears that the ridges have been interwoven and the river has disappeared into the ridges. Such a series of mountain ridges are known as interlocking spurs.

Question 13 What is a cascade?
Answer:

Cascade:

A series of step-like waterfalls that originate when the river flows over an area with alternating bands of hard and soft rock beds is known as a cascade. E.g. Jonha waterfalls in Ranchi, Jharkhand.

Question 14 What is a canyon?
Answer:

Canyons:

Canyons are formed when the river flows through a dry, rainless region where the rate of lateral erosion is far less than the rate of vertical erosion. Prolonged downcutting by the rivers through the soft rocks forms long and narrow steep-sided valleys. These valleys formed resemble the shape of the letter T and are known as canyons. Example—Grand Canyon.

The limit of maximum downward erosion by a river is known as the base level of erosion. The base level of erosion can be further divided into grand base level, temporary base level and local base level. The sea level becomes the grand base level beyond which no dryland can further erode. There may also be a temporary base level of a river course depending on the presence of lakes or beds of hard and soft rocks along the course. The local base level of erosion on the other hand depends on the confluence of the tributary stream with the mainstream.

Class 10 Geography Chapter 1 West Bengal Board

Question 16 What are endogenetic forces?
Answer:

Endogenetic forces:

The forces that act from within the earth are called endogenetic forces. These forces cause two types of movement in the earth, namely, vertical movement and horizontal movement. These movements give birth to various relief features such as plateaus, plains, lakes, folds, faults, etc. Volcanic eruptions and earthquakes are also a result of endogenetic forces.

Question 17 What are exogenetic forces?
Answer:

Exogenetic forces:

The forces which act on the surface of the earth externally and cause changes in landforms, are called exogenetic forces. These forces are also known as denudational forces. Exogenetic forces are constantly engaged in the destruction of relief features which have been formed due to the endogenetic forces. Rivers, glaciers, winds, underground water, and sea waves, are some exogenetic forces that work to change the landforms on the earth’s surface.

Question 18 What do you mean by gradation?
Answer:

Gradation:

The process of acquiring a smooth and graded profile of landform that lies in equilibrium is called gradation. Gradation includes three processes. The higher landforms are eroded and smoothened in the first phase. In the second phase, the eroded materials are transported by the agents of erosion. In the third phase, the eroded materials are deposited in lowlands or depressions to obtain a graded profile. Thus, gradation helps to eliminate the vertical irregularities of relief on the surface of the earth.

Question 19 What is degradation?
Answer:

Degradation:

The process of lowering the height of a landform by different exogenetic forces is known as degradation. It is a destructive force. Weathering, mass wasting and erosion are the processes that cause degradation.

Question 20 What is aggradation?
Answer:

Aggradation:

The process of increasing the height of a landform by deposition of materials eroded from elsewhere, is known as aggradation. It is a constructive process. Aggradation leads to the formation of alluvial fans and cones, flood plains, etc.

Class 10 Geography Chapter 1 West Bengal Board

Question 21 Mention a few instances in which humans and animals act as agents of erosion.
Answer:

At times, human beings and animals also act as active agents of erosion. Mining, construction and agricultural activities cause widespread localised erosion. Burrowing animals such as rabbits, and beavers also act as agents of erosion.

Question 22 What are peneplains?
Answer:

Peneplains:

The featureless plains dotted with small undulations formed at the end of the cycle of erosion by rivers are known as peneplains. The river erodes the high landforms over a considerable period of time and lowers them. The soft rocks are eroded away faster and the hard rocks stand out on the surface as they are eroded less. These hard rocks standing out as highlands on a plain surface are known as monadnocks. E.g.-The Chotanagpur region is a peneplain, and the Pareshnath and Panchet hills lie as monadnocks.

Question 23 What is the middle course of a river?
Answer:

The middle course of a river:

The river emerges onto the plains from its mountainous or upper course and henceforth this course of the river on the plains is known as its middle course. All along this course, the speed of the river reduces comparatively but the volume of the water carried decreases. Transportation of the eroded materials from the upper course is the main activity of the river in this course. Deposition of the eroded materials is also partially seen along this course. Example-The course of the river Ganga between Haridwar and Rajmahal hills is its middle course.

Question 24 Which is the lower course or delta course of a river?
Answer:

The course of the river flowing through the plains when reaches its mouth is known as its lower course. The speed of the river in this course is vastly reduced due to the gentle slope of the land. The flow also becomes sluggish due to the huge amount of sediment that is carried with the water as a bed load. This leads to the deposition of the sediments near the mouth forming deltas. Example-The portion of the river Ganga, lying between Rajmahal hills to the mouth in the Bay of Bengal is known as the lower course of the river.

Class 10 Geography Chapter 1 West Bengal Board

Question 25 What is Plunge Pool?
Answer:

Plunge Pool:

In mountainous regions, waterfalls are created where the river drops from a considerable height with great velocity. Small depressions or hollows known as potholes are created at the base of the waterfalls due to the pounding of rock fragments brought down by the water. These potholes gradually grow bigger in size to form Plunge Pools.

Question 26 Why is the Lohachara island submerging?
Answer:

The Lohachara island at the mouth of the river Hooghly is gradually submerging because—

1. The sea level is rising.
2. Severe cyclonic storms are hitting the area frequently.
3. The mangrove forests are being cut down and thus the coasts are being exposed to erosion.

Question 27 What do you know about South Talpatti island?
Answer:

South Talpatti island:

The South Talpatti island also known as New Moore island existed 2 km away from the mouth of the river Hariyabhanga in the Sunderbans. The cardinal location of the island was 21°37’00″N and 89°08’30” S. The island emerged in the aftermath of the Bhola cyclone in 1970. According to satellite images, the island was about 2500 sq. km in area. The island is currently submerged due to the rise in the sea level as reasoned by scientists.

Question 28 What is the current condition of Ghoramara island?
Answer:

The current condition of Ghoramara island:

The Ghoramara island lies 92 km south of Kolkata, north of the Sagar islands at the mouth of river Hooghly and east of the mouth of river Haldi in the Bay of Bengal. This is an island in the Sundarban region. In 1951, the size of the island was 38.23sq. km, but by 2011, the size reduced to a mere 4.37sq.km. Experts predict that the island will totally disappear due to submergence in the near future.

Question 29 What do you mean by rejuvenation?
Answer:

Rejuvenation:

Rejuvenation means acceleration of the erosive work of the rivers due to various factors. This lengthens the period for the cycle of erosion of the rivers. A river may be rejuvenated due to earth movements that cause upliftment or depression of land, substantial fall in the sea level, river capture, etc. Landforms created due to the rejuvenation of rivers include knick points, valley-in-valley topography, incised meanders, paired terraces, etc.

Question 30 What is a knick point?
Answer:

Knick point:

After the rejuvenation of a river, the point lying between the old slope and the new slope is known as the knick point. Waterfalls are formed at the knick points as the difference in the level of the old slope and the new slope creates a considerable difference in height for the water to jump. The knick point gets eroded gradually with time and matches the graded profile of the region.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms knick point

 

Question 31 What do you mean by abrasion?
Answer:

Abrasion:

Abrasion or corrasion is a type of erosion. The natural agents of erosion like rivers, glaciers and wind bring down rock fragments, pebbles, sand and stones that rub against the rock beds on the surface of the earth. This is known as the process of abrasion. Thus, the surface is polished and eroded fast by the removal of loosened materials.

Class 10 Geography Chapter 1 WBBSE

Question 32 What are rapids?
Answer:

Rapids:

Waterfalls of smaller dimensions are known as rapids. They are usually found upstream from the main falls or are even found independently. For example—Rapids are seen in the mountainous course of many Himalayan rivers.

 

Chapter 1 Exogenetic Processes And Resultant Land Forms If The Statement Is True, Write True And False, Write False Against The Following

 

Question 1. The main work of the river in its mountainous course is erosion.
Answer: True

Question 2. The work of the river starts above the snowline.
Answer: False

Question 3. Colca Canyon formed by the river Colca is one of the deepest in the world.
Answer: True

Question 4. Potholes are created in the river beds due to abrasion and attrition.
Answer: True

Question 5. The sea level is the last limit of erosion.
Answer: True

Question 6. The Grand Canyon lies in the course of the river Colorado.
Answer: True

Question 7. The rate of side cutting is more than the rate of downcutting in the gorges and canyons.
Answer: False

Question 8. Natural levees are created on the banks of the rivers only in the lower course.
Answer: False

Question 9. The largest river island in India is Majuli.
Answer: True

Question 10. Gorges are seen in dry regions and canyons are seen in moist tropical regions.
Answer: False

Question 11. The scientific study of the river is known as Potamology.
Answer: True

Question 12. The river Ganga is an example of an ideal river.
Answer: True

Question 13. Rapids are larger in dimension than cascades.
Answer: False

Question 14. The waterfalls gradually recede towards the source of the river.
Answer: True

Question 15. Waterfalls are mostly formed at the knick points of the rivers.
Answer: True

Question 16. Oxbow lakes are seen in the upper course of a river.
Answer: False

Question 17. Flood plains are a common depositional feature beside most of the large rivers of the world.
Answer: True

Question 18. The islands of Sundarbans are gradually submerging.
Answer: True

Question 19. Canyons are U-shaped valleys.
Answer: False

Question 20. Alluvial cones in the course of the river Ganga are formed from sediment deposits brought down by the river near Haridwar.
Answer: True

Question 21. The oxbow lakes are known as ‘tal’ in Uttar Pradesh.
Answer: True

Question 22. The Suparibhanga island of the Sundarbans is subjected to gradual submergence.
Answer: True

Question 23. The deltaic flow of river Ganga extends from Haridwar to its mouth at the Bay of Bengal.
Answer: False

Question 24. Plucking is solely a process and mechanism of fluvial erosion.
Answer: False

Question 25. The process of degradation increases the height of the landforms.
Answer: False

Question 26. Potholes are formed at the base of the waterfall.
Answer: False

Question 27. The confluence of the Alakananda and Bhagirathi rivers is at Devprayag.
Answer: True

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Fill In The Blanks With Suitable Words

 

Question 1. A fault lying across the river in a mountainous region gives rise to a_______
Answer: Waterfall

Question 2. _______ Are created due to erosion by rivers in the mountainous or upper course.
Answer: Gerges/Canyons

Question 3. In the upper course of a river, downcutting of valleys mainly occurs due to_______
Answer: Abrasion

Question 4. Cliffs present in the course of a river form large waterfalls called_______
Answer: Cataracts

Question 5. The longest river in the world is a river _______
Answer: Nile

Question 6. The largest river in the world in terms of volume of water is a river _______
Answer: Amazon

Question 7. The islands of New Moore and Ghoramara have submerged due to _______
Answer: Rise in the sea level

Question 8. An example of an endogenetic process of landform formation is _______
Answer: Plate Movement

Question 9. Erosion by rivers and glaciers is a _______ process of creating landforms.
Answer: Exogenetic

Question 10. Two important works in exogenetic processes are erosion and _______
Answer: Deposition

Question 11. The river erodes least in the _______ course.
Answer: Lower

Question 12. The upper course of the river Ganga extends from Gomukh to _______
Answer: Haridwar

Question 13. The Livingstone waterfalls lie on the river _______
Answer: Congo

Question 14. The Victoria waterfalls of Africa are an example of a _______
Answer: Cataract

Question 15. The fertile region in between two rivers is called a _______
Answer: Doab

Question 16. The huge depressions created at the base of a waterfall are called _______
Answer: Plunge pools

Question 17. The term meander came from the river _______
Answer: Buyuk Meanderes

Question 18. The delta formed by the river Seine is a _______ delta.
Answer: Estuarine

Question 19. The rate of flow of water in a river per cubic metre per second is measured by the unit _______
Answer: Cumec

Question 20. Holes formed by abrasion on the riverbed are called _______
Answer: Pot Holes

Question 21. According to the name of _______ the river, the zigzag course of a river is known as a meander.
Answer: Meanders

Question 22. The process of modifying landforms by the combined action of erosion and weathering is called _______
Answer: Denudation

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Answer in one or two words

 

Question 1. How far does the upper course of river Ganga lie?
Answer: Gomukh to Haridwar.

Question 2. On which course of the river depositional activities are the least?
Answer: Upper or mountainous course.

Question 3. What is the curved flowing path of a river called?
Answer: Meander.

Question 4. What is the depositional feature of a river looking like a fan called?
Answer: Alluvial fan.

Question 5. Name the type of lake which is formed by being cut off from the river in its middle course.
Answer: Oxbow lake.

Question 6. Name the place where the river meets the sea.
Answer: Estuary.

Question 7. What is the sediment carried by the river called?
Answer: Bedload.

Question 8. Name the process of erosion in which air bubbles trapped in small spaces implode to erode rocks.
Answer: Cavitation.

Question 9. Which is the world’s longest estuary?
Answer: Gulf of Ob (at the mouth of River Ob).

Question 10. What are the exogenetic forces also known as?
Answer: Destructive forces.

Question 11. Which is the largest drainage basin in the world in terms of area?
Answer: Amazon drainage basin.

Question 12. What is the cause behind the gradual submergence of the islands of Ghoramara, Lohachara, etc.?
Answer: Rise in sea level.

Question 13. What is a river with all its courses well-defined called?
Answer: Ideal river.

Question 14. What are the valleys carved out by rivers called?
Answer: River valleys.

Question 15. Name two islands of the Sundarbans that are on the verge of submergence.
Answer: Suparibhanga and Kapasgadi.

Question 16. Who was the first to use the term grade’ in geology?
Answer: Geologist Gilbert.

Question 17. Who propounded the concept of gradation in geology?
Answer: Geologists Chamberlain and Salisbury.

Question 18. Name the main source of energy for the exogenetic processes.
Answer: Sun.

Question 19. What is the process of removal of weathered rocks to other places called?
Answer: Erosion.

Question 20. What is the process of lowering the height of landforms called?
Answer: Degradation.

Question 21. What is the process of falling loose materials like rocks and soil along the slope called?
Answer: Mass wasting.

Question 22. What kind of a process is gradation?
Answer: Exogenetic process.

Question 23. Which type of weathering is the most prominent in desert regions? Right Column
Answer: Mechanical weathering.

Question 24. What is the process of weathering, erosion, transportation and deposition together known as?
Answer: Denudation.

Question 25. Which island of Sundarban was completely submerged due to global warming?
Answer: New Moore

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Match The Left Column With The Right Column


1.

Left Column  Right Column  
1. Waterfalls A. Mouth of river
2.  Delta B. Waterfalls of smaller dimension
3. Alluvial cone C. Peneplains
4. Rapids D. Upper course of the river
5. Monadnocks E. Foothills of mountains

Answer:1-D,2-A,3-E,4-B,5-C

2.

Left Column   Right Column
1. Triangular delta  A. River Tiber
2. Abandoned delta B.River seine
3. Estuarine delta C. Yellow River
4. Bird foot delta D. River Ganga
5. Cuspate delta E. River Mississippi

Answer:1-D,2-C,3-B,4-E,5-A

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Topic 2 Works Of Glaciers

 

Question 1 Describe a few landforms formed due to erosional works of glaciers.
Answer:
The glaciers erode the valley or region through which it flows and form several landforms. A few of them are as follows—

1. Cirque: The glacier erodes by the processes of plucking and abrasion At the source of the glacier, the mountain wall is eroded heavily and the landform thus formed looks like a huge armchair. This is known as a cirque Rock basin formed at the floor of the cirques gets filled up with water after deglaciation and is known as cirque lakes or tarn lakes.

Cirques are known by different names at different places Cirques can be divided into three parts—

1. Steep wall at the back,
2. Semi-circular depression in the middle
3. Threshold or hunch at the lower part. The cirques may get filled with snow-melt water and form lakes For Example—Such landforms are seen in the glacial regions of the Himalayas, Alps, etc.

2. Arete: In the snow-covered mountainous region, two or more glaciers can originate from different slopes of a single mountain Thus a number of cirques will be formed in the same mountain Due to headward erosion, the cirques may get deeper, and the portion between two adjacent cirques lie like a steep, sharp narrow wall. This is called an arete. If the mountain has three or more aretes it forms a pyramidal peak. The tip or peak of such a pyramidal peak is called a horn. E.g. — The Matterhorn peak.

3. Hanging valleys: In a glaciated region, the main or trunk glacier carries a greater volume of ice than the tributary glaciers. Thus the main glacier has greater erosive power than the smaller tributary glaciers.

Hence, the main glacier forms deeper valleys and the tributary glaciers form comparatively less deep valleys. These are not visible as long as the ice cover remains. When the glaciers melt or recede, the small valleys are found to be hanging over the huge deep valleys, due to different rates of erosion during their formation. Such valleys are called hanging valleys.

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms land forms

4. U-shaped valley: In a mountain glacier, the glacier descends from the cirque and flows through the valley. The intensity of side erosion or lateral erosion is almost the same as the intensity of vertical erosion of the glacial valley by the processes of abrasion and plucking. Thus, the valley developed looks like the letter ‘U’. These valleys are called U-shaped valleys.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms u shaped valley

 

5. Fjord: In regions where the mountain glaciers meet the coast directly, the valleys may be eroded so deep that the base or bed of the valley may lie lower than the sea level. When the ice melts or recedes these depressions get filled up with seawater. Such regions look like valleys that have been submerged in ocean water, while the ridges stand out. These submerged valleys are known as fjords. Such a coast is known as a fjord coast. Examples of fjords are seen in Norway and Finland.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Fjord

 

6. Roches mountaineer: In the path of a glacier, if a hard rock stands like an obstruction, the glacier rides over it while crossing it. In this process, the side over which it rides gets smoothened and polished by the rocks and pebbles.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms roches mountonneee

 

7. Crag and tail: Along the path of the glacier if there lies a volcanic rock it projects above the ground as a resistant rock. These volcanic rocks offer resistance to the flow of ice and thus the side facing the direction of flow becomes steep due to erosion. This is known as a crag. The other side being sheltered by the ice becomes elongated and has a gentle slope. This elongated side is known as the tail. Crag Hard rock outcrop

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Crag and tail

 

8. Glacial stairways: When the glaciers descend from very high mountains into valleys, they develop steps or stairs along the walls of the valleys through the processes of abrasion and plucking. The steps may develop due to unequal distribution of load in the glacier or alternate alignment of hard and soft rock beds. These steps are known as glacial stairways. Further, small depressions formed in these steps get filled up with snowmelt water, later. These depressions are known as paternoster lakes.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Paternoster lakes

 

Question 2 Describe a few landforms formed by the depositional works of glaciers.
Answer:

The depositional works of glaciers can be broadly classified into two parts—

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms flow chart

 

1. Depositional landforms altitudes:

1. Moraines: The debris of rocks and pebbles that the glaciers carry as they flow through the valleys, get deposited in parts along the sides, bed or at the end of the glaciers. These are known as moraines. They are named side moraines or lateral moraines, medial moraines and end or terminal moraines based on their locational aspect.

2. Karnes: At the end of the glacier, as the ice melts, the rocks, pebbles, sand and gravel brought down by the glacier get accumulated and are deposited in triangular shapes, resembling deltas of rivers. They are called kames. Narrow flat-topped terraces like ridges are called kame terraces.

2. Depositional landforms in lower altitudes:

1. Glacial erratics: The glaciers bring down rocks and boulders along with them in their course. When they melt, these rocks and boulders may get carried to distant places with the snow-melt water, and get deposited there. These rocks have no similarities with the local rocks of that region. Such rocks are called glacial erratics.

2. Eskers: The rocks, sand, clay, pebbles, etc. brought down by glaciers may get deposited like low ridges at the foothills of the mountains. They may be curved and branched. These ridges are called eskers. E.g.— Punkaharju esker in Finland.

3. Drumlins: When boulder clay is deposited in large heaps that look like inverted boats, they are known as drumlins. A number of Compare the works of rivers and glaciers drumlins lying in a region look like a ‘basket of eggs topography’.

 

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Drumlins

 

4. Boulder clay: The accumulation of sand, clay, rocks and boulders at the base of the valley after the glacier melts is known as boulder clay.

5. Outwash plains: At the end moraine, where the glacier melts and gives rise to the river, the rocks, pebbles, clay and sand brought down by the glacier are carried as bed load by the river water and spread over extensive areas. The plains thus formed are called outwash plains. The big chunks of hard ice that come along with the rock debris, make depressions, in the ground. These are called kettles. When the hard ice melts, these depressions get filled up with water and form kettle lakes.

6. Knobs: Rocks and pebbles brought down by glaciers and carried along with flowing water are deposited on the outwash plains like domes or low hillocks, they are called knobs.

Question 3 Compare the works of rivers and glaciers.
Answer:

The comparison between the works of rivers and glaciers is as follows—

 

Point of comparison Works of rivers Works of glaciers
Age of landforms The landforms are older than those formed by glaciers. The landforms are newer than those formed by rivers.
Methods of erosion 1. Friction,
2. Abrasion,
3. Attrition,
4. Saltation,
5. The solution,
6. Hydraulic action
1. Plucking,
2. Abrasion
Shape of valleys V-shaped or l-shaped valleys are formed depending on the volume of water and the nature of the rocks. U-shaped valleys are formed. Size and depth vary according to the volume of ice.
Nature of eroded materials The eroded rocks are rounded and smoothened. The eroded rocks are rough, and uneven and don’t have any fixed shape.
Course of flow The course is divided into upper, middle and lower courses. No definite classification of the course of flow.
Location of depositions of eroded materials Depositions mostly occur in lowlands, plain lands or depressions in the middle and lower courses. Maximum deposition occurs at the delta near the mouth. Depositions occur in different places in the course of flow at the same time.
Erosional landforms Gorge, canyon, waterfall, pothole, V-shaped valley, l-shaped valley, etc. U-shaped valley, cirque, arete, pyramidal peak, horn, hanging valley, Roches mouton nee, crag and tail, etc.
Depositional landforms Flood plain, natural levee, delta, etc. Moraine, kame, esker, drumlin, etc.
Area of influence Works of rivers are seen almost everywhere through which rivers flow except in dry desert regions and cold snow-covered regions. Works of glaciers are seen only in snow-covered mountainous regions and polar regions, above the snowline.

 

Question 4 How are pyramidal peaks and hanging valleys formed?
Answer:

Pyramidal peaks and hanging valleys formed:

Hanging valleys: In a glaciated region, the main or trunk glacier carries a greater volume of ice than the tributary glaciers. Thus the main glacier has greater erosive power than the smaller tributary glaciers.

Hence, the main glacier forms deeper valleys and the tributary glaciers form comparatively less deep valleys. These are not visible as long as the ice cover remains. When the glaciers melt or recede, the small valleys are found to be hanging over the huge deep valleys, due to different rates of erosion during their formation. Such valleys are called hanging valleys.

Question 5 Differentiate between river valleys and glacial valleys.
Answer:

The differences between river valleys and glacial valleys are as follows-

 

Point of Difference  River valleys  Glacial valleys 
Location River valleys are seen in almost every region through which a river flows, except dry desert regions and snow-covered regions. Glacial valleys are seen only in high altitudes and high latitudes where snow persists throughout the year.
Shape  l-shaped valleys in dry and arid regions due to more downcutting than side-cutting. V-shaped valleys in moist or semi-dry regions due to side cutting along with downcutting. U-shaped valleys due to similar intensities of downcutting and side cutting.
Length The river valleys are quite extensive based on the length of the river courses. The glacial valleys are comparatively shorter in length.
Bends  Most of the river valleys have numerous bends as the river itself flows through various bends in the middle and lower course. The number of bends in the case of glacial valleys is far less.
Nature of rocks The rocks and pebbles brought down by the rivers collide against one another and the valley floor and are disintegrated into smaller rocks and further into sand and silt. The rocks brought down by the glaciers are broken down by the processes of abrasion and are deposited as uneven, rough sediments.

 

 

Question 6 Why are waterfalls formed from where the corrie is formed, the ice seems to tear hanging valleys.
Answer:

In hilly regions through which glaciers flow, the main glacier being longer, wider and more extensive erodes much more than the small tributary glaciers. Thus, the valley of the main glacier is deeper than the valleys of the small tributary glaciers.

When the ice melts, the small glacial valleys seem to hang over the main valley due to differences in height. The rivers formed due to the melting of the glaciers flow through these glacial valleys. The water pouring in from the tributary glacial valleys into the main valley jumps downwards due to differences in elevation, thus creating waterfalls.

Example— Vasudhara waterfalls near Badrinath. The rivers flowing through this region gradually erode the glacial valleys and try to reduce the slope of the land.

Question 7 How are crevasses and bergschrunds formed?
Answer:

In high mountainous regions, where heavy snowfall occurs, the ice gets compacted gradually and gives rise to glaciers. Several erosional and depositional features are formed in glaciers.

Bergschrund: At the source of the glacier, apart from the headwall of the corrie as the glacier begins to flow. This creates a long, narrow and deep fault or trench near the wall of the corrie in the snow. This is known as the bergschrund.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms crevasse and bergs chrucd

 

Crevasses: As the glacier advances, it crosses many types of slopes on its way. This may create several cracks on the surface of the glacier which are comparatively shallow. These are known as crevasses. Both bergschrunds and crevasses remain covered with a thin film of fresh snow. Thus, they can be of great danger to mountaineers.

Question 8 What are varves?
Answer:

Varves:

Varves are circular deposits of sediments found in glacial lakes. Each valve has two layers of deposits. The light-coloured sandy deposits and the dark-coloured silt deposits. In the summer reason, when the snow melts and the speed of the glacial melt water is greater, the heavy sediments are deposited, while the lighter ones are carried in suspension. As the winter sets in, the rate of melting is lowered and also there is less meltwater flowing.

As a result, the sediments in suspension are also deposited. Every year a new set of sediments are deposited in different circles. Enumerating the number of circles helps to calculate the age of the lake.

Question 9 How is an ideal glacier formed?
Answer:

An ideal glacier is formed by the following processes—

1. Sublimation: The ice crystals directly change into vapour by this process.

2. Crystallisation: The small crystals of snow are broken and compacted into large crystals to form ice. This ice serves as the source of a glacier.

3. Melting: Sometimes the ice melts partially into the water, and sometimes the water crystallises into ice. These processes lead to the formation of glaciers.

4. Regelation: This is the phenomenon of melting ice under high pressure and freezing again when the pressure is reduced. This influences the structure of the ice crystals and leads to the formation of glaciers.

5. Compaction: As more and more snowfall occurs the lower layers of snown get compacted into ice this helps in the information of glaciers.

Question 10 What are moraines? Classify the moraines.
Answer:

Moraines:

The glaciers erode materials from the walls and beds of the valleys as they flow downwards. These rock debris are deposited along the sides, end or ground of the glacial valley as glacial till or deposits in the form of ridges. These are known as moraines.

Classification: The moraines can be generally divided into four types based on their locational aspect.

1. Moraines deposited along the sides of the glacier are called side moraines or lateral moraines.

2. Two lateral moraines meet to form the medial moraine. They are found on the top and on the inner side of an existing glacier.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms types of moraines

 

3. The end moraine or terminal moraine is formed due to depositions at the end of the glacier, where it starts to melt.

4. The moraine deposited on the base or on the floor of the valley is called a ground moraine.

Question 11 Why do valleys rivers while carving glaciers out T carve or out’V’ ‘U’ shaped valleys?
Answer:

The rivers have great speed in the mountainous region. The intensity of downcutting is more than the intensity of side cutting. regions the valley carved out are ‘I’ shaped and while flowing through the wet regions the shape of the valleys resembles the letter V.

In the case of glaciers, the intensity of side-cutting of valleys is similar to that of downcutting. Rocks are broken and removed by the process of plucking and abrasion. Thus, the shape of the valley formed resembles the letter ‘U’.

Question 12 Mention the importance of glaciers as a source of sweet and fresh drinking water.
Answer:

A glacier is not only a frozen river of ice but also influences the landform and climate. the environment of the glacial region. It can be considered as a reserve for freshwater pres in the frozen form. About 97.20% of the water present on the earth’s surface is salty and unfit for use. The rest 2.80% of the water is fresh. Out of this share, about 0.0001% of the water flows through rivers, 0.9999% lies as underground water, and 1% remains frozen as ice.

This means that about 75% of usable fresh water is trapped in the glaciers. Out of this about 90% or more lie in Antarctica. Rivers like Ganga, Yamuna, Indus and Brahmaputra rise from the glaciers. Thus, the glaciers in the high mountains are important in being reserves of freshwater in frozen form.

Question 13 Why are the roches moutonnees smooth on one side and rough on the other?
Answer:

In a glaciated region, if a large boulder, or rock comes in the way of the glacier, the side over which the glacier moves forward is smoothened and polished by the process of abrasion. The opposite side over which the glacier descends is plucked and eroded and weathered. Thus, one slope of the Roches moutonnees is smooth while the opposite side is rough, uneven and plucked.

Question 14 How are glacial stairways formed?
Answer:

When the glaciers descend from very high mountains into valleys, they develop steps or stairs along the walls of the valleys through the processes of abrasion and plucking. The steps may develop due to unequal distribution of load in the glacier or alternate alignment of hard and soft rock beds. These steps are known as glacial stairways.

Question 15 Differentiate between mountaineers and drumlins. Differentiate between kame and delta.
Answer:

The differences between kame and delta are as follows—

 

Point of difference Roches mountaineers Drumlins
Type of landform Formed due to erosional work of glaciers. Formed due to the depositional work of glaciers and flowing water.
Shape One side is smooth while the other side is rough. Looks like inverted boats.
Location They are formed in high mountainous regions. They are deposited at the foothills of mountains.
Component Formed of the hard rock mass. Formed of glacial till (rocks, pebbles, etc.) carried by glaciers.

 

Question 16 Differentiate between Kame and delta.
Answer:

The difference between Kame and delta are as follows-

 

Point of difference Kame Delta
 Location  Foothills of mountains.  The mouth of the river.
Texture of The rocks and The silt and clay
deposits pebbles are coarse and big. are very fine and smooth.
Size of the feature Small size. Usually very big in size.

 

Question 17 Differentiate between continental glaciers and valley glaciers
Answer:

The difference between glacier and valley glaciers

 

Point of difference Continental glacier Valley glacier 
Concept A huge mass of ice lying over vast areas of the continent Mass of ice lying in the valley of mountainous regions.
Size Vast and huge. Comparatively small.
Direction of movement Flows in all directions from the centre. Flows in one direction according to the slope of the land.
Depth Very deep. Comparatively less deep.

 

Question 18 Differentiate between bergschrund and crevasses
Answer:

The difference between bergschrund and crevasses are as follows-

Point of difference   Bergschrund Crevasses
Concept Deep narrow trench formed between the mountain wall and the glacier. Cracks formed on the surface of the glacier.
Extent From the surface of the glacier to its base. From the surface of the glacier to a certain depth, depending on the curvature of the surface.
Structure Lies vertically downwards and looks like a long nail. Lies horizontally and across the direction of the flow of the glacier. Usually, a    number of parallel crevasses lie together.

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Short Answer Type Questions

 

Question 1. What is the snowline?
Answer:

Snowline:

Huge snowfall occurs in high altitudes as well as polar regions The imaginary line above which the snow never melts totally or below which the snow starts melting is called the snowline. Snowline marks the beginning of the permafrost region. In low or middle latitudes, the snowline may exist j at S000-6000 m altitude But in polar, regions, it lies at the sea level itself.

Question 2. classify the glaciers
Answer:

Glaciers can be generally classified into two categories —

1. mountain or valley glaciers and
2. continental glaciers H W. Ahlmann further classified glaciers into 3 broad categories and 11 subtypes based on their thermal and morphological characteristics The three broad categories are-
3. Mountain or valley glaciers, (T) Continental glaciers, (J) Piedmont glaciers.

Question 3. What are mountain or valley glaciers?
Answer:

Mountain or valley glaciers:

The glaciers that flow through the valleys in high mountainous regions are called valleys or mountain glaciers. E.g- Gangotri

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Mountain galcier

 

Question 4. What are continental glaciers? Give examples.
Answer:

Continental glaciers:

When the extensive areas of the continent remain covered with snow, irrespective of high or low altitude, they are known as continental glaciers. Example—The snow cover of Greenland and Antarctica is called continental glaciers.

Question 5. What are piedmont glaciers?
Answer:

Piedmont glaciers:

The glaciers formed due to the coalescence of several mountains or valley glaciers at the foothills of the mountains, are called piedmont glaciers.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Piedmont glacier

 

Question 6. What are avalanches?
Answer:

Avalanches:

In snow-covered mountainous and glacial regions, sometimes huge volumes of ice may slide down mountain slopes due to their large weight and gravitational pull. These are called avalanches. They can be so powerful at times, that they may cause earthquakes and devastate forests or habitations coming their way.

Question 7. What is an iceberg?
Answer:

Iceberg:

The huge blocks of ice that float on the oceans are called icebergs. In higher latitudes, generally, huge blocks of ice break away from the continental glaciers and float in the adjacent oceans. They move towards lower latitudes with the help of ocean currents. Only 1/9 th part of an iceberg floats above the water. The rest remain submerged. The famous ship Titanic was wrecked on its first voyage due to its collision with a huge iceberg.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Piedmont glacier

 

Question 8. What are end moraines?
Answer:

End moraines:

Terminal or end moraines are depositions of glacial till due to the ablation of ice brought down by the glaciers. These moraines are deposited at the snouts. They are horseshoe-shaped and have concave slopes.

Question 9. What are eskers?
Answer:

Eskers:

Eskers are depositional landforms found in the lowlands or foothills of mountains or valley glaciers. When the debris (rocks, pebbles, stone, etc.) brought down by glaciers gets deposited like low-lying ridges (about 15 m in height) with branches, they are called eskers.

Question 10. What are pyramidal peaks?
Answer:

Pyramidal peaks:

At the source of the mountain glaciers, deep armchair-like depressions are formed on the walls of the mountains due to erosion. These are called cirques or corries. The steep narrow wall between two adjacent cirques or corries is known as aretes. If there are three or more cirques on the different faces of the mountain, the aretes meet at a steep and sharp point or peak. This is called a pyramidal peak. Example— Matterhorn peak is a famous pyramidal peak in the Alps.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant pyramidal peak

 

 

Question 11. What do you mean by boulder clay?
Answer:

Boulder clay:

In a mountainous or valley glacier, the glacier brings a huge volume of debris along with the snow to the lower reaches. As the glaciers melts, this debris is deposited in various forms on the lowlands. The sand, clay and boulders deposited together are known as boulder clay.

Question 12. What are drumlins?
Answer:

Drumlins:

When the rocks, sand and clay brought down by the glaciers get deposited into dome-like features that look like inverted boats, they are called drumlins. An area covered with drumlins is also called a basket of eggs topography.

Question 13. What Is a glacial erratic?
Answer:

Glacial erratic:

In a glacial region, when big rocks are carried too far away distances along with the snow and are deposited there after the glacier melts, the rocks are known as glacial erratics. These rocks are found to have no similarity with the local rocks. Example—Glacial erratics are seen in the high mountainous regions of Pahelgaon in Kashmir.

Question 14. What is a glacier? Name the glaciers that are sources of the river Ganga and Yamuna.
Answer:

Glacier:

Aglacierisamassorriveroficemovingslowly under the impact of gravity. In high altitudes and polar regions, where heavy snowfall occurs, glaciers are formed due to the accumulation of snow above the snowline. The river Ganga rises from the Gangotri glacier and the river Yamuna rises from the Yamunotri glacier.

Question 15. What is an ice shelf?
Answer:

Ice shelf:

The thick layer of hard ice that remains attached to the land at one end and seems to float on the ocean like an extended shelf is known as an ice shelf. E.g.—Ross and Ronne-Filchner ice shelves of Antarctica.

Question 16. What do you mean by ‘basket of eggs topography’?
Answer:

Basket of eggs topography:

When the rocks, pebbles, sand and clay brought down by the glacier get deposited on the lowland like inverted boats, the topography looks like a number of eggs spread over the land. These are known as drumlins and the topography is known as ‘basket of eggs topography’. Example-Such groups of drumlins are seen in Ireland and Scotland.

Question 17. What do you mean by ice sheet?
Answer:

Ice sheet:

Glaciers are classified into valley glaciers, piedmont glaciers and continental glaciers. Out of these, the continental glaciers are in fact extensive ice sheets. In the polar regions, vast areas are covered with thick layers of ice like a sheet or cover. Thus, the area known as a narrow wall between them is known as an arete. Aretes are sharpened peaks resembling the shape of saw teeth.

Question 22. What is a kame?
Answer:

Kame:

At the edge or near retreating ice sheets the rocks, stones, pebbles, sand, clay etc., brought down by the glacier accumulate in dumps like triangular deltas. These are known as kames.

Question 23. What are paternoster lakes?
Answer:

Paternoster lakes:

In high mountainous areas, the glacial valleys seem to develop a number of steps or stairs through the processes of abrasion or plucking. Further, several depressions or hollows are created on these steps or stairs due to glacial erosion. These depressions later get filled with water when the glacier melts. These are known as paternoster lakes.

Question 24. What are knobs and kettles?
Answer:

Knobs: The rocks and pebbles brought down by glacial erosion flow down along with the rivers and spread on the outwash plains. If these materials accumulate like small domes on the plainlands, they are called knobs. Kettles: The big chunks of ice that flow down with the glacier-melt rivers, spread on the outwash plains and create hollows or depressions. These are called kettles. The hollows get filled with water as the ice chunks melt, and thus form kettle lakes. E.g.— ‘Knob and Kettle’ topography is seen in many regions in northern Europe.

Question 25. What is the speed of glaciers?
Answer:

Speed of glaciers:

The glaciers move very slowly. The speed of the glaciers depends upon the slope of the land, the volume of ice, seasonal variations, gravitational pull, etc. Example—The glaciers of the Alps mountains move at an average speed of 5.5 cm per day. The Himalayan glaciers move at a speed of 2.5 7.5cm per day.

Question 26. Why does the end of a glacier look like a tongue?
Answer:

In a valley glacier, the middle part of the body of ice moves forward faster as it experiences friction solely from the valley base. On the other hand, the sides of the glacier experience friction from the base as well as the valley walls. Thus, the rate of movement of glacial ice decreases from the centre towards the edge. This causes the end
of the glacier to look like a tongue. This is also known as glacial snout.

Question 27. What is firn?
Answer:

Firn:

In cold regions, where temperatures drop below the freezing point, snowfall occurs instead of rainfall. The snow falls like the feathers of birds and spread over the ground to form an ice field. An increased volume of snow gets compacted under the pressure of the overlying snow. This partially compacted granular snow is known as firn, which is the intermediate stage between snow and glacial ice.

Question 28. What are Roche mountaineers?
Answer:

Roche mountaineers:

In a mountainous region, due to erosional works of glaciers, large asymmetrical domes with smooth and steep walls may be formed. These landforms are known as Roche mountaineers. Example—Several Roche mountaineers are seen in the glaciated valleys of the Kashmir Himalayas.

Chapter 1 Exogenetic Processes And Resultant Land Forms If The Statement Is True, Write True And If False, Write False, Against The Following

Question 1. Floating blocks of ice found in oceans are called icebergs.
Answer: True

Question 2. The Malaspina glacier of Alaska is an example of a piedmont glacier.
Answer: True

Question 3. Nunataks are seen in polar regions.
Answer: True

Question 4. The lakes formed in the depressions found in the glacial stairways are called paternoster lakes.
Answer: True

Question 5. The submerged glacial valleys formed due to erosion by continental or mountain glaciers are called fjords.
Answer: True

Question 6. The region clustered with drumlins is also called ‘basket of eggs topography’.
Answer: True

Question 7. Clay containing many large stones and boulders formed by the deposition of debris from melting glaciers and ice sheets is called boulder clay.
Answer: True

Question 8. Ice deposits are found above the snowline only in winter.
Answer: False

Question 9. Waterfalls are formed from the meltwater of hanging valleys after deglaciation.
Answer: True

Question 10. The altitude of the snowline varies with latitude.
Answer: True

Chapter 1 Exogenetic Processes And Resultant Land Forms Fill in the blanks with suitable
words

Question 1. Eskers are depositions of glacial debris comprising sand and gravel looking like low
Answer: Ridges

Question 2. The longest glacier in the world is Antarctica.
Answer: Lambert

Question 3. One of the largest valley glaciers in the world is
Answer: Bread more

Question 4. The largest glacier in India is
Answer: Saichen

Question 5. Glacier is a slow-moving mass of ice formed on the mountains or near the poles due to the accumulation of snow.
Answer: River

Question 6. Fjords are seen in the latitudes of the coastal regions.
Answer: Higher

Question 7. The tongue-like extension of the glacier is known as the
Answer: Snout

Question 8. U-shaped glacial valleys are also called
Answer: glacial troughs

Question 9. The snow-less peaks in an ice-covered region are called
Answer: Nunataks

Question 10. Aretes are formed by the process of
Answer: Abrasion

Chapter 1 Exogenetic Processes And Resultant Land Forms Answer In One Or Two Words

Question 1. What does a landform comprising several drumlins look like?
Answer: Basket of eggs topography.

Question 2. What kind of glacier is Siachen in India?
Answer: Mountain or valley glacier.

Question 3. Where are Roches moutonnees found in India?
Answer: Glaciated valleys of Kashmir.

Question 4. What kind of a peak is Mt. Makalu in Nepal?
Answer: Pyramidal peak.

Question 5. What is the debris brought down by glaciers called?
Answer: Moraines.

Question 6. Name the type of moraine formed due to depositions of sediments along the internal margins of two glaciers?
Answer: Medial moraine.

Question7.What is the compaction of granular snow called?
Answer: Firn.

Chapter 1 Exogenetic Processes And Resultant Land Forms Match The Left Column With The Right Column Answer

1.

Left Column  Right Column  
1. Shiviling A. Glacier in Antarctica
2.  Siachen B. Snowless peaks
3. Nunataks C.Largest piedmont glacier
4. Malaspina D. Arete
5. Lambert E. Largest glacier in India

Answer: 1-D,2-E,3-B,4-C,5-A

2.

Left Column  Right Column  
1. Fjord A. Yosemite valley
2.  Hanging valley B. Basket of eggs Topography
3. pyramidal peak C. Roass ice self
4. Ice self D. Nanda devi
5. Drumlins E.Sogne

Answer: 1-E,2-A,3-D,4-C,5-B

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Topic 3 Works Of Winds Long Answer Type Question

 

Question 1 Describe some of the landforms formed by wind erosion.
Answer:

The work of wind can be most prominently seen in the hot dry desert regions.

The landforms formed by erosional activities of wind are—

1. Ventifact: In desert regions, when the windward side of a rock becomes smooth and polished due to abrasion caused by wind blowing from a single direction, it is called a ventifact. The other faces of the rock remain rough and unpolished.

2. Dreikanter: In desert regions, if the wind direction changes with changes in seasons, abrasion polishes all the faces of the rocks at different times of the year from different directions. Thus, rocks with three polished and smoothened sides are formed. Such a rock is called a dreikanter.

3. Mushroom rock: In desert regions, the effect of abrasion is more actively felt at the lower heights than at the upper heights. In a rock mass composed of soft rock beds at the bottom and harder rocks at the top, the lower rock beds are eroded faster than the upper beds due to abrasion. Thus, the landform formed has a narrow base and a flat broad top. This resembles a mushroom and is known as a mushroom rock.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms mashroom rock

 

4. Zeugen: In desert regions where soft and hard rock beds lie parallel to the earth’s surface, the soft rocks are eroded and soft rock Hard rock Furrows hollows are formed. The hard rocks lie above them like caps. Thus, a landform created with a broader base than the top resembling a capped inkpot is known as a zeugen.

Yardang: In desert regions, if hard and soft rock beds lie parallel to each other in alternate ctr the soft rocks get eroded very fast due to abrasion. The hard rocks are less eroded and lie as hanging ridges stretching parallel to each other separated by grooves. Such a feature is known as a yardang.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Zeugen

 

 

5. Yardang:  In desert regions, if hard and soft rock beds lie parallel to each other in alternate strips, the soft rocks get eroded very fast due to abrasion. The hard rocks are less eroded and lie as hanging ridges stretching parallel to each other separated by grooves. Such a feature is known as a yardang.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms yardang

 

6. Furrow: In desert regions, high-velocity winds carry rock fragments and pebbles along with them, that work as tools of erosion. When these rock fragments hit against the large standing rocks, they form long narrow grooves on the rocks due to erosion. These narrow long grooves formed on the standing rocks are known as furrows.

7. Millet seeds sand: In desert regions, as the wind blows over the rocky surface, the rock fragments hit against each other and break down into smaller fragments that resemble the seeds of millets. These small fragments are thus called millet seeds sand. Formation of the millet seeds sand leads to the formation of sand particles due to further erosion.

8. Blowouts: The speedy winds in desert regions often blow out or deflate sand particles from a region. Thus, a number of small or big depressions are formed known as blowouts or depression hollows. These are known as ‘hands’ in Rajasthan. The hands may get filled with water to form saltwater lakes called playa lakes.

9. Pavements: These are extensive stretches of stony surfaces formed in the desert due to the deflation of the wind. Pavements consist of angular or rounded rocky fragments in a matrix of finer sand, silt and clay-sized materials. They are locally known by various names in various places. In the Sahara desert, they are known as reg or hammada.

Question 2 Describe some of the depositional landforms formed by wind action.
Answer:

The depositional landforms formed by wind action are as follows—

1. Dunes: In sandy deserts, if the winds carrying huge amounts of sand are obstructed by the presence of trees, plants, rocks or bushes, the wind loses speed which leads to the deposition of sand. Gradually, the sand accumulates into large heaps and forms sand dunes.

Dunes are classified into the following types—

1. Barchans: The barchan is a transverse sand dune that is found in the desert region. It stands across the direction of the wind. It looks like a crescent moon. The middle part of the barchan can be 15-30m high. It has two horns on either side which move forward as the wind blows.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms barcahn

 

2. Seif dunes: Longitudinal dunes parallel to the direction of wind form the seif dunes, Barchans gradually transform into seif dunes when the sand from the central portion gets eroded away and the two horns form two separate dunes.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms seif dunes

 

3. Star dunes: In desert regions, winds blow from different directions during different times of the year. Thus, dunes are formed in different directions. Star dunes are formed by variable winds. They grow vertically and do not migrate laterally. A star dune has multiple slip faces, a central peak and three or more arms extending radially.

1. Akle dunes: A number of barchans lying side by side like a chain from akl6 dunes. They look like a long serpentine ridge. The front part of the curve of the ankle dunes is called languid, and the rear part is known as the paranoid.

2. Transverse dunes: Elongated dunes lying at right angles to the direction of the prevailing wind are known as transverse dunes. These dunes have a steep leeward side and a gently sloping windward side. They appear as wave-like features.

3. Parabolic dunes: These dunes develop in partially stabilised sandy terrains and form a U shape. Parabolic dunes have a convex nose which migrates downwind. They are longer and narrower than barchans and are always associated with blowouts.

2. Loess plain: Loess plain is composed of yellowish soil particles that are blown by the wind from the deserts and deposited elsewhere. The loess plain contains particles that are very fine textured and rich in quartz silt, clay and carbonate minerals. The soil particles do not have any similarity with the rocks and soil present in the region where they have been deposited.

3. Ripple marks: These are wave-like small-scale depositional features formed by wind action. They can be of two types—
transverse ripples and longitudinal ripples.

Question 3 Write about the processes of wind action in a desert in the desert.
Answer:

The processes of wind action in a desert in the desert:

The work of the wind is most prominent in desert regions. Wind performs three actions in desert regions—erosion, transportation and deposition.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land orms work of wind

 

1. Erosion:

The wind carries out erosion by the following processes—

1. Abrasion: The wind carries particles of rocks, pebbles, sand, etc., of different sizes along with it as it blows. These particles collide with the landforms on the earth’s surface and create scratch marks, hollows and furrows. Erosion by this process is called abrasion. Landforms formed due to abrasion are—mushroom rocks, yardang, zeugen, ventifact, dreikantar, etc.

2. Deflation: In the process of deflation, the wind blows away sand and smaller rock particles from one place to another. Landforms formed by deflation are—blowouts, pavements, etc.

3. Attrition: The rock fragments, pebbles, etc., present in the blowing wind collide with each other and break into smaller fragments and finally convert into sand particles. The process of this breaking down of rock fragments into fine particles of sand due to their collision with each other is known as attrition.

2. Transportation: Wind transports the broken rock fragments and other finer particles by the following methods—

1. Suspension: The small and light particles of sand and dust remain suspended in the air and are thus transported to long distances by wind.

2. Saltation: The medium-sized particles of rock fragments are heavy and cannot be transported in suspension. Even if lifted by the wind, they are carried to shorter distances and dropped on the ground wherever the wind is obstructed.

3. Creeping: The larger particles of rock fragments cannot be lifted by the wind due to their heavy weight. They are dragged along the surface while the wind blows. This method of transportation is known as creeping. deserts. Dune migration is harmful as vast regions of agricultural fields, grazing land, human settlement, etc., are buried under huge heaps of sand.

2. Overgrazing: The areas adjacent to the desert receive more rainfall than the desert regions. Thus, it leads to the growth of grasslands. In the absence of agricultural activities, the people of the desert region take to cattle rearing. Overgrazing of animals on these grasslands turns these adjacent areas also into deserts.

3. Rampant cutting down of trees: Indiscriminate felling of trees in the areas adjacent to the desert regions, leads to the expansion of deserts.

4. Unscientific methods of cultivation: Following unscientific methods of cultivation in the areas adjacent to the deserts affects the fertility of these regions. As a result, the adjacent areas are also turned into deserts.

3. Deposition: Any hindrance in the form of trees, bushes, rocky boulders, etc., in the path of the blowing wind may affect the velocity of the wind. As a result, the sand and broken rocky fragments being carried to distances are dropped wherever they are obstructed. These sand accumulations grow in dimension and form several depositional features. Example-Various sand dunes, loess plains, etc.

Question 4 Why are the deserts of the world facing severe expansion? Suggest remedial measures to prevent this.
Answer:

At present, the deserts of the world are facing severe expansion.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms expansion of desesrts

 

The reasons leading to such an event are as follows—

1. Migration of dunes: Migration or shifting of sand dunes causes the expansion of deserts. Dune migration is harmful as vast regions of agricultural fields, grazing land, human settlement, etc., are buried under huge heaps of sand.

2. Overgrazing: The areas adjacent to the desert receive more rainfall than the desert regions. Thus, it leads to the growth of grasslands. In the absence of agricultural activities, the people of the desert region take to cattle rearing. Overgrazing of animals on these grasslands turns these adjacent areas also into deserts.

3. Rampant cutting down of trees: Indiscriminate felling of trees in the areas adjacent to the desert regions, leads to the expansion of deserts.

4. Unscientific methods of cultivation: Following unscientific methods of cultivation in the areas adjacent to the deserts affects the fertility of these regions. As a result, the adjacent areas are also turned into deserts.

5. Drought: Areas adjacent to the deserts when affected by frequent droughts, turn into deserts. The water table in these regions is severely lowered and the vegetation also stands affected.

6. Global warming: Worldwide increase of temperature due to global warming has affected the temperature, amount of rainfall received, etc., of the regions adjacent to the desert. Decreased amounts of rainfall received and high temperatures are turning the adjacent areas into a desert.

Measures to prevent the expansion of deserts are as follows—

1. Afforestation: Planting of trees suitable to the desert environment along the margins of the desert and in the areas adjacent to the desert. to high wind speed, sand being continuously removed from a place creates several small and big hollows or depressions on the ground. These are called deflation hollows or blowouts. In Rajasthan, they are locally known as Dhand.

2. Controlled grazing: Overgrazing should be checked in the areas adjacent to the deserts.

3. Other sources of fuel: The use of a wood source of fuel should be reduced. Alternative sources of fuel should be looked at regions drought-resistant crops should be grown using modern methods of irrigation.

5. Conservation and judicious use of water: Rainwater harvesting should be extensively practised in the areas adjacent to the desert to mitigate the problem of water shortage. Judicious use of water should also be promoted.

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Short Explanatory Answer Type Questions

 

Question 1 Write down the characteristics of Barchans.
Answer:

The dunes formed transverse to the direction of the blowing wind in the shape of a crescent, is known as a barchan.

Characteristics: The characteristics of barchans are listed below—

1. The windward slope of the barchan is gentle and convex while the leeward slope is steep and concave.

2. The edges of the barchan look like two horns on either side of the crescent.

3. Barkhans are usually 15-30m high. Some barkhans may be as high as 200m.

4. A number of barkhans may develop like a chain in plain regions in the desert. However, they are all temporary and may shift with the change in wind direction.

5. Barchans advance on a regular basis at a constant rate when the sand supply is adequate.

Question 2 Write the characteristics of seif dunes.
Answer: The long, narrow sand dunes formed parallel to the direction of the wind in a desert region, are called seif dunes. another place

Characteristics:

1. Seif dunes can be a few kilometres long and a few hundred metres high.

2. A number of seif dunes may be formed parallel to each other.

3. Sometimes, due to very speedy winds, the middle portion of the barchans may get eroded or blown away, and the horns at the edges of the barchans may get transformed into seif dunes.

4. The gap between two adjacent seif dunes is a called corridor. The wind blows at a great speed through these corridors.

5. The top of the seif dunes are sharp and are like saw teeth.

Question 4 What is a loess plain?
Answer:

Loess plain:

The yellowish fine sandy particles blown off from the desert regions and deposited elsewhere are known as loess. The particles of loess are fine textured and rich in quartz silt, clay and carbonate minerals. The fine textured soil particles are blown away from the deserts and the outwash plains and deposited at distant regions, forming a new landform known as a loess plain.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms Expansion of deserts

 

Example—In central Asia, every year, a heavy amount of sandy soil is eroded from the Gobi desert by the northeast monsoon winds. They are deposited in the Hwang Ho river valley of northern China. This Loess plains formed deposition of sand Plains formed by the deposition of silt in the river basin of River Hwang Ho form a loess plain. The depth of the plainland thus formed is 30-200m. Examples of other loess plains are—the loess plain formed in the southern region of Israel by blowing off the soil from the Sahara desert region of Africa; the loess plain formed in the Mississippi-Missourie river in the USA, etc.

Question 5 Differentiate between yardang and barchan.
Answer:

The differences between yardang and barchan are as follows-

 

Point of difference Yardang Barchan
Nature Erosional landforms formed by wind action. Depositional landform formed by wind action.
Appearance Looks like steep sided deeply undercut overhanging rock ridge. Looks like a crescent moon, with two horns at the edge of the barchan.
Component Hard resistant rocks. Huge heaps of sand.
Height Usually, 8m high. It may even attain a height of 60m in the deserts of Iran. Usually, 25-30m high.

 

The landforms formed by the deflation of wind are—

1. Deflation hollows: In desert regions, due to high wind speed, continuously removed from a place creates depressions on the ground. These are called deflation hollows or blowouts. In Rajasthan, they are locally known as Dhand.

2. Oasis: At times the depressions formed due to the deflation action of the wind become their depth reach so deep that As a result, the underground water table. sand over there becomes due to the presence of water, few trees and little moisture and plants grow around the region. Such a landscape is known as an oasis.

 

WBBSE Solutions Class 10 geography and environment Exogenetic process and resultant land forms formation of oasis by the process of deflaction

 

3. Desert Pavements: These are extensive stretches of stony surfaces formed in the desert due to the deflation of the wind. Pavements consist of angular or rounded rocky fragments in a matrix of finer sand, silt and clay-sized materials. They are locally known by various names in various places. In the Sahara desert, they are known as reg or hammada.

Question 7 Where is the erosional action of wind most predominant?
Answer:

In arid regions of the world where the rainfall received is less than 25cm, growth of natural vegetation is negligible or almost absent the erosional action of the wind is most predominant. The land surface remains open and uncovered. There are almost no obstructions to the blowing wind. Hence the winds blow at a great speed. Also, the high diurnal range of temperature leads to the disintegration of rocks. These rock fragments are carried with the wind further eroding the landscape by the process of abrasion.

Question 8 Why is the action of wind also active in the coastal regions?
Answer:

Action of wind is highly active in the coastal regions because—

1. Extensive coastline: The sea breeze blowing over the open seas come towards the land and blow away the sand from the coast. Thus, the open and extensive coastline assist in the erosional and depositional works of the wind.

2. Sea waves: The sea waves splash against the coast continuously, and tend to break the rocks and stones into tiny particles, that can be easily blown away by the wind.

3. Deposition of sand: The sand present along the coast can be blown away, carried and deposited elsewhere when the winds are obstructed and lose speed. These landforms are called sand dunes. Example—Such dunes can be seen in the Digha and Contai regions of West Bengal.

3. Desert Pavements: These are extensive stretches of stony surfaces formed in the desert due to the deflation of the wind. Pavements consist of angular or rounded rocky fragments in a matrix of finer sand, silt and clay-sized materials. They are locally known by various names in various places. In the Sahara desert, they are known as reg or hammada.

Question 9 How is sand formed in the deserts?
Answer:

In the desert regions, the diurnal and annual ranges of temperature are very high. This enhances weathering by mechanical methods, where the large rocks are gradually broken down into small rock fragments. Also, abrasion of rocks leads to further breakdown of rocks into sand particles. Lack of rainfall helps to speed up the whole process. Thus, sand is formed in the deserts.

Question 10 Differentiate between barchans and seif dunes. Or, State three”Seifseif dune” dunes. and “Barkhan”.
Answer:

The differences between barchans and seif dunes are as follows-

 

Point of difference  Barchans  Seif dunes 
Shape  Look like a crescent moon Look like a sword straight, narrow and long
Relation to wind direction  Present as oblique dunes across the wind direction Present as straight or longitudinal dunes parallel to the direction of the wind
Special feature  Two horns lie at the edge of the Barnes No such horns are present

 

Question 11 Differentiate between pediment and bajada.
Answer:

The differences between pediment and bajada are as follows—

 

Points of difference  Pediment  Bajada
Concept A gently sloping landform formed in j desert regions at the foothills of 1 mountain. A plain land formed between pediment and playa by the accumulation of sand, clay and pebbles.
Gradient  The general gradient ranges between r-r. The gradient in the upper part ranges between and becomes almost in the lower part.
Nature Tit is formed jointly by the erosional 1 work of the wind and water. It is solely a depositional feature.

 

Question 12 Differentiate between monadnocks and inselbergs.
Answer:

The differences between monadnocks and inselbergs are as follows—

 

Points of difference  Monadnocks  Inselbergs
Concept low hillocks lying on a peneplain region, formes on peneplain region, Formed of hard resistant rock. Low hillocks lying on a peneplain region, formed of hard resistant rocks.
Agent of erosion  Formed by erosional activities of flowing water Formed by erosional activities of wind and flowing water.
location  Found in humid regions Found in arid regions

 

Chapter 1 Exogenetic Processes And Resultant Land Forms Short Answer Type Questions

 

Question 1. What are wadis?
Answer:

Wadis:

The small, shallow dry river valleys found in the deserts are called wadis. The wadis remain dry for most of the time and get filled at times of sudden rain in the desert. They often shift from one position to another or get lost in the sand. Eg.— Wadi Al-Batin of Saudi Arabia is a famous wadi.

Question 2. What do you mean by a pediment?
Answer:

Pediment:

In desert regions, the winds are the strongest agent of erosion. The small rocks, pebbles, sand particles etc., that blow with the wind help in eroding large boulders or mountains to low landforms. A pediment is a plain formed at the foothills of mountains in a desert by the joint action of erosion and deposition by the wind as well as flowing water. It remains covered with rocks and boulders.

Question 3. What are dunes?
Answer:

Dunes:

In deserts, the winds are very strong and can lift and carry large amounts of sand as they blow. But if the winds are obstructed by trees, rocks, boulders, bushes, hillocks, etc., they lose speed and drop the sand at the place of obstruction. Thus, the sand gets accumulated as high dumps over long stretches of land. These landforms are known as sand dunes. Dunes also form due to the presence of a dominant direction in which the wind blows.

Question 4. What is a barchan?
Answer:

Barchan:

The barchan is a transfer sand dune that is found in the desert region. It stands across the direction of the wind. It looks like a crescent moon. The middle part of the barchan can be 15-30m high. It has two horns on either side which move forward as the wind blows.

Question 5. What is a hammada?
Answer:

Hammada:

Hard rocky sand-free surface in a desert is known as a hammada. It is formed when the sand has been blown away by winds.

Question 6. Where are sand dunes found?
Answer:

Sand dunes are found in regions that have huge accumulations of sand, some thorny bushes acting as obstructions and vast open lands. Such conditions are found in hot dry desert regions and coastal regions.

Question 7. What is a garage?
Answer:

Garage:

In a desert region, the wind is the most active agent of erosion. The wind erodes mainly by the process of abrasion, where the rocks and pebbles carried by the wind collide against the lower parts or base of a high boulder or a hill. The soft rocks at the base get eroded faster and the hard rocks on the top remain as it is. Thus, the landform develops a narrow base and a broad top. This looks like a mushroom and thus is known as a mushroom rock. Such mushroom rocks are known as gara in the Sahara region.

Question 8. What is loess? Or, Define Loess.
Answer:

Loess:

Loess are the yellowish soil particles that are blown by the wind from the deserts and deposited elsewhere. Loess contains particles that are very fine textured and rich in quartz silt, clay and carbonate minerals. The soil particles do not have any similarity with the rocks and soil present in the region where they have been deposited. The plains formed of the loess deposits are called loess plains.

Question 9. What is an oasis?
Answer:

Oasis:

In desert regions, a huge depression may be created due to the blowing away of sand by the wind regularly. The depression becomes so deep that the surface of the region reaches the level of the underground water table. Thus, water is easily available here, and the soil remains moist. This region is known as the oasis, as the availability of water helps in the growth of trees around the depression and makes this region look green. An oasis is like a garden in the desert region.

Question 10.What are ventifact and dreikanter?
Answer:

Ventifact: In a desert region, if the wind blows from one direction, the large rocks are polished on one side (the side facing the wind) by the process of abrasion, while the other sides remain uneven and rough. Such a rock is known as a ventifact.

Dreikanter: If the wind blows from different directions, all the faces of the rocks standing out are polished by the process of abrasion. Thus, a landform with three polished faces is formed. This is known as dreikanter.

Question 11. What is a durian?
Answer:

Durian:

In a desert region, due to changes in the direction of winds, the sand dunes shift from one place to the other. These moving or shifting dunes are called ‘durians’ in the desert region of Rajasthan.

Question 12. What are seif dunes?
Answer:

Seif dunes:

Seif’ means sword in Arabic. The long and narrow dunes like swords formed in the deserts are called seif dunes.
The seif dunes are formed in sandy deserts parallel to the direction of the wind. These are practically the longitudinal dunes. According to scientist Bagnold, the barchans in the desert region get gradually converted to seif dunes.

Question 13. What are blowouts or deflation hollows? Or, How are the “deflation hollows” formed?
Answer:

Blowouts or deflation hollows are sandy depressions found in desert regions. They are formed by the removal of sand from a region by the wind. They are commonly found in arid regions or coastal regions where there is the sufficient sand cover. Example—Qattara Depression, Egypt.

Question 14. What do you mean by playa lakes?
Answer:

Playa lakes:

The saltwater lakes found in desert regions are called playa lakes. They are known as ‘hands’ in Rajasthan and ‘shafts’ in Sahara. The ephemeral streams that originate from the surrounding mountains drain into these lakes. The non-perennial rivers of the desert region may also drain into these playa lakes.

Class 10 Geography Chapter 1 Notes WBBSE

Question 15. What is a bajada?
Answer:

Bajada:

The gently sloping plain land lying between the pediment and the playa in a desert region is called a bajada. It may be formed at the foothills of mountains by the accumulation of clay, silt and pebbles. The alluvial cones formed at the foothills of mountains in a fluvial aeolian environment may join with each other and form a bajada.

Question 16. Why does abrasion occur at a height of a few metres above the earth’s surface?
Answer:

Abrasion is the process in which the rock pieces, pebbles and sand blown by the wind rub against or collide against the rocky hills or walls on the earth’s surface and thus erode them. Abrasion occurs only till a few metres above the ground because the large rock pieces cannot be lifted too high above the ground by the winds. The presence of erosive tools carried by the wind is maximum at the lower columns of air than at a height.

Question 17. What are star dunes?
Answer:

Star dunes:

In desert regions, winds blow from different directions during different times of the year. Thus, dunes are formed in different directions. Star dunes are formed by variable winds. They grow vertically and do not migrate laterally. A star dune has multiple slip faces, a central peak and three or more arms extending radially.

Question 18. What do you mean by Agassi?
Answer:

Agassi:

The seif dunes lie parallel to one another and the gap or passage between two adjacent seif dunes is called a corridor. These corridors are devoid of sand and lie as pavements or vast stony plains in the desert. These are called reg. Such reg or corridors between parallel dunes are known as gassy in Sahara, Africa. These corridors are used as caravan paths for travelling through the deserts.

Question 19. What do you mean by erg?
Answer:

Erg:

The vast stretches in the desert made up of sand accumulations are known as ergs. Ergs are formed where the wind is most active and the amount of sand present is huge. These depressions of wind accumulations were formerly filled with alluvium.

Class 10 Geography Chapter 1 Notes WBBSE

Question 20. Name some deserts of the mid-latitudes.
Answer:

Some deserts of the mid-latitudes are— Gobi, Taklamakan and the desert of Turkestan in Asia, the Colorado desert in North America, etc. The number of deserts in mid-latitudes is more than the number of deserts in low latitudes.

Question 21. Name some deserts of the low latitudes.
Answer:

The low-latitude deserts are found within 20°-30° latitudes in both hemispheres. These deserts have developed on the western margins of the continents. E.g.— Sahara, and Kalahari in Africa; the Arabian desert, the Baluchistan desert and Thar desert in Asia; Soneran in North America, the Great Australian desert in Australia, etc.

Question 22. What is adobe?
Answer:

Adobe:

In North America, loess deposits are found in the valleys of the Mississippi and Missouri rivers. Scientists believe that this landform had been formed in the Pleistocene Age when sand from the moraines and outwash plains was blown off and deposited here. These loess deposits are known as adobe in North America. Loess is extensively found in Nebraska, Illinois, Iowa, etc.

Chapter 1 Exogenetic Processes And Resultant Land Forms If The Statement Is True, Write True And False Write ‘False Against The Following

Question 1. Erg is an area of a large accumulation of sand, formerly piled up with alluvium.
Answer: True

Question 2. Oases are created due to the abrasion of wind.
Answer: False

Question 3. Barchans are a special type of transverse dunes.
Answer: True

Question 4. The pediment is a type of plain.
Answer: True

Question 5. The lakes found in desert topography are called playas.
Answer: True

Question 6. The leeward slope of the ventifact is smooth and sharp.
Answer: False

Question 7. The dreikanter has all three sides eroded and polished.
Answer: True

Question 8. The large hollow or depression created in the Sahara desert due to the blowing away of sand is known as Qattara.
Answer: True

Question 9. Inselbergs are erosional landforms of glaciers.
Answer:  False

Question 10. Interlocking spurs are formed due to wind erosion.
Answer:  False

Question 11. The crescent sand dunes are known as seif dunes.
Answer: False

Question 12. The landforms looking like mushrooms found in deserts are called yardangs.
Answer: False

Question 13. The shifting dunes are called barchans.
Answer: False

Question 14. The saltwater lakes of deserts are called wadis.
Answer: False

Question 15. The Taklamakan desert lies in China.
Answer: True

Question 16.’Mesa’ means ‘chair’ in Spanish.
Answer: False

Question 17. Seif dunes are formed parallel to the direction of the wind.
Answer: True

Class 10 Geography Chapter 1 Notes WBBSE

Chapter 1 Exogenetic Processes And Resultant Land Forms Fill In The Blanks With Suitable Words

 

Question 1. Loess comes from a German word meaning
Answer: Loose materials

Question 2. In desert regions, the presence of rocks is in a tabular form.
Answer: Zeguen

Question 3. The rock-covered plain formed at the foothills of mountains in desert regions due to the combined action of wind and flowing water is called
Answer: Pediment

Question4.The dunes have two horns and look like a crescent moon.
Answer: Barchan

Question 5. The salt lakes of the Marusthali region are known as
Answer: Dhand

Question 6. The salt lakes of the desert are known as
Answer: playa

Question 7. Whaleback landforms are also known is predominantly seen
Answer: Draas

Chapter 1 Exogenetic Processes And Resultant Land Forms Answer In One Or Two Words

Question 1. Which shape do the sharp and pointed yardangs tend to look like?
Answer: Needle.

Question 2. Which is the largest desert in the world?
Answer: Sahara.

Question 3. What is the space between two seif dunes called?
Answer: Corridor.

Question 4. Where are the largest loess depositions found in the world?
Answer: Hwang Ho valley of China.

Question 5. What does the word ‘butte’ mean?
Answer: Hillocks or domes.

Question 6. Where is the work of winds predominant?
Answer: In desert regions and coastal regions.

Question 7. What are straight dunes also known as?
Answer: Seif dunes.

Question 8. Which is the deepest blowout in the world?
Answer: Qattara in Egypt.

Chapter 1 Exogenetic Processes And Resultant Land Forms Match The Left Column With The Right Column Answer

Class 10 Geography Chapter 1 Notes WBBSE

1.

Left Column  Right Column  
1. Loess A. Rocky Sand free surface
2. Hammada B. Qattara in Egypt
3. Blow out C. Gobi desert in asia
4. Oasis D. Loose materials
5. Mid-Latitude deserts E. Riyadh

Answer: 1-D,2-A,3-B,4-E,5-C

2.

Left Column  Right Column
1. Draas A. Dunes contain
2. Seif dunes B. Hwang ho river
3. Coastal dunes C. Thar desert
4. Shifting dunes D. Sahara desert
5. loess E. Dhrian

Answer: 1-D,2-C,3-A,4-E,5-B

WBBSE Solutions for Class 10 Geography and Environment

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