WBBSE Class 9 Geography Solutions Chapter 4 Geomorphic Processes and Landforms of the Earth

Detailed explanations in West Bengal Board Class 9 Geography Book Solutions Chapter 4 Geomorphic Processes and Landforms of the Earth offer valuable context and analysis.

WBBSE Class 9 Geography Chapter 4 Question Answer – Geomorphic Processes and Landforms of the Earth

Very Short Questions and Answers : (1 mark for each question)

Question 1.
Which is the second highest peak in India?
Answer:
Mt. Kangchenjunga.

Question 2.
What is the topmost part of a mountain called?
Answer:
Peak.

Question 3.
The Himalayan mountains have originated from which geosyncline?
Answer:
Tethys.

Question 4.
Give an example of a volcano in India.
Answer:
Barren Island.

Question 5.
What is the average altitude of a mountain?
Answer:
1,000 metre.

Question 6.
What is block mountain called in German?
Answer:
Horst.

Question 7.
What is the upper part of a fold mountain called?
Answer:
Anticline.

Question 8.
Which is India’s largest plateau?
Answer:
Deccan Plateau.

Question 9.
Which is the largest delta in the world?
Answer:
Ganga-Brahmaputra Delta.

Question 10.
Which is the largest mountain chain in the world?
Answer:
The Andes.

Question 11.
Give an example of an erosional plateau in India?
Answer:
Chota Nagpur Plateau.

Question 12.
By which name is Pamir Plateau also known?
Answer:
‘Roof of the World’.

Question 13.
Which activity/movement leads to the formation of fold mountains?
Answer:
Orogeny.

Question 14.
Which is the highest peak of the Aravallis?
Answer:
Guru Shikhar.

Question 15.
Which activity/movement leads to the formation of rift valleys?
Answer:
Epeirogeny.

Question 16.
What is the intervening valley between two block mountains called?
Answer:
Rift valley.

Question 17.
What is an ancient plateau also known as?
Answer:
Shield.

Question 18.
What is the main reason for the formation of an uplifted plain?
Answer:
Geotectonic activity.

Question 19.
What is the meaning of ‘Deccan Trap’?
Answer:
Steps of the Deccan.

Question 20.
Which is the largest plain in the world?
Answer:
Siberian Plain.

Question 21.
Give an example of an exogenic force/agent of erosion.
Answer:
Work of a river/fluvial action.

Question 22.
Give an example of a block mountain in India.
Answer:
Satpuras.

Question 23.
Where are gr. abens seen?
Answer:
In the low-lyi ing basin between two faults.

Question 24.
What is Pang aea?
Answer:
The only lai idmass that existed in the ancient world.

Question 25.
Give examples of two mountain knots in Asia.
Answer:
Pamir Knot and, Armenian Knot.

Question 26.
Give an exam, ole of an ancient fold mountain.
Answer:
Caledonian mour itains of North America.

Question 27.
Give an example of a structural plain.
Answer:
Turan Lowland.

Question 28.
Give an example of a karst topography in India.
Answer:
Borra Caves in An dhra Pradesh.

Question 29.
What is the residual hill in a peneplain called?
Answer:
Monadnock.

Question 30.
In which geological period were the Himalayas formed?
Answer:
Tertiary.

Short Questions and Answers : (2 marks for each question)

Question 1.
What are landforms? What are the major landforms on the earth’s surface?
Answer:
Landforms are the outer appearances on the earth’s surface with typical geometric shapes and physical features resulting from weathering and erosion carried out by different agents like rivers (fluvial), glaciers, wind, waves. The major landforms on the earth’s surface are mountains, plateaus and plains. Notable examples in India are the Himalayas, the Deccan Plateau and the Indo-Gangetic Plain respectively.

Question 2.
What are geotectonic activities?
Answer:
The tectonic disturbances/activities originating under the earth’s crust (in the interior) that lead to the formation of primary relief features or landforms on the earth’s surface are known: as geotectonic activities. These are of two types-1. epeirogenic, and 2. orogenic movem ents.

Question 3.
What are epeirogenic movements?
Answer:
The vertical movemerits on the earth’s crust due to tectonic activities in the earth’s interior are known as epeirogenic movement. Faults are created on the earth’s crust and certain parts of it either move up or down as a result of such movements.

Question 4.
What are orogenic movements?
Answer:
The horizontal movements on the earth’s crust due to tectonic activities in the earth’s interior are known as orogenic movements.
They are also called mountain-building movements. Fold mount ains are formed and the crust is deform ed due to such movements. The Himalaya in-Alpine orogeny is a classic example of this ..

Question 5.
What is meant by isostat ic imbalance?
Answer:
The different landform s (like mountains, plateaus and plains) exist on the earth’s surface while maintaini ng a certain balance among each other, known as isostatic balance (since the ear th’s solid crust floats on the viscous mant le below it). If this balance is disturbed (fue to some reason, the movement that follows is known as isostatic imbalance.

Question 6.
What is meant by gec icentric or endogenic process?
Answer:
The initial process wt iereby the landforms are formed (relief of the 1st order) is known as geocentric or enclogenic process. For example, geotectonic activity, volcanicity, plate movement occur suddenly in the earth’s interior and ha je their influence on the landforms of the e-arth’s crust.

Question 7.
What is exogenic or ext erior process?
Answer:
The different forces of: nature or agents of erosion which act on the earth’s outer surface are called texogenic or exterior processes. For example, weathering and erosion. Since they a re acting continuously over a long period of time, they play a major role in forming different types of landform on the earth’s crust.

Question 8.
What are fold mountains?
Answer:
When the sediments of the ocean floor come under pressure and are crumpled up due to orogenic movement, they are uplifted to form fold mountains (having peaks). For example, the Himalayas, the Rockies, the Andes, the Alps etc.

Question 9.
What are ancient/old and young fold mountains?
Answer:
The fold mountains which are very old according to geological age have been affected by erosion over millenia and, as a result, their heights have decreased. For example, the Aravalli in India. On the other hand, the young fold mountains have formed much later according to geological age and they are higher than the old fold mountains. For example, the lofty Himalayas.

Question 10.
What is plate margin?
Answer:
Large parts of the earth’s crust which are constantly moving and constitute the continent and ocean floors are called plates. The margin or border of two such plates is called plate margin.

Question 11.
What are the different types of plate margins?
Answer:
There are mainly 3 types of plate margins

1. converging or destructive plate margins (plates moving towards each other)
2. diverging or constructive plate margins (plates moving away from each other)
3. transform or conservative or parallel plate margins (plates moving or sliding along each other, but in opposite directions) and are neither destructive nor constructive in nature.

Question 12.
What are suture lines?
Answer:
The margin where two continental plates meet and join each other is known as a suture line. Fold mountains are formed along such lines and the mountains gradually increase in height with further lateral pressure exerted by the plate movements (moving towards each other).

Question 13.
What is a geosyncline?
Answer:
The long and narrow portions of the sea floor where there is continuous deposition of sediments (such as silt, sand, pebbles) are called geosynclines. Due to lateral/ horizontal pressure coming from both sides, the sediments are crumpled up and form fold mountains. For example, the young fold mountains of the Himalayas have formed in such a geosyncline (called the Tethys Sea).

Question 14.
What are erosional mountains?
Answer:
When high and extensive rocky landmasses are subjected to erosion by various forces of nature (like weathering, river, wind), the residual/remaining part of such mountains are called erosional or residual mountains. They are much lower in height but retain the features of a mountain. For example, the Aravalli Hills in India.

Question 15.
What is a depositional or aggradational hill?
Answer:
Molten magma comes out from beneath the earth’s surface through cracks and fissures, as a result of tectonic movement. Over time, layers of magma accumulate over each other, forming a hill. For example, Mt. Fujiyama of Japan.

Question 16.
What is fault?
Answer:
Due to the alternative processes of expansion and contraction occurring during epeirogenic movements, cracks are formed on the rock layers of the earth. If the adjacent rock layers separate along these almost vertical cracks and get displaced, they give rise to faults.

Question 17.
What are block mountains or horst?
Answer:
When a block of landmass is uplifted along a fault as a result of epeirogenic movement, it forms a flat-topped hill called block mountain. For example, the Satpura Hill of India, Vosges of France, Black Forest of Germany.

Question 18.
What is a rift valley or graben?
Answer:
When a block of landmass subsides along two faults as a result of epeirogenic movements, this subsided block is called a rift valley or graben. For example, the Narmada river of India, lying adjacent to the Satpura hills, and the Rhine river valley of Germany, which lies between the Vosges and Black Forest block mountains.

Question 19.
What is an intermontane plateau?
Answer:
When fold mountains are formed as a result of tectonic activity, the intervening low land, lying between high fold mountains is known as an intermontane plateau. For example, the Plateau of Tibet lying between the Himalayas and Kunlun mountains.

Question 20.
Where do you find dissected plateaus in India?
Answer:
Parts of Chota Nagpur Plateau, Deccan Plateau and Meghalaya Plateau are dissected plateaus.

Question 21.
What is the Deccan Trap?
Answer:
The step-like landform seen in the Deccan Plateau is known as Deccan Trap. The Swedish term ‘trap’ means ‘step’. Such a landform has developed as a result of erosion for a long time on the basaltic rocks (formed due to lava accumulation through fissure eruption).

Question 22.
Where are depositional or aggradational plains found in India?
Answer:
In the northwestern part of the Deccan Plateau (including Maharashtra Plateau) and covering a large part of south India, we find depositional plains formed as a result of accumulation of lava (due to fissure eruption from beneath the earth’s surface) and basically formed of basaltic rocks.

Question 23.
Where are flood plains found in India?
Answer:
In the lower reaches and also in the middle courses of the main rivers of North India, we find flood plains. For example, on both sides of river Ganges, viz., near Patna and Munger in Bihar.

Question 24.
What is a plain?
Answer:
A large expanse of land, having gentle undulations, at the sea level or at a slightly higher altitude (less than 300 m), is called a plain. For example, the Ganges Plains.

Question 25.
Where would you find the world’s largest delta?
Answer:
The world’s largest delta is found between the lower reaches of rivers Ganges and Brahmaputra.

Question 26.
What is meant by uplifted plain?
Answer:
When a plain is formed as a result of the upliftment of any existing plain, as a result of tectonic activity, it is known as an uplifted plain.

Question 27.
What is meant by subdued plain?
Answer:
When any highland (having the characteristics of a plain) subsides to a lower level due to tectonic activity, it forms a subdued plain.

Question 28.
What is a pediment?
Answer:
In the arid (dry) or desert area, we find a gently sloping foothill zone formed by accumulation of sediments consisting of boulders and pebbles. This region is known as a pediment. ‘Pedi’ means foothill and ‘mont’ means hill or mountain. For example, pediments are formed in the foothill region of the Atlas mountains in North Africa.

Question 29.
What is a mountain peak?
Answer:
The high conical top of a mountain is called its peak. For example, Mt. Everest (8,848 m above sea level) is the highest peak of the Himalayas. A mountain may have several peaks.

Question 30.
What are anticlines and synclines?
Answer:
The upper parts of a fold mountain are called anticlines and the lower parts (valleys) are called synclines.

Question 31.
What is a shield?
Answer:
An ancient plateau (created about 100 crore years ago) which has formed due to agelong weathering and erosional processes acting upon the initial landmass is known as a shield. They are geologically stable. For example, the Canadian and Brazilian Shields.

Question 32.
What are flood plains?
Answer:
When the river is in spate, the water overflows its banks on either side and the lowlying tracts of land get flooded. Later on, when the water recedes, the silt carried by this water settles down on these plains, giving rise to fertile flood plains on either side of the river. For example, the Ganges Plains (in the middle and lower courses of the river).

Question 33.
Write a note on the importance of plains.
Answer:

1. Agriculture is extensively carried out in the plains.
2. Transport lines can easily be constructed on the plains because of the flat land and soft soil.
3. Since agriculture and transport are developed here, industries can be developed on the plains.
4. About 90 % of the world’s population lives in the plains.

Question 34.
Why is ‘peneplain’ named so?
Answer:
When an ancient plateau is subjected to age-long weathering and erosion by various agents like rivers, winds, it is reduced to a lower level and looks almost like a plain. Such landforms are called ‘peneplains’ (meaning ‘almost a plain’). Most of the area is a flat, level land, with low hills called monadnocks scattered here and there. For example, parts of the Chota Nagpur Plateau is a peneplain.

Question 35.
Why is Pamir called the ‘Roof of the World’?
Answer:
Pamir is the world’s highest plateau with an average altitude of 4,800 m above sea level. This plateau has an almost flat top wih steep slopes on all sides resembling a roof. This is why Pamir is called the ‘Roof of the World’.

Question 36.
Give examples of one uplifted and one subdued plain.
Answer:
1. Uplifted plain: The coastal plain of Gulf of Mexico.
2. Subdued plain: The plain of Turan.

Question 37.
What is the Tethys Sea?
Answer:
According to geologists, from the later part of the Carboniferous period till the early part of the Cretaceous period, the Tethys Sea was located in between Gondwanaland to the south and Laurasia or Angaraland to the north. Later on, the sediments deposited in the bed of sea gave rise to the formation of the Himalayas (a young fold mountain range) as a result of plate movements.

Question 38.
What is a monadnock?
Answer:
Some low altitude conical hills scattered in a peneplain, which stand out because they are made up of hard resistant rocks, are called monadnocks. For example, Susunia Hill, Tagore Hill of Chota Nagpur Plateau.

Question 39.
What is meant by geotectonic disturbance or diastrophism?
Answer:
When any part of the earth’s surface is uplifted or subsides as a result of tectonic activity, it is called a geotectonic disturbance. This happens as a resuit of tectonic disturbance and isostatic or eustatic disturbance. Epeirogenic and orogenic (mountain-building movement) movements cause changes in the landforms on the earth’s surface.

Question 40.
What is a caldera?
Answer:
The opening through which volcanic ash, lava, and gases gush out during a volcanic eruption is called a crater. A large-sized opening is called a caldera. Sometimes a crater may collapse and subside to from a caldera.

Question 41.
Why is a convergent plate margin known as a destructive plate margin?
Answer:
When two tectonic plates move towards each other, the margin or margin is called convergent plate margin. If a heavier plate (viz., an oceanic plate made up of sima) slides under a lighter plate (viz., a continental plate made up of sial), the sediments on its margins get crumpled up and give rise to fold mountains. Parts of the heavier plate may subside and enter the semi-molten magma below where the solid part of the plate (crust) is melted down and lost. These areas are also prone to earthquakes. This is the reason why they are known as destructive plates.

Question 42.
What is meant by a hotspot?
Answer:
Parts of some weak or thin plates lying in the central part of the plates become very hot as a result of radioactivity taking place there. Later on, as a result of uprising convection currents, magma may force its way upwards and this lava may form volcanic mountains. There are about 25 such hotspots all over the earth’s surface.

Question 43.
What are the ‘Pillars of Light’, located in the Mediterranean Sea?
Answer:
In the Lipari Island of Italy in the Mediterranean Sea, frequent volcanic eruptions occur from the volcanic mountain known as Stromboli. This light can be seen from great distances during the night. The sailors of the ships during ancient times plying on the Mediterranean Sea used to determine their direction with reference to these lights. Thus, they are known as ‘Pillars of Light’.

Short Questions and Answers : (3 marks for each question)

Question 1
How are volcanic mountains formed?
Answer:
The factors that lead to the formation of volcanic mountains are as follows-
1. When magma comes out through the weak zones of two converging tectonic plates, it forms volcanic mountains.
2. When a gap is created between two diverging tectonic plates, magma comes out from below to fill up this gap, resulting in the formation of volcanic mountains.
3. In some cases, magma comes out through the hotspots (i.e., centres of radioactivity). The upward movement of this magma is facilitated by the upward moving convection currents generated in the mantle below the earth’s crust. Examples of such volcanic mountains are-Mt. Fujiyama in Japan, Mt. Vesuvius in Italy, Barren Islands in India. These mountains become increasingly high as a result of further volcanic activity and accumulation of lava in those regions.

Question 2
Classify volcanic mountains based on the nature of volcanic activity. Give examples.
Answer:
Volcanic mountains can be classified into three majors categories based on the nature of volcanic activity. It is shown in the following table-

Question 3
What are the characteristics of volcanic mountains?
Answer:
The features of volcanic mountains are-

1. Shape: They are usually conical or triangular in shape.
2. Presence of a crater: A big opening on the top or peak of the mountain is usually present, which is known as a crater.
3. Multiple craters: Larger volcanic mountains may have more than one crater or multiple craters.
4. Connection between the crater and the mantle in the inner depths of the earth: The crater is connected by an elongated pipe-like structure to the magma chamber of the mantle at greater depths below it.
5. Slope: A volcanic mountain has steep slopes on all sides.
6. Altitude: The volcanic mountains are of medium height.

Question 4.
How are glacial plains and loess plains formed?
Answer:
Formation of glacial plains: The sediments called moraines consisting of gravels, pebbles, cobbles and rock fragments, which have been brought down by moving glaciers and deposited at the foothills, form glacial plain. The Prairies of North America and the European Plains have been formed in this manner.
Formation of loess plains: Fine particles of sand and silt, blown by winds, are transported to distant places and deposited in lowlying places, thereby forming loess plains. The fine sand particles from the Gobi desert of Central Asia, being blown away by winds and carried away to the distant Hwang Ho basin of China, get deposited and form loess plains there.

Question 5.
What are the influences of mountains on human life?
Answer:
Mountains play a vital role in human life. Some of these are-
1. Dense forests provide rich resources in high mountainous regions.
2. Hydroelectricity is generated from swiftflowing mountain rivers.
3. High mountains act as a climatic barrier and play a major role in controlling the climate of any region, including temperature (by preventing cold winds from entering the country) and rainfall (by causing relief or orographic rainfall on the windward side of a mountain). A glaring example of this is the Himalayas influencing the climate of India.
4. Lumbering, animal husbandry and livestock rearing, tourism, etc., flourish in mountainous regions though agriculture is not possible here due to the rough terrain (except in case of terrace farming on mountain slopes).
5. Population is sparse in these areas as steep slopes and rocky terrain make construction of roads difficult. Lack of accessibility hampers the growth of big settlements in these mountainous regions.

Question 6.
Delineate the causes of formation of plateaus.
Answer:
The following three major causes lead to the formation of plateaus-
1. Geotectonic activity: The ancient landmasses on the earth’s crust separate and move away from each other and gain in height as a result of plate movements. These higher landmasses form plateaus. For example, the Arabian Plateau, the Deccan Plateau in south India, etc.

2. Weathering and erosion (due to various agents): Landmasses of higher altitudes are worn down and reduced in height due to the combined effect of weathering and erosion by water, wind, solar insolation, glaciers, etc. As a result, plateaus are formed which are usually flat (tableland) in nature with scattered hills and low peaks here and there. For example, the Chota Nagpur plateau in eastern India.

3. Deposition/Accumulation of lava: Magma or lava from beneath the earth’s crust comes out through cracks or fissures present in the crust. On coming in contact with the atmosphere, they cool down and solidify as horizontal layers of rocks and form lava plateaus. For example, the lava plateau of northwestern Deccan Plateau.

Question 7
What is the influence of plateaus on human life?
Answer:
Plateaus have various influences on human life. Some of these are-
1. Most of the ancient plateaus are rich in mineral resources, e.g., Chota Nagpur Plateau in India, the Canadian Shield, etc.
2. Hydroelectricity can be generated from swift-flowing rivers which flow along the steep slopes of plateaus, viz., most of the big rivers flowing through the Deccan Plateau are utilised for generating hydroelectricity.
3. Due to the uneven and rocky nature of the plateaus, agricultural activity is hampered.

Question 8
Why are plateaus rich in mineral resources?
Answer:
The plateaus which are formed by igneous or metamorphic rocks, are usually rich in mineral resources. When the molten magma comes out and spreads horizontally on the earth’s surface in layers and begins to cool, minerals like iron ore, aluminium, etc., consitituting these solidified rocks are formed here.
Again, minerals like gold, silver, copper are formed in the plateau regions constituted by metamorphic rocks.
The Chota Nagpur Plateau in India is rich in such mineral resources and thus this region is known as the ‘Mineral Reserve of India’.

Question 9.
Why are fossils found in fold mountains?
Answer:
The sediments deposited under the sea have remains of dead plants and animals embedded within their layers. When these sediments are pressurised, they eventually transform into rocks. Later on, these sedimentary rocks are prone to horizontal pressure from either side and they crumble up and form fold mountains. Thus the fold mountains composed of such sedimentary rocks have fossils embedded in them.

Question 10.
Discuss the characteristics of block mountains with examples.
Answer:
The characteristics of block mountains are as follows –
1. When the earth’s crust between two fault lines is forced to rise up (due to horizontal pressure from either side) it forms a block mountain or horst. The lowlying parts on either side are called rift valleys or graben. For example, the Satpura range is a horst and the rivers Narmada and Tapi flow along the rift valleys on either side.
2. When the part of the earth’s crust subsides along two faults lines, due to divergent forces, a rift valley or garben is formed. For example, the river Rhine in Germany flows along such a rift valley and the Black Forest and Vosges represent the block mountains or horst on either side of it.
3. Block mountains have steep slopes and flattened tops.
4. The height and extent of block mountains are moderate and these mountains are devoid of peaks.

Question 11.
Mention any three types of plateaus with examples.
Answer :
Three types of plateaus and their respective examples are as follows-

Name of Plateau	Example
1. Intermontane plateau	Tibetan Plateau, Iranian Plateau
2. Dissected or erosional/residual plateau	Chota Nagpur Plateau, parts of Karnataka Plateau (Malnad) of India
3. Lava plateau	Deccan Trap in south India, Columbia Snake Plateau in USA

Question 12.
How are volcanic or depositional/ accumulative mountains formed? Give examples.
Answer:
Molten magma comes out to the earth’s surface through some deep cracks or channels as a result of differential heating in the earth’s interior, movement of continental and oceanic plates, earthquakes, etc. In due course of time, this lava accumulates in and around such openings and gradually increases in height, leading to the formation of mountains. For example, Mt. Fujiyama in Japan, Mt. Vesuvius in Italy, etc.

Question 13
What are rift valleys/grabens and block mountains/horsts?
Answer:
Rift Valleys/Grabens: When the surface of the earth between two adjacent fault lines vertically subsides to a lower level, it forms a rift valley or graben. For example, the Rhine valley in Germany lying between the two horsts, Black Forest and Vosges on either side, is a rift valley or graben.
Block Mountains/Horsts: When the surface of the earth between two fault lines is forced to rise above the existing level, forming a mountain, it is called block mountain or horst. For example, the Satpuras in India.
Both of these dominant landforms are formed as a result of faults.

Question 14.
What are the features of erosional/ residual mountains?
Answer:
Following are the features of erosional/ residual mountains-

1. The extent of this type of mountain is limited
2. they are low in height
3. they have gentle slopes since erosion takes place over a long period of time
4. the mountain tops are rounded or dome-shaped,
5. these mountains are made up of all three types of rocks
6. they are made up of hard and resistant ancient rocks.

Question 15.
What are the characteristics of intermontane plateaus?
Answer:
Intermontane plateaus formed as a result of tectonic movements have the following characteristics-

1. This type of plateau is usually surrounded by fold mountains.
2. These plateaus attain great heights.
3. They are usually formed by sedimentary rocks.
4. These plateaus are high and are structurally complex. For example, Plateau of Tibet, Plateau of Anatolia, etc.

Question 16.
What is Benioff Zone?
Answer:
As a result of the horizontal movement of two plates, when the heavier plate subsides or goes under the lighter plate, that area or zone is called the subduction zone or Benioff Zone. This zone has been named after the scientist Benioff.
Characteristics: Melting down of solid plates (comprising the earth’s crust), convection currents in the magma (present in the mantle), earthquakes and volcanicity are all common features of this zone.
Example: As a result of the horizontal movement of the Eurasian plate towards the Pacific Oceanic plate, the heavier Pacific Oceanic plate has gone under the Eurasian continental plate and formed a Benioff Zone here.

Question 17.
What is the ‘Pacific Ring of Fire’?
Answer:
The majority of the world’s volcanoes are situated around the Pacific Ocean. Out of these, about 500 active volcanoes (about 70 per cent of the world’s volcanoes) are situated all around the Pacific Ocean like a ring. When these volcanoes erupt (quite frequently) it seems to resemble a ring of fire. This circular belt of volcanoes extend from South America’s Cape Horn to the Andes mountains, via the Rocky Mountains of North America and then extend to the west through the Aleutian Islands, Kamchatka Peninsula, Japan and Philippines.

Question 18.
Why are volcanic mountain regions prone to earthquakes?
Answer:
Earthquakes are common in volcanic mountainous regions because–
1. When volcanic mountains are formed along the margins of converging or destructive plates, two plates collide and this results in the occurrence of earthquakes.
2. When hot and molten magma comes out from the asthenosphere or mantle in the gap created by two diverging plates, earthquakes may occur due to its pressure.
3. When volcanic mountains are formed in the hotspot zones, magma, gases, etc., come out from the interior of the earth towards the earth’s surface. The resulting upward force and pressure make these areas prone to earthquakes.

Question 19
Why are volcanic or igneous matter found in fold mountain regions?
Answer:
The front portion of the heavier oceanic plate slides under the lighter continental plate at about 30°-80° angular plane. As a result, the sediments in this colliding zone buckle up under pressure and form fold mountains. At the same time, the portion of the solid oceanic plate which goes beneath to reach the mantle, is heated up and melts. This molten magma comes up to the earth’s crust in this subduction zone, where fold mountains are in the process of formation. This is the reason why volcanic or igneous matter is found here.

Question 20.
Why are erosional mountains also known as residual mountains?
Answer:
The landforms are sculpted and altered over a long period of time under the influence of different physical factors which cause weathering and erosion. Due to this, the higher mountainous areas formed of relatively weaker and softer rocks are eroded and reduced to mountains with lower altitudes. On the other hand, the harder resistant rocks of the mountains are less eroded and stand out as smaller mountains or uplands. The mountains which are reduced by erosion to lower levels or heights are therefore known as erosional or residual mountains or hills. The ancient mountains like the Aravallis in India, Appalachians in North America are the type of mountains which have been reduced in height due to erosion over the ages.

Write the differences between the following –

Question 1.
Hills and Mountains
Answer:
The difference between hills and mountains are as follows-

Points of diference	Hills	Mountains
1. Height	Hills are usually 300-1,000 metre above sea level.	Mountains are usually more than 1,000 metre above sea level.
2. Slope	The slopes of hills are relatively moderate (less steep).	The slopes of mountains are relatively high (steep to very steep).
3. Extent	Hills are lesser in extent, for example, Susunia Hills in West Bengal, India.	Mountain are larger in extent, for example, the Himalayan mountains in India.

Question 2
Mountains, Plateaus and Plains
Answer:
The differences between mountains, plateaus and plains are as follows-

Question 3
Fold mountain and Block mountain
Answer:
The differences between fold mountain and block mountain are as follows-

Points of difference	Fold Mountain	Block Mountcin
1. Origin	Due to orogenic movement, the sediments in the ocean floor come under lateral pressure and are crumpled, thus giving rise to fold mountains.	Due to epeirogenic movement, landmasses move vertically upwards between two fault lines and form block mountains.
2. Upper part	These are rugged and conical in shape.	It is almost a flat or slightly undulating landform.
3. Altitude	Fold mountains are relatively high, for example, the Himalayan mountains in India.	Block mountains are relatively low, for example, the Satpura range in India.

Question 4
Endogenic and Exogenic process
Answer:
The differences between endogenic and exogenic processes are as follows-

Points of difference	Endogenic Process	Exogenic Process
1. Concept	Internal forces originating in the earth’s interior which influence the primary relief features on the earth’s surface are called endogenic processes.	Physical forces on the surface (like water, wind, glacier, sea waves, etc.) that modify the landform features on the earth’s surface are called exogenic processes.
2. Time taken	These processes act slowly or suddenly, for example, plate movement (slow) and volcanicity (sudden).	These processes act slowly and continuously, for example, landforms produced as a result of weathering and erosion.
3. Landform	Major landforms on the earth’s crust are formed (original or initial landforms) by this process.	Major changes occur in the main landforms of the earth (modified landforms) by this process.

Question 5
Depositional or Aggradational mountain and Erosional or Degradational mountain
Answer :
The differences between depositional/aggradational mountain and erosional/degradational mountain are as follows-

Points of difference	Depositional/Aggradational Mountain	Erosional/Degradational Mountain
1. Origin	Molten magma comes up from beneath the earth’s surface and gets accumulated as lava deposits on the earth’s surface after cooling and solidifying, forming this type of mountain.	An ancient mountainous region is subjected to weathering and erosion by various agents like rivers, wind, etc., and its altitude is reduced. These are erosional mountains.
2. Appearance	These are usually conical in shape.	These are usually dome-shaped.
3. Change in altitude	With further volcanic eruptions, such mountains gain in height, for example, Mt. Vesuvius of Italy.	These mountains gradually decrease in height, for example, the Aravalli Hills of India.

Question 6
Epeirogenic movement and Orogenic movement
Answer:
The differences between epeirogenic and orogenic movements are as follows-

Points of difference	Epeirogenic Movement	Orogenic Movement
1. Definition	The movements which result in formation of continents are known as epeirogenic movements.	The movements which result in the formation of fold mountains (by folding of sediments or rock layers) are known as orogenic movements.
2. Nature	It is a type of vertical movement.	It is a type of horizontal movement.
3. Change in rock layers	Vertical upliftment or subsidence of rock layers takes place in this case.	Rock layers are displaced horizontally in this case.
4. Contraction and expansion	Rocks are not subject to contraction or expansion in this case.	Rocks are subject to contraction and expansion in this case.
5. Effect	Faults, cracks and fissures are formed.	Different types of folds are formed.
6. Resultant landforms	Block mountains, rift valleys, seas, plateaus, etc., are formed.	Mainly fold mountains are formed.

Question 7.
Volcanic and Erosional mountains
Answer:
The differences between volcanic and erosional mountains are as follows-

Points of difference	Volcanic Mountain	Erosional Mountain
1. Causes of Formation	When hot molten magma comes out from beneath the earth’s surface through a vent and cools down and solidifies on the surface, this type of mountain is formed.	As a result of weathering and erosion carried out by different agents like rivers, glaciers, wind, etc., the original mountains are reduced in height, and these are called erosional mountains.
2. Type of rocks	These mountains are made up of igneous rocks only.	These mountains are usually made up of igneous and metamorphic rocks, and also sedimentary rocks.
3. Age	The age of these mountains ranges from young to old.	These mountains are usually ancient
4. Altitude	Their altitude gradually increases with further volcanic activity and subsequent deposits.	Their altitude gradually decreases as a result of continuous weathering and erosion.
5. Appearance	They are usually conical or domeshaped.	They are usually flat-topped or rounded in shape.
6. Forces required for formation	These are formed as a result of tectonic forces (endogenic) acting below the earth’s surface.	Exogenic forces of weathering and erosion-physical agents like rivers, glaciers, wind, etc., are instrumental in the formation of these mountains.

Give reasons for the following –

Question 1.
Most of the world’s population resides in plains.
Answer:
The reasons why most of the world’s population reside in plains are as follows-
1. Availability of water: Since the major perennial rivers flow over the plains, there is constant supply of drinking water, water for domestic purposes, water to be used for irrigation and industrial purposes, etc.
2. Job opportunities: Due to the easy availability of fertile soil, flat land, developed transport system, etc., there is ample scope for agricultural pursuit and industrial development, and hence a lot of job opportunities.
3. Advantages of infrastructure: Since settlements have developed on the flat land, infrastructural facilities like education and health facilities, and a proper transport system have developed.

Question 2.
Settlements do not come up near volcanic mountains.
Answer:
The reasons are as follows-

1. Possibility of volcanic eruptions: Volcanic eruptions can occur at any time from active and dormant volcanoes, leading to huge loss of life and property.
2. Prone to earthquakes: Since these areas are tectonically unstable, plate movements happening here lead to earthquakes which cause disasters.
3. Infertile soil: As a result of accumulation of lava and ash, the soil is rendered infertile and hence not conducive for cultivation and as such, growth of settlements.

Question 3.
Heavy industries cannot develop in mountainous areas.
Answer:
The reasons are as follows-
1. Rugged topography: Transport and communication lines are difficult to construct on such landforms.
2. Sparse settlements: Due to the rugged topography, cold climate, infertile soil, etc., very few settlements come up in such areas. As a result, industry based products have a very low demand here.
3. Other obstacles: Lack of sufficient funds, dearth of advanced technology, etc., have hindered growth of industries here.

Question 4.
Fold mountain regions are prone to earthquakes.
Answer:
The reasons are as follows-
1. Plate movements: When two convergent tectonic plates collide, fold mountains are formed in the plate margin area and the area is thus prone to earthquakes.
2. Upliftment: When the plates move, the folded mountains that are formed rise gradually and these areas are prone to frequent earthquakes.
3. Landslides: When landslides occur in high fold mountains, earthquakes may occur under its influence.

Long Questions and Answers : (5 marks for each question)

Question 1.
Describe the different types of geotectonic movements.
Answer:

The different physical phenomena and processes giving rise to various landforms and their continuous evolution and change are known as geotectonic movements or processes. They may be categorised as-

Endogenic Process: The slow as well as the sudden changes occurring on the earth’s surface as a result of the force or pressure created in the earth’s interior is known as endogenic process. It has been derived from the Greek word ‘endon’ meaning interior or inside. These processes may again be divided into two categories- 1. slow movement or process, and 2. sudden movement.

1. Slow movement or process: The movements in the earth’s interior, giving rise to slow movements or processes in sculpting and changing the landform features on the earth’s surface, are slow movements or processes. They are of two types-
Epeirogenic movement: The movements which are responsible for the formation of continents and oceans are called epeirogenic movements. It has been derived from the Greek word ‘epeiros’ meaning continent. These movements or processes act in a vertical manner and give rise to faults on the earth’s surface.

Orogenic movement: The movements which cause the folding of rocks and formation of fold mountains are called orogenic movements. It has been derived from the Greek word ‘oros’ meaning mountain. The force or pressure acts in a horizontal or lateral manner in this case.

2. Sudden movement: The movements take place very rapidly and all of a sudden. Earthquakes and volcanicity are caused due to such type of movements.

Exogenic Process: The different physical features aiding in weathering and erosion and deposition, resulting in the evolution of landforms, form the exogenic process. It has been derived from the Greek word ‘exo’ meaning exterior or outside. The major exogenic processes are-
1. Weathering: The fragmentation and chemical reactions of rocks due to the action of various climatic factors (like temperature, rainfall, etc.) is called weathering. Mechanical and chemical weathering are the two major types.

2. Mass wasting: When the fragments of rocks, pebbles, mud, etc., slide down the mountain or hill slopes due to gravity, the process is called mass wasting.

3. Erosion: The process whereby various agents of erosion like river, glacier, wind, sea wave, etc., act on the landform, resulting in its modification (viz., formation of mountains, plateaus, plains, etc.), is called erosion. The process of erosion involves both weathering and transportation of the fragmented rocks, pebbles, etc.

4. Deposition: When the action of physical agents (like river, glacier, wind, sea waves, etc.) bring about the aggradation and modification of landforms, the process is called deposition. For example, the formation of loess plains by the action of winds.

Question 2.
Discuss the formation of fold mountains in relation to Plate Tectonic Theory.
Answer:
The Plate Tectonic Theory was first propagated by a French scientist Xavier Le Pichon in 1968. The main idea behind this theory is that the earth’s crust is made up of a number of large plates which are on an average about 100 km in depth and each of them extend over lakhs of kilometre. The plates comprising the continents are called continental plates and those of the ocean floors are called oceanic plates. These solid crustal plates are floating on the mantle which is in a viscous state. Due to the convection currents circulating in the mantle and other tectonic movements that these plates move continuously. As a result, in the plate margin areas, various landforms have formed. Usually there are 3 types of plate margins –
1. Converging plate margin: The plates move towards each other along this plate margin.

2. Diverging plate margin: The plates move away from each other along this plate margin.
3. Transform plate margin: The adjacent plates move along each other in a parallel manner (but in opposite directions) along this plate margin.

Converging plate margins are mainly of 3 types –

1. When two continental plates move towards each other, it is called continentalcontinental plate margin.
2. When one continental and one oceanic plate move towards each other, it is called continental-oceanic plate margin.
3. When two oceanic plates move towards each other, it is called oceanic-oceanic plate margin.
Out of these three types, the first two plate margin movements are responsible for the formation of fold mountains. The process of formation of fold mountains are as follows-

1. Continental-Continental plate margin: A narrow and shallow seabed lying between two continental plates is called a geosyncline. Rivers and streams from both the adjoining continents deposit their silt on this seabed and gradually fill it up. As the converging continental plates come closer, the geosyncline narrows down and the intervening sediments come under great pressure resulting in crumpling up and folding of these sediments in the geosyncline. This is how fold mountains are formed.

For example, when the Indian Plate and the Eurasian Plate moved towards each other, the sediment of the Tethys Sea lying in between was subjected to pressure from both sides and was forced to crumple and rise to form folds, resulting in the formation of the Himalayan mountain ranges.

2. Continental-Oceanic plate margin: When the continental and oceanic plates approach each other, the heavier oceanic plate subsides below the lighter continental plate in a downward bend (like a bow) along the plate margin (see Fig. 4.6). This zone is called subduction zone or Benioff Zone. Consequently, as the two plates come nearer to each other, the lateral or horizontal pressure exerted is so much that the sediments deposited in the plate margin are crumpled up and they rise upwards, resulting in the formation of fold mountains. For example, the Rocky Mountains have been formed as a result of folding of the sediments along the margin of the American Plate (continental plate) and Pacific Plate (oceanic plate).

Question 3.
Define mountains and classify them.
Answer:

Rocky regions extending over vast areas, with an average height of over 1,000 metre above sea level and having peaks are called mountains. For example, the Himalayas, Vindhyas and Satpura mountain ranges in India.

Classification: Mountains can by broadly divided into 4 types –
1. Fold mountains: When the sediments on the ocean floor are subjected to lateral pressure due to tectonic movements, they are compressed, folded and forced to rise up and form fold mountains. The higher convex parts of these mountains are called anticlines and the lower concave parts are called synclines.
On the basis of origin, fold mountains are mainly of two types-

Ancient/Old fold mountains: Examples of such mountains are the Aravallis in India, Appalachian mountain ranges of United States of America, etc.
Young fold mountains: Examples of such mountains are the Himalayas in India, Alps in Europe and the Rocky Mountains in North America.

2. Volcanic mountains: When molten magma comes out from the earth’s interior through cracks and fissures, and after cooling down accumulates to great heights, they form volcanic mountains. They are also called depositional mountains. For example, Fujiyama in Japan and Mt. Vesuvius in Italy, etc.

On the basis of their shape, different types of volcanic mountains, like conical, domeshaped etc., have formed all over the world. Again, on the basis of the kind and frequency of volcanic activity, such mountains can be classified as extinct, dormant and active volcanoes.

3. Block mountains: When any part of the earth’s surface is forced upwards between two faults on either sides of it, they form flat-topped block mountains or horsts. For example, the Black Forest and Vosges rise much above their adjacent Rhine valley. The Satpuras in India is another example of block mountain.

4. Erosional Mountain: When any fold mountain, block mountain or upland area is reduced in elevation due to weathering and erosion by various agents such as rivers, wind, glaciers over a long time, it forms erosional or residual mountains. For example, the Aravallis in India and Henry Mountains in North America.

Question 4.
Describe the different stages of formation of fold mountains.
Answer :
According to geologists, many fold mountains were formed throughout the world, known as ancient or old fold mountains, before the formation of the young fold mountains of recent geological age like the Himalayas and the Alps. The fold mountains were formed basically in three stages and there was an intervening break or inactive period between two such stages. These stages were-

1. Silurian and Devonian Period: According to geological time scale, it was some time in the mid-Paleozoic era, i.e., between the Silurian and Devonian sub-periods (37.2 million to 44.5 million years ago) that the Atlantic Ocean was compressed as a result of the two converging plates of America and Europe. The mountain created as a result of folding is known as the Caledonian Fold Mountains. It is as a result of this that fold mountains have also developed in northern Ireland, Scotland and Scandinavian islands. After this, there was a period of lull when no activity took place.

2. Carboniferous Period: At the end of the Paleozoic era in the sub-period of Carboniferous and Permean (29 to 35 million years ago), the Altyde (Hercynian) fold mountains were developed as a result of crumpling up of sediments. The American and Hercynian mountains located in the southern part of Caledonian Fold Mountains in Europe and the Appalachian Mountains in North America were formed during this period. The Ural Mountains in Russia and Tien Shan and Nan Shan mountains in Asia were also formed during this time.

3. Tertiary Period: Folds also developed during the Tertiary period (2 million to 6.6 million years ago) after the Altyde orogeny (mountain-building era). As a result, new mountain ranges were formed in the southern part of Altyde mountain ranges and these are called Alpine orogeny. The Alps, Himalayas, Rockies and Andes mountain ranges were all formed during this period. The old fold mountain ranges are now reduced to lower heights as a result of erosion by different physical factors over a long time. They have now turned into low and dissected erosional plateaus. For example, the Caledonian range in Europe.

Question 5.
Classify the different types of landforms. Describe the characteristics of fold mountains. [2+3]
Answer:
Landforms are the outer appearances on the earth’s surface with typical geometric shapes and physical features resulting from weathering and erosion carried out by different agents like rivers (fluvial), glaciers, winds, waves, etc.

Usually, based on the height, shape, structure, slope and undulations of the land, landforms can be classified into 3 major divisions (1) mountains, (2) plateaus, and (3) plains. These can again be sub-divided into further classes as shown in the chart above.

Characteristics of Fold Mountains:

1. Significance of nomenclature: Since the mountains form as a result of folding and rising up of sedimentary rocks, they are called fold mountains.
2. Required force: Fold mountains form as a result of tectonic force (orogeny or mountain-building movements).
3. Main components: The two main parts of fold mountains are anticlines and synclines.

4. Predominant rocks: Though the major components of fold mountains are sedimentary rocks, igneous and metamorphic rocks are also found locally.
5. Area of extension: Fold mountains are lofty and extend over wide areas. For example, the Himalayas are 8,848 m above sea level and extend over the whole of northern part of India (from west to east).
6. Presence of fossils: Being formed of sedimentary rocks (usually in oceanic environment), they have remains of plants and animals embedded in the rock layers known as fossils.
7. Multiple peaks: Fold mountains have multiple peaks. For example, Mt. Everest, Makalu, Phalut, Kangchenjunga, etc., are the famous peaks of the Himalayas.

8. Other characteristics:

• Fold mountain areas are prone to earthquakes.
• The plate movements, being a continuous activity, gradually lead to the increase in height of these mountains.
• They have steep slopes.
• They are conical in shape.
• They are distinguished by the undulations (ups and downs) in their relief features and are sometimes inaccessible.

Question 6.
Explain the formation of volcanic mountains. Mention the characteristics of volcanic mountains. [3+2]
Answer:
Origin of volcanic mountains: When the hot molten magma comes out to the earth’s surface through cracks and fissures in the earth’s crust, it cools down and accumulates, thereby gaining height and forming mountains, they are called volcanic mountains. Mt. Fujiyama in Japan, Mt. Vesuvius in Italy, etc., are examples of such mountains. Their formation can easily be related to the Plate Tectonic theory.

1. Converging plate margins: When two converging plates approach each other, the margin between them is called converging plate margin. When they collide, the relatively heavier plate sinks below the lighter plate. When it reaches the mantle, it becomes hot and melts. Subsequently, this hot molten magma is forced up through the cracks and fissures and it comes out to the earth’s surface (through volcanic activity). In due course of time, this lava cools down, accumulates, and rises up to form volcanic mountains.

2. Diverging plate margins: When two plates move away from each other in opposite directions, they are called diverging plates. From the gap created as a result of this movement, hot molten magma comes out and eventually fills it up, forming volcanic mountains here.

Characteristics of volcanic mountains:

1. Shape: Volcanic mountains are usually triangular or conical in shape.
2. Presence of crater: A volcanic mountain has one or more than one crater at its top.
3. Connected to the magma chamber: The volcanic mountain is connected to the magma chamber in the earth’s interior through a tube-like structure (called the ‘vent’).
4. Slope: Volcanic mountains usually have steep slopes.
5. Altitude: They are moderate in altitude. However, their altitude increases with subsequent volcanic activity and accumulation of more lava on its top.
6. Structure: Volcanic mountains usually form in unstable parts of the earth, for example, along the moving plate margins.
7. Rocks: Volcanic mountains are usually formed of acidic and alkaline igneous rocks.
8. Settlements: Being usually inaccessible, with cold climate due to high altitude and lack of fertile soil, volcanic mountain areas are usually devoid of or have scattered settlements.

Question 7.
Classify volcanic mountains on the basis of their shape and structure.
Answer:
On the basis of shape and structure, volcanic mountains can be divided into 4 categories. They are as follows –

Question 8.
Explain the formation of block mountains and mention some of their characteristics.
Answer:
Origin of Block Mountains: When any part of the earth’s surface is uplifted along fault lines due to epeirogenic movements, they assume the appearance of a mountain known as block mountain. They are flat-topped and rise above the surrounding areas. For example, the Satpura mountains in India.

Block mountains are formed mainly due to the following three reasons-

1. The intervening land between two fault lines are forced to rise upwards to form a block mountain.
2. When the two blocks along two fault lines subside below the earth’s surface, the intervening block takes the shape of a block mountain.
3. When the land between two fault lines subsides, the areas on its two sides stand out as two block mountains.

Characteristics of Block Mountains:

1. Time taken for formation: The formation of a block mountain takes place all of a sudden.
2. Altitude: Block mountains are lower in height compared to fold mountains.
3. Summit: The top portion or summit of block mountains are flat.
4. Slope of the land: They have steep slopes on all sides.
5. Rift Valley/Graben: Block mountains or horsts have rift valleys or grabens lying adjacent to them.
6. Extent: Block mountains are not as widespread the fold mountains.

7. Rocks: Block mountains are made up of sedimentary and metamorphic rocks.
8. Tectonic movement: Block mountains are formed as a result of epeirogenic movement.

Question 9.
Explain the formation of erosional mountains and mention their characteristics.
Answer:
Formation of Erosional Mountains: When one or more of the characteristic features of a mountain is seen in an eroded mountain or upland (being eroded by rivers, glaciers, winds, sea waves, etc.), they are called erosional or residual mountains. For example, the Aravalli Hills in India (actually it is an ancient fold mountain). This type of mountain is formed in two ways-
1. Differential texture (hardness) of rocks: Any high mountain, hill or upland is made up of both hard and soft rocks. The soft rocks, being weaker and more prone to erosion, are easily eroded and reduce in altitude, while the hard and resistant rocks stand out as mountains and hills. The Aravalli Hills in India are examples of this type.

2. Volcanic activity or intrusion in the sedimentary rocks: When, due to volcanic activity or diastrophism, igneous rocks are intruded upon especially vertically (as dykes), this molten magma gradually cools down to form igneous rocks within the sedimentary rock layers. In due course of time, when the upper sedimentary rock layers are eroded, these igneous rocks are exposed to the surface. Since they are hard and resistant rocks, they form residual mountains. For example, the Henry Mountain in North America.

Characteristics of Erosional Mountains:

1. Origin: Forms as a result of erosional process over a long time by different agents of erosion like rivers, glaciers, winds, etc.
2. Altitude: Erosional mountains are usually low in height and since they are in a continuous process of erosion, they gradually decrease in elevation.
3. Summit: The summit or top of erosional mountains are rounded since they have been eroded.
4. Rocks: They are usually made up of hard igneous and metamorphic rocks.
5. Slope: The slopes of erosional mountains are not steep.
6. Ruggedness: The ruggedness of these mountains is quite high.
7. Age: Erosional mountains are geologically quite old.

Question 10.
Discuss the importance of mountains with examples.
Answer:
The importance of mountains are as follows-
1. Origin/Source of rivers and streams: Many small streams and big rivers have their origin in the meltwaters of the snowcapped mountains. These rivers have great influence on human life and civilisation. For example, the big rivers like the Indus, Ganges, Yamuna, Teesta, etc., have their sources in the snow-capped peaks of the Himalayas.

2. Climate control:

• Being very high, the upper reaches of mountains have cold climate and snowfall is common here.
• The windward side of the mountain act as a climatic barrier to the moisture bearing winds and orographic or relief rainfall occurs here, while on the opposite side there is no rainfall.
• A mountain controls the direction of winds too. For example, the Himalayas prevent the cold Siberian winds from entering India.

3. Source of hydroelectric power: The snowfed rivers of the mountainous regions are perennial and have water throughout the year. The streams having strong water currents are also ideal for producing hydroelectricity.

4. Natural vegetation: The dense forests in the mountainous regions are sources of valuable timber, honey, medicinal plants, fruits, etc. Due to the ruggedness of the terrain, the mountainous regions are sparsely populated.

5. Tourism industry: Snowfields, waterfalls, springs, swift-flowing streams and rivers, valleys, ridges, gardens with beautiful fruits, flowers and orchids appeal to the eyes of many tourists who love to visit these mountainous areas, making them areas of major tourist attraction. For example, Simla, Kashmir (valley), Darjeeling, Gangtok, etc., in the Himalayas are popular tourist spots.

6. Animal husbandry: Grazing animals on the green pastures of mountain slopes are the major activities of nomadic tribes of mountainous regions. For example, the Gujjars and Goddi tribes of Kashmir.

7. Provides security: The lofty mountains act as barrier to the intruders from neighbouring countries who try to enter illegally.

8. Other importance:

• Mountains are ideal places for mountain climbers and trekkers.
• Fossils which are found embedded in the sedimentary rocks of mountains provide important clues to ancient life.
• The origin of mountains are quite significant to geologists and geographers who are involved in research work.
• The different environments associated with varying landforms, climate, soil and natural vegetation of mountains have greatly influenced man’s adaptation to nature.
• Civilisation and culture are also influenced by different environments in mountainous areas.

Question 11.
What is meant by a plateau? Classify plateaus. [1 + 4]
Answer:
Plateaus: Table-like landforms which are usually more than 300 metre above sea level, almost flat on the top with steep slopes, are called plateaus. They are also called tablelands. Sometimes low hills are found on these flattopped plateaus. For example, Chota Nagpur Plateau, Deccan Plateau, Ladakh Plateau in India.

Classification: Plateaus are usually divided into 4 types-
1. Intermontane Plateau: During the process of building of fold mountains (due to tectonic movements), the intervening area between two mountains comes under pressure and is forced to rise up and form plateaus. Since these plateaus are encircled by mountains, they are called intermontane plateaus. For example, Plateau of Tibet, Plateau of Anatolia in Turkey, Plateau of Iran, etc. The Plateau of Tibet is enclosed by Kunlun mountain in the north, and Karakoram, Tien Shan and Himalayan mountains to its south.

2. Dissected Plateau: Ancient plateaus are continuously eroded by the various agents of erosion like rivers, glaciers, winds, etc., and subsequently get reduced in height. The numerous rivers and their tibutaries and branches further divide the area into smaller blocks. Such a landform which is broken down by rivers is called dissected plateau or erosional plateau. For example, Chota Nagpur Plateau and Malnad Plateau (part of Karnataka Plateau) in India.

3. Continental Plateau: When ancient landforms on the earth’s surface separate from each other as a result of tectonic activity, they form plateaus. They are also called shield areas and are resistant to earthquakes. For example, the Deccan Plateau in south India and the Arabian Plateau.

4. Lava Plateau: Molten magma from the earth’s interior comes up to the surface through cracks and fissures in the weaker zones of the crust and gets deposited there. This lava slowly cools down and solidifies to form lava plateaus. For example, Lava Plateau or Deccan Trap region in north-western part of south India, Colombia Snake Plateau in the United States of America, etc.

Question 12
Give a detailed account of dissected plateau and intemontane plateau. [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]
Answer :
Dissected Plateau:
1. Definition: When any large and ancient plateau undergoes erosion by various physical factors like rivers, winds, etc., for a long time, and is divided into smaller parts or is dissected, it is called dissected plateau.
2. Origin: Plateaus are usually made up of hard and soft rocks. Various agents erosion like rivers, winds, etc., erode the softer rocks and create deep gorges or valleys. On the other hand, the hard and resistant rocks remain as dissected plateaus.

Characteristics:

• Dissected plateaus are usually formed as a result of erosion.
• They are moderate in height.
• After erosion, dissected plateaus form ‘mesas’ and ‘buttes’.

Examples: Chota Nagpur Plateau, Karnataka Plateau, Malnad region, Bundelkhand and Bagelkhand in Madhya Pradesh.

Intermontane Plateau:
Definition: When a plateau is located between two or more mountains, it is called an intermontane plateau.
Origin: When a mountain rises up due to plate movements, its middle portion rises above its surrounding parts to form a plateau.

Characteristics:

• Intermontane plateaus reach up to great heights.
• The formation of these plateaus are associated with the formation of fold mountains.
• These plateaus are extensive in nature.

Examples: Plateau of Tibet, Plateau of Iran, Pamir Plateau, etc. The Tibetan Plateau is encircled by Kunlun mountain in the north, Karakoram mountains in the southwest and the Himalayas in the south.

Question 13.
Describe continental plateau and lava plateau. [2 \(\frac{1}{2}\)+2 \(\frac{1}{2}\)]
Answer:
Continental Plateau:
Definition: When parts of an ancient plateau separate from each other as a result of tectonic activity and form plateaus, they are called continental plateaus.

Origin: As a result of tectonic activity, parts of ancient plateaus get separated from each other. After erosion by various agents like rivers, glaciers, winds, etc., for a long time, these turn into plateaus. Since they cover extensive areas over continents, they are called continental plateaus. They are also known as ancient plateaus or shields.

Characteristics:

• They are quite old according to geological age (more than 100 million years).
• They have formed as a result of erosion over a long period.
• The land is stable in continental plateau regions.
• These plateaus are rich in mineral reasources.

Examples: Brazilian Plateau, Deccan Shield in India, Canadian Shield, etc. South Africa, Antarctica, Greenland, etc., also have widespread areas of such plateaus.

Lava Plateau:

Definition: During volcanic eruptions, the molten magma comes out to the earth’s surface and accumulates there to form lava plateaus.

Origin: When magma comes out through cracks and fissures and accumulates on the earth’s surface, the plateau that starts forming is called a lava plateau. When this happens on several occasions, the entire area gains height and a lava plateau is thus formed.

Characteristics:

• This is a type of depositional plateau.
• It is formed as a result of volcanic activity.
• Basalt is a common rock here.
• The hills located on such plateaus also have flattened tops.

Examples: Deccan Plateau in south India, Malwa Plateau in northwestern India, Columbia Snake Plateau in the United States of America, etc.

Question 14.
Discuss the significance of plateaus with examples.
Answer:
Storehouse of mineral resources: Many types of mineral resources like iron ore, coal, copper ore, limestone, etc., are available here in large amounts. The Chota Nagpur plateau is called the ‘Storehouse of India’s mineral resources’.

Supply of hydroelectric power: Since the rivers flowing over plateaus are swiftflowing (due to the undulating topography), these rivers can easily be used for generating hydroelectricity. This is prevalent especially in the Deccan Plateau in south India.

Deveiopment of industries: Abundance of raw materials (mineral resources), electricity (hydro and thermal) and availability of cheap labour, make these areas ideal for the development of industries.

Abundance of natural vegetation: Settlements in plateau areas are usually very sparse. As a resuit, most parts of the plateaus are covered with dense forests. These forests provide timber, honey, wax, flowers, fruits, etc., in large amounts.

Grazing lands for animals: Since most of the large plateau regions of the world have dry and arid climate, there are vast expanses of green pastures, which are ideal for grazing animals. This provides the chief livelihood to the people living in plateaus.

Development of tourism industry: Springs, waterfalls, mining areas, industrial areas, forest-based livelihood, and the scenic beauty of these regions attract both domestic and international tourists.

Other Importance:

1. The rocks, mineral resources, landforms, etc., of plateau regions are important areas of research for geologists.
2. The livelihood, culture, socio-economic condition of the tribal people residing in the plateaus are significant for the study of Geography. These are some of the significant roles of a plateau.

Question 15.
Classify plains and analyse the origin and development of each of them.
Answer:
Classification of Plains: Plains can broadly be divided into 3 categories-

1. Origin of depositional plain: Of the three types of plains based on origin, this type is most important. Depositional Plain is of five types, namely-

Alluvial plain/flood plain: When silt is deposited on the two sides of an overflowing river (during floods) or in a delta region, they form alluvial plains or flood plains. For example, Ganges Plain in India, Hwang Ho Plain in China, etc.

Loess plain: When sand is blown away to distant places from another region and deposited in some lowlying area, a loess plain is formed. For example, the loess plain of Hwang Ho basin has been formed by the sand of the Gobi desert.

Bajada or desert plain: The sand, pebbles and small rock fragments are carried down the slopes of mountains and get deposited in the foothill zone forming Bajadas. For example, Bajada in the foothill zone of Atlas Mountain adjoining Sahara Desert of North Africa.

Lava plain: Molten magma comes out of the earth’s interior through cracks and fissures on the earth’s surface. Here, it cools down and solidifies to form plains. These plains are called lava plains. For example, the lava plain located in the northern part of the Deccan Plateau.

Glacial plain: During the Glacial Age, continental ice sheets have eroded the uneven topography over which it moved and have eventually flattened the relief and formed glacial plains. For example, the Prairie region of North America and the glacial plain of northern Europe.

2. Origin of erosional plain: Plains are formed in two ways as a result of erosion caused by agents like river, glacier, wind, etc.-

• peneplain
• pediment.

1. Peneplain: When a landmass is reduced in elevation as a result of erosion over a long time, it is called a peneplain, which means ‘almost a plain’. For example, parts of Chota Nagpur Plateau in India.

Pediment: Due to the action of strong winds in arid regions, sand is deposited in the foothill zone of mountains and hills, forming a plain. This is called pediment. For example, the foothill zone of Atlas Mountain of the Sahara region in Africa.

Plains formed due to geotectonic activity: Some plains have formed as a result of geotectonic activity. For example

• uplifted plain.
• subdued or lowlying plain.

The sea floor is uplifted due to diastrophism or tectonic activity and is exposed to the surface. These are called uplifted plains and when the uplands subside, they form subdued plains. The coastal plain of Mexico Sea in North America (uplifted plain) and the Turan Lowland (subdued plain) are some examples.

Answer:
Structural Plain:
1. Definition: When any landmass gets either uplifted or it subsides as a result of geotectonic activity (epeirogeny), it forms a structural plain.

2. Types: Structural plains are of 2 types

• uplifted plain
• subdued plain.

3. Origin:

• When any shallow seabed is uplifted near a coast due to tectonic activity, it forms an uplifted plain.
• When any elevated landmass subsides as a result of tectonic activity, it forms a subdued plain.

4. Characteristics:

1. These plains are formed as a result of geotectonic activity.
2. Such plains are generally formed near coasts.
3. These plains are formed all of a sudden.

5. Examples: The coastal plain of Mexico Sea in the United States of America and the Turan lowland are examples of uplifted and subdued plains respectively.

Erosional Plains:

1. Definition: When any ancient highland is affected by erosion by various agents like rivers, glaciers, winds, etc., over a long period, they lose their elevation gradually and form erosional plains.
2. Origin: Any upland or plateau is formed of both hard and soft rocks. In due course of time, due to continuous erosion over long periods, the landform is modified into a gently sloping plain.
3. Characteristics:

1. Such plains are formed as a result of erosion of uplands.
2. Some isolated rounded hills made up of hard and resistant rocks called monadnocks lie here and there.
3. Erosional plains are not fertile.

4. Examples: Some parts of the Chota Nagpur Plateau are erosional plains.

Question 17.
Give an account of different types of depositional plains.
Answer:

Alluvial plains: Silt and sand which get deposited on both the banks of a river (flood plains) or in delta regions form depositional plains. For example, Ganges Plains, Hwang Ho Plain, etc. Alluvial plains are again divided into 4 types.

Flood plains: When a river overflows its banks during floods every year, fresh silt is laid on both sides of the river in the plains. These are called flood plains. For example, the middle and lower courses of river Ganges and the Brahmaputra valley have many such flood plains.

Delta plains: A triangle-shaped landform formed in the lower course of a river where it enters the sea is called a delta. The plain which forms at such a delta is called a delta plain. For example, the world’s biggest delta has developed in the lower part of the Ganga-Brahmaputra river where it meets the sea (Bay of Bengal).

Coastal plains: When silt, sand, pebbles, washed away by sea waves, winds, rivers get deposited in the shallow sea, a coastal plain is formed. For example, the Palestine Plain has formed by the action of waves and oceanic deposits and the Western and Eastern Coastal Plains of India have formed by the action of rivers, winds, etc.

Lake or Lacustrine plains: These are formed by deposition of silt, sand, pebbles, etc., on any lake bed. They are also called lacustrine plains. For example, the Great Basin in the United States of America and lake plains of Red river basin in Canada.

Loess plains: When sand particles are blown away form one place and deposited in lowlying places at a great distance, they are called loess plains. For example, the loess plain of China’s Hwang Ho river basin has been formed by the sand of the Gobi Desert.

Bajada or desert plains: When sand, pebbles, etc., are deposited in the foothill areas of any hill or mountain, they form desert plains. For example, Bajadas have formed in the foothills of the Atlas Mountain adjoining the Sahara Desert.

Lava plains: Hot molten magma comes out through cracks and fissures of the earth’s surface and gets deposited to form lava plains. For example, the lava plains in the northern part of the Deccan Plateau.

Glacial plains: The continental ice sheets of the Glacial Age have eroded the earth’s surface on which it moved and created glacial plains. The Prairie region of North America and the Glacial Plain of northern Europe are such examples.

Question 18.
Discuss the significance of plains with examples.
Answer :
Benefits of agricultural activity: The fertile silt-laden plains formed by river deposition are ideal for practising agriculture and that is why the main livelihood of the people residing here is agriculture. For example, large amounts of paddy, sugarcane, etc., are cultivated in the Ganges Plain.

Improved transport and communication system: Being a level or flat land, plains are ideal for constructing roads and railways. Waterways (rivers) can also be used as a mode of transport, thereby leading to a developed system of transport and communication.

Conducive climate: Compared to mountains and plateaus, climate is quite pleasant in the plains. Temperature is not extreme here and rainfall is also high due to presence of rivers, canals, creeks, lakes, ponds, etc.

Settlements: The flat land, fertile soil, developed transport and communication system, conducive climate, opportunities of employment, etc., have all led to the growth of settlements here. For example, the Ganges Plain of north India.

Development of industries: Flat land, pleasant climate, developed transport and communication system, availability of labour (the plains being a densely populated area), availability of raw materials, etc., have all contributed to the development of industries in the plains.

Advantage of urbanisation: Due to the above mentioned advantages, the plains are the places of urban development and culture. The transformation of rural to urban ways of life is called urbanisation. Major cities like Delhi, Kolkata, Mumbai, Chennai, etc., have all developed in the plains.

Other importance:

1. It is advantageous to develop grazing lands where animals are reared in the parts of the plains which are uncultivable.
2. Fisheries have a great scope of developing here, due to the presence of numerous rivers, wetlands and proximity to the sea (in case of coastal plains).
3. The culture of the area is enhanced due to the fact that it is a densely populated area where education, healthcare facilities, etc., have much scope for development.
4. Business, trade and commerce also flourish in the plains because they are developed areas from the point of view of agriculture and industries.