NCERT Class 11 Geography Chapter 7 Landforms and Their Evolution

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NCERT Class 11 Geography Chapter 7 Landforms and Their Evolution

Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 11 Geography Solutions are part of All Subject Solutions. Here we have given NCERT Class 11 Geography Part I: Fundamentals of Physical Geography, Part II: Indian: Physical Environment, Part III: Practical Work in Geography. NCERT Class 11 Geography Chapter 7 Landforms and Their Evolution Notes, NCERT Class 11 Geography Textbook Solutions for All Chapters, You can practice these here.

Landforms and Their Evolution

Chapter: 7

GEOGRAPY [ PART – I ]

SHORT ANSWER TYPE QUESTIONS

Q.1. What is geomorphology?

Ans. Geomorphology is the genetic study of landforms. It is concerned with the origin and evolution of landforms.

Q.2. Name the geomorphologists who considered that landforms were the best indicators of earth’s history.

Ans. S.W. Wooldridge and M.M. Davis.

Q.3. Which forces are involved in the creation of landforms?

Ans. Internal and external forces are involved in the creation of landforms.

Q.4. Name various types of weathering.

Ans. The various types of weathering are:

1. Mechanical weathering.

2. Chemical weathering.

3. Biological weathering.

Q.5. Arrange the following from smaller to bigger form: Stream, gully, river, rill.

Ans. Rill, gully, stream, river.

Q.6. Which are the first order landforms?

Ans. The first order landforms are continents and ocean basins.

Q.7. What is a relief?

Ans. Physical landscape, the actual configuration of the earth the surface.

Q.8. On which type of rocks the action of carbonation is more effective?

Ans. Limestone.

Q.9. What will be the transporting capacity of a river if the velocity of its water is doubled?

Ans. 64 times.

Q.10. Which is the largest canyon of the world?

Ans. Grand Canyon of Colorado river in U.S.A.

Q.11. What is a fiord?

Ans. It is a glacial trough formed near the sea filled with water.

Q.12. What types of landforms are generally found in the eastern and western coasts of India?

Ans. The west coast of India is a high rocky retreating coast. Erosional forms dominate in the west coast. The east coast of India is a low sedimentary coast. Depositional forms dominate in the east coast.

Q.13. What is weathering?

Ans. Weathering means the weakening or breaking up or rotting and the disintegration of rocks at or over the earth’s surface.

Q.14. How are cirques formed?

Ans. Cirques are semi-circular hollows at the sides of a mountain. The moving ice produces depression on the slopes of mountains. Plucking and frost-wedging deepens and widens these depressions. An arm chair-shaped basin with back wall is formed. These are known as cirques.

Q.15. How are mushroom-shaped rocks formed?

Ans. Mushroom-shaped rocks are produced by undercutting of the wind. Under cutting erodes the softer rocks at the base of rocks. It results in the formation of thin pillars. These rock pillars are called rock pedestals. Blocks of hard rocks are on thin pillars. An umbrella-shaped rock is formed. It is a called mushroom rock.

Q.16. How is a cliff formed?

Ans. Steep slopes facing the sea are called cliffs. Due to constant and direct strike of waves a notch is formed and is widened. An overhanging rock projects seawards. After sometime large blocks of rock fall into sea. A vertical wall-like cliff is formed.

Q.17. Describe the formation of the sea caves.

Ans. At the base of cliffs, the sea caves are formed. Softer rocks at base are quickly eroded. Holes are produced in the cliff by the wave action. These holes are enlarged to form sea caves. When two caves are united together from the opposite sides, an arch is formed.

Q.18. How is a V-shaped valley formed?

Ans. A V-shaped valley is formed by the vertical erosion of the river. Side cutting and down cutting of river had go on simultaneously. The valley is depend as well as widened. In this way a broad V-shaped valley is developed.

Q.19. On what factors does the erosional work of the river depend?

Ans. The erosional work of the river depends upon the following factors:

(i) Volume of water.

(ii) Velocity of water.

(iii) Load of the river.

(iv) Slope of the river.

(v) The nature of the rocks.

SHORT ANSWER TYPE QUESTIONS

Q.1. What do incised meanders in a rocks and meanders in plains of alluvium indicate?

Ans. The incised meanders in rocks and meanders in plains indicate the status of original land surface over which streams have developed.

Q.2. How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in the deserts?

Ans. Winds move along the desert floors with great speed and the obstructions in their path create turbulence. Storm winds are formed which are very destructive. Winds cause deflation, abrasion and impact. Deflation includes lifting and removal of dust and smaller particles from the surface of the rocks from the surface of the rocks. The impact is the simply the shear force of momentum which occurs when sand is blown into or against a rock surface. These are the ways in which wind action creates a number of interesting erosional and depositional features in the deserts.

Winds are not the only agent responsible for the erosional features of the deserts. Alongwith winds the running water is also important for this.

Q.3. Underground flow of water is more common than surface run-off in limestone areas. Why?

Ans. Underground flow of water is more common than surface water in the limestone areas. It is because the chief constituent of limestone is calcium carbonate which is soluble in pure water and easily soluble in carbonate water. Surface run-offs and infiltration into the ground starts the solution process along the fractures and joints.

Q.4. Glacial valleys show up many linear depositional forms. Give their locations and names.

Ans. The linear depositional formed by glacier are called maraines. These are terminal moraines, lateral moraines and ground moraines.

Q.5. Explain the evolution of valley sinks or uvalas.

Ans. A sink hole is on opening more or less circular at the top and funnel-shaped towards the bottom with sizes varying in area from a few sq.mt. to a hectare and with depth from a less than half a metre to thirty metres or more. Quite often the surface run-off simply goes down swallow and sink holes and flow as underground streams and re-emerge at a distance down-stream through a cave opening. A doline is a collapse sink. When sinkholes and dolines join together because of slumping of materials along their margins or due to roof collapse of caves, long narrow to wide trenches called valley sinks or uvalas form.

Q.6. (i) Distinguish between stalagmites and stalactites 

Ans. 

Stalagmites	Stalactites
1.These grow from the floor.	1.These grow from the roof.
2. They have broad base.	2. They have narrow base.
3. These are formed due to evaporation of water.	3. These are formed due to condensation.
4. These have broad edge.	4. They are sharp edge.

(ii) Differentiate Sinkholes and Uvallas.

Ans. 

Sinkholes	Uvallas
A sinkhole is an opening more or less circular at the top and funnel shaped towards the bottom.	When sinkholes and dolines join together because of slumping of material along their margines the Uvallas are formed.

Q.7. Give difference between Gorge and Canyon.

Ans. 

Gorge	Canyon
1.It has setup sides.	1.It has step like sides.
2. Equal width of top and bottom are found in the gorge.	2. These are wider at the top and narrow at the bottom.
3. These are small in length.	3. These are longer in length.
4. They are found in semi arid lands. For example,Brahmaputra Gorge.	4. These are found in dry areas. For example, Grand Canyon.

Q.8. What do you mean by saltation?

Ans. Depending upon the velocity of wind, different sizes of grains are moved along the floors by rolling and carried in suspension and in this process of transportation itself, the materials get sorted. These are called saltation.

Q.9. Distinguish between:

(i) Work of wind and work of river.

Ans. 

Work of Winds	Work of Rivers
1.The work of Wind is important in desert.	1.The work of river is important in humid regions.
2. Wind carries the material to long distance.	2. The work of river is limited to its basin only.
3. The work of wind depends on the wind velocity.	3. The work of river depends on the slope of the landmass.
4. Wind erosion is done at slow rates.	4. The erosion by rivers is very rapid.

(ii) Alluvial Fans and Deltas.

Ans. 

Alluvial Fans	Deltas
1. Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of low gradient.	1. Deltas are formed when the load carried by the rivers is dumped and spread into the sea.
2. Alluvial fans are associated with the young regimes of the running water.	2. Deltas are associated with the old regimes of the running water.
3. Deposits making up alluvial fans are not sorted well.	3. Deposits making up deltas are well sorted with clear stratification.

(iii) V-shaped valley and U-shaped valley.

Ans. 

V-shaped valley	U-shaped valley
1. V-shaped valley are carved out by river in their youthful stages.	1. U-shaped valleys are casual by glaciers in hilly regions.
2. They are original in nature, i.e. they are formed by the erosional actions of the rivers.	2. They are modified forms of pre-existing valleys.
3. Their shapes are of the letter ‘V’ of English alphabet.	3. Their shapes are that of the letter ‘U’ of the English alphabet.
4. They are associated with gorges, canyon etc.	4. They are associated with hanging valleys.

(iv) Continental glacier and valley glacier.

Ans. 

Continental Glacier	Valley Glacier
1. Continental glaciers are found in Antarctica and Greenland.	1. The valley glaciers are found over the Alps and the Himalayas.
2. These are found in polar regions.	2. These glaciers are found on the high mountains.
3. These are also covered in ice sheets.	3. These do not cover large areas.
4. These cover large areas.	4. These are also called mountain glaciers.

(v) Delta and Estuary.

Ans. 

Delta	Estuary
1. A delta is a triangular shaped land formed at the mouth of a river.	1. An estuary is a funnel shaped channel formed at the mouth of a river.
2. It is formed by deposition when there is a absence of tides and currents.	2. It is formed when deposition does not take place due to strong tides and currents.
3. Ganges-Brahmputra form a large delta.	3. Narmada and Tapi do not form deltas.

LONG ANSWER TYPE QUESTIONS

Q.1. Landforms have a past, present and future. Discuss.

Ans. The surface of the earth has a great variety of physical features. Each physical feature has a form-dynamic and unique and, is known as landform. No landform is permanent. Each landform is changing.

Since the earth came into existence land- forms are being created by a large number of internal and external forces. Agents of change are always active in this work such as erosion and deposition of rock material. Filling the basins and valleys, brings changes in the surface of land. Deposition follows erosion and the depositional surface too are ultimately subjected to erosion. The geomorphic agents such as running water, ice and wind etc. are acting over a long periods of time, and produce systematic changes leading to sequential development of landforms. We know that most of geomorphic processes are imperceptible functions and can only be seen or measured through their results. The results are landforms and their characteristics. It is said, in geomorphology, the present is key to the past. In other words, the analysis of the present day characteristics of a landform will reveal us about its past history. In this way, landforms have present, past and future.

Q.2. Describe the landforms formed by the action of wind deposition.

Ans. The following landforms are formed due to the wind deposition:

1. Sand dunes : Sand dunes are hills of wind-blown sand. These are found in the areas like sandy coasts in deserts, on the sandy shores of lakes and along river banks.

The sand dunes are formed in following conditions:

1. Large supply of sand.

2. Strong winds.

3. Obstruction in the way of wind.

Sand is deposited at the base of an obstruction such as bushes and gradually a large amount of sand is deposited. Sand is thrown on the windward side by the strong winds. Thus a sand dune is formed with a crest. It has a long gentle windward slope and a steep leeward slope with ripple marks.

Sand dunes are of three types:

1. Longitudinal dunes: These are long narrow ridges of sand. These are called silts in Sahara.

2. Transverse dunes: These are formed perpendicular to the wind direction. They look like waves of sand. They are semicircular in shape.

3. Barchans: Barchans are crescent or moon-shaped sand dunes formed in a perpendicular direction to the wind. The windward side is convex and gentle while the leeward side is steep. Its ends are called horns. These resemble a sickle or bow. The sand-dunes keep on advancing and many towns and buildings have been burried under these sand dunes.

Q.3. How do glaciers accomplish the work of reducing high mountains into low hills and plains?

Ans. Erosion by glaciers is tremendous because of friction caused by sheer weight of the ice. The material plucked from the land by glaciers get dragged along the floors of the valley and cause great damage through abrasion and plucking. Glaciers can cause significant damage to even unweathered rocks and can reduce high mountains into low hills and plains.

During this process various landforms are formed.

These are:

1. Cirques.

2. Horns and serrated ridges.

3. Glacial V-shaped valleys.

4. Ice-scoured plains.

Q. 4. Running water is by far the most dominating geomorphic agent in shaping the earth’s surface in humid as well as in arid climates. Explain.

Ans. In humid regions, there are two components of running water. One is overland flow on general land surface as a sheet. Another is linear flow as streams and rivers in valleys. During youthful stage a number of erosional forms are developed by the running water such as U-shaped valleys, gorges, canyons etc. With time, stream channels over steep gradients turn gentler due to continued erosion, and as a consequence lose their velocity, facilitating active deposition. During their terminal stages i.e. old stages, the running water makes deltas. During the middle stages, a number of landforms like river terraces, alluvial fans, flood plains, natural levees etc. are formed.

In arid regions, though rain is scarce, it comes down torrentially in a short period of time. The desert rocks devoid of vegetation, exposed to mechanical and chemical weathering processes due to drastic diurnal temperature changes, decay faster and the torrential rains help in removing the weathered material very easily. The weathered material debris in deserts is not only moved by winds but also by rain/sheet wash. Thus, we can say that the running water is by far the most dominating geomorphic agent in shaping the earth’s surface in humid as well as arid regions.

Q.5. Limestones behave differently in humid and arid climates. Why? What is the dominant and almost exclusive geomorphic process in limestone areas and what are its results?

Ans. Limestones are permeable rocks with thinly bedded and highly jointed and cracked planes. So when the surface water percolates in, it vertically it starts moving horizontally through the bedding planes, joints or through the materials themselves, causing the limestones to erode, thus creating a variety of insignificant, not easily perceptible land forms. In arid regions water table is quite low below the surface and there is less amount of surface water.

It is due to this differential availability of water in these two areas, that makes limestone to behave differently. The most dominant and almost exclusive type of geomorphic process in limestone areas is that of processes of solution and deposition by the action of the groundwater. The erosional landforms produced by the action of the groundwater are pools, sinkholes, lapies and limestone pavements. In areas of alternating beds of rocks with limestones caves are also formed. The depositional landforms in limestone areas by the action of ground water are stalctites, stalagmites and pillars.

Q. 6. Define a glacier. Describe the different types of glaciers.

Ans. Glaciers are rivers of ice-snow fields are the parents of the glaciers. Thus a glacier is a large mass of moving ice. It is tongue shaped. The end of the glacier is called snout. The movement of glacier is due to the following factors:

(i) Pressure of the ice.

(ii) Slope of the land.

(iii) The pull of gravity.

Types of glacier: Glacier can be divided into two major types according to location size and length.

(i) Valley glacier: These glaciers rise from high mountains. These are also called mountain glaciers. These glacier were fond first in Alps so these are also called Alpine glacier. The longest of the Indian glacier is Siachin glacier which is 72 km long.

(ii) Continental glaciers: These are the largest of all glaciers. They cover vast areas in polar regions. These are called Ice Sheets. About 25000 years ago ice sheets covered most of North America and Europe. At present two ice sheets still exist in Greenland and Antarctica.

Q.7. Explain the erosion done by glaciers.

Ans. Erosion by glaciers is tremendous because of friction caused by sheer weight of the ice. The material plucked from the land by glaciers get dragged along the floors or sides of the valleys and cause great damage through abrasion and plucking. Glaciers can cause significant damage to even un-weathered rocks and can reduce high mountains into low hills and plains. Stalagmites may take the shape of a column, a disc, with either a smooth, rounded bulging end or a miniature crater like depression. The stalagmite and stalactites eventually fuse to give rise to columns and pillars of different diameters.

As glaciers continue to move, debris gets removed, divides get lowered and eventually the slope is reduced to such an extent that glaciers will stop moving leaving only a mass of low hills and vast outwash plains along with other depositional features.

EROSIONAL LANDFORMS

Cirque: Cirques are the most common of landforms in glaciated mountains. The cirques quite often are found at the heads of glacial valleys. The accumulated ice cuts these cirques while moving down the mountain tops.

Horns and Serrated Ridges: Horns form through head ward erosion of the cirque walls. If three or more radiating glaciers cut headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.

Glacial Valleys/Troughs: Glaciated valleys are trough-like and U-shaped with broad floors and relatively smooth, and steep sides.