NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

Landforms and their Evolution NCERT Solutions for Class 11 Geography Chapter 7

Landforms and their Evolution Questions and Answers Class 11 Geography Chapter 7

Question 1.
Multiple choice questions :
(i) In which of the following stages of landform develop¬ment, downward putting is dominated?
(a) Youth stage
(b) Late mature stage
(c) Early mature stage
(d) Old stage
Answer:
(a) Youthstage.

NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution

(ii) A deep valley characterised by steep step-like side slopes is known as
(a) U-shaped valley
(b) Gorge
(c) Blind valley
(d) Canyon
Answer:
(d) Canyon.

(iii) In which one of the following regions the chemical weathering process is more dominant than the mechanical process?
(a) Humid region
(b) Limestone region
(c) Arid region
(d) Glacier region
Answer:
(b) Limestone region.

(v) Which one of the following sentences best defines the term ‘Lapies’?
(a) A small to medium sized shallow depression.
(b) A landform whose opening is more or less circular at the top and funnel shaped towards bottom.
(c) A landform forms due to dripping water from surface.
(d) An irregular surface with sharp pinnacles, grooves and ridges.
Answer:
(d) an irregular surface with sharp pinnacles, grooves and ridges.

NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution

(v) A deep, long and wide trough or basin with very steep concave high walls at its head as well as in sides is known as
(a) cirque
(b) glacial valley
(c) lateral moraine
(d) esker
Answer:
(a) cirque.

Question 2.
Answer the following questions in about 30 words each :

(i) What do incised meanders in rocks and meanders in plains of alluviam indicate?
Answer:
Meandering courses over flood plains and delta plains are found where stream gradients are very gentle. But very deep and wide meanders can also be found cut in hard rocks. Such meanders are called incised meanders. Meander loops develop over original gentle surfaces in the initial stages of development of streams.

(ii) Explain the evolution of valleys sinks or uvaias.
Answer:
A sinkhole is an opening more or less circular at the top and funnel-shaped towards bottom with sizes vary ing in areas. When sink-holes 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 uvaias form.

(iii) Underground flow of water is more common than surface run-off in limestone areas. Why?
Answer:
Surface runoff gradually diminishes and is diverted to underground passages developing subterranean drainage. If there is enough water, surface drainage too will develop. Surface runoff and infiltration into the ground starts the solution process along the fractures, faults, bedding planes and other zones of weakness. Subterranean drainage begins to develop.”Solution on the surface and through the ground results in shallow holes and sinkholes.

NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution

(iv) Glacial valleys show up many linear depositional forms. Give their locations and names.
Answer:
The linear depositional formed by the glacier are called moraines. These are terminal moraines, lateral moraines and ground moraines. A deep valley characterised by steep step-like side slopes is known as :

  • U-shaped valley.
  • Gorge.
  • Blind valley.
  • Canyon.

(v) How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in deserts?
Answer:
Wind is one of the two dominant agents in hot deserts. The desert floors get heated up too much and too quickly because of being dry and barren. The heated floors heat up the air and results in upward movements in the hot lighter air with turbulence, whirlwinds, updrafts and downdrafts.

Winds move along the desert floors with great speed. There are storm winds which are very destructive. Winds cause deflation, abrasion and impact. Wind action creates a number of t – interesting erosional and depositional features in the deserts.

Question 3.
Answer the following questions in about 150 words each :
(i) “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.
Answer:
Running water is considered the most important geomorphic agent in bringing about the degradation of land surface. There are two components of running water:
(1) overland flow on general land surface as a sheet, and
(2) linear flow as streams and rivers in the valleys. Most of the erosional landforms made by running water are associated with vigorous and youthful rivers flowing over steep gradients. With time, stream channels over steep gradients turn gentler due to continued erosion. The greater is the deposition, downward cutting becomes less dominant and lateral erosion of banks increases and, as a consequence, the hills and the valleys are reduced to plains.

NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution

Overland flow causes sheet erosion. Depending upon theirregularities of the land surface, rills, gullies, valleys are formed. In arid regions, rain is scarce. It comes down torrentially in a short period of time. These regions owe their formation to mass wasting and running water as sheet floods. Stream channels are broad, smooth and indefinite and flow for a brief time after rains.

Landscape evolution is primarily concerned with the formation and extension of pediments. Such rocky floors form as a result of erosion of mountainfront through a combination of lateral erosion by streams and sheet flooding through the extension of pediments. These low featureless plains are called pediplains.

(ii) Limestones behave differently in humid and arid climates. Why? What is the dominent and almost exclusive geomorphic process in limestone areas and what are its results?
Answer:
The result of the work of ground water cannot be seen in all types of rock. But in rocks like limestones or dolomites, rich in calcium carbonate, the surface water as well as ground water through the chemical process of solution and precipitation develop varieties of landforms. These two processes of solution and precipitation are active in limestones or dolomites occuring either exclusively or interbedded with other rocks.

Any limestone region showing typical landforms produced by the action of ground water through the process of solution and precipitation is called karst topography. Limestone is calcium carbonate which is slightly soluble in pure water. Due to erosional activity, shallow holes, small to large sinkholes, dolines, cavities and tunnels and trenches form on the surface of limestones.

NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution

If there is enough water (humid climate), surface drainage too will develop, and mass wasting also plays a role in the degradation of limestone rocks. Surface runoff and infiltration into ground starts the solution process along the fractures, faults, bedding planes and other zones of weakness. Solution on the surface and through the ground results in the formation of swallow holes and sinkholes.

Cavities and tunnels develop underground. Sinkholes and dolines not only increase in their number but also in their diameter. They enlarge and merge creating long and wide trenches. The trenches widen and suffer headward erosion through mass wasting. Gradually, most of the surface of the limestone is eaten away by these pits and trenches leaving it extremely irregular and forming grooves and fluted lapies. The lapie field may turn into somewhat smooth limestone pavements.

In areas of arid climate, where the alternating beds of rocks (shales, sandstones, quartzites) with limestones or dolomites, are dense, massive and occuring as thick beds, cave formation is prominent. It is along ; these bedding planes that limestone dissolves and long and narrow to wide gaps called caves result. Caves normally have an opening through which cave stream discharges out, called tunnels.

Many beautiful depositional forms develop within the limestone caves,.known as depositional landforms. Stalagmites rise up from the floor of the caves. These are formed due to dripping water from the surface, of the stalactite, immediately below it. Stalagmites may take the shape of a column, disc, crater like depression. The stalagmites and stalactites fuse to give rise to columns and pillars of different diameters with smooth or fluted surface.
NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution 1

(iii) How do glaciers accomplish the work of reducing high mountains into low hills and plains?
Answer:
Masses of ice moving as sheets over the land are called glaciers. The movement of glaciers isfslow. Glaciers move because of the force of gravity. Erosion by glaciers is tremendous because of the friction caused by the sheer weight of the ice. The material plucked from the land by glaciers gets dragged along the floor or sides of the valleys and cause great damage through abrasion and plucking. Glaciers can cause significant damage and can reduce high mountains into low hills and plains.

NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution

The accumulated ice, while moving down the mountaintops, cuts and scoops amphitheatre-like basins called cirques. Ice masses move down the cirques and join together to move along a valley. If three or more radiating glaciers cut headward until their cirques meet, high, sharp-pointed and steep-sided peaks called horns form. 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 landform in glacialiated mountains. They are found at the heads of glacial valleys.

Horns and serrated ridges : Homs form through headward erosion of the cirque-walls. The divides between cirque side walls or head walls get narrow because of progressive erosion and turn into serrated or saw-toothed ridges.

Glacial valleys/troughs : Glaciated valleys are trough like and U-shaped with broad floors and over steepened sides. Very deep glacial troughs filled with sea water and making up shorelines are called fiords.

Ice-scoured plains: Striations, grooves and polished surfaces, rock basins and rounded rock knobs are found on ice-scoured plains with patches of glacial drift deposits.

Depositional landforms – Large quantity of eroded material accompanies a glacier. Strip of dirt and rock that flows with the ice and is deposited along the side of valley is known as lateral moraine.
NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution 3

When the lateral moraine of two glaciers merge, they form a single medieval moraine in the middle. Plucking of bedrocks by the over-riding glacier beds to this formation of glacial trough a channel at the valley glacier. The glacial trough is filled up by water and gives rise to trough lake.

NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution

The glacial troughs formed near the sea get filled in by the sea water giving rise to fiords. At the head of each trough, a semi¬circular basin is formed called cirque. Below the snow lines, the glacier melts and materials carried by it are deposited. Eskers, drumlins, out- wash plain and many other features are noticeable in the area.

error: Content is protected !!