NCERT Solutions Class 9 Social Science Chapter 2 Shaping of the Earth s Surface

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 9 · SOCIAL SCIENCE

NCERT Solutions

Chapter 2: Shaping of the Earth's
Surface

NCERT Textbook — Understanding Society: India And Beyond

BOOK PAGES SECTIONS QUESTIONS MEDIUM

13 – 38 13 38 English

Solutions, notes, sample papers & more at 60 pages

Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

CLASS 9 · SOCIAL SCIENCE · UNDERSTANDING SOCIETY: INDIA AND BEYOND

NCERT Solutions — Chapter 2: Shaping of the Earth's
Surface
Complete NCERT Solutions for Class 9 Social Science Chapter 2 Shaping of the Earth's Surface from
Understanding Society: India and Beyond, Grade 9 Part 1. Every question the chapter prints is answered — The
Big Questions, the LET'S MAP activity, all eight LET'S EXPLORE boxes, the THINK ABOUT IT box on the
Chamoli flood, the Before we move on… recap and all 15 Questions and activities — with the plate-
boundary mechanism explained, labelled diagrams drawn, and the evidence read off Figs. 2.1 to 2.30.

TEXTBOOK BOOK PAGES

Understanding Society: India and Beyond (Class 13 – 38
9)

SECTIONS QUESTIONS

13 38

MEDIUM

English

The Big Questions — Page 13
Chapter opening

THE BIG QUESTIONS

Q1 What shapes the Earth's surface?

ANSWER

Two sets of forces shape it, and they work against each other all the time.
1. Internal (endogenic) forces — these come from the heat inside the Earth. That heat sets up
convection currents in the mantle, which move the tectonic plates. Plate movement produces
earthquakes, volcanic eruptions, folding and faulting, and these build relief: mountains, valleys,
ocean basins and plateaus.
2. External (exogenic) forces — these work on the surface: weathering, erosion and
deposition, carried out by running water, glaciers, wind, waves and underground water. These
wear down what the internal forces have raised, and fill up the hollows. The chapter calls them
the agents of gradation, because they grade — level — the surface.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Why it happens: the Earth is hot inside. Fig. 2.2 labels this as the total interior heat
flow and shows where it comes from — crust 24%, upper mantle 22%, lower mantle
32%, core 22% (24 + 22 + 32 + 22 = 100%). That heat has to escape, and as it moves
outward by advection, convection and conduction it keeps the mantle stirring. The
stirring mantle drags the plates, and everything else follows from that.

The surface you see at any moment is the balance of the two. The Himalaya is still being
pushed up by the collision of plates while rivers, glaciers and frost are cutting it down at the
same time. If the internal forces stopped, the external agents would eventually grind the
continents flat.

Check it yourself: the chapter's closing paragraph on page 37 says exactly this —
internal forces "create mountains, valleys, and ocean basins, while external forces
like weathering, erosion, and deposition slowly wear them down and reshape them".

Q2 What is plate tectonics? What are the effects of plate movement?

ANSWER

Plate tectonics is the theory in earth science — given by W.J. Morgan — which explains the
movement of the Earth's crust. It says that the outermost layer of the Earth is not one single
piece but is broken into several large and small slabs called tectonic plates, which move slowly
over the semi-molten layer beneath them.
What the theory rests on:

The crust plus the upper mantle form the rigid lithosphere (about 100 km thick, Fig. 2.1).
Beneath it is the asthenosphere (about 200 km), a hot, mobile layer of partially molten rock.
A rigid layer floating on a layer that can flow is exactly what makes movement possible.
Plates are of three kinds — continental plates (carrying continents), oceanic plates
(carrying ocean floors) and mixed plates (carrying both). The major ones named on page 15
are the Pacific, Eurasian, African, North American, South American, Indo-Australian and
Antarctic plates.
They move at only a few centimetres per year — about the speed at which your fingernails
grow — but over millions of years that adds up to thousands of kilometres.

What makes them move: convection currents in the mantle. Heat from within causes molten
material to rise; the cooler material near the top sinks; this endless circulation pushes and pulls
the plates in different directions.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

divergent: new crust convergent: B sinks

Plate A Plate B Plate C

hot material rises, spreads sideways

cooler material sinks and returns

Asthenosphere — hot, partly molten, and able to flow

Lithosphere = crust + upper mantle (about 100 km, Fig. 2.1); it rides on the
asthenosphere (about 200 km).

How the mantle moves the plates: a convection cell rises under Plate A and Plate B and pushes them
apart, and sinks where Plate B meets Plate C, dragging one plate down. Drawn from the description
on page 15 and the loops in Fig. 2.2.

The effects of plate movement depend on which way two plates move at the boundary
between them:

BOUNDARY MOVEMENT WHAT HAPPENS TO THE LANDFORMS AND
CRUST EVENTS

Convergent (continent Towards each Neither slab is dense enough to Fold mountains — the
meets continent) other sink, so the rock between them is Himalaya
squeezed and crumpled upward

Convergent (ocean Towards each The oceanic plate sinks beneath Volcanic activity and
meets continent) other the continental plate earthquakes

Divergent Away from each Magma rises from below into the Mid-ocean ridges — the
other gap and forms new crust Mid-Atlantic Ridge

Transform Sliding past No crust is created and none Earthquakes — the San
each other destroyed Andreas Fault, USA

Beyond these, plate movement also explains the distribution of continents and oceans, and
the fact that most earthquakes and volcanoes are concentrated along plate boundaries —
especially around the Pacific Ocean, the Ring of Fire.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface l AglaSem · NCERT Solutions

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Why the theory matters: page 16 gives the practical reason — because we know

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where the boundaries are, we can identify earthquake- and volcano-prone regions in
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How are landforms formed and how are they classified?
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Q3

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ANSWER
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A landform is a natural feature on the Earth's surface formed by weathering, erosion,

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deposition and the movement of the Earth's crust (the definition in the margin on page 13).

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How they are formed — in two stages.
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1. Internal

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material away; deposition drops it somewhere else. Over long periods this cuts valleys,
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opens caves, builds deltas and beaches.
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How they are classified. The chapter classifies them in two useful ways.
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(a) By the agent of gradation that made them — this is the order the chapter itself follows:

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AGENT EROSIONAL LANDFORMS DEPOSITIONAL LANDFORMS

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Running water Oxbow lakes, floodplains, deltas, levees,

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meanders (lateral erosion of the outer alluvial fans, bars on the inner bank

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Waves and Sea cliffs, wave-cut (shore) platforms, sea Beaches, sand bars
caves, arches, stacks
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currents

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ascirques, aretes, hanging
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U-shaped valleys,l Moraines — lateral, medial, terminal
valleys, fjords

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Wind Yardangs, ventifacts, deflation hollows Dunes — barchan, longitudinal, star,
(blowouts), desert pavements parabolic
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Caves, sinkholes or dolines, underground Stalactites,

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rivers

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(b) By the force behind them — landforms of internal origin (fold mountains, rift valleys,
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volcanic cones, ocean basins) and landforms of external origin (all the ones in the table above).

a s em group is carved out or laid down.
The first group is built up; the second

a l story in one river, because the same river does different work
Running water shows thegwhole
along its course:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

V-shaped valley, rapids

waterfall

delta, levees, alluvial fan

meanders, oxbow lake, floodplain

UPPER COURSE — erosion dominates
MIDDLE — transport LOWER — deposition

The same river, three kinds of work. Steep gradient in the upper course means strong downward
erosion; a gentler gradient in the middle course means sideways erosion and the start of deposition;
almost no gradient at the mouth means deposition only.

Why the classification by agent works so well: each agent carries material in a
different way, so it leaves a different signature. Ice is stiff and carries rock of every
size, so it gouges a broad U-shaped trough. Water is fluid and cuts fastest at the
point of the stream, so it saws a narrow V. Wind can lift only fine particles, so it
leaves the coarse stones behind as a desert pavement. Look at the shape and you
can name the agent.

Q4 How are humans and other living beings connected to these landforms?

ANSWER

Closely — landforms decide where people can farm, settle, travel and earn a living, and they
decide which plants and animals can survive there.
Landform by landform, as the chapter sets it out:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

LANDFORM HOW PEOPLE AND OTHER LIVING BEINGS DEPEND ON IT

Waterfall Tourism and the local economy; hydroelectric power, because the force of falling
water can be harnessed; trekking and photography; cultural or religious significance
in many regions

Meander Fertile soil deposited along the banks supports agriculture; villages and towns grow
on the gentle slopes near meanders; navigation, irrigation and tourism. The Grand
Anicut (Kallanai) in Tamil Nadu is the chapter's example of a river used for
irrigation

Delta Rich alluvial soil — ideal for rice and jute; the mix of fresh and salt water creates
diverse aquatic life, so fishing thrives; dense settlement, trade and river transport
— but also a real flood risk

Beach Tourism, relaxation, swimming; fishing grounds; sand and shells; and a natural
barrier against strong waves and coastal erosion

Glacial landforms U-shaped valleys and cirques bring trekking, skiing and mountaineering; fjords
make deep natural harbours and fishing grounds; fertile glacial soil in some valleys;
glaciers are crucial sources of fresh water feeding the rivers that sustain people
downstream

Moraines Fertile soil for agriculture; they can form natural dams and lakes used for water
supply, irrigation and sometimes hydroelectric power

Dunes Natural barriers against desertification and wind erosion; tourism and adventure
sports; protection of coastal settlements from sea winds and waves; sand for
construction

Yardangs, They influence settlement and agriculture in arid regions and attract tourists and
ventifacts geologists studying desert landscapes

Caves, Sources of fresh water; tourism; cultural or religious significance; stalactites and
underground stalagmites draw geologists and adventurers
rivers

The connection also runs through history. Page 22 makes the point: the fertile plains of the
Ganga, Nile, Brahmaputra and Indus gave rise to agricultural societies and early cities.
Mountains acted both as barriers and as protectors — the Himalayas shielded India from
invasions but still allowed cultural exchange through passes such as the Khyber Pass. Deserts
such as the Thar limited large settlements but encouraged trade routes such as the Silk Route.
Coasts and harbours supported trade and travel, helping kingdoms in south India flourish.
And it runs the other way too. When a landform is damaged, livelihoods go with it. Page 21
lists it plainly: erosion strips the fertile topsoil farmers need, so yields fall; it washes away land,
houses and roads near rivers and coasts; it destabilises land for construction and mining; and it
hurts tourism and fishing when beaches, rivers and fertile lands are destroyed.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

The underlying reason: a landform is not just scenery — it is a package of soil,
water, slope and shelter. Deltas give soil and water and no slope, so they carry
dense populations. Steep mountains give slope and shelter but little soil, so
populations there stay thin and rely on grazing, forests and, today, tourism.

Q5 How do disasters associated with different landforms impact human lives?

ANSWER

Every landform carries its own hazard, and the damage follows the shape of the land.

DISASTER WHERE IT BELONGS IMPACT ON HUMAN LIFE

Landslide Steep, weathered hill Houses and villages buried; roads and bridges cut, so
slopes relief cannot reach; farmland and terraces lost; rivers
blocked, which can flood upstream

Avalanche Steep snow-covered Trekkers, skiers, soldiers and road crews buried;
mountain slopes mountain roads and settlements cut off in winter

GLOF (Glacial Lake Glacial valleys with A wall of water arrives with no warning; downstream
Outburst Flood) moraine- or ice-dammed villages, bridges and hydel projects destroyed
lakes

Dust storm Deserts and semi-arid Topsoil blown away, crops buried or scorched; visibility
plains lost, so road, rail and air travel stop; breathing problems

Earthquake Plate boundaries and Buildings collapse on the people inside them — Fig. 2.5
fault zones shows the extensive damage of the Gujarat earthquake of
2001

Volcanic eruption Convergent boundaries, Ash buries fields, houses and roads and collapses roofs
the Ring of Fire under its weight — Fig. 2.6

The chapter's own case. The flood that struck Chamoli district in Uttarakhand in February
2021 shows the full pattern: many people and livestock lost their lives; there was severe damage
to buildings, roads, bridges and hydel projects; and connectivity to villages was badly affected.
Notice that the losses are of three kinds — lives, property and connectivity — and the third
one is what makes rescue in mountains so difficult.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Why the impact is so uneven: a hazard becomes a disaster only where people and
property are exposed to it. The same magnitude of earthquake causes far more
deaths in a densely populated region with weak buildings than in an empty one —
which is exactly the point the box on page 17 makes about India.

Tip: for every disaster in this chapter, learn it as a chain — trigger → landform
condition → damage → mitigation. Heavy rain (trigger) on a deforested steep slope
(condition) buries a road (damage), and afforestation plus proper drainage
(mitigation) breaks the chain.

LET'S MAP — Page 16

Page 8 of 60

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface
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Fig. 2.3, world map showing major plates and their direction of movement
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LET'S MAP

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a s emany two plates from the map above and complete the table given below. (Name
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Pick
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Q1
of the plate | Continents | Ocean)

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Eurasian

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North American

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plate
plate

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Pacific plate

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African

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plate

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a plate
Indo-Australian
plate

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Antarctic plate Antarctic plate

Major Plates: ag
North American plate African plate Eurasian plate South American plate
Indo-Australian plate Pacific plate Antarctic plate Minor Plates
plate boundary direction in which the plate is moving

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Arrows meeting head-on mark a convergent boundary; arrows pointing away from each other mark a

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divergent boundary; arrows sliding past each other mark a transform boundary.

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Fig. 2.3, page 16 — the world's major plates and the direction in which each one is

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moving. The plate names sit where the book prints them, and the arrows show the
direction of movement of each plate as the book's arrows do; the dashed red lines mark

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the plate boundaries, added so that you can see where one plate ends and the next

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ANSWER

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Read the plate outlines and the arrows in Fig. 2.3 first, then fill the table. Any two plates are

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acceptable — here are two worked examples, with the rest of the major plates given so you can
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check

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NAME OF THE PLATE CONTINENTS OCEAN

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Indo-Australian plate Asia (the Indian subcontinent) and Australia Indian Ocean

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South American plate
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South America Atlantic Ocean (its western half)

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The other major plates in Fig. 2.3, for reference:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

NAME OF CONTINENTS OCEAN
THE PLATE

North American North America, Greenland Atlantic Ocean (western half), part of the
plate Arctic Ocean

Eurasian plate Europe and most of Asia Atlantic Ocean (eastern half), Arctic
Ocean

African plate Africa Atlantic Ocean (eastern half) and the
western Indian Ocean

Pacific plate Almost none — a small strip of North Pacific Ocean
America along the Californian coast

Antarctic plate Antarctica Southern Ocean, and the southern edges of
the Pacific, Atlantic and Indian Oceans

What the two rows tell you: the Indo-Australian and South American plates both
carry land and sea floor, so they are mixed plates in the chapter's three-fold
classification. The Pacific plate is the clearest oceanic plate — it is almost entirely
ocean floor. That is why the Pacific rim, where this heavy oceanic plate meets lighter
continental plates, is ringed by volcanoes and earthquakes.

Check it yourself on the map: read the arrows for the plate you picked. Over India
the arrows on the Indo-Australian plate point north and north-east, straight into
the Eurasian plate — which is precisely where the Himalaya stands. On either side of
the mid-Atlantic the arrows point away from each other, one set west and one set
east. Around Antarctica they point outwards in every direction.

LET'S EXPLORE — Page 16

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Comparing the plate map (Fig. 2.3) with the earthquake and volcano map (Fig. 2.4)

LET'S EXPLORE

Q1 Examine the plate map (Fig. 2.3) with the earthquake and volcano map (Fig. 2.4).
What correlation do you observe?

Eurasian
North American plate
plate

Pacific plate African
plate
South American
plate
Indo-Australian
plate

Antarctic plate Antarctic plate

Major Plates: North American plate African plate Eurasian plate South American plate
Indo-Australian plate Pacific plate Antarctic plate Minor Plates
plate boundary direction in which the plate is moving

Arrows meeting head-on mark a convergent boundary; arrows pointing away from each other mark a
divergent boundary; arrows sliding past each other mark a transform boundary.

Fig. 2.3, page 16 — the world's major plates and the direction in which each one is
moving. The plate names sit where the book prints them, and the arrows show the
direction of movement of each plate as the book's arrows do; the dashed red lines mark
the plate boundaries, added so that you can see where one plate ends and the next
begins.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Ring of Fire
(around the Pacific Ocean)

Active Volcanoes
Earthquake Origin

Every dense band of dots and triangles lies along a plate boundary of Fig. 2.3.
This map is centred on the Pacific Ocean; Fig. 2.3 is centred on the Atlantic, so the
two maps show the same world cut open at different places.

Fig. 2.4, page 17 — the distribution of earthquakes and volcanoes, on a map centred on
the Pacific Ocean. Red dots are earthquake origins and black triangles are active
volcanoes; they are drawn along the same belts as in the book, though not one dot for
one dot.

ANSWER

The correlation is almost exact: the dots and triangles in Fig. 2.4 trace the plate
boundaries of Fig. 2.3. Earthquake origins (red dots) and active volcanoes (black triangles) are
not scattered evenly over the Earth — they form narrow belts, and every belt sits on a line where
two plates meet.
Match them belt by belt:

Around the whole rim of the Pacific — from New Zealand up through Indonesia, the
Philippines, Japan, Kamchatka, across the Aleutians, and down the west coast of North and
South America — Fig. 2.4 shows the densest band of both dots and triangles anywhere on
the map. In Fig. 2.3 this is the edge of the Pacific plate against the Eurasian, Indo-Australian,
North American, South American and Antarctic plates. This belt is the Ring of Fire.
A second belt runs west to east through the Mediterranean, Turkey, Iran, the Himalaya and
on to Indonesia. In Fig. 2.3 this is the boundary where the African and Indo-Australian
plates press north into the Eurasian plate.
A thin line of red dots runs down the middle of the Atlantic, exactly where Fig. 2.3 shows
the North and South American plates separating from the Eurasian and African plates.
Notice this belt has many earthquakes but few marked volcanoes — it is the Mid-Atlantic
Ridge, and its eruptions happen underwater.
A line of volcanoes runs down East Africa, where the African plate is being pulled apart.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

The interiors of the plates are almost empty — central Siberia, the Sahara, the Australian
interior, the Canadian shield, peninsular India, most of the deep ocean floor.

Why the correlation exists: an earthquake is stored strain released suddenly, and
strain builds only where rock is being pushed, pulled or sheared — that is, at a
boundary. A volcano needs a path for magma to reach the surface, and the cracked
crust of a boundary provides exactly that: at a divergent boundary magma rises into
the gap, and at a convergent boundary the sinking plate supplies molten material
from below. In the middle of a plate the crust is neither strained nor cracked, so it is
quiet.

Did you notice? The two maps are drawn on different centres — Fig. 2.3 is centred
on the Atlantic, Fig. 2.4 on the Pacific. Find a common landmark (say Japan, or the tip
of South America) on both before you start comparing.

LET'S EXPLORE — Page 17

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface l AglaSem · NCERT Solutions

The Ring of Fire in Fig. 2.4
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LET'S EXPLORE

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a s em the map showing the distribution of earthquakes and volcanoes (Fig. 2.4).
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Observe
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Q1
Can you identify which continents and countries are located around the Ring of Fire
with the help of an atlas or a globe?

co m
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g l as
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co m
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m l as
m .co a g
l a se Ring of Fire

a g (around the Pacific Ocean)

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m.co agl
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a g Earthquake Origin

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Every dense band of dots and triangles lies along a plate boundary of Fig. 2.3.

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This map is centred on the Pacific Ocean; Fig. 2.3 is centred on the Atlantic, so the

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two maps show the same world cut open at different places.

o m g l a
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the Pacific Ocean. Red dots are earthquake origins and black triangles are active
volcanoes; they are drawn along the same belts as in the book, though not one dot for
one dot.
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ANSWER agl
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Method first: in Fig. 2.4 trace the horseshoe-shaped band of dense red dots and black triangles

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that rings the Pacific Ocean. Then lay that band over the political map in your atlas and list what

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it crosses, going round the ring.
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Continents touched by the Ring of Fire — four: Asia, North
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ring altogether.)

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Countries, going round the ring:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

SIDE OF THE COUNTRIES ON THE RING
PACIFIC

Western Pacific (Asia) Indonesia, Philippines, Malaysia (east), Papua New Guinea, Japan, Taiwan, China
(east coast), Republic of Korea, Russia (Kamchatka and the Kuril Islands)

South-western Pacific Solomon Islands, Vanuatu, Fiji, Tonga, New Zealand

Northern Pacific United States (Alaska and the Aleutian Islands)

Eastern Pacific (North and Canada (west coast), United States (Washington, Oregon, California), Mexico,
Central America) Guatemala, El Salvador, Nicaragua, Costa Rica, Panama

Eastern Pacific (South Colombia, Ecuador, Peru, Bolivia, Chile, Argentina (Andean edge)
America)

Why the ring is a ring: look back at Fig. 2.3. The Pacific plate is a single huge
oceanic plate, and almost its entire edge is a boundary with some other plate —
Eurasian, Indo-Australian, North American, South American, Antarctic. Because
oceanic crust is thin and heavy (5 km against 30 km for continental crust, Fig. 2.1), it
sinks beneath the lighter continental plates all round. Sinking plates make both
violent earthquakes and the magma for volcanoes. So the shape of the ring is simply
the shape of one plate's boundary.

Check it yourself: India does not lie on the Ring of Fire — it sits on the Indo-
Australian plate, well inside it. India's earthquake belt comes from a different
boundary: the collision with the Eurasian plate along the Himalaya.

LET'S EXPLORE — Page 17
Does India have a risk of earthquakes? (Fig. 2.5)

LET'S EXPLORE

Q1 Can you find out which region is more vulnerable to earthquakes?

ANSWER

Yes — the Himalayan belt in the north and north-east is India's most vulnerable region,
followed by the Kachchh region of Gujarat and the Andaman and Nicobar Islands.
The reasoning, from the maps in this chapter:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Fig. 2.3 shows the arrows on the Indo-Australian plate pointing north into the Eurasian
plate. That collision has not stopped — it is what raised the Himalaya and it is still going on.
Fig. 2.4 confirms it independently: a continuous line of earthquake origins runs along the
Himalayan arc, from Jammu and Kashmir through Himachal Pradesh, Uttarakhand, Nepal,
Sikkim and the north-eastern states, and continues down through the Andaman Islands into
Indonesia.
Fig. 2.5 gives a worked example of the damage — the Gujarat earthquake of 2001, in the
Kachchh region, far from the Himalaya but on an active fault zone within the plate.

Ranking the regions by risk:

REGION WHY IT IS AT RISK

The Himalayan belt and the Sits directly on the convergent boundary where the Indo-Australian plate is
north-east pushing under the Eurasian plate — the highest risk in the country

Kachchh, Gujarat An active fault zone inside the plate; the source of the 2001 earthquake shown
in Fig. 2.5

Andaman and Nicobar Islands On the same plate boundary as it curves south into Indonesia

The Indo-Gangetic plain Close to the Himalayan source, and its thick soft alluvium shakes far more
strongly than hard rock does

The peninsular shield (most of Old, stable crust in the middle of the plate — the lowest risk, though not zero
central and south India)

Try this: place a piece of tracing paper over the earthquake map in Fig. 2.4, mark
only the dots that fall on India, then compare your tracing with a physical map of
India. The line of dots will lie along the Himalaya — the mountains and the
earthquakes have the same cause.

Q2 Why do you think human lives are at risk?

ANSWER

Because, as the box says, India is a densely populated country — so a single large earthquake
reaches an enormous number of people at once. Past earthquakes here have already killed
thousands.
The reasons, in order of importance:

1. Population density. The Indo-Gangetic plain, close to the Himalayan source, is one of the
most crowded regions on Earth. The same shaking that would harm a few hundred people in
an empty region can reach millions here.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

2. It is buildings that kill, not the shaking itself. Fig. 2.5 shows exactly this — the ground is
not torn open; what covers the ground is the rubble of collapsed buildings. Heavy
unreinforced masonry, unplanned multi-storey construction and poor foundations turn a
tremor into a burial.
3. Soft ground amplifies the shaking. The plains are built of thick river alluvium, which shakes
much more violently than solid rock, so damage extends far from the source.
4. Earthquakes cannot be predicted. There is no warning, so people are indoors and asleep
when it strikes.
5. Secondary effects follow. Landslides on Himalayan slopes, blocked roads, broken water and
power lines, and fires prolong the disaster long after the shaking stops. Damage to the
environment — the box's own words — comes with the damage to life.

The idea behind all of this: risk is not the hazard alone. Risk = hazard (how strong
and how likely the earthquake is) × exposure (how many people and buildings are
there) × vulnerability (how badly they are built). India cannot change the first — the
plates will keep moving — but it can change the third, which is why earthquake-
resistant building codes save more lives than anything else.

LET'S EXPLORE — Page 18

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

The photograph in Fig. 2.6 — deposition by volcanic eruption

LET'S EXPLORE

Q1 What do you think caused this situation?

What the photograph shows — a whole hillside village buried under grey ash.
Everything in the picture is the same dust-grey: the roofs, the walls, the
ground, the tree trunks and the hill behind. Almost no colour survives —
only a blue plastic bucket, a scrap of red cloth on a wall and one patch of
bare brick.
Small houses of timber, corrugated sheet and tile stand on either side of a
narrow lane that runs up the middle of the picture. Several have collapsed
— roofs caved in, walls pushed over, planks and beams spilled into the
lane.
Tall bare trees, stripped of every leaf, rise through the ash; drifts of ash lie
banked against the walls and bury the lane, with loose boulders sitting on
top of it.
Behind the village a smooth grey hill rises, streaked with dark gullies
where the ash has slid downhill. There is no one in the picture — no
people, no animals, no vehicles.

Fig. 2.6, page 18 — “Photograph showing the deposition by volcanic eruption”. Described
here; see the textbook for the photograph itself.

ANSWER

A volcanic eruption — the caption of Fig. 2.6 confirms it: the photograph shows the deposition
left by a volcanic eruption.
The evidence in the photograph itself:

Everything — the ground, the roofs, the walls, the tree trunks, the hillside behind — is coated
in the same uniform grey. Only something that fell out of the air could coat every surface
equally like that.
The houses are half-buried and several roofs have sagged or broken; the grey material is
deep enough to bury the lower parts of the walls.
The trees are stripped bare of leaves and still standing. A flood or a landslide would have
knocked them over; a hot ash fall kills the leaves but leaves the trunk upright.
The whole slope behind the village is smothered, and the sky is hazy — ash is still in the air.

So: a nearby volcano erupted, threw out ash and fine fragments, and the wind carried them
over the settlement, where they settled as a thick grey blanket.

Page 18 of 60

as e
a g
Class 9 Social Science Chapter 2 Shaping of the Earth's Surface l AglaSem · NCERT Solutions

co m
m.
What could that grey powder be?
e
Q2

m l as
.co a g
ANSWER
a s em
a l
It isgvolcanic ash — the fine dust of the eruption.
When magma reaches the surface, the dissolved gases in it expand violently and shatter the

. c om
molten rock into tiny fragments. Those fragments cool almost instantly in the air into fine, gritty
ag
particles of rock and glass, and that is whatm
s e falls as ash. It is not soft like wood ash: it is sharp,

a g
abrasive and surprisingly heavy — whichla is why the roofs in the photograph have collapsed
under it.

co m
se
Why the colour is grey: the fragments are freshly shattered rock and volcanic glass,
m.
o m l a
.cout of a whole landscape and everything below it looksagthe same shade.
not burnt material. Ash has no single colour of its own, so a thick fall drains the

se m
colour

g l a
a
s
Did you know? Once it weathers, volcanic ash breaks down into some of the most
m a
.co agl
fertile soil on Earth — which is why people keep returning to live on the slopes of

se m
a
volcanoes even after an eruption like this one.

a g l

co m
What does it tell us about the Earth's internal forces?
m .
e
Q3

m l as
.co a g
a s emANSWER

a gl It tells us that the Earth is hot and active inside, and that its internal heat can reach the surface
with enough force to remake a landscape in hours.
se m
com g l a
. a
Four things this photograph proves:
m
ase
agl
1. The interior is hot enough to melt rock. Ash is shattered molten rock. Fig. 2.2 shows where
that heat comes from and how it travels outward — by advection, convection and conduction
— with the crust and mantle together supplying 78% of the total interior heat flow and the
core the remaining 22%.
. c om
s e m remove material; this
2. Internal forces are constructive. External agents like wind and rivers

. om has added a whole new layer of it. Over time, repeated
ceruption a g la ash and lava falls build
a s em volcanic cones, plateaus and islands.
agl 3. They act suddenly. Weathering and erosion take thousands of years to change a valley. An
c
eruption buries a village in a single day. Both are shaping the Earth, but on completely
m .
m a s e
co agl
different timescales.

m .
se
4. They are tied to plate boundaries. A volcano needs a crack in the crust for magma to

l a
agplate, and where plates pull apart. That is why Fig. 2.4 shows
escape through, and page 15 tells us where such cracks are — where an oceanic plate sinks
beneath a continental
volcanoes lined up along boundaries and almost none in plate interiors.

co m
m .
m ase
.co


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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

The larger lesson: the surface we walk on is only a thin, cool skin — 5 km thick
under the ocean and about 30 km under the continents (Fig. 2.1) — over 6,375 km of
hot interior. A photograph like this is the interior making itself visible.

LET'S EXPLORE — Page 21
Erosion caused by (a) water and (b) wind — Fig. 2.9

LET'S EXPLORE

Q1 Observe the photographs (Fig. 2.9) and also note the types of erosion. How are
farmers affected by erosion due to water and wind?

b
rain wind lifts the dry, loose topsoil
and carries it away as dust

crop field crop field

topsoil
blocks of soil
subsoil break off the sides

the fertile soil is
gully carried away bare, dry field — no crop to hold the soil down
a

(a) Erosion caused by water (b) Erosion caused by wind
Rain and run-off cut a gully into the edge of a field. A dust storm over dry farmland. The air is thick
Blocks of soil break away and the fertile topsoil is with
blown off a bare field, soil
and the trees behind are
leaving bare,washed off,
stony ground behind. half hidden
in the haze of flying dust.

Fig. 2.9, page 20 — the book prints two photographs: (a) erosion by water and (b) erosion
by wind. They are redrawn here as labelled sketches of what each photograph shows;
see the textbook for the photographs themselves.

ANSWER

First, the two photographs.

Page 20 of 60

Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

PHOTOGRAPH WHAT YOU CAN SEE TYPE OF
EROSION

Fig. 2.9 (a) A bare slope cut into deep, branching channels with steep Water erosion — gully
raw sides, and a thin stream at the bottom. There is a little erosion by running
grass surviving only at the very top, where the ground has water
not yet been cut into.

Fig. 2.9 (b) Dry pale grassland with a few trees, and the air thick with Wind erosion — fine
drifting brown dust so that the far trees are almost hidden. soil being lifted and
The ground is bare between the tufts of grass. carried away

How farmers are affected — water erosion:

Rain water running downhill first strips the fertile topsoil, which is the only layer that holds
the nutrients and organic matter crops need. Yields fall even though the field looks
unchanged.
If it continues, the sheet of running water concentrates into rills and then gullies, as in
photograph (a). A gullied field cannot be ploughed at all; the land is lost outright and the plot
is cut into unusable pieces.
The eroded soil is dumped downstream, silting up canals, tanks and reservoirs and
reducing the water available for irrigation.
Along rivers and coasts, erosion washes away land, houses and roads — page 21 lists this as
a direct loss of property.

How farmers are affected — wind erosion:

Wind lifts the finest particles first — exactly the clay and humus that make soil fertile —
and leaves behind coarse sand. The field slowly turns from soil into sand.
Blowing sand buries young crops and sand-blasts standing plants, damaging leaves and
stems.
Seed and fertiliser broadcast on a loose dry field are simply blown away, so the farmer's
investment is lost before the crop starts.
Repeated wind erosion leads towards desertification, after which the land cannot be
farmed at all.

Why both begin the same way — bare soil. Erosion needs loose particles and an
agent to move them. A crop canopy or grass cover breaks the force of falling
raindrops and slows the wind at ground level, and roots bind the particles together.
Remove the cover — by deforestation, overgrazing, or leaving a field bare between
crops — and both water and wind can start work at once. That is why every remedy
in this chapter is about putting a cover or a barrier back.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Check it yourself: page 21 also names the answers Indian farmers worked out long
ago — contouring (continuous contour trenches dug along the contour lines of a
hillside to slow, hold and soak in rainwater), bunding (earthen embankments along
the contour to cut run-off), terracing (level steps cut into a hillside) — and the Zabo
system of Nagaland, where earthen bunds on hill slopes and check dams across
small streams slow the water, trap sediment and recharge groundwater.

LET'S EXPLORE — Page 25
The Sundarbans delta (Fig. 2.13)

LET'S EXPLORE

Q1 Have you heard about the Sundarbans delta? Try and explore its uniqueness and
find out why it is popular with tourists.

ANSWER

Method: this is a find-out question, so build the answer in three parts — (i) what kind of
landform it is and how it formed, (ii) what makes it different from every other delta, (iii) what a
visitor actually goes there to see. Use an atlas for the location, and the chapter's own section on
deltas (page 24) for the geography.
What a good answer must contain: the rivers that built it and the sea it opens into; the fact
that it is shared between India (West Bengal) and Bangladesh; the mangrove forest and why
mangroves grow there and not elsewhere; the Royal Bengal tiger; its recognition as a protected
area; the livelihoods it supports; and the hazards it faces.
Sample answer:
The Sundarbans is the delta built where the Ganga, Brahmaputra and Meghna meet the Bay
of Bengal. It is the largest delta in the world, and it is shared between West Bengal in India
and Bangladesh. As Fig. 2.13 shows, the rivers here split into a maze of distributaries that wind
between hundreds of low, muddy islands — exactly the fan-shaped, sediment-built landform
described on page 24.
What makes it unique is that it is not farmland but forest — the largest mangrove forest on
Earth. Mangroves are trees that can live with their roots in salt water, and they send up
breathing roots through the mud. They can grow here because a delta gives them what nothing
else does: soft new sediment, shallow water, and the daily mixing of river water with sea water.
The name Sundarbans is usually traced to the sundari tree that grows there.
Tourists come for the wildlife and the waterways. The Sundarbans is the only mangrove forest in
the world with a population of Royal Bengal tigers, which are famous for swimming between
the islands. Visitors also see estuarine crocodiles, spotted deer, snakes and a great variety of

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

birds. Because there are no roads between the islands, the whole visit is made by boat through
narrow creeks — an experience found nowhere else. It is a national park and a protected
biosphere, which is itself a draw.
The delta also shows both sides of what page 24 says about deltas. It gives fertile land, fishing,
honey collection and boat transport to the people who live there — and it is very prone to
flooding, cyclones and the erosion of its islands, so life on it is never secure.

Why the mangroves matter beyond tourism: the mangrove belt takes the first
force of every cyclone that comes up the Bay of Bengal. It is a delta protecting itself,
and protecting the towns behind it. This is the same idea as the beach acting as a
natural barrier on page 25.

THINK ABOUT IT — Page 29
The Chamoli flood of February 2021 (Fig. 2.20)

THINK ABOUT IT

Q1 A devastating flood struck the Chamoli district in Uttarakhand in February 2021 in
which many people and livestock lost their lives. There was severe damage to
buildings, roads, bridges, and hydel projects, and connectivity to villages was
adversely affected. Can you find out the reasons that led to the sudden and
unexpected flood?

ANSWER

The flood came from the mountain itself, not from rain. That is the key to the whole event —
it happened in February, in the middle of winter, when there is no monsoon and no snowmelt
to speak of. So the water had to be released suddenly from something already stored high up.
The chain of reasons:

1. A mass of rock and ice broke away high on a steep slope. The Chamoli area lies in the
high Himalaya, where slopes are very steep, the rock is fractured, and repeated freezing and
thawing prises it apart — the physical weathering described on page 19.
2. The falling mass shattered on impact and mixed with ice and snow. The heat of the fall
melted part of the ice, turning solid debris into a fast-moving slurry of water, mud and
boulders.
3. The slurry poured into a narrow valley. A steep, narrow Himalayan valley cannot spread a
flood out sideways, so the water rose into a wall instead of a sheet, and travelled
downstream at great speed.
4. It reached the Rishiganga and Dhauliganga rivers, and struck what lay in the valley
floor — bridges, roads and two hydel project sites, where workers were inside tunnels. This
is why the loss of life was concentrated and sudden.

Page 23 of 60

ase
a g
Class 9 Social Science Chapter 2 Shaping of the Earth's Surface l AglaSem · NCERT Solutions

c om
Why it was "sudden and unexpected":
.
m a s em warning
There was no rainfall warning to go by, because rain was not the trigger. Flood

. co the weather, and the weather that day was ordinary. agl
systems watch
The s
a em was high, remote and unmonitored — nobody was watching that slope.
l flood travelled down a steep gradient, so the time between the collapse and its arrival in
source

agThe
the villages was minutes, not hours.

. c om ag
a s
The deeper reason — why the Himalayaem is fragile at all: it is a young fold
aglby the collision of the Indo-Australian and Eurasian
mountain, still being pushed up
plates (page 15). Young mountains are high, steep and made of rock that has been

c o m
crushed and fractured by that same collision. Add glaciers and daily freeze–thaw,
.
m roads,
s e
and the slopes are loaded with loose material waiting to move. Building
tunnels o
. c and
a gla directly in the
m hydel projects at the bottom of such valleys puts people
a s
pathemof whatever comes down.
a gl
m
Connect it forward: pages 33–35 name the three hazards that combine in an event
a s
em
.co
like this — a landslide or rock-and-ice avalanche starting it, and a GLOF as the
agl
a s
aglthe ice and moraine dams that hold them.
closely related danger, since rising temperatures are enlarging glacial lakes across
the Himalaya and weakening

com
m .
se
Try this: find newspaper reports of the Chamoli event and note down the times —

o m g l a
.cis exactly what an early-warning system has to work inside.
when the collapse happened and when the water reached each village. That time
m a
ase
gap

agl
se m
com g l a
LET'S EXPLORE — Page 32
m . a
ase
agl
Landforms around your school or home

LET'S EXPLORE

c o m
.
mtry to identify which
s
Observe the landforms around your school or residence and
e
comagent may have created them. gla
Q1

. a
as em
agl ANSWER
c
m .
Method. Do not start by naming landforms — start by asking three questions about each
m a s e
. co agl
feature you can see, and let the answers name the agent.

e m
l as
1. What shape is it? A narrow V-shaped cut, a broad U-shaped trough, a rounded hollow, a
g
ridge, a flat step? a

com
m .
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.co


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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

2. What is it made of? Solid rock, rounded pebbles, angular gravel, fine sand, sticky clay?
Rounded stones have travelled in water; angular ones have not travelled far; sorted sand of
one size means wind or waves.
3. Which way does it face, and what is nearby? A river, the sea, a hill slope, a bare dry plain, a
limestone quarry?

What a good answer needs: at least three features you have actually seen; the agent for each;
and the one piece of evidence that made you decide. Then use this table to check yourself.

IF YOU SEE … THE AGENT IS BECAUSE
PROBABLY …

A stream in a V-shaped notch, with Running water Water cuts downward at a point and
rounded pebbles in its bed rounds stones by rolling them

A flat strip of fine silt beside a river, Running water — deposition Silt is dropped when a river
farmed and slightly raised at the bank (floodplain and levee) overflows and loses speed

Small channels or gullies cutting a Running water — erosion Run-off concentrates into channels
bare slope after rain wherever the soil is bare

A sandy shore, low ridges of sand Waves and currents Waves both deposit sand and
behind it, or a rock cliff facing the sea undercut rock at the shoreline

Ripples or low mounds of clean sand Wind Wind sorts particles by size, so dune
on a dry plain sand is all of one grade

A broad U-shaped valley, or scattered A glacier, in the past Only ice carries huge boulders far
boulders quite unlike the local rock and widens a valley into a U

A limestone area with hollows, Underground water Slightly acidic water dissolves
springs, or a cave limestone from within

A steep road cutting with fresh debris Gravity, helped by Weathered rock loses support and
at its foot weathering slips downslope

Sample answer: Behind my school there is a low hill and a small stream. In the stream bed the
stones are smooth and rounded and the channel is a narrow V, so the agent here is running
water. Where the stream leaves the hill it spreads out and the ground is flat and silty, and
farmers grow vegetables on it — that is deposition by the same stream, a small alluvial fan. On
the bare part of the hill slope, where the trees were cut, the last monsoon left a set of small
gullies about knee-deep: again running water, but eroding this time, and only where the soil
had lost its cover. Near the school gate the rock in the compound wall has cracked where a
peepal root has grown into it — that is biological weathering, not erosion, because the pieces
have not moved anywhere.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Tip: the single most useful test in the field is the difference the chapter draws on
pages 19–20. If the broken material is still lying where it broke, you are looking at
weathering. If it has been carried somewhere else, you are looking at erosion.

LET'S EXPLORE — Page 32
Completing the disaster exercises on pages 33–36

LET'S EXPLORE

Q1 Complete the exercises given at the end of each type of disaster with the help of
newspapers, atlases, and books. Make a list of disaster-prone areas from India and
the world and enlist mitigation measures quoting recent examples.

ANSWER

Method: for each of the four disasters the chapter describes, fill the three blanks it prints —
Prone areas, Mitigation measures, Recent examples. Take the prone areas from your atlas (they
follow the landform, so look for the right kind of terrain), take the mitigation measures from the
causes listed in the chapter itself — every cause suggests its own remedy — and take the recent
examples from newspapers of the last year or two, writing down the date and place each time.
The completed exercises:
1. Landslides (page 33)

Prone areas India — the Himalayan states (Jammu and Kashmir, Himachal Pradesh, Uttarakhand,
Sikkim), the north-eastern hills, the Western Ghats (Kerala, Karnataka, Maharashtra) and
the Nilgiris. World — the Andes, the Alps, the Rockies, the mountainous parts of Nepal,
China, Japan, Indonesia and Colombia.

Mitigation Afforestation and grass cover so roots bind the slope; terracing and retaining walls; proper
measures drainage so water does not build up inside the slope; controlled blasting and correct slope angles
when cutting roads; banning construction on steep slopes and along drainage paths; hazard-zone
mapping; rain-gauge based early warning; and educating residents to recognise warning signs —
cracks in the ground or in walls, tilting trees and poles, and suddenly muddy stream water.

Recent Landslides in the Himalayan and Western Ghat districts recur every monsoon. Write down
examples two from this year's newspapers with the district and date.

2. Avalanches (page 34)

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Prone areas India — the high Himalaya of Jammu and Kashmir, Ladakh, Himachal Pradesh,
Uttarakhand and Sikkim, especially high passes and army posts. World — the Alps
(Switzerland, France, Austria, Italy), the Rockies, the Andes, and the mountains of Japan
and Norway.

Mitigation Snow and weather monitoring with avalanche bulletins; avalanche barriers, snow fences and
measures deflecting walls above roads and settlements; planting and protecting slope forests; controlled
release of unstable snow before it builds up; closing high roads and passes after heavy snowfall or
a sudden warm spell; and training for trekkers, skiers and soldiers, including the use of beacons
and probes.

Recent Avalanches on high Himalayan passes and near border posts are reported most winters.
examples Add one recent case with its date and location.

3. GLOFs (page 35)

Prone areas India — the glacier-fed valleys of Uttarakhand, Himachal Pradesh, Sikkim, Arunachal
Pradesh and Ladakh. World — Nepal, Bhutan, Tibet, Pakistan, the Peruvian Andes,
Iceland and Alaska.

Mitigation Satellite monitoring of glacial lakes so a growing lake is spotted early; lowering dangerous lakes
measures by siphoning or by cutting a controlled outlet channel; strengthening the moraine dam; automatic
water-level sensors linked to sirens downstream; keeping settlements, roads and hydel projects
out of the flood path; and evacuation drills in downstream villages.

Recent The Chamoli disaster of February 2021 in Uttarakhand, described in the THINK ABOUT
examples IT box on page 29, is the chapter's own case. Add any newer event you find in the
newspapers.

4. Dust storms (page 36)

Prone areas India — Rajasthan and the Thar, Gujarat, Haryana, Punjab, Delhi and western Uttar
Pradesh, mainly in the hot months before the monsoon. World — the Sahara and the
Sahel, the Arabian Peninsula, Iran, Central Asia, western China, the interior of Australia
and the dry plains of the United States.

Mitigation Shelter belts and windbreaks of trees along field edges; keeping a stubble or crop cover on the soil
measures instead of leaving it bare; stabilising dunes with grasses and shrubs; controlling overgrazing;
contour ploughing across the wind direction; sand fences; weather warnings so schools, road and
air traffic can be halted; and masks and eye protection for people who must be outdoors.

Recent Pre-monsoon dust storms over north-western India are reported almost every summer.
examples Note one, with the date and the states affected.

Page 27 of 60

Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

The pattern worth noticing: every mitigation measure in these four boxes belongs
to one of three families — hold the material in place (trees, bunds, walls, fences),
take the water away safely (drains, controlled outlets, siphons), or keep people
out of the path (zoning, early warning, evacuation). If you know the cause, you can
work out the measure for yourself; you do not have to memorise the list.

Tip: for the "recent examples" line, always write place + district + month + year and
the source newspaper. A dated example is evidence; an undated one is only a claim.

Before we move on … — Page 37
The chapter's recap points, expanded

BEFORE WE MOVE ON …

Q1 The Earth is made up of layers, namely, the crust, mantle, and core.

ANSWER

What this recap means, expanded:

Page 28 of 60

as e
a
Class 9 Social Science Chapter 2 Shaping of the Earth's Surface
g l AglaSem · NCERT Solutions

co m
em.
as
Drawn to scale

m l
.co
(thicknesses in km)

a g
m
Crust

ase
Crust

agl
Mantle

6375 km — surface to centre
Mantle 2900 km

co m
e m . ag
as
Outer Core

a g l Inner Core Outer core 2200 km

co m
e m.
as
Inner core 1250 km

m l
.co g
The Earth cut open

m a
l a se The top 300 km of that column, magnified (bands not to scale)

a g Oceanic crust 5 km Continental crust 30 km
Lithosphere = crust + upper mantle, about 100 km — this rigid layer is what is broken into plates

m a s
.co agl
Asthenosphere, about 200 km — hot, mobile, partly molten rock on which the plates ride

the rest of the mantle continues below

se m
g l a
a
Crust Asthenosphere Outer core
Thickness varies from 30–40 km under A hot, mobile layer of partially A fluid layer mainly consisting of
continents to 5–7 km under the ocean. molten rock. iron and nickel.

m
Lithosphere Mantle Inner core

. co
The rigid outer layer of the Earth that The mostly solid layer between the A solid, hot spinning metal ball that

m
includes the crust and upper mantle. crust and the Earth's outer core. is the densest part of the Earth.

m as e
.co g l
Fig. 2.1, page 14 — the Earth's interior. The thicknesses are the approximate values printed in the

a
sem
book.

a
agl Crust — the outermost layer, the one we live on. Fig. 2.1 gives its thickness as 30–40 km

se m
m a
under the continents but only 5–7 km under the ocean. That difference is not a detail:

.c o a g l
m
thin, heavy oceanic crust is exactly what sinks at a convergent boundary, while thick, light
continental crust does not. se
la between the crust and the outer core, about 2900 km thick
aglayer
Mantle — the mostly solid
in Fig. 2.1. It is very thick and very hot, and it is where the convection currents run.

. c om
Core — the innermost part, in two pieces: an outer core (about 2200 km), a fluid layer

s e m hot, spinning metal
mainly of iron and nickel, and an inner core (about 1250 km), a solid,

. omthat is the densest part of the Earth.
cball a gla
a em
s Two layers cut across this three-fold division, and they are the ones plate tectonics actually
ag l
.c
needs:

s e m
m a
agl
Lithosphere — the rigid outer shell, about 100 km thick: the crust plus the upper part of the
. co
m
mantle. This is the layer that is broken into plates.

l a se
Asthenosphere — about 200 km thick, a hot, mobile layer of partially molten rock lying
ag Because it can flow, the plates above can move.
beneath the lithosphere.

co m
m .
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.co


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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Check the figures against the radius in Fig. 2.1:

crust + mantle (2900) + outer core (2200) + inner core (1250)

= 2900 + 2200 + 1250 = 6350 km
Fig. 2.1 marks the distance from surface to centre as 6375 km — the two agree, as they

should, since the caption says the values are approximate.

Why the layers differ: they are sorted by density. The heaviest material — iron and
nickel — sank to the centre, and the lightest rock floated to the top as the crust. That
is why the inner core is the densest part of the Earth and the crust the lightest, and
why continental crust rides higher than oceanic crust.

Q2 Interior forces of the Earth (earthquakes, volcanoes, folding, and faulting) are
responsible for the movement of the crust.

ANSWER

What this recap means, expanded. These four are the visible signs of one hidden cause — the
slow movement of the plates driven by convection currents in the mantle.

INTERIOR WHAT IT DOES TO THE CRUST WHERE IT HAPPENS
FORCE

Folding Rock layers are squeezed sideways and Convergent boundaries where two
buckle into waves instead of breaking continental plates collide — the Himalaya

Faulting Rock cracks and one block slips past or Wherever the crust is stretched or sheared
over another; blocks are raised or — rift valleys, transform boundaries
dropped

Earthquakes Strain stored in locked rock is released in All three kinds of boundary; the San
a sudden slip, and the ground shakes Andreas Fault is the transform example

Volcanoes Magma reaches the surface and builds Where an oceanic plate sinks under a
new land out of lava and ash continental one, and where plates pull
apart

Why these forces are called constructive: all four add relief — they raise land,
thicken crust, build cones and open basins. They work against the external agents,
which do the opposite. Every landscape you see is a snapshot of that contest.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Note the direction of the logic: the recap line says these forces are responsible for
the movement of the crust. It is more exact to say that the movement of the plates
and these four phenomena share a single cause — the heat escaping from the
Earth's interior, shown in Fig. 2.2 — and that folding, faulting, earthquakes and
eruptions are how that movement shows itself at the surface.

Q3 External forces like weathering and erosion carve smaller landforms over the
Earth's surface which affect human life in multiple ways.

ANSWER

What this recap means, expanded. The internal forces make the big shapes; the external
forces do the carving that decides what the land is actually like to live on.
The two are not the same process, and the chapter is careful about the difference:

WEATHERING EROSION

What Rock breaks into smaller pieces Material is worn away
happens and carried off

Movement? No — the pieces stay where they are Yes — movement is the
whole point

Types Physical (heating and cooling, water, wind, ice expansion), Water, wind, glacial,
chemical (substances in the air and in rain), biological (plants coastal — Fig. 2.9
and animals) — Fig. 2.8

Result Broken rock, and the beginning of soil Valleys, cliffs, caves,
deltas — the shaped
landscape

The order matters: weathering has to come first. Erosion can only carry away material that has
already been loosened. That is why the two are always described together as the pair that wears
down mountains, carves valleys, forms plains and creates caves, cliffs and river deltas.
And the effect on human life is direct. Weathering makes the soil that farming depends on.
Erosion, unchecked, takes that same soil away: page 21 lists the consequences — lower yields
for farmers, land, houses and roads washed away near rivers and coasts, unstable ground for
construction and mining, and losses to tourism and fishing when beaches, rivers and fertile
lands are destroyed.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Why the same process can help and harm: erosion in one place is deposition in
another. The silt stripped from a hillside is the silt that builds the fertile floodplain
and delta downstream. Whether it is a loss or a gain depends on where you are
standing.

Q4 The surface of the Earth is carved by agents of gradation like running water, waves
and tides, glaciers, wind, and underground water.

ANSWER

What this recap means, expanded. Agents of gradation are the natural forces that wear
down, transport and deposit material, and so level or smooth the surface over time. Gradation
means bringing to a common grade — lowering the high ground and filling the hollows.

AGENT WHAT IT DOES (PAGE 22) ITS SIGNATURE LANDFORMS

Running water Erodes rocks and soils to form V-shaped valleys, waterfalls, rapids, meanders,
valleys and plains oxbow lakes, floodplains, deltas, levees, alluvial
fans

Glaciers Scrape and carry huge amounts of U-shaped valleys, cirques, aretes, hanging valleys,
material, carving U-shaped valleys fjords, moraines

Wind Shapes deserts by eroding and Yardangs, ventifacts, deflation hollows, desert
depositing sand pavements, dunes

Waves and tides Erode coastlines to form cliffs, Sea cliffs, shore platforms, sea caves, arches,
beaches and bays stacks, beaches, sand bars

Underground Dissolves rocks such as limestone, Caves, stalactites, stalagmites, pillars, sinkholes,
water creating caves and sinkholes underground rivers — Karst topography

Why each agent leaves a different shape: each one carries material differently. Ice
is rigid and holds everything it picks up, so it grinds a broad U-shaped trough. Water
is fluid and cuts hardest along the line of fastest flow, so it saws a narrow V. Wind
can lift only fine grains, so it sorts the desert — carrying dust away, piling sand into
dunes, and leaving the coarse stones as a desert pavement. Groundwater does not
carve at all; it dissolves, so its landforms are hollows and dripstone. Recognise the
shape and you can name the agent.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Q5 Disasters like landslides, avalanches, glacial lake outflows, and sandstorms are
associated with specific landforms.

ANSWER

What this recap means, expanded. A disaster does not strike just anywhere. Each one needs a
particular landform to be possible at all — so knowing the landform tells you the hazard in
advance.

DISASTER LANDFORM IT MAIN CAUSES GIVEN IN THE CHAPTER
NEEDS

Landslide Steep slopes with loose Heavy continuous rainfall (water seeps in, adds weight, reduces
or weathered rock friction); earthquakes and eruptions; deforestation, mining,
road building and unplanned hillside construction; poor
drainage and improper land use

Avalanche Steep snow-covered Heavy snowfall in a short time on weakly bonded layers; a
mountain slopes sudden rise in temperature that melts snow and reduces
friction; strong winds piling snow unevenly; earthquakes and
vibrations; skiing, trekking and construction

GLOF (glacial Glacial valleys holding Rapid glacier melting from rising temperatures raising the lake
lake outflow) lakes behind ice or level; heavy rain or snow adding water; earthquakes,
moraine dams avalanches or landslides striking the lake or weakening the
dam, which then collapses

Dust storm Deserts and semi-arid Strong winds lifting dry soil; prolonged drought and low
plains with loose, dry rainfall; sparse vegetation from deforestation, overgrazing or
soil poor farming; climate change and extreme weather

The common thread: in every one of the four, something is held in place only by
friction — soil on a slope, snow on a slope, water behind a moraine dam, dust on dry
ground. Add water, heat, shaking or wind and the friction gives way all at once. That
is why these disasters are sudden, and why mitigation almost always means
increasing the friction (roots, bunds, barriers) or removing the load (drainage,
controlled release) before it fails.

Note the human share: three of the four lists above contain human causes —
deforestation, mining, unplanned construction, overgrazing, poor farming. These
are hazards we make worse ourselves, which also means they are hazards we can
reduce.

Page 33 of 60

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co m
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Questions and activities — Pages 37–38
m as e
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End-of-chapter exercise
a g l
a s em
aQ1gl What are the sources of energy that are required to cause movements associated
with the internal forces of the Earth?

co m
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as
ANSWER

a g l
The energy comes from the heat stored inside the Earth — what Fig. 2.2 labels the total
interior heat flow. As that heat escapes outward it stirs the mantle, and the stirring mantle
moves the plates.
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Share of the Earth's total interior heat flow

agl Crust 24% Magma zones

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Heat transport mechanism

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Advection

Lower mantle
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Convection

convection cells in the mantle Conduction

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Outer core 22% Heat from the core melts rock in the

m a
mantle. The molten material rises,

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convection in the outer core cools, and sinks again — the loops

agl
drawn here. These convection
currents drag the plates above them.

m
conduction out of the inner core

se
Inner core

com g l a
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Fig. 2.2, page 15 — movement of material below the crust. The percentages are the shares of the
Earth's total interior heat flow printed in the book, and the loops are its convection cells.

c o m
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Where the heat comes from. Fig. 2.2 divides the total interior heat flow

. com a gla
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24 + 22 + 32 + 22 = 100% a

co m
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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Read that carefully, because it corrects a common idea. The core supplies only about a fifth of
the heat; the crust and mantle together supply 24 + 22 + 32 = 78%. So the Earth's engine is not
just a hot ball at the centre warming everything above it — heat is being produced through the
crust and mantle themselves as well.
How that heat is carried outward. Fig. 2.2 names three mechanisms:

Conduction — heat passing through solid rock from hot to cold, without the rock moving.
Shown by the straight red arrows through the crust.
Convection — the important one for plate movement. Hot material in the mantle expands,
becomes lighter and rises; cooler material near the top is denser and sinks. The loops
drawn in Fig. 2.2 are these convection cells, and page 15 says plainly that they "push and pull
the tectonic plates, causing them to move in different directions".
Advection — heat carried along by material actually moving from place to place, as when
magma rises into the magma zones marked in red just below the crust.

Why heat can move a continent: a temperature difference makes a density
difference, and a density difference in a layer that can flow makes it circulate — the
same reason hot water rises in a pan and cool water sinks. The asthenosphere is
partially molten, so it can flow. The rigid plates sit on top of that flow and are
dragged along with it. Gravity helps: once the edge of a cold, dense plate starts to
sink into the mantle, its own weight keeps pulling the rest of the plate after it.

Tip for the exam: answer in two parts — the source (the Earth's interior heat, with
Fig. 2.2's shares) and the mechanism (convection currents in the mantle, aided by
conduction and advection). A one-word answer, "heat", misses half the question.

Q2 Relate various physiographic divisions you have studied in the earlier grades with
various endogenic forces responsible for their origin.

ANSWER

Endogenic forces are the internal forces of the Earth — plate movement, folding, faulting,
earthquakes and volcanic activity. Every major physiographic division of India can be traced
back to one of them.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

PHYSIOGRAPHIC ENDOGENIC HOW IT WORKED
DIVISION FORCE
RESPONSIBLE

The Himalaya and the Plate collision and The Indo-Australian plate moved north into the
northern mountains folding at a convergent Eurasian plate. Neither could sink, so the sediments
boundary and rock between them were squeezed and
crumpled upward into fold mountains. Fig. 2.3 shows
the arrows still pointing north — which is why the
range is still rising and still shaking.

The Northern Plains Plate collision The same collision left a deep trough between the
(indirectly), then rising Himalaya and the old peninsular block. The
deposition Indus, Ganga and Brahmaputra have been filling
that trough with alluvium ever since. The basin is
endogenic; the filling is exogenic.

The Peninsular Plateau Ancient crustal It is one of the oldest and most stable blocks of crust
movement, faulting in the world. Later, block faulting raised ranges such
and volcanic activity as the Satpura and dropped the Narmada and Tapi
valleys between them, and huge lava flows spread
over the north-west of the plateau to form the
Deccan trap country.

The Western and Faulting and uplift of The steep, straight western edge is a faulted margin,
Eastern Ghats the plateau edge which is why the Western Ghats drop sharply to the
coast while the Eastern Ghats are lower and broken
by rivers.

The Coastal Plains Uplift and subsidence Vertical movements of the crust raised parts of the
of the continental sea floor and drowned others; rivers then built
margin deltas on top — the Sundarbans of Fig. 2.13 among
them.

The Indian Desert Uplift of the crust; Its rock floor is an extension of the peninsular block.
(Thar) then wind action The dunes and deflation hollows on top of it are the
work of wind — again, endogenic base, exogenic
surface.

The Andaman and Convergent plate They are the tops of a submarine ridge raised where
Nicobar Islands boundary and volcanic plates converge — the same arc that continues into
activity Indonesia, which is why Fig. 2.4 shows the belt of
earthquakes and volcanoes passing straight through
them. The mud volcano at Baratang, described on
page 19, lies in this island group.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

The general rule: endogenic forces supply the relief — they decide where the land
is high and where it is low. Exogenic agents then supply the detail — the valleys,
plains, deltas and dunes cut into and laid over that relief. Almost every division
above is a partnership of the two, and naming which force did which part is exactly
what this question asks for.

Q3 Why and where do earthquakes occur frequently? Is it possible to predict
earthquakes?

ANSWER

Why they occur. Tectonic plates are moving all the time, but their edges are rough and are
locked together by friction. The plates keep pushing, and strain builds up in the locked rock.
When the strain finally exceeds the strength of the rock, the two sides slip suddenly. The stored
energy is released as vibrations that travel outward — and the ground shakes. That is an
earthquake.
Where they occur frequently — along plate boundaries. Fig. 2.4 shows it directly: the
earthquake origins form narrow belts, and every belt lies on a boundary in Fig. 2.3.

BELT BOUNDARY TYPE CHARACTER OF THE
EARTHQUAKES

The Ring of Fire around Convergent — oceanic plates The most numerous and the most violent;
the Pacific sinking beneath continental plates volcanoes here too

Mediterranean – Convergent — African and Indo- Large, destructive; this is India's belt
Himalaya – Indonesia Australian plates pressing into
Eurasia

The mid-ocean ridges, Divergent Frequent but generally smaller and
e.g. the Mid-Atlantic mostly under the sea

The San Andreas Fault, Transform Frequent, shallow and damaging; few
USA volcanoes, because no magma is supplied

Plate interiors — peninsular India, central Siberia, the Sahara, inland Australia — are
comparatively quiet, because the crust there is neither being squeezed nor pulled nor sheared.
Is it possible to predict earthquakes? No — not in the exact sense the word "predict"
usually means. Nobody can say that an earthquake of a given size will strike a given place on a
given day. There are two reasons: the rock that will break lies many kilometres underground
where we cannot watch it directly, and the exact moment of failure depends on tiny details of
the rock and the friction on the fault.
But a great deal is possible, and it saves lives:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Long-term forecasting. We know where earthquakes will happen, because we know where
the boundaries are. India's seismic zoning map divides the country by expected shaking so
that buildings can be designed for it.
Early warning of seconds. The first, faster waves from an earthquake can be detected and
an alert sent electronically before the slower, more destructive waves arrive — enough to
stop trains and shut gas lines.
Preparedness — earthquake-resistant construction, drills, and public awareness. This is the
only defence that reliably works.

Why "where" is easy but "when" is not: the where is fixed by geography — plate
boundaries do not move about. The when depends on the moment a rough patch of
rock finally gives way, and that is like asking exactly when a stretched rubber band
will snap. You know it will; you cannot say on which second.

Did you know? Page 18 notes that earthquakes were studied in India long ago as
bhūkampa, "the shaking of the Earth". In the Bṛihatsaṁhitā, Varāhamihira devoted a
section to them, noting that changes in wind, rain, clouds, animal behaviour and
planetary alignments might signal them, and attributing them to four elemental
forces — Vāyu (wind), Agni (fire), Indra (heaven/thunder) and Varuṇa (water). It was
an early attempt to look for observable warning signs — the same instinct that
drives earthquake research today.

Q4 “Plate movements are responsible for the distribution of earthquakes and
volcanoes.” Explain.

ANSWER

The statement is correct, and Figs. 2.3 and 2.4 together are the proof. If earthquakes and
volcanoes had some other cause, they would be scattered across the globe. They are not — they
lie in narrow belts, and those belts are the plate boundaries.
Step 1 — the evidence. Put the two maps side by side. Every dense band of red dots and black
triangles in Fig. 2.4 falls on a line where two plates meet in Fig. 2.3: right round the rim of the
Pacific, along the Mediterranean–Himalaya–Indonesia line, down the middle of the Atlantic, and
along East Africa. The interiors of the plates are nearly empty. A match that close cannot be
coincidence.
Step 2 — the mechanism, boundary by boundary.

Page 38 of 60

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface l AglaSem · NCERT Solutions

c o m
.
1. Divergent — plates move apart
m ridge of new crust s em
2. Convergent — ocean meets continent
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magma rises into the gap

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Mid-Atlantic Ridge
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3. Convergent — continent meets continent
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4. Transform — plates slide past
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fold mountains — the Himalaya

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fault line — San Andreas

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The three plate boundaries (with convergence shown in its two forms). Panels 1–3 are cross-sections;

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move.

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Convergent, continent against continent. Neither slab is dense enough to sink, so the

a gl crust between them is squeezed, crumpled and thickened into fold mountains — the
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Himalaya. The rocks jam and slip repeatedly, so this belt has severe earthquakes. There is
little melting, so few volcanoes.
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Convergent, ocean against continent. Oceanic crust is thin and heavy (5 km, against 30 km

g l asso it sinks beneath the continental plate. The descending slab
for continental crust, Fig. 2.1),
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com
volcanoes and earthquakes. This is why the Pacific rim is called the Ring of Fire.

.
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Divergent. The plates pull apart, magma rises into the gap and forms new crust, building

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mid-ocean ridges such as the Mid-Atlantic Ridge. The cracking crust
o moderate earthquakes, and the eruptions happen
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why Fig. 2.4 shows a line of red dots down the Atlantic with few triangles beside it.
a g
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Transform. The plates slide past each other, so no crust is created or destroyed and there is

m .
no magma. The result is earthquakes without volcanoes, as along the San Andreas Fault.
m a s e
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Step 3 — the conclusion. Each type of movement produces a different combination of

l a se each type occurs at a known place on the map. Therefore the
earthquakes and volcanoes, and
ag is the pattern of earthquakes and volcanoes. That is why page 16
pattern of plate movement

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says the theory is important for identifying earthquake- and volcano-prone regions and
managing the disasters that arise there.

Q5 Draw and label a diagram of a meander and a delta.

ANSWER

Draw each one in plan view — as seen from above — and label the parts the chapter names.
Use the labels of Fig. 2.11 for the meander and Fig. 2.12 for the delta.
(a) Meander — a winding curve or bend in the middle or lower course of a river, formed by
lateral erosion and deposition of sediments.

2 Steep bank (outer bend) — fast flow, erosion

3 River

4 Bar (inner bend) — slow flow, deposition

1 Oxbow lake — a cut-off meander loop

Cross-section through the bend (why the two banks differ)
gentle slope steep bank,

sediment piles up (bar) undercut by the current

deepest, fastest water hugs the outer bank

A meander in plan and in section. The river swings to the outside of every bend, so it erodes there
and deposits on the inside — and the loop grows sideways year after year until its neck is cut through
and an oxbow lake is left behind.

Why a river bends at all, and why the bend deepens: water flowing round a curve
is thrown to the outside, so the current is fastest and the channel deepest against
the outer bank. Fast water erodes — the bank is undercut and becomes steep. On
the inner bank the water is slow and shallow, so it drops the sediment it was
carrying and builds a bar. Erosion on one side and deposition on the other means
the whole loop migrates outward, exactly as page 24 says.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

(b) Delta — the landform built at the mouth of a river where it enters a sea, ocean or lake and
deposits the sediment it has carried from upstream, until the deposits form a fan-shaped or
triangular area of land.

2 Distributaries

3 Islands / bars
1 River (main channel)

4 Sea

Land built by the river

The whole deposit takes a fan-shaped or triangular outline — hence the name “delta”.

A delta in plan view, labelled as in Fig. 2.12. One channel arrives from the left and splits into
distributaries that wander between low islands and bars of freshly deposited sediment before
reaching the sea.

Why a delta forms where it does: a river carries sediment only as long as it is
moving fast. At the mouth it meets standing water, loses its speed almost at once,
and has to drop its load. The deposit blocks its own channel, so the river splits round
the obstacle into distributaries — and repeats the process at each new mouth. That
is how the fan grows outward into the sea.

When you draw these in your book: use the numbered labels from Figs. 2.11 and
2.12 — meander: 1 Oxbow lake, 2 Steep bank, 3 River, 4 Bar; delta: 1 River, 2
Distributary, 3 Islands/Bars, 4 Sea. Mark the direction of flow with an arrow, and add
a red arrow on the outer bank and a green one on the inner bank of the meander to
show erosion and deposition.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Q6 How are deforestation and erosion associated with each other? Explain.

ANSWER

They are linked as cause and effect: deforestation removes the protection that keeps soil
in place, and erosion is what follows. Page 33 names deforestation among the human
activities that "disturb the natural balance of slopes", and page 36 names sparse vegetation
cover due to deforestation as a cause of dust storms.
What a forest actually does for the soil — four separate jobs:

1. The canopy breaks the fall of rain. A raindrop striking bare soil hits it hard enough to knock
the particles loose. Leaves intercept the drops, so the water reaches the ground gently.
2. Roots bind the soil. A network of roots holds the particles together and anchors the whole
layer to the rock beneath it.
3. Litter on the forest floor slows the run-off. Slower water carries less material, and more of
it soaks in instead of racing downhill.
4. Trees slow the wind at ground level, so fine dry particles are not lifted away.

Remove the trees and all four fail at once:

Deforestation

→ bare soil exposed to raindrops and wind

→ no roots to bind the particles, no litter to slow the flow

→ run-off increases, soaks in less, and concentrates into rills

→ rills deepen into gullies (Fig. 2.9a); fine soil is blown away by wind (Fig. 2.9b)

→ fertile topsoil lost, slopes destabilised

And the damage does not stop at the soil. The chapter traces the chain further:

Water that no longer soaks in seeps into loose rock instead, adding weight and reducing
friction — one of the main causes of landslides (page 33).
The eroded material is carried into rivers and reservoirs, silting them up and adding to
flooding downstream.
In dry regions, the bare, exposed land loses its fine particles to the wind, feeding dust
storms and leading towards desertification (page 36).
Farmers lose topsoil and yields fall; land near rivers and coasts is washed away (page 21).

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Why the relationship also runs backwards: erosion makes deforestation harder to
reverse. Once the topsoil has gone, there is little for a seedling to root in, so the
forest does not come back on its own. This is why the mitigation lists in this chapter
always pair afforestation with physical works — bunds, terraces and check dams —
that hold the soil long enough for the new trees to take hold. Page 21 gives India's
own examples: contouring, bunding, terracing, dams and canals described in the
Vedas, the Kṛiṣhiparāśhara, Kauṭilya's Arthaśhāstra and the Vṛikṣhāyurveda, and the
Zabo system of Nagaland with its earthen bunds on hill slopes and check dams
across small streams.

Q7 Develop a plan to protect the land in your local area from erosion.

ANSWER

Method. A plan has to fit the land it is written for, so build it in four steps: (1) survey — find
where soil is actually being lost; (2) diagnose — decide whether the agent is water or wind; (3)
choose measures that match; (4) say who will do what, and how you will check whether it
worked.
What a good plan must contain: the name of your area and its terrain; the evidence of erosion
you have seen with your own eyes; the agent responsible; at least three measures with a reason
for each; the people or bodies who must act (school, gram panchayat, farmers, forest
department, municipality); and a way to measure success.
Sample answer:
Step 1 — Survey. Walk the area after a heavy shower and mark on a rough sketch map: bare
slopes, rills and gullies, spots where roots are exposed above the soil, gullies at the ends of
drains, muddy water in the local stream, and any field where sand is drifting.
Step 2 — Diagnose. Muddy run-off, rills and gullies, and exposed roots mean water erosion.
Drifting sand, dust in the air and coarse grit left on the surface mean wind erosion. Most places
have some of both.
Step 3 — The measures.

Page 43 of 60

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface l AglaSem · NCERT Solutions

co m
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MEASURE WHERE TO USE IT WHY IT WORKS

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Afforestation and grass Bare slopes, gully heads,
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Canopy softens the rain, roots bind the soil, litter

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cover stream banks, the school slows the run-off

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compound

Contour bunding and Cultivated hill slopes Earthen embankments and trenches along the

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contour trenches (CCT) contour hold rainwater where it falls, so it soaks in

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Terracing
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water never gathers speed

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Check dams across small Gullies and seasonal Slow the water, trap sediment behind the wall and

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streams nullahs recharge groundwater — the Zabo idea from

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Nagaland

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a windbreaks
Shelter belts and Field edges in dry, open
country
Rows of trees cut the wind speed near the ground
so fine soil is not lifted

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Cover crops and stubble Fields between harvest Never leave the soil bare — bare soil is the one
mulching and sowing
a s em thing every kind of erosion needs

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Controlled grazing; no Common land and Removes the human causes listed on pages 33 and
hillsides
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construction on steep 36 before they act

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Proper drains along Road cuttings and built-up Concentrated run-off from a road is a common

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agl Step 4 — Who does what, and how we check. The school Eco Club plants and waters saplings
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on the bare slope and keeps the drains clear; the gram panchayat or municipal ward takes up

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the bunds, check dams and road drains; farmers
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try contour ploughing and a cover crop on one
a
l a se the depth of one gully with a scale every month, and note
plot each as a demonstration. To check results, photograph the same three spots at the start

ag
and end of each monsoon, measure
whether the stream water runs clearer after rain than it did last year.

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The principle behind every item on the list: erosion needs three

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oman agent (moving water or wind) and a slope or aagdistance for the material to

as em travel down. Break any one of the three and erosion stops. Cover crops remove the
agl first; windbreaks and bunds weaken the second; terraces and check dams cut the
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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Q8 Which disasters do you think you might experience in your region? Discuss a
mitigation plan in your classroom.

ANSWER

Method. Do not guess. Work it out from the land you live on, because — as the chapter shows
on pages 33–36 — each disaster needs a particular landform. Answer in three steps: name your
region's terrain, list the hazards that terrain allows, then write the mitigation plan for the most
likely one.
What a good answer needs: your region and its landform; two or three hazards that genuinely
apply, with the reason each is possible there; a mitigation plan divided into before / during /
after; and the names of the people and bodies who would have to act.
Match your region to its hazards:

IF YOU LIVE IN LIKELY DISASTERS BECAUSE
…

The Himalayan or Landslides, earthquakes, avalanches, Steep young fold mountains on an active
north-eastern hills GLOFs, flash floods convergent boundary, with glaciers
above

The Northern Plains River floods; strong earthquake Flat land, large rivers, thick soft alluvium
shaking; pre-monsoon dust storms in close to the Himalayan source
the west

Rajasthan and the Dust storms, drought, desertification Loose dry soil, sparse vegetation, strong
dry west summer winds

The coasts and deltas Cyclones, storm surges, coastal erosion, Low flat land at sea level, exposed to
tsunami on the east coast waves and currents

The Western Ghats Landslides and flash floods in the Steep faulted slopes with very heavy
and Nilgiris monsoon rainfall

The peninsular Drought; local flooding; mild Old stable crust, but uneven rainfall
plateau earthquakes

Kachchh, Gujarat Earthquakes (Fig. 2.5, 2001), cyclones An active fault zone within the plate
on the coast

Sample answer (for a town in the Himalayan foothills): My region is hilly, with steep slopes
cut by a road and by streams that swell in the monsoon, so the disasters most likely here are
landslides and earthquakes, with the risk of a flash flood in the valley.
Our classroom mitigation plan for landslides:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Before — plant and protect trees on the bare slopes above the school; keep drains and weep
holes open so water does not build up inside the slope; do not allow building on steep slopes
or in the path of the nullah; learn the warning signs (new cracks in walls or ground, tilting
trees and poles, suddenly muddy stream water, unusual sounds from the hillside) and report
them to the tehsil office; keep a family emergency kit and an agreed meeting point.
During — stay calm and ignore rumours; stay together with your companions; move away
quickly from the landslip path and out of the valley below it; inform the nearest tehsil or
district headquarters.
After — do not touch or walk over loose material, fallen electrical wires or poles; check for
injured and trapped people; do not move an injured person without first aid unless they are
in immediate danger; do not drink water directly from rivers, springs or wells, which may be
contaminated.

Who acts: the school (drills, tree planting, awareness posters), the gram panchayat or municipal
ward (drainage, retaining walls, building rules), the district disaster management authority
(warning and rescue), and every family (kit, meeting point, knowing the signs).

How to run the classroom discussion: divide the class into four groups — hazard
mapping, prevention, warning and response, and after-care. Each group presents for
five minutes, then combine the four into one page and put it on the school notice
board. A plan nobody has read is not a plan.

Q9 Prepare a model of landforms created by underground water.

ANSWER

What you are modelling. The landforms of underground water are together called Karst
topography (page 31). They form where the rock is limestone or another soluble rock, and
where slightly acidic rainwater seeps through it, dissolving the rock from within. Your model
must show both halves of the process — the hollows dissolved out and the dripstone built
back up.
The landforms to include, from page 31:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

LANDFORM WHAT IT IS MADE BY

Cave A hollow space formed as acidic water dissolves Solution — rock removed
the rock

Stalactite An icicle-shaped formation hanging from the Deposition — rock added, drop
ceiling of a cave by drop

Stalagmite A formation rising from the floor of a cave Deposition, from the same drips
landing below

Pillar Formed where a stalactite and a stalagmite meet Deposition, over a very long time
and join (Fig. 2.24)

Sinkhole (doline) A depression formed when the ground collapses Collapse, after solution has
into an underground cavity hollowed out the roof

Underground A river flowing through the cave system Solution and erosion together
river

1 Sinkhole (doline)

Limestone
2 Stalactites — hang from the ceiling

5 Cave

6 Underground river

4 Pillar 3 Stalagmites — rise from the floor

The karst landforms of page 31 in one section: rainwater sinks through the limestone, dissolves out a
cave, and the water dripping inside slowly rebuilds rock as stalactites, stalagmites and pillars. Where
the roof over a cavity gives way, a sinkhole opens at the surface.

How to make the model (materials you already have):

1. The block of rock. Take a shoebox or a tray. Build up a solid mass of clay, plaster of Paris or
papier-mâché to about three-quarters of the height. Colour the outside pale grey and label it
limestone.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

2. The cave. Before it sets, press a crumpled ball of newspaper or a small plastic bottle into the
middle to make a chamber, then remove it once the material has hardened. Cut away one
end of the box so the cave can be seen in section, and leave a cave mouth on that face.
3. Stalactites and stalagmites. Roll thin cones of clay. Glue the pointed ones to the ceiling
(stalactites) and the blunt ones to the floor (stalagmites) directly below them. Join one pair to
make a pillar. A trick that looks very real: dribble thin plaster from a spoon onto the ceiling
and let it hang as it sets.
4. The sinkhole. On the top surface, press a rounded hollow above one end of the cave and
colour its inside like bare rock, with green paper grass around the rim.
5. The underground river. Lay a strip of blue paper or foil along the cave floor and out
through the mouth.
6. Label everything with pins and paper flags: limestone, sinkhole, cave, stalactite, stalagmite,
pillar, underground river, cave mouth — the labels of Figs. 2.24 and 2.25.

The science to write on the model card: rainwater takes in gases from the air and
the soil and becomes slightly acidic. As it seeps down through joints in the limestone
it dissolves the rock, widening the cracks into passages and then chambers. Inside
the cave the water hangs as a drop from the ceiling; some of the dissolved rock is
left behind when the drop evaporates, so the ceiling grows downward as a stalactite,
and the rest is deposited where the drop lands, so the floor grows upward as a
stalagmite. Given long enough, the two meet and become a pillar. Underground
water therefore does both jobs at once — it removes rock in one place and rebuilds
it a few centimetres away.

Try this demonstration: put a piece of chalk (which is a form of limestone) in a glass
of water and another in a glass of lemon juice or vinegar. The one in the acid fizzes
and wears away far faster. That is Karst topography happening in a glass — and it is
why the chapter files caves under chemical weathering and erosion.

Q10 What precautionary measures will you take if you are staying in an earthquake-
prone region?

ANSWER

Take them in three stages, because an earthquake gives no warning — everything useful has to
be done before it happens.
Before the earthquake

Build or retrofit to resist shaking. This is the single most important measure, because Fig.
2.5 shows what kills people — collapsing buildings, not the ground itself. Follow earthquake-
resistant building codes; use reinforced columns and beams and tied brickwork; avoid heavy

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface l AglaSem · NCERT Solutions

stone or concrete roofs on weak walls; and do not add unauthorised extra floors.
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Make the inside of the house safe. Fasten cupboards, shelves, mirrors and water heaters
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near the door.
Agree a family plan — a meeting
number, and who will fetch the youngest child.

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During the earthquake
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If you are in a vehicle, stop in the open, away from bridges and flyovers, and stay inside.
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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Q11 Prepare a map showing landform-associated disasters that happened in the
current calendar year.

ANSWER

Method. This is a data-collection and mapping exercise, and it is judged on accuracy and clarity,
not decoration. Work through it in five steps.

1. Collect. Keep a notebook for a few weeks and record every disaster report you find in
newspapers, on official bulletins or in the news. For each one write down: the disaster, the
exact place, the district and state, the date, and the source. Never enter an event you cannot
date and source.
2. Sort by type, using the chapter's own four categories plus earthquakes: landslide,
avalanche, GLOF, dust storm, earthquake. Add flood and cyclone if your region needs them.
3. Choose the base map. An outline political map of India with state boundaries works best;
add a world outline map on the same sheet if you are collecting global events too.
4. Design the symbols before you start plotting. One symbol per disaster type, a different
colour for each, all of the same size — for example a brown triangle for a landslide, a white
star for an avalanche, a blue circle for a GLOF, a yellow square for a dust storm, a red star for
an earthquake. Put them in a legend in the corner.
5. Plot and finish. Place each symbol at the correct location, number it, and give a numbered
table below the map with date, place and a one-line description. Add a title, the legend, a
north arrow and the scale.

What a good map will show — and what you should write underneath it. Once your
symbols are on the sheet, they will not be scattered evenly. Look for the pattern and write two
or three sentences about it, because that is the real point of the exercise:

EXPECT TO FIND BECAUSE

Landslides clustered along the Himalaya, the north-east and the Steep slopes plus heavy monsoon rainfall
Western Ghats

Avalanches and GLOFs only in the high Himalaya They need snow and glacial lakes, which exist
nowhere else in India

Dust storms in Rajasthan, Gujarat, Haryana, Punjab and Delhi, Dry loose soil, sparse vegetation and strong pre-
mostly in the hot months monsoon winds

Earthquakes along the Himalayan arc, in Kachchh and in the The convergent plate boundary of Figs. 2.3 and
Andaman Islands 2.4

Cyclone damage on the east coast, floods in the plains Low, flat coastal land and large rivers

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

The conclusion your map will demonstrate: disasters are not distributed randomly
— they follow landforms. Your finished map should look like a physical map of
India seen through its hazards, which is exactly what the chapter claims on page 32
and what the plate maps in Figs. 2.3 and 2.4 show at world scale.

Tip: mark the month next to each symbol. You will discover a seasonal pattern too —
landslides and floods in the monsoon, avalanches in winter, dust storms in the pre-
monsoon heat.

Q12 Create a poster showing landforms that are considered to be sacred or important
in your region, and add the folk stories associated with them.

ANSWER

Method. Start from the land, not from the internet. Walk or think through your own district and
list the natural features people treat with respect — a hill, a river confluence, a spring, a cave, a
waterfall, a grove, a rock. Then find the story attached to each by asking older people in your
family and neighbourhood, and note who told you.
What a good poster must contain:

A title and the name of your region.
Four to six landforms, each with a picture or a careful sketch.
For each one: its name, the type of landform in the chapter's vocabulary (hill, cave,
waterfall, river confluence, spring, sea cliff, sacred grove), the folk story or belief in two or
three sentences, and who told you or where you read it.
A closing line on why it matters — what these beliefs do for the landform itself.
A small map of your district with the sites marked.

Sample answer (adapt it to your own region):

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

LANDFORM TYPE WHY IT IS HELD SACRED OR IMPORTANT

The hill above our Residual hill A shrine stands on the summit and a fair is held there every year.
town Elders say the hill "watches over" the town, and no tree on it may
be cut.

The confluence of the River People bathe here on festival days. The story is that the two
two streams confluence streams are sisters who meet once and travel on together — which
is why the spot is used for family rituals.

The spring at the foot Spring — Said never to have dried up even in the worst drought. Villagers
of the ridge groundwater keep the area around it clean and do not wash clothes there.

The cave in the Cave — Karst Stalactites inside are described in local stories as a stone forest. A
limestone hill lamp is lit at the mouth on one day each year.

The old grove near Sacred grove Nothing may be taken from it, not even a fallen branch. It is the
the fields last patch of original forest left in the area.

Closing line for the poster: "These stories are not only beliefs — they are rules. A hill that may
not be cleared does not slide; a grove that may not be cut holds its soil; a spring that must be
kept clean keeps giving water. Our folk stories have been protecting our landforms for
generations."

Why this activity belongs in this chapter: page 22 makes the point that landforms
have shaped human history — rivers and plains produced early cities, mountains
acted as barriers and protectors, deserts pushed people onto trade routes, coasts
opened trade with distant lands. Sacred landforms are the same relationship seen
from the other side: the culture that a landform produced, turned back into care for
the landform. Recording these stories is a way of recording that link before it is lost.

Tip: write down the name and age of everyone you interview and the date. That
turns your poster from a collection of stories into a piece of documentation your
school can keep.

Q13 Document a case of a disaster that hit your region in the past, highlighting its
effects on various human activities.

ANSWER

Method. Documenting is different from describing. You need sources — newspaper reports
from the time, official records, photographs, and interviews with people who lived through it —
and you must say where each fact came from.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Structure your report under these headings:

1. The event — what happened, exactly where, and on what date.
2. The landform setting — the terrain that made this disaster possible, in the chapter's terms
(a steep slope, a floodplain, a low coast, a fault zone).
3. The causes — natural and human, using the cause lists on pages 33–36.
4. The effects on human activities — the heart of the report, set out activity by activity.
5. The response — rescue, relief, rebuilding; what worked and what did not.
6. Lessons and what has changed since.
7. Sources — newspapers with dates, and the names of people you interviewed.

Use this grid for section 4, so nothing is missed:

HUMAN ACTIVITY WHAT TO RECORD

Agriculture Crops lost, fields buried under sand or debris, livestock killed, irrigation channels
broken

Housing and settlement Houses damaged or destroyed, families displaced, how long they stayed in relief
camps

Transport and Roads, bridges, railway lines and phone links cut; villages left unreachable and for
communication how many days

Trade and industry Shops and markets shut, workdays lost, small businesses that never reopened

Tourism Visitors cancelled, hotels and guides without work in the season that followed

Water, power and health Water sources contaminated, power lines down, hospitals overloaded, disease
afterwards

Education Schools damaged or used as relief camps, days of teaching lost

Environment Forest and soil lost, river course changed, wildlife affected

Sample answer (an outline you can follow, using the chapter's own case): The Chamoli
flood of February 2021 struck the valleys of the Rishiganga and Dhauliganga in Uttarakhand.
Landform setting: steep, glaciated Himalayan valleys in a young fold mountain range, where a
narrow valley concentrates any flood into a wall of water. Causes: a mass of rock and ice fell from
a high slope, mixed with melting ice and debris, and surged down the valley — a winter event
with no rainfall to warn of it. Effects on human activities: as the THINK ABOUT IT box on page 29
records, many people and livestock lost their lives; buildings, roads and bridges were severely
damaged; hydel projects were destroyed, with workers trapped in the tunnels; and
connectivity to villages was adversely affected, so relief could not reach them and daily
trade, schooling and medical care stopped for days. Response: rescue teams worked at the
tunnel sites; helicopters supplied cut-off villages; temporary bridges restored access. Lessons:

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface l AglaSem · NCERT Solutions

the need for monitoring of high glacial slopes and lakes, for early-warning sirens downstream,
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mountain range.

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Tip:
"What did you do first?" The answer tells you more about preparedness than any
statistic.
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Q14 Translate the given poster on landslide into your native language and display it in

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ANSWER

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What the poster says. Before translating, read the English poster on page 38 carefully. Its title
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and it is divided into three columns:

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BEFORE DURING AFTER
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TV and read the newspaper for any companions; if you notice warning move away from the landslip path and
alerts; keep drains clean and keep signs such as unusual sounds like
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holes open; watch out for warning trees cracking or boulders knocking injured and trapped persons; do NOT

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such as subsidence of a together — move away from the move

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landslip path or downstream valley rendering first aid unless he or she is in
muddy river water; do NOT quickly, and inform the nearest immediate danger; do NOT drink
construct near steep slopes and near Tehsil or District HQ. contaminated water directly from rivers,
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springs, wells etc.
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1. Translate meaning, not words. A safety poster has to be understood at a glance by
someone who is frightened, so use the simplest everyday words of your language, not
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formal or literary ones.

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2. Keep the three-column layout, the picture and the colour coding. The layout is part of the
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5. Check your draft with an adult who speaks the language well, then write it large and neatly,
and display it where a
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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Sample answer — the poster in Hindi (students of other languages should follow the same
pattern in theirs):
भूस्खलन — सुरि त रहने के िलए अभी तैयार रहें। समझदार बने,ं तैयार रहें।

पहले दौरान बाद मे ं

ऐसे अिधक पेड़ लगाएँ जो िम ी को बाँध कर शांत रहे,ं घबराएँ नही ं, अफ़ वाहों पर ध्यान ढीली िम ी-मलबे तथा िबजली के तारों या
रखें; रे िडयो सुन,े ं टी.वी. दे खें और समाचार-पत्र न दे ं; अपने सािथयों के साथ रहे;ं यिद खंभों को न छु ए ँ और न उन पर चले ं;
पढ़ े ं तािक िकसी चेतावनी की जानकारी िमले ; कोई असामान्य आवाज़ सुनाई दे — जैसे भूस्खलन के रास्ते और नीचे की घाटी से
नािलयाँ साफ़ रखें और छे द खुले रखें; चेतावनी पेड़ों के चटकने या पत्थरों के टकराने की तुर ंत दू र हटें; घायल और फँ से हुए लोगों की
के संके तों पर ध्यान दे ं — जैसे भवन का धँस ना, — तो भूस्खलन के रास्ते और नीचे की तलाश करे ं; घायल व्यि त को पाथिमक
च ानों में दरारे ं, नदी के पानी का गँद ला होना; घाटी से तुर ंत दू र हट जाएँ, और िनकटतम उपचार िदए िबना न िहलाएँ, जब तक िक
खड़ी ढलानों के पास और पानी के बहाव के तहसील या िज़ला मुख्यालय को सूिचत उसे तुर ंत ख़तरा न हो; नदी, झरने या कु एँ
रास्ते पर िनम ण न करे ं। करे ं। का दू िषत पानी सीधे न िपएँ।

Why translating it is the point of the activity: a warning works only in the
language people think in. Most of the people most at risk from landslides live in hill
villages and read their own language first. Turning the poster into that language —
and putting it on a wall at home — is a small piece of real disaster mitigation, not
just a classroom exercise.

Q15 Divide the class into three groups. Each group will work on one project (water,
wind, and glacier). The project should highlight the causes, impact on human life
and the environment, and mitigation measures.

ANSWER

Method. All three groups should use the same four headings, so that the projects can be
compared side by side when they are presented: (1) the agent and how it works, (2) the
landforms it creates, (3) its impact on human life and the environment — both good and bad, (4)
mitigation measures. Give each group a wall chart, one map and one model or photograph set.
Group 1 — WATER

How it works: running water erodes, transports and deposits. Steep upper course —
downward erosion; gentler middle course — lateral erosion and the start of deposition;
almost flat lower course — deposition only.
Landforms: V-shaped valleys, waterfalls, rapids; meanders, oxbow lakes, floodplains; deltas,
levees, alluvial fans. Add coastal water too — sea cliffs, shore platforms, caves, arches,
stacks, beaches and sand bars.
Impact — the good: the most fertile land on Earth. Deltas grow rice and jute; meander
banks support farming and settlement; rivers give irrigation (the Grand Anicut, Kallanai, in
Tamil Nadu) and navigation; waterfalls give hydroelectricity and tourism; beaches support
fishing and tourism and shield the coast from waves.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Impact — the harm: loss of fertile topsoil and falling yields; gullied land that cannot be
farmed; land, houses and roads washed away along rivers and coasts; silting of canals and
reservoirs; floods in deltas and plains; landslides where water saturates a slope.
Mitigation: afforestation; contour bunding and contour trenches; terracing; check dams (the
Zabo system of Nagaland); embankments and proper drainage; keeping construction out of
drainage paths; mangrove protection on deltaic coasts.

Group 2 — WIND

How it works: strong winds pick up and carry loose particles of sand and soil in dry regions,
wearing rock down by sandblasting and dropping the sand where the wind slows.
Landforms: erosional — yardangs (streamlined rock ridges), ventifacts (rocks polished by
sandblasting), deflation hollows or blowouts, desert pavements. Depositional — dunes:
barchan (crescent-shaped, limited sand, one wind direction), longitudinal (long ridges
parallel to the wind), star (many arms, winds from several directions) and parabolic (U-
shaped, often held in place by vegetation).
Impact — the good: dunes act as natural barriers against desertification and wind erosion;
they protect coastal settlements from sea winds and waves; they support tourism and
adventure sports; dune sand is used in construction; yardangs and ventifacts attract tourists
and geologists.
Impact — the harm: fertile fine soil blown away; crops buried or sand-blasted; dust storms
that stop road, rail and air traffic and harm breathing; oases and settlements encroached by
moving dunes; desertification.
Mitigation: shelter belts and windbreaks of trees; stabilising dunes with grasses and shrubs;
keeping a cover crop or stubble on the soil; controlling overgrazing; contour ploughing
across the wind; sand fences; dust-storm warnings.

Group 3 — GLACIER

How it works: a glacier moves slowly over the land, scraping and carrying huge amounts of
material and dropping it (as till) where the ice melts.
Landforms: erosional — U-shaped valleys, cirques (bowl-shaped hollows at the head of a
glacier), aretes (sharp ridges between valleys), hanging valleys (where a smaller glacier met a
larger one), fjords (deep narrow inlets where the sea has flooded a glacial valley).
Depositional — moraines: lateral along the sides, terminal at the end marking the furthest
advance, and medial where two glaciers join and their lateral moraines meet in the middle.
Impact — the good: glaciers are crucial sources of fresh water, feeding the rivers that
sustain populations downstream; U-shaped valleys and cirques support trekking, skiing and
mountaineering; fjords make harbours and fishing grounds; fertile glacial soil in some
valleys supports agriculture; moraines give fertile soil and form natural dams and lakes used
for water supply, irrigation and hydroelectric power.
Impact — the harm: avalanches on steep snow slopes; GLOFs when a moraine or ice dam
collapses; the Chamoli disaster of February 2021 as the case study; and, as glaciers retreat
with rising temperatures, a long-term threat to the rivers that depend on them.

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

Mitigation: satellite monitoring of glacial lakes; lowering dangerous lakes by siphoning or a
controlled channel; strengthening moraine dams; automatic water-level sensors and sirens
downstream; keeping settlements, roads and hydel projects out of the flood path; avalanche
barriers and bulletins; and reducing the emissions that are warming the glaciers.

What the three projects together should show: the same three-part story runs
through all of them — an agent erodes in one place, transports, and deposits in
another. The eroded area loses soil and becomes hazardous; the area of deposition
gains fertile land. Human beings benefit from the second and suffer from the first,
and every mitigation measure in all three lists is an attempt to slow the agent down
at the point where it is doing the damage.

Tip for the presentation: end with a single comparison table on the board — agent
| how it carries material | erosional landform | depositional landform | main hazard |
key mitigation. Filling that table in together is the best revision of the whole chapter.

Chapter at a glance
The Earth has three main layers — crust, mantle and core. The crust together with the
upper mantle makes the rigid lithosphere (about 100 km thick in Fig. 2.1); below it lies the
hot, partly molten asthenosphere (about 200 km), which is what lets the plates move at all.
The lithosphere is broken into tectonic plates — continental, oceanic and mixed — that
creep along at a few centimetres a year. Fig. 2.3 names seven major plates: Pacific, Eurasian,
African, North American, South American, Indo-Australian and Antarctic.
Plates move because of convection currents in the mantle: heated material rises, cooler
material sinks, and the circulating mantle pushes and pulls the plates. Fig. 2.2 splits the
total interior heat flow between crust (24%), upper mantle (22%), lower mantle (32%) and
core (22%), and shows it travelling outward by advection, convection and conduction.
The three plate boundaries explain where the big landforms sit — convergent (fold
mountains such as the Himalaya; volcanoes and earthquakes where an oceanic plate sinks
under a continental one), divergent (new crust and mid-ocean ridges such as the Mid-
Atlantic Ridge) and transform (earthquakes such as along the San Andreas Fault).
Comparing Fig. 2.3 with Fig. 2.4 shows earthquakes and volcanoes tracing the boundaries,
above all the Ring of Fire.
External forces then carve the raised land. Weathering breaks rock in place (physical,
chemical, biological); erosion also carries the broken material away. The agents of
gradation — running water, glaciers, wind, waves and groundwater — lower the high
ground and fill the hollows, and each leaves its own family of landforms: waterfalls,
meanders, oxbow lakes and deltas (rivers); beaches, sea cliffs, caves, arches and stacks

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Class 9 Social Science Chapter 2 Shaping of the Earth's Surface AglaSem · NCERT Solutions

(waves); U-shaped valleys, cirques, aretes, fjords and moraines (glaciers); yardangs,
ventifacts, deflation hollows and dunes (wind); caves, stalactites, stalagmites and sinkholes
— Karst topography (groundwater).
Landforms shape human life, and their hazards too: landslides, avalanches, GLOFs and
dust storms, along with the earthquakes and eruptions of plate boundaries — the Chamoli
flood of February 2021 and the Gujarat earthquake of 2001 are the chapter's own examples.

Page 58 of 60

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