Jacob Sir Poetry, Poems and education : 11 th geography book

BOOK -1

FUNDAMENTALS OF PHYSICAL GEOGRAPHY

CHAPTER 1 GEOGRAPHY AS A DISCIPLINE

1 “What is geography”?

In very simple words, it can be said that geography is the description of the earth.

2. The term geography was first coined by Eratosthenese, a Greek scholar (276-194 BC.).

3. A geographer explains the phenomena in a frame of cause and effect relationship, as it does not only

help in interpretation but also foresees the phenomena in future .

5. Geography as a discipline is concerned with three sets of questions: WHAT, WHERE and WHY?

6. Geography is a discipline of systhesis. Geography attempts SPATIAL synthesis and history attempts

TEMPORAL synthesis.

7. The present world is being perceived as a global village. The distances have been reduced by better

means of transportation and increasing accessibility.

8. All the sciences, whether natural or social, have one basic objective, of Understanding the Reality.

9. The major approaches to study geography have been (i) Systematic and (ii) Regional.

10. The Systematic geography approach is the same as that of general geography. This approach

was introduced by Alexander Von Humboldt, a German geographer (1769-1859)

In systematic approach , a phenomenon is studied world over as a whole, and then the

identification of typologies or spatial patterns is done

11. The Regional geography approach was developed by another German geographer, Karl

Ritter (1779-1859)

In the regional approach, the world is divided into regions at different hierarchical levels and

then all the geographical phenomena in a particular region are studied

12. The word ‘dualism’ simply means the state of being divided (i.e. same subject exist in two

different forms).

13. Dualism finally leads to ‘dichotomy’ which means the bifurcation of any subject into branches of

knowledge.

14. Branches of Geography ( based on Systematic approach)

MCQ :

1.GIS stands for

[a] Geography Integrated System

[b] Geography Included Study

[c] Geographic Information System

[d] Geographic Inclusive Study

2.The science of drawing maps is called

[a] Calligraphy

[b] Cartography

[c] Bibliography

[d] Epigraphy

3.The term geography was coined by

[a] Aristotle

[b] Socrates

[c] Eratosthenes

[d] Thales

4.Which of the following is not a natural science?

[a] Pedology

[b] Botany

[c] Geology

[d] Sociology

5._________________ helps humans to loosen the shackles of the physical

environment.

[a] Society

[b] Technology

[c] Courage

[d] Valour

Assertion (A) Time is an important factor in pedogenesis

Reason (R) Time provides maturity to soils and helps in development of soil profiles.

[a] A and R are true and R is the correct explanation of A.

[b] A and R true but R is not the correct explanation of A.

[c] A is false but R is true.

[d] A is true but R is false.

SOURCE BASED QUESTIONS

Read the following passage and answer the questions that follow:

Geography is a discipline of synthesis. It attempts spatial synthesis, and history attempts temporal synthesis.

Its approach is holistic in nature. It recognises the fact that the world is a system of independencies. The

present world is being perceived as a global village. The distances have been reduced by better means of

transportation increasing accessibility. The audio-visual media and information technology have

enriched the data base. Technology has provided better chances of monitoring natural

phenomena as well as the economic and social parameters. Geography as an integrating discipline has

interface with numerous natural and social sciences. All the sciences, whether natural or social, have one basic

objective, of understanding the reality. Geography attempts to comprehend the associations of phenomena as

related in sections of reality.

Every discipline concerned with scientific knowledge is linked with geography as many of their

elements vary over space. Geography helps in understanding the reality in totality in its spatial

perspective. Geography. thus, not only takes note of the differences in the phenomena from place to

place but integrates them holistically which may be different at other places. A geographer is

required to have a broad understanding of all

the related fields, to be able to logically Integrate them. This integration can beunderstood with some

examples. Geography Influences historical events. Spatial distance Itself has been a very potent

factor to alter the course of history of the world. Spatial depth provided defence to many countries,

particularly in the last century. In traditional warfare countries with large size in area, gain time at

the cost of space. Thedefence provided by oceanic expanse around the countries of the new world

has protected them from wars being imposed on their soil. If we look at the historical events world

over, each one of them can be interpreted geographically. In India, Himalayas have acted as great

barriers and provided protection but the

passes provided routes to the migrants and invaders from Central Asia. The sea coast

has encouraged contact with people from East and Southeast Asia, Europe and Africa.

Navigation technology helped European countries to colonise a number of countries ofAsia and

Africa, including India as they got accessibility.

Which of the following technology has made the world a global village?

[a] Internet

[b] Air transport

[c] Satellite communication

[d] All of the above

Which of the following is the most important feature of geography?

[a] It is derived from three discipline

[b] It is dynamic in nature

[c] It has no interface with natural sciences

[d] Geography does not help in understanding reality.

10. Which of the following has helped in understanding geographical phenomenon more

Assertion (A) Climate does not influence life of human beings.

Reason (R) Temperature and precipitation affects density of forests and quality of

grassland.

[a] A and R are true and R is the correct explanation of A.

[b] A and R true but R is not the correct explanation of A.

[c] A is false but R is true.

[d] A is true but R is false.

accurately?

[a] Technology

[b] Social science

[c] Governments

[d] Mineral

1 2 3 4 5 6 7 8 9 10

c b c d b a C d b a

SHORT ANSWER QUESTIONS (3 MARKS)

11. What is geography ?

Ans: The word’geography’ is a combination of two words Geo+geography . Geo means the earth and

graphy means the science.

Thus geography means the earth science. Man and his environment have assumed a dominant role over

the earth.

12.Write differences between deterministic Vs Possibilistic school of thoughts.

Deterministic school of thoughts Possibilistic school of thoughts

Control of nature on man Crucial role of human beings on environment.

Environment or nature plays a dominant role Human beings play dominant role

Major supporter of idea: Ratzel and Huntington Major supporter of idea: vidal-de-la-blache,

L.febvre.

13. What are the sets of questions , geography is concerned with?

Ans: Geography as a discipline is concerned with three sets of questions:

a) What ? --This question is related to identification of natural and cultural features.

b) Where ? – this is related to the distribution of natural and cultural features.

c) Why?—The casual relationship between features and phenomena.

14. Distinguish between systematic and regional geography

Systematic geography Regional geography

Studies specific natural and social phenomena Studies spatial effects

Includes spatial patterns and structures on earth

surface

Single factors and multifactor regions

Branches: Physical , Human, biogeography Branches: Regional studies, regional analysis,

regional development and regional planning.

15 Why is geography considered the study of areal differentiation?

Ans: numerous earth phenomena are similar and many are dissimilar. Hence, geography is considered the

study of areal differentiation.

LONG ANSWER QUESTIONS (5 MARKS)

16. Discuss the scope of geography.

Ans Geography is regarded as mother of all sciences.

a) Humans in their early stages of civilized life had to interact with an omnipotent and omnipresent

nature.

b) Human suffered from serious limitations imposed by nature because nature was overpowering

c) Humans used technological means to control nature were primitive and toothless.

d) The need for a discipline ,which looked at the causes and consequences of the arrangement of

various natural and cultural features of earth surface existed before as it exists even today.

e) Geography is, therefore, a truly holistic and interdisciplinary field of study. (any other points.

Explain the points )

17 Describe the systematic geography and its brances.

Ans: Systematic geography is a study of specific natural or social phenomena that give rise to certain

spatial patterns and structure on the earth’s surface.

a) Physical geography:

i. Geomorphology

ii. Climatology

iii. Hydrology

iv. Soil geography

b) Human geography:

i. Social/Cultural geography

ii. Population and settlement geography

iii. Economic geography

iv. Historical Geography

v. Political geography

c) Biogeography:

i. Plant geography

ii. Zoo geography

iii. Ecology/Ecosystem

iv. Environmental geography

18 Give an account of Regional geography .

Ans : Regional geography starts with the effects of one or the other processes of systematic geography.

a) Regions are based on a single factor like relief

b) Regions are based on a single factor like relief, rainfall, vegetation, per capita income, literacy and

so on and so faith.

c) They are also multifactor regions.

d) They have no rationales other than convenience for planning and development purpose.

(Explain points to meet the requirement)

19 Discuss the importance of physical geography.

Ans : Physical geography covers all that is domains of earth.

a) Lithosphere covers land forms, drainage, relief and physiography

b) Atmosphere deals with climates, composition and structure of atmosphere.

c) Hydrosphere studies wate features- water real, oceans, seas, lakes.

d) Biosphere – insets on living things such as plants, animals micro-organisms and human beings

and their sustaining mechanism like food-chain, ecological balance etc.

20. Describe geography as an integrating discipline.

Ans : Geography is a discipline of synthesis.

a) Geography attempts spatial synthesis.

b) Approach of geography is holistic in nature.

c) Geography as an integrating discipline has interface with various natural and social sciences.

(explain points to meet the requirement)

CHAPTER 2 THE ORIGIN AND EVOLUTION OF EARTH

QUESTIONS

[1] Who gave the nebular hypothesis?

[a] Immanual Kant

[b] Aristotle

[c] Chamberlain

[d] none of these

[2] ____________ provided evidence that universe is expanding.

[a] Eratosthenes

[b] Edwin Hubble

[c] Socrates

[d] Aristotle

[3] Initially, earth had a thin atmosphere mostly containing

[a] Hydrogen

[b] Helium

[c] both

[d] none of them

[4] Who among the following gave the ‘steady state’ concept of universe?

[a] Fred Hoyle

[b] Chamberlin & Moulton

[c] Edwin Hubble

[d] Eratosthenes

[5] Light year is a unit to measure

[a] Distance

[b] Speed

[c] Velocity

[d] Density

[6] _________ is an interstellar cloud of dust, hydrogen, helium and other ionized gases.

[a] Supernova

[b] Pulsar

[c] Nebula

[d] White Dwarf

[7] What is Jovian or Gas Giant planets?

[a] Inner planets

[b] Outer planets

[c] none of these

[d] both of these

[8] Identify the correct sequence of stages of formation of star.

[i] Small rounded objects developed by the process of cohesion are called planetesimals.

[ii] The gravitational force within a nebula leads to formation of core of gas and dust.

[iii] Large number of small planetesimals accrete to form fewer large bodies in the formof planets.

Choose the correct option:

[a] i, ii, iii

[b] ii, i, iii

[c] iii, i, ii

[d] iii, ii, i

[9] Which of the following is correct order of planets starting from the sun?

[a] Mercury, Neptune, Mars, Earth

[b] Mercury, Mars, Earth, Neptune

[c] Mars, Mercury, Earth, Neptune

[d] Mercury, Earth, Mars, Neptune

[10] All planets were formed about ____ billion years ago.

[a] 2.6 billion years ago

[b] 3.6 billion years ago

[c] 4.6 billion years ago

[d] 5.6 billion years ago

[11] ‘Big splat’ is related to origin of which of the following celestial body?

[a] Sun

[b] Asteroids

[c] Haleys comet

[d] Moon

[12] Astronomical unit is

[a] Average distance between sun and earth

[b] Average distance between sun and moon

[c] Average distance between moon and earth

[d] Average distance between mars and earth

[13] Due to ___________ process the earth forming material got separated into different

layers.

[a] Degassing

[b] Differentiation

[c] Lithification

[d] Solifluction

[14] The process through which the gases were outpoured from the interior of earth

[a] Degassing

[b] Differentiation

[c] Lithification

[d] Solifluction

[15] When did the event of Big Bang take place?

[a] 13.6 million years ago

[b] 13.7 billion years ago

[c] 4.6 billion years ago

[d] 4.6 million years ago

SOLUTIONS

1. A 2. B 3. C 4. 5. A

6. C 7. B 8. B 9. B 10. C

11. D 12. A 13. B 14. A 15. B

SHORT ANSWER QUESTIONS

Question 1. What do you mean by the big splat?

Answer: The origin of the moon as a satellite of the earth is the result of big collision which is called “the

big splat”.

Question 2.Which hypothesis was given by Hoyle?

Answer: Hoyle gave concept of steady state. It considered the universe to be roughly the same at any

point of time. However, with greater evidence becoming available about the expanding universe, scientific

community at present favours argument of expanding universe.

Question 3.What do you mean by dwarf planets?

Answer:According to International Astronomical. Union (LAU) on August 24,2006, a planet is a celestial

body that orbits around the sun has sufficient mass so that it assumes a hydrostatic equilibrium (nearly

round) shape.The non-satellites bodies fulfilling these two rules are called dwarf planets. Pluto is now

considered a dwarf planet. Ceres, Eris, Makemake, Haumea are some other dwarf planets.

Question 4.What are different stages of development of atmosphere?

Answer:In the early stage the atmosphere with hydrogen and helium is supposed to have been stripped

off as a result of intense solar winds. In the second stage during the cooling of the earth, gases and water

vapour were released from the interior solid earth. Continuous volcanic eruptions contributed water

vapour and gases to the atmosphere. As the earth cooled, the water vapour released started getting

condensed. Third stage was the stage of photosynthesis.

Question 5.Name different hypothesis associated with the formation of the earth.

Answer: Nebular Hypothesis: It was given by Laplace.

Collision Hypothesis: It was given by Sir James and Harold Jeffrey.

Accretion Hypothesis: It was given by Schmidt and Carl Weizascar.

The Big Bang Theory: It was given by Edwin Hubble.

LONG ANSWER QUESTIONS

1. Explain different phases of evolution of planets.

Evolution of planets can be understood in three stages:

1. Formation of Disc; The stars are localised lumps of gas within a nebula. The gravitational force within

the lumps leads to the formation of a core to the gas cloud and a huge rotating disc of gas and dust

develops around the gas core.

2. Formation of Planetesimals: In the next stage, the gas cloud starts and getting condensed and the

matter around the core develops into small rounded objects. These small rounded objects by the process

of collision develop into what is called planetesimals. Larger bodies start forming by collision and

gravitational attraction causes the materials to stick together. Planetesimals are a large number of

smaller bodies.

3. Formation of Planets: In the final stage, these large number of small planetesimals accrete to form

fewer large bodies in the form of planets.

Write an explanatory note on the ‘Big Bang Theory’. Answer:

The Big Bang Theory, also called as expanding universe hypothesis.

1. In the beginning, ail matter forming the universe existed in one place in the form of a ‘tiny ball” with an

unimaginably small volume, infinite temperature and infinite density.

2. At the Big Bang “tiny ball” exploded violently. This led to a huge expansion.

3. The event of big bang took place 13.7 billion years before the present.

4. The expansion continues even to the present day.

5.As it grew, some energy was converted into matter.

6.Within first three minutes from the Big Bang event, the first atom began to form.

7. Within 300,000 years from the Big Bang, temperature dropped to 4,500k and gave rise to atomic

matter.

8. The universe became transparent.

Question 3. Explain the earliest theory associated with the origin of the earth.

Answer:

1. One of the earlier and popular arguments was by German philosopher Immanuel Kant. Mathematician

Laplace revised it in 1796. It is known as Nebular Hypothesis.

2. According to this theory there was a hot and rotating gas cloud called Nebula in the space.

3. Gradual cooling caused contraction in size of Nebula, but its speed increased due to angular

momentum.

4. The outer layer was separated from the remaining part of Nebula.

5. The centre of Nebula became ‘Sun’ and the planets were formed of the smaller units.

6. In 1950, Otto Schmidt in Russia and Carl Weizasear in Germany revised the ‘nebular hypothesis’,

7. He considered that the sun was surrounded by solar nebula containing mostly the hydrogen and

helium along with what may be termed as dust.

8. The friction and collision of particles led to formation of a disk-shaped cloud and the planets were

formed through the process of accretion.

Question 4. Write an explanatory note of evolution of earth’s atmosphere and hydrosphere.

Answer:

1. The early atmosphere, with hydrogen and helium, was stripped off as a result of the solar winds.

2. During the cooling of the earth, gases and water vapour were released from the interior solid earth.

3. The early atmosphere largely contained water vapour, nitrogen, carbon di oxide, methane, ammonia,

and very little of free oxygen.

4. As the earth cooled, the water vapour released started getting condensed.

5. The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further

decreased causing more condensation and more rains.

6. The rainwater falling onto the surface got collected in the depressions to give rise to oceans.

7. The earth’s oceans were formed 4,000 million years ago.

8. Around 3,800 million years ago, life began to evolve.

9. 2,500-3,000 million years before the present, the process of photosynthesis got evolved.

10. Life was confined to the oceans for a long time.

11. Eventually, oceans were saturated with oxygen, and 2,000 million years ago, oxygen began to flood

the atmosphere.

Q.5 Describe the origin of life on earth.

[1] Initially the earth or even the atmosphere of the earth was not conducive for the development of life.

[2] Life originated as a kind of chemical reaction, which first generated complex organic molecules and

assembled them.

[3] This assemblage was such that they could duplicate themselves converting lifeless matter into living

substance.

[4] Life began to evolve 3800 million years ago.

CHAPTER 3 INTERIOR OF EARTH

Sources of Information about the Earth’s Interior

There are two sources for information about interior of the earth –

a) Direct Sources: 1. Mining 2. Drilling 3. Volcanic Eruption

b) Indirect Sources: 1. Seismic waves 2. Gravitational field 3. Magnetic field 4. Meteors

EARTH QUAKE

It is the shaking of the earth, natural event. It is caused due to release of energy which generates waves

that travel to all directions.

Focus: It is point inside the earth surface from where an earthquake starts. It is always hidden inside the

earth. Focus of an earthquake may be found at the depth of 100-200 km.

Epicenter: It is a point on the earth surface which records the seismic waves for the first time. Maximum

destruction from an earthquake is caused on the epicenter. Epicenter is located just perpendicular to the

focus.

Measurement of earthquakes: 1. Richter Scale 2. Mercalli Scale

Causes :a) movement of plates, b) rising of magma, c) folding and faulting, d) violent volcanic eruption.

Earthquake Waves:

P and S waves are combinedly called as ‘Body Wave’ as they move inside the body of the earth.

P wave is the fastest wave. It is also called as longitudinal wave. P waves move parallel to the direction of

wave. These waves can move in both solid and liquid.

S wave is slower than P wave. It is also called as transverse wave. It moves perpendicular to the direction

of the wave. These waves move only in solid and disappear in liquid.

L wave is the slowest wave. It moves on the earth surface. It causes maximum destruction on the earth

surface.

VOLCANISM

Volcano means the vent from which magma and other substances erupt to the surface.

TYPES OF VOLCANOES: Classification of volcanoes based on nature of eruption and land forms developed

on the surface.

SHIELD VOLCANO

1. Largest of volcanoes.

2. Hawaiian Islands are best examples.

3. Basalt lava flow.

4. Lava is very fluid

5. They are not steep.

COMPOSITE VOLCANOES

1 Cool and more viscous lava.

2. Explosive eruptions.

3. They erupt pyroclastic and ashes along with lava.

4. Layers are formed.

CALDERA

1. Most explosive type of volcanoes.

2. These volcanoes collapse onto themselves.

3. collapsed depressions are called caldera.

4. The magma chamber is huge and close to surface.

FLOOD BASALT PROVINCES

1. Consists of highly fluid lava

2. Some parts of the world are covered by thousands of sq.km of basalt

3. there can be series of flows

4. Average thickness is more than 50 km

5. Individual flow is 100 of sq.k.m

6. Ex. Deccan plateau

MID OCEANIC RIDGES VOLCANOES

1. Found in oceanic surfaces

2. More than 70,000 km length

3. Frequent volcanic eruptions

4. Ex. Mid Atlantic ridge

INTRUSIVE VOLCANIC LANDFORMS

When lava comes out forms volcanic rocks, some part cools down in the lower portion forms plutonic

rocks.

[1] BATHOLITH: A large part of the magma material that cools in the deeper depth of the crust. They are

dome shaped, cover large areas. They come out when erosion takes place. They are granite bodies.

[2] LACO

MULTIPLE CHOICE QUESTIONS

1. The earth’s radius is about

[a] 5370 kms

[b] 6370 kms

[c] 8000 kms

[d] 9000 kms

2. The __________ is the point within the earth where an earthquake rupture starts.

[a] hypocentre

[b] epicentre

[c] fault

[d] fold

3. _____________ instrument is used to record the motion of the ground during an earthquake.

[a] Anemometer

[b] Rain Gauge

[c] Seismograph

[d] Barometer

4. Identify the incorrect statement.

[a] Velocity of earthquake waves changes as they travel through materials with different densities.

[b] The denser the material, the lower is the velocity.

[c] Their direction also changes as they reflect or refract when coming across materials with different

densities

[d] None of the above

5. The upper portion of mantle is called:

[a] Lithosphere

[b] Thermosphere

[c] Mesosphere

[d] Asthenosphere

6. Deccan traps in India is an example of:

[a] Shield Volcanoes

[b] Composite Volcanoes

[c] Flood basalt province

[d] Caldera

7. A saucer shaped, concave to the sky, volcanic landform:

[a] Batholith

[b] Lacoliths

[c] Lapolith

[d] Phacolith

8. Assertion: Shield volcanoes are very steep.

Reason: In shield volcanoes magma made up of basalt is very fluid.

[a] A and R are true and R is the correct explanation of A.

[b] A and R true but R is not the correct explanation of A.

[c] A is false but R is true.

[d] A is true but R is false.

9. The crust and mantle are separated by which of the following discontinuities?

[a] Gutenberg discontinuity

[b] Moho discontinuity

[c] Conrad discontinuity

[d] Lehman discontinuity

10. Which of the following layers is known as NiFe?

[a] Mantle

[b] Continental crust

[c] Oceanic crust

[d] Core

SOLUTIONS

1.B 2. A 3. C 4. B 5. D

6. C 7. C 8. C 9. B 10. D

SHORT ANSWER QUESTIONS

Q.1 Differentiate between body waves and surface waves.

Ans Body Waves:

[a] These are generated due to release of energy at the focus.

[b] They move in all directions travelling through the body of earth.

[c] These are less destructive than the surface waves.

Surface Waves:

[a] The body waves interact with the surface rocks and generate these waves.

[b] These waves move along the surface.

[c] These waves are most destructive earthquake waves.

Q.2 Discuss the direct sources of information about the interior of the earth.

Ans. [a] Mining: Extraction of valuable minerals provides information.

[b] Drilling: Provides large volume of information through the analysis of materials collected at different

depth.

[c] Volcanic eruptions: During volcanic eruption magma becomes available for analysis.

Q.3 What is gravity anomaly?

Ans. The reading of the gravity at different places is influenced by many other factors. These readings

differ from the expected values. Such a difference is called gravity anomaly. Gravity anomalies give us

information about the distribution of mass of the material in the crust of the earth.

Q.4 Describe the volcanic activity and the major features associated with it.

Ans [1] Vulcanicity is an endogenous process through which the heated materials (solid, liquid or

gaseous) move from the interior towards the surface of the earth.

[2] High relief features like mountains, cones, domes etc. which are known as positive relief features. The

low lying features like Caldera, Crater, etc. are called negative relief features.

[3] Crater. A crater is a funnel-shaped hollow formed At the centre of volcano. It is formed by an

explosion. A crater filled with water is known as a crater lake, such as Lonar lake in Maharashtra.

[4] Caldera. Calderas are very large volcanic depressions. Calderas are formed by explosion and collapse.

The top of the cone is blown off and a broad depression or crater is formed.

Q.5 What are shadow zones?

Ans Areas on earth where no earthquake waves are reported, such areas are called shadow zones.

Shadow zone of P waves: 105° to 145° from focus

Shadow zone of S waves: 105 ° to 105° from focus

LONG ANSWER QUESTIONS

Q.1 what are earthquake waves? Describe their types and characteristics.

Ans. Earthquake waves provide the most reliable information regarding the structure of the earth.

The vibrations recorded during an earthquake are called waves.

These waves are recorded by an instrument known as Seismograph.

There are three types of earthquake waves:

1. Longitudinal Waves. These waves are similar to sound waves. These can travel in solid, liquid and

gaseous mediums. These are also termed as Primary waves or P waves. The particles travel to and fro in

the direction of the waves. These waves travel at a speed of 5 to 12 km. per second. These waves reach

the surface of the Earth at the earliest.

2. Transverse Waves. These are known as Secondary waves or S-waves. In these waves, particles move

right angles to the direction of waves. These waves are slow and travel only in solid medium.

3. Surface Waves. These waves travel on the surface of the Earth and produce disastrous effects of

earthquakes. These are called Long waves or L-waves. These are also known as Rayleigh waves or Rwaves. Their intensity decreases with depth. These waves move along the boundaries between solid,

liquid and gaseous mediums. These waves are the last to reach the earth surface. These are the most

destructive waves.

Q.3 Explain the layered structure of earth.

Ans: [1] Crust:

Outermost solid layer, brittle in nature,

Oceanic crust is younger and thin

Continental crust is older and thick

Density is 3 gm/cm3

[2] The mantle

1. Second layer from the top of the earth

2. It extends from Moho-discontinuity to a depth of 2900 km.

3. The upper portion of the mantle is called ASTHENOSPHERE ( Astheno= weak it extends up to 400 km)

4. It is the source of magma

5. Average density is 3.4g/cm3

6. Crust and upper most part of the mantle is called Lithosphere. Its thickness is 10 -200km

7. Lower mantle is in solid state

[3] The core

1. It extends from 2900 km to 6300 km depth

2. Outer core is liquid while inner core is solid

3. Outer core density is 5 g/ inner core is 13 g/

4. Made of heavy metals such as nickel and iron

Q.2 What do you understand by intrusive forms? Briefly describe various intrusive forms.

Ans. Depending on the location of cooling of lava igneous rocks are classified as volcanic rocks (cooling at

the surface) and plutonic rocks (cooling in the crust).

The lava that cools within the crustal portions assumes different forms. These forms are called intrusive

forms.

(1) Batholiths. A large body of magmatic material that cools in the deeper depth of crust develops in the

form of large domes. They appear on surface only after the denudational processes remove the overlying

materials. They cover large areas and at times assume depth that may be several kilometres. These are

granitic bodies. Batholiths are cooled portion of magma chambers.

(2) Lacoliths. These are large dome shaped intrusive bodies with a level base and connected by a pipe like

conduit from below. It resembles the surface volcanic domes of composite volcano, only located at deeper

depths.

(3) Lapolith: In case if develops into a saucer shape, concave to sky body, it is called lapolith.

(4) Phacolith: A wavy mass of intrusive rocks at times is found at the base of synclines or at the top of

anticline in folded igneous country. Such wavy materials are called the phacoliths.

(5) Sill: The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the

thickness of material. The thinner ones are called sheets while the thick horizontal deposits are called

sills.

(6) Dykes. When the lava makes it way through cracks and through the fissures developed in the land it

makes almost perpendicular to the ground. Such structures are called dykes.

CHAPTER 4 DISTRIBUTION OF CONTINENTS AND OCEANS

1. Continents cover 29% of the surface of the earth and the remainder 71% is under oceanic waters.

2. Alfred Wegener-a German meteorologist put forth a comprehensive argument in the form of "the

continental drift theory" in 1912. This was regarding the distribution of the oceans and the continents.

3. According to Wegener, all the continents formed a single continental mass and mega ocean surrounded

the same. The super continent was named PANGAEA, which meant all earth. The mega-ocean was called

PANTHALASSA, meaning all water.

4. Wegener argued that, around 200 million years ago, the super continent, Pangaea, began to split.

Pangaea first broke into two large continental masses as Laurasia and Gondwanaland forming the

northern and southern components respectively. Subsequently, Laurasia and Gondwanaland continued to

break into various smaller continents that exist today.

5. The radiometric dating methods developed in the recent period have facilitated correlating the rock

formation from different continents across the vast ocean.

6. The ocean floor may be segmented into three major divisions based on the depth as well as the forms of

relief. These divisions are continental margins, deep-sea basins and mid-ocean ridges.

7. Concept of sea floor spreading was proposed by Hess in 1961 who believed that new lava pushes out

the plates from the mid-oceanic ridge.

8. It was in 1967, McKenzie and Parker and also Morgan, independently collected the available and came

out with another concept termed Plate Tectonics.

MULTIPLE CHOICE QUESTIONS

[1] ______________ was the first person to propose the possibility of drifting of continents.

[a] Alfred Wegner

[b] Alexander Von Humboldt

[c] Abraham Ortelius

[d] Antonio Pellegrini

[2] Which of the following techniques helps us to determine the age of rocks?

[a] Archaeological findings

[b] Inscriptions

[c] Radiometric dating

[d] Calendars

[3] In 1930 _____________ discussed the possibility of convection currents operating in the mantle portion.

[a] Alfred Wegner

[b] Arthur Holmes

[c] Abraham Ortelius

[d] Antonio Pellegrini

[4] Who among the following proposed the concept of sea floor spreading?

[a] Harry Hess

[b] Mackenize

[c] Morgan

[d] Parker

[5] Formation of deccan trap happened around

[a] 6 billion years ago

[b] 60 billion years ago

[c] 60 million years ago

[d] 6 million years ago

[6] Earth’s lithosphere is divided into ___________ major and several minor plates.

[a] Six

[b] Seven

[c] Ten

[d] Eleven

[7] Identify the incorrect statement.

[a] A tectonic plate is a massive irregularly-shaped slab of solid rock.

[b] A plate is generally composed of either continental or oceanic lithosphere.

[c] A plate may be referred to as continental or oceanic plate.

[d] The thickness of tectonic plate varies between 5-200 kms.

[8] According to Wegner the forces responsible for drifting of continents were caused by

[a] gravitational force and tidal force

[b] pole fleeing force and tidal force

[c] electromagnetic force and pole fleeing force

[d] electromagnetic force and gravitational force

[9] Sedimentary rocks formed out of deposits of glaciers are called

[a] Sandstone

[b] Mica

[c] Tillite

[d] Azurite

[10] Identify the incorrect statement:

[a] Alfred Wegner propounded continental drift theory in 1912.

[b] All continents formed a single continental landmass-Panthalassa.

[c] 200 years ago the super continent began to split.

[d] Super continent broke into Laurasia and Gondwanaland.

SOLUTION

1. c 2. c 3. b 4. a 5. c

6. b 7. b 8. b 9. c 10. b

SHORT ANSWER QUESTIONS

Q. 1. What do you mean by Tillite? Where are these found?

Ans. Tillite are the sedimentary rocks formed out of deposits of glaciers.

At the base the system has thick tillite indicating extensive and prolonged glaciation.

The counter parts of this succession are found in Africa. Falkland Island, Madagascar, Antarctica and

Australia.

Q.2 What is meant by sea floor spreading?

Ans. Widening of ocean floor is called sea floor spreading.

The mid-oceanic ridges are cracks on the floor of ocean. Theyemitsmagma actively.

Molten matter forms a new crust. The crust spreads away from the ridges.

Q.3 What is meant by Polar Wandering?

Ans There has been periodic change in the position of magnetic pole. This is known as polar wandering.

It is recorded in rocks by way of permanent magnetism.

The polar wandering clearly demonstrates that the continents have frequently moved and changed

directions of their motion from time to time.

Q.4 What are abyssal plains?

Ans. These are extensive plains that lie between the continental margins and mid-oceanic ridges. The

Abyssal plains are the areas where the continental sediments that move beyond the margins get

deposited.

Q5. What are Continental Margins?

Ans. These form the transition between continental shores and deep-sea basins. They include continental

shelf, continental slope, continental rise and deep-oceanic trenches.

Q6. What are convection currents?

Ans. Convection currents are generated due to radioactive elements causing thermal differences in the

mantle portion.

Q7. How was Himalaya formed?

Ans. India started her northward journey about 200 million years ago at the time when Pangaea broke.

India collided with Asia about 40-50 million years ago That causing rapid uplift of the Himalayas.

LONG ANSWER QUESTIONS

Question.1 Explain tectonic plate theory and different plate margins.

Answer:

1. The theory of plate tectonics was introduced by McKenzie, Parker and, Morgan in 1967.

2. A tectonic plate is also called as lithosphere plate.

3. It is a massive irregularly shaped slab of solid rock.

4. Consists of oceanic and continental sphere.

5. Plates move horizontally over the asthenosphere.

6. Average thickness is 100 km of oceanic part and 200 km of continental part.

7. It may be oceanic or continental.

8. Pacific plate is largest oceanic plate whereas Eurasian plate is the largest continental plate.

9. These plates are moving constantly throughout geological time not the continent, believed by Wegener.

10. It creates three types of boundaries.

(i) Divergent boundaries:

New crust is generated

Plates move away from each other

Tensional forces are generated

Faults develop

These are called spreading sites

Ex. Mid Atlantic ridge

(ii) Convergent boundaries:

Crust is destroyed

Plates move towards each other.

Folds develop

Sinking of plate is called “subduction zone”.

There are three ways in which subduction occurs

(i) between an oceanic and continental plates;

(ii) between two oceanic plates; and

(iii) between two continental plates.

(iii) Transform boundaries:

Where the crust is neither produced nor destroyed as the plates slide horizontally past each other.

Q2. Explain the basic concept of continental drift theory.

Ans. Alfred Wegener-a German meteorologist put forth a à comprehensive argument in the form of "the

continental drift theory" in 1912.

This was regarding the distribution of the oceans and the continents.

According to Wegener, all the continents formed a single continental mass and mega ocean surrounded

the same.

He called the super continent as PANGAEA, which meant all earth.

He named mega-ocean as PANTHALASSA meaning all water.

According to him, around 200 million years ago, the super continent, Pangaea, began to split. Pangaea

first broke into two large continental masses as Laurasia and Gondwanaland forming the northern and

southern components respectively.

Subsequently, Laurasia and Gondwanaland continued to break into various smaller continents that exist

today.

Q.3 What are the evidences in support of sea floor spreading?

Ans. (i) Along the mid- oceanic ridges, volcanic eruptions are common and they bring huge amounts of

lava to the surface in this area.

(ii) The rocks equidistant on either side of the crest of mid-oceanic ridges show remarkable similarities in

terms of period of formation, chemical compositions and magnetic properties.

(iii) The ocean crust rocks are much younger than the continental rocks oceanic crust 200 million years

old. continental rock formations 3,200 million years old.

(iv) The sediments on the ocean floor are unexpectedly very thin.

(v) The deep trenches have deep-seated earthquake occurrences while in the mid- oceanic ridge areas,

the quake foci have shallow depths.

Q.4 What are the evidences in support of the continental drift theory?

Ans. (a) The Matching of Continents (Jig- Saw-Fit): The shorelines of Africa and South America facing each

other have a remarkable and unmistakable match.

(b) Rocks of Same Age Across the Oceans: The belt of ancient rocks of Brazil coast who matches with

those from western Africa. This suggests that the ocean did not exist prior to that time.

Gondwana type sediments clearly demonstrates that these landmasses had remarkably similar histories.

(d) Placer Deposits: The gold bearing veins are in Brazil and it is obvious that the gold deposits of the

Ghana are derived from the Brazil plateau when the two continents lay side by side.

(e) Distribution of Fossils: Lemurs occur in India, Madagascar and Africa led some to consider a

contiguous landmass "Lemuria" linking these three landmasses. Mesosaurus was a small reptile adapted

to shallow brackish water.

CHAPTER 6

Geomorphic Processes

The earth’s surface is being continuously subjected to by external forces originating within the earth’s

atmosphere and by internal forces from within the earth. The external forces are known as exogenic

forces and the internal forces are known as endogenic forces. The endogenic forces are mainly land

building forces and the exogenic processes are mainly land wearing forces.

Geomorphic Processes

The endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and

bringing about changes in the configuration of the surface of the earth are known as geomorphic

processes.

A process is a force applied on earth materials affecting the same. An agent is a mobile medium (like

running water, moving ice masses, wind, waves and currents etc.) which removes, transports and

deposits earth materials. Running water, groundwater, glaciers, wind, waves and currents, etc., can be

called geomorphic agents.

Endogenic Processes

The energy emanating from within the earth is the main force behind endogenic geomorphic processes.

This energy is mostly generated by radioactivity, rotational and tidal friction and primordial heat from

the origin of the earth.

Diastrophism

All processes that move, elevate or build up portions of the earth’s crust come under diastrophism. They

include:

(i) orogenic processes involving mountain building

(ii) epeirogenic processes involving uplift or warping of large parts of the earth’s crust;

(iii) earthquakes involving local relatively minor movements;

(iv) plate tectonics involving horizontal movements of crustal plates.

Orogeny is a mountain building process

Epeirogeny is continental building process.

Through the processes of orogeny, epeirogeny, earthquakes and plate tectonics, there can be faulting and

fracturing of the crust. All these processes cause pressure, volume and temperature (PVT) changes which

in turn induce metamorphism of rocks.

Volcanism

Volcanism includes the movement of molten rock (magma) onto or toward the earth’s surface and also

formation of many intrusive and extrusive volcanic forms.

Exogenic Processes

>The exogenic processes derive their energy from atmosphere determined by the ultimate energy from

the sun and also the gradients created by tectonic factors.

>Force applied per unit area is called stress. Stress is produced in a solid by pushing or pulling. This

induces deformation. Forces acting along the faces of earth materials are shear stresses (separating

>forces). It is this stress that breaks rocks and other earth materials.

>The shear stresses result in angular displacement or slippage.

>Temperature and precipitation are the two important climatic elements that control various processes.

>All the Exogenic geomorphic processes are covered under a general term, denudation.

The word ‘denude’ means to strip off or to uncover. Weathering, mass wasting/movements, erosion and

transportation are included in denudation.

>The exogenic geomorphic processes vary from region to region. The density, type and distribution of

vegetation which largely depend upon precipitation and temperature also exert influence indirectly on

exogenic geomorphic processes. Within different climatic regions there may be local variations of the

effects of different climatic elements due to altitudinal differences, aspect variations and the variation in

the amount of insolation received by north and south facing slopes as compared to east and west facing

slopes. Further, due to differences in wind velocities and directions, amount and kind of precipitation, its

intensity, the relation between precipitation and evaporation, daily range of temperature, freezing and

thawing frequency, depth of frost penetration, the geomorphic processes vary within any climatic region.

Weathering

Weathering is defined as mechanical disintegration and chemical decom-position of rocks through the

actions of various elements of weather and climate.

As very little or no motion of materials takes place in weathering, it is an in-situ or on-site process.

There are three major types of weathering processes:

(i) Chemical;

(ii) Physical or mechanical;

(iii) Biological weathering processes.

Special Effects of Weathering

Exfoliation

Flaking off of more or less curved sheets of shells from over rocks or bedrock results in smooth and

rounded surfaces

Significance of Weathering

1. Weathering processes are responsible for breaking down the rocks into smaller fragments and

preparing the way for formation of soils,

2. Forests depend upon the depth of weathering mantles.

3. Erosion cannot be significant if the rocks are not weathered.

4. Weathering of rocks and deposits helps in the enrichment and concentrations of certain valuable ores

of iron, manganese, aluminum, copper etc.

Mass Movements

These movements transfer the mass of rock debris down the slopes under the direct influence of

gravity.The movements of mass may range from slow to rapid, affecting shallow to deep columns of

materials and include creep, flow, slide and fall.

Mass movements are aided by gravity and no geomorphic agent like running water, glaciers, wind, waves

and currents participate in the process of mass movements.

That means mass movements do not come under erosion.

Landslides

These are relatively rapid and perceptible movements. Like Slump ,debris slide, Debris fall , Sliding, Rock

fall.

>In our country, debris avalanches and landslides occur very frequently in the Himalayas. There are many

reasons for this.

1. The Himalayas are tectonically active. They are mostly made up of sedimentary rocks and

unconsolidated and semi-consolidated deposits. The slopes are very steep. Compared to the

Himalayas, the Nilgiris bordering Tamilnadu, Karnataka, Kerala and the Western Ghats along the

west coast are relatively tectonically stable and are mostly made up of very hard rocks; but, still,

debris avalanches and landslides occur though not as frequently as in the Himalayas, in these hills.

2. Many slopes are steeper with almost vertical cliffs and escarpments in the Western Ghats and

Nilgiris. Mechanical weathering due to temperature changes and ranges is pronounced. They

receive heavy amounts of rainfall over short periods. So, there is almost direct rock fall quite

frequently in these places along with landslides and debris avalanches.

Erosion and Deposition

>Erosion involves acquisition and transportation of rock debris.

>It is erosion that is largely responsible for continuous changes that the earth’s surface is undergoing.

>Denudation processes like erosion and transportation are controlled by kinetic energy.

>The erosion and transportation of earth materials is brought about by wind, running water, glaciers,

waves and ground water.

>Of these the first three agents are controlled by climatic conditions.

>The work of the other two agents of erosion-waves and ground water is not controlled by climate.

>In case of waves it is the location along the interface of litho and hydro sphere — coastal region — that

will determine the work of waves,

> The work of ground water is determined more by the lithological character of the region. If the rocks

are permeable and soluble and water is available only then karst topography develops.

Deposition is a consequence of erosion. The erosional agents loose their velocity and hence energy on

gentler slopes and the materials carried by them start to settle themselves. The coarser materials get

deposited first and finer ones later. By deposition depressions get filled up. The same erosional agents

viz., running water, glaciers, wind, waves and groundwater act as aggradational or depositional agents

also.

Soil Formation Soil is a complex mixture of mineral and organic products forms.

>Soil is a dynamic medium in which many chemical, physical and biological activities go on constantly.

Soil is a result of decay; it is also the medium for growth. It is a changing and developing body.

Process of Soil Formation

Soil formation is also called Pedogenesis depends first on weathering.

Pedology is soil science. A pedologist is a soil-scientist.

Soil-forming Factors

Five basic factors control the formation of soils:

(i) Parent material

(ii) Topography

(iii) Climate

(iv) Biological activity

(v) Time.

Parent Material - Parent material is a passive control factor in soil formation. Soil formation depends

upon the texture and structure as well as the mineral and chemical composition of the Parent rock.

Topography

Soils will be thin on steep slopes and thick over flat upland areas. Over gentle slopes where erosion is

slow and percolation of water is good, soil formation is very favourable. Soils over flat areas may develop

a thick layer of clay with good accumulation of organic matter giving the soil dark colour.

Climate The climatic elements involved in soil development are :

(i) Moisture in terms of its intensity, frequency and duration of precipitation-evaporation and

humidity

(ii) Temperature in terms of seasonal and diurnal variations.

Removal of silica from the soil is known as desilication.

Temperature acts in two ways — increasing or reducing chemical and biological activity. Chemical

activity is increased in higher temperatures, reduced in cooler temperatures (with an exception of

carbonation) and stops in freezing conditions. That is why, tropical soils with higher temperatures show

deeper profiles and in the frozen tundra regions soils contain largely mechanically broken materials.

Biological Activity

The vegetative cover and organisms that occupy the parent materials from the beginning and also at later

stages help in adding organic matter, moisture retention, nitrogen etc. Dead plants provide humus, the

finely divided organic matter of the soil. Some organic acids which form during humification aid in

decomposing the minerals of the soil parent materials.

Intensity of bacterial activity shows up differences between soils of cold and warm climates. Humus

accumulates in cold climates as bacterial growth is slow. The influence of large animals like ants, termites,

earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework

the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil

that comes out of their body changes.

Time

Time is very important controlling factor in soil formation. A soil becomes mature when all soil-forming

processes act for a sufficiently long time developing a profile. Soils developing from recently deposited

alluvium or glacial till are considered young and they exhibit no horizons or only poorly developed

horizons. No specific length of time in absolute terms can be fixed for soils to develop and mature.

MCQs

1.Which one of the following processes is a gradational process?

(a) Deposition

(b) Diastrophism

(d) Erosion.

2.Which one of the following materials is affected by hydration process?

(a) Granite

(b) Clay

(d) Salts.

3.Debris avalanche can be included in the category of:

(а) Landslides

(b) Slow flow mass movements’

(d) Subsidence.

4.Which of the following is a type of mass movement?

(a) Slow movements

(b) Rapid movements

(d) All of the above.

5.Which of the following is not a cause of soil erosion?

(a) Rock Material

(b) Landform

(d) Deposition.

6.Which of the following is a form of weathering?

(a) Physical

(b) Chemical

(d) All of the above.

7.What term is used for the reaction of carbonate and bicarbonate with minerals?

(a) Carbonate

(b) Carbonation

(d) All of the above.

8.Weathering is important for:

(a) Air

(b) National economy

(d) Earth

9.Which type of weathering occurs due to growth of ice within pores and cracks of rocks during repeated

cycles of freezing and melting?

(a) Frost weathering

(b) Landslides

(d) Crystallisation.

10.Which of the following is an example of endogenic forces?

(a) Erosion

(b) Volcanism

(d) Balance.

11.Which of the following is not associated with diastrophism?

(a) Orogenic processes

(b) Epeirogenic processes

(d) Balance.

12.Which of the following is a systematic process?

(a) Weathering

(b) Diastrophism

(d) Balanced erosion.

13.What are geomorphic causes of erosion?

(a) Flowing water

(b) Underground water

(d) All of the above.

14.Which of the following process is not associated with physical weathering?

(a) Frost wedging

(b) Expansion

(d) Thawing.

15.All earth materials having a sloping surface and tend to produce movement of matter in down slope

direction. It is called:

(a) Soil erosion

(b) Landslides

(d) Slump.

16.Which of the following is affected by hydration?

(a) Granite

(b) Soil

(d) Rocks.

17Where’does oxidation take place?

(a) Where there is ready access to the atmosphere and oxygenated waters.

(b) Where there are plants.

(d) In mountainous regions.

(d) (d) (c) (d) (d) (d) (b) (b) (a) (b)

(d) (d) (d) (c) (a) (b) (a)

Q 1.Assertion (A) In dry climates, because of high temperature, evaporation exceeds precipitation and

hence ground water is brought up to the surface by capillary action and in the process the water

evaporates leaving behind salts in the soil. Such salts form into a crust in the soil known as hardpans.

Reason ( R ) In tropical climates and in areas with intermediate precipitation conditions, calcium

carbonate nodules (kanker) are formed.

 [a] A and R are true and R is the correct explanation of A.

 [b] A and R true but R is not the correct explanation of A.

 [c] A is false but R is true.

 [d] A and R both true .

 Ans: [d]

Q 2. Assertion (A) The erosion and transportation of earth materials is brought about by wind, running

water, glaciers, waves and ground water.

Reason (R) Of these the first three agents are controlled by climatic conditions.

 [a] A and R are true and R is the correct explanation of A.

 [b] A and R true but R is not the correct explanation of A.

 [c] A is false but R is true.

 [d] A and R both true .

 Ans: [b]

Short Answer Questions

Q 1. What factors have caused diastrophism?

Answer: All processes that move, elevate or build up portions of the earth’s crust come under

diastrophism. They include:

 Orogenic processes

 Epeirogenic processes

 Earthquakes

 Plate tectonics: It involves horizontal movements of crustal plates.

Q 2. Why is the surface of the earth uneven?

Answer: The difference in the internal forces operation from within the earth which built up the crust

have been responsible for the variations in the outer surface of the crust. Due to variations in geothermal

gradients and strength, the actions of endogenic forces are not uniform and hence the tectonically

controlled original crystal surface is uneven.

Q 3. How does biological weathering take place?

Answer: Biological weathering takes place by:

 Animals: Animals like rabbits, rats, termides, etc. make burrows and holes in the rocks.

They consumes large quantity of soils and rocks for making their habitat and destruction of

food. This loosens the rock strata and disintegration occurs.

 Vegetation: Long and teanatious roots of plants work down into cracks of rocks. The roots

of shrubs and trees reach deep into them and this lodge large blocks.

 Human Activities: Mining, deforestation, indiscriminate cultivation of land and construction

activities contribute to weathering.

Q 4. Deposition is the result of erosion. Explain.

Answer: Deposition is a consequence of erosion. The erosional agents loose their velocity and hence

energy on gentler slopes and the materials carried by them start to settle themselves. In other words,

deposition is not actually the work of any agent. The coarser materials get deposited first and finer ones

later. By deposition depressions get filled up. The same erosional agents viz., running water, glaciers,

wind, waves and groundwater act as aggradational or depositional agents also.

Q 5. Without gravity and gradient will there be no erosion? Prove it.

Answer: Gravity besides being a directional force activates down slope movement of matters and also

causes stresses on earth material.

 Without gravity and gradients there would be no mobility and hence no erosion, no

transportation and no deposits as gravitation stresses are as important as the other

geomorphic process.

Q 6. Explain the mass movements which are slow.

Answer:

 Soil creep: It is one type under this category which can occur on moderately steep, soil

covered slope. We may find some of evidence of extremely, slow down slope movement of

soil.

 Rock creep: The disintegrated rock material creeps down the slope under the influence of

gravity.

 Solifluction: It takes place in cold areas where there is heavy snowfall in winter. It involves

slow downslope flowing soil mass or fine grained rock debris saturated or lubricated with

water.

Q 7. Write the difference between:

(i) Exogenic and endogenic forces

Answer:

S.no.Exogenic Forces Endogenic Forces

1. The external forces are known as Exogenic

forces. The internal forces are known as Endogenic forces.

Solar energy is the sole driving force behind all

the Exogenic processes. E.g. Erosion, Flood,

Mining, etc.

Gravity is the sole driving force behind all the

Endogenic process. E.g. Earthquake, Volcanic

Eruption, etc.

(ii) Orogenic movements and epeirogenic movements

S.no.Orogenie Movements Epeirogenic Movements

1. In the process of Orogenie the crust is

severely deformed into folds.

Due to Epeirogenic they may be single

deformation.

2. It is mountain building process. It is continental building process.

3. It affects long and narrow belt of earth’s crust. It involves uplift or wrapping of large parts of

earth’s crust.

(iii) Physical weathering and chemical weathering

S.no.Physical Weathering Chemical Weathering

1. Physical force disintegrates the rocks. Rocks are decomposed by chemical changes.

2. No chemical change occurs. Not much physical change occurs but chemical change

occurs due to air and water.

3. More effective in dry and cold areas. Effective in hot and humid areas.

4. Insulation, frost and pressure are the

agents.

Oxidation and reduction carbonation, hydration and soil

are the agents.

5. Rocks are affected at the greater depth. Rocks are affected on the surface only.

6. Even the strong minerals are affected by

physical weathering. Chemical resistance minerals are not affected.

Long Answer Type Questions

Q 1. Explain different types of chemical weathering.

Answer: Different types of chemical weathering includes:

1. Oxidation and Reduction: Oxidation is the effect of oxygen in air and water on the rocks. The

atmospheric oxygen in rainwater unites with minerals in rocks specially with iron compounds. When

oxidised minerals are placed in an environment where oxygen is absent, reduction takes place. It exists

below water table, in area of stagnant water in more hot and humid climates.

2. Carbonation: When the carbon dioxide in atmosphere dissolves in water it form carbonic acid that

affects the rocks, it is carbonation. It has acidic affect and dissolves calcium carbonates and magnesium

carbonates such as gypsum, marble, limestone.

3. Hydration: When the hydrogen of water dissolves in rocks hydration occurs. Certain minerals in rocks

increase their volume and become heavy when observe water contains hydrogen. They break due to its

increased pressure and the colour also changes.

4. Solution: Rainwater is able to dissolve certain minerals and leaching of the soil occurs. Normally solids

are also removed during leaching. For e.g.: gypsum, rock salt, etc. undergo solution.

Q 2. Explain different types of physical weathering.

Answer: Different types of physical weathering includes:

 Exfoliation: Due to differential heating and resulting expansion and contraction of surface

layers and their subsequent exfoliation from the surface results in smooth rounded

surfaces in rocks. In rocks like granites, smooth surfaced and rounded small to big boulders

called tors form due to such exfoliation.

 Frost: It is an active agent in cold climatic regions in high altitudes and the cracks are filled

with water during the day time, this water is frozen at night when temperature falls below

freezing point.

 Pressure: Many igneous and metamorphic rocks crystallize deep in the interior under the

combine influence of high pressure and temperature. The salt near surface pores cause

splitting of the grains within the rocks which eventually falls off, this result into granules

disintegration.

Q 3. Is it essential to distinguish between geomorphic agents and geomorphic processes? If yes, explain

the difference.

Answer: Yes, it is essential to distinguish between geomorphic agents and geomorphic processes because

former is the cause and latter is the stepwise process.

 Geomorphic agent: An agent is a mobile medium (like running water, moving ice masses,

wind, waves and currents, etc.) which removes, transports and deposits earth materials.

Running water, groundwater, glaciers, wind, waves and currents, etc., can be called

geomorphic agents.

 Geomorphic Processes: The Endogenic and Exogenic forces causing physical stresses and

chemical actions on earth material and bringing about changes in the configuration of the

surface of the earth is known as Geomorphic Process.

Q 4. What is the sole driving force behind all the exogenic processes? Explain how?

Answer: The solar energy is the sole driving force behind all exogenic processes. Exogenic processes

derive their energy from atmosphere determined by the ultimate energy from the sun and also the

gradients created by tectonic factors.

1. Various minerals in rocks possess their own limits of expansion and contraction.

2. With rise in temperature, every mineral expands and pushes against its neighbour and as

temperature falls, a corresponding contraction takes place. Because of diurnal changes in the

cause splitting of individual grains within rocks, which eventually fall off. This process of falling

off of individual grains may result in granular disintegration or granular foliation. Salt

crystallisation is most effective of all salt-weathering processes.

3. In areas with alternating wetting and drying conditions salt crystal growth is favoured and the

neighbouring grains are pushed aside. Sodium chloride and gypsum crystals in desert areas heave

up overlying layers of materials and with the result polygonal cracks develop all over the heaved

surface. With salt crystal growth, chalk breaks down most readily, followed by limestone,

sandstone, shale, gneiss and granite etc.

Q 5. What factors activate the process of mass movement?

Answer: Following factors activate the process of mass movement.

 Removal of support from below to materials above through natural or artificial means;

 Increase in gradient and height of slopes;

 Overloading through addition of materials naturally or by artificial filling;

 Overloading due to heavy rainfall, saturation and lubrication of slope materials;

 Removal of material or load from over the original slope surfaces;

 Occurrence of earthquakes, explosions or machinery;

 Excessive natural seepage;

 Heavy drawdown of water from lakes, reservoirs and rivers leading to slow outflow of water from

under the slopes or river banks;

 Indiscriminate removal of natural vegetation.

CHAPTER 7

Landforms and their Evolution

Small to medium tracts or parcels of the earth’s surface are called landforms.

Several related landforms together make up landscapes, (large tracts of earth’s surface). Each landform

has its own physical shape, size, materials and is a result of the action of certain geomorphic processes

and agent(s).

Running Water

lateral erosion of valley sides becomes a lowland of faint relief with some low resistant remnants called

monadnocks standing out here and there.

This type of plain forming as a result of stream erosion is called a peneplain.

Erosional Landforms

Valleys

Valleys start as small and narrow rills; the rills will gradually develop into long and wide gullies; the

gullies will further deepen, widen and lengthen to give rise to valleys.

Types of valleys

V-shaped valley

Gorge: A gorge is a deep valley with very steep to straight sides. A gorge is almost equal in width at its top

as well as its bottom. Gorges form in hard rocks

Canyon: canyon is characterised by steep step-like side slopes and may be as deep as gorge. A canyon is

a variant of gorge. canyons commonly form in horizontal bedded sedimentary rocks.

Potholes and Plunge Pools

Over the rocky beds of hill-streams more or less circular depressions called potholes. Once a small and

shallow depression forms, pebbles and boulders get collected in those depressions and get rotated by

flowing water and consequently the depressions grow in dimensions.

At the foot of waterfalls also, large potholes, quite deep and wide, form because of the sheer impact of

water and rotation of boulders. Such large and deep holes at the base of waterfalls are called plunge

pools.

Incised or Entrenched Meanders

Because of active lateral erosion, streams flowing over gentle slopes, develop sinuous or meandering

courses. It is common to find meandering courses over floodplains and delta plains where stream

gradients are very gentle. But very deep and wide meanders can also be found cut in hard rocks. Such

meanders are called incised or entrenched meanders.

River Terraces

River terraces are surfaces marking old valley floor or floodplain levels. They may be bedrock surfaces

without any alluvial cover or alluvial terraces consisting of stream deposits. River terraces are basically

products of erosion as they result due to vertical erosion by the stream into its own depositional

floodplain. There can be a number of such terraces at different heights indicating former river bed levels.

The river terraces may occur at the same elevation on either side of the rivers in which case they are

called paired terraces..

Depositional Landforms

Alluvial Fans

Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of low

gradient. Normally very coarse load is carried by streams flowing over mountain slopes. This load

becomes too heavy for the streams to be carried over gentler gradients and gets dumped and spread as a

broad low to high cone shaped deposit called alluvial fan.

Deltas

Deltas are like alluvial fans but develop at a different location. If this load is not carried away far into the

sea or distributed along the coast, it spreads and accumulates as a low cone.The coarsest materials settle

out first and the finer fractions like silts and clays are carried out into the sea. As the delta grows, the

river distributaries continue to increase in length and delta continues to build up into the sea.

Floodplains, Natural Levees and Point Bars

Deposition develops a floodplain just as erosion makes valleys. Floodplain is a major landform of river

deposition. Large sized materials are deposited first when stream channel breaks into a gentle slope.

Thus, normally, fine sized materials like sand, silt and clay are carried by relatively slow moving waters in

gentler channels usually found in the plains and deposited over the bed and when the waters spill over

the banks during flooding above the bed. A river bed made of river deposits is the active floodplain.

Natural levees and point bars are some of the important landforms found associated with floodplains.

Natural levees are found along the banks of large rivers. They are low, linear and parallel ridges of coarse

deposits along the banks of rivers, quite often cut into individual mounds.

Point bars are also known as meander bars. They are found on the concave side of meanders of large

rivers and are sediments deposited in a linear fashion by flowing waters along the bank. They are almost

uniform in profile and in width and contain mixed sizes of sediments.

Meanders

In large flood and delta plains, rivers rarely flow in straight courses. Loop-like channel patterns called

meanders develop over flood and delta plains.

As meanders grow into deep loops, the same may get cut-off due to erosion at the inflection points and

are left as ox-bow lakes.

Groundwater

Physical or mechanical removal of materials by moving groundwater is insignificant in developing

landforms. The results of the work of groundwater cannot be seen in all types of rocks. But in rocks like

limestones or dolomites rich in calcium carbonate, the surface water as well as groundwater through the

chemical process of solution and precipitation deposition develop varieties of landforms. These two

processes of solution and precipitation are active in limestones or dolomites occurring either exclusively

or interbedded with other rocks.

Any limestone or dolomitic region showing typical landforms produced by the action of groundwater

through the processes of solution and deposition is called Karst topography.

The karst topography is also characterised by erosional and depositional landforms.

Erosional Landforms

Pools, Sinkholes, Lapies and Limestone Pavements

Small to medium sized round to sub-rounded shallow depressions called swallow holes form on the

surface of limestones through solution.

Sinkholes are very common in limestone/karst areas. A sinkhole is an opening more or less circular at the

top and funnel-shapped towards the bottom with sizes varying in area from a few sq. m to a hectare and

with depth from a less than half a metre to thirty metres or more.The term doline is sometimes used to

refer the collapse sinks.When sink holes and dolines join together because of slumping of materials along their margins or due to

roof collapse of caves, long, narrow to wide trenches called valley sinks or Uvalas.

Gradually, most of the surface of the limestone is eaten away by these pits and trenches, leaving it

extremely irregular with a maze of points, grooves and ridges or lapies.

Caves

Water percolates down either through the materials or through cracks and joints and moves horizontally

along bedding planes. It is along these bedding planes that the limestone dissolves and long and narrow

to wide gaps called caves. Caves normally have an opening through which cave streams are discharged.

Caves having openings at both the ends are called tunnels.

Depositional Landforms

Many depositional forms develop within the limestone caves. The chief chemical in limestone is calcium

carbonate which is easily soluble in carbonated water (carbon dioxide absorbed rainwater). This calcium

carbonate is deposited when the water carrying it in solution evaporates or loses its carbon dioxide as it

trickles over rough rock surfaces.

Stalactites, Stalagmites and Pillars

Stalactites hang as icicles of different diameters. Normally they are broad at their bases and taper

towards the free ends showing up in a variety of forms.

Stalagmites rise up from the floor of the caves. In fact, stalagmites form due to dripping water from the

surface or through the thin pipe, of the stalactite, immediately below it.

Stalagmites may take the shape of a column, a disc, with either a smooth, rounded bulging end or a

miniature crater like depression.

The stalagmite and stalactites eventually fuse to give rise to columns and pillars of different diameters.

Glaciers

Masses of ice moving as sheets over the land or as linear flows down the slopes of mountains in broad

trough-like valleys are called glaciers.The movement could be a few centimetres to a few metres a day or

even less or more. Glaciers move basically because of the force of gravity.

We have many glaciers in our country moving down the slopes and valleys in Himalayas. Higher reaches

of Uttaranchal, Himachal Pradesh and Jammu and Kashmir, are places to see some of them. Do you know

where one can see river Bhagirathi is basically fed by meltwaters from under the snout (Gaumukh) of the

Gangotri glacier. In fact, Alkapuri glacier feeds waters to Alakananda river. Rivers Alkananda and

Bhagirathi join to make river Ganga near Deoprayag.

Erosion by glaciers is tremendous because of friction caused by sheer weight of the ice. The material

plucked from the land by glaciers (usually large-sized angular blocks and fragments) get dragged along

the floors or sides of the valleys and cause great damage through abrasion and plucking. Glaciers can

cause significant damage to even un-weathered rocks and can reduce high mountains into low hills and

plains.

Erosional Landforms

Cirque

Cirques are the most common of landforms in glaciated mountains. The cirques quite often are found at

the heads of glacial valleys. The accumulated ice cuts these cirques while moving down the mountain

tops. They are deep, long and wide troughs or basins with very steep concave to vertically dropping high

walls at its head as well as sides. A lake of water can be seen quite often within the cirques after the

glacier disappears. Such lakes are called cirque or tarn lakes.

Horns and Serrated Ridges

Horns form through head ward erosion of the cirque walls. If three or more radiating glaciers cut

headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.

The divides between cirque side walls or head walls get narrow because of progressive erosion and turn

into serrated or saw-toothed ridges sometimes referred to as arêtes with very sharp crest and a zig-zag

outline.

The highest peak in the Alps, Matterhorn and the highest peak in the Himalayas, Everest are in fact horns

formed through headward erosion of radiating cirques.

Glacial Valleys/Troughs

Glaciated valleys are trough-like and U-shaped with broad floors and relatively smooth, and steep sides.

The valleys may contain littered debris or debris shaped as moraines with swampy appearance. There

may be lakes gouged out of rocky floor or formed by debris within the valleys.

There can be hanging valleys at an elevation on one or both sides of the main glacial valley. The faces of

divides or spurs of such hanging valleys opening into main glacial valleys are quite often truncated to give

them an appearance like triangular facets.

Very deep glacial troughs filled with sea water and making up shorelines are called fjords/fiords.

Depositional Landforms

The unassorted coarse and fine debris dropped by the melting glaciers is called glacial till.

Some amount of rock debris small enough to be carried by such melt-water streams is washed down and

deposited. Such glacio-fluvial deposits are called outwash deposits. The rock fragments in outwash

deposits are somewhat rounded at their edges.

Moraines

They are long ridges of deposits of glacial till.

Terminal moraines are long ridges of debris deposited at the end (toe) of the glaciers.

Lateral moraines form along the sides parallel to the glacial valleys.

The lateral moraines may join a terminal moraine forming a horse-shoe shaped ridge.

Many valley glaciers retreating rapidly leave an irregular sheet of till over their valley floors. Such

deposits varying greatly in thickness and in surface topography are called ground moraines.

The moraine in the centre of the glacial valley flanked by lateral moraines is called medial moraine. They

are imperfectly formed as compared to lateral moraines.

Eskers

When glaciers melt in summer, the water flows on the surface of the ice or seeps down along the margins

or even moves through holes in the ice. These waters accumulate beneath the glacier and flow like

streams in a channel beneath the ice. Such streams flow over the ground (not in a valley cut in the

ground) with ice forming its banks. Very coarse materials like boulders and blocks along with some minor

fractions of rock debris carried into this stream settle in the valley of ice beneath the glacier and after the

ice melts can be found as a sinuous ridge called esker.

Outwash Plains

The plains at the foot of the glacial mountains or beyond the limits of continental ice sheets are covered

with glacio-fluvial deposits in the form of broad flat alluvial fans which may join to form outwash plains of

gravel, silt, sand and clay.

Drumlins

Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till with some masses of

gravel and sand. The long axes of drumlins are parallel to the direction of ice movement. They may

measure up to 1 km in length and 30 m or so in height. One end of the drumlins facing the glacier called

the stoss end is blunter and steeper than the other end called tail. The drumlins form due to dumping of

rock debris beneath heavily loaded ice through fissures in the glacier. The stoss end gets blunted due to

pushing by moving ice. Drumlins give an indication of direction of glacier movement.

Waves and Currents

When waves break, the water is thrown with great force onto the shore, and simultaneously, there is a

great churning of sediments on the sea bottom. Constant impact of breaking waves drastically affects the

coasts. Storm waves and tsunami waves can cause far-reaching changes in a short period of time than

normal breaking waves.

High Rocky Coasts

Along the high rocky coasts, the rivers appear to have been drowned with highly irregular coastline. The

coastline appears highly indented with extension of water into the land where glacial valleys (fjords) are

present. The hill sides drop off sharply into the water. Shores do not show any depositional landforms

initially. Erosion features dominate.

Along high rocky coasts, waves break with great force against the land shaping the hill sides into cliffs.

With constant pounding by waves, the cliffs recede leaving a wave-cut platform in front of the sea cliff.

Waves gradually minimise the irregularities along the shore.

The materials which fall off, and removed from the sea cliffs, gradually break into smaller fragments and

roll to roundness, will get deposited in the offshore.

Bars are submerged features and when bars show up above water, they are called barrier bars.

Barrier bar which get keyed up to the headland of a bay is called a spit.

When barrier bars and spits form at the mouth of a bay and block it, a lagoon forms.

The lagoons would gradually get filled up by sediments from the land giving rise to a coastal plain.

Low Sedimentary Coasts

Along low sedimentary coasts the rivers appear to extend their length by building coastal plains and

deltas. The coastline appears smooth with occasional incursions of water in the form of lagoons and tidal

creeks. The land slopes gently into the water. Marshes and swamps may abound along the coasts.

Depositional features dominate.

When waves break over a gently sloping sedimentary coast, the bottom sediments get churned and move

readily building bars, barrier bars, spits and lagoons. Lagoons would eventually turn into a swamp which

would subsequently turn into a coastal plain. The maintenance of these depositional features depends

upon the steady supply of materials. Storm and tsunami waves cause drastic changes irrespective of

supply of sediments. Large rivers which bring lots of sediments build deltas along low sedimentary

coasts.

The west coast of our country is a high rocky retreating coast. Erosional forms dominate in the west coast.

The east coast of India is a low sedimentary coast. Depositional forms dominate in the east coast.

Erosional Landforms

Cliffs, Terraces, Caves and Stacks

Wave-cut cliffs and terraces are two forms usually found where erosion is the dominant shore process.

Almost all sea cliffs are steep and may range from a few m to 30 m or even more. At the foot of such cliffs

there may be a flat or gently sloping platform covered by rock debris derived from the sea cliff behind.

Such platforms occurring at elevations above the average height of waves is called a wave-cut terrace.

The lashing of waves against the base of the cliff and the rock debris that gets smashed against the cliff

along with lashing waves create hollows and these hollows get widened and deepened to form sea caves.

The roofs of caves collapse and the sea cliffs recede further inland. Retreat of the cliff may leave some

remnants of rock standing isolated as small islands just off the shore. Such resistant masses of rock,

originally parts of a cliff or hill are called sea stacks. Like all other features, sea stacks are also temporary

and eventually coastal hills and cliffs will disappear because of wave erosion giving rise to narrow coastal

plains, and with onrush of deposits from over the land behind may get covered up by alluvium or may get

covered up by shingle or sand to form a wide beach.

Depositional Landforms

Beaches and Dunes

Beaches are characteristic of shorelines that are dominated by deposition, but may occur as patches along

even the rugged shores. Most of the sediment making up the beaches comes from land carried by the

streams and rivers or from wave erosion. Beaches are temporary features. The sandy beach which

appears so permanent may be reduced to a very narrow strip of coarse pebbles in some other season.

Most of the beaches are made up of sand sized materials. Beaches called shingle beaches contain

excessively small pebbles and even cobbles.

Just behind the beach, the sands lifted and winnowed from over the beach surfaces will be deposited as

sand dunes. Sand dunes forming long ridges parallel to the coastline are very common along low

sedimentary coasts.

Bars, Barriers and Spits

A ridge of sand and shingle formed in the sea in the off-shore zone (from the position of low tide

waterline to seaward) lying approximately parallel to the coast is called an off-shore bar. An off-shore bar

which is exposed due to further addition of sand is termed a barrier bar. The off-shore bars and barriers

commonly form across the mouth of a river or at the entrance of a bay. Sometimes such barrier bars get

keyed up to one end of the bay when they are called spits (Figure 7.15). Spits may also develop attached

to headlands/hills. The barriers, bars and spits at the mouth of the bay gradually extend leaving only a

small opening of the bay into the sea and the bay will eventually develop into a lagoon. The lagoons get

filled up gradually by sediment coming from the land or from the beach itself (aided by wind) and a broad

and wide coastal plain may develop replacing a lagoon.

Winds

Wind is one of the two dominant agents in hot deserts.The wind action creates a number of interesting

erosional and depositional features in the deserts.

Erosional Landforms

Pediments and Pediplains

Landscape evolution in deserts is primarily concerned with the formation and extension of pediments.

Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris, are

called pediments.

Through parallel retreat of slopes, the pediments extend backwards at the expense of mountain front, and

gradually, the mountain gets reduced leaving an inselberg which is a remnant of the mountain. That’s

how the high relief in desert areas is reduced to low featureless plains called pediplains.

Playas

Plains are by far the most prominent landforms in the deserts. In basins with mountains and hills around

and along, the drainage is towards the centre of the basin and due to gradual deposition of sediment from

basin margins, a nearly level plain forms at the centre of the basin. In times of sufficient water, this plain

is covered up by a shallow water body. Such types of shallow lakes are called as playas where water is

retained only for short duration due to evaporation and quite often the playas contain good deposition of

salts. The playa plain covered up by salts is called alkali flats.

Deflation Hollows and Caves

Weathered mantle from over the rocks or bare soil, gets blown out by persistent movement of wind

currents in one direction. This process may create shallow depressions called deflation hollows. Deflation

also creates numerous small pits or cavities over rock surfaces. The rock faces suffer impact and abrasion

of wind-borne sand and first shallow depressions called blow outs are created, and some of the blow outs

become deeper and wider fit to be called caves.

Mushroom, Table and Pedestal Rocks

Many rock-outcrops in the deserts easily susceptible to wind deflation and abrasion are worn out quickly

leaving some remnants of resistant rocks polished beautifully in the shape of mushroom with a slender

stalk and a broad and rounded pear shaped cap above. Sometimes, the top surface is broad like a table top

and quite often, the remnants stand out like pedestals.

Depositional Landforms

Sand Dunes

Types of sand dunes

1. Crescent shaped dunes called barchans with the points or wings directed away from wind direction

2. Parabolic dunes form when sandy surfaces are partially covered with vegetation.

3. Seif is similar to barchan with a small difference. Seif has only one wing or point.

4. Longitudinal dunes form when supply of sand is poor and wind direction is constant.

5. Transverse dunes are aligned perpendicular to wind direction.

Multiple choice questions

Q 1. In which of the following stages of landform development, downward cutting is dominated?

(a) Youth stage

(b) Late mature stage

(d) Old stage

Q 2. A deep valley characterised by steep step-like side slopes is known as

(a) U-shaped valley

(b) Gorg

(d) Canyon

Q 3. In which one of the following regions the chemical weathering process is more dominant than the

Mechanical process?

(a) Humid region

(b) Limestone region

(d) Glacier region

Q 4. Which one of the following sentences best defines the term ‘Lapies’?

(a) A small to medium sized shallow depression

(b) A landform whose opening is more or less circular at the top and funnel shaped towards bottom

(d) An irregular surface with sharp pinnacles, grooves and ridges

Q 5. A deep, long and wide trough or basin with very steep concave high walls at its head as well as in

sides is known as:

(a) Cirque

(b) Glacial valley

(d)Esker

Q 6.Outwash plains are formed by:

(a) Rivers

(b) Glacier

(d) Wind

Q 7. What are most important landforms in desert areas?

(a) Chardong

(b) Interbedded rocks

(d) Valleys

Q 8. They are deep, long and wide troughs or basins with very steep concave to vertically dropping high

walls at its head as well as sides. What are they?

(a) Cirque

(b) Horne

(d) Drumlin

Q 9. Which type of landforms are formed by rivers in youth stage?

(a) Desert

(b) Cirque

(d) V-shaped valley.

Q 10. In mature stage, loop like channel patterns develop in rivers. These are called:

(a) Meanders

(b) Canyon

(d) Cirque

Q 11. On the mouth, the river flows not on one but many sides. It is called:

(a) Meanders

(b) Canyon

(d) Cirque.

Q 12 Very coarse materials like boulders and blocks along with some minor fractions of rock

debriscarried into this stream settle in the valley of ice beneath the glacier and after the ice melts can be

found as asinuous ridge called what?

(a) Meanders

(b) Esker

(d) Cirque.

Q 13. Which types of landforms are formed by rivers in their mature stage?

(a) Meanders, deltas and concave bank

(b) V-shaped valley and waterfall

(d) U-shaped valley and gorge.

Q 14. In which stage streams divides are broad and flat with marshes, swamp and lakes?

(a) Youth stage

(b) Mature stage

(d) Old stage.

Q 15.Which of the following landform is not made by rivers?

(a) V-shaped valley

(b) Waterfall

(d) Sand dunes.

Q 16. Which of the following is not created by the rivers?

(a) V-shaped valley

(b) Waterfall

(d) Sand dunes.

Q 17. Which of the following landform is made by deposition work of ground water?

(a) Lapies

(b) Pools

(d) Stalagmites.

Q 18. Which of the following landform is not made by glaciers?

(a) Cirque

(b) Horn

(d) Barkhans

a d b a a a c a d a

c b a a d d d d

SHORT ANSWER QUESTIONS

Q 1. How do landforms transform?

Answer: Stability of sea level; tectonic stability of landmasses and climate, which influence the evolution

of landforms. Any disturbance in any of these three controlling factors can upset the systematic and

sequential stages in the development and evolution of landforms.

Q 2. Where are alluvial fans formed?

Answer: Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of

low gradient.

Q 3. Name the landforms made by groundwater.

Answer: Pools, sinkholes, lapies and limestone pavements, caves, stalactites, stalagmites and pillars

stalactites are formed by groundwater.

Q 4. What do you mean by meanders?

Answer: In mature stage, loop like channel patterns develop in rivers. These are called meanders.

Q 5. How do ocean barriers prevent storm and tsunami?

Answer: The coastal off-shore bars offer the first buffer or defence against storm or tsunami by absorbing

most of their destructive force.

Q 6. What do you mean by saltation?

Answer: Depending upon the velocity of wind, different sizes of grains are moved along the floors by

rolling and carried in suspension and in this process of

transportation itself, the materials get sorted. These are called saltation.

Q 7. How are pediments formed?

Answer: Pediments are formed through the erosion of mountain front through a combination of lateral

erosion by streams and sheet flooding.

LONG QUESTION

Q 1. Explain the landforms that are seen in upper part of the river?

Answer: In upper part of the river, many beautiful and attractive landforms are

formed. Some of them are as follows:

1 V-shaped valleys

2 Gorge

3 Canyon

4 Waterfall

5 Plunge pools Explain each

Q 2. Explain the landforms made by erosion caused by groundwater?

Answer: Important landforms made by erosion are as follows:

1. Pools

2. Sinkholes

3. Lapies

4. Limestone Pavements

5. Caves Explain each

Q 3.Explain the depositional landforms made by rivers?

Answer: Depositional Landform made by rivers:

1. Alluvial Fans:

2. Deltas

3. Floodplains

4. Natural Levees

5. Point Bars Explain each

Q 4. Explain the erosional landforms created by waves and currents?

Answer: Cliffs, Terraces, Caves and Stacks are important landforms created by erosion

caused by waves and currents.

1 Wave-cut cliffs

2 Terraces

3 Sea stacks

4 caves Explain each

Q 5. Explain the different stages of a river ?

Answer: A river passes through three stages like a human being: youth, mature and old.

1. Youth Stage: Streams are less in number.

* Showing shallow V-shaped valleys with no floodplains

* Streams divides are broad and flat

* With marshes, swrnmp and lakes.

* Waterfalls and rapids may exist where local hard rock bodies are exposed.

2. Mature Stage: Streams are plenty with good integration.

* The valleysare still V-shaped but deep

* Trunk streams are broad enough to have wider floodplains within which streams may flow in meanders

confined within the valley.

* The flat and broad inter stream areas and swamps and marshes of youth disappear and the

streamdivides turn sharp.

3. Old Stage: Smaller tributaries during old age are few with gentle gradients.

* Streams meander freely over vast floodplains showing natural levees, oxbow lakes, etc.

* Dividesare broad and flat with lakes, swamps and marshes.

* Most of the landscape is at orslightly above sea level.

CHAPTER 8

COMPOSITION AND STRUCTURE OF ATMOSPHERE

Atmosphere is a mixture of different gases and it envelopes the earth all round. It contains life-giving

gases like oxygen for humans and animals and carbon dioxide for plants

99 per cent of the total mass of the atmosphere is confined to the height of 32 km from the earth’s

surface. The air is colourless and odourless and can be felt only when it blows as wind.

Composition of the Atmosphere

The atmosphere is composed of gases, water vapour and dust particles.

oxygen will be almost in negligible quantity at the height of 120 km.

carbon dioxide and water vapour are found only up to 90 km from the surface of the earth.

Gases

Carbon dioxide is meteorologically a very important gas as it is transparent to the incoming solar

radiation but opaque to the outgoing terrestrial radiation. It absorbs a part of terrestrial radiation and

reflects back some part of it towards the earth’s surface. It is largely responsible for the green house

effect. The volume of other gases is constant but the volume of carbon dioxide has been rising in the past

few decades mainly because of the burning of fossil fuels. This has also increased the temperature of the

air.

Ozone is another important component of the atmosphere found between 10 and 50 km above the earth’s

surface and acts as a filter and absorbs the ultra-violet rays radiating from the sun and prevents them

from reaching the surface of the earth.

Water Vapour

Water vapour is also a variable gas in the atmosphere, which decreases with altitude. In the warm and

wet tropics, it may account for 4% of the air by volume, while in the dry and cold areas of desert and

polar regions, it may be less then1% of the air. Water vapour also decreases from the equator towards the

poles. It also absorbs parts of the insolation from the sun and preserves the earth’s radiated heat. It thus,

acts like a blanket allowing the earth neither to become too cold nor too hot.

Dust Particles

Atmosphere has a sufficient capacity to keep small solid particles, which may originate from different

sources and include sea salts, fine soil, smoke-soot, ash, pollen, dust and disintegrated particles of

meteors.

Dust and salt particles act as hygroscopic nuclei around which water vapour condenses to produce

clouds.

Structure of the Atmosphere

The column of atmosphere is divided into five different layers depending upon the temperature

condition. They are: troposphere, stratosphere, mesosphere, thermosphere and exosphere.

1. The troposphere is the lowermost layer of the atmosphere. Its average height is 13 km and extends

roughly to a height of 8 km near the poles and about 18 km at the equator.

*This layer contains dust particles and water vapour.

*All changes in climate and weather take place in this layer.

*The temperature in this layer decreases at the rate of 1°C for every 165m of height.

*This is the most important layer for all biological activity.

2. The zone separating the tropsophere from stratosphere is known as the tropopause.

*The air temperature at the tropopause is about minus 800C over the equator and about minus 45oC over

the poles.

*The temperature here is nearly constant, and hence, it is called the tropopause.

3. The stratosphere is found above the tropopause and extends up to a height of 50 km.

*It contains the ozone layer. This layer absorbs ultra-violet radiation and shields life on the earth from

intense, harmful form of energy.

4. The Mesosphere lies above the stratosphere, which extends up to a height of 80 km.

* In this layer, once again, temperature starts decreasing with the increase in altitude and reaches up to

minus 100°C at the height of 80 km.

5. The upper limit of mesosphere is known as the mesopause.

6. The Ionosphere: is located between 80 and 400 km above the mesopause.

* It contains electrically charged particles known as ions, and hence, it is known as ionosphere. Radio

waves transmitted from the earth are reflected back to the earth by this layer.

* Temperature here starts increasing with height.

7. The Thermosphere : The uppermost layer of the atmosphere above the thermosphere is known as the

exosphere

Elements of Weather and Climate

The main elements of atmosphere which are subject to change and which influence human life on earth

are temperature, pressure, winds, humidity, clouds and precipitation.

MCQs

Q 1. which one of the following layer contains electrically charged particles known as icons?

A Ionosphere B Troposphere

C Mesosphere D Stratosphere

Q 2. Which one of the following element of the atmosphere are subject to change and influence life on

earth?

A Relief B Precipitation

C Soil D Plants

Q 3.. Which one of the following gases constitutes the major portion of the atmosphere ?

(a) Oxygen (b) Argon

Q 4. Which one of the following gases is most important for life?

(a) Oxygen (b) Argon

Q 5. What percentage of carbon di oxide is found in the atmosphere?

(a)0.036% (b)0.93%

( c)0.002% (d) 0.3%

Q 6. The Mesosphere lies above the

a) Troposphere (b) Mesosphere

Q 7. Excesss carbon di oxide in the atmosphere will cause

(a) Earth’s temperature to rise (b) Earth’s temperature to rise

( c) Decrease in weather phenomena (d) Thick ozone layer

Q 8. Which layer of the atmosphere is free from water vapour and clouds?

(a) Troposphere (b) Mesosphere

a b c c a c b c

SHORT ANSWER QUESTIONS

Q 1. Name the elements of weather.

Ans : The atmospheric conditions which make up weather of a place are known as elements of

weather.These are (i) Temperature (ii) Pressure (iii) Winds (iv) Sunshine (v) Humidity (vi)Rainfall ( vii)

Mist and fog.

Q 2. Name the major controlling factors of Climate.

Ans : The factors which change the climate from place to place are called as elements of climate. These are

(i) Latitude (ii) Altitude (iii) Distribution of land and water (iv) Pressure(v) Ocean currents ( vi)

Prevailing winds (vii ) mountain barriers

Q 3. “Water vapour acts like a blanket “ Discuss

Ans: Water vapour decreases from equator towards the poles. It absorbs parts of insolation from the sun

and thus reducing the amount reaching the earth’s surface. It also preserves the earth’s radiated heat. It

thus, acts like a blanket allowing the earth neither to become too cold nor too hot. Conditions od stability

and instability are greatly influenced by the role of water vapour.

Q 4. Why is the height of troposphere greatest at the poles?

Ans :The height of troposphere varies from one place to another. It is 8 km at the poles and 20 km at the

equator. The equator receives the maximum insolation . The heated surface give rise to strong convection

currents. These currents transport the heat to greater heights. The light air rises and increases the zone of

troposphere. In other areas due to low temperature descending winds reduce the height of troposphere.

Q 5. Explain important features of ionosphere.

Ans. The ionosphere is the ionized part of Earth's upper atmosphere from about 60 km (37 mi) to

1,000 km (620 mi) altitude, a region that includes the thermosphere and parts of the mesosphere and

exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric

electricity and forms the inner edge of the magnetosphere. It has practical importance because,

among other functions, it influences radio propagation to distant places on the Earth.

Q 6. How does the composition of air keep changing in upper layers of the earth?

Ans: The air in our atmosphere is composed of molecules of different gases. The most common

gases are nitrogen (78%), oxygen (about 21%), and argon (almost 1%). While the composition doesn't

change much as you travel up through the lower layersof the atmosphere, what does change is the

number of molecules.

Q 7. What is the role of dust particles in atmosphere?

Ans: Every solid substance is composed of very small particles. When these small particles of

matter are scattered, they become dust particles. There are different ways by which dust is

formed. When solids break, dust is formed. The biggest role of dust particles is that they help in the

formation of rains. The water vapor in the clouds condense on dust particles in the form, of water

drops. These drops fall on to the earth as rains. The absence of dust particles can delay the rain.

Likewise, mist, fog etc. are also formed due to the presence of dust particles in, the atmosphere.

Long Answer Type Questions

Q 1. Describe the role of water vapour in the weather processes.

Water vapour is the result of evaporation from water bodies on the earth. Water vapour represents

about 2% of the air by volume. The presence of water vapour in the atmosphere is of primary

importance in weather phenomena:

i. It reduces the amount of insolation reaching the earth’s surface by absorption.

ii. It acts as an insulating blanket by preserving the earth radiation. It allows the earth

neither to become too cold nor too hot.

iii. Water vapour condenses into clouds and fogs.

iv. Water vapour is the main source of the energy-giving rise to cyclons storms etc.

v. Water vapour both releases and consumes latent heat of condensation which cools and

warms the air.

vi. Water vapour makes the air-stable and unstable.

vii. Water vapour is the basic cause of all condensation and precipitation.

Q 2. What is summer solastice and winter solstice? Explain

Ans: The summer solstice (or estival solstice), also known as mid summer occurs when one of the

Earth's poles has its maximum tilt toward the Sun. It happens twice yearly, once in each hemisphere

(Northern and Southern). For that hemisphere, the summer solstice is when the Sun reaches its

highest position in the sky and is the day with the longest period of daylight. At the pole, there is

continuous daylight around the summer solstice. On the summer solstice, Earth's maximum axial tilt

toward the Sun is 23.44°. Likewise, the Sun's declination from the celestial equator is 23.44°. The

summer solstice occurs during the hemisphere's summer. This is the June solstice in the Northern

Hemisphere and the December solstice in the Southern Hemisphere. Depending on the shift of the

calendar, the summer solstice occurs sometime between June 20 and June 22 in the Northern

Hemisphere and between December 20 and December 23 in the Southern Hemisphere. The same

dates in the opposite hemisphere are referred to as the winter solstice

]

Q 3. Differentiate between Troposphere and stratosphere .

Ans:

Tropospher

Stratospher

It is the lowermost layer of the atmosphere.

It is the second layer of the atmosphere above the

earth.

Its height varies from 8 km at the poles to 18 km at

the equator. Its height goes up to 50 km.

In this layer, the temperature decreases at a rate of

1°C per 165 meters.

In this layer, the temperature is very low and

mainly constant.

It is a zone of convection currents. It is the non-convective zone of the atmosphere.

Most of the water vapours, clouds, and dust

particles are found in this layer.

Clouds, dust particles and water vapours are

practically absent in this layer.

Atmospheric disturbances are confined to this zone. This zone is free from atmospheric disturbances.

Q 4. Differentiate between weather and climate.

Ans: WEATHER CLIMATE

1. Weather stands for actual atmospheric

conditions for a short period ( a day or a

week)

1. Climate is the aggregate of atmospheric

conditions for a longer period ( say 35 years)

2. The weather changes from day to day, ths

cannot be generalized

2.Theclimateis everlasting and static. It does

not change so frequently.

3. Weather depends upon the dominant

element at a particular time say Rainfall,

temperature etc.

3. Climate is the composite picture of all the

elements spread over a longer period.

4. Weather refers to a particular place 4. Climate refers to a particular area

5. Weather is uncertain and we can only

forecast for a short time ahead

5. Climate has a high degree of accuracy and it

is similar year after year

SOURCE BASED QUESTIONS

The atmosphere is composed of gases, water vapour and dust particles. Nitrogen constitutes 78.8%,

oxygen contributes 20.94% and argon contributes 0.93% in atmosphere. Other gases include carbon

dioxide, helium, ozone, methane, hydrogen, krypton, xenon and neon, etc. Nitrogen and oxygen together

constitute 99% of the atmosphere. Neon, krypton, xenon are scarce gases. The proportion of gases

changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible

quantity at the height of 120 km. Similarly, carbon dioxide and water vapour are found only up to 90 km

from the surface of the earth. Carbon dioxide is meteorologically a very important gas as it is transparent

to the incoming solar radiation but opaque to the outgoing terrestrial radiation. It absorbs a part of

terrestrial radiation and reflects back some part of it towards the earth’s surface. It is largely responsible

for the green house effect. Ozone is another important component of the atmosphere. It is found between

10 and 50 km above the earth’s surface and acts as a filter. It absorbs the ultra-violet rays radiating from

the sun. It prevents them from reaching the surface of the earth.

Q 1. What is the importance of Ozone layer?

Ans. Ozone layer shields the earth from intense, harmful ultra violet rays

Q 2. Why carbon di oxide is meteorologically a very important gas?

Ans.Because it is transparent to incoming solar radiation but opaque to outgoing terrestrial

radiation.

Q 3. Which gas is responsible for Green house effect?

A. Carbon di oxide B. Nitrogen

C. Helium D. Oxygen

Ans: A. Carbon di oxide

Q 4. Which two gases are the main constituents of atmosphere?

A. Oxygen and argon B. Nitrogen and Argon

C. Oxygen and Carbon di oxide D. Nitrogen and Oxygen.

Ans: D. Nitrogen and Oxygen.

Chapter- 9

Solar Radiation, Heat Balance and Temperature

Insolation : The amount of solar radiation received on earth is called insolation. The energy is received in

the form of short waves.

This radiant energy of the sun is received at the rate of 1.94 calories per sq. cm. per minute at the surface

of the earth.

Aphelion and Perihelion:-

Perihelion Aphelion

1) Perihelion is the point in an orbit that

is the nearest point to the sun.

a) Aphelion is the point in an orbit that

is the farthest point from the sun.

2) the Earth comes closest to the sun on

3rd January every year

b) the Earth comes to the farthest point

of its orbit on 4th July every year

3) At this point, the distance between

the Earth and the sun is about 91.4

million miles/ 147 million km.

c) At this point, the distance between

the Earth and the sun is about 94.5

million miles/ 152 million km.

FACTORS AFFECTING INSOLATION:

The amount and the intensity of insolation vary during a day, in a season and in a year. The factors that

cause these variations in insolation are

(i) The rotation of earth on its axis;

(ii) The angle of inclination of the sun‘s rays;

(iii) The length of the day;

(iv) The transparency of the atmosphere;

(v) The configuration of land in terms of its aspect.

HEATING AND COOLING OF THE ATMOSPHERE:

The different ways of heating and cooling the atmosphere: -

1. Conduction

2. Convection

3. Radiation

4. Advection

Heat Budget of the Planet Earth: -

INCOMING SOLAR RADIATION-

a. The earth does not accumulate or loose

heat. It maintains its temperature.

b. This can happen only if the amount of

heat received in the form of insolation

equals the amount lost by the earth

through terrestrial radiation.

c. Consider that the insolation received at

the top of the atmosphere is 100 percent.

d. While passing through the atmosphere

some amount of energy is reflected,

scattered, and absorbed.

e. Only the remaining part reaches the

earth surface.

f. Roughly 35 units are reflected to space

even before reaching the earth ‘s surface.

g. Of these, 27 units are reflected from the

top of the clouds

h. Only 2 units from the snow and icecovered areas of the earth.

i. The remaining 65 units are absorbed,14

units within the atmosphere and 51 units

by the earth ‘s surface.

TERRESTRIAL RADIATIONa) The earth radiates back 51 units in the form

of terrestrial radiation.

b) 17 units are radiated to space directly

c) the remaining 34 units are absorbed by the

atmosphere

d) 6 units absorbed directly by the atmosphere,

e) 9 units through convection and turbulence

f) 19 units through latent heat of condensation

g) 48 units absorbed by the atmosphere (14

units from insolation +34 units from

terrestrial radiation) are also radiated back

into space.

TEMPERATUREThe interaction of insolation with the atmosphere and the earth’s surface creates heat

which is measured in terms of temperature.

Factors Controlling Temperature Distribution: -

i. The latitude of the place

ii. The altitude of the place

iii. Distance from the sea, the air mass circulation

iv. The presence of warm and cold ocean currents

v. Local aspects

Isotherms- Isotherms are lines joining places having equal temperature.

INVERSION OF TEMPERATURE: -

i. Normal lapse rate: temperature decreases with increase in elevation.

ii. Inversion of temperature: normal lapse rate is inverted.

iii. The inversion takes place in hills and mountains due to air drainage.

Air drainage -The cold air acts almost like water and moves down the slope to pile up deeply in pockets

and valley bottoms with warm air above under the influence of gravity. This is called air drainage

Plank’s law states that hotter a body, the more energy it will radiate and shorter the wavelength of that

radiation.

Specific heat is the energy needed to raise the temperature of one gram of substance by one Celsius

EXERCISEMultiple choice questions1) Which one of the following means the rate of decrease of temperature with height?

a) Terrestrial radiation b) Albedo of the earth

c) Heat budget d) Normal lapse rate

2) Which one of the following is important in heating the lower layer of the atmosphere?

a) Conduction b) Insolation

c) Convection d) Advection

3) On 22th December, receives direct rays of the sun as the south pole tilts towards it.

a) Tropic of Capricorn b) Equator

c) poles d) Tropic of cancer

4) Which one of the following means vertical heating of the atmosphere?

a) Conduction b) Convection

c) Transition d) Advection

5) What is the role of air drainage in the atmosphere?

a) Influence the gravity b) Influence temperature

c) Produce dust and smoke d) Protects plants from frost damage

6) The main reason that the earth experiences highest temperatures in the subtropics in the

northern hemisphere rather than at the equator is:

a) Subtropical areas have longer day hours in the summer than the equatorial areas

b) Subtropical areas have an enhanced "greenhouse effect" compared to equatorial areas

c) Subtropical areas are nearer to the oceanic areas than the equatorial locations

d) Subtropical areas tend to have less cloud cover than equatorial areas

7) On which date the earth is nearest to the sun:

a) 6th January b) 3rd January

c) 4th January d) 5th January

8) The transfer of the amount of visible radiation by the earth is called as its .

a) Scattering b) Dispersion

c) Albedo d) Refraction

9) The earth is farthest from the sun on:

a) 4th July b) 6th July

c) 7th July d) 5th July

10)The insolation received by the earth is in short waves forms and heats up its surface is calleda) Conduction b) Insolation

c) Terrestrial radiation d) Advection

MCQ: Answers (10)

1) (d) Normal lapse rate

2) (a) Conduction

3) (a) Tropic of Capricorn

4) (b) Convection

5) (d) Protects plants from frost damage

6) (a) Subtropical areas have longer day hours in the summer than the equatorialareas

7) (b) 3rd January

8) (c) Albedo

9) (a) 4th July

10)(a) Terrestrial radiation

Very Short Answer Type Question

1. What is albedo?

While passing through the atmosphere some amount of energy is reflected, scattered and absorbed.

Only the remaining part reaches the earth surface. The reflected amount of radiation is called the

albedo of the earth.

2. What is terrestrial radiation?

Answer: The insolation received by the earth is in short wave forms and heats up its surface. The

earth after being heated itself becomes a radiating body and it radiates energy to the atmosphere in

long wave form. This energy heats up the atmosphere from below. This process is known as

terrestrial radiation.

3. Differentiate between Perihelion and Aphelion.

Answer: During its revolution around the sun, the earth is farthest from the sun, on 4th July. This

position of earth is called Aphelion. And on 3rd January, the earth is the nearest to the sun. This

position is called Perihelion.

SHORT ANSWER TYPE QUESTIONS

4. Explain the factors affecting insolation at the surface of earth.

Answer: The factors affecting insolation at the surface of earth are: -

1. The rotation of earth on its axis: The fact that the earth on its axis makes an angle of 6614 with

the plane of its orbit round the sun has a greater influence on the amount of insolation received at

different latitudes.

2. The angle of inclination of the sunrays: The higher the latitude the greater is the angle they make

with the surface of the earth resulting in slant sunrays. The areas covered by vertical rays are always

less than the slant rays. If more areas is covered the energy gets distributed and the net energy

received per unit area decreases. Thus, the slant rays are required to pass through greater depth of

the atmosphere resulting in more absorption, scattering and diffusion.

3. The transparency of the atmosphere: The atmosphere is largely transparent to the short wave

solar radiation. The incoming solar radiation passes through the atmosphere before striking the

earth‘s surface. Within the troposphere water vapour, ozone and other gases absorb much of the near

infrared radiation.

4. The configuration of land in terms of its aspect: The insolation received at the surface varies

from about 320 watt/ m2 in the poles. Maximum insolation is received over the subtropical deserts,

when the cloudiness is the least. Equator receives less rainfall as compared to tropics.

LONG ANSWER TYPE QUESTIONS

5. Explain the heating and the cooling mechanism of atmosphere.

Answer:

a) Conduction: Transfer of heat molecules from hot to cold substances through contact is known

as conduction.

b) Convection: In this process transfer of heat takes place only in liquid or gaseous

condition of the substance. The molecules become light and rise the vacant spaces are

filled by the cooler mass

c) Radiation: In this process heat is transferred directly from space to atmosphere.

d) Advection: The process of the horizontal transfer of heat by winds is calledadvection. is the

outcome of advection process.

6. Study the following graph and answer the questions that follows:

6.1 What amount of radiation is reflected back to the outer space directly without reaching the surface?

Ans: 35 units

6.2 What is the total amount of terrestrial radiation originating from the surface of the earth?

Ans: 51 units

6.3 What is the total amount of energy that passes through the earth‘s atmosphere?

Ans: 65 units

6.4 How much solar insolation is directly absorbed by the atmosphere?

Ans: 34 units

Chapter-10

Atmospheric Circulation and Weather System

ATMOSPHERIC PRESSUREThe weight of a column of air contained in a unit area from the mean sea level to the topof the

atmosphere is called the atmospheric pressure.

a) The atmospheric pressure is expressed in units of Millibars. At sea level the average

b) atmospheric pressure is 1,013.2 Millibars. Due to gravity the air at the surface is denser

c) and hence has higher pressure.

d) Air pressure is measured with the help of a mercury barometer or the aneroid barometer

e) The pressure decreases with height.

f) wind which moves from high pressure areas to low pressure areas.

VERTICAL VARIATION OF PRESSUREa) In the lower atmosphere the pressure decreases rapidly with height. The decrease amounts to

about 1 mb for each 10 m increase in elevation. It does not always decrease at the same rate.

b) The vertical pressure gradient force is much larger than that of the horizontal pressure

gradient. But it is generally balanced by a nearly equal but opposite gravitational force.

Hence, we do not experience strong upward winds.

HORIZONTAL DISTRIBUTION OF PRESSUREHorizontal distribution of pressure is studied by drawing isobars at constant levels.

Isobars are lines connecting places having equal pressure.

a) Low- pressure system is enclosed by one or more isobars with the lowest pressure in the centre.

b) High-pressure system is also enclosed by one or more isobars with the highest pressure in the

centre.

WORLD DISTRIBUTION OF SEA LEVEL PRESSUREa. Near the equator the sea level pressure is low and the area is known as equatorial low.

b. Along 30° N and 30° S are found the high-pressure areas known as the subtropical highs.

c. Further pole wards along 60° N and 60° S, the low-pressure belts are termed as the sub

polar lows.

d. Near the poles the pressure is high and it is known as the polar high.

e. These pressure belts are not permanent in nature. They oscillate with the apparent

movement of the sun.

f. In the northern hemisphere in winter, they move southwards and in the summer

northwards.

FORCES AFFECTING THE VELOCITY AND DIRECTION OF WIND1. PRESSURE GRADIENT FORCE

a. It is the rate of change of pressure with respect to distance.

b. The pressure gradient is strong where the isobars are close to each other and is weak

where the isobars are apart.

2. FRICTIONAL FORCE

a. The force generated by two surfaces that contacts and slide against each other is called

Frictional Force.

b. It has great impact on the speed of wind. It has highest impact on the elevation of 1-3 km

and lower over the sea surface.

3. CORIOLIS FORCE

a. The rotation of the earth about its axis affects the direction of the wind. This force is called

the Coriolis force. It deflects the wind to the right direction in the northern hemisphere

and to the left in the southern hemisphere.

b. The deflection is more when the wind velocity is high.

c. The higher the pressure gradient force, the more is the velocity of the wind and the larger

is the deflection in the direction of wind.

d. At the equator, the Coriolis force is zero and the wind blows perpendicular to the isobars.

GENERAL CIRCULATION OF THE ATMOSPHERE

The pattern of the movement of the planetary winds is called the general circulation of the atmosphere.

The pattern of planetary winds largely depends on:

(i) latitudinal variation of atmospheric heating;

(ii) emergence of pressure belts;

(iii) the migration of belts following apparent path of the sun;

(iv) the distribution of continents and oceans;

(v) the rotation of earth.

LAND AND SEA BREEZES-

-During the day the land heats up

faster and becomes warmer than the

sea. Therefore, over the land the air

rises giving rise to a low pressure

area, whereas the sea is relatively

cool and the pressure over sea is

relatively high. Thus, pressure

gradient from sea to land is created

and the wind blows from the sea to

the land as the sea breeze.

- In the night the

reversal of condition takes place. The

land loses heat faster and is cooler

than the sea. The pressure gradient is

from the land to the sea and hence

land breeze results.

MOUNTAIN AND VALLEY WINDS-

- In mountainous regions, during the day the

slopes get heated up and air moves upslope

and to fill the resulting gap the air from the

valley blows up the valley. This wind is

known as the valley breeze.

- During the night the slopes get cooled and

the dense air descends into the valley as the

mountain wind.

-The cool air, of the high plateaus and ice

fields draining into the valley is called

katabatic wind.

AIR MASSESAn air mass is a large volume of air in the atmosphere that is mostly uniform in temperature and

moisture. Following types of air masses are recognised:

(i) Maritime tropical (mT);

(ii) Continental tropical (cT);

(iii) Maritime polar (mP);

(iv) Continental polar (cP);

(v) Continental arctic (cA).

(vi) Tropical air masses are warm and polar air masses are cold

FRONTS:

When two different air masses meet, the boundary zone between them is called a front.

The process of formation of the fronts is known as frontogenesis.

There are four types of fronts:

a) Cold : When the cold air moves towards the warm air mass, its contact zone is called the cold

front,

b) Warm : if the warm air mass moves towards the cold air mass, the contact zone is a warm front.

c) Occluded : If an air mass is fully lifted above the land surface, it is called the occluded front.

d) Stationary : When the front remains stationary, it is called a stationary front.

TROPICAL CYCLONESTropical cyclones are violent storms that originate over oceans in tropical areas and large scale

destruction caused by violent winds, very heavy rainfall, and storm surges.

OTHER NAMES OF TROPICAL CYCLONESa) Cyclones in the Indian Ocean,

b) Hurricanes in the Atlantic,

c) Typhoons in the Western Pacific and South China Sea, and

d) Willy-willies in the Western Australia.

The conditions favourable for the formation and intensification of tropical storms are:

(i) Large sea surface with temperature higher than 27°C;

(ii) Presence of the Coriolis force;

(iii) Small variations in the vertical wind speed;

(iv) A pre-existing weak low-pressure area or low-level-cyclonic circulation;

(v) Upper divergence above the sea level system.

EXTRA TROPICAL CYCLONEIt is developed in the mid and high latitude beyond tropics which causes abrupt changes in the

weather conditions over area in the middle and high latitudes.

THUNDERSTORMIt is a storm resulting from strong rising air currents; heavy rain or hail along with thunder and

lightning. It is caused by intense convection on moist hot days.

TORNADOWhen severe thunderstorms sometimes spiralling wind descends like a trunk of an elephant with

great force, with very low pressure at the centre, causing massive destruction on its way. Such a

phenomenon is called a tornado. It is generally occurred in middle latitudes.

EXERCISE

MULTIPLE CHOICE QUESTIONS1. The Inter Tropical Convergence Zone normally occurs:

(a) Near the Equator

(b) Near the Tropic of Cancer

(d) Near the Arctic Circle.

Answer:

(a) Near the Equator

2. The direction of wind around a low pressure in northern hemisphere is:

(a) Clockwise

(b) Perpendicular to isobars

(d) Parallel to isobars.

Answer:

3. What does a cell in tropics called?

(a) Polar cell

(b) Hadley cell

(d) Frost cell.

Answer:

(b) Hadley cell

4. What is tropical cyclone in Australia called?

(a) Hurricanes

(b) Typhoons

(d) Willy-willies,

Answer:

(d) Willy-willies

5. Circular flow of air in low pressure area is called:

(a) Cyclonic circulation

(b) Pascal

(d) Western storm.

Answer:

(a) Cyclonic circulation

6. What is the unit for measuring pressure?

(a) Barometer

(b) Millibars and Pascal

(d) Isobars.

Answer:

(b) Millibars and Pascal

7. Which instrument is used for measuring pressure?

(a) Mercury barometer or the aneroid barometer

(b) Pascal

(d) Seismograph.

Answer:

(a) Mercury barometer or the aneroid barometer.

8. The cool air, of the high plateaus and ice fields draining into the valley is called:

(a) Mountain wind

(b) Valley breeze

(d) Cold front.

Answer:

SHORT ANSWER TYPE QUESTIONS1. How many types of fronts are there?

Answer:There are four types of fronts:

a) Cold

b) Warm

c) Stationary

d) Occluded.

2. What do you mean by extra tropical cyclones?

Answer:The systems developing in the mid and high latitude, beyond the tropics are called the

middle latitude or extra tropical cyclones.

3. What do you mean by Geostrophic wind?

Answer:When isobars are straight and when there is no friction, the pressure gradient force is

balanced by the Coriolis force and the resultant wind blows parallel to the isobar. This wind is

known as the geostrophic wind.

4. What is air mass? In how many categories are air masses categorized on the basis of their source

regions?

Answer:The air with distinctive characteristics in terms of temperature and humidity is called an

air mass. In other words, it is defined as a large body of air having little horizontal variation in

temperature and moisture.

The homogenous surfaces, over which air masses form, are called the source regions. The air

masses are classified according to the source regions into five major source regions. These are:

a) Warm tropical and subtropical oceans: Maritime tropical (mT);

b) The subtropical hot deserts: Continental tropical (cT);

c) The relatively cold high latitude oceans: Maritime polar (mP);

d) The very cold snow-covered continents in high latitudes: Continental polar (cP);

e) Permanently ice-covered continents in the Arctic and Antarctica: Continental arctic (cA).

5. What is a tropical cyclone? Give its two examples. What are the favourable conditions for its

formation?

Answer:Tropical cyclones are violent storms that originate over oceans in tropical areas and

move over to the coastal areas bringing about large-scale destruction caused by violent winds,

very heavy rainfall, and storm surges.

Cyclones in the Indian Ocean and Hurricanes in the Atlantic are its biggest examples. Tropical

cyclones originate and intensify over warm tropical oceans.

The conditions favourable for the formation and intensification of tropical storms are:

a) Large sea surface with temperature higher than 27 C;

b) Presence of the Coriolis force;

c) Small variations in the vertical wind speed;

d) A pre-existing weak low-pressure area or low-level-cyclonic circulation;

e) Upper divergence above the sea level system.

6. What are the features of El-Nino?

Answer:EI-Nino is a complex weather system that appears once every three to seven years,

bringing drought, floods, and other weather extremes to different parts of the world.

Features:

a) The system involves oceanic and atmospheric phenomena with the appearance of warm

currents off the coast of Peru in the Eastern Pacific and affects weather in many places

including India.

b) EI-Nino is merely an extension of the warm equatorial current which gets replaced

temporarily by cold Peruvian current or Humbolt current.

c) These current increases the temperature of water on the Peruvian coast by

10 C.

This results in:

a) The distortion of equatorial atmospheric circulation;

b) Irregularities in the evaporation of sea water;

c) Reduction in the number of planktons which further reduces the number of fish in thesea.

7. Draw a simplified diagram to show the general circulation of the atmosphere over the

globe.What are the possible reasons for the formation of subtropical high pressure over

30° N and S latitudes?

Answer: The general circulation of the atmosphere also sets in motion the ocean water circulation

which influences the earth ‘s climate and affects the oceans.

a. The air at the Inter Tropical Convergence Zone (ITCZ) rises because of convection caused by high

insolation and a low pressure is created. The winds from the tropics converge at this low-pressure

zone.

b. The converged air rises along with the convective cell. It reaches the top of the troposphere up to

an altitude of 14 km. and moves towards the poles. This causes accumulation of air at about 30° N

and S.

c. Part of the accumulated air sinks to the ground and forms a subtropical high. Another reason for

sinking is the cooling of air when it reaches 30° N and S latitudes.

d. Down below near the land surface the air flows towards the equator as the easterlies. The

easterlies from either side of the equator converge in the Inter Tropical Convergence Zone (ITCZ).

e. Such circulations from the surface upwards and vice-versa are called cells. Such a cell in the

tropics is called Hadley Cell.

f. In the middle latitudes the circulation is that of sinking cold air that comes from the poles and the

rising warm air that blows from the subtropical high. At the surface these winds are called

westerlies and the cell is known as the Ferrell cell.

g. At polar latitudes the cold dense air subsides near the poles and blows towards middle latitudes

as the polar easterlies. This cell is called the polar cell.

These three cells set the pattern for the general circulation of the atmosphere. The transfer of heat

energy from lower latitudes to higher latitudes maintains the general circulation.

SOURCE BASED QUESTIONSQ1. Read the extract given below and answer the questions follows:

General Atmospheric Circulation and its Effects on Oceans Warming and cooling of the Pacific

Ocean is most important in terms of general atmospheric circulation. The warm water of the

central Pacific Ocean slowly drifts towards South American coast and replaces the cool Peruvian

current. Such appearance warm water off the coast of Peru is known as the El Nino. The El Nino

event is closely associated with the pressure changes in the Central Pacific and Australia. This

change in pressure condition over Pacific is known as the southern oscillation. The combined

phenomenon of southern oscillation and El Nino is known as ENSO. In the years when the ENSO is

strong, large-scale variations in weather occur over the world. The

arid west coast of South America receives heavy rainfall; drought occurs in Australia and

sometimes in India and floods in China. This phenomenon is closely monitored and is used for

long range forecasting in major parts of the world.

Q1. The warm water of the central Pacific Ocean slowly drifted towards which coast?

Ans: South American coast

Q1. Appearance of warm water off the coast of Peru is known as

Ans: ELNINO

Q1. The combined phenomenon of southern oscillation and El Nino is known as

Ans: ENSO

Q1. The El Nino event is closely associated with which place?

Ans: Central pacific and Australia

Chapter-11

Water in the Atmosphere

HUMIDITYAir contains water vapour, which varies from 0 to 4% by volume of the atmosphere. Water vapour

present in the air is known as humidity.

Humidity is expressed in two ways:

Absolute humidity1) The actual amount of the water vapour present in the atmosphere is known as the absolute

humidity.

2) It is the weight of water vapour per unit volume of air and is expressed in terms of grams per

cubic metre.

Relative humidity- The percentage of moisture to its full capacity at a given temperature is known as the

relative humidity.The ability of the air to hold water vapour depends entirely on its temperature

The moisture in the atmosphere is present in the three forms, i.e., solid, liquid, and gaseous.

Saturated-The air containing moisture to its full capacity at a given temperature is said to be saturated.It

means that the air at the given temperature is incapable of holding any additional amount of moisture at

that stage.

Dew point -The temperature at which saturation occurs in a given sample of air is known as dew point.

EVAPORATION and CONDENSATIONEVAPORATION1) Evaporation is a process by which water is transformed from liquid to gaseous state. Heat is the

main cause for evaporation.

2) The temperature at which the water starts evaporating is referred to as the latent heat of

vaporization. Increase in temperature increases water absorption and retention capacity of the

given parcel of air.

3) Movement of air replaces the saturated layer with the unsaturated layer.

CONDENSATION1) The transformation of water vapour into water.

2) Condensation is caused by the loss of heat.

Condition for formation of Condensation1) When moist air is cooled, it may reach a level when its capacity to hold water vapour ceases.

Then, the excess water vapour condenses into liquid form.

2) Condensation also takes place when the moist air comes in contact with some colder object

and it may also take place when the temperature is close to the dew point.

3) Condensation, therefore, depends upon the amount of cooling and the relative humidity of the

air.

Dew

1) When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects

such as stones, grass blades and plant leaves, it is known as dew.

2) The Ideal Conditions for Its Formation are clear sky, calm air, high relative humidity, and cold

and long nights. For the formation of dew, it is necessary that the dew point is above the freezing

point.

Frost

1) Frost forms on cold surfaces when condensation takes place below freezing point (00C), i.e. the

dew point is at or below the freezing point.

2) The excess moisture is deposited in the form of minute ice crystals instead of water droplets.

3) The Ideal Conditions For The Formation of white frost are the same as those for the formation

of dew, except that the air temperature must be at or below the freezing point.

Fog and Mist

1) Fog is a cloud with its base at or very near to the ground. Because of the fog and mist, the visibility

becomes poor to zero.

2) The only difference between the mist and fog is that mist contains more moisture than the fog.

3) In mist each nuceli contains a thicker layer of moisture. Mists are frequent over mountains as the

rising warm air up the slopes meet a cold surface.

4) Fogs are drier than mist and they are prevalent where warm currents of air come in contact with

cold currents. Fogs are mini clouds in which condensation takes place around nuclei provided by

the dust, smoke, and the salt particles.

SMOG –

1) In urban and industrial centres smoke provides plenty of nuclei which help the formation of fog

and mist.

2) Such a condition when fog is mixed with smoke, is described as SMOG.

CLOUDSCloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water

vapour in free air at considerable elevations.

TYPES OF CLOUDSAccording to their height, expanse, density and transparency or opaqueness clouds are grouped under

four types :(i)Cirrus; (ii)Cumulus; (iii)Stratus; (iv)-Nimbus.

1) Cirrusa) Cirrus clouds are formed at high altitudes (8,000 - 12,000m).

b) They are thin and detached clouds having a feathery appearance. They are always white in

colour.

2) Cumulusa) Cumulus clouds look like cotton wool. They are generally formed at a height of 4,000 -

7,000 m.

b) They exist in patches and can be seen scattered here and there. They have a flat base.

3) Stratus -

a) As their name implies, these are layered clouds covering large portions of the sky.

b) These clouds are generally formed either due to loss of heat or the mixing of air masses

with different temperatures.

4) Nimbusa) Nimbus clouds are black or dark grey. They form at middle levels or very near to the

surface of the earth.

b) These are extremely dense and opaque to the rays of the sun. Sometimes, the clouds are so

low that they seem to touch the ground. Nimbus clouds are shapeless masses of thick

vapour.

PRECIPITATIONThe process of continuous condensation in free air helps the condensed particles to grow in size. When

the resistance of the air fails to hold them against the force of gravity, they fall on to the earth’s surface in

the form of precipitationi.e. rainfall or snowfall

a) The precipitation in the form of water is called rainfall,

b) when the temperature is lower than the 0°C, precipitation takes place in the form of fine flakes of

snow and is called snowfall.

SLEET

a) Sleet is frozen raindrops and refrozen melted snow-water.

b) When a layer of air with the temperature above freezing point overlies a subfreezing layer near

the ground, precipitation takes place in the form of sleet.

HAILSTONES –

a) When drops of rain after being released by the clouds become solidified into small rounded solid

pieces of ice and which reach the surface of the earth are called hailstones.

b) These are formed by the rainwater passing through the colder layers.

c) Hailstones have several concentric layers of ice one over the other.

TYPES OF RAINFALLCyclonic rains

a) Cyclonic rainsare caused when the warm

moist air comes in contact with cool dry air.

b) At the end of summer, the air above the

water heats up and rises creating an area of

low pressure. So, the high pressure cold air

starts rushing in.

c) When this cold air meets the warm air, it

forms a high-speed spiral that rises up and

causes rain along the coasts.

CONVECTIONAL RAINa) The, air on being heated, becomes light and

rises up in convection currents. As it rises,

it expands and loses heat and

consequently, condensation takes place

and cumulous clouds are formed.

b) Such rain is common in the summer or in

the hotter part of the day.

c) It is very common in the equatorial regions

and interior parts of the continents,

particularly in the northern hemisphere.

OROGRAPHIC RAIN (RELIEF RAIN)-

a) When the saturated air mass comes

across a mountain, it is forced to

ascend and as it rises, it expands; the

temperature falls, and the moisture is

condensed. It is also known as the

relief rain.

b) The chief characteristic of this sort of

rain is that the windward slopes

receive greater rainfall.

c) After giving rain on the windward

side, when these winds reach the

other slope, they descend, and their

temperature rises. Then their

capacity to take in moisture increases

and hence, these leeward slopes

remain rainless and dry.

d) The area situated on the leeward side,

which gets less rainfall is known as

the rain-shadow area.

WORLD DISTRIBUTION OF RAINFALLa) In general, as we proceed from the equator towards the poles, rainfall goes on decreasing steadily.

b) The coastal areas of the world receive greater amounts of rainfall than the interior of the

continents.

c) The rainfall is more over the oceans than on the landmasses of the world because of being great

sources of water.

d) Between the latitudes 35° and 4° N and S of the equator, the rain is heavier on the eastern coasts

and goes on decreasing towards the west.

e) But, between 45° and 65° N and S of equator, due to the westerlies, the rainfall is first received on

the western margins of the continents and it goes on decreasing towards the east.

f) Wherever mountains run parallel to the coast, the rain is greater on the coastal plain, on the

windward side and it decreases towards the leeward side.

MAJOR PRECIPITATION REGIMES OF THE WORLDBased on the total amount of annual precipitation, major precipitation regimes of the world are identified

as follows.

a) The equatorial belt, the windward slopes of the mountains along the western coasts in the cool

temperate zone and the coastal areas of the monsoon land receive heavy rainfall of over 200 cm

per annum.

b) Interior continental areas receive moderate rainfall varying from 100 - 200 cm per annum. The

coastal areas of the continents receive moderate amount of rainfall.

c) The central parts of the tropical land and the eastern and interior parts of the temperate lands

receive rainfall varying between 50 - 100 cm per annum.

d) Areas lying in the rain shadow zone of the interior of the continents and high latitudes receive

very low rainfall-less than 50 cm per annum. Seasonal distribution of rainfall provides an

important aspect to judge its effectiveness.

e) In some regions rainfall is distributed evenly throughout the year such as in the equatorial belt

and in the western parts of cool temperate regions.

EXERCISEMULTIPLE CHOICE QUESTIONS1.Which one of the following is an important feature of Nimbus cloud?

a) Layer clouds covering large portion of the sky

b) Extremely dense and opaque to the rays of the sun

c) Flat base

d) Feathery appearance

2.Which one of the following is the highest cloud in the sky?

a) Cirrus

b) Nimbus

c) Cumulus

d) Stratus

3.The actual amount of the water vapour present in the atmosphere known as:

a) Relative humidity

b) Dew point

c) Saturated

d) Absolute humidity

4.The air that contains moisture to its full capacity:

a) Absolute humidity

b) Saturated air

c) Specific humidity

d) Relative humidity

5.The temperature at which the water starts evaporating is referred as:

a) Latent heat of vapourisation

b) Dew point

c) Condensation

d) Sublimation

6.Which one of the following is the most important constituent of the atmosphere for human

beings?

a) Oxygen

b) Water vapour

c) Dust particle

d) Nitrogen

7.Which one of the following type of rainfall is common in the equatorial region and interior parts

of the continents?

a) Cyclonic

b) Frontal

c) Convectional

d) Orographic

8.Which one of the following means a frozen raindrops and refrozen melted snow water?

a) Snowfall

b) Sleet

c) Rainfall

d) Hailstones

9.Which one of the following processes is responsible for transforming the liquid into vapor?

a) Evaporation

b) Transpiration

c) Precipitation

d) Condensation

10.Consider the following statements about troposphere

a. It contains approximately 99% of atmosphere’s water vapour and aerosols.

b. It is deeper in the tropics upto 12 miles and shallower near the polar regions, at 4.3 miles

in summer and indistinct in winter.

c. Tropopause is the region of temperature inversion.

Which of the above statement(s) is/are correct?

a) Only 1

b) Only 2

c) 1 and 3

d) All of these

MCQ: Answers -

(b) Extremely dense and opaque to the rays of the sun

(a) Cirrus

(d) Absolute humidity

(b) Saturated air

(a) Latent heat of vapourisation

(b) Water vapour

(b) Sleet

(a) Evaporation

(d)All of these

SHORT ANSWER TYPE QUESTIONSQuestion 1. What is smog?

Answer: Such a condition when fog is mixed with smoke, is described as smog.

Question 2. How are clouds classified?

Answer: According to their height, expanse, density and transparency or opaqueness clouds are grouped

under four types: cirrus, cumulus; stratus; nimbus. A combination of these four basic types can give rise

to the following types of clouds: high clouds cirrus, cirrostratus, cirrocumulus; middle clouds—

altostratus and altocumulus; low clouds—stratocumulus and nimbostratus and clouds with extensive

vertical development cumulus and cumulonimbus.

Question3. What are the suitable conditions for making of dew?

Answer: The ideal conditions for its formation are clear sky, calm air, high relative humidity, and cold and

long nights. For the formation of dew, it is necessary that the dew point is above the freezing point.

Question 4. Name and define three important types of rainfall.

Answer: On the basis of origin, rainfall may be classified into three main types:

a) The convectional rain

b) Orographic or relief rain and

c) Cyclonic or frontal rainfall

(Explanation of each point)

Question 5. Name the three types of precipitation.

Answer: There are many forms of precipitation like dew, fog, rainfall, snowfall, hailstones etc.

a) Rainfall: The precipitation in the form of water is called rainfall.

b) Snowfall: When the temperature is lower than the 0°C, precipitation takes place in the form of fine

flakes of snow and is called snowfall.

c) Hailstones: Sometimes, drops of rain after being released by the clouds become solidified into

small rounded solid pieces of ice and which reach the surface of the earth are called hailstones.

Question 6. How are clouds formed? Classify them.

Answer:

Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the

water vapour in free air at considerable elevations.

According to their height, expanse, density and transparency or opaqueness clouds are grouped

under four types:

a) Cirrus,

b) Cumulus,

c) Stratus, And

d) Nimbus.

(Explanation of each point)

LONG ANSWER TYPE QUESTIONSQuestion 1. Discuss the salient features of the world distribution of precipitation.

Answer: Salient features of the world distribution of precipitation are given below:

1. Different places on the earth ‘s surface receives different amounts of rainfall in a year and that too in

different seasons. In general, as we proceed from the equator towards the poles, rainfall goes on

decreasing steadily. The coastal areas of the world receive greater amounts of rainfall than the interior of

the continents. The rainfall is more over the oceans than on the landmasses of the world.

2. Between the latitudes 35° and 40° N and S of the equator, the rain is heavier on the eastern coasts and

goes on decreasing towards the west. But, between 45° and 65° N and S of equator, the rainfall is first

received on the western margins of the continents and it goes on decreasing towards the east.

3. In some regions rainfall is distributed evenly throughout the year such as in the equatorial belt and in

the western parts of cool temperate regions. .

Based on the total amount of annual precipitation, major precipitation regimes of the world are identified

as follows: -

a) The equatorial belt, the windward slopes of the mountains along the western coasts in the cool

temperate zone and the coastal areas of the monsoon land receive heavy rainfall of over 200 cm

per annum.

b) Interior continental areas receive moderate rainfall varying from 100-200 cm per annum. The

coastal areas of the continents receive moderate amount of rainfall.

c) The central parts of the tropical land and the eastern and interior parts of the temperate lands

receive rainfall varying between 50-100 cm per annum.

d) Areas lying in the rain shadow zone of the interior of the continents and high latitudes receive

very low rainfall-less than 50 cm per annum.

2. Read the following passage and answer the questions that follow:-

Water vapour present in the air is known as humidity. It is expressed quantitatively in different ways. The

actual amount of the water vapour present in the atmosphere is known as the absolute humidity. It is the

weight of water vapour per unit volume of air and is expressed in terms of grams per cubic metre. The

ability of the air to hold water vapour depends entirely on its temperature. The absolute humidity differs

from place to place on the surface of the earth. The percentage of moisture present in the atmosphere as

compared to its full capacity at a given temperature is known as the relative. humidity. With the change of

air temperature, the capacity to retain moisture increases or decreases and the relative humidity is also

affected. It is greater over the oceans and least over the continents. The air containing moisture to its full

capacity at a given temperature is said to be saturated. It means. that the air at the given temperature is

incapable of holding any additional amount of moisture at that stage. The temperature at which

saturation occurs in a given sample of air is known as dew point. The amount of water vapour in the

atmosphere is added or withdrawn due to evaporation and condensation respectively. Evaporation is a

process by which water is transformed from liquid to gaseous state. Heat is the main cause for

evaporation. The temperature at which the water starts evaporating is referred to as the latent heat of

vaporization. Increase in temperature increases water absorption and retention capacity of the given

parcel of air. Similarly, if the moisture content is low, air has a potentiality of absorbing and retaining

moisture. Movement of air replaces the saturated layer with the unsaturated layer. Hence, the greater the

movement of air, the greater is the evaporation. The transformation of water vapour into water is called

condensation. Condensation is caused by the loss of heat. When moist air is cooled, it may reach a level

when its capacity to hold water vapour ceases. Then, the excess water vapour condenses into liquid form.

If it directly condenses into solid form, it is known as sublimation.

2.1 Relative humidity is greatest in which region of the earth?

Ans: Rainforest

2.2 Through which process moisture is added in the atmosphere?

Ans: Evaporation

2.3 Saturation of air occurs at a particular temperature. This temperature is known as –

Ans: Dew point

2.4 Which factor will affect the relative humidity of a place?

Ans: Temperature

Chapter- 12

World Climate and Climate Change

The world climate can be studied by organizing information and data on climate and synthesizing them in

smaller units for easy understanding, description and analysis.

APPROACHES TO CLASSIFYING WORLD CLIMATE1) Empirical Approach- Empirical classification is based on observed data, particularly on

temperature and precipitation.

2) Genetic Approach- Genetic classification attempts to organize climates according to their causes.

3) Applied Approach- Applied classification is for specific purpose.

KOEPPEN’ S SCHEME OF CLASSIFICATION OF CLIMATEa) The most widely used classification of climate is the empirical climate classification scheme

developed by V. Koeppen.

b) Koeppen identified a close relationship between the distribution of vegetation and climate.

c) He selected certain values of temperature and precipitation and related them to the distribution

of vegetation and used these values for classifying the climates.

d) He introduced the use of capital and small letters to designate climatic groups and types.

e) Koeppen recognized five major climatic groups, four of them are based on temperature and one

on precipitation.

The capital letters: A, C, D and E delineate humid climates and B dry climates.

Climate Groups According to KoeppenThe climatic groups are subdivided into types, designated by small letters, based on seasonality of

precipitation and temperature characteristics.

Group Characteristics

A – Tropical Average temperature of the coldest month is 18 C or higher

B – Dry Climates Potential evaporation exceeds precipitation

C – Warm

Temperate

The average temperature of the coldest month of the (Mid-latitude)

climates years is higher than minus 3oC but below 18oC

D – Cold Snow

Forest Climates The average temperature of the coldest month is minus 3° C or below

E – Cold Climates Average temperature for all months is below 10’ C

H – High Land Cold due to elevation

CLIMATE TYPES ACCORDING TO KOEPPENCAUSES OF CLIMATE CHANGEThe causes for climate change are many:

They can be grouped into :-

a) Astronomical causes

b) Terrestrial causes

Astronomical causesa) The changes in solar output associated with sunspot activities. Sunspots are dark and cooler

patches on the sun which increase and decrease in a cyclical manner.

b) According to some meteorologists, when the number of sunspots increase, cooler and wetter

weather and greater storminess occur.

c) decrease in sunspot numbers is associated with warm and drier conditions. Yet, these findings are

not statistically significant.

Terrestrial causesa) Volcanic eruption throws up lots of aerosols into the atmosphere. These aerosols remain in the

atmosphere for a considerable period of time reducing the sun’s radiation reaching the Earth’s

surface.

b) After the recent Pinatoba and El Cion volcanic eruptions, the average temperature of the earth fell

to some extent for some years.

c) The most important anthropogenic effect on the climate is the increasing trend in concentration

of greenhouse gases in the atmosphere which is likely to cause global warming.

GLOBAL WARMINGa) Due to the presence of greenhouse gases, the atmosphere is behaving like a greenhouse.

b) The atmosphere also transmits the incoming solar radiation but absorbs most of the long wave

radiation emitted upwards by the earth’s surface.

c) The gases that absorb long wave radiation are called greenhouse gases.

d) The processes that warm the atmosphere are often collectively referred to as the greenhouse

effect.

Greenhouse Gases (GHGs)-

The primary GHGs of concern today are carbon dioxide (CO2), Chlorofluorocarbons (CFCs), methane

(CH4), nitrous oxide (N2 O) and ozone (O3). Some other gases such as nitric oxide (NO) and carbon

monoxide (CO) easily react with GHGs and affect their concentration in the atmosphere.

KYOTO PROTOCOL (1997)-

This protocol went into effect in 2005, ratified by 141 nations.

Kyoto protocol bounds the 35 industrialized countries to reduce their emissions by the year 2012 to 5 per

cent less than the levels prevalent in the year 1990. Efforts have already been initiated to control the

emission of GHGs and to arrest the trend towards global warming.

KYOTO DECLARATION-

(a) Implement and/or further elaborate policies and measures in accordance with its

(i) Enhancement of energy efficiency in relevant sectors of the national

(ii) Protection and enhancement of sinks and reservoirs of greenhouse gases not controlled by the

Montreal Protocol, taking into account its commitments under relevant international environmental

agreements: promotion of sustainable forest management practices, afforestation, and reforestation:

(iii) Promotion of sustainable forms of agriculture in light of climate change

(iv) Research on. and promotion, development and increased use of. new and renewable forms of energy,

of carbon dioxide sequestration technologies and of advanced and innovative environmentally sound

technologies:

(v) Progressive reduction or phasing out of market imperfections, fiscal incentives, tax and duty

exemptions and subsidies in all greenhouse gas emitting sectors that run counter to the objective of the

Convention and

(vi) Encouragement of appropriate reforms in relevant sectors aimed at promoting policies and measures

which limit or reduce emissions of greenhouse gases not controlled by the Montreal Protocol:

(vii) Measures to limit and/or reduce emissions of greenhouse gases not controlled by the Montreal

Protocol in the transport sector.

(viii) Limitation and/or reduction of methane emissions through recovery and use in waste management,

as well as in the production, transport, and distribution of energy.

EXERCISEMULTIPLE CHOICE QUESTION1.Koeppen’s system of classification of climates can be termed as:

a. Applied

b. Systematic

c. Genetic

d. Empirical.

2.Most of the Indian Peninsula will be grouped according to Koeppen’s system under:

a. “Af”

b. “BSh”

c. “Cfb”

d. “Am”

3.Which one of the following years is supposed to have recorded the warmest temperature the world

over?

a. 1990

b. 1998

c. 1885

d. 1950.

4.Which one of the following groups of four climates represents humid conditions?

a. A—B—C—E

b. A—C—D—E

c. B—C—D—E

d. A—C—D—F

5.Which protocol was held for reducing the emission of GHGs into the atmosphere in 1997?

a. RioJannero Earth Summit

b. Johnsonburg meets

c. Kyoto Protocol

d. Copenhagen Meet

6.What absorbs ultra-violet rays in stratosphere?

a. Ozone

b. Ions

c. Methane

d. Nitrogen

7.At which place the highest shade temperature of 58° C was recorded in Libya on 13 September 1922?

a. Tripoli

b. A1 Aziziyah

c. Taiwan

d. Tikari.

SHORT ANSWER QUESTIONSQuestion 1.

In which areas do we find tropical humid (Af) climate? What are its features?

Answer:

a) Tropical wet climate is found near the equator. The major areas are the Amazon Basin in South

America, western equatorial Africa and the islands of East Indies.

b) Features:

c) Significant amount of rainfall occurs in every month of the year as thunder showers in the

afternoon.

d) The temperature is uniformly high and the annual range of temperature is negligible.

e) The maximum temperature on any day is around 30 C while the minimum temperature is around

20 C.

f) Tropical evergreen forests with dense canopy cover and large biodiversity are found in this

climate.

Question 2.

Explain about tropical wet and dry climate (Aw).

Answer:

a) Tropical Wet and Dry Climate (Aw): Tropical wet and dry climate occurs north and south of Af

type climate regions.

b) It borders with dry climate on the western part of the continent and Cf or Cw on the eastern part.

c) Extensive Aw climate is found to the north and south of the Amazon Forest in Brazil and adjoining

parts.

Question 3.

In how many groups has Koeppen classified the climate?

Answer:

Koeppen has classified climate into five groups: four are based on temperature and one is based on

humidity. The capital letters: A, C, D and E delineate humid climates and B dry climates.

Question 4.

What is the astronomical theory of Milankovitch oscillations?

Answer:

It is an astronomical theory of Milankovitch oscillations, which infer cycles in the variations in the earth’s

orbital characteristics around the sun, the wobbling of the earth and the changes in the earth’s axial tilt.

All these alter the amount of insolation received from the sun, which in turn, might have a bearing on the

climate.

Question 5.

How does volcano affect the climate?

Answer:

Volcanic eruption throws up lots of aerosols into the atmosphere. These aerosols remain in the

atmosphere for a considerable period of time reducing the sun’s radiation reaching the Earth’s surface.

After the recent Pinatoba and El Cion volcanic eruptions, the average temperature of the earth fell to

some extent for some years.

Question 6.

Explain about tundra climate.

Answer:

The tundra climate (ET) is so called after the types of vegetation, like low growing mosses, lichens and

flowering plants. This is the region of permafrost where the sub soil is permanently frozen. The short

growing season and water logging support only low growing plants. During summer, the tundra regions

have very long duration of day light.

Question 7.

What is Kyoto Protocol?

Answer:

International efforts have been initiated for reducing the emission of GHGs into the atmosphere. Kyoto

protocol is the most important and was proclaimed in 1997. This protocol went into effect in 2005,

ratified by 141 nations. Kyoto protocol bounds the 35 industrialised countries to reduce their emissions

by the year 2012 to 5 per cent less than the levels prevalent in the year 1990.

LONG ANSWER TYPE QUESTIONS

Question 1.

Explain the major climate categories by Koeppen.

Answer:

The first level recognises six major climatic types with each group being designated by a capital letter.

These major climate categories have the following broad characteristics:

a) Tropical moist climates: These are very warm climates found in the tropics that experience high

quantities of precipitation. The primary distinguishing characteristic of these climates is that all

months have average temperatures above 18° C (64° F).

b) Dry climates: These are climates that experience little precipitation during most of the year.

Further, potential losses of water from evaporation and transpiration greatly exceed atmospheric

input.

c) Moist mid-latitude climates with mild winters: In these climates, summer temperatures are

warm to hot and winters are mild. The primary distinguishing characteristic of these climates is

that the coldest month has an average temperature between 18° C (64° F) and -3° C (27 °F).

d) Moist mid-latitude climates with cold winters: In these climates, summer temperatures are

warm and winters are cold. The primary distinguishing characteristic of these climates is the

average temperature of warmest month exceeds 10° C (50° F), and average temperature of

coldest is below -3° C (27° F).

e) Polar climates: These climates have very cold winters and summers, with no real summer

season. The primary distinguishing characteristic of these climates is the warmest month has an

average temperature below 10° C (50° F).

f) Highland climates: These are climates that are strongly influenced by the effects of altitude. As a

result, the climate of such locations is rather different from places with low elevations at similar

latitudes.

CHAPTER-13

WATER

GIST OF THE LESSON:-

Hydrological Cycle

Oceans – submarine relief , distribution of temperature and salinity

GENERAL

Waterisanessentialcomponentofalllifeformsthatexistoverthesurfaceoftheearth.

HYDROLOGICALCYCLE:

Thehydrologicalcycle,isthecirculationofwaterwithintheearth’shydrosphereindifferentformsi.e.the

liquid,solidandthegaseousphases.Italsoreferstothecontinuousexchangeofwaterbetweentheoceans,at

mosphere, landsurfaceandsubsurface and theorganism.

DISTRIBUTIONOFWATERONEARTH:

About71percentoftheplanetarywaterisfoundintheoceans.Theremainingisheldasfreshwateringlacie

rsandicecaps,groundwatersources,lakes,soilmoisture,atmosphere,streamsandwithinlife.

SCARCITYOFWATERANDITSCONSERVATION:

Itistobenotedthattherenewablewaterontheearthisconstantwhilethedemandisincreasing

tremendously.Weneedtotakenecessarystepstoconservethedrinkingwaterbyusingvariousmodern

methodsandtechniques.

RELIEFOFTHEOCEANFLOOR:

Thegeographershavedividedtheoceanicpartoftheearthintofiveoceans,namelythePacific,theAtlantic,

theIndian,SouthernoceanandtheArctic.Thevariousseas,bays,gulfsandotherinletsarepartsofthesefourla

rge oceans.

Theoceanfloorexhibitscomplexandvariedfeaturesasthoseobservedovertheland.Thefloorsoftheocea

nsareruggedwiththeworld’slargestmountainranges,deepesttrenchesandthelargestplains.

Thesefeaturesareformed,likethoseofthecontinents,bythefactorsoftectonic,volcanicanddep

ositionalprocesses.

DivisionsoftheOceanFloors:

Theoceanfloorscanbedividedintofourmajordivisions:(i)theContinentalShelf;(ii)theContinentalSlo

pe;(iii) the Deep Sea Plain; (iv)the Oceanic Deeps. Besides these divisionsTherearealsomajorandminorrelieffeaturesintheoceanfloorslikeridges,hills,seamounts,guyots,

trenches,canyons, etc.

ContinentalShelf:

● Thecontinentalshelfistheextendedmarginofeachcontinentoccupiedbyrelativelyshallowseasan

dgulfs.

● Itistheshallowestpartoftheoceanshowinganaveragegradientof1°orevenless.

● Theshelftypicallyendsataverysteepslope,calledtheshelfbreak.

● Thewidthofthecontinentalshelvesvariesfromoneoceantoanother.Theaveragewidthofco

ntinentalshelves is about 80 km.

● Massivesedimentarydepositsreceivedoveralongtimebythecontinentalshelves,becometheso

urceof fossil fuels.

ContinentalSlope:

● Thecontinentalslopeconnectsthecontinentalshelfandtheoceanbasins.

● Itbeginswherethebottomofthecontinentalshelfsharplydropsoffintoasteepslope.

● Thegradientofthesloperegionvariesbetween2-5°.

● Thedepthofthesloperegionvariesbetween200and3,000m.

● Theslopeboundaryindicatestheendofthecontinents.

● Canyonsandtrenchesareobservedinthisregion.

DeepSeaPlain:

● Deepseaplanesaregentlyslopingareasoftheoceanbasins.

● Thesearetheflattestandsmoothestregionsoftheworld.

● Thedepthsvarybetween3,000and6,000m.

● Theseplainsarecoveredwithfine-grainedsedimentslikeclayandsilt.

OceanicDeepsorTrenches:

● These areas are the deepest parts of the oceans.

● The trenches are relatively steep sided, narrow basins.

● Theyaresome3-5kmdeeperthanthesurroundingoceanfloor.

● As many as 57 deeps have been explored so far; of which 32 are in the Pacific Ocean; 19in

theAtlantic Ocean and 6 in the Indian Ocean.

MinorReliefFeatures:

Apartfromtheabovementionedmajorrelieffeaturesoftheoceanfloor,someminorbutsignificantfeatures

predominate in different parts of the oceans.

Mid-OceanicRidges:

Amid-oceanic ridge is the chains of mountains separated by a large depression.

The mountain ranges can have peaks as high as 2,500 m and some even reach above

theocean’ssurface.

Example- MidAtlantic Ridge

Seamount:

It is a mountain with pointed summits, rising from the seafloor that does not reach the surface ofthe

ocean. Seamounts are volcanic in origin. These can be 3,000-4,500 m tall. The Emperorseamount, an

extension of the Hawaiian Islands in the Pacific Ocean, is a good example.

SubmarineCanyons

These are deep valleys, found cutting across the continental shelves and slopes, often extendingfrom

the mouths of large rivers. The Hudson Canyon is the best known submarine canyon in theworld.

Guyots

It is a flat topped seamount. They show evidences of gradual subsidence through stages tobecome

flat topped submerged mountains. It is estimated that more than 10,000 seamounts and guyots exist

in the Pacific Ocean alone.

AtollThese are low islands found in the tropical oceans consisting of coral reefs surrounding a central

depression. It may be a part of the sea (lagoon), or sometimes form enclosing a body of fresh,brackish,or

highly saline water.

TEMPERATUREOFOCEANWATERS:Oceanwatersgetheatedupbythesolarenergyjustasland.Theprocessof

heatingandcoolingof the oceanic water is slower than land.

FactorsAffectingtheDistributionTemperature

(i)Latitude (ii) Unequal distribution of land and water

(iii) Prevailing wind (iv) Ocean currents:

VerticalDistributionofTemperature:

The temperature-depth profile for the ocean water shows how the temperature decreases withthe

increasing depth. This boundary region, from where there is a rapid decrease of temperature, is

called the thermocline.

The temperature structure of oceans over middle and low latitudes can be described as a

three-layer system from surface to the bottom.

● The first layer represents the top layer of warm oceanic water and it is about 500m

thickwith temperatures ranging between 20° and 25° C.

● The second layer called the thermocline layer lies below the first layer and is characterizedby

rapid decrease in temperature with increasing depth. The thermocline is 500 -1,000 mthick.

● Thethirdlayerisverycoldandextendsuptothedeepoceanfloor.

HorizontalDistributionofTemperature:The average temperature of surface water of the oceans is

about 27°C and it gradually decreases from the equator towards the poles at an average rate of 0.5°C per

latitude.The oceans in the northern hemisphere record relatively higher temperature than in the

southern hemisphere.

● Thehighesttemperatureisrecordedslightlytowardsnorthofequator.

The average annual temperatures for the northern and southern hemisphere are around 19° C and 16° C

respectively. This variation is due to the unequal distribution of land and water in the northern and

southern hemispheres.

SALINITY OF OCEAN WATERS

Salinity is the term used to define the total content of dissolved salts in sea water.

It is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater. It is usually

expressed as parts per thousand (o/oo) or ppt.

Salinity of 24.7o/oo has been considered as the upper limit to demarcate ‘brackish water’.

Factors affecting ocean salinity:

● The salinity of water in the surface layer of oceans depends mainly on evaporation

andprecipitation.

● Surface salinity is greatly influenced in coastal regions by the fresh water flow from

rivers,and in Polar Regions by the processes of freezing and thawing of ice.

● Wind, also influences salinity of an area by transferring water to other areas.

● The ocean currents contribute to the salinity variations.

HORIZONTALDISTRIBUTIONOFSALINITY:

● The salinity for normal open ocean rangesbetween 33o/oo and 37 o/oo. In the land

lockedRedSea,itisashighas41o/oo,whileintheestuariesandtheArctic,thesalinityfluctuatesfro

m 0 - 35o/oo, seasonally.

● In hot and dry regions, where evaporation is high, the salinity sometimes reaches to

70o/oo.

● Salinity decreases from 35 o/oo - 31 o/oo on the western parts of the northern hemisphere

because of the influx of melted water from the Arctic region. In the same way, after 15° -20°

south, it decreases to 33 o/oo .

● TheaveragesalinityoftheAtlanticOceanisaround36o/oo.Thehighestsalinityis recorded

between 15° and 20° latitudes.

● Maximumsalinity(37o/oo)isobservedbetween20°Nand30°Nand20°W-60°W.Itgradually

decreases towards the north.

● TheaveragesalinityoftheIndianOceanis35o/oo.Thelowsalinitytrendisobservedinthe Bay of

Bengal due to influx of river water. On the contrary, the Arabian Sea showshighersalinity

due tohigh evaporation andlow influx offresh water.

VerticalDistributionof Salinity:

● Salinity changes with depth, but the way it changes depends upon the location of the sea.

● Salinity at the surface increases by the loss of water to ice or evaporation, or decreased by the

input of fresh waters, such as from the rivers.

● Salinity at depth is very much fixed, because there is no way that water is ‘lost’, or the saltis

‘added.’ There is a marked difference in the salinity between the surface zones and thedeep

zones of the oceans.

● Thelowersalinitywaterrestsabovethehighersalinitydensewater.

● Salinity,generally,increaseswithdepthandthereisadistinctzonecalled

thehalocline(comparethiswiththermocline),wheresalinityincreasessharply.

● Other factors being constant, increasing salinity of seawater causes its density to increase.

Highsalinityseawater,generally,sinksbelowthelowersalinitywater.Thisleadsto

stratification by salinity.

MCQ QUESTIONS

Q1. The average seasonal temperatures of surface Water of the oceans have been represented through

a. Isobath b. Isohytes c. Isotherms d. Isobar

Q2. The major source of Temperature of the Ocean Water is

a. volcanic eruption b. Black body radiation c. Sun d. central point of Earth

Q3. The Transitional Zone between the land and actual Sea bottom is known as

a. Continental shelf b. Continental Slope c. Deep sea Plain d. Canyon

Q4. The Average Salinity in the Oceans and The Seas is --------------------------

a. 30 %o b. 35%o c. 40%o d. 39%o

Q5. The average width of Continental Shelf is……..

a. 80km b.200km c. 150km d. 250km

Q6. Which of the following layer s of the Ocean characterized by Rapid rate of Decrease of Temperature

with increasing depth?

a. Top layer b. The Thermo cline layer c. The third layer d. The bottom layer

Q7. Which one of the following is the largest Ocean:

a. Indian Ocean b. Atlantic Ocean c. Pacific Ocean d Arctic Ocean

Q8. Which of the following is an area of steep slope extending just after the continental shelf?

a. Continental slope b. Continental Shelf c. Sea plain d. Oceanic Ridges

Q9. The highest value of Salinity (330%o) is found in

a. Salt Lake b. Dead Sea c. Caspian Sea d. Von Lake

Q10. Salinity is expressed as the amount of Salt in grams dissolved in Sea Water Per

a. 10 grams b. 100 grams c. 1000 grams d. 10000 grams

Answer

1 c 2 c 3 a 4 b 5 a 6 b 7 c 8 a 9 d 10 c

THREE MARKS QUESTIONS

Q1. Why do we call the earth a Blue Planet?

Ans: Water is very essential component of all life forms that exist only over the earth surface. In our Solar

system, Water is only present in planet the Earth has an abundant supply of water e on its surface. Hence

our Planet is called the ‘Blue Planet’.

Q2. What are the major relief features of the Ocean basin?

Ans: The major relief features of the Ocean floor are

a. Continental Shelf b. Continental Slope c. Abyssal plains d. Oceanic Trenches.

Q3.What is the source of Oceanic Temperature and how does the water heat?

Ans: The main source of temperature of the Oceanic Water is the Sun. The Oceanic Water is heated by

absorption of radiation from the Sun and by Convection of Heat through the Ocean bottom from the

interior of the earth.

Q4. What is the importance of Salinity?

Ans: Salinity influences the composition and movement of Sea water, distribution of marine fauna,

temperature, density, evaporation, thermal expansion, humidity, absorption of radiation and

compressibility.

Q5. What are the differences between Thermocline and halocline?

Ans: This boundary region, from where there is a rapid decrease of temperature, is called the

Thermocline.

Salinity, generally, increases with depth and there is a distinct zone called the halocline

FIVE MARKS QUESTIONS

Q1. What is Hydrological Cycle? Which components and Processes are responsible for Water Cycle?

The hydrological cycle is the Circulation of Water in different forms the liquid, Solid, and the gaseous

phases within Earths Hydrosphere. It also refers to the continuous exchange of water between the

Oceans.

Components Processes

WaterstorageinOceans Evaporation

EvapotranspirationSublimatio

WaterinAtmosphere Condensation

Precipitation

WaterstorageinIceandSnow Snow

meltingRunofftoStrea

SurfaceRunoff StreamflowInfil

tration

FreshwaterStorage

GroundWaterStorage GroundWaterDischargethroughspring

Q2. Differentiate between Continental Shelf and Continental Slope.

Subject ContinentalShelf ContinentalSlope

Definition Itisanextendingmarginof

each Continentoccupied by

relativelyShallowseasandgulf

It is the edge ofContinent;

steep sidedextending from

thecontinentalshelftothe

deepseaplane.

Slope It’sslopeis10oreven lessItsis2to50

Depth Itsdepthupto200m It’s200to2000m

Area Itrepresents8.5%oftotal

areaoftheOceanbasin.

Itrepresents7.6%oftotal

areaoftheOceanbasin.

Q3. Discuss briefly Which Factors affecting the Distribution of Salinity in Oceans.

Ans: There is a Wide range of variation in the spatial distribution of Salinity within Oceans and The Seas.

The Factors Affecting the amount of Salt in different Seas and Oceans. They are as follows-----

1. Evaporation: There is direct positive relationship between the rate of evaporation and Salinity. Grater

the Evaporation higher the Salinity and vice versa. As for example, salinity is higher near the Tropics.

2. Precipitation: It is inversely related to salinity, Higher the Precipitation, lower the salinity.

3. Influx of river Water: Big voluminous rivers pour down immense volume of Water into the Oceans and

thus salinity is reduced at their mouths. As for example low Salinity is found near the mouth of Ganga

River

4. Circulation of Oceanic Water: Ocean circulation affects the spatial distribution of Salinity by mixing Sea

waters.Beside those factors Atmospheric pressure and Wind Direction also helps the distribution of

Salinity.

Q4. Discuss briefly the minor Reliefs of the Oceans.

Ans: Some Minor Reliefs are in different parts of the Oceans. Mid Oceanic ridges:

It is narrow shaped large, high and submerged mountain ranges. It indicates the divergent plate

boundary. Its high is 1000 to 3000 m .As for Example Mid Oceanic Ridge in Atlantic Ocean.

Seamount: It is a mountain with pointed summits, rising from the seafloor that does not reach the surface

of the ocean. Seamounts are volcanic in origin. These can be3000 to 4500 m tall.

Submarine Canyon: Long, narrow and very deep valleys or trenches located on the continental shelves

and slopes with vertical walls resembling the continental canyons are called submarine canyons.

Guyots: Flat topped sea mount in deep sea basin is known as Guyots. They show evidences of gradual

subsidence through stages to become flat topped submerged mountains. It is estimated that more than

10,000 seamounts and guyots exist in the Pacific Ocean alone.

Atoll: These are low islands found in the tropical oceans consisting of coral reefs surrounding a central

depression. It may be a part of the sea (lagoon).

Q5. Which factors are responsible for unequal distribution of temperature in Oceans?

Ans: The factors which affect the distribution of temperature of ocean water are:

a) Latitude: the temperature of Surface water decreases from the equator towards the poles because

the amount of insolation decreases pole ward.

b) Unequal distribution of land and water: The Oceans in the northern hemisphere receive more

heat due to their contact with large extent of land than the Oceans in the Southern hemisphere.

c) Prevailing Wind the winds blowing from the land towards the Oceans drive warm surface water

away from the coast resulting in the upwelling of cold water from below. It results longitudinal variation

in the temperature.

d) Ocean Currents: Ocean currents also influence the temperature of the Ocean. Warm currents raise

the temperature in cold areas while the cold currents decrease the temperature in warm ocean areas. As

for example Gulf Stream raises the temperature of east coast of North America.

Q6. Describe the horizontal distribution of oceanic salinity.

●The salinity for normal Open Ocean ranges between 33o/oo and 37o/oo. In the land locked Red Sea, it is

as high as 41 o/oo, while in the estuaries and the Arctic, the salinity fluctuates from 0 - 35 o/oo,

seasonally.

●In hot and dry regions, where evaporation is high, the salinity sometimes reaches to 70o/oo.

●Salinity decreases from 35o/oo to 31o/oo from the western parts of the northern hemisphere because

of the influx of melted water from the Arctic region. In the same way, after 15° - 20° south, it decreases to

33o/oo.

●The average salinity of the Atlantic Ocean is around 3o/oo. The highest salinity is recorded between 15°

and 20° latitudes.

●Maximum salinity (37o/oo) is observed between 20° N and 30° N and 20° W - 60° W. It gradually

decreases towards the north.

●The average salinity of the Indian Ocean is 35o/oo. The low salinity trend is observed in the Bay of

Bengal due to influx of river water. On the contrary, the Arabian Sea shows higher salinity due to high

evaporation and low influx of fresh water.

CHAPTER- 14

MOVEMENTS OF OCEAN WATER

Gist of the chapter:The ocean water is dynamic.The horizontal and vertical motions are common in

ocean water.The horizontal motion refers to the Ocean Currents and Waves. The vertical motion refers to

Tide.

GENERAL

Wave

1 - Waves are actually the energy, not the water as such, which moves across the ocean surface.

2 - Wind provides energy to the waves.

3 - The motion of the surface water seldom affects the stagnant deep bottom water of the ocean.

4- As a wave approaches the beach it slows down.

5- The largest waves are found in the open oceans.

6- Waves may travel thousands of KM before rolling ashore, breaking and dissolving as surf.

7-Steep waves are very young ones and are probably formed by local winds.

8- Slow and steady waves originate from faraway places, possibly from another hemisphere.

9- Height of wave is determined by wind.

10-Wave travel because wind pushes the water body in its course while gravity pulls the crests of the

waves downward. The falling water pushes the former troughs upward, hence crests and troughs are

formed.

Tides

1- The periodical rise and fall of the sea level once or twice a day, mainly due to gravitational attraction of

the Sun and the Moon is called tide

2- Movement of ocean water caused by wind and atmospheric pressure are called Surges, which are not

regular like tides.

3- Tidal bulges occur on the Earth. For these two tidal bulges together the gravitational force and

centrifugal force are responsible.

4- On the side of the earth facing the moon a tidal bulge occur due to gravitational attraction of the moon

while on the opposite side the gravitational force is less as it is farther away, the centrifugal force causes

tidal bulge on the other side.

5- The tidal bulge on wide continental shelves have greater height. When tidal bulges hit the mid oceanic

islands they become low.

6- Type of Tides based on frequency are- semi-diurnal, Diurnal and Mixed Tide

7- Tides based on the Sun, the Moon and the Earth position are- Spring tide and Neap tide.

8- The tides are very important for navigators, desiltation of sediments from rivers estuaries and to

generate electricity.

Ocean Currents

1 Ocean currents are like river flow in oceans. They represent a regular volume of water in a definite path

and direction.

2 Ocean currents are influenced by two type of forces-

(A) Primary forces (Heating by Solar energy, Wind, Gravity and Coriolis force)

(B) secondary forces (Density, salinity etc)

3 The speed of current is measured in knot.

4 Near the surface the currents are strongest and at a depth currents are generally slow.

5 Types of ocean current based on their depth of water are-surface currents and deep water current.

6 Ocean current based on temperature are- cold current and warm current.

Major ocean currents.

Indian Ocean currents