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GEOGRAPHYGEOGRAPHYGEOGRAPHYGEOGRAPHYGEOGRAPHY(P(P(P(P(PARARARARARTTTTT-I)-I)-I)-I)-I)

CONTENTS

1. Our Universe ........................................................................................... 7

2. Interior Infrastructure of Earth ............................................................ 16

3. Mineral & Rocks .................................................................................... 21

4. Forces Effecting the Earth Movements ............................................... 25

5. Weathering & Erosion. .......................................................................... 27

6. Geogmorphological Landforms ........................................................... 30

7. Volcanoes Earthquakes ......................................................................... 34

8. Erosional and Depositional Landforms............................................... 39

9. Drainage System & Patterns ................................................................ 44

10. Atmosphere. ........................................................................................... 46

11. Climatic Classification........................................................................... 58

12. Hydrosphere .......................................................................................... 60

13. Soil........................................................................................................... 69

14. Natural Vegetation ................................................................................ 73

15. Population .............................................................................................. 79

16. Human Settlement................................................................................. 84

17. Agriculture. ............................................................................................ 89

18. Fisheries................................................................................................ 100

19. Minerals ................................................................................................ 103

20. Industries.............................................................................................. 108

21. Energy Resources ................................................................................ 117

22. Transport .............................................................................................. 122

Sl. No. TOPICS Pg. No.

GENERAL GEOGRAPHY

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[7] Chronicle IAS Academy

OUR UNIVERSEOUR UNIVERSEOUR UNIVERSEOUR UNIVERSEOUR UNIVERSE

The big bang theory explains the origin of ouruniverse. According to this theory, 15 billion yearsago, cosmic matter was in a compressed state fromwhich expansion started by a primordialexplosion. The super-dense ball broke to formgalaxies, which again broke to form stars andfinally stars broke to form planets including earth.

Since the outer space is limitless, conventionalunits for measuring distances are not suitable.Hence new units as follows are used:

Light Year: Distance covered by light inone year in vacuum at a speed of 3x108

m/s. One light year is equal to 9.46 1012 kilometers.

Astronomical Unit: The Mean distancebetween the Sun and the Earth (1.49 x108 km). One light year is equal to 60,000AU.

Cosmic Year: Sun's period of revolutionaround the galactic centre (250 millionyears). Also called as 'galactic year'

Parsec: Distance at which the mean ra-dius of the Earth's orbit subtends anangle of one second of an arc. It is equalto 3.26 light years.

Galaxies

These are huge congregation of stars that holdtogether by force of gravity e.g. the Milky Way,Andromeda galaxy, large and small magellaniccloud, Ursa Minor system, sculptor system, etc.Milky Way or Akashganga is our home galaxy.Our solar system is located in this galaxy.

Stars

Stars are self luminous bodies that accountfor 98 percent of the matter in a galaxy. In theuniverse, some stars appear small but emit moreenergy than the other stars of the Milky Way.Such stars are called 'Quasars'. When the densegalactic nucleus is compressing to form a star, thisstage in star formation is called a 'protostar' stage.Due to high temperature hydrogen converts to

helium and heat and light is emitted. Thus a staris formed. When the hydrogen of a star is depleted,its outer regions swell and redden. This stage of astar is called a 'Red Giant'. Our sun will turn intoa 'Red Giant' in 5 billion years. 'Novae Stars' arestars whose brightness increases suddenly by 10to 20 magnitudes due to explosion and then thestars again fade into normal brightness. 'SuperNovae' are stars whose brightness suddenlyincreases by more than 20 magnitudes. After theexplosion, the dense core of comparatively smallerstars is called the 'white dwarf'. The dense coreof the comparatively larger stars is called the'Neutron star'. The neutron star rotates at a highspeed emitting radio waves. Such stars are called'Pulsar'. 'Black hole' stage of the star occurs whenthe ancient star collapses. Gravity becomes sointense in the hole that nothing escapes, evenlight.

Constellations

In the sky at night there are various patternsformed by different groups of stars. These arecalled constellations. Ursa Major or Big Bear isone such constellation. One of the most easilyrecognizable constellations is the small bear orSaptarishi (Sapta-seven, Rishi-sages). It is a groupof seven stars that forms a part of the large UrsaMajor Constellation.

Solar System

The sun along with its eight planets, asteroidsand comets comprise the 'solar system'. The planetsare divided into inner or terrestrial planets whichhave higher densities e.g. Mercury, Venus, Earthand Mars and outer planets which have lowerdensities e.g. Jupiter, Saturn, Uranus andNeptune.

The Sun

The sun is in the center of the solarsystem.

It is made up of extremely hot gases par-ticularly hydrogen.

The sun is 109 times bigger than the

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Origin

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earth and weighs 2 1027 tonnes. The sun is about 150 million km away

from the earth. The light from the sunreaches earth in about 8 minutes.

The glowing surface of the sun is called'Photosphere'. Above the 'Photosphere'is red coloured 'Chromosphere'. Beyondthe Chromosphere is the 'Corona', vis-ible during eclipses.

The temperature of the photosphere isabout 6000C and that of the Chromo-sphere is about 32400C, and that of thecorona about 2,700,000C. The core ofthe sun has a temperature about 15million degrees Kelvin. But that tremen-dous heat is not felt so much by us be-cause despite being our nearest star, it isfar away from us.

It takes 250 million years to completeone revolution round its centre. Thisperiod is called 'Cosmic year'.

Sun spots' are dark patches notched onthe surface of the sun. They appear darkbecause they are cooler i.e. they have atemperature of about 1500C.

The 'Aurora Borealis' or northern lightsare multicoloured lights that sweepacross the sky in waves and are visiblein the arctic region. The 'Aurora Aus-tralis' or southern lights are similarlyvisible near the Antarctica region.

The Moon

The moon is the only satellite of the earth. Its size is approximately one-fourth that

of the earth. It has a diameter of 3475km.

Its orbit is elliptical. The maximum dis-tance (apogee) of the moon from theearth is 406,000 km and the minimumdistance (perigee) is 364,000 km.

The moon moves around the earth inabout 27 days. It takes exactly the sametime to complete one spin. As a result,only one side of the moon is visible to uson the earth.

The bright parts of the moon are moun-tains whereas the dark patches are low-lying plains.

Asteroids

Asteroids are a series of very small planets orfragments of planets lying between the orbit ofMars and that of Jupiter. They number about

45,000. 'Ceres' whose length is about 1000km isthe largest one. They revolve around the sun inthe same way as the planets.

Meteors and Meteorites

The meteors are the remains of comets whichare scattered in the interplanetary space of thesolar system. On contact with the earth'satmosphere, they burn due to friction. Thosewhich completely burn out into ash are calledmeteors or 'shooting star.' Those which do notburn completely and strike the earth in the formof rocks are called 'meteorites'.

Planetary System

There are eight planets in our solar system.They are: Mercury, Venus, Earth, Mars, Jupiter,Saturn, Uranus and Neptune. Earlier, Pluto wasconsidered as a planet. But recently it has lost thisstatus. All the eight planets of the solar systemmove around the sun in fixed paths. These pathsare elongated. They are called orbits. A new planet2003 UB 313 has been discovered recently in oursolar system. It is bigger than Pluto and farthestfrom the Sun.

A. Mercury

1. Mercury is the smallest and the nearestplanet to the Sun.

2. It takes only about 88 days to completeone round along its orbit.

3. It has no atmosphere and no satellite.

4. Its days are scorching hot and nights arefrigid.

B. Venus

1. Venus is considered as 'Earth's-twin'because its size and shape are very muchsimilar to that of the earth.

2. It is also called the 'morning' or 'eveningstar'.

3. It is probably the hottest planet because itsatmosphere contains 90-95% of carbondioxide. The day and night temperaturesare almost the same.

4. The atmospheric pressure is 100 times thatof the earth.

5. It has no satellite.

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C. The Earth

1. The earth is the third nearest planet to theSun.

2. In size, it is the fifth largest planet.

3. It is slightly flattened at the poles. That iswhy its shape is described as a Geoid.

4. From the outer space, the earth appearsblue because its two-thirds surface iscovered by water. It is, therefore, called ablue planet.

D. Mars

1. It is marked with dormant volcanoes anddeep chasms where once water flowed.

2. It has a thin atmosphere comprising ofNitrogen and Argon.

3. Beneath its atmosphere, Mars is barren,covered with pink soil and boulder.Because of this it is known as 'red planet'.

4. It has two satellites namely 'Phobos' and'Demos'.

5. The highest mountain here is Nix Olympiawhich is three times higher than MountEverest.

6. Recent explorations have thrown light onthe possibility of existence of life here.

E. Jupiter

1. It is the largest planet of the solar system.

2. Its atmosphere contains hydrogen, helium,methane and ammonia.

3. It contains two and a half times the massof all the other planets combined.

4. It reflects more than three times the energyit receives from the sun.

5. It has the great red spot which is anenormous eddy in the turbulent cloud cover.It also contains dusty rings and volcanoes.

6. It has 16 satellites like Ganymede, Aayo,Europa, Callisto etc.

F. Saturn

1. It is the second largest planet of the solarsystem.

2. It has a celebrated rings composed ofthousands of rippling, spiraling bands oficy rock and dust just 200 feet thick and

270,000 km in diameter.

3. It has 21 known satellites. Among themTitan, Phobe, Tethys and Mimas areimportant.

4. Its moon, Titan has nitrogen atmosphereand hydrocarbons, the necessity of life butno life exists.

G. Uranus

1. It is the only planet that lies on its side.Hence, one pole or the other faces the sunas it orbits.

2. It is one of the coldest planets because ofhaving an average temperature of -223?C.

3. Its atmosphere is made of mainly hydrogen.The landscape is barren and there is frozenmethane cloud.

4. There are 9 dark compact rings around theplanet and a corkscrew shaped magneticfield.

5. It has 15 satellites; prominent ones areAerial, Ambrial, Titania, Miranda etc.

6. It rotates north to south.

H. Neptune

1. It is the most distant planet from the sun.

2. There are five rings of Neptune. The outerring seems to be studded with icy moonletswhile the inner ring appears narrow andnearly solid.

3. It has 8 satellites like Titron, Merid, N-1,N-2, N-3 etc.

4. Its atmosphere mostly containshydrocarbon compounds. The atmosphereappear blue, with quickly changing whiteicy methane clouds often suspended highabove an apparent surface.

Pluto from Planet to Plutoid

Pluto, demoted from planet status in 2006,got a consolation prize - it and other dwarf planetslike it will be called plutoids. Plutoids are celestialbodies in orbit around the Sun at a distancegreater than that of Neptune that have sufficientmass for their hydrostatic equilibrium (near-spherical) shape. The two known plutoids arePluto and Eris. It is expected that more plutoidswill be named as science progresses and newdiscoveries are made.

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Motions of the Earth

The earth has two main motions: (i) Rotationand (ii) Revolution.

The axis of the earth, which is an imaginaryline, makes an angle of 66 with its orbital plane.

The plane formed by the orbit is known asthe orbital plane. The earth receives light fromthe sun. Due to the spherical shape of the earth,only half of it gets light from the sun at a time.The portion facing the sun experiences day whilethe other half away from the sun experiencesnight. The circle that divides the day from nighton the globe is called the circle of illumination.This circle does not coincide with the axis as yousee in the given figure.

Rotation: The earth rotates around its axis.The axis is an imaginary line passing through thecentre of the earth. The earth completes onerotation in 23 hours, 56 minutes, 4.09 seconds tobe exact. The earth rotates from west to east. Theperiod of rotation is known as the earthday.

Effects of the Rotation of the Earth

(i) Causation of day and night

(ii) A difference of 1 hour between twomeridians which are 15apart.

(iii) Deflection of ocean currents and winds.

(iv) Rise and fall of tides every day

Revolution: It is earth's motion in its ellipticalorbit around the sun. One revolution is completedin 365 1/4 days, resulting in one extra day everyfourth year. The year, consisting of 366 days iscalled a "leap year" having 29 days in the monthof February.

A year is usually divided into summer, winter,spring and autumn seasons. Seasons change dueto the change in the position of the earth aroundthe sun.

On 21st June, the Northern Hemisphere istilted towards the sun. The rays of the sun falldirectly on the Tropic of Cancer. As a result, theseareas receive more heat. The areas near the polesreceive less heat as the rays of the sun are slanting.The North Pole is inclined towards the sun andthe places beyond the Arctic Circle experiencecontinuous daylight for about six months. Sincea large portion of the Northern Hemisphere isgetting light from the sun, it is summer in theregions north of the equator. The longest day andthe shortest night at these places occur on 21stJune. At this time in the Southern Hemisphere allthese conditions are reversed. It is winter seasonthere. The nights are longer than the days. Thisposition of the earth is called the SummerSolstice.

On 22nd December, the Tropic of Capricornreceives direct rays of the sun as the South Poletilts towards it. As the sun's rays fall vertically atthe Tropic of Capricorn (23 S), a larger portionof the Southern Hemisphere gets light. Therefore,

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it is summer in the Southern Hemisphere withlonger days and shorter nights. The reversehappens in the Northern Hemisphere. Thisposition of the earth is called the Winter Solstice.

On 21st March and September 23rd, directrays of the sun fall on the equator. At this position,neither of the poles is tilted towards the sun; so,the whole earth experiences equal days and equalnights. This is called an equinox.

On 23rd September, it is autumn season inthe Northern Hemisphere and spring season inthe Southern Hemisphere. The opposite is the caseon 21st March, when it is spring in the NorthernHemisphere and autumn in the SouthernHemisphere. Thus, we find that there are daysand nights and changes in the seasons because ofthe rotation and revolution of the earthrespectively.

Some terminologies related to revolution are: Perihelion: The position of the earth

when it is at its nearest point to the sun.The earth reaches its perihelion on about3rd January at a distance of about 147million km from the sun.

Aphelion: The position of the earthwhen it is at its greatest distance fromthe sun. The earth reaches its aphelionon 4th July when it is at a distance of152 million km from the sun.

Perigee: The point in the orbit of themoon when it is nearest to the earth.

Apogee: The point in the orbit of themoon when it is farthest from the earth.

Effects of the Revolution of the Earth

(i) Change of seasons.

(ii) Variation in the lengths of day and nightat different times of the year.

(iii) Shifting of wind belts.

(iv) Determination of latitudes.

Lattitude and Longitude

Latitude:

Latitude of a place on the earth is the angulardistance of the place from the equator. 1 oflatitude is approximately equal to 111 km.

Parallels of Latitude: They are circles drawnon the globe parallel to the equator. All the placeson a parallel of latitude will have the same

latitudinal angle.

Important Parallels of Latitude

1. Equator 0

2. Tropic of Cancer 23 N

3. Tropic of Capricorn 23S

4. Arctic circle 66N

5. Antarctic circle 66S

Heat Zones of the Earth

The mid-day sun is exactly overhead at leastonce a year on all latitudes in between the Tropicof Cancer and the Tropic of Capricorn. This area,therefore, receives the maximum heat and is calledthe Torrid Zone.

The mid-day sun never shines overhead onany latitude beyond the Tropic of Cancer and theTropic of Capricorn. The angle of the sun's raysgoes on decreasing towards the poles. As such,the areas bounded by the Tropic of Cancer andthe Arctic Circle in the Northern Hemisphere, andthe Tropic of Capricorn and the Antarctic Circlein the Southern Hemisphere, have moderatetemperatures. These are, therefore, calledTemperate Zones.

Areas lying between the Arctic Circle and theNorth Pole in the Northern Hemisphere and theAntarctic Circle and the South Pole in theSouthern Hemisphere, are very cold. It is becausehere the sun does not rise much above thehorizon. Therefore, its rays are always slanting.These are, therefore, called Frigid Zones.

Great Circles: Any circle which divides aglobe into hemispheres is a great circle. Theequator is a great circle and Greenwich meridiantogether with meridian 180 make another greatcircle. The number of great circle is limitless. Greatcircle can extend in any direction: east to west,north to south, north east to south west, and soon. Great circles are of equal length.

Longitude:

The longitude shows the distance of a pointeast or west of the Prime Meridian which is at 0and passes through Greenwich, near London. Foreach degree of longitude there is a difference offour minutes in time.

Longitude and Time: The best means of

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measuring time is by the movement of the earthand the moon. The sun regularly rises and setsevery day, and naturally, it is the best time-keeperthroughout the world.

When the Prime Meridian has the sun at thehighest point in the sky, all the places along thismeridian will have mid-day or noon. As the earthrotates from west to east, those places east ofGreenwich will be ahead of Greenwich time andthose to the west will be behind it. The rate ofdifference can be calculated as follows. The earthrotates 360 in about 24 hours, which means 15an hour or 1 in four minutes. Thus, when it is 12noon at Greenwich, the time at 15 east ofGreenwich will be 15 4 = 60 minutes, i.e., 1 hourahead of Greenwich time, which means 1 p.m.But at 15 west of Greenwich, the time will bebehind Greenwich time by one hour, i.e., it willbe 11.00 a.m. Similarly, at 180, it will be midnightwhen it is 12 noon at Greenwich.

Greenwich Mean Time: The local time atGreenwich or any place on the Prime Meridian.All meridians to the east of Greenwich meridianhave sunrise before that meridian. Local timesalong these meridians are therefore ahead ofG.M.T. Meridians to the west of Greenwichmeridian have sunrise after this meridian andtherefore their local times are behind G.M.T.

Standard Time: A particular meridian oflongitude passing through a country is chosen asthe reference meridian. The local time along thismeridian, calculated with respect to GreenwichMean Time in terms of its longitude is taken asthe Standard Time for that country.

Why do we have standard time?

The local times of places which are on differentmeridians are bound to differ. For example, it willbe difficult to prepare a time-table for trains whichcross several longitudes. In India, for instance,there will be a difference of about 1 hour and 45minutes in the local times of Dwarka in Gujaratand Dibrugarh in Assam. It is, therefore, necessaryto adopt the local time of some central meridianof a country as the standard time for the country.

Indian Standard Time: Time along 82 Emeridians, calculated with respect to G.M.T.India, for being a large country, is unusual inhaving a single time zone all over the country. Itis 5 hours ahead of G.M.T.

International Date Line: An imaginaryzigzag line on the globe, approximately along the180 meridian of longitude. When a personcrosses this line from East to West, he gains oneday and when he crosses from West to East, heloses one day.

Solar Day: It is the time interval betweensuccessive crossings of the sun across the meridianof the celestial sphere of any fixed place in thesame direction. This is equal to 24 hours.

Sidereal Day: The period of rotation of theearth about its axis. This is calculated with respectto any fixed star. It is 4 minutes less than 24 hours.

Solar Year (Tropical year): It is the averageinterval between successive returns of the sun inits apparent motion along the ecliptic to a fixedposition on the celestial sphere of any fixed place.This is equal to 365.24 mean solar days.

Sidereal Year: The period of revolution of theearth around the sun. It is calculated withreference to any fixed star. It is approximatelyequal to 365.26 days.

To account for 1/4 of a day in a year, theleap year system is adopted in the Gregoriancalendar. To account for the excess of 11 minutesin a year, the centurial year is considered a leapyear only when it is divisible by 400.

Earth in Figures

1. Age 4,550 million years

2. Mass 5.976 1024 kg.

3. Mean density 5.518 kg/litres.

4. Total Surface Area 510,000,000 km2.

5. Land Area 29.2% of the total

surface area.

6. Water Area 70.8% of the total

surface area.

7. Highest point

(Mt. Everest) 8,848 m

8. Lowest point

(Dead Sea) 397 m.

9. Greatest Ocean Depth 11,033 m(Mariana Trench)

10. Mean EquatorialDiameter 12,756 km.

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11. Equatorialcircumference 40,076 km.

Theories of Origin of Earth

1. Buffon-Hypothesis: Based on sun-cometcollision.

2. Kant-Gaseous Mass Theory: Based onNewton's law of gravitation.

3. Chamberlain-Moulton: PlanetesimalHypothesis.

4. Jeans & Jeffery: Tidal Hypothesis: Basedon sun-giant star attraction.

5. Alfven: Electromagnetic Hypothesis.

6. Russell and Littleton: Binary StarHypothesis.

7. Ross-Gun-Fission Hypothesis: Rotationaland Tidal hypothesis.

8. F. Hoyle: Super Nova Hypothesis.

9. Big Bang Theory: Latest idea.

Major domains of the earth

Earth is the only planet which has life.Human beings can live here because the lifesustaining elements of land, water and air arepresent on the earth. The surface of the earth is acomplex zone in which three main componentsof the environment meet, overlap and interact.The solid portion of the earth on which we live iscalled the lithosphere. The gaseous layers thatsurround the earth, is the atmosphere, whereoxygen, nitrogen, carbon dioxide and other gasesare found. Water covers a very big area of theearth's surface and this area is called thehydrosphere. The hydrosphere comprises waterin all its forms, that is, ice, water and watervapour. The biosphere is the narrow zone wherewe find land, water and air together, whichcontains all forms of life.

A. Lithosphere

The solid portion of the earth is called thelithosphere. It comprises the rocks of the earth'scrust and the thin layers of soil that containnutrient elements which sustain organisms. Thereare two main divisions of the earth's surface. Thelarge landmasses are known as the continentsand the huge water bodies are called the oceanbasins. All the oceans of the world are connectedwith one another. The level of seawater remains

the same everywhere. Elevation of land ismeasured from the level of the sea, which is takenas zero.

The highest mountain peak Mt. Everest is8,848 metres above the sea level. The greatestdepth of 11,022 metres is recorded at MarianaTrench in the Pacific Ocean.

Continents

There are seven major continents. These areseparated by large water bodies. These continentsare - Asia, Europe, Africa, North America, SouthAmerica, Australia and Antarctica.

Asia is the largest continent. It covers aboutone-third of the total land area of the earth. Thecontinent lies in the Eastern Hemisphere. TheTropic of Cancer passes through this continent.Asia is separated from Europe by the UralMountains on the west. The combined landmassof Europe and Asia is called the Eurasia (Europe+ Asia).

Europe is much smaller than Asia. Thecontinent lies to the west of Asia. The Arctic Circlepasses through it. It is bound by water bodies onthree sides.

Africa is the second largest continent afterAsia. The Equator or 0 latitude runs almostthrough the middle of the continent. A large partof Africa lies in the Northern Hemisphere. It isthe only continent through which the Tropic ofCancer, the Equator and the Tropic of Capricornpass. The Sahara Desert, the world's largest hotdesert, is located in Africa. The continent is boundon all sides by oceans and seas. The world'slongest river, the Nile, flows through Africa.

North America is the third largest continentof the world. It is linked to South America by avery narrow strip of land called the Isthmus ofPanama. The continent lies completely in theNorthern and Western Hemisphere. Three oceanssurround this continent.

South America lies mostly in the SouthernHemisphere. The Andes, world's longestmountain range, runs through its length fromnorth to south. South America has the world'slargest river, the Amazon.

Australia is the smallest continent that liesentirely in the Southern Hemisphere. It is

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surrounded on all sides by the oceans and seas. Itis called an island continent.

Antarctica, completely in the SouthernHemisphere, is a huge continent. It is larger thanthe combined area of Europe and Australia. TheSouth Pole lies almost at the centre of thiscontinent. As it is located in the South PolarRegion, it is permanently covered with thick icesheets. There are no permanent humansettlements. Many countries have researchstations in Antarctica. India also has researchstations there. These are named as Maitri andDakshin Gangotri.

B. Hydrosphere

The earth is called the blue planet. More than71 per cent of the earth is covered with waterand 29 per cent is with land. Hydrosphere consistsof water in all its forms. As running water inoceans and rivers and in lakes, ice in glaciers,underground water and the water vapour inatmosphere, all comprise the hydrosphere. Morethan 97% of the Earth's water is found in theoceans and is too salty for human use. A largeproportion of the rest of the water is in the formof ice-sheets and glaciers or under the ground anda very small percentage is available as fresh waterfor human use.

Oceans

Oceans are the major part of hydrosphere.They are all interconnected. The ocean waters arealways moving. The three chief movements ofocean waters are the waves, the tides and theocean currents. The four major oceans are thePacific Ocean, the Atlantic Ocean, the IndianOcean and the Arctic Ocean, in order of their size.

The Pacific Ocean is the largest ocean. It isspread over one-third of the earth. MarianaTrench, the deepest part of the earth, lies underthe Pacific Ocean. The Pacific Ocean is circularin shape. Asia, Australia, North and SouthAmericas surround it.

The Atlantic Ocean is the second largestOcean in the world. It is 'S' shaped. It is flankedby the North and South Americas on the westernside, and Europe and Africa on the eastern side.The coastline of Atlantic Ocean is highly indented.This irregular and indented coastline providesideal location for natural harbours and ports.From the point of view of commerce, it is thebusiest Ocean.

The Indian Ocean is the only ocean namedafter a country, that is, India. The shape of oceanis almost triangular. In the north, it is bound byAsia, in the west by Africa and in the east byAustralia.

The Arctic Ocean is located within the ArcticCircle and surrounds the North Pole. It isconnected with the Pacific Ocean by a narrowstretch of shallow water known as Bering Strait.It is bound by northern coasts of North Americaand Eurasia.

C. Atmosphere

The earth is surrounded by a layer of gascalled the atmosphere. This thin blanket of air isan integral and important aspect of the planet. Itprovides us with the air we breathe and protectsus from the harmful effects of sun's rays. Theatmosphere extends up to a height of about 1,600km.

The atmosphere is divided into five layersbased on composition, temperature and otherproperties. These layers starting from earth'ssurface are the troposphere, the stratosphere, themesosphere, the thermosphere and the exosphere.

The atmosphere is composed mainly ofnitrogen and oxygen, which make up about 99per cent of clean, dry air. Nitrogen 78 per cent,oxygen 21 per cent and other gases like carbondioxide, argon and others comprise 1% by volume.

The density of the atmosphere varies withheight. It is maximum at the sea level anddecreases rapidly as we go up. The climbersexperience problems in breathing due to thisdecrease in the density of air. The temperaturealso decreases as we go upwards.

The atmosphere exerts pressure on the earth.This varies from place to place. Some areasexperience high pressure and some areas lowpressure. Air moves from high pressure to lowpressure. Moving air is known as wind.

D. Biosphere

The biosphere is the narrow zone of contactbetween the land, water and air. It is in this zonethat life exists. All the living organisms includinghumans are linked to each other and to thebiosphere for survival. The organisms in thebiosphere may broadly be divided into the plantkingdom and the animal kingdom.

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The three domains of the earth interact witheach other and affect each other in some way orthe other. For example, cutting of forests forfulfilling our needs of wood, or clearing land foragriculture may lead to fast removal of soil fromslopes. Similarly earth's surface may be changeddue to natural calamities like earthquakes ortsunamis.

Discharge of waste material into lakes andrivers makes the water unsuitable for human use.It also damages other forms of life. Emission fromindustries, thermal power plants and vehicles,pollute the air. Carbon dioxide (CO2) is animportant constituent of air. But increase in theamount of CO2 leads to increase in globaltemperatures. This is termed as global warming.There is thus, a need to limit the use of resourcesof the earth to maintain the balance of naturebetween the domains of the lithosphere, theatmosphere and the hydrosphere.

Points to Remember

1. Mercury, Venus, Earth and Mars areknown as' Inner Planets' whereas Jupiter,Saturn, Uranus and Neptune are knownas "Outer plants".

2. Planets bigger than the earth are Jupiter,Saturn, Uranus and Neptune.

3. Earth and Venus have almost same size,hence these two are known as' Twinplanets"

4. All planets rotate in the same direction inwhich they revolve except Venus andUranus.

5. Saturn is surrounded by three luminous,concentric rings.

6. Earth has the maximum density of 5.52 inthe solar system while the Saturn has theleast density of 0.69.

7. According to gravity Jupiter stands firstfollowed by Neptune, Uranus, Saturn andEarth.

8. Mercury and Venus have no satellite.9. Neptune's atmosphere has poisonous gases

like methane, ammonia, etc.10. Comets revolve around the Sun and when

broken are converted into "Meteors".11. Earth is spherical in shape with

compression at the poles and a bulge atthe equator. Hence earth is an oblatespheroid or called a Geoid.

12. A solar day is greater than a sidereal dayby 4 minutes.

13. Each degree of latitude is equals to 111 km.14. A person crossing International Date Line

from the East to West loses one day.15. Mercury is the nearest planet to Sun.16. Venus is the nearest planet to Earth.17. Venus is the hottest planet; its atmosphere

contains 97% CO2.18. Jupiter is the biggest planet.19. Venus is the brightest planet.20. Earth is the blue planet.21. Mars is the Red planet.22. Venus is the Morning and Evening Star.23. Pluto is the double planet.24. Saturn and Uranus are known as the

planets with rings.25. Mercury has the maximum diurnal range

of temperature.26. Saturn has maximum no. of satellites.27. Pluto has the most eccentric orbit.28. Jupiter is the fastest rotating planet.29. Venus is the slowest rotating planet.30. Venus has the same period of rotation as

revolution.31. The length of the day is nearly same on the

planet Mars as that of the Earth.32. Jupiter, Saturn, Uranus and Neptune are

the Jovian planets.33. The angle of inclination of Mars is nearly

same as that of Earth.34. Jupiter, Saturn, Uranus and Neptune are

the outer planet.35. Mercury, Venus, Earth and Mars are the

inner planets.36.Venus rotates from East to West.37.Uranus rotates from North to South.

38. Mercury is the fastest revolving planet.39. Pluto is the slowest revolving planet.40. Planet revolves around the sun in Anti-

clockwise direction.41. "Hydra" is the largest constellation.42. The nearest galaxy. "Andromeda" is 22,

00,000 Light years away.43. Existence of galaxies beyond Milky Way

was first demonstrated by Edwin Hubble.44. Galaxies are also called "Islands of universe"

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The interior of the earth can be understoodonly by indirect evidences as no one has reachedthe interior of the earth. The surfaceconfiguration of the earth is largely a product ofthe processes operating in its interior. A properunderstanding of the physiographic characterof a region remains incomplete unless the effectsof both endogenic processes as well as exogenicprocesses are studied.

Sources of information about the interior

The earths radius is 6,370 km. Reaching thecentre of the earth and make observations orcollect samples of the materials is almostimpossible. Under such conditions, most of ourknowledge about the interior of the earth islargely based on analogies and inferences. Yet,a part of the information is obtained throughdirect observations and analysis of materials.

Direct Sources

The readily available solid earth material issurface rock we get from mining areas. Besidesmining, scientists world over are working on twomajor projects such as Deep Ocean DrillingProject and Integrated Ocean DrillingProject. The deepest drill at Kola, in ArcticOcean, has so far reached a depth of 12 km.These drilling projects have provided largevolume of information through the analysis ofmaterials collected at different depths. Volcaniceruption forms another source of obtainingdirect information. As and when the magmacomes out to the surface of the earth duringvolcanic eruption it becomes available forlaboratory analysis.

Indirect Sources

Analysis of properties of rocks and magmaindirectly provides information about theinterior. Through mining we know thattemperature and pressure increase with theincreasing depth. It is also known that the densityof the material also increases with depth.

Scientists have estimated the values oftemperature, pressure and the density ofmaterials at different depths.

Meteor is another source of information aboutthe interior of the earth. However, the material,that becomes available for analysis from meteors,is not from the interior of the earth. It is onlysimilar to that of the earth. Meteors are solidbodies developed out of materials same as, orsimilar to, earth. So, by analogy meteors providevaluable information about the earths interior.

Other indirect sources include gravitation,magnetic field and seismic activity. Thegravitational force is greater near the poles andless at the equator. It also differs according to themass of material. Thus the uneven distribution ofmaterial within the earth influences its value. Thereadings of the gravity, may, at places differ fromthe expected values. Such a difference is calledgravity anomaly. Gravity anomalies give usinformation about the distribution of mass of thematerial in the crust of the earth.

Seismic/Earthquake Waves

The study of seismic waves provides acomplete picture of the layered interior. Anearthquake in simple words is shaking of theearth. It is a natural event. It is caused due torelease of energy, which generates waves thattravel in all directions. The energy wavestravelling in different directions reach the surface.

Earthquake waves are basically of two types-body waves and surface waves. Body waves aregenerated due to the release of energy at the focusand move in all directions travelling through thebody of the earth. They interact with the surfacerocks and generate new set of waves calledsurface waves. These waves move along thesurface. The velocity of waves changes as theytravel through materials with different densities.Denser the material, higher is the velocity.

There are two types of body waves. Theyare called P and S-waves. P-waves move faster

INTERIOR INFRASTRUCTUREINTERIOR INFRASTRUCTUREINTERIOR INFRASTRUCTUREINTERIOR INFRASTRUCTUREINTERIOR INFRASTRUCTURE

OF THE EARTHOF THE EARTHOF THE EARTHOF THE EARTHOF THE EARTH


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and are the first to arrive at the surface. These arealso called primary waves. The P-waves aresimilar to sound waves. They travel through allmaterials gaseous, liquid and solid. S-waves arriveat the surface with some time lag. These are calledsecondary waves. S-waves can travel onlythrough solid materials. This characteristic of theS-waves has helped scientists to understand thestructure of the interior of the earth.

Different waves travel in different manners.P-waves vibrate parallel to the direction of thewave. This exerts pressure on the material in thedirection of the propagation. As a result, itcreates density differences in the material leadingto stretching and squeezing of the material.Other waves vibrate perpendicular to thedirection of propagation. The direction ofvibrations of S-waves is perpendicular to thewave direction in the vertical plane. Hence, theycreate troughs and crests in the material mediumthrough which they pass. Surface waves areconsidered to be the most damaging waves.

Shadow Zone

Earthquake waves are recorded inseismographs located at far off locations.However, there are certain areas where thewaves are not reported. Such a

zone, where the waves are not recorded, is calledthe shadow zone. The study reveals that foreach earthquake, there exists an altogetherdifferent shadow zone. Given figure shows theshadow zones of P and S-waves.

It was observed that seismographs, locatedwithin 105 from the epicentre, recorded thearrival of both P and S-waves. But, beyond 140from epicentre, they record the arrival of P-waves,but not that of S-waves. Thus, a zone between

105 and 140 from epicentre is identified as theshadow zone of P-waves. However, the entirezone beyond 105 does not receive S-waves. Thusshadow zone of S-wave is much larger than thatof the P-waves. The shadow zone of P-wavesappears as a band around the earth between 105and 140 away from the epicentre whereas thatof S-wave is a continuous zone.

Structure of the interior

Just like an onion, the earth is made up ofseveral concentric layers with one inside another.The important zones include:

The crust: The outer layer of the earth isknown as the crust. It comprises about 0.5% ofthe earths body. Its thickness ranges from 5 to 40km. The crust is thicker beneath the continentsthan beneath the oceans. It is made up of twolayers: upper lighter layer (density=2.7 g/cc)called the sial (silica + aluminium) and a lowerdenser layer (density=3.0 g/cc) called sima (silica+ magnesium). The average density of the earthssurface is less than 3 gm/c.c. The upper layer ofthe crust is mainly composed of crystallineigneous and metamorphic rocks, acidic innature. The lower layer of the crust containsbasaltic & ultra-basic rocks. Conrad discontinuityseparates the outer and the inner crusts.

The mantle: Below the crust of the earth isa thick

layer called mantle. This layer extends upto adepth of 2900 km. The mantle consistspredominantly of solid olivine rocks made up ofsilicates of magnesium and iron and displayingplastic properties. Its average density is 56.8. Thislayer is separated from the crust by MohorovicicDiscontinu- ity. The outer and the inner mantleare separated by another discontinuity namedRepetti discontinuity.

The core: Beyond a depth of 2900 km liesthe core of the earth. It is named as barysphere

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and also nife (nickel and ferrous). Averagethickness is 4671 kms. Average density is 17.2.By volume it constitutes 17% of the earths body.The temperature of the core is about 200c. Thecore is believed to be a reason for the earthsmagnetism. It is separated from the mantle byGutenburg-Wiechert Discontinuity.

Lithosphere & Aesthenosphere: Beneath

the upper mantle there is a soft layer in whichthe mantle rock is at the temperature close tothe melting point. It sets in at an average depthof about 80 km which is well below the base ofthe continental crust. This layer is called asAesthenosphere and the rigid layer above itis called as lithosphere. The aesthenosphereextends to a depth of about 400 km.

Composition and properties of different layers of the earth

Name of the Chemical Average Density Physical Propertieslayer Composition Thickness (g cm-3)

(km)

A.(i) Crust Sial 6 to 45 2.2 to 2.9 Solid part oflithosphere; partly molten under thecontinents.

(ii) Inner part of Outer silicate 45 to 100 The solid crust andlithosphere layer, Basaltic upper mantle

B Aesthenosphere 50 to 400 It transmits both S-and P-wave but withreduced velocities.

C.(i) Upper Mantle Sima (Peridotite 100 to 1700 3.1 to 4.75 Slightly solid and(mainly under iron- magnesium- slightly plasticoceans) rich silicate rock) material close to

melting point.

(ii) Lower Mantle Wholly Sima 1700 to2900 4.75 to 5.6 Transition zone of(Olivine- mixed metals andUltrabasic rocks) silicate

D.(i) Outer core Nife 2900 to 4980 9.9 - 12.3 Liquid or in a plasticstate. Fe, Ni and Smixture.

(ii) Inner core Barysphere (heavy 4980 to 6400 13.5 Iron and nickel. Solidmetallic rocks) and rigid due to

tremendous overlyingpressure.

Temperature: In upper 100 km theincrease in temperature is estimated at the rateof 12C per km descend. In the next 300 km,the increase is of 2C per km and below thatthe rate of increase is 1C per km. In the corethe temperature is about 2000C. But at thesame time there is a huge pressure of overlyinglayers of the earths interior. So even underextremely high temperature towards thecentral part of the earth the liquid nature ofthe earth core has acquired the properties of asolid and is probably in a plastic state.

Composition of the Earth

1. Iron 35%

2. Oxygen 30%

3. Silicon 15%

4. Magnesium 13%

5. Nickel 2.4%

6. Sulphur 1.9%

7. Calcium 1.1%

8. Aluminium 1.1%

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Continental drift

The theory of continental drift, expoundedby Alfred Wegener in 1915, holds that portionsof the original continent which comprised theentire landmass of the world underwent a seriesof horizontal displacement before the presentcontinents were formed.

According to this theory, about 280 millionyears ago, the entire landmass formed one supercontinent, called Pangea. According toWegener, after the breaking of the supercontinent pangae, the movement of thecontinents took place in two directions- onetowards the equator due to centrifugal force ofthe earth which gave rise to fold mountains likethe Himalayas, the alps, etc. and another towardswest due to tidal force of sun and the moon whichgave rise to Andes and Rockies.

A glance at the world map shows that S.America particularly Brazil can be fitted into theGulf of Guinea of Africa; Antarctica can roughlybe fitted into S. Australian coast and S.E-Africancoast. Similarly NW-Australian coast and E-Indian coast are liable to fit. After the drifts somewater bodies developed between them. Geologicalevidences prove that S. America and Africa wereprobably joined together till the upper Triassic.Biological history of certain animals likemarsupials and placental mammals also throwsignificant light on the continental drift.

Plate Tectonics

Plate tectonics deals with rock structureswhich are in the form of the plates and it is notonly the continents which are in motion but theoceans as well. These plates include not only theearths upper crust but also the part of densermantle below. They have an average thicknessof 100 km. They float on the plastic upper mantle

called aesthenosphere and carry thecontinents and oceans on their back. The edgesof the plates are designed as boundaries andmargins, where movements occur.

Major plates of the world are:

1. American plate2. Pacific plate3. Antarctic plate4. African plate5. European plate and6. Australian plate.

Some minor plates are:

1. Caribbean plate.2. Cocas plate3. Nazca plate4. Juan de Fuca plate5. Philippine plate, etc.

All these plates are in constant motion bothin relation to each other and with regard to theearths motion. Some movements are responsiblefor the volcanic activities, seismic and other platedisturbances on the margins of the plates.

Types of movements of plates

A. Convergence: When the oceaniclithosphere moves towards the continentallithosphere, due to its thickness the continentalcrust is unable to go down and it is the oceaniccrust which is involved in subduction. Thedownwent plate of the oceanic crust melts andproduces magma. This magma rises

slowly and emerges as intrusive igneous rock inthe form of volcanic mountains on thecontinental crust. Thus origin of volcanicmountains like Andes takes place.

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When the two oceanic lithospheres lie onboth side of subduction, then either of the twoplates may subduct. The subducted part meltsand the magma rises above the oceanic surfaceand volcanic islands are formed in arc form likeAleutian island, Kuril Island, Ryuku Island, etc.

When the continental lithosphere lies onboth sides of subduction, the sediments getscrapped off the descending plate margin. In thenext stage the two continents collide, squeezingthe sediment mass and throwing it intocomplicated fold and high alpine ranges likeHimalayas and Alps are formed.

B. Divergence/continental rupturing: It is

also termed as ocean floor spreading. Deepbeneath the continental plate a column of heatedmantle rock begins to rise and reach the plateabove, causing the plate to fracture, which iscalled continental rupture. At first blockmountains are formed. Next a long narrow valleycalled rift valley appears. The widening crackin its center is continuously filled in with magmarising from the mantle below. The magmasolidifies to form new crust and also a newoceanic crust and lithosphere.

C. Parallel movements of plates: Parallelplates, as they slide past each other along acommon boundary, do not create a new crustor destroy the old one but they producetransform faults which are fractures in rockformation. Fractures imply displacement ofrocks. As the plates continue to move, the lockedrocks snap. They shift violently back toequilibrium like a bent - stick breaking. Thisviolent shift causes earth - quakes.

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MINERALS & ROCKSMINERALS & ROCKSMINERALS & ROCKSMINERALS & ROCKSMINERALS & ROCKSCHRONICLEIAS ACADEMYA CIVIL SERVICES CHRONICLE INITIATIVE

Minerals

A mineral is a naturally occurring substancethat is solid and stable at room temperature,representable by a chemical formula, usuallyabiogenic, and has an ordered atomic structure

Mineral are divided as follows:

A. Metallic Minerals

These minerals contain metal content andcan be sub-divided into three types:

(i) Precious metals: gold, silver, platinum etc.

(ii) Ferrous metals: iron and other metals oftenmixed with iron to form various kinds ofsteel.

(iii) Non-ferrous metals: include metals likecopper, lead, zinc, tin, aluminium etc.

B. Non-Metallic Minerals

These minerals do not contain metal content.Sulphur, phosphates and nitrates are examplesof non-metallic minerals. Cement is a mixture ofnon-metallic minerals.

Some Major Minerals and Their Characteristics

Feldspar

Silicon and oxygen are common elements inall types of feldspar and sodium, potassium,calcium, aluminium etc. are found in specificfeldspar variety. Half of the earths crust iscomposed of feldspar. It has cream to salmonpink colour. It is used in ceramics industries.

Quartz

It is one of the most important componentsof sand and granite. It consists of silica. It is ahard mineral virtually insoluble in water. It iswhite or colourless and used in radio and radar.It is one of the most important components ofgranite. Pyroxene

Pyroxene consists of calcium, aluminum,

magnesium, iron and silica. Pyroxene forms 10per cent of the earths crust. It is commonly foundin meteorites. It is in green or black colour. Amphibole

Aluminium, calcium, silica, iron, magnesiumare the major elements of amphiboles. They form7 per cent of the earths crust. It is in green orblack colour and is used in asbestos industry.Hornblende is another form of amphiboles. Mica

It comprises of potassium, aluminium,magnesium, iron, silica etc. It forms 4% of theearths crust. Commonly found in igneous andmetamorphic rocks, it is used in electricalinstruments. Olivine

Magnesium, iron and silica are majorelements of olivine. It is used in jewellery. It isusually a greenish crystal, often found in basalticrocks. Other minerals like chlorite, calcite,magnetite, haematite, bauxite and barite are alsopresent in some quantities in the rocks.

Rocks

The earths crust is composed of rocks. Arock is an aggregate of one or more minerals.Rock may be hard or soft and in varied colours.For example, granite is hard, sandstone is soft.Gabbro is black and quartzite can be milky white.Rocks do not have definite composition ofmineral constituents. Feldspar and quartz are themost common minerals found in rocks.

The crustal rocks are classified on the basisof mode of formation, physical and chemicalproperties, location etc. On the basis of mode offormation the rocks are divided into threecategories (i) igneous rocks (ii) sedimentaryrocks (iii) metamorphic rocks.

A) Igneous rocks

As igneous rocks form out of magma andlava from the interior of the earth, they areknown as primary rocks. The igneous rocks are

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formed when magma cools and solidifies. Whenmagma in its upward movement cools and turnsinto solid form it is called igneous rock. Theprocess of cooling and solidification can happenin the earths crust or on the surface of the earth.

Igneous rocks are characterized on the basisof texture. Texture depends upon size andarrangement of grains or other physicalconditions of the materials. If molten material iscooled slowly at great depths, mineral grains maybe very large. Sudden cooling (at the surface)results in small and smooth grains. Intermediateconditions of cooling would result inintermediate sizes of grains making up igneousrocks. Granite, gabbro, pegmatite, basalt,volcanic breccia and tuff are some of theexamples of igneous rocks.

Igneous rocks are roughly hard rocks andwater percolates with great difficulty. They donot have strata and are less affected by chemicalweathering. They dont contain fossils. Thenumber of joints increases upwards. They aremostly associated with volcanic activity.

They are classified on several grounds asmentioned below:

(a) On the basis of silica content:

(i) Acidic igneous rocks have more silica e.g.Granites

(ii) Basic igneous rocks have less silica e.g.Gabbro.

(b) On the basis of chemistry andmineralogical composition:

(i) Felsic igneous rock (feldspar is dominant)

(ii) Mafic igneous rock (magnesium and ferrousare dominant)

(iii) Ultra mafic igneous rock (Peridotite anddunite are dominant).

(c) On the mode of occurrence:

(i) Intrusive igneous rocks they arecooled and solidified below the surface of theearth. They are further divided into plutonic andhypabyssal igneous rocks. Plutonic rocks cooldeep beneath the earth e.g. Granite. Hypabyssalrocks cool just beneath the earth surface e.g.Batholith, laccolith, phacolith, lapolith, sills,dykes, etc.

(ii) Extrusive igneous rocks are formed dueto cooling and solidification of hot and moltenlava at the earths surface e.g. Basalt, Gabbro,obsidian.

B) Sedimentary rocks

The word sedimentary is derived from theLatin word sedimentum, which means settling.Rocks (igneous, sedimentary and metamorphic)of the earths surface are exposed todenudational agents, and are broken up intovarious sizes of fragments. Such fragments aretransported by different exogenous agencies anddeposited. These deposits through compactionturn into rocks. This process is called lithification.In many sedimentary rocks, the layers ofdeposits retain their characteristics even afterlithification. Hence, we see a number of layersof varying thickness in sedimentary rocks likesandstone, shale etc.

Depending upon the mode of formation,sedimentary rocks are classified into three majorgroups: (i) mechanically formed - e.g. sandstone,conglomerate, shale, loess etc. (ii) organicallyformed - e.g. chalk, limestone, coal etc. (iii)chemically formed e.g. chert, halite, potash etc.

These rocks are formed due to aggregationand compaction of sediments. These rockscontain fossils of plants and animals. They cover75 percent of surface area of the globe. Howeverthey form only 5 percent of the volume of earthscrust. They contain several layers or strata butthese are seldom crystalline rocks. They areseldom found in original and horizontal manner.They may be well consolidated, poorlyconsolidated and even unconsolidated. They arecharacterized by different sizes of joints. Mostsedimentary rocks are porous and permeable.

The formation of sedimentary rocks takes placein three stages:

Transportation: after weathering anderosion the fragments of parental rocksare transported by the agents of erosionlike stream, wind, air, etc.

Deposition: transported materials aredeposited in sea, lakes, etc. The particlesare deposited in parallel layers and theirprocess of layer formation is calledstratification.

Consolidation: when the number of layer

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is large, the weight of upper layer begins to affectthe lower layers and the further compressionsolidifies the sediments into rocks.

They are classified under different schemes:

1. On the basis of nature of sediments:

(a) Mechanically formed or clastic rocks e.g.Sandstones. Conglomerates, clay rock,shale, loess.

(b) Chemically formed sedimentary rocks e.g.gypsum, salt rock.

(c) Organically formed sedimentary rocks e.g.Limestone, dolomites, coal, peats, etc.

2. On the basis of transporting agents:

(i) Argillaceous or aqueous rocks: (a) Marinerocks, (b) Lacustrine rocks, (c) Riverinerocks

(ii) Aeolian rocks e.g. Loess.

(iii) Glacial sedimentary rocks e.g. Till, moraine.

C). Metamorphic rocks

The word metamorphic means change ofform. These rocks form under the action ofpressure, volume and temperature (PVT)changes. Metamorphism occurs when rocks areforced down to earths interior by tectonicprocesses or when molten magma rising throughthe crust comes in contact with the crustal rocksor the underlying rocks are subjected to greatamounts of pressure by overlying rocks.Metamorphism is a process by which alreadyconsolidated rocks undergo recrystallization andreorganization of materials within original rocks.

Mechanical disruption and reorganizationof the original minerals within rocks due tobreaking and crushing without any appreciablechemical changes is called dynamicmetamorphism. The materials of rockschemically alter and recrystallize due to thermalmetamorphism. There are two types of thermalmetamorphism - contact metamorphism andregional metamorphism.

In contact metamorphism the rocks come incontact with hot intruding magma and lava andthe rock materials recrystallize under hightemperatures. Quite often new materials formout of magma or lava are added to the rocks.

In regional metamorphism, rocks undergorecrystallization due to deformation caused bytectonic shearing together with high temperatureor pressure or both. In the process ofmetamorphism in some rocks grains or mineralsget arranged in layers or lines. Such anarrangement of minerals or grains inmetamorphic rocks is called foliation or lineation.

Sometimes minerals or materials of differentgroups are arranged into alternating thin to thicklayers appearing in light and dark shades. Sucha structure in metamorphic rocks is calledbanding and rocks displaying banding are calledbanded rocks. Types of metamorphic rocksdepend upon original rocks that were subjectedto metamorphism.

Metamorphic rocks undergo completealteration in the appearance of pre-existing rocksdue to change in mineral composition and texturethrough temperature and pressure changes.Gneiss, granite, slate, schist, marble, quartzite etc.are some examples of metamorphic rocks. Theyare classified as mentioned below:

1. Contact or thermal metamorphism: heremetamorphism occurs when the mineralcomposition of the surrounding rocks is changeddue to intense heat e.g. Limestone is changed tomarble.

2. Regional or dynamic metamorphism:here pressure plays an important role so thatrocks are altered in their forms in an extensivearea.

Rock Cycle

Rocks do not remain in their original formfor long but may undergo transformation. Rockcycle is a continuous process through which oldrocks are transformed into new ones. Igneousrocks are primary rocks and other rocks(sedimentary and metamorphic) form from theseprimary rocks. Igneous rocks can be changedinto metamorphic rocks. The fragments derivedout of igneous and metamorphic rocks transforminto sedimentary rocks. Sedimentary rocksthemselves can turn into fragments and thefragments can be a source for formation of othersedimentary rocks. The crustal rocks (igneous,metamorphic and sedimentary) once formedmay be carried down into the mantle (interiorof the earth) through subduction process (parts

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or whole of crustal plates going down underanother plate in zones of plate convergence). Thesame can melt down due to increase intemperature in the interior and turn into moltenmagma, the original source for igneous rocks.

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FORCES EFFECTING THEFORCES EFFECTING THEFORCES EFFECTING THEFORCES EFFECTING THEFORCES EFFECTING THE

EAREAREAREAREARTH MOTH MOTH MOTH MOTH MOVEMENTSVEMENTSVEMENTSVEMENTSVEMENTS


The forces which affect the earthsmovement are involved in the creation,destruction, recreation and maintenance ofvarious types of relief features of varyingmagnitudes. On the basis of origin these forcesare divided into (i) endogenetic forces and (ii)exogenetic forces. While endogenetic forcescreate relief features on the earths surface, theexogenetic forces through their erosional anddepositional activities destroy them and help inthe planation process.

Endogenetic forces

Term endogenic refers to internal processesand phenomena that occur beneath the Earth'ssurface. These forces are divided into suddenforces and diastrophic forces.

(a) Sudden forces: events like earthquake andvolcanic eruption occur suddenly and theresultant forces work very quickly. Theyare constructive forces as they create cones,lakes, plateaus, lava plains etc.

(b) Diastrophic forces: they include bothvertical and horizontal movements.

(i) Vertical movement: they includeemergence and subsidence of land masses.Emergence may occur due to upliftment ofthe whole continent or part there of orupliftment of coastal land of the continents.Submergence may occur when the landnear the sea coast subsides below sea level.

(ii) Horizontal movement: these forces workinto two ways

a) In opposite direction - this includestensional or divergent forces which createfaults, rupture, fracture, cracks etc.

b) Towards each other - This includescompressional or convergent forces whichcreate folding, warping etc.

Folding:

It is the process whereby the rock strata arebent into a series of arches (anticlines) and toughs

(syncline) as a result of horizontal earthmovements which cause compression within thecrust. The anticlines of the folds generally formthe mountains and the adjacent synclines formthe valleys. Most of the mountain ranges of theworld consist of Fold Mountains e.g. the Alps,the Andes, the Rockies and the Himalayas.

Geometry of Folds - Folds are described bytheir form and orientation. The sides of a foldare called limbs. The limbs intersect at the tightestpart of the fold, called the hinge. A lineconnecting all points on the hinge is called thefold axis. In the diagrams above, the fold axesare horizontal, but if the fold axis is nothorizontal the fold is called a plunging

fold and the angle that the fold axis makes witha horizontal line is called the plunge of the fold.An imaginary plane, that includes the fold axisand divides the fold as symmetrically as possible,is called the axial plane of the fold.

Types of Folds

Not all folds are equal on both sides of theaxis of the fold. Those with limbs of relativelyequal length are termed symmetrical, and thosewith highly unequal limbs are asymmetrical.Asymmetrical folds generally have an axis at anangle to the original unfolded surface theyformed on. Other kinds of folds are:

Anticlines - Up folds.

When the upper part of the fold is erodedaway, the oldest rocks are in the center ofthe fold, and the youngest rocks are on

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each side. Also, the rocks dip (or slope)away from the central axis of the fold.

Synclines - Down folds.When the upper part of the fold is erodedaway, the youngest rocks are in the centerof the fold, and the oldest rocks are oneach side. Also, the rocks dip toward thecentral axis of the fold.

Monoclines - a bend in otherwisehorizontal strata.

Isoclinal folds have undergone greaterstress that has compressed the limbs of thefolds tightly together.

The limbs of overturned folds dip in thesame direction, indicating that the upperpart of the fold has overridden the lowerpart. Depending

on where the exposure is in an overturnedfold, the oldest strata might actually be ontop of the sequence and be misinterpretedas the youngest rock unit.

Recumbent folds, found in areas of thegreatest tectonic stress, are folds that areso overturned that the limbs are essentiallyhorizontal and parallel.

Chevron: angular fold with straight limbsand small hinges.

Faulting:

It is the process by which the tensional earthmovements under the effect of considerablepressure create a fracture in the earth's crust.Faulting gives rise to relief features like blockmountains (horsts), rift valleys, etc. A rift valleyis a long, relatively narrow depression formed

by the sinking of a block of land between twomore or less parallel faults. Examples: EastAfrican rift valley, Narmada and Tapti valleys.

Columns of faulting bring four distinguishablelandforms as:

I. Rift valley: it is the result of the subsidenceof the central column. When the centralcolumn of the two fault-lines subsides, therift valley is made. "Damodar valley" is suchan example.

II. Ramp valley: when both side columns areraised and the central column is standstill,then the made landform is ramp valley."Brahmaputra" river passes through a rampvalley.

III. Block Mountain: this is the result of thesubsidence of side column. The centralcolumn gets

steep rim along the fault scarps and theraised landform is Block Mountain."Satpura hills" of India is such an example.

IV. Horst: Horst is a similar landform but issupposed to be due to upward force frombeneath the central column. Side-columnsare standstill. "Harz Mountain" of Germanyis an example.

Exogenetic forces

Exogenic forces refer to external processesand phenomena that occur on or above theEarth's surface. Comet and meteoroid impacts,the tidal force of the moon and sun's radiationsare all exogenic. Weathering effects and erosionare also exogenic processes. They also affect theplanation processes. These are also calleddenudational or destructive forces. The erosionalprocess is affected by running water, groundwater, glaciers, sea waves etc. These processesform erosional and depositional land forms.

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WEAWEAWEAWEAWEATHERING &THERING &THERING &THERING &THERING &

EROSIONEROSIONEROSIONEROSIONEROSION


Weathering

Weathering is the process of disintegrationand decomposition of rocks while erosion is theprocess of removal, transportation anddeposition of the weathered particles. Theseprocesses together are known as Denudation.

Weathering is defined as mechanicaldisintegration and chemical decomposition ofrocks through the actions of various elements ofweather and climate. Weathering process bringsmechanical disintegration and chemicaldecaying of rocks. Weather conditions are themost decisive phenomenon hence the nameweathering. However the type and rate ofweathering are also influenced by rock structure,topography and vegetation. Weathering is astatic process. It is also the process of soil genesis.It is of three types:

I. Mechanical Weathering: When a regionundergoes mechanical weathering, rocks arebroken into small pieces. Physical or mechanicalweathering processes depend on some appliedforces. The applied forces could be: (i)gravitational forces such as overburden pressure,load and shearing stress; (ii) expansion forcesdue to temperature changes, crystal growth oranimal activity; (iii) water pressures controlledby wetting and drying cycles.

Many of these forces are applied both at thesurface and within different earth materialsleading to rock fracture. Most of the physicalweathering processes are caused by thermalexpansion and pressure release. These processesare small and slow but can cause great damageto the rocks because of continued fatigue therocks suffer due to repetition of contraction andexpansion.

This mechanical disintegration takes place indifferent ways.

(a) Frost Action: Frost weathering occurs dueto growth of ice within pores and cracks ofrocks during repeated cycles of freezing and

melting. This process is most effective athigh elevations in mid-latitudes wherefreezing and melting is often repeated.Glacial areas are subject to frost wedgingdaily. In this process, the rate of freezing isimportant. Rapid freezing of water causesits sudden expansion and high pressure.

The resulting expansion affects joints, cracksand small inter granular fractures tobecome wider and wider till the rock breaksapart.

(b) Thermal Expansion and Contraction:Various minerals in rocks possess their ownlimits of expansion and contraction. Withrise in temperature, every mineral expandsand pushes against its neighbour and astemperature falls, a correspondingcontraction takes place. Because of diurnalchanges in the temperatures, this internalmovement among the mineral grains of thesuperficial layers of rocks takes placeregularly. This process is most effective indry climates and high elevations wherediurnal temperature changes are drastic.Though these movements are very smallthey make the rocks weak due to continuedfatigue.

The surface layers of the rocks tend toexpand more than the rock at depth andthis leads to the formation of stress withinthe rock resulting in heaving and fracturingparallel to the surface. Due to differentialheating, the resulting expansion andcontraction of surface layers and theirsubsequent exfoliation from the surfaceresults in smooth rounded surfaces of rocks.

In rocks like granites, smooth surfaced androunded small to big boulders called torsform due to such exfoliation. In the area ofhot deserts, the diurnal range oftemperature brings the expansion andcontraction of surface rocks, leading to theirdisintegration into smaller pieces.

(c) Exfoliation: This is the expansion by

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unloading process. Unloading occurs whenlarge igneous bodies are exposed throughthe erosional removal of overlying rock andthe reduction in the pressure. On beingexposed to the surface they expand slightlyin volume. This leads to the peeling of thickshells like an onions layers from the parentrock.

(d) Spalling: When there is a sudden showerin the hot desert area, the highly heatedrocks when struck by sudden drizzledevelop numerous cracks.

(e) Cavernous Weathering: It occurs generallyin hot arid region and also in the rocks ofcoastal area.

(f) Salt Weathering: Salts in rocks expand dueto thermal action, hydration andcrystallization. Many salts like calcium,sodium, magnesium, potassium and bariumhave a tendency to expand. Expansion ofthese salts depends on temperature andtheir thermal properties. High temperatureranges between 30C and 50C of surfacetemperatures in deserts favour such saltexpansion.

Salt crystals in near-surface pores causesplitting of individual grains within rocks,which eventually fall off. This process offalling off of individual grains may resultin granular disintegration or granularfoliation.

Salt crystallization is most effective of allsalt-weathering processes. In areas withalternating wetting and drying conditionssalt crystal growth is favoured and theneighbouring grains are pushed aside.Sodium chloride and gypsum crystals indesert areas heave up overlying layers ofmaterials and with the result polygonalcracks develop all over the heaved surface.With salt crystal growth, chalk breaks downmost readily, followed by limestone,sandstone, shale, gneiss and granite etc.

(g) Sheeting: The development of cracks andfractures, parallel to the ground surface,caused by removal of superincumbent load.

(h) Cambering process: Due to expansioncaused by unloading of super-incombitantload and consequent release of confiningpressure.

(i) Flaking: Different heating of outer andlower shells of a rock mass causes flaking.

II. Chemical Weathering: It changes the basicproperties of the rock. Principal processesof chemical weathering are:

(a) Solution: Here the rocks are completelydissolved. This process involves removal ofsolids in solution and depends uponsolubility of a mineral in water or weakacids.

On coming in contact with water manysolids disintegrate and mix up as suspensionin water. Soluble rock forming minerals likenitrates, sulphates and potassium etc. areaffected by this process. So, these mineralsare easily leached out without leaving anyresidue in rainy climates and accumulatein dry regions. Minerals like calciumcarbonate and calcium magnesiumbicarbonate present in limestones aresoluble in water containing carbonic acid(formed with the addition of carbon dioxidein water), and are carried away in wateras solution. Carbon dioxide produced bydecaying organic matter along with soilwater greatly aids in this reaction. Commonsalt (sodium chloride) is also a rock formingmineral and is susceptible to this process ofsolution.

(b) Oxidation and Reduction: In weathering,oxidation means a combination of amineral with oxygen to form oxides orhydroxides. Oxidation occurs where thereis ready access to the atmosphere andoxygenated waters. The minerals mostcommonly involved in this process are iron,manganese, sulphur etc. Though it is auniversal phenomenon but it is moreapparent in rocks containing iron.

In the process of oxidation rock breakdownoccurs due to the disturbance caused byaddition of oxygen. Red colour of iron uponoxidation turns to brown or yellow. Whenoxidized minerals are placed in anenvironment where oxygen is absent,reduction takes place. Such conditions existusually below the water table, in areas ofstagnant water and waterlogged ground.Red colour of iron upon reduction turns togreenish or bluish grey.

(c) Hydration: Hydration is the chemical

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addition of water. Most of the rock-formingminerals absorb water. Minerals take upwater and expand. This not only increasestheir volume but also produces chemicalchanges resulting in the formation of newminerals which are softer and morevoluminous. E.g. this process convertshematite into limonite. Calcium sulphatetakes in water and turns to gypsum, whichis more unstable than calcium sulphate.

This process is reversible and long,continued repetition of this process causesfatigue in the rocks and may lead to theirdisintegration. Many clay minerals swelland contract during wetting and dryingand a repetition of this process results incracking of overlying materials. Salts in porespaces undergo rapid and repeatedhydration and help in rock fracturing. Thevolume changes in minerals due tohydration will also help in physicalweathering through exfoliation andgranular disintegration.

(d) Carbonation: Carbonation is the reactionof carbonate and bicarbonate with mineralsand is a common process helping thebreaking down of feldspars and carbonateminerals. Carbon dioxide from theatmosphere and soil air is absorbed bywater, to form carbonic acid that acts as aweak acid. Calcium carbonates andmagnesium carbonates are dissolved incarbonic acid and are removed in a solutionwithout leaving any residue resulting incave formation.

(e) Hydrolysis: The mineral of the rocks andwater molecules react in such a way thatnew mineral compounds are formed.Silicate minerals are most affected bydefrosts.

(f) Chelation: Chelation is a complex organicprocess by hydrocarbon molecules.Chelation is form of Chemical weatheringby plants.

These weathering processes are interrelated.Hydration, carbonation and oxidation gohand in hand and hasten the weatheringprocess.

III. Biological Weathering: This type ofweathering is performed by the tree roots,animals and human beings. As the plantroots grow, they wedge the rocks apart andcause the widening of joints and otherfractures. Micro animals like earthworms,ants, termites and other burrowing animals

move materials to or near the surface wherethey are more closely subjected to chemicalweathering.

Erosion

Erosion is concerned with the various waysin which the mobile agencies acquire and removerock debris. The acquisition of materials by themobile agencies and their transport, i.e. corrasionand transportation are considered to be theintegral part of erosion. The principal erosionalagents are running water, groundwater, glaciers,wind and coastal waves. Each of the agents doeserosion by distinctive processes and gives rise todistinctive landforms. There are five commonaspects of erosion by the above mentionedagents.

(1) The acquisition of rocks fragments.

(2) Wearing away of rocks fragments.

(3) The breaking down of the rock particles bymutual wear while in transit.

(4) Transportation of the acquired rock debris.

(5) Ultimately the deposition in the low lyingareas.

Mass Wasting

Mass wasting is the movement of materialdown a slope under the influence of gravity. Itis a transitional phenomenon betweenweathering and erosion. Mass Wasting is ofVarious Types: Land-slide, Debris avalanche,Earth-flow, Mud-flow, and Sheet-flow etc.

(a) Soil creep: In soil covered slope extremelyslow downslope movement of soil and overburden may be found. This process is calledas soil creep.

(b) Talus cones: Steep rocks walls of gorgesand high mountains shed countless rockparticles under the attack of physicalweathering processes.

(c) Earth Flows: In humid climate region, ifslope are steep, masses of water-saturatedsoil due to over burden or weak bedrockmay side down slope during a period offew hours.

(d) Mud flow: Rapid flowage of mud streamdown a canyon floor and spreading out onplain at the foot of a mountain range iscalled as mud flow.

(e) Landslide: The downslope movement ofregolith of bed rock is called as landslide.

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Mountains

A mountain is defined as a naturalelevation of the earth surface rising more or lessabruptly from the surrounding level andattaining an altitude which, relative to theadjacent elevation, is impressive or notable.Mountains can be classified on the basis of theirstructure or their origin.

A. Structural classification:

I. Fold Mountains: These mountains haveoriginated due to compressional tectonicforces and have been thrown up to formfold mountains e.g. Himalayas, Andes, Alpsetc. The folds consist of two inclined partscalled limbs, the upfold is called anticlineand the downward portion is calledsyncline.

All young folded mountains have originatedfrom geosynclines. Geosynclines are long narrowand shallow water depressions characterized bysedimentation and the subsequent subsidence.The conversion of geosynclines into foldedmountains requires geologically long time withdefinite phases of mountain building process-

(b) Orogenesis: After horizontal compressionhas completed its task, vertical uplift starts.This is the real stage of mountain building.

(c) Glyptogenesis: In this phase thecharacteristic land forms are sculptured byerosion.

On the basis of age the Fold Mountains can begrouped into:

(i) New or Young fold Mountains: Example:The Alps, the Himalayas, the Circum-Pacificoceanic Mountains, etc. The main featuresof these mountains are the complex foldingof the rocks, faulting, volcanic activities, andthe erosion caused by running water, ice,winds, etc.

(ii) Old Fold Mountains: Example: TheCaledonian and Hercynian mountains of

central Europe, the Pennines, the Highlandof Scotland, etc. These mountains werefolded in very ancient times, and thensubjected to denudation and uplift. Manyfaults were formed and the layers of therock were wrapped. Many mountains existas relicts due to erosion.

II. Block Mountains: They are originated bytensile forces leading to formation of riftvalleys. They are also called horstmountains e.g. black forest, Vosges,Vindhya, Satpura, Sierra Nevada etc. Whenthe crust cracks due to tension orcompression faulting takes place. A sectionof the landform may subside or rise abovethe surrounding level giving rise to Riftvalley or Graben and Block Mountains orHorst. The Block Mountains have a steepslope towards the rift valley but the slopeon the other side is long and gentle.

III. Dome Mountains: They are originated bymagmatic intrusion and upwarping ofcrustal surface e.g. lava domes, Batholithdomes etc.

IV Mountain of Accumulation: They areoriginated by accumulation of volcanicmaterial e.g. cinder cones, composite conesetc. These are formed by the emission anddeposition of lava and so they are alsocalled volcanic mountains. The slope of themountains becomes steep and the heightincreases due to the development of thecones of various types like Cinder cones,Composite Cones, Acid lava cones, Basiclava cones, etc. Some of the examples ofthis type are Popocatepetl of Mexico, MountRainier of Washington, Lessen Peak ofCalifornia, the Vesuvius of Italy, theFujiyama in Japan, the Aconcagua in Chileetc.

V Circum Erosional or Relict Mountain: e.g.Vindhyachal ranges, Aravallis, Satpura,Eastern and Western Ghats, Nilgiris,Parasnath, Girnar, Rajmahal. These

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mountains have been subjected toweathering and erosion for a long time andlowered down. They represent the old stageof mountain life cycle.

B. Classification on the basis of MountainBuilding periods

Pre-Cambrian Mountains: Rocks ofthese mountains are older than the Cam-brian era, and are found in older stableblocks or old shields which are nowmetamorphosed. Some of those oldshields are Laurentia, Fennoscandinevia(Europe), Angaraland (Asia),Gondwanaland (Asia), etc.

Caledonian Mountains: (320 m.yrs.):Mountains of Scandinavia, Scotland, N.America, Aravallis, Mahadeo, Satpurafall under this category. This mountainbuilding process started at the end ofthe Silurian period or at the beginningof the Devonian period.

Hercynian Mountains: (240m.yrs.):These Mountains were formed duringPermian and Permo-Carboniferous pe-riod. They include Appalachian in N.America, Meseta in Spain, Vosges andBlack Forest in Germany, Harz, Donetzarea of Ural , Altai, Kinghan ,TienShan, Alai, Nan-Shan, etc. MesetaMountains in Morocco; the High AtlasMountains also represent this category.

Alpine Mountains (30m.yrs.): It startedby the end of the Mesozoic era and con-tinued upto the Tertiary period. Theseare the highest mountains of the world.Being newer, the erosional forces couldnot erode them into a Peneplain like theHimalayas, the Alps, the Rockies, theAndes, the Atlas, etc.

Stages of Mountains Building: The lifehistory of mountains can be divided into youth,maturity and old stage. Following are thecharacteristics of mountains in different stages:-

A. The Youth Mountains:

1. The rivers are youthful and the valleys aredeep and their flow is fast.

2. Landslide and volcanic activities arecommon.

3. The mountains are high.

4. The slopes are steep and the piedmont isbare.

5. The sky line is irregular.

B. The Maturity of Mountains:

1. The rivers are mature and many water-gaps exist in the area.

2. The height of the mountains is not much.

3. The peaks are rounded, generally coveredby thick vegetation.

4. Landslides are uncommon and noearthquakes are experienced.

5. Slopes are not steep. Pebbles and rockfragments are accumulated in the piedmontarea.

C. The Old-Age of Mountains:

1. The rivers have attained old age.

2. Monadnocks are found denuded and are acommon sight.

3. The mountains are low. Peneplaincondition seems imminent.

4. The area is broad, low and leveled whichhas wavy hills at some places.

Plateau

Plateaus are extensive upland areascharacterized by flat and rough top surface andsteep walls which rise above the neighbouringground surface at least for 300 m.

On the basis of mode of formation the plateauscan be classified into:

1. Plateaus Formed by Running Water: Manyparts of the Deccan of India (KaimurPlateau, Rewa Plateau, Rohtas Plateau,Bhander Plateau), Brazilian Plateau.

2. Plateaus formed by Glacial Erosion:Plateau of Greenland and Antarctica,Garhwal Plateau.

3. Plateaus formed by Glacial Deposition:Russian Plateau, Finland Plateau, Merg ofKashmir.

4. Aeolian plateaus: Loess Plateau of China,Potwar Plateau of Rawalpindi in Pakistan.

5. Plateaus formed by endogenic processes:(a) Intermontane Plateaus: Tibetan Plateau,

Bolivian Plateau, Peruvian Plateau,Columbian Plateau, Mexican Plateau.

(b) Piedmont Plateaus: Appalachian Pla-

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teau, Patagonian Plateau, Colorado Pla-teau.

(c) Dome Plateaus: Ozark Massif (USA),Chhotanagpur Plateau.

(d) Lava Plateaus: Columbian Plateau,Mahabaleshwar Plateau.

(e) Continental Plateau: Deccan plateau,Ranchi plateau, Shillong plateau, Colum-bia Plateau, Mexican Plateau etc. etc.

(f) Coastal Plateau: Coromandal coastalupland of India.

(g) Rejuvenated Plateau: Missouri Plateau(USA).

(h) Mature Plateau: Ranchi Plateau,Hazaribagh Plateau, Appalachian Pla-teau (USA).

(i)Young Plateau: Idaho Plateau (USA),Colorado Plateau (USA),Mahabaleshwar Plateau, Khandala up-land (Maharashtra).

Plains

Plains can be defined as flat areas with lowheight. They may be above or below sea levele.g. coastal plains of Netherlands.

The plains may be classified as under:

1. Formation of plain due to deposition ofsediments over submerged coastlands e.g.Coromandal coastal plains.

2. River deposited plains e.g. north Indianplains

3. Piedmont alluvial plain e.g. Bhabar plain

4. Flood plains e.g. Khadar and Bhangarplains

5. Lava plains e.g. plains of New Zealand,Iceland etc.

6. Glaciated plains e.g. north west Eurasianplain.

A. Erosional Plains

1. Plains of Fluvial Erosion: The plainsformed by river erosion have a lot ofvariation because of the stages oferosional development, the initial slope andthe structure of basal rocks.

(a) The Dissected Plains of the Youth: TheColorado, Kansas, Nebraska, east of theRockies belong to this category of plains.The broad water-divides, large valleys arethe main characteristics of s

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