UPPSC Target PT 90 days Planner

When few months are left for UPPSC Prelims 2021, it becomes very important for every aspirant to be on their toes and follow an organized plan which will help them clear this exam and keep them at ease during the preparation phase.

UPPSC Target PT in 90 Days Planner will provide you with a daily time table, which will comprise of the following:

  • Daily Value added Article
  • Daily subject specific Quiz according to the given schedule
  • Snippets (UP through MAP) for maximizing your Prelims score.

Day 26: Geography - Geography (Day 26 to 36)

Origin of Universe, Geomorphology

Theories on origin of the Universe

  • Nebular Hypothesis:(Initial arguments were given by German philosopher Immanuel Kant Mathematician Laplace revised it in 1796). The hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.
  • Planetesmial Hypothesis:In 1900, Chamberlain and Moulton considered that a wandering star approached the sun. Sir James Jeans and later Sir Harold Jefirey supported the argument.
  • At a later date, the arguments considered of a companion to the sun to have been coexisting. These arguments are called binary theories.
  • In 1950, Otto Schmidt in Russia and Carl Weizascar in Germany somewhat revised the ‘nebular hypothesis’.
  • Big Bang Theory/ Expanding Universe Hypothesis: It was given by Edwin Hubble. According to “Big Bang Theory” everything in the universe emerged from a point known as ‘Singularity’ 15 billion years ago. Later on, this point expanded and inside it galaxies move apart due to which empty space between them expanded. All matter in the universe was created at one instant in fixed moment of time. A single fire ball existed along with wispy clouds of matter. When it exploded, it formed cluster of galaxies which exploded to form stars and then stars exploded to form planets.

Solar System 

  • The solar system comprises the Sun and its eight planets which are believed to have been developed from the condensation of gases and other lesser bodies.
  • All the planets revolve round the Sun in elliptical orbits.
  • Alternatively, the first four are called Terrestrial, meaning earth-like as they are made up of rock and metals, and have relatively high densities. The rest four are called Jovian or Gas Giant planets. Jovian means Jupiter-like. Most of them are much larger than the terrestrial planets and have thick atmosphere, mostly of helium and hydrogen.
  • Till recently (August 2006), Pluto was also considered a planet. However, in a meeting of the International Astronomical Union, a decision was taken that Pluto like other celestial objects (2003 UB313) discovered in recent past may be called‘dwarf planet’.
  • The eight bodies officially categorized as planets are often further classified in several ways:

By composition:

  • Terrestrial or rocky planets: Mercury, Venus, Earth, and Mars.
  • The terrestrial planets are composed primarily of rock and metal and have relatively high densities, slow rotation, solid surfaces, no rings and few satellites.
  • Jovian or gas planets: Jupiter, Saturn, Uranus, and Neptune:
  • The gas planets are composed primarily of hydrogen and helium and generally have low densities, rapid rotation, deep atmospheres and lots of satellites.

By size:

  • Small planets:Mercury, Venus, Earth, Mars. (The small planets have diameters less than 13000 km.)
  • Giant planets:Jupiter, Saturn, Uranus and Neptune. (The giant planets have diameters greater than 48000 km. The giant planets are sometimes also referred to as gas giants.)

By position relative to the Sun:

  • Inner planets:Mercury, Venus, Earth and Mars.
  • Outer planets:Jupiter, Saturn, Uranus, Neptune. The asteroid belt between Mars and Jupiter forms the boundary between the inner solar system and the outer solar system.
  • Kuiper Belt: The Kuiper Belt (sometimes referred to as the Kuiper-Edgeworth Belt) is an area of the outer solar system that is estimated to stretch across 20 astronomical units (AU) of space.
  • It contains small solar system bodies made mostly of ices.
  • The ices are frozen volatiles (gases) such as methane, ammonia, nitrogen and water.
  • It also is home to the known dwarf planets Pluto, Haumea and Makemake.
  • The Kuiper-Edgeworth Belt is named for the astronomers Gerard Kuiper.
  • The Kuiper Belt extends from roughly the orbit of Neptune (at 30 AU out to about 55 astronomical units) from the Sun.
  • Oort cloud: The Oort cloud is an extended shell of icy objects that exist in the outermost reaches of the solar system.
  • It is named after astronomer Jan Oort, who first theorized its existence.
  • The Oort cloud is roughly spherical, and is thought to be the origin of most of the long-period comets that have been observed.
  • Objects in the Oort cloud are also referred to as Trans-Neptunian objects. This name also applies to objects in the Kuiper Belt.

THE EARTH

  • When the solar system settled into its current layout about 4.5 billion years ago, Earth formed when gravity pulled swirling gas and dust in to become the third planet from the Sun. Like its fellow terrestrial planets, Earth has a central core, a rocky mantle and a solid crust.
  • Earth is the third planet from the Sun and is the largest of the terrestrial planets.
  • The Earth is the only planet in our solar system not to be named after a Greek or Roman deity.
  • In size, it is the fifth largest planet. It is slightly flattened at the poles. That is why its shape is described as a
  • The Moon (or Luna) is the Earth’s only natural satellite. The Moon is in synchronous rotation with Earth meaning the same side is always facing the Earth.

Evidence of the Earth’s Sphericity

  1. Ship’s visibility: When a ship appears over the distant horizon, top of the mast is seen before the hull & vice a versa.
  2. Sunrise & Sunset: Sun rises & sets at different times in different places. As earth rotates from west to east, places in east see sun earlier than those in the west.
  3. Lunar eclipse: Shadow cast by earth on the moon during the lunar eclipse is always circular.
  4. Driving poles on level ground on curved earth: Engineers while driving poles of equal length at regular intervals on the ground have found that they do not give a perfect horizontal level. Centre pole normally projects slightly above the poles at either end because of curvature of the Earth. Hence they have to make certain corrections for this inevitable curvature i.e. 8” to a mile.
  5. Aerial Photographs: Pictures taken from high altitudes by rockets & satellites show clearly the curved edge of the earth. This is perhaps the most convincing & up to date proof of earth’s sphericity.

Latitudes and Longitudes

Latitudes

  • The Equator is an imaginary line around the middle of the Earth. It is halfway between the North and South Poles, and divides the Earth into the Northern and Southern Hemispheres.
  • The Earth is widest at its Equator. The distance around the Earth at the Equator, its circumference, is 40,075 kilometers (24,901 miles).
  • Orbital plane is the plane formed by the orbit. The axis of the Earth is an imaginary line that makes an angle of 66½° with its orbital plane.
  • Latitudes and Longitudes are imaginary lines used to determine the location of a place on earth. Parallels of Latitudes are the angular distance of a point on the earth’s surface, measured in degrees from the center of the Earth.
  • As the earth is slightly flattened at the poles, the linear distance of a degree of latitude at the pole is a little longer than that at the equator.
  • Besides the equator (0°), the north pole (90°N) and the south pole (90°S), there are four important parallels of latitudes–
    • Tropic of Cancer (23½° N) in the Northern Hemisphere.
    • Tropic of Capricorn (23½° S) in the Southern Hemisphere.
    • Arctic Circle at 66½° North of the Equator.
    • Antarctic Circle at 66½° South of the Equator.

Latitudinal Heat zones of the Earth

  • The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat and is called the Torrid Zone.
  • The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. As such, the areas bounded by the Tropic of Cancer and the Arctic circle in the northern hemisphere, and the Tropic of Capricorn and the Antarctic circle in the southern hemisphere, have moderate temperatures. These are, therefore, called Temperate Zone.
  • Areas lying between the Arctic circle and the north pole in the northern hemisphere and the Antarctic circle and the south pole in the southern hemisphere are very cold. It is because here the sun does not raise much above the horizon. Therefore, its rays are always slanting. These are, therefore, called Frigid Zone.

Longitudes

  • Longitude is the angle east or west of a reference meridian between the two geographical poles to another meridian that passes through an arbitrary point.
  • All meridians are halves of great circles, and are not parallel to each other.
  • They converge only at the north and south poles. A line passing to the rear of the Royal Observatory, Greenwich (near London in the UK) has been chosen as the international zero-longitude reference line and is known as the Prime Meridian.
  • Places to the East are in the Eastern Hemisphere, and places to the West are in the Western Hemisphere.
  • The antipodal meridian of Greenwich serves as both 180°W and 180°E. There are 360° of the meridians and the longitude of prime meridian is 0°.
  • Length of all meridians is equal. The distance between two meridians is farthest at the equator and it decreases as we move towards poles and becomes zero at poles.
  • They determine local time in relation to G.M.T. or Greenwich Mean Time, which is sometimes referred to as World Time.

Longitude and Time

  • Since the earth makes one complete revolution of 360° in one day or 24 hours, it passes through 15° in one hour or 1° in 4 minutes.
  • The earth rotates from west to east, so every 15° we go eastwards, local time is advanced by 1 hour. Conversely, if we go westwards, local time is retarded by 1 hour.

International Date Line (IDL)

  • The International Date Line (IDL) is an imaginary line on earth’s surface defining the boundary between one day and the next.
  • The International Date Line is located halfway around the world from the prime meridian (0° longitude) or about 180° east (or west) of Greenwich, London, UK, the reference point of time zones. It is also known as the line of demarcation.
  • A traveler going eastwards gains time from Greenwich until he reaches the meridian 180°E, when he will be 12 hours ahead of G.M.T.
  • Similarly in going westwards, he loses 12 hours when he reaches 180°W. There is thus a total difference of 24 hours or a whole day between the two sides of the 180° meridian.

Circle of Illumination

  • The circle of illumination is the circle that divides the day from night on the globe.
  • Earth goes around the sun in an elliptical orbit. Note that throughout its orbit, the earth is inclined in the same direction.

Interior of the Earth

To understand the various endogenetic activities and their effects on the exogenetic land forms, it becomes very important to know about the interior of the Earth. The information regarding the earth’s interior can be known through various sources. Some of them are discussed below:

Direct Sources

  • The most easily available solid earth material is surface rock or the rocks we get from mining areas.
  • Volcanic eruption forms another source of direct information. As and when the molten material (magma) is thrown onto the surface of the earth, it becomes available for laboratory analysis. However, it is di?cult to ascertain the depth of the source of such magma.

Indirect Sources

  • Analysis of properties of matter provides indirect information about the interior of the Earth.
  • Another source of information is the meteors that at times reach the earth.
  • The other indirect sources include:
    • The gravitation force(g) is not the same at different latitudes on the surface. It is greater near the poles and less at the equator. This is because of the distance from the center at the equator being greater than that at the poles. The gravity values also diaer according to the mass of material. The uneven distribution of mass of material within the earth influences this value. The reading of the gravity at different places is influenced by many others factors.
    • Seismic Activity:Some of the indirect evidences of seismic activity are:
    • Study of ancient rocks and parts of interior now exposed to surface due to erosive activity.
    • Study of lava erupted from volcanism from the interiors of the earth.

Seismological Evidences

The most authenticate source of knowledge about earth’s interior is through detailed study of earthquake waves. The seismic waves can be classified into two categories:

1. Surface waves: These waves travel through the surface of the earth. Due to their amplitude, they are most destructive waves causing extensive damage on the surface of the earth.

    • Types of Surface Waves:
    • Love waves (L-waves)- its fastest surface waves and move on ground side to side. It is confined to surface of the crust love wave is wounded by Seismograph.
    • Rayleigh waves-Rayleigh waves rolls along the ground just like a wave roll across a lake or an ocean.

2. Body waves: These waves travel through the interiors of the earth. While travelling through interiors, their characteristics such as velocity and wavelength changes according to the density of the medium in which they are travelling. The body waves are recorded at different seismograph stations located at different places throughout the surface of earth. Body waves can be further categorized into

    • Primary Waves:Also known as P-waves. These are longitudinal or compressive in nature. These waves can pass through solid as well as liquid medium. The velocity of these waves increases with increasing density and rigidity of the medium. (They travel faster in solid than in liquids)
    • Secondary waves:Also known as S-waves. These are transverse or distortional in nature. These waves cannot pass through liquid medium. Their velocity also increases with increasing rigidity of the medium.
  • Nature of Body Waves:
    • These waves (both P and S waves) travel faster in rigid medium.
    • Among P and S waves the velocity of P waves is more.
    • These waves while passing from one medium to another medium of different density experiences refraction (bending from original path) similar to the light waves.
  • Observations from the study of body waves:
    • The velocity of body waves initially increases continuously denoting the increasing density of material with increasing depth in the part of outer layer of earth known as core.
    • After around 100 km of depth, the velocity of both the waves shows a drastic decrease which denotes the less rigidity of the layer. This layer was named as asthenosphere and is made of plastic material.
    • The body waves velocity increases, again denoting the increasing density with depth in mantle.
    • After certain depth, the S-waves disappear and again re-emerge at surface of earth at an angle of 105°.The area where S-waves are not received is known as S-waves shadow region and lies between 105° on both sides. This concludes the presence of a liquid layer which forms outer core.
    • The P-waves continue its journey and its velocity increases drastically representing very dense material in inner core. Due to high degree of refraction the P-waves are not recorded between 140° and 105°, and hence the region is known as P-waves shadow region.
    • The velocity and wavelength of waves in different regions give a concrete evidence of composition of different layers of interior of earth.

Earth’s Interior

Based on all the evidences from Seismic data and their analysis, the earth’s interior has been divided into three layers.

Crust

  • This is the outermost layer of the earth. Its depth varies from 16 km – 40 km.
  • It is thicker at continents (30 - 40 km) and its thickness underneath the ocean basin varies from 5-10 kms.
  • At continental crust, the uppermost part is mainly sedimentary rocks followed by granite and gneisses rocks which overlie the basaltic rocks. The oceanic crust however is devoid of sedimentary or granitic cover and mainly consists of basaltic rocks.
  • Thus, continental and oceanic crusts di?er in nature where continental crust is mainly granitic while oceanic crust is mainly basaltic in composition.

Mantle

  • This is the intermediate layer below crust. It extends upto 2900 km depth.
  • It is composed of dense and rigid rocks having predominance of minerals like magnesium and iron. These rocks are similar to peridotite.

Core

  • It is the innermost layer of earth. It is divided into outer core and inner core.
  • Outer Core: It extends from 2900 km to 5100 km depth from sea level. This is primarily made of iron with a small proportion of nickel, which is in liquid condition. At this depth, the S-waves suddenly disappear. Also, the velocity of P-waves abruptly decreases. Despite such a high pressure, outer core is in liquid form because of the presence of silicon which decreases the melting point of iron
  • Inner Core: It lies beyond 5100 km depth. The average density increases to 13. This is mainly composed of pure iron and nickel in solid state. The outer liquid core moving around solid inner core of iron acts as a giant self-exciting dynamo which is responsible for magnetic field of earth.

Discontinuities within the Earth’s Interior

Conrad discontinuity: The Conrad discontinuity corresponds to the sub-horizontal boundary in continental crust at which the seismic wave velocity increases in a discontinuous way. This boundary is observed in various continental regions at a depth of 15 to 20 km, between outer and inner crust however it is not found in oceanic regions.

Mohorovicic discontinuity: The Mohorovicic Discontinuity, or “Moho,” is the boundary between the crust and the mantle.

Repetti discontinuity: This discontinuity is found between upper and lower Mantle. This is marked by general decrease in velocity of seismic waves between upper and lower mantle.

Gutenberg discontinuity: The Gutenberg discontinuity occurs within Earth’s interior at a depth of about 1,800 mi (2,900 km) below the surface, generally between mantle and core ,where there is an abrupt change in the seismic waves (generated by earthquakes or explosions) that travel through Earth.

Lehmann discontinuity: The Lehmann discontinuity is an abrupt increase of P-wave and S-wave velocities at the depth of 220±30 km, discovered by seismologist Inge Lehmann. It appears beneath continents, but not usually beneath oceans, and does not readily appear in globally averaged studies. It is generally found between outer and inner core.

Evolution of Oceans and Continents

The Theory of Continental drift

German meteorologist Alfred Wegener observed similarities among the continents that suggested the landmasses might have once been connected.

Coastal fit: The “jig-saw” fit of opposing coasts of continents across Atlantic Ocean. The eastern coast of South America fits into western coast of Africa. Similar case is with eastern coast of North America fitting into western coast of Europe.

Fossil evidences: There is a similarity in the fossils found in distant lands across oceans and sometimes at places where it should not be. Glaciation evidences found in landmasses such as Brazil, South Africa and peninsular India indicates that once these landmasses were in polar or subpolar region which is consistent with Wegner’s hypothesis of Pangea located somewhere near South pole.

Geological evidences: The rocks and minerals found in distant lands were found to be having similarity in their structure and age. The coal deposits found in Alps region were similar to those found in North America.

Later, other evidences also came out which supported Wegner’s Continental Drift Theory. Those evidences are:

Paleomagnetism: These form the most reliable proof of the continental drift. The rocks found at any place preserve the magnetic properties like magnetic declination, inclination and polarity of that place during their time of cooling and rock formation. The socks of similar paleomagnatic evidence found at different location.

These observations led Alfred Wegner to formulate his “Theory of Continental Drift”, through which he tried to explain these anomalies.

Hypothesis

  • All the continents were once combined as a single landmass called Pangea, which means “all lands” in Greek, during Carboniferous period.
  • Pangea was surrounded by a vast water body which he called Panthalassa.
  • Pangaea broke into two landmasses namely northern part which became Lauratia and the southern part namely Gondwanaland. A water body developed between these two landmasses known as Tethys Sea. The two landmasses drifted northward and westward.
  • The northward movement was due to the gravitational attraction force exerted by the earth’s equatorial bulge. Wegner called this “pole fleeing”. The westward movement of landmasses was attributed to the tidal force exerted by moon and the sun.
  • During the drifting of both the landmasses, they again broke due to differential dragging force into different continents.

Criticism of Wegner’s Continental Drift Theory

  • The driving force that Wegner suggested for the drift of landmasses was questioned. It has been argued that the tidal force of Moon and Sun cannot be of the magnitude to move such huge landmasses. If it were of so large magnitude then the rotation of earth would have been stopped due to effect of these forces.
  • The assumption of Wegner that Sial floated over Sima and the formation of fold mountains which according to him were due to scrapping of ofSima and their folding was contradicted on the basis that it was not possible for a lighter Sial to scrap Sima and if any scrapping had been there, it would be of Sial not Sima.
  • Another assumption of Wegner based on Suess theory that ocean floors are exposed part of Sima ( or mantle) does not hold ground now, as it is now evidently proved that they are part of crust only, not the exposed part of mantle.
  • The fossil evidence given by Wegner was countered by another “Theory of Parallel evolution”, according to which it was possible for particular specie to evolve at two different places at the same period of time.

Sea - Floor Spreading

  • According to Harry Hess, the hot magma rises from mantle to the surface by convection currents at the site of Mid Oceanic Ridges (MOR) and then diverges along two limbs on either side of MOR. This diverging limb drags the crust lying above it, causing them to diverge too. The diverging limb descends inside the crust at the boundary of continental crust dragging again the oceanic crust causing ocean crust to melt and destroyed at the site of trenches.
  • Since a new crust is formed at the site of MORs, it is considered as constructive zone while at trenches, the oceanic crust is destroyed and hence the site is a destructive zone. This means that oceanic crust is continuously being destroyed and new crust being formed. This explains why rocks of continental crust are much older than those found at oceanic crust although oceanic crust was the basis of all. In other way, “Oceanic crust is destructible while continents are forever”.

Plate Tectonics Theory

By combining the sea floor spreading theory with continental drift and information on global seismicity, the new theory of Plate Tectonics became a coherent theory to explain crustal movements. According to the theory, plates are composed of lithosphere, about 100 km thick that “float” on the ductile asthenosphere. As of now there are six major plates and six minor plate’s identified.

Major Plates

  • Indian plate or Indo-Australian plate
  • Pacific plate
  • American plate (divided into North American plate and South American plate)
  • African plate
  • Eurasian plate
  • Antarctica plate

While the continents do indeed appear to drift, they do so only because they are part of larger plates that float and move horizontally on the upper mantle asthenosphere. The plates behave as rigid bodies with some ability to flex, but deformation occurs mainly along the boundaries between plates. The plate boundaries can be identified because they are zones along which earthquakes occur. Plate interiors have much fewer earthquakes.

Plate Boundaries

There are three types of plate boundaries:

Divergent Plate boundaries

  • These are areas where plates move away from each other, forming either mid-oceanic ridges or rift valleys. These are also known as constructive boundaries.
  • Regions of Divergent Boundaries
    • East African Rift (Great Rift Valley) in eastern Africa
    • Mid-Atlantic Ridge system separates the North American Plate and South American Plate in the west from the Eurasian Plate and African Plate in the east
    • Gakkel Ridge is a slow spreading ridge located in the Arctic Ocean
    • East Pacific Rise, extending from the South Pacific to the Gulf of California
    • Baikal Rift Zone in eastern Russia
    • Red Sea Rift
    • Aden Ridge along the southern shore of the Arabian Peninsula
    • Carlsberg Ridge in the eastern Indian Ocean
    • Gorda Ridge of the northwest coast of North America
    • Explorer Ridge of the northwest coast of North America
    • Juan de Fuca Ridge of the northwest coast of North America
    • Chile Rise of the southeast Pacific

Convergent Plate Boundaries

  • Convergent boundaries are areas where plates move toward each other and collide. These are also known as compressional or destructive boundaries.
  • Subduction zones occur where an oceanic plate meets a continental plate and is pushed underneath it. Subduction zones are marked by oceanic trenches. The descending end of the oceanic plate melts and creates pressure in the mantle, causing volcanoes to form.
  • Obduction occurs when the continental plate is pushed under the oceanic plate, but this is unusual as the relative densities of the tectonic plate’s favours subduction of the oceanic plate. This causes the oceanic plate to buckle and usually results in a new mid ocean ridge forming and turning the obduction into subduction.
  • Orogenic belts occur where two continental plates collide and push upwards to form large mountain ranges. These are also known as collision boundaries
  • Regions of Convergent Boundaries-Few of the regions are mentioned below:
  • The oceanic Nazca Plate subducts beneath the continental South American Plate at the Peru–Chile Trench.
  • Just north of the Nazca Plate, the oceanic Cocos Plate subducts under the Caribbean Plate and forms the Middle America Trench.
  • Cascadia subduction zone is where the oceanic Juan de Fuca, Gorda and Explorer Plates subduct under the continental North American plate.
  • Oceanic Pacific Plate subducts under the North American Plate (composed of both continental and oceanic sections) forming the Aleutian Trench.

Transform Plate Boundaries

Occur when two plates grind past each other with only limited convergent or divergent activity.

  • Regions of Transform Boundaries
    • The San Andreas Fault in California is an active transform boundary. The Pacific Plate (carrying the city of Los Angeles) is moving northwards with respect to the North American Plate.
    • The Queen Charlotte Fault on the Pacific Northwest coast of North America.
    • The Motagua Fault, which crosses through Guatemala, is a transform boundary between the southern edge of the North American Plate and the northern edge of the Caribbean Plate.
    • New Zealand’s Alpine Fault is another active transform boundary.
    • The Dead Sea Transform (DST) fault which runs through the Jordan River Valley in the Middle East.
    • The Owen Fracture Zone along the southeastern boundary of the Arabian Plate

Orogeny

  • A portion of land rising considerably above the surrounding country either as a single eminence (Kilimanjaro) or in range (Himalayas, Rockies, Andes), is known as ‘mountain’.
  • Orogeny (Orogenesis): A period of mountain building involving the process of intense upward displacement of the earth’s crust, usually associated with folding, thrust faulting and other compressional processes.

Fold Mountains

  • Fold Mountains are formed at convergent boundaries at the meeting point of two tectonic plates.
  • Fold Mountains are formed as a result of the compression of tectonic plates, which leads to the formation of large fold-like structures on the earth’s crust.
  • Fold Mountains primarily exist as mountain ranges, and the majority of the earth’s well-known mountain ranges are examples of Fold Mountains.

Characteristics of Fold Mountains

  • Fold Mountains belong to the group of youngest mountains of the earth.
  • The presence of fossils suggests that the sedimentary rocks of these folded mountains were formed after accumulation and consolidation of silts and sediments in a marine environment.
  • Fold Mountains extend for great lengths whereas their width is considerably small.
  • Generally, Fold Mountains have a concave slope on one side and a convex slope on the other.
  • Fold Mountains are found along continental margins facing oceans.
  • Fold Mountains are characterized by granite intrusions on a massive scale.
  • Recurrent seismicity is a common feature in folded mountain belts.
  • High heat flow often finds expression in volcanic activity.
  • These mountains are by far the most widespread and also the most important.
  • They also contain rich mineral resources such as tin, copper, gold.

Types of Folds

According to the shape, the folds are of many types:

Symmetrical Folds: These are ordinary folds. The limbs of the folds are equally inclined on either side.

Asymmetrical Fold: One of the limbs is more inclined than the other.

Monoclinal Fold: In this fold, one limb makes a right angle with the surface but the other limb is ordinarily inclined.

Isoclinal Fold: The two limbs are so much inclined in such a way that they appear equally inclined and parallel to each other.

Recumbent Fold: In this fold the two limbs are so much inclined that they become horizontal.

Overturned Fold: In this fold one limb is overturned over the other limb. The difference between the overturned and recumbent folds is that the overturned limbs are not horizontal like those of recumbent fold.

Plunging Fold: If the axis of the fold is not parallel to the horizontal but makes an angle with it, it is known as Plunging Fold.

Fan Fold: It is a great anticline which has many small anticlines and synclines. It is also known as Anticlinorium. A great syncline having many small anticlines and synclines is called Synclinorium.

Open Fold: If the angle between the limbs of a fold is obtuse, the fold is called Open Fold.

Closed Fold: If the angle between the limbs of a fold is acute, it is called Closed Fold.      

Block Mountains

  • Block Mountains are formed when two tectonic plates move away from each other causing cracks on the surface of the Earth. When parallel cracks or faults occur, the strip of land or the block of land between them may be raised resulting in the formation of Block Mountains. The upward block is called a horst. Examples, Black forest and the Vosges of Rhineland.
  • Block Mountains are also formed when the crust of the Earth sinks on both sides of two parallel faults. Therefore, a block mountain can be found between two rift valleys. The land which sinks is known as graben. Examples, East African rift valleys.

Residual Mountains

  • These are mountains evolved by denudation.
  • Where the general level of the land has been lowered by the agents of denudation some very resistant areas may remain and these form residual mountains, e.g. Mt. Manodnock in U.S.A.
  • Residual Mountains may also evolve from plateaus which have been dissected by rivers into hills and valleys. Examples of dissected plateaux, where the down-cutting streams have eroded the uplands into mountains of denudation, are the Highlands of Scotland, Scandinavia and the Deccan Plateau.

Volcanism

  • A volcano is an opening in the earth’s crust through which gases, molten rocks materials (lava), ash, steam etc. are emitted outward in the course of an eruption.
  • Such vents or openings occur in those parts of the earth’s crust where the rock strata are relatively weak.
  • Volcanic activity is an example of endogenic process. Depending upon the explosive nature of the volcano, different land forms can be formed such as a plateau (if the volcano is not explosive) or a mountain (if the volcano is explosive in nature).

Types of Lava

  • Basic lavas: There are highly fluid. They are dark coloured like basalt, rich in iron and magnesium but poor in silica. They are affect extensive areas, spreading out as thin sheets. The resultant volcano is gently sloping with a wide diameter and form a fattened shield or dome.
  • Acidic lavas: There lavas are highly viscous with a melting point. They are light-coloured, of low density, and have a high percentage of silica. They flow slowly and seldom travel far. The resultant cone is therefore steep sided.

Types of Volcanoes

Classification of Volcanoes according to shape

Cinder cones-are circular or oval cones made up of small fragments of lava from a single vent that has been blown up.

  • Cinder cones result from eruptions of mostly small pieces of scoria and pyroclastic that builds up around the vent. Most cinder cones erupt only once.
  • Cinder cones may form as flank vents on larger volcanoes, or occur on their own.

Composite Volcanoes: These are steep-sided volcanoes composed of many layers of volcanic rocks, usually made from high-viscosity lava, ash and rock debris.

  • These types of volcanoes are tall conical mountains composed of lava flows and other ejected in alternate layers, the strata that give rise to the name.
  • Composite volcanoes are made of cinders, ash, and lava. Cinders and ash pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the process repeats.

Shield volcanoes are volcanoes shaped like a bowl or shield in the middle with long gentle slopes made by basaltic lava flows.

  • These are formed by the eruption of low-viscosity lava that can flow a great distance from a vent.
  • They generally do not explode catastrophically.
  • Since low-viscosity magma is typically low in silica, shield volcanoes are more common in oceanic than continental settings.
  • The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland, as well.

Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as the lava piles up near the volcanic vent.

  • They are built by slow eruptions of highly viscous lava.
  • They are sometimes formed within the crater of a previous volcanic eruption.
  • Like composite volcano, they can produce violent, explosive eruptions, but their lava generally does not flow far from the originating vent.

According to flow of magma and its place of cooling

  • Extrusive volcanism:Magma is expelled onto surface.
  • Intrusive Volcanism:Magma solidifies in the shallow crust near the surface. It can be exposed after weathering.
  • Plutonic Volcanism:Magma solidifies deep inside the earth’s crust

Classification of Volcanoes on the basis of Periodicity

  • Active Volcanoes:When volcanic materials like lava, gases, ash, cinder, pumice etc. are ejected constantly from the vent. Most of the active volcanoes are found in the Circum-Pacific Belt which is known as the ‘Ring of Fire’. A few examples of active volcanoes are: Etna and Visuvius, Mount Pelee (Martinique), Mount Karmai (Alaska), Mount Saint Helens, Nevado Del Ru’z (Columbia), Mount Unzen (Japan), Mount Pinatubo (Philippines), Mount Redoubt (Alaska) and Mount Mayon (Philippines). The Stromboli volcano emits so much fire and incandescent gases that it is known as ‘the Light House of the Mediterranean Sea’.
  • Dormant Volcanoes:Those that have been known to erupt and show signs of possible eruption in the future. These are not extinct. For example: The Vesuvius erupted in 79 AD, 1631, 1803, 1872, 1906, 1927, 1928 and 1929. Violent eruptions of dormant volcanoes are generally preceded and accompanied by earthquakes, some of which have been very destructive. Example Mt. Kilimanjaro.
  • Extinct Volcanoes:A volcano that was active in the geological past and no longer has any active vulcanicity. The Crater is filled with water. For example: St. Arthur’s Sea (Edinburgh) and the numerous Crater Lakes in the Andes and Rockies Mountains. Some of the volcanoes that are today dormant may become active. For example: Monte Somma which erupted 700 years back are now considered extinct by the inhabitants.

World distribution of Volcanoes

The Circum Pacific Belt

  • Due to subduction of the Pacific plate below the Asiatic plate, the large number of volcanic eruptions are found circling Pacific Ocean known as Ring of Fire, which extends through the Andes of South America, Central America, Mexico, the Cascade Mountains of Western United States, the Aleutian Islands, Kamchatka, the Kuril Isles, Japan, the Philippines, Celebes, New Guinea, the Solomon Islands, New Caledonia and New Zealand where about 80 active volcanoes are found.
  • The Circum-Pacific belt meets the mid- continental belt in the East Indies. This belt is characterised by high volcanic cones and volcanic mountains.
  • The volcanoes of the Aleutian Island, Hawaii Island and Japan are found in Chains.
  • Cotapaxi is the highest volcanic mountain (6035m) in the world.
  • Other important volcanoes found in this belt are Fuziyama, Shasta, Rainer and Hood.
  • Volcanic eruptions occur in this belt because of the subduction of the Pacific plate below the Asiatic plate.

The Mid-Continental Belt

  • Having various volcanoes of the Alpine Mountain Chain, Mediterranean Sea (Stromboli, Vesuvius, Etna etc.), volcanoes of the Aegean Sea, Mt. Ararat, Elburz and Hindukush. There are several volcanic free zones found along the Alps and the Himalayas, come under this belt. Kilimanjaro, Elgon, Birunga and Rungwe etc. are the volcanoes found in the Rift Valleys of Africa.
  • In the region where the boundaries of Persia, Afghanistan, and Baluchistan meet, there are several volcanic cones of large size, and one or two of them emit steam and other gases. This region has also a few extinct volcanoes.

The Mid Atlantic Belt

  • It includes the volcanoes of the Mid-Atlantic Ridge which are associated with the Atlantic Ocean and are located either on swells or ridges rising from the sea floor or on or near the edge of the continent where it slopes abruptly into the deep oceanic basins.
  • The volcanoes formed along the Mid-Atlantic Ridge actually represent the splitting zone of the American plate moving towards west and the Eurasian plate moving towards east representing the zones of crystal movement.
  • In the splitting zone there is constant upwelling of Magma hence known as crustal weakness.
  • Volcanoes in this belt are generally of fissure-eruption type such as Volcanoes of Lesser Antilles, Azores, and St. Helens etc.

Earthquakes

  • An earthquake is the shaking or trembling of the earth’s surface, caused by the sudden movement of a part of the earth’s crust.
  • They result from the sudden release of energy in the Earth’s crust that creates seismic waves or earthquake waves.

Causes of Earthquakes

  • Volcanic Eruptions:Volcanic eruptions are the main cause of earthquake caused by gas explosions or the upcoming and fissuring of volcanic structures. For example: Karakota (1883), Cotopaxi, Chimborazo, Kilimanjaro, Fujiyama etc.
  • Faulting (Displacement of Rocks):Earthquakes occur when movement of earth takes place along a line of fracture (FAULT). Examples: San Andres Fault of California (Los Angeles) and earthquakes of 1994 at Northridge, California.
  • Plate Tectonics:The 6 major and 9 minor plates of the earth crust are constantly moving at different rates. The boundaries of these plates are the primary location of earthquakes, example: the Ring of Fire. Shallow focus earthquakes occur on the Oceanic Ridges and in the Oceanic Trenches, deep focus earthquakes occur.
  • Anthropogenic Factors (Human’s over Integration with Nature):Extraction of minerals and the dams built on time to time disturbing the earth’s balance – Marathon Dam (Greece) – 1929, Koyna (Maharashtra 1962), Hoover Dam (1935), Mangla Dam (Pakistan), Kariba Dam (Zambia), Manic Dam (Canada), Kurobe Dam (Japan).

Measuring Earthquakes

  • Seismometers are the instruments which are used to measure the motion of the ground, which including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources.
  • A Seismograph is also another term used to mean seismometer though it is more applicable to the older instruments.
  • The recorded graphical output from a seismometer/seismograph is called as a seismogram. (Note: Do not confuse seismograph with seismogram. Seismograph is an instrument while seismogram is the recorded output)
  • There are two main scales used in the seismometers:

Mercalli Scale

The scale represents the intensity of earthquake by analyzing the after effects like how many people felt it, how much destruction occurred etc. The range of intensity is from 1-12.

Richter Scale

The scale represents the magnitude of the earthquake. The magnitude is expressed in absolute numbers from 1-10. Each whole number increase in Richter scale represents a ten times increase in power of an earthquake.

Earthquake Zones in the World

Circum-Pacific Zone: This zone is mainly distributed along the subsidence zone along trenches, where oceanic plate subducts under continental plate. Enormous amount of energy is released in earthquakes which occur in this zone. The depth of focus may vary greatly in accordance with Benioff zones which can result in focus as deep as 300 to 700 km below sea level.

The Mediterranean and Trans-Asiatic zone: This zone runs along the fold mountain chains from Alpine system of Europe through Asia, Iran and Himalayan mountain system. These earthquakes owe their origin to collision of continental plates and resulting buckling of plates. These earthquakes have generally shallow to intermediate focus.

The Mid-Oceanic Ridges and the African Rift System: This runs along the mid-oceanic ridges through the oceans. These have generally shallow focus.

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