DFA Geography Book PDF

GEOGRAPHY BOOK CONTENT 1. UNIVERSE pg 4 2. ROCKS AND MINERALS pg 11 3. CONCEPTS OF GEOMORPHOLOGY pg 23 4. LANDFORMS AND ITS EVOLUTION pg 34 5. CLIMATOLOGY pg 44 6. ATMOSPHERIC CIRCULATION & WEATHER SYSTEMS pg 54 7. OCEANOGRAPHY pg 63 8. PHYSIOGRAPHY OF INDIA pg 74 9. DRAINAGE SYSTEM OF INDIA pg 79 10. CLIMATE OF INDIA pg 88 11. MAPS OF INDIA AND WORLD pg 102 12. AGRICULTURE pg 115 13. MINERAL RESOURCES pg 141 14. TRANSPORT pg 161 15. MIGRATION pg 174 3 TARGET PT 2020 5 DAY - 16 1 UNIVERSE 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 Jeffrey 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 4 6 TARGET PT 2020 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. Korolev Crater About: European Space Agency’s (ESA) Mars Express mission has discovered an icy crater on Mars which has been named as Korolev Crater. 5 TARGET PT 2020 7 Korolev Crater has been located by Mars Express Mission near the north pole of the Red Planet It is filled with a mound of water ice 60 kilometers across and nearly 2 kilometers thick. The water ice is a permanent feature. It has been anticipated that the crater traps a layer of cold air that prevents the ice melting even during the six-month-long northern summer on Mars, making this a yearlong winter wonderland. Significance: Water on Mars has long been debated as the sign of existence of life on Mars, further existence of this huge reservoir of water will give thrust to it. To date, no proof has been found of past or present life on Mars but Cumulative evidence shows that during the ancient Noachian time period, the surface environment of Mars had liquid water and may have been habitable for microorganisms. Although, the existence of habitable conditions does not necessarily indicate the presence of life. THE EARTH 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 Geoid. 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 Ship’s visibility: When a ship appears over the distant horizon, top of the mast is seen before the hull & vice a versa. 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. Lunar eclipse:Shadow cast by earth on the moon during the lunar eclipse is always circular. 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. 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 6 8 TARGET PT 2020 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 hemisphereare 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 timefrom Greenwich until he reaches the meridian 180°E, when he will be 12 hours ahead of G.M.T. 7 TARGET PT 2020 9 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 landforms, 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 diﬃcult 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 differ 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: 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. Rayleigh waves- Rayleigh waves rolls along the ground just like a wave roll across a lake or an ocean. 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 8 10 TARGET PT 2020 ! 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 differ 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 denseand 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. 9 TARGET PT 2020 11 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. ********** 10 12 TARGET PT 2020 DAY - 17 2 ROCKS AND MINERALS Rocks The Earth’s crust is composed of rocks. A rock is an aggregate of one or more minerals. Rock may be hard or soft and in varied colors. For example, granite is hard, soapstone is soft. Gabbro is black and quartzite can be milky white. Rocks do not have deflnite composition of mineral constituents. Feldspar and quartz are the most common minerals found in rocks. Petrology is science of rocks. A petrologist studies rocks in all their aspects viz., mineral composition, texture, structure, origin, occurrence, alteration and relationship with other rocks. Type of Rocks There are many different kinds of rocks which are grouped under three families on the basis of their mode of formation. They are: ! Igneous Rocks — solidifled from magma and lava; ! Sedimentary Rocks — the result of deposition of fragments of rocks by exogenous processes; ! Metamorphic Rocks — formed out of existing rocks undergoing recrystallization. Igneous Rocks As igneous rocks form out of magma and lava from the interior of the earth, they are known as primary rocks. The igneous rocks (Ignis – in Latin means ‘Fire’) are formed when magma cools and solidifles when magma in its upward movement cools and turns into solid form it is called igneous rock. The process of cooling and solidiflcation can happen in the earth’s crust or on the surface of the earth. Igneous rocks are classifled based on texture. Texture depends upon size and arrangement of grains or other physical conditions of the materials. If molten material is cooled slowly at great depths, mineral grains may be very large. Sudden cooling (at the surface) results in small and smooth grains. Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks. Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks. Types of Igneous Rocks: Based on place and time taken in cooling of the molten matter, igneous rocks can be divided into Plutonic and Volcanic rocks. 11 TARGET PT 2020 13 Plutonic Rocks or intrusive rocks: Sometimes, the molten matter is not able to reach the surface and instead cools down very slowly at great depths. Slow cooling allows big-sized crystals (large grains) to be formed. Granite is a typical example. These rocks appear on the surface only after being uplifted and denuded. Lava or Volcanic Rocks or Extrusive rocks: These are formed by rapid cooling of the lava thrown out during volcanic eruptions. Rapid cooling prevents crystallization; as a result such rocks are fl ne-grained. Basalt is a typical example. The Deccan traps in the peninsular region are of basaltic origin. Basic rocks contain a greater proportion of basic oxides, e.g. of iron, aluminum or magnesium, and are thus denser and darker in color. Based on the presence of acid forming radical, silicon, igneous rocks are divided into Acid Rocks and Basic Rocks. Acid Rocks: These are characterized by high content of silica—up to 80 per cent, while the rest is divided among aluminum, alkalis, magnesium, iron oxide, lime etc. These rocks constitute theSial portion of the crust. Due to the excess of silicon, acidic magma cools fast and it does not flow and spread far away. High mountains are formed of this type of rock. These rocks have a lesser content of heavier minerals like iron and magnesium and normally contain quartz and feldspar. Add rocks are hard, compact, massive and resistant to weathering. Basic Rocks: These rocks are poor in silica (about 40 per cent); magnesia content is up to 40 per cent and the remaining 40 per cent is spread over iron oxide, lime, aluminum, alkalis, potassium etc. Due to low silica content, the parent material of such rocks cools slowly and thus, flows and spreads far away. This flow and cooling gives rise to plateaus. Presence of heavy elements imparts to these rocks a dark color. Basalt is a typical example, others being gabbro and dolerite. Not being very hard, these rocks are weathered relatively easily. Sedimentary Rocks The word ‘sedimentary’ is derived from the Latin word sedimentum, which means settling. Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents, and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called lithiflcation. In many sedimentary rocks, the layers of deposits retain their characteristics even after lithiflcation. Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale etc. Depending upon the mode of formation, sedimentary rocks are classifled into three major groups: ! Mechanically formed— sandstone, conglomerate, limestone, shale, loess etc. are examples; ! Organically formed— geyserite, chalk, limestone, coal etc. are some examples; ! Chemically formed— chert, limestone, halite, potash etc. are some examples. 12 14 TARGET PT 2020 Metamorphic Rocks The word metamorphic means ‘change of form’. These rocks form under the action of pressure, volume and temperature (PVT) changes. Metamorphism occurs when rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks or the underlying rocks are subjected to great amounts of pressure by overlying rocks. Metamorphism is a process by which already consolidated rocks undergo recrystallization and reorganization of materials within original rocks. Mechanical disruption and reorganization of the original minerals within rocks due to breaking and crushing without any appreciable chemical changes is called dynamic metamorphism. The materials of rocks chemically alter and recrystallize due to thermal metamorphism. There are two types of thermal metamorphism — contact metamorphism and regional metamorphism. In contact metamorphism the rocks come in contact with hot intruding magma and lava and the rock materialsrecrystallize under high temperatures. Quite often new materials form out of magma or lava are added to the rocks. In regional metamorphism, rocks undergo recrystallization due to deformation caused by tectonic shearing together with high temperature or pressure or both. In the process of metamorphism in some rocks grains or minerals get arranged in layers or lines. Such an arrangement of minerals or grains in metamorphic rocks is called foliation or lineation. Sometimes minerals or materials of different groups are arranged into alternating thin to thick layers appearing in light and dark shades. Such a structure in metamorphic rocks is called banding and rocks displaying banding are called banded rocks. Types of metamorphic rocks depend upon original rocks that were subjected to metamorphism. Metamorphic rocks are classifled into two major groups — foliated rocks and non-foliated rocks. Gneissoid, granite, syenite, slate, schist, marble, quartzite etc. are some examples of metamorphic rocks. Types of Metamorphic Rocks: Gneissis foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals. Quartziteis a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz. Schist is metamorphic rock with well-developed foliation. It often contains signiflcant amounts of mica which allow the rock to split into thin pieces. Marbleis a non-foliated metamorphic rock that is produced from the metamorphism of limestone. It is composed primarily of calcium carbonate. Slateis a foliated metamorphic rock that is formed through the metamorphism of shale. It is a low grade metamorphic rock that splits into thin pieces. Soapstoneis a metamorphic rock that consists primarily of talc with varying amounts of other minerals such as micas, chlorite, amphiboles, pyroxenes and carbonates. It is a soft, dense, heat- resistant rock that has a high speciflc heat capacity. These properties make it useful for a wide variety of architectural, practical and artistic uses. Minerals The earth is composed of various kinds of elements. These elements are in solid form in the outer layer of the earth and in hot and molten form in the interior. About 98 per cent of the total crust of the earth is composed of eight elements like oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium The rest is constituted by titanium, hydrogen, phosphorous, manganese, sulphur, carbon, nickel and other elements. 13 TARGET PT 2020 15 What is a mineral? A mineral is a naturally occurring organic or inorganic substance, having an orderly atomic structure and a deflnite chemical composition and physical properties. A mineral is composed of two or more elements. But, sometimes single element minerals like sulphur, copper, silver, gold, graphite, etc. are also found. The basic source of all minerals is the hot magma in the interior of the earth. When magma cools, crystals of the minerals appear and a systematic series of minerals are formed in sequence to solidify so as to form rocks. The minerals which contain metals are called as metallic minerals (eg: Haematite) and the metallic minerals which are profltably mined are called as the ores. The crust of the earth is made up of more than 2000 minerals, but out of these, only six are the most abundant and contribute the maximum. These six most abundant minerals are feldspar, quartz, pyroxenes, amphiboles, mica and olivine. Types of Mineral Metallic Minerals These minerals contain metal content and can be sub-divided into three types: Precious metals:gold, silver, platinum etc. Ferrous metals:iron and other metals often mixed with iron to form various kinds of steel. Non-ferrous metals:include metals like copper, lead, zinc, tin, aluminum etc. Non-Metallic Minerals These minerals do not contain metal content. Sulphur, phosphates and nitrates are examples of non- metallic minerals. Cement is a mixture of non-metallic minerals. Physical Characteristics of Minerals External crystal form— determined by internal arrangement of the molecules — cubes, octahedrons, hexagonal prisms, etc. Cleavage — tendency to break in given directions producing relatively plane surfaces — result of internal arrangement of the molecules — may cleave in one or more directions and at any angle to each other. Fracture— internal molecular arrangement so complex there are no planes of molecules; the crystal will break in an irregular manner, not along planes of cleavage. Lustre— appearance of a material without regard to color; each mineral has a distinctive lustre like metallic, silky, glossy etc. Color— some minerals have characteristic color determined by their molecular structure — malachite, azurite, chalcopyrite etc., and some minerals are colored by impurities. For example, because of impurities quartz may be white, green, red, yellow etc. Streak — color of the ground powder of any mineral. It may be of the same color as the mineral or may differ — malachite is green and gives green streak, fluorite is purple or green but gives a white streak. Transparency — transparent: light rays pass through so that objects can be seen plainly; translucent — light rays pass through but will get diffused so that objects cannot be seen; opaque — light will not pass at all. Structure— particular arrangement of the individual crystals; fine, medium or coarse grained; fibrous — separable, divergent, radiating. Hardness — relative resistance being scratched; ten minerals are selected to measure the degree of hardness from 1-10. They are: 14 16 TARGET PT 2020 ! Talc; ! Gypsum; ! Calcite; ! Fluorite; ! Apatite; ! Feldspar; ! Quartz; ! Topaz; ! Corundum; and ! Diamond. Compared to this for example, a fingernail is 2.5 and glass or knife blade is 5.5. Specific gravity— the ratio between the weight of a given object and the weight of an equal volume of water; object weighed in air and then weighed in water and divide weight in air by the difference of the two weights. Soil Soil can be deflned as the solid material on the Earth’s surface that results from the interaction of weathering and biological activity on the parent material or underlying hard rock. The naturally occurring soil is influenced by parent material, climate, relief, and the physical, chemical and biological agents (micro-organisms) in it. A soil is made up of four elements: inorganic fraction (derived from the parent material), organic material, air and water. The abundance of each component and its importance in the functioning of the soil system vary from horizon to horizon and from one soil to another. Soil Characteristics Soil Texture Soil texture is a term used to describe the distribution of the different sizes of mineral particles in a soil. Textures range from clay, sand, and silt at the extremes, to a loam which has all three sized fractions present. The main influence of texture is on permeability which generally decreases with decreasing particle size. A clayey soil may thus be described as flne, a sandy soil as course, while a silty soil is intermediate. Soil Air The air content of a soil is vital, both to itself and to organic life within it. A certain amount of air is contained between the individual particles except for the waterlogged soils. The air in the soil helps in the process of oxidation which converts part of the organic material into nitrogen in a form readily available to the plants. Soil water Depending on the texture of the soil, water moves downward by percolation. The amount of water in the soil varies from almost nil in arid climates which makes life virtually impossible for organisms, to a state of complete water logging which excludes all air, causes a reduction of bacteriological activity, and limits decomposition. In damp climates, especially in high latitudes where the evaporation rate is low, water tends to move predominantly downward, particularly in coarse-grained sandy soils. This dissolves the soluble 15 TARGET PT 2020 17 minerals in the soil, together with soluble humus material and carries both downward, a process called leaching or eluviations. A typical leached soil is known as podzol, a Russian word meaning ash because the surface layer is often grayish or ash-coloured. In a hot, arid climate, evaporation exceeds precipitation for greater part of the year, so the water tends to move upward and the soil dries out. Consequently, in some areas, a thin salty layer is formed on the surface. This process of Salinization. Soil color Generally, soil color is determined by the amount of organic matter and the state of the iron. Soil color is also related to soil drainage, with free draining, well AERATED soils (with pore space dominated by oxygen) having rich brown colors. In contrast, poorly draining soils often referred to as gleys, develop under ANAEROBIC conditions (the pore space dominated by water) and have grey or blue-grey colors. Such colors are the result of oxidation-reduction; iron is the main substance affected by these processes. If the iron is released in an anaerobic environment, then it stays in the reduced state giving it the grey blue color of waterlogged soils. Factors Responsible for Soil Formation Soil formation is the combined effect of physical, chemical, biological, and anthropogenic processes on soil parent material. Parent material This is the material from which the soil has developed and can vary from solid rock to deposits like alluvium and boulder clay. It has been defined as ‘the initial state of the soil system’. The parent material cans influence the soil in a number of ways: color; texture; structure; mineral composition and permeability/drainage. Soil may form directly by the weathering of consolidated rock in situ (a residual soil), saprolite (weathered rock), or it may develop on superficial deposits, which may have been transported by ice, water, wind or gravity. These deposits originated ultimately from the denudation and geologic erosion of consolidated rock. Consolidated material is not strictly parent material, but serves as a source of parent material after some physical and /or chemical weathering has taken place. Soils may form also on organic sediments (peat, muck) or salts (evaporates). The chemical and mineralogical compositions of parent material determine the effectiveness of the weathering forces. Climate Temperature varies with latitude and altitude, and the extent of absorption and reflection of solar radiation by the atmosphere. Solar radiation (direct radiation and diffuse radiation) increases with elevation, differs seasonally, and is influenced by cloud cover or other atmospheric disturbance (e.g. air) pollution). The absorption of the solar radiation at the soil surface is affected by many variables such as soil color, vegetation cover, and aspect. In general, the darker the soil color, the more radiation is absorbed and the lower the albedo. The effect of vegetative cover on absorption varies with density, height, and color of the vegetation. Hence the absorption differs in areas with decidious trees (soil surface is shaded by trees most of the year) and arable land (soil surface is not shaded throughout the year). Light, or whitish-colored, soil surfaces tend to reflect more radiation. When incoming solar radiation is reflected, there is less net radiation to be absorbed and heat the soil. Snow is especially effective in reflecting the incoming solar radiation. Temperature affects the rate of mineral weathering and synthesis, and the biological processes of growth and decomposition. Weathering is intensified by high temperatures, hence weathering is stronger in the tropics than in humid regions. Biological processes are intensified by rising temperatures. Reaction rates are roughly doubled for each 10°C rise in temperature, although enzyme-catalyzed reactions are sensitive to high temperatures and usually attain a maximum between 30° and 35°C. 16 18 TARGET PT 2020 Biological Factors The soil and the organisms living on and in it comprise an ecosystem. The active components of the soil ecosystem are the vegetation, fauna, including microorganisms, and man. Vegetation ! The primary succession of plants that colonize a weathering rock culminates in the development of a climax community, the species composition of which depends on the climate and parent material, but which, in turn, has a profound influence on the soil that is formed. ! Deciduous forest seems to accelerate soil formation compared to grassland on the same parent material under similar climatic conditions. Meso-/Macrofauna ! Earthworms are the most important of the soil forming fauna in temperate regions, being supported to a variable extent by the small arthropods and the larger burrowing animals (rabbits, moles). ! Earthworms are also important in tropical soils, but in general the activities of termites, ants, and beetles are of greater significance, particularly in the sub humid to semiarid savanna of Africa and Asia. Micro-organisms ! The organic matter of the soil is colonized by a variety of soil organisms, most importantly the micro-organisms, which derive energy for growth from the oxidative decomposition of complex organic molecules. ! During decomposition, essential elements are converted form organic combination to simple inorganic forms (mineralization). ! Types of micro-organisms comprise bacteria, actinomycetes, fungi, algae, protozoa, and soil enzymes. Man ! Man is perhaps now the most influential of all organisms. He affects the soil by such activities as: ploughing, irrigating, mining, clearing, disposing and leveling. Time ! Time is a factor in the interactions of all the above factors as they develop soil. Over time, soils evolve features dependent on the other forming factors, and soil formation is a time-responsive process dependent on how the other factors interplay with each other. Relief ! Relief is not static; it is a dynamic system (its study is called geomorphology). Relief influences soil formation in several ways: It influences soil profile thickness i.e. as angle of slope increases so does the erosion hazard. Gradient affects run-off, percolation and mass movement. It influences aspect which creates microclimatic conditions Stages of Soil Formation Soil formation is a long slow process. It’s estimated that an inch of soil takes 500 to 1000 years to form. Soil is constantly being formed. Stage One ! This is the rock pulverizing stage. Here the forces of wind, rain, freezing and thawing water, earthquakes, volcanos all work to slowly pulverize rocks into smaller particles that can make up a soil. At the end of this stage a combination of sand, silt and clay sized particles forms. These form a mineral soil like substance but are unable to support life. ! They are missing nitrogen. It may seem nitrogen should be the least of a being’s worries. After all the air we breathe is made up of about 78% nitrogen gas. The problem is that plants cannot use nitrogen in this form. For them it needs to be converted to either ammonia which is a combination of nitrogen and hydrogen or nitrates - a combination of nitrogen and oxygen. 17 TARGET PT 2020 19 Stage Two ! This is the early stage of soil formation. Here life is added specifically by lichens. ! Lichens are a symbiotic relationship of algae and fungus. The algae have the very important role of fixing the nitrogen, changing it from nitrogen gas to a form, the plant can use. It also captures the sunlight and creates sugars and oxygen. The fungus provides a place for the algae to live, along with water and the mineral nutrients it needs. Stage Three ! At this time the little pockets of soil have formed to the extent that some larger plants, plants with roots can have a go at growing. ! The first pioneers will be short lived but as their bodies are added to the layers of soil forming, the soil becomes more capable of supporting life. Humus builds and soil horizons begin to form. Stage Four ! The soils are developed enough to support thick vegetation. Soil Forming Processes The four major processes that change parent material into soil are additions, losses, translocations, and transformations. Additions ! The most obvious addition is organic matter. As soon as plant life begins to grow in fresh parent material, organic matter begins to accumulate. Organic matter gives a black or dark brown color to surface layer. ! Other additions may come with rainfall or deposition by wind, such as the wind-blown or eolian material. By causing rivers to flood, rainfall is indirectly responsible for the addition of new sediment to the soil on a flood plain. Losses ! Most losses occur by leaching. Water moving through the soil dissolves certain minerals and transports them into deeper layers. Some materials, especially sodium salts, gypsum, and calcium carbonate, are relatively soluble. They are removed early in the soil’s formation. As a result, soil in humid regions generally does not have carbonates in the upper horizons. ! Fertilizers are relatively soluble, and many, such as nitrogen and potassium, are readily lost by leaching, either by natural rainfall or by irrigation water. ! Solid mineral and organic particles are lost by erosion. Such losses can be serious because the material lost is usually the most productive part of the soil profile. Translocations ! Translocation means movement from one place to another. In low rainfall areas, leaching often is incomplete. Water starts moving down through the soil, dissolving soluble minerals as it goes. There isn’t enough water, however, to move all the way through the soil. When the water stops moving, then evaporates, salts are left behind. Soil layers with calcium carbonate or other salt accumulations form this way. If this cycle occurs enough times, a calcareous hardpan can form. ! Translocation upward and lateral movement is also possible. Even in dry areas, low-lying soils can have a high water table. Evaporation at the surface causes water to move upward. Salts that are dissolved in solution will move upward with the water and deposit on the surface as the water evaporates. Transformations ! Transformations are changes that take place in the soil. Microorganisms that live in the soil feed on fresh organic matter and change it into humus. Chemical weathering changes parent material. Some minerals are destroyed completely. Others are changed into new minerals. Many of the clay-sized particles in soil are actually new minerals that form during soil development. 18 20 TARGET PT 2020 ! Other transformations can change the form of certain materials. Iron oxides (ferric form) usually give soils a yellowish or reddish color. In waterlogged soils, however, iron oxides loose some of their oxygen and are referred to as being reduced. The reduced form of iron (ferrous) is quite easily removed from the soil by leaching. After the iron is gone, generally the leached area has a greyish or whitish color. Soil Classification Soil Classification concerns the grouping of soils with a similar range of properties (chemical, physical and biological) into units that can be geo-referenced and mapped. Soils are divided into: (i) zonal, (ii) intrazonal, (iii) azonal categories. Zonal A soil whose characteristics are dominated by the influence of climate and vegetation is known as a zonal soil. These soils occur on gently undulating land where drainage is free and where the parent material is of neither extreme texture nor chemical composition. They occur in latitudinal zones. There are seven main types of zonal soils: Tundra Soils: ! These soils extend over the tundra region, covering northern parts of North America, southern fringes of Greenland and northern Eurasia. The exact character of these soils depends on the ground ice position, slope and the vegetation. If the slope is stable, peaty soils are formed due to slow organic and chemical action. In case of steep slopes, thin soils result. Podzols: ! These soils occur south of the tundra region in North America, northern Europe and Siberia and are associated with conifers and heath plants. In these soils, the horizon-A is colloidal and humus rich, horizon-E is bleached and ash- grey, horizon-B is brown clayey. Depending on the composition of horizon-B, the soils could be humus- podzol, iron-podzol or gleypodzol. These soils are generally infertile and require lime and fertilisers if put to agricultural use. Brown Forest Soils: ! These soils occur south of the podzol region in milder climates of eastern to USA, northern Europe and England. These soils are associated with deciduous forests and derive their brown appearance from the equitable distribution of humus and sesquioxides. ! There is less leaching, because there is no downward movement of sesquioxides. The brown forest soils are generally less acidic. Lateritic Soils/Latosols/Ferralsols: ! These soils cover large areas of Asia, Africa, South and Central America and Australia. These soils are generally associated with tropical and sub-tropical climates with a short wet and long dry season and thick vegetation. ! During the dry season, in these areas, there is intense physical and chemical weathering and organic activity. During the wet season, an intense leaching causes washing down of humus, organic and mineral colloids, clay and other soluble material. ! The upper horizons are, as a result, acidic with minimum organic content. The insoluble oxides of iron and aluminum give the upper layers a characteristic red color. The lower horizons are clayey. The lateritic soils are generally poorly differentiated but have deep horizons and are suitable for mining. These soils are generally infertile due to low base status. Chernozem/Prairie/Steppe: ! These soils are associated with grasslands receiving moderate rainfall in northern USA, the Commonwealth of Independent States (former USSR), Argentina, Manchuria and Australia. ! The chernozems are characterised by high mineral content and low organic content. Calcium carbonate is quite high in the proflle. The upper horizons are dark, mineral-matrix-base rich. The humus content is around 10%. The parent material of chernozems may be ‘loess’ (wind eroded sediments). The soft, crumb structure imparts fertility to these soils. 19 TARGET PT 2020 21 ! The chestnut soils occur on the arid side of chernozems, and are associated with low-grass steppe. The lime content is still higher in these soils compared to the chernozems. ! The prairies represent the transitional soils between chernozems and the brown forest soils and reflect the element of increasing wetness. These soils are characterized by less leaching, no calcium content and taller, coarser grasses. In the corn regions of the USA, prairie soils are quite fertile. Grumusols/Reddish Brown Soils: ! These are dark clayey soils of savanna grasslands which occur on the drier margins of the laterites. These regions experience warm climate with wet-dry seasons. ! There are no eluviated and alluvial horizons but the wholesolum is base-rich which gives these soils a dark appearance. These soils support scattered trees, low scrubs and grasses. During the dry season, these soils show cracks. Desert (Seirozems and Red Desert) Soils: ! Seirozems or grey desert soils occur in mid-latitude deserts of Colorado and Utah states of USA, in Turkmenistan, Mongolia and Sinkiang. These soils occur on the extreme sides of chestnut soils and have a low organic content. Lime and gypsum are closer to the surface. Being rich in bases, the seirozems are good for irrigation. ! The red desert soils occur in the tropical deserts of the Sahara, West Asia, Pakistan, South Africa and Australia. These soils are characterized by lack of vegetation and lack of leaching. The insoluble oxides of iron and aluminum give these soils a red color. The red desert soils are generally base rich, sandy and gravelly. Intrazonal Soils ! Intrazonal soils is a soil which has been influenced in its development less by climate and vegetation than by other local factors, such as defective drainage, excessive evaporation or an unusual parent material (such as lime stone), terrain or age. ! They can be sub-divided into: Hydromorphic: Bog soils are formed under cool, temperate, continental climates. In these soils the upper layer is peaty while the lower layer is gleyey Calcimorphic:Wherever the limestone is exposed, rendzinas are formed which are dark, organic rich and good for cultivation in humid regions. Halomorphic:These soils occur mostly in deserts. Azonal Soils A soil which has not been suﬃciently subjected to soil –forming processes for the development of a mature profile and so is little changed from the parent rock material. Azonal soils do not have B horizon because it is too immature. Thus, the A horizon lies immediately above the C horizon. Examples are soil forming on scress, recently deposited alluvium, sand dunes, and newly deposited glacial draft, wind-blown sand, marine mud flats and volcanic soils. Soils of India Since Independence, scientific surveys of soils have been conducted by various agencies. Soil Survey of India, established in 1956, made comprehensive studies of soils in selected areas like in the Damodar Valley. The National Bureau of Soil Survey and the Land Use Planning an Institute under the control of the Indian Council of Agricultural Research (ICAR) did a lot of studies on Indian soils. In their effort to study soil and to make it comparable at the international level, the ICAR has classified the Indian soils on the basis of their nature and character as per the United States Department of Agriculture (USDA) Soil Taxonomy. On the basis of genesis, colour,composition and location, the soils of Indiahave been classified into: 20 22 TARGET PT 2020 Alluvial soils Black soils Red and Yellow soils Laterite soils Arid soils Saline soils Peaty soils Forest soils. Alluvial Soils Alluvial soils are widespread in the northern plains and the river valleys. These soils coverabout 40 per cent of the total area of the country. They are depositional soils, transported and deposited by rivers and streams. Through a narrow corridor in Rajasthan, they extend into the plains of Gujarat. In the Peninsular region, they are found in deltas of the east coast and in the river valleys. In the Upper and Middle Ganga plain, two different types of alluvial soils have developed, viz. Khadar and Bhangar. Khadar is the new alluvium and is deposited by floods annually, which enriches the soil by depositing fine silts. Bhangar represents a system of older alluvium, deposited away from the flood plains. Both the Khadar and Bhangar soils contain calcareous concretions (Kankars). These soils are more loamy and clayey in the lower and middle Ganga plain and the Brahamaputra valley. The sand content decreases from the west to east. Black Soil Black soil covers most of the Deccan Plateau which includes parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and some parts of Tamil Nadu. In the upper reaches of the Godavari and the Krishna, and the northwestern part of the Deccan Plateau, the black soil is very deep. These soils are also known as the ‘Regur Soil’ or the ‘Black Cotton Soil’. The black soils are generally clayey, deep and impermeable. They swell and become sticky when wet and shrink when dried. Chemically, the black soils are rich in lime, iron, magnesia and alumina. They also contain potash. But they lack in phosphorous, nitrogen and organic matter. The colour of the soil ranges from deep black to grey. Red and Yellow Soil Red soil develops on crystalline igneous rocks in areas of low rainfall in the eastern and southern part of the Deccan Plateau. The soil develops a reddish colour due to a wide diffusion of iron in crystalline and metamorphic rocks. It looks yellow when it occurs in a hydrated form. The fine-grained red and yellow soils are normally fertile, whereas coarse-grained soils found in dry upland areas are poor in fertility. They are generally poor in nitrogen, phosphorous and humus. Laterite Soil Laterite has been derived from the Latin word ‘Later’ which means brick. 21 TARGET PT 2020 23 The laterite soils develop in areas with high temperature and high rainfall. These are the result of intense leaching due to tropical rains. With rain, lime and silica are leached away, and soils rich in iron oxide and aluminum compound are left behind. Humus content of the soil is removed fast by bacteria that thrive well in high temperature. These soils are poor in organic matter, nitrogen, phosphate and calcium, while iron oxide and potash are in excess. Hence, laterites are not suitable for cultivation; however, application of manures and fertilizers are required for making the soils fertile for cultivation. Laterite soils are widely cut as bricks for use in house construction. Arid Soils Arid soils range from red to brown in colour. They are generally sandy in structure and saline in nature. In some areas, the salt content is so high that common salt is obtained by evaporating the saline water. Due to the dry climate, high temperature and accelerated evaporation, they lack moisture and humus. Nitrogen is insuﬃcient and the phosphatecontent is normal. Lower horizons of the soilare occupied by ‘kankar’ layers because of the increasing calcium content downwards. Saline Soils They are also known as Usara soils. Saline soils contain a larger proportion of sodium, potassium and magnesium, and thus, they are infertile, and do not support any vegetative growth. They have more salts, largely because of dry climate and poor drainage. They occur in arid and semi-arid regions, and in waterlogged and swampy areas. Their structure ranges from sandy to loamy. They lack in nitrogen and calcium. Peaty Soils They are found in the areas of heavy rainfall and high humidity, where there is a good growth of vegetation. Thus, large quantity of dead organic matter accumulates in these areas, and this gives a rich humus and organic content to the soil. Organic matter in these soils may go even up to 40-50 per cent. Forest Soils As the name suggests, forest soils are formed in the forest areas where suﬃcient rainfall is available. The soils vary in structure and texture depending on the mountain environment where they are formed. They are loamy and silty on valley sides and coarse-grained in the upper slopes. In the snow-bound areas of the Himalayas, they experience denudation, and are acidic with low humus content. The soils found in the lower valleys are fertile. ********** 22 24 TARGET PT 2020 DAY 3- 18 CONCEPTS OF GEOMORPHOLOGY Evolution of Oceans and Continents The Theory of Continental 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 The distribution of glacial features can be best polar or subpolar region which is consistent explained if the continents were part of Pangaea. 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. 23 TARGET PT 2020 25 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 off of Sima 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 24 26 TARGET PT 2020 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 Antartica 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 25 TARGET PT 2020 27 ! 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 off the northwest coast of North America ! Explorer Ridge off the northwest coast of North America ! Juan de Fuca Ridge off the northwest coast of North America ! Chile Rise off 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 subductsbeneath 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 Mountains: 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. 26 28 TARGET PT 2020 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. 27 TARGET PT 2020 29 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 flattened 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 pyroclasticthat 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. 28 30 TARGET PT 2020 ! 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 volcanoesare 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 domesare 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, volcanism may be categorized into: ! 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-Pacifi c 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 Sommawhich erupted 700 years back are now considered extinct by the inhabitants. World distribution of Volcanoes The CircumPacific 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. 29 TARGET PT 2020 31 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, Etnaetc.), 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. 30 32 TARGET PT 2020 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). Seismic Waves or Earthquake Waves The seismic waves can be classified into two categories: 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 earth. ! Types of Surface Wave Love waves (L-waves): It is 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. Stoneley waves: Stone waves propagate along a solid - fluid boundary and also along solid - solid boundary. Standing waves: Standing waves are the result of free oscillation of earth. When two waves moving opposite to each other interfere standing waves are produced. 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. 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. 31 TARGET PT 2020 33 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 Distribution of earthquakes and volcanoes 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. 32 34 TARGET PT 2020 The Mid-Oceanic Ridges and the African Rift System:This runs along the mid-oceanic ridges through the oceans. These have generally shallow focus. Earthquake Zones in India Bureau of Indian Standardsbased on the past seismic history, grouped the country into four seismic zones, viz. Zone-II, -III, -IV and –V. Of these, Zone V is the most seismically active region, while zone II is the least.The Modified Mercalli (MM) intensity, which measures the impact of the earthquakes on the

DFA Geography Book PDF

Document Details

Tags

Related

Summary

Full Transcript

Upgrade to continue