Physical Geography PDF

Sl.No. Topic 1. Introduction and the Origin of the Earth 2. Evolution of Earth 3. Rocks 4. Geomorphology 5. Volcanoes 6. Earthquakes 7. Landforms 8. Soil 9. Oceanography 10. Climatology 11. World Climate 12. Appendix...

Sl.No. Topic 1. Introduction and the Origin of the Earth 2. Evolution of Earth 3. Rocks 4. Geomorphology 5. Volcanoes 6. Earthquakes 7. Landforms 8. Soil 9. Oceanography 10. Climatology 11. World Climate 12. Appendix  1. Introduction and the 1.4 Star Formation: Origin of the Earth Due to uneven distribution of matter and energy in the early universe led to 1.1 Origin of earth: initial density differences in gravitational forces and it caused the Nebular hypothesis by Immanuel Kant Later matter to get drawn together bases for revised by Laplace development of galaxies. A galaxy starts to form by The planets were formed out of a cloud accumulation of hydrogen gas in the material associated with a youthful form of a very large cloud called sun which was slowly rotating. nebula. Later revised by Carl Weizascar and Nebula localised clumps of gas That Otto Schmidt. led to formation of gaseous bodies→ Sun was surrounded by solar nebula formation of stars. containing mostly hydrogen, helium and other dust particles. The friction 1.5 Formation of Planets: and collision of particles led to the formation of disk shaped cloud. Stages in the Development of Planets: Planets are formed through accretion(growth by gradual accumulation of matter) 1.2 Origin of Universe: Big bang theory/expanding universe hypothesis: by Edwin Hubble. Stages - As the time passes galaxies further move apart. Though space between the galaxies is increasing there is no expansion of galaxies. The stars are localized lumps of gas within a nebula, gravitational force 1.3 Stages in development of universe within the lumps lead to formation of a core to the gas cloud and a huge All the matter was a tiny ball of rotating disc of gas and dust unimaginably small volume, with developed around the gas core. infinite temperature and infinite Gas cloud ->condenses->matter density. around the core develops into small At the Big Bang the "tiny ball" exploded round objects by the process of violently which led to huge expansion. cohesion->planetesimals. Within 300,000 years from the Big These large number of small Bang, temperature dropped to 4,500 K planetesimals accrete to form a fewer (Kelvin) and gave rise to atomic large bodies in the form of planets. matter. The universe became transparent. 002  Note: 1.6 Solar system: The corona's high temperatures are a Our solar system consists of the sun bit of a mystery. Imagine that you're (the star), 8 planets, more than 200 sitting next to a campfire. It's nice and moons, millions of smaller bodies like warm. But when you walk away from asteroids and comets and huge the fire, you feel cooler. This is the quantity of dust-grains and gases. opposite of what seems to happen on Mercury, Venus, Earth and Mars are the Sun. called as the Inner planets/Terrestrial Astronomers have been trying to solve planets, as they lie between the sun this mystery for a long time. The and the belt of asteroids the other four corona is in the outer layer of the Sun's planets are called the outer atmosphere-far from its surface. Yet planets/Jovian planets the corona is hundreds of times hotter than the Sun's surface. Fig: Solar System A dark patch on the surface of Sunspot the Sun. Sun–The solar atmosphere consists of the photosphere, chromosphere, and the corona A stream of energized, charged particles, primarily electrons The bright outer layer of the Solar Wind and protons, flowing outward Photosphere Sun that emits most of the from the Sun. radiation Just above the photosphere, Chromosphere it is a relatively thin layer of burning gases - A distinctive atmosphere of plasma that surrounds the Sun and other celestial bodies A magnetic storm on the Sun - Usually hidden by the which appears to be a very Corona bright light of the Sun's Solar Flares bright spot and is a gaseous surface, making it difficult to surface eruption. see without using special instruments - Can be seen during a total solar eclipse 003 Planet Description - The smallest planet in our solar system - The closest planet to the Sun at a distance of about 36 million miles - One day on Mercury takes 59 Earth days.- Revolution around the Sun in just 88 Earth days Mercury - Has no moons. - The two spacecraft of ESA-JAXA's BepiColombo are en route to Mercury. - NASA's Mariner 10 was the first mission to explore Mercury. - NASA's MESSENGER was the first to orbit the innermost planet. - The second closest planet to the Sun at a distance of about 67 million miles - One day on Venus lasts 243 Earth days - Spins backwards, with its Sun rising in the west and setting in the east. - Has no moons and no rings. - The brightest planet in the solar system and is the third brightest object visible from Venus Earth after the Sun and the Moon. - Sometimes called Earth’s sister planet or Earth’s twin because of their similar size, mass, proximity to the Sun, bulk composition, and presence of similar physical features such as high plateaus, folded mountain belts, and numerous volcanoes. - In ancient literature, Venus was often referred to as the morning star and evening star. - Moon - only natural satellite of the Earth. - Darwin suggested that the Earth and Moon formed a single rapidly rotating body. The whole mass became a dumbbell-shaped body and later it broke. Earth - Present scientists believe that the formation of the Moon is an outcome of “the big splat” which blasted a large part of Earth into space. - This blasted material continued to orbit the Earth and formed into the Moon. - Dark patches, it possesses an atmosphere of mostly carbon dioxide. - Often referred to as the “Red Planet” because of the reddish iron oxide prevalent on its surface. Mars - Has two irregularly shaped moons, Phobos and Deimos, which are thought to be captured asteroids. - Martian year is 687 days and Martian day is 24h 37m. - Largest outer planet; composed of hydrogen, helium, and methane. - It has circular light and dark bands with outer rings, very cold (-130°C). - Rotates once about every 10 hours (a Jovian day), but takes about 12 Earth years to Jupiter complete one orbit of the Sun (a Jovian year). - In 1979 the Voyager mission discovered Jupiter’s faint ring system. All four giant planets in our solar system have ring systems. - It has 53 named moons and another 26 awaiting official names. 004  Planet Description - Composed mostly of hydrogen and helium. - Takes about 10.7 hours (no one knows precisely) to rotate on its axis once - a Saturn “day” - and 29 Earth years to orbit the Sun. - Has 53 known moons with an additional 29 moons awaiting confirmation of their discovery Saturn - a total of 82 moons. - Has the most spectacular ring system, with seven rings and several gaps and divisions between them. - Few missions have visited Saturn: Pioneer 11 and Voyagers 1 and 2 flew by; but Cassini orbited Saturn 294 times from 2004 to 2017. - A distance of about 1.8 billion miles- Takes about 17 hours to rotate once (a Uranian day), and about 84 Earth years to complete an orbit of the Sun (a Uranian year). - An ice giant. Most of its mass is a hot, dense fluid of "icy" materials – water, methane, and ammonia – above a small rocky core. Uranus - Has 27 known moons, and they are named after characters from the works of William Shakespeare and Alexander Pope. - Has 13 known rings. The inner rings are narrow and dark, and the outer rings are brightly colored. - Voyager 2 is the only spacecraft to fly by Uranus. - Like Venus, Uranus rotates east to west. - Orbits the Sun at a distance of about 2.8 billion miles - Takes about 16 hours to rotate once (a Neptunian day), and about 165 Earth years to orbit the Sun (a Neptunian year). - An ice giant. Most of its mass is a hot, dense fluid of "icy" materials Neptune – water, methane, and ammonia – above a small rocky core. - Has 14 known moons which are named after sea gods and nymphs in Greek mythology. - Voyager 2 is the only spacecraft to have visited Neptune. The Kuiper belt is a great ring of debris Celestial bodies: Any natural body similar to the asteroid belt, but outside of the Earth's atmosphere. consisting mainly of objects composed Asteroids: Small rocky body orbiting the primarily of ice. sun. Large numbers of these, ranging enormously in size, are found between Inner versus outer planets. the orbits of Mars and Jupiter. Inner Planets Outer Planets Dwarf Planet: Dwarf planets are heavenly bodies that are too small to be - Mercury, Venus, - Jupiter, Saturn, Uranus, considered a planet but too large to fall Earth, Mars Neptune under smaller categories. The International Astronomical Unit defines a - Solid, rocky - Gaseous, ringed planet as something that obeys the - Warmer - Colder following criteria: - Smaller - Larger ○ To be in orbit around the Sun - Mostly made of - Made of methane, ○ Has enough gravity to pull its own metals hydrogen, helium mass into a round shape ○ Has cleared its orbit of smaller objects 005  Comets: a celestial object consisting 2.2 Evolution of Atmosphere: of a nucleus of ice and dust and, when There are three stages in the evolution near the sun, a ‘tail’ of gas and dust of the present atmosphere. First stage is marked by the loss of particles pointing away from the sun. primordial atmosphere.. Second stage, the hot interior of the earth contributed to the evolution of the atmosphere. Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis. The early atmosphere largely contained water vapor, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen. The process through which the gases were outpoured from the interior is called degassing. Continuous volcanic eruptions contribute water vapor and gases to Meteors/Meteoroids: A meteor is an the atmosphere. asteroid or other object that burns and vaporizes upon entry into the Earth's 2.3. Evolution of Hydrosphere: atmosphere; meteors are commonly known as "shooting stars." If a meteor As the earth cooled, the water vapour released started getting condensed. survives the plunge through the The carbon dioxide in the atmosphere atmosphere and lands on the surface, got dissolved in rainwater and the it's known as a meteorite. temperature further decreased causing more condensation and more rains. 2. Evolution of Earth The rainwater falling onto the surface got collected in the depressions to give rise to oceans. 2.1 Evolution of Lithosphere: The earth's oceans were formed within The earth was mostly in a volatile 500 million years from the formation state during its primordial stage. of the earth. Due to gradual increase in density the However, around 2,500-3,000 million temperature inside has increased. years before the present, the process As a result, the material inside started of photosynthesis got evolved. Life was getting separated depending on their confined to the oceans for a long time. Oceans began to have the densities. contribution of oxygen through the This allowed heavier materials (like photosynthesis. process of iron) to sink towards the centre of the Eventually, oceans were saturated Earth and the lighter ones to move with oxygen, and 2,000 million years towards the surface. With passage of ago, oxygen began to flood the time, it cooled further and solidified atmosphere. and condensed into a smaller size. This later led to the development of the outer surface in the form of a crust. 006 2.4 Structure of Earth: 2.4.2.1. Asthenosphere: The upper portion of the mantle is The structure of the earth’s interior is called asthenosphere. made up of several concentric layers. Asthenosphere is a plastic zone in Broadly three layers can be mantle identified—Crust, Mantle and the Core It is considered to be extending up to 400 km. It is the main source of magma and is more fluidic in nature 2.4.3. Core: Lies between 2900 km and 6400 km below the earth's surface. Accounts for 16 per cent of the earth's volume. Core has the heaviest mineral materials of highest density. It is composed of nickel and iron [Nife]. 2.4.1. Crust: The outer core is liquid while the inner Crust is the outer thin layer with a total соrе is solid. thickness normally between 30-50 Gutenberg Discontinuity lies between km. The thickness of the crust varies the mantle and the outer соге. under the oceanic-thinner (5-30 Km) and continental areas- thick (50-70 2.5 Composition of Earth Crust: Km). The mean density of oceanic crust is Sl. No. Element Weight (%) 2.7g/cm³ 1 Oxygen 46.6 Basalt is found in oceanic crust. The continental crust is thicker in the 2 Silicon 27.72 areas of major mountain systems. 3 Aluminium 8.13 It forms 5-10 percent of the earth's 4 Iron 5 volume. Mohorovic (Moho) discontinuity forms 5 Calcium 3.63 the boundary between crust and outer 6 Sodium 2.83 -outer mantle. 7 Potassium 2.59 The continents are composed of Sial while the oceans are composed of 8 Magnesium 2.09 Sima 9 Others 1.41 2.4.2. Mantle: 2.5.1 Chemical composition of the Earth: The mantle extends to a depth of 2,900 km. The crust and the uppermost part Element Chemical Composition (%) of the Iron 34.6 mantle are called lithosphere. Its thickness ranges from 10-200 km. Oxygen 29.5 The lower mantle extends beyond the Silicon 15.2 asthenosphere. It is in solid state. The density of mantle varies between Magnesium 12.7 2.9 and 3.3. Nickel 2.4 It is composed of solid rock and magma. Sulphur 1.9 It forms 83 per cent of the earth's Titanium 0.05 volume 007 2.5.2 Sources of information about earth 2.6.2 Revolution of Earth: interior: The motion of the earth around the 1. Direct sources- surface rock obtained sun which spins in an elliptical orbit is by Ocean drilling, mining and volcanic called revolution. eruptions. It takes 365¼ days (one year) to 2. Indirect sources- revolve around the sun. Analysis of properties of matter like Six hours saved every year are added temperature which increase with the to make one day (24 hours) over a increasing distance from the surface span of four years. This surplus day is towards interior in deeper depths, added to the month of February. Thus pressure and density of material also every fourth year, February is of 29 increases with depth. days instead of 28 days. Such a year Meteors these solid bodies structure with 366 days is called a leap year. and material is similar to earth. Revolution leads to change in Seasons. Gravity anomaly which gives us the information about distribution of mass 2.7 Seasons: of material in the crust of earth. It is greater near the poles and less at 2.7.1 Summer Solstice: equator. On 21st June, the Northern hemisphere Magnetic surveys give information is tilted towards the sun. The rays of about magnetic material distribution the sun fall directly on the Tropic of in crustal portion. Cancer. As a result, these areas Seismic activity important source receive more heat. about interiors of earth The areas near the poles receive less heat as the rays of the sun are 2.6 Motions of Earth: slanting. The north pole is inclined towards the 2.6.1 Rotation of Earth: sun and the places beyond the Arctic Earth rotates along its axis from west Circle experience continuous daylight to east. for about six months. It takes approximately 24 hrs to Since a large portion of the northern complete on rotation. hemisphere is getting light from the Days and nights occur due to rotation sun, it is summer in the regions north of the earth. of the equator. The longest day and The circle that divides the day from the shortest night at these places night on the globe is called the circle occur on 21st June. of illumination. At this time in the southern Earth rotates on a tilted axis. Earth’s hemisphere all these conditions are rotational axis makes an angle of 23.5° reversed. It is winter season there. The with the normal i.e. it makes an angle nights are longer than the days. This of 66.5° with the orbital plane. Orbital position of the earth is called the plane is the plane of earth’s orbit summer solstice. around the Sun. Rotation Movement of earth on its axis 2.7.2 Winter Solstice: – 24 hours – Earth day. On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it. As the sun’s rays fall vertically at the Tropic of Capricorn (23½° s), a larger portion of the southern hemisphere gets light. 008  Therefore, it is summer in the southern Latitude Longitude hemisphere with longer days and shorter nights. The reverse happens in Their length decreases All longitudes are the northern hemisphere and it from equator to poles equal in length experiences winter. This position of the Prime meridian 0° and earth is called the winter solstice. Equator has the International Date Line maximum length also 180° E or 180° W are 2.7.3 Equinox: called as great circle On 21st March and September 23rd, important longitudes direct rays of the sun fall on the Equator, Tropic of equator. At this position, neither of the Cancer 23.5° N, Tropic poles is tilted towards the sun; so, the of Capricorn 23.5° S, whole earth experiences equal days Arctic circle 66.5° N, and equal nights. This is called an Antarctic circle 66.5° S, equinox. On 23rd September, it is autumn North Pole 90° N and season [season after summer and South Pole 90° S are before the beginning of winter] in the important latitudes northern hemisphere and spring They help in season [season after winter and Used to determine determining the before the beginning of summer] in time and date at a the southern hemisphere. intensity of sunlight location The opposite is the case on 21st March, received at a point when it is spring in the northern They divide Earth into hemisphere and autumn in the torrid, temperate, and southern hemisphere. frigid zones Rotation -> Days and Nights. Revolution -> Seasons. Both are used to determine the location of a point on Earth. The location is identified with Coordinates 2.8 Latitudes and longitudes: Latitude Longitude The angular distance The angular distance of a place east or of a place north or Latitude: Angular distance measured west of the prime south of the equator north or south of the equator. Project a meridian line from a given point ‘p’ on the Prime meridian = 0° earth’s surface to the centre of the Equator = 0° Latitude Longitude earth. Angle between this line and the Latitudes are named Longitudes are equatorial plane is the measure of south and north of named east or west latitude of point ‘p’. Latitude varies from 00 to 900 north equator of prime meridian and south. 009  Longitude: Angular distance between the meridian passing through a given point and the prime meridian. A longitude varies from 00 to 1800 east or west. International Date Line is where the date changes by exactly one day when it is crossed. A traveller crossing the date line from east to west loses a day and while crossing the dateline 2.8.1 Greenwich Meridian Time: from west to east he gains a day. Equator is centrally placed between 2.8.3 Indian Standard Time: the poles; any meridian could be taken to begin the numbering of The standard meridian of India is the longitude. 82.5º east longitude which passes It was finally decided in 1884, by through Allahabad. This is five and a international agreement, to choose as half hours ahead of 0º meridian the zero meridian the one which (Greenwich). passes through the Royal Astronomical Observatory at 2.8.4 Day Light Saving Greenwich, near London. This is the Prime Meridian (0°) from Many parts of North America and which all other meridians radiate Europe follow what is called Daylight eastwards and westwards up to 180°. Saving Time (DST). They help to determine local time. It’s a practice by which all the clocks in One revolution of 360° earth takes these places are moved forward by an 24-hours, therefore in 1-hour it hour during the summer months and traverses 15° or in 4 mins 1° brought back during the winter to Places east of Greenwich see the sun utilise the long lasting sunlight in earlier and gain time summer and save energy. (EAST-GAIN-ADD), whereas places India follows a single time zone of west of Greenwich see the sun later 82.5°E, Northeast region are and lose time (WEST-LOSE-SUBTRACT) demanding for a separate time zone as the sun rises as early as four in the 2.8.2 International Date Line: morning and in winter it sets by four in the evening. The International Date Line serves as the "line of demarcation" between two consecutive calendar dates. It passes through the mid-Pacific Ocean and roughly follows 180 degrees at the Bering Strait, Fiji, Tonga and other islands longitude, north-south line on the Earth. It is located halfway round the world from the prime meridian. 010  Time Unit Period/Epoch Time (Ma) Major Events Eon Holocene 0.01 Earliest Homo sapiens Quaternary -0.01 to 0 Age of Mammals, Extinction of dinosaurs and Era Cenozoic 65 many other species Tertiary 65 to 1.6 First flowering plants, First birds Period Pleistocene 1.6 Pliocene 5.3 Miocene 23.8 Oligocene 33.7 Eocene 55 Paleocene 65 Era Mesozoic 252 Dinosaurs dominant Cretaceous 145 First flowering plants Jurassic 201 First birds Triassic 252 First mammals Extinction of trilobites and many other marine Era Paleozoic 541 animals Period Permian 286 First reptiles Carboniferous 359 Large coal swamps, Amphibians abundant Devonian 419 First amphibians, First insect fossils Silurian 443 Fishes dominant Ordovician 485 First land plants First multicelled organisms, First organisms Cambrian 541 with shells, Abundant Ediacaran faunas Collectively called Precambrian, comprises Eon Proterozoic 2500 about 87% of the geological time scale Palaeozoic 541 to 252 Eon Archean 3800 First one-celled organisms Eon Hadean 4600 Origin of the earth Major Events Age of oldest rocks 011  3. Rocks 3.1 Classification of Rocks: - Formed under the action Igneous rocks of pressure, volume, and Sedimentary rocks temperature (PVT) Metamorphic rocks changes. Type of Rock Features - Formed from magma and lava; known as primary - Metamorphism involves rocks. recrystallization and - Examples: Granite, Gabbro, reorganization of materials. Pegmatite, Basalt. - Crystalline structure. Igneous - Extrusive Rocks: Formed by Rocks rapid cooling of lava during - Foliation or lineation: volcanic eruptions (e.g., Grains or minerals arranged Basalt - The Deccan Traps). in layers or lines. - Intrusive Rocks: Formed by slow cooling at great depths, allowing large crystals to form (e.g., Metamorphic Granite). - Banding: Alternating thin Rocks - Formed from the process and thick layers of minerals of denudation (weathering in light and dark shades. and erosion) followed by compaction and lithification. - Cover 75% of Earth’s crust Examples of but occupy only 5% Metamorphism: volumetrically. - Consist of layers with - Granite → Gneiss fossils of plants and animals. Sedimentary - Clay → Shale → Schist - Mechanically Formed: Rocks Sandstone, Conglomerate, Limestone, Shale, Loess. - Sandstone → Quartzite - Organically Formed: Coal, some Dolomites, some - Clay → Shale → Slate Limestones (formed from plant or animal debris). - Coal → Anthracite → - Chemically Formed: Rock Graphite Salt, Iron Ore, Chert, Flint, some Dolomites, some - Limestone → Marble Limestones. 012  This energy due to geothermal 4. Geomorphology gradients and heat flow from within induces diastrophism (slow movements) and volcanism (sudden Geomorphology is the study of the movements) in the lithosphere, physical features of the surface of the thereby causing PVT (pressure, earth and their relation to its volume and temperature) changes. geological structures. Geomorphic Process The formation 4.1.1. A. Diastrophism/ Slow Movements: and - deformation of landforms on the Diastrophic forces refer to forces surface of the earth are a continuous generated by the movement of the process which is due to the continuous solid material of the earth's crust. influence of external and internal All processes like plate tectonics, forces. orogenesis, epeirogenesis, earthquake 4.1 Earth Movements and Landforms: etc. that move, elevate or build up Earth is undergoing deformations due to, portions of the earth's crust come diastrophism. under 1. The heat generated by the radioactive Epeirogenic or Continent Movements: elements in earth's interior. Forming 2. Movement of the crustal plates due to Epirogenic movement is vertical tectogenesis. movement of the earth along the 3. Forces generated by rotation of the radius of earth crust. earth. It is continental building process which 4. Climatic factors like winds, involves uplift ог warping/subsidence precipitation, pressure belts etc. of large parts of the earth's crust. Uplift: Due to vertical movement of the earth some earth crust emerges there by leading to elevations / upliftment. Raised beaches, elevated wave-cut terraces, sea caves and fossiliferous beds above sea level are evidences of uplift. Ex: The Sierra Nevada in North America, Black Forest Mountains in Germany are examples of uplift mountains. Raised beaches along the Kathiawar, Nellore, and Tirunelveli Based on the above diagram we can see coasts. earth movements can be majorly classified into, Subsidence: 1. Endogenic movement Due to vertical movement of the earth some 2. Exogenic movement earth crust submerges there by leading subsidence. 4.1.1. Endogenic Movements: Ex: Movements inside the earth's crust or 1. Mammoth cave system in Kentucky, interaction of matter and temperature Karst topography in southern china, generates these forces. The earth Andes of South America. movements are mainly of two types: 2. Presence of peat and lignite beds diastrophism/ slow and the sudden below the sea level in Tirunelveli and movements. the Sundarbans is an example The energy emanating within the subsidence. of earth by radioactivity, rotational and 3. The Andamans and Nicobar have tidal forces, friction and primordial been isolated from the Arakan coast heat from early earth are the main by submergence of the intervening force behind these movements. land. 013 4.1.1.B. Orogenic or the Mountain- Building Ex: Vindhya and Satpura Mountains, rift Movements: valleys of Nile, Narmada and Tapi etc. Note: Orogenic movements movements are Earthquake and volcanoes are covered in horizontal which involves mountain detail later chapters. building through severe folding and faulting, act tangentially to the earth 4.1.2 Theories of Endogenetic Forces: surface. 4.1.2.A. Continental Drift Theory: These horizontal movements can be This theory was suggested by Alfred through forces of compression and Wegener in 1920's. forces of tension. According to Wegener's Continental Drift Theory, there existed one big 1. Forces of Compression: landmass which he called Pangaea Are the forces which push rock strata which was covered by one big ocean against a hard plane from one side or called Panthalassa from both sides. These compressional forces lead to the bending of rock layers and thus lead to the formation of Fold Mountains. Ex: Himalayas, the Rockies (N. America), the Andes (S. America), the Alps (Europe) etc. 2. Forces of tension: Work horizontally, but in opposite directions. Under intense tensional forces, the rock stratum gets broken or fractured which results in the formation of cracks and fractures in the crust. The displacement of rock upward ог A sea called Tethys divided the downward from their original position Pangaea into two huge landmasses: along such a fracture is termed as Laurentia (Laurasia) to the north and faulting. Faulting results in rift valleys Gondwanaland to the south of Tethys. and Block Mountains.” Drift started around 200 million years Note: The uplifted blocks are termed as ago (Mesozoic Era), and the Horsts and the lowered blocks are called continents began to break up and drift Graben. away from one another. 014 i. Force for Continental Drift: These currents are generated due to The drift was in two directions, radioactive elements causing thermal 1. Equator wards due to the interaction of differences in mantle. forces of gravity, pole-fleeing force According to this theory, the intense (earth has bulge at the equator due to heat generated by radioactive rotation of earth) and buoyancy. substances in the mantle seeks a path 2. Westwards due to tidal currents to escape, and gives rise to the because of the earth's motion. formation of convention currents in Tidal force is due to the attraction of the mantle. the moon and the sun that develops Wherever rising limbs of these tides in oceanic waters. currents meet, oceanic ridges are ii. Evidence in support of Continental Drift: formed on the sea floor and wherever South America and Africa seem to fit in the falling limbs meet, trenches are with each other, especially, the bulge formed. of Brazil fits into the Gulf of Guinea. Greenland seems to fit in well with 4.1.2.C. Sea Floor Spreading: Ellesmere and Baffin islands. The idea that the seafloor itself moves The west coast of India, Madagascar as it expands from a central axis was and Africa seem to have been joined proposed by Harry Hess. i.e identical species of plants and Continued with convectional theory animals are found on either side. i.e.. intense heat tries to escape leads North and South America on one side to convectional current meeting of and Africa and Europe on the other fit rising limbs causes ridges and falling along the mid-Atlantic ridge. limbs trenches. The Caledonian and Hercynian mountains of Europe and the Appalachians of USA seem to be one continuous series. Criticism: Coastlines are a temporary feature and are liable to change. Continental Drift Theory shifts India's position too much to the south, distorting its relation with the Mediterranean Sea and the Alps The mountains do not always exhibit geological affinity. Seafloor spreading is a process that 4.1.2.B. Conventional Theory: occurs at mid-ocean ridges, where Arthur Holmes in 1930s discussed the new oceanic crust is formed through possibility of convection currents in volcanic activity and then gradually the mantle. moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere, basaltic magma rises up the fractures and cools on the ocean floor to form new sea floor. Older rocks will be found farther away from the spreading zone while younger rocks will be found nearer to the spreading zone. 015  4.2 Types of plate boundaries: Plate Boundaries are of three types, based on the nature of interaction. 4.1.2. D. Plate Tectonic Theory: In 1967, McKenzie and Parker suggested the theory of plate tectonics. According to the theory of plate tectonics, the earth's lithosphere is broken into distinct plates which are floating on asthenosphere (upper mantle). Plates move horizontally asthenosphere as rigid units. over the The lithosphere includes the crust and Boundary Features of the Interaction top mantle with its thickness range Interaction varying between 5-100 km in oceanic Constructive Edge / Divergent parts and about 200 km in the Edge continental areas - Occurs when two tectonic Lithospheric plates (crustal plates, plates move away from each tectonic plates) vary from minor other. plates to major plates, continental Divergence - Leads to the formation of plates (Arabian plate) to oceanic mid-oceanic ridges and rift plates (Pacific plate), sometime a valleys. combination of both continental and - Earthquakes are common oceanic plates (Indo-Australian along divergent boundaries. plate). Destructive Edge / Convergent D.1 Rates of Plate Movement: Edge The Arctic Ridge has the slowest rate - Occurs when two tectonic (less than 2.5 cm/yr.), and the East plates collide with each other. Pacific Rise in the South Pacific [about - Results in crumpling and 3,400 km west of Chile), has the folding of the crust, leading to the formation of folded fastest rate (more than 15 cm/yr.). Convergence mountains. Indian plate's movement during its - Example: Himalayan journey from south to equator was one Boundary Fault. of the fastest plate movements. - When one plate is oceanic, it subducts beneath the continental plate, creating trenches. - Formed when two plates slide past each other horizontally. - Involves the grinding of plates against each other, leading to Transform deformation of existing Fault landforms. - No creation or destruction of landforms. - Example: San Andreas Fault (USA). 016 4.2.1 Convergent boundaries are of 3 types 5. Volcanoes 1. Ocean-Ocean Convergent Plate Boundary: Volcanism includes the movement of When two oceanic plates meet and molten. rock (magma) onto or toward collide against each other, the denser of the earth's surface the two plates is pulled under the other A volcano is formed when the molten. and is subducted. magma in the earth's interior escapes It descends into the asthenosphere through the crust by vents and leading to generation of new magma. fissures in the crust, accompanied by steam, gases (hydrogen sulphide, The resulting body of many volcanoes sulphur dioxide, hydrogen chloride, and volcanic rocks is called an island carbon dioxide) and pyroclastic volcanic arc. material. Examples of such arcs are Japan, the Pyroclastic-adjective of or denoting Philippines, the Tonga Islands, the rock fragments or ash erupted by a Aleutian Islands, and the West Indies volcano, especially as a hot, dense, Islands etc. destructive flow 5.1 Classification of Volcanoes: 2. Ocean-Continental Convergent Boundary: When an oceanic plate collides with a 1. Based on the frequency of eruption continental plate, the oceanic plate is Active Volcanoes- Erupt frequently or always pulled under and subducted have erupted recently or are in action because it is denser than the currently. Eg: Barren Islands. continental plate. Dormat Volcanoes- Not erupted in When the oceanic plate is subducted recent times but at least erupted once in human history under the continental plate, it leads to Extinct Volcanoes- Not erupted in the generation of new magma, which human history upwells and forms volcanoes on the non-subducting plate, or the 2. Based on the Mode of eruption continental plate. Centre Typer Volcanoes- Eruption The resulting body of such an through a vent or opening. Forms different types of hills or conical forms. interaction leads to the formation of Most of the Volcanoes of the world are continental volcanic arcs. of this type The most visible example is Andes Fissure Type Volcanoes- Magma flows Mountains off the west coast of the U.S. through a deep elongated crack. 3. Continent Continent convergent Boundary Forms thick horizontal sheet of lava or When the continent and continent low dome shaped volcano with a converge, the crust at both the sides is broad base. Eg: Deccan Traps 3. Based on the characteristics of lava. too light and buoyant to be subducted, Volcanoes of basic lava- Lava will be so neither plate is subducted in rich in metallic minerals and has continent-continent convergent greater fluidity, i.e. less viscosity. Lava boundary. flows far and wide with greater speed. Both continental masses press against They form shield volcanoes. the other, and both become Volcanoes with Acidic Lava- Rich in compressed and ultimately fused into a silica and has a relatively high melting point. They are highly viscous and single block with a folded mountain belt solidify quickly. They form high forming between them. volcanic structures with steep slope Example: Himalayas known as composite volcanoes. 017 5.2 Types of Lava: 5.4 Extrusive Landforms: 1. Acidic light coloured, highly viscous, flow slowly, steep-sided, lead to Hot magma from inside the Earth flows explosion throwing out pyroclasts or out (extrudes) onto the surface as bombs, forming spine or plug at craters lava or explodes violently into the 2. Basic-hottest, highly fluid, rich in iron atmosphere to fall back as pyroclastic. and magnesium, lack silica, dark colour, This is as opposed to intrusive rock highly fluid, flow quietly, forms thin formation, in which magma does not sheets and spread over large area reach the earth surface. forming shield or dome. 5.4.1 Types of Extrusive landforms: Volcanoes are also classified as Lava Plains and Basalt Plateaux fluid Intrusive and Extrusive landforms Snake basin, USA; Deccan; Iceland - Lava domes or shield volcanoes cones Mauna Loa and Kilauea. - volcanic Ash and cinder cones less fluid - crater and steep slope - - large small volcano in groups Mt. Nauvoo (Naples) and Mt. - Paricutin (Mexico) Lava tongues and lava dammed lakes bridges. - confined in valleys Lava Lava tunnels Volcanic dust fine particles. Dust and Ash - black snow Composite Cones are most commonly called as Stratocones with main conduit and subsidiary dykes and pipes. 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. Molten magma intrusion horizontally along the bed of sedimentary planes is called sills. Molten magma intrusion vertically along the walls of igneous rocks are called as dykes. 5.3 Types of igneous intrusions: Dome-shaped igneous mound with Laccolith a bulging upper surface. Lopolith Saucer-shaped igneous intrusion. Mt. Etna (Sicily, Italy) best example of parasitic cone. Phacolith Lens-shaped mass of igneous rock. Interesting composite volcano-Mt. Stromboli (Lighthouse of Huge mass of igneous rock that Mediterranean) Batholith forms large underground formations. 018 5.5 Distribution of Volcanoes: 6. Earthquakes Circum-Pacific ring of fire or Pacific ring of fire includes 2/3rd of world volcanoes. An earthquake is the shaking or Although there are a few active trembling of the earth's surface, volcanoes found along the Atlantic, caused by the sudden. movement of a Mediterranean costs part of the earth's crust resulting in release of energy that creates seismic waves. It occurs when the surplus accumulated stress in rocks in the earth's interior is relieved through the weak zones over the earth's surface in form of kinetic energy of wave motion causing vibrations (at times devastating) on the earth's surface. 6.1 Terms: Point within the Earth where Focus an earthquake originates. 5.6 Geyser and Hot Springs: Point on the Earth's surface Geyser - fountain of hot water and vertically above the focus; Epicentre superheated steam from earth beneath maximum damage is caused in which water is heated beyond boiling at the epicentre. point with explosion. World major geyser are concentrated in A line connecting all points on Iceland, Rotorua (N. Island, New Isoseismic the surface of the Earth where Zealand), Yellowstone National Park Line the intensity of an earthquake (USA) Old Faithful world's best-known geyser. is the same. Hot Springs or thermal springs water rises to the surface without any Igneous A geological structure with a explosion and consist of dissolved Mound dome-shaped upper surface. minerals. Ex: Hawaii and Japan. Wave Velocity 5 to 8 km per second through the outer part of the crust but travel faster with depth. Earthquake magnitude is measured by Richter scale, intensity is measured by Mercalli. 6.2 Causes: 1. Compressional or tensional stresses built up at the margins of the huge moving lithospheric plates. 2. Sudden release of stress along a fault, or fracture in the earth's crust. 3. Constant change in volume and density of rocks due to intense temperature and pressure in the earth's interior. 4. Human induced earthquake 019 6.3 Earthquake Waves: These waves are of high frequency Seismic waves are produced when some waves. form of energy stored in Earth’s crust is Travel at varying velocities suddenly released, due to slipping of land, (proportional to shear strength) these waves will travel in all directions. through the solid part of the Earth’s Earthquake waves are of two types — Body crust, mantle. waves and Surface waves. 6.3.B. Surface Waves: 1. L waves: Confined to the surface of the crust, Love waves produce entirely horizontal motion. They are much slower than body waves but are faster than Rayleigh. 2. Rayleigh waves: These waves follow an elliptical motion. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or Body waves are generated due to the an ocean. Because it rolls, it moves the release of energy at the focus and move in ground up and down and side-to-side all directions travelling through the body of in the same direction that the wave is the earth. Hence, the name body waves. moving. Most of the shaking felt from an Body waves interact with the surface rocks earthquake is due to the Rayleigh and generate new set of waves called wave. surface waves, these waves move along the surface and are also more destructive (Rayleigh) than body waves. 6.3.A. Body Waves: There are two types of body waves - 1. Primary waves or P waves (longitudinal) Also called as the longitudinal or compressional waves. Analogous to sound waves. Particles of the medium vibrate along the direction of propagation of the wave. P-waves move faster and are the first to arrive at the surface. These waves are of high frequency. They can travel in all mediums. Velocity of P waves in Solids > Liquids > Gases. Their velocity depends on shear strength or elasticity of the material. 2.. Secondary waves or S waves (transverse) (least destructive) Also called as transverse or distortional waves. Analogous to water ripples or light waves S-waves arrive at the surface with some time lag. A secondary wave cannot pass through liquids or gases. 020 6.4.1 Propagation of Earthquake Waves in 6.5 Distribution of Earthquakes: Earth’s Interiors: 6.5.1 Exogenic Movements: The velocity of waves changes as they Exogenic processes are a direct result travel through materials with different of stress induced in earth materials elasticity. due to various forces that come into The more elastic the material is the higher existence due to sun’s heat. is the velocity. Earth materials become subjected to Their direction also changes as they reflect molecular stresses caused due to or refract when coming across materials temperature changes. with different densities. Chemical processes normally lead to P-waves vibrate parallel to the direction of loosening of bonds between grains. the wave. Temperature and precipitation are the As a result, it creates density differences in two important climatic elements that the material leading to stretching and control various processes by inducing squeezing of the material. stress in earth materials. The direction of vibrations of S-waves is Geomorphic agent: An exogenic perpendicular to the wave direction in the element of nature (like water, ice, vertical plane. wind, etc.) capable of acquiring and Hence, they create troughs and crests in transporting earth materials can be the material through which they pass. called a geomorphic agent. Denudation- the process of wearing 6.4.3 Emergence of Shadow Zone: away the earth that causes general The seismic shadows are the effect of lowering and levelling out of the seismic waves striking the core-mantle surface. boundary. P and S waves radiate spherically away 6.5.2 Denudation Involves 4 Processes: from an earthquake's hypocenter (or 1. Weathering- gradual disintegration of focus) in all directions and return to the rocks by atmospheric or weather surface by many paths. forces. S waves, however, don't reappear beyond 2. Erosion – active wearing of earth an angular distance of ~103° (as they are surface by agents like water, wind, ice don’t pass through liquid material) and P etc. waves don't arrive between ~103° and 140° 3. Transportation- removal of eroded due to refraction at the mantle-core debris to new positions. boundary. 4. Deposition – dumping of debris in certain parts of earth. Warm wet climate promotes rapid chemical weathering while dry climate provide good conditions for physical weathering 6.5.2.A Chemical Weathering: Extremely slow and gradual decomposition of rocks due to exposure to air and water Regolith - mineral remains of decomposed rocks. When a soil cover on the rock exists, chemical weathering of the rock enhances because the soil absorbs rainwater and keeps the underlying rock in contact with this moisture. 021 6.5.2.A.i Types of Chemical weathering: 2. Repeated wetting and drying 1. Solution Stresses are naturally greatest near Many minerals are dissolved by water the surface and where there are sharp especially with rain water which contains angles in the rock, finally it leads to enough carbon dioxide to make it a weak peeling off of rock’s outer layer called acid. as exfoliation. Ex: in limestone region, rocks made of Exfoliation also takes place by calcium carbonate get dissolved in rain repeated wetting and drying of rocks water, widening joints resulting in surface as during wetting its outer crumbling of rocks. layer absorbs moisture and expand; 2. Oxidation when they dry this moisture Weathering by reaction of oxygen in evaporates and they quickly shrinks, presence of air and water with minerals finally leading to peeling of outer layer present in the rock. of the rock. Ex: rocks contain certain amount of iron, 3. Frost which in contact with air changes into iron At high altitudes and cold climates oxide leading to rust. where during day cracks and joints 3. Decomposition by Organic Acids inside rock fill with water and during Soils consist of certain bacteria which night they get frozen. With repeated thrive on the rock surface, they produce freeze / thaw cycles, rock breaks into acids when dissolved in water. pieces. Ex: Microorganisms, mosses or lichens. 4. Biotic factors 4. Carbonation Vegetation grows into crevices of rock Reaction of carbonate and bicarbonate cracks or in courtyards as plant grows with minerals which helps in breaking roots penetrate weaken the rock. down of feldspars and carbonate minerals. 5. Salt weathering 5. Hydration Salts in rocks expand due to thermal Chemical addition of water. Minerals action, hydration and crystallisation. absorb water and expand which causes an increase in volume of material itself or 6.6 Mass Movement: rock. Movement of weathered material down the slope due to gravitational 6.5.2.B Physical Weathering: forces. Also known as Mechanical Weathering, it is Movement can be slow or sudden, physical Disintegration of rocks depending on the slope gradient, weight of debris and lubricating moisture supplied by rainwater 6.5.2.B.i Types of physical weathering: 1. Temperature changes Mainly in dry desert areas, hot at day and cold by night, Leads to expansion and contraction of rock setting up stresses in the rock. Finally leading to its disintegration 022 6.6.1 Types of mass movements are, 6.8 Ground Water: A. Slow movement Hydrological cycle is process of 1. Soil creep circulation of water between land, sea Slow and gradual process continuous and atmosphere. movement of downhill slopes Ground water plays major role in Common in damp soils where water act as weathering and mass movement. lubricant 2. Soil Flow: 6.8.1 Volume of ground water depends on Soil is saturated with water and individual climate particles are suspended in water, they start Dry climate – precipitation is moving like a liquid. evaporated quickly and little moisture The gradual movement of wet soil or other percolate into ground. material down a slope, especially where Humid areas – most water runs off frozen subsoil acts as a barrier to the and sinks into ground percolation of water. Porous Rocks – sandstone – many B. Rapid movements pore spaces exists (water is absorbed 1. Earthflow: and stored) Movement of water saturated clayey or Permeable or pervious rocks - allow silty earth materials down low angle water to pass through them terraces. Flow of water that contains large Impermeable – Clay is highly porous amounts of suspended particles and silt. as made of many fine particles but 2. Mudflow: spaces are very small and particle Flow of water that contains large amounts cannot move. of suspended particles and silt. 6.8.2 Water Table: Water moves down by gravity and reach impermeable layer through which it cannot pass. If no outlet is there, water accumulates above impermeable rocks and saturates the rocks. Water store in the permeable rock is known as aquifer. Surface of saturated area is called water table. Water table is far below surface in hill tops but close to surface in valleys and flat lowlying areas causing water 6.7 Landslides (Slumping and Sliding): logging. Occur on steep slopes, slope undercut by river or sea or by lubricating action of rain water. Slumping is permeable layer overlie over impermeable clay, which acts as a slippery surface. 023 6.8.3 Springs: 7. Landforms A spring is a point at which water flows from an aquifer to the Earth's surface. It is a component of the hydrosphere. Minerals become dissolved in the water as 7.1 Landforms Created by Running it moves through the underground rocks. Water: This is why spring water is often bottled and sold as mineral water. 7.1.1 Course of a river 6.8.4 Wells: Hole is bored until it reaches water table of Course of permanent depth with continuous flow of Description Features River water - Gorges and Canyons: Deep clefts between escarpments or cliffs resulting from Predominant weathering and action in erosion. vertical - River Capture: corrosion. Natural diversion of Gorges and one stream's canyons are headwaters into Young formed another channel. Stage during this Aquifer is saturated to the brim of the - Rapids, Cataracts, stage due to basin. and Waterfalls: weathering Water is trapped in the aquifer under Strong currents, and the pressure and when well is bored, pressure obstacles, and of water downwards forces the water up erosive steps in the the bore hole to gush as fountain. activity of the streambed, with After sometime pressure decreases and river. waterfalls pumping is not required. This water is unsuitable for agriculture as it representing is hot and contains lots of mineral salts. vertical drops. Both are sites of vigorous erosion. The river starts - Meanders: meandering Winding curves or as it moves bends in a river. Middle or through its - River Cliffs and Valley valley. The Slip-off Slopes: Course erosion is Formed due to less vertical lateral erosion and and more deposition. lateral. 024  Course of Description Features Feature Description River - Flood Plains: River terraces occurring at Low-lying ground Paired Terraces the same elevation on adjacent to a river, either side of the river. The river prone to flooding. reaches its - Ox-bow Lakes: mature U-shaped lakes Unpaired River terraces occurring at Lower or stage, formed when a wide Terraces different elevations. Plain depositing meander is cut off. Course sediments - Delta: A triangular and forming tract of sediment broad deposited at the floodplains. river's mouth, where it diverges into several outlets. 7.1.3 Depositional landforms of running water: Feature Description Formed when streams flowing 7.1.2 Erosional land forms of running water: from higher levels break into foot slope plains of low Alluvial Fans gradient. The load is dumped Feature Description as a broad low to high cone-shaped deposit called an Circular depressions on alluvial fan. rocky beds of hills formed Potholes due to steam erosion aided by abrasion of rock fragments. Large and deep holes at the Plunge Pools base of waterfalls. Low, linear, and parallel ridges Natural of coarse deposits along the Result from vertical erosion Levees banks of rivers. River Terraces by the stream into its own depositional floodplain. 025  7.2.2 Landforms of Glaciations: Feature Description Sediments deposited in a linear fashion by flowing waters along Feature Description Point Bars the bank, found on the convex side of meanders of large rivers. A depression where Corrie, Cirque Thread-like streams of snow accumulates. water that rejoin and Knife-edged ridges Braided Channels subdivide repeatedly, Aretes and formed when two creating a braided Pyramidal Peaks corries cut back on pattern. each other. A deep vertical crack that opens up at the Bergschrund head of a glacier when snow begins to leave the corrie. A U-shaped valley characterized by high, steep sides and a rounded or flat valley bottom, often found in 7.2 Landforms of glaciations: U-shaped Glacial areas with high 7.2.1 Glaciers: Trough mountains. Examples A glacier is a large, perennial include Zezere Valley accumulation of crystalline ice, snow, rock, (Portugal), Leh Valley sediment, and often liquid water that (India), and Nant originates on land and moves down slope Francon Valley under the influence of its own weight and (Wales). gravity. Only two major ice caps are present today Antarctica and Greenland U-shaped valleys that At the foot of the mountain glacier, several are elevated above glaciers may converge to form an extensive ice-mass called piedmont their main valleys, glacier with a steep wall at the point where the Hanging Valleys two valleys meet, often forming waterfalls. These valleys are typically found in high-altitude, mountainous regions. 026  Feature Description Elongated, teardrop-shaped hills Formed from debris Drumlins of rock, sand, and carried by a glacier. gravel formed under Lateral moraines form moving glacier ice. at the sides of the ice Long, winding ridges Moraines flow, and terminal Eskers of stratified sand and moraines form at the gravel. foot, marking the Plains formed of maximum advance of glacial sediments the glacier. deposited by Outwash Plains meltwater outwash at the t