Earth movements
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Earth movements Earth movements Document Transcript

    • EARTH MOVEMENTS:The earth turns around itself once a day. The earth turns around the sun once a year. There are four different methods to describe a year. The earth 'wobbles' around his own axis. This is called precession. The angle of the earth axis varies with the plane of the sun and the planets. also, see below The earth wobbles its tail. This is called 'Precession of the equinoxes' This means that the eath axis makes a rotation. According to most 'alternative archeology' sites this movement takes 25920 years. According to NASA it takes 'about 26000 years'.
    Endogenetic forces:<br />The forces coming from within the earth are called as endogenetic forces which cause two types of movements in the earth, <br /> (i) Horizontal movements, and <br />(ii) Vertical movements.<br /> These movements motored by the endogenetic forces introduce various types of vertical irregularities which give birth to numerous varieties of relief features on the earth's surface, eg., mountains, plateaus, plains, lakes, faults, folds, etc. The origin of endogenetic forces is related to thermal conditions of the interior of earth. The endogenetic forces and related horizontal and vertical movements are caused due to contraction and expansion of rocks' because of varying thermal conditions and temperature changes inside the earth. The endogenetic forces and movements are divided, on the basis of intensity, into two major categories:<br />(i)Sudden forces(ii)Diastrophic forces<br />
    • Sudden forces are the result of long period preparation deep within the earth. Their cumulative effects on the earth's surface are quick and sudden. Geologically, these sudden forces are termed as 'constructive forces' because these create certain relief features on the earth's surface.
    • Diastrophic forces include both vertical and horizontal movements which are caused due to forces deep within the earth. These diastrophic forces operate very slowly and their effects become discernable after thousands and millions of years. These forces also termed as constructive forces, affect larger areas of the globe and Produce meso-level reliefs, for example, mountains, plateau, plains, lakes, big faults, etc. These diastrophic forces are further subdivided into two groups, namely,
    • (A)epeirogenetic movements and
    • (B)orogenetic movements.
     <br />(A)Epeirogenetic movements: <br /> Epeirogenetic word consists of two words, viz: 'epiros' (meaning thereby con-tinent) and 'genesis' (meaning thereby original). Epeirogenetic movement causes upliftment and subsidence of continental masses through upward movements are, vertical movements. These forces and resultant movements affect larger parts of the continents. These are further divided into two types: upward movement and downward movement. <br /> <br />(B) Orogenetic movement: <br /> The word orogenetic has been derived from two Greek words, 'pros' (meaning thereby mountain) and 'genesis' (meaning thereby origin or formation). Orogenetic movement is caused due to endogenetic forces working in horizontal movements. Horizontal forces and movements are also called as tangential forces. Orogenetic or horizontal forces work in two ways, namely, (i) in opposite direction, and (ii) towards each other. This is called 'tensional force' when it operates in opposite directions. Such type of force and movement are also called as divergent forces. Thus, tensional forces create rupture, cracks, fracture and faults in the crustal parts of the earth. The-force when operates face to face, is called compression force or convergent force. Compressional force causes crustal bending leading to the formation of fields or crustal warping leading to local rise or subsidence of crustal parts. Crustal bending: When horizontal forces work face to face, the crustal rocks are bent due to resistant compressional and tangential forces. It is in two ways: (i) warping, and (ii) folding. The process of crustal warping affects larger areas of the crust wherein the crustal parts are either warped (raise),upward or downward. The upward rise of the crustal part due to compressive force resulting from convergent horizontal movement is called upwarping. While the bending of the crustal part downward in the form of a basin or depression is called down warping.<br /> <br />FOLDS:<br /> Folds are wave-like bends formed due to tangential compressive forces resulting from horizontal movement caused by the endogenetic force originating deep within the earth. The two sides of a fold are called limbs of the fold. The limb which is shared companion syncline is called middle limb. The plane which Dissects the angle between the two limbs or middle limb of the syncline is called the axis of fold or axial plane. On the basis of anticline and syncline, these axial planes are called as axis of anticline and axis of syncline respectively. The inclination of rock beds with respect to horizontal plane is termed as 'dip', the angle of dip is measured with an instrument called clinometers. The strike of an inclined bed is the direction of any horizontal line along a bedding plane. The direction of dip is always at right angle to the strike.<br />Anticlines:The unfolded rock beds are called anticlines. Synclines:Downfold rock beds due to compressive forces caused by horizontal tangential forces <br />are called synclines. Anticlinorium:It refers to those folded structures in the regions of folded mountains where there are a series of minor anticlines and synclines within one extensive anticline. <br />Synclinorium:It represents such a folded structure which includes an extensive syncline having numerous minor anticlines and synclines. <br />Monoclinal folds:These are those in which one limb inclines moderately with regular slope while the other limb inclines steeply at right angle and the slope is almost vertical. <br />Isoclinal folds:When the compressive forces are so strong that both the limbs of the fold become parallel but not horizontal.<br />Recumbent folds:These are formed when the compressive forces are so strong that both the limbs of the fold become parallel as well as horizontal. <br />Overturned folds:These are those folds in which one limb of the fold is thrust upon another fold due to intense compressive forces. Limbs are seldom horizontal. <br />Plunge folds: <br /> These are found when the axis of the fold, instead of being parallel to the horizontal plane, becomes tilted and forms plunge angle which is the angle between the axis and the horizontal plane. <br />Fan folds:<br /> These with anticlinorium or obtuse angle.<br />Open folds: <br /> These are those in which' the angle between the two limbs of the fold is more than 90 degree but less than 180 degree<br />Closed folds: <br /> These are those folds in which the angle between the two limbs of a fold is acute angle. Such folds are formed because of intense compressive force. <br />EARTHQUAKES:<br /> <br /> The earthquakes in India are due to the drifting -called Indian Plate. Scientists divide the globe into a number of major tectonic plates that drift very slowly. As these plates slide against each other a tremendous amount of energy is released causing heavy destruction.<br /> There was a time – some 225 million years ago-when the continents were not separated by oceans. The earth’s surface knew only one massive continent, called Panagea. The some 200 million years ago, Pan agea split into two major continents, one of them Gondwana-land (which contains Africa, South America, India and Australia). Gondwanaland continued to split into smaller land masses, one of them is the Indian Plate. It drifted at a speed of 9 m per century towards the Eurasian plate. <br />Where these giant plates met under enormous pressure, the Himalayans were formed.<br />TYPES:<br />Natural Earthquakes caused by endogenic forces.<br /> (i) Volcanic -caused due to volcanic eruptions, e.g., Mt Etna.<br /> (ii) Tectonic -caused due to stress and strain along Earth’s plates or dislodging of rocks during faulting. <br />(iii) Isostatic -caused by isostatic imbalance due to sudden geological activity at a regional scale. (iv) Plutonic –earthquakes originating deep inside the earth between 250 to 650 km deep.<br /> There are many fault -lines in the Earth’s crust. A fault is where blocks of curst on either side are moving relative to one another. The typical average rate is around a millimeter per year. <br /> The strongest seismic waves are generated at the initial break -point. The closer to the break-point, the greater the energy and the greater the potential for destruction, if the break -point is called the earthquake focus, and the point on the surface directly above it is referred to as the epicenter. Slip further along the fault and readjustments close to the focus usually cause a series of smaller aftershocks, which continue for days (even years in extreme cases) after the initial earthquake. Such kinds of energy release are called waves because of the way they move. Most of the damage caused by an earthquake is not done by the P - waves and S-waves. These waves travel through the body of the Earth, and their energy is spread over a rapidly increasing volume as they propagate. It is other waves of the sort that travel along the surface of the ground that do most of the harm. These include up -and-down waves and strong side -to-side shaking waves. The P-and S-body waves travel faster than the surface waves warning of the arrival of the more damaging surface waves.<br />Seismic Scale<br /> The Richter scale is a logarithmic scale, devised in 1935 by geophysicist Charles Richter, for representing the energy released by earthquakes. More relevant as a measure of earthquake strength is the intensity, for which the modified Mercalli scale is used.<br />Volcanoes<br /> A volcano is a mountain or hill with an opening on top known as a crater. Hot melted rock (magma), gases, ash, and other material from iniside the Earth mix together a few kilometers underground, rising up through cracks and weak spots in the mountain. Every once in a while, the mixture may blast out, or erupt, through the crater. The magma is called lava when it reaches the air. Lava may be as hot as 1000 degree Centigrade. Gradually the lava cools and solidifies on the earth surface making new landforms. In some eruptions, huge fiery clouds rise over the mountain, and glowing rivers of lava flow down its sides. In other eruptions, red -hot ash and cinders shoot out from the mountain top, and large chunks of hot rock are blasted high into the air. A few eruptions are so violent eruptions occur on volcanic islands. Such islands are the tops of volcanic mountains that have been built up from the ocean floor by repeated eruptions. Other eruptions occur along narrow cracks in the ocean floor. In such eruptions, lava flows away from the cracks, building up the sea bottom.<br />Types of Volcanoes<br /> (i)Active-that which is alive now. e.g. Etna, Stromboli, Pinatubo, etc. <br />(ii)Dormant that which has not erupted for quite some time. e.g. Vesuvius,<br /> Barren Islands. <br />(iii)Extinct - which has not erupted for several centuries/millennia or may not occur in near future too.<br />MODE OF ERUPTION:<br />(i)Central/Explosive-e.g. Hawaiian type, Vesuvius type, Pelean type, etc.<br />(ii)Fissure/Quite eruption: in which lava flow or flood, mud flow and fumaroles.<br />PLATE TECTONICS<br /> Plate Tectonics, it is the continents that are in motion, but the oceans as well. This is so, because the top crust of the Earth is not a complete single shell of granite and basalt, but a mosaic of several rigid segments, called plates.<br /> The theory of plate tectonics explains how the Earth’s crust is moving in vast, rigid sections (plates) and is a modern revolution in our understanding of the planet. These plates include not only the Earth’s solid upper crust, but also parts of the denser mantle below called Asthenosphere, and carry the continents and oceans on their backs like mammoth rafts.<br />The plates with an average thickness of 100 km float on the Asthenosphere and move continuously against one another at a rate of upto 20cm a year. Continents form only a part of the plates, the surrounding oceans form the rest of the plates. It is the plates containing both continents and oceans that move. The relation of inter -plate movement is defined by the type of plate margin: Constructive, Destructive or Conservative plate movement.<br /> <br />Divergent Plate Boundaries :The mid-ocean ridges are one of the three basic types of plate boundaries. We call them divergent plate boundaries because the plate material on either side of the margin is spreading apart. The spreading is a result of forces pulling the oceanic lithosphere on either side of the ridge in opposite directions. The forces are produced by mantle convection and gravity.<br />As the plates are pulled apart, magma is extracted from the mantle to fill in the void. The magma cools and records the magnetic field characteristics. The process is slow but relentless <br />The oceanic crust is shown with "magnetic stripes" indicating the polarity of Earth's magnetic field at the time that part of the ocean formed. The region where oceanic.<br />lithosphere is manufactured is topographically high because of the high temperatures associated with the thin lithosphere. The thermal expansion of the material beneath the ridge maintains the high elevation and produces a gravitational force that helps slide the two plates apart (this force is called ridge push).<br />The ridges are regions of earthquake activity. As you should expect, the pulling apart of the two plates is expressed by normal faulting events, which are usually very shall, less than 15<br />kilometers deep because the high temperature beneath the ridge causes the rocks to deform more easily beneath that depth (and hence you can't store the strain energy to produce an earthquake).<br />If you study the map of ocean age, you will notice that there are places where the regions of different age ocean are juxtaposed and segments of the ridge are offset. The offsets occur on transform faults, which form the second type of plate boundary.<br />Conservative (Transform) Plate Boundaries<br />Transform margins are conservative in the sense that along these margins material is translated, not created or destroyed. Faulting along transform margins is strike-slip. The sense of motion along transform margins joining two divergent margins can be tricky. Even though the ridge segments are offset in a left-lateral sense, because of spreading, the direction of motion across the fault is right-lateral.<br /> The San Andreas fault system in California is well-studied example of a transform plate margin and forms the boundary between the Pacific and North American plates. As the system evolved, part of coastal California has been "captured" by the Pacific plate and as a result the Los Angeles region (which is on the Pacific plate) is moving towards the San Francisco region (which is on the North American plate) at about four centimeters per year.<br />Convergent Plate Boundaries<br />The oldest ocean floor is about 220 Ma, much younger than much of the continents. We know that the oceans have been around much longer than 200 Ma so the implication is that the entire sea floor is recycled in a few hundred million years. Now if the ocean floor is growing in some places, but the overall surface are of the planet is constant, somewhere ocean floor must be destroyed.<br />The places where the destruction takes place are called convergent plate boundaries, or subduction zones. Convergent margins are the boundaries formed when two plates collide and there are three possibilities depending on whether continental or oceanic lithosphere is involved in the process. The cartoon below depicts the collision of oceanic continental lithosphere.<br /> The oceanic material is forced down into the mantle because it is more dense than the continent. In fact, the reason the continents are so much older than the ocean floor is that the continental crust is composed of material too light to sink into the mantle. The subduction of oceanic lithosphere explains the locations of deep earthquakes and many volcanoes. The earthquakes are located in the down going slab of oceanic lithosphere, which remains cool enough to store enough strain to allow brittle failure in the rocks at such great depths<br />.<br />The largest earthquakes occur in these regions of plate convergence, and are usually low-angle reverse or thrust events located near the surface. We classify earthquakes that are shallower than 70 km as "shallow" those between 71 and 300 km are called "intermediate" depth, and those deeper than that, are called "deep". The deepest earthquakes extend to about 700 km depth.<br />Alfred Wegener – proposed that in the distant past, the Earth’s continents were all joined as a single landmass.<br />
    • South America and Africa would fit remarkably well, shoreline to shoreline.
    • If the Americas were moved next to Africa and Europe, there would be a match of ancient continental rocks and tectonic (fold and fault) structures.Pangaea – when Wegener placed all the continents togetherlike a puzzle, it formed a large landmass which he called Pangaea
    Fossil Clues:<br />
    • Fossils of similar plants and animals have been found on continents that are now very far apart, but were perhaps once joined together.
    Climate clues:<br />
    • Evidence of glaciers can be found on land that is now tropical, because that land was once located in a colder region of our planet.
    Rock Clues:<br />
    • Similar rock structures can be found on continents that are now far apart, again suggesting that they could have once been joined. Rocks found in the eastern US are similar to those found in western Europe.
    THE EARTH’S LOOK IN THE PAST:<br />EARTH MOVEMENTS AROUND THE SUN: The planets revolve around the sun in ellipses, with the sun at one focus of their ellipse. For Earth this ellipse is a circle - earth's distance from the sun varies by less than 2%. According to Kepler's second law of planetary motion, the line from the sun to the earth sweeps out equal areas in equal times. This means that if area A is equal to area B; then tA = tB ( see figure on the right).Since the distance covered during tA is longer than the distance covered during tB, it follows that Earth must move faster during tA than during tB.Therefore when the earth is closer to the sun it travels faster and if it is further away from the sun it travels slower. Earth is closest to the sun in January - about 147.5 million km and furthest from the sun in June at about 152.6 million km.<br />REFERENCES:<br />.American Geophysical Union (AGU) <br />For over 75 years, American Geophysical Union (AGU) researchers, teachers, and science administrators have dedicated themselves to advancing the understanding of the Earth and its environment in space and making the results available to the public.<br />Ask a Geologist (USGS) <br />Have a geological question? Here is your chance to ask it.<br />Dynamic Earth Tutorial (USGS) <br />An excellent online, interactive plate tectonics tutorial from the United States Geological Survey.<br />Global Earth History <br />The Global Earth history site uses a series of plate-tectonic reconstructions to show the broad patterns of Phanerozoic Earth history. <br /> <br />SUBMITTED TO,<br />Prof.B.V.Suresh<br />DOS in Earth Science<br /> <br />SUBMITTED BY,<br />Divyashree.S<br />2nd year M.Sc.3rd semester<br />Dos in Food Science and Nutrition <br />