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Plate Tectonics

Plate Tectonics. Paul Blackburn 11-16-12 Turner 1 st Period. Wegner’s theory of Continental Drift & the Supercontinent Theory. Continental Drift Wegner’s theory-the continents were slowly drifting around the Earth. Evidence- the glacier till deposits indicate erratic glacier motion.

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Plate Tectonics

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  1. Plate Tectonics Paul Blackburn 11-16-12 Turner 1st Period

  2. Wegner’s theory of Continental Drift & the Supercontinent Theory • Continental Drift • Wegner’s theory-the continents were slowly drifting around the Earth. • Evidence- the glacier till deposits indicate erratic glacier motion. • Problems with theory- the lack of mechanism. • Supercontinent Theory • Supercontinent Cycle- a geological cycle where the Earth’s continents alternatively merge into a single supercontinent. • Pangaea was a supercontinent consisting of all seven modern continents. Panthalassa was the humongous ocean that surrounded the landmass. • Accretion- the increase in size of a tectonic plate. • Rifting- the process in which continental crust is extended and thinned. • Plate movements can move glaciers over land causing changes in temperature. Also, movement can cause volcanoes making evolution more difficult.

  3. Theory of Plate Tectonics • Theory of Plate Tectonics • Lithosphere- the rigid outermost shell of Earth. • Asthenosphere- the highly vicious, mechanically weak region of the upper mantle of Earth. • Plates move because of the intense heat in the core causes molten rock to move in the convection cell. • The three types of plate boundaries are divergent, convergent and transform. • Isostasy- ideal theoretical balance of all large portions of Earth’s lithosphere. • Isostatic adjustments- the phenomenon of how the earth readjusts to a stable shape after its loading by ice sheets. • Stress- the force put on plates when they collide or slide past each other.

  4. Divergent Boundary • Sea-floor Spreading • Landforms- Mid-Atlantic Ridge and Southwest Indian Ridge • Paleomagnetism • Magnetic reversals- the process by which the North pole is transformed into a South pole and the South pole becomes a North pole. • Magnetic Symmetry- when the magnetic poles are symmetrical. • Normal Faults • Landforms- Teton Fault

  5. Convergent Boundary • Subduction Zones • When an oceanic plate pushes into and subducts under a continental plate, the overriding continental plate is lifted up and a mountain range is created. • Landforms- Andes Mtns. • When two oceanic plates converge one is usually subducted under the other and in the process a deep oceanic trench is formed. • Landforms- Ring of Fire • Collision Zones • When two continents meet head-on, neither is subducted because the continental rocks are relatively light and, like two colliding icebergs, resist downward motion. • Compression and Uplift-The degree to which a substance has decreased in size after being or while being subject to stress. • Landforms- Colorado Plateau

  6. Volcanoes • Magma- molten material beneath or within the earth’s crust. • Three conditions under which magma forms: • A decrease in pressure at mid-ocean ridges. • An increase in pressure at a hot spot. • The increase in the amount of water in the asthenosphere. • Lava- hot molten rock erupted from a volcano. • Volcano- an opening in earths crust through which molten lava, ash, and gases are ejected. • Common locations for volcanoes include Hawaii, Japan, and Yellowstone National Park. • The major zone of active volcanoes encircling the Pacific Ocean is called the Pacific Ring of Fire.

  7. Volcanoes (continued) • Pyroclastic material- a cloud of ash, lava fragments carried through the air, and vapor. • Viscosity- a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress • The build up of explosive materials such as gases and volcanic ash and rock will create explosive volcanos. These items build up until they pop like a balloon.

  8. Types of Vocanoes- There are four types of volcanos: Shield, Cinder Cones, Composite, Caldera. • Shield- Large base, gentle sloping sides. Quite eruptions • Cinder Cones- Steep slopes, but not very tall. Explosive eruptions. • Composite- Large, mountainous, steep slopes. Explosive eruptions. • Caldera- Magma chamber collapses creating a basin. May fill with water creating crater lakes.

  9. Belknap Shield Volcano Kilauea Cinder Cone Volcano Mount Fuji (Composite Volcano) Mount Okmok (Caldera)

  10. Transform Boundary • Reverse faults- a geologic fault in which the hanging wall has moved upward relative to the footwall. • Strike-slip faults- a fault in which surfaces on opposite sides of the fault plane have moved horizontally and parallel to the strike of the fault. • Tension- the act or process of stretching something tight. • Sheer stress- a form of stress that subjects an object to which force is applied to skew, tending to cause shear strain. • Landforms- San Andreas Fault

  11. Earthquakes • Elastic rebound- a theory of earthquakes that envisages gradual deformation of the fault zone without fault slippage until friction is overcome, when the fault suddenly slips to produce the earthquake. • Seismology- the scientific study of earthquakes and elastic waves. • Seismograph- an instrument used to detect and record earthquakes. • Focus- the point within the earth where an earthquake rupture starts. • Epicenter- the point on earth’s surface vertically above the focus.

  12. Seismic Waves • Body waves- seismic wave that moves through the interior of the earth, as opposed to surface waves that travel near the earth's surface. P and S waves are body waves. Each type of wave shakes the ground in different ways.

  13. Seismic Waves (continued) • P waves- a seismic body wave that shakes the ground back and forth in the same direction and the opposite direction as the direction the wave is moving. Also called compressional wave.

  14. Seismic Waves (continued) • S waves- a seismic body wave that shakes the ground back and forth perpendicular to the direction the wave is moving. Also called a shear wave.

  15. Seismic Waves (continued) • Surface waves- a seismic wave that is trapped near the surface of the earth. • Seismic waves can determine earth’s interior in two different ways. First, seismic waves have their direction of motion changed (refracted) by variations in the interior density. Thus, by studying the way such waves propagate in the Earth we can learn something about density variations. Second, the fact that P-waves propagate in liquids but S-waves do not allows us to determine if portions of the interior are liquid.

  16. Earthquakes • Magnitude- the intensity of an earthquake represented by a number on an arbitrary scale. • Intensity- a measure of the size of an earthquake based on observation of the effects of the shock at the earth's surface. Specified on the Mercalliscale. • Intensity- a seismic scale used for measuring the intensity of an earthquake. • Tsunami- A long high sea wave caused by an earthquake or other disturbance. (Ex: Indian Ocean 2004)

  17. Other Related Landforms • Dome Mountains- Black Dome Mountain Castle Dome Mountains • Hot Spots-

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