PLATE MOVEMENT

1. PLATE MOVEMENT PLATE TECTONICS AND CONTINENTIAL DRIFT

2. Continental Drift When the early explorers began to discover the shapes of the continents, mapmakers noticed how well the shapes of North and South America fit together with Europe and Africa. Later on, geologists discovered fossils of species of land-based plants and animals on continents separated by large oceans.

3. Continental Drift Fossils of plants and animals on widely separated land masses led Alfred Wegener to hypothesize that the continents had once been joined.

4. Continental Drift In 1912, Alfred Wegener proposed a hypothesis of continental drift to explain these puzzling observations. Wegener called the ancient supercontinent Pangaea.

5. Continental Drift Continental drift explains why the continents seem to fit together. It also explains why the fossils from a single region appear across the globe. Wegener was unable to explain how the continents could plow through the solid rock of the sea floor or what force could move entire continents. As a result, most geologists rejected continental drift.

6. Continental Drift The continents move slowly across Earth's surface over time.

7. Sea-floor Spreading Sea-floor spreading is the process by which new oceanic crust is created at mid-ocean ridges as older crust moves away. As sea-floor spreading occurs, old oceanic plates sink into the mantle in the process of subduction.

8. Sea-floor Spreading The Mid-Ocean Ridge When scientists mapped the ocean floor, they found a chain of underwater mountains which they called the mid-ocean ridge. It forms the world’s longest mountain chain.

9. Sea-floor Spreading Formation of Oceanic Crust Sea-floor spreadingis the process by which new oceanic crust is created at mid-ocean ridges as older crust moves away. • The mid-ocean ridge is a huge crack where magma pushes upward. • The parts of the ocean floor on both sides of the central valley are moving apart. • Magma from the mantle wells up and solidifies to form new oceanic crust.

10. Mid-ocean ridge Volcano Trench Oceanic crust Continental crust Oceanic lithosphere Asthenosphere Continental lithosphere Sediment Magma Asthenosphere Sea-floor Spreading During sea-floor spreading, oceanic crust forms at the mid-ocean ridge. This crust gradually moves toward a subduction zone, where old crust sinks beneath a trench.

11. Sea-floor Spreading Subduction of Oceanic Plates As sea-floor spreading occurs, old oceanic plates sink into the mantle in the process of subduction. Subduction zones are near the edges of oceanic plates. As a plate sinks through a subduction zone, it bends, forming a depression in the ocean floor called a trench.

12. Sea-floor Spreading Subduction occurs because, as an oceanic plate moves away from the mid-ocean ridge, it gradually cools and becomes more dense. During subduction, the force of gravity slowly pulls the dense edges of oceanic plates into the mantle, destroying old ocean floor. Sea-floor spreading and subduction together act like a giant conveyor belt. https://igppweb.ucsd.edu/~gabi/sio15/supps/slab-ridge.gif

13. The Theory of Plate Tectonics Convection currents form in the mantle as hot rock rises, cools and spreads out, and then sinks back into the mantle at subduction zones. These sinking slabs of dense lithosphere and heat from within Earth drive the circulation of convection currents in the mantle.

14. Convection currents Lithosphere Outercore Innercore Mantle The Theory of Plate Tectonics Heat flows from Earth’s hot interior toward the cooler surface mainly through large convection currents in the mantle. Plates are the uppermost part of a global convection system.

15. The Theory of Plate Tectonics The heat that drives convection in the mantle comes from two sources. • Earth was very hot when it first formed, and some of the heat moving upward in convection currents is due to the gradual cooling of its interior. • A second source of heat is the result of the decay of radioactive isotopes that are distributed throughout the mantle and crust.

16. Plate Boundaries There are about a dozen major tectonic plates. Most major plates contain both continental and oceanic crust. The edges of plates meet at plate boundaries. As the plates move apart, collide, or slide past each other, they cause changes in Earth’s surface.

17. Plate Boundaries The lithosphere is broken into about a dozen large plates, which move slowly over Earth’s surface.

18. Divergent Boundary Convergent Boundary Transform Boundary Lithosphere Asthenosphere Lithosphere Plate Boundaries Plates meet at three types of boundaries: divergent boundaries, convergent boundaries, and transform boundaries.

19. Mountain Building Some mountains form when two plates with continental crust at their edges collide along a convergent boundary. • Neither plate is subducted during such collisions. • The crust buckles, folds, and thickens, pushing up tall mountains.

20. Mountain Building Mountains can also form along diverging plate boundaries. • The mid-ocean ridge system forms one long chain of mountains on the ocean floor. • In places, the mountains of the mid-ocean ridge rise above sea level. One example is the island of Iceland in the North Atlantic Ocean.

21. Mountain Building The Andes, which extend along the western side of the South American plate, have risen as a result of a collision between that plate and the Nazca Plate

22. The tsunami triggered by the 2004 Sumatra earthquake caused extensive damage to coastal areas in Southeast Asia.

23. An earthquakeis a movement of Earth’s lithosphere that occurs when rocks in the lithosphere suddenly shift, releasing stored energy. The energy released during an earthquake is carried by vibrations called seismic waves.

24. As a result of the earthquake, nearly 200,000 people died in Asia and Africa. Many people were killed or injured when coastal areas were hit by a tsunami. • A tsunami is a large sea wave generated by an underwater earthquake, volcano, or landslide. • When the 2004 Sumatra earthquake ruptured the sea floor, it pushed up a large volume of water, resulting in a tsunami.

25. Stress in Earth’s Crust Earthquakes happen because of the ways that plate movements affect the lithosphere. The forces of plate movement cause deformation, or changes in the shape or volume of a mass of rock.

26. Stress in Earth’s Crust This portion of the San Andreas fault runs through the Carrizo Plain in south-central California. A fault is a break in a mass of rock along which movement occurs. • The two slabs of rock on either side of a fault move in relation to each other. • Many faults occur along plate boundaries.

27. Stress in Earth’s Crust Stress can squeeze rock together, producing folds in layers of rock. A fold is a bend in layers of rock. • Folds form where rocks are squeezed together but do not break. • Rocks tend to fold rather than break when they are under high temperature or pressure.

28. Earthquakes and Seismic Waves The buildup of stress along a fault provides the energy that powers an earthquake. • The location beneath Earth’s surface where an earthquake begins is called the focus, also known as the hypocenter. • The location on Earth’s surface directly above the focus is called the epicenter. • Seismic waves move out in all directions from the focus.

29. Fault Epicenter Seismic waves Focus Earthquakes and Seismic Waves When an earthquake occurs on a fault, seismic waves move out from the focus. The epicenter lies on the surface, directly above the focus.

30. Earthquakes and Seismic Waves The Physics of Earthquakes Within Earth’s crust, forces cause the two sides of a fault to move past each other. Sometimes the rocks along the two sides of a fault may snag and remain locked because of friction between the two fault surfaces. Tremendous stress builds up in these areas.

31. Earthquakes and Seismic Waves When rocks are strained beyond their limit, they break and grind past each other, releasing huge amounts of energy in the form of an earthquake. As the rocks break and move, potential energy is transformed into kinetic energy in the form of seismic waves.

32. Earthquakes and Seismic Waves Types of Seismic Waves Earthquakes produce three main types of seismic waves: P waves, S waves, and surface waves. https://i.pinimg.com/originals/a0/4d/89/a04d894db011e06f8611fee2ea7cffb0.jpg

33. Earthquakes and Seismic Waves P waves are longitudinal waves similar to sound waves. • As longitudinal waves move through a material, particles vibrate in the direction of the waves’ motion. • P waves compress and expand the ground like an accordion. • P waves are the fastest seismic waves. • P waves can travel through both solids and liquids. https://i.pinimg.com/originals/a0/4d/89/a04d894db011e06f8611fee2ea7cffb0.jpg

34. Earthquakes and Seismic Waves S waves are transverse waves, like light and other electromagnetic radiation. • S waves cause particles to vibrate at right angles to the direction the waves move. • Unlike P waves, S waves cannot travel through liquids. https://i.pinimg.com/originals/a0/4d/89/a04d894db011e06f8611fee2ea7cffb0.jpg

35. P wave S wave Compression Expansion Direction of wave Direction of wave Particle motion Particle motion Earthquakes and Seismic Waves P waves are longitudinal waves. S waves are transverse waves.

36. Earthquakes and Seismic Waves Surface waves are waves that develop when seismic waves reach Earth’s surface. • Surface waves move more slowly than P waves and S waves. • They usually produce larger ground movements and greater damage. • Some surface waves are transverse waves, and others have a rolling motion at Earth’s surface that is similar to ocean waves. https://www.kullabs.com/uploads/SeisWaveAnim.gif https://i.pinimg.com/originals/a0/4d/89/a04d894db011e06f8611fee2ea7cffb0.jpg

37. Earthquakes and Seismic Waves https://i.pinimg.com/originals/a0/4d/89/a04d894db011e06f8611fee2ea7cffb0.jpg

38. Seismographic Data Scientists have mapped Earth’s interior, analyzing how seismic waves move through its layers. • Wave speeds and paths are affected by the temperature, composition, and density of the rocks they pass through. • Seismic waves interacting with boundaries between different kinds of rock are reflected, refracted, or diffracted.

39. Seismographic Data Geologists infer that Earth’s outer core is liquid because S waves cannot pass through it. They can also tell that the core is mostly iron because P waves travel through it at a speed that matches laboratory experiments on iron.

40. Seismographic Data Earth’s liquid outer core blocks S waves and bends P waves. The result is a shadow zone on the surface where no direct seismic waves from an earthquake are detected.

41. When Mount St. Helens erupted, trapped gases caused the north side of the mountain to explode. Volcanic ash was ejected high into the atmosphere.

42. https://image.slidesharecdn.com/volcanoespowerpoint-130311134209-phpapp01/95/volcanoes-powerpoint-3-638.jpg?cb=1363009363https://image.slidesharecdn.com/volcanoespowerpoint-130311134209-phpapp01/95/volcanoes-powerpoint-3-638.jpg?cb=1363009363

43. A volcanois a mountain that forms when magma reaches the surface. Volcanoes can result from several different geological processes and can take a variety of forms. The process that leads to a volcanic eruption begins deep inside Earth. Magma rises because it is less dense than the solid rock around and above it.

44. Formation of a Volcano How a Volcano Erupts • Magma is under pressure and contains dissolved gases, including carbon dioxide and water vapor. • Lower pressure near the surface allows the gases in magma to expand rapidly. • An eruption occurs when the gases bubble out through a crack in the crust, propelling magma to the surface.

45. Formation of a Volcano Structure of a Volcano • Before an eruption, magma often collects in a pocket called a magma chamber. • Magma slowly accumulates in the magma chamber until enough pressure builds up to start an eruption. • Then, magma rises to the surface in a narrow, vertical channel called a pipe.

46. Formation of a Volcano • An opening in the ground where magma escapes to the surface is called a vent. • Often there is one central vent at the top of a volcano. Sometimes there are other vents that open along a volcano’s side. • At the top of the central vent in most volcanoes is a bowl-shaped pit called a crater.

47. Formation of a Volcano • After an eruption, a volcano’s magma chamber and main vent may empty of magma, creating a hollow shell. • If this shell collapses inward, it creates a huge depression, called a caldera, at the top of the volcano.

48. Formation of a Volcano When a volcanic mountain erupts, magma under pressure is forced upward from the magma chamber. Magma flows onto the surface as lava. Crater Vent Magma chamber Lava Pipe

49. Quiet and Explosive Eruptions Magma can vary in viscosity, the resistance to flow. Magma with high viscosity is thick and resists flowing. Magma with low viscosity is thin and flows easily.

50. Quiet and Explosive Eruptions There are three main factors that determine the viscosity of magma: temperature, water content, and silica content. • Higher temperatures lower the viscosity of magma, so it flows more easily. • Water in magma helps it flow more easily. • Magma that is high in silica has high viscosity.