Plate movements (teach)


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Describes the various plate movements, their causes and effects.

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Plate movements (teach)

  1. 1. How Plate Movements Create LandformsBy Moira Whitehouse PhD
  2. 2. Understanding how the plates of theEarth move help us understand howsome landforms on Earth are built.The forces of plate movements areconstructive forces—forces that buildnew landforms on the surface of theEarth.
  3. 3. Remember howthe crust of theEarth is brokeninto huge piecesof rock calledplates. Theseplates fit togetheraround the globelike a giant jigsawpuzzle.
  4. 4. The plates move as they float on the hot, melted rock found in the mantle.Creative CommonsWikipedia Commons
  5. 5. The Earth’s crust consists of the oceanic andthe continental crusts, both of which float onthe magma (melted rock). • The oceanic crust is the layer of rock which forms the floor of an ocean. It is about 4-7 miles thick. • The continental crust is the layer of rock which forms the continents and those areas magma of shallow seabed close to the shore. The continental crust is much thicker than the oceanic crust--about 19 miles thick.
  6. 6. The continental crust is mainly made of arock called granite.The oceanic crust is made of mostlybasalt, a very dense rock that is muchheavier than the granite of the continentalcrust.As a result, the oceanic crust sinks deeperinto the magma (the molten rock) whenthe continental and oceanic crust meet.
  7. 7. This rockis mainlygranite. This rock magma is mainly basalt.
  8. 8. Wikipedia commonsFirst of all, notice that most plates have both Wikipedia Commonsoceanic and continental crust and that fewhave only oceanic crust.
  9. 9. Wikipedia CommonsWikipedia commons Notice the arrows to see how the plates interact.
  10. 10. You may have noticed that plates can movein one of three ways: 1. together 2. apart 3. side by side
  11. 11. This map of volcano and earthquake activitymirrors a map of plate boundaries. Image for educational use http//serc.carleton.educ
  12. 12. Two continental plates colliding
  13. 13. USGSWhen two continental plates collide, the rockwhere the two plates meet rises and foldsforming jagged mountains.
  14. 14. These collisions produce Earth’s mostspectacular mountain ranges and deepestvalleys.Mountain ranges that were formed in thisway include the Himalayas where theIndian Plate is moving into the EurasianPlate.The Himalayas are the highest mountains inthe world, towering as high as 29,000 feet.
  15. 15. Wikipedia commons
  16. 16. Wikipedia CommonsHimalayan Mountains from the air
  17. 17. Pictures of folded mountains. The Himalayas, the Andes in South America, the Alps, the Rocky Mountains and the Appalachian Mountains are all folded mountains.Pics4learning
  18. 18. When continental plates meet and pushup “new” mountains, the land behind themountain chain often is also up lifted.However, it doesn’t break or fold. As aresult a high flat area is formed---aplateau.The Tibetan Plateau was created when theIndian Plate and Eurasian Plate collided.The Himalayan Mountains formed alongthe edge of the collision, and the unbrokenplateau behind them rose as a “flat table”.
  19. 19. USGS
  20. 20. Continental andoceanic plates colliding
  21. 21. When an oceanic plate moves into a continental plate, it slides under because it is denser and thus, heavier.The extreme heat andpressure causes theleading edgeof the oceanicplate to melt. USGSThe resulting magma rises and gathers inpools under the continental crust.
  22. 22. As a result:First, a deep ocean trench forms where theoceanic plate moves under the continentalplate.Second, when enough magma collects in thepools under the continental plate, andenough pressure develops, a volcano erupts.
  23. 23. Image courtesy of FEMAUSGS
  24. 24. An example of an oceanic plate is movingunder a continental plate would be on thewestern coast of South America. •The Nasca Plate (oceanic plate) is moving under the South American Plate. Result: the Andes Mountains. Many volcanoes and earthquakes occur in this region.
  25. 25. Wikipedia commons
  26. 26. Image courtesy of National Geographic Andes Mountains
  27. 27. Another place, closer to home, where anoceanic plate is moving under acontinental plate is on the west coast ofUnited States.There a small oceanic plate called the Juande Fuca Plate is subducting (moving under)under the North American Plate.
  28. 28. This subduction isoccurring on thecoast of Washingtonstate, Oregon andnorthern California.The Juan de FucaPlate, what is left ofan old oceanicplate, is pushingunder the NorthAmerican Plate.
  29. 29. This subductionresults in thebuilding of theCascade MountainRange. Well-known volcanoesin this range areMount St.Helens, MountAdams and MountHood.
  30. 30. Wikipedia commons Mount St. Helens erupting in 1980
  31. 31. Now we will consider where two platespull apart.We will look at what happens when twooceanic plates move apart.
  32. 32. Oceanic plates moving apart
  33. 33. When two oceanicplates moveapart, magma from themantle flows upwardfilling the gap betweenthe two plates. Whenthe lava hits the coldwater it solidifies asbasalt rock. Image courtesy of USGSIf this process occurs over a long, long time, anew mountain range is built. This type ofmountain chain is called a midoceanic ridge.
  34. 34. Wikipedia commons
  35. 35. Wikipedia CommonsHere we see magma building up to form achain of mountains as two oceanic plates pullapart.As a result of this process, new oceanic crust iscontinuously being built.
  36. 36. This is what is happening in the middle of the Atlantic Ocean. The North American plate and the Eurasian plates are pulling apart in the North Atlantic and the South American plate and the African plate in the South Atlantic.usgs
  37. 37. Magma oozing outof these “pullaparts” overmillions and millionsof years has builtand is still buildingan underwatermountain rangedown the middle ofthe Atlantic Oceancalled the Mid- http://www.navmetoccom.Atlantic Ridge.
  38. 38. Iceland is an example of an island formed by magma that came from between diverging oceanic plates. It sits on top of the Mid- Atlantic Ridge.USGS
  39. 39. Photos from Iceland
  40. 40. Image from NASAHere we see a chain of mountains being builtunder all Earth’s oceans where ocean plates move apart.
  41. 41. As the ocean plates move apart, the oceansare getting wider--a few centimeters eachyear.As a result, oceans all over the world areincreasing in size. However, at the sametime, new continents are building at thefaults (cracks) that run down the middleof these oceans.
  42. 42. Tectonic platesthat move side by side
  43. 43. Now we will consider where two platesslide side by side: This type of movement commonly produces earthquakes.
  44. 44. Sometime the touching surfaces get stuck. As the movement of the plates continues, pressure builds up.When pressure to move is greater than theforce holding the surfaces still, a suddenviolent thrust occurs. This is an earthquake.Earthquakes are common where plates slide byone another.
  45. 45. We have our own transform fault. Along thewest coast of North American, the PacificPlate is sliding past the North America Platecreating a fault called the San Andreas Fault.In fact, the Pacific Plate is very graduallycarrying the western-most part ofCalifornia northward.The city of Los Angeles rides on top ofthe oceanic Pacific plate.
  46. 46. Let’s look at that image of the plates again.Wikipedia Commons
  47. 47. Here you cansee the PacificPlate movingnortheast andtheNorthAmericanPlate slidingsouthwestcreating the SanAndreas Fault.
  48. 48. In some parts ofCalifornia, you can actuallysee the San Andreas Faultline where the two platesare sliding by one another.The land to the west of theSan Andreas Fault is slowlymoving north. The land tothe east of the fault ismoving south. Aerial view of the fault USGS
  49. 49. 1906 San Francisco earthquake Wikipedia commons 1994 collapse of Los Angeles overpass
  50. 50. “Hot spot”volcanic activity
  51. 51. Most earthquakes and volcanic eruptionsoccur where plates move together, apartor side by side.However, a few volcanoes erupt in themiddle of plates.
  52. 52. Red dots are some of the hotspots found around the world. usgsFor example, the Hawaiian Islands, which areentirely of volcanic origin, have formed in themiddle of the Pacific Ocean more than 3,200km from the nearest plate boundary.
  53. 53. How do theHawaiian Islandsand othervolcanoes thatform in theinterior of platesfit into the platetectonicspicture? mccum934
  54. 54. Scientists believe that below the crust inthese areas, a hot plume of magma risesfrom deep within the Earth. When the plumesbreaking through the Earth’s surface a volcanoerupts. These plumes are thought to bestationary relative to the plates that moveover them. So as the platemoves on the present volcano becomesextinct and a new one develops above theplume forming new land.
  55. 55. Source: Maurice Krafft, Centre deVolcanologie, France)
  56. 56. Image courtesy of National GeographicMount Kilauea in Hawaii erupting
  57. 57. Now let us review.Look at each landform shown.Be ready to show by moving your handsand by telling us how each landform wasformed.
  58. 58. Wikipedia CommonsHimalayan Mountains from the air
  59. 59. Wikipedia commons Mount St. Helens erupting in 1980
  60. 60. Image courtesy of National GeographicMount Kīlauea volcano erupting in Hawaii.
  61. 61.
  62. 62. Image from NASAA chain of mountains being built under all Earth’s oceans.