Plate Tectonics and Mountain Building

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Plate Tectonics andMountain Building
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Clues to Earths Interior

• We must rely on indirect clues since we cant see
  into earths interior. These clues suggest that
  earth is made of layers of different materials
• Seismic waves change speed and direction
  dependent on the material and density of the
  material they are traveling through. Waves are
  disturbances that carry energy through matter or
  space and are released during earthquakes
• Surface rocksrocks that appear on the surface
  have not always been there. Earth forces pushed
  them from deep inside the earth

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Earths Layers

• Inner Core
• Dense, solid iron, hot5000 degrees C, great
  pressure (earths center of gravity
• Outer Core
• Molten metal, stops one type of seismic wave and
  slows down another
• Mantle
• Largest layer in area solid like putty or melted
  plastic
• Crust
• thin, outermost layer thickest under continents,
  thinnest, but densest under ocean
• LITHOSPHEREThe earths crust and part of the
  rigid upper mantle that is divided into about 30
  plates that float on the ASTHENOSPHERE, or the
  part of the mantle below the lithosphere. The
  asthenosphere flows very slowly, and due to
  convection currents and gravity, causes the
  plates to move on the surface of the earth.

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Layers of Earth
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PLATE BOUNDARIES

• Plates that Move Apart ? ?
• Diverging boundaries caused by tension forces
• New crust forms when magma is pushed up from the
  mantle and fills gaps
• Can happen at mid ocean ridgesMid Atlantic Ridge
  is the longest mountain range in the world
• Can happen on landWhen 2 continental plates pull
  apart, a rift valley forms such as in Eastern
  Africa

Mid Ocean Ridge
Rift Valley
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• Plates that Move Together ? ?
• Caused by compression forces
• Converging continental plates have similar
  densities which Is less than the mantle
  underneath, so the crust piles up, buckles, or
  fold upon itself
• Converging Continental/Oceanic Plates-Denser
  oceanic place is forced under less dense
  continental plate. Subduction zone formed
• Converging Oceanic PlatesDenser plate is forced
  under less dense plate. Subduction zone is
  formed. Volcanic activity is common

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Subduction Zones
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Transform Boundaries

• Occur when plates move past each other
• Shearing causes faults (weak spots in rocks) and
  earthquakes
• San Andreas fault is on a transform boundary

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Uplifting of Earths CrustMountain Building

• Mountains fall into 4 main categories
• The ruggedness (sharp peaks, height) depends on
  if the mountains are still forming
• The Himalayas are still forming at the rate of
  several centimeters per year
• Longest mountain range in the world is the
  mid-ocean ridge that wraps almost around the
  world, through the Atlanta, Artic, and Indian
  Oceans

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Mountian Types

• Fault-Block
• Form from huge blocks of tilted rock separated
  from surrounding rock by faults
• Caused by tension (pulling) forces
• Examples Grand Tetons in Wyoming, Sierra Nevada
  in California
• Folded
• Form when crust buckles and folds over on itself
• Caused by compression (pushing) forces
• ExamplesAppalachian Mountains
• 250 million years old
• Oldest range in NA and one of the longest (AL to
  Canada)
• Upwarped
• Form when forces in the earth push the crust up
• ExamplesRocky Mountains, Adirondacks

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• Volcanic Mountains
• Volcanoes occur when molten lava and ash escape
  through a hole in the earth. The material
  gradually builds up and forms a mountain
• A. Subduction volcanoes form on land
• Formed when one tectonic plate is forced under
  another
• Magma comes from high in the mantle
• Some volcanoes of this type can build up several
  meters of layers of ash and cinders in 24 hours
• ExampleMt. St. Helens
• B. Hot Spot Volcanoes form on seafloor
• Form from material from near the earths core
  that is forced up through the mantle and forms a
  hot spot in the crust
• Volcanic Islands such as Hawaii form here
• These mountains are larger and have more gently
  sloping sides than subduction volcanoes

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This is how a hot spot formed the islands of
Hawaii
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The Ring of Fire