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Plate Tectonics and Mountain Building


LITHOSPHERE The earth's crust and part of the rigid upper mantle that is divided ... that float on the ASTHENOSPHERE, or the part of the mantle below the lithosphere. ... – PowerPoint PPT presentation

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Title: Plate Tectonics and Mountain Building

Plate Tectonics andMountain Building
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

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
  • 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.

Layers of Earth
  • 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

Mid Ocean Ridge
Rift Valley
  • 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

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

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

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
  • Upwarped
  • Form when forces in the earth push the crust up
  • ExamplesRocky Mountains, Adirondacks

  • 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
  • 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

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