Chapter 8: Plate Tectonics - PowerPoint PPT Presentation

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Chapter 8: Plate Tectonics

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Chapter 8: Plate Tectonics 8.1: Earth has several layers 8.2: Continents change position over time 8.3: Plates move apart 8.4: Plates converge or scrape past each other – PowerPoint PPT presentation

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Title: Chapter 8: Plate Tectonics


1
Chapter 8 Plate Tectonics
  • 8.1 Earth has several layers
  • 8.2 Continents change position over time
  • 8.3 Plates move apart
  • 8.4 Plates converge or scrape past each other

2
8.4 Plates converge or scrape past each other
  • Before, you learned
  • Plates move apart at divergent boundaries
  • In the oceans, divergent boundaries mark where
    the sea floor spreads apart
  • On land, continents split apart at divergent
    boundaries
  • Now, you will learn
  • What happens when two continental plates converge
  • What happens when an oceanic plate converges with
    another plate
  • What happens when one plate scrapes past another
    plate

3
Tectonic plates push together at convergent
boundaries
  • Recall new crust forms at divergent boundaries
  • At convergent boundaries, plates push together
    and crust is folded or destroyed
  • A plate with older, denser oceanic crust will
    sink beneath another plate
  • The crust melts in the athenosphere and is
    destroyed
  • Subduction when one plate sinks beneath another
  • Sub-, under and ducere, to lead led under

4
Continental-Continental Collision
  • Both crusts are the same density, so neither
    plate can sink beneath the other
  • The edges crumple and fold
  • Push together two blocks of clay one or both
    will buckle
  • Folded crust may push up high enough to form a
    mountain
  • Ex European Alps where the African and European
    Plates are colliding
  • Ex Himalaya Indian Plate colliding with the
    European
  • These mountains keep rising higher plates are
    still moving

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6
Oceanic-Oceanic Subduction
  • Occurs where an older plate with oceanic crust
    sinks (subducts) under another with newer oceanic
    crust
  • Older plate is colder and more dense than the
    younger plate subducts into the asthenosphere

7
Oceanic-Oceanic Subduction
  • Deep-Ocean Trenches like deep canyons that form
    in the ocean floor as a plate sinks
  • Most are found in the Pacific Ocean
  • Ex Marina Trench Pacific Plate sinking under
    the Philippine Plate
  • Deepest place in the worlds ocean 11,000m
    (36,000ft) into the sea floor

8
Oceanic-Oceanic Subduction
  • Island Arcs chains of volcanic islands that form
    on the top plate, parallel to a deep-ocean trench
  • Ocean crust of the sinking plate melts and magma
    rises through the top plate
  • Overtime, flows can build up a series of islands
  • Ex Philippine Islands, Aleutian Islands
    (Alaska), islands of Japan

9
Oceanic-Continental Subductions
  • Occurs when ocean crust sinks under continental
    crust ocean crust is colder and denser than
    continental crust
  • Deep-Ocean Trenches
  • In the Pacific Ocean, the Pacific Plate is
    sinking under the North American Plate can cause
    underwater earthquakes

10
Oceanic-Continental Subductions
  • Coastal Mountains as oceanic crust sinks under a
    continent, the continental crust buckles to form
    a range of mountains
  • Similar to island arcs, parallel a deep-ocean
    trench
  • Some of theses mountains are volcanoes (when
    melted oceanic crust rises through the top plate)
  • Ex Cascade Mountains in Oregon and Wash.
  • As the Juan de Fuca Plate began sinking under the
    North American Plate
  • Mount St. Helens active volcanoes

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12
Tectonic Plate Boundaries
  • Divergent Boundaries new crust formed
  • Convergent Boundaries crust folds/destroyed
  • Transform Boundaries
  • Plates move past each other in opposite
    directions
  • Edges scrape and grind against each other
  • Occur mostly on the sea floor near mid-ocean
    ridges
  • Can occur on land San Andreas Fault
  • Runs from the Gulf of California to San Francisco
  • Pacific Plate and North American Plate are moving
    opposite directionsLos Angeles will be a suburb
    of San Francisco in about 10 million years!!

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16
The theory of plate tectonics helps geologists
today
  • Changed scientists view of Earth the lithosphere
    has been in motion for millions of yearsand can
    help predict what may happen in the future
  • Eastern U.S the deformed and folded rocks in the
    Appalachian Mountains are evidence of an ancient
    convergent boundary
  • These rocks are the same as those in northwest
    Africa!
  • Indicate these mountains formed when North
    America collided with Africa and Eurasia as part
    of Pangaea
  • As they pulled apart formed rift valleys (U.S.
    east coast)
  • Predictions
  • more earthquakes are likely where plates slide
    past each other
  • volcanic activity where plates are sinking
    beneath other plates
  • mountains will continue to rise where plates push
    together
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