Bell Ringer

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Bell Ringer

• Wednesday 8/19/09
• List three examples of evidence of continental
  drift theory.
• What are the three basic types of plate movement?

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UNDERSTANDING PLATE MOTION
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Four types of plate boundaries

• Divergent boundaries-new crust generated as
  plates pull away from each other.
• Convergent boundaries-crust is destroyed as one
  plate dives under another
• Transform boundaries- crust is not created or
  destroyed as the plates slide horizontally past
  each other
• Plate boundary zones-broad belts where boundaries
  are not well defined and effects are unclear

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Illustration of Main Types of Boundaries
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Divergent Boundaries

• Plates move a part-magma pushes up from mantle
  forming new crust
• Best known-Mid-Atlantic Ridge
• Rate of spreading
• 2.5 cm per year
• (25 km in a million years)
• Iceland is splitting between
• the North American plate
• Eurasian plate.

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Divergent Boundaries

• Consequences of plate movement as seen around
  Krafla Volcano in NW part of Iceland
• Ground cracks have widened
• and new ones appear every
• month.
• Sometimes this rifting was
• accompanied by volcanic activity.

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Convergent Boundaries

• Earths unchanging size implies that crust is
  being destroyed at the same rate as it is being
  created.
• Destruction(recycling) of crust takes place along
  convergent boundaries where plates are moving
  toward each other and sometimes one plate sinks
  under another
• Where sinking of a plate occurs is called a
  subduction zone

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Types of Convergence

• Oceanic-continental convergence-creates deep
  trenches under the ocean and up lifts mountains

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Oceanic-continental Convergence

• Off the coast of south America along the
  Peru-Chili trench, the oceanic Nazca Plate is
  pushing into and being subducted under the
  continental part of the South American
  Plate-causes lifting of Andes Mountains.
• Strong, destructive
• Earthquakes
• occur here.

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Bell Ringer

• Thursday 8/20/09
• What type of plate boundary slides horizontally
  past one another?
• List at least one type of convergent boundary.

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Oceanic-continental Convergence

• Oceanic-continental convergence also sustain many
  of the Earths most active volcanoes,such as
  those in the Andes,the Pacific North-west of US
  and those that ring the pacific ocean.

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Oceanic-oceanic Convergence

• When two oceanic plates converge, one is usually
  subducted under the other and in the process a
  trench is formed.

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Oceanic-oceanic Convergence

• Subduction process results in the formation of
  volcanoes.
• Over millions of years lava and volcanic debris
  pile up on the ocean floor until a submarine
  volcano rise to form an island volcano.
• These are usually strung out into chains called
  island arcs.

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Continental-continental Convergence

• When two continents meet neither is subducted
  because continental rocks are relatively light
  and, like colliding icebergs, resist downward
  motion
• Instead the crust tends to buckle and be pushed
  upward and sideways.

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Continental-continental Convergence

• The collisions of India into Asia caused the
  Eurasian Plate to crumble up and override the
  India Plate.
• This pushed up the Himalayas and the Tibetan
  Plateau to its present height.

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Continental-continental Convergence

• The Himalayas are 8,854 m above sea level
• The Plateau is 4,600m above sea level

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Collision of Indian Eurasian Plates
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Cross Section of Two Plates
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How Plate Movement has Changed our Planet in the
Past
Pangea Split into 2 continents, then changed
until it looked like Earth today
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To Our Present Day
Will We Continue to Change?
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How Earth Might Look in the future
Pangea Ultima
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Information Pictures

• USGS-www.pubs.usgs.gov/publications/text/understan
  ding.