Download 3.3 Plates Move Apart

Plates Move Apart
Learn about:
Different plate boundaries
What happens when plates move
apart.
How the direction and speed of
plates can be measured.
Plate Boundaries
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There are three kinds of plate boundaries
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Divergent
Convergent
Transform
Both the kind of boundary and the kind of
plate affects how plates interact
Divergent Boundary
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Most divergent Boundaries occur on the
ocean sea floor.
Types of Divergent Boundaries
(What happens there?)
1.
Oceanic – Oceanic Divergence
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2.
Mid-Ocean Ridges
Rift Valleys
Continental – Continental Divergence
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Rift Valleys
Oceanic-Oceanic Divergence
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This is where two oceanic plates were
diverging forming new crust
Oceanic-Oceanic Divergence
(Continued)
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This is where oceanic plates are being
ripped apart magma comes up from deep
within the earth’s crust and forms pillow
basalts and under water vents
The Mid Atlantic Ridge
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The Mid Atlantic Ridge is an example of oceanicoceanic divergence
Over millions of years the continents have
moved enough to create an ocean
The ridge also contains the longest mountain
chain in the world
(6214 miles long)
(15 miles wide)
(6 miles deep)
http://www.wwnorton.com/college/geo/egeo/flash/2_5.swf
Mid- Atlantic Ridge (continued)
Review Oceanic-Oceanic Divergent
Boundaries
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With your neighbor, review what happens
at Divergent Oceanic-Oceanic Boundaries
Remember to put these concepts into your
own words.
How can you best remember the
information?
(You have 2 minutes)
Continent-Continent Divergence
Boundary
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Continental plates diverge in the same
way as Oceanic plates
Cliffs and ridges are more easily visible in
continental divergence
Continental- Continental divergent
Boundary
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Same as Oceanic – Oceanic Boundaries rift
vallies will occur.
What is different?
In this case, rift valley’s happen on land.
Two piece of land are pulled apart, revealing
magma. (it will cool and harden)
Creating what is called a continental rift valley (it
could fill with water, making a lake.)
Rift Valleys
East African Rift Valley
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The East African Rift Valley formed when a
three way split almost tore Africa apart
Example of a Continental rift valley.
East African Valley (On land Rift Valley)
Review the difference!
What is the difference between?
 Oceanic – Oceanic divergence and
 Continental – Contiental divergance
 (you have 1 minute)
3.4 Convergent Boundaries
Learn:
What happens when:
two continental plates converge
 An oceanic plate converges with another
plate
 One plate scrapes past another.
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Types of Convergent Boundaries
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Continental – Continental Collision
Contiental – Oceanic Subduction
Oceanic – Oceanic Convergent
Continental-Continental
Convergence

When two continental crusts collide the
pressure builds up and they form Mountains
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Since both plates are approximately equal density
neither subducts and no volcanoes are formed
Oceanic-Oceanic Convergence
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When oceanic plates collide a subduction zone
occurs
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One plate goes under the other deep beneath the
ocean floor
 (creating a deep ocean trench.)
Island Arcs- can form when oceanic plates
converge
Japan

Japan is part of an Island Arc formed by
oceanic-oceanic convergence
Continental – Oceanic Convergent Boundary
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Occurs when ocean crust and continental crust
are pushed together
What happens there? (Subduction Zone)
Subduction – one plate is pushed under another.
Which Plate always goes under? And why?
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Subduction Zone?
What kinds of landforms are created at a
Subduction Zone?
•Deep Ocean Trenches
•Volcanoes (after a long period of time.)
•Coastal Mountain Ranges (Parallel to
the Coast.)
(see next slide for an illustration)
Transform Faults
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Transform faults occur along divergent
oceanic and continental plate boundaries
Plates slide past each other building up
tension until the tension is released during
an earthquake
San Andreas Fault
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The San Andreas fault is a surface fault
line going through San Francisco
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In 1906 an Earthquake hit San Francisco
setting breaking gas and water lines and
causing fires that could not be stopped
Hot Spots
Another type of tectonic activity are
areas called hot spots
 A hot spot is where magma rises to
the earths crust melting the land and
forming a line of volcanoes as the
earth’s crust moves past it
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Hot Spots
Hawaii
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In oceans hot spots form Island chains
Since the hot spot is under mafic rocks the
lava flows smoothly down the mountain
creating shield volcanoes like Hawaii
Yellowstone National Park
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Hotspots below continents are highly
explosive and form craters called calderas
The force required for Felsic rock is so
great the eruption vaporizes the land and
sends ash over large parts of continents