Transcript Plate Tectonics - Exploits Valley High

Plate Tectonics
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Tectonic plates move or float on top of
the upper mantle.
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However they do not float freely.
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The plates are forced in specific
directions by the flow of magma
beneath.
Plate Tectonics – cont’d
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Plates move with the flow of magma.
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The magma closer to the core heats and then
rises towards the surface as its density
decreases.
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Once the rising magma reaches the
lithosphere it moves in opposite directions.
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The magma forms convectional currents.
Plate Tectonics – Convection Currents
Divergent Boundaries
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Tensional Forces occur where two tectonic
plates are pulled apart. The tension is created
as the plates move away from each other.
Ridge Zones sometimes occur where two
plates move apart. The magma rises between
the plates and forms a ridge.
Again caused by convectional currents in
the magma
Tensional Forces – Ridge Zones
This diagram above shows “Sea Floor Spreading”
Where’s the TENSION?
Convergent Boundaries
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Compressional Forces occur where two
tectonic plates come together. They
compress against each other.
Subduction Zones sometimes occur where
compressional forces result from two plates
colliding and one plate slips under the
other.
Again caused by convectional currents in
the magma
Compressional Forces – Subduction
Where’s the Subduction /
Compression?
More about Plate Tectonics
 our
text p. 10 - 12
 watch

it at:
http://www.pbs.org/wgbh/aso/tryit/t
ectonics/intro.html