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Driving Forces of Plate Movement
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Title Slide: Driving Forces of Plate Movement
Slide 2: Heat Transfer
To understand how the Earth’s lithospheric plates move, it is important to know how thermal
energy or heat is transferred.
Slide 3: Heat Transfer
Inside the Earth, there are three mechanisms by which heat is transported through the
mantle:
Radiation, Conduction and Convection
Slide 4: Heat Transfer
First,
..Radiation-this is the transfer of heat by electromagnetic waves.
Second,
..Conduction is a form of heat transfer by which particles of matter have direct contact with one
another.
The third type of heat transfer is
..Convection is heat transfer by the movement of heated liquid. This method is the heat transfer
method this lesson will focus on.
Slide 5: Plate Movement
..Scientists still do not entirely understand the process of how tectonic plates move.
..However, most scientists agree that convection currents play a large role in this process.
Slide 6: Convection Currents
..Convection currents occur within Earth's mantle. This process is said to be the driving
force for plate tectonics.
..There are actually two types of convection currents occurring within the Earth. The first
deals with creating the Earth’s magnetic field and the second one is the process for
tectonic plate movement.
Slide 7: Earth’s Magnetic Field
..Deep within the Earth, the outer core experiences convection currents when fluid
metals, primarily iron and nickel turn over.
..This is what helps create the Earth’s magnetic field.
..The movement of the metals forms electrical currents, which in turn generate magnetic
fields.
Slide 8: Mantle Convection Currents
..As heat from the inner and outer core heat the lower portion of the mantle, a second set of
convective currents form.
..This mantle convection is extremely slow, as the mantle is a thick semi-solid material.
Slide 9: Mantle Convection Currents
..As semi-molten rock in the mantle is heated, it becomes less dense and begins to rise
closer to the surface of the Earth.
..As it reaches the undersurface of the crust above, it spreads out carrying the plates of
the lithosphere with it.
..As the rock cools and becomes more dense, it gradually sinks back deeper into the
mantle to be re-heated
Slide 10: Convection Currents Diagram
Be sure to view the “slab pull” that occurs between the ridge and the trench. This is
where the lithospheric plate is moving away from the crustal ridge. As the oceanic plate
moves it cools and becomes more dense―sinking back into the Earth.
Slide 11: Convection Currents
Rifts
..Rifts or cracks are created in the oceans where magma comes from inside the Earth.
..Rifts occur where two plates come together.
.. When the magma rises it pushes the ocean plates apart. A rift is being formed today in
Iceland as the island nation is being spread apart and filled in by volcanic activity.
Slide 12: Trenches
..Trenches are places where the ocean plates slip under the continental plates.
..As the upper part of the plate moves outward toward the trench, the lower part moves
back toward the rift.
Slide 13: Subduction
..The process of making the new plate and getting rid of the old is called Subduction
[image of oceanic crust subducting under the continental crust]