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Causes of Plate Movement
After completing this section, the student will relate convection currents in the
asthenosphere to plate movement (Standard PI – 042) and use evidence to
support the Theory of Continental Drift (Standard PI-040)
We know that the Earth’s surface
is made up of moving plates.
Most earthquakes and volcanoes occur at plate
We don’t know what causes the plates
to move. Scientists have proposed 3
theories to explain how the plates
• Mantle Convection
• Ridge Push
• Slab Pull
Mantle Convection
Heat from the Earth’s inner and
outer cores is transferred by a
process called mantle convection
Magma that is hotter is less dense
and rises. As it moves, it pulls a
lithospheric plate with it
As the magma cools, it becomes more dense and
sinks, forming a convection current
Many scientists think that mantle
convection does not completely
explain how plates move
It doesn’t account for the force needed to move
the plates
Ridge Push
The molten magma that rises at a
mid-ocean ridge is very hot and
heats the rocks around it
As the lithosphere is heated, it
expands and becomes elevated above
the surrounding area
Gravity causes the older, denser
rock to slide away from the ridge
Slab Pull
At a subduction boundary, one plate is
more dense and heavier than another
The heavier plate begins to slide under the other
As the dense plate slides down
into the mantle, it pulls the rest
of the plate with it
The force that the sinking edge of the
plate exerts on the rest of the plate is
called slab pull
Many scientists consider this to be a better
theory than mantle convection or ridge push