Transcript Plate Tectonics - Exploits Valley High
Plate Tectonics
Tectonic plates move or float on top of the upper mantle.
However they do not float freely. The plates are forced in specific directions by the flow of magma beneath.
Plate Tectonics – cont’d
Plates move with the flow of magma. The magma closer to the core rises heats and then towards the surface as its density decreases.
Once the rising magma reaches the lithosphere it moves in opposite directions. The magma forms convectional currents .
Plate Tectonics – Convection Currents
Divergent Boundaries
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
the plates and forms a
ridge.
between Again caused by
the magma convectional currents in
Tensional Forces – Ridge Zones This diagram above shows “Sea Floor Spreading”
Where’s the TENSION?
Convergent Boundaries
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