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PLATE TECTONICS
Lithospheric plates
• Lithosphere is made up of 12 large plates and about 20 smaller ones
• Plates are solid and float on the asthenosphere
• Convection currents in the asthenosphere make the plates move
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Continental and Oceanic plates
• Continental plates are usually less dense
• Oceanic plates are under the ocean and made of more dense rock
Plate Boundaries
There are 3 main types of plate boundaries:
• Divergent ( moving apart)
• Convergent (moving together)
• Transform (moving past each other)
Divergent Boundaries
• On land - produce rift valleys
• Under the ocean - mid-ocean ridges such as in the Atlantic
• As the plates separate, magma rises into the space and hardens
• Volcanoes and shallow earthquakes occur
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Convergent boundaries
• One plate may move under the other (subduction zone)
• Deep earthquakes and volcanoes occur
• Mountains form when one plate is pushed up
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Types of convergent boundaries
• Oceanic - oceanic: creates chains of islands (ex. Phillipines)
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• Oceanic - continental: oceanic plate subduct under continental plate; creates deep ocean trenches and coastal mountain ranges
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• Continental - continental: mountain ranges ex. Himalaya
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Transform boundaries
• Plates slide past each other causing fault lines and earthquakes
• Ex. San Andreas Fault
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