Below are revision notes for plate tectonics. If you require more detailed information take a look at the plate tectonics geotopic.
Earthquakes and volcanoes can be explained by the theory of plate tectonics. The crust of the earth is made up of a series of large plates (seven main plates and lots of smaller ones). There are two types of plates - continental and oceanic.
Convectional activity within the mantel cause the plates to move. A plate margin marks the boundary between two plates. There are three main plate boundaries:
- destructive
- passive, also known as conservative
- constructive
At a destructive plate margin two plates move towards each other. Two plates move past each other, side by side, at a passive margin. At a constructive margin two plates move apart.
As plates move apart at a constructive margin magma rises creating new crust. Volcanoes form along these margins. An example of a constructive margin is the margin between the Eurasian plate and the North American plate where the Mid-Atlantic ridge has formed. This margin also created Iceland!
At a destructive margin an oceanic plate is forced under a continental plate. As the oceanic plate subducts the continental plate friction causes the crust to melt. Magma rises and causes volcanoes. Earthquakes also occur along these plate margins. An example of where this happens is the Pacific plate and the Eurasian plate. Mount Pinatubo was formed at this margin.
At a conservative margin two plates slide past each other. This does not happen smoothly! Friction causes the plates to stick. Pressure builds which is eventually released causing an earthquake.
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