GCSE Revision - Plate Tectonic Theory

The diagram opposite shows the structure of the earth. It is similar to an apple in that at the centre of the earth is its core which is surrounded  by a mass of molten rock called the mantle. Above this is the surface of the earth known as the crust which floats on the mantle.

The surface of the earth is not one continuous layer but is made up of a number large plates. As these plates move due to convention currents in the mantle they create fold mountains, volcanoes and earthquakes

Below is a map showing the main plates as well as the four types of plate boundary found. To get a better understanding of what happens at these plate boundaries click on the diagrams to access animations of the processes at work. Likewise click on the globe so see how the convection currents affect the crust of the earth.




Destructive Plate Boundary

 This is where a continental and oceanic plate are moving towards each other. As they meet the oceanic is forced down where it melts in the subduction zone. The molten rock rises through cracks in the rock and and creates a composite volcano. Other features of the destructive plate boundary are violent earthquakes and fold mountains such as in the Andes Mts.

Constructive Plate Boundary
This is where two plates diverge and pull apart. As a gap appears between the two plates, lava can escape in a line or fissure. The lava creates new oceanic crust and forms mid-ocean ridges such as the one that runs down the centre of the Atlantic Ocean. Volcanoes can be found in certain locations but they are more gentle than at destructive plate boundaries. Mild or gentle earthquakes also occur. Iceland is the result of this type of plate boundary.

Conservative Plate Boundaries
At these boundaries two plates slide past each other as in the case below. In fact both are moving in the same direction but as the Pacific Plate is moving faster, it gives the impression that they are moving in different directions. Severe earthquakes occur at this type of plate boundary.

Collision Plate Boundary
These occur when two plates are converging but are both continental plates. As continental plates cannot be destroyed, the land between the two plates is pushed upwards to form mountains such as the Himalayas. Only earthquakes take place here as there are no volcanoes.