8.1.4 The Formation of Composite Volcanoes Diagram (17-18)
A vent in the earth's crust.
Where one plate is forced to move under another. This occurs at destructive plate boundaries.
1. As the plates move towards each other because of convection currents in the mantle, the denser oceanic plate subducts under the continental plate.
2. The oceanic plate melts as it subducts.
3. This magma chamber which has been created weakens the continental crust and pushes upwards to form a vent.
4. Pressure builds until it is released in a violent eruption.