Volcanoes/earthquakes

• Constructive Plate Boundary

  The convection currents cause the plates to move apart from each other. This is when magma heated from the core rises an cools dragging the plates apart. When the plates separate magma rises creating shield volcanoes. Weak earthquakes can sometimes occur as the plates move apart because pressure is not being built up

  Example: Mid-Atlantic Ridge
• Destructive Plate Boundary

  The oceanic plate gets subducted under the continental plate because the oceanic plate is denser. As the plates collide it is pushed upwards forming fold mountains. As the plates slide friction happens causing pressure to build. The plates then slip past each other in an abrupt movement causing strong earthquakes. As the oceanic plate subducts friction and heat in the mantle melts the crust forming composite volcanoes to erupt. 

  Example: South American plate and Nazca plate
• Why do people continue to live in hazardous areas?

  People could have a lack of income so may not have enough money to move somewhere else. The benefits could also outweigh the risks such as fertile soil or minerals.
• Conservative Plate Boundary

  Convection currents cause the plates to move in opposite ways or at different speeds but in the same direction. This is when magma heated from the core rises and cools dragging the plates apart. Earthquakes are formed because friction is caused when the plates move apart and then a build up of tension. When the tension is released there is a sudden movement/tremor.

  Example: San Andreas Fault, California, USA
• Collision Plate Boundary

  Two continental plates move towards each other due to convection currents. The plates are equal density and so neither can sink. They are forced upwards forming fold mountains. No crust in mantle so there is no melting therefore no volcanoes. As plates collide earthquakes can occur.

  Example: Himalayas
• Advantages of living near volcanoes

  Attract tourists (hot springs) which means that people can get jobs leading to the multiplier effect

  Gold can be found in volcanoes and sold for a lot of money
• Disadvantages of volcanoes

  Houses/businesses collapse meaning people become homeless or displaced in poorer countries
• Theory of Plate movement

  Ridge push - the plate rises due to convection currents and is pulled away from the ridge due to gravity.

  Slab pull - the plate is pulled down into the mantle by gravity.