Geography- Physical


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  • Created by: Olly
  • Created on: 05-04-11 15:18

Plate Boundaries

Constructive eg, Mid Atlantic Ridge (10,000km)

  • Plates are pulled apart by convection currents 
  • Reduction in pressure leads to the mantle melting and forming magma
  • Thinning crust may bow upwards due to pressure below & low density
  • Magma produces submarine volcanoes
  • Transform faults are produced at right angle to the ridge system

Low level explosivity eruptions and NO SUBDUCTION

Conservative eg, San Andreas fault

  • Pressure comes from the friction that is made from the plates sliding past each other. 

No volcanoes, no new landoforms as there is no melting of a subducted plate

San Andreas- Pacific plate moving NW/ American plate moving SE 

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Plate boundaries continued.

Hot Spot eg, Hawaii

Plumes of magma are rising from the asthenosphere, eventhough they are not necessarily near a plate boundary.

  • If the crust is thin/weak the magma may escape as a volcanic eruption.
  • Lava is basaltic and free-flowing.
  • Earthquakes- smooth and regular.

Continental-Continental eg, Himalayas

  • 2 plates collide with each other and are forced upwards creating fold mountains. 
  • No volcanoes as no magma is rising towards the surface.

Himalayas- Indo-australian plate is moving north(5cm per year)/Eurasian plate is moving south and they collide.

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More plate boundaries

Oceanic-Continental eg, Peru-chile trench

  • Oceanic plates slides beneath the continental plate and melts at the subduction zone.
  • Volcanoes are explosive as there is more pressure due to there being more plate to get through.

Peru-chile trench- Nazca plate subducts the SA plate. Andes are formed (fold).

Oceanic-Oceanic eg, Japan Trench

  • Older of the 2 oceanic plates subducts and erupt immediately with 50% silica content.
  • Island arc is formed (magma breaks through).

Japan Trench(Marina islands)- Pacific plate subducts the Philippine plate.

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