Plate Boundaries

• Plate boundaries


  • Convergent
  • Divergent
  • Transform
• Convergent plate boundaries


  Plates move towards each other
• Divergent plate boundaries


  Plates move away from each other
• Transform plate boundaries


  Plates move alongside each other
• Divergent margins - Mid ocean ridges


  1. Plates pull apart in ocean areas

  2. Space between plates filled with basaltic lava to form a ridge

  3. Volcanoes found along this ridge

  4. E.g. Mid Atlantic ridge where African and South American plates diverge
• Divergent margins - Rift valleys

  1. Plates move apart in continental areas

  2. Areas of crust fracture and drop down to form a rift

  3. E.g. The Great African Rift Valley
• Divergent margins - Volcanic islands

  1. As plates diverge, magma rises up through the gap in submarine volcanoes

  2. When enough magma has erupted it will reach the surface and form an island

  3. E.g. Surtsey, Iceland
• Divergent plate boundaries


  • Shallow focus earthquakes (0-70km deep)
• Convergent plate boundaries - Oceanic-Oceanic

  1. Denser plate subducts under the other creating a trench

  2. As descending plate melts, magma rises to the surface and forms a chain of volcanic islands (island arcs)

  3. E.g. Mariana Trench - Pacific plate subducted beneath Philippine plate
• Convergent plate boundaries - Oceanic-Continental

  1. Denser oceanic plate subducted below less dense continental plate

  2. Subduction causes deepening of ocean at plate boundary forming a trench

  3. Sediments and rocks crumple, fold and are uplifted along leading edge of continental plate (fold mountains)

  4. E.g. Peru-Chile trench, The Andes
• Convergent plate boundaries - Oceanic-Continental


  • Angle of subduction 30-70 degrees
  • Intense pressure and friction as oceanic plate descends
  • Faulting and fracturing in Benioff zone where angle is close to 45 degrees
  • Releases energy in form of intermediate and deep focus earthquakes
• Convergent plate boundaries - Continental-Continental

  1. Little subduction due to similar densities

  2. Colliding plates and sediment between them uplift and form high fold mountains

  3. E.g. The Himalayas, The Alps
• Convergent plate boundaries - Continental-Continental


  • Shallow focus earthquakes
• Transform plate boundaries


  1. Frictional resistance causes build-up of pressure

  2. Pressure causes rocks to fracture, releasing energy as earthquakes

  3. E.g. San Andreas fault in California
• Volcanic activity is absent at transform boundaries