Processes at Plate Margins

• Convection Currents

  The earth is made of tectonic plates which used to be 1 continent called pangea. The same coastlines align like a jigsaw as they got separated by continental drift. Plates move in 2 ways - ridge push (away) and slab pull (slide over) due to convection currents (cycles of heat). The direction of convection currents is the same as the direction the plates move.
• Constructive (Divergent) Plate Margins

  Two oceanic plates diverge, e.g. the Mid-Atlantic Ridge

  • Magma cools, forming new land in the form of volcanoes
  • Plates move apart, Magma forces its way to the surface along the ridge
  • As it breaks through overlying crust, it causes earthquakes
  • Magma at constructive margins is very hot and fluid
  • Lava errupting has to flow a long way before cooling
  • Creates tropically broad and flat shield volcanoes.
• Destructive (Convergent) Plate Margin

  An oceanic plate is subducted under a continental plate as the oceanic is too dense, destroying land e.g. the Nazca Plate and American Plate

  • Where 2 plates meet, a deep ocean trench is formed
  • Friction causes strong earthquakes and oceanic melts
  • As oceanic moves down into the crust it melts, creating magma which is thicker
  • It breaks through to the surface to form steep sided, composite volcanoes
  • Erruptions are often very violent and explosive
• Conservative (Transform) Plate Margin


  Two continental plates move past each other at different rates. No land is created or destroyed e.g. the San Andreas Fault

  • Friction between plates causes earthquakes
  • Faster moving plate slides in the same direction as the slower plate
  • Earthquakes occur as stresses gradually build up over many years
  • Can be destructive as are close to the earth's surface
  • Suddenly released stress as plates slip and shift
  • No volcanoes as no magma