Plate Boundaries

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Also known as convergent boundaries or compressional boundaries.

  • These cause violent volcanoes and earthquakes, as well as deep-ocean trenches and fold mountains.
  • An oceanic plate and continental plate move towards each other.
  • The denser oceanic plate dives under the lighter continental one, creating a deep ocean trench.
  • As the oceanic plate goes deeper into mantle it melts in the subduction zone, due to friction and the increased temperature.
  • The newly molten rock is lighter that that which surrounds it, so it will rise towards the surface and cause volcanoes on the earth's surface.
  • The continental crust is crumpled by the collision of the two plates creating Fold Mountains.
  • If the magma rises offshore it will form an Island Arc, like the West Indies and Japan.

A good example of a destructive plate boundary is where the Nazca plate dives underneath the South American plate. This has caused volcanoes, earthquakes and the formation of the Andes Mountain Range.

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Also known as divergent or tensional boundaries.

  • Although often not as violent as those on destructive plate boundaries, volcanoes and earthquakes do occur on constructive plate boundaries. They also cause mid-ocean ridges to form.
  • Two plates move away from each other.
  • Molten rock (magma) rises from the mantle to fill the gap between the two plates. This forms a mid-ocean ridge.
  • Volcanoes can also form here, along the edges of the plate boundary, due to the rising magma. These volcanoes are called shield volcanoes.

A good example of a constructive plate boundary can be found where the NorthAmerican plate is moving away from the Eurasian plate. This has caused theMid-Atlantic ridge to form and has created Iceland through volcanic activity.

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Also known as passive plate boundaries.

  • The main effects of a conservative plate boundary are earthquakes, which can be fairly violent and frequent.
  • Two plates slide past each other, without creating or destroying any land.
  • As they move past each other they often get stuck, building up great pressure until finally they jolt past each other. This sudden movement is what causes earthquakes.

The best-known example of a conservative plate boundary is the San Andreas Fault, where the North American and Pacific plates are actually moving in the same direction, but at a different speed.

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  • Where two continental crusts collide neither can sink.
  • Instead they push into each other forcing material to be folded up into huge mountain ranges.
  • Often this movement and pressure can cause earthquakes, but no volcanoes will occur on these boundaries.
  • The best example is found where the Indian plate collided with the Eurasian plate to form the Himalayas.

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