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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.
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.
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.
- 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.