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Waves

Plate Tectonics - Plates colliding.

An oceanic plate moves away from a mid-ocean ridge,
and collides with a continental plate.
The oceanic plate (basalt) is thinner and denser
than the continental plate (granite).

When the two plates collide,
the oceanic plate is forced underneath the continental plate,
down towards the hot mantle.
This "forcing underneath" is called "subduction".
The place where it happens is called a "subduction zone",
(see next page). 

As you can imagine,
two huge pieces of the Earth's crust crashing into each other
generates an enormous amount of energy.
Rocks are heated, crushed, deformed, folded,
and some are melted and recycled
(see the Rock Cycle at GCSE Chemistry).
During the process,
metamorphic rocks are formed and mountains are built.
Volcanoes and earthquakes are common features.

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