The outer layer of the Earth is called the crust. It is not one
complete layer, but made up of pieces called plates, which sit next
to each other like crazy paving.
Because the rocks below the crust are partly molten (melted) and
moving, the plates move and push against each other. Sometimes,
one plate will move beneath another, and where this occurs, a deep
submarine trench is formed between the two plates. The trench is
like a long, narrow hollow in the surface of the Earth. Sometimes
plates will move apart, causing a gap which molten rock rises to
fill. Sometimes, the plates slide past each other. A famous example
of this is the San Andreas fault in California, which moves about
5 or 6 cms each year.
A fault is a break in the Earth's surface or, on a smaller scale,
a break in a rock formation
Most of the volcanoes, earthquakes and mountains in the world occur
near the edges of plates, and all of these are the results of movement
inside the Earth.
During this constant movement rocks are created.
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