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What happens when Tectonic Plates Separate from each other?

Plates under land masses are called continental plates.
Plates under the ocean are called oceanic plates.
Oceanic plates grow outwards from an underwater
plate boundary. The plate boundary is a mid-ocean ridge.
An example of a mid-ocean ridge is the Mid-Atlantic ridge.

Sea Floor Spreading

What is Sea Floor Spreading?

 Plates moving away from each other at a mid-ocean ridge
is called sea floor spreading. Hot magma rises up through the
plate boundary, and it cools rapidly in the cold sea water
forming basalt mountains. As the oceanic plates move apart
they leave a very deep trench and more magma rises to
fill the gap. New oceanic crust is continually being formed.
The basalt mountains are therefore the same on each side of
the ridge, since they were formed at the same time from the
same rising magma. See the evidence for this on the next page.

Hot magma may burst violently out of a mid-ocean ridge
from underwater volcanoes.
Volcanoes and earthquakes under the ocean can cause
enormous waves called "tsunami", pronounced "tsoo-nar-mee".
These waves can do great damage when they reach land.

Where the oceanic plate meets a continental plate, the
plates collide. The oceanic plate is forced down
into the mantle and it melts. It is recycled forming new magma.
The oceanic plates are not more than 200 million years old.
That's about how long it takes for the largest plate to be recycled.

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