Divergent boundary - A tectonic boundary where two plates are moving away from each other and new crust is forming from magma that rises to the Earth's surface between the two plates. The middle of the Red Sea and the mid-ocean ridge (running the length of the Atlantic Ocean) are divergent plate boundaries.


Ocean vs. Ocean : when two oceanic plates collide ,
the plate that is older , therefore colder and denser ,
is the one that will sink. Once again a subduction zone is formed.
above the subducting plate a chain of volcanic mountains form.
This time the volcanoes rise out of the ocean.
The Volcanic mountain is called island arcs.

Sea-floor spreading is the process in which the ocean floor is extended when two plates move apart. As the plates move apart, the rocks break and form a crack between the plates. Earthquakes occur along the plate boundary. Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcano.
seafloor.jpg
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http://www.platetectonics.com/book/page_5.asp
http://library.thinkquest.org/17457/platetectonics/4.php