How do ocean ridges and deep sea trenches support the theory of seafloor spreading?

Tectonic Plate Theory (go to ask.com or even wikipedia.com). Ridges are places where continental plates are colliding (mountain-building), and trenches are where they are pulling apart. The volcanoes that created (and still create) Iceland are erupting in the offshore trench where the North American and European plates are pulling apart, and there's even a 300-yard gash on the island itself that is in fact where that trench extends out of the ocean onto land.

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