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TITLE: Heat Below, Mountains Above

[Photo: Spreading Ridge]
The Mid-Atlantic Ridge rises as high as 2.5 km (1.6 mi) above the ocean floor. Why are spreading ridges so tall? Because the mantle rocks beneath them are hot and therefore buoyant. As these rocks expand and bulge upward, they elevate the sea floor into a ridge.

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits