the Mid-Atlantic Ridge

ATLANTIC OCEAN: The hourglass shaped Atlantic covers approximately 20 percent of the Earth's surface and is the second largest of the four oceans. It extends from the North Pole southward for 10,000 miles to the Antarctic continent, and covers 41 million square miles. Width of the Atlantic varies from 1,769 miles between Brazil and Liberia and approximately 3,000 miles between Norfolk, VA, and Gibraltar.

More is known of the Atlantic than any other ocean because of heavy commercial and military ship traffic connecting Europe and North America. Average depth is 12,000 feet and the greatest depth is 28,374 feet in the Puerto Rico Trench. If Alaska's Mount McKinley (20,320 feet) was to rise from the floor of the Puerto Rico trench, its peak would still be about 1.5 miles below the surface of the Atlantic.

The Mid-Atlantic Ridge divides the sea floor nearly through the center and stretches from the polar regions of the North to Antarctica in the South. The Mid Atlantic Ridge was created by the splitting apart of the super continent of Pangaea 190 million years ago. The ridge lies about 10,000 feet below water level except in a few areas where it surfaces as islands. This mountain range is as much as 500 miles wide. Rugged valleys extend outward from the ridge line to the abyssal plains.

The Mid-Atlantic Ridge is a continuous feature of the basin floor with one exception. There is a significant break in the ridge near the equator at the Romanche furrow where the crest of the ridge dips 15,000 feet below the surface. This break in the mountain chain allows deep water to flow freely between the Atlantic's east and west sides. The unrestricted movement provides a thorough circulation of the ocean basin that has a pronounced effect on deep water currents, density and temperature.

http://pao.cnmoc.navy.mil/pao/Educate/OceanTalk2/indexoceans.htm