The Grand Canyon is 1,700 meters deep. The mid-ocean ridge extends from Iceland through the entire length of the Atlantic Ocean. It continues into the Indian Ocean and then into the Pacific. The mid-ocean ridge consists of mountains beneath the sea. Over much of its length, the center of this ridge is split by a rift valley.
Many earthquakes occur near the rift valley in the center of the ocean.
The floor of the rift valley gives off heat more rapidly than do other parts of the sea floor. The greater heat flow and earthquake activity suggest that the mid-ocean ridge is active geologically. As the ocean floor is moved toward the continents, it is forced beneath the continental masses at some points, thus forming the trenches. Other major features of oceanic basins are continental shelves, submerged extensions of the continental masses, usually lying at depths of less than 200 m. The depths and widths of the continental shelves vary considerably.