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Usually, when you look at a world map, the continents are shown with mountains, valleys, and plains, and the oceans are shown as flat blue surfaces. But that doesn't give a true picture of the ocean. When you take a closer look past the surface of the water and down to the seafloor, ocean basins are anything but flat. Ocean floors have just as many mountains, valleys, and plains as the continents do.
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| The World Ridge System as seen on a bathymetry map. The continents have been darkened to emphasize the topography of the ocean basins. |
| Light blue | 1,000Ð2,000 meters | continental shelves
oceanic plateaus |
| Blue | 2,000Ð3,300 meters | ocean floor mountains |
| Purple | 3,400Ð5,000 meters | valleys
deep plains. |
| Yellow | line drawn on map
(no depth indication) | midocean ridge system |
You're probably wondering about the features highlighted by the yellow lines in the middle of the ocean basins. Those lines indicate a chain of volcanoes called the midocean ridge system. At a total length of 50,000 kilometers, the midocean ridge system is the longest continuous chain of volcanoes on the planet. This chain of volcanoes forms as the result of plate spreading. As the oceanic plates spread apart from each other, cracks are created that are immediately filled in with magma (molten rock) from the mantle below. Twenty cubic kilometers of new oceanic crust are created along this interconnected network of volcanoes every year. If all this new rock were poured into the Grand Canyon, the Grand Canyon would be filled in every eight to ten years.
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