Seafloor Bathymetry - During the war, battleships and submarines carried echo sounders to locate enemy submarines. Echo sounders produce sound waves that travel outward in all directions, bounce off the nearest object, and then return to the ship. The round-trip time of the sound wave is then recorded. By knowing the speed of sound in seawater, scientists can calculate the distance to the object that the sound wave hit. During the war, the sound wave rarely encountered an enemy submarine, and so most of the sound waves ricocheted off the ocean bottom.
After the war, scientists pieced together the bottom depths to produce a map of the seafloor. This is known as a bathymetric map and is similar to a topographic map of the land surface. While a bathymetric map measures the distance of the seafloor below sea level, a topographic map gives the elevation of the land surface above sea level. Bathymetric maps reveal the features of the ocean floor as if the water were taken away.
The bathymetric maps that were produced at this time were astonishing! Most people had thought that the ocean floor was completely flat but the maps showed something completely different. As we know now, majestic mountain ranges extend in a line through the deep oceans. Amazingly, the mountain ranges are connected as if they were the seams on a baseball. These mountain ranges are named mid-ocean ridges. The mid-ocean ridges and the areas around them rise up high above the deep seafloor.
Another astonishing feature is the deep sea trenches that are found at the edges of continental margins or in the sea near chains of active volcanoes. Trenches are the deepest places on Earth. The deepest trench is the Marianas Trench in the southwestern Pacific Ocean, which plunges about 11 kilometers 35,840 feet (35,840 feet) beneath sea level. Near the trenches, the seafloor is also especially deep.
Besides these dramatic features, there are lots of flat areas, called abyssal plains, just as the scientists had predicted. But many of these plains are dotted with volcanic mountains. These mountains are both large and small, pointy and flat-topped, by themselves as well as in a line. When they first observed the maps, the amazing differences made scientists wonder what had formed these features.
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