Features of the Seafloor Read and use the information to complete the response below. Before World War II, people thought the seafloor was completely flat and featureless. There was no reason to think otherwise. But during the war, battleships and submarines carried devices called echo sounders. An echo sounder produces sound waves that travel outward in all directions. The sound waves bounce off underwater objects and the seafloor and return to the ship. The purpose of using echo sounders during the war was to detect enemy submarines. However, most of the sound waves did not hit submarines. Instead, they traveled to the bottom of the ocean and provided data that could be used to MAP THE SEAFLOOR. Scientists were surprised to learn that there are long, continuous ridges of huge MOUNTAINS IN THE MIDDLE OF THE OCEANS. For example, a mid-ocean ridge runs approximately north-south through the center of the Atlantic Ocean. Scientists were also surprised to find out that there are very DEEP TRENCHES around the edges of continents near chains of active volcanoes. Explain in paragraph form how echo sounders were used to learn about the seafloor. *