THE OCEAN FLOOR COMPRISES TWO SECTIONS: the continental shelf and slope, and the deep-ocean floor. The continental shelf and slope are part of the continental crust, but may extend far into the ocean. Sloping quite gently to a depth of about 460 feet (140 m), the continental shelf is covered in sandy deposits shaped by waves and tidal currents. At the edge of the continental shelf, the seabed slopes down to the abyssal plain, which lies at an average depth of about 12,500 feet (3,800 m). On this deep- ocean floor is a layer of sediment made up of clays, fine oozes formed from the remains of tiny sea creatures, and occasional mineralrich deposits. Echo-sounding and remote sensing from satellites has revealed that the abyssal plain is divided by a system of mountain ranges, far bigger than any on land—the mid-ocean ridge. Here, magma (molten rock) wells up from the Earth’s interior and solidifies, widening the ocean floor. As the ocean floor spreads, volcanoes that have formed over hot spots in the crust move away from their magma source; they become extinct and are increasingly submerged and eroded. Volcanoes eroded below sea level remain as seamounts (underwater mountains). In warm waters, a volcano that projects above the ocean surface often acquires a fringing coral reef, which may develop into an atoll as the volcano becomes submerged.
The ocean floor
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GEOLOGY AND GEOGRAPHY AND METEOROLOGY
published on 7:28 AM
THE OCEAN FLOOR COMPRISES TWO SECTIONS: the continental shelf and slope, and the deep-ocean floor. The continental shelf and slope are part of the continental crust, but may extend far into the ocean. Sloping quite gently to a depth of about 460 feet (140 m), the continental shelf is covered in sandy deposits shaped by waves and tidal currents. At the edge of the continental shelf, the seabed slopes down to the abyssal plain, which lies at an average depth of about 12,500 feet (3,800 m). On this deep- ocean floor is a layer of sediment made up of clays, fine oozes formed from the remains of tiny sea creatures, and occasional mineralrich deposits. Echo-sounding and remote sensing from satellites has revealed that the abyssal plain is divided by a system of mountain ranges, far bigger than any on land—the mid-ocean ridge. Here, magma (molten rock) wells up from the Earth’s interior and solidifies, widening the ocean floor. As the ocean floor spreads, volcanoes that have formed over hot spots in the crust move away from their magma source; they become extinct and are increasingly submerged and eroded. Volcanoes eroded below sea level remain as seamounts (underwater mountains). In warm waters, a volcano that projects above the ocean surface often acquires a fringing coral reef, which may develop into an atoll as the volcano becomes submerged.
