Abyssal hills are low hills that occur on the deep ocean floor. Large stretches of the Atlantic and Indian Ocean floors and more than three-quarters of the Pacific floor are covered by such hills, which rise no higher than about 1,000 meters (3,000 ft). They tend to occur as a series of parallel ridges 1–10 km across, and represent the roughed topography of mid-ocean ridges subdued by burial beneath thick layers of sediment.
Abyssal plains are very flat areas of the deep ocean floor which may extend for more than 1,000 km (600 miles). They typically have slopes with gradients of less than 1 in 1000 and are found off continental margins where sediments can enter the deep sea unobstructed. They are common in the Atlantic and Indian Oceans, but rare in the Pacific, where deep trenches and island arcs serve as barriers to the transport of sediment from the continents.
Related category• ECOLOGY
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