Abyssal Floor

The abyssal floor is the deep part of the ocean that lies between 3,000 and 6,000 m. The continents cover 29 percent of the earth, but the abyssal floor covers 30 percent; it extends from the sides of midocean ridges to the base of the continental rise. With deep-sea exploration, principally using seismic profiling techniques, this part of the ocean floor can be divided into two sections: abyssal plains and abyssal hills. Abyssal hills vary in height from 75 to 1,000 m above the seafloor. Maps of the seafloor show that they cover 50 percent of the Atlantic and 80 percent of the Pacific Ocean floor; they are considered to be the earth's most widespread topographic feature. Circular or elliptical and 1 to 8 km in width at their base, they are probably mostly volcanic, although some could also be the result of faulting. Located on the flanks of midocean ridges and on parts of the ocean floor separated from continents by trenches, they are most abundant in the Pacific Ocean.

Abyssal plains are extremely flat features of the ocean floor that are completely covered by sediments transported from the continents by turbidity currents. In all probability these sediments also bury abyssal hills; it is most likely that the hills are found on most of the ocean floor. Where the margins of the ocean basin are ringed by trenches and intersected by rises, sediments from the continents are trapped and cannot spread over the seafloor.

—Sidney Horenstein

See also: Continental Slope and Rise; Oceans; Seamounts


Hamblin, W. Kenneth, and Eric H. Christiansen. 2000. The Earth's Dynamic Systems. Upper Saddle River, NJ: Prentice Hall; Lampitt, R. S., et al. 2001. "Material Supply to the Abyssal Seafloor in Northeast Atlantic." Progress in Oceanography 50, nos. 1-4: 27-63; Press, Frank, and Raymond Siever. 2000. Understanding Earth, 3d ed. New York: W. H. Freeman; Rice, A. L. 1991. "Fining Bottom." Sea Frontiers 37, no. 2: 28-33; Siebold, E., and W. H. Beyer. 1993. The Sea Floor: An Introduction to Marine Geology. Berlin: Springer Verlag;

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