Abyssal plains are the vast, flat, sediment-covered areas of the deep ocean floor. They are the flattest, most featureless areas on Earth, and have a slope of less than one foot of elevation difference for each thousand feet of distance. The lack of features is due to a thick blanket of sediment that covers most of the surface.

These flat abyssal plains occur at depths of over 6,500 ft (1,980 m) below sea level. They are underlain by the oceanic crust, which is predominantly basalt—a dark, fine-grained volcanic rock. Typically, the basalt is covered by layers of sediment, much of which is deposited by deep ocean turbidity currents (caused by the greater density of sedimentladen water), or biological materials, such as minute shells of marine plants and animals, that have "rained" down from the ocean's upper levels, or a mixture of both.

Other components of abyssal plain...