oceanic plateau

oceanic plateau, large submarine elevation rising sharply at least 200 m (660 feet) above the surrounding deep-sea floor and characterized principally by an extensive, relatively flat or gently tilted summit. Most oceanic plateaus were named early in the 20th century prior to the invention of sonic sounding, and many of these features have been shown by modern bathymetric data to be portions of the oceanic ridges. Thus, the Albatross Plateau of the eastern equatorial Pacific now is recognized as belonging to the East Pacific Rise and has been shown to possess a much more irregular summit than early data indicated.

Most plateaus are steplike interruptions of the continental slopes and appear to be downwarped or downfaulted blocks of former continental shelves. These marginal plateaus are exemplified by the Blake Plateau off the southeastern United States. This plateau’s flat surface lies between 700 and 1,000 m (2,300 and 3,300 feet) below sea level, is more than 300 km (185 miles) wide, and covers approximately 130,000 square km (50,000 square miles) of seafloor. The crust underlying the plateau, although relatively thin and veneered by flat-lying marine sediments, is otherwise continental in character.

Other plateaus, such as the coral-capped plateaus of the South China Sea, occur in the ocean well beyond the continental margins. They stand above the surrounding deep-sea floor as isolated topographic highs and are believed to be composed of continental rock cores overlain by flat-lying marine sediments. Presumably, these mid-ocean plateaus are minor fragments of continent that have been isolated during continental drift and seafloor spreading.