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List of submarine topographical features : ウィキペディア英語版 | List of submarine topographical features
List of submarine topographical features, oceanic landforms and topographic elements. ==Abyssal plain== An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between and . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains are among the flattest, smoothest and least explored regions on Earth. Abyssal plains are key geologic elements of oceanic basins (the other elements being an elevated mid-ocean ridge and flanking abyssal hills). In addition to these elements, ''active'' oceanic basins (those that are associated with a moving plate tectonic boundary) also typically include an oceanic trench and a subduction zone. Abyssal plains cover more than 33% of the ocean floor (about 23% of Earth’s surface),〔Harris, P.T., MacMillan-Lawler, M., Rupp, J., Baker, E.K., 2014. Geomorphology of the oceans. Marine Geology 352, 4-24.〕 but they are poorly preserved in the sedimentary record because they tend to be consumed by the subduction process.〔 The abyssal plain is formed when the lower oceanic crust is melted and forced upwards by the asthenosphere layer of the upper mantle. As this basaltic material reaches the surface at mid-ocean ridges, it forms new oceanic crust. Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt. Much of this sediment is deposited from turbidity currents that have been channeled from the continental margins along submarine canyons down into deeper water. The remainder of the sediment is composed chiefly of pelagic sediments. Use of a continuously recording fathometer enabled Tolstoy & Ewing in the summer of 1947 to identify and describe the first abyssal plain.〔〔 This plain, located to the south of Newfoundland, is now known as the Sohm Abyssal Plain. Following this discovery many other examples were found in all the oceans.
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