1.An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 3000 and 6000 meters. Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth’s surface. 2. A guyot is an isolated underwater volcanic mountain sea mount, with a flat top over 200 meters below the surface of the sea. 3.the continental shelf, which is an underwater extension of the coastal plain. The continental shelves are the regions of the oceans best known. 4.A submarine canyon is a steep-sided valley cut into the sea floor of the continental slope, sometimes extending well onto the continental shelf. Some submarine canyons are found as extensions to large rivers; however most of them have no such association. 5.A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges (chains), typically having a valley known as a rift running along its spine, formed by plate tectonics. 6.An island arc is a type of archipelago, often composed of a chain of volcanoes, with arc-shaped alignment, situated parallel and close to a boundary between two converging tectonic plates.