Submarine landform is the general name of the surface morphology of the solid earth covered by seawater. The slope of the deep-sea plain is less than one thousandth, and the flatness exceeds that of the continental plain. The whole seabed can be divided into three basic geomorphic units: continental margin, ocean basin and mid-ocean ridge, and several sub-seabed geomorphic units.

ocean basin

Located between the mid-ocean ridge and the continental margin, one side is connected with the gentle slope of the mid-ocean ridge, and the other side is adjacent to the continental ridge or trench, accounting for 45% of the total ocean area. The sea basin is divided by normal topography such as ocean ridges, forming a number of submarine depressions with a water depth of about 4000 ~ 5000 meters, which are called sea basins. A long submarine depression with large width and gentle slope is called a trough. Deep-sea plains and deep-sea hills are developed at the bottom of the basin. A long submarine highland is called a seamount or ridge, a wide and gentle submarine highland is called a seamount, and a flat-topped submarine highland with steep slopes around it is called a sea platform.

continental margin

It is a transitional zone between the mainland and the ocean floor, accounting for about 22% of the total ocean area. Usually divided into Atlantic continental margin (also known as passive continental margin) and Pacific continental margin (also known as active continental margin). The former consists of three units: continental shelf, continental slope and continental uplift. The terrain is broad and gentle, and it is more common in the peripheral areas of the Atlantic Ocean, Indian Ocean, Arctic Ocean and Southern Ocean. The latter has a narrow continental shelf, steep continental slope and undeveloped continental uplift, but it is replaced by a trench, which can be divided into trench-island arc-marginal basin series and the Andean continental margin near the continental margin, mainly distributed in the Pacific Rim and also found in the northeastern margin of the Indian Ocean.

Mid-ocean ridge

Submarine landforms, like terrestrial landforms, are the result of the combined action of internal and external forces. Submarine topography is usually the direct product of internal forces, which is closely related to submarine expansion and plate tectonic activities. The mid-ocean ridge axis is the center of submarine expansion. The deep sea floor lacks the compression and folding mountain system on land, and the formation of seamounts and seamounts is mostly related to volcanoes and fault blocks. External forces also play a role in shaping the seabed topography. Strong sedimentation can transform the original rugged volcano and tectonic terrain and form a deep-sea plain. Submarine canyon is the most spectacular manifestation of turbidity current erosion, but in the process of shaping submarine topography, except for continental margin, erosion is far less important than land. Waves, tides and currents have a profound influence on the topography of coastal and shallow sea areas.