Plain of Accumulation
The long-term subsidence of the Earth’s crust or the formation of basin-like depressions of various scales provides sites for compensatory deposition of a wide range of materials to form extensive plains of accumulation. For example, the bottom of the Bohai Sea and the coastal plains in Hebei Province are sinking at a rate of 1 cm per year, and the settlement since the Quaternary (two million years ago) has reached 800–1,000 m. However, the rate of fluvial deposition has exceeded the subsidence rate; hence, the plain has been expanding and advancing into the Bohai Sea, turning the marine area into extensive arable fields. Based on the cause of deposition, this type of plain can be categorised into floodplains, alluvial plains, lacustrine plains and marine depositional plains. The most extensive accumulation plains in the world are located in coastal areas, such as the North China Plain.