Simple geography questions

The North China Plain starts from the Taihang Mountains and Funiu Mountains in the west, to the Yellow Sea, the Bohai Sea and the Shandong hills in the east, leans on the Yanshan Mountains in the north, and is connected to the plains of the middle and lower reaches of the Yangtze River near the Huaihe River in the south. It spans Hebei, Henan, Shandong, Beijing, Tianjin has five provinces and cities, covering an area of ??about 310,000 square kilometers, and is the second largest plain in my country.

The North China Plain is mainly formed by the alluvial deposits of the Yellow River, Haihe River and Huaihe River, so it is also called the Yellow-Huaihai Plain. The North China Plain has a broad terrain, with altitudes mostly below 50 meters. It slopes from west and southwest to east and northeast, and is divided into three landscape zones: foothill alluvial, alluvial fan plain, alluvial plain and coastal lowland. They extend from the foothills to the sea. , generally distributed in a semi-ring shape.

The North China Plain was formed from a crustal movement - the Yanshan Movement - 130 million years ago. This movement caused the western and northern parts of Hebei to rise into mountains and the eastern part to subside into a bay. As North China rises in the west and falls in the east, the Luan River, Hai River, Yellow River and other rivers flowing from the mountains and plateaus in the north and west accumulate a large amount of sediment brought from the Loess Plateau in front of the mountains, forming a series of large and small rivers. Small alluvial fan. Over time, these alluvial fans connected to each other and then gradually expanded, eventually forming the vast North China Plain.

The North China Plain is a Cenozoic fault depression area on the North China continental platform. The base of the plain was formed in the Archean and Proterozoic Era, and the caprock structure was mainly affected by the Yanshan Movement. During the Mesozoic Era, the North China Plain was an uplifted area, and fault basins developed locally. Since the Cenozoic, fault-blocking has been active, and a series of secondary fault basins have been formed in the Early Tertiary Period; during the Late Tertiary and Quaternary Periods, the accumulation range has gradually expanded, forming a contiguous great plain. At the same time, The fault-block mountains on the edge of the plain are relatively uplifted, and the outline of the great plain is becoming increasingly clear. During the Cenozoic Era, the area sank relatively and received thicker sediments, with local sedimentation reaching up to 1,000 meters.

Because the North China Plain is connected by alluvial fans of many rivers, many low-lying lands are formed between the alluvial fans. Any area between alluvial fans and between rivers is relatively low-lying and has many lakes and swamps. To the north of the Yellow River alluvial fan, between Baoding and Dagu, Tianjin, is the center of low-lying land distribution in the Haihe Plain. The famous Baiyangdian, Wen'an Depression and Dawa are all distributed in this area; the eastern edge of the Yellow River alluvial fan contacts the Shandong hills. Another low-lying center of the Huanghuai Plain, famous lake groups such as Weishan Lake and Dongping Lake in western Shandong are located in this area. There is also a low-lying land between Fuyang River, Ziya River and Zhangwei Canal. Low-lying areas with poor drainage are not only vulnerable to floods and waterlogging, but also because of high groundwater levels, a large amount of soluble salts present in groundwater and lower soil layers during dry seasons rise to the surface with capillary water and accumulate in the soil, easily forming saline-alkali soil.