When was the alluvial plain of the lower reaches of the Yellow River formed

The basement of the plain was formed in the Archean and Proterozoic, and the caprock structure was mainly influenced by the Yanshan movement. During the Mesozoic Era, the North China Plain was an uplift area, and fault basins were developed locally. Since the Cenozoic, faulting has been active, and a series of secondary faulted basins were formed in the early Tertiary period. During the Late Tertiary and Quaternary periods, the accumulation area gradually expanded, forming a contiguous large plain, and at the same time, the fault block mountains at the edge of the plain were relatively uplifted, and the contours of the great plain became more and more distinct.

The Cenozoic was relatively subsident, receiving thicker sediments, and the local sediments reached thousands of kilometers. The altitude of the North China Plain is less than 100 meters, and the terrain is gentle and sloping. From the foothills to the coast, there are various landform types, such as alluvial inclined plain, alluvial alluvial fan plain, alluvial plain, alluvial lacustrine plain, marine alluvial plain, and marine sedimentary plain.

The landforms shaped by the Yellow River, Huaihe River, Haihe River, Luanhe River and other rivers constitute the main body of the North China Plain, namely the alluvial fan plain of the Yellow River, the middle and lower reaches of the Huaihe River Plain, the middle and lower reaches of the Haihe River Plain, and the alluvial fan plain of the lower reaches of the Luanhe River.

The alluvial plain of the lower reaches of the Yellow River was formed in the Late Tertiary and Quaternary periods. During this period, the Yellow River underwent fault-block action, forming fault-block basins, and then over time, the sedimentary extent continued to expand, forming contiguous large plains. At the same time, the edge of the plain is relatively uplifted, and the outline of the great plain is becoming more and more distinct.

Hekou Town in the Inner Mongolia Autonomous Region to Taohuayu in Zhengzhou, Henan Province is the middle reaches of the Yellow River, which is the main area of flood and sediment of the Yellow River, and there are 30 large tributaries that flow in. Hekou Town to Yumen is the longest continuous canyon on the main stream of the Yellow River, most of the tributaries in the river section flow through the loess hilly and gully area with serious soil erosion, it is the main sediment of the Yellow River, especially the coarse sediment, the average annual sediment volume of the whole river is 1.6 billion tons, of which 900 million tons ** in this interval.

The main stream of the Yellow River runs from Taohuayu to the Bohai Sea, and is called the lower reaches of the Yellow River. The downstream river channel is an above-ground hanging river, and there are few tributaries. At present, the riverbed in the lower reaches of the Yellow River is 3-5m higher than the ground of the embankment, which is more than the plains on both sides.

Except for the low mountains and hills between Dongping Lake and Jinan on the south bank, the rest rely on embankments to keep water back. Historically, there have been frequent breaches, which have brought heavy disasters to the Chinese nation. In the past 40 years, the Yellow River has transported an average of about 1 billion tons of sediment to the estuary area every year, and the average annual net land area is 25 square kilometers and 30 square kilometers.

Lower reaches of the Yellow River: The lower reaches are mainly formed by the accumulation of rivers, so they form an estuary delta, and the Yellow River has a large sediment content, forming an above-ground hanging river.

Hanging river on the ground. The reason why the lower reaches of the Yellow River form a "hanging river on the ground" is that the lower reaches of the Yellow River flow through the North China Plain, with a smaller slope and a slow flow rate. An average of about 1.6 billion tonnes of sediment is transported from the midstream to the lower reaches each year, of which about 400 million tonnes are deposited in the downstream riverbed, raising the riverbed two volumes above the plain beyond the oak bank embankment.

The river is constrained by artificial embankments, forming the famous overground river. The highest above-ground river in China is the section of the Yellow River flowing through Kaifeng, which is located at the mouth of Liuyuan on the south bank of the Yellow River, 10 kilometers north of Kaihu Jufeng City, where the river is 8,000 meters wide and the embankment is about 15 meters high.

Because the Yellow River rushes out of Zhengzhou Mountain, into the plain, the drop suddenly becomes smaller, a large number of sediments next to the sediment state, resulting in the Kaifeng section of the Yellow River riverbed at a rate of 10 centimeters per year to increase, day by day, the riverbed here has been higher than the ground level of Kaifeng urban area 7 8 meters, the highest point up to more than 10 meters.

With the continuous siltation of sediment and the continuous rise of the riverbed, the embankments on both sides of the bank are also increasing day by year. Because the Yellow River is protected by the embankments on both sides of the river, it flows through the high place in the north of Kaifeng City, resembling the Tianhe River, so this artificial wonder is called "Hanging River".

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It is a great honor to answer for you, the Huang River is the longest and largest Huangse River in China, and the reasons for the formation of soil in its downstream areas are mainly related to the following points: Huang River alluvium: The Huang River is a large Huang soil plateau river in China, and the sediment has fallen into the downstream area over the years, forming a large area of river beaches, islands and estuarine deltas.

With the accumulation of sediment and the precipitation of materials, the soil in the downstream area is gradually formed. Soil erosion: The undulating terrain and loose soil in the Huang River Basin, coupled with strong soil erosion, lead to the instability of the riverbed, and the accumulation of sediment and erosion alternately.

Affected by the sediment accumulation and soil erosion of the Huang River, the clay of the soil in the lower reaches of the Huang River has increased, and the lower reaches of the Huang River are very rich in sedimentary rocks, which also have a great impact on soil formation. Geological origin: The lower reaches of the Huang River are mainly composed of huang soil and clay, which are mainly composed of huang soil, huang clay, sand, pebbles and peat.

The geological conditions of the lower reaches of the Huang River play a very important role in soil composition and structure. In conclusion, the formation of soil in the lower reaches of the Huang River was mainly affected by the sedimentation and erosion of the Huang River, soil erosion, geological genesis and other factors. The combination of these factors forms the unique soil environment and geographical landscape of the lower reaches of the Huang River.

The middle reaches of the Yellow River flow through the Loess Plateau, where soil erosion is serious and the Yellow River has a high sediment content. A large amount of sediment flows to the lower reaches of the Yellow River, where the terrain is low and flat, the river channel widens, the water flow slows down, and the sediment is deposited to form an above-ground river over time.

The main reason

Due to the serious destruction of vegetation on the Loess Plateau in the middle reaches, a large amount of soil erosion is caused by the flow of water into the Yellow River, which is the Yellow River with a great sediment content to the downstream areas. As the river widens and the water flow slows, a large amount of sediment is deposited. Over the years, the riverbed has gradually been raised, forming an "above-ground river".

The main reasons for the formation of "above-ground rivers" in the lower reaches of the Yellow River are:

a.The midstream is low, and the downstream is high.

b.The slope of the downstream is gentle, and a large amount of sediment is deposited on the river bottom.

c.The middle reaches of the river are wide and the water flow is slow.

d.Soil erosion and destruction of vegetation downstream.

Answer: BThe reason why the lower reaches of the Yellow River became an above-ground river is ( ).

a.The terrain is high, and it is flanked by basins.

b.The sediment of the Yellow River is deposited, and the riverbed is constantly rising.

c.The construction on both sides of the Yellow River is made of earth, so that the ground is underground.

d.The sinking of the earth's crust on both sides of the Yellow River caused the ground to fall.

Answer: B

Alluvial plains are formed in the middle and lower reaches of large rivers by the accumulation of large amounts of alluvium brought by rivers. Under the condition of long-term tectonic subsidence, the alluvial plain can accumulate very thick alluvium, and the North China Plain is formed by the subduction of the Pacific plate to the Eurasian plate, which causes the post-arc tension and the dispersion of the continental margin, resulting in the extensional structure.

Since the Tertiary period, the thickness of sediments in the North China Plain has reached a maximum of 5,000 m, and a minimum of about 1,500 m. The basement of the alluvial plain is often undulating, and most of them are uplifts and depressions formed by tectonic faults.

Conditions for the formation of alluvial plains

In terms of geological structure, it must be a relatively subsident or relatively stable Li Li area, which refers to a huge thick alluvial plain in the relatively subsidence area, and an alluvial plain with a small thickness in the relatively stable area.

There shall be a valley or flat land with a considerable width of disturbance in the topography;

There must be sufficient sediment**.

The littoral plain is an alluvial sedimentary plain with fine sediments and a large area of lakes and marshes. Due to periodic tidal intrusion, the interlacing of marine deposits and alluviums is formed, and coastal sand dikes, shell dikes, lagoons and other landforms are also common.

Alluvial plains of our country

Taking China as an example, on the first topographic step of the Qinghai-Tibet Plateau is the bead-shaped wide valley alluvial plain of the Maquan River in the upper reaches of the Brahmaputra River, with an altitude of more than 4,550 meters. Located on the plateau of the second topographic step, there are the alluvial plain of the Hetao in the middle reaches of the Yellow River and the alluvial plain of the Weihe River in Guanzhong, which are 1300 300 meters high. However, more of them are the plains in the middle and lower reaches of the rivers distributed on the lowest topographic steps in the east, such as the Northeast Plain, the Huang-Huai-Hai Plain, the Middle and Lower Reaches of the Yangtze River Plain, the Pearl River Delta Plain, etc., which are mostly below 200 meters.

In the lower reaches of the Yellow River near the estuary, there is a phenomenon of above-ground rivers, because the middle reaches of the Yellow River pass through the Loess Plateau, and because of the twists and turns of the river channel, the hydraulic erosion is serious, and the sediment accumulates in the flat North China Plain in the lower reaches.

The middle and lower reaches of the Yangtze River Plain (Jianghan Plain, Yangtze River Delta).

The middle and lower reaches of the Yangtze River Plain is known as the Yangtze River Delta.

We collectively refer to the multiple plains formed by the impact of the Yangtze River as the middle and lower reaches of the Yangtze River Plain.

These include (from west to east): the plain formed by the Han River and Jingjiang River becomes the Han River Plain, the Dongting Lake Plain formed by Dongting Lake and the Yangtze River, the Poyang Lake Plain formed by Poyang Lake and the Yangtze River, the Suzhou-Anhui Plain formed by many tributaries of the lower reaches of the Yangtze River, and the Yangtze River Delta, where sediment carried by the Yangtze River accumulates at the mouth of the Yangtze River.

The middle and lower reaches of the Yangtze River plain.

The middle and lower reaches of the Yangtze River Plain, spanning the six provinces of Hubei, Hunan, Jiangxi, Anhui, Jiangsu, Zhejiang and Shanghai, are mainly composed of the Hanjiang River Plain, the Dongting Lake Plain, the Poyang Lake Plain, the Suzhou-Anhui Plain and the Yangtze River Delta, which is the largest plain in China.

The middle and lower reaches of the Yangtze River plain.

the Hanjiang River Plain, Dongting Lake Plain, Poyang Lake Plain, Suzhou-Anhui Plain and the Yangtze River Delta; These are all alluvial formations of the Yangtze River.

The middle and lower reaches of the Yangtze River Plain, as well as Chongming Island at the mouth of the Yangtze River, are also.

The middle and lower reaches of the Yangtze River Plain, including many small plains, are collectively referred to as the middle and lower reaches of the Yangtze River Plain.