How the loess of the Yellow River Plateau is formed 5

Loess Plateau In the north of our country, there is a loess plateau with an area of about 600,000 square kilometers, which is famous for its huge area, rugged terrain and deep loess.

How did the Loess Plateau form?

For more than 100 years, many scientists have devoted themselves to the study of this problem and put forward dozens of hypotheses: some believe that the "hometown" of loess is not local, and that the loess is carried to the Loess Plateau by wind (called the loess wind theory); Some believe that the flowing water carries the loess to the Loess Plateau (called the Loess Hydrogenic Theory); Some people believe that the "hometown" of loess is in the local area, and it is weathering that "crushes" the original rocks and gravel, and then the remnants evolve into loess in situ (called the theory of weathering residue), and so on.

In the past two or three decades, more scientists have agreed with the theory of loess aeoliation. Because after research, scientists have found that the farther away from the deserts in Mongolia, Central Asia and northwest China, the finer the particles of loess; From northwest to southeast, the distribution pattern of Gobi, desert, sand loess, loess and clay loess is present, and the mineral composition of each zone is completely consistent with the mineral composition of sand and gravel in desert areas, but it is very different from the local rock composition. The loess is inselectively covered on the mountains of the Loess Plateau, and its thickness gradually thins from northwest to southeast. Fossils of terrestrial animals and plants of the arid steppe type have also been found in the loess.

According to the explanation of the theory of loess wind, the Loess Plateau is formed in this way: in the desert areas of Mongolia, Central Asia and northwest China, the climate is dry, the temperature difference is very large, due to the effect of thermal expansion and cold contraction, the rocks, gravel, etc. are "processed and crushed" into fine sand and dust. A strong northwesterly wind will whirl millions of tons of fine sand and dust into the sky and move south with the wind.

As a result, the coarse-grained ones settled down first to form a desert, while the fine-grained ones were drifted to the northern foot of the Qinling Mountains. After two or three million years of transportation and accumulation, the Loess Plateau was finally formed.

Science is constantly evolving, and in recent years scientists have discovered many phenomena that cannot be explained by the loess aeolian theory. For example, the content of coarse silt in loess decreases from northwest to southeast, while the content of clay increases from northwest to southeast. This shingle-like distribution transition is more like a masterpiece of the flood and so on.

In this regard, Chinese scientist Li Mingguang put forward a new theory -- the theory of catastrophe water formation on the Loess Plateau. He used a large amount of evidence to confirm that the Loess Plateau was formed by flooding, loess sedimentation and neotectonic uplift brought about by Himalayan movements. His views have attracted attention.

The reasons for the yellowing of the Yellow River are: there is little recharge water in the basin and the runoff of the river is small; The Loess Plateau is prone to water and land erosion, the soil layer is easy to be washed away, the vegetation is seriously damaged, there are many heavy rains in summer, and grazing is heavy.

Governance: afforestation, soil consolidation and sand control; Construct water conservancy projects on the Loess Plateau, control sand in small watersheds, and improve water quality in small watersheds; cross-basin water diversion to help the Yellow River in water scarcity;

The reasons for the formation of the Loess Plateau are as follows:

1.The Loess Plateau is one of the most special geographical and largest areas in China, which has formed a unique landform and ecological environment due to its special geological conditions and historical evolution process. The formation of the Loess Plateau is mainly influenced by the following aspects:

2.First of all, the Loess Plateau is located on the edge of eastern Chinese mainland, in the middle of the "transition from the Sichuan Basin to the North China Plateau", which determines that its geological conditions are very complex. From a tectonic point of view, the area has undergone many geological upheavals, such as karst landforms and rare karst landscapes due to the movement of the earth's tectonic plates.

3.Secondly, the climatic conditions of the Loess Plateau are very harsh, hot and dry summer, cold and long hail in winter, coupled with strong winds and dry climate influences, which can easily lead to soil erosion and wind erosion, and these natural conditions interact with human behavior, so that the soil organic matter content decreases, the sediment content increases, and the water loss is serious, and the phenomenon of serious water loss accelerates the formation of the Loess Plateau.

4.Finally, the topographical features of the Loess Plateau also played an important role in the formation process. Due to the steep terrain, undulating ground and local geomorphological differences, many special landforms such as hills, ravines and small basins have appeared on the Loess Plateau.

The influence of these geomorphological factors has accelerated the formation process of the Loess Plateau.

5.In summary, the formation of the Loess Plateau is the result of the interaction between natural conditions and human activities, including complex geological structures, harsh climatic conditions and special geomorphological features, etc., which eventually led to the unique landform and environment of the Loess Plateau.

6.Due to the influence of many geological upheavals and climatic processes, rich karst and karst landscapes have been formed on the Loess Plateau, and many unique biological communities and vegetation types have also emerged.

However, the development of modern human society has had a huge impact on the environment of the region, and excessive reclamation and destruction have made soil erosion and desertification on the Loess Plateau more severe. Therefore, it is necessary to strengthen protection and restoration, implement a sustainable development model, promote the restoration and reconstruction of the ecological environment, and ensure the sustainable development of this important area of the Loess Plateau.

The formation of the Loess Plateau is mainly due to the accumulation of wind, and the surface morphology of the Loess Plateau is formed by the erosion of flowing water. About 8 million years ago, the Loess Plateau was a vast lake with vast deserts on the west bank and barren mountains to the south and east. Due to the dry and cold climate, the wind was raging, and the noisy sky and flying sand and dust fell to the lake and sank to the bottom of the lake.

Over time, the lake became less and less water, and the loess was lifted out of the water, gradually forming a plateau. With the drying up of the lake and the formation of the plateau, the climate has gradually become colder, and the tropical animals have slowly become extinct, forming the current geographical environment and ecological environment, which is the formation process of the Loess Plateau. Therefore, the Loess Plateau is formed by the interaction between wind and dust and lake water under special geographical environment and special conditions.

The formation process of the Loess Plateau is as follows:

It is formed due to the accumulation of wind, and the strong winter monsoon in the eastern monsoon region of Asia comes from the inland areas of the middle and high latitudes, that is, the Siberian and Mongolian plateaus, and the wind brings a large amount of sand and dust, which is blocked by the Taihang Mountains, Qinling Mountains and other mountains, and the sand and dust are deposited to form the Loess Plateau. The surface morphology of the surface is formed by the erosion of flowing water, because the Loess Plateau is located in the monsoon climate zone, the precipitation is concentrated in summer, it is easy to have heavy rainfall, and a relatively large surface runoff is formed, due to the large undulation of the terrain and the fast flow of water, the soil quality of the loess itself is very loose, the vegetation coverage rate is low, the lack of protection of the soil, the erosion of the flowing water is very strong, and the rugged surface form of the Loess Plateau is formed.

The formation of the Loess Plateau is mainly due to the accumulation of wind, and the surface morphology of the Loess Plateau is formed by the erosion of flowing water.

The Loess Plateau was originally a lake area, about 15 million years ago, the landform here underwent great changes, the earth plate pushed from the southern Indian Ocean and the Eurasian plate collided, so that the entire lake area was slowly pushed up, the bottom of the lake was raised, and the lake water poured down, to the bottom depression of the east, flowing to the East China Sea. The huge flood brought the soil to the North China Plain, which laid the most important foundation for the formation of the North China Plain in the future.

Over time, the loess lake area became higher and higher, and the lake became less and less shallower, and finally, in about 8 million years, the lake finally dried up, and the loess was lifted out of the ground, and gradually became a plateau. It has become the landform of today's loess high slope. With the drying up of the lake, the formation of the plateau, the climate has gradually become colder, and the current geographical environment and ecological environment have been formed, which is the formation process of the Loess Plateau.

Geomorphological features of the Loess Plateau:

The Loess Plateau is divided into ravines and ravines, and the mountains, faulted valleys and basins are alternately distributed. The terrain is undulating, and from a distance it looks uneven and fragmented. The topography of the Loess Plateau is high in the northwest and low in the southeast, and it descends in a wave-like manner from northwest to southeast.

The Loess Plateau is divided into three parts: eastern, central and western, bounded by Liupan Mountain and Luliang Mountain: the western part of the Loess Plateau west of Liupan Mountain, with an altitude of 2000 3000 meters, is the highest area of the Loess Plateau.

Liupan Mountain and Luliang Mountain. The central part of the Loess Plateau, with an altitude of 1000 2000 meters, is the main body of the Loess Plateau. In the eastern part of the Loess Plateau east of Luliang Mountain, the terrain drops to 500 1000 meters, and the river valley plain occupies a large proportion.

According to this, the Loess Plateau can be divided into mountain area, loess hilly area, loess plateau area, loess plateau area, and river valley plain area.

The reason for the formation of the Loess Plateau is mainly due to the accumulation of wind.

The primary loess of the Loess Plateau is a wind-dust accumulation under the dry and cold climate conditions of the Quaternary glacial period, and the secondary loess is transformed by flood and alluvium of the primary loess. During the Quaternary loess accumulation period, with the climatic rotation of the glacial and interglacial periods, the loess layer showed the replacement of loess and paleosoil. According to the paleosoil in the loess, the loess layer can be divided into Wucheng loess, Lishi loess, Malan loess and Holocene loess from bottom to top.

Loess is an aeolian accumulation accumulated in an arid and semi-arid environment under the blowing and carrying of the wind, and after long-distance transportation and sorting, its material composition has a high degree of uniformity. Under the action of the northwest wind, a large amount of sand and dust is carried to the Loess Plateau area, and due to the weakening of the wind, it is deposited, year after year, and finally forms a thick loess accumulation.

Folk customs of the Loess Plateau

1. Xintianyou.

"Xintianyou" is a kind of folk song card that is widely popular on the Loess Plateau. The style of "Xintianyou" is simple, concise and heroic, and has a strong charm of the Northwest Plateau. The words of "Xintianyou" are plain and easy to understand, generally two sentences and one paragraph, ranging from 70 words per sentence, to use metaphorical techniques.

There are dozens of songs in Xintianyou, most of them are high-pitched, loud, strong, and have a wide range of contents, most of which are improvised songs, most of which sing about love and express the desire for a better life. The more famous tunes include "Walking to the West Exit" and so on.

2. Ansai waist drum.

The Ansai waist drum is a unique folk large-scale dance art form with a history of more than 2,000 years. The Ansai waist drum shows the simple and bold character of the farmers of the Northwest Loess Plateau, and shows a unique artistic personality. Its heroic and rugged movements, strong and unrestrained majestic dancing, fully reflect the simple, simple, brave and mighty personality of the people of the northern Shaanxi Plateau.

The Ansai waist drum performance can be performed by a few or thousands of people, and it is magnificent.

The above content reference: Encyclopedia - Loess Plateau.

From the analysis of the development history of the Loess Plateau, there are great differences in the material and external transportation capacity of the loess in the Early and Middle Pleistocene and the late Pleistocene. At present, the location of the source area, that is, the area with the most complete development of loess, was a basin in the Early and Middle Pleistocene, and the material in the basin mainly came from the weathered crust of the surrounding mountains.

According to the early and middle Pleistocene loess layers, the bottom of the loess layer is often a silt layer or a mixed zone (red and yellow mixed subclay), the loess itself is relatively dense, and its internal structural characteristics such as microbedding and clay clay masses are determined, so it is determined that the external force is mainly water. As for the late Pleistocene, the loess area has been uplifted from the basin to the plateau, and considering that the desert in the north and northwest of the plateau has been well developed, the loess material ** at this time is mainly the northern desert area, and the moving force is mainly wind. This can be confirmed from the loose structure and single composition of Malan loess.

In addition to the formation of loess such as water and wind, the most important thing is that an indispensable condition for the formation of loess is that there must be a weathering process after the accumulation of loess materials, that is, the loess process. Therefore, in addition to biological effects, the causes of loess are the most important reasons for the formation of loess under specific dry and early or semi-arid continental climate conditions. Therefore, in this sense, the loess genesis should be regarded as a compound cause.

At the beginning of the 20th century, the geological circles in China and even the world had a heated discussion on the causes of the Loess Plateau, and put forward various theories such as the theory of wind formation, water formation, residual accumulation and multiple genesis. Later, it was believed that loess has a complex formation process, but the aeolian process is the main process of loess formation.