2. The surface morphology of the Loess Plateau is formed by flowing water erosion. Because the Loess Plateau is located in the monsoon climate zone, the precipitation is concentrated in summer, which is prone to heavy rain, resulting in relatively large surface runoff. Moreover, because of the undulating terrain, the speed of running water is relatively fast, and the loess itself is very loose and the vegetation coverage rate is low, it has no protective effect on the soil. Therefore, the flowing water erosion in this area is very strong, forming the rugged surface morphology of the Loess Plateau.
Question 2: Why the Loess Plateau was formed 1. The Loess Plateau was formed by wind accumulation. The strong winter monsoon in the East Asian monsoon region originated in the inland areas of middle and high latitudes, namely Siberia and Mongolia Plateau. The wind brought a lot of dust, which was blocked by Taihang Mountain, Qinling Mountain and other mountains and deposited to form the present Loess Plateau.
2. The surface morphology of the Loess Plateau is formed by flowing water erosion. Because the Loess Plateau is located in the monsoon climate zone, the precipitation is concentrated in summer, which is prone to heavy rain, resulting in relatively large surface runoff. Moreover, because of the undulating terrain, the speed of running water is relatively fast, and the loess itself is very loose and the vegetation coverage rate is low, it has no protective effect on the soil. Therefore, the flowing water erosion in this area is very strong, forming the rugged surface morphology of the Loess Plateau.
Question 3: The reason for the formation of the Loess Plateau is very simple. The Loess Plateau is formed by aeolian deposits.
Explain in detail:
After the Indian plate moved northward and collided with the Eurasian plate, the Indian continental crust was inserted under the Asian continental crust to prop up the latter. As a result, the shallow sea of the Himalayas disappeared, the Himalayas began to form and gradually lifted, and the Qinghai-Tibet Plateau was also squeezed and lifted by the Indian plate. After this process lasted more than 60 million years, by about 2.4 million years ago, the height of the Qinghai-Tibet Plateau had exceeded 2,000 meters.
The great change of surface morphology directly changed the pattern of atmospheric circulation. Before that, the Pacific Ocean was in the east of Chinese mainland, Siberia in the north and Himalaya in the south were occupied by shallow seas respectively, and the Mediterranean Sea in the west also extended to far places in Central Asia at that time, so most flat Chinese mainland could get enough moist air from the ocean, and the climate was warm and humid. Northwest China and Central Asia are mostly subtropical areas, and there are no large areas of deserts and Gobi.
However, the east-west Himalayan mountains stopped the warm and humid air mass in the Indian Ocean from moving northward. With the passage of time, the northwest of China has become more and more arid, gradually forming a large area of desert and Gobi. This is the birthplace of dust accumulated on the Loess Plateau. The huge Qinghai-Tibet Plateau just stands in the westerly belt of the northern hemisphere, and its height has been increasing for 2.4 million years. The width of the Qinghai-Tibet Plateau accounts for about one third of the westerly belt, which divides the surface of the westerly belt into two branches. The south branch flows eastward along the south side of the Himalayas, and the north branch flows eastward from the northeast edge of the Qinghai-Tibet Plateau. This kind of high-altitude airflow exists at an altitude of 3500-7000 meters all the year round and becomes the main driving force for carrying dust. At the same time, due to the uplift of the Qinghai-Tibet Plateau, the East Asian monsoon has also been strengthened. The winter wind blowing from northwest to southeast, together with westerly jet, formed the Loess Plateau in the north of China.
In the desert and Gobi in the northwest of China and the inland of Central Asia, the rocks here disintegrate into pieces faster than other places because of the drastic change of temperature. Geologists divide it into gravel (more than 2 mm), sand (2-0.05 mm), silt (0.05-0.005 mm) and clay (less than 0.005 mm) according to its diameter. Clay and sediment particles can be carried to an altitude of more than 3,500m, enter the westerly belt, be transported to the southeast by westerly jet, and gradually fall until the middle and lower reaches of the Yellow River.
For two or three million years, the process of transporting sand from northwest to southeast in this part of Asia has never stopped. A lot of sand falls in the area where the Loess Plateau is located, and even many mountains in North China, such as Wutai Mountain and Taihang Mountain, have loess accumulation at the top. Of course, the scouring effect of several large rivers and countless valleys in northern China, including the Yellow River, is just the opposite of the accumulation of loess. Otherwise, the loess plateau will not be like this, and the thickness will not exceed 409.93 meters. The North China Plain east of Taihang Mountain is also a subsidence area of sand, but it is a subsidence area, and at the same time many rivers have developed, so the falling sand is either washed away by the rivers or buried by the sediment brought by the rivers.
There are hundreds of records about rain soil, rain loess, rain yellow sand and rain haze in China ancient books. The earliest record of "rainy soil" can be traced back to 1 150 BC: the sky is yellow and foggy, and sand falls from the sky like rain. What is recorded here is actually a sandstorm.
The location of rainy soil is mainly in the Loess Plateau and its vicinity. The ancients regarded this kind of thing as a strange catastrophe phenomenon and thought it was a sign of "harmony between man and nature" It is recorded in the Natural History compiled by Zhang Hua in the Jin Dynasty: "When Xia Jie was in the deep valley, the night palace was mixed with men and women, and he did not go out to listen to politics for ten days. It was a windy day and filled the empty valley overnight. "
During the period of 1966- 1999, there were 60 sandstorms lasting more than two days in China. Academician Liu Dongsheng of the Chinese Academy of Sciences thinks that the Loess Plateau should be regarded as a laboratory for sandstorms, which has accumulated records of sandstorms for millions of years. Sandstorms from the northwest desert and Gobi are scattered all over the sky, leaving a thin layer of loess on the Loess Plateau every year.
Question 4: The causes of ravines in the Loess Plateau. There are many gullies and valleys on the Loess Plateau, which are caused by soil erosion. Loess is a fine-grained soil with loose and upright texture, belonging to silty loam with low organic matter and clay content. Therefore, the role of soil-forming particles depends largely on calcium carbonate in loess. Calcium carbonate is easy to dissolve in rainwater, because rainwater contains carbonic acid, which reacts with calcium carbonate to dissolve calcium carbonate, losing the function of bonding soil particles, thus causing loess to be easily dispersed and washed away in rainwater.
On the other hand, the loess plateau has loose soil, large slope, sparse vegetation, heavy rain in summer, and running water has a strong erosion effect on the soil. As long as even tiny gullies appear, they will deepen and widen rapidly, and the gullies will continue to develop and extend. Ditches cut and dismembered the Loess Plateau like countless swords. At the same time, the crust of the Loess Plateau is still rising, and rivers and ditches are still being cut underground, further aggravating the ups and downs of this plateau.
Question 5: Why did the Loess Plateau form? Genesis of Loess Plateau
Geologically, the Variscan movement at the end of Paleozoic caused the fold and uplift of the Mongolian geosyncline, while the Yanshan movement only experienced extensive and moderate flexure and fracture. Himalayan movement and neotectonic movement caused the plateau to uplift as a whole, and large-scale basalt eruption occurred, filling low-lying areas and forming lava platforms, which were widely distributed in the eastern part of the plateau. The platform is stepped and slightly undulating.
Loess comes from the vast arid and desert areas such as Gansu, Ningxia and Mongolian Plateau in the north and northwest and even Central Asia. The rocks in these areas expand when heated during the day, contract when cooled at night, and gradually weather into stones, sand and clay of different sizes. At the same time, in these areas, whenever the northwest wind prevails in winter and spring, the wind suddenly rises, flying sand and stones, and dust covers the sky. Coarse stones remain in place and become "Gobi", while finer sand grains fall in nearby areas and gather into deserts, and tiny silt and clay fly to the southeast one after another. When the wind weakened or was blocked by the winding Qinling Mountains, they stopped accumulating, and after hundreds of thousands of years of accumulation, a vast loess plateau was formed.
The ravines on the Loess Plateau are vertical and horizontal, which are caused by soil erosion. Loess is a fine-grained soil with loose and erect texture, belonging to silty loam with low organic matter and clay content. Therefore, the role of soil particles is mostly calcium carbonate in loess. Calcium carbonate is easy to dissolve in rainwater, because rainwater contains carbonic acid, which reacts chemically with calcium carbonate, dissolving calcium carbonate and losing the function of bonding soil particles, thus causing loess to be easily dispersed and washed away in rainwater.
On the other hand, the loess plateau has loose soil, large slope, sparse vegetation, heavy rain in summer, and running water has a strong erosion effect on the soil. As long as even tiny gullies appear, they will deepen and widen rapidly, and the gullies will continue to develop and extend. Gullies cut and dismembered the Loess Plateau like countless swords. At the same time, the crust of the Loess Plateau is still rising, and rivers and ditches are still being cut underground, further aggravating the ups and downs of this plateau.