"What are the characteristics of the Loess Plateau?

(Loess Plateau)

In the north of China, it starts from the Taihang Mountains in the east, and goes to the Wusheng Mountains in the west, connects the Qinling Mountains in the south, and arrives at the Great Wall in the north, and mainly includes Shanxi, Shaanxi, and part of the provinces of Gansu, Qinghai, Ningxia, and Henan, with an area of 400,000 square kilometers, and is the world's largest loess accumulation area. The loess is 50-180 meters thick, with an arid climate, concentrated precipitation, sparse vegetation and serious soil erosion. The Loess Plateau is rich in minerals, with large reserves of coal, oil and bauxite.

North wind send soil

On the origin of loess, for a long time, Chinese and foreign scholars have had different arguments. Among them, the "wind into say" is more convincing. That loess from the north and northwest of Gansu, Ningxia and Mongolia Plateau to Central Asia and other vast arid desert areas. These areas of rock, daytime heat expansion, night cooling contraction, gradually weathered into different sizes of stone, sand and clay. At the same time these areas, whenever the northwest wind prevails in the winter and spring seasons, the wind rises, flying sand, dust. Coarse stone remains in place to become the "Gobi", the finer grains of sand falling in the vicinity of the area, gathered into a slice of desert, fine powdered sand and clay, have to the southeast, when the wind weakened or detour of the Qinling Mountains will be blocked to stop the accumulation down, after hundreds of thousands of years of accumulation on the formation of the vast Loess Plateau. According to the loess accumulation of different environments, can be divided into three periods of China's Huangshi development: the early Pleistocene, equivalent to the first ice age, the climate is drier than the new tertiary, the occurrence of Wucheng loess accumulation; in the Pleistocene, the second ice age, the climate further drying, the accumulation of the Liashi loess, a wide range of soil layer thickness; late Pleistocene, the third ice age, the climate is more dry and cold, the accumulation of the Malan loess, the thickness of the small, but distribution Although the thickness was small, the distribution was wider, and it was called Shimoshu loess in the south. Into the Holocene, the climate turned warm and humid, loose loess layer, by running water erosion, the formation of gullies and gullies, beams, mounts widely spread broken surface.

Science is constantly developing, and in recent years scientists have discovered many phenomena that cannot be explained by the theory of loess wind formation. For example, the loess in the coarse powder sand content decreases from northwest to southeast, the clay content is increasing from northwest to southeast, this from northwest to southeast of the regular arrangement of the stacked tile ladder-like distribution of transition, rather than the plane fuzzy transition. This kind of stacked tile ladder-like distribution transition is more like the masterpiece of the flood, etc.

In order to understand how to use the flood, we need to have the following information.

In order to understand the Loess Plateau's "face" process, experts deliberately to the Loess Plateau in the western Gansu Jingning County, Qin'an County, Dingxi County and other places to collect the Loess Plateau 6 typical geological section of the loess specimens, from which more than 700 pieces of sporoderma samples and 209 pieces of epidermal sporoderma samples, which nearly 1,000 sporoderma samples approximately These nearly 1,000 spore samples recorded the vegetation change of the Loess Plateau from 46,000 years B.C. to the present. Through the measurement of carbon 14, 34 dates were obtained in 6 typical profiles***. After analysis, the experts found that the maximum number of spore particles isolated from the 20 grams of samples collected from the Loess Plateau reached about 1,112, while the minimum number was less than 50, showing the process of great changes in the environment and vegetation over 40,000 years.

Li Chunhai said, from the analysis of spores, found in the pine, spruce, fir, hemlock, oak, chrysanthemums and dozens of other plants spore records, experts believe that the Loess Plateau in the beginning of the time is not surnamed "yellow" in the 46,000 years of history, more than half of the time, the Loess Plateau is a component of forests and grasslands! During this time, the Loess Plateau has experienced a number of rapid "face changes" --- through the grasslands, forest steppe, coniferous forests, and desertification of grasslands and deserts and other conversions.

The formation of the Loess Plateau and the uplift of the Tibetan Plateau, accelerated the speed of erosion and weathering, in the low-lying areas around the plateau piled up a lot of pebbles, sand and finer particles. Whenever a gale rises, a scene of flying sand and dust is created in the western region. The swept-up sand and dust settles in turn, and the fine-grained dust finally lands in the Loess Plateau region, creating a deserted strip of land.

After the Indian plate moved northward and collided with the Asian-European plate, the crust of the Indian continent was inserted under the crust of the Asian continent and topped the latter. Thus, the shallow sea in the Himalayan region disappeared, and the Himalayas began to form and rise gradually, and the Tibetan plateau was also uplifted by the squeezing effect of the Indian plate.

However, the east-west oriented Himalayas blocked the Indian Ocean warm and humid air masses moving northward, over time, China's northwestern region is more and more arid, and gradually formed a large area of desert and the Gobi. This is where the sand and dust that built up the Loess Plateau originated. The massive Tibetan Plateau rises right into the westerly belt of the Northern Hemisphere and has been growing in height for 2.4 million years. The Tibetan Plateau is about one-third the width of the Westerly Wind Belt, and divides the near-surface layer of the belt into two branches, north and south. The southern branch flows eastward along the southern flank of the Himalayas, and the northern branch begins to flow eastward from the northeastern edge of the Tibetan Plateau. This high-altitude airflow exists year-round at an altitude of 3,500-7,000 meters, and has become the main driving force for transporting sand and dust. At the same time, the East Asian monsoon has been strengthened by the uplift of the Tibetan Plateau, and winter winds blowing from the northwest to the southeast, along with westerly rapids, have created a loess plateau in northern China.

Types of landforms

The three major landform types of mountains, plains and rivers are the mainstay of the Loess Plateau. The mountains towering over the plateau are like isolated islands in the ocean. For example, west of the Liupan Mountains, Longzhong Plateau on the Qu Wushan, Huajialing, Horsebit Mountain, Longdong Shaanbei Plateau on the Ziwuling, Baiyushan, Huanglongshan and so on. Plain (or loess) refers to the flat loess plateau ground, famous for Dongzhi Plateau in eastern Gansu and Luochuan Plateau in northern Shaanxi. The loess is wide and suitable for mechanized farming, and is an important agricultural area. However, the loess is susceptible to erosion by flowing water, and gullies develop, dividing the loess into long strips, which become mountain beams, called "Liang" land. If the beams are cut by the gullies, they are scattered and isolated, and the shape is like a bun-shaped hill, which is locally known as a "mount". By the "beam" and "mount" composed of loess hills, above the bottom of the nearby ditch is mostly in the 100 to 200 meters, soil erosion is serious, is the Yellow River sediment source area. Chuan is a deep-cut river valley plain under the loess surface. In the Liangxuan area, groundwater is exposed and converged into a small river, and the sediment brought by the river is deposited here, forming a small plain on both sides of the river, which is called "Chuan". There are also terraces on both sides of Chuan, i.e. "palm" and "staff" land. Palm is the source of the basin-like plains on the Chuan, unlike the strip distribution of the staff.

The Yellow River in its middle and upper reaches flows through the world's largest loess plateau. Loess Plateau soil layer is deep, loose soil, broken terrain, frequent rainstorms, soil erosion is extremely serious, is the main source of sediment of the Yellow River. Especially the Yellow River Hekou town to Tongguan this section of the river, the Yellow River in the process of crossing this section of the Loess Plateau, many tributaries into the Yellow River, the Yellow River "dyed" yellow. It has been determined that the sediment entering the Yellow River in this section accounts for 90% of the river's sand.

From the point of view of the earth, loess is mainly distributed in Central Asia to China's northwest, north and northeast of China, the world's largest loess plateau is located in the upper and middle reaches of the Yellow River region of the Loess Plateau. It extends roughly from the Yinshan Mountains in the north, to the Qinling Mountains in the south, to the Riyue Mountains in the west, and to the Taihang Mountains in the east, spanning six provinces of Qinghai, Ningxia, Gansu, Shaanxi, Shanxi, and Henan, with an area of 640,000 square kilometers. Loess cover thickness is generally below 100 meters, and to the east of Longdong, north of Shaanxi, west of Jinxian loess layer is the thickest, east of Liupan Mountain to the west side of Luliang Mountain, loess thickness between 100 meters to 200 meters, the thickest in Lanzhou, up to more than 300 meters. Loess distribution area and thickness, are among the world's top.

Erosion

Mainly caused by torrential gullies and valleys scouring the loosened loess. Loess particles are small, loose texture, upright and contain calcium carbonate, water easily dissolved, collapse. Ground slope, sparse vegetation, and summer rainstorms, resulting in strange peaks, steep walls, caves, caves, natural bridges and other micro-geomorphisms, but also contributes to the expansion of the gullies, accelerating soil erosion. At the same time, it is also related to the recent crustal uplift, which makes the gully bed continuously cut and side erosion, gully erosion intensified retroactively, and accordingly the valley slopes are constantly expanding, so the gully land is increasingly fragmented. In addition to the above natural factors, and human activities, especially the indiscriminate cultivation and logging, destruction of natural vegetation and other social factors are closely related. After the founding of New China, the Loess Plateau has taken a series of comprehensive measures to control soil erosion, planting trees, grass, the slope of the arable land into horizontal terraces, as well as water conservancy projects and other measures, the Loess Plateau has undergone a welcome change.

Increase the construction of the "Three Norths" protection forest, increase the area covered by vegetation and the coverage rate. Especially for the looser soil of the Loess Plateau, the forest cover must be higher than the national average of 22%, only in this way can be more effective in preventing soil erosion.

Differences in landforms

Based on the formation process and characteristics of landforms, it can be divided into the following parts: ① Longzhong Plateau. One is called Longxi Plateau. Located west of the Liupan Mountains, is a Cenozoic argillic basin, is a basin-type plateau, elevation 1500 to 2000 meters. Terrain fragmentation, more beams, mounts, gullies and valleys, ridge and plate terrain. ② Longdong, northern Shaanxi plateau. Including the Liupan Mountains to the east, west of the Luliang Mountains, north of the Weihe North Mountain, south of the Great Wall area. It is also a basin-type plateau, with an elevation of 800 to 1200 meters. After strong erosion, except for a few remaining loess plateaus (Dongzhi Plateau and Luochuan Plateau), most of the area has become broken beams and mounts and hills. There are only a few bedrock low mountains protruding above the plateau, like an island. ③ Shanxi Plateau. Including the Wutai Mountains, Hengshan Mountain south, north of the Funiu Mountains, west of the Taihang Mountains, east of the Luliang Mountains in the region. It consists of a series of folded fault block mountains and trapped basins. The mountains include Lvliang, Hengshan, Wutai, Zhongtiao and Taihang, and the basins include Datong, Xinxian, Taiyuan, Linfen and Yuncheng. In addition to the river valley plains, most of the area in the altitude of 1000 to 1500 meters, stony mountains constitute the main body of the plateau, loess accumulation is limited to the basin and the valley between the mountains, the distribution of the area accounts for about 40% of the region. The Weihe Plain is known as the Guanzhong Plain. It is located between the northern mountains of the Wei River and the Qinling Mountains, starting from Baoji in the west.

Energy Base

The Loess Plateau is extremely rich in coal resources, ranking first in the country in terms of reserves and production. Coal resources are not only large in quantity and quality, but also have better mining conditions. Among them, the coal reserves available for open-pit mining amounted to 20 billion tons. About half of the country's mega coal fields with proven reserves are located here. Shanxi Province is the largest coal base in China. The Shenfu coal field in northern Shaanxi Province and the Changqing oil field are also important parts of the Loess Plateau energy base. The Loess Plateau region is centrally located, as the country's energy base, is a constant supply of coal and electricity to the country, people figuratively called it the country's "boiler room".

History

Since the Qin and Han Dynasties, the Loess Plateau has experienced three high tides of deforestation and reclamation, the first of which was the large-scale Qin and Han Dynasties "Tunken" (border guards organized reclamation) and "immigrant real border" reclamation. This big "reclamation" so that the forests in northern Jin and northern Shaanxi have been destroyed on a large scale. The second is the implementation of the Ming dynasty of large-scale "reclamation", so that the northern Loess Plateau ecological environment has been unprecedented havoc. According to evidence, the beginning of the Ming Dynasty in the Loess Plateau in northern Shaanxi (Yan'an, Suide, Yulin area) and Jinbei vigorously implement the "cantonment" system, and even forced the provisions of each border guards to deforest the task of clearing land. From here it is not difficult to see, the Ming Dynasty, the implementation of the "cantonment" system of environmental damage is serious. The third big reclamation is the Qing dynasty, the Qing dynasty has been the implementation of incentives to reclaim the land system, reclamation category from the north of Shaanxi, Jinbei and north to southern Inner Mongolia, the northern Loess Plateau and the Ordos Plateau millions of acres of grassland was reclaimed as farmland, so that a large area of land sandy, soil erosion intensified.