The Evolutionary Process Of The Landform And Soil Erosion During Historical Period In Loess Plateau

Loess Plateau as a special regional unit of landform is concerned because of its serious soil erosion and ecological problem. The evolutionary process is related to the soil erosion in the plateau and the relation between the recent landform and the soil erosion is based upon its past condition. So the study of the evolutionary process of the landform and soil erosion can not only enriches the study on the physical geography, but also fills in the gaps of the plateau's physical geomorphology and helps the rebuild of ecologic environment in Loess Plateau. According to the styles of landform, the plateau is divided into five main types. Based on making of the field survey, semi-position observation, historical document research, environment exam and applying of knowledge of C14 Chronology, Geography analyze and GPS, RS, GIS technology, the paper obtained some research results, the main task and key results are follow :1.The paper comprehensively commented on the researching condition of the evolutionary process of landform and soil erosion during historical period in Loess Plateau. The paper also studied the regional characteristics of landform and soil erosion , studied geology, climate, vegetation, population and land using which affected landform process and soil erosion changes in Loess Plateau.2. The channel of Xi'an section of Weihe River has been moving to north and the rate of moving speed were pointed out. The river's first terrace was formed from early Holocene to late Chun-Qiu dynasty and the flood plain was made later. The location of Weihe River was fixed. The river bed moving speed in Holocene is 0.80-0.87m/a,besides the speed is different between eastern and western, the paper analyzed its reasons. On the contrary, the channel of Bahe River has been moving to west as Lishan Mountain's rising, the moving amount is 2150~2200m from West Han to Sui-Tang dynasty, and Bahe River's bed has been steady after Sui-Tang Dynasty.3.The evolution of the Loess Taiyuan (platform Land) is the stage of making gullies, through the study of Qixinghe River Drainage Basin, most gullies of them were formed after Jin dynasty. The soil erosion was weak before East Han dynasty and got stronger after that times relatively. During Yuan, Ming, Qing dynasties and early last century, the soil erosion became most serious and its gullies developing was the strongest . So planting is a major measure to water and soil conservation in the Loess Taiyuan.4.Landslide is a main factor to produce the geological hazards, landslide also is the main forms of landform evolutionary process and soil erosion during historicalinperiod in edge of Loess Taiyuan. The paper obtained that soil erosion average amount by gullies in edge of Loess Taiyuan is 102.68-529.12t/a from Qin dynasty to early 20th century; from early 20th century to now it has enlarge to 980.29-2125.89t/a. In historical period, excavated edge slope of Loess Taiyuan by human being is the important role for its landform evolutionary process and soil erosion.5.There are four erosion stages since mid-late Pleistocene in Luochuan Yuan -83 stage to form Heimugou, Holocene to be serious erosion stage, the average speed of gully evolution of Heimugou in Holocene is 0.3740m/a,on contrary in 1768-1957 A.D. is 4.3386m/a which is 11.6 times of the average speed of Heimugou in Holocene. The paper studied Luochuan Yuan's gullies evolution since Yuan Dynasty. The research indicating: since Yuan Dynasty, gully development speed and soil erosion intensity have the trend of aggravation. In the period when precipitation is comparatively rich, the gully development speed and soil erosion intensity are comparatively stronger. It is the principal reason why natural erosion and man-made erosion lead to gully development and soil erosion violently since modern and contemporary age. Gully's landform evolution process is from the bystreet gully to the V-shaped gully, finally to the U- shaped gully. The districts of "U"-gully and "V"-gully are major to control against soil erosion in the...