CAUSE OF STRUCTURE DIFFERENCE OF LOESS LAYER AND ITS EFFECT ON NATUEAL ENVIRONMENT

The present paper studies on how to harness the silted Yellow River.The ability of erosion resistance of loess layer and the effect of human′s activity on the ability are discussed.And it is concluded that the water disaster caused by the Yellow River is mainly resulted from strong erosion of mud and sand in loess area by human′s cultivation and planting.The relationship between basement fracture system and erosion of loess layer area in Shaanxi Gansu Ningxia Block is analyzed(Fig.1).The harnessing plan is derived from the analysis.By the analysis several conclusions are obtained as follows.(1) The main cause of the disaster of the Yellow River is the destruction of loess layer.(2) Loess layer itself has certain ability of erosion resistance,but human′s activity such as farming decreases the ability.(3) The fracture degree of loess layer depends also on the texture background and the structure of loess layer.(4) The deep studies on the structure of the loess layer are very helpful to the nature environment area partition.(5) The non uniformity of inner structure of Shaanxi Gansu Ningxia Block is the outcome of the action of crustal wavy masaic structures.(6) Naural property of environment is the first consideration in study on disaster reduction.