Geomorphology And Affecting Factors Analysis Of Alluvial Fans In North China

More and more research proves that alluvial fan is affected by many environmental factors such as tectonic activity, climatic conditions, base level change, drainage basin geology, geomorphology and plant covering of drainage basin, human activities; therefore, alluvial fan research bears great significance to theory of geomorphology and practicalities.Climatic conditions vary greatly in North China, and alluvial fans lying along margins of basins between mountains or at mountain front. Research areas of this dissertation include Lvliang Mountain, Helan Mountain and Qilian Mountain. The shape, structure, mass composition and deposition process of these alluvial fans are researched through field exploration and laboratory experiments. Remote Sensing and GIS technologies are also used. Characteristics of alluvial fans at margins of faulted basin are researched. Alluvial fans in different faulted basins of Lvliang Mountain are compared; Alluvial fans in three different regions are also compared. Agricultural land on alluvial fans is researched at chapter 5 of this dissertation.Great differences between alluvial fans in different regions are found. Alluvial fans at Lvliang Mountain are characterized by smaller size, channel-fill deposition and sheet-flood deposition. There has sharply contrast between alluvial fans at the north sector and at the south sector of Helan mountain: alluvial fans with larger area and steeper slope at south sector bear debris flow, but alluvial fans at north sector, which have smaller size and gentler slope, were formed mainly by stream flow. Alluvial fans at Qilian Mountain often have larger size, and their deposition process is stream flow. The main bodies of these alluvial fans were formed during Late Pleistocene.Research of alluvial fans at Houma basin reveals how alluvial fans are affected by faulted basins. It is found that the shape, structure and deposition process of alluvial fans relate well to its position in faulted basin. Fan head incision, channel-fill deposits in drainage basin, emergence of bedrock can be criteria of tectonic activity of boundary fault.Comparison of alluvial fans in Taiyuan basin, Linfen basin and Houma basin shows that tectonic activity and Fen river base level account for the differences of alluvial fans in these three basins, and they also affect deposition process, channel-fill deposits in drainage basin and fan head incision. Comparison of alluvial fans in three regions shows that climatic conditions and deposition process impact fan size greatly.Research of agricultural land on alluvial fans shows that fine deposits mainly determine the agricultural land; and fine deposits are determined by particular deposition process and geomorphology of alluvial fans together; as an allochthonic deposit, loess plays an important role in the development of agricultural land on alluvial fans.