The Alluvial Fans along the Eastern Foot of Helan Mountain
MO Duowen\ ZHU Zhongli\ WAN Linyi (Department of Urban and Environmental Sciences, Peking University,Beijing,100871)
There are many alluvial fans developed along the eastern foot of Helan Mountain. Under the control of climate, mountain features and the Huanghe River, the fans have many different characters comparing with the fans of other region, such as conglomerate with boulders on the surface, big slope and abrupt slope change, salt lake or swamp, sand dunes at the margin of the fans. And also there are many different features among the fans themselves. Dawukou alluvial fan, located at the north end of the study area, has fine sediments, big fan area, flat slope and typical morphology. In front of the middle segment of the mountain, there is Dashuigou alluvial fan with coarse sediment, moderate slope and less fan area. Helankou alluvial fan, at the south segment of the mountainside, consists of coarse sediment, steep slope and moderate fan area. This paper describes the geomorphology, sediments, fan size, fan figure and depositional structure of the fans along the eastern foot of Helan Mountain. In study of the relationship of the fan features and the source basin features we got such relations as: A \-f=6\^245 A \-d 1.09 h 1.33 and r =10\^67 A d -0.27 h 0.39 ( A \-f:fan area, A\- d:source basin area, h :relief, r :fan slope). And we concluded that the main factor affecting the fan area and slope of this region is the relief of Helan mountain.