Abstract: 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 Heln Mountain. In study of the relationship of the fan features and the source basin features we got such relations as: A_f =6.245A_d^1.09h^1.33 and r=10.67A_d^-0.27h^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.

Key words: alluvial fan, Helan mountain, relief

摘要： 贺兰山东麓是我国冲积扇发育比较典型的地区之一，受独特的气候和山地特征以及黄河冲积平原的影响，该地区冲积扇发育有着不同于其他地区的特点：扇体主要以砂砾石物质为主形成，砾石滩地与前缘坡地呈突然转折，前缘形成咸水湖沼和沙地，扇体坡度较大，扇体前缘基本沿直线分布等。而且本地区冲积扇在发育上也存在着较大的差异：北段的大武口冲积扇物质组成较细，坡度较平缓，面积较大。中段的大水沟等四个扇体组成物质较粗，坡度较大，而面积较小。南段的贺兰口等4个扇体则物质粗，坡度大，面积中等。本文介绍了贺兰山东麓冲积扇的形态、规模、地貌、物质、沉积结构构造等。并对流域特征与扇体特征的关系以及其他影响冲积扇的发育特征的因素进行了探讨，发现扇体面积与流域面积、地势起伏度有以下关系：A_f=6.245A_d^1.09h^1.33。扇体坡度与流域面积和地势起伏度的关系式为：r=10.67A_d^-0.27h^0.39。可见山地地势起伏对贺兰山东麓冲积扇的影响相对较大。同时，气候、构造和黄河冲积平原也影响着扇体发育。

关键词: 冲积扇, 贺兰山, 地势起伏度