花東縱谷沖積扇的地形學研究

Abstract

Huatung (Hualien-Taitung) Longitudinal Valley locates between Central Range and Coastal Range with a length of 183 km and width of 3-4km. With conspicuous fault scarps and abundant debris supply , alluvial fans are developed well in this valley. There are 31 fans with over 2 km2 in size and over 2[] in slope. Due to the continual uplift, most of the fans have been undercut into composite fans. There are 2-3 steps in southern fans whereas 1 step in northern fans, and also, the amounts of dissection of southern fans are greater than that of northern fans. These differences, thus, may provide an usable reference for differential uplift in Huatung area. By product-moment correlation, there are some relations between fan variables, such as a significant relation with fan area and fan width, slope and height. Further, the factors of drainage area, relief ratio, stream length and intermountain basin area have strong correlation with the variables of fan area, slope, width and degree of dissection. Based on the discriminant analysis, the sediment space, uplift rate, geologic age, precipitation, stream order and slope failure area are the dominating factors to the existence of fan. By factor analysis and canonical correlation analysis the results can be concluded that drainage area, stage of fan, sediment space, amount of uplift and relief ratio of drainage basins are the common factors which influence the fan morphology. It is difficult to examine the evolutionary hypothesis and climatic hypothesis in this area due to the insufficient chronologic and climatic data. But from the strong relation between fans and drainage basins, the fan development in this area can be interpretated by equilibrium hypothesis.