蘭陽地區沖積扇的地形學研究
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Date
1995-03-??
Authors
張瑞津
石再添
楊淑君
林譽方
陳翰霖
董德輝
Journal Title
Journal ISSN
Volume Title
Publisher
地理學系
Department of Geography, NTNU
Department of Geography, NTNU
Abstract
蘭陽地區是臺灣沖積扇發達地區之一，區內共有30個沖積扇，位於縱谷內13個，平原區者17個。縱谷上游諸扇呈四階複成扇，且扇項有逐次下移的現象，可推知本區現今山麓的河下切率，大於集水域的上升速率。另由扇體堆積的縱剖面呈凸透鏡狀，可推知沖積扇形成之同時，集水域的地盤仍持續隆升。由沖積扇的形態與堆積物特徵的相關分析，沖積扇面積愈大，流幅愈大，坡度愈緩，堆積物淘選度愈佳，圓度愈大。根據集水域的地形、地質、氣候各項特徵所作之判別分析，得知主流等級、起伏比、隆升率、年平均降雨量、面積高度積分、溪口距、山間盆地面積為決定沖積扇存在的要因。經因子分析地盤隆升率、集水域面積、起伏比，扇面時期為影響沖積扇形態的要因。由沖積扇特徵特徵與集水域各地形、地質、氣候諸要素的關係觀之，本區沖積扇的演育頗適合以侵蝕輪迴說及動態平衡說加以解釋均似合適。
Lanyang area including longitudinal valley and alluvial plain is located between the northern part of Central Range and Snow Mountain. With conspicuous fault scarps and abundant debris supply, alluvial fans are developed well in this area. There are 30 fans with area over 1 ha. each, 13 of them are distributed in the longitudinal valley and the rest are in the peidmont surrounding the alluvial plain. In the longitudinal valley, most of the fans have been undercut to be composit fans. There are 4 steps in the upper valley where as 2 steps in the down valley. The fact of the fan head trench shifting down could reveal that the down cutting rate of stream channel is greater than the uplift rate of mountain area. The cross profile of fan deposition is shaped in lenticular could be resulted from the continul uplift of the mountain area. By product-moment correlation, some fan variables are corretaled closely, such as fan area has a significant relation with width, slope and sorting and roundness of sediments. Based on the discriminant analysis, the stream order, relief ratio, uplift rate, precipitation, hypsometric integral, the distance between valley mouth and intermountain basin areas are the dominating factors to the existence of the fan. By factor analysis, uplift rate, drainage area, relief ratio and stage of fan are the main factors influencing the fan morphology. From the relation between fan and drainage basin, the evolution of the fan can be interpretated by both the equillibrium model and the erosional cycle model.
Lanyang area including longitudinal valley and alluvial plain is located between the northern part of Central Range and Snow Mountain. With conspicuous fault scarps and abundant debris supply, alluvial fans are developed well in this area. There are 30 fans with area over 1 ha. each, 13 of them are distributed in the longitudinal valley and the rest are in the peidmont surrounding the alluvial plain. In the longitudinal valley, most of the fans have been undercut to be composit fans. There are 4 steps in the upper valley where as 2 steps in the down valley. The fact of the fan head trench shifting down could reveal that the down cutting rate of stream channel is greater than the uplift rate of mountain area. The cross profile of fan deposition is shaped in lenticular could be resulted from the continul uplift of the mountain area. By product-moment correlation, some fan variables are corretaled closely, such as fan area has a significant relation with width, slope and sorting and roundness of sediments. Based on the discriminant analysis, the stream order, relief ratio, uplift rate, precipitation, hypsometric integral, the distance between valley mouth and intermountain basin areas are the dominating factors to the existence of the fan. By factor analysis, uplift rate, drainage area, relief ratio and stage of fan are the main factors influencing the fan morphology. From the relation between fan and drainage basin, the evolution of the fan can be interpretated by both the equillibrium model and the erosional cycle model.