Dynamic landscape evolution of the Taiwan orogen from fluvial channel morphology
Date Issued
2016
Date
2016
Author(s)
Chen, Cheng-Hung
Abstract
Landscape evolution is fundamentally coupled with processes within river channel networks, thus understanding the changes in river systems would provide important constraints on geomorphic and tectonic developments. Most previous studies assumed that river networks and watershed boundaries are stable through time. However, if rivers on both sides of the drainage divide have different erosion rates, the divide may move due to the erosion rate difference. In this study, we used a new method (the fluvial geomorphic index χ) to analyze the river networks of the Taiwan orogen. By comparing the χ values of river tributaries on both sides of the drainage divide, we can obtain the information of the divide stability. Based on the results of χ values, satellite image analysis, river steepness index, and field investigations, the major river basins of the Taiwan orogen appear to be adjusting their sizes and shape. The main drainage divide of the Hsuehshan Range may move from southeast to northwest. This movement is likely produced by the general tectonic setting of the area and the activity of the Northern Ilan structure. The results from the Zengwun River basin show that some parts of the drainage area had been captured by another river, thus the rivers change the flow direction from southward to westward probably due to river captures. From south to north in western Taiwan, the χ values of river basins gradually reach an equilibrium. This suggests changing the flow direction would make the channels more stable. Moreover, this development is likely produced by the general tectonic evolution processes of the fold and thrust belt in western Taiwan. The identification of past and ongoing changes in river networks creates a new opportunity to explore connections between geological and geomorphic systems. We hope this study would provide more information for reconstructing river basins in the past and understanding their developments in the future.
Subjects
Landscape evolution
Geomorphic index χ
River steepness index
Divide moving
River capture
Type
thesis
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