Dynamic landscape evolution of the western Taiwan orogen

Abstract:

Landscape evolution is fundamentally coupled with processes of river channel networks, thus understanding the changes in river systems would provide important constraints on geomorphic and tectonic developments. In the western part of the Taiwan orogen, we observed a major flow direction transition of the main trunks at the southern drainage divide of the Chuoshui River. South of this transition, river systems are sub-parallel and flow to the south, but to the north all main trunks flow to the west. This is consistent with the southwestward propagation of the collision in Taiwan, and implies that the landscapes in the northern part are more “matured” than in the southern part. Therefore, the river systems in Taiwan appear to have the tendency to develop from south-flowing to west-flowing from south to north. Based on such hypothesis, we hope to reconstruct the evolution patterns of river basins and their mechanisms of western Taiwan in this study.

We used a new method, the fluvial geomorphic index χ, to analyze the river networks in western Taiwan. By comparing the χ values of river tributaries on both sides of the drainage divide, we can obtain the information of the divide stability. In the southern part of western Taiwan, most of the main water divides are unstable. 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. We hope this study would provide more information for reconstructing river basins in the past and understanding their developments in the future.