Transient fluvial landscape and preservation of low-relief terrains in an emerging orogen: Example from Hengchun Peninsula, Taiwan

The oblique collision of Taiwan orogen led to a progressive southward uplift and emergence of a submarine accretionary wedge. The Hengchun Peninsula located at the southernmost tip of Taiwan island represents the most recently emerged landform of an antecedent submarine surface. In this study we examine the geomorphic evolution of this newly emerged and uplifted landscape. The extraction of geomorphic parameters (knickpoint distribution, steepness index of rivers) indicates a transient nature of the landscape but shows that a simple model of regressive erosion consecutive to sudden uplift is unsatisfactory. Knickpoint migration modeling shows that only the upstream Sizhong basin can be explained by this single process. On the other hand, the occurrence of a relict landscape (Mutan Ponds low relief) developed at low elevations and, today uplifted in the core of the peninsula, has strongly influenced the drainage evolution. Numerous knickpoints are linked to capture processes around the Mutan Ponds area, indicating a dynamic reorganization of the drainage system. We propose that the landscape of the Hengchun Peninsula is in a transient stage and results from a combination between rejuvenation and drainage rearrangement caused by the late stage of emergence of the south of Taiwan.