INVESTIGATING LOW-RELIEF TOPOGRAPHY IN TAIWAN'S CENTRAL RANGE

Taiwan’s Central Range is a young, tectonically active orogen that typically exhibits rapidly incising rivers, steep landslide-prone hillslopes, and overall high topographic relief. Recently, regions of anomalous topography have been identified within the Central Range that are characterized by low slopes, low relief and lower erosion rates. The exact cause of these anomalous regions remains unclear; in recent years, researchers have proposed river capture and drainage divide migration method for their formation, which runs counter to the hypothesis that they represent uplifted relict topography. In this contribution, we use an updated 20-m Digital Elevation Model for Taiwan and perform topographic and geospatial analysis to systematically map and investigate regions of low hillslope gradients (<25 degrees) and low topographic relief (<440 m over a 1-km window) across the entire Central Range. Regions of anomalous topography range in size from 0.2-5 km² and are typically found along the central divide of the Central Range, with additional clusters found near the Hsueshan Range, Beinan Shan, and southern Taiwan. Anomalous topography is found at a wide range of elevations far below the Late Pleistocene ELA (including examples <1000 m elevation), occur within both the black schist of the Tananao Complex and slates of the Lushan Formation, and lie within topography that experience rainfall rates ranging from 2 m/yr to over 3 m/yr, indicating that glaciation, lithology, and precipitation gradients are not primary explanations of all anomalous topography. Although small scale examples of river capture with lower relief do exist within the Central Range, most examples lie in the upper portions of watersheds consistent with ongoing transient incision and landscape adjustment to uplift. Ongoing work will further investigate the relationship between anomalous topography, river capture and possible uplifted relict topography. Overall, this contribution is helping to refine ideas about the erosion and the uplift history of Taiwan.