The Relationship between Basin Hypsometric Integral Scale Dependence and Rock Uplift Rate in a Range Front Area: A Case Study from the Coastal Range, Taiwan

摘要

The hypsometric curve and hypsometric integral (HI) of drainage basins are common tectonic geomorphologic indices. Generally, the hypsometric curve is convex and the HI is high in areas of strong rock uplift. However, previous research indicates that an inverse correlation exists between the HI and rock uplift in the mountain-piedmont junction in California. It has also been proposed that the basin HI in the range front area has scale dependence, which increases the difficulty of inferring tectonic uplift. We therefore examined the effects of tectonic uplift and basin scale on basin HI in the southern Coastal Range of eastern Taiwan. The results showed that basin size could affect the HI. First-order Strahler basins are smaller and have higher HIs, whereas second- and third-order basins are larger and have lower HIs, indicating some form of scale dependence. The coefficient of logarithmic regression between mean area and mean HI of every subbasin was calculated to determine the scale dependence index (SDI). The lower the SDI, the higher the scale dependence. The SDI was utilized to distinguish basins' topographic tendencies between range interior and range front. We also applied the igneous-area ratio to define spatial tendencies of basins' lithology distributions. The lower the igneous-area ratio, the greater the spatial tendency toward range front will be. Basins in the middle of the south Coastal Range tended to approach a range interior steady state, with higher SDIs and a positive correlation between HI and rock uplift rate. Basins in the north and south of the south Coastal Range tended to be at a range front nonsteady state, with lower SDIs and a negative correlation between HI and rock uplift rate. The correlations may be applicable to estimate the rock uplift rate.