How erosional efficiency modulates landscape response to drainage reorganization: New empirical evidence from the Andes

Abstract

The fluvial network in active mountain ranges is considered to evolve from longitudinal to transverse-dominated drainage systems. This hypothesis links to the forelandward migration of the orogen, while crustal thickening modifies the range's flank slopes, enhancing erosional efficiency. We probe such a proposition with new empirical observations from the Colombian Andes by studying the recent capture of the longitudinal Suárez and Chicamocha Rivers by the transverse Sogamoso River. Firstly, by integrating published low-temperature thermochronology and quantitative topographic metrics like χ, we found that rejuvenated rock uplift in the Cocuy and Yariguies ranges delays the transition from longitudinal to transverse-dominated drainage systems by compensating the across-divide contrasts in erosion. To further constrain the spatiotemporal response of the Suárez and Chicamocha Rivers after the discrete capture, we computed sediment-gauge erosion rates in conjunction with rainfall-normalized channel steepness and Gilbert metrics. We observe stark contrasts in erosion rates between the Chicamocha (maximum of 148.22 ± 44.86 m/Myr) and Suárez Rivers (maximum of 71.9 ± 21.5 m/Myr). Higher erosion rates in the former are expressed with widely distributed slope-break knickpoints that migrated further upstream with catchment expansion at the expense of the less efficiently erosive Suárez River basin. We interpret these erosional differences as a lithological control on the pace of topographic response to an external perturbation (discrete capture), given low-lying sedimentary rocks delay the erosional response of the Suárez River basin. Our research therefore emphasizes the role that lithology poses in keeping the landscape in an unsteady topographic condition.