Tectonics controls on fluvial landscapes and drainage development in the westernmost part of Switzerland: Insights from DEM-derived geomorphic indices

Abstract

Abstract This work focuses particularly on the geomorphological evidence for the tectonic controls on the development of the present-day fluvial landscapes in the westernmost part of Switzerland. The tectonic deformation was evaluated on the basis of a combined analysis of several classical geomorphic indices (hypsometric curves and integrals, transverse topographic symmetry index, and channel s bottom gradients) through high-precision DEM processing. A new optimization strategy was applied for defining geomorphic anomalies related to tectonic activity along the channels of three rivers, based on a combined investigation of topographic swath, longitudinal profiles, geological and geophysical observations. The results show that the abnormally high values of hypsometric integral are spatially occurred on the hanging walls of thrust faults, while abnormally low ones are spatially observed in the same locations of paleo-ice stream pathways. Observations obtained from transverse topographic symmetry index display asymmetries in the most of the studied drainage basins with a predominant SE direction of lateral migration. This direction is in agreement with the dominant dip-direction of the bedding planes within the study area. Abnormal changes in the channel s bottom gradients, which almost coincide in space with pronounced change in the depth of the subsurface geologic layers and in the geophysical properties, are marked by distinct topographic relief in areas where rivers flow above blind and emergent faults. Our analysis not only confirms that there is a significant tectonic control on the evolution of drainage systems, but also revealed a possible evidence for the reactivation of some inherited faults.