Erosion of a tectonically uplifting coastal landscape, NE Sicily, Italy

Abstract

We investigate the relative importance of tectonic uplift, climate, and bedrock resistance as controls upon channel morphology in the active orogen of NE Sicily. The study area displays spatial variations in uplift rate, precipitation, and bedrock resistance. The significance of each of these gradients was tested using established morphometric relationships. Twenty catchments were investigated using the 28-m Aster digital elevation model (DEM) for longitudinal profile analysis, Google EarthTM to determine channel widths, and Schmidt Hammer readings to quantify bedrock strength. Based on channel morphologies and hillslope gradients, the basins exhibit three distinct reaches: upper, middle, and lower. The upper reaches of the bedrock channels display concave longitudinal profiles, positive correlation between uplift rate and steepness, and exponents in the width–area relationship of 0.4–0.5, indicating that uplift is the major control on the morphology of this reach. The middle reaches, however, display sublinear longitudinal profiles, weak correlation between uplift rate and channel steepness, and no systematic width–area relationship. We interpret this to be caused by the presence of a shear zone, which, through fracturing, has tectonically increased the bedrock erodibility, irrespective of its lithology. In the lower reaches, the channels are alluvial. Neither channel concavity nor steepness seems to be affected by the spatial variation in precipitation in any of the reaches, indicating that climate does not noticeably affect channel morphology. These observations suggest a strong tectonic influence on channel evolution in this active mountainous region. Our study illustrates how reach-scale morphometric analysis can aid understanding of how fluvial systems vary with potential controlling parameters.