The use of the Stream Length–Gradient index in morphotectonic analysis of small catchments: A case study from Central Italy

The aim of this work is to test an integrated quantitative geomorphic approach based on Stream Length–Gradient Index (SL Index) analysis within the small catchment of the Tarugo River in the Northern Marchean Apennines (Central Italy). The Tarugo River basin, 92 km2 wide, strikes SW–NE across the Marchean Ridge and the western sector of Marchean Piedmont. The area is characterized by a series of NW–SE trending, NE verging thrust folds affecting the Meso–Cenozoic bedrock that pass upward from dominantly carbonate to dominantly terrigenous rocks. The area investigated has been affected since the Pliocene by extensional tectonics, accompanying a regional uplift decreasing in rate north-eastwards. In this work the SL Index analysis has been integrated with the spatial analysis of the Amplitude of relief (Ar) and compared to geological and geomorphological field data. Results of this work indicate that the SL Index is a valid tool to detect the long wavelength structural effect on topography as well as the incipient local response to regional processes (i.e. regional uplift) that is often undetectable by other morphotectonic parameters. In contrast, the SL Index analysis seems not be a valid tool for discriminating the local lithological influence from the tectonic one.