MSI (morphometric slope index) for analyzing activation and evolution of calanchi in Italy

The “calanchi” (singular calanco) are a typical example of Italian badlands, widespread in areas with hills of clay-rich sediments and rocks. They appear as a very dense and rapidly evolving drainage system characterized by an alternating pattern of narrow furrows and sharp crests. The calanchi can be considered as small hydrographical basins, characterized by two possible drainage patterns, parallel and dendritic. The two patterns show both linear and areal erosion processes. In this study, calanchi with dendritic drainage patterns were analyzed in three different areas representative of the Italian Peninsular: Atri in the Abruzzi region, Mount Ascensione in the Marche region, and Orcia Valley in the Tuscany region. For each calanchi, the pre-erosion topographic surface was reconstructed and the value of MSI (morphometric slope index) was calculated for the surface. The volume of eroded material was estimated by comparing the pre-calanchi and present surfaces. We assumed that slope morphometry influences the type of erosion processes, and the efficacy of these processes with respect to the amount of eroded material is a function of their duration. We deduced that calanchi inception was contemporaneous, because the duration of the processes was common to all landforms, and probably due to a common climate input. Moreover, the relations among MSI, eroded volume and erosion processes indicate that, over a long period, areally distributed surface processes contribute more to total sediment yields than channel flows.