Relationships between a new slope morphometric index and calanchi erosionin northern Sicily, Italy

The Italian badlands, or “calanchi”, are common landforms in Mediterranean areas including central andsouthern Italy. Calanchi landforms may be compared to small hydrographic basins. These landforms arecharacterised by dense, hierarchical and rapidly evolving drainage systems carved into steep clayey slopesand by a sharply alternating pattern of furrows and narrow, generally sharp crests.This work presents a study of morphometric characteristics and a statistical analysis for two sites in northernSicily (Italy), on outcrops of silty-clay deposits affected by active erosion processes, which give this area a typicalcalanchi landscape. In particular, factors closely linked to the characteristics of the hydrographic network andslope morphometry were considered and analysed. The initial geometry of the slopes was reconstructed andstatistically compared with that of the current calanchi slopes including the drainage network.A new morphometric index (Morphometric Slope Index, MSI) was defined to represent the initial slope geometryas awhole. This indexwas found to be effective in defining the structure of hydrographic networks, summarisingthe characteristics and type of slope evolution, and quantifying the rate of soil erosion. The rate wasdetermined based on both linear (gully erosion) and areal (landslides, sheet and rill erosion) morphogeneticprocesses, and our analysis based on MSI indicates the dominance of areal erosion. MSI could also be used forbasins larger than calanchi to represent the characteristics of geomorphic processes.