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

Abstract

The Italian badlands, or “calanchi”, are common landforms in Mediterranean areas including central and southern Italy. Calanchi landforms may be compared to small hydrographic basins. These landforms are characterised by dense, hierarchical and rapidly evolving drainage systems carved into steep clayey slopes and 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 northern Sicily (Italy), on outcrops of silty-clay deposits affected by active erosion processes, which give this area a typical calanchi landscape. In particular, factors closely linked to the characteristics of the hydrographic network and slope morphometry were considered and analysed. The initial geometry of the slopes was reconstructed and statistically 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 geometry as awhole. This indexwas found to be effective in defining the structure of hydrographic networks, summarising the characteristics and type of slope evolution, and quantifying the rate of soil erosion. The rate was determined based on both linear (gully erosion) and areal (landslides, sheet and rill erosion) morphogenetic processes, and our analysis based on MSI indicates the dominance of areal erosion. MSI could also be used for basins larger than calanchi to represent the characteristics of geomorphic processes.