Recent alluvial fans in Calabria (southern Italy)

Abstract

The present work aims at identifying the location of recent debris-flow-dominated alluvial fans at a regional scale in Calabria (southern Italy). Here, alluvial fans widely occur as both tributary junction and mountain front types and represent a potential hazard to human settlements and transportation links near or on them. The alluvial fans inventory map at 1:250,000 scale was obtained by means of a stereoscopic interpretation of aerial photos shot in 1954–1955. To establish the activity of the detected alluvial fans, recent documentary evidence (scientific reports, local newspapers and journals, and Internet blogs) on debris-flow events and historical satellite imagery available on Google Earth, covering the period 2001–2014, were analysed. Subsequently, the activity of the alluvial fans over the last 60 years has been divided into four classes. A total of 1170 alluvial fans have been mapped, 545 (46.58%) of which have been active over the last 60 years. The alluvial fans with a length from apex to toe < 200 m predominate, constituting 70% of the total. In the feeder basins, the dominant lithologies are represented by medium to high-grade metamorphic rocks and igneous rocks, gravel and debris and, shales and low-grade metamorphic rocks. Finally, the inventory map shows that 103 settlements are located on alluvial fans, 18 of which are active or have been active during the last 60 years. This map is a useful tool for land planning policy and for the assessment of risk deriving from debris-flows on the alluvial fans of the Calabria region.