Late Quaternary catchment evolution and erosion rates in the Tyrrhenian side of central Italy

- Holocene geomorphological evolution of the Formone river catchment (Tuscany, Italy)
- New data on soil erosion rate during last 14,000 yrs
- First absolute chronological constrains on the alluvial deposits of the study area
- GIS computation of erosion volume and rate

This work assessed the geomorphological evolution and erosion rates in a small clayey catchment of Tyrrhenian central Italy, providing chronological constraints for the fluvial deposits of the area for the first time. The study area is the catchment of the Formone stream, a left tributary of the Orcia River (Tuscany, Italy). A 5 km-long section of the valley, up to its confluence with the Orcia, was studied. It has an area of ca. 12 km2 and elevations between ca. 300 and 600 m a.s.l. Two soil samples have been radiocarbon dated. One was located at the top of a fluvial terrace (~ 20 m above the present thalweg), and the other was located near the water divide of a small tributary catchment: they yielded ages of 2780 ± 40 and 14,050 ± 70 yrs B.P., respectively.These chronological constraints allowed us to reconstruct the geomorphological evolution of the area through topographic and GIS analyses, and to estimate late Quaternary erosion rates. The ages provided a chronological reference for the terraced fluvial deposits of the Formone and the upper Orcia catchments. The resultant erosion rates are consistent with those in the literature both for the Tyrrhenian side of central Italy and for Mediterranean Europe. Moreover, the results confirmed that very intense erosion processes occurred as a consequence of the Pleistocene-Holocene climatic change, as observed in the peri-Adriatic belt of central Italy.