The gravitational landscape of Montespertoli (Valdelsa Basin, Tuscany, Italy): State of activity and characteristics of complex landslides

The town of Montespertoli (Florence Province) is located on a NW–SE ridge that separates the Valdelsa River Basin to the west from the Val di Pesa Basin to the east. The bedrock is characterised by alternations of alluvial, transitional, and marine deposits with a maximum gradient of 5°. The slopes surrounding the town are affected by a series of rock slides, flows, and complex landslides, usually roto-translational slides that evolve into rock flows. The headward evolution of the landslide escarpments threatens the stability of several buildings and streets. The conditions leading to the activation of these gravitational movements are mainly based on the lithological setting and downcutting of river valleys. In addition, recent inappropriate water management plays an important role locally. The aim of this study is to illustrate the importance of gravitational phenomena in the modelling of areas with this type of structural setting, which is very common in many Italian regions, and to identify the geometry and state of activity of gravitational movements. To verify the activity of the movements in recent decades, multitemporal analysis was carried out using orthophotos of four different periods: 1954, 1988, 1996, and 2013. Based on the results, a classification of the degree of activity of the landslides was introduced, which can be applied at the regional scale by the regional authority. Several researchers proposed to utilise Synthetic Aperture Radar (SAR) technology. The use of aerial photos is of advantage because these photos are easily available at a very low price, as needed by professional geologists.