Geomorphological surveys and software simulations for rock fall hazard assessment: a case study in the Italian Alps

Abstract. In northern Italy, fast-moving landslides represent a significant threat to the population and human facilities. In the eastern portion of the Italian Alps, rock falls are recurrent and are often responsible for casualties or severe damage to roads and buildings. The above-cited type of landslide is frequent in mountain ranges, is characterised by strong relief energy and is triggered by earthquakes or copious rainfall, which often exceed 2000 mm yr⁻¹. These factors cause morphological dynamics with intense slope erosion and degradation processes.

This work investigates the appraisal of the rock-fall hazard related to the presence of several large unstable blocks located at the top of a limestone peak, approximately 500 m NW with respect to the Village of Cimolais.

Field surveys recognised a limestone block exceeding a volume of 400 m³ and identified this block as the most hazardous for Cimolais Village because of its proximity to the rocky cliff.

A first assessment of the possible transit and stop areas has been investigated through in-depth traditional activities, such as geomorphological mapping and aerial photo analysis. The output of field surveys was a detailed land use map, which provided a fundamental starting point for rock fall software analysis. The geomorphological observations were correlated with DTMs derived by regional topography and Airborne Laser Scanning (ALS) surveys to recognise possible rock fall routes.

To simulate properly rock fall trajectories with a hybrid computer program, particular attention was devoted to the correct quantification of rates of input parameters, such as restitution coefficients and horizontal acceleration associated to earthquakes, which historically occur in this portion of Italy.

The simulation outputs regarding the distribution of rock fall end points and kinetic energy along rock falling paths highlight the hazardous situation for Cimolais Village. Because of this reason, mitigation works have been suggested to immediately reduce the landslide risk. This proposal accounts for the high volume of blocks, which, in case of a fall, render the passive mitigation measures already in place at the back of Cimolais worthless.