## 4 Case Studies  
### Santa Caterina  
The rock cliff over the beach of Santa Caterina is located in the municipality of Sant'Agnello (Naples province, northern coast of the Sorrento Peninsula), in Campania region (Figure 5). Due to presence of a small marina, and to beauty of the area, which attracts a wide number of tourists during the summer season, the beach is highly frequented. From a geological-structural standpoint the Sorrento Plain represents a tectonic graben, between two limestone horsts of Cretaceous age. The graben was filled during Wurm with materials from an explosive volcanic eruption, dated about 39,000 years ago [66], within the Phlegorean volcanic district. The volcanic products were emplaced through huge, high temperature, pyroclastic surges and flows, that entirely filled the pre-existing morphologies. These pyroclastic products belong to the formation of the _Campanian Grey Tuff_ (or _Campanian Ignimbrite_), consisting of yellow-greyish ashes, associated to black scoriae and lava fragments. After the emplacement, the formation of sanidine and zeolite crystals (zeolitization processes) caused lithification of the pyroclastic material. Cooling processes in the pyroclastic mass generated the development of sub-vertical and strongly inclined joints that, combined with the bedding, create the main discontinuity planes, fragmenting the tuff rock mass. Concerning morphology, the slope is an approximately 50-m high rock cliff, the terrace of pyroclastic aggradation of the Sorrento Plain bounding toward the sea. The rock cliff shows a retrogressive evolution through rapid slope movements with different failure mechanisms (falls, toppling, slides, wedges). The cliff is directly hit by sea waves, and this action produces a further erosional action, involving both mechanical action and weathering processes [67; 68], thus contributing to degrade the rock mass. Eventually, other negative factors working toward  
Figure 5: Location of the Santa Caterina cliff, in Campania, southern Italy. instability of the cliff are represented by natural factors such as earthquakes, wind, rainfall, and the alteration in the first meters of slope exerted by the tree roots. Regarding the factors of anthropogenic origin, in the past the rock cliff was interested by quarrying activity to extract the tuff. These activities are testified by presence of artificial cavities and passages, where it is possible to observe a net decrease in the mechanical properties of the rock mass [69; 70; 71; 72; 73], with development of release tension cracks and widening in the aperture of the fissures. In general, the area is characterized by sub-vertical scarps in tuff deposits crossed by multiple discontinuity sets, which intersections determine the formation of isolated, potentially unstable, slabs, wedges, and blocks. Dimensions of the rock blocks are widely variable, from cubic decimeters to cubic meters, in function of the spacing of the main discontinuity sets within the rock mass. Due to the relevant socio-economical interest of the area and to site logistics, it was decided to proceed with an evaluation of the stability conditions through a geo-structural analysis on point cloud acquired with a combined approach through the use of both laser scanner and drone. Such integrated approach was necessary in order to overcome the logistic and morphological problems present at the site, since the tuff cliff is definitely active, and, as such, not accessible from below for long sectors. First, a laser survey by means of RIEGL VZ400 was carried out, through acquisition of three _scan positions_ for a total number of 12 scans. Following the preliminary visits to the study area, useful to check the site logistics and its features, including the presence of people and its frequency during the different hours of the day, the survey was planned in order to schedule the best temporal windows, with the aim at avoiding any possible interference. Further, the planning phase included the choice of the precise locations for the control targets.