3D structural analysis of the cave of Saint Michael at Minervino Murge, Bari (Italy) – a typical case of karst environment in Puglia

The presence of surface and subterranean landforms (caves, sinkholes, etc.) produced by karst processes in the Apulian territory is among the most typical features of the local landscape. Numerous examples can be counted throughout the region, especially in the Murge plateau, one of the three karst sub-regions of Apulia. Here the rock, being composed mainly of carbonates, has been affected in multiple stages by karst, which more visible results nowadays consist of numerous cavities, some of which show evidence of instability problems. At the present day, especially for those caves which are open to the public, it is necessary to perform stability analysis aimed at evaluating the stability conditions at the sites. In the Murge area, the cave of Saint Michael at Minervino Murge is among the most famous, belonging to the set of caves dedicated to the figure of Saint Michael the Archangel, which also includes the UNESCO protected site at Monte Sant’Angelo, in the Gargano Promontory of northern Apulia, a major Catholic pilgrimage site. At Minervino Murge, the cave consists of a wide room hosting a deep and wide stairway leading to the altar dedicated to Saint Michael, and an innermost, smaller, environment which entirely keeps its naturality. Besides the religious and historical interests, the whole cave needs a detailed analysis of the stability of the rock mass, both for the protection of its architectural and archaeological values and for the safeguard of the pilgrims. At this aim, we performed various digital surveys by means of laser scanners and drones equipped with high-resolution cameras. The results of these scans are going to be processed in order to understand the geometry of the entire cave and to properly determine the main volumes of unstable blocks, as well as the likely kinematics of movement. Given the height of the cave, remote sensing techniques are particularly suitable for such an analysis, allowing to obtain from a distance the relevant data, rather than investigating the site with traditional geomechanical survey methods. Furthermore, the facility of acquisition of the remote sensing data will allow repetitiveness of the surveys, thus permitting monitoring over different time windows, in order to check periodically the most dangerous situations and to properly exploit this site of historical importance and religious worship.