## 4 Case Studies
### Castellana Caves  
The Castellana Caves are located in the SE Murge of Apulia (southern Italy; Figure 9), and are one of the most famous Italian karst areas [74; 75; 76], with more than 300,000 tourists yearly, as the most visited show cave in Italy. Apulia backbone consists of Jurassic-Cretaceous limestones and dolostones, unconformably overlain Tertiary and Quaternary clastic carbonates, with stratigraphic successions varying in different parts of the region, depending upon paleo-geography of the individual sectors. Since the Lower Pleistocene, Apulia was subjected to a general uplifting, until reaching its present configuration, that is a blocky structure fragmented by high dip faults [77; 78; 79]. An extensive network of underground caves and karst conduits, and widespread karst landforms at the surface as well, characterize the three main karst sub-regions (from north to south, Gargano, Murge, and Salento). As in other sectors of the Apulian karst, and in many other karst areas worldwide [80; 81; 82; 83; 84; 85; 86; 87; 14; 88], the development, elongation, and spatial distribution of karst landforms in the Castellana area, both at the surface and underground, is strongly controlled by the main tectonic lineations [75; 89]. First explored by Professor [PERSON] in January 1938, the Castellana Caves were exploited as show cave soon after [90; 91; 92], due to beauty of the underground passages and richness in the speleothems decorating the karst systems, whilst in the decades later the explorations added further passages to the overall development, that therefore reached a length greater than 3300 m, with maximum depth of \(-122\) m [93]. The karst system has a prevailingly sub-horizontal pattern, with wide caverns  
Figure 9: Location of the Castellana Caves, in Apulia, southern Italy. ranging in height from a few to some tens of meters, and intervening, structurally controlled corridors. The karst system at Castellana opens in the Upper Cretaceous Altamura Limestone formation, showing moderately spaced bedding planes [94]. The carbonate rock mass is fractured, with local arching and deformations in the strata, and thick weathered zones at the contact with elastic sediments or where the carbonates are wetted by trickling or condense water, and weathered material is protected against mechanical erosion [95]. The contact with fine-grained sediments is particularly important, since it contributes to provide the moisture required for dissolution. Corrosive moisture has been in fact invoked as the main reason for limestone weathering in several cases, including the drenching of clay pebble surfaces [96; 97; 98]. Besides bedding of strata, showing a sub-horizontal attitude, four main discontinuity systems can be identified at Castellana, the prevailing system always being in the range N 130-150 [99]. The most spectacular view of the system is the 55 m deep _Grave_, a natural opening created by a collapse sinkhole [100; 101; 102; 103], through progressive falls from the vault. The name derives from the pre-Latin term _grava_, meaning pit or hole, and is locally used to indicate deep entrance to cave systems [104]. This type of feature, generally produced through collapse or cover-collapse sinkhole processes, is very common in the Apulian karst [74; 75; 105; 106; 107; 108]. At Castellana, given the relevance of the _Grave_ (the most iconic symbol of the Castellana Caves, with the typical picture showing the solar ray entering the sinkhole at middle morning), its location above parts of the tourist path, and the need to evaluate the stability conditions, this site was surveyed by means of the laser scanner RIEGL VZ400 (Figure 1). During the survey, a high-density geo-referenced point cloud (430,000 million points, with 21,500 pt/m\({}^{2}\) density) was produced (Figure 10). The survey consisted of 42 scans from 20 scan positions (eight located at the surface, 12 within the cavern).