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Sinkholes are the main hazard related to underground voids of both natural and anthropogenic origin. Instabilities developing underground may propagate upwards in a dramatic manner and reach the surface in the form of a sinkhole. The Apulia region in southern Italy is an interesting case study due to the outcropping of soluble rocks throughout the region. These rocks are affected by karst processes and have a high number of anthropogenic cavities. The latter were excavated by humans at different times for a variety of purposes. The worrying recent increase in the number of sinkhole events registered in Apulia led us to collect information on natural and anthropogenic sinkholes in Apulia. We focused on anthropogenic cavities, mostly excavated in Plio-Pleistocene calcarenites, and characterized the rock masses before using two- and three-dimensional parametric numerical analyses to model the instability processes, with the aim of exploring the failure mechanisms that lead to the occurrence of sinkholes. The parametric studies allowed us to carry out a preliminary evaluation of the stability conditions through simple charts designed for use in the field.

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Abstract. The Tremiti Archipelago (Southern Adriatic Sea), also called Insulae Diomedae from the name of the Greek hero who first landed there, is an area of high landscape and historical value. It is severely affected by significant geomorphologic processes dominated by mass movements along the coast that constitute the most important and unpredictable natural hazard for the population and cultural heritage. Coastal erosion is favoured by the peculiar geological and structural setting, seismic activity, weathering, development of karst processes, and wave action.The present paper reports on descriptive and qualitative evaluation of the factors controlling landslides and coastline changes based on medium-term in situ observation, detailed surface surveys at selected locations since 1995, and historic and bibliographic data.The Tremiti Archipelago is part of an active seismic area characterised by a shear zone separating two segments of the Adriatic microplate that have shown different behaviour and roll back rates in the subduction underneath the Apennines since middle Pleistocene.Although coastal morphology can be basically considered to be the result of wave action, the continual action of subaerial processes contributes effectively to the mechanism of shoreline degradation. Weathering mainly affects the marly calcisiltites and calcilutites of the Cretaccio Fm. and the friable and low cemented calcarenites and biomicrites of the San Nicola Fm. The cliffs are characterised by different types of failure such as lateral spreads, secondary topples, rock falls and slides. At the Isle of San Nicola, landslides are controlled by the contrast in competence, shear strength and stiffness between the Pliocene re-crystallised dolomitic calcarenites and calcisiltites and the Miocene marly calcilutites and calcisiltites. At the Isles of San Domino and Caprara rock falls are attributed to the undercutting of waves at the base of the cliffs.