The Mediterranean Basin is characterized by a significant variability in tectonic behaviour, ranging from subsidence to uplifting. However, those coastal areas considered to be tectonically stable show coastal landforms at elevations consistent with eustatic and isostatic sea level change models. In particular, geomorphological indicators—such as tidal notches or shore platforms—are often used to define the tectonic stability of the Mediterranean coasts. We present the results of swim surveys in nine rocky coastal sectors in the central Mediterranean Sea using the Geoswim approach. The entire route was covered in 22 days for a total distance of 158.5 km. All surveyed sites are considered to have been tectonically stable since the last interglacial (Marine Isotope Stage 5.5 [MIS 5.5]), because related sea level markers fit well with sea level rise models. The analysis of visual observations and punctual measurements highlighted that, with respect to the total length of surveyed coast, the occurrence of tidal notches, shore platforms, and other indicators accounts for 85% of the modern coastline, and only 1% of the MIS 5.5 equivalent. Therefore, only 1% of the surveyed coast showed the presence of fossil markers of paleo sea levels above the datum. This significant difference is mainly attributable to erosion processes that did not allow the preservation of the geomorphic evidence of past sea level stands. In the end, our research method showed that the feasibility of applying such markers to define long-term tectonic behaviour is much higher in areas where pre-modern indicators have not been erased, such as at sites with hard bedrock previously covered by post-MIS 5.5 continental deposits, e.g., Sardinia, the Egadi Islands, Ansedonia, Gaeta, and Circeo. In general, the chances of finding such preserved indicators are very low.

The photogrammetric method is widely used in coastal areas and in submerged environments. Time-lapse images collected with unmanned aerial vehicles are used to reproduce the emerged areas, while images taken by divers are used to reproduce submerged ones. Conversely, 3D models of natural or human-made objects lying at the water level are severely affected by the difference in refractive index between air and seawater. For this reason, the matching of 3D models of emergent and submerged coasts has been very rarely tested and never used in Earth Sciences. The availability of a large number of time-lapse images, collected at the intertidal zone during previous snorkel surveys, encouraged us to test the merging of 3D models of emerged and submerged environments. Considering the rapid and effective nature of the aforementioned program of swim surveys, photogrammetric targets were not used during image acquisition. This forced us to test the matching of the independent models by recognizing prominent landforms along the waterline. Here we present the approach used to test the method, the instrumentation used for the field tests, and the setting of cameras fixed to a specially built aluminum support console and discuss both its advantages and its limits compared to UAVs. 3D models of sea cliffs were generated by applying structure-from-motion (SfM) photogrammetry. Horizontal time-lapse images, collected with action cameras while swimming parallel to the coastline at nearly constant velocity, were used for the tests. Subsequently, prominent coastal landforms were used to couple the independent models obtained from the emergent and submerged cliffs. The method was pilot tested in two coastal sites in the north-eastern Adriatic (part of the Mediterranean basin). The first site was a 25 m sea wall of sandstone set within a small harbor, while the second site was a 150 m route below plunging limestone cliffs. The data show that inexpensive action cameras provide a sufficient resolution to support and integrate geomorphological field surveys along rocky coastlines.

Tidal notches, long regarded as reliable indicators of mean sea level, have been extensively studied along carbonate coasts in the central Mediterranean Sea. Previous studies revealed a correlation between the genesis of tidal notches and tidal range, lithology, cliff foot depth, and wave energy. In the 2020 Geoswim campaigns at Lampedusa, the southernmost island of the Pelagie archipelago (Italy), and in Gozo Island (Malta), ‘anomalous’ tidal notches were identified. Unlike normal notches observed elsewhere, those in Lampedusa’s southern bays exhibited a particular behaviour—constantly deepening in the inner part of the bays, reaching a maximum depth of approximately 30 cm below sea level and narrowing inwards. Similar phenomena were previously observed near Marseille (France). As confirmed by the literature, all these areas are tectonically stable. Time-lapse images, alongside measurements of morphometric parameters, were collected during the survey. Our hypothesis indicates that a combination of marine factors influenced by local marine conditions driven by the local morphology of the small bays exposed to southern quadrants contribute to the formation of these unique landforms. The latter manifests higher lowering erosion rates slightly below the mean sea level in sheltered areas, challenging conventional notions about tidal notch formation.

Storms and storm surges could increase their impact on rocky coasts in the next years due to global warming. In recent years, the study of boulders moved by storm waves seems to have played an important role. A key indicator that can follow extreme storm events on rocky shores includes coastal boulders detached from the bedrock. These deposits became in focus of a several studies since play a significant role in coastal hazard assessment. First studies regarded deposits of boulder related to tsunami events, but recently many sites with large clasts related to storm waves have been discovered, also in semi-enclosed shallow basin, such as the Adriatic Sea, in the Mediterranean area.In this study we widened the mapping of boulders recently studied at Premantura promontory (southern Istria, Croatia) in order to better assess the role of coastal morphology in boulder sedimentation. In particular, we present and discuss the role of boulder deposits in several islets close to the promontory, also considering that at the island of Sekovac boulders are definitively of artificial origin and later moved by extreme waves.The investigation of the position, size, and mass of each boulder was created through the application of Uncrewed Aerial Vehicle Digital Photogrammetry (UAV-DP) and Structure from Motion (SfM) technique, defining the GCPS points, and providing high-resolution data.  Boulders were identified and categorized using UAV-DP products, and their validation was done through the comparison with outputs of traditional geomorphological investigations such as field surveys including direct axis measurement and the use of Google Earth images for boulder mapping.

Tidal notches, long regarded as reliable indicators of mean sea level, have been extensively studied along carbonate coasts in the central Mediterranean Sea. Previous studies revealed a correlation between the genesis of tidal notches and tidal range, lithology, cliff foot depth and wave energy. In the 2020 Geoswim campaign at Lampedusa, the southernmost island of the Pelagie archipelago (Italy), 'anomalous' tidal notches were identified. Unlike normal notches observed elsewhere, those in Lampedusa's southern bays exhibited a particular behavior —constantly deepening in the inner part of the bays, reaching a maximum depth of approximately 30 cm below sea level and narrowing inwards. Similar phenomena were previously observed by [1] near Marseille (France) and in Gozo Island (Malta). Time-lapse images, alongside measurements of morphometric param-eters, were collected during the survey. Despite the rapid morphological changes of the notches within the bay, the tectonic stability of the studied areas was confirmed by literature and data. Our hypothesis indicates that a combination of marine factors, influenced by local meteomarine conditions driven by the local morphology of the small bays exposed to southern quadrants con-tribute to the formation of these unique landforms. The latter manifest higher lowering erosion rates slightly below mean sea level in sheltered areas, challenging conventional notions about tidal notch formation.