Evaluating Characteristics of an Active Coastal Spreading Area Combining Geophysical Data with Satellite, Aerial, and Unmanned Aerial Vehicles Images

Abstract

The northern region of the Maltese archipelago is experiencing lateral spreading landslide processes. This region is characterized by cliffs with a hard coralline limestone outcropping layer sitting on a thick layer of clay. Such a geological configuration causes coastal instability that results in lateral spreading which predispose to rockfalls and topplings all over the cliff slopes. The aim of this research was to develop a methodology for evaluating cliff erosion/retreat using the integration of geomatics and geophysical techniques. Starting from a 3D digital model of the Selmun promontory, generated by unmanned aerial vehicle (UAV) photogrammetry, it was possible to map the fractures and conduct geophysical measurements such as electrical resistivity tomography and ground penetrating radar for the identification and mapping of vertical fractures affecting the hard coralline limestone plateau, and to create a 3D geological model of the study area. In addition to this, high-accuracy orthophotos from UAV that were captured between 1957 and 2021 were georeferenced into a GIS and compared to aerial and satellite images. The movement and evolution of boulders and cracks in rocks were then vectorized to highlight, track and quantify the phenomenon through time. The results were used to derive a qualitative assessment of the coastal variations in the geometric properties of the exposed discontinuity surfaces to evaluate the volumes and the stop points of the observed rockfalls. The outcomes of this research were finally imported in a GIS which offers an easy approach for the collection and processing of coastal monitoring data. In principle, such a system could help local authorities to address social, economic and environmental issues of pressing importance as well as facilitate effective planning in view of a risk mitigation strategy.

Rockfall Susceptibility Assessment and Landscape Evolution of San Nicola Island (Tremiti Islands, Southern Adriatic Sea, Italy)

“…In this context, slope phenomena are due to the detachment and sliding of dolomitic blocks, of meter to decameter size, isolated by intersecting fracture systems. Similar contexts are found in the insular environ-ments of Malta [76][77][78] and Mallorca [79], where the landscape results from the interplay of tectonics, slope processes, and marine action. This situation is comparable with the geomorphological dynamics of San Nicola Island.…”

Satellite-Derived Bathymetry for Selected Shallow Maltese Coastal Zones

“…The extraction of bathymetry from satellite images acquired over time can be used to comprehend temporal changes in sedimentation patterns that shape the seafloor in coastal systems. This information is particularly valuable for research on coastal erosion and sedimentation and can result in morphodynamic models that provide managers with a tool capable of predicting the dynamic evolution of coastal sediment and make informed management decisions [52][53][54].…”

Engineering Geological and Geophysical Investigations to Characterise the Unstable Rock Slope of the Sopu Promontory (Gozo, Malta)

“…The coastal plateau in question was surveyed using UAV photogrammetric acquisition, meticulously planned and executed to fully capture the topographic details of the cliff and slope (Figure 2). Unmanned Aerial Vehicle (UAV) photogrammetry is a powerful tool for generating high-resolution 3D models of various landscapes, including coastal scenery [30][31][32] and other landforms [33].…”