Long-term monitoring to support landslide inventory maps. The case of the north-western coast of the island of Malta

The aim of this paper is to show the results of 8 years of research activities carried on the north-western coast of the Island of Malta, with particular reference to the outputs of monitoring and interferometric analysis as a support for the implementation of a landslide inventory. The study area is characterized by the presence of limestones overlapping clayey terrains, thus favoring the presence of large rock spreading phenomena, which often evolve into block slides. Field surveys resulted in approximately 86 landslides, distributed between the coastline and structural cliffs which flank limestone plateaus. In order to support geomorphological investigations, a GPS (Global Position System) monitoring network was deployed over two coastal sites. Slow rates of surface deformations varying from few millimeters per year to some centimeters per year were recorded. Since the extension of the GPS network over the entire north-western coast and for such a high number of landslides is not feasible in terms of cost-benefit relations, we applied PSI (Persistent Scatterers Interferometry) to validate the geomorphological map. DinSAR data analysis confirmed the displacement rates measured by the GPS monitoring network and provided useful information about the style of activity of a large number of landslides affecting the north-western coastline of Malta. The outcomes supported the satisfactory capabilities of an integrated approach, which coupled conventional geomorphological procedures with monitoring techniques to bring out an exhaustive landslide inventory, even for slow or very slow mass movements, essential for related hazard assessment. .