Benefits from the outputs of UAV Digital Photogrammetry technique in the investigation of lateral spreads and block slides

Uncrewed Aerial Vehicle Digital Photogrammetry (UAV-DP) is transforming geoscience research by providing an affordable and efficient technique of acquiring High-Resolution (HR) data for terrain analysis and environmental monitoring. Researching lateral spreads and block slides poses significant challenges due to their extremely slow dynamics, necessitating long-term investigations and detailed field surveys, which are frequently unsafe, time-consuming and expensive. This study explores the efficacy of the use of a micro drone (weighing 300 gr) in investigating gravity-induced landforms and processes related to lateral spreads and block slides in the northern sector of the Island of Malta (Mediterranean Sea). The research focuses on the inventory of persistent joints and downslope megaclast deposits at four sites located along the NW coast of Malta, where spectacular lateral spreads evolve into widespread block slides. Lateral spreads enlarge persistent joints that partially isolate limestone blocks along plateau edges, which subsequently slide or fall downslope, creating the unique "Rdum" landscapes characteristic of Malta. Using Google Earth (GE) imagery and UAV-based Digital Photogrammetry (UAV-DP), the study precisely identified and categorized persistent joints and detached blocks. Regarding boulder accumulations, the outputs of UAV-DP revealed about 9,000 megaclasts compared to about 5,000 identified using GE, representing a 76% increase due to the DP-derived orthomosaics and 3D models generated. The application of the UAV-DP technique, with a total cost of approximately $5,000, proved significantly more efficient and accurate than traditional GE imagery datasets. These results demonstrate the method’s suitability for being extended to other rocky coastal areas affected by slow-moving landslides.