Integrating geophysical techniques and 3D modelling for lateral spreading : analysis and coastal risk mitigation in the Northern Region of ‘Rdum il-Qammieħ’

Abstract

This project investigates the geomorphological evolution and geohazard implications of coastal instability at ‘Rdum il-Qammieħ’, a prominent promontory on the northwestern coast of Malta. The study focuses on monitoring for lateral spreading which is a form of landslide where Upper Coralline Limestone detaches and slides over the underlying Blue Clay. This geological interface, compounded by regional tectonics and environmental forces, presents critical risks to both ecological and infrastructural assets. Based on Unmanned Aerial Vehicle photogrammetry, historical imagery, and Geographic Information System (GIS) tools, the research developed a high-resolution 3D model and an orthomosaic to map slope angles, block displacements, fracture mapping and surface deformations. CloudCompare and MeshLab helped in identifying high-risk zones marked by tension cracks, rotational slides, and seaward-tilted blocks. These physical indicators align with the region's structural framework, where structural discontinuities contribute to cliff segmentation and block mobility. A stereographic projection analysis confirmed a dominant South West dip direction (227°) and a strike of 137°, supporting interpretations of outward-tilting strata and block detachment patterns. The research further incorporates ecological assessments, highlighting how geomorphological processes threaten native species in Natura 2000 zones. Through hazard classification, the study delineates zones of critical, moderate, and low instability, offering a coastal risk map for use in policy and site management. A multi-temporal analysis was performed by georeferencing aerial photographs from 1964 to 2024, revealing long-term patterns of cliff retreat and block detachment. This historical mapping was validated using Root Mean Square (RMS) error thresholds, with lower values indicating higher georeferencing fidelity which is crucial for detecting subtle morphological changes over time. Observations noted, included back-tilted blocks, fracture mapping, and rockfall debris, confirm that the instability at ‘Rdum il-Qammieħ’ is both progressive and ongoing. Although large-scale collapses are currently infrequent, clear signs of incipient failure are evident, underscoring the need for continuous monitoring and informed intervention strategies The research offers an evaluation of terrain instability at ‘Rdum il-Qammieħ’, combining geomatics, geophysics, and ecological perspectives to inform proactive coastal risk management in Malta. Additionally, the findings contribute valuable insights into the mechanics of lateral spreading within Mediterranean karstic landscapes.