Correlation between erosion patterns and rockfall hazard susceptibility in hilltop fortifications by terrestrial laser scanning and diagnostic investigations

A holistic methodology combining conventional diagnostic investigations and kinematic analysis performed on 3D laser scanning survey is here proposed for rockfall hazard assessment and erosion patterns study, to map critical sectors and evaluate potential impacts on the conservation of cultural heritage sites built on unstable rock masses. Experiments carried out on the fortifications of Citadel, Gozo (Malta), led us to classify the susceptibility of the cliff surfaces to instability mechanisms, recognizing the wedge failure as the highest hazardous one. Observations on thin section of the rock textural properties and measurements of the resistance to abrasion completed the laser-based analysis, clarifying the intrinsic weakness of the outcropping limestones. Levels of conservation criticality were assigned to the rock mass sectors located underneath the historical buildings, and on site monitoring system was installed to follow the evolution of the crack patterns.