Combining field data with infrared thermography and DInSAR surveys to evaluate the activity of landslides: the case study of Randazzo Landslide (NE Sicily)

Infrared thermography and DInSAR surveying methodologies have been integrated and compared to study the state and distribution of activity of one of the largest landslides of northeastern Sicily, Italy, which is characterized by a slow retrogressive evolution. The Randazzo Landslide was triggered by heavy rainfalls in 1996 and its activity caused the disruption of a strategic transportation corridor, along with the formation of a landslide dam in the Alcantara Valley. After more than 20 years, the slope is still affected by instability and worrying signs of reactivations (e.g., deformation and cracking of road pavement) were surveyed in the field. The application of infrared thermography during the landslide survey allowed detecting peculiar features according to the different thermal pattern of the elements occurring along the slope. In particular, areas with different surface temperature were associated to vegetated spots, steep portions, bare sectors, and contact between different lithologies. Incipient portions and ancient landslide bodies were located, proving the utility of this experimental approach to the surveying of unstable slopes. Information on the entity, in terms of velocity, of the recent landslide displacements were provided by a DInSAR monitoring, which allowed ascertaining the presence of movements affecting several sectors of the landslide, mainly matching with the areas highlighted by thermal images. Achieved outcomes represent a scientifically relevant datum providing important information on the surveyed landslide from the risk management point of view and proving the utility of integrating infrared thermography and DInSAR methodologies for the study of complex movements.