Coastal retreat is a non-recoverable phenomenon that—together with a relevant proneness to landslides—has economic, social and environmental impacts. Quantitative data on geological and geomorphologic features of such areas can help to predict and quantify the phenomena and to propose mitigation measures to reduce their impact. Coastal areas are often inaccessible for sampling and in situ surveys, in particular where steeply sloping cliffs are present. Uses and capability of infrared thermography (IRT) were reviewed, highlighting its suitability in geological and landslides hazard applications. Thanks to the high resolution of the cameras on the market, unmanned aerial vehicle-based IRT allows to acquire large amounts of data from inaccessible steep cliffs. Coupled structure-from-motion photogrammetry and coregistration of data can improve accuracy of IRT data. According to the strengths recognized in the reviewed literature, a three-step methodological approach to produce IRTs was proposed.

The mechanical strength is a fundamental characteristic of rock masses that can be empirically related to a number of properties and to the likelihood of instability phenomena. Direct field acquisition of mechanical information on tall cliffs, however, is challenging, particularly in coastal and alpine environments. Here, we propose a method to evaluate the compressive strength of rock blocks by monitoring their thermal behaviour over a 24-h period by infrared thermography. Using a drone-mounted thermal camera and a Schmidt (rebound) hammer, we surveyed granitoid and aphanitic blocks in a coastal cliff in south-east Sardinia, Italy. We observed a strong correlation between a simple cooling index, evaluated in the hours succeeding the temperature peak, and strength values estimated from rebound hammer test results. We also noticed different heating-cooling patterns in relation to the nature and structure of the rock blocks and to the size of the fractures. Although further validation is warranted in different morpho-lithological settings, we believe the proposed method may prove a valid tool for the characterisation of non-directly accessible rock faces, and may serve as a basis for the formulation, calibration, and validation of thermo-hydro-mechanical constitutive models.

Detailed geological mapping, field observations and structural analyses demonstrate that Early Ordovician (‘Sardic’) deformation occurred in the early Palaeozoic successions that are now incorporated in the Variscan Nappe zone of SE Sardinia. This deformation is represented by folds that formed at a shallow depth, lack a significant syn-folding axial planar foliation, and do not affect the overlying Late Ordovician – Devonian sedimentary sequence. These deformation features can be related to the development of the Sardic Unconformity and to calc-alkaline volcanism in several now-scattered terranes of Ordovician northern Gondwana. This reflects a convergent geodynamic setting that in the study sector appears to have failed to reach a continental collisional end-stage. Associating the structural data from this study with those of several published research studies, a preliminary evaluation about which tectonic setting could better fit is proposed. These conditions affected the eastern side of the northern Gondwana margin more or less contemporaneously with the opening of the Rhéic Ocean and the closure of the Qaidam Ocean, before the amalgamation of the Hunia terranes.