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Rocky coastal regions are often inaccessible due to steep slopes and high relief. Remotely sensed data can, therefore, be useful, but they often have low spatial and temporal resolution and, in the case of airborne LiDAR, if not publically available, are costly to obtain. This paper reports on the use of high-resolution images from unmanned aerial vehicles (UAVs) and Structure-from-Motion (SfM) photogrammetric techniques, supplemented by a series of orthophotos and aerial LiDAR, to examine changes in rocky coastal cliffs from 2002 to 2018. The study was conducted over an 800 m-long, orthogneiss-dominated coastal section in northwestern Galicia, Spain. Cliff changes are due, primarily, to rockfalls, resulting from weathering and wave undercutting, which cause talus deposits to accumulate at the cliff foot. These deposits provide temporary protection to the cliff from wave action, until destabilized and removed by wave erosion and shallow landslides. Cliff recession rates are affected by changing conditions within a cycle and are dependent, in part, on when a survey is conducted. The data suggest that rates of cliff recession are increasing in this region and that the plan shape of the coast, which consists of headlands and bays, is continuing to evolve. Most coastal landslides in this region help to transport and dispose of talus fallen from the cliff. In contrast to landslides that remove intact materials from the cliff face, and are, therefore, primary erosional mechanisms, talus landslides are triggered by wave erosion and probably simultaneously, by storm wave spray and splash, rather than by heavy rainfall. [ABSTRACT FROM AUTHOR]

A mathematical model was used to predict the effect of climate change on soft and hard rock coasts in a 2 m tidal environment. Erosional equations represented the effect of wave impact and bottom generated shear stresses in the intertidal and subtidal zones. Model runs were made for: 2900 years with constant sea level; a further 100 years, representing the last century, with either constant or slow sea level rise (0.2 m per century); and another 100 years, representing the present century, with either slow or fast (1 m per century) sea level rise, and with either no change in storm frequency or with a 10% increase in the frequency of the highest waves. The results suggest that rising sea level will trigger faster rates of cliff recession, whereas increased storm wave frequency may have only a fairly minor effect on erosional efficacy. Model runs were used to derive a series of predictive equations relating cliff recession during the present and last centuries. [ABSTRACT FROM AUTHOR]