## 1 Introduction  
Globally coastal areas balance in a highly dynamic regime formed by a variety of complex natural processes [1] and human intervention [2]. The evolution of these constantly changing environments is affected by numerous natural geomorphic mechanisms such as erosion, mass wasting, deposition, wave action, as well as tectonic and volcanic activity [3]. Despite these processes and the risks associated with them, coastal areas contain a large part of the world's population [4] and an important portion of socio-economic activities [5], including trade, tourism, transportation and others. This activity heavily influences [6] some segments of the coastline. Coastal zones are home to many interests including economic (ports, fishing, navigation), recreation, water quality and nature conservation. Assets developed in coastal areas can be very valuable [7] and the disruption of some of the activities can be very costly [8]. There are examples where the interests and exploitation schemes of these areas are conflicting with each other or lead to expansion into areas of high risk [9; 10; 11]. Thus, coastal zones are often characterized by both high exposure of valuable assets [8], as well as high hazard levels as a result of the various dynamic processes that take place. Particularly, in seismically active areas, high inclination, deformation of geological formations and strong earthquakes lead to instability phenomena [12; 13; 14] that are often associated with significant damage to property and infrastructure [15; 16] and loss of human lives [17; 18]. On many occasions, these failures can become a very significant threat in coastal areas. The complexity of the processes together with the high risk caused by such mass-movement events create a demand for in-depth knowledge and understanding of the mechanisms (both natural and anthropogenic) that drive them [19]. For example, it is crucial to understand the role of discontinuities in geological formations that affect their integrity and stability, acting as catalysts in various geographic processes, including landslides. Monitoring this and other structural properties of rock formations is important to predict slope behavior in coastal areas. Coastal slope failures are a significant source of hazard and a constraint for human activities in rocky coastal areas [20]. The most prevalent process responsible for the high risk of coastal cliffs is slope mass movements [21]. The extent and economic impact of this problem tend to increase over time, due to the general increasing trend in the use of coastal areas, especially steep and rocky coastlines, which correspond to one-third of the coasts worldwide [22; 23]. The value of land in these locations is constantly increasing due to the high demand for exploitation, especially beaches of special beauty, which are often formed at the base of cliffs and are a tourism product of high value. There are also issues related to the presence of urban areas and archaeological and historical heritage sites close to the top of the cliffs [24; 25]. In this context, coastal evolution and its processes have been examined through a variety of techniques, some of which belong to the field of remote sensing [26]. New techniques, such as photogrammetry and laser scanning, have shown interesting capabilities in studying changing terrain and particularly geomorphic processes, including slope stability and structural integrity [27; 28]. For example, unmanned aerial systems (UASs) and UAS-aided photogrammetry have been used before in applications in coastal areas including surveying topographical changes [29], cliff erosion [30], coastline changes [31], and coastal floods [32; 33; 34]. In the field of mass movement, previous studies [35; 36] have demonstrated that UAS, with the proper processing of data, can provide fairly accurate results [37; 38]. Similarly, Terrestrial Laser Scanning (TLS) has demonstrated its capabilities in slope stability [39] including applications in coastal zones [40; 41].