# UAV-Based Evaluation of Rockfall Hazard in the Cultural Heritage Area of Kipinas Monastery, Greece
Specifically, the utilization of the Structure from Motion (SfM) methodology enabled the production of ultra-high-resolution orthomosaic and Digital Terrain Models (DTMs) of hazardous regions by intersecting the matched features between the overlapping offset images [51] and interpreting them as detailed 3D point clouds. This dense 3D visual interpretation allows the main discontinuities to be identified and mapped with either a manual or a semi-automatic approach [52,53,54,55,56,57,58,59,60,61,62], and consequently volume displacements to be calculated in order to predict future movements, in areas prone to rockfall events, via computer-based methodologies. Hence, the compound of these innovative remote sensing technologies with traditional engineering geological field surveys can lead to an accurate, precise and time-effective local scale modeling of rockfall events. The principal aim of this research is to perform an in-depth qualitative rockfall hazard analysis and a preliminary approach of risk analysis, based on a UAV-derived dataset of the area. In order to achieve this goal, a new rockfall hazard and risk rating system is presented, by reviewing and modifying the existing ones from the literature, based on morphological and structural information of the rock mass derived from the analysis of the 3D point cloud. The factors of vulnerability and commercial impact were also taken into account for the risk estimation. In order to achieve these goals, this study focuses on the cultural heritage area of Kipinas Monastery in Epirus, Greece, situated in northern Tzoumerka, south of Kalarites village. The morphology of the site consists of high (\(\geq\)60 m), very steep slopes (\(\geq\)80\({}^{\circ}\)). The topography is characterized as mountainous in general (altitude from 580 m up to 730 m). The geological setting, where Kipinas Monastery is located, consists of only one formation, Jurassic limestones [63]. These grey limestones range from thick to medium bedded along the cliff but in some distinctive locations, alongside the bedding, some zones of the formation can be identified more as thin bedded up to foliated due to increased regional tectonic strain. Additionally, an important aspect of this formation is the influential karst development in it. As the monastery is built on this limestone, within the walls of it a large entrance to a karst cave (cupola) can be identified. In this unwelcoming location, Kipinas Monastery was literally chiseled and built into the surrounding rock mass around 1212 A.D., constituting one of Greece's most beautiful and impressive churches. However, in this location, various rockfall events have occurred in past years, with fallen blocks identified near the tarmac of the road that leads to the monastery. In general, the impact of rockfall events on archaeological sites, historical monuments and generally on cultural heritage areas in the Greek territory is significant, since most of the landscapes are mountainous and the sites are usually found near steep rock slopes. Considering the significant tourist activity in such locations, the risk adds up to be significantly increased. The principal reason leading to the implementation of a qualitative approach instead of a quantitative one, in this area, is the absence of pre-existing data, mainly temporal data related to rockfall events. Hence, the current research demonstrates a powerful approach to conduct a detailed hazard and risk assessment, by using data that were obtained incredibly fast via the UAV, and with the least possible prior information about former rockfall-related events in an area of interest.