## 6 Conclusions  
This application shows that UASs can be an important addition in surveys of geomorphological processes, providing an efficient, rapid, and accurate way of performing terrain observations, detecting changes in a post-extreme event environment, and allowing for a deeper understanding of how these processes work. The presented approach has a range of advantages. It was shown to be especially helpful for studying a site on demand with minimum disruption and requirements during the post-disaster period. In addition, although these capabilities are appropriate in the context of monitoring disaster events and mapping their impact on the natural and built environment, the efficiency of this application is an important indicator that they can function in a continuous monitoring scheme in a framework of systematically repeated surveys. The described UAS-based methodology presents a quite simple and convenient way of comparing datasets from different time periods and achieving a co-registration of very high accuracy. The accuracy in the final photogrammetric product--including the co-registration between multi-temporal datasets--proved to be very crucial in terms of accurate measurement of distances between the original point clouds and eventually the volume of mass movement through mudflows, which leads consequently to the quantification of the surface alteration. On this basis that the application allows accurate observations of erosion and deposition processes, volumetric estimates of the geomorphic changes and the delineation of the affected and the unaffected areas were obtained. Both methods, either C2C or DoD, provide realistic and reliable results in terms of the quantification of surface material relocation. Detailed change detection, along with the volume calculations, are much more effective with the use of photogrammetric techniques, as long as the dataset co-registration procedure is successful and accurate. Overall, the complexity of mass wasting processes in light of the threat of climate change, together with the high vulnerability of the region (particularly highly visited areas), show that there is a need for a better understanding of the risks of slope failures and various instabilities caused by extreme weather events. UASs have the potential to contribute to monitoring these effects and improve our understanding of the geomorphic processes. The high-resolution of results allows for microzonation of a study area, which is the foundation for allowing these high-value sites to be able to retain their use and their socio-economic activities with minimum disruption, while at the same time keeping high standards of safety. New technologies, such as the one applied in the present study, provide such solutions with certain limitations and can be an important step toward sustainable development. Conceptualization, E.V. and S.M. ; methodology, E.V., E.K., A.K., S.L. and C.F. ; software, E.V., E.K. and A.K. ; validation, E.V., E.K. and A.K. ; formal analysis, E.V., M.D., S.M. and A.K. ; investigation, E.V., E.K., A.K., S.L. and C.F. ; resources, E.V. ; data curation, E.V. and A.K. ; writing--original draft preparation, E.K., E.V., M.D., S.M. and E.L.; writing--review and editing, E.K., E.V., M.D. and S.M. ; visualization, E.V., E.K., A.K., S.L. and M.D. ; funding acquisition, E.L. All authors have read and agreed to the published version of the manuscript. This research was funded by the \"LAERTIS--Innovative Risk Management System in the Region of Ionian Islands\" project included in the Priority Axis \"Environmental Protection and Sustainable Development\" of the Regional Operational Programme \"Ionian Islands 2014-2020\" (grant number MIS: 5010951), which is funded by the European Regional Development Fund (ERDF) and National Resources under the National Strategic Reference Framework (NSRF) 2014-2020. **Key Words:** Data availability Statement: Not applicable.