## 4 Results  
The analysis shows that within the time period studied (between July and October 2020) a significant change has occurred, attributed to the Medicare Ianos event, as based on rainfall and earthquake data, no other important event occurred in this period. The survey showed that a large part of the slope, which hosts the roadway that leads to the waterfront and the beach area itself, together with several retaining walls, was covered by debris flows from higher up the slope. Distinct instabilities across the study site were visible in the DoD output, including debris cones and extensive mudflows triggered by the high-intensity rainfall of the Ianos event. Based on the approach followed, it was possible to delineate the activated area and measure it through comparison of the ortho-photographs, allowing the precise calculation of the magnitude of the area that was covered with debris. A high-resolution comparison between the two DSMs (performed by using the ArcGIS add-in algorithm, called geomorphic change detection, or GCD) [84]) illustrated noteworthy elevation changes (shown in Figure 10). Figure 9: Sparse point cloud showing the UAS camera locations during the image acquisition and the position of the seven pseudo-GCPs. This observation in turn led to detailed area and volume calculations using the DoD method [83; 85] (shown in Figure 11), providing results with an accuracy in the order of a few centimeters. Specifically, we determined that the total area that suffered changes due to the storm was 59,418.60 m\({}^{2}\), of which 40,678.20 m\({}^{2}\) was covered with debris (mostly in the central section of the area). Furthermore, an area of 6,618.25 m\({}^{2}\), situated along the parking lot near the beach, was covered with debris, blocking the outlet of a small stream draining part of northwest Cephalonia (Figure 11). Figure 11: The results of the processing of the affected area over Myrtos beach with the DoD technique. The color scale shows the calculated vertical changes. Blue areas show elevation loss (erosion) and therefore the sources of material, whereas red areas of the figure show elevation gain (deposition), which in many locations exceeds a thickness of 5 m.  
Figure 10: Comparison of digital surface models created from imagery captured (**a**) before and (**b**) after the destructive event. The total change in terms of volume was calculated to be 45,575.05 m\({}^{3}\) (with an uncertainty of \(\pm\)824.79 m\({}^{3}\)). The larger portion of this change in terms of volume was associated with a flow of debris in the central part of the study site. Around this location, the elevation values recorded in the pre-and post-lanos event DSMs were found to be quite modified, either negatively (erosion) or positively (deposition). It was calculated that a volume of 15,318.73 (\(\pm\)3158.05) m\({}^{3}\) was deposited at new locations within Myrtos beach and 30,256.33 (\(\pm\)5089.74) m\({}^{3}\) was removed from its original location after Janos. Detection of vertical changes allows the delineation of areas with erosion and scouring, as well as areas with deposition. In fact, a comparison of observations and phenomena after the seismic sequence in Cephalonia in early 2014 [47] with change detection results from the present study reveals that the greatest impact from the occurrence of both phenomena was located in the same segments of the slope. In particular, it was found that the paths followed by the debris flows in the Medicare Janos event correspond with the paths followed by the rock fragments that were detached from the slope during the 2014 earthquakes, before they ended up at the base of the slope, a few tens of meters from the shore [47].