## 5 Data Collection in IVR and Following GIS Data Analysis
Although Phase 3 is the only one missing in the mine, the boundary between phases P0, P1 and P2 can only be seen where the famous section is located at the entrance of the mine (Figure 10e), due to extensive debris flows that cover the lower parts of the cliffs. The Polygon tool allowed us to map and define the areal coverage of anthropogenic debris and machineries, as well as natural debris flows. Considering the level of vegetation that grows on these surfaces we can assume their relative temporal relationship, with 3 being the oldest and 1 the newest (Figure 10a,c,d). Finally, using the Ruler tool, we quantified the Minoan phases' thickness at several part of the mine, along the vertical cliff, focusing on P2 and P4 phases that are the most exposed. We collected a total of 80 measurements along the vertical mine cliffs, quantifying, for the first time, the maximum thickness of 17.8 m and of 7.2 m for P2 and P4, respectively. The Camera tool was used to capture several pictures all over the area, with the aim of showing the main characteristic landforms inside the mine (Figure 10). In addition to the above, we evaluated the overall volume of excavation materials in the area, processing the two digital surface models we obtained in the present work, in ArcGIS Pro, as follows:  
First, the SfM-derived DSM was cleaned, removing values that correspond to debris flows, anthropogenic debris and the machineries located near the entrance. The generated raster elevation file was then improved by filling the cleaned part with interpolated values, obtained with the Inverse Distance Weighting (IDW) method, using the Elevation Void Fill tool (Figure 11a). Second, aerial photo-derived DSM was clipped according to the upper boundary of excavation mapped in IVR, after being converted into a polygon (Figure 11b). Using the CutFill tool, the two abovementioned final elevation files (focusing within the excavation boundary for both), we produced a new raster that corresponds on the one hand to the common area shared between them and on the other hand only to excavation materials, having an estimated volume of 1,660,141.89 m\({}^{3}\) (Figure 11c). Apart from estimating the overall excavated volume, an effort was made to use the boundary between eruption Phases 2 and 4, which was digitized, for the first time, on a 3D model with the excellent texture resolution of 1 cm/pixel, to create a surface. Outputs (lines and points) from IVR survey, were imported into ArcGIS Pro to first estimate the boundary plane and then the volume of phase 4 (Figure 12). The hypothetical plane created through Topo to Raster tool is flat, with elevations that vary approximately between 105 m to the west and 147 m to the northeast, while dipping towards the south. The estimated total volume of P4 excavation materials rises to 794,386.02 m\({}^{3}\). Figure 11: Workflow followed in order to calculate the total volume of excavation materials. (**a**) The DSM generated by UAV photos and SfM techniques (left) was cleaned, removing anthropogenic debris and debris flows, and the removed values were replaced by interpolated ones (right), (**b**) the DSM generated by 1960s aerial photos (left) was clipped to excavation boundary (right), (**c**) 3D representation of the final surfaces generated from (**a**,**b**) on the left and on the right the common area between the two models that corresponds to excavation materials.