## 2. Medicane Ianos-Induced Landslides
### 2.1. Landslides in Thessaly
#### 2.1.2. Remote Sensing-Based Landslide Inventory  
To investigate and map the distribution of landslides in the Karditsa, Thessaly area, we used post-event acquisitions of Copernicus Sentinel-2 optical satellite imagery. Sentinel-2A/B multispectral imagery has a ground resolution of 10-60 m and covers wide swaths, thus enabling the rapid imaging of the affected area. Multiple Sentinel-2 frames were selected for the post-event period, and acquired 20, 25 and 30 September 2020, as large parts of the area were covered by clouds in the 20 and 25 September frames. Imagesacquired before the event, on 5, 10 and 15 September 2020, were used as references in order to visually identify and map landslides (Figures 2 and 3). The minimum size of landslides mapped was limited by the satellite imagery resolution (10 m for Sentinel-2), and consequently smaller-sized slides or rockfalls were not possible to identify and were not included. In addition, it was not feasible to classify most of the landslides into different types based on this remote sensing procedure. A small portion of slope failures was classified by the field surveys as presented in following section, validating the outcome of the statistical analysis presented in Figure 4.  
Due to the small size of the majority of the identified landslides (most having a size of 2-4 pixels in Sentinel-2 imagery), landslide polygons were not digitized in this preliminary inventory. Digitizing was focused on marking the initiation point/headscarp (long avalanches or earthquakes) or the approximate center of the landslide feature when the former was not possible due to small size and image resolution. For assistance during manual picking of landslides, we used additional analysis products, such as change analysis rasters (MAD-Multivariate Alteration Detection Transformation [25]) and multi-temporal single band RGB composites (Figure 2). Co-registration issues present between Sentinel-2 frames were resolved using GeFolki registration algorithm [26].  
This preliminary inventory (Figure 3) includes 1697 landslides, limited to a narrow mountainous area of Karditsa and part of Evritania regions. Examination of Sentinel-2 imagery over the Pindos mountain region showed no or few sparse landslides, outside this area. The largest concentration of landslides was found around Amarantos village, southeast of Plastira lake, with up to 15 landslides per square kilometer (Figure 3).  
Figure 2: Example of manually mapping landslides within the study area using Sentinel-2 imagery. Pre- and post-event true color Sentinel-2 images (**a**,**b**) and an overlay (**c**) of mapped landslide points with red color (mostly headscarp points). Change detection MAD processing (**d**,**e**) assisted visual picking of headscarp points (**f**).  
Figure 3: (**a**) Mapped landslides (black dots) triggered by Medicare Ianos during 17-19 September 2020, and simplified lithology of the area (see text for references). (**b**) Density map of Ianos landslides (using a radius of 1000 m); two major concentrations of landslides west of Lake Plastira and around Amarantos village.