## 4 Hazards Analysis
### Landslide Hazard Assessment  
Landslides refer to the downward movement of rock, soil, or debris along a slope under the influence of gravity. These events can be triggered by natural causes, such as earthquakes and heavy rainfall, or by human activities, like deforestation or poorly constructed infrastructure. Landslides may occur gradually with minimal damage, or suddenly with severe consequences, including destruction of property and loss of life. On Lefkas Island, landslides frequently occur on steep, remote slopes, particularly along the western coastline. Although official records are limited, event data were collected from local news sources [28], the \"LAERTIS\"--Innovative Operational Risk Management System in the Region of the Ionian Islands\", conducted by the Department of Geology and Geoenvironment of the National and Kapodistrian University of Athens research project [29], and other scientific studies [30; 31]. These records are shown in Figure 10.  
To assess landslide hazard, we applied the Analytical Hierarchy Process (AHP), a widely used multi-criteria decision-making method [21]. The process began by identifying ten relevant factors influencing landslide susceptibility on the island. Each factor was ranked based on its contribution to landslide risk, using the Reverse Ranking Method (where 1 = least influence, 10 = highest), as shown in Table 1. The weight of each factor was based on a review of established methodologies and existing studies conducted in similar geological settings across Greece, e.g., [32; 33]. A consistency ratio (CR) of 0.0997 confirmed the reliability of the comparisons. The factors used in the model are as follows (Table 2, Figure 10):  
* Slope: Susceptibility increases with slope steepness. However, on very steep slopes, greater than 45\({}^{\circ}\), formations that are cohesive and rocky can ensure slope stability in terms of sliding but are vulnerable to collapsing. Slopes between 16 and 30\({}^{\circ}\) are most prone to landslides [32]. The steepest slopes (>35\({}^{\circ}\)) are concentrated in the southern part of the island. Figure 9: Spatial distribution of parameters used to obtain Flood Hazard Map: Recent deposits (**a**) and morphological slopes (**b**) in 25 m resolution. The Flood Hazard Map of Lefkas Island (**c**) presents mainly areas with low hazard, where medium- and high-hazard zones cover Lefkada, Vasiliki, Karia, and Nidri areas. * Lithology: According to [33], the landslide susceptibility of Greece can be divided into three zones--western, central, and eastern--based on the general geotechnical behavior of dominant geological formations. Lefkas Island, located in Western Greece, falls within the zone considered most prone to landslides. This elevated risk is linked to the lithological composition and structural characteristics of the region. The most vulnerable formations are loose, thin Quaternary deposits, which are highly susceptible to sliding. To a lesser extent, limestone and flysch formations also contribute to slope instability, primarily through rockfalls. * Distance From Faults: Landslides are more frequent near active fault zones, which are widespread on the island. * Land Use: Vegetation helps stabilize slopes. In Lefkas, only approximately one-third of the surface is well vegetated, making much of the island more vulnerable. * Distance From the Road Network: Proximity to roads increases landslide risk due to slope modifications, poor drainage, and excavation. Although all settlements on Lefkas Island are connected by roads, the main road network consists primarily of a single route that encircles the island. * Distance From the Drainage Network: Areas near rivers or streams are more prone to erosion, especially during heavy rainfall. Lefkas has a well-developed drainage network (Figure 4) covering most of the island. * Precipitation: The island receives between 845 and 918 mm of annual rainfall, which can saturate soils and trigger slope instability. * Soil Depth: Deeper soils are generally more prone to failure.