Geomorphological and Hydrological Analysis of Landslide-Prone Basins: A Case Study from Mount Pelion, Central Greece

Landslides rank among the most devastating natural hazards globally, causing widespread socio-economic disruptions and posing significant threats to human lives, infrastructure, and ecosystems. These events are primarily triggered by extreme weather conditions, such as heavy rainfall, and result from complex interactions between hydrological conditions, soil saturation, and terrain instability. This study focuses on southeastern Thessaly, specifically Mount Pelion in central Greece, a region with high geomorphological complexity and significant landslide susceptibility. Situated between the Aegean Sea and the Pagasetic Gulf, Mount Pelion’s diverse landscape, shaped by its unique climatic and geological features, makes it an ideal case study for exploring the relationships between morphometric and hydrological parameters and landslide activity.

The region's geological formations range from the Quaternary to the Triassic periods. While Quaternary deposits, composed mainly of sandy clays and gravels, are typically stable and found in torrent beds and coastal areas, the unstable Neo-Paleozoic to Triassic formations dominate the region. These formations, which include schists, quartzites, gneisses, and marbles, account for over 90% of historical landslides, highlighting their critical role in slope instability. 

This research presents a detailed geomorphological and hydrological analysis of 15 basins within the region, utilizing a variety of morphometric parameters. These include basin area, perimeter, elevation metrics, stream density, ruggedness indices, and shape indices like the Gravelius index and circularity ratio. Statistical analyses, including Pearson and Spearman correlation tests, were conducted to evaluate the influence of these parameters on landslide occurrences. The study also incorporated SHAP (SHapley Additive exPlanations) analysis to quantify the global impact of key features on landslide susceptibility predictions. 

Positive correlations between landslide occurrences and variables such as basin area (p: 0.981), stream length (p: 0.964), and perimeter (p: 0.948) emphasize the role of large basins with extensive hydrological networks and complex boundaries in increasing landslide susceptibility. Elevation metrics, including maximum elevation (p: 0.765) and mean elevation (p: 0.713), further underscore the vulnerability of high-altitude terrains with steep slopes. Conversely, negative correlations were observed for compact basin shapes (Gravelius index: p: -0.745, s: -0.923) and lower relief ratios (p: -0.676, s: -0.773), indicating that compact and less steep basins are less prone to landslides due to efficient runoff and reduced infiltration. The SHAP analysis further identified basin area (F), relief ratio (Rv), stream flow length (SF), and ruggedness index (Rn) as the most influential features driving landslide risk, with high values of these parameters significantly increasing susceptibility. Features like maximum elevation (Hmax) showed moderate positive impacts, while perimeter (P) and stream length (SL) exhibited lesser influence.

In conclusion, this study offers a robust framework for understanding the geomorphological behavior of basins and its impact on landslide susceptibility. By linking key parameters to slope instability, it contributes to the development of effective mitigation strategies and supports sustainable management of landslide-prone regions. Insights from this analysis hold practical value for disaster risk reduction, resource management, and long-term resilience planning in geologically complex landscapes like southeastern Thessaly.