From Seafloor Morphodynamics to geohazard quantification: a multidisciplinary study of submarine canyon evolution along the Ionian Calabrian Margin

The evolution of submarine canyon systems along the Ionian Calabrian Margin (ICM) in the central Mediterranean Sea, is poorly understood as their unique morphological expression and occurrence is not fully clear. By focusing on the relationships between tectonic activity, sedimentary processes, and shallow fluid migration we investigated various scale and processes currently shaping the seabed. The ICM represents a complex forearc basin characterised by active tectonics and rapid margin uplift, where the interplay of structural, sedimentological, and fluid-related factors governs seafloor morphology and slope stability. Through the integration of multibeam and autonomous underwater vehicles (AUV)-based bathymetry datasets, high-resolution seismic profiles, and remotely operated vehicle (ROV) imagery, this work provides new insights into the mechanisms driving canyon development, headwall retreat, and slope failure processes in an area of significant geohazard potential. Bathymetric and seismic data revealed that canyon evolution is strongly controlled by the spatial distribution of structural high, shallow gas migration pathways and the proximity to ephemeral terrestrial rivers. Seismic profiles revealed the presence of acoustic blanking zones, chimneys and mounded features, indicating active or recent fluid seepage and demonstrating a close relationship between subsurface free gas and the occurrence of submarine drainage systems. The evidence suggests that canyon initiation occurs through the coalescence of fluid-escape depressions, which progressively evolve into gullies and mature canyon systems through retrogressive headward erosion. The morphology and structural setting of the ICM thus highlight the coupling between structural highs, shallow fluid migration, and sediment supply in shaping the present-day seabed. The use of newly acquired ultra-high-resolution datasets from AUV and ROV surveys provided the opportunity to identify centimetre- to metre-scale geomorphic features indicative of active erosional and instability processes along canyon walls, particularly within the Squillace Canyon system. These data reveal that fracture networks act as precursors to wall failure, evolving into spalling surfaces that promote further retrogressive failures. In addition, biological activity exerts an unexpected yet significant control on wall stability: benthic organisms colonize freshly exposed surfaces, producing intense bioturbation and localized weakening that can lead to the development of new unstable sectors. The comparable temporal scales of benthic community development and offshore infrastructure lifespans underscore the practical relevance of these small-scale erosional processes for risk assessment and early-stage infrastructure planning. To further quantify slope stability mechanisms, three-dimensional slope stability models were developed by coupling geotechnical analysis with seabed mapping from multibeam and seismic datasets. These models demonstrate that pre-conditioning factors such as sediment density, acoustic velocity, and slope gradient alone are insufficient to trigger landslides under static conditions. However, when earthquake-related cyclic loading is introduced, the modelled factors of safety (FoS) fall below unity, particularly in areas characterized by multiple overlapping slide scars. This finding emphasizes the critical role of seismic shaking in triggering slope failures and highlights the inherent instability of the Calabrian forearc under dynamic loading conditions. In conclusion, this study provides a comprehensive, multi-scale analysis of the processes governing submarine canyon initiation and evolution along the Ionian Calabrian Margin. By integrating geomorphological, geophysical, and geotechnical datasets, it demonstrates how tectonics, fluid flow, sediment dynamics, and biological activity act at different timescales to shape a rapidly evolving continental margin.