Reassessing Coastal Boulder Deposits in Southwestern Crete using UAV and LiDAR-Based Field Investigations

Coastal boulder deposits along the southwestern coast of Crete (Greece) have been widely interpreted as evidence of past tsunami impact, based on their size, position and geomorphic setting. However, distinguishing tsunami-transported boulders from those emplaced by other high-energy coastal processes remains challenging, particularly where field documentation is limited. In this study, we present a reassessment of selected boulder sites in southwestern Crete previously described in the literature, with the aim of assessing the extent to which existing tsunami interpretations are supported by new high-resolution field observations. Our methodological approach integrates UAV-based surveys, mobile LiDAR scanning, detailed field mapping and targeted sampling to systematically document boulder dimensions, orientations, elevations, spatial distribution and local geomorphic and geological context. Our acquired datasets allow a more detailed evaluation of boulder emplacement than previously available. While several observations are consistent with high-energy marine inundation, detailed documentation of boulder positioning, imbrication patterns, elevation ranges and local topography reveals substantial variability in depositional settings than previously captured. At some locations, field observations indicate that the available evidence does not uniquely constrain a single emplacement mechanism. In addition to tsunami-related processes, other high-energy coastal dynamics, such as storm wave action, cliff-derived block falls or multi-phase transport, may have contributed to the observed boulder distributions. These observations complement earlier studies by broadening the empirical basis for evaluating coastal boulder deposits and by indicating where previous tsunami interpretations may benefit from additional consideration.

Our findings underline the value of site-specific, high-resolution field assessments aimed at systematically documenting as many boulders as possible at each site. We examined 15 sites regarding boulder deposits which results in several hundred individual LiDAR-Scans of coastal boulders. By expanding the available data archive, this approach supports more reliable, transparent and reproducible interpretations and helps clarifying remaining ambiguities that require additional constraints. The study contributes to an improved understanding of coastal boulder emplacement in the eastern Mediterranean and provides a refined empirical foundation for tsunami hazard reconstructions and the interpretation of extreme-wave proxies in tectonically active coastal regions.