3D Mesh Analysis of Coastal Boulder Deposits in Southern Peloponnese: Investigation of a Possible Tsunamigenic Origin

Coastal boulder deposits (CBD) along the Greek coastlines have long been considered indicators of past extreme-wave events, such as tsunamis. In this study, we aim to refine previous volume and mass estimates of CBD and reassess their possible tsunamigenic origin. To achieve this, CBDs were analyzed using advanced calculations for hydrodynamic conditions, that not solely focus on masses, but include LiDAR-scanned geometrical shapes and variations of coefficients that rely on their physical properties.

Therefore, we studied CDB near the Bay of Vatika by using built-in smartphone LiDAR sensors. In combination with rock density analysis, their masses were obtained. The CBD are distributed along a ~600 m-long coastal stretch. The largest boulders (≥38 t) are located on bedrock near the shore. Smaller boulders (>100 kg) are located up to ~200 m inland, partly embedded in sandy sediments and covered by vegetation, and were found up to 6-7m above sea level. It is indicated that the sandy sediments underneath boulders were transported as suspended load and deposited alongside them. Orientations of >330 measured CDB’s longest axes dominated in NNW-SSE direction. Rock pools indicate overturning during transport, imbrications and accumulations in clusters indicate extreme-wave events as transport mode. OSL analysis is intended to provide a chronology and confirm prior age estimations for the CBDs (~910-1150 yrs. BP).

With reference to the existing literature, we found that former volume analyses on CBDs in the study areas significantly overestimated the masses, thus we provide new data to refine calculated wave parameters and tsunami wave heights.