Solid rocks on the nearshore seabed – the distribution and potential impact on coastal processes in the Kołobrzeg region, the Southern Baltic

The Southern Baltic seabed is mainly composed of marine sediments situated on glacial and fluvioglacial deposits. In the Kołobrzeg region, however, solid rocks are located at the shallow subbottom. In order to determine the exact distribution of the rocks, some analyses of sonar images, underwater photos, sediment samples, seismoacoustic profiles and bathymetric data have been performed. The outcrops of Jurassic sandstones and mudstones have been documented. The geological structure of the area is presented, while the fact that the present seafloor relief is determined by the shallow uneven top surface of the Jurassic rocks is emphasized. The seabed has been classified as rock platform-constrained. The seafloor is a sediment-poor abrasion platform, within which marine sandy sediments are transported, mainly toward offshore, on the firm, stiff or hard surface of glacial deposits and Jurassic solid rocks. This results in a lack of material for the reconstruction of the beach after storms. Many of the commonly used methods for studying the condition and changes of the coast cannot be used in this type of terrain due to the presence of a thin and discontinuous dynamic layer lying on the erosion-resistant rocks of the geomorphologically complex seafloor.