Submarine landslides on the slope of a sandy barrier: A case study of the tip of the Hel Peninsula in the Southern Baltic

Abstract

The aim of the study is to present the occurrence of landslides on the submarine slope of a sandy barrier. The scale and significance of this phenomenon is discussed. The study area is the Hel Peninsula. It is a 35 km long young sandy spit. The landform is prograding into the deep part of Gdańsk Bay, and the underwater extension of its tip is a steep sandy slope. The tip is still poorly investigated, as it was a military area closed to researchers until 2003. The first detailed survey of the tip on the seabed was conducted aboard the research vessel “IMOR”. A multibeam echosounder, a sub-bottom profiler and a side-scan sonar were used, while grab and core samples of sediment were obtained. Many forms, commonly created as the result of underwater mass movement, were recognized and determined (main scarps, main bodies, landslide steps, landslide foots, series of small slides, “sheet” slides and structural slides). On the one hand, the landslide processes that occur in the tip of the Hel Peninsula are related to the natural development of sandy spits. On the other hand, they threaten the shore’s stability. The genesis of the landslides is still not known.