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

Abstract

part ment of Geo mor phol ogy and Qua ter nary Ge ol ogy, Baayńskiego 4, 80-952 Gdańsk, Po land Rudowski, S., Rucińska-Zjadacz, M., Wróblewski, R., Sitkiewicz, P., 2016. Sub ma rine land slides on the slope of a sandy bar rier: a case study of the tip of the Hel Pen in sula in the South ern Bal tic. Geo log i cal Quar terly, 60 (2): 407-416, doi: 10.7306/gq.1291 The aim of the study is to pres ent the oc cur rence of land slides on the sub ma rine slope of a sandy bar rier. The scale and sig-nif i cance of this phe nom e non is dis cussed. The study area is the Hel Pen in sula. It is a 35 km long young sandy spit. The landform is prograding into the deep part of Gdańsk Bay, and the un der wa ter ex ten sion of its tip is a steep sandy slope. The tip is still poorly in ves ti gated, as it was a mil i tary area closed to re search ers un til 2003. The first de tailed sur vey of the tip on the sea bed was con ducted aboard the re search ves sel "IMOR". A multibeam echosounder, a sub-bot tom profiler and a side-scan so nar were used, while grab and core sam ples of sed i ment were ob tained. Many forms, com monly cre ated as the re sult of un der wa ter mass move ment, were rec og nized and de ter mined (main scarps, main bod ies, land slide steps, landslide foots, se ries of small slides, "sheet" slides and struc tural slides). On the one hand, the land slide pro cesses that oc cur in the tip of the Hel Pen in sula are re lated to the nat u ral de vel op ment of sandy spits. On the other hand, they threaten the shore's sta bil ity. The gen e sis of the land slides is still not known. Key words: un der wa ter mass move ments, sandspit, dig i tal ter rain model, side-scan so nar, sub-bot tom pro fil ing.

Seismic architecture of the tip of the Hel Peninsula, Poland

“…Other data used in the present research included side-sonar measurements and sea-floor viewing with the ROV TV system on the tip slopes (Rucińska-Zjadacz 2015; Rudowski et al 2016) and information from the analysis of sparse shallow core samples with a length of 3 m (Rucińska-Zjadacz 2015; Rudowski et al , 2016.…”

“…Furthermore, the authors of the present article used high-resolution seismoacoustic profiles obtained with the subbottom profiler (frequency 3.5-5 kHz) using precise positioning with the DGPS RTK system in connection with the appropriate navigation systems Hydro and Track Point. The profiles were made between 2004 and 2013 by the Operational Oceanography Department of the Maritime Institute in Gdańsk (Rucińska-Zjadacz, Rudowski 2008Rudowski , 2009Rucińska-Zjadacz 2015;Rudowski et al 2015Rudowski et al , 2016.…”

“…The incentive for the research were the results obtained from the earlier, detailed investigations of the underwater slope of the Hel Peninsula tip (Rucińska-Zjadacz, Rudowski 2008Rudowski , 2009Rucińska-Zjadacz 2015;Rudowski et al 2015Rudowski et al , 2016. The investigations revealed great impact of the surface mass movements on the structure and the evolution of the tip.…”

“…The submarine slope of the tip of the Hel Peninsula is a unique form when compared with underwater slopes of other sand barriers due to its steep inclination (5-8 o on average, and locally almost 20 o ) and its height (ca. 50 m) (Rucińska-Zjadacz, Rudowski 2009;Rudowski et al 2016). There are other spits entering deep waters of non-tidal water bodies, for example the Long Point spit on Lake Erie (Davidson-Arnott, Conliffe Reid 1994).…”

“…However, no mass movements were identified and described on such spits. In the case of such a steep inclination of the tip slopes a variety of forms connected with mass movements developed on the slope surface (Rucińska-Zjadacz 2015; Rudowski et al 2016).…”