This paper summarizes four years of geological research in the Pomerania Bay and Oder Bank. As a result of the synthesis of new and archival data,we have compiled maps, cross-sections and models depicting the geological structure of the Quaternary and its basement, and the relief of structural surfaces. Two main seismostratigraphic sedimentary complexes are distinguished. The first corresponds to Pleistocene glacial and interstadial deposits. The second one is composed of Late Glacial and Holocene lacustrine-swamp and marine sediments. The outline of geochemical condition of the sea bottom is also presented. The content of the elements is always below the acceptable concentration and the origin of the elements is geogenic. Special attention has been given to mineral resources on the bottom surface and to documenting deposits of sand containing heavy minerals. The characterization of areas with sands suitable for beach nourishment and valorization of deposits and prospective areas have also been of great importance. The history of the development of the geological structure and palaeogeography of the area is the summary of the results.
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Investigations of the geological structure and seabed dynamics as well as the morphological and sedimentological effects of sand extraction generated by different mining techniques were carried out in Polish waters of the Baltic Sea, NW of the Gulf of Gdańsk, at a water depth of 15-17 m. Three research cruises took place: just before, directly after and 11 months after dredging operations. Seismoacoustic profiling, a multibeam echosounder, a side-scan sonar, a 3 m vibro-corer and a box-corer were used during the research cruises. The grain size distribution and 137Cs content of the sand samples were determined. Marine shells were dated by the AMS14C technique and pollen analyses were carried out on samples of muddy sands lying below the marine sand. A 2 to 4.5 m thick layer of marine sands lies on the boulder till and locally on late Pleistocene ice margin lake deposits. The 137Cs content indicates that the 0.4-0.8 m thick sand layer is mobile during storms. After the dredging operations, four pits with diameters from 80 to 120 m, depths from 3 to 4.5 m and slopes with gradients up to 30-55° were measured. Several smaller irregularly shaped pits and double furrows 30-150 m in length and 0.3-0.5 m in depth were found. The sonar mosaic also shows a 50-100 m buffer zone of fine sand around the pits which flowed over the dredger's side with water and settled on the bottom. During one year after the dredging operation the furrows generated by trailer suction hopper dredging as well as the fine sand cover around the pits disappeared completely. The four post-dredging pits left by stationary suction dredging were shallower by 2-2.5 m, their diameters increased by 40-50 m, the gradient of the slopes was reduced by up to 5-10°, and the total volume was only about 3.5% smaller than directly after dredging.
Celem artykułu było przedstawienie zasadniczych problemów kartograficznych przy rozpoznawaniu i dokumentowaniu osuwisk oraz terenów potencjalnie zagrożonych ruchami masowymi w obszarach miejskich Gdańska i Gdyni. Określenie lokalizacji i stopnia aktywności osuwisk oraz zagrożeń związanych z ich ponownym uruchomieniem wspomoże władze lokalne we właściwym zagospodarowaniu przestrzeni oraz wypełnieniu obowiązków dotyczących problematyki ruchów masowych wynikających z odpowiednich ustaw i rozporządzeń. Rozpoznanie lokalizacji i zasięgu osuwisk jest pomocne w tworzeniu planów odnoszących się do ryzyka osuwiskowego, czyli w ograniczeniu w znacznym stopniu szkód i zniszczeń wywołanych rozwojem osuwisk oraz zaniechaniu łub dostosowaniu budownictwa drogowego i mieszkaniowego w warunkach panujących w obrębie osuwisk.
EN
The aim of this article is to depict the fundamental cartographic difficulties towards appropriate recognition and evidence of landslides and areas potentially at risk of mass wasting, within urban zones of Gdańsk and Gdynia. Designation of landslide location, activity, and assessing a threat of landslide reactivation, is going to support the local authorities spatial planning accuracy - an obligation resulting from the adequate laws and regulations. A proper recognition of landslide location and coverage helps to apply suitable arrangements, aiming to reduce the damage caused by landslide development, as well as omission, or adaptation of road construction and housing, within areas being at risk of mass wasting and landslide activity.
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