Coastal flooding in Kołobrzeg (Kolberg) area, southern Baltic Sea, in the light of historical and geological data

Abstract

The Baltic Sea is not a typical tsunami area, but there are reports of coastal flooding, with its traces preserved in deposits from Germany, Finland and Sweden, and more recently from Poland. In this study an attempt was made to verify historical and legendary accounts of the ‘Sea Bear’ (‘der Seebär’) phenomenon. In the descriptions of folk accounts, the phenomenon has the features such as suddenness, speed, short duration, independence from the atmospheric conditions on land and sea. The search for coastal flooding deposits was conducted around the town of Kołobrzeg (Kolberg), located on the southern coast of the Baltic Sea. For the study area in chronicle record exist information about two events (17 September 1497 and 1 March 1779). For both events no record has been found in geological profiles, probably due to strong anthropogenic transformation of the subsurface layers. However there is quite precise information from chronicle records on the extent of the event from 17 September 1497 and on the thickness of the sandy layer left by the flooding. Based on this information in the Kołobrzeg area the range of the sand layer was 1400 m from the seashore, and its thickness locally reached approximately 10 cm. The flood height estimated according to the above-presented assumptions was 4.9 m a.s.l. In the Baltic Sea area, coastal flooding is possibly due to atmospheric forcing which can be responsible for an external waves event and devastating long waves, which have the same spatial and temporal scale as typical tsunami waves.