10. Postglacial Evolution of the Odra River Mouth, Poland-Germany

As revealed by multidisciplinary research, the Odra River mouth area was evolving during the Late Glacial and Holocene by changing from glacio-fluvial to fluvio-limnic to marine through to the present lagoonal area. In the Late Pleistocene, the pre-Odra River was rolling westward along the Toruń-Eberswalde ice-marginal valley to discharge, farther away and like the rivers Elbe and Rhine, to the Atlantic. After the Scandinavian icesheet retreat (ca. 14.5 ky BP), the ancient river was flowing north-west to discharge to the Baltic Sea, most likely close to the eastern part of today’s Island of Rügen. Initially, the Odra was a braided river of a type, with many wandering channels and sandbanks. In the early Holocene, the river became anastomosing, with stabilised channels. In the mid-Holocene, the Odra was most likely meandering through swamps and bogs. In the late Atlantic period, during the Littorina transgression (ca. 7 ky BP), the river valley was invaded by the sea water and was transformed into a marine embayment extending southward down to today’s city of Szczecin. The river mouth area became an estuary. During the marine transgression, erosion processes affected two islands composed of glacial sediments: the Wolin and the Usedom. Erosion of the islands and the intensifying longshore transport produced two sandy spits which grew in size and gradually blocked the embayment, turning it into a lagoon. At present, the Odra River mouth area shows characteristics of a lagoon.