| Summary: | The former Viking settlement Birka is located on Björkö Island in Lake Mälaren, the third largest lake in Sweden. Birka is a well-known archeological site that onshore has been carefully examined. The lake floor of the waters surrounding the island has been less investigated but has a great potential to host not yet discovered archeological objects from this former hub for seafarers. Therefore, a geophysical survey including multibeam sonar mapping and subbottom profiling was carried out mainly along the shores of western Björkö Island. Processing and analysis of these collected data form the basis of this thesis. The main aims of this study are to produce a suite of geological maps and stratigraphic profiles that are used to geologically interpret the uppermost sediment stratigraphy and the bathymetry of the area. In addition, the processed data are investigated for archeological objects. The result shows that the acoustic records of the sediment stratigraphy reaches back to glacial clay formed as a consequence of the retreat of the Late Weichselian ice sheet, and that the uppermost sediment units probably are from the time after the isolation of Lake Mälaren from the Baltic Sea. The bathymetry and backscatter results have revealed that this relatively shallow study area contains several objects that potentially could be of interest from an archeological point of view. These objects include several unidentified objects in the Björkö strait and two unregistered shipwrecks where ground truthing data need to be collected to determine their respective origin.
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