The Interplay of Neotectonics and Climate Change as Triggers for Coastal Hazards — Examples from the Baltic

Vertical displacement of the earth's crust and climatically driven eustasy serve as main components driving the relative sea level (RSL) change during the Quaternary. Whereas the eustatic change mirrors mainly climatic factors, the vertical displacement of the earth's crust has to be regarded as a result of isostatic processes superimposed by the regional tectonic regime or land-subsidence due to local factors. Using a simple model the eustatic and isostatic component of RSL data can be separated. Comparing these components by a "coastal index" the dominating factor of coastline development at sites under investigation — either vertical crustal displacement or climatically controlled eustatic change — can be determined. Based on this index shorelines can be classified identifying particularly tectonically stable coastal zones where morphogenesis is influenced mainly by the sea level rise and hydrographically determined zones of coastal erosion and lateral sediment transport. The Baltic Sea serves as a model area bridging between the areas of the uplifting Fennoscandian Shield and the subsiding southern Baltic lowlands. Subsidence superimposed with climatically driven sea level rise and meteorologically induced coastal flooding provokes permanent coastal retreat at the southern sinking coasts. Predictions of coastal hazards are made applying our model parameterized with neotectonical and long term sea level change data superimposed with extreme sea level data measured during the flood of 1872.