The discovery of extensive landslide scars in the southern Baltic Sea during the Swedish Geological Survey's sea floor mapping has raised questions regarding the timing and triggering factors of landslide events. The primary goal of the study is to conduct a comprehensive analysis about the areal extent and timing of submarine landslides in the southern Baltic Sea, with focus on their potential to trigger tsunamis that potentially impact coastal regions. The research draws inspiration from historical events such as the Storegga slide off the coast of Norway ca. 8150 years ago which resulted in a tsunami that propagated across vast areas, leaving notable geological traces.

By examining evidence from the Baltic Sea region, the study aims to shed light on the potential occurrence of tsunamis in this previously unexplored context. Various indicators, including disrupted stratigraphic offshore sediment profiles, a sudden sea level rise, and the abrupt inundation of Mesolithic settlements, suggest that a significant event in the region have occurred in the past.

Considering ongoing global warming and anticipated rises in sea levels, the southern Baltic Sea, lacking land uplift post-deglaciation, is particularly vulnerable to such changes. In essence, this research not only contributes to a deeper understanding of geohazards in the Baltic Sea but also holds implications for coastal infrastructure planning in the face of climate change and the imperative need for sustainable mitigation strategies.

The project is divided into three Work Packages (WP 1-3):

WP 1: Offshore and modelling. Marine geophysical mapping (utilizing multibeam and sub-bottom profiling) and sediment coring will be conducted in the southern Baltic Sea. The mapping data will facilitate the reconstruction of slide sites and the creation of a 3D model of the seafloor geology. This model will enable the calculation of slide mass volumes and displacement, providing input for tsunami modelling. Laboratory analyses of sediment cores will employ automated core logging of physical properties, X-ray CT scanning, undrained shear strength measurements, geochemical profiling, and biostratigraphy. Radiocarbon dating will be used to establish a chronological framework for the slide event. Numerical simulations will be executed to model the tsunami wave propagation, wave amplitude and the resulting coastal inundation along the coastlines for different submarine landslide scenarios.

WP 2: Coastal. Investigation of coastal geological and archaeological evidence related to tsunami run-up around the southern Baltic Sea coasts (Blekinge area in Sweden and Pärnu area/Gulf of Riga in Estonia) will be conducted. This will involve the dating of evidence from both published and newly acquired sites/data. Coastal lake sediment stratigraphies will be analysed using traditional methods (micro-/macro-fossils) as well as innovative approaches (environmental-DNA and organic geochemistry).

WP 3: Societal Risk Assessment. Indicators of further slide events are studied on a landscape level to form a susceptibility map. Using data from WP 1 and WP 2, we will compile information on submarine and coastal infrastructure in the identified risk zone, conducting an initial vulnerability assessment.