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Browsing by Author "Åberg, Susanne"

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  • Åberg, Susanne (2013)
    The Litorina Sea is the latest Baltic Sea stage, which has dated to begin about 9000−7500 years ago. The sea phase developed after the Ancylus Lake when the straits of Denmark opened, and it is a distinctive phase within the Baltic Sea history. This MSc thesis aims to create a GIS based database about the highest stand of the Litorina Sea in Finland and to reconstruct its extent by interpolating it's shorelines with the resolutions of 10 and 25 meters. The purpose was also to make an updated version of the highest Litorina Sea shoreline map by Eronen and Haila 1992. The highest shoreline of the Litorina Sea can be observed in ancient shoreline relicts such as stone belts, beach ridges, cliffs and terraces. The widest extent of the Litorina Sea's brackish water can be detected from isolation horizons within mire and lake sediments. It can be distinguished as Clypeus limit or physically as a chance where the clays of the Ancylus Lake turn into clays of the Litorina Sea. The highest shoreline of the Litorina Sea is diachronous and its level in different regions of Finland varies due to the uneven uplift and inclining of the shorelines. It is important to note that the highest shoreline of the Litorina Sea has occurred in some regions at the beginning of the Litorina Sea stage like in Ostrobothnia or later by the time of the Litorina transgression in other places like in southern Finland. Depending on the location, the highest shoreline of the Litorina Sea occurred about 8000−6500 year ago due to its diachronity and the impact of transgression. All known shoreline and isolation observations were collected from the literature in the database with the help of LiDAR DEM with a resolution of two meters, and DEM 25. Observations were used to create a database with the information of coordinates and observed altitude. The aim was also to find new shoreline sites. Altogether 564 shoreline observations and 102 isolation observations were collected in the database and they were classified to five classes according to their reliability. The highest shoreline of the Litorina Sea (LI) was reconstructed with the help of the best observation points by using vector based TIN interpolation. Two different resolution LI representing rasters were created by subtracting the formed TIN model from two separate DEM models: DEM 10 and DEM 25. Calculated raster grids represent the relative altitude and the depth of the Litorina Sea at its highest stage in different areas. These rasters were classified into two classes, which other class represents area covered with water and other represents land area, and they were converted into polygons. Modeling was challenging because observations were not evenly distributed among the sphere of influence of the Litorina Sea. The altitude of LI increases in north-west direction from about 21 m in Virolahti area to about 32 m in Helsinki area, 45-52 m in Turku and Pori and to 100 m in Ostrobothnia area. Highest observation altitude of the Litorina Sea is in Ylitornio in the slopes of the Huitaperi at the level of 108.4 m. The results of the modeling resemble earlier maps of the highest shoreline of the Litorina Sea but they are more detailed. On the other hand the 25 m resolution map is still very coarse reflecting the errors of DEM 25 model. However, the 10 m resolution map is rather detailed, but it still needs some enhancement. Ancient Shoreline Database and associated fine-resolution maps are published to facilitate and promote the research related to the highest stage of the Litorina Sea.