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Browsing by Author "Åberg, Annika"

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  • Åberg, Annika (2013)
    Observations of the highest shoreline of the Baltic Sea have been collected over decades but only recently it has been possible to create an ArcGIS based database that covers whole Finland. An ancient shoreline database (ASD) was created in this study, in which shoreline observations from earlier publications were collected and analysed. The map was created in two resolutions (10 and 25 m) using TIN (Triangulated Irregular network) as an interpolation method. The highest shoreline of the Baltic Sea basin designates the post-glacial shoreline level that separates sub- and supra-aquatic areas. The highest shoreline is diachronous and shorelines have formed during various stages of the Baltic Sea, i.e. from the Baltic Ice Lake to the Ancylus Lake between 12 000-8500 BP. Shoreline landforms that can be connected to the highest shoreline are washed hillsides, deltas, stone belts, esker tops, cliffs, beach terraces, beach ridges and lake ramparts. Shoreline observations were collected in ASD as point type data, in which every observation has location, altitude and other related information. Three different DEMs (Digital Elevation Model) were used to measure altitudes. Two of them, DEM 10 m and DEM 25 m cover whole area of Finland and along with them were used LiDAR DEM, which only covers those parts of Finland that were published in 2011 or earlier. DEM 25 m has resolution 25 meters and it has been used to measure the altitude of shorelines in areas where LiDAR DEM is not available. DEM 10 m is newer DEM with 10 meter resolution and it is only used at the end of the database collecting. New shoreline observations were also scouted using MDOW hillshade and LiDAR DEM. A total of 935 highest shoreline observations were collected in the ASD and 69 dummies were defined, which were used to backfill missing areas outside the ASD. Best shoreline observations were used to interpolate a surface that represents the highest shoreline using TIN-model. The TIN-surface was subtracted from DEM 10 m and DEM 25 m that were converted into rasters and result maps were two different resolution raster maps, which were converted to polygons. The observations of the Baltic Ice Lake, the Yoldia Sea and the Ancylus Lake were used in same interpolation regardless the fact that the level of the Baltic Ice Lake dropped 28–25 meters at around 11 600 BP. Result maps largely correspond with the map of Eronen and Haila that were published in 1992. The map based on DEM 10 m has clearly better resolution and it gives new information of the border of the sub- and supra-aquatic areas in Finland. DEM 25 m is mainly beneficial in large scale because it is coarser than DEM 10 m. TIN-model interpolates the drop of The Baltic Ice Lake well enough but additional shoreline observations would be needed for more precise outcome. The highest shoreline of the Baltic Ice Lake district in this study is 163 m a.s.l. close to the First Salpausselkä in the vicinity of Hollola and the highest shoreline of the Ancylus Lake is located in the city of Rovaniemi where it reaches 220 m a.s.l.