L’archipel de Kvarken (Finlande) et la Haute côte (Suède) sont situés dans le golfe de Botnie, qui prolonge la mer Baltique vers le nord. Les 5 600 îles et îlots se singularisent principalement par les curieuses moraines à crête bosselées, ou moraines de Geer, formées par la fonte de la nappe de glace continentale composées il y a entre 10 000 et 24 000 ans. L’archipel de Kvarken s’élève de manière continue du niveau de la mer du fait d’un relèvement glacio-isostatique rapide, lorsqu’une terre précédemment comprimée par le poids d’un glacier se relève après la disparition de ce dernier, fait de ce taux de relèvement dans la région l’un des plus élevés au monde. Du fait de l’avancée du littoral, des îles apparaissent et s’unissent, des péninsules grandissent, des lacs se forment depuis les baies et deviennent des marais et des fagnes tourbeuses. La Haute côte a aussi été largement façonnée par l’association de processus de glaciation, de recul des glaciers et d''émergence de nouvelles terres. Depuis le retrait final des glaces de la Haute côte, il y a 9 600 ans, le relèvement est de l''ordre de 285 m, ce qui correspond au « rebond » manifeste le plus important jamais observé. La Haute côte est un site exceptionnel pour la compréhension des processus importants qui ont formé les glaciers et les zones de relèvement de la surface de la Terre.
Björköby - Finland
[Uniquement en anglais]
The site lies within the specific area known as the 'High Coast' of Sweden, and is located on the west shore of the southern Gulf of Bothnia, a northern extension of the Baltic Sea. The High Coast is a mosaic of human and natural landscapes with agriculture, fishing and tourism as the main economic activities. It has a long history of human use dating from late Stone Age dwellings and remains of an Iron Age village.
Physically, the archipelago has irregular topography with a series of lakes, inlets and flat hills rising to 350 m. Vegetation is typical of the west Eurasian taiga with a mix of alpine, boreal forest and wetland communities. It displays marked altitudinal zonation and great spatial variability, with high floristic diversity, due to the complex pattern of soils and substrate on an uplifted, high-relief land surface. The offshore islets support small seabird populations. The main natural values of the High Coast are geological and relate to the glacial history of the area. Since the retreat of the last ice cap, 18,000-9600 BP, the land began to uplift. The geomorphology of the region is largely shaped by the combined processes of glaciation, glacial retreat and the emergence of new land from the sea which continues today at a rate of 0.9 m per century. In conclusion, the High Coast is one of many places in the world that is experiencing uplift as a result of deglaciation. Isostatic rebound is well illustrated and the distinctiveness of the site is the extent of the total isostatic uplift which, at 294 m, exceeds others. The geological, topographical and climatic conditions also combine to make the High Coast a distinctive vegetation boundary zone, with a rare blend of southern plants with northern boreal, western oceanic and eastern continental species.
The High Coast contains large mammal species, such as bear, lynx and moose, which are widespread in Scandinavia. Whereas the coastal birdlife is typical of the region, the terrestrial birdlife is rich and varied due to the altitudinal range and topographic diversity which also provide habitats attractive to some rare birds of southern origin. Invertebrate fauna is not well known, although insects may be richer than elsewhere because of the floristic diversity. The biological character of the marine environment is a consequence of several major controlling influences such as: brackish waters of very low salinity; the most sharply contoured submarine topography in the Baltic, extending to depths in excess of 200 m close inshore; little tidal influence, with shifting water levels determined mainly by changing weather conditions of air pressure and wind; and seasonal ice cover. The resultant mosaic of shallow, sheltered embayment and deep, open waters provides a range of habitats for a mix of marine, brackish and freshwater species, low in species diversity but high in population numbers for some macrofauna species.
The special feature of the marine realm, imparting the greatest scientific significance, represents the submarine extension of the topographical continuum of landscapes undergoing isostatic uplift.
Continual elevation of the land results in inlets becoming progressively cut off from the sea, transforming them into estuaries and ultimately lakes. The terrestrial influence progressively extends seawards into the Bothnian Sea. This process has major effects for the associated plants and animals that must constantly adapt to the changing environments. The whole creates a landscape of great scenic value and aesthetic appeal.
Archaeological sites, some remarkably well preserved, reveal 7,000 years of human agrarian and maritime settlement in the High Coast, all confined by the steep topography into a narrow coastal strip of 2-3 km. Displacement of coastal settlements by isostatic land uplift has created a relict cultural landscape with evidence of different peoples at successive levels above the sea. The oldest remains, from the Stone Age of 5000 BC, now stand at 150 m above sea level, and corresponding Bronze Age and Iron Age are found, respectively, at 30 m and 15 m above the present shoreline. Adaptation of peoples to conditions created by land uplift means the geological history and cultural history are, thus, closely entwined.
The remarkable imprint of 7,000 years of human occupancy on a landscape experiencing the world's highest isostatic uplift is a significant cultural heritage asset, and one that is important to preserve for future generations. However, cultural landscapes and prehistoric remains are widespread throughout Scandinavia. Source : UNESCO/CLT/WHC