<P> The Baltic Sea, with its unique brackish water, is a result of meltwater from the Weichsel glaciation combining with saltwater from the North Sea when the straits between Sweden and Denmark opened . Initially, when the ice began melting about 10,300 BP, seawater filled the isostatically depressed area, a temporary marine incursion that geologists dub the Yoldia Sea . Then, as post-glacial isostatic rebound lifted the region about 9500 BP, the deepest basin of the Baltic became a freshwater lake, in palaeological contexts referred to as Ancylus Lake, which is identifiable in the freshwater fauna found in sediment cores . The lake was filled by glacial runoff, but as worldwide sea level continued rising, saltwater again breached the sill about 8000 BP, forming a marine Littorina Sea which was followed by another freshwater phase before the present brackish marine system was established . "At its present state of development, the marine life of the Baltic Sea is less than about 4000 years old", Drs . Thulin and Andrushaitis remarked when reviewing these sequences in 2003 . </P> <P> Overlying ice had exerted pressure on the Earth's surface . As a result of melting ice, the land has continued to rise yearly in Scandinavia, mostly in northern Sweden and Finland where the land is rising at a rate of as much as 8--9 mm per year, or 1 meter in 100 years . This is important for archaeologists since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore . </P> <P> The term Würm is derived from a river in the Alpine foreland, approximately marking the maximum glacier advance of this particular glacial period . The Alps were where the first systematic scientific research on ice ages was conducted by Louis Agassiz at the beginning of the 19th century . Here the Würm glaciation of the last glacial period was intensively studied . Pollen analysis, the statistical analyses of microfossilized plant pollens found in geological deposits, chronicled the dramatic changes in the European environment during the Würm glaciation . During the height of Würm glaciation, c. 24,000--c . 10,000 BP, most of western and central Europe and Eurasia was open steppe - tundra, while the Alps presented solid ice fields and montane glaciers . Scandinavia and much of Britain were under ice . </P> <P> During the Würm, the Rhône Glacier covered the whole western Swiss plateau, reaching today's regions of Solothurn and Aarau . In the region of Bern it merged with the Aar glacier . The Rhine Glacier is currently the subject of the most detailed studies . Glaciers of the Reuss and the Limmat advanced sometimes as far as the Jura . Montane and piedmont glaciers formed the land by grinding away virtually all traces of the older Günz and Mindel glaciation, by depositing base moraines and terminal moraines of different retraction phases and loess deposits, and by the pro-glacial rivers' shifting and redepositing gravels . Beneath the surface, they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow . </P>

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