Urstromtal
Anurstromtal(plural:Urstromtäler) is a type of broad glacialvalley,for example, in northernCentral Europe,that appeared during theice ages,or individualglacial periodsof an ice age, at the edge of the Scandinavianice sheetand was formed by meltwaters that flowed more or less parallel to the ice margin.Urstromtälerare an element of theglacial series.The term is German and means "ancient stream valley". Although often translated as "glacial valley", it should not be confused with a valley carved out by a glacier. More accurately some sources call them "meltwater valleys"[1][2]or "ice-marginal valleys".[3]
Emergence and structure
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Important for the emergence of theUrstromtäleris the fact that the general lie of the land on theNorth German Plainand inPolandslopes down from south to north. Thus the ice sheet that advanced from Scandinavia flowed into a rising terrain. The meltwaters could therefore only flow for a short distance southwards over thesandurs(outwash plains) before having to find a way to theNorth Seabasin that was parallel to the ice margin. At that time, the area that is now the North Sea was dry as a result of the low level of the sea.
As elements of the glacial series,Urstromtälerare intermeshed with sandur areas for long stretches along their northern perimeters. It was over these outwash plains that the meltwaters poured into them.Urstromtälerare relatively uniformly composed ofsandsandgravels;the grain size can vary considerably, however. Fine sand dominates especially in the upper sections of theUrstromtalsediments. The thickness of theUrstromtalsediments also varies a great deal, but is mostly well over ten metres.
Urstromtälerhave wide and very flat valley bottoms that are between 1.5 and 20 kilometres wide. The valley sides, by contrast are only a few to a few dozen metres high. The bottom and the edges of anUrstromtalmay have been significantly altered by more recent processes, especially the thawing ofdead iceblocks or the accumulation ofsand dunes.In thepost-glacial period,manyUrstromtälerbecame bogs due to their low lying situation and the high water table.
Central Europe
[edit]
InCentral Europe,there are severalUrstromtälerfrom various periods.
- Breslau-Magdeburg-BremenUrstromtal;(Poland,Germany); formed during theSaale glaciation
- Glogau-BaruthUrstromtal;(Poland, Germany); formed during theWeichselian
- Warsaw-BerlinUrstromtal;(Poland, Germany); formed during the Weichselian
- Thorn-EberswaldeUrstromtal;(Poland, Germany); formed during the Weichselian
- The termElbeUrstromtalrefers to theElbe valleyroughly at the height ofGenthinto the Elbe estuary atCuxhaven.The meltwaters of the three above-mentioned WeichselianUrstromtälerflowed successively through this valley towards the North Sea basin.
- The term RhineUrstromtalfor theRhinevalley fromDüsseldorfto its mouth on the North Sea is disputed. The Rhine was certainly a route for meltwaters during the Saale glaciation. The structure of the valley is however clearly older and was formed by recenttectonics.
- In theAlpineglaciation zone of Central Europe the termUrstromtalis not used. In this region, theDanubeand, periodically, theRhinecarried the meltwaters away.
Some sections of the aforementioned main valleys have been given their own names. The LusatianUrstromtaland the AllerUrstromtalare parts of the Breslau-Magdeburg-BremenUrstromtal.The Baruth, Berlin and EberswaldeUrstromtälerare common short names for the associated sections of theUrstromtalinBrandenburg.
In addition to the large main valleys there are also numerous smaller meltwater valleys (Urstromtalungen). Their appearance is similar to that of the greatUrstromtäler,but they are considerably shorter. They are also not linked to a sandur and aterminal moraine.
Urstromtälerof Central Europe (Poland, Germany and Denmark especially) were directly connected to the North Atlantic Ocean, via theChannel River,during Pleistocene maximum glaciations, i.e. at times of confluence of the British and Fennoscandian ice-sheets in the intervening North Sea.[4][5]
Features
[edit]Urstromtälershould not be confused withtunnel valleys.The latter are formed beneath, not in front of, the ice mass. In addition most tunnel valleys run from north to south. The principal direction ofUrstromtäleris from east to west. TodayUrstromtälerare only partly used by rivers, because the majority have found shorter routes to the sea (like theOderandVistula). The straight troughs of theUrstromtälerbetween the rivers were used for canal routes due to their low gradient, for example for theElbe–Havel Canalor theOder–Havel Canal.
Because the land inNorth Americaand on theRussian Plaintilts towards the south, the formation ofUrstromtälerthere during the ice age did not take place. TheMississippi Riverand its tributaries carried the meltwaters of the North American ice sheet away. In Eastern Europe the meltwaters flowed down the river basins of theDnieper,DonandVolga.
Urstromtäler,whether sandy or boggy, posed considerable obstacles to movement in theMiddle Ages.As a result, thetrade routesconverged on points where the valley could be crossed comparatively easily. These hubs thus became favourite sites for the founding of towns or castles. Examples from the German state of Brandenburg includeBerlin,Fürstenwalde,LuckenwaldeandBaruth/Mark,and from Lower Saxony the town ofVorsfeldeandWolfsburg Castle.
See also
[edit]References
[edit]- ^Böse, Margot (2005).The Last Glaciation and Geomorphologyin: Koster, E. (ed.):The Physical Geography of Western Europe,Oxford University Press, p. 61
- ^Selected Soil Associations,Berlin Digital Environmental Atlas, accessed on 23 Dec 2011
- ^Jürgen Ehlers, Philip Leonard Gibbard (ed.) (2004).Quaternary glaciations: extent and chronology, Part 3,Elsevier, London, Oxford, San Diego, Amsterdam. p. 139.ISBN0-444-51462-7
- ^Toucanne, S.; Zaragosi, S.; Bourillet, J.F.; Cremer, M.; Eynaud, F.; Van Vliet-Lanöe, B.; Penaud, A.; Fontanier, C.; Turon, J.L.; Cortijo, E.; Gibbard, P.L. (2009)."Timing of massive 'Fleuve Manche' discharges over the last 350 kyr: Insights into the European ice sheet oscillations and the European drainage network from MIS 10 to 2"(PDF).Quaternary Science Reviews.28(13–14): 1238–1256.Bibcode:2009QSRv...28.1238T.doi:10.1016/j.quascirev.2009.01.006.
- ^Toucanne, S.; Zaragosi, S.; Bourillet, J.F.; Marieu, M.; Cremer, M.; Kageyama, M.; Van Vliet-Lanöe, B.; Eynaud, F.; Turon, J.L.; Gibbard, P.L. (2010)."The first estimation of Fleuve Manche palaeoriver discharge during the last deglaciation: Evidence for Fennoscandian ice sheet meltwater flow in the English Channel ca 20-18 ka ago"(PDF).Earth and Planetary Science Letters.290(3–4): 459–473.Bibcode:2010E&PSL.290..459T.doi:10.1016/j.epsl.2009.12.050.
Literature
[edit]- H. Liedtke:Die nordischen Vereisungen in Mitteleuropa.2nd ed., Trier 1981,ISBN3-87994-204-8,307 p.
- H. Liedtke, J. Marcinek (ed.):Physische Geographie Germanys.3rd ed., Gotha 2002,ISBN3-623-00860-5,786 p.
- Johannes H. Schroeder (ed.):Führer zur Geologie von Berlin und Brandenburg, No. 2, Bad Freienwalde – Parsteiner See.2nd improved edition. Geowissenschaftler in Berlin und Brandenburg e. V., Selbstverlag, Berlin 1994,ISBN3-928651-03-X,ISSN0941-2980
- Johannes H. Schroeder (ed.):Führer zur Geologie von Berlin und Brandenburg, No. 5, Nordwestlicher Barnim – Eberswalder Urstromtal.Geowissenschaftler in Berlin und Brandenburg e. V., Selbstverlag, Berlin 2004,ISBN3-928651-06-4,ISSN0941-2980
- Johannes H. Schroeder (ed.):Führer zur Geologie von Berlin und Brandenburg, No. 9, Oderbruch – Märkische Schweiz – Östlicher Barnim.Geowissenschaftler in Berlin und Brandenburg e. V., Selbstverlag, Berlin 2003,ISBN3-928651-11-0,ISSN0941-2980
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