Glaciation of Würm
The glaciation of Würm is the name given to the manifestations of the last total Glaciation of the Pléistocène in the the Alps.
HistoryIt was defined by A. Penck and E. Brückner (1901-1909), which gave him the name of a tributary of the the Danube ( c.f. Würm ), like the preceding alpine glaciations (Riss, Mindel, Günz, Donau). Its definition rests on the observations of the geological consequences of the significant drops of the average temperatures over one long period (fluvio-glacial tablecloth, Moraine S) in the alpine solid mass.
ChronologyThe glaciation würmienne corresponds roughly to stages 2,3,4 and 5a-d of the isotopic Chronologie developed since the years 1950. Its lower limit is generally fixed at 115 000 BP (beginning of the stage 5d) but certain authors consider that it begins with stage 4 (75 000 BP). Its higher limit corresponds at the end of stage 2 and at the beginning of the Holocène, there is approximately 10 000 years. The glacial maximum was reached there is approximately 20 000 years.
Würm is more or less Synchrone other glaciations of the northern Hemisphere, of which the Wisconsinien in North America, the Weichselien in Northern Europe, the Vistulien in Germany of North and the Devensien in British Isles. Würm name has only one local chronological significance, limited to the area located around the the Alps.
ConsequencesThe glaciation of Würm is a demonstration of a cooling which related to more or less directly all planet. This cooling in particular had as a consequence a fall of the sea level of a hundred meters (Marine regression) and the establishment of a periglacial climate in Europe, outcome with deep modifications of fauna and flora.
Grounds emerged between 50.000 years and 40.000 years then between 25.000 years and 12.000 years.
- Ainsi appeared grounds, such as that of the Béringie being located between the Siberia and the Alaska, allowing a mégafaune (mammoths, équidés, camélidés, deer tribe) and populations human hunters-gatherers to pass from a continent to the other.
- Of the terrestrial bridges also appeared between the Australia, the Tasmanie and the New Guinea thus forming a large continent of the name of Sahul.
- terrestrial Bridges also between the archipelago of the Filipino and the Indonesia.
- Enfin terrestrial continuity enters the Japan and the Korea.
For certain authors, on the level of the low latitudes the glaciations are correlated at rain stages i.e. wetter periods: thus, the desert of the the Sahara knew episodes relatively sprinkled during the Préhistoire.
Traces of the ice caps of the Quaternary oneThe glaciation of the quaternary era left many visible traces in areas which, today, are not covered any more by the ices. The accumulation of Loess and silts of glacial origin meets on vast surface in North America, the plates and the plains of average Europe and in septentrional China. In the southern hemisphere, it relates to especially Argentina (Pampa). Transported by the wind, the loesses end up forming a more or less thick cover (up to 200 meters in China) and makes fertile the areas concerned.
The plain of Geest (Germany) and the Polish plain are concerned with the morainic deposits of the Quaternary one; that gives landscapes of moors (Moor of Lunebourg) or hills (Mazurie Polish) framing rivers which run towards north. The area of Börde (in Germany) or that Shanxi (valley of the Huang He in China) is papered loess and is consequently fertile. The withdrawal of the ice cap gives rise to landscapes of marsh (Marais of Polésie in Ukraine) or lakes (Lac Ladoga, Lac Onega in Russia; Big lakes in North America).
With Quaternary, the Ice cap, which covered many mountains, including in the intertropical zone, left behind him modelled completely characteristic accumulation and of erosion. The bone, Drumlin and glaciated valleys mark many landscapes in the periglacial areas.
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