Glaciation

A glaciation or glacial period is at the same time a paleoenvironmental phase cold and a geological period of the Ground during which a big part of the continents east englacée.

Description

The glaciations initially were highlighted thanks to their morphological traces (Moraine S, erratic blocks) in the alpine valleys at the end of the 19th century.

Since the years 1950, the study of the relationship between different the Isotope S from the Oxygène in the sediments taken by coring at the bottom of the oceans confirmed and specified the existence of many more or less cyclic climatic fluctuations (cf marine isotopic Stades and isotopic Chronologie ).

Origin

The causes of the glaciations were the object of many debates, since the phenomenon was clearly identified at the 19th century. The modern theories often retain a relationship to the periodic oscillations of the Orbite of the Earth (cf the Paramètres of Milanković), associated with hypothetical and periodic variations in the solar radiation or the effects of a displacement of important continental masses towards the polar regions.

Consequences

During one glacial period, the phenomena according to occur following climatic cooling:
  • formation of ice cap : Inlandsis settle gradually on the zones Continent ales of high the Latitude S, with a maximum thickness of about 3 km, and flowing towards their margins.
  • lowers sea level (Glacio-eustasie) : the storage of ice on the continents causes the fall of the level of the oceans (about 120 m for the Glaciaire last) and causes the emergence of part of the continental shelves.
  • vertical tectonic movements (Glacio-isostasy) : under the weight of the ice, vertical movements Tectonique S affect the englacées zones and their margins (depression during the glaciation, rising or rebound at the time of the deglaciation).
  • modification of oceanic circulation : the oceanic Circulation world is completely transformed (with influences reciprocal, complex and ignored in detail, on the climate).

Traces of old glaciations

The Earth keeps the trace of old glaciations. The Glaciation Varanger, in particular, was particularly important. The ice at that time seems to have covered almost all planet, until the equator. We also know traces of glaciations during:
  • the Huronien (of -2  400 My with -2  100 My)
  • the Cryogénien (of -950 My to -570 My)
  • the Andéen-Saharan (of -450 My to -420 My)
  • the Karoo (of -360 My to -260 My)

Traces of the ice caps of the quaternary one

The glaciations of the Quaternaire left many visible traces in areas which, today, are not covered any more by the ices. The accumulation of Loess and silts of glacial and periglacial origin meet on vast surfaces 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), making fertile the areas concerned and posing problems of stability (very fast erosion).

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 of Shanxi (valley of the Huang He in China) is papered loess. 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

Recent glacial cycles

The end of the Cénozoïque is marked by the return of glaciations known as Quaternaire S, of approximately -2.7 million years to today. The quaternary glaciations correspond to the installation of a colder climate and to the cyclic return of cold periods (known as Glaciaire S) and moderate (Interglaciaire S). It there has approximately 10.000 years, began the Interglacial one which continues today and which corresponds to the Holocène. The higher Pléistocène corresponds to the last Interglaciaire cycle/Glaciaire (of approximately 120  000 with 10  000 years).

Various chronologies

The chronology of the glacial cycles answers the stratigraphic rules and the definition of Stratotype S, usable in the area where they were defined. The alpine chronology, if it has the merit to be the established first, is based on the morphological traces left by the moraines. Only thus are correctly recorded the particularly strong glaciations or most recent (push of the glacier destroying with each cycle the oldest traces). Thus, only four major cycle is recorded, with difficulty corrélables (except for the Glaciaire last) with the other continental recordings.


Period older of Pleistocene

Last glaciation

The Glacial last (approximately 120  000 with 10  000 years) is named Glaciation of Würm in the Alps, Weichsel in Northern Europe and Wisconsin in North America.

Principal the Ice cap situaient :

These areas preserve the geomorphological traces of them.

The case of the “small Ice Age”

See also: Small Ice Age

The northern hemisphere knew a Net cooling, started in second half of the 14th century - with a thermal minimum at the 17th century - which persisted until the beginning of the 19th century. Called “ small glaciation ” or “ Small Age Ice ”, it acts one period centered on the “Minimum of Maunder” (1645 - 1715 itself), which seems to correspond to a weak solar activity (its spots was not very visible besides). It was marked by a series of Hiver S particularly rigorous, accompanied by Disette S and Famine s.
The climate in Iceland and with the Greenland was completely pleasant during three the first hundred years which followed the Colonisation Viking. It then strongly cooled, prohibiting agriculture there and making there disappear the forests. However, it is about a cold climatic fluctuation to interior of the Interglaciaire Holocène, of as much better highlighted than he is recent, and cannot be regarded as one glacial period.

See too

Related articles

External bonds

  • small glaciation and its effects on the habitat eskimo

  • minimum of Maunder on the site of the Observatory of Nice
  • quaternary glaciations
  • Dryas
  • glaciations former to the quaternary era
  • " Climate through the history of Terre" an animation of the international polar Foundation explaining the glacial eras.

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