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Periglacial
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A periglacial Lake is one formed where the natural drainage of the Topography is obstructed by an Ice Sheet , Ice Cap or Glacier .


PERIGLACIATION

Periglaciation is the corresponding noun. It means 'periglacial conditions', that is principally, an area of Permafrost - intense freezing, perhaps with freeze/thaw of the surface. That is to say, the surface layer melts briefly in summer. Periglaciation occurs near mountain glaciers. At lower levels it forms a zone of cold around continental glaciers in areas of high latitudes, covering perhaps 20% of the earth’s land surface.


Effects

Periglacial conditions in the Pleistocene created landscapes and Geological conditions moulded by Frost Action ; the repeated freezing and thawing of material over many years. Around a third of the earth's land surface can be considered as having been subject to periglacial conditions at some time.

Periglaciation results in a variety of ground conditions but especially those involving irregular, mixed deposits created by Ice Wedge s, Solifluction , Gelifluction , Frost Creep and Rockfall s.

The resulting Ecological Community is known as Tundra .


Factors affecting location

  • Latitude – temperatures tend to be higher towards the equator. Periglacial environments tend to be found in higher Latitude s. Since there is more land at these latitudes in the north, most of this effect is seen in the northern hemisphere. However, in lower latitudes, the direct effect of the sun's radiation is greater so the freeze-thaw effect is seen but permafrost is much less widespread.

  • Altitude – Air temperature drops by approximately 1 °C for every 100 m rise above sea level. This means that on mountain ranges, modern periglacial conditions are found nearer the Equator than they are lower down.

  • Ocean Currents – Cold surface currents from polar regions, reduce mean average temperatures in places where they exert their effect so that ice caps and periglacial conditions will show nearer to the Equator as in Labrador for example. Conversely, warm surface currents from tropical seas increases mean temperatures. The cold conditions are then found only in more northerly places. This is apparent in western North America which is affected by the North Pacific current. In the same way but more markedly, the Gulf Stream affects Western Europe.

  • Continentality – Away from the moderating influence of the ocean, seasonal temperature variation is more extreme and freeze-thaw goes deeper. In the centres of Canada and Siberia, the permafrost typical of periglaciation goes deeper and extends further towards the Equator. Similarly, solifluction associated with freeze-thaw extends into somewhat lower latitudes than on western coasts.