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Friday, February 25, 2011

PERIGLACIAL ENVIRONMENTS

The term ‘periglacial’ was first used by Polish geomorphologist Walery von Lozinzki in 1909 to describe frost
weathering conditions in the Carpathian Mountains of Central Europe. In 1910, the idea of a ‘periglacial zone’
was established at the Eleventh Geological Congress in Stockholm to describe climatic and geomorphic conditions in areas peripheral to Pleistocene ice sheets and glaciers.
This periglacial zone covered tundra regions, extending as far south as the latitudinal tree-line. Inmodern usage, periglacial refers to a wider range of cold but non-glacial conditions, regardless of their proximity to a glacier. It includes regions at high latitudes and below the altitudinal and latitudinal tree-lines: polar deserts and semi-deserts, the High Arctic and ice-free areas of Antarctica, tundra zones, boreal forest zones, and high alpine periglacial zones, which extend in mid-latitudes and even low latitudes.The largest alpine periglacial zone is the Qinghai–Xizang (Tibet) Plateau of China.

Periglacial environments characteristically experience intense frosts during winter months and snow-free ground during summer months. Four distinct climates produce such conditions – polar lowlands, subpolar low
lands, mid-latitude lowlands, and highlands (Washburn 1979, 7–8): 

1 Polar lowland climates have a mean temperature of the coldest month less than 3◦C.They are associated with zones occupied by ice caps, bare rock surfaces, and tundra vegetation. 

2 Subpolar lowland climates also have a mean temperature of the coldest month less than 3◦C, but the temperature of the warmest month exceeds 10◦C. In theNorthernHemisphere, the 10◦Cisothermfor the warmest month sits roughly at the latitudinal treeline, and subpolar lowland climates are associated with the northern boreal forests.

3 Mid-latitude lowland climates have a mean temperature of the coldest month less than 3◦C, but the mean temperature ismore than 10◦C for at least four months of the year.

4 Highland climates are cold owing to high elevation.They vary considerably over short distances owing to aspect. Daily temperature changes tend to be great.
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