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periglaciation
Periglaciation (adjective: "periglacial," also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and other structures.〔Slaymaker O., 2011. Criteria to distinguish between periglacial, proglacial and paraglacial environments. Quaestiones Geographicae 30(1): 85–94. DOI 10.2478/v10117-011-0008-y.〕 Tundra is a common ecological community in periglacial areas.
==Extent of periglaciation==
Some earth scientists have likened the extent of periglaciation to that of permafrost. Under this definition large areas in Siberia, Canada and Alaska and smaller areas in Fennoscandia, Tibet, Iceland, Greenland, Antarctica and the Andes are periglaciated. Not all scientists agree with this definition as many areas without permafrost show significant action of processes related to the freezing of water.
Periglaciation occurs principally in areas of permafrost. These areas experience intense freezing with an active layer of freeze/thaw near the surface which thaws 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.
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.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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