アジアの山岳永久凍土と周氷河環境

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Asian high mountains involve a large area and a wide variety of periglacial environments. This paper reviews distribution, landscapes and geomorphic processes of mountain permafrost and periglacial belts in the Asian mountains. The lower limit of mountain permafrost descends northwards at a rate of about 160 m per degree of latitude. At the same latitudes, arid continental mountains have a lower limit about 1, 000 m higher than humid mountains, which contrasts with the subpolar mountain permafrost in Scandinavia. The altitudinal extent of the mountain permafrost belt commonly exceeds 700 m in the arid continental mountains, while it is generally less than 700 m in the humid continental and Pacific mountains. A non-permafrost but deep seasonal frost area usually lies between the lower limit of permafrost and the timberline. In the arid continental mountains, despite a vast extent of the periglacial environments, the lack of moisture minimizes frost action that produces typical periglacial landforms. However, the large height of the permafrost belt, when combined with local moisture sources, can produce very long rock glaciers and block streams. In the humid Himalaya, steep rockwalls impede the development of stony patterned ground and lobes in the upper part of the periglacial belt, while they favour debris production that feeds debris-covered glaciers. Low summit levels and creeping pine shrubs combine to narrow the periglacial belt in the Pacific high mountains. However, high freeze-thaw frequency aided by high moisture availability in these mountains leads to shallow but rapid frost weathering, heave and creep, resulting in extensive small-scale stony periglacial features. A systematic understanding of the periglacial environments in the Asian mountains requires field monitoring of the rates and mechanisms of periglacial processes with standardized modern technology.
社団法人東京地学協会の論文
2002-08-25

アジアの山岳永久凍土と周氷河環境

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