スイスアルプスの周氷河環境と地形変動 : ―15年間の観測の総括と展望―

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Spacio-temporal variability of contemporary periglacial environments in the Swiss Alps is summarized on the basis of 15 years of field observations of rock weathering, permafrost creep, and soil movements, as well as other recent studies. Diurnal and annual freeze-thaw cycles loosen wet rock joints, which subsequently produce rockfalls. A large episodic rockfall can temporarily raise the rate of rockwall retreat. Rock debris derived from different parent rocks controls the types of rock glacier having different compositions, thermal characteristics, and dynamics. Some rock glaciers at the lower limit of permafrost are accelerating due to intensified mobility, but they may eventually become inactive because of permafrost thawing and the lack of debris supply. On slopes mantled with fine debris, small-scale stripes and lobes tend to develop on the upper part due to thin debris and good drainage, whereas larger scale lobes increase downslope as a result of thicker debris, poor drainage, and gentler slopes. The former mainly responds to shallow diurnal freeze-thaw cycles, whereas the latter reflects frost heave and gelifluction during deeper annual freezing-thawing. A prolonged supply of meltwater further triggers rapid mudflows superimposed on slow solifluction. Climate warming may decrease periglacial activity in seasonal frost areas, whereas in marginal permafrost areas it promotes permafrost warming that temporarily accelerates permafrost creep and/or permafrost thawing that possibly triggers large rockfalls and debris flows.

スイスアルプスの周氷河環境と地形変動 : ―15年間の観測の総括と展望―

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