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Distributive Features and Controlling Factors of Permafrost and the Active Layer Thickness in the Bayan Har Mountains along the Qinghai-Kangding Highway on Northeastern Qinghai-Tibetan Plateau
详细信息   
摘要
Permafrost on the Qinghai-Tibet Plateau(QTP) is elevational,where the permafrost accounts for approximately 75% of the elevational permafrost in the Northrn hemisphere.Located in the transition zone from the Qinghai-Tibet Plateau higher than 4 500 m a.s.l.to the Loess Plateau at less than 2 000 m a.s.l.,the Bayan Har Mountains(BHM) have typical alpine permafrost.The intensive uplifts of the BHM have resulted in a great variety in climate,permafrost and landscapes on the north and south slopes.Based on field investigations and ground temperature measurements between 2008-2012,the distributive features and controlling/influencing factors of permafrost in the BHM are revealed in detail in this paper.Most permafrost in the BHM is warm(>-1℃),except that at some mountain tops such as Chalaping and the Bayan Har Mountain Pass.The ground temperature in the BHM is principally controlled by elevations.The lowest MAGT of-1.8℃ and the thickest permafrost of 74 m are found at Chalaping higher than 4 700 m a.s.l.The lapse rate of MAGT with rising elevation is 6℃/km on the north slopes and 4℃/km on the south slopes,respectively.The MAGTs are-0.2℃ in Borehole YNG-1 at the north-slope toes,and + 0.3℃ in Borehole QSH-1 at the south-slope toes.Permafrost thins rapidly downwards at both slope toes.The MAGTs are lower than-0.5℃ at elevations above 4 570 m a.s.l.on the south slopes and above 4 527 m a.s.l.on the north slopes.The MAGTs are lower than-1℃ at elevations above 4 670 m a.s.l.on the south slopes and above 4 615 m a.s.l.on the north slopes.The zone boundaries of-0.5℃ in mean annual ground temperatures largely coincide with the lower limits of sporadic(discontinuous) permafrost,and zone boundaries of-1℃ correspond to the lower limits of continuous permafrost.The active layer thickness,which usually affected by the lithology(soil types) and moisture conditions,is about 1 m at the Bayan Har Mountain Pass and Chalaping on the north slopes.It increases with declining elevation.However,on the south slopes,it is greatly influenced by some local factors,such as vegetative coverage and soil moisture contents.For example,the active layer is more than 4 m deep in Borehole CLQ-1 at 4 642 m a.s.l.,where the surface vegetation coverage is low,and soils and alpine meadows are broken by rodent and insect activities.

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