Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tReaction of strata of seasonal permafrost to climatechanges remains ambiguous in different landscapeconditions. Seasonal thawing depth increased from 3.2 m in1974 up to 6.0 in 2001, but then that process stopped. In2002, the mentioned figure decreased to 4.6 m., and for thelast 5 years, it has remained stable, with small interannualoscillations within the limits of 4.6–4.9 mSince 1975 to 1998, in high mountains (at an altitude of3000 m), the changing of seasonal freezing depth on slopeson different expositions has not been supervised, but itsincrease was marked during the last 4 years: by 1.0 m atnorthern and 0.3 m at southern slopes.A steady trend of reduction of seasonal freezing depth hasbeen observed in mid-hill terrain up to the top forest border(from 1400–1500 to 2700 m) for the period 1974–1998.Data relating the value of mentioned characteristic on twoopposite, but equal by construction, slopes of the centralpart of the Zailiyskiy Alatau Range at absolute altitude of2570 m can be viewed here. So during mentioned period,on loamy-detritus soils of the northern slope, the seasonalfreezing depth decreased by 25 cm, and on idem ground ofthe southern one, it reduced by 21 cm.The tendency in changing of frost penetration depth onnorthern and southern slopes was not shown for the periodsince 1975 up to 1998 at absolute height of 3000 m. However,the increasing tendency of seasonal freezing depth on slopeswith different expositions has been marked for the last 3years. That is connected with the reduction of snowiness.Thus, it has increased for 1 m on northern and for 0.3 m onsouthern slopes.The revealed tendency of reduction of seasonal frostpenetration depth for mid-hill terrains continued till 2002.It has been stable since 2003 to present time, and has beenchanging just slightly during the years.Under all other equal conditions, interannual fluctuationsof freezing intensity and its depth depend on two factors:distinctions of soils temperatures before frost penetration,and terms ratio between the beginning of ground freezingand snow cover formation.General glacier recession in the Tien Shan conducts toan output of moraine sediments up to the surface. They aretransferring from subglacial status to a subaerial one. Thisprocess essentially changes an orientation of cryogenic andpost-cryogenic processes on fresh moraines. When smallglaciers recede, permafrost moraine layers are released. Insubaerial conditions, they are subjected to thawing on 1–2 mdepth from the surface during summer seasons; that is, thelayer of seasonal thawing appears.During large glacier receding, long-term frost penetrationof the transparent and blind talik systems occurs alongsidewith the mentioned process. Transformation of themoraines from subglacial to subaerial condition generates amodification of character of relief formation; new processesand effects appear. There is an especially distinguishingthermokarst among them and different modifications.The thawing of buried ice, accompanied with partialthawing of accommodating permafrost moraines, conductsto subsidence formation, which is filled usually with thewater from melted snow. In such a way, thermokarst lakesare forming. Some of the subglacial lakes originate fromwater-current ponding by the sediments of cryogeniclandslips. Thus, fresh moraines are the same kind of arenafor intensive formation of lakes of various genesis, sizes, andconfigurations. There were only 10 lakes, (with the capacityof each one over 10,000 cubic meters) in the middle of 1960on the northern slope of the Zailiyskiy Alatau. In 1980, thatnumber has increased to 41, and by 1990, to 60. The last10 years of aero-visual supervision of the glacial belt testifythat their quantity significantly increased.In addition to the lakes, soliflucton processes are developingon fresh moraines, and also active subglacial rock glaciersare forming. Loose, fragmental deposits of fresh morainesincrease the supply area of subglacial rock glaciers that hadbeen formed earlier, in that way stimulating the moving ofthe last ones. Icings are emerged and destroyed; structuralgrounds are formed; and frost weathering processes areactivated on fresh moraines.282