Ninth International Conference on Permafrost ... - IARC Research

Cryogenic Formations of the Caucasus and the Significance of Their Impact on theNatural Phenomena of the RegionIgor V. BondyrevVakhushti Bagrationi Institute of Geography, Ministry of Education and Sciences of Georgia, TbilisiCryogenic or periglacial phenomena are widespreadwithin the high mountain Caucasian region. The modernarea of spreading cryogenic processes on the south slopeof the Central Caucasus (Georgia) forms 3300 km 2 andwithin the Republic of North Osetia-Alanya, 5400 km 2 , butin Kabardino-Balkaria, 4600 km 2 (1, 2). These processesare widely spread as well on the territory of the PontidesMountains and the Iranian upland, covering 14,200 km 2 . Theset of factors defining the genesis and morphology of theforms of periglacial relief changes depending on the heightof the area. Three hypsometric levels are singled out:1. The upper belt occupies the whole area of the nivalzone and is limited from underneath by snow line lyingat the height of 3000–3200 m a.s.l. Frost weathering andgravitational talus processes, which play the leading role information of present-day relief forms, take place here.2. The middle belt is situated below snow line andpractically coincides with the alpine and sub-alpine landscapezones (1750–2300 m). Here prevail slope (solifluction,rock-streams, stone and snow avalanches, talus trains, mudflows, etc.) and plane (polygonal-structural groundboulderpavement, thufurs).3. Relict cryogenic formations (fluvioglacial deposits,cryoturbation, etc.) are spread in the lower belt down to1400–1600 m a.s.l.The given formations are characterized by the followingregularities of their spatial distribution:1. Formations related to rocky ground occupy the beltof tops, ridges of watersheds, and steep slopes of highmountains.2. Formations related to rudaceous ground and pebbles aremainly placed on gentle slopes and at the foot of mountainridges and massifs within 2700–1900 m a.s.l.3. Formations related to fine detrital and rock debris arewell observed on the high mountain plateaus in the zone ofNeocene-quaternary volcanism.4. Formations related to loamy and turf/soddy surfacescover quite a large area, mostly alpine and sub-alpinemeadows and alluvial soils of high mountain zones (seethe scheme of classification of periglacial formations of theCaucasus).Widespread morainic mantles and sheets and gravitationaltalus processes define the existence of numerous “fossil”glaciers (dead ice), on their part testifying to the regressionof the glaciation process. The value of seasonal freezing ofground soil is an important feature for determining mainrelief-forming processes in high mountains. Information onthese parameters helps with decisions about engineeringgeological,building, agro-biological, and other problems.We offered theoretical determination for the values ofseasonal freezing depth for different points in periglacialareas in Georgia, having minimum information on thoseareas. For this purpose, the formula of Budnikov was usedwith some amendments of ours on the high-mountainousrelief character, the height of snow cover, and influence ofwind (2, 3, 6, 8). Comparison of meteorological yearbookrecords of the Hydrometeorological Institute of Georgiawith ours on the depth of seasonal freezing showed littlediscrepancy (not more than 3–6 cm). The gained recordsare well founded only for subhorizontal surfaces deprivedof mantle and vegetative cover, with similar mechanicalcomposition and equal humidity value. Calculations werecarried out per formula:h=5kTable 1. Experimental evaluation of the rate of frosty weathering of mountain rocks (5).Number ofversionMeanamplitude oftemperaturefluctuationduring theexperimentArea offrozensurface(sm 2 )Initialweightofsample(г)WeightoffrozensampleNumber of“freezingthawing”cycleTn −Weight ofdisintegratedparticlesn1( + )50 LtH ⋅VVelocity ofdisintegration offrozen surface aday/gr/m 2 .a day/(1)(1)Velocity ofdisintegration/mm/year/1 – overmoistured28.2°С 22.56 31.70 31.74 80 0.73 4.0514 0.2882 – dry 31.34 41.10 41.47 80 0.07 0.2819 0.0403 – overmoistured34.23 41.94 42.03 70 0.53 2.2079 0.6724 – dry 37.84 25.19 25.45 70 0.10 0.3790 0.04729