Regional Problems of Earth's Cryology The

EARTH’S CRYOSPHERE SCIENTIFIC JOURNAL

Kriosfera Zemli, 2018, vol. XXII, No. 3, pp. 3–15 http://www.izdatgeo.ru

REGIONAL PROBLEMS OF EARTH’S CRYOLOGY

DOI: 10.21782/EC2541-9994-2018-3(3-15) THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU S.N. Buldovich, E.N. Ospennikov, V.Z. Khilimonyuk Lomonosov Moscow State University, Faculty of Geology, 1, Leninskie Gory, Moscow, 119991, Russia; [email protected] The paper discusses results of the study of geocryological (permafrost) conditions in the eastern part of the Olekma-Chara Plateau at the watershed divide of the Tokko River and its tributary, the Choruoda River, carried out within the ﬁ eld study of the sites of mineral showings (deposits), whose permafrost conditions are extremely contrasting. The combined impact of hydrogeological factors acting in the middle altitude environment is found to be largely responsible for the unique permafrost conditions in the study area. Olekma-Chara Plateau, geocryological conditions, hydrological conditions, permafrost, annual average soil temperatures, geocryological processes

INTRODUCTION The study area, located in the southwest of the Moscow State University, which conducted a compre- Republic of Sakha (Yakutia) and subsumed into the hensive permafrost-hydrogeological and permafrost- eastern part of the Olekma-Chara Plateau, is under- engineering geological survey within the Aldan-Timp- lain by permafrost which had been largely underex- ton interfl uve area. Later, in 1973–1985, this expedi- plored until the middle of the twentieth century, with tion conducted medium-scale surveys (1:50 000 and the information about it ranging from sketchy (i.e. 1:200 000) in the areas of coal deposits within the derived from results of comprehensive geological- Chulman Plateau, southern Yakutia [Kudryavtsev, geophysical expeditions) to unavailable. The system- 1975]. Results of the exogenous geological processes atic geocryological study began in the 1930s and and phenomena surveys (1:200 000 and 1:500 000 1940s and gained traction in the decades to follow. In scales) in the territory of the Aldan-Timpton inter- southern areas of permafrost distribution the studies fl uve in the late 70s–early 80s of the last century were were conducted by the Aldan permafrost research analyzed and discussed in [Ospennikov et al., 1980]. station (PRS) staff of the Permafrost Institute of the It is noteworthy that the Olekma-Chara Plateau USSR Academy of Sciences (V.M. Ponomarev, area has been hitherto least studied in southern Yaku- S.E. Su khodolskii, S.M. Fotiev, N.A. Vel’mina, tia, specifi cally, its part adjacent to the Tokko river G.N. Fi losofov, V.R. Alekseev and others). The 1951– valley [Ershov, 1989]. With regard to permafrost as- 1954 regional survey works as part of permafrost-hy- pects, the studies, in themselves, were reduced to the drogeological studies of the Aldan-Timpton inter- information about ground temperature regime in per- fl uve area were conducted by the Yakutia Complex mafrost zones obtained by M.N. Zheleznyak and Expedition (A.I. Efimov, P.I. Melnikov, I.D. Belo- others [Dorofeev et al., 1981; Zheleznyak, 1998, 2005; krylov and others) of the USSR Academy of Sciences Semenov and Zheleznyak, 2013]. Proceeding from Council for the study of Russian natural productive these, the average annual temperature of rocks in- forces. In the 1960s, these endeavors were continued creases in the direction from the watershed divides to by the Udokan Expedition of the Permafrost Insti- the river valley bottoms, where the rocks for the most tute of the USSR Academy of Sciences, during which part remain in the unfrozen state. a team of researchers headed by I.A. Nekrasov inves- During the 2009 Expedition, the researchers tigated geocryological conditions of the Udokan from the Department of Geocryology, Moscow State Ridge along with the Chara, Verkhne-Kalar and University conducted geocryological surveys along Nizhny Ingamatkit intermountain basins. with the 1:25 000 mapping of one of the sites located More complete data and materials on the forma- within the Verkhe-Tokkin area. The results allowed tion of permafrost and its regional variability in south- the fi rst ever comprehensive permafrost characteris- ern Yakutia were obtained during the works of the tics of the study area and provided new insights into 1961–1964 Expedition of the Faculty of Geology of its entire geocryological situation.

3 S.N. BULDOVICH ET AL.

BRIEF CHARACTERIZATION vers, the tributaries to the Olekma river. All streams OF THE GEOEVIRONMENTAL SETTING are fi lled with water only during the spring snowmelt The study area is located in the watershed area and prolonged spells of summer rains. Otherwise, of the Tokko River and its tributary, the Charuoda most of the time the stream-beds remain dry. Their River (Fig. 1). thalweg marks range between 1100 and 1180 m. The area topography (relief) is medium-moun- The climate of the area, which is defi ned as sharp- tain, characterized by 1200–1400 m absolute eleva- ly continental, is largely controlled by the mountain- tions on the watershed surfaces and deeply embedded ous terrain, as well as by the band of air masses trans- (to 200–300 m) bottoms of the river valleys, with the fer shift from western to eastern direction, i.e. to the slope steepness reaching 25–30°. The river network East Pacifi c [Karausheva, 1977]. This area is charac- of the area, composed by small watercourses, is sub- terized by long cold winters and short summers with sumed into the basins of the Tokko and Charuodo ri- the average values described as: the mean annual tem-

Fig. 1. Location map of the investigated area of the eastern part of the Olekma-Chara Plateau, on the watershed divide of the Tokko Rv. and its tributary Chorouda (South- ern Yakutia).

4 THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU perature is –7.8 °C; the annual amplitude of the mean tions. As is the case with watersheds and slopes oc- monthly temperature fl uctuations reaches 57 °C; the cupying most of the study area and underlain by per- annual precipitation ranges between 330 and 680 mm, mafrost to significant depths, the feeding of generally increasing with height. groundwaters by infi ltration waters is precluded. At Most of the precipitation falls during the sum- this, subsurface waters are recharged dominantly mer season (50–70 %), while only 7–15 % accounts from surface runoff during the warm season. In the for winter. The snow cover exists from September bottoms of river valleys, where the groundwater feed- through May, with its depth reaching 0.7–0.9 m or ing sources are amassed, groundwaters are widely de- greater, at the foot of slopes, particularly in their veloped in alluvial and fl uvioglacial sediments. Judg- wooded areas. The snow cover density varies from ing from the nature of circulation, these are porous 0.12 to 0.18 g/cm3, averaging 0.13 g/cm3. Due to in- phreatic waters, which discharge through the fault tensive snowdrift transport at the watersheds, the zones into the underlying aquifer complex of lower snow cover depth (average density: 0.145 g/cm3) Proterozoic sediments. According to drilling data does not exceed 0.2–0.4 m there. (depth range: up to 150 m), the rocks are either in the Soils and vegetation developed in the area belong permafrost state to a depth of hundreds of meters, or to the mountain-tundra, mountain-shrub-tundra, drained in most of the investigated area. As such, the mountain-sparse woodland, and mountain-valley situation is typical of the interfl uve and slope areas types. The area is differentiated by sparse marshy and of the valley bottoms. Locally, in eastern part of landscapes, observed in some segments of the Levy the study area, the position of water table of the con- Usu Creek valley bottom. Judging from the regional sidered aquifer is found to be close to the surface, vegetation cover pattern, the territory is labeled as though. the light coniferous taiga province of the middle taiga The deposits’ deep drainage within the study subzone. The presence of permafrost and seasonally area is, undoubtedly, exerted by the proximity of a frozen rocks slows down the biochemical reactions major regional drain, the Tokko river (∼7–8 km to fl ow in the soil horizon during a short vegetative sea- the west from the investigated site) with absolute el- son, along with the formation of soil profi le, causing evations of the valley tahlweg of about 650 m within thereby the dominance of thin, primitive and skeletal the considered intercept along the course of the river. soils across the area. With the spot elevations ranging between 1000 and Geological structure. In the geological framework 1400 m, the investigated site (as part of Tabornoe de- of the area, the most ancient structural stage is com- posit) represents a topographically elevated area and posed by Archean rocks: crystalline shales, gneisses, therefore the sedimentary rocks here are expected to amphibolites, quartzites. The upper structural stage have drained to signifi cant depths. The thickness of is represented by folded and metamorphosed lower the zone of aeration, even beneath the bottoms of the Proterozoic sediments, dominated by the metamor- valleys can reach 200–300 m, and signifi cantly deeper phosed terrigenous deposits, mainly sandstones and in the watershed areas (400–500 m). At this, the frac- siltstones. The intrusive Archean, early Proterozoic, tured solid rock mass is ubiquitously and completely late Proterozoic and late Jurassic rocks are made up saturated with water below the Tokko river stream- by amphibolites, gabbroids, pyroxenes, diabases and bed occurrence level. granitoids. The tectonic setting of the territory is described as the system of thrust-faults, partially com- GEOCRYOLOGICAL CONDITIONS pensated by dislocations, extending roughly W–E and in N–E direction. The fi eld study of permafrost aspects of the area The unconsolidated (loose) deposits structure is conducted by the authors within the research into its dominated by eluvial, deluvial, colluvial, delluvial- engineering-geocryological conditions, revealed that deserption and to a lesser extent by diluvial sediment the geocryological structure of the study area is de- types, cumulatively composing a continuous cover termined, in addition to regional features of the radia- atop the watershed surface and slopes of river valleys. tion balance, by the snow and vegetation covers, by The glacial and aqueoglacial deposits co-existing absolute elevation and dissection of the terrain, and with the river-channel and fl oodplain sediments in considering the composition of upper horizons of the valley bottoms are represented by a strata of soils, and the action of surface and ground waters. poorly sorted indistinctly layered boulder-pebble de- The authors performed both the numerical and math- posits, which compose the upper part of the section of ematical modeling of the natural setting of the area a through (antecedent) valley of Levy Usu and within the WARM program [Khrustalev et al., 1994], Tyomny creeks. as a series of one-dimensional heat problems aiming The hydrogeological conditions are characterized to measure the impact from natural insulation (snow by the distribution of crevice waters (within crevices and vegetative covers) on the thermal conditions of of intrusive and metamorphic rocks) and fracture- sedimentary rocks. The variations of average annual vein waters confi ned to the zones of tectonic disloca- temperature of rocks throughout the area are largely

5 S.N. BULDOVICH ET AL.

within the active layer (AL) is directed from the slopes into the drained rocks of the valley taliks, pro- viding additional convective heat input and sediment warming. As such, the absorption of both the surface and near-surface runoff waters by the unfrozen loose sediments in river valleys during summer represents a characteristic feature of the study area, which is associated with a high water-transmissive capacity of alluvial and fl uvioglacial sediments serving as the valley infi ll material, given their relatively big thickness and high longitudinal slopes. The zone of high-frac- tured underlying rocks also becomes part of the fi ltration section. The implications are that the river chan- nels in the Tabornoe deposit area are fi lled with water only during periods of snowmelt and heavy rains, when the water coming from the slopes exceeds the water-transmission capacity of the underfl ow depos- Fig. 2. A relationship between the average rock its. It is therefore likely that the additional input of temperatures T and snow cover depth hi (maximum value for winter) inferred from the mathematical heat convection is remarkably involved in the forma- modeling. tion of the per se unfrozen, water-permeable rocks in the valley bottoms within the study area. 1 – hs = 0; 2 – hs = 0.1 m; 3 – hs = 0.2 m. The interplay of all the considered environmental controls create the complexity of the geocryological situation of the study area. governed by the combined infl uence of snow and ve- The average annual sediment temperature at getation. the base of the zero annual amplitude in the South- Figure 2 shows the eff ect of the interplay of these Ugui gold-bearing area varies from positive to essen- factors on the average annual temperature of rocks, tially lower negative values (–4…–6 °С and lower) indicating along with the simulation results, that the [Ershov, 1989; Zheleznyak, 2005]. Despite the pres- contribution from the ground covers, specifically, ence of local deviations, the general trend refl ects a snow cover is the largest to the temperature fi eld of decrease in rocks temperature, propagating from the rocks. Virtually, the entire (fairly wide) range of ave- valley bottoms to the watershed zones. rage annual temperatures of rocks (–5.5...2.0 °C), es- The average annual rock temperature distribu- tablished by the thermometric measurements in wells tion pattern in the specifi ed natural conditions of the within the Tabornoe deposit area, is overlapped by studied area has hitherto been largely understudied. diff erent combinations of the combined impact of the Some major features of the formation of geocryologi- snow and vegetation covers. cal conditions were established during the permafrost The formation of average annual sediment tem- survey (scale: 1:25 000) conducted by the authors. perature of rocks (°С) is contributed by different The drilling data and results of temperature surveys natural controls*, such as: in wells indicate extremely contrasting distribution – altitude position ±(0.5–1.5); of average temperatures of rocks in the area: from – slope exposition and steepness ±(0.5–2.0); –5.0…–5.5 °С on elevated watershed surfaces (1300– – snow cover +(2.0–10.0); 1400 m) to 1.0...2.0 °C in the valleys of rivers and – vegetation cover –(0.5–3.0); creeks (1100–1200 m). – bogging –(0.5–3.5); A diff erence in rock temperatures within one val- – moisture infiltration and condensation ley side can reach 6–7 °C at a relatively small diff er- +(0.2–1.5). ence in elevation (~200–300 m). A wide distribution The impact from bogginess, despite the potenti- of unfrozen rocks with temperatures from 0...0.3 to ally large amount of heat exposure, in fact is inconspi- 1.0...1.5 °C has been established in the bottoms of cuous due to a very limited distribution of wetlands. river valleys. These are confi ned to the rudaceous al- Assumingly signifi cant thermal eff ect comes from luvial and glacial deposits, whose areas of distribution the fi ltration fl ow in the river valleys during the sum- can exceed 500–800 m in width. Such a wide extent mer low-water periods, with completely absent sur- of unfrozen deposits in the valley bottoms with eleva- face runoff in streams in the study area (i.e. stream- tions exceeding 1050 m could hardly be envisaged beds are dry), when cumulative groundwater runoff before the commencement of the research.

* The inﬂ uences from the snow and vegetation covers were estimated by the authors on the basis of numerical-mathematical modeling, while other controls were estimated using method developed by V.A. Kudryavtsev [Kudryavtsev et al., 2016].

6 THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU

At this, the presence of permafrost in the areas of the warming eff ect of the snow cover directly depends the first floodplain terrace with developed moss on the intensity of heat exchange between rocks and ground cover was confi dently identifi ed in the bot- the environment and tends to be less with the de- toms of the valleys. Unfrozen deposits can coexist creasing contribution from the latter. A moss pillow with and sporadic (island) permafrost in the valley with a thickness of 0.2 m brings the critical thickness bottoms, although relatively small in size in this case, of the snow cover down to 0.6 m. with vertical thickness in the fi rst tens of meters and That big and even greater snow cover depth is their average annual temperatures approximating to reported from the river valley bottoms within the ex- 0 °C. The thawed zones of the valleys, judging by tent of fi r-larch woods, where relatively thick moss or their large extent in plan view represent through ta- lichen ground covers are common. The performed liks in relation to permafrost thickness. mathematical modeling (Fig. 2) thus allows to expla- A comparative analysis with the morphologically in, in principle, how the interplay of snow and vegeta- identical Aldan-Chulman Upland area has shown tion covers benefi ts both the wide distribution of tha- that the absolute elevations inherent in the relief of wed rocks in the valleys, and the presence of sporadic the study area (1000–1400 m) fall into the high-alti- permafrost in areas with a developed moss cover. tude transition zone close to the “ceiling” of the hi gh- It is nevertheless possible that the formation of altitude air temperature inversion distribution. In taliks in the bottoms of the valleys composed by this zone, the inversion nature of temperatures distri- coarse alluvial and glacial deposits is largely contrib- bution (refl ecting their rise with height) gives way to uted by the warming eff ect of convective heat transfer a normal decrease in temperatures as the altitude in- caused by groundwater fi ltration fl ows. The hydro- creases, generally showing no pronounced trend in air logical regime of watercourses in this area is unique, temperature variations with height (thermopause inasmuch as the surface runoff transpires here only phenomenon). during the short periods of snowmelt and heavy rains, Meanwhile, the orographic inversion at the while the rest of the summer is completely devoid of 1300–1600 m altitude interval with a gradient of the runoff process. The coarse sediments of the valley –0.4…–0.6 °С/100 m is evidenced in the natural set- bottoms thus absorb the entire amount of precipita- tings of the Olekma-Chara Plateau [Zheleznyak, tion from the catchment area of the valley and redi- 2005]. However, because of a specifi c relief dissection rect it to the subsurface drainage system (underfl ow in the Tabornoe deposit area (⁓200–300 m), the runoff ). At this, the high summer temperatures and a high-altitude inversion diff erentiation of the mean measurable mean summer rainfall suggest that the an nual air temperatures (MAAT) does not account convective heat transfer processes have high thermal for more than 1.0–1.5 °C. energy level. That large diff erence in rock temperatures with- A continuous permafrost is distributed through- in the study area have been therefore caused by the out the entire Tabornoe deposit area, with the excep- contributions from the ground covers, primarily, the tion of the bottoms of streamfl ow valleys, whereas snow accumulation pattern. The snow-survey as part neither watershed divide – nor hillslope-confined of the research, has revealed a notable increase in the through taliks have been discovered during the re- snow cover depth (from 0.1–0.3 to 0.6–0.8 m or search. Given that none of the boreholes have com- more) with a decrease in spot elevations in the di- pletely penetrated permafrost strata, there is no direction from the watershed divides to the valleys, rect evidence for the permafrost thickness within this prompting thereby a signifi cant warming eff ect of the area, which therefore has to be inferred from the aver- snow and affi liated rise in rocks temperatures. The big age annual temperatures of rocks and from the tem- picture is superimposed by the vegetation types perature fi eld measurements in the upper part of per- (shrubs, woody vegetation) largely aff ecting the pat- mafrost. terns of snow accumulation, as well as by the specifi cs Using the data on areal distribution of rock tem- of the radiation and heat balance on the slopes of dif- peratures resulting from the permafrost survey and ferent exposure and steepness. taking into account actual spot elevations, the Note that the snow cover depth of about 0.4– WARM program [Khrustalev et al., 1994] was applied 0.5 m on the exposed surface of sedimentary rocks is to perform a two-dimensional simulation of the tem- considered critical, seeing as any further increase in perature fi eld of rocks measured along a characteristic its depth trigger the rocks temperature transition profi le laid through the valley of one of major creeks into a positive domain, which rules out the existence in the study area and comprising five geothermal of permafrost here. In the presence of ground vegeta- wells, with one of them drilled to a depth of 140 m tion cover, acting as an additional layer of insulation, enabling thermometric studies. The diff erence in ele- the warming effect of snow, all other things being vations within a stretch from the divide to the valley equal, becomes markedly reduced. This is associated bottom is 200 m (abs. elev. 1320–1120 m); the width with a signifi cant decrease in the depth of zero annual (horizontal equivalent) of slope is 500 m, while the amplitude at sites overgrown by vegetation, whereas valley bottom is 80 m in width. According to the

7 S.N. BULDOVICH ET AL. ther mometric measurements in wells, the average an- taliks of purely conductive origin (i.e. without in- nual temperature of rocks almost linearly increases volvement of convective heat generated by ground- down the slope: from –5.5 to 0 °C at its foot and up to water) have proven to be able to exist even in the val- 1.5 °C in the valley bottom. leys of the smallest watercourses in the area. Given Permafrost thickness. The data from [Zhelez- that relatively high average annual temperatures of nyak, 2005] indicate that ancient Proterozoic sand- rocks can develop under the infl uence of only one fac- stones composing the main part of the geological sec- tor – increased snow accumulation, through taliks of tion have enhanced thermal conductivity up to 3.7– purely thermal origin (snowgenic) are expected to 4.8 W/(m⋅K). The density of geothermal heat fl ux form in the valleys of small watercourses. from the subsoil is 30–40 mW/m2 within the study Interestingly, the simulation also revealed a spe- area [Zheleznyak, 2005, Fig. 4.4]. We therefore used cific pattern of subhorizontal redistribution of the both the values for thermal conductivity of rocks deep heat fl ux in the upper parts of the section, caused (4.2 W/(m⋅K)) and deep heat fl ux (35 mW/m2) in by the relief dissection and spatial diff erentiation of the modeling. rock temperatures. The latter is considered a major The result allowed to obtain the following spa- natural control, which determines the complex na- tial configuration of the permafrost strata (PS) ture of the geothermal heat fl ux redistribution. Due (Fig. 3): permafrost thickness below the watershed to the sharply reduced temperatures of rocks at the divide measures 450 m; the PS decreases towards the watersheds against the backdrop of those in the val- valley, where it completely pinches out at the foot of leys, the heat flux concentration gravitated to the the slope, which proves the lower limit of permafrost topmost parts of the watershed divides rather than to to be almost 200–250 m lower than the valley thaweg. the bottoms of the valleys, exactly the way it should The obtained spatial confi guration of the perma- occur when aff ected by the terrain dissection alone. frost distribution is in good agreement with the avai- Within the implemented modeling (Fig. 3), which lable thermometric data. The deepest well emplaced takes into account the linear change in the average along the profi le is located in the middle of the slope annual temperature on the slope surface, the density (about 1220 m in height) and has a depth of 140 m. of heat fl ux released by the rocks through the water- At this, rocks temperature at the depth of zero annual shed surface is 67 mW/m2; in the center of the slope amplitude (17 m) is –2.8 °C, which tends to increase it is close to a deep-earth value of 35 mW/m2, while with depth and equals –1.7 °C at the bottomhole. at the valley bottom the heat fl ux passing through the This temperature coincides with the rocks tempera- surface is generally directed downward, into the rock ture at the same point of rock massif derived from mass, and equals –125 mW/m2. In the valleys, this mathematical modeling of its temperature field additional input of heat fl ux into the rocks is redis- (Fig. 3). tributed towards the cooled watershed divides, con- The calculations for diff erent model scenarios re- tributing to the deep-earth component of geothermal vealed one important feature of the PS confi guration: heat. Within depth interval of about 600–800 m from within the accepted boundary conditions, specifi cally, the watershed surface, the impact of surface inhomo- with the linearly increasing average annual tempera- geneities of boundary conditions tends to wane, and ture of rocks within the hillslopes to zero values at the density of the ascending heat fl ux becomes lev- the foot of hills, the valley talik has remained to be a eled off across the area. through talik even at a small width of the valley bot- The obtained results also show that the concept tom (some fi rst tens of meters). Therefore, through of greater stability of frozen rocks in depression zones of the relief in comparison with watershed divides in the territory of southern Yakutia, advocated by D.O. Sergeev and others [2005] is just unworkable. It is quite the contrary: given a persistent relationship between the lowest average annual temperatures and high ice content of the upper horizons of the section of rocks, the watersheds, in themselves, appear the most stable in terms of evolution. The seasonal thaw depth of rocks is basically determined by the following factors: relatively high summer temperatures, ground vegetation, moisture (ice) content and thermophysical properties of sediments. Proceeding from the results obtained, the specifi city of seasonal thaw of rocks within the study area is described below. Fig. 3. The confi guration of permafrost strata in- On the divide surfaces of the upper and middle ferred from the mathematical modeling. parts of the slopes affected by seasonal thawing,

8 THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU which, contrary to expectations, was relatively shal- consistent with the data on the cryogenic structure of low, averaging 1–2 m. Partial thawing of thin cover of the deposits in the areas adjacent to southern Yaku- drained loose eluvial (sedentary) deposits occurring tia. on mountain rocks, may be accounted for the horizon As was shown above, loose permafrost represent- of altiplain ice identifi ed in the lower part of the ac- ed by both syngenetically and epigenetically frozen tive layer (AL). The presence of a signifi cant amount sediments has a relatively limited spatial extent. Syn- of ice inclusions in the fi rst meters of the section was cryogenic permafrost composed by alluvial deposits reported from all wells while drilling. The established occupy small areas and is confi ned to the valleys of by [Zabolotnik and Zabolotnik, 2014] pattern of the large creeks (Rudny, Tyomny) and minor rivers thaw depth decrease in rocks with a height gradient (Maly Usu). These deposits include fi ne-dispersed of 0.85–1.28 m per 1000 m for southern Yakutia was sediments of the fl oodplain and old river bed facies: not observed in the considered territory, which may clay- and sand-loams, often peaty and gleyed, with be explained by the specifi c changes in the composi- interlayers and lenses of peat, as well as peat mantles tion of rocks. Thus, given an extensive development up to 1.0–1.5 m thick. Their cryogenic texture is pre- of corrom covers (stone rivers) on the slopes and dominantly layered and layered-reticulate. Total vol- stone debris at the divides with similar structure of umetric ice content of these deposits varies between the AL rocks (blocky-rubbly beds with almost totally 10–15 % and 40–50 % in mineral soils and up to 90– missing fi ller material in-between), the depth of sea- 95 % in peats. sonal thaw there also slightly changes with its thick- Most of the alluvial and fl uvioglacial deposits, ness averaging in the range of 0.8–1.5 m, regardless of composed by boulder-pebble, pebble, pebble-gravel, the absolute elevations of the terrain. Within the rest sandy, and sandy loam varieties were subjected to epi- of the territory, specifi cally in the river valley bot- genetic freezing, while presently, most of them remain toms (on the fl oodplain and fi rst above-the-fl oodplain in the unfrozen state. In southeastern part of the terraces) where moss cover is relatively thick, the study area, though, north of the heads of Levy Gross thaw depths of rocks range in the 0.3–0.7 m interval. and Pravy Gross creeks, they are frozen and their tex- Noteworthy, however, is that at the time of their pos- tural characteristics are largely dominated by ice-ce- sible drilling (the beginning of July), the reported ac- ment and crusts, as well as by basal cryotectures (at tive layer thickness (ALT) is still far from its maxi- relative humidity close to 100 % moisture-holding mum. Besides, the exposed rocks in some cases may capacity). be the remnants of a layer of seasonally freezing rocks The most complex cryogenic structure is associ- formed during the winter. ated with the epigenetically frozen lacustrine-boggy Seasonal refreezing of rocks appears inherent sediments (mainly biogenic), forming covers in the only in river valleys, where unfrozen rocks are fairly river valley bottoms. The frozen peat is dominated by extensively developed within the valley bottoms. The porphyry, lenticular-layered, lenticular- reticulate, greatest depths of seasonal freeze of the AL rocks banded, plicate, ataxite, cortical and massive cryo- reach 3.5 m; however, judging from the monitoring genic textures. Given diff erent cryogenic textures are results, the thawing of seasonally frozen layer pro- involved, ice content changes in relatively narrow ceeds quite intensively and terminates mainly in the range in peat layers, and usually does not exceed 10– fi rst half of summer. As such, the measurable ALT is 20 % (from 72 to 93 %), whereas it is 2–2.5 times primarily caused by low pre-winter moistening of higher in mineral dispersed soils. rocks, suggesting a rapid drainage of alluvial and fl u- Epigenetically frozen diluvial and diluvial-soli- vioglacial deposits residing in the river valleys to a fl uction deposits in the perennially frozen state are considerable depth during the fall. characterized by massive, rarely lenticular-layered, Cryogenic structure of permafrost underlying cryogenic textures. Volumetric ice content appears the study area is the least studied characteristic. Nei- higher in rubbly horizons from this group (40–50 % ther deep drilling, nor examination of the existing of the total rock volume), while it is lower (25–40 %) outcrops have added to clarity therein. The rocks in syngenetically frozen solifl uction-aff ected loamy outcropping in the left side of Rudny Creek, in the sediments, which usually have lenticular-layered gullies along the road to the east of the quarry, as well cryostructure. as in the walls of quarries of building materials, did Massive, crust-forming and rarely thin lenticu- not expose the ice-rich PS either. Neither inclusions lar-layered cryogenic textures are typical of eluvial of ice were found in drill cores recovered while drill- and deluvial deposits. In areas abounding with rock ing wells (thermometric and hydrological). However, caldrons and polygons which are usually character- ice-rich rocks were discovered along the geological ized by complete water saturation of clastic rocks, traverse during the test pit excavations in the fl ood- basal cryogenic texture is dominant. plain sediments and old river bed alluvium, and in Diluvium-deserption deposits of corroms noted biogenic sediments in the southeast of the territory. for altiplain ice (the underlying ice band acting as The obtained characteristics of ice inclusions are fully transporting medium for rock debris), are partially

9 S.N. BULDOVICH ET AL. distended and characteristically exhibit high ice con- (Fig. 4, c). In the study area, stone fi elds on the slopes tent (10–30 % of total rock volume), as is the case tend to form a mosaic system, where they alternate with altiplain ice, which is also typical of eluvial-de- with wooded zones, in chessboard order. luvial deposits at high-altitude (1200–1350 m) wa- Stone streams as linear forms of the stone debris tershed divides and is encountered at a depth of on the slopes with the length to width ratio of more 1.5–2.0 m from the surface, where it is overlain by than 1:2, are commonly confi ned to the bottoms of crushed-block eluvial-deluvial beds. small ravine and shallow gullies on the slopes. Exogenous geological processes and phenom- The microrelief of rock glaciers is often compli- ena observed in the study area are divided into three cated by gullies, cirque depressions, terrace-like groups: cryogenic geological processes (frost weath- bluff s and benches. Their surface is composed of small ering, frost cracking, frost heaving of the rocks, ic- and medium-sized platy blocks of sandstones. Char- ing), gravitational processes (rock sloughing and acteristically, a significant part of the blocks have cryodeserption, formation of avalanches, mud fl ows, their main axis vertically oriented, while the rest bear and corroms) and thermohydrogenic process (ther- indications of “ridging”, when the blocks located up moerosion) and the affi liated phenomena. the hill, creep over those underlying. Unlike the formation of corroms, gravitational The structure of the corrom section is diff erenti- processes having a relatively limited area of distribu- ated by clastic material decreasing in size from top to tion, develop on steep (>25–30°) slopes, and are com- bottom, while the content of dispersed infi ll material monly represented by screes, a product of stream cur- (usually sand- and clay-loams) increases. Thus, in the rent washing away weathered and broken bedrock pit, located on the west-facing slope of the slope of material, which is emplaced along the rivers’ banks Tyomny Creek (steepness: 30–40°), the following se- and at the base of the near-divide steep slopes. quences are exposed from its top down (Fig. 4, d): The scree-prone slopes are also inherent to an- 0–0.5 m – blocks of sandstone, platy in shape, sub- cient corrie (cirque) glaciers, localized in the upper vertically oriented, with dimensions up to 0.6–0.8 m reaches of Levy Gross Creek, in the near-divide part with thickness of 8 cm. The surface of blocks is covered of the Pravy Gross and Small Usu creeks intefl uve, with crustose lichen, light green and black in color. The etc. The corrie glacier tends to be open here in the infi ll material is absent. Dusting of vegetable detritus as N–E and N–W directions, with the slope steepness partially decomposed remains of lichens and pine nee- reaching 35–40°. The unstable parts of the slopes are dles is observed between the blocks; associated with the locations of snowfi elds, implying 0.5–1.0 m – blocks of sandstone without infi ll ma- their signifi cant role in the slope deposits weathering terial, averaging 0.2–0.4 m in size in plan view, and (Fig. 4, a). 3–6 cm in thickness. In the left-hand part of the walls of Snow avalanches and mudfl ows, in themselves, the pit the blocks are in vertical position. The right- hand part is dominated by low-tilted boulders (<15° to represent paragenetic processes developing at diff er- the center of the wall). Interlayers of fi ne landwaste are ent time at the same sites of the study area: in ancient observed between the blocks, characterized by weak and cirques, steeply dipping heads of the streams and nar- medium degree of abrasion; row valleys. They give rise either to snow avalanches 1.0–1.6 m – small boulders and rubble of sandstone, (in winter), or to mudfl ows (in summer), when a large with platy shape. The location of debris is disordered. amount of precipitation has been received. Traces of Fine landwaste is found in the right-hand part of the these processes are commonly observed in almost all wall, along with ruble with inclusions of small blocks (up parts of the study area (Fig. 4, b). At the present to 20 %). The debris is exceedingly wet from the surface stage, mudfl ow activity is showing some signs of miti- side. A layer of boulders and rubble in the left-hand part gation. Features of the structure of one of the mud- of the front wall of the pit is fi lled with dark brown plant fl ow cones (in the tributary to Taborny Creek) and detritus exhibiting a high degree of decomposition; the revegetation pattern indicate that in the past 1.6–1.7 m – small blocks of sandstone with light 20–30 years, the descents of mudflows and debris grayish or light brown sandy loam with fi ne landwaste as have ceased, while the mudfl ow cone have become infi ll material, which is very wet. eroded by temporary watercourse formed in the an- It should be emphasized that the corrom mate- cient glacial cirque located up the slope. rial gradually reduces in size to become small rubble Corrom-forming processes are developing ubiqui- and gravel in the lower part of the section of clastic tously on the slopes. The corrom-overlain area mea- rocks. The fragments receive sufficiently perfect sures many tens of square kilometers. By their in-plan roundness due to their friction against each other in outlines, they are divided into stone fi elds and stone the course of repeated freezing and thawing in the streams. context of excessive moisture. As such, the structure Stone fi elds are the debris of blocks of hard-rock, of the corrom section signifi cantly reduces internal occupying an area whose length across and along the friction between the fragments, and, accordingly, the slope is approximately equal. Alternatively, the length stability of the entire corrom cover during undercut- across the slope may be bigger than the latter ting of slopes by seismic shocks.

10 THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU

Fig. 4. Gravitational exogenous processes and phenomena: a – talus slopes of ancient corrie glaciers (heads of Vysoky Cr.); b – avalanche chute and debris cone (left side of the unnamed right tributary to the Tokko Rv.); c – corroms-ﬁ eld on the slope of the altiplain ice in the upper reaches of Rudny Cr.,; d – vertical section of the corrom on the valley slope of Tyomny Cr.; e – rock debris (felsenmeers) at the watershed divide (Olekma-Chara Plateau, the Tokko Rv. basin). Photograph by E.N. Ospennikov.

A distinctive feature of the corrom structure is composition of rocks and their resistance to weather- the altiplain ice that ﬁ lls all the voids between the ing. Corroms readily develop in places of the out- fragments below the AL base. Altiplain ice shows ob- cropping Archean igneous and metamorphic rocks vious signs of freezing from the surface of the sur- (granites, granite-gneisses). They also form on slo- rounding fragments (chains of air bubbles are drawn pes of diff erent steepness and exposure, occupying normal to the surface of blocks and are amassed in more than 40–50 % of their area. In respect with the central parts of ice inclusions as they are dis- rocks less resistant to weathering (sandstones, silt- placed thereto by the suprapermafrost waters freez- stones), corroms tend to develop on the slopes with ing in the corrom body). The distribution of cor- steepness more than 10–15° and occupy much small- roms in the study area is primarily governed by the er areas.

11 S.N. BULDOVICH ET AL.

Stone ﬁ elds are the product of cryo-elluvial pro- The structure of stone polygons often includes cessing of the AL rocks on watershed surfaces. They relatively well-rounded fragments resulting from the are morphologically divided into stone polygons and processing of fragments near the permafrost table felsenmeers (Fig. 4, e). through thermal and cryogenic heaving, aggravated The study area is dominated by stone polygons by processes of repeated freeze/thaw of water. The and their variety – stone caldrons, with the rock ma- variability of particle size distribution of the debris terial mobilized either in relatively narrow bands (up material are consistent with the patterns established to 2–5 m), forming polygons of irregular shape, or in for corroms. The stone polygons distribution across caldrons, located at the intersection of their sides. the study area is determined primarily by the bed- The structure of stone polygons in many ways rep- rocks composition and their resistance to weathering. licates both the main structural features of corroms, These are most common in areas of developed crystal- and the material composing stone polygons, which line Archean rocks. In the segments composed by shows close affi nity with the composition of parent Proterozoic sandstones, their extent is to some extent rocks. The structure of the section is diff erentiated lowered, and so is the predominant particle size of the by stratification, which is inverse relative to the material composing the stone bands. nor mal eluvium structure, as the debris material de- Another factor aff ecting the pattern of distribu- crease in size from top downwards. tion of stone ﬁ elds is the height of watershed divides.

Fig. 5. Cryogenic and thermos-hydrogenic exogenous processes and phenomena: а – thermoerosion washout on the motor-and-tractor road in the upper reaches of Rydny Cr.; b – soliﬂ uction tongue in the upper part of the slope of the right side of the Pravy Gross Cr. valley; c – soli- ﬂ uction splash in the slope bottom of the tributary to Taborny Cr. (Olekma-Chara Plateau, the Tokko Rv. basin). Photograph by Е.N. Ospennikov.

12 THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU

The processes of frost sorting tend to be intensifi ed posits. Thus, massive varieties of Proterozoic sand- with increasing altitude, while the processes of soil stones of the Olonnokon Formation often form a formation become suppressed. As a result, the extents thick-platy structures up to 1.5–2.0 m in size, where- of stone fi elds distribution also increase. At this, the as schistose sandstones produce smaller ones. Silt- felsenmeers representing continuous covers of block stones, when experiencing weathering, form small material are steadily gaining ground. Stone scattering platy blocks up to 0.4–0.6 m in size and platy rubble in the watershed divides (felsenmeers and stone poly- up to 10–15 cm in diameter with sandy-loamy aggre- gons), and corroms on the slopes have a common ge- gates. These petrographic types are characterized by netic nature, specifi cally, because of the leading pro- the thickness of weathering zone increasing on aver- cess of their formation is the clastic material expul- age to 8–10 m, within which the rocks are intensely sion onto the surface under the action of thermal and ferruginous and often pierced by closely-spaced fi ne cryogenic heaving. As a result of the transition from cracks. The actual thickness of cryo-eluvial bodies on watershed surfaces to slopes, stone polygons and watersheds usually does not exceed 1.5–3.0 m. felsenmeers grade into corroms, forming a single sys- The intensity of rocks weathering varies signifi - tem of stone covers. cantly depending on the surface exposure. On the Thermal erosion (as the only thermo-hydrogenic slopes of the southern exposure, the products of process) in the study area practically does not occur weathering have for the most part greater thickness, under natural conditions. Despite the orographic and their sediment composition is the most dispersed. (dissected terrain with slopes of more than 5°) and On the contrary, a coarser cover of Pleistocene–Ho- climatic (relatively large amount of summer precipi- locene material is developed on the north-facing tation) conditions, favorable for the emergence of this slopes with shallow seasonal thaw depth, where the process, the planar and linear erosion of rocks is pre- weathering is described as less intense. cluded by thin loose cover, its coarse material compo- Frost cracking plays a signifi cant role in origina- sition, as well as a relatively well-developed vegetation of a number of other cryogenic geological phe- tion cover. nomena – corroms, stone fi elds, stone polygons and Consequently, both erosion and thermal erosion caldrons, as well as fi ne polygonal forms of the relief. processes have developed mainly in the form of small Frost cracking in surface sediments and associated washouts in areas of vegetation disturbed by tracked polygonal relief are most pronounced in areas un- vehicles and along roads. The size of erosion forms de- derlain by relatively low-temperature (less than pends primarily on the composition and thickness of –2…–3 °C) permafrost with a thick layer of dispersed loose sediments. Therefore, erosion develops for most deposits (primarily in bottoms of gentle slopes), and part in the bottoms of the creek valleys, composed by are most remarkably expressed as stone polygons on sandy and sand-loam sediments, as well as on gentle the surface of gently convex watershed divides. slopes and slopes with medium steepness (Fig. 5, a). In these environments, the polygons vary on average from 5 × 5 to 10 × 10 m in size; while cracks Cryogenic geological processes proper with a length ranging from 20 to 40 m and a visible Processes of cryogenic weathering prepare the depth of penetration of 2–3 m, do not exceed a few conditions for the development of many phenomena, centimeters in width. The penetration depth of cracks such as landslides, screes, corroms, etc., whereas the is determined by the thickness of loose deposits (elu- harsh continental climate and the deep penetration of vial-diluvial). Low variability of the main parameters freezing and thawing of rocks determines physical as- of polygonal network developed in the area is ex- pects of the intensive development of frost (cryogen- plained by the annual temperature amplitudes on the ic) weathering. The nature of weathering and the soil surface, being a major control of the size of poly- composition of products of disintegration are largely gons, vary within small limits due to the relatively controlled by the composition, texture and structure uniform distribution of the snow cover. The excep- of the bedrock. Thus, depending on the mineralogical tions are the watershed divides where the snow is ei- and structural varieties, some rocks form large-boul- ther blown off or subjected to compaction. Ice wedg- der streams (granite-gneisses, granites), others yield es typical of southern Yakutia and localizing in the small blocks, rubble and landwaste (siltstone) during bottoms of river valleys, do not develop within the the weathering. Nepheline syenites erode even more study area mainly due to the unfrozen state of rocks readily, seeing as nepheline has low resistance to composing them and because of a lack of organo- weathering, which is not the case with afanite dia- genic rocks prone to shattering. bases (Torsky complex of late-Riphean intrusions) Frost heave of rocks within the investigated area particularly resistant to weathering (the affected represents one of the most common cryogenic geo- depth does not exceed a few meters from the surface). logical processes, resulting in the formation of heave The dependence of rocks disintegration on their mounds, spot-medallions, stone caldrons and poly- composition and structural features is best manifest- gons and other exogenous phenomena in different ed by the weathering of sedimentary terrigenous de- geocryological environments. The process of heaving

13 S.N. BULDOVICH ET AL. is accompanied by intensive restructuring of the sur- tion processes: given that the rooting zone binds the face microrelief. The most common are the water mi- moistened rocks, their creep down the slope is largely gration induced frost heave mounds. arrested. In the deposit area, the development of soli- Frost-heaved peat mounds are found on the an- fl uction is also impeded due to small amounts of fi ne cient sites of the first floodplain terrace, in the material in the rocks. swampy upper reaches of creeks and rivers in eastern Consequently, neither solifl uction processes have part of the territory, the most remote from the Tokko had wide occurrence, nor distinct solifl uction land- river valley. The size of frost-heaved mounds is not forms developed within the study area. However, the big, seeing as their height rarely exceeds 0.3–0.5 m, former tend to be occurring as low intensity processes while the area at the base is sized from 1.5 × 2 to almost ubiquitously, with their manifestations found 3 × 5 m. All heaved mounds within the study area mainly on gently sloping parts of the near-watershed emerge seasonally and are reported completely tha- divides, mostly at the base, where they are promoted wed by the end of the summer period. One of the by higher moisture content of rocks and may culmi- forms of the frost heaving process is the expulsion of nate in the formation of tongue-shaped solifl uction stone material, resulting in frost sorting of the materi- lobes. These are elongated down the slope as slightly al of loose formations and deposits in the active layer. convex positive forms of microrelief with a relatively Despite the fact that no hydrolaccoliths have been pronounced bench (tread) in the lower part of the found during the fi eldwork in the area, their seasonal tongue and a fl at rear part, almost merging with the small-size replicas can probably be formed in winter in slope surface (Fig. 5, b). Such solifl uction tongues the completely freezing-through creeks and rivers, usually measure 8–15 m in length and from 2 to 4 m specifi cally, in the lower parts of slopes. The absence in width; the frontal slope (riser) height is about 0.2– of perennial heaved mounds is accounted for the fai- 0.4 m. With soil and vegetation layer missing on their lure of multi-year freezing of the talik areas, whereas surface, fi ne earth does not transpire either, and is de- rocks in the existing taliks are usually drai ned during tectable only from a depth of about 0.2 m below sur- their freezing in winter. The study area has been prac- face. tically unaff ected by thermokarst development, which The essentially diff erent solifl uction features ob- is accounted for a limited distribution of ice-rich served in the lower parts of slopes, in themselves, usu- rocks, as well as for the fact that the thickness of dis- ally represent fragments of rubble and small blocks persed deposits, which are usually characterized by scattered around on the sodded surface of slope high ice content (biogenic, old river beds and fl ood- (Fig. 5, c) and have a shape of very gently sloping plain alluvial), remain mostly in the unfrozen state. dome, 1–2 m in diameter and 0.2–0.3 m in height. Nevertheless, some small-sized thermokarst subsid- From the surface they are made up by small-block ences are found at the head of Gross creek, in areas of clasts. Along the foot of the slope such features are glacial deposits distribution, as well as on watersheds, organized in chains, sometimes separated from each where they take the form of funnel-shaped structures other by tens of meters. Their origin can be defi ned as formed by locally melted out altiplain ice. the injection induced solifl uction, which form as a re- Icing (aufeis), which is formed by the freezing of sult of the expulsion (“splash”) of stone material dur- outflowing either suprapermafrost groundwater of ing the freezing of the strongly water-wet active layer the AL or groundwater from the underfl ow taliks, has in winter, when thawed rocks become squeezed be- limited distribution in the area. Patches of aufeis from tween the permafrost table and the base of the re- suprapermafrost waters in this area are usually a freezing layer of the rocks, which experienced thaw- product of uneven freezing of the aquifers in slope de- ing during the summer. The developing therewith posits and ravine alluvium. Being small in size (its ground pressure leads to the rupture of the frozen area measures fi rst hundred square meters; the thick- rock shelter and promotes the expulsion of thawed ness of ice likely not exceeding 1 m), they are rela- rocks onto the slope surface. The configuration of tively rare and found mainly in the ravine bottoms such landforms gradually acquire fi nal shape, as fi ne and at the foot of the slopes. The role played by the earth (melkozem) is washed away from their surface processes of icing is not critical for the formation of during the summer season. terrain in the area. The impact of icing on the relief was observed as a relatively small-size ice-coated CONCLUSIONS glade and reliably traced only in the upper reaches of the Maly Usu Creek valley. The phenomenon of the environmental settings Solifl uction (soil creep). The development of soil in the Tabornoe deposit area consists in specifi c fea- creep in the investigated area is most favored by the tures of the geocryological conditions established in medium-steepness and partly gentle slopes, made up the course of this research. Some of them were found from the surface by gravel and small boulders with to be fairly nonintuitive. sand-loam and sandy aggregates, however, the devel- 1. An extremely high contrasting distribution of opment of vegetation cover discourages the solifl uc- the average annual temperature of rocks is observed

14 THE PHENOMENON OF GEOCRYOLOGICAL CONDITIONS IN THE EASTERN PART OF THE OLEKMACHARA PLATEAU across the entire area. Inasmuch as the watershed di- karst, cryogenic heaving of rocks and icing, are large- vides outtop (by about 250 m) the valley bottoms, ly impeded by the predominance of unfrozen rocks in the temperature of rocks change from –5…–6 to the valley bottoms, as well as the absence of suffi- 1…2 °С with decreasing elevations, which can happen ciently thick dispersed deposits. Whereas the pro- within one slope of a valley (in plan view) within the cesses of waterlogging and bog formation, most inher- length of fi rst hundreds meters. The spatial confi gura- ent in and paragenetically associated with cryogenic tion of permafrost is therefore very complex: its thick- geological processes and phenomena, are poorly de- ness in watershed areas can exceed 400–500 m, rapid- veloped, given the specifi c hydrogeological situation, ly decreasing down the slope, while in the valley bot- which is characterized, in particular, either by good toms permafrost is either totally missing or have a drainage of the river valley bottoms or the predomi- sporadic distributuon. nance of highly dissected relief that precludes the ex- 2. Despite considerable absolute elevations of cessive waterlogging of the surface. thalwegs in the valleys (>1050–1100 m), the latter are characterized by a wide distribution of unfrozen References rocks. At this, the valley taliks reach hundreds of me- Dorofeev, I.V., Zheleznyak, M.N., Volod’ko, B.V., et al., 1981. ters in width, and almost all of them are interpreted Geothermal Conditions of the Chara-Tokko Interfl uve. In: to be through in relation to permafrost. Apart from a Tematicheskie i regionalnye issledovania myorzlykh tolshch highly warming eff ect of the snow cover during the Severnoy Evrazii [Thematic and regional studies of perma- winter season, the summer-time processes accompa- frost strata]. IMZ SO AN SSSR, Yakutsk, pp. 65–74. (in nying additional convective heat input into the rocks Russian) during the surface water absorption by coarse alluvial Ershov, E.D. (Ed.), 1989. Geocryology of the USSR. Central deposits of the valleys are involved in the formation Siberia. Nedra, Moscow, 414 pp. (in Russian) of taliks. Karausheva, A.I., 1977. Climate and Microclimate of the Ko- 3. The mathematical modeling enabled the au- dar–Chara–Udokan Area. Gidrometeoizdat, Leningrad, 128 pp. (in Russian) thors to establish the principal possibility of the for- Khrustalev, L.N., Emel’yanov, N.V., Pustovoit, G.P., Yakov- mation of through taliks in the considered environ- lev, S.V., 1994. The program for calculating the thermal in- mental settings even in narrow valleys of small water- teraction of engineering structures with permafrost WARM. courses. Whilst their persistent existence can be Certifi cate No. 940281, PosAPO. (in Russian) maintained solely by conductive heat exchange, with- Kudryavtsev, V.A. (Ed.), 1975. South Yakutia: Permafrost and out additional heat input from the ground waters. Hydrogeological Conditions of the Aldan Mining-industrial 4. The established specifi c pattern of redistribu- Region. Moscow University Press, Moscow, 444 pp. (in Rus- tion of the deep heat fl ux concentrating in the direc- sian) tion of the cooled watersheds, where the fl ux density Kudryavtsev, V.A., Garagulya, L.S., Buldovich, S.N., et al., 2016. has shown almost two-fold increase at the surface, Principles of Permafrost Forecasting in Geotechnical Inves- tigations. Geoinfo, Moscow, 512 pp. (in Russian) against the background deep-earth value. In this case, the heat fl ux in the valley bottoms has a downward Ospennikov, E.N., Trush, N.I., Chizhov, A.B., Chizhova, N.I., 1980. Exogenic Geological Processes and Phenomena (South trend and is redistributed towards the watershed di- Yakutia). Moscow University Press, Moscow, pp. 147–178. vides, where it is stacked with the depth component. (in Russian) 5. A relatively small depth of seasonal thaw of Semenov, V.P., Zheleznyak, M.N., 2013. Geothermal conditions rocks and its low variability are noted for diff erent of the Vilyuy syneclise. Kriosfera Zemli XVII (4), 3–10. types of geocryological conditions, which explains Sergeev, D.O., Tipenko, G.S., Romanovsky, V.E., Romanov- the monotonous structure of the loose cover formed sky, N.N., Berezovskaya, S.L., 2005. The infl uence of moun- within the corroms and stone fi elds on watershed di- tain relief and vertical geocryological zoning on permafrost vides, predominating across the study area. thickness evolution in South Yakutia. Kriosfera Zemli IX (2), 6. Cryo-elluvial and cryogenic slope processes 33–42. and phenomena (e.g. felsensees and stone polygons, Zabolotnik, S.I., Zabolotnik, P.S., 2014. Conditions of ground seasonal thawing and freezing in South Yakutia. Kriosfera corroms, snow avalanches and mudfl ows, solifl uction) Zemli XVIII (1), 23–30. are the most widespread and actively developing in Zheleznyak, M.N., 1998. Geothermal Conditions of Permafrost the area of South-Ugui group of deposits, due to the Zone in the Western Portion of the Aldan Basin. Izd-vo SO relatively severe geocryological conditions in the wa- RAN, Yakutsk, 90 pp. (in Russian) tershed divides and slopes. Zheleznyak, M.N., 2005. Geothermal Field and Permafrost Zone The proper cryogenic geological processes and of the Southeastern Part of the Siberian Platform. Nauka, phenomena, such as formation of ice wedges, thermo- Novosibirsk, 227 pp. (in Russian) Received May 26, 2016