A landslide-affected slope was chosen to study the ionic migration in the active layer and upper portion of permafrost. The research was conducted in two stages, in 1994 and 2001. Several boreholes, in dry and wet environments of the shearing surface of a 1989-landslide, were drilled. A background borehole on an undisturbed site was sampled as well. Each sample, collected from the core, underwent a conventional chemical cation-anion analysis. The results showed desalinization of the active layer and upper permafrost, which occurred in 7 years. Different migration rates noted for various salts determine change of ionic composition from marine pattern to continental, because mobile ions are washed away by surface and subsurface runoff, while the less mobile ones are accumulating in the upper portion of the active layer due to capillary rise and at the active layer base on a geochemical barrier

Leibman, M. O.

Rogov, V. V.

Streletskaya, I. D.

Streletskii, D. A.

OceanRep

1 INTRODUCTIONSaline frozen deposits, widely distributed at YamalPeninsula, leave their prints on every natural and anthro-pogenic process occurring in the region. A specific typeof the tundra vegetation with a “warmer” appearance(high willows, richer biomass compared with zonal veg-etation) develop at the sites where the saline deposits areexposed at the surface due to the landslide process. Thelandslide process removes the upper fresh, often sandysoils down slope and exposes the clayey saline perenni-ally frozen soils (Leibman 1995). The landslide activa-tion and permafrost exposure is accompanied by thevertical migration and horizontal wash away of readilysoluble salts (Leibman & Streletskaya 1996; Tentyukov1998; Ukraintseva et al. 2000).The objective of the present work is the suggestinga dynamic pattern for the process of ionic migration ina case study on a landslide slope within the coastal-marine plain, Yamal Peninsula, Russia.2 STUDY AREAThe area under study is located at the interfluve of Se-Yakha and Mordy-Yakha rivers (Fig. 1). The terri-tory is represented by a hilly plain with narrow water-sheds and extensive gentle slopes. Marine terraceshave the maximum altitude up to 58 m. Narrow val-leys of rivers and small creeks, ravines and gulliesintensively dissect the territory.Marine sedimentation prevailed in the area duringthe Middle and Late Pleistocene. A thick stratum ofmarine clayey deposits was accumulated in the courseof marine transgression (Ershov 1995). The polarbasin’s water surface continually decreased, and itsshoreline moved northwestward. Marine deposits,being turned into a subaerial state, began to freeze upin Late Pleistocene.The main relief-forming process at the study area aswell as at other coastal plains of permafrost zone isthermal denudation on slopes, including cryogeniclandslides, thermal erosion, nivation, etc. (French 1996,Kaplina 1975, Leibman et al. 1991, 1997, Lewkowicz1988, 1990, Zhigarev 1975).Active natural cryogenic processes typical of theregion on study, expose the sediments containing1117Redistribution of ions within the active layer and upper permafrost, Yamal, RussiaD.A. Streletskii, I.D. Streletskaya & V.V. RogovLomonosov Moscow State University, Faculty of Geography, Moscow, RussiaM.O. LeibmanEarth Cryosphere Institute SB RAS, Tyumen, RussiaABSTRACT: A landslide-affected slope was chosen to study the ionic migration in the active layer and upperportion of permafrost. The research was conducted in two stages, in 1994 and 2001. Several boreholes, in dry andwet environments of the shearing surface of a 1989-landslide, were drilled. A background borehole on an undis-turbed site was sampled as well. Each sample, collected from the core, underwent a conventional chemical cation-anion analysis. The results showed desalinization of the active layer and upper permafrost, which occurred in 7 years. Different migration rates noted for various salts determine change of ionic composition from marine pat-tern to continental, because mobile ions are washed away by surface and subsurface runoff, while the less mobileones are accumulating in the upper portion of the active layer due to capillary rise and at the active layer base ona geochemical barrier.Permafrost, Phillips, Springman & Arenson (eds)© 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7Figure 1. Yamal Peninsula, star points to the study area.soluble salts, microelements and lenses of brine, andsubject them to destruction. That, in the end, affectsessentially the chemical composition of sediments aswell as superficial and active layer water (Leibman &Streletskaya 1996, Ukraintseva et al. 2000).3 RESEARCH METHODSA field study has been carried out in Central Yamal,“Vaskiny Dachi” research station. The site wasaffected by a landslide event in 1989 (Leibman 1995).Samples were collected from the core of shallowboreholes and their ionic composition tested to ana-lyze redistribution of water-soluble salts, caused byinvolving of the upper section of permafrost into sea-sonal thaw as a result of a landslide process.Several shallow boreholes were drilled in 1994(Leibman & Streletskaya 1996). Considered are twoboreholes located on a shearing surface, borehole #2at the wet site, in the sediment accumulation zone, andborehole #3 in the dry site, the zone of active erosion,and thus well-drained (Fig. 2a, b).The same landslide area was under study in summer2001. Sampling was undertaken in a backgroundborehole #1 on an undisturbed surface to characterizea stable slope without redistribution due to a land-slide. Boreholes #2bis and #3bis correspond to oldones #2 at the wet site, and 3 at the dry site, respec-tively. The results of repeated chemical tests are com-pared to reveal the dynamics of the ionic migrationthrough a geological section in various landscape-geochemical conditions.4 RESULTS AND DISCUSSIONBackground boreholes #1 (2001) characterize theactive layer and upper permafrost. It is clear from thediagram (Fig. 3a), that there are two horizons of salini-zation. Near-surface salinization is due to salt migra-tion upward in winter (Naletova, 1996 ) and capillaryrise in summer (Anisimova, 1981). The second nearthe active layer base is resulting from the permafrosttable accumulating salts as a geochemical barrier(Leibman & Streletskaya 1996).The soluble salt content in perennially frozendeposits at the depth from about 95 cm downward, ispractically similar in all three boreholes (0.6–0.8%).This, probably, proves the similarity of the initial ionicdistribution at the landslide and background sitebefore the landslide event.The active layer of the shearing surface contains asa whole more soluble salts (0.3–0.6%) than the undis-turbed area (0.04–0.2%), and the amount of saltsincreases with the depth (borehole #2, Fig. 3b; and #3,Fig. 3c).The distribution of soluble salts through the activelayer of the shearing surface is rather similar at the dryand wet conditions. Specific pattern is connected withwashing away of soluble salts under filtration andaccumulation due to capillary rise as well as at theundisturbed site but at a different rate. The mainprocess for the wet site (Fig. 3b) is capillary rise ofions to the surface and evaporation (Anisimova 1981),and then washing away by surface run-off. Intensity of this process is seen from rather low soluble-saltcontent at the active layer base (0.5% at 65 cm,Fig. 3b) compared with the dry site (0.65% at75 cm, Fig. 3c). In addition, the lower horizon at theactive layer base of the wet site, looses its salts due tosubsurface runoff over the permafrost table along thepost-cryogenic fissured zone where the rate of filtra-tion in clayey ground is abnormally high (Leibmanet al. 1993, Naletova 1996).Comparing ionic composition data for 1994 and2001, one can see the dynamic pattern for redistribu-tion of ions in the active layer and upper permafrost.At the wet site of the shearing surface the salt contentis much less in 2001 compared with 1994 (Fig. 3b, bore-holes #2 and 2bis). Most active desalinization is above1118Figure 2. Borehole position: a, profile; b, plan.the active layer base of 1994. This can be explained byabundant cryostructure formation in the active layer ofthe wet site, better developed post-cryogenic fissuredzone, and thus more intensive run-off. Though there areno samples at the active layer top, it can be surmised thatupper accumulation zone (at the depth of 20 cm) in2001 should be much less pronounced compared with1994 due to re-vegetation of the surface and preventingof wash out of evaporites.The dynamics of total salinity at the dry shearingsurface (Fig. 3c, borehole #3, 3bis) is characterized bythe binomial accumulation pattern. The upper accumu-lation horizon is less expressed, while the active layerbase horizon shows the highest among the study sitescontent of soluble salts. Most likely this can beexplained by an accumulation at geochemical barrierunder low run-off in the lack-of-water conditions ofthe dry site.Re-distribution of separate ions (mainly anions) isdifferent from total soluble-salt redistribution, depend-ing on the migration ability of anions. Cations are notdiscussed because the pattern of their distributionwith depth does not change qualitatively, though thecontent of cations decrease. Re-distribution of anionsis shown on Figure 4 (bicarbonate-ion), Figure 5 (sulfate-ion), and Figure 6 (chloride-ion).There is a non-uniform distribution of anions inpermafrost at the undisturbed site (Figs. 4a, 5a, 6a)with a peak near the geochemical barrier at the activelayer base.At both sites of the shearing surface (Fig. 4b, c)bicarbonate has minimum content near the surfaceand in permafrost while in most of the active layer thecontent of this anion is maximum. Bicarbonate con-tent decreased in 2001 at both sites, as compared with1994, but at the wet site to a larger degree. The accumulation zone for sulfate-ion at geochem-ical barrier is most expressed at the wet site (Fig. 5b)where maximum is noted at the active layer base ofthe relevant year. Remarkable is abrupt increase ofsulfate content at the surface of the dry site (Fig. 5c).This is explained by several reasons: (1) capillary riseof soluble salts is more active at the dry site, (2) chlo-rides are the most mobile and first washed away, and(3) the content of bicarbonates is low from the begin-ning. Thus, sulfates are the main component of evap-orites on the surface of the dry site.The total content of chloride-ion is the highestamong other anions due to marine type of initial sal-inization in the study deposits. The main distributionpattern is persistent decrease with depth up to theactive layer base. But there is a specific feature withinthe active layer of the wet site. Here at a depth about20 cm other anions have maximum in 1994 (Figs. 4b,5b), while chloride content shows minimum (Fig. 6b).Unfortunately there is no data at this depth for 2001.1119c0204060801001201401600,00 0,50 1,00total salinity, %cmtotal amount of salts, % (1994)total amount of salts, % (2001)active layer -1994active layer-2001b0204060801001201401601800,00 0,50 1,00total salinity, %cmtotal amount of salts, % (1994)total amount of salts, % (2001)active layer 1994active layer-2001 a0204060801001201401601800,00 0,50 1,00total salinity, %cmtotal amount of salts, % (2001) active layer Figure 3. Total content of soluble salts (a dry residue) inthe deposits of the active layer and upper permafrost at: a,undisturbed site (borehole 1, 2001); b, wet site of the shear-ing surface (borehole 2 in 1994 and 2bis in 2001); c, at thedry site of the shearing surface (borehole 3 in 1994 and 3bisin 2001).Chloride content does not change much in 2001 com-pared with 1994 in permafrost, but there is rather ahigh difference in 1994 and 2001 at the active layer ofthe wet site (Fig. 6b) or near the surface at the dry one(Fig. 6c). Thus, geochemical barrier at the active layerbase for this anion is not efficient. Capillary rise is,probably, the main factor of redistribution for chloride.As demonstrated by the field study, the change incontent of cations and anions between 1994 and 20011120c0204060801001201401600,00 0,50 1,00 1,50 2,00mg-equ/100 gcmHCO3-(1994) HCO3-(2001)active layer-2001active layer -1994a0204060801001201401601800,00 0,50 0,501,00 2,00mg-equ/100 gcmHCO3-(2001)active layer  b0204060801001201401601800,00 0,50 1,00 1,50 2,00mg-equ/100 gcmHCO3-(1994) HCO3-(2001)active layer -2001active layer -1994Figure 4. Content of bicarbonate-ion in the deposits ofthe active layer and upper permafrost at: a, undisturbed site(borehole 1, 2001); b, wet site of the shearing surface (bore-hole 2 in 1994 and 2bis in 2001); c, at the dry site of theshearing surface (borehole 3 in 1994 and 3bis in 2001).a0204060801001201401601800,00 1,00 2,00 3,00 4,00 5,00mg-equ/100 gcmcmSO4--(2001)active layer c0204060801001201401600,00 1,00 2,00 3,00 4,00 5,00mg-equ/100 gcmSO4--(1994) SO4--(2001)active-layer-2001active layer-1994b0204060801001201401601800,00 1,00 2,00 3,00 4,00 5,00mg-equ/100 gSO4--(1994) SO4--(2001)active layeractive-Figure 5. Content of sulfate-ion in the deposits of theactive layer and upper permafrost at: a, undisturbed site(borehole 1, 2001); b, wet site of the shearing surface (bore-hole 2 in 1994 and 2bis in 2001); c, at the dry site of theshearing surface (borehole 3 in 1994 and 3bis in 2001).follows migration rates of various ions. At undis-turbed surface all anions have the same distributionpattern with maximum in the zone of maximum sea-sonal thaw depth (geochemical barrier), at the shear-ing surface this regularity is broken by re-distributionof chloride-ion. This ion due to a high migration ratemoves fast from permafrost into the active layer and is washed away by surface and active layer runoff.Sulfate and bicarbonate form a second zone of accu-mulation at the depth of 20–30 cm. This zone is mostexpressed at the dry site and more actively reducing atthe wet one due to a higher runoff. Chloride marksthis zone by a reduced rate of washing away.5 CONCLUSIONSSampling and ionic analyses of active layer and upperpermafrost deposits at a landslide-affected slope showthe following.1 Shearing surface compared with undisturbed slopeis characterized by reduced content of soluble saltsin both active layer and upper portion of perma-frost, thus landslide process causes desalinizationof near-surface saline marine deposits.2 Different rates and dynamical pattern of ion redis-tribution at the wet and dry sites of the shearingsurface depend on the migration rates of ions incombination with water filtration and movementrates.3 Since 1994, in 7 years, two zones of accumulationwere formed in the new active layer. One at thegeochemical barrier of the active layer base iseffective only for bicarbonate and sulfate ions,while the upper one in addition to other anions, isfeebly distinct for chloride as well.4 The initially marine type of salinization in perenni-ally frozen deposits involved in the seasonal thawafter the landslide event turns into continental dueto a high rate of washing away chloride-ion.REFERENCESAnisimova, N.P. 1981. Cryohydrochemical peculiarities ofthe permafrost zone. Novosibirsk: Nauka (in Russian).Ershov, E.D. (ed.) 1995. Fundamentals of geocryology 1.Moscow: Moscow University Press (in Russian).French, H.M. 1996. The Periglacial Environment. London:Longman. Kaplina, T.N. 1975. Cryogenic slope processes. Moscow:Nauka (In Russian).Leibman, M.O. 1995. Preliminary results of cryogeniclandslides study on Yamal Peninsula, Russia. Perma-frost and Periglacial Processes 6(3): 259–264.Leibman, M.O. & Streletskaya, I.D. 1996. Migration ofchemical elements and ions in the active layer andupper permafrost in connection with the process ofthermal denudation on Yamal Peninsula. In E.D.Ershov,R.M.Kamenskii & V.V.Baulin, (eds) Materials of theFirst Conference of Russian Geocryologists 2:390–398. Moscow: Moscow University Press (inRussian).1121c0204060801001201401600,00 2,00 4,00 6,00 8,00 10,00 12,00mg-equ/100 gcmCl-(1994) Cl-(2001)active-layer-2001active-layer-1994b0204060801001201401601800,00 2,00 4,00 6,00 8,00 10,00 12,00mg-equ/100 gcmCl-(1994) Cl-(2001)active layer-2001 active layer -1994a0204060801001201401601800,00 2,00 4,00 6,00 8,00 10,00 12,00mg-equ/100 gcmCl-(2001)active layer  Figure 6. Content of chloride-ion in the deposits of theactive layer and upper permafrost at: a, undisturbed site(borehole 1, 2001); b, wet site of the shearing surface (bore-hole 2 in 1994 and 2bis in 2001); c, at the dry site of theshearing surface (borehole 3 in 1994 and 3bis in 2001).Leibman, M.O., Lakhtina, O.V., Miklyaev, S.M. & Titova, I.R.1991. Pattern of relief-forming cryogenic process dis-tribution at Western Yamal Peninsula. In: Denudation incryolithozone: 92–99. Moscow: Nauka (In Russian).Leibman, M.O., Rivkin, F.M. & Saveliev, V.S. 1993.Hydrogeological aspects of cryogenic slides on theYamal peninsula. Permafrost. Proceedings of the SeventhInternational Conference, Beijing, 5–9 July 1993 1.Leibman, M.O., Streletskaya, I.D. & Konyakhin, M.A.1997. Assessment of surface dynamics atBovanenkovo gas field (Central Yamal Peninsula) dur-ing the period 1949 to 1990. Geomorphology 2: 45–48(In Russian).Lewkowicz, A. 1988. Slope processes. In M.J. Clark (ed)Advances in periglacial geomorphology: 325–368.Chichester, UK: Wiley.Lewkowicz, A. 1990. Morphology, frequency and magnitudeof active layer detachment slides, Fosheim peninsulaEllesmere Island, N.W.T., Permafrost-Canada. Proc. ofthe Fifth Canadian Permafr. Conf. Quebec: CollectionNordicana 54.Naletova, N.S. 1996. Mass transfer and cryogenic textureand structure formation in freezing saline soils. Candi-date of science thesis. Moscow: Moscow University,Faculty of Geology.Tentyukov, M.P. 1998. Geochemistry of landscapes ofCentral Yamal. Ekaterinburg (in Russian).Ukraintseva, N.G., Leibman, M.O. & Sreletskaya, I.D. 2000.Peculiarities of landslide process in saline frozendeposits of central Yamal, Russia. In E. Bromhead, N. Dixon and L-L Ibsen (eds), Landslides. Proc. VIIIInternational Symposium on Landslides 3, London:Thomas Telford.Zhigarev, L.A. 1975. Thermodenudational processes anddeformative behavior of thawing ground. Moscow:Nauka (In Russian).1122

Redistribution of ions within the active layer and upper permafrost, Yamal, Russia

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