LandslidesDOI 10.1007/s10346-014-0488-7Received: 6 July 2013Accepted: 7 April 2014© Springer-Verlag Berlin Heidelberg 2014

Sebastian Tyszkowski I Halina Kaczmarek I Michał Słowiński I Elena Kozyreva I DariuszBrykała I Artiom Rybchenko I Viktoria A. Babicheva

Geology, permafrost, and lake level changes as factorsinitiating landslides on Olkhon Island (Lake Baikal,Siberia)

Abstract Permafrost decline, observed in the last few decades as aresult of climate change, causes an activation of cryogenic land-slide processes. This study on Olkhon Island in Lake Baikal(Eastern Siberia), located within the discontinuous permafrostzone, was aimed to determine how strongly the landslide formsfound there are associated with climatic conditions and if they canreact to climate change. It was also important to identify whichtype of landslides in this area is the most sensitive indicator of theobserved changes and to what extent they can react to them. Forthis purpose, landslides were identified, and their morphology,geological structure, and thermal parameters were assessed. Theresults show that the key process is the increase in thickness of theactive layer, partly due to the presence of Miocene lake clays andchanges in water level in Lake Baikal.

Keywords Landslide . Permafrost . Solifluction . Climatechange . Olkhon Island . Eastern Siberia

IntroductionOlkhon Island, the largest one in Lake Baikal, is one of the mostgeodynamically active areas in Eastern Siberia. According to theglobal landslide hazard zonation, the Baikal rift zone is character-ized by a moderate degree of landslide hazard (Nadim et al. 2006),mostly because the area was classified as “very high hazard” on thebasis of seismic hazard maps. They show the likely peak groundacceleration (PGA) with 475-year return period (10 % probabilityof exceedance in 50 years) from the Global Seismic HazardAssessment Program (GSHAP) (Fig. 1).

However, apart from the seismic factor, landslide developmentis also affected by the climate, reflected in the presence of perma-frost and function of the active layer. The climate change observedin the last few decades, global warming in particular, results inthawing of permafrost, which causes an increase in landslideactivity (Couture and Pollard 2007; Crozier 2010). Reduction ininterstitial ice and permafrost, caused by increased temperature,leads to reduced cohesion of jointed rock masses, debris, and soil(Crozier 2010). Many observations suggest that a similar problemapplies also to Eastern Siberia.

Siberian ecosystems are likely sensitive to global warming ow-ing to the reduced area with permafrost (Koven et al. 2012). Themain factors causing the rapid disappearance of permafrost arelong-term changes in air temperature, which is confirmed byrecords in the Baikal region, where the mean annual surface airtemperature increased in the twentieth century (Voropay et al.2011). The regional increasing trends in air temperature exceedglobal trends 1.5–2.5-fold. Permafrost thaw under the influence ofglobal climate change is most visible at high latitudes in northernRussia (Smith et al. 2005; Romanovsky et al. 2007; Grosse et al.2011), and Yukon in Canada (Huscroft et al. 2004; Wang et al.

2009). In many parts of Eastern Siberia, especially in the south,permafrost is now at the brink of degradation as a result of 30–40 years of climate warming, and a further rise in air temperatureand/or increase in snow cover thickness will initiate its degrada-tion (Romanovsky et al. 2007). In the permafrost zone, thicknessof the active layer is increasing, and in the areas that are frozenonly seasonally, the depth of freezing is declining (Frauenfeld et al.2004). In 1956–1990 in Eastern Siberia, there was a significantincreasing trend of 0.26 °C/decade in annual mean soil tempera-ture at the depth of 1.6 m, and it was only slightly lower thanthe increasing trend in air temperature of 0.29 °C/decade(Romanovsky et al. 2007). The increasing trend in soil tem-perature in those areas was clearly strengthened in the 1990s(Trofimova 2006). Particularly important in terms of global climatechange is the fact that the study site lies at the southern limit ofdiscontinuous permafrost (defined as van Everdingen 1998), whoserange in Russia has been greatly reduced in the last decades (Pavlovand Malkova 2008).

The available literature on cryogenic processes on slopes con-cerns primarily Alaska, Canada (Lewkowicz 1988, 2007; Lyle andHutchinson 2006), Russia (Czudek and Demek 1970; Leibman1995, 1997; Leibman and Egorov 1996; Frauenfeld 2004;Khomutov and Leibman 2014), and model studies (Harris et al.2001, 2008). In a work concerning landslides in northern Russia,Leibman (1995) reviews the literature on downslope movement inpermafrost regions, noting that slope movements can be dividedinto two types. The first type includes solifluction (and gelifluctionin North American literature). Solifluction is the slow soil move-ment with limited tearing of the turf cover, and gelifluction is theslow downslope flow of unfrozen earth materials on a frozensubstrate (van Everdingen 1998). The second type of slope move-ments is cryogenic landslides, defined as quick movement of soilblocks or earth flows coupled with turf and moss cover (describedin North American literature as active layer slope failures, activelayer detachments, active layer glide, slumps, and skinflows).

This study was aimed to determine if (and if yes, to whatextent) landslides on Olkhon Island may react to global climatechange. It is also important to assess which type of landslides inthis area is the most sensitive indicator of the observed changes.

Study areaOlkhon is the largest island in Lake Baikal (Eastern Siberia)(Fig. 2), which is one of the largest and oldest lakes in the world.The island has an area of 742 km2 and is 71 km long and 12 kmwide. Its shoreline is 225 km long. The western part of the island isseparated from land only by a shallow, broad strait, known as theSmall Sea. The relief of the island is mountainous, with altitudesvarying from 455 to 1,274 m in the northeastern part of the island.The southern part of the island and nearly the whole western

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shores, with gentle slopes (inclination usually 5°–15°), are coveredby steppes, while the rest of the island are covered by taiga.

The core of the island consists of Early Palaeozoic rocks, mostlystrongly metamorphosed marbles, quartzites, and crystallineschists: gneisses, granitic gneisses, and amphibolites (Fig. 3). Therocks are dissected by numerous tectonic fractures; many of themare still active and are some of the deepest ones in this region

(Ivanov et al. 2013). Locally, along the western shore of the island,Palaeozoic rocks are covered by Miocene loams and clays, as wellas Pleistocene sands and lacustrine–riverine gravels, being rem-nants of an elevated terrace of Lake Baikal. Olkhon Island, locatedwithin the Baikal rift zone, is one of the most dangerous regions inRussia in terms of seismic activity. Earthquakes with intensities ofup to X or XI (i.e., devastating or catastrophic) on the MSK-64

Fig. 1 Peak ground acceleration (m/s2) map with 10 % probability of exceedance in 50 years for Northern Euroasia (GSHAP results)

Fig. 2 Location of the study area. Digital elevation model (based on SRTM digital elevation data and digitized topographic map)

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scale and magnitudes ofM>7.6 have occurred here in the past andprobably will occur in the future (Mel’nikova et al. 2010).Significant earthquakes were observed in various parts of LakeBaikal on average of every 50 years or so: in 1862 (intensity X, M7.5), 1903 (intensities VIII–IX, M 6.7), and 1959 (intensity IX, M6.8) (Galaziy and Lut 2000; Baikal Branch of Geophysical SurveySB RAS).

The heterogeneous geological structure causes differences ingeomorphological processes taking place on the island. In theeastern part, there are many remnants of old rock flows and mixedrock/debris flows, ascending from elevated rock massifs, and theshore forms a tall wall with rockfalls. By contrast, the western partof the island is dominated by forms associated with aeolian andlandslide processes, and its gentle slopes form an abrasion–accu-mulation coast.

Olkhon Island has a strongly continental climate, with annualmean air temperature ranging from −0.4 °C in the central part to−1.3 °C in the northern part of the island (Berkin et al. 2009).Monthly mean air temperatures are negative from November tillApril, with lowest values in January and February, reaching up to−20 °C. Mean temperature in July is the highest, close to 15 °C(Galaziy 1993). Mean annual precipitation is 225 mm, mostly inApril–October. Snow cover on the island was only 2–29 cm thick in1964–2000 (Тrоfimоvа 2006). The climate of Olkhon is character-ized by lower precipitation and milder winters and colder sum-mers than the areas around Lake Baikal. On the island, seasonalfreezing of the ground lasts 7 months and reaches to the depth of2.4–2.8 m, with intensive thawing in summer (Trofimova 2006).

Very much like in other parts of the globe, air temperaturetends to increase. Annual mean air temperature on Olkhon in1966–2006, as compared to 1947–1965, increased by about 1 °C,from −1.4 to −0.4 °C in the northern part of the island and from−2.2 to −1.3 °C in the central part (Berkin et al. 2009). Climate

warming in Eastern Siberia results in increased precipitation,especially in winter. Snow cover increased in this area by 20 mmbetween 1961–1990 and 1991–2005 (Anisimov et al. 2007), whichenhanced the effect of climate change on soil temperature(Sherstyukov 2008).

Olkhon Island is located at the southern limit of the discontin-uous and sporadic permafrost zone. Permafrost is found in rivervalleys, wetlands, and on north-facing slopes. It is up to 30 mthick. Seasonally, the permafrost layer thaws to the depth of 0.5–1.0 m in peatlands up to 3 m and more in mineral soils. Permafrostin that region is extremely unstable. Its temperature varies from−0.2 to −0.5 °C, and even small deviations of environmentalconditions may result in degradation of this layer (Palshin 1968).

In 1956, in Irkutsk, the first one of the five planned dams wasbuilt on the river Angara, which is the only outflow of Lake Baikal.The dam is located at 65 km from the Angara source. Its construc-tion was aimed at impoundment of the upper section of theAngara and its transformation into the Irkutsk Reservoir (filledin 1956–1958) and a 1.2-m rise in water level of Lake Baikal, ascompared to the mean water level (Trzchinskij et al. 2009).

As a result of creation of the reservoir, annual water levelfluctuations in the lake have changed. Before creation of thereservoir, they did not exceed 0.80 m, whereas in 1956–2001,they varied from 0.62 (1972) to 1.83 (1973), and maximum am-plitude was 2.21 m. Since 2001, they range from 0.62 to 0.93 m(Lake level 2012). Because of the impoundment, beaches on theshores of Lake Baikal and river mouths were frequently flooded,and the processes of shore erosion and/or sediment accumula-tion were intensified.

MethodsThe initial selection of the study area for more detailed analyseswas based on the comparison of old aerial photographs with

Fig. 3 Geological map of OlkhonIsland (modified from Konoplev1964 and Lunina et al. 2010)

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modern satellite images. On the same basis, dimensions of indi-vidual landslides were also assessed. Further research, conductedin the field, included primarily geological and geomorphologicalmapping near the landslides, combined with hand drilling andsampling. Major parameters of the landslides were measured: formsize and slope as well as scarp height and orientation. From theopencast workings and exposed landslide walls, samples for geotech-nical research were taken. Soil temperature was measured to themaximum depth of 3.5 m. On the basis of the established monitoringnetwork, current horizontal movements were measured.

To assess climate change in the last few decades in the studyarea, monthly mean values of daily temperature in 1951–2011 werecompared for weather stations Khuzhir (53° 12′ N, 107° 20′ E,altitude 462 m) at Olkhon and Irkutsk (52° 27′ N, 104° 35′ E,altitude 467 m). On this basis, we calculated mean annual airtemperature and mean air temperature in April–September.Long-term variation in air temperature was described by meansof linear regression equations, and the increase in temperature wasassessed on the basis of directional coefficients.

Landslides’ descriptionLandslides on Olkhon are found nearly exclusively along theshores of the island, and their type depends on geological structureand land relief. The dominant type of mass movements on high,rocky shores is rockfalls. They are most conspicuous on the steepsoutheastern cliffs which are 150–500 m high, with slope angle of25°–50° (Fig. 4). The high shores, with periodically active land-slides, are found along a 35-km section of southeastern shoreline,which accounts for 17 % of the total shoreline length of the island.Locally, also rockfalls and rapid debris flows are observed in thispart of the shoreline. Forms of this type appear every 15 years orso, as a result of rainstorms or snowmelt. Rockfalls are alsoobserved on cliffs of the northwestern shoreline, in places withrock outcrops (igneous or metamorphic). Also, screes with loose,weathered rock debris can be found there. Mass movements of thistype can be directly activated on a larger scale by seismic activityin this region.

Another type of mass movements is rotational landslides, ob-served at the northwestern shores, with gentle grassy slopes (in-clination of 9°–20°) (Fig. 5). They are small forms (surface areaabout 500–3,500 m2) (Table 1), 1–3 m thick, with relative height of5–20 m and mean sliding surface inclination of 10°–15°. In mor-phology of these landslides, the main scarp is most conspicuous,2–4 m high, with slope angle of 45°–55°. Additionally, two to threesecondary scarps may be noticeable. Foot in most of the landslidesslopes down directly into Lake Baikal. During storms, especiallywhen the lake level is high, toe is partly washed away, and terminalparts of landslide toes look like vertical cliffs, about 0.5 m high.

The landslides develop as a result of a single displacement, as arotational slide of the whole mass of the material, with preservedinternal structure. The collected cores show that these formsfunction above the groundwater table. A vast majority of themdevelop within the top layer of residual clays in local depressions,whose relief corresponds with synclines (or depressions) withinthe rock substrate. They are often formed in places where thebedrock is close to the ground surface, but the sliding surface islocated above its upper limit. The observed rotational landslidesvary in age. After the first major displacement, secondary creep isnot observed. Moreover, within forms of this type, there are nosigns of other types of mass movements.

In respect of current geodynamic processes, a particularlyinteresting type of landslides on Olkhon is associated withclimatic conditions (cryogenic landslides), i.e., presence ofpermafrost and seasonal, deep freezing of the ground—functionof the active layer. Forms of this type develop on the western shoresof the island, nearly exclusively on the slopes falling directlyinto Baikal, whose angle does not exceed 12°–15°. Such land-slides are most frequent in the central part of the westernshore of the island, near the village of Kharantsy on theKharalday Bay and Bayan-Shungen Bay, forming the KharantsyLandslides Complex (KLC) (Fig. 6).

These landslides vary in surface area from about 40,000 to135,000 m2 (Figs. 7 and 8). Borders between individual forms areusually associated with differences in activity of adjacent forms.

Fig. 4 Southeastern rocky shore ofOlkhon Island, dominated by rockfalls and debris flow

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The landslides are 150–300 m long and 140–460 m wide. Theirheight ranges from 20 to 55 m. Both borders and morphology inthe lower and central parts are conspicuous, while in many forms,the main scarp is poorly defined. Landslides start from smallswellings of the ground, which in the central part, reach a relativeheight of 2 m, emphasized by secondary scarps dissected by nu-merous cracks up to 0.5 m deep.

In the monitored area, two mechanisms of mass movementscan be distinguished, often observed within a single landslideform. The first type, much more strongly reflected in land relief,includes forms associated with the presence of permafrost andwith the process of its decline.

In many cases, in respect of land relief and origin, the land-slides are similar to those described by Leibman (1995) as shearing

slides (active layer detachment failures in ACGR, 1988), as well asactive layer glide and slumps described by Lewkowicz (1988).

Forms developed in this way are characterized by a deep loca-tion of the sliding surface, estimated to reach 3–5 m, so that theyare well defined in the terrain. Scarp height sometimes exceeds5 m. Old inactive, active, and partly reactivated forms often coexistclose to each other.

This has resulted in decreased soil cohesion, caused by melt-water and easier infiltration, and increases the depth of the soillayer influenced by groundwater. The ground, anyway, because ofits structure is highly sensitive to landslides, is now active andstrongly hydrated and plastic at even greater depths, so it is subjectto sliding. This process can be even more intensive if the slidingsurface is located at the upper permafrost table. The potential for

Fig. 5 Example of a small rotational landslide in northeastern part of the island, with an area of about 3,500 m2

Table 1 Listing typical objects of study with the main features

Landslidetype

Area(ha)

Landslidelength (m)

Landslidewidth (m)

Heightrange (m)

Main scarpheight (m)

Overalllandslideangle (°)

Landslidedirection (°)

Impact ofcryogenicfactors

Rotational 0.30 43 80 12 3.0 15 110 No

Rotational 0.15 20 70 8 1.5 12 340 No

Rotational 0.06 30 20 7 1.0 10 100 No

Rotational 0.35 70 57 15 2.5 13 80 No

Rotational 0.27 50 40 20 4.0 15 10 No

Rotational 0.08 35 28 5 1.0 10 20 No

Cryogenic 13.5 300 440 38 0.0 10 10 Yes

Cryogenic 8.5 250 310 40 1.5 14 5 Yes

Cryogenic 5.4 170 280 25 2.0 14 350 Yes

Cryogenic 1.1 150 130 45 4.0 15 350 Yes

Cryogenic 2.5 140 180 25 0.0 13 340 Yes

Cryogenic 8.5 220 390 50 3.5 16 320 Yes

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deformation of many fragments of the slope is decreased orcompletely depleted, so that the process of large deformations ofthe surface is finished. Their remnants are mostly main scarps aswell as secondary and lateral borders in displaced material.

The solifluction flows on the Olkhon Island are still very active,as displacements appear in the active layer, especially in upperparts of slopes at the island shores. Activation and development ofsuch forms are associated with displacement of the surface, thawedlayer of the ground, on the still frozen substrate. This processreaches the depth of 2–1.8 m. Thickness of the active zone in-creases with rising air temperature. Thickness of displaced masswithin the developing landslides is 0.5–1.0 m in the upper, up to2 m in the central, and up to 3 m in the lower part. In many cases,it is difficult to distinguish unambiguously the fragments trans-formed by solifluction from those transformed by skinflows, be-cause it is often impossible to assess the rate of displacement.

An interesting modification is mixed-type landslides, where soli-fluction is combined with rotation. In their upper parts, solifluctionsheets are noticeable, while below them, at a distance of 80–150 m,rotational landslides have been formed in recent years, with well-defined scarps (maximum 5–8 m high). Within landslides of themixed type, a lack of well-defined borders indicates a combinationof sliding and very intensive creeping of the material. Both mecha-nisms of mass movements co-occur within one form.

The comparison of monthly mean values of daily temperature in1951–2011 for the weather stations Khuzhir at Olkhon and Irkutsk(Fig. 9) confirm general trends of climate change in this region. Forboth weather stations, annual mean air temperatures as well as meantemperatures in April–September tend to increase. Annual meantemperature rose 0.37 °C/decade in Irkutsk and 0.29 °C/decade inKhuzhir. In April–September, the changes in air temperature wereslightly lower: 0.25 °C in Irkutsk and 0.31 °C in Khuzhir.

Fig. 6 Kharantsy Landslides Complex, with marked study sites S1 and S2

Fig. 7 Typical landslide of Kharantsy Landslides Complex—study site S1, with an area of about 28,000 m2

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Geological settingThe slope where the complex of landslides (KLC) has devel-oped is composed of Neogene–Quaternary clays, constitutingthe tectonically uplifted lacustrine sediments of Baikal, andcompact and semi-compact residual clays. This complex, about10 km long and 2.0–2.5 m wide, lies directly on the crystallinebedrock.

The soils are characterized by very good sorting. Their majorfractions are clay (46 %) and very fine silt (48 %) (Fig. 10). Thesoils have the following mechanical parameters: plastic limit(PL=35 %), liquid limit (LL=94%), and plasticity index (PI=59 %).High Skempton activity (A=1.26) makes the soils highly sensi-tive to the presence of water. Most of them, in the layer tothe depth of 0.5 m, are in a plastic state. They are characterizedby varied mass density (up to 1.9 g/cm3) and gravimetric watercontent (up to 90 %).

Fig. 8 Typical landslide of Kharantsy Landslides Complex—study site S2, with an area of about 34,000 m2

Fig. 9 Monthly a mean air temperature in 1951–2011 in April–September andannual b mean air temperature in 1951–2011 for the weather stations Irkutsk(red line) and Khuzhir on Olkhon (blue line). Sources of meteorologicaldata for Irkutsk: All-Russian Research Institute of HydrometeorologicalInformation—World Data Center, weather service Reliable Prognosis 5;meteorological data for Khuzhir: monthly meteorological data from the localweather station (in Russian) Fig. 10 Typical grain size distribution of Miocene clays from the study sites

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In more active landslides, seepage is noticeable in the upperpart of the slope, and small water bodies exist in depressions ofsecondary scarps. Because of the presence of impermeable mate-rials in the substrate, water infiltration is difficult. Water canpenetrate down only due to the system of cracks and crevices inthe colluvium.

As mentioned above, landslides are markedly activated duringthawing of the active layer. It is important to assess the scope ofthis process. The cores taken in July and August 2009, in themiddle of summer, confirmed the presence of remnants of sea-sonally frozen soil at the depth of about 2.0–3.5 m. Their temper-ature was −0.2 °C.

Considering the low precipitation on Olkhon, water in the areaof landslides derives mostly from thawing of frozen ground inspring. The top of the still frozen ground becomes an impermeablesubstrate, so that water flows down on its top, and its presence isat the same time, the main cause of water supply to the alreadythawed colluvium. As the ground gradually thaws to greaterdepths, the water starts to infiltrate the colluvium slowly. In spring,landslides are supplied with water through low precipitation andrelatively small surface runoff. Its efficiency increases in Augustand September, when precipitation amounts to 60–100 mm, i.e.,40–50 % of annual precipitation (2010–2012), (Weather Service,http://rp5.ru), with negligible evapotranspiration. The catchmentarea in individual landslides varies in size from 2.6 to 10 ha.

In respect of dynamics, solifluction flows in the studied com-plex are visibly active. During 2 years (2010–2012), horizontaldisplacement on the single form monitored in this respect, in the10-cm subsurface soil layer, ranges from a maximum of 70 mm inthe upper to 30 mm in the central, and 0 mm in the lower part ofthe studied form. Displacement of the ground reached to the depthof 0.64 m in the central and 1.15 m in the upper part of the form.Slope toes of all the forms found here reach to the beach (Fig. 11),at a distance of 0 to 5–10 m, where they are partly washed away bywaters of Lake Baikal. Terminal parts of landslide toes are activecliffs, varying in height from several centimeters to 3 m. Therecorded vertical movements within other landslides in the KLCreached the highest values (3-year mean 0.5–0.6 m) in the zone ofup to 75 m above the cliff edge, while no dislocation was observedin the lower parts of landslides.

Aerial photographs taken in 1953, i.e., before impoundment ofLake Baikal, compared with modern satellite images (2006) show

that, in that period, new landslides appeared within the KLC inareas that were stable earlier, while the existent forms wereenlarged.

The shoreline of Lake Baikal is subject to abrasion within theKLC. This is evidenced by the prevalence of active cliffs developedwithin landslide toes reaching to the beach, separated by relativelynarrow (about 15 m wide) stable cliff fragments, in stable parts ofthe slopes. Landslide toes, after they enter the beach, are graduallywashed away when lake water level is high. Consequently, theshoreline is very irregular, and its location is variable, dependingon the volume of the displaced material that were displaced to thebeach and on the water level in the lake. On the basis of theanalysis of the above-mentioned photogrammetric materials, itcan be concluded that recession of the shoreline, i.e., the extentof shore abrasion, reached 10 m since the impoundment of LakeBaikal in this section (Kozyreva and Radziminovich 2008).

DiscussionThe landslides described here remain closely linked with thepresence of permafrost and the shearing mechanism. Solifluctiontakes place there, but these are mostly rapid processes, includingactive layer detachment failures—both forms described byLewkowicz (1988) as skinflow and active layer glide—and rota-tional slides in the form of slumps.

Permafrost that was found in the study area is associatedparticularly with north-facing, poorly drained slopes. However,many authors (e.g., Washburn 1967; Benedict 1976; Ballantyneand Harris 1994, after Matsuoka 2011) show that solifluction actsalso on slopes where moist fine-grained soils are periodicallyfrozen and thawed, sometimes not associated with the presenceof permafrost. Thus, irrespective of how deep the permafrost tableis located, the climate affects landslide development on Olkhonand is equally important as geological structure.

When comparing the Olkhon landslides, it must be emphasizedthat “results of one piece of research on slopes may be applicableonly to (a) particular set of climatic, geologic, geomorphic, hydro-logic, and vegetative parameters, and these may be representativeof a very small geographic area” (Lewkowicz 1988, p. 327). Most ofthe published studies of cryogenic landslides present results fromcontinuous permafrost zones, often of the ice-rich type. Currently,we have not detected this type of permafrost on Olkhon Island,although Palshin (1968) showed that volumetric water content of

Fig. 11 Landslide toes on the beach, partly washed away by waters of Lake Baikal

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the ground in this area, in the places where permafrost occurs,clearly increased with depth from 27–35 to 40–54 % at the upperlimit of frozen ground. Nevertheless, some similarities can benoticed.

The landslides classified as active layer detachment, presentmostly in the upper and sometimes central parts of the slope,share some characteristics with the forms described by Leibman(1995, 1997) and Lewkowicz (1988), interpreted as skinflow. OnOlkhon, they are thicker than those described on the YamalPeninsula (Leibman 1995, 1997; Khomutov and Leibman 2014),which were 0.25–1.0 m thick. However, Lewkowicz (1988) regarded1.5–2.0 m as typical values for southern areas. Their greater thick-ness on Olkhon results from a milder climate, probably related tohigher temperatures. Also, slope angle is similar at the sites wherethese forms appear: from 12° to as low as 6°.

In the central and lower parts of slopes, internal displacementsof ground correspond mostly to the slide, rather than to the flowtype of movement. They are analogous to the forms classified asactive layer glide and slumps described by Lewkowicz (1988). Thelatter also arise with the participation of the active layer, often onslopes steeper than 10°. Lewkowicz (1988) reported that the activelayer glide appeared to be equivalent to block slide, detachmentfailure, and active layer detachment. Their origin is usually attrib-uted to the presence of ice-rich permafrost, sudden snowmelt,forest fire, or heavy summer rainfall (Lewkowicz 1988; Leibman1995). Moreover, Leibman (1995) emphasized the role of ground icemeltwater, which results especially from rapid thawing of the icepresent in the active layer.

On Olkhon Island, the subsurface layer of the ground is thawedfor 5–6 months, in May–October (Trofimova 2006). In that period,air temperature rapidly increases with maximum values exceeding20 °C as early as in May and as late as at the end of August(Weather Service, http://rp5.ru).

In the development of slumps in the study area, a significantrole is played by abrasive undercutting of the slope toe by watersof Lake Baikal. The process of abrasion was intensified as a resultof the rising of the water level in Lake Baikal, associated with thecreation of the reservoir. A similar phenomenon was described byHughes (1972) in the discontinuous permafrost zone in river val-leys, with the contribution of bank erosion at the slope toe.

In favorable climatic conditions, the presence of fine-grained(lacustrine) sediments promotes development of cryogenic land-slides (Dyke 2004; after Lyle et al. 2005). Lewkowicz (1988) indi-cates that active layer glides may be reasonably widespread onmoderate slopes in fine-grained soils in the boreal forest zone. Inthe literature, however, there are mostly descriptions of sensitivityof fine-grained soils to freezing in areas of ice-rich permafrost, butthis phenomenon is observed also in other areas, where fine-grained sediments are frozen. Thus, this applies also to landformsin the KLC, which develop in Neogene lake clays.

This seems to be of major importance for landslide develop-ment in the KLC, especially that areas with the highest intensity ofgeodynamic processes on the island coincide with the range ofdistribution of Neogene deposits.

Consequently, the question is if further development of suchforms on Olkhon will reflect current changes in permafrost con-dition and in the scope of the active layer, resulting from climatechange. The influence of climate change on permafrost slopes is anissue drawing significant attention today (Dyke and Brooks 2000;

Huscroft et al. 2004; Lyle et al. 2005). On Olkhon Island, however,they may be less spectacular than those observed in the case of ice-rich permafrost.

The observed climate change on Olkhon Island since the mid-1960s, e.g., a rise in air temperature (Berkin et al. 2009) and snowcover thickness (Anisimov et al. 2007; Sherstyukov 2008), resultsin a slow increase in soil temperature (Trofimova 2006). Thedetailed data on soil temperature presented below are based onresearch by Trofimova (2006). As mentioned above, on OlkhonIsland, seasonal freezing of the ground lasts 7 months and reachesto the depth of 2.4–2.8 m, with intensive thawing in summer. Thetemperature of −5 °C reaches to the depth of 1.0–1.3 m, while−10 °C reaches to the depth of 0.3–0.5 m. Maximum temperaturesvary depending on depth: 18–16 °C at 0.2 m, 15 °C at 0.8 m, 10 °C at2.6 m, and 9–7 °C at 3.2 m. Maximum temperature at deeper layersis recorded with a delay of about 30 days/m of depth (Trofimova2006). This indicates that maximum temperature at the groundsurface is recorded in July, while at the depth of 3.2 m, in October.Mean annual temperature in the whole vertical soil profile onOlkhon Island in 1964–2000 was 2.9 °C, and like air temperature,it tends to increase, on average 0.45 °C every 10 years. In the 1990s,the increase was much higher and reached 0.6 °C, whereas meanannual air temperature in that period increased 0.36 °C. Soiltemperature in the lower part of the soil profile (at the depth of3.2 m) remained stable very long. However, its remarkable, con-tinuous increase has been observed since 1989 (Trofimova 2006).

The subsurface layer of the ground is thawed to the depth of upto 1.6 m for 5–6 months, in May–October (Trofimova 2006). Inthat period, air temperature rapidly increases, with maximumvalues exceeding 20 °C as early as in May and as late as at theend of August (Weather Service, http://rp5.ru).

It can be assumed that if the tendency for climate warming ismaintained in the Baikal region (Voropay et al. 2011), soil temper-ature will increase, and the layer of active heat accumulation in theground will be broader as a result of lowering of its lower limit.These changes could cause permafrost degradation, which is al-ready observed in the Baikal region, Mongolia, and China(Gavrilova 2007). Thus, also on Olkhon Island, a rise in landslideactivity can be expected due to permafrost thawing, which leads todeepening of the active layer of the ground as well as due to anincrease in solifluction dynamics.

Important factor for landslide development was the above-mentioned 1.2-m rise in lake level, which caused an increase ingroundwater level in the shore zone. This could locally acceleratethawing of the ground and prolong the functioning of the activezone, thus prolonging also active solifluction. A direct effect of therise in lake water level was also the increased shore abrasion,resulting in removal of the displaced mass from landslide toesand thus causing changes in slope stability and landslide activa-tion. Similar examples were described, e.g., by Wei et al. (2006).The current character of the shore zone of Olkhon Island, e.g., thepresence of stabilized accumulated forms at the shores and ofinactive cliffs along stable slopes that are not subject to landslides,shows that abrasion intensity is diminished. This process currentlytakes place in periods of high water level in the lake or duringstorms and involves mostly the sections of the shore where land-slide activity is currently observed. However, the lack of colluvia incores taken within the beach, only 3–4 m away from landslide toes,indicate that, in general, the whole mass of the displaced material

Landslides

that moved down to the beaches is later washed away, and themaximum scope of landslides is marked by the active cliff devel-oped at the terminal parts of landslide toes.

In summary, as noted by Crozier (2010), current monitoring ofsensitive “geoindicator” sites (e.g., permafrost limits and coast-lines) will continue to provide valuable data on the mechanismsand rates of change, and many pieces of evidence indicate that theOlkhon Island is one of such sites.

ConclusionsResults of this study indicate that many of the investigated landslideson Olkhon Island, especially within the KLC, are cryogenic. Ananalysis of climatic data collected on Olkhon (in this study), andtheir comparison with other data from Siberia, show progressingclimate warming in that part of Asia. In relation to permafrostdegradation and deeper seasonal thawing of active layer, we canexpect further intensive development of landslides on OlkhonIsland, especially of active layer detachment failures, active layerglide, and slumps. Moreover, when the slope toe is cut or disturbedby some other forces, the slope movement may be more significant,and water level fluctuations in Lake Baikal can be such an additionalfactor. Consequently, in the future, the geodynamics of the study areamay be increased, as processes resulting from climate change willenhance one another. Landslides on Olkhon Island, especially thosewithin the KLC, are sensitive, so they will react to the changes mostquickly and need to be monitored.

AcknowledgmentsThis study was part of the project “Exogenous processes ashuman pressure indicators in water bodies and their zone ofinfluence—continuation” (2011–2013). It was partly supported bythe Ministry of Science and Higher Education, Warsaw, Poland(grants N N306 033033 in 2007–2009, N N306 086037, and N N306085037 in 2009–2012) and by the Virtual Institute for IntegratedClimate and Landscape Evolution (ICLEA) of the Helmholtz Asso-ciation. Authors would like to thank V. A. Pellinen from the Instituteof the Earth’s Crust, Russian Academy of Science, for the help inobtaining weather data from the weather station in Khuzhir atOlkhon. Authors would also like to thank anonymous reviewersfrom Landslides for reviewing the paper, which has helped to im-prove it significantly, and they wish to express their appreciation forthe kind support received from the Editor.

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S. Tyszkowski ()) : H. Kaczmarek : M. Słowiński : D. BrykałaDepartment of Environmental Resources and Geohazards, Institute of Geography andSpatial Organization,Polish Academy of Sciences,Kopernika 19, 87-100, Toruń, Polande-mail: sebtys@wp.pl

M. SłowińskiGFZ German Research Centre for Geosciences, Section 5.2—Climate Dynamics andLandscape Evolution,Telegrafenberg, 14473, Potsdam, Germany

E. Kozyreva : A. Rybchenko : V. A. BabichevaLaboratory of Engineering Geology and Geoecology, Siberian Branch,Institute of the Earth’s Crust Russian Academy of Sciences,Lermontov Street 128, 664033, Irkutsk, Russia

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