Late-Holocene evolution of a floodplain impounded by the Smrdutá landslide,Carpathian Mountains (Czech Republic)

Abstract

Landslides affecting narrow mountainous valleys might significantly determine sedimentation dynamics of floodplains. We present here a detailed study of the sedimentary archive within a landslide-controlled impounded floodplain (Smrdutá site, Czech Flysch Carpathians) using geochronological (¹⁴C and ¹³⁷Cs), sedimentological and pollen evidence. A sedimentary sequence deposited above the landslide dam points to three highly discontinuous and instantaneous depositional events dated to 4.6 and 2.0 cal. ka BP, whereas the last cycle started approximately in the 17–18th centuries and has continued to recent times. Such sedimentary pulses characterized by the duration of several decades to a few centuries originated as a consequence of the blockage and/or reduction of the valley floor width by successive long-runout landslides from a slope formed by tectonically and lithologically anisotropic flysch bedrock. Stages of mass movement activity revealed by the Smrdutá landslide correlate well with major humid late-Holocene oscillations suggesting its high sensitivity to century-scale climatic deteriorations. The character of lithological units forming individual sedimentary pulses, erosional hiatuses and sedimentary traces caused by the July 1997 extreme flood indicate a decisive role of large flood events during accretion and erosion of the floodplain-impounded section.

Keywords

Czech Republic Flysch Carpathians landslide dam late Holocene recurrent landslide sedimentary archive

Introduction

Landslides are important agents driving morphological and sedimentary evolution of floodplains of many mountainous rivers (García-García et al., 2011; Korup, 2005; Pánek et al., 2010). On-site imprints of landslides on valley floors may vary from a simple riparian impact, when landslides act as sediment sources, to complete valley obliteration (Korup, 2005). Despite recent progress in the knowledge of the influence of landslides on the morphometry of valley floors and persistency of landslide dams (Ermini and Casagli, 2003; Korup, 2005; Korup et al., 2006), documented sedimentary records and chronology of landslide dam-related impoundments are still relatively scarce (e.g. Borgatti et al., 2007; García-García et al., 2011; Geertsema and Clague, 2006; Pratt-Sitaula et al., 2007). However, landslide-related blockages of valley floors found in regions with otherwise poor Holocene record (and discontinuous alluvial deposits) might provide excellent palaeoenvironmental records imprinted in lacustrine and palustrine deposits (Borgatti et al., 2007; Bryndal et al., 2003; Pánek et al., 2010). Deposits trapped behind landslide dams also contain useful information concerning the timing of causal landslides (or several successive events of landsliding) responsible for valley blockages (Haczewski and Kukulak, 2004; Pánek et al., 2010). This aspect of the study of landslide-related impoundments is especially valuable since appropriate organic material necessary for direct radiocarbon dating of landslide material is usually very scarce (Lang et al., 1999).

We present here results of high-resolution dating of a late-Holocene sedimentary sequence deposited behind the large landslide dam in the Hostýnské vrchy Mts (Czech part of the Outer Western Carpathians). The Czech part of the Outer Western Carpathians lacks any detailed chronological information concerning late-Holocene evolution of slopes and valley floors. Therefore, we attempt here to partly fill this gap for the westernmost section of the Carpathian mountain system. The main aims of our study are (1) to present the sedimentary regime of a mountainous floodplain affected by long-term activity of recurrent landslide(s) and (2) to constrain chronology of a large flysch long-runout landslide in the context of late-Holocene climatic changes. Our intention is to find out whether the history of a single landslide reflects palaeoclimatic settings of the western domain of the Flysch Carpathians, derived previously by various types of proxy data (Margielewski, 2006; Margielewski et al., 2010, 2011; Starkel et al., 2006). Besides these implications, we also evaluate possible limitations of sedimentary archives stored within dynamic settings of landslide-dammed impoundments.

Regional setting

The studied valley impoundment comprises c. a 100 m long and 40 m wide stretch of an alluvial plain of the Bystřička valley found in the Hostýnské vrchy Mts in the eastern part of the Czech Republic (Figure 1). It is situated in the humid temperate climatic zone (elevation 550 m a.s.l.) characterized by mean air temperature c. 7°C and annual precipitation totals around 800 mm. The landslide-dammed impoundment under study was firstly mentioned by Baroň (2007). It evolved behind a c. 18 m high landslide dam (type II according to Costa and Schuster, 1988) that originated as a consequence of the blockage by long-runout landslide(s) with the source on the right valley slope called locally Smrdutá (Figure 1b). The landslide itself is characterized by a length of 670 m, of which nearly 500 m have a character of lobate debris accumulation containing several boulders that reach >10 m in a-axis (Figures 1, 2b, c). The upper limit of the landslide area is represented by a sandstone rocky headscarp up to 20 m in height (Figures 1b, 2a). The landslide body is divided by secondary scarps into several distinct landslide zones (Figure 1b). In accordance with the classification of mass movement performed by the International Geotechnical Societies’ UNESCO Working Party on World Landslide Inventory (Dikau et al., 1996), the Smrdutá slope failure is a compound landslide with signs of both translational and rotational movements. Underlying bedrock consists of Cretaceous–Eocene flysch of the Magura Unit where the headscarp is formed by thickly bedded sandstones and conglomerates of the Rusava Member belonging to the Zlín Formation, whereas a major part of the accumulation zone is underlain by sandstones and claystones of the Hostýn Member of the Soláň Formation (Stráník et al., 1999) (Figure 1b). The contemporary impoundment surface is characterized by a periodically inundated wetland overgrown with Alnus glutinosa and Sambucus nigra (Figure 2d). Adjacent slopes (including the landslide body) are covered by a forest composed of Fagus sylvatica with an admixture of Acer pseudoplatanus, Ulmus glabra, Picea abies, Sorbus aucuparia and Abies alba.

Figure 1.

(a) Localization of the studied area within the NW part of the Outer Western Carpathians (digital elevation model SRTM 3′′ used as background). (b) Geological settings of the Smrdutá landslide and its surrounding (Stráník et al., 1999) with an inserted cross-section of the slope failure. 1: Sandstones and conglomerates of the Rusava Member belonging to the Zlín Formation (Eocene); 2: sandstones and claystones of the Hostýn Member belonging to the Solánˇ Formation (Upper Cretaceous–Eocene); 3: landslide headscarps (a: rocky; b: soil-mantled); 4: landslide bodies graded in accordance with their relative ages (a: oldest landslide; c: youngest landslide); 5: swampy surface of landslide-dammed floodplain; 6: floodplain; 7: large (>10 m) rock block; 8: stony accumulation. (c) Thickness of predominantly fine-grained deposits accumulated because of blockages by successive landslides from the Smrdutá site.

Figure 2.

Typical morphological features of the Smrdutá landslide and adjacent impounded floodplain. (a) Rocky headscarp; (b) giant rock blocks in the middle part of the landslide body; (c) stony accumulation in the area of the landslide dam; (d) impounded swampy floodplain just above the landslide dam.

The fold-and-thrust belt of the Outer Western Carpathians consists of a flysch accretional wedge originated during late-Miocene compressive tectonics, when nappe stacks including predominantly Cretaceous and Palaeogene strata were thrust over the Northern European Platform (Danišík et al., 2008; Menčík et al., 1983). Anisotropic flysch strata consisting of alternating competent sandstones and plastic shales with high density of discontinuities (bedding planes, joints and faults) are highly prone to landsliding, especially because of elevated pore-water pressures during extreme hydrometeorological events (Krejčí et al., 2002; Margielewski, 2006; Margielewski et al., 2011). The surroundings of the study area were heavily affected by landslide activity especially during heavy rainfall in July 1997 (five-day precipitation totals reached 375 mm in the neighbouring Valašské Meziřící station), when more than 1500 landslides were activated in the Czech part of the Western Carpathians (Krejčí et al., 2002). Other historical examples of landslides in the region include events in January 1919 (rapid snowmelt and rainfalls), August 1967 (consequence of long-term elevated precipitation totals), April 2006 (rapid snowmelt and rainfalls) and May 2010 (heavy rainfalls).

Materials and methods

Coring and sampling

The depth of the impounded valley above the landslide dam was checked using a probe in spring 2010 to reconstruct the thickness of deposits. The thickest sedimentary section was chosen for coring and complex analyses involving dating, and sedimentological and pollen analyses. The deepest part of the impoundment (Figure 1c, 49°22′15.42″N, 17°45′09.97″E, 555 m a.s.l.) was drilled by means of a percussion Eijkelkamp sampler with a synthetic foil liner (63 mm diameter). The total 473 cm long section contained lacustrine, palustrine, colluvial and alluvial deposits. Further coring was impossible since the boulder (probably channel-type) accumulation could not be penetrated. Additional sampling using an Eijkelkamp peat sampler (60 mm diameter) was performed in the uppermost 100 cm thick layer in order to obtain as much as possible of the youngest uncompressed deposits. The core sections were cut in the laboratory into 2.5 cm thick slices for further analyses. A total of nine samples of organic remnants (including eight plant fragments and one Coleoptera remnant) were carefully selected for radiocarbon dating.

Dating

An age–depth model of the impounded sedimentary section was built for deposits older than ~150 years using radiocarbon (¹⁴C) dating, whereas in case of the youngest deposits (the upper c. 100 cm thick layer of the sequence), the activity of ¹³⁷Cs and ²¹⁰Pb radionuclides was used. Results of the radiocarbon and ¹³⁷Cs dating enabled the creation of the age–depth curve using the P-sequence deposition model in the OxCal v 4.1.7 software (Bronk Ramsey, 2009).

Radiocarbon dating (seven AMS and one conventional LSC) was performed in the Gliwice Radiocarbon Laboratory of the Institute of Physics, Silesian University of Technology, Poland (samples marked as GdA and GdS in Table 1). One additional AMS dating was carried out at the University of Georgia, Center for Applied Isotope Studies, USA (sample marked as UGAMS in Table 1). Radiocarbon dates were converted into calendar ages using IntCal 09 calibration curve (Reimer et al., 2009) in OxCal v 4.1.7 software (Bronk Ramsey, 2009; Table 1). Calibrated radiocarbon dating results expressed as medians of probability density functions are indicated as cal. BP (before the year 1950) in this study. For calculations of linear sedimentation rates, we used single estimates where medians of calibrated radiocarbon probability density functions were used as appropriate central values of calibrated dates (Engel et al., 2010; Telford et al., 2004).

Table 1.

Radiocarbon dates obtained in this study.

Lab. code	Depth (cm)	Dated material	¹⁴C age (BP)	Cal. age (95.4% range, cal. BP)	Median age (cal. BP)	¹⁴C dating method^a
GdS-1094	473	Wood	4065 ± 80	4840–4350	4580	LSC
GdA-1994	385	Plant piece	4015 ± 30	4570–4410	4480	AMS
GdA-1995	343	Charcoal	4030 ± 30	4580–4420	4480	AMS
GdA-1996	326	Leaf	3990 ± 30	4530–4410	4480	AMS
GdA-1997	257	Plant piece	2075 ± 20	2120–1990	2040	AMS
GdA-1998	202	Cone piece	2015 ± 30	2050–1880	1960	AMS
GdA-1999	190	Leaf	2020 ± 30	2060–1890	1970	AMS
UGAMS 8590	143	Coleoptera fragment	1900 ± 40	1930–1720	1850	AMS
GdA-2000	101	Cone piece	130 ± 30	280–0	130	AMS

AMS: Accelerator Mass Spectrometry method; LSC: Liquid Scintillation Counting method.

¹³⁷Cs activity measurement helped to constrain depositional rates for the uppermost 50 cm thick layer of the profile. A total of 20 measurements (for each 2.5 cm slice) were determined through laboratory gamma emission at 662 kEv in the Department of Geological Sciences (Masaryk University). The mass activity of ¹³⁷Cs was measured using a PCAP (Nucleus, USA) laboratory gamma-ray spectrometer with a NaI (Tl) scintillation detector, 9 Bq/kg detection limit and 30 min measurement time. ¹³⁷Cs is an anthropogenic radionuclide occurring in the environment since the 1950s and it is still easily detectable in soil samples (Appleby, 2008). In the case of nine samples, the dating was completed from the interval of 0–140 cm also with unsupported ²¹⁰Pb activity measurement in the Cosmogenic Isotope and Radiochemistry Laboratory, GNS, New Zealand (performed by gamma ray spectroscopy using an Ortec HPGe GWL-110230 well detector).

Regarding the results of sedimentological, pollen and chronological analyses, the studied sedimentary section was visually subdivided into eight individual lithological units reflecting particular facies regimes and physical properties. The units were chronologically determined according to the Holocene stratigraphical subdivision of Mangerud et al. (1974). Lithostratigraphy and sedimentation rates of the youngest section determined by ¹³⁷Cs dating method (c. since 1954) were related to discharge data (maximum annual discharge Q _max) of the nearest hydrological profiles on streams monitored by the Czech Hydrometeorological Institute.

Physical composition and pollen analysis

Basic physical properties of sediments were determined for each 2.5 cm thick slice of the studied section applying the methods of loss on ignition (LOI) at 550°C, particle-size distribution and magnetic susceptibility (χ).

LOI was measured in order to derive the percentage of organic/minerogenic material. The measurement was conducted in a muffle furnace at a temperature of 550°C in accordance with a standard methodology proposed e.g. by Heiri et al. (2001). Particle-size distribution was measured both by laser diffraction (using wet dispersion) and wet-sieving methods. Laser diffraction measurement was performed for <2 mm fractions by Mastersizer 2000E from Malvern company supported by Mastersizer 2000 v. 5.40 software. Wet sieving was conducted for coarser fractions using Fritsch 3a PRO equipment accompanied by Autosieb software. Standard granulometric indexes – mean grain size and sorting index (standard deviation) were calculated according to the Arithmetic Method of Moments within the GRADISTAT software and expressed in μm (Blott and Pye, 2001). Mass magnetic susceptibility was determined using Kappabridge KLF-4 (AGICO Ltd.) and recalculated to sample mass.

Pollen analysis was applied for sediments at a 5 cm interval in the uppermost 100 cm thick layer of the section and a 10 cm interval for deeper part of the core. Pollen samples were prepared (3 g sediments) using standard procedures (Berglund and Ralska- Jasiewiczowa, 1986). The results of pollen analysis are presented as a percentage pollen diagram. The percentage values were calculated on the basis of arboreal and non-arboreal pollen sum (AP+NAP) excluding only demonstrably aquatic taxa and spore plants. The percentages of the spores (ferns and mosses) were calculated on the basis of AP + NAP + sum of corresponding spores = 100%. Besides pollen quantity, the study included stomata of plant, algae, fungi (hyphae and spores of fungal parasites which live in association with the host plants, commonly the roots) and Rhizopoda (amoebae fauna, Booth, 2002; Ogden, 1981; Opravilová and Hájek, 2006; Schönborn and Peschke, 1990). Charcoal particles were found in samples at the depths of 150–5 cm. The concentration of pollen in samples (total counts) is shown on S = 4 cm². These data reveal the speed of sediment accumulation, hiatus and the stages of high hydrological activity. Corroded and broken pollen is presented in the form of a corrosion curve. The diagram was zoned visually to local pollen assemblage zones (LPAZ) on the basis of both the presence and abundance of ecologically important taxa.

Results

Chronology and sedimentation rates of the impoundment

Radiocarbon ages obtained in the studied section are clustered in three pronounced time intervals, which imply that the impoundment was filled rapidly during three distinct and chronologically separated sedimentary pulses (Table 1, Figure 3).

Figure 3.

Age–depth model and lithological scheme of the studied sedimentary sequence. Grey italic numbers denote calibrated median ages (topmost numbers) and particular two-sigma probability distributions. Hiatuses are denoted by dotted lines. Sedimentary facies: 1: alluvial channel deposits; 2: landslide/earthflow diamict; 3: high-energy sandy deposits; 4: organic-rich silts deposited in swampy and/or shallow limnic environment; 5: alluvial overbank deposits; 6: sandy inclusions; 7: erosional contacts between lithological units.

The oldest sedimentary sequence of 473–320 cm was dated by one conventional LSC and three AMS radiocarbon dating procedures to the time interval between 4580 and 4480 cal. BP, which corresponds to the early Subboreal (SB1) chronozone. All dated samples reveal very similar ages that overlap in two-sigma ranges. This indicates very fast accumulation at a depositional rate of ~1.53 cm/yr. The second cluster of radiocarbon ages also overlapping in two-sigma ranges (four AMS dating procedures) covers an interval of 255–107 cm and reveals the time range of 2040–1850 cal. BP. This second sedimentary pulse characterized by the sedimentation rate of ~0.78 cm/yr took place in the terminal part of the early Subatlantic (SA1) chronozone. The onset of the third (most recent) sedimentary pulse represented by an interval of 107–0 cm was determined using one AMS dating procedure to the age of 130±30 ¹⁴C BP. Similarly to other calibrated radiocarbon ages coming from the last 150 years, this age shows high scatter of probabilities (see e.g. Roberts, 1998; Walker, 2005). The age was therefore verified via comparison with pollen data where the rise in the percentage of NAP pollen as a consequence of extensive deforestation during the 17th century represents a distinct independent time marker. This shows that two-sigma calibration of the age falling to the interval of ad 1675–1778 is the most reliable interval of the beginning of the third sedimentation pulse. Estimation of the sedimentation rate calculated considering this uncertainty gives the value 0.32–0.46 cm/yr.

The youngest sedimentary sequence was chronologically refined by the measurement of the activity of ¹³⁷Cs and ²¹⁰Pb radionuclides (Figure 4). The curve of the ¹³⁷Cs mass activity created for the uppermost 50 cm thick layer of the profile shows a distinct peak in the depth of 20 cm below the surface. We attribute this elevated concentration of ¹³⁷Cs to the Chernobyl disaster of ad 1986, whereas a secondary peak identified in the depth of 45 cm could be related to c. ad 1963. Most sedimentary sections of the world (e.g. Humphries et al., 2010; Mizugaki et al., 2006; Saravan Kumar et al., 1999; Yan et al., 2002) reveal two more or less distinct peaks of ¹³⁷Cs concentration – at c. ad 1963 (maximum intensity of thermonuclear weapon tests) and at c. ad 1986 (Chernobyl catastrophic explosion). The most pronounced peak of the ¹³⁷Cs concentration in Central Europe is usually related to atmospheric fallout from the Chernobyl catastrophic explosion of ad 1986 (Nehyba et al., 2011). Regarding the position of the ad 1986 peak at a depth of 20 cm, the average sedimentation rate of the last three decades is c. 0.83 cm/yr. Results obtained by ¹³⁷Cs dating were completed with the determination of ²¹⁰Pb activity for the upper 150 cm of the profile. However, since the concentration of unsupported ²¹⁰Pb in our sedimentary section does not fit the exponential curve, it fails to be reliably converted to any chronological model. Results of ²¹⁰Pb concentration measurement were therefore excluded from the age–depth model and they only serve partially to the discussion of the results.

Figure 4.

Selected physical/sedimentological properties of the uppermost 50 cm layer of the studied sedimentary sequence and its possible correlation with the flood record (Q _max).

Lithological units

Individual lithological units are described from the basal part of the section upward and are marked with numbers 1–8 (Figure 3).

Unit 1 (>473 cm)

Basal unit 1 was sampled only in its uppermost section because it consists predominantly of poorly sorted gravels (>50%) and pebbles preventing the penetration to lower sections using a percussion corer (Figure 5). Individual clasts (some of them >5 cm in a-axis) are rounded or subrounded, which points to their fluvial origin. With the highest probability, the deposition represented a gravel bar which was accumulated before >4580 cal. BP as it is indicated by the lowermost radiocarbon-dated sequence from overlying unit 2.

Figure 5.

Sedimentological properties of the studied sedimentary section.

Unit 2 (473–320 cm)

The overlying unit is represented by dark grey sandy silt with negligible clay content (<6%) (Figure 5). The lower part of this unit (473–440 cm) can be characterized as massive silt containing a low percentage of sand (<10%). The upper part of the sequence (460–315 cm, percentage of sand >15%) has a laminated texture with several intercalations of sandy deposits indicating multiple minerogenic delivery of flood deposits into an aquatic, shallow lake environment. As for these intercalations, there is an especially distinct 2 cm thick layer of poorly sorted coarse sand situated in the interval of 336–338 cm. The laminated sequence revealing a record of repeated hydrometeorological events is also well documented by multiple oscillations of LOI and χ curves. The whole (153 cm thick) unit 2 was deposited very quickly, most likely within several decades between 4580 and 4480 cal. BP (four radiocarbon dates coming from various depths of the sequence are within two-sigma error limits), i.e. in humid conditions of the early Subboreal (SB1) chronozone. This indicates the first generation of landslide damming of the Bystřička valley that can be detected in the studied sedimentary section.

Unit 3 (320–255 cm)

The third unit is poorly sorted grey sediment of predominantly polymodal grain-size distribution (Figure 5). Lower (315–298 cm) and upper (265–255 cm) parts of the unit are characterized by silty gravels enclosing sandy silt with scattered subangular clasts (298–265 cm). The whole section reveals a relatively high (5–8%) content of clay. On the basis of granulometry, the sediment is characterized by very low LOI (<5% of organic matter) and a pronounced peak on the magnetic susceptibility curve. As revealed by a hiatus in the pollen record (see the next section), unit 3 lies on the underlying deposits with unconformity (c. 2.5 ka of missing sedimentary record). From the point of view of chronology, unit 3 deposits could be placed just before the onset of sedimentation of the overlying unit, i.e. 2040 cal. BP. The sedimentological properties of unit 3 suggest that it is a distal facies of landslide/earthflow, which was responsible for the second generation of blockage in the studied stretch of the Bystřička valley.

Unit 4 (255–213 cm)

This unit is represented by dark grey sandy silt with a relatively high content of organic matter (20–25%) and low χ values (Figure 5). This granulometrically homogenous section can be interpreted as palustrine mud, relatively quickly deposited as a consequence of the second generation of landslide damming. An AMS date from the bottom (2040 cal. BP) of this sequence constrains the second blockage of the valley to the early Subatlantic chronozone (SA1-2). The whole section was deposited within several decades (c. 80 years), which is supported by dating the top layer of deposits to 1960 cal. BP.

Unit 5 (213–185 cm)

Unit 5 consists predominantly of poorly sorted grey silty sands with an admixture of gravel (<6%) accumulated instantaneously c. 1970 cal. BP. The sandy layer is characterized by a very low content of organic matter (LOI<10%) and relatively low χ values (Figure 5). This intercalation is formed by very distinct high-energy sediment (sensu Kotarba, 1996), which was accumulated quickly, most likely during one flood event at the termination of the early Subatlantic (SA1) chronozone. Instantaneous deposition is also evidenced by two nearly identical AMS ages (overlapping in one sigma error limits), which delimit upper and lower boundaries of the unit (1970 and 1960 cal. BP, respectively).

Unit 6 (185–107 cm)

Grey sandy and clayey sandy silt reflects a return to calm backwater sedimentation, predominantly in shallow lake conditions. The section is characterized by gradual upward refinement of the sediment (25% sand in the lower part, 10% sand in the top zone), decreasing percentage of organic material and increasing χ values (Figure 5). The uppermost part of the section is formed by c. 10 cm thick minerogenic layer consisting of silt with a slightly elevated percentage (6–7%) of clay and a low content of sand (<10%). Unit 6 presents the continuation of sedimentation of units 4 and 5 and it was deposited between 1970 and 1850 cal. BP.

Unit 7 (107–17 cm)

Gray sandy silt of unit 7 situated in the interval of 107–17 cm is characterized by a graded sequence with a high content of sand (30–45%) in its basal part and upward refinement tendency with <25% of sand in the upper half of the section (Figure 5). The deposits have typically raised LOI around 25%. Magnetic susceptibility values reveal negligible fluctuations in the majority of the unit, except for the interval of 20–17 cm showing a pronounced exponential increase of χ. The onset of the sedimentation of unit 7 can be placed at 130±30 ¹⁴C BP (two-sigma range: ad 1675–1778) equalling the culmination of the ‘Little Ice Age’ (Grove, 1988). A hiatus in the pollen record and a chronological gap between the radiocarbon dates suggest that the lower boundary of unit 7 is erosional. A level situated c. 3 cm below the top of the sequence was determined by ¹³⁷Cs peak to ad 1986. Sedimentologically, the deposits of unit 7 can be characterized as overbank facies formed on the surface of mire from the adjacent Bystřička river channel during flood-generated inundations.

Unit 8 (17–0 cm)

The uppermost sequence formed by gray, poorly sorted sandy silt overlies unit 7 with distinct unconformity. In comparison with the upper part of the underlying unit 7, the topmost sediment is characterized by significantly lower LOI (<15%) and a higher content of sand (>30%) showing a gradual increase in the sand percentage upward. In accordance with a tendency to particle-size coarsening, the deposits reveal a pronounced increase in χ values attaining the highest values of the whole sedimentary section (Figure 5). Chronologically, unit 8 postdates the year ad 1986.

Pollen record

Here we describe individual local pollen assemblage zones defined on the basis of the interpretation of the pollen diagram displayed in Figure 6.

Figure 6.

Percentage pollen diagram of the studied sedimentary section. Wavy lines on the right side of the diagram mark hiatuses. For explanations of the sedimentary log see Figure 3.

LPAZ – Pal-1(a, b): Picea-Q. mixtum (473–320 cm)

The main tree pollen is Picea (max. 22.8%), Tilia (28.8%), Quercus (17.8%), Acer (14.7%), Corylus (16.5%) and also Fagus (16.4%), and Carpinus (6.2%). Abies (0.9–7.7%) is present constantly. The NAP is presented by the pollen of wet herbs (Ranunculus, Cyperaceae, Poaceae) and ruderal plants (Artemisia and Chenopodiaceae). In the sediments of this zone (Pal-1a), there are semi-aquatic plants (Thypha latifolia, T. angustifolia, T. minima, Alisma, and Limosella aquatica), which grow in wetland habitats such as marshes, mud and wet sand close to water, and partly in water as deep as 0.5–1.0 m. Spores of various ferns are marked. Human activity and/or presence of landslide-deforested open spaces are evidenced by Rumex acetosa/acetosella, Cichoriaceae, Plantago lanceolata, Sedum, and Astragalus type pollen and signal pollen grains of Centaurea cyanus and Spergularia type. Increased pollen values of Salix were identified at the end of the zone (Pal-1b), while the pollen of water vegetation had disappeared. Fungi (Glomus, Herpotrichia, сonidia of Bipolaris sorokiniana), fern sporangia, stomata and corroded pollen were found at the beginning, in the middle and at the end of this zone. Pollen concentration falls in these parts. Pediastrum boryanum and Rhizopoda (Clathrulina, Assulina) appear occasionally.

LPAZ – Pal-2: Abies-Fagus (255–185 cm)

The value of Fagus reaches 38.7% in AP and that of Abies 48.8%. The pollen curves of Acer, Tilia, Fraxinus and Ulmus are closing. The values of fern spores increase considerably, while the values of herb pollen decrease. Sporadic grains of Rumex acetosa/acetosella and Urtica point to the presence of humans or naturally deforested parts of the landscape. Fungi (Glomus, Tilletia) and corroded pollen is detected.

LPAZ – Pal-3: Abies (185–100 cm)

The pollen values of Abies (59%) reach their maximum, whereas the pollen values of Fagus fall to 6.9%. The presence of partly deforested open landscape is identified by the increase in the pollen of Rumex acetosa/accetosella, Cichoriaceae, Plantago lanceolata, Plantago major/media and Fagopyrum. The values of semiaquatic plants (Typha latifolia. T. angustifolia, T. minima, Alisma) and aquatic plants (Lemna, Nymphaea) increase again.

LPAZ – Pal-4: Fagus-Abies-NAP (100–73 cm)

The proportion of Fagus pollen increases abruptly to 46%, while Abies decreases to 19%. The value of Poaceae and other herbs in NAP (18.3%) increases, cereal pollen appears (Cerealia undif. pollen, Avena/Triticum and Secale, Centaurea cyanus). The pollen of Plantago lanceolata, Rumex acetosa/acetosella, Urtica, Ranunculus and Cichoriaceae is present constantly. The pollen of Salix, Sambucus, and Juglans also appears. The pollen of aquatic plants is absent.

LPAZ – Pal-5: Pinus-Abies-NAP (73–22 cm)

Pinus (41.4%), Abies (21.4%) and NAP (28.9%) dominate. The pollen curve of Salix rises gradually. NAP (40.0%) includes considerably increasing values of Poaceae, Cyperaceae, Equisetum and ruderal herbs (Artemisia, Chenopodiaceae, Brassicaceae, Cichoriaceae, Asteraceae, Selena). The pollen value of anthropogenic indicators (Cerealia undif. pollen, Avena/Triticum and Secale, Centaurea cyanus, Fagopyrum, Polygonum aviculare, Cannabis, Sedum, Plantago lanceolata, and Rumex acetosa/acetosella) also continues to increase. Remains of Equisetum, fungi and Rhizopoda were found in sediments.

LPAZ – Pal-6: Alnus-Pinus-Picea-NAP (22–0 cm)

The pollen values of anthropogenic herbs decrease (NAP 25.4%). The main tree pollen includes Alnus (36.0%), Pinus (29.0 %), and Picea (25.0 %) with lower values of Abies, Fagus and Quercus pollen (the sum does not exceed 15%). There is an increased value for fern spores.

Discussion

Implications for sedimentary dynamics

The studied sedimentary section of landslide-dammed impoundment in the western part of the Flysch Carpathians (Hostýnské vrchy Mts) reveals that an almost 5 m thick sequence of late-Holocene, predominantly palustrine, shallow lake and fluvial deposits accumulated during three distinct, chronologically limited sedimentary pulses. Such instantaneous depositional events took place before c. 4.6 and 2.0 cal. ka BP, whereas the last sedimentation cycle started in the 17–18th centuries and has continued to modern times. The recent depositional cycle was probably induced by incomplete damming of the valley (occlusion), which reduced the energy of the stream and led to enhanced aggradation of slackwater facies. Since the core under investigation terminates at the imbricated layer of alluvial deposits containing large clasts, the presence of older palustrine/lacustrine cycles in deeper levels (i.e. >5 m) cannot be discounted. The number of inferred landslide blockages should thus be considered as a minimum.

The sedimentary record of the impoundment is discontinuous, showing both accumulation and erosional episodes. It reveals the dynamic setting of a mountainous alluvial plain controlled by changes in the local base level represented by a landslide toe episodically damming the valley. Highly episodic sedimentation behind the landslide barrier and a relatively short longevity of the dam reflects typical behaviour of landslide-dammed lakes which have so far been described in many places throughout the world (Costa and Schuster, 1988; Ermini and Casagli, 2003, etc.). Our detailed study of the dammed alluvial plain suggests that sedimentation behind such barriers could be diverse, including palustrine and lacustrine muds with frequent intercalations of high-energy sandy flood deposits. Specific sedimentary dynamics is evidenced also by the presence of several erosional contacts between lithological units (Figure 3). Inferred sedimentation rates in the impoundment are an order higher than in landslide peat bogs (Margielewski, 2006) and several times higher than in the case of vertical accretion in typical Central European alluvial plains (e.g. Stolz, 2011). It can rather be compared with recent sedimentation in artificial water reservoirs (e.g. Nehyba et al., 2011). Furthermore, the inferred sedimentation rates in the impoundment should be considered minimal, as erosion contacts of individual sedimentary pulses show a lack of significant ortions of individual sedimentary sequences. Similar to high-mountain environments (Hewitt, 2006), our example shows that local obstacles can pose major factors modifying the sedimentation regime within mountainous alluvial plains.

Older fine-grained sedimentation cycles involving 4.6 and 2.0 cal. ka BP events originated as a consequence of landslide damming of the valley floor. Rapid sedimentation of up to ~century-long cycles involving dark sandy silts reveals a shallow lake (<1 m as indicated e.g. by the presence of Typha latifolia, T. angustifolia, T. minima, Alisma, Limosella aquatica) and/or swampy depositional environments. The variation in pollen concentrations is other evidence of fast accumulation and siltation of the reservoir. Both sedimentary pulses involve pollen spectra containing species typical of open deforested landscapes (e.g. Artemisia, Chenopodiaceae, Chamaenerion, Rumex acetosa/acetosella, Cichoriaceae, Plantago lanceolata, Sedum, Astragalus, etc.). Beside the presence of human activities, these pollen signals to a greater degree reflect the clearing of forests by successive landslide activity.

The existence of relatively thick overbank deposits (void of aquatic pollen spectra) characterizing the youngest sequence suggests that the landslide body also affected sedimentation within the alluvial plain via the downstream narrowing of the valley bottom. However, the youngest phase of accelerated sedimentation starting in c. the 17–18th centuries should, at least partially, also be attributed to increased human activity connected with the Wallachian colonization of the Carpathians (Jančík, 1958; Kukulak, 2003). During this event significant portions of hillslopes in the region were deforested for sheep grazing, which caused accelerated gullying and sheet erosion (Stankoviansky, 2003). A pronounced increase of the percentage of NAP pollen (Poaceae, Cyperaceae, Asteraceae, Artemisia, Chenopodiaceae), the presence of species indicating anthropogenic activity (Cerealia undif. pollen, Avena/Triticum and Secale, Centaurea cyanus, Fagopyrum, Polygonum aviculare, Cannabis, Sedum, Brassicaceae) together with the occurrence of charcoal and corroded pollen strongly evidence that lithological units 7 and 8 were deposited under a significant influence of man in the conditions of accelerated sheet/gully erosion. A distinct change in sedimentation (delivery of minerogenic deposits, particle-size coarsening, increase in the sedimentation rate and anomalously high χ) within the last sedimentation pulse is clearly visible in case of the uppermost 17 cm thick layer of the studied section (unit 8). This sedimentary unit postdates a pronounced peak of ¹³⁷Cs activity determined to ad 1986. The base of this unit could probably be correlated with the exceptional flood event of July 1997, which was the most important hydrometeorological extreme in the Czech part of the Western Carpathians of the 20th century (Krejčí et al., 2002). Culmination discharges in neighbouring rivers measured during this event exceeded Q _max for the period of 1950–2010 two or three times (Figure 4). The distinctiveness of the youngest deposits formed mainly as a consequence of the 1997 event shows a major role of extreme floods during the formation of impounded alluvial stretches. Erosion of older deposits and an exceptionally high accumulation rate could partly explain low near-surface ²¹⁰ Pb activity and the non-exponential character of its relation with the depth (see, e.g., Saravan Kumar et al., 1999). When compared with older depositional evidence, the catastrophic flood of July 1997 left one of the most important traces within the studied sedimentary section.

Magnetic susceptibility variations measured through the section reveal a relationship with the sediment lithology. The clayey horizons show higher χ values as a result of a higher concentration of magnetic minerals derived either from the Palaeogene bedrock or from eroded soil horizons developed in the Bystřička Stream catchment. Anomalous magnetic enhancement detected in the topmost 20 cm thick layer of the studied section is related to increased concentration of anthropogenic magnetic pollution produced in nearby Ostrava smelting works during the last century. Magnetic particles from the air settled on the surface in the stream catchment were later eroded and re-deposited probably during the 1997 flood event.

Implications for landslide chronology

The character of the sedimentary sequence developed behind the landslide blockage together with overall geomorphic properties of the Smrdutá slope failure suggest the existence of successive catastrophic slope failures which originated during the events dated to c. 4.6 and 2.0 cal. ka BP. The onset of the last event was determined to the 17–18th centuries.

Multiple recurrences of catastrophic, long-runout landslides are not uncommon and have also been described from other regions (Aa et al., 2007; Bisci et al., 1996; Lee et al., 2009; Ocakoglu et al., 2009). Some of these mass movements are periodically accelerated by earthquakes (Ocakoglu et al., 2009). However, there is also a potential for highly localized slope instabilities in seismically nearly inactive settings such as the Outer Western Carpathians (Pánek et al., 2011). In such regions, the presence of favourably oriented geological structures in combination with tectonically weakened and weathered bedrock might provoke recurrent slope movement periodically triggered by intensive and/or prolonged rainfalls (Hartvich and Mentlík, 2010; Margielewski et al., 2011; Pánek et al., 2011). In such circumstances, dated landslides might serve as relevant palaeoclimatological proxies as has been demonstrated by numerous examples from around the world (e.g. Alexandrowicz and Alexandrowicz, 1999; Bookhagen et al., 2005; Borgatti et al., 2007; Gioia et al., 2011; Margielewski, 2006; Margielewski et al., 2010, 2011; Soldati et al., 2004, etc.).

Stages of mass movement activity revealed by the Smrdutá landslide are strongly related to major late-Holocene humid oscillations suggesting its high sensitivity to century-scale climatic deteriorations (Figure 7). Activations dated to 4.6 and 2.0 cal. ka BP together with the last event determined to the interval spanning from the 17th to 18th centuries correlate with cold and, in Central Europe, generally humid periods of the late Holocene. The landslide event dated back to 4.6 cal. ka BP (early Subboreal – SB1) corresponds generally with the onset of the Neoglacial period and could be correlated with one of the most important global cold events stated by Wanner et al. (2011) to 4.8–4.5 cal. ka BP. This event was also accompanied by a depression of the δ¹⁸0 recorded within the GISP 2 ice core (Grootes et al., 1993). In Central Europe this period was characterized by a cold and very humid climate evidenced by high water levels of lakes (Magny, 2004; Pazdur et al., 1995; Ralska-Jasiewiczowa, 1989), flood activity (Starkel et al., 2006), landslides (Margielewski 2006, Prager et al., 2008) and increased delivery of minerogenic material into peat bogs (Margielewski, 2006; Margielewski et al., 2011).

Figure 7.

Correlation of the landslide activations of the Smrdutá landslide with regional and global proxy data (data sources: 1: chronozones according to Mangerud et al., 1974; 2: Starkel et al., 2006; 3: Magny, 2004; 4: Margielewski, 2006; 5: Margielewski et al., 2011; 6: Grootes et al., 1993).

Although the second landslide event determined to c. 2.0 cal. ka BP is not directly related to any global climatic event, the evidence from the Central Europe suggests correlation with the extremely humid beginning of the Subatlantic chronozone (SA1) documented by another stage of high lake level stands, flood activity and contamination of peat bogs by minerogenic deposits (Magny, 2004; Margielewski, 2006; Margielewski et al., 2011; Ralska-Jasiewiczowa, 1989; Starkel et al., 2006). Margielewski (2006) reports eight dated bedrock landslides from the territory of Polish Flysch Carpathians to the time interval of c. 2.2–1.8 cal. ka BP.

The last stage of the landslide movement determined to the 17–18th centuries occurred in one of the most significant Holocene periods of climate deterioration corresponding with the culmination of the LIA (Roberts, 1998; Wanner et al., 2011). However, in contrast with glaciated high mountains (e.g. Holm et al., 2004), it is not certain whether the LIA really represented a period of regionally enhanced landslide activity in Flysch Carpathians (as is the case for other medium–high mountains in Central Europe). This uncertainty is caused by a still relatively low number of numerically dated landslides in this region. Despite this, the LIA activation of the Smrdutá long-runout landslide indicates its potential for future activation in current natural conditions.

Conclusions

The sedimentary sequence deposited above the Smrdutá landslide dam in the western part of Flysch Carpathians (Czech Republic) reveals a record of three highly discontinuous depositional events dated to 4.6 and 2.0 cal. ka BP, whereas the last cycle started approximately in the 17–18th centuries and has continued up to recent times. Such sedimentary pulses characterized by the duration in the order of several decades to a few centuries originated as a consequence of the blockage and/or reduction of the valley floor width by successive long-runout landslides from the slope formed by tectonically weakened and lithologically anisotropic flysch bedrock. Periodic activation of the landslide body correlates both with global phases (events dated to 4.6 cal. ka BP and LIA) and Central European phases (2.0 cal. ka BP event) of climate deterioration connected in the studied region mainly with long-lasting and/or high intensity rainfall. Our example is thus another example of the high sensitivity of mountain landslides to climatic changes. Highly dynamic sedimentation within the blocked impoundment presented by depositional changes and hiatuses suggests a major influence of the longevity of the landslide dam and erosive/accumulation potential of large flood events. This is evidenced by an abrupt depositional change connected with the extreme event of July 1997, which left one of the most distinctive traces within the whole sedimentary sequence. In comparison with this event, similar high-energy flood deposits have also been identified within ancient sedimentary pulses (4.6 and 2.0 cal. ka BP events) supporting a decisive role of extreme hydrometeorological events in the formation of impounded mountainous alluvial plains in humid late-Holocene phases.

Footnotes

Acknowledgements

Thanks are extended to Monika Hradecká for English style corrections, to Petr Tábořík and Karel Šilhán for help during fieldwork, and to Zdzisław Jary, Jerzy Raczyk and Krzysztof Rękas from the Department of Physical Geography, Institute of Geography and Regional Development, University of Wrocław for giving access to laser diffraction equipment. We also gratefully acknowledge reviewers for valuable comments that have substantially improved the manuscript.

Funding

This research was supported by the project of the Czech Science Foundation no. GAP209/10/0309: ‘The effect of historical climatic and hydrometeorological extremes on slope and fluvial processes in the Western Beskydy Mts and their forefield’ and by the University of Ostrava Foundation SGS6/PřF/2011. The institutional funding was partly provided by the Institute of Geology AS CR, v.v.i. (AV0Z30130516).

References

Sjåstad

Sønstegaard

. (2007) Chronology of Holocene rock-avalanche deposits based on Schmidt-hammer relative dating and dust stratigraphy in nearby bog deposits, Vora, inner Nordfjord, Norway. The Holocene 17: 955–964.

Alexandrowicz

(1999) Recurrent Holocene landslides: A case study of the Krynica landslide in the Polish Carpathians. The Holocene 9: 91–99.

Appleby

(2008) Three decades of dating recent sediments by fallout radionuclides: A review. The Holocene 18: 83–93.

Baroň

(2007) Výsledky datování hlubokých svahových deformací v oblasti Vsetínska a Frýdeckomístecka. Geologické Výzkumy na Moravě a ve Slezsku 14: 10–12 (in Czech).

Berglund

Ralska-Jasiewiczowa

(1986) Pollen analysis and pollen diagrams. In: Berglund

(ed.) Handbook of Holocene Palaeoecology and Palaeohydrology. Chichester: John Wiley, pp. 455–484.

Bisci

Burattini

Dramis

. (1996) The Sant’Agata Feltria landslide (Marche Region, central Italy): A case of recurrent earthflow evolving from a deep-seated gravitational slope deformation. Geomorphology 15: 351–361.

Blott

Pye

(2001) GRADISTAT: A grain size distribution and statistics package for the analysis of unconsolidated sediments. Earth Surface Processes and Landforms 26: 1237–1248.

Bookhagen

Thiede

Strecker

(2005) Late Quaternary intensified monsoon phases control landscape evolution in the northwest Himalaya. Geology 33: 149–152.

Booth

(2002) Testate amoebae as paleoindicators of surface-moisture changes on Michigan peatlands: Modern ecology and hydrological calibration. Journal of Paleolimnology 28: 329–348.

10.

Borgatti

Ravazzi

Donegana

. (2007) A lacustrine record of early Holocene watershed events and vegetation history, Corvara in Badia, Dolomites (Italy). Journal of Quaternary Science 22: 173–189.

11.

Bronk

Ramsey C

(2009) Bayesian analysis of radiocarbon dates. Radiocarbon 51: 337–360.

12.

Bryndal

Cabaj

Margielewski

. (2003) Record of the Neoholocene palaeoenvironmental changes in the Polish Carpathians: A case study of the Siekerczyna landslide (Beskid Wyspowy Mts, Outer Carpathians). Folia Quaternaria 74: 75–96.

13.

Costa

Schuster

(1988) The formation and failure of natural dams. Geological Society of America Bulletin 100: 1054–1068.

14.

Danišík

Pánek

Matýsek

. (2008) Apatite fission track and (U-Th)/He dating of teschenite intrusions gives time constraints on accretionary processes and development of planation surfaces in the Outer Western Carpathians. Zeitschrift für Geomorphologie, NF Hauptbänd 52: 273–289.

15.

Dikau

Brunsden

Schrot

. (eds) (1996) Landslide Recognition. Identification, Movement and Causes. Wiley, pp. 1–251.

16.

Engel

Nývlt

Křížek

. (2010) Sedimentary evidence of landscape and climate history since the end of MIS 3 in the Krkonoše Mountains, Czech Republic. Quaternary Science Reviews 29: 913–927.

17.

Ermini

Casagli

(2003) Prediction of the behaviour of landslide dams using a geomorphological dimensionless index. Earth Surface Processes and Landforms 28: 31–47.

18.

García-García

Sánchez-Gómez

Navarro

. (2011) Formation, infill, and dissection of a latest-Pleistocene landslide-dammed reservoir (Betic Cordillera, Southern Spain): Upstream and downstream geomorphological and sedimentological evidence. Quaternary International 233: 61–71.

19.

Geertsema

Clague

(2006) 1000-year record of landslide dams at Halden Creek, northeastern British Columbia. Landslides 3: 217–227.

20.

Gioia

Di Leo

Giano

. (2011) Chronological constraints on a Holocene landslide in an intermontane basin of the southern Apennines, Italy: Morphological evolution and palaeoclimate implications. The Holocene 21: 263–273.

21.

Grootes

Stuiver

White

JWC

. (1993) Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice core. Nature 366: 552–554.

22.

Grove

(1988) The Little Ice Age. London: Routledge.

23.

Haczewski

Kukulak

(2004) Early Holocene landslide-dammed lake in the Bieszczady Mountains (Polish East Carpathians) and its evolution. Studia Geomorphologica Carpatho-Balcanica 38: 83–96.

24.

Hartvich

Mentlík

(2010) Slope development reconstruction at two sites in the Bohemian Forest Mountains. Earth Surface Processes and Landforms 35: 373–389.

25.

Heiri

Lotter

Lemcke

(2001) Loss on ignition as method for estimating organic and carbonate content in sediments: Reproducibility and comparability of results. Journal of Paleolimnology 25: 101–110.

26.

Hewitt

(2006) Disturbance regime landscapes: Mountain drainage systems interrupted by large rockslides. Progress in Physical Geography 30: 365–393.

27.

Holm

Bovis

Jakob

(2004) The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia. Geomorphology 57: 201–216.

28.

Humphries

Kindness

Ellery

. (2010) ¹³⁷Cs and ²¹⁰Pb derived sediment accumulation rates and their role in the long-term development of the Mkuze River floodplain, South Africa. Geomorphology 119: 88–96.

29.

Jančík

(1958) Odlesňování Těšínska v minulosti. Sborník Československé akademie zemědělských věd – Lesnictví 4: 1019–1036 (in Czech).

30.

Korup

(2005) Geomorphic imprint of landslides on alpine river systems, southwest New Zealand. Earth Surface Processes and Landforms 30: 783–800.

31.

Korup

Strom

Weidinger

(2006) Fluvial response to large rock-slope failures: Examples from the Himalayas, the Tien Shan, and the Southern Alps in New Zealand. Geomorphology 78: 3–21.

32.

Kotarba

(1996) Sedimentation rate in the High Tatra lake during the Holocene – Geomorphic interpretation. Studia Geomorphologica Carpatho-Balcanica 30: 51–56.

33.

Krejčí

Baroň

Bíl

. (2002) Slope movements in the Flysch Carpathians of Eastern Czech Republic triggered by extreme rainfalls in 1997: A case study. Physics and Chemistry of the Earth 27: 1567–1576.

34.

Kukulak

(2003) Impact of mediaeval agriculture on the alluvium in the San River headwaters (Polish Eastern Carpathians). Catena 51: 255–266.

35.

Lang

Moya

Corominas

. (1999) Classic and new dating methods for assessing the temporal occurrence of mass movements. Geomorphology 30: 33–52.

36.

Lee

Davies

Bell

(2009) Successive Holocene rock avalanches at Lake Coleridge, Canterbury, New Zealand. Landslides 4: 287–297.

37.

Magny

(2004) Holocene climate variability as reflected by mid-European lake-level fluctuations and its probable impact on prehistoric human settlements. Quaternary International 113: 65–79.

38.

Mangerud

Andersen

Berglund

. (1974) Quaternary stratigraphy of Norden, a proposal for terminology and classification. Boreas 3: 85–104.

39.

Margielewski

(2006) Records of the Late Glacial–Holocene palaeoenvironmental changes in landslide forms and deposits of the Beskid Makowski and Beskid Wyspowy Mts Area (Polish Outer Carpathians). Folia Quaternaria 76: 1–149.

40.

Margielewski

Kołaczek

Michczyński

. (2011) Record of the meso- and neoholocene palaeoenvironmental changes in the Jesionowa landslide peat bog (Beskid Sądecki Mts Polish Outer Carpathians). Geochronometria 38: 138–154.

41.

Margielewski

Krąpiec

Valde-Nowak

. (2010) A Neolithic yew bow in the Polish Carpathians. Evidence of the impact of human activity on mountainous palaeoenvironment from the Kamiennik landslide peat bog. Catena 80: 141–153.

42.

Menčík

Adamová

Dvořák

. (1983) Geologie Moravskoslezských Beskyd a Podbeskydské pahorkatiny (Geology of the Moravskoslezské Beskydy Mts and Podbeskydská pahorkatina Hilly land). Praha: Ústřední Ústav Geologický (in Czech, with English summary).

43.

Mizugaki

Nakamura

Araya

(2006) Using dendrogeomorphology and ¹³⁷Cs and ²¹⁰Pb radiochronology to estimate recent changes in sedimentation rates in Kushiro Mire, Northern Japan, resulting from land use change and river channelization. Catena 68: 25–40.

44.

Nehyba

Nývlt

Schkade

. (2011) Depositional rates and dating techniques of modern deposits in the Brno reservoir (Czech Republic) during the last 70 years. Journal of Paleolimnology 45: 41–55.

45.

Ocakoglu

Acikalin

Gokceoglu

. (2009) A multistory gigantic subaerial debris flow in an active fault scarp in NW Anatolia, Turkey: Anatomy, mechanism and timing. The Holocene 19: 955–965.

46.

Ogden

(1981) Observations of clonal cultures of Euglyphidae (Rhizopoda, Protozoa). Bulletin of the British Museum (Natural History) Zoology 41: 137–151.

47.

Opravilová

Hájek

(2006) The variation of testacean assemblages (Rhizopoda) along the complete base-richness gradient in fens: A case study from the western Carpathians. Acta Protozool 45: 191–204.

48.

Pánek

Hradecký

Smolková

. (2010) The largest prehistoric landslide in northwestern Slovakia: Chronological constraints of the Kykula long-runout landslide and related dammed lakes. Geomorphology 120: 233–247.

49.

Pánek

Šilhán

Tábořík

. (2011) Catastrophic slope failure and its origins: Case of the May 2010 Girová Mountain long-runout rockslide (Czech Republic). Geomorphology 130: 352–364.

50.

Pazdur

Fontugne

Goslar

. (1995) Lateglacial and Holocene water-level changes of the Gościąż Lake, Central Poland, derived from carbon isotopes studies of laminated sediment. Quaternary Science Reviews 14: 125–135.

51.

Prager

Zangerl

Patzelt

. (2008) Age distribution of fossil landslides in the Tyrol (Austria) and its surrounding areas. Natural Hazards and Earth Systems Science 8: 377–407.

52.

Pratt-Sitaula

Garde

Burbank

. (2007) Bedload-to-suspended load ratio and rapid bedrock incision from Himalayan landslide-dam lake record. Quaternary Research 68: 111–120.

53.

Ralska-Jasiewiczowa

(ed.) (1989) Environmental changes recorded in lakes and mires of Poland during the last 13000 years, Part III. Acta Palaeobotanica 29: 1–120.

54.

Reimer

Baillie

MGL

Bard

. (2009) IntCal09 and Marine09 radiocarbon age calibration curves, 0–50,000 years cal BP. Radiocarbon 51: 1111–1150.

55.

Roberts

(1998) The Holocene: An Environmental History. Oxford: Basil Blackwell.

56.

Saravan Kumar

Navada

Rao

. (1999) Determination of recent sedimentation rates and pattern in Lake Naini, India by ²¹⁰Pb and ¹³⁷Cs dating techniques. Applied and Radiation Isotopes 51: 97–105.

57.

Schönborn

Peschke

(1990) Evolutionary studies on the Assulina-Valkanovia complex (Rhizopoda, Testaceafilosia) in Sphagnum and soil. Biology and Fertility of Soils 9: 95–100.

58.

Soldati

Corsini

Pasuto

(2004) Landslides and climate change in the Italian Dolomites. Catena 55: 141–161.

59.

Stankoviansky

(2003) Historical evolution of permanent gullies in the Myjava Hill Land, Slovakia. Catena 51: 23–239.

60.

Starkel

Soja

Michczyńska

(2006) Past hydrological events reflected in Holocene history of Polish rivers. Catena 66: 24–33.

61.

Stolz

(2011) Budgeting soil erosion from floodplain sediments of the central Rhenish Slate Mountains (Westerwald), Germany. The Holocene 21: 499–510.

62.

Stráník

Tyráček

Dvořák

(1999) Geologická mapa ČR 25-14 Valašské Meziříčí 1:50 000 (Geological map CR 25-14 Valasske Mezirici in scale 1:50 000). Praha: Český geologický ústav (in Czech).

63.

Telford

Heegaard

Birks

HJB

(2004) The intercept is a poor estimate of a calibrated radiocarbon age. The Holocene 14: 296–298.

64.

Walker

(2005) Quaternary Dating Methods. Chichester: John Wiley & Sons.

65.

Wanner

Solomina

Grosjean

. (2011) Structure and origin of Holocene cold events. Quaternary Science Reviews 30: 3109–3123.

66.

Yan

Shi

Gao

. (2002) ¹³⁷Cs dating of lacustrine sediments and human impacts on Dalian Lake, Qinghai Province, China. Catena 47: 91–99.