Recent progress of dating techniques has greatly improved the age determination of various types of landslides. Since the turn of the 21st century, the number of dated landslides throughout the world ...has increased several fold and the introduction of modern dating methods (e.g. cosmic ray exposure dating) has enabled the dating of new landslide features and elements. Based on the analysis of >950 dated landslides (of which 734 have been dated since the year 2000), it is clear that the predominant traditional strategies have continued to rely on the radiocarbon method; however, there is a remarkable trend of using cosmic ray exposure techniques for dating both the accumulation (e.g. landslide boulders) and the depletion (e.g. landslide scarps) parts of landslides. Furthermore, an increasing number of slope failures is determined by a multi-dating approach, which enables the verification of particular dating methods. Although coherent regional landslide chronologies are still relatively scarce in comparison with extensive databases of fluvial, glacial and/or eolian landforms, they offer important insights into temporal landslide distribution, long-term landslide behavior and their relationships with paleoenvironmental changes. The most extensive data sets exist for the mountain areas of North America (Pacific Coast Ranges), South America (Andes), Europe (Alps, Scottish Highlands, Norway, Carpathians and Apennines), the Himalaya-Tibet orogeny and the Southern Alps of New Zealand. Dated landslides in the plate interiors are lacking, especially in South America, Africa and Australia. Despite the fact that some dating results are well correlated with major regional and continental-scale changes in the seismic activity, moisture abundance, glacier regimes and vegetation patterns, some of these results contradict previously established straightforward hypotheses. This indicates the rather complex chronological behavior of landslides, reflecting both intrinsic (e.g. gradual stress relaxation within a rock mass) and external factors, including high-magnitude earthquakes or heavy rainfalls.
Deep-seated gravitational slope deformations (DSGSDs) are slow moving, hillslope-scale mass movements featuring characteristic landforms such as double-crested ridges and upslope-facing scarps that ...occur in diverse landscapes throughout the world. Although these deformations have been studied since the 1960s, significant insights to the rates of DSGSDs have only been gained within the last two decades owing to progress in geochronology, remote sensing and instrumental monitoring. Absolute age and monitoring data indicate that DSGSD movements are observable over long-term (≥102years) and short-term (<102years) intervals. Apart from creep, an episodic deformation also plays a crucial role, especially in regions with earthquakes and heavy rainfall. Our review also supports the notion of DSGSDs as precursors of catastrophic rock slope failures, given that many of the world's largest rock avalanches have occurred in areas with diagnostic DSGSD features, indicating that sudden collapse was preceded by a prolonged stage of slope sagging. Detailed studies on DSGSDs have therefore the potential for better prediction of catastrophic rock slides and rock avalanches.
Future research directions include constraining the lifespan of DSGSDs with absolute age dating and precise high-resolution monitoring of spatio-temporal displacement across DSGSD bodies. It is of great importance to include absolute time scales in the numerical models of DSGSDs. Furthermore, combining remote sensing techniques such as Synthetic Aperture Radar Interferometry with high-resolution LiDAR scanning and near-surface geophysics offers a promising toolkit for collecting very detailed and accurate data on the short-term deformation rates of DSGSDs.
We used culture-based and culture-independent approaches to discover diversity and ecology of anaerobic jakobids (Excavata: Jakobida), an overlooked, deep-branching lineage of free-living ...nanoflagellates related to Euglenozoa. Jakobids are among a few lineages of nanoflagellates frequently detected in anoxic habitats by PCR-based studies, however only two strains of a single jakobid species have been isolated from those habitats. We recovered 712 environmental sequences and cultured 21 new isolates of anaerobic jakobids that collectively represent at least ten different species in total, from which four are uncultured. Two cultured species have never been detected by environmental, PCR-based methods. Surprisingly, culture-based and culture-independent approaches were able to reveal a relatively high proportion of overall species diversity of anaerobic jakobids-60 or 80%, respectively. Our phylogenetic analyses based on SSU rDNA and six protein-coding genes showed that anaerobic jakobids constitute a clade of morphologically similar, but genetically and ecologically diverse protists-Stygiellidae fam. nov. Our investigation combines culture-based and environmental molecular-based approaches to capture a wider extent of species diversity and shows Stygiellidae as a group that ordinarily inhabits anoxic, sulfide- and ammonium-rich marine habitats worldwide.
Large-scale, low-gradient ancient landslides estimated at 5.4–18.9 km
2 in area and ∼
0.2–1.2 km
3 in volume have been studied in the northern hilly periphery of the Crimean Mountains (Ukraine). They ...originated on slopes along wide water gaps of rivers (Belbek, Kacha, Alma and Biyuk–Karasu) crossing the cuestas of the northern foothills. The slopes generally consist of slightly northward tilting Miocene (mainly Sarmatian) limestones overlying weak, clay-rich Lower Neogene–Palaeogene substratum with a significant content of smectite. Although the region is characterised by the least active contemporary morphodynamics within the Crimean Mountains, the landslides which were studied are of the same size or even larger than various types of landslides occupying active geomorphic domains of the highest mountain range in the southernmost part of the peninsula. The landslides are generally a spreading type, but the sliding mechanics were probably very complex, involving toppling, rotational slides, gravitational folding and translational block slides. All the landslides which were studied are located in the vicinity of regional faults and three of them have headscarps aligned along faults. A common feature is also a location close (within several km) to the Mesozoic suture zone which is the most important tectonic feature in the northern periphery of the Crimean Orogene. This suture was formerly classified as aseismic; however, evidence of strong, low-frequency palaeoearthquakes was collected during the last decade within both the Mesozoic suture and the low-lying northern part of the Crimean Peninsula. Radiocarbon dating of deposits associated with the landslides has revealed at least two phases of increased landslide-activity during the Late Glacial chronozone and Holocene epoch. The main landslide phase presumably took place at some time between the Late Glacial and Atlantic chronozones. Minor reactivation of landslide toes occurred during the Subatlantic chronozone and some of them have been active up to recent times. The first major landslide phase was possibly triggered by an earthquake, whereas late Holocene activity can be attributed both to seismic and hydroclimatic factors.
This paper presents the results of two separate geophysical investigations undertaken across the Sudetic Marginal Fault zone in the Bohemian Massif. This fault zone represents one of the most ...important tectonic features in central Europe. The first, preliminary, investigation used electrical resistivity tomography (ERT) to define the exact position of the main fault at two localities (Kamenička & Bílá Voda). Both profiles revealed a resistivity gradient that divided a complex of crystalline rocks with high resistivities from sedimentary deposits with low resistivities. From these data, sites were selected for palaeoseismic trenching. This trenching provided detailed information regarding the surveyed structures and lithologies. The second, more extensive, investigation used electrical resistivity tomography and gravimetric survey in order to extend the previously recognised features both laterally and to depth. The fault is displayed by the presence of an expressive resistivity gradient, even on profiles undertaken in more homogeneous lithologies. Finally, the most intensive investigations were conducted at Bílá Voda, where highly detailed ERT was undertaken on the floor of the trench. From this, it was possible to trace approximately logged geological structures to far greater depths and assess sedimentary thicknesses. A gravimetric survey was also undertaken adjacent to the trench. From modelling the gravitational effects of the fault zone, it is shown that the fault dips about 75° NE and that the vertical offset of Miocene vs. bedrock on the fault is approximately 200
m. The presented study has demonstrated the value of undertaking two phases of geophysical exploration separated by a trenching investigation. It is considered that this methodology is particularly suitable for the study of active tectonics in analogous intraplate settings where fault slip-rate is low.
► ERT & gravimetric survey determined precise position of fault trace. ► Geophysical survey combined with trenching maximises effectiveness of methodology. ► Used research design enables to follow fault trace both laterally and to the depth. ► High-resolution ERT on trench floor gives more accurate geological interpretation. ► Gravity modelling suggests fault dip and vertical offset on Sudetic Marginal Fault.
The occurrence and evolution of crevice-type caves is one of the most spectacular phenomena in the progression of slope failures in distinct types of rocks. Crevices are common manifestations of ...disintegration of anisotropic flysch rocks in the area of the Carpathians. This paper presents the issues of the close connection between the evolution of gravitational slope deformations and the formation of crevice-type caves. Furthermore, it presents a contemporary view on the regional distribution of crevice-type caves in this area and outlines the recent progress and future possibilities of the investigation of this phenomenon. Based on the vertical distribution of different morphological zones within the caves and the main modes of their evolution, we can distinguish three basic types of crevice-type caves: (i) translational/spreading type, (ii) toppling type and (iii) rotational type. Rozsedlinové jeskyně jako indikátory svahových poruch: Přehled s důrazem na flyšové Karpaty Česka, Polska a Slovenska Vznik a vývoj rozsedlinových jeskyní je jedním z nejviditelnějších fenoménů spojených s výskytem svahových defomrací v nejrůznějších typech hornin. Rozsedliny se velice často vytvářejí ve flyšových horninách jako například v oblasti Karpat, které jsou tvořeny střídáním subhorizontálně uložených vrstev pískovců, prachovců a jílovců. Článek prezentuje propojení mezi vývojem svahových deformací a výskytem a vývojem rozsedlinových jeskyní, poskytuje přehled o genezi a vývoji rozsedlinových jeskyní jakožto důležitého geomorfologického elementu gravitačně rozrušených svahů flyšových Karpat, prezentuje náhled na soudobou problematiku výzkumu a odhaduje cesty jeho budoucího vývoje.
Deep-seated gravitational deformations are significant denudational agents of rock slopes at the margins of karstified plateaus of the Crimean Mountains (Ukraine). The aim of this article is to study ...long-term evolution of a giant rock slope failure close to the Black Sea coast in the southwestern tip of the mountains near Foros Town. The failure evolved in highly anisotropic limestones overlying plastic flysch layers where the main headscarp follows a strike-slip fault. We tested a new chronological strategy based on super(1) super(4)C and U-/Th-series dating of speleothems from unroofed caves exposed in the headscarp area of the slope failure. This approach made it possible to state maximum age of the slope collapse in individual parts of the deformed slope. Obtained results indicate that extension of discontinuities together with their karstification can be traced to >300 ka BP, whereas evolution of the main headscarp started ~110 ka BP and since then it has propagated in the eastward direction. The youngest slope failure in the easternmost part of the studied collapse is of Late Holocene age. Our study indicates that conditions for large rock slope failures in carbonate areas can be prepared by speleogenesis or combined effects of propagation of cracks and their solution-based expansion. Furthermore, large rock slope failures can be important factors for the genesis of unroofed caves.
In the Kamienne Mountains the largest concentration of apparently relict landslides in the Sudetes range occurs. On the northern slopes of Mt Garbatka mass movements re-shaped two adjacent slope ...hollows and a wide depositional area is located down the valley. The main landslide body is nearly 1km long and 200–300m wide. Its flattened surface morphology and the occurrence of large dispersed allochtonous boulders in the distal part suggests a flow-like movement, initiated by shallow translational slides in the upper slopes. The thickness of colluvium, determined by an ERT survey, may reach 10m. Geomorphic signatures of mass movement are subdued, suggesting that considerable time has elapsed since the origin of the landslide and that large-scale mass movements are likely pre-Holocene in age. This is consistent with the results of an extensive soil survey within the landslide body and on the surrounding slopes. Similarity of soil properties and well-developed horizonation of profiles both within the landslide and outside it shows that no major disturbance has taken place during the soil formation period. Dendrogeomorphological research, in turn, yielded evidence of numerous growth disturbances recorded in tree rings of Norway spruce growing on the landslide body. These signals are interpreted that the slope surface is not entirely stable under current environmental conditions. Flow or creep of landslide material is not very likely, given the characteristics of cover materials, and it is hypothesized that dendrochronological signals develop in response to ground deformation through piping and throughflow. Landslide hazard in the valley below Mt Garbatka appears low at present but to claim complete stability would be premature.
•Relict landslide is characterized in terms of geomorphology, soils, and activity.•A complex approach helps to establish pre-Holocene age and evaluate hazards.•Two separate phases of activity are suggested.•Tree ring record indicates ongoing ground instability probably related to piping.
PDF
