Tomáš Pánek

Recent progress in landslide dating A global overview

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.

Between a Pod and a Hard Test: The Deep Evolution of Amoebae

Abstract Amoebozoa is the eukaryotic supergroup sister to Obazoa, the lineage that contains the animals and Fungi, as well as their protistan relatives, and the breviate and apusomonad flagellates. Amoebozoa is extraordinarily diverse, encompassing important model organisms and significant pathogens. Although amoebozoans are integral to global nutrient cycles and present in nearly all environments, they remain vastly understudied. We present a robust phylogeny of Amoebozoa based on broad representative set of taxa in a phylogenomic framework (325 genes). By sampling 61 taxa using culture-based and single-cell transcriptomics, our analyses show two major clades of Amoebozoa, Discosea, and Tevosa. This phylogeny refutes previous studies in major respects. Our results support the hypothesis that the last common ancestor of Amoebozoa was sexual and flagellated, it also may have had the ability to disperse propagules from a sporocarp-type fruiting body. Overall, the main macroevolutionary patterns in Amoebozoa appear to result from the parallel losses of homologous characters of a multiphase life cycle that included flagella, sex, and sporocarps rather than independent acquisition of convergent features.

Geomorphic evidence of ancient catastrophic flow type landslides in the mid-mountain ridges of the Western Flysch Carpathian Mountains (Czech Republic)

Abstract Ancient flow type landslides are relatively frequent fossil forms of the relief in mid-mountain conditions of the Czech Carpathian Mountains. Sixty rather distinctive displays of debris flows, rock avalanches, and debris avalanches have been mapped in the uppermost part of the territory. Unlike contemporary sporadic and low volume debris flows, ancient (Pleistocene and Lower Holocene) accumulations are a few orders of magnitude more extensive and were of considerable geomorphologic significance in forming the steep sections of mountain valleys and slopes. This geomorphic pattern does not hold for flow type slides, the source of which is material released as a consequence of numerous deep-seated landslides. Due to deep disruption of slopes, a few high-magnitude flow type landslides (e.g., rock avalanches), quite rare in flysch mid-mountain conditions, also occurred in the Late Holocene.

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

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.

Diversity of Heterolobosea

Heterolobosea is a small group of amoebae, amoeboflagellates and flagellates (ca. 140 described species). Since heterolobosean amoebae are highly reminiscent of naked lobose amoebae of Amoebozoa, they were for a long time treated as members of Rhizopoda (Levine, 1980). The class Heterolobosea was established in 1985 by Page and Blanton (Page & Blanton, 1985) by uniting unicellular Schizopyrenida with Acrasida that form multicellular bodies. Later, it was suggested that Heterolobosea might be related to Euglenozoa (e.g., Trypanosoma, Euglena) instead of other amoebae (Cavalier-Smith, 1998; Patterson, 1988). This assumption based on the cell structure was supported also by early multigene phylogenetic analyses (Baldauf et al., 2000). Currently, the Heterolobosea is nested together with Euglenozoa, Jakobida, Parabasalia, Fornicata, Preaxostyla, Malawimonas, and Tsukubamonas within the eukaryotic supergroup Excavata (Hampl et al., 2009; Rodriguez-Ezpeleta et al., 2007; Simpson, 2003; Yabuki et al., 2011). The excavate organisms were originally defined on the basis of the structure of flagellar system and ventral feeding groove (Simpson & Patterson, 1999). However, Heterolobosea have lost some of these structures (Simpson, 2003).

Recurrent landslides predisposed by fault-induced weathering of flysch in the Western Carpathians

Abstract The interrelationship between slope deformation and fault-induced weathering as a predisposing factor for the development of sliding is analysed through several case studies from the Western Carpathians in the Czech Republic. The study area comprises flysch nappes with alternating sandstone and shale of different permeability. These lithological structures are affected by systems of faults. Recurring slope instability is found associated with zones of deep weathering in tectonically weakened areas. Climatic variability of landslide activity can be identified during the Holocene by means of radiocarbon dating and pollen analysis. Areas affected by recurring landsliding suggest gradual and cyclic landslide frequency.

Giant landslides and highstands of the Caspian Sea

The history of Quaternary sea-level changes in the Caspian Sea, the world’s largest lake, is partly enigmatic, and so is the geomorphic response of its coasts. Late Pleistocene transgressions during the Early Khvalynian (ca. 40–25 ka) inundated extensive portions of the flat, low-lying semi-desert of western Kazakhstan. Cliffs cut during these highstands form a prominent escarpment tens of kilometers to several hundred kilometers from the present coast of the Caspian Sea. Satellite images, digital terrain analysis, and field mapping reveal that >300 giant landslides intersect with this escarpment. More than 100 of these slope failures mobilized volumes >10 8 m 3 along basal failure planes with gradients as low as ∼5°. All landslides share characteristics of lateral rock spreads involving competent limestones overlying weak and plastic claystones. From relative stratigraphy and new 14 C data, we infer that catastrophic slope failure of over 41 km 3 occurred mostly during Pleistocene Caspian sea-level highstands, while several landslides may have been reactivated or entirely originated during the Holocene. This largest cluster of terrestrial mass wasting in a tectonically quiescent setting offers an opportunity to understand how landslides erode low-relief landscapes subject to oscillating sea levels.

Nuclear genetic codes with a different meaning of the UAG and the UAA codon

BackgroundDepartures from the standard genetic code in eukaryotic nuclear genomes are known for only a handful of lineages and only a few genetic code variants seem to exist outside the ciliates, the most creative group in this regard. Most frequent code modifications entail reassignment of the UAG and UAA codons, with evidence for at least 13 independent cases of a coordinated change in the meaning of both codons. However, no change affecting each of the two codons separately has been documented, suggesting the existence of underlying evolutionary or mechanistic constraints.ResultsHere, we present the discovery of two new variants of the nuclear genetic code, in which UAG is translated as an amino acid while UAA is kept as a termination codon (along with UGA). The first variant occurs in an organism noticed in a (meta)transcriptome from the heteropteran Lygus hesperus and demonstrated to be a novel insect-dwelling member of Rhizaria (specifically Sainouroidea). This first documented case of a rhizarian with a non-canonical genetic code employs UAG to encode leucine and represents an unprecedented change among nuclear codon reassignments. The second code variant was found in the recently described anaerobic flagellate Iotanema spirale (Metamonada: Fornicata). Analyses of transcriptomic data revealed that I. spirale uses UAG to encode glutamine, similarly to the most common variant of a non-canonical code known from several unrelated eukaryotic groups, including hexamitin diplomonads (also a lineage of fornicates). However, in these organisms, UAA also encodes glutamine, whereas it is the primary termination codon in I. spirale. Along with phylogenetic evidence for distant relationship of I. spirale and hexamitins, this indicates two independent genetic code changes in fornicates.ConclusionsOur study documents, for the first time, that evolutionary changes of the meaning of UAG and UAA codons in nuclear genomes can be decoupled and that the interpretation of the two codons by the cytoplasmic translation apparatus is mechanistically separable. The latter conclusion has interesting implications for possibilities of genetic code engineering in eukaryotes. We also present a newly developed generally applicable phylogeny-informed method for inferring the meaning of reassigned codons.

CREVICE-TYPE CAVES AS INDICATORS OF SLOPE FAILURES: A REVIEW PAYING A SPECIAL ATTENTION TO THE FLYSCH CARPATHIANS OF CZECHIA, POLAND, AND SLOVAKIA

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.

Recent Landform Evolution in the Moravian–Silesian Carpathians (Czech Republic)

Topographic changes in the Moravian-Silesian Carpathians have been due to variations of natural conditions (climatic changes, accelerated rates of exogenic geomorphic processes during the Little Ice Age), but mainly to the growing intensity of human activities (tillage, deforestation, accelerated soil erosion, urban sprawl). In this geomorphologically highly sensitive region, land-use changes exerted a great influence on the intensity and type of exogenic geomorphological processes in the last millennium. Their impact is studied on archive maps. The density of slope deformations (like deep-seated slope failures, lateral spreading, toppling, sackung, translational and rotational landslides, earthflows, debris flows, and rockfalls) in the study area is the highest in the Czech Republic. Other geomorphic processes presented in this overview are erosion by water on the surface and underground (piping), wind erosion, and a range of anthropogenic processes (urbanization, mining, industry, water management, and transport).