Birgit Terhorst

GIS-based assessment of landslide susceptibility on the base of the Weights-of-Evidence model

The major scope of the study is the assessment of landslide susceptibility of Flysch areas including the Penninic Klippen in the Vienna Forest (Lower Austria) by means of Geographical Information System (GIS)-based modelling. A statistical/probabilistic method, referred to as Weights-of-Evidence (WofE), is applied in a GIS environment in order to derive quantitative spatial information on the predisposition to landslides. While previous research in this area concentrated on local geomorphological, pedological and slope stability analyses, the present study is carried out at a regional level. The results of the modelling emphasise the relevance of clay shale zones within the Flysch formations for the occurrence of landslides. Moreover, the distribution of mass movements is closely connected to the fault system and nappe boundaries. An increased frequency of landslides is observed in the proximity to drainage lines, which can change to torrential conditions after heavy rainfall. Furthermore, landslide susceptibility is enhanced on N-W facing slopes, which are exposed to the prevailing direction of wind and rainfall. Both of the latter geofactors indirectly show the major importance of the hydrological conditions, in particular, of precipitation and surface runoff, for the occurrence of mass movements in the study area. Model performance was checked with an independent validation set of landslides, which are not used in the model. An area of 15% of the susceptibility map, classified as highly susceptible, “predicted” 40% of the landslides.

Palaeopedology and magnetic susceptibility of a loess–palaeosol sequence in southwest Germany

Abstract A loess–palaeosol sequence that formed during the last and the penultimate glacial–interglacial cycle was studied by pedological, geochemical and rock magnetic methods. Particular emphasis was placed on magnetic susceptibility in order to derive a climatic signal. Problems of separating the influence of palaeo-relief, hydrological influence and climate complicate the interpretation, but the results show that minimal levels of soil formation cause a distinct enhancement of the magnetic properties. Higher magnetic susceptibility signals characterise the more oxidized parts of the palaeosols. Alternatively, hydromorphic processes operating on the ferrimagnetic minerals cause a decrease in magnetic susceptibility, reflecting both past climate and changes in the palaeoenvironment. Extremely low-susceptibility values characterise the reduced greyish zones of the interglacial Bt horizons. Additional complications are introduced because magnetic susceptibility may change along the horizons of one soil profile. Eluvial horizons tend to have lower concentrations of ferrimagnetic minerals than the loess parent material, whereas the corresponding illuvial horizons show an increase. It is considered that palaeoclimatic interpretation based solely on magnetic susceptibility must be treated with great caution.

Casting new light on the chronology of the loess/paleosol sequences in Lower Austria

This paper presents a review on recently dated sections in well-known loess/paleosol sequences of Lower Austria. The dating results indicate that there was loess deposition during the Upper Würmian Pleniglacial as recorded in the profile Joching. However, most obtained ages are older than the Last Glacial Maximum (LGM) and therefore erosional processes, which led to the removal of younger deposits can be supposed. Soil formation between ~28 ka and ~35 ka mainly resulted in the formation of Cryosols. Hence, in the studied profiles, there is no evidence for more intense interstadial pedogenesis during this time span. This might be of particular relevance to the stratigraphy of ‘Stillfried B’ (sensu Fink). The 2 age cluster lies between ~35 ka and ~57 ka i. e. the Middle Pleniglacial (Würmian) and is dominated by loess deposits intercalated with different Cryosols. This period is also characterized by colluvial processes. There is a significant hiatus between ~57 ka and ~106 ka, a fact which might be due to long lasting and intensive erosional processes in the study areas. The oldest measured age of the Last Glacial is 106 ± 12 ka for the loess on top of ‘Stillfried A’ in Paudorf (Paudorfer Bodenbildung). Immediately below this pedocomplex and equivalents to it, ages of 124 ± 25 ka (Göttweig-Aigen), 159 ± 20 ka (Paudorf 1), and 170 ± 16 ka (Joching) were obtained in loess. Furthermore, there is evidence for older Middle Pleistocene deposits in Stratzing, Paudorf 2, Göttweig-Furth and Langenlois. (Löss-/Paläoboden sequenzen in niederösterreich im Licht neuer chronologischer Ergebnisse) Kurzfassung: Der vorliegende Artikel gibt einen Überblick über neu datierte Abschnitte in bekannten Löss/Paläoboden-Sequenzen Niederösterreichs. Die Ergebnisse der Datierungen im Profil Joching deuten darauf hin, dass es im letzten Hochglazial zur Lösssedimentation kam. Die meisten erfassten Alter sind jedoch älter als das letzte Hochglazial, was auf Erosionsprozesse hindeutet, die zur Abtragung der jüngeren Lösse geführt hat. In dem Abschnitt zwischen ~28 ka and ~35 ka wurden überwiegend Tundragleye gebildet. Eine intensivere interstadiale Bodenbildung ist nicht nachzuweisen. Dieses Ergebnis kann auch für die stratigraphische Einstufung von ‚Stillfried B‘ (sensu Fink) von Bedeutung sein. Der folgende chronologische Abschnitt liegt zwischen ~35 ka and ~57 ka in Lösssedimenten mit eingeschalteten Tundragleyen. Auch dieser Abschnitt ist durch Umlagerungsprozesse charakterisiert. Im Zeitraum von ~57 ka bis ~106 ka befindet sich eine markante Zeitlücke, die vermutlich auf langandauernde und intensive Erosionsprozesse im Untersuchungsgebiet zurückzuführen ist. Die älteste Datierung in den Sedimenten des letzten Glazials mit 106 ± 12 ka befindet sich in Paudorf direkt über dem ‚Stillfried A‘Komplex (Paudorfer Bodenbildung). Direkt unter diesem Pedokomplex, bzw. vergleichbaren Pedokomplexen treten in Lössablagerungen Alter von 124 ± 2 5 ka (Göttweig-Aigen), 159 ± 20 ka (Paudorf 1), and 170 ± 16 ka (Joching) auf. Darüber hinausgehende Alter konnten in Stratzing, Paudorf 2, Göttweig-Furth und Langenlois nachgewiesen werden.

The influence of Pleistocene landforms on soil-forming processes and soil distribution in a loess landscape of Baden-Württemberg (south-west Germany).

Abstract Geomorphodynamic and pedogenetic processes were studied in a dry valley (the Borten Valley) within a typical loess region near Heilbronn. Land use in this area is very intensive and causes serious soil erosion problems. Soil mapping showed the degree of erosion of Luvisols and the resulting mosaic of different erosion and accumulation patterns. Soil profiles on slopes have been eroded and soils with relict properties in valley bottoms and on lower slope positions (Gleyic Chernozems and intergrades to Luvisols) have been covered by colluvial sediments. These paleosols provide evidence for Holocene soil evolution. The transformation of Gleyic Chernozems to Luvisols depended mainly on geomorphology and hydrological conditions. The preservation of paleosols also allows the landscape before anthropogenic deforestation to be reconstructed.

Estimation of Direct Landslide Costs in Industrialized Countries: Challenges, Concepts, and Case Study

This paper presents a short summary of the challenges and concepts in previous landslide loss studies and introduces a methodological framework for the estimation of direct landslide costs in industrialized countries. A case study of landslide losses for federal roads in the Lower Saxon Uplands (NW Germany) exemplifies the application of this methodology in a regional setting.

Slope Stability and Slope Formation in the Flysch Zone of the Vienna Forest (Austria)

The Rhenodanubian Flysch of the northern Vienna Forest is composed of various layers of sandstones, marly shales, calcareous marls, and clay shists, which are covered by Quaternary periglacial cover beds and loess deposits. This area at the margin of the eastern Alps represents an undulating landscape of the Austrian low-mountain regions. The Vienna Forest Flysch region is considered to be susceptible to landslides. Both petrography of the bedrock and soil mechanical properties of the Quaternary sediments control the current slope dynamics in the study area. In a temporal context it is evident that the stability of slopes exceeding is controlled by a succession of several steps of slope formation. On the basis of field surveys, laboratory analyses, and slope stability modelling, results from investigations on recent landslides demonstrate five different phases of slope formation. In general, after passing these phases the stability of studied slopes is increased, due to the different soil mechanical properties of the potential sliding masses.

A landslide inventory system as a base for automated process and risk analyses

Landslide research requires consistent and widespread data. Many countries within the European Union have national landslide inventories to fulfill these demands for their respective research. However, those inventories were usually not intended to provide the technical basis for automated process and risk analyses during their design phase. The ongoing development of Germany’s national landslide database offers the opportunity to do this differently. This paper introduces a landslide inventory system called WISL suitable for data handling as well as for novel automated process and risk analyses on a national scale. WISL is designated to form the technical infrastructure for a German national database. Its core consists of an open source relational database management system (PostgreSQL), standardized input and registration methods as well as integrated analyses modules, which avoid large data movement and allow for rapid risk analyses. We present proof-of-concept results of endangered infrastructure related to automated risk mappings based on topography and proximity of active landslides. The use of open source software and the application of a standardized input and data acquisition system for experts, coupled with custom analysis modules, constitutes a step toward automated risk maps by a mere ‘button-press’. Future developments for the inventory lie in the field of refining and inventing analysis modules and collecting data, for which WISL provides a firm technical base.

Multi-methodological Studies on the Large El Capulín Landslide in the State of Veracruz (Mexico)

During the last decade, the State of Veracruz (Mexico) experienced a series of intense rainfall seasons with more than 1000 registered landslides. As a consequence, more than 45,000 people had to be evacuated and resettled. Even though the mountainous areas of Veracruz are highly prone to landslides, neither susceptibility maps nor any other relevant information (distribution of landslides, geology, etc.) with high spatial resolution is available. The high social impact of the most recent landslide hazards points out the necessity of detailed investigations in the affected areas. The aim of this study is to improve the understanding of process dynamics for the landslides and to provide the base for future susceptibility mapping. As an example, a young landslide with a high complexity of nested processes from the year 2013 is selected for detailed investigations in the east Trans Mexican Volcanic Belt in the State of Veracruz, related to the complexity of the studied landslide a multi-methodological approach is applied, which includes geomorphological mapping, sediment characterization as well as geophysical methods (electrical resistivity tomography, seismic refraction tomography). Field results indicate that the studied landslide must be regarded as a reactivated older landslide body, with a variety of intricate processes and numerous secondary slides. Detailed investigations provide deep insights in the dynamics and interactions of landslide processes related to their natural and anthropogenic settings.