Richard Dikau

Classic and new dating methods for assessing the temporal occurrence of mass movements

Abstract Establishing landslide chronologies is essential both for understanding causes of mass movements as part of fundamental geomorphological research, and for the assessment of landslide hazards as part of applied geomorphology. We discuss the applicability of different methods for determining landslide chronologies, frequencies and dynamics in relation to the type of material being dated, sampling location and type of mass movement. The emphasis is on the possibilities and limitations of the different dating methods. Established methods such as radiocarbon dating, lichenometry and dendrochronology are briefly discussed. The paper focuses, however, on (1) new analytical techniques like Accelerator Mass Spectrometry (AMS), Thermally Ionising Mass Spectrometry (TIMS) and laser fusion, which have led to significant improvements of established dating methods and on (2) new dating methods like Optically-Stimulated-Luminescence (OSL) dating and Alpha-Recoil-Track (ART) dating.

Spatial distribution of sediment storage types and quantification of valley fill deposits in an alpine basin, Reintal, Bavarian Alps, Germany

Spatial patterns of sediment storage types and associated volumes using a novel approach for quantifying valley fill deposits are presented for a small alpine catchment (17 km 2 ) in the Bavarian Alps. The different sediment storage types were analysed with respect to geomorphic coupling and sediment flux activity. The dominant landforms in the valley in terms of surface area were found to be talus slopes (sheets and cones) followed by rockfall deposits and alluvial fans and plains. More than two-thirds of the talus slopes are relict landforms, completely decoupled from the geomorphic system. Notable sediment transport is limited to avalanche tracks, debris flows, and along floodplains. Sediment volumes were calculated using a combination of polynomial functions of cross sections, seismic refraction, and GIS modelling. A total of, 66 seismic refraction profiles were carried out throughout the valley for a more precise determination of sediment thicknesses and to check the bedrock data generated from geomorphometric analysis. We calculated the overall sediment volume of the valley fill deposits to be 0.07 km 3 . This corresponds to a mean sediment thickness of 23.3 m. The seismic refraction data showed that large floodplains and sedimentation areas, which have been developed through damming effects from large rockfalls, are in general characterised by shallow sediment thicknesses (<20 m). By contrast, the thickness of several talus slopes is more than twice as much. For some locations (e.g., narrow sections of valley), the polynomial-generated cross sections resulted in overestimations of up to one order of magnitude; whereas in sections with a moderate valley shape, the modelled cross sections are in good accordance with the obtained seismic data. For the quantification of valley fill deposits, a combined application of bedrock data derived from polynomials and geophysical prospecting is highly recommended. D 2003 Elsevier B.V. All rights reserved.

Principles of semantic modeling of landform structures

Landforms, which result from the interplay of physical, chemical, and biological processes acting on the surface, function as static boundary conditions for processes in geomorphology, hydrology, meteorology and other fields. The description, parameterization, and modeling of landform structure, as well as the terminology used, are fitted to the requirements of the disciplines and are, therefore, often strongly divergent. As a consequence, representations of landform structure for different disciplines are often not compatible and require frequent revisions and adaptations. Principles of the semantic approach to the problem are presented in this paper. The main objective is a semantically correct description of landform which is useful to all disciplines related to surface structure. The approach considers geometric form as a basic property, extended by topological considerations and semantic definitions. The potential, limitations, and open questions of the semantic-based approach are discussed using hillslopes as a case study. The focus of the paper is on semantic representation and only thereafter are the special features of DEMs, tools, and implementations considered.

The temporal stability and activity of landslides in Europe with respect to climatic change (TESLEC): main objectives and results

Abstract The major aim of the European project “The temporal stability and activity of landslides in Europe with respect to climatic change (TESLEC)” was to investigate the interrelationship between landslides, climate and time. The research was focused on three main objectives: (1) developing criteria for the recognition of landslides, (2) reconstructing past distributions of landslide incidents and their relationship to climatic change parameters, and (3) developing a hydrological and slope stability modelling framework using different test sites. The results of the project are related to these major objectives and include: (1) a technical manual for landslide recognition, (2) records of landslide activity, and (3) an evaluation of different hydrological and slope stability models. Landslide activity since 1950 has been generally high at all test sites. In some areas, there has almost been a continuous activity observed since the beginning of the monitoring. The records before 1950 are incomplete and probably indicate a lack of data rather than a lack of landslide activity. Whether the observed active landslides are carrying a climate signal cannot be stated for all test sites with high confidence, since some relationships between climate and landslides are uncertain. Thus, for the present, the complexity of the relationships between climate and landsliding seems to make it not feasible to establish “universal laws” all over Europe. On the other hand, it was possible to establish for some areas a cumulative rainfall-duration threshold for the reactivation of landslides. Future scenarios of regional precipitation were derived from downscaled general circulation model (GCM) experiments and used within simple slope hydrological and slope stability models. The evaluation of hydrological and slope stability models shows that physically based models are not always the best solution due to the model complexity and data requirements. For shallow landslides, more simple tank models are sometimes the better alternative. Future model development should strengthen considerations of fissure flow, sudden changes in permeability, larger landslide volumes and complex landslide topography.

TOWARDS A UNIFORM CONCEPT FOR THE COMPARISON AND EXTRAPOLATION OF ROCKWALL RETREAT AND ROCKFALL SUPPLY

Abstract. Rates of rockwall retreat and rockfall supply are fundamental components of sediment budgets in steep environments. However, the standard procedure of referencing rockwall retreat rates using only lithology is inconsistent with research findings and results in a variability that exceeds three orders of magnitude. The concept proposed in this paper argues that the complexity inherent in rockfall studies can be reduced if the stages of (i) backweathering, (ii) filling and depletion of intermediate storage on the rock face and (iii) final rockfall supply onto the talus slopes are separated as these have different response functions and controlling factors. Backweathering responds to preweathering and weathering conditions whereas the filling and depletion of intermediate storage in the rock face is mainly a function of internal and external triggers. The noise apparent in backweathering rates and rockfall supply can be reduced by integrating the relevant controlling factors in the response functions. Simple conceptual models for the three stages are developed and are linked by a time‐dependent ‘rockfall delivery rate’, which is defined as the difference between backweathering and rockfall supply, thus reflecting the specific importance of intermediate storage in the rock face. Existing studies can be characterized according to their ‘rockfall delivery ratio’, a concept similar to the ‘sediment delivery ratio’ used in fluvial geomorphology. Their outputs can be qualified as trigger‐dependent rockfall supply rates or backweathering rates dependent on (pre‐)weathering conditions. It is shown that the existing quantitative backweathering and rockfall supply models implicitly follow the proposed conceptual models and can be accommodated into the uniform model. Suggestions are made for how best to incorporate non‐linearities, phase transitions, path dependencies and different timescales into rockfall response functions.

Rockglacier acceleration in the Turtmann valley (Swiss Alps): Probable controls

Temporal variations in mountain permafrost creep are discussed within a regional study on rockglacier 1 In order to emphasize the autonomy of the phenomenon, the term ‘rockglacier’ is expressed as one word in this article, in accordance with Barsch 1988. kinematics. On all investigated active rockglaciers in the Turtmann valley, a distinct acceleration of horizontal velocities has been recorded since the early 1990s. Since variations in rockglacier movement are mainly discussed in the context of temperature fluctuations in the current literature, the link between surface velocities and temperature development is investigated at two different scales. The signal of rockglacier speed-up in the period 1993–2001 (here termed as ‘regional signal’ since all rockglaciers show this behaviour) fits well with the general increase in air temperature recorded during the 1990s. On the local scale, the pattern of BTS values coincides well with the surface-velocity pattern, but in areas with high velocities the BTS temperatures are clearly below −3°C. Thus, marginal permafrost occurrence is not indicated in this data and the high velocities probably do not result directly from ‘warming’ permafrost conditions, as is suggested by other studies.

Landform - Structure, Evolution, Process Control

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SENSITIVITY AND PATH DEPENDENCE OF MOUNTAIN PERMAFROST SYSTEMS

price are net prices, subject to local VAT. Prices indicated with * include VAT for books; the €(D) includes 7% for Germany, the €(A) includes 10% for Austria. Prices indicated with ** include VAT for electronic products; 19% for Germany, 20% for Austria. All prices exclusive of carriage charges. Prices and other details are subject to change without notice. All errors and omissions excepted. J.-C. Otto, R. Dikau (Eds.) Landform Structure, Evolution, Process Control

Solifluction meets vegetation: the role of biogeomorphic feedbacks for turf‐banked solifluction lobe development

Verleysdonk, S., Krautblatter, M. and Dikau, R., 2011. Sensitivity and path dependence of mountain permafrost systems. Geografiska Annaler: Series A, Physical Geography, 93, 113–135. DOI: 10.1111/j.1468‐0459.2011.00423.x Abstract This article is an attempt to transfer a classical geomorphological concept – the sensitivity concept by Brunsden and Thornes – onto mountain permafrost systems. Focus is put on the impulses applied on the system and its subsequent response. The system state, the ratio between sensitivity and resistivity, as well as all system components and the external impulses are understood to be variable in space and time. In order to address sensitivity and path dependence in mountain permafrost systems, not only the present system configuration but also their historical development and possible future attractors have to be analysed. Important elements are the system configuration, variable impulses and thresholds, processes and process rates and internal feedbacks. The Zugspitze in the Northern Calcareous Alps at the German/Austrian border is chosen as a test site for the applicability of the sensitivity concept on mountain permafrost systems due to the high quantity of research conducted there and the significant impact of climate change on the periglacial system. Further aspects include the consequences of the Eibsee Bergsturz event in 3700 bp in terms of path dependence and geomorphic response time. With this conceptual approach, we hope (1) to enhance the interlinkage between periglacial geomorphology and other sub‐disciplines of geomorphology, (2) to contribute to the strengthening of the conceptual basis of periglacial geomorphology, and, therefore, (3) to strengthen the possibilities for holistic exchange within the cryospheric research community.

Concepts and approaches to long term and large scale modelling of fluvial systems

Vegetation is an important factor influencing solifluction processes, while at the same time, solifluction processes and landforms influence species composition, fine-scale distribution and corresponding ecosystem functioning. However, how feedbacks between plants and solifluction processes influence the development of turf-banked solifluction lobes (TBLs) and their geomorphic and vegetation patterns is still poorly understood. We addressed this knowledge gap in a detailed biogeomorphic investigation in the Turtmann glacier foreland (Switzerland). Methods employed include geomorphic and vegetation mapping, terrain assessment with unmanned aerial vehicle (UAV) and temperature logging. Results were subsequently integrated with knowledge from previous geomorphic and ecologic studies into a conceptual model. Our results show that geomorphic and vegetation patterns at TBLs are closely linked through the lobe elements tread, risers and ridge. A conceptual four-stage biogeomorphic model of TBL development with ecosystem engineering by the dwarf shrub Dryas octopetala as the dominant process can explain these interlinked patterns. Based on this model, we demonstrate that TBLs are biogeomorphic structures and follow a cyclic development, during which the role of their components for engineer and non-engineer species changes. Our study presents the first biogeomorphic model of TBL development and highlights the applicability and necessity of biogeomorphic approaches and research in periglacial environments. Copyright