No abstract

Frozen ground characteristics resolved by annual, seasonal/monthly and daily electrical resistivity monitoring are presented based on case studies from three alpine sites in the Swiss Alps with different surface conditions and subsurface process dynamics. Data acquisition is achieved by different set-ups ranging from low-cost to automated and more expensive monitoring strategies. To ensure the reproducibility of measurement results a robust setup is required within the rough surface conditions of alpine environments, and this constitutes a fundamental precondition for time-lapse measurements.The selected different monitoring approaches allow for a detection and analysis of processes related to frozen ground dynamics on varying timescales. The interpretation of the geophysical data is improved by temperature measurements from various data loggers and borehole data. All three approaches allowed detection of the interface between frozen and unfrozen ground. The variation of the frequency of measurements enabled exploration of the specific permafrost-related problems. At one site, the multi-annual resistivity distribution at the end of the thawing period revealed fairly stable permafrost conditions, while at the second site, year-round measurements showed extremely divergent evolution of resistivity values in the subsurface throughout the measurement period, which could be ascribed to different site-specific environmental parameters. Using measurements with daily resolution at the third field site, the rapid decrease in subsurface resistivity values due to the infiltration of meltwater in spring could be documented. The presented results show that the different monitoring set-ups have their justification and are able to monitor timedependent subsurface dynamics within the scale of their temporal resolution.The operation of an automated monitoring system allows for very efficient observation especially of short-time processes within the active layer and the frozen ground below, the major advantage in comparison to non-automated monitoring approaches. However, the system is cost-intensive, requires an extensive infrastructure, and is more prone to environmental forces. For monitoring the inter-annual and long-term permafrost evolution, application of a fixed monitoring set-up that is accessible throughout the year and measured manually has proven to be a robust and cost-efficient alternative. Focusing on the long-term permafrost evolution, set-ups using fixed electrodes and measurements conducted as needed with a brought-along cable is a legitimate approach. Hence, for studies in alpine permafrost environments, choice of the monitoring set-up remains a question of the scientific problem, infrastructure facilities, and cost-efficiency.

Abstract. This study aimed to optimise the application, efficiency and interpretability of quasi-3D resistivity imaging for investigating the heterogeneous permafrost distribution at mountain sites by a systematic forward modelling approach. A three dimensional geocryologic model, representative for most mountain permafrost settings, was developed. Based on this geocryologic model quasi-3D models were generated by collating synthetic orthogonal 2D arrays, demonstrating the effects of array types and electrode spacing on resolution and interpretability of the inversion results. The effects of minimising the number of 2D arrays per quasi-3D grid were tested by enlarging the spacing between adjacent lines and by reducing the number of perpendicular tie lines with regard to model resolution and loss of information value. Synthetic and measured quasi-3D models were investigated with regard to the lateral and vertical resolution, reliability of inverted resistivity values, the possibility of a quantitative interpretation of resistivities and the response of the inversion process on the validity of quasi-3D models. Results show that setups using orthogonal 2D arrays with electrode spacings of 2 m and 3 m are capable of delineating lateral heterogeneity with high accuracy and also deliver reliable data on active layer thickness. Detection of permafrost thickness, especially if the permafrost base is close to the penetration depth of the setups, and the reliability of absolute resistivity values emerged to be a weakness of the method. Quasi-3D imaging has proven to be a promising tool for investigating permafrost in mountain environments especially for delineating the often small-scale permafrost heterogeneity, and therefore provides an enhanced possibility for aligning permafrost distribution with site specific surface properties and morphological settings.

The Southern Kalahari Drainage network is in a key position to analyze spatiotemporal changes in the tropical easterly and the temperate westerly circulation over the Southern African subcontinent. However, due to the prevailing aridity, paleoenvironmental archives within the southwestern Kalahari are sparse and often discontinuous. Hence, little is known about Holocene environmental change in this region. This study focuses on reconstructing paleoenvironmental change from the timing and provenance of fluvial deposits located within the Molopo Canyon, which connects the Southern Kalahari Drainage to the perennial flow regime of the Orange River. To gain insight into temporal aspects of fluvial morphodynamics within the Molopo Canyon, the entire variety of fluvial landforms consisting mainly of slope sediments, alluvial fans and alluvial fills were dated using Optically Stimulated Luminescence (OSL). We additionally applied a provenance analysis on alluvial fill deposits to estimate potential sediment source areas. Source areas were identified by analyzing the elemental and mineralogical composition of tributaries and eolian deposits throughout the course of the lower Molopo. The results allow the first general classification of fluvial landscape development into three temporally distinct deposition phases in the southern Kalahari: (1) A phase of canyon aggradation associated with short lived and spatially restricted flash floods during the early to mid-Holocene; (2) A phase of fan aggradation indicating a decrease in flood intensities during the mid-to late Holocene; (3) A phase of canyon aggradation caused by the occurrence of supraregional flood events during the Little Ice Age. We interpret the observed spatiotemporal deposition patterns to latitudinal shifts of the tropical easterly circulation in the early to mid-Holocene and the temperate westerly circulation in the late Holocene. However, despite marked changes in the provenance and timing of fluvial deposits in the Molopo Canyon throughout the Holocene, our analysis did not detect a contribution of sediments originating from the Kalahari interior to the deposition of alluvial fills. These results suggest that the Southern Kalahari drainage remained endorheic and therefore disconnected from the Orange River throughout the Holocene.

Abstract. Die Region um Ebermannstadt ist stark anfällig für Massenbewegungen. Eine Rutschung aus dem Jahr 1957 wurde geomorphologisch kartiert und mit geophysikalischen Messungen (Gleichstromgeoelektrik sowie Refraktionsseismik) untersucht. Die Ziele der Untersuchungen waren eine Rekonstruktion der Beobachtungen von 1957 sowie deren Vergleich mit der heutigen Oberfläche und dem oberflächennahen Untergrund. Die Ergebnisse zeigen, dass die früheren Beobachtungen auch heute noch Gültigkeit besitzen. Darüber hinaus ist es möglich, einzelne Rutschungselemente und Prozesse zu differenzieren. Die Studie zeigt zudem die Verbreitung von alten Rutschmassen, welche in die Rutschung von 1957 eingebunden waren. Eine erneute Remobilisierung dieser Ablagerungen kann nicht ausgeschlossen werden.