Markus Keuschnig

DETECTION OF MOUNTAIN PERMAFROST BY COMBINING HIGH RESOLUTION SURFACE AND SUBSURFACE INFORMATION – AN EXAMPLE FROM THE GLATZBACH CATCHMENT, AUSTRIAN ALPS

Otto, J.‐C., Keuschnig, M., Götz, J., Marbach, M. and Schrott, L., 2012. Detection of mountain permafrost by combining high resolution surface and subsurface information – an example from the Glatzbach catchment, Austrian Alps. Geografiska Annaler: Series A, Physical Geography, 94, 43–57. doi:10.1111/j.1468‐0459.2012.00455.x Abstract Permafrost distribution in mid‐latitude mountains is strongly controlled by solar radiation, snow cover and surface characteristics like debris cover. With decreasing elevation these factors have to counterbalance local positive air temperatures in order to enable permafrost conditions. We combine high resolution surface data derived from terrestrial laser scanning with geophysical information on the underground conditions using ground penetrating radar and electrical resistivity tomography and ground surface temperature data in order to understand the effects of surface characteristics on permafrost distribution in an Alpine catchment, Austrian Alps (Glatzbach, 47°2′23.49″N; 12°42′33.24″E, 2700–2900 m a.s.l.). Ground ice and permafrost is found above an elevation of 2780 m a.s.l. on north‐east facing slopes in 2009, previous studies detected permafrost at the same site at 2740 m a.s.l. in 1991. Analysis of surface roughness as a proxy for grain size distribution reveals that the lower boundary of discontinuous and sporadic permafrost is lowered on rough surfaces compared to fine‐grain zones. At the same location modelled potential summer solar radiation in coarse grain zones is reduced by up to 40% compared to surfaces of fine grain sizes. The mostly patchy permafrost distribution at the Glatzbach can therefore be attributed to local surface cover characteristics, particularly regolith grain size and its influence on solar radiation. We conclude that the analysis of ground surface characteristics using very high resolution terrain data supports the assessment of permafrost in Alpine areas by identifying rough surface conditions favouring permafrost occurrence.

Geoelectrical monitoring of frozen ground and permafrost in alpine areas: field studies and considerations towards an improved measuring technology

Processes that control permafrost warming in Alpine regions are still not completely understood. Recently, geoelectrical monitoring has emerged as a useful tool to investigate thawing and freezing processes. However, high resistive environments and harsh environmental conditions pose very unfavourable conditions for automated resistivity measurements. Based on the results of several test studies, an improved data acquisition system for geoelectrical monitoring of frozen soils was developed. Furthermore, the implementation of algorithms for statistical analysis of raw data time series led to a significant improvement in the reliability of inversion results. At two Alpine sites, namely Molltaler Glacier and Magnetkopfl/Kitzsteinhorn, the adapted system was tested at soil temperature conditions between 0°C and –12°C. Data was continuously collected at both locations over nearly a full seasonal cycle. The results showed an almost linear dependency of resistivity and temperature at values above –0.5°C. At lower temperatures, the relation was non-linear, indicating that the reduction of porosity due to the shrinking of connected brine channels was the dominating process that determined the value of resistivity. Based on the derived results, further improvements were suggested, especially for measurements at soil temperatures below –4.5°C as low injection currents make it extremely challenging to gather these.

Permafrost-Related Mass Movements: Implications from a Rock Slide at the Kitzsteinhorn, Austria

Rock instability in high mountain areas poses an important risk for man and infrastructure. At 3 p.m. on 18 August 2012 a rock slide event was documented at the Kitzsteinhorn, Austria. The release zone was detected on a north-exposed rock face below the cable car summit station (3.029 m). Analysis of terrestrial laser scanning (TLS) data delivered an accurate identification of the release zone yielding a rock fall volume of approximately 500 m3. Cubic Blocks with lengths of up to 4 m and block masses of up to 125 t were released during the event. The failure plane is located in a depth of approximately 3–4 m and runs parallel to the former rock surface (mean inclination 47°). Comparison with borehole data located less than 50 m from the release zone shows that failure plane depth is consistent with active layer depth. The event documentation is supplemented with observations of rock and air temperature, data on precipitation and snow depth, electrical resistivity tomography data, observed active layer depth and geological/geotechnical background data. The comprehensive ambient data suggests the influence of high temperatures and water availability for the triggering of the rock slide.

Analyzing the Sensitivity of a Distinct Element Slope Stability Model: A Case Study on the Influence of Permafrost Degradation on Infrastructure Stability

Since the 19th century, the warming rate in the European Alpine region has been twice as high as the average global rate. Warming-related permafrost degradation has been shown to cause a reduction of bedrock bearing capacities, potentially leading to the destabilization and eventually to the failure of high-alpine infrastructure. The presented study investigates permafrost-related changes of bedrock properties and their stability-relevant effects on high-alpine infrastructures. The Kitzsteinhorn summit and its highly frequented cable car station (3029 m a.s.l., Austria) is home to the interdisciplinary Open Air Lab Kitzsteinhorn (OpAL), where the consequences of climate change, based on a long-term monitoring of surface, subsurface and atmospheric parameters are investigated. In a rock-ice mechanical model, degradation of permafrost causes changes in rock fracture toughness and rock friction, affects ice fracturing and creep as well as the behavior of rock-ice interfaces. A first numerical distinct element model of the mechanical behavior of rock slope and the infrastructure was set up, based on OpAL datasets and a civil engineering assessment of the cable car setup. By conducting a thorough rock mechanical model sensitivity analysis, it was tested how individual model parameters affect the rock slope stability below the cable car summit station. The accurate knowledge of the most sensitive parameters and their empirical variation range generates a better process understanding of destabilisation in permafrost-affected rock walls. This facilitates efficient stabilization measures for affected high-alpine infrastructures. Here we show, that the stability of infrastructure on permafrost-affected bedrock is not only passively determined by mechanical changes in the underlying frozen rock mass, but infrastructure also actively affects thermal conditions and rock stability in a relevant way.

Climate Change Impacts on High Alpine Infrastructures: An Example from the Kitzsteinhorn (3200 m), Salzburg, Austria

Numerous rock fall events in the European Alps suggest an increasing occurrence of mass movements due to rising temperatures. In recent years particularly during extensive hot periods large numbers of rock fall events have been reported (e.g. hot summers of 2003, 2005 and 2012). Governed by climate change two major changes can be observed at the summit region of the Kitzsteinhorn, Austria: Intensive glacier retreat and changes of permafrost conditions. The combination of these two major changes leads to an increasing exposure of potentially hazardous areas and higher risks for man and infrastructure. Close to the summit, infrastructure was built in the 1960s, including a cable car station at 3029 m on a north exposed rock face w under permafrost conditions. Due to the decreasing surface area of the glacier and the deepening of the annual active layer, meter thick slabs of the slope became unstable and started sliding down slope parallel to bedding planes. In order to avoid a continuous and deep-reaching destabilization of the entire slope, an intensive rehabilitation program has been established. This program consists of short-, mid- and long-term measures with technical installations (drainage, rock support, etc.) and an intensive monitoring program (including laser scanning, continuous geophysical, geotechnical and temperature monitoring).

Adapting to Climate Change in a High Mountain Environment: Developing a Monitoring Expert System for Hazardous Rock Walls

The research project MOREXPERT (“Monitoring Expert System for Hazardous Rock Walls”) investigates short and medium term responses of slope stability to climatic changes in high alpine rock walls. The study contributes to the question how man and infrastructure are potentially affected by these responses. Based on a combination of geophysical, geotechnical and borehole measurements, surface and subsurface conditions are monitored within the study area at the Kitzsteinhorn (3.203 m), Hohe Tauern, Austria. Factors controlling slope stability in steep bedrock, most notably freeze/thaw and permafrost dynamics, are identified and analysed with respect to changing climatic conditions. The fundamental goal of this research project is the development of a general decision support system for slope stability assessment in steep bedrock. Due to its flexible structure the decision support system is intended to be adaptable for application to rock walls of other regions.