WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland

Switzerland

WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland

Switzerland
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Bebi P.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Graf F.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Rickli C.,Swiss Federal Institute of forest
Earth Surface Processes and Landforms | Year: 2016

Forests can decrease the risk of shallow landslides by mechanically reinforcing the soil and positively influencing its water balance. However, little is known about the effect of different forest structures on slope stability. In the study area in St Antönien, Switzerland, we applied statistical prediction models and a physically-based model for spatial distribution of root reinforcement in order to quantify the influence of forest structure on slope stability. We designed a generalized linear regression model and a random forest model including variables describing forest structure along with terrain parameters for a set of landslide and control points facing similar slope angle and tree coverage. The root distribution measured at regular distances from seven trees in the same study area was used to calibrate a root distribution model. The root reinforcement was calculated as a function of tree dimension and distance from tree with the root bundle model (RBMw). Based on the modelled values of root reinforcement, we introduced a proxy-variable for root reinforcement of the nearest tree using a gamma distribution. The results of the statistical analysis show that variables related to forest structure significantly influence landslide susceptibility along with terrain parameters. Significant effects were found for gap length, the distance to the nearest trees and the proxy-variable for root reinforcement of the nearest tree. Gaps longer than 20 m critically increased the susceptibility to landslides. Root reinforcement decreased with increasing distance from trees and is smaller in landslide plots compared to control plots. Furthermore, the influence of forest structure strongly depends on geomorphological and hydrological conditions. Our results enhance the quantitative knowledge about the influence of forest structure on root reinforcement and landslide susceptibility and support existing management recommendations for protection against gravitational natural hazards. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd. 2016 10.1002/esp.3887 Research Article Research Articles Copyright © 2015 John Wiley & Sons, Ltd..


Phillips M.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Wolter A.,ETH Zurich | Luthi R.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Amann F.,ETH Zurich | And 2 more authors.
Earth Surface Processes and Landforms | Year: 2016

In February 2014, a rock pillar with a volume of around 150 000 m3 collapsed at Piz Kesch in the Eastern Swiss Alps. A reconstruction of the conditions prior to the event and of the event itself is presented on the basis of different sources of data. The methods applied include photogrammetry, terrestrial laser scanning, structural geological analysis, examination of meteorological data, carbon-14 (14C) dating of organic material in permafrost ice from a tension crack and numerical modelling of likely modes of failure. Despite a complete lack of in situ measurements in the rock wall prior to the event and of direct observations during the event, the available data allow the determination of the approximate timing of the event as well as the structural predisposition, the probable mode of failure and the timescale of several millennia involved in the triggering of the failure of the rock pillar. The interdisciplinary analysis of this event contributes towards understanding the complex interaction of processes involved in large rock slope failures currently occurring in warming mountain permafrost regions. © 2016 John Wiley & Sons, Ltd.


Zenklusen Mutter E.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Phillips M.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland
Permafrost and Periglacial Processes | Year: 2012

This study investigates and compares active layer characteristics determined from ground temperature measurements at ten borehole sites in various types of Alpine permafrost terrain. Active layer thickness (ALT) remained fairly constant at the individual boreholes over the past five to 14 years, but was highly variable among the sites due to local terrain characteristics. To allow intra-site comparisons, a characteristic depth within the active layer was determined for each site. The temperature series either measured or interpolated for that depth were used to investigate different thermal stages during the annual thawing and refreezing cycle. The relation between air temperature thawing-degree days and ALT was investigated on an annual, seasonal and daily basis. The results show that at least daily data are required to establish the relevant characteristics of active layer development. Periods of slow advance of the thaw plane, interpreted as being due to the presence of ice-bearing layers within the active layer, are particularly important to the final ALT. Rapid active layer deepening, however, can occur due to the formation of taliks caused by lateral thermal disturbances below the active layer. © 2012 John Wiley & Sons, Ltd.


Steinkogler W.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Gaume J.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Lowe H.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Sovilla B.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Lehning M.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland
Journal of Geophysical Research F: Earth Surface | Year: 2015

It is well known that snow avalanches exhibit granulation phenomena, i.e., the formation of large and apparently stable snow granules during the flow. The size distribution of the granules has an influence on flow behavior which, in turn, affects runout distances and avalanche velocities. The underlying mechanisms of granule formation are notoriously difficult to investigate within large-scale field experiments, due to limitations in the scope for measuring temperatures, velocities, and size distributions. To address this issue we present experiments with a concrete tumbler, which provide an appropriate means to investigate granule formation of snow. In a set of experiments at constant rotation velocity with varying temperatures and water content, we demonstrate that temperature has a major impact on the formation of granules. The experiments showed that granules only formed when the snow temperature exceeded -1°C. No evolution in the granule size was observed at colder temperatures. Depending on the conditions, different granulation regimes are obtained, which are qualitatively classified according to their persistence and size distribution. The potential of granulation of snow in a tumbler is further demonstrated by showing that generic features of the experiments can be reproduced by cohesive discrete element simulations. The proposed discrete element model mimics the competition between cohesive forces, which promote aggregation, and impact forces, which induce fragmentation, and supports the interpretation of the granule regime classification obtained from the tumbler experiments. Generalizations, implications for flow dynamics, and experimental and model limitations as well as suggestions for future work are discussed. © 2015. American Geophysical Union. All Rights Reserved.


Luethi R.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Phillips M.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Lehning M.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland
Permafrost and Periglacial Processes | Year: 2016

Although non-conductive heat flow plays an important role in the evolution of rock glacier temperature and dynamics, few studies have quantified it. At the Ritigraben rock glacier (Switzerland), intra-permafrost talik formation was observed at around 12m depth and related to snowmelt and rainfall infiltration. Our aim is to attribute the talik formation to physical processes by quantifying the heat required to explain the observed dynamics of the temperature profile. We combined measured borehole temperatures, meteorological data and borehole logs with physics-based modelling experiments using the one-dimensional SNOWPACK model. The simulations were run with a simulated heat sink/source controlled by modelled snow cover, measured meteorological data and borehole temperature measurements. This allowed us to estimate non-conductive heat flow for different synthetic ground profiles with varying physical properties based on borehole logs. Our model results corroborate the assumption that purely conductive heat exchange is incompatible with the observed talik formation. We attribute the talik to advective and conductive heating by infiltrating water (which causes local heating rates to the order of 1Wm-3) and circulating air (which causes cooling to the order of 0.1Wm-3). © 2016 John Wiley & Sons, Ltd.


Kenner R.,WSL Institute for Snow and Avalanche Research SLF Davos Dorf Switzerland | Magnusson J.,Norwegian Institute for Water Research
Permafrost and Periglacial Processes | Year: 2016

To elucidate the factors that influence rock glacier distribution, we created a rock glacier inventory for two regions in the Swiss Alps (the Albula Alps and the Glarner Alps) and identified their spatial characteristics by adding topographical and meteorological data to a GIS. We evaluated the influence of mean annual precipitation (MAP), mean annual air temperature, head wall erosion, glacier coverage, lithology, slope, aspect, elevation and snow cover on rock glacier occurrence and characteristics, taking into account the interactions between these factors. MAP, lithology and head wall erosion significantly influenced rock glacier distribution, and the interaction of precipitation and lithology seemed to play a key role. Wind-driven snow redistribution influenced rock glacier frequency on hillslopes with different aspects. Rock glaciers interact with all of the factors analysed and exhibit complex relations with their regional environments. © 2016 John Wiley & Sons, Ltd.

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