The behavior of ice in frozen rock masses is an important control on rock slope stability but the knowledge of the formation, extent and evolution of ice-filled fractures in steep bedrock permafrost ...is limited. Therefore, this study aims at characterizing the site specific ambient seismic vibration recorded at the Matterhorn Hörnligrat fieldsite over the course of more than three years. The observed normal mode resonance frequencies vary seasonally with four distinct phases: persistent decrease during summer (phase I), rapid increase during freezing (phase II), trough-shaped pattern in winter (phase III) and a sharp peak with a rapid decay during the melting/thawing season (phase IV). The relation between resonance frequency and rock temperature exhibits an annually repeated pattern with hysteretic behavior. The link between resonance frequency, fracture width and rock temperature indicates that irreversible fracture displacement is dominant in summer periods with low resonance frequency. These findings suggest that the temporal variations in resonance frequencies are linked to the formation and melt of ice-fill in bedrock fractures.
•Over three years of recorded ambient seismic vibrations in bedrock permafrost.•Distinct seasonal patterns in resonance frequency were observed.•Obtained resonance frequency agrees with the resonance of cantilever beam.•Variations of ice-fill in fractures change the geometry of the resonating rock mass.•Temporal variations in resonance frequency are linked to ice-fill in fractures.
Le Cervin dont la pyramide parfaite est une image quasi-obsédante en Suisse, est une montagne emblématique dans l'histoire de l'alpinisme depuis sa conquête en 1865. Mais c'est aussi l'objet ...d'importantes recherches géologiques et géomorphologiques : place dans l'architecture tectonique de la chaîne alpine, formation par le recoupement de grands cirques glaciaires, fonte du pergélisol de paroi. Revêtant à la fois une valeur scientifique et emblématique en Suisse, il peut être considéré comme un géomorphosite bien caractérisé.
The Matterhorn, a famous mountain in the Swiss Alps is a well characterized geomorphosite, presenting both an important scientific interest and aesthetic, cultural and economic values in Switzerland. ...The main scientific issues concerning the Matterhorn are its place in the tectonic history of the Alps, the carving of a residual pyramid by glacial erosion and the effects of melting of high mountain permafrost on mountaineering. To answer those questions, two “tools” were used, the field work and the bibliographic investigations. The Matterhorn played, from its first ascent in 1865 until today, a very special role in the history of mountaineering, and its remarkable shape has become iconic in Switzerland. As a consequence, the Matterhorn can be analyzed through four time scales:(1) the deep time of tectonics during the Cenozoic era, which saw the thrusting and piling up of the “Pennine nappes,” due to the collision between African and European plates; (2) the Quaternary period of glacial erosion, which carved the Matterhorn into its distinctive pyramidal peak shape;(3) the Anthropocene time of the thawing of high mountain permafrost; and (4) the era of humans or mountaineering, which spans over than 150 years, from the first ascent in 1865 to the recent achievements of modern mountaineering.
Amplification of seismic energy in steep topography plays an important role controlling the location of earthquake-induced landslides. Alpine mountains represent extreme topography, therefore large ...amplification may be anticipated, however suitable data needed to probe the limits of topographic effects in these demanding locations are rare. Here we present new ambient vibration data from seismic stations on the summit and ridge of one of the tallest freestanding mountains in the Swiss Alps – the Matterhorn – comparing these to a nearby local reference. Results show elevated spectral power at mountain stations between 0.4 and 1 Hz, and directional site-to-reference spectral amplitude ratios up to 14, which we attribute in part to topographic resonance. We used ambient vibration modal analysis and numerical eigenfrequency modeling to identify the fundamental mode of the Matterhorn at 0.42 Hz, as well as evidence for a second, mutually-perpendicular mode at a similar frequency. We identified high modal damping ratios of ∼20% for these modes, which we ascribe to radiative energy loss. A short campaign measurement at another mountain of comparable shape but smaller scale showed similar modal properties with a higher fundamental frequency of 1.8 Hz and peak spectral ratios of 6. Tracking of resonant frequencies over one year at the Matterhorn revealed no measurable seasonal variations related to near-surface environmental changes (e.g. temperature, ice). Our results demonstrate large spectral amplifications linked to resonance of high-relief mountain landforms, which is likely to be a widespread effect making such areas more prone to co-seismic rock damage and landslides.
•We identified resonant modes of two mountains based on ambient seismic data.•Analyzed spectral, polarization and modal attributes plus eigenfrequency models.•The larger of these sites, the Matterhorn, has a fundamental frequency of 0.42 Hz.•Both sites exhibit large site-to-reference spectral ratios and high modal damping.•Spectral amplification and fundamental frequency were consistent over time.
Among other techniques, aerial and terrestrial photogrammetry have long been used to control the displacements of landslides and glaciers as well as for the detection of terrain morphological ...changes. Unmanned Aerial Systems (UAS) are today an efficient tool to perform data acquisition in rough or difficult terrain, both safely and quickly, avoiding hazards and risks for the operators while at the same time containing the survey costs. Since 2012 ARPAVdA (the Regional Environmental Protection Agency of Aosta Valley, Italy) periodically surveys with UAS photogrammetry the Gran Sometta rock glacier, the Agency main monitoring site for the climate change impacts on high-mountain areas and related infrastructures.
A Digital Surface Model (DSM) and an orthophoto of the rock glacier are produced after each survey flight. In order to accurately georeference them in a stable reference system, a Global Navigation Satellite System (GNSS) campaign is carried out at each epoch, to update the coordinates of signalised Ground Control Points (GCPs), since they partly lay in unstable (moving) areas. In late August 2015 a survey flight has been executed with a senseFly eBee RTK, with differential corrections sent from a ground reference station. The block has been adjusted without GCP using, as control information, only the projection centres coordinates encoded in the images. The RMS of the differences found on twelve Check Points were about 4cm in horizontal and 7cm in elevation, i.e. practically the same accuracy found using GCP. Differences between the DSMs produced at the same epoch with block orientation performed with GCP and with GNSS-determined projection centres were also investigated.
To evaluate the rock glacier displacement fields between two epochs, corresponding features were at first manually identified on the orthophotos by a trained operator. To avoid the manual time-consuming procedure and increase the density of displacement information, two automatic procedures, the former using Least Squares Matching (LSM) and the latter a proprietary implementation of Semi-Global Matching (SGM) have been implemented. Both techniques were applied to pairs of orthophotos as well as to pairs of DSMs at different epochs. A discussion of the characteristics of the implemented methods is provided and the results of the comparison of the two methods with manual measurements are illustrated. Overall, results using DSM matching provided higher completeness of the displacement field than orthophoto matching, especially if long-term (year-to-year) comparisons are considered. At the same time, SGM in both cases produced less mismatches and more smooth and reliable displacement fields than LSM.
Understanding rock slope kinematics in steep, fractured bedrock permafrost is a challenging task. Recent laboratory studies have provided enhanced understanding of rock fatigue and fracturing in cold ...environments but were not successfully confirmed by field studies. This study presents a unique time series of fracture kinematics, rock temperatures and environmental conditions at 3500 m a. s. l. on the steep, strongly fractured Hörnligrat of the Matterhorn (Swiss Alps). Thanks to 8 years of continuous data, the longer-term evolution of fracture kinematics in permafrost can be analyzed with an unprecedented level of detail. Evidence for common trends in spatiotemporal pattern of fracture kinematics could be found: a partly reversible seasonal movement can be observed at all locations, with variable amplitudes. In the wider context of rock slope stability assessment, we propose separating reversible (elastic) components of fracture kinematics, caused by thermoelastic strains, from the irreversible (plastic) component due to other processes. A regression analysis between temperature and fracture displacement shows that all instrumented fractures exhibit reversible displacements that dominate fracture kinematics in winter. Furthermore, removing this reversible component from the observed displacement enables us to quantify the irreversible component. From this, a new metric – termed index of irreversibility – is proposed to quantify relative irreversibility of fracture kinematics. This new index can identify periods when fracture displacements are dominated by irreversible processes. For many sensors, irreversible enhanced fracture displacement is observed in summer and its initiation coincides with the onset of positive rock temperatures. This likely indicates thawing-related processes, such as meltwater percolation into fractures, as a forcing mechanism for irreversible displacements. For a few instrumented fractures, irreversible displacements were found at the onset of the freezing period, suggesting that cryogenic processes act as a driving factor through increasing ice pressure. The proposed analysis provides a tool for investigating and better understanding processes related to irreversible kinematics.
In high mountain areas, permafrost is important because it influences the occurrence of natural hazards, because it has to be considered in construction practices, and because it is sensitive to ...climate change. The assessment of its distribution and evolution is challenging because of highly variable conditions at and below the surface, steep topography and varying climatic conditions. This paper presents a systematic investigation of effects of topography and climate variability that are important for subsurface temperatures in Alpine bedrock permafrost. We studied the effects of both, past and projected future ground surface temperature variations on the basis of numerical experimentation with simplified mountain topography in order to demonstrate the principal effects. The modeling approach applied combines a distributed surface energy balance model and a three-dimensional subsurface heat conduction scheme. Results show that the past climate variations that essentially influence present-day permafrost temperatures at depth of the idealized mountains are the last glacial period and the major fluctuations in the past millennium. Transient effects from projected future warming, however, are likely larger than those from past climate conditions because larger temperature changes at the surface occur in shorter time periods. We further demonstrate the accelerating influence of multi-lateral warming in steep and complex topography for a temperature signal entering the subsurface as compared to the situation in flat areas. The effects of varying and uncertain material properties (i.e., thermal properties, porosity, and freezing characteristics) on the subsurface temperature field were examined in sensitivity studies. A considerable influence of latent heat due to water in low-porosity bedrock was only shown for simulations over time periods of decades to centuries. At the end, the model was applied to the topographic setting of the Matterhorn (Switzerland). Results from idealized geometries are compared to this first example of real topography, and possibilities as well as limitations of the model application are discussed.
The PermaSense project is an ongoing interdisciplinary effort between geo-science and engineering disciplines and started in 2006 with the goals of realizing observations that previously have not ...been possible. Specifically, the aims are to obtain measurements in unprecedented quantity and quality based on technological advances. This paper describes a unique >10-year data record obtained from in situ measurements in steep bedrock permafrost in an Alpine environment on the Matterhorn Hörnligrat, Zermatt, Switzerland, at 3500 ma.s.l. Through the utilization of state-of-the-art wireless sensor technology it was possible to obtain more data of higher quality, make these data available in near real time and tightly monitor and control the running experiments. This data set (https://doi.org/10.1594/PANGAEA.897640, Weber et al., 2019a) constitutes the longest, densest and most diverse data record in the history of mountain permafrost research worldwide with 17 different sensor types used at 29 distinct sensor locations consisting of over 114.5 million data points captured over a period of 10 or more years. By documenting and sharing these data in this form we contribute to making our past research reproducible and facilitate future research based on these data, e.g., in the areas of analysis methodology, comparative studies, assessment of change in the environment, natural hazard warning and the development of process models. Finally, the cross-validation of four different data types clearly indicates the dominance of thawing-related kinematics.
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