scholarly journals Internal structure of two alpine rock glaciers investigated by quasi-3-D electrical resistivity imaging

2017 ◽  
Vol 11 (2) ◽  
pp. 841-855 ◽  
Author(s):  
Adrian Emmert ◽  
Christof Kneisel
Keyword(s):  
Electrical Resistivity ◽  
Internal Structure ◽  
Swiss Alps ◽  
Electrical Resistivity Imaging ◽  
Rock Glacier ◽  
Ground Ice ◽  
Resistivity Imaging ◽  
Wide Range ◽  
Rock Glaciers ◽  
Ice Content

Abstract. Interactions between different formative processes are reflected in the internal structure of rock glaciers. Therefore, the detection of subsurface conditions can help to enhance our understanding of landform development. For an assessment of subsurface conditions, we present an analysis of the spatial variability of active layer thickness, ground ice content and frost table topography for two different rock glaciers in the Eastern Swiss Alps by means of quasi-3-D electrical resistivity imaging (ERI). This approach enables an extensive mapping of subsurface structures and a spatial overlay between site-specific surface and subsurface characteristics. At Nair rock glacier, we discovered a gradual descent of the frost table in a downslope direction and a constant decrease of ice content which follows the observed surface topography. This is attributed to ice formation by refreezing meltwater from an embedded snow bank or from a subsurface ice patch which reshapes the permafrost layer. The heterogeneous ground ice distribution at Uertsch rock glacier indicates that multiple processes on different time domains were involved in the development. Resistivity values which represent frozen conditions vary within a wide range and indicate a successive formation which includes several advances, past glacial overrides and creep processes on the rock glacier surface. In combination with the observed topography, quasi-3-D ERI enables us to delimit areas of extensive and compressive flow in close proximity. Excellent data quality was provided by a good coupling of electrodes to the ground in the pebbly material of the investigated rock glaciers. Results show the value of the quasi-3-D ERI approach but advise the application of complementary geophysical methods for interpreting the results.

scholarly journals Internal structure of two alpine rockglaciers investigated by quasi-3D electrical resistivity imaging (ERI)

2016 ◽  
Author(s):  
Adrian Emmert ◽  
Christof Kneisel
Keyword(s):  
Electrical Resistivity ◽  
Internal Structure ◽  
Geophysical Methods ◽  
Swiss Alps ◽  
Electrical Resistivity Imaging ◽  
Active Layer Thickness ◽  
Ground Ice ◽  
Resistivity Imaging ◽  
Wide Range ◽  
Ice Content

Abstract. Interactions between different formative processes are reflected in the internal structure of rockglaciers. Its detection can therefore help to enhance our understanding of landform development. For an assessment of subsurface conditions, we present an analysis of the spatial variability of active layer thickness, ground ice content and frost table topography at two different rockglacier sites in the Eastern Swiss Alps by means of quasi-3D electrical resistivity imaging (ERI). This approach enables an extensive mapping of subsurface structures and hence the performance of a spatial overlay between site-specific surface und subsurface characteristics. At Nair rockglacier, we discovered a gradual descent of the frost table in a downslope direction and a homogenous decrease of ice content which follows the observed surface topography. This is attributed to ice formation by refreezing meltwater from an embedded snowbank or from a subsurface ice patch which reshapes the permafrost layer. The heterogeneous ground ice distribution at Uertsch rockglacier indicates that multiple processes on different time domains were involved in rockglacier development. Resistivity values which represent frozen conditions vary within a wide range and indicate a successive formation which includes several rockglacier advances, past glacial overrides and creep processes on the rockglacier surface. In combination with the observed rockglacier topography, quasi-3D ERI enables us to delimit areas of extensive and compressive flow in close proximity. Excellent data quality was provided by a good coupling of electrodes to the ground in the pebbly material of the investigated rockglaciers. Results show the value of the quasi-3D ERI approach but advice the application of complementary geophysical methods for interpreting the results.

scholarly journals Towards accurate quantification of ice content in permafrost of the Central Andes – Part II: an upscaling strategy of geophysical measurements to the catchment scale at two study sites

2021 ◽  
Author(s):  
Tamara Mathys ◽  
Christin Hilbich ◽  
Lukas U. Arenson ◽  
Pablo A. Wainstein ◽  
Christian Hauck
Keyword(s):  
Geophysical Data ◽  
Distribution Model ◽  
Permafrost Degradation ◽  
Rock Glacier ◽  
Ground Ice ◽  
Data Set ◽  
Refraction Seismic ◽  
Geophysical Surveys ◽  
Rock Glaciers ◽  
Ice Content

Abstract. With ongoing climate change, there is a pressing need to better understand how much water is stored as ground ice in areas with extensive permafrost occurrence and how the regional water balance may alter in response to the potential generation of melt water from permafrost degradation. However, field-based data on permafrost in remote and mountainous areas such as the South-American Andes is scarce and most current ground ice estimates are based on broadly generalised assumptions such as volume-area scaling and mean ground ice content estimates of rock glaciers. In addition, ground ice contents in permafrost areas outside of rock glaciers are usually not considered, resulting in a significant uncertainty regarding the volume of ground ice in the Andes, and its hydrological role. In part I of this contribution, Hilbich et al. (submitted) present an extensive geophysical data set based on Electrical Resistivity Tomography (ERT) and Refraction Seismic Tomography (RST) surveys to detect and quantify ground ice of different landforms and surface types in several study regions in the semi-arid Andes of Chile and Argentina with the aim to contribute to the reduction of this data scarcity. In part II we focus on the development of a methodology for the upscaling of geophysical-based ground ice quantification to an entire catchment to estimate the total ground ice volume (and its estimated water equivalent) in the study areas. In addition to the geophysical data, the upscaling approach is based on a permafrost distribution model and classifications of surface and landform types. Where available, ERT and RST measurements were quantitatively combined to estimate the volumetric ground ice content using petrophysical relationships within the Four Phase Model (Hauck et al., 2011). In addition to introducing our upscaling methodology, we demonstrate that the estimation of large-scale ground ice volumes can be improved by including (i) non-rock glacier permafrost occurrences, and (ii) field evidence through a large number of geophysical surveys and ground truthing information. The results of our study indicate, that (i) conventional ground ice estimates for rock-glacier dominated catchments without in-situ data may significantly overestimate ground ice contents, and (ii) substantial volumes of ground ice may also be present in catchments where rock glaciers are lacking.

scholarly journals Towards accurate quantification of ice content in permafrost of the Central Andes, part I: geophysics-based estimates from three different regions

2021 ◽  
Author(s):  
Christin Hilbich ◽  
Christian Hauck ◽  
Coline Mollaret ◽  
Pablo Wainstein ◽  
Lukas U. Arenson
Keyword(s):  
Remote Sensing ◽  
Hydrological Cycle ◽  
Field Measurements ◽  
Central Andes ◽  
Rock Glacier ◽  
Ground Ice ◽  
Catchment Scale ◽  
Refraction Seismic ◽  
Rock Glaciers ◽  
Ice Content

Abstract. In view of the increasing water scarcity in the Central Andes in response to ongoing climate change, the significance of permafrost occurrences for the hydrological cycle is currently being discussed in a controversial way. The lack of comprehensive field measurements and quantitative data on the local variability of internal structure and ground ice content further enhances the situation. We present field-based data from six extensive geophysical campaigns completed since 2016 in three different high-altitude regions of the Central Andes of Chile and Argentina (28 to 32° S). Our data cover various permafrost landforms ranging from ice-poor bedrock to ice-rich rock glaciers and are complemented by ground truthing information from boreholes and numerous test pits near the geophysical profiles. In addition to determining the thickness of the potential ice-rich layers from the individual profiles, we also use the quantitative 4-phase model to estimate the volumetric ground ice content in representative zones of the geophysical profiles. The analysis of 52 geoelectrical and 24 refraction seismic profiles within this study confirmed that ice-rich permafrost is not restricted to rock glaciers, but is also observed in non-rock-glacier permafrost slopes in the form of interstitial ice as well as layers with excess ice, resulting in substantial ice contents. Consequently, non-rock glacier permafrost landforms, whose role for local hydrology has so far not been considered in remote-sensing based approaches, may be similarly relevant in terms of ground ice content on a catchment scale and should not be ignored when quantifying the potential hydrological significance of permafrost. We state that geophysics-based estimates on ground ice content allow for more accurate assessments than purely remote-sensing-based approaches. The geophysical data can then be further used in upscaling studies to the catchment scale in order to reliably estimate the hydrological significance of permafrost within a catchment.

Pushing the limits of electrical resistivity tomography measurements on a rock glacier at 5500 m a.s.l. on the Tibetan Plateau: Successes and Challenges

2020 ◽  
Author(s):  
Nora Krebs ◽  
Anne Voigtländer ◽  
Matthias Bücker ◽  
Andreas Hördt ◽  
Ruben Schroeckh ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Tibetan Plateau ◽  
Internal Structure ◽  
Electrical Resistivity Tomography ◽  
High Resistivity ◽  
Mountain Range ◽  
The Tibetan Plateau ◽  
Rock Glacier ◽  
Resistivity Tomography ◽  
Rock Glaciers

<p>Geophysical methods provide a powerful tool to understand the internal structure of active rock glaciers. We applied Electrical Resistivity Tomography (ERT) to a rock glacier at an elevation of 5500 m a.s.l. in the semi-arid Nyainqêntanglha mountain range on the Tibetan plateau, China.  The investigations comprised three transects across the rock glacier and its catchment, each spanning over a distance of 296 m up to 396 m, equipped with 75 up to 100 electrodes respectively. Our measurements were successful in revealing internal structures of the rock glacier, but were also accompanied by challenges.</p><p>We successfully detected first-order permafrost structures, such as a shallow about 4 m thick active layer of low electrical resistivity values that was underlain by potentially ice rich zones of high resistivity. Further high-resistivity zones were found and interpreted as dense bed rock of adjacent slopes that undergird the loose rock glacier debris.</p><p>Challenges, we faced in the application of ERT, were mainly posed by the morphology and internal structure of the rock glacier itself. Coarse debris created a rough surface that prevented a uniform setup with accurate 4 m spacing. The presence of loosely nested blocks of pebble size up to boulders with large interspaces resulted in high contact resistances. The consequent low injection current densities and possible noisy voltage readings downgraded part of the data, causing low data density and resolution. Coupling was partly improved by attaching salt-watered sponges to the electrodes and adding more conductive fine-grained materials to the electrodes. The detected high resistivity ice layer impeded deep penetration of electrical currents, which caused that the lower limit of the permanently frozen zone could not be defined.</p><p>Despite these challenges, the captured ERT profiles are an indispensable contribution to the sparse field data on the internal structure of rock glaciers on the Tibetan plateau. Our results contribute to a better understanding of the prospective evolution of rock glaciers in dry, high mountain ranges under a changing climate.</p>

Towards accurate quantification of ground ice content in permafrost of the Central Andes: geophysics-based estimates from three different regions

2021 ◽  
Author(s):  
Christin Hilbich ◽  
Tamara Mathys ◽  
Christian Hauck ◽  
Lukas Arenson
Keyword(s):  
Remote Sensing ◽  
Central Andes ◽  
The Other ◽  
Data Sets ◽  
Rock Glacier ◽  
Ground Ice ◽  
Other Hand ◽  
Rock Glaciers ◽  
Ice Content ◽  
Permafrost Regions

<p>Continued climate change is projected to cause significant temperature increase, yielding substantial water shortage especially in the semi-arid mountain regions of the Central Andes. The role of permafrost occurrences for the hydrological cycle in the Central Andes is currently discussed in a controversial way. On the one hand, permafrost in general, and especially rock glaciers are considered key stores of frozen water in view of the recession of glaciers, and degrading permafrost is expected to partly compensate the decreasing glacial discharge in future. On the other hand, the methodology to quantify ground ice resources in Andean permafrost regions as well as the time scales involved for significant discharge from permafrost bodies are currently disputed.</p><p>Comprehensive and quantitative field-based data on the local variability of internal structure, ground ice content and the hydrological contribution of different permafrost landforms are mostly lacking, and the current debate mostly focuses on rock glaciers as the prominent ice-rich permafrost landforms, as they can easily be identified by remote sensing.</p><p>To ameliorate this lack of ground truth data, we present a quantitative analysis of > 50 Electrical Resistivity Tomography and > 20 Refraction Seismic Tomography profiles from several permafrost sites in different geomorphologic settings, including ice-rich and ice-poor permafrost occurrences. The surveys were conducted between 2016 and 2019 in three different regions of the Central Andes of Chile and Argentina (28 - 32° S) in the framework of several Baseline studies in mining environments. For some sites borehole and test pit data are available and used to validate the quantitative estimates of ground ice contents by the 4-phase model (Hauck et al. 2011).</p><p>We demonstrate the value of geophysical surveys to detect ice-rich permafrost in various landforms (also beyond rock glaciers), and to estimate ground ice volumes in permafrost regions. Our data show, that remote-sensing based approaches tend to significantly overestimate ice volumes of rock glaciers, and on the other hand, that ice-rich permafrost is not restricted to rock glaciers, but also observed in non-rock-glacier permafrost slopes in the form of interstitial ice and layers with excess ice. In regions with widespread occurrence of such permafrost slopes, even relatively thin ice-rich layers can sum up to substantial total ground ice contents, which can be close to the volumes observed in rock glaciers. Consequently, non-rock-glacier permafrost terrain, whose role for local hydrology is basically neglected in remote-sensing based approaches, may be of equal hydrological significance regarding stored ground ice volumes on the catchment scale in some cases, and shall not be ignored.</p><p>The presented data may therefore serve as one of the first available field-based and validated data sets regarding the presence and total quantities of ground ice, and as input for modelling studies about the relative contributions of rock glacier and non-rock glacier permafrost to runoff in the Central Andes.</p><p> </p><p>References</p><p>Hauck C, Böttcher M and Maurer H 2011. A new model for estimating subsurface ice content based on combined electrical and seismic data sets. The Cryosphere 5(2): 453-468.</p>

Informed experimental design for electrical resistivity imaging

2011 ◽  
Vol 9 (5) ◽  
pp. 469-482 ◽  
Author(s):  
Vanessa Nenna ◽  
Adam Pidlisecky ◽  
Rosemary Knight
Keyword(s):  
Electrical Resistivity ◽  
Experimental Design ◽  
Electrical Resistivity Imaging ◽  
Resistivity Imaging

scholarly journals Verification of geophysical models in Alpine permafrost using borehole information

2000 ◽  
Vol 31 ◽  
pp. 300-306 ◽  
Author(s):  
Daniel S. Vonder Mühll ◽  
Christian Hauck ◽  
Frank Lehmann
Keyword(s):  
Geophysical Methods ◽  
Swiss Alps ◽  
Rock Glacier ◽  
Surface Microtopography ◽  
Refraction Seismics ◽  
Geophysical Surveys ◽  
Ground Conditions ◽  
Lateral Extent ◽  
Ice Content ◽  
Difficult Terrain

AbstractAt two permafrost sites in the Swiss Alps a range of geophysical methods were applied to model the structure of the subsurface. At both sites, borehole information was used to verify the quality of the model results. On the Murtèl-Corvatsch rock glacier (2700 m a.s.L; upper Engadine) a 58 m deep core drilling was performed in 1987. D. c resistivity measurements, refraction seismics, ground-penetrating radar (GPR) and gravimetric surveys allowed the shape of the permafrost table beneath the marked surface microtopography to be determined and the lateral extent of a deeper shear horizon to be established The validity of each method was verified by the borehole information (cores, density log and temperature). A coherent model of the rock-glacier structure was developed. At the Schilthorn (2970 m a.s.L; Bernese Oberland), it was not clear whether permafrost is in fact present. Various geophysical surveys (d.c. resistivity tomography, refraction seismics, GPR and EM-31) gave results that were not typical of permafrost environments. A 14 m percussion drilling revealed warm permafrost and a very low ice content. These geotechnical and geothermal data allowed reinterpretation of the geophysical results, improving modelling of ground conditions. The paper demonstrates that in the difficult terrain of Alpine permafrost, boreholes may be critical in calibration and verification of the results of geophysical methods. The most useful combinations of geophysical techniques proved to be (a) seismics with d.c. resistivity, and (b) gravimetry with GPR.

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