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>

Inventory of active rock glaciers in the western Nyainqêntanglha Range, Tibetan Plateau

2021 ◽  
Author(s):  
Eike Reinosch ◽  
Markus Gerke ◽  
Björn Riedel ◽  
Antje Schwalb ◽  
Qinghua Ye ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
High Reliability ◽  
Surface Velocity ◽  
Windward Side ◽  
Mountain Range ◽  
The Tibetan Plateau ◽  
Automated Classification ◽  
Rock Glacier ◽  
North West ◽  
Rock Glaciers

<p>The western Nyainqêntanglha Range on the Tibetan Plateau (TP) reaches an elevation of 7162 m and is characterized by an extensive periglacial environment. Here, we present the first rock glacier inventory of the central TP containing 1433 rock glaciers over an area of 4622 km². The rock glaciers are identified based on their surface velocity. The surface velocity is derived from Sentinel-1 satellite data of 2016 to 2019 via InSAR time series analysis. 16.4 % of the inventoried rock glaciers are classified as active with a surface velocity above 10 cmyr<sup>-1</sup> and 80.0 % are classified as transitional with 1 to 10 cmyr<sup>-1</sup>. The western Nyainqêntanglha Range forms a climate divide between the dry continental climate brought by the Westerlies from the north-west and the Indian Summer Monsoon to the south. 89.7 % of all active rock glaciers and 74 % of the free ice glacial area are located on the southern side. The higher moisture availability on the southern (windward) side of the mountain range is likely the cause of a higher rock glacier occurrence and the greater activity.</p><p>Manually identifying and outlining rock glaciers is time consuming and subjective. To ensure a high reliability and comparability of our inventory, we therefore combined a manual approach with an automated classification. Three analysts worked in tandem to generate the manual outlines according to the guidelines of the IPA action group on ‘Rock glacier inventories and kinematics’. A subset of these outlines acted as training areas for a pixel-based maximum likelihood classification. Both the manual and the automated classification were performed based on DEM parameters (elevation, slope etc.), optical datasets (Sentinel-2 and NDVI) and surface velocity (generated with InSAR). 87.8 % of all manually outlined rock glaciers were identified successfully at a true positive rate of 69.5 %. 18 additional rock glaciers were added to the inventory based on the automated classification. This combined approach is therefore beneficial to generate a complete inventory. The automated classification can, however, not replace the expertise of an analyst as it greatly overestimates the actual rock glacier area.</p>

Internal structure and conditions of permafrost mounds at Umiujaq in Nunavik, Canada, inferred from field investigation and electrical resistivity tomography

2008 ◽  
Vol 45 (3) ◽  
pp. 367-387 ◽  
Author(s):  
Richard Fortier ◽  
Anne-Marie LeBlanc ◽  
Michel Allard ◽  
Sylvie Buteau ◽  
Fabrice Calmels
Keyword(s):  
Electrical Resistivity ◽  
Internal Structure ◽  
Prior Information ◽  
Electrical Resistivity Tomography ◽  
Reference Model ◽  
High Resistivity ◽  
Unfrozen Water ◽  
Resistivity Tomography ◽  
Unfrozen Water Content ◽  
Resistivity Model

A systematic approach was used for the interpretation of the electrical resistivity tomography carried out on two permafrost mounds at Umiujaq in Nunavik, Canada, to assess their internal structure and conditions. Prior information under the form of a geocryologic model of the permafrost mounds was integrated in the inversion of the pseudo-section of apparent electrical resistivity. The geocryologic model was developed from the synthesis of previous field investigations, including shallow and deep sampling, temperature and electrical resistivity logging, and cone penetration tests performed in the permafrost mounds. Values of electrical resistivity were ascribed to the different layers making of the geocryologic model to define a synthetic resistivity model of the permafrost mounds used as a reference model to constrain the inversion. The constrained resistivity model clearly show the presence of ice-rich cores in the permafrost mounds underscored by high resistivity values in excess of 30 000 Ωm, while the unfrozen zones surrounding the permafrost mounds are characterized by resistivity values lower than 1000 Ωm. The spatial distribution of unfrozen water and ice contents in the permafrost mounds were also assessed according to empirical relationships between the electrical resistivity and water contents. The ice content is highly variable and can be as high as 80% in the ice-rich cores, while the unfrozen water content varies between 2% and 5%. The integration of prior information in the inversion process leads to a more realistic constrained resistivity model showing sharp resistivity contrasts expected at the boundaries such as the permafrost table and base.

scholarly journals Electrical resistivity tomography applied to geologic, hydrogeologic, and engineering investigations at a former waste-disposal site

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. B231-B239 ◽  
Author(s):  
Jonathan E. Chambers ◽  
Oliver Kuras ◽  
Philip I. Meldrum ◽  
Richard D. Ogilvy ◽  
Jonathan Hollands
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Site Investigation ◽  
High Resistivity ◽  
Potential Zone ◽  
Resistivity Tomography ◽  
L2 Norm ◽  
Resistivity Model ◽  
2D And 3D ◽  
2D Resistivity

A former dolerite quarry and landfill site was investigated using 2D and 3D electrical resistivity tomography (ERT), with the aims of determining buried quarry geometry, mapping bedrock contamination arising from the landfill, and characterizing site geology. Resistivity data were collected from a network of intersecting survey lines using a Wenner-based array configuration. Inversion of the data was carried out using 2D and 3D regularized least-squares optimization methods with robust (L1-norm) model constraints. For this site, where high resistivity contrasts were present, robust model constraints produced a more accurate recovery of subsurface structures when compared to the use of smooth (L2-norm) constraints. Integrated 3D spatial analysis of the ERT and conventional site investigation data proved in this case a highly effective means of characterizing the landfill and its environs. The 3D resistivity model was successfully used to confirm the position of the landfill boundaries, which appeared as electrically well-defined features that corresponded extremely closely to both historic maps and intrusive site investigation data. A potential zone of leachate migration from the landfill was identified from the electrical models; the location of this zone was consistent with the predicted direction of groundwater flow across the site. Unquarried areas of a dolerite sill were imaged as a resistive sheet-like feature, while the fault zone appeared in the 2D resistivity model as a dipping structure defined by contrasting bedrock resistivities.

scholarly journals Exploring the regolith with electrical resistivity tomography in largescale surveys: electrode spacing related issues and possibility

2020 ◽  
Author(s):  
Laurent Gourdol ◽  
Rémi Clément ◽  
Jérôme Juilleret ◽  
Laurent Pfister ◽  
Christophe Hissler
Keyword(s):  
Electrical Resistivity ◽  
Apparent Resistivity ◽  
Large Scale ◽  
Electrical Resistivity Tomography ◽  
Subsurface Layer ◽  
Electrode Spacing ◽  
High Resistivity ◽  
Constant Thickness ◽  
Resistivity Tomography

Abstract. Within the Critical Zone, regolith plays a key role in the fundamental hydrological functions of water collection, storage, mixing and release. Electrical Resistivity Tomography (ERT) is recognized as a remarkable tool for characterizing the geometry and properties of the regolith, overcoming limitations inherent to conventional borehole-based investigations. For exploring shallow layers, a small electrode spacing (ES) will provide a denser set of apparent resistivity measurements of the subsurface. As this option is cumbersome and time-consuming, smaller ES – albeit offering poorer shallow apparent resistivity data – are often preferred for large horizontal ERT surveys. To investigate the negative trade-off between larger ES and reduced accuracy of the inverted ERT images for shallow layers, we use a set of synthetic conductive/resistive/conductive three-layered soil–saprock/saprolite–bedrock models in combination with a reference field dataset. Our results suggest that an increase in ES causes a deterioration of the accuracy of the inverted ERT images in terms of both resistivity distribution and interface delineation and, most importantly, that this degradation increases sharply when the ES exceeds the thickness of the top subsurface layer. This finding, which is obvious for the characterization of shallow layers, is also relevant even when solely aiming for the characterization of deeper layers. We show that an oversized ES leads to overestimations of depth to bedrock and that this overestimation is even more important for subsurface structures with high resistivity contrast. To overcome this limitation, we propose adding interpolated levels of surficial apparent resistivity relying on a limited number of ERT profiles with a smaller ES. We demonstrate that our protocol significantly improves the accuracy of ERT profiles when using large ES, provided that the top layer has a rather constant thickness and resistivity. For the specific case of large-scale ERT surveys the proposed upgrading procedure is cost-effective in comparison to protocols based on small ES.

Application of Electrical Resistivity Tomography on Glaciers and Rock-Glaciers in the Western Alps

2005 ◽  
Author(s):  
M. Marchisio ◽  
A. Bianchi ◽  
X. Bodin ◽  
P. Ciuffi ◽  
L. D‘Onofrio ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Western Alps ◽  
Resistivity Tomography ◽  
Rock Glaciers

scholarly journals A Comparison of Frequency Domain Electro-Magnetometry, Electrical Resistivity Tomography and Borehole Temperatures to Assess the Presence of Ice in a Rock Glacier

2020 ◽  
Vol 8 ◽  
Author(s):  
Jacopo Boaga ◽  
Marcia Phillips ◽  
Jeannette Noetzli ◽  
Anna Haberkorn ◽  
Robert Kenner ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Frequency Domain ◽  
Layer Thickness ◽  
Active Layer ◽  
Electrical Resistivity Tomography ◽  
Temperature Data ◽  
Active Layer Thickness ◽  
Rock Glacier ◽  
Resistivity Tomography ◽  
Borehole Temperature

Alpine permafrost is currently warming, leading to changes such as active layer deepening and talik formation. Frequency domain electro-magnetometry (FDEM) measurements were tested as a simple and efficient method to investigate ground characteristics along two transects on the ice-rich Schafberg rock glacier in the Eastern Swiss Alps. The results were compared with electrical resistivity tomography (ERT) and ground temperature data acquired simultaneously in boreholes. FDEM provides information on the electrical properties of the ground, allowing to investigate ground-ice distribution. Our device allowed measurements to a depth of around 7 m. In ice-rich permafrost, FDEM can provide an approximation of the active layer thickness, and ice-free zones within the permafrost such as intra-permafrost taliks can be identified. This rapidly applicable geophysical method can be used to monitor ground ice distribution easily and efficiently, making it an ideal complement to borehole temperature data, which only provide point information and are costly to install and maintain. At the Schafberg site the three methods FDEM, electrical resistivity tomography and borehole temperature measurements provided similar results, with regard to active layer thickness and the presence of unfrozen zones within the ice-rich permafrost.

scholarly journals Stabilization Methodology in Foundation Soils by ERT-3D Application in Estepona, South Spain

2021 ◽  
Vol 11 (10) ◽  
pp. 4455
Author(s):  
Alfonso Gutiérrez-Martín ◽  
José I. Yenes ◽  
Marta Fernández-Hernández ◽  
Ricardo Castedo
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Shallow Foundations ◽  
Simplified Model ◽  
High Resistivity ◽  
Combined System ◽  
Resistivity Tomography ◽  
Field Campaign ◽  
Non Invasive ◽  
Dipole Configuration

The paper proposes a novel methodology for the stabilization of shallow foundations, with a simplified model combined with 3D electrical resistivity tomography (ERT-3D and consolidation injections. To determine its usefulness, the method has been applied in a case located in Estepona (southern Spain). The chosen tomography model is the dipole–dipole configuration, with an optimized distance between electrodes of 0.80 m for a better visualization of the foundation subsoil; with this parameterization, a total of 72 electrodes were installed in the analyzed case. In this work, the depth of the anomaly in the building’s supporting subsoil was detected ranging from 2.00 m to 3.90 m deep. The study also delineates areas of high resistivity variations (50–1000 Ω m) in the middle and eastern end of the field. These data have been validated and corroborated with a field campaign. The results of the ERT-3D monitoring are presented, once the investment data has been processed with the RES3DINV software, from the beginning to the end of the stabilization intervention. The novelty occurs with the interaction between the tomography and the foundation consolidation injections, until the final stabilization. This is a very useful methodology in case of emergency consolidation, where there is a need to minimize damage to the building. Thus, people using this combined system will be able to practically solve the initial anomalies of the subsoil that caused the damages, in a non-invasive way, considerably lowering the value of the resistivities.

scholarly journals Ground penetrating radar and electrical resistivity tomography for locating buried building foundations: A case study in the city centre of Thessaloniki, Greece

2016 ◽  
Vol 47 (3) ◽  
pp. 1355
Author(s):  
G. Vargemezis ◽  
N. Diamanti ◽  
I. Fikos ◽  
A. Stampolidis ◽  
Th. Makedon ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Ground Penetrating Radar ◽  
Electrical Resistivity Tomography ◽  
Geophysical Methods ◽  
Geological Structure ◽  
City Centre ◽  
High Resistivity ◽  
Resistivity Tomography ◽  
Ground Penetrating ◽  
The City

Ground penetrating radar (GPR) and electrical resistivity tomography (ERT) surveys have been carried out in the city centre of Thessaloniki (N. Greece), for investigating possible locations of buried building foundations. Geophysical survey has been chosen as a non-destructive investigation method since the area is currently used as a car parking and it is covered by asphalt. The geoelectrical sections derived from ERT data in combination with the GPR profiles provided a broad view of the  subsurface.  Regarding  ERT,  high  resistivity  values  can  be  related  to  buried building remains, while lower resistivity values are more related to the surrounding geological materials. GPR surveying can also indicate man-made structures buried in the ground. Even though the two geophysical methods are affected in different ways by the subsurface conditions, the processed underground images from both techniques revealed great similarity. High resistivity anomalies and distinct GPR signals were observed in certain locations of the area under investigation, which are attributed to buried building foundations as well as the geological structure of the area.

scholarly journals A 2D electrical resistivity tomography survey of a vineyard plot of the Gaillac appellation (France): interpretation with respect to possible implications on vine water supply

OENO One ◽  
2010 ◽  
Vol 44 (2) ◽  
pp. 51
Author(s):  
Pierre Courjault-Radé ◽  
Muriel Llubes ◽  
José Darrozes ◽  
Marguerite Munoz ◽  
Eric Maire ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Water Supply ◽  
Electrical Resistivity Tomography ◽  
Lower Layer ◽  
Temporal Variations ◽  
Climatic Conditions ◽  
Morphological Data ◽  
Subsurface Water ◽  
High Resistivity ◽  
Resistivity Tomography

<p style="text-align: justify;"><strong>Aims</strong>: The aim of this 2D electrical resistivity tomography (ERT) survey performed on a vineyard plot of the Gaillac appellation was to investigate spatial and temporal variations in subsurface water supply in relation with pedo-geological and morphological features.</p><p style="text-align: justify;"><strong>Methods and results</strong>: The ERT surveys were carried out under two contrasted - dry and humid - climatic conditions. All the resistivity profiles showed the superposition of two layers: a lower layer characterized by very low resistivity values (&lt; 40 <strong>Ω</strong>.m) corresponding to a marly molassic subsoil overlaid by an upper layer characterized by moderate to high resistivity values (300 <strong>Ω</strong>.m to 1500 <strong>Ω</strong>.m) corresponding to a silty-sandy and gravely-pebbly soil sequence. The resistivity values of the molassic subsoil stayed very low independently of water supply conditions whereas those of the soil sequence decreased by a factor 2 (300/750 <strong>Ω</strong>.m versus 750/1500 <strong>Ω</strong>.m) when the plot was close to field capacity.</p><p style="text-align: justify;"><strong>Conclusion</strong>: The ERT results coupled with pedological and morphological data strongly suggest that the water flow is preferentially restricted at the molassic subsoil/soil sequence interface, short-lived and of low amplitude.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: Consequently, the water supply regime, which points out a potential risk of drought stress for vine crops, implies a minimization strategy when choosing vegetal material and viticultural management operations</p>

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