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.

Active layer and bedrock mapping in permafrost with Electrical Resistivity Tomography and Induced Polarization – A case study from Svalbard 

2021 ◽  
Author(s):  
Asgeir Kydland Lysdahl ◽  
Sara Bazin ◽  
Andreas Olaus Harstad ◽  
Regula Frauenfelder
Keyword(s):  
Electrical Resistivity ◽  
Physical Properties ◽  
Water Content ◽  
Active Layer ◽  
Electrical Resistivity Tomography ◽  
Unfrozen Water ◽  
Resistivity Tomography ◽  
Unfrozen Water Content ◽  
Run Off ◽  
Permafrost Soils

<div> <p> </p> <p>Design and construction of infrastructure in frozen permafrost soils demands for detailed investigation of the ground characteristics prior to the construction process. Variations in ground temperature affect the physical properties of permafrost, such as amount of unfrozen water content and ice content. In addition, aggradation and degradation of permafrost induce changes of its physical properties. Ground-based Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) surveying can be used to characterize near-surface ground conditions to a few tens of meters depth, especially when calibrated by boreholes. </p> </div><div> <p>Measured electrical resistivity is temperature‐dependent, which makes ERT a suitable tool in permafrost investigations. The temperature dependence is most pronounced for temperatures below freezing point. Electrical resistivity rises exponentially during freezing, when unfrozen water content within a substrate decreases. The electrical resistivity is, thus, very sensitive to phase changes between water and ice and we usually observe a lack of resistivity contrast at lithological interfaces. Direct translation from resistivity to lithology is, therefore, seldomly possible in permafrost. While ERT is successful for mapping the active layer, further interpretation of resistivity profiles is thus impeded by the lack of resistivity contrast within the permafrost. Indeed, the lithological structures are hidden by the strong resistivity of the frozen layer. By adding complementary information, IP measurements can help separate effects due to freezing and lithology. The IP effect can be measured in the time-domain, simultaneously with the ERT measurements, and with the same equipment. The IP effect occurs after abruptly interrupting the current flow between the current electrodes. The voltage across the potential electrodes does not drop to zero instantaneously, but  decays exponentially. The decay time can be used to estimate the chargeability of the ground. </p> </div><div> <p>Here, we present three examples where combined ERT- and IP-surveying was used to detect the interface between sediments and bedrock within permafrost soils, and to investigate potential environmental hazards related to run-off paths from existing and planned landfills. Study sites were an active landfill near the town of Longyearbyen, and two potentially new landfills near Longyearbyen and Barentsburg, respectively (the latter one for surplus masses resulting from coal mining). As permafrost traditionally had been seen as a natural flow barrier for such landfills, understanding its degradation owing to climate change was considered key in the planning of future sites. Eight profiles were carried out in September 2018, when expected active layer thicknesses were at their maxima. Two-dimensional inversion was performed with the commercial software RES2DINV for the resistivity data and Ahrusinv for the chargeability data.  </p> </div><div> <p>The results of our case studies show the benefit of simultaneous ERT- and IP-measurements, to both map active layer depths and determine sediment depths in permafrost areas. They also gave valuable insights in understanding potential environmental hazards related to run-off from the landfill, as a consequence of water entering the landfill in the summer period. ERT/IP surveys are flexible and relatively easy to deploy. The technique is non-destructiv and is, therefore, also suitable for maintenance studies in vulnerable arctic Tundra environments. </p> <p> </p> </div>

scholarly journals Detailed detection of fast changes in the active layer using quasi-continuous electrical resistivity tomography (Deception Island, Antarctica)

2019 ◽  
Author(s):  
Mohammad Farzamian ◽  
Gonçalo Vieira ◽  
Fernando A. Monteiro Santos ◽  
Borhan Yaghoobi Tabar ◽  
Christian Hauck ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Snow Cover ◽  
Active Layer ◽  
Electrical Resistivity Tomography ◽  
Deception Island ◽  
Freezing And Thawing ◽  
Resistivity Tomography ◽  
Thaw Depth ◽  
Set Up ◽  
The Impact

Abstract. Climate induced warming of permafrost soils is a global phenomenon, with regional and site-specific variations, which are not fully understood. In this context, a 2D automated electrical resistivity tomography (A-ERT) system was installed for the first time in Antarctica at Deception Island, associated to the existing Crater Lake site of the Circumpolar Active Layer Monitoring Network (CALM-S) I) to evaluate the feasibility of installing and running autonomous ERT monitoring stations in remote and extreme environments such as Antarctica, II) to monitor subsurface freezing and thawing processes on a daily and seasonal basis and to map the spatial and temporal variability of thaw depth, and III) to study the impact of short-lived extreme meteorological events on active layer dynamics. Measurements were repeated at 4-hour intervals during a full year, enabling the detection of seasonal trends, as well as short-lived resistivity changes reflecting individual meteorological events. The latter is important to distinguish between (1) long-term climatic trends and (2) the impact of anomalous seasons on the ground thermal regime. Our full-year dataset shows large and fast temporal resistivity changes during the seasonal active layer freezing and thawing and indicates that our system set-up can successfully map spatiotemporal thaw depth variability along the experimental transect at very high temporal resolution. Largest resistivity change took place during the freezing season in April when low temperatures induce an abrupt phase change in the active layer in the absence of a snow cover. The seasonal thawing of the active layer is associated with a slower resistivity decrease during October due to the presence of a snow cover and the corresponding zero-curtain effect. Detailed investigation of the daily resistivity variations reveals several periods with rapid and sharp resistivity changes of the near-surface layers due to the brief surficial refreezing of the active layer in summer or brief thawing of the active layer during winter as a consequence of short-lived meteorological extreme events. These results emphasize the significance of the continuous A-ERT monitoring set-up which enables to detect fast changes in the active layer during short-lived extreme meteorological events. Based on this first complete year-round A-ERT monitoring data set in Deception Island, we believe that this system shows high potential for autonomous applications in remote and harsh polar environments such as Antarctica.

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>

scholarly journals Detailed detection of active layer freeze–thaw dynamics using quasi-continuous electrical resistivity tomography (Deception Island, Antarctica)

2020 ◽  
Vol 14 (3) ◽  
pp. 1105-1120
Author(s):  
Mohammad Farzamian ◽  
Gonçalo Vieira ◽  
Fernando A. Monteiro Santos ◽  
Borhan Yaghoobi Tabar ◽  
Christian Hauck ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Snow Cover ◽  
Active Layer ◽  
Electrical Resistivity Tomography ◽  
Deception Island ◽  
Freezing And Thawing ◽  
Resistivity Tomography ◽  
Thaw Depth ◽  
The Impact ◽  
First Time

Abstract. Climate-induced warming of permafrost soils is a global phenomenon, with regional and site-specific variations which are not fully understood. In this context, a 2-D automated electrical resistivity tomography (A-ERT) system was installed for the first time in Antarctica at Deception Island, associated to the existing Crater Lake site of the Circumpolar Active Layer Monitoring – South Program (CALM-S) – site. This setup aims to (i) monitor subsurface freezing and thawing processes on a daily and seasonal basis and map the spatial and temporal variability in thaw depth and to (ii) study the impact of short-lived extreme meteorological events on active layer dynamics. In addition, the feasibility of installing and running autonomous ERT monitoring stations in remote and extreme environments such as Antarctica was evaluated for the first time. Measurements were repeated at 4 h intervals during a full year, enabling the detection of seasonal trends and short-lived resistivity changes reflecting individual meteorological events. The latter is important for distinguishing between (1) long-term climatic trends and (2) the impact of anomalous seasons on the ground thermal regime. Our full-year dataset shows large and fast temporal resistivity changes during the seasonal active layer freezing and thawing and indicates that our system setup can resolve spatiotemporal thaw depth variability along the experimental transect at very high temporal resolution. The largest resistivity changes took place during the freezing season in April, when low temperatures induce an abrupt phase change in the active layer in the absence of snow cover. The seasonal thawing of the active layer is associated with a slower resistivity decrease during October due to the presence of snow cover and the corresponding zero-curtain effect. Detailed investigation of the daily resistivity variations reveals several periods with rapid and sharp resistivity changes of the near-surface layers due to the brief surficial refreezing of the active layer in summer or brief thawing of the active layer during winter as a consequence of short-lived meteorological extreme events. These results emphasize the significance of the continuous A-ERT monitoring setup which enables detecting fast changes in the active layer during short-lived extreme meteorological events. Based on this first complete year-round A-ERT monitoring dataset on Deception Island, we believe that this system shows high potential for autonomous applications in remote and harsh polar environments such as Antarctica. The monitoring system can be used with larger electrode spacing to investigate greater depths, providing adequate monitoring at sites and depths where boreholes are very costly and the ecosystem is very sensitive to invasive techniques. Further applications may be the estimation of ice and water contents through petrophysical models or the calibration and validation of heat transfer models between the active layer and permafrost.

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