Ice or rock matrix? Improved quantitative imaging of Alpine permafrost evolution through time-lapse petrophysical joint inversion

2021 ◽  
Author(s):  
Johanna Klahold ◽  
Christian Hauck ◽  
Florian Wagner
Keyword(s):  
Liquid Water ◽  
Joint Inversion ◽  
Time Lapse ◽  
Swiss Alps ◽  
Permafrost Degradation ◽  
Rock Matrix ◽  
Validation Data ◽  
Water Ice ◽  
Borehole Temperature ◽  
Ice Content

<p>Quantitative estimation of pore fractions filled with liquid water, ice and air is one of the prerequisites in many permafrost studies and forms the basis for a process-based understanding of permafrost and the hazard potential of its degradation in the context of global warming. The volumetric ice content is however difficult to retrieve, since standard borehole temperature monitoring is unable to provide any ice content estimation. Geophysical methods offer opportunities to image distributions of permafrost constituents in a non-invasive manner. A petrophysical joint inversion was recently developed to determine volumetric water, ice, air and rock contents from seismic refraction and electrical resistivity data. This approach benefits from the complementary sensitivities of seismic and electrical data to the phase change between ice and liquid water. A remaining weak point was the unresolved petrophysical ambiguity between ice and rock matrix. Within this study, the petrophysical joint inversion approach is extended along the time axis and respective temporal constraints are introduced. If the porosity (and other time-invariant properties like pore water resistivity or Archie exponents) can be assumed invariant over the considered time period, water, ice and air contents can be estimated together with a temporally constant (but spatially variable) porosity distribution. It is hypothesized that including multiple time steps in the inverse problem increases the ratio of data and parameters and leads to a more accurate distinction between ice and rock content. Based on a synthetic example and a field data set from an Alpine permafrost site (Schilthorn, Swiss Alps) it is demonstrated that the developed time-lapse petrophysical joint inversion provides physically plausible solutions, in particular improved estimates for the volumetric fractions of ice and rock. The field application is evaluated with independent validation data including thaw depths derived from borehole temperature measurements and shows generally good agreement. As opposed to the conventional petrophysical joint inversion, its time-lapse extension succeeds in providing reasonable estimates of permafrost degradation at the Schilthorn monitoring site without <em>a priori </em>constraints on the porosity model.</p>

scholarly journals Quantitative imaging of water, ice and air in permafrost systems through petrophysical joint inversion of seismic refraction and electrical resistivity data

2019 ◽  
Vol 219 (3) ◽  
pp. 1866-1875 ◽  
Author(s):  
F M Wagner ◽  
C Mollaret ◽  
T Günther ◽  
A Kemna ◽  
C Hauck
Keyword(s):  
Electrical Resistivity ◽  
Liquid Water ◽  
Field Data ◽  
Joint Inversion ◽  
A Priori ◽  
Seismic Refraction ◽  
Rock Matrix ◽  
Data Set ◽  
Water Ice ◽  
Borehole Temperatures

SUMMARY Quantitative estimation of pore fractions filled with liquid water, ice and air is crucial for a process-based understanding of permafrost and its hazard potential upon climate-induced degradation. Geophysical methods offer opportunities to image distributions of permafrost constituents in a non-invasive manner. We present a method to jointly estimate the volumetric fractions of liquid water, ice, air and the rock matrix from seismic refraction and electrical resistivity data. Existing approaches rely on conventional inversions of both data sets and a suitable a priori estimate of the porosity distribution to transform velocity and resistivity models into estimates for the four-phase system, often leading to non-physical results. Based on two synthetic experiments and a field data set from an Alpine permafrost site (Schilthorn, Bernese Alps and Switzerland), it is demonstrated that the developed petrophysical joint inversion provides physically plausible solutions, even in the absence of prior porosity estimates. An assessment of the model covariance matrix for the coupled inverse problem reveals remaining petrophysical ambiguities, in particular between ice and rock matrix. Incorporation of petrophysical a priori information is demonstrated by penalizing ice occurrence within the first two meters of the subsurface where the measured borehole temperatures are positive. Joint inversion of the field data set reveals a shallow air-rich layer with high porosity on top of a lower-porosity subsurface with laterally varying ice and liquid water contents. Non-physical values (e.g. negative saturations) do not occur and estimated ice saturations of 0–50 per cent as well as liquid water saturations of 15–75 per cent are in agreement with the relatively warm borehole temperatures between −0.5  and 3 ° C. The presented method helps to improve quantification of water, ice and air from geophysical observations.

scholarly journals Applicability of time-lapse refraction seismic tomography for the detection of ground ice degradation

2010 ◽  
Vol 4 (1) ◽  
pp. 77-119 ◽  
Author(s):  
C. Hilbich
Keyword(s):  
Seismic Tomography ◽  
Time Lapse ◽  
Swiss Alps ◽  
P Wave ◽  
Permafrost Degradation ◽  
Travel Times ◽  
Ground Ice ◽  
Refraction Seismic ◽  
Velocity Changes ◽  
Ice Content

Abstract. The ice content of the subsurface is a major factor controlling the natural hazard potential of permafrost degradation in alpine terrain. Monitoring of changes in ground ice content is therefore similarly important as temperature monitoring in mountain permafrost. Although electrical resistivity tomography monitoring (ERTM) has proved to be a valuable tool for the observation of ground ice degradation, results are often ambiguous or contaminated by inversion artefacts. In theory, the P-wave velocity of seismic waves is similarly sensitive to phase changes between unfrozen water and ice. Provided that the general conditions (lithology, stratigraphy, state of weathering, pore space) remain unchanged over the observation period, temporal changes in the observed travel times of repeated seismic measurements should indicate changes in the ice and water content within the pores and fractures of the subsurface material. In this paper, the applicability of refraction seismic tomography monitoring (RSTM) as an independent and complementary method to ERTM is analysed for two test sites in the Swiss Alps. The development and validation of an appropriate RSTM approach involves a) the comparison of time-lapse seismograms and analysis of reproducibility of the seismic signal, b) the analysis of time-lapse travel time curves with respect to shifts in travel times and changes in P-wave velocities, and c) the comparison of inverted tomograms including the quantification of velocity changes. Results show a high potential of the RSTM approach concerning the detection of altered subsurface conditions caused by freezing and thawing processes. For velocity changes on the order of 3000 m/s even an unambiguous identification of significant ground ice loss is possible.

scholarly journals Time-lapse refraction seismic tomography for the detection of ground ice degradation

2010 ◽  
Vol 4 (3) ◽  
pp. 243-259 ◽  
Author(s):  
C. Hilbich
Keyword(s):  
Seismic Tomography ◽  
Time Lapse ◽  
Phase Changes ◽  
Swiss Alps ◽  
P Wave ◽  
Permafrost Degradation ◽  
Travel Times ◽  
Refraction Seismic ◽  
Velocity Changes ◽  
Ice Content

Abstract. The ice content of the subsurface is a major factor controlling the natural hazard potential of permafrost degradation in alpine terrain. Monitoring of changes in ice content is therefore similarly important as temperature monitoring in mountain permafrost. Although electrical resistivity tomography monitoring (ERTM) proved to be a valuable tool for the observation of ice degradation, results are often ambiguous or contaminated by inversion artefacts. In theory, the sensitivity of P-wave velocity of seismic waves to phase changes between unfrozen water and ice is similar to the sensitivity of electric resistivity. Provided that the general conditions (lithology, stratigraphy, state of weathering, pore space) remain unchanged over the observation period, temporal changes in the observed travel times of repeated seismic measurements should indicate changes in the ice and water content within the pores and fractures of the subsurface material. In this paper, a time-lapse refraction seismic tomography (TLST) approach is applied as an independent method to ERTM at two test sites in the Swiss Alps. The approach was tested and validated based on a) the comparison of time-lapse seismograms and analysis of reproducibility of the seismic signal, b) the analysis of time-lapse travel time curves with respect to shifts in travel times and changes in P-wave velocities, and c) the comparison of inverted tomograms including the quantification of velocity changes. Results show a high potential of the TLST approach concerning the detection of altered subsurface conditions caused by freezing and thawing processes. For velocity changes on the order of 3000 m/s even an unambiguous identification of significant ice loss is possible.

Quantification of ground ice through petrophysical joint inversion of seismic and electrical data applied to alpine permafrost

2020 ◽  
Author(s):  
Coline Mollaret ◽  
Florian M. Wagner ◽  
Christin Hilbich ◽  
Christian Hauck
Keyword(s):  
Electrical Resistivity ◽  
Melting Point ◽  
Joint Inversion ◽  
Geophysical Methods ◽  
Ground Truth ◽  
Ground Ice ◽  
Ground Truth Data ◽  
Water Ice ◽  
Refraction Seismic ◽  
Ice Content

<p>Quantification of ground ice is particularly crucial for understanding permafrost systems. The volumetric ice content is however rarely estimated in permafrost studies, as it is particularly difficult to retrieve. Geophysical methods have become more and more popular for permafrost investigations due to their capacity to distinguish between frozen and unfrozen regions and their complementarity to standard ground temperature data. Geophysical methods offer both a second (or third) spatial dimension and the possibility to gain insights on processes happening near the melting point (ground ice gain or loss at the melting point). Geophysical methods, however, may suffer from potential inversion imperfections and ambiguities (no unique solution). To reduce uncertainties and improve the interpretability, geophysical methods are standardly combined with ground truth data or other independent geophysical methods. We developed an approach of joint inversion to fully exploit the sensitivity of seismic and electrical methods to the phase change of water. We choose apparent resistivities and seismic travel times as input data of a petrophysical joint inversion to directly estimate the volumetric fractions of the pores (liquid water, ice and air) and the rock matrix. This approach was successfully validated with synthetic datasets (Wagner et al., 2019). This joint inversion scheme warrants physically-plausible solutions and provides a porosity estimation in addition to the ground ice estimation of interest. Different petrophysical models are applied to several alpine sites (ice-poor to ice-rich) and their advantages and limitations are discussed. The good correlation of the results with the available ground truth data (thaw depth and ice content data) demonstrates the high potential of the joint inversion approach for the typical landforms of alpine permafrost (Mollaret et al., 2020). The ice content is found to be 5 to 15 % at bedrock sites, 20 to 40 % at talus slopes, and up to 95 % at rock glaciers (in good agreement to the ground truth data from boreholes). Moreover, lateral variations of bedrock depth are correctly identified according to outcrops and borehole data (as the porosity is also an output of the petrophysical joint inversion). A time-lapse version of this petrophysical joint inversion may further reduce the uncertainties and will be beneficial for monitoring and modelling studies upon climate-induced degradation.</p><p> </p><p>References:</p><p>Mollaret, C., Wagner, F. M. Hilbich, C., Scapozza, C., and Hauck, C. Petrophysical joint inversion of electrical resistivity and refraction seismic applied to alpine permafrost to image subsurface ice, water, air, and rock contents. Frontiers in Earth Science, 2020, submitted.</p><p>Wagner, F. M., Mollaret, C., Günther, T., Kemna, A., and Hauck, C. Quantitative imaging of water, ice, and air in permafrost systems through petrophysical joint inversion of seismic refraction and electrical resistivity data. Geophysical Journal International, 219 (3):1866–1875, 2019. doi:10.1093/gji/ggz402.</p>

Non-equilibrium modeling hysteresis of water freezing: Ice thawing in partially saturated porous building materials

2019 ◽  
Vol 43 (2) ◽  
pp. 61-98 ◽  
Author(s):  
Dariusz Gawin ◽  
Francesco Pesavento ◽  
Marcin Koniorczyk ◽  
Bernhard A Schrefler
Keyword(s):  
Liquid Water ◽  
Building Materials ◽  
Freezing Point ◽  
Model Parameters ◽  
Scanning Calorimetry ◽  
Water Ice ◽  
Partially Saturated ◽  
Ice Content ◽  
Model Equations ◽  
Non Equilibrium

This article presents a novel mathematical model of hygro-thermal processes in a porous material, partially saturated with liquid water, exposed to temperatures below the freezing point of pore water. Water–ice phase transition is modeled by means of a kinetic approach considering water supercooling and thermodynamic non-equilibrium of the phases, what allows taking into account a hysteresis of ice content during freezing–thawing of moist porous materials. The model equations are solved for two numerical examples. The first one deals with laboratory differential scanning calorimetry test of a cement mortar saturated with water and exposed to temperatures below the freezing point of water (down to −40°C). The results are used for experimental validation of the proposed model, confirming its accuracy and practical usefulness. In the second example, the mesh refinement test is performed and the influence of the solid–liquid water phase change model parameters on the simulation results for a 1D model problem concerning water freezing–thawing are analyzed and discussed.

Permafrost monitoring by reprocessing and repeating historical geoelectrical measurements

2020 ◽  
Author(s):  
Christian Hauck ◽  
Christin Hilbich ◽  
Coline Mollaret ◽  
Cécile Pellet
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Geophysical Methods ◽  
Swiss Alps ◽  
Permafrost Degradation ◽  
Resistivity Tomography ◽  
Climate Signal ◽  
Data Source ◽  
Ice Content

<p>Geophysical methods and especially electrical techniques have been used for permafrost detection and monitoring since more than 50 years. In the beginning, the use of Vertical Electrical Soundings (VES) allowed the detection of ice-rich permafrost due to the clear contrast between the comparatively low-resistive active layer and the high-resistive permafrost layer below. Only after the development of 2-dimensional tomographic measurement and processing techniques (Electrical Resistivity Tomography, ERT), in the late 1990’s, electrical imaging was widely applied for a large range of different permafrost applications, including ice content quantification and permafrost monitoring over different spatial scales. Regarding ERT monitoring, the comparatively large efforts needed for continuous and long-term measurements implies that there are still only few continuous ERT monitoring installations in permafrost terrain worldwide. One of the exceptions is a network of six permafrost sites in the Swiss Alps that have been constantly monitored in the context of the Swiss Permafrost Monitoring Network (PERMOS) since 2005, enabling the analysis of the long-term change in the ground ice content and associated thawing and freezing processes (Mollaret et al. 2019).</p><p>On the contrary, a much larger number (estimated to be > 500) of permafrost sites exist worldwide, where singular ERT (or VES) measurements have been performed in the past - many of them published in the scientific literature. These data sets are neither included in a joint database nor have they been analysed in an integrated way. Within a newly GCOS Switzerland-funded project we address this important historical data source. Whereas singular ERT data from different permafrost occurrences are not easily comparable due to the local influence of the geologic material on the obtained electrical resistivities, their use as baseline for repeated measurements and subsequent processing and interpretation in a climatic context is highly promising and can be effectuated with low efforts.</p><p>In this presentation we will show evidence that singular ERT surveys in permafrost terrain can indeed be repeated and jointly processed after long time spans of up to 20 years, yielding a climate signal of permafrost change at various sites and on different landforms. Examples are given from various field sites in Europe and Antarctica, and the results are validated with borehole data, where available. We believe that a joint international data base of historical ERT surveys and their repetitions would add an important data source available for permafrost studies in the context of climate change.</p><p> </p><p>Mollaret, C., Hilbich, C., Pellet, C., Flores-Orozco, A., Delaloye, R. and Hauck, C. (2019): Mountain permafrost degradation documented through a network of permanent electrical resistivity tomography sites. The Cryosphere, 13 (10), 2557-2578.</p>

Lichens of the Oasis Molodyozhnyi and adjacent areas (Enderby Land, Antarctic)

2013 ◽  
Vol 47 ◽  
pp. 167-178 ◽  
Author(s):  
M. P. Andreev
Keyword(s):  
Liquid Water ◽  
Climate Conditions ◽  
Water Ice ◽  
Buellia Frigida ◽  
Antarctic Continent ◽  
Harsh Climate ◽  
The Antarctic ◽  
First Time ◽  
Lichen Flora

Lichen flora and vegetation in the vicinity of the Russian base «Molodyozhnaya» (Enderby Land, Antarctica) were investigated in 2010–2011 in details for the first time. About 500 specimens were collected in 100 localities in all available ecotopes. The lichen flora is the richest in the region and numbers 39 species (21 genera, 11 families). The studied vegetation is very poor and sparse, but typical for coastal oases of the Antarctic continent. The poorness is caused by the extremely harsh climate conditions, insufficient availability of liquid water, ice-free land, and high insolation levels. The dominant and most common lichens are Rinodina olivaceobrunnea, Amandinea punctata, Candelariella flava, Physcia caesia, Caloplaca tominii, Lecanora expectans, Caloplaca ammiospila, Lecidea cancriformis, Pseudephebe minuscula, Lecidella siplei, Umbilicaria decussata, Buellia frigida, Lecanora fuscobrunnea, Usnea sphacelata, Lepraria and Buellia spp.

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.

4D-Quantification of alpine permafrost degradation in a bedrock ridge using multiple inversion schemes and deformation measurements

2021 ◽  
Author(s):  
Maike Offer ◽  
Riccardo Scandroglio ◽  
Daniel Draebing ◽  
Michael Krautblatter
Keyword(s):  
Climate Change ◽  
Mechanical Stability ◽  
Regularization Parameter ◽  
Time Lapse ◽  
Permafrost Degradation ◽  
Thermal Dynamics ◽  
Near Surface ◽  
Data Error ◽  
Near Surface Geophysics ◽  
Thawing Rate

<p>Warming of permafrost in steep rock walls decreases their mechanical stability and could triggers rockfalls and rockslides. However, the direct link between climate change and permafrost degradation is seldom quantified with precise monitoring techniques and long-term time series. Where boreholes are not possible, laboratory-calibrated Electrical Resistivity Tomography (ERT) is presumably the most accurate quantitative permafrost monitoring technique providing a sensitive record for frozen vs. unfrozen bedrock. Recently, 4D inversions allow also quantification of frozen bedrock extension and of its changes with time (Scandroglio et al., in review).</p><p>In this study we (i) evaluate the influence of the inversion parameters on the volumes and (ii) connect the volumetric changes with measured mechanical consequences.</p><p>The ERT time-serie was recorded between 2006 and 2019 in steep bedrock at the permafrost affected Steintälli Ridge (3100 m asl). Accurately positioned 205 drilled-in steel electrodes in 5 parallel lines across the rock ridge have been repeatedly measured with similar hardware and are compared to laboratory temperature-resistivity (T–ρ) calibration of water-saturated samples from the field. Inversions were conducted using the open-source software BERT for the first time with the aim of estimating permafrost volumetric changes over a decade.</p><p>(i) Here we present a sensitivity analysis of the outcomes by testing various plausible inversion set-ups. Results are computed with different input data filters, data error model, regularization parameter (λ), model roughness reweighting and time-lapse constraints. The model with the largest permafrost degradation was obtained without any time-lapse constraints, whereas constraining each model with the prior measurement results in the smallest degradation. Important changes are also connected to the data error estimation, while other setting seems to have less influence on the frozen volume. All inversions confirmed a drastic permafrost degradation in the last 13 years with an average reduction of 3.900±600 m<sup>3</sup> (60±10% of the starting volume), well in agreement with the measured air temperatures increase.</p><p>(ii) Average bedrock thawing rate of ~300 m<sup>3</sup>/a is expected to significantly influence the stability of the ridge. Resistivity changes are especially evident on the south-west exposed side and in the core of the ridge and are here connected to deformations measured with tape extensometer, in order to precisely estimate the mechanical consequences of bedrock warming.</p><p>In summary, the strong degradation of permafrost in the last decade it’s here confirmed since inversion settings only have minor influence on volume quantification. Internal thermal dynamics need correlation with measured external deformation for a correct interpretation of stability consequences. These results are a fundamental benchmark for evaluating mountain permafrost degradation in relation to climate change and demonstrate the key role of temperature-calibrated 4D ERT.</p><p> </p><p>Reference:</p><p>Scandroglio, R. et al. (in review) ‘4D-Quantification of alpine permafrost degradation in steep rock walls using a laboratory-calibrated ERT approach’, <em>Near Surface Geophysics</em>.</p>

scholarly journals Semi-automated calibration method for modelling of mountain permafrost evolution in Switzerland

2016 ◽  
Vol 10 (6) ◽  
pp. 2693-2719 ◽  
Author(s):  
Antoine Marmy ◽  
Jan Rajczak ◽  
Reynald Delaloye ◽  
Christin Hilbich ◽  
Martin Hoelzle ◽  
...  
Keyword(s):  
Large Scale ◽  
Calibration Method ◽  
Swiss Alps ◽  
Climate Projections ◽  
European Alps ◽  
Permafrost Degradation ◽  
Future Evolution ◽  
Mountainous Regions ◽  
Automated Calibration ◽  
The Future

Abstract. Permafrost is a widespread phenomenon in mountainous regions of the world such as the European Alps. Many important topics such as the future evolution of permafrost related to climate change and the detection of permafrost related to potential natural hazards sites are of major concern to our society. Numerical permafrost models are the only tools which allow for the projection of the future evolution of permafrost. Due to the complexity of the processes involved and the heterogeneity of Alpine terrain, models must be carefully calibrated, and results should be compared with observations at the site (borehole) scale. However, for large-scale applications, a site-specific model calibration for a multitude of grid points would be very time-consuming. To tackle this issue, this study presents a semi-automated calibration method using the Generalized Likelihood Uncertainty Estimation (GLUE) as implemented in a 1-D soil model (CoupModel) and applies it to six permafrost sites in the Swiss Alps. We show that this semi-automated calibration method is able to accurately reproduce the main thermal condition characteristics with some limitations at sites with unique conditions such as 3-D air or water circulation, which have to be calibrated manually. The calibration obtained was used for global and regional climate model (GCM/RCM)-based long-term climate projections under the A1B climate scenario (EU-ENSEMBLES project) specifically downscaled at each borehole site. The projection shows general permafrost degradation with thawing at 10 m, even partially reaching 20 m depth by the end of the century, but with different timing among the sites and with partly considerable uncertainties due to the spread of the applied climatic forcing.

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