Geophysical analysis of an area affected by subsurface dissolution &ndash; case study of an inland salt marsh in northern Thuringia, Germany

Wadas, Sonja Halina; Buness, Hermann; Rochlitz, Raphael; Skiba, Peter; Günther, Thomas; Grinat, Michael; Tanner, David Colin; Polom, Ulrich; Gabriel, Gerald; Krawczyk, Charlotte M.

doi:https://doi.org/10.5194/egusphere-2022-164

Preprints

https://doi.org/10.5194/egusphere-2022-164

Preprints

02 May 2022

Geophysical analysis of an area affected by subsurface dissolution – case study of an inland salt marsh in northern Thuringia, Germany

Sonja Halina Wadas¹, Hermann Buness¹, Raphael Rochlitz¹, Peter Skiba^2,a, Thomas Günther¹, Michael Grinat¹, David Colin Tanner¹, Ulrich Polom¹, Gerald Gabriel^1,3, and Charlotte M. Krawczyk^4,5 Sonja Halina Wadas et al.

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¹Leibniz Institute for Applied Geophysics, Stilleweg 2, 30655 Hannover, Germany
²Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany
³Leibniz University Hannover – Institute of Geology, Callinstraße 30, 30167 Hannover, Germany
⁴GFZ – German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
⁵Technical University Berlin – Institute for Applied Geosciences, Ernst-Reuter-Platz 1, 10587 Berlin, Germany
^aformerly at: Leibniz Institute for Applied Geophysics, Stilleweg 2, 30655 Hannover, Germany

Received: 07 Apr 2022 – Discussion started: 02 May 2022

Abstract. The subsurface dissolution of soluble rocks, also called subrosion, can affect areas over a long period of time and pose a severe hazard. We show the benefits of a combined approach using P-wave- and S_H-wave reflection seismics, electrical resistivity tomography, transient electromagnetics, and gravimetry for a better understanding of the subrosion process. The study area, ’Esperstedter Ried’ in northern Thuringia, Germany, located south of the Kyffhäuser hills, is a large inland salt marsh that developed due to dissolution of soluble rocks at approximately 300 m depth.We were able to locate buried subrosion structures, subrosion zones, faults and fractures, and potential fluid pathways, aquifers and aquitards based on seismic and electromagnetic surveys. Further improvement of the subrosion model was accomplished by analyzing gravimetry data that indicates subrosion-induced mass movement as shown by local minima of the Bouguer anomaly for the Esperstedter Ried. Forward modelling of the gravimetry data, in combination with the seismic results, delivered a cross section through the inland salt marsh from north to south. We conclude that the tectonic movements during the Tertiary, which led to the uplift of the Kyffhäuser hills and the formation of faults parallel and perpendicular to the low mountain range, were the initial trigger for subrosion. The faults and the fractured Triassic and Lower Tertiary deposits serve as fluid pathways for groundwater to leach the deep Permian Zechstein deposits, since subrosion is more intense near faults. The artesian-confined salt water ascends towards the surface along the faults and fracture networks, and formed the inland salt marsh over time. In the past, subrosion of the Zechstein formations formed several, now buried, sagging and collapse structures, and, since the entire region is affected by recent sinkhole development, subrosion is still ongoing. From the results of this study, we suggest that the combined geophysical investigation of subrosion areas can improve the knowledge of control factors, risk areas, and thus local subrosion processes.

Sonja Halina Wadas et al.

Status: final response (author comments only)

RC1:
'Comment on egusphere-2022-164', Anonymous Referee #1, 27 May 2022

The manuscript deals with geophysical surveys and interpretation in an area affected by sinkhole processes in Germania. The topic is certainly of interest to Solid Earth, and the article is worth to be published, being an interesting piece of work; I was particularly happy to have the chance to read it.

I have listed in the accompanying file a number of small edits, and requests of clarification on some issues that are not clear to me. Overall, I therefore require minor revisions and invite the Authors to carefully read my comments on the pdf file. Here, I just summarize the main points where the Authors should make an effort to further improve the quality and clarity of the paper, in my opinion.

The main problem with the manuscript is the extensive use throughout the article of the term “subrosion”, which I strongly discourage. This because the term is not established in the scientific literature about sinkholes, and represents a potential source of confusion. I would suggest to use, as in the first line of the article, subsurface dissolution (which in many cases include also the leaching process).

At a greater detail, the existence of a well-established classification (proposed by Gutierrez et al., 2014, with recent developments by Parise, 2019, 2022) should be considered as reference point, and the interpretation of the geophysical surveys including the attribution to mechanism of origin, should be done in accordance with the categories of the classification above. In many parts of the manuscript I pointed out the confusion deriving from using the term subrosion, I really hope the Authors could take into account such observations and comments.

As for the sinkhole classification, as mentioned above there have been in the last years some updates published in the Encyclopedia of Caves (3^rd edition) and in the Treatise on Geomorphology (2^nd edition). I would suggest to quote also these recent developments. Below the complete references:

Parise M., 2019, In: White W.B., Culver D.C. & Pipan T. (Eds.), . Academic Press, Elsevier, 3^rd edition, ISBN ISBN 978-0-12-814124-3, p. 934-942.

Parise M., 2022, . In: Shroder J.J.F. (Ed.), . Elsevier, Academic Press, pp. 200–220. https://dx.doi.org/10.1016/B978-0-12-818234- 5.00029-8. ISBN: 9780128182345.

The issue of salt springs in the Khyffauser hills (line 73) is very interesting, and might deserve some additional detail. Is there any reference to hydrogeological works in this area? Could these (if existing) could be useful for a deeper understanding of the sinkhole problems?

Comment on Figure 1: do we need so many different colors if you then summarize them in single formations?The map is quite complex and not easily readable, I suggest to simplify it in 6 colours (the 6 groups listed in the legend) to improve readability.

There is inconsistency among the initial figures as regards the formations shown. Figure 1 groups them in a way different from figure 2, and this makes difficult for the reader to understand the link among different figures and what is stated in the text. Author should decide which grouping is the best for their manuscript and adapt to that subdivision all the figures and the text.

Lines 241-216:

Authors are here describing their interpretation of a sinkhole identified by sinkhole profiles. In line 216, they state it is a collapse sinkhole. This is just an example to outline how misleading is the use of the term "subrosion" (used few lines before by the Authors) that, on the other hand, would let the reader think to a completely different mechanism of origin, that is dissolution or suffosion. I once more insist on not using such a misleading term.

Risk: the term risk is not used in the proper way, in my opinion. In natural hazards, risk comprises all damage caused by natural processes, and include the economical and societal costs. These are not dealt with in the present manuscript, and the term risk is used with a meaning that should be (in my interpretation) corresponding to susceptibility, or, if including also temporal information, on hazard. I suggest therefore to change in the manuscript, and in the abstract as well, the word risk.

Reference list: please check the reference Schriel & Bulow (1926). It is exactly the same, and repeated as 1926a and 1926b.

In relation to the comments above, and to those in the attached pdf, I suggest to add the following references:

Abou Karaki N., Fiaschi S., Paenen K., Al-Awabdeh M. and Closson D., 2019, Exposure of tourism development to salt karst hazards along the Jordanian Dead Sea shore. Hydrol. Earth Syst. Sci., 2323, 2111-2127.

Bruthans J., Asadi N., Filippi M., Vilhelm Z. & Zare M., 2008 - Erosion rates of salt diapirs surfaces: An important factor for development of morphology of salt diapirs and environmental consequences (Zagros Mts., SE Iran). Environmental Geology, 53 (5): 1091-1098.

Bruthans J., Filippi M., Zare M., ChuraÌcÌkovaÌ Z., Asadi N., Fuchs M. & AdamovicÌ J., 2010 - Evolution of salt diapir and karst morphology during the last glacial cycle: effects of sea-level oscillation, diapir and regional uplift, and erosion (Persian Gulf, Iran). Geomorphology, 121: 291-304.

De Waele J., Piccini L., Columbu A., Madonia G., Vattano M., Calligaris C., D’Angeli I.M., Parise M., Chiesi M., Sivelli M., Vigna B., Zini L., Chiarini V., Sauro F., Drysdale R. and Forti P., 2017, Evaporite karst in Italy: a review. International Journal of Speleology, vol. 46 (2), p. 137-168.

Dreybrodt, W., 2004. Dissolution: evaporite and carbonate rocks. In: Gunn, J. (Ed.), Encyclopedia of Caves and Karst Science. Fitzroy Dearborn, New York, pp. 295–300.

Fazio N.L., Perrotti M., Lollino P., Parise M., Vattano M., Madonia G., & Di Maggio C., 2017, A three-dimensional back analysis of the collapse of an underground cavity in soft rocks. Engineering Geology, vol. 238, p. 301-311.

Filippi M., Bruthans J., Palatinus L., Zare M. and Asadi N. 2011. Secondary halite deposits in the Iranian salt karst: general description and origin. International Journal of Speleology, 40 (2), 141-162.

Goldscheider N. & Bechtel T.D., 2009, The housing crisis from underground—damage to a historic town by geothermal drillings through anhydrite, Staufen, Germany. Hydrogeology Journal, vol.17, p. 491-493.

Iovine G., Parise M. & Trocino A., 2010, Breakdown mechanisms in gypsum caves of southern Italy, and the related effects at the surface. Zeitschrift fur Geomorphologie, vol. 54 (suppl. 2), p. 153-178.

KAUFMANN, G. 2014. Geophysical mapping of solution and collapse sinkholes. Journal of Applied Geophysics, 111, 271–288.

KAUFMANN, G. & ROMANOV, D. 2016. Structure and evolution of collapse sinkholes: combined interpretation from physico-chemical modelling and geophysical field work. Journal of Hydrology, 540, 688–698.

KAUFMANN, G., NIELBOCK, R. & ROMANOV, D. 2015b. The Unicorn Cave, Southern Harz Mountains, Germany: from known passages to unknown extensions with the help of geophysical surveys. Journal of Applied Geophysics, 123, 123–140.

Kaufmann, G., Romanov, D., Tippelt, T., Vienken, T., Werban, U., Dietrich, P., Mai, F., Börner, F., 2018. Mapping and modelling of collapse sinkholes in soluble rock: The MuÌnsterdorf site, northern Germany. Journal of Applied Geophysics 154, 64–80.

KAUFMANN, G. & ROMANOV, D, 2018, Geophysical observations and structural models of two shallow caves in gypsum/anhydrite-bearing rocks in Germany. In: Parise M., Gabrovsek F., Kaufmann G. & Ravbar N. (Eds.), Advances in Karst Research: Theory, Fieldwork and Applications. Geological Society, London, Special Publications, 466, p. 341-357.

Margiotta S., Negri S., Parise M. & Valloni R., 2012, Mapping the susceptibility to sinkholes in coastal areas, based on stratigraphy, geomorphology and geophysics. Natural Hazards, vol. 62 (2), p. 657-676, DOI 10.1007/s11069-012-0100-1.

Margiotta S., Negri S., Parise M. & Quarta T.A.M., 2016, Karst geosites at risk of collapse: the sinkholes at Nociglia (Apulia, SE Italy). Environmental Earth Sciences, vol. 75 (1), p. 1-10, DOI: 10.1007/s12665-015-4848-y.

Parise M., Closson D., Gutierrez F. & Stevanovic Z., 2015, Anticipating and managing engineering problems in the complex karst environment. Environmental Earth Sciences, vol. 74, p. 7823-7835.

Perrotti M., Lollino P., Fazio N.L. & Parise M., 2019, Stability charts based on the finite element method for underground cavities in soft carbonate rocks: validation through case-study applications. Natural Hazards and Earth System Sciences, vol. 19, p. 2079-2095.

Watson R.A., Holohan E.P., Al-Halbouni D., Saberi L., Sawarieh A., Closson D., Alrshdan H., Abou Karaki N., Siebert C., Walter T.R. and Dahm T., 2019, Sinkholes and uvalas in evaporite karst: spatio-temporal development with links to base-level fall on the eastern shore of the Dead Sea. Solid Earth, 10, 1451-1468.

White, W.B., 2002. Karst hydrology: recent developments and open questions. Eng. Geol. 65, 85–105.

Zumpano V., Pisano L. & Parise M., 2019, An integrated framework to identify and analyze karst sinkholes. Geomorphology, vol. 332, p. 213-225.

For all the considerations above, I recommend minor revision.

Citation: https://doi.org/10.5194/egusphere-2022-164-RC1
- AC1: 'Reply on RC1, RC2 and EC1', Sonja Wadas, 15 Aug 2022
  
  Author response to reviewer and editor comments
  
  We would like to thank the Editor, Elias Lewi, and the two reviewers, Alireza Malehmir and one anonymous, for their useful comments that helped to improve the manuscript. We have tried to answer all comments and questions as best as we could and incorporated them into the manuscript accordingly.
  A detailed tabular overview of the reviewer comments, sorted by chapters, and our corresponding answers, together with a manuscript version with the highlighted changes (tracked changes) can be found in the attached Zip-Folder 'Table of Comments & Answers & Manuscript with tracked changes'.
  
  With best regards,
  
  Sonja Halina Wadas - on behalf of all Co-Authors
  
  Citation: https://doi.org/10.5194/egusphere-2022-164-AC1
RC2:
'Comment on egusphere-2022-164', Alireza Malehmir, 03 Jun 2022

This is an interesting work combining various geophysical methods and boreholes to study sinkholes and their potential hazards. The work is quite complete and the interpretations are sounds.

My main issue is the lack of details on the seismic data and the processing works. While the P-wave sections have good quality and show distinct and promising reflections, the SH sections are rather poor and risky to rely on. It would be good to spot any of the reflectivity in the shot gathers and show where they have ended up in the final sections. I am otherwise afraid to say that the SH sections have failed where the much of introduction attempts to say it would provide high-resolution images of the subsurface. Following this, I think much of the SH section interpretations are overdone or mainly based on the P-wave and gravity modelling work, which is fine but then the text and introduction should be adjusted.

As for the text:

Some resharpening of the text should be needed like

P-wave and SH-wave, can be P- and S-wave …

Avoid using get and replace with "obtain"

what is 5 km2 "sink"? Looks strange wording.

As for extreme slow S-wave velocity please also note our works presented recently at NSG-EAGE 2021 with S-wave reflections imaged in the vertical component data when spatial and temporal sampling was done in a great resolution (Malehmir, 2019 and 2021). You may also look into our work where we combined a similar approach for fault mapping in Sweden: Post-glacial reactivation of the Bollnäs fault, central Sweden – a multidisciplinary geophysical investigation (Solid Earth, 2016)

Avoid naming so many commercial names and software in the main text and move them to the acknowledgments.

You mean 3 repeated shot records vertically stacked?

It is NMO corrections (plural) and static corrections

Use of semicolon between references looks a bit odd as it breaks the sentence.

Citation: https://doi.org/10.5194/egusphere-2022-164-RC2
- AC1: 'Reply on RC1, RC2 and EC1', Sonja Wadas, 15 Aug 2022
  
  Author response to reviewer and editor comments
  
  We would like to thank the Editor, Elias Lewi, and the two reviewers, Alireza Malehmir and one anonymous, for their useful comments that helped to improve the manuscript. We have tried to answer all comments and questions as best as we could and incorporated them into the manuscript accordingly.
  A detailed tabular overview of the reviewer comments, sorted by chapters, and our corresponding answers, together with a manuscript version with the highlighted changes (tracked changes) can be found in the attached Zip-Folder 'Table of Comments & Answers & Manuscript with tracked changes'.
  
  With best regards,
  
  Sonja Halina Wadas - on behalf of all Co-Authors
  
  Citation: https://doi.org/10.5194/egusphere-2022-164-AC1
EC1:
'Comment on egusphere-2022-164', Elias Lewi, 14 Jun 2022
An interesting attempt is made to present an integrated geophysical survey. Even though it is common to give less detailed information in data processing in integrated geophysical survey, the comment of reviewer no. 2, especially in relation to SH waves needs to be considered seriously. Similarly, I have some additional comments in relation to the gravity data processing and interpretation that are attached herewith below. The authors should address and accommodate all the comments and resubmit the manuscript to consider it for publication.
Page 9
ETRS89, which is the European Terrestrial Reference System 1989, is an Earth-Centered, Earth-Fixed reference system, which is based on the GRS80 ellipsoid. On the other hand, DHHN92 is a height system above mean sea level (“Höhen über Normalhöhennull, in DHHN2016”). From the first paragraph under section 4.4 it can be understood that the authors used the Somigliana’s closed form formula to compute the normal gravity and they have computed the Complete Bouguer Anomaly using the formula given by Hinze et al. (2005). In that case, the effect of the geoid undulation on the data will not be taken care because the normal gravity is computed on GRS80 and the height used to compute the Complete Bouguer Anomaly is an orthometric height. In other words, the effect of the height between the ellipsoid and the geoid is not removed, though it will most probably, shift all data points constantly as your area is small. However, from the computational point of view it is still a mistake, and this constant shift should either be mentioned or the processing should be done using geometric height. This is well explained in the paper which the authors have cited (i.e. Hinze et al., 2005). They should have used height above the ellipsoid not above mean sea level. In that case also they have to remove the EGM96 geoid undulation from the DEM model as most of these models have geoid undulation from EGM96. As they haven’t mentioned which DEM model, they have used it is hard to comment on this.

As height has a deceive influence on gravity data reduction, it will be good if the authors explain how height errors have propagated unto the Bouguer anomaly so that it is possible to appreciate the interpretation.

Which DEM is being used? As the different DEM models have different accuracies, it will be great if the DEM used is mentioned to appreciate the interpretations.

The authors have stated that they have used a filtering method in the gravity data processing without mentioning the type of filter. The type of filter and the parameters used have an impact on the result and it will be good if the authors specify the type of filter and the parameters set for filtering to appreciate the interpretations. What changes has the filtering process has brought.

Page 19
In the model of the gravity data, there are small sharp edges, which I think are directly taken from the controlled source seismic profile. I am sure that this can’t be detected and resolved by the surface gravity survey and it would have been good to present what is only detectable and resolvable by gravity method.

General
As gravity data modeling is highly non-unique, it would have been appreciated if the authors try to describe the methods, they have used to constrain the density of the different layers and their shape. The integrated approach including borehole information can be a very good spring board for this analysis.
Citation: https://doi.org/10.5194/egusphere-2022-164-EC1
- AC1: 'Reply on RC1, RC2 and EC1', Sonja Wadas, 15 Aug 2022
  
  Author response to reviewer and editor comments
  
  We would like to thank the Editor, Elias Lewi, and the two reviewers, Alireza Malehmir and one anonymous, for their useful comments that helped to improve the manuscript. We have tried to answer all comments and questions as best as we could and incorporated them into the manuscript accordingly.
  A detailed tabular overview of the reviewer comments, sorted by chapters, and our corresponding answers, together with a manuscript version with the highlighted changes (tracked changes) can be found in the attached Zip-Folder 'Table of Comments & Answers & Manuscript with tracked changes'.
  
  With best regards,
  
  Sonja Halina Wadas - on behalf of all Co-Authors
  
  Citation: https://doi.org/10.5194/egusphere-2022-164-AC1

Sonja Halina Wadas et al.

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Short summary

The dissolution of rocks (subrosion) poses a severe hazard because it can cause subsidence and sinkhole formation. Based on results from our study area in Thuringia, Germany, using P- and S_H-wave reflection seismics, electrical resistivity- and electromagnetic methods and gravimetry, we develop a geophysical investigation workflow. This workflow enables to identify the initial triggers of subrosion and its control factors, such as structural constraints, fluid pathways, and mass movement.


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