the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Jan 2024
Review article: Retrogressive thaw slump theory and terminology
Abstract. Retrogressive thaw slumps (RTSs in plural and RTS in singular) are spectacular landforms that occur due to the thawing of ice-rich permafrost or melting of massive ground ice often in hillslope terrain. RTSs occur in the Arctic, Subarctic as well as high mountain (Tibetan Plateau) permafrost regions and are observed to expand in size and number due to climate warming. As the observation of RTS is receiving more and more attention due to their important role in permafrost thaw, impacts on topography, mobilization of sediment, carbon, nutrients, and contaminants, and their effects on downstream hydrology and water quality, the thematic breadth of studies increases and scientists from different scientific backgrounds and perspectives contribute to new RTS research. At this point, a wide range of terminologies originating from different scientific schools is being used and we identified the need to provide an overview of theoretical approaches, terms, and variable characteristics of RTS to clarify terminologies and create common ground for understanding RTS processes, dynamics, and feedbacks. We here review the theoretical geomorphological background of RTS formation and landform characteristics to provide an up-to-date understanding of the current views on terminology and underlying processes. The presented overview can be used not only by the international permafrost community but also by scientists working on ecological, hydrological, and biogeochemical consequences of RTS occurrence as well as remote sensing specialists developing automated methods for mapping RTS dynamics. The framework will foster a better understanding of the nature and diversity of RTS phenomena and provide a useful base for experts in the field but also ease the introduction to the topic of RTSs for scientists who are new to it.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Status: closed
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RC1: 'Comment on egusphere-2023-2914', Anonymous Referee #1, 18 Feb 2024
Nesterova et al. present an overview of taxonomies to describe retrogressive thaw slumps, their morphological characteristics and associated geomorphic processes. To bridge the disparate terminologies, the authors present and contrast taxonomies from the Russian and Western literature.
I laud the overall goal and see this contribution as an important step toward reconciling the disparate schools. However, it is difficult to say to what extent the present manuscript achieves this goal. The manuscript could be strengthened by clear definitions for all the terms it introduces, by drawing a sharp boundary between definitions and observations, and by more precise language. Currently, there is a risk the article will only be of interest to a niche audience. Clear definitions and descriptions would strengthen the manuscript substantially, as they would enable researchers from diverse backgrounds to thoroughly appraise the existing literature. Because similar issues pervade periglacial science (e.g., patterned ground), it could serve as a role model for review papers on various types of landforms, processes, etc.
1) Definitions
I encourage the authors to include clear definitions that enable a researcher with limited prior knowledge of these taxonomies to classify a given landform. If no prior or conflicting definitions are available, your guidance will be all the more valuable. Currently, almost none of the landforms are defined. I provide a few examples in the following.
a) The Canadian RTS glossary entry is included here and criticized for, among other things, not including stabilized landforms. What would be a useful definition? What is the definition implicitly used in the remainder of the manuscript? Is an RTS a landform (as suggested by the glossary entry) or is RTS also a process (as mentioned in the conclusion, but barely developed in the main body of the document)?
b) Shallow landslides: No definition of a "cryogenic translational landslide" is provided. Do these have to be translational (as the name suggests), by definition? Is the triggering by high pore-water pressure required by definition, or is this commonly observed or inferred for landforms that fall within the definition? For the ice whose melt induces pressurization: Does it have to be seasonal (and how can you tell, i.e., is this a useful definition) and does it have to be at the base of the active layer. A clear definition would help me determine whether detachments of the organic layer in discontinuous permafrost are CTLs, or shallow landslides on slopes underlain by taliks. The same concerns apply to cryogenic earthflows.
c) Thermocirques and thermoterraces: The paragraph starting at line 421 seems to assume the reader knows what is being referred to. In general, the distinction appears to be based on genesis rather than morphology, but it is not clear to me to what extent they are to be discriminated based on the morphology. For instance, Fig. 7b shows a thermocirque along a lake. Where did it initiate, and unless precise information is available, how was its present-day morphology taken into consideration to classify it as a thermocirque? If the location of initiation is the determining factor, a length scale could be informative: e.g., <=3 vs >3 m from the waterline at the time of initiation (averaged over at least 1 day).
2) Description vs. definition
I was struggling to distinguish which statements were definitional vs. descriptive. This relates partially to the lack of clear definitions (see 1), but also to ambiguous language. These ambiguities further made it impossible for me to identify the theoretical foundations alluded to in the title. I would expect any scientific theory to make testable predictions, based on a coherent set of clearly defined processes/quantities/observables.
Several examples of ambiguous language are provided below.
- The authors note there is little evidence that "aspect defines RTS occurrence." I suspect this is a descriptive statement, meaning that the observed regional associations between aspect and slump occurrence are variable.
- On line 74, it is stated that slumps "develop in a polycyclic fashion". This statement is presented as a universally valid declaration. Does slumping have to be polycyclic?3) Precise language advised
I think the manuscript would benefit from more precise language in many places. Vague statements are difficult to falsify.
Consider specifying the spatial and temporal scales in the descriptions. For instance, in line 395, CTLs are described as rapid. How rapid? Elsewhere, they are described as "very dynamic". What does this mean?
It is claimed that the "spatial distribution of ground ice determines the spatial extent of RTS." This is a strong deterministic statement, but the subsequent paragraph does not provide quantitative information. Do the climatic conditions play any role, or sediment properties? What are the relevant spatial and temporal scales?
It is claimed that "ablation happens only in summer when the air temperature is above 0C". Can it happen in the fall? Can it happen under strong radiation (e.g., Tibetan Plateau) when the 2m air temperature is <0C? See e.g. Lewkowicz 87.4) Scope
a) Paraglacial phenomena
Slumps on moraines or debris-covered glaciers were not considered in the manuscript, but they were not explicitly ruled out either.
b) Stabilization
A binary distinction between active thaw slumps and stabilized thaw slumps is made, with active thaw slumps featuring exposed ice (e.g., 3.5.1). Conversely, Kokelj et al. 2015 and Zwieback et al. 2020, amongst others, described thaw slumps that remained active on ~annual time scales despite featuring intermittent or even a persistent sediment cover. Would a more nuanced view on sediment cover and stabilization strengthen the manuscript?
c) Subjacent taliks and bay formation
The manuscript briefly mentions Kokelj et al. 2005, without describing the mechanisms involved. Also consider highlighting consequences of subsidence in the slump floor and below the adjacent waterbody, such as bay formation.Minor points
l 166: It may be useful to consider differences between regions and landforms. For instance, many slumps on Banks Island feature a break in slope in the headwall, while many in the Anderson Plain/Tuktoyaktuk Coastlands do not.
l 230: What is a "cliff retreatment"? What do you mean by lower and upper edge?
l 271: isolation->insulation
l 408: Soils often exhibit plastic or pseudoplastic behaviorCitation: https://doi.org/10.5194/egusphere-2023-2914-RC1 - AC1: 'Reply on RC1', Nina Nesterova, 12 Jul 2024
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RC2: 'Comment on egusphere-2023-2914', Anonymous Referee #2, 16 May 2024
As review 2, who was asked and accepted late, I both have read the manuscript and review 1. In my review I try not to repeat many of the comments from review 1, which all are valid, and I totally agree with those statements.
I was very interested in the title and the importance of RTS in a time of permafrost degradation and thaw, making these landforms a very visible witness of climate change. While acknowledging the attempt to review these features, I struggle with the paper outline and writing. The following issues arise, partly also mentioned by reviewer 1:
- The paper first introduces RTS incl. history (chapter 1), then it defines RTS (chapter 2) and describes common morphological features (chapter 3), while the discuss two divergent views of RTS, starting again with an historical background (chapter 4). This is confusing, and should be changed before publication, and I do not follow the motivation to structure the paper like that. I would recommend moving parts of the “historical background” into the start of the review, maybe into the Introduction. For a review paper this is an interesting knowledge to start with.
- The authors should review the common knowledge and discuss divergent views in a discussion chapter (which now is short and not really a discussion) or focus the paper on the different views in Russian and American literature as an example of divergent views, and come with recommendation on a common strategy. Now, the study is neither of those two.
- Because of that the paper is very hard to follow, the start of the manuscript is chopped in few descriptive chapters of landform details without illustration (move Fig. 1), incl a large table (maybe better off in an appendix). The second part is interesting incl. figure 3 is kind of illustrative, but is bot clearly connected to the first part.
- Concerning the discussion around landform and process, it reminds me a bit around discussion related to other landforms, such as rock glaciers, which is not always fruitful. In my understanding is RTS as term is similar to e.g. debris flow, this means a landslide process resulting in a landforms, which shape differs related to setting geological material the process is happening.
- Do a thorough check of the references, e.g. Yershov (1998) in line 308 is not in the reference list. But I did not check everything here.
- Precise language is important in review papers, as also review 1 mentioned. E.g. l. 135 makes no sense if the list all aspect instead of writing that “there is no preferred slope orientation”. Also check definitions, e.g. you use the for me unknown term “baydzheraks” in l. 151 before you define it in chapter 3.5.6.
I really recommend a manuscript like this, and if thoroughly revised I am confident it will be read, commented and cited.
Citation: https://doi.org/10.5194/egusphere-2023-2914-RC2 - AC2: 'Reply on RC2', Nina Nesterova, 12 Jul 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-2914', Anonymous Referee #1, 18 Feb 2024
Nesterova et al. present an overview of taxonomies to describe retrogressive thaw slumps, their morphological characteristics and associated geomorphic processes. To bridge the disparate terminologies, the authors present and contrast taxonomies from the Russian and Western literature.
I laud the overall goal and see this contribution as an important step toward reconciling the disparate schools. However, it is difficult to say to what extent the present manuscript achieves this goal. The manuscript could be strengthened by clear definitions for all the terms it introduces, by drawing a sharp boundary between definitions and observations, and by more precise language. Currently, there is a risk the article will only be of interest to a niche audience. Clear definitions and descriptions would strengthen the manuscript substantially, as they would enable researchers from diverse backgrounds to thoroughly appraise the existing literature. Because similar issues pervade periglacial science (e.g., patterned ground), it could serve as a role model for review papers on various types of landforms, processes, etc.
1) Definitions
I encourage the authors to include clear definitions that enable a researcher with limited prior knowledge of these taxonomies to classify a given landform. If no prior or conflicting definitions are available, your guidance will be all the more valuable. Currently, almost none of the landforms are defined. I provide a few examples in the following.
a) The Canadian RTS glossary entry is included here and criticized for, among other things, not including stabilized landforms. What would be a useful definition? What is the definition implicitly used in the remainder of the manuscript? Is an RTS a landform (as suggested by the glossary entry) or is RTS also a process (as mentioned in the conclusion, but barely developed in the main body of the document)?
b) Shallow landslides: No definition of a "cryogenic translational landslide" is provided. Do these have to be translational (as the name suggests), by definition? Is the triggering by high pore-water pressure required by definition, or is this commonly observed or inferred for landforms that fall within the definition? For the ice whose melt induces pressurization: Does it have to be seasonal (and how can you tell, i.e., is this a useful definition) and does it have to be at the base of the active layer. A clear definition would help me determine whether detachments of the organic layer in discontinuous permafrost are CTLs, or shallow landslides on slopes underlain by taliks. The same concerns apply to cryogenic earthflows.
c) Thermocirques and thermoterraces: The paragraph starting at line 421 seems to assume the reader knows what is being referred to. In general, the distinction appears to be based on genesis rather than morphology, but it is not clear to me to what extent they are to be discriminated based on the morphology. For instance, Fig. 7b shows a thermocirque along a lake. Where did it initiate, and unless precise information is available, how was its present-day morphology taken into consideration to classify it as a thermocirque? If the location of initiation is the determining factor, a length scale could be informative: e.g., <=3 vs >3 m from the waterline at the time of initiation (averaged over at least 1 day).
2) Description vs. definition
I was struggling to distinguish which statements were definitional vs. descriptive. This relates partially to the lack of clear definitions (see 1), but also to ambiguous language. These ambiguities further made it impossible for me to identify the theoretical foundations alluded to in the title. I would expect any scientific theory to make testable predictions, based on a coherent set of clearly defined processes/quantities/observables.
Several examples of ambiguous language are provided below.
- The authors note there is little evidence that "aspect defines RTS occurrence." I suspect this is a descriptive statement, meaning that the observed regional associations between aspect and slump occurrence are variable.
- On line 74, it is stated that slumps "develop in a polycyclic fashion". This statement is presented as a universally valid declaration. Does slumping have to be polycyclic?3) Precise language advised
I think the manuscript would benefit from more precise language in many places. Vague statements are difficult to falsify.
Consider specifying the spatial and temporal scales in the descriptions. For instance, in line 395, CTLs are described as rapid. How rapid? Elsewhere, they are described as "very dynamic". What does this mean?
It is claimed that the "spatial distribution of ground ice determines the spatial extent of RTS." This is a strong deterministic statement, but the subsequent paragraph does not provide quantitative information. Do the climatic conditions play any role, or sediment properties? What are the relevant spatial and temporal scales?
It is claimed that "ablation happens only in summer when the air temperature is above 0C". Can it happen in the fall? Can it happen under strong radiation (e.g., Tibetan Plateau) when the 2m air temperature is <0C? See e.g. Lewkowicz 87.4) Scope
a) Paraglacial phenomena
Slumps on moraines or debris-covered glaciers were not considered in the manuscript, but they were not explicitly ruled out either.
b) Stabilization
A binary distinction between active thaw slumps and stabilized thaw slumps is made, with active thaw slumps featuring exposed ice (e.g., 3.5.1). Conversely, Kokelj et al. 2015 and Zwieback et al. 2020, amongst others, described thaw slumps that remained active on ~annual time scales despite featuring intermittent or even a persistent sediment cover. Would a more nuanced view on sediment cover and stabilization strengthen the manuscript?
c) Subjacent taliks and bay formation
The manuscript briefly mentions Kokelj et al. 2005, without describing the mechanisms involved. Also consider highlighting consequences of subsidence in the slump floor and below the adjacent waterbody, such as bay formation.Minor points
l 166: It may be useful to consider differences between regions and landforms. For instance, many slumps on Banks Island feature a break in slope in the headwall, while many in the Anderson Plain/Tuktoyaktuk Coastlands do not.
l 230: What is a "cliff retreatment"? What do you mean by lower and upper edge?
l 271: isolation->insulation
l 408: Soils often exhibit plastic or pseudoplastic behaviorCitation: https://doi.org/10.5194/egusphere-2023-2914-RC1 - AC1: 'Reply on RC1', Nina Nesterova, 12 Jul 2024
-
RC2: 'Comment on egusphere-2023-2914', Anonymous Referee #2, 16 May 2024
As review 2, who was asked and accepted late, I both have read the manuscript and review 1. In my review I try not to repeat many of the comments from review 1, which all are valid, and I totally agree with those statements.
I was very interested in the title and the importance of RTS in a time of permafrost degradation and thaw, making these landforms a very visible witness of climate change. While acknowledging the attempt to review these features, I struggle with the paper outline and writing. The following issues arise, partly also mentioned by reviewer 1:
- The paper first introduces RTS incl. history (chapter 1), then it defines RTS (chapter 2) and describes common morphological features (chapter 3), while the discuss two divergent views of RTS, starting again with an historical background (chapter 4). This is confusing, and should be changed before publication, and I do not follow the motivation to structure the paper like that. I would recommend moving parts of the “historical background” into the start of the review, maybe into the Introduction. For a review paper this is an interesting knowledge to start with.
- The authors should review the common knowledge and discuss divergent views in a discussion chapter (which now is short and not really a discussion) or focus the paper on the different views in Russian and American literature as an example of divergent views, and come with recommendation on a common strategy. Now, the study is neither of those two.
- Because of that the paper is very hard to follow, the start of the manuscript is chopped in few descriptive chapters of landform details without illustration (move Fig. 1), incl a large table (maybe better off in an appendix). The second part is interesting incl. figure 3 is kind of illustrative, but is bot clearly connected to the first part.
- Concerning the discussion around landform and process, it reminds me a bit around discussion related to other landforms, such as rock glaciers, which is not always fruitful. In my understanding is RTS as term is similar to e.g. debris flow, this means a landslide process resulting in a landforms, which shape differs related to setting geological material the process is happening.
- Do a thorough check of the references, e.g. Yershov (1998) in line 308 is not in the reference list. But I did not check everything here.
- Precise language is important in review papers, as also review 1 mentioned. E.g. l. 135 makes no sense if the list all aspect instead of writing that “there is no preferred slope orientation”. Also check definitions, e.g. you use the for me unknown term “baydzheraks” in l. 151 before you define it in chapter 3.5.6.
I really recommend a manuscript like this, and if thoroughly revised I am confident it will be read, commented and cited.
Citation: https://doi.org/10.5194/egusphere-2023-2914-RC2 - AC2: 'Reply on RC2', Nina Nesterova, 12 Jul 2024
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Marina Leibman
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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