the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Feb 2024
Glacial Vermicular Ridge Features on Axel Heiberg Island, Nunavut, Canada
Abstract. Vermicular Ridge Features (VRFs) comprise a series of ridges and troughs with a circular, sinuous, and anastomosing morphology composed of clast-rich sandy diamict. VRFs were first reported on the south coast of Devon Island, Nunavut, Canada, in the Dundas Harbour region. Here, we document the presence of VRFs near Mokka Fjord on Axel Heiberg Island, Nunavut, Canada. We utilize field observations, ultra high resolution LiDAR, and ground penetrating radar to characterize and compare the morphometry and sedimentology of VRFs near Mokka Fjord to other periglacial, paraglacial, and glacial landforms. VRFs near Mokka Fjord have a diameter ranging from 6 to 37 m and reach up to 1.5 m in height. They comprise clast-rich glaciofluvial sediment and till. A leading periglacial (i.e., segregation ice features/lithalsas) and glacial (i.e., ring-ridge moraines and kame/kettled terraces) origin are presented. We interpret Mokka Fjord VRFs to be an ice-marginal feature resulting from paraglacial ablation of buried glacial ice producing a hummocky ring-ridge moraine comprised of ice marginal and supra- and englacial debris. This formation mechanism would infer a largely polythermal glacial environment with limited water supply. Likely from occasional warm-based periods at the ice margins which may allow sediment output and ice burial from basal ice debris redistribution or the thinning and subsequent burial of snout ice from glaciofluvial outwash.
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RC1: 'Comment on egusphere-2024-227', Anonymous Referee #1, 22 Feb 2024
I am afraid that the genetic model proposed in this paper for the formation of VRFs is untenable and hence I have proposed a rejection.
I have attached an annotated pdf with specific comments on the text.
Whereas this paper presents a lot of good field data on some interesting landforms, the interpretive and analytical aspects are unconvincing and much of the material misconceived. Fundamental to this is the lengthy argument presented to reject a permafrost/periglacial origin of the landforms and then a very short and weakly justified case for a glacial origin. The latter appears to be based on a dated understanding of the glacial literature which is compounded by a lack of critical discussion of that literature with respect to ridge rimmed landforms, of which there are many types but few of which actually resemble those described by the authors. VRFs are common throughout the Canadian Arctic and occur on valley floors and coastal lowlands covered in deglacial sediments. Spatially they grade in and out of low-centred polygons and circles, the changing morphology being dictated by local material properties and standing water characteristics. In places you can see where old water channels link up with the depressions between parallel winding ridges, indicating that running water had some role in their evolution amongst developing ground ice features. The fact that the VRFs reported in this paper mostly lie on glaciofluvial outwash terraces clearly demonstrates that they have been constructed on those terraces after they formed - hence they cannot be derived from underlying dead ice even if it is present. Where stagnant glacier ice is present, the materials in which VRFs form has been released by supraglacial melt out. Any structure imparted on the material at this stage is subject to topographic reversal and flowage - no downwasting, debris-covered glacier surface has ever been reported to contain VRFs. Even if they did form they would not survive with such morphological clarity due to the continued melt-out of underlying ice. Moreover, once the material is thicker than the active layer it is subject to permafrost and periglacial processes for at least 8 ka. Reports on the surficial geology and landforms of deglaciated terrain in the Canadian Arctic show that VRFs are inextricably linked to low centred ice wedge polygons, pingos and linear pingo complexes and lithalsa-type landforms developed in lowlands containing diamictic and poorly-sorted sand and gravel deposits laid down during and after deglaciation. They are therefore genetically related to those landforms. No evidence has been presented in this paper to justify any other interpretation. Nor has a specific glacial process been proposed in any detail other than differential ablation, which would form chaotic hummocky moraine or linear controlled moraine at best, not winding ridges.
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AC1: 'Reply on RC1', Shannon Hibbard, 26 Feb 2024
Thank you for taking the time to review our manuscript. We appreciate your thorough examination of our work and your feedback. We have thoroughly searched the literature and consulted with experts who have studied periglacial processes in the Arctic for decades and we can find no previously published studies on this landform. We would greatly appreciate any references you could provide. For additional review into glacial landforms, please see Hibbard et al. (2021) at https://doi.org/10.1016/j.geomorph.2021.107947. Similar features are detailed in Tables 1 (our manuscript) and 2 (Hibbard et al., 2021). In our manuscript, we discuss VRFs at Mokka Fjord as potentially lithalsa-type frost mounds or ring-ridge moraines/kettled terraces. Our interpretation is based on field observations, geological context, and literature review. While a conclusive mechanism may require further study, we present our preferred formation mechanism.
Citation: https://doi.org/10.5194/egusphere-2024-227-AC1 -
RC2: 'Reply on AC1', Anonymous Referee #1, 28 Feb 2024
I'm afraid citing Hibbard et al. 2021 doesn't really help the case for a justification as it is based on the same problematic argument. I can provide you with some paper titles that include these features as part of permafrost assemblages but what is more fundamentally problematic is that you have not identified exactly what process-form regime you think is operating if these features are glacial. Can you sketch up conceptual model? That process often brings up problematic issues as you try to re-assemble the process-form regime. These features would not be as clearly defined or intricate if they had emerged from buried glacier ice - moreover, they are formed on outwash, which has been deposited over buried glacier ice where it does actually exist. Hence the ridges must have formed in the overburden, independent of glacier ice melt out. Here are some papers that include these forms being inextricably linked morphologically to permafrost features, but you are correct that they have not received detailed attention - hence it is a pity that your valuable attention has been devalued by a pre-conceived notion of a glacial genesis.
French et al. 1982 - Ground ice stratigraphy and late Quaternary events, SW Banks Island - Proc. 4th Can. Permafrost Conf. p81-90
Pissart 1967 - Les pingos de l'ile Prince Patrick - Geographical Bulletin 9, 189-217
Pissart & French 1977 - The origin of pingos in regions of thick permafrost, western Canadian arctic. Quaestiones Geographicae 4, 149-160
French 1976 - Pingo investigations, Banks Island, District of Franklin. GSC Paper 76-1A, 235-238
Pissart 1975 - Banks Island, NWT - pingos, wind action, periglacial structures. GSC Paper 75-1A, 479-481
Also take a look at the relict pingo literature, especially Pissart's work on the remnants of periglacial mounds in the Hautes Fagnes. Recent papers like Ross et al 2019 that propose glacial origins for these relict features are fundamentally flawed for the same reason as yours - they have not provided a glacial process-form regime that explains the landforms.
Finally, Wolfe et al 2014, which you do cite, provide a clear illustration of exactly the same forms as yours, which the interpret as lithalsas. The interesting thing about the high arctic forms that you have studied is that they are inextricably linked to low centred ice wedge polygons/ovoids, lithalsas and elongate pingo chains and hence are genetically related. I too have colleagues who have spent decades working in the arctic, as I have myself, and we would never consider these forms as anything other than permafrost landforms.
Citation: https://doi.org/10.5194/egusphere-2024-227-RC2 -
AC2: 'Reply on RC2', Shannon Hibbard, 14 Mar 2024
Thank you for providing additional references.
The studies by Pissart and French in 1976 and 1977 regarding pingo investigations on Banks Island in the Canadian Arctic have been referenced and discussed within the manuscript. While I suggest that Mokka Fjord VRFs may share a similar periglacial origin, the features they studied differ morphometrically from Mokka Fjord VRFs (see morphologic comparison in Table 1 of Hibbard et al., 2021).
Similar disparities are found in the descriptions of pingos by Pissart in 1967 and French et al. in 1982. Not only do their morphology and morphometry vary (their landforms are larger in all dimensions), but observations such as sediment grading towards the pingo ice core, presence of marine shells and forams, and the steep dipping of beds at the pingo core were not evident at Mokka Fjord (though further field investigations are necessary at this site). Pissart (1967) additionally notes the uncertainty surrounding the origin of these landforms, with suggestions that the landscape may resemble that of glacial origins, thereby indicating that considering other formation mechanisms, such as glacial origins, is not unwarranted. It's also worth mentioning that Mokka Fjord VRFs are unique in their smaller scale compared to the features studied by others.
Additionally, Pissart’s work on the Hautes Fagnes and Wolfe et al. 2014 are referenced in the manuscript and morphological comparisons are made in Table 1.
That being said, while there are notable distinctions between the landforms documented by Pissart on Banks Island and Prince Patrick Island compared to those addressed in this manuscript, there are also significant parallels. These landforms share similar depositional environments, situated within glacial outwash plains comprising sands and gravels alongside glacial meltwater channels and terraces prone to fluvial taliks and permafrost aggradation following deglaciation. Furthermore, the landforms described by Pissart are located near features bearing a striking resemblance to those found in Mokka Fjord. However, the descriptions provided in these papers do not explicitly describe these nearby analogous landforms. While I acknowledge the validity of the lithalsa/frost mound argument, I maintain that a glacial origin is plausible, hence the extensive discussion on both possibilities. I am happy to provide a step-by-step schematic depiction of the two proposed formation mechanisms, with a focus on buried ice origin, a point also echoed by Reviewer #2 and the editor.
Lastly, my reference to Hibbard et al. 2021 was not intended as a justification but rather to offer additional references to morphologically similar glacial features, as per your inquiry.
Citation: https://doi.org/10.5194/egusphere-2024-227-AC2 -
RC4: 'Reply on AC2', Anonymous Referee #1, 14 Mar 2024
I can only re-iterate the points already made, which are still un-resolved. Based upon the morphology and location of these features they cannot be glacial in origin. Even where they overlie buried glacier ice, which by strict definition is now ground ice, they are forming in the overburden under modern periglacial conditions. You do indeed cite some periglacial literature but you don't critically evaluate it in the context of your preferred genesis. Again I have to point out that you have not critically discussed a glacial origin either and have not cited the most up to date and relevant glacial literature on the subject of hummocky and sinuous landforms. And on the subject of the inclusion of shells and foraminifera, these would only be present if 1) landforms were below the marine limit and 2) the raised marine sediments did actually originally contain shells and foraminifera - this is not a diagnostic criteria. I would welcome your compilation of a schematic, conceptual model of how you envisage these landforms are being created glacially - I look forward to engaging with that hypothesis in the future.
Citation: https://doi.org/10.5194/egusphere-2024-227-RC4 -
AC3: 'Reply on RC4', Shannon Hibbard, 25 Mar 2024
We appreciate the time and effort you and the other reviewer have invested in reviewing our manuscript. Your insightful comments have led us to think more deeply about how we present our ideas and data synthesis, with a focus on competing hypotheses. We acknowledge that, at this stage, it would be premature to favor one hypothesis over the other without additional fieldwork and predictive modeling.
In light of your feedback, we intend to revise our manuscript to present both hypotheses impartially, without advocating for a preferred interpretation. To aid in the understanding of these hypotheses, we will include a new figure that delineates the landscape evolution and formation mechanisms for both propositions.
Furthermore, we will expand our discussion to consider the implications of each hypothesis on our understanding of past Holocene climate and its implications for a polythermal environment in more depth.
Citation: https://doi.org/10.5194/egusphere-2024-227-AC3
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AC3: 'Reply on RC4', Shannon Hibbard, 25 Mar 2024
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RC4: 'Reply on AC2', Anonymous Referee #1, 14 Mar 2024
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AC2: 'Reply on RC2', Shannon Hibbard, 14 Mar 2024
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RC2: 'Reply on AC1', Anonymous Referee #1, 28 Feb 2024
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AC1: 'Reply on RC1', Shannon Hibbard, 26 Feb 2024
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RC3: 'Comment on egusphere-2024-227', Anonymous Referee #2, 29 Feb 2024
This paper provides a contribution to the discussion about periglacial vs glacial origin of vermicular ridge features in the Canadian high Arctic.
The authors make a huge and solid effort in field work and data collection, on the ground and remotely. They also give a good description of a complicated set of landforms.
I think this paper has potential, but I suggest a major revision, with an in-depth discussion of the possible formation mechanisms. Especially, the authors should provide a schematic step-by-step drawing/description of their chosen formation suggestion (or two contradictory ones). That is, about the possible origins of buried ice, that seems to be the key in figuring out formation mechanisms. About formation timing of the terrasses where these features are located, thus the transport of the glacifluvial material you describe, and how this relates, in time and space, to the possible buried ice.
Line 34: can you really say that many of these were associated with massive ice? What does massive mean? Only ice would be sufficient?
First section, any references to the ongoing debate about the Canadian high Arctic?
Line 89 of our field study
In Line 330 you give a crucial part of your argumentation: “Axel Heiberg Island lies within a recently deglaciated landscape where large amounts of dead glacial ice are likely preserved in the continuous permafrost zone under the protection of surface debris cover”. Could you please elaborate on this argument and give references? You describe some of the glacial history in chapter 2, Geologic and Geomorphic Setting, but nothing that tells the likeliness of large amounts of dead glacial ice. In chapter 6, Summary and Conclusions, first section, you suggest the presence of buried ice, but that the origin of the ice is unknown.
An interesting point is that you did not observe grain sorting where you were digging. Would you say this applies to the entire area?
5.2 Glacial Origins, Line 393 and onwards: please read the references you give, and which formation hypothesis is given in which reference, and sort them correctly in 1) leftover from stagnant ice, and 2) subglacial diapirism (or if needed, add a third formation class).
Citation: https://doi.org/10.5194/egusphere-2024-227-RC3 -
AC4: 'Reply on RC3', Shannon Hibbard, 11 Apr 2024
Thank you for your thoughtful comments and suggestions. We appreciate your recognition of our data collection, as well as your constructive feedback on areas where our manuscript can be improved.
We agree with your suggestion to provide a more in-depth discussion of the possible formation mechanisms. We plan to include a schematic step-by-step drawing and description of our proposed formation suggestions. This will cover the possible origins of buried ice, which is key to understanding the formation mechanisms. We will also discuss the timing of terrace formation and the transport of glacifluvial material, and how these relate, in time and space, to the possible buried ice.
Regarding your comment on Line 34, we hypothesize that these features are the product of topographic inversion following the disintegration of buried massive ice rather than interstitial ice. We will provide a figure demonstrating this process.
To the best of our knowledge, we are not aware of any previously published articles referencing VRF-like features (except Hibbard et al., 2021 where we first observed these features on Devon Island). However, many VRF-like features are found across the northern hemisphere which we reference in Table 1 and throughout the discussion section. Many of these features’ origins are debated (and there is an ongoing topic on differentiating glacial and periglacial ice and landforms in the permafrost and glacial communities) and we will be sure to make the ongoing debate/discussion clearer.
Regarding your comment on Line 330, we can certainly elaborate on the discussion on the glacial history and presence/absence of buried glacial ice in the area and provide additional references.
Correct, we did not observe grain sorting. However, we did not do a grain size analysis to confirm this at this location (we did a grain size analysis on Devon Island VRFs and did not observe grain sorting there either, described in Hibbard et al., 2021). We continue our study with the assumption that grain sorting is not present across the entire deposit.
We will carefully review the references given in Section 5.2 (Glacial Origins) and ensure that each formation hypothesis is correctly associated with its respective reference.
We appreciate your time and effort in reviewing our work and look forward to the possibility of providing revisions based on your feedback. Thank you!
Citation: https://doi.org/10.5194/egusphere-2024-227-AC4
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AC4: 'Reply on RC3', Shannon Hibbard, 11 Apr 2024
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EC1: 'Comment on egusphere-2024-227', Chris R. Stokes, 26 Mar 2024
Firstly, I'd like to thank both reviewers for their comments on this manuscript. It is clear that the formation of these features is somewhat enigmatic but I feel that the manuscript has clear potential to advance our understanding and so I have closed the discussion and would like to encourage the authors to provide a detailed response to the reviewer comments, along the lines they have suggested in the public discussion. I would also add that whilst I consider it important to provide a more rigorous treatment of competing hypotheses, it is not necessary that the authors are completely impartial and that it might still be appropriate to favour a specific hypothesis if it motivates future work on these features. I'll leave that for them to decide, of course.
Chris Stokes
Citation: https://doi.org/10.5194/egusphere-2024-227-EC1
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