New experiments to probe the role of fractures in bedrock on river erosion rate and processes

Fournereau, Marion; Guerit, Laure; Steer, Philippe; Kermarrec, Jean-Jacques; Leroy, Paul; Lanos, Christophe; Hivert, Hélène; Astrié, Claire; Lague, Dimitri

doi:10.5194/egusphere-2025-1541

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https://doi.org/10.5194/egusphere-2025-1541

Preprints

24 Apr 2025

| 24 Apr 2025

New experiments to probe the role of fractures in bedrock on river erosion rate and processes

Marion Fournereau, Laure Guerit, Philippe Steer, Jean-Jacques Kermarrec, Paul Leroy, Christophe Lanos, Hélène Hivert, Claire Astrié, and Dimitri Lague

Abstract. River erosion via abrasion and plucking is a fundamental process that impacts, among others, landscape evolution, sediment transport, and hillslope dynamics. It results from complex interactions between climate, tectonics, topography and the erodibility of bedrock. Despite its significant role, bedrock erodibility remains poorly understood as it is thought to aggregate several parameters. Among these, fractures in bedrock are assumed to exert a strong control over erosion and thus, on landscape evolution. However, there is no systematic study of the impact of fracture geometry and density on bedrock river erosion.

Due to the complex interactions at play, we investigate this question via an experimental approach. We develop an erosion mill apparatus designed to erode a fractured concrete disk with a diameter of 17 cm. We simulate fractures by embedding a 3D-printed plastic mesh in the concrete, using BVOH—a plastic that softens in cold water—creating mechanical heterogeneities with a controlled pattern. We explore 10 different geometries and run 4 additional experiments without fractures for control. We record the topographic evolution every 2 minutes by photogrammetry and derive erosion maps by measuring elevation changes between successive scans. To our knowledge, this is the first study of its kind. Our results show that while fractures influence the relative contributions of abrasion and plucking, no clear relationship emerges between average erosion rates and fracture density or dip angle. However, we observe that the occurrence of plucking is related to the density and the dip angles of fractures, and is favoured by intermediate density that scales with the size of the impactors, and intermediate dip angle that ease the removal of blocks. We suggest that the main impact of plucking is to change the location of erosion, increasing the eroded surface area rather than accelerating overall erosion rates. However, but as plucking accounts for at most one-third of the total erosion, its occurrence does not significantly affect average erosion rates. These findings emphasize the role of fractures on erosion mode and location rather than erosion rates, and highlight the need to further explore the impact of fractures on riverbed erosion.

Received: 31 Mar 2025 – Discussion started: 24 Apr 2025

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Journal article(s) based on this preprint

16 Mar 2026

New experiments to probe the role of fractures in bedrock on river erosion rate and processes

Marion Fournereau, Laure Guerit, Philippe Steer, Jean-Jacques Kermarrec, Paul Leroy, Christophe Lanos, Hélène Hivert, Claire Astrié, and Dimitri Lague

Earth Surf. Dynam., 14, 191–210, https://doi.org/10.5194/esurf-14-191-2026,https://doi.org/10.5194/esurf-14-191-2026, 2026

Short summary

Marion Fournereau, Laure Guerit, Philippe Steer, Jean-Jacques Kermarrec, Paul Leroy, Christophe Lanos, Hélène Hivert, Claire Astrié, and Dimitri Lague

Interactive discussion

Status: closed

RC1: 'Comment on egusphere-2025-1541', Alexander Neely, 01 May 2025

I attach suggestions in the pdf.
Good luck with the rest of the submission and review!
Don't hesitate to contact if you have questions.

Citation: https://doi.org/10.5194/egusphere-2025-1541-RC1
RC2: 'Comment on egusphere-2025-1541', Anonymous Referee #2, 10 Jun 2025

See the attached commentary on this paper.

Citation: https://doi.org/10.5194/egusphere-2025-1541-RC2
AC1: 'Comment on egusphere-2025-1541', Marion Fournereau, 18 Jul 2025

Please find attached the document containing our detailed responses to the comments from both reviewers.

Citation: https://doi.org/10.5194/egusphere-2025-1541-AC1

Interactive discussion

Status: closed

RC1: 'Comment on egusphere-2025-1541', Alexander Neely, 01 May 2025

I attach suggestions in the pdf.
Good luck with the rest of the submission and review!
Don't hesitate to contact if you have questions.

Citation: https://doi.org/10.5194/egusphere-2025-1541-RC1
RC2: 'Comment on egusphere-2025-1541', Anonymous Referee #2, 10 Jun 2025

See the attached commentary on this paper.

Citation: https://doi.org/10.5194/egusphere-2025-1541-RC2
AC1: 'Comment on egusphere-2025-1541', Marion Fournereau, 18 Jul 2025

Please find attached the document containing our detailed responses to the comments from both reviewers.

Citation: https://doi.org/10.5194/egusphere-2025-1541-AC1

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by Marion Fournereau on behalf of the Authors (21 Jul 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (31 Jul 2025) by Anastasia Piliouras

RR by Alexander Neely (18 Aug 2025)

RR by Anonymous Referee #3 (16 Sep 2025)

Suggestions for revision or reasons for rejection

I found this paper to contain intriguing experimental results, attractive figures and thoughtful consideration of experimental design confounding variables. The experiments are an important contribution to the field of experimental approaches to bedrock erosion, and the authors were thorough in explaining the rationale of experimental design and the technical aspects of the experimental setup, and they provide a meticulous accounting of the results. However, the manuscript must correct two major issues before it can be considered suitable for publication.
First, the manuscript feels long and wordy which limits reader comprehension. At the macro level, this stems from disorganization in the results and discussion, as well as an introduction that describes at length systems that are not relevant to the experiments at hand. These three sections require more focus to tighten them to keep the reader’s mind from wandering – at times there is commentary in Results and new methods introduced in the Discussion. The results section should succinctly describe what was observed, and then the Discussion section should contextualize those findings within previous experimental results and field observations. My advice to address this is to revise the manuscript such that every paragraph begins with a topic sentence stating either a fact or a knowledge gap which will then frame the remainder of the paragraph text. The Introduction especially feels like paragraphs begin and end at random. Ideally, a reader should be able to skim a manuscript by reading the first sentence of each paragraph and get the gist of the motivation for the study, its results, and implications. Topic sentences in the Results should state a result.
At the micro level, many sentences in the Results contain extraneous phrases (e.g. “we now explore…” “Another way to document these patterns is…”, Lines 311-313) that should be removed to sharpen the focus on the results of the study. I provide some line-by-line advice for both macro and micro fixes.
Second, the paper fails to convincingly connect their experiments to the “real world.” Part of this stems from spending too many words diving into the details of the experimental results without justifying to the reader early or often enough that these experiments are close enough to how real rivers behave that it is worth peering so closely and deeply into these experimental results (see above). But there are too few words in the Discussion that connect specific results to observations about plucking and abrasion observed in the field – it seems like the authors take for granted that the reader will believe that their blocks and spiraling water behave enough like real rocks and rivers to implicitly connect their results to natural phenomena, but if one is not convinced, large swaths of the Discussion are challenging to accept. I point out these instances in line-by-line advice below.
Line 40 and throughout: I also love Anderson and Anderson, but is there a review paper or similar that might be a better citation than a textbook throughout this manuscript?
Line 40 and throughout: “well-known” does not need a hyphen. There are numerous instances where punctuation and phrasing are a little off (e.g. word choice of “maximum” in Line 44, comma after “turn” in Line 61). Checking with an English language editor will clear some of these stumbles.
Line 65 “…thereby promoting the detachment and mobilization of blocks by plucking.” Does this need a citation?
Paragraph starting with Line 77: It’s not clear to me that hillslope fracturing is relevant to this study. Would be clarified with a topic sentence that perhaps uses quantifying hillslope fracture density etc. as an example of attempts in the past to measure what this study can experimentally control, but I’m not sure it’s an appropriate direction for the introduction.
Line 87-88: Can you elaborate/be more specific about this timescale?
Line 107-108: An odd place for the first definition of plucking in the introduction; move earlier.
Line 111-112: This is the first mention of the role of fracture network geometry specifically (not just density). This topic was not laid out in the Introduction despite it being the focus of the experiments. Distill the existing Introduction into half its current length and then add more background on fracture network geometry to reflect the remaining focus of the paper.
Lines 125-130: The geometry description would benefit from also having a cartoon/diagram. Right now the concrete disk as sketched lacks detail to show the different geometries you’ve set up.
Line 150: “…but it can also be different.” Clarify/elaborate?
Line 152: Is this the proper citation format for this resource?
Line 177: “parts of the disk can be removed” by people? Sediment? Can be? Did occur? Rephrase for clarity here.
Line 195: watch phrasing “10 times this protocol”
Line 204-205: what does this sentence mean? Data? Uncertainty? Clarify.
Figure 3: I don’t like the bold lines being connected to disks, it is more intuitive that the bold lines represent some mean (which I think you should show for each fracture density). You can just annotate specific data lines with text to connect back to Figure 2. Instead I would use bold lines as averages.
Figure 4b and c: it feels like maybe the 125 m-1 fracture density sample is a bit of an outlier, as is the particularly high erosion rate sample with 150 m-1 fracture density, but some interpretation is made of these patterns. I would recommend being more cautious interpreting any trends with fracture density (e.g. interpretation that erosion has a max at 150 m-1 when it really might just increase with increasing fracture density if that one point is an outlier).
Line 299: Cite “period of weakening” precedence?
Lines 311-313: example of phrase to be cut to streamline.
Line 326: Well, it’s not monotonic, but more of a step function, and really not much of a trend at all if the 160 degree sum sample is an outlier.
Line 354: Rephrase “we have no clue”
Line 363-364: Check phrasing/word choice here.
Lines 383-384: Cut
Paragraph beginning with 385: this paragraph and the one following it mostly feels like Results. You are just making slightly different plots of your Results. The same goes for Section 4.3, and honestly both of these subheadings would make appropriate Results subheadings, and your Results subheadings would be better suited for either topic sentences in the Results or as topic sentences in the Discussion.
Lines 415-416: How similar is the impact and fracture scale to real rivers? If this were in the Results it would be early for interpretations, but since we’re in the Discussion, please contextualize your results with field observations so that the reader can know if these results are relevant to the real world.
Lines 425-455: Just re-emphasizing that this is all Results, or 80% of it is results that should then be referenced in the Discussion when providing the interpretations.
Lines 469-473: This sentence needs more support from the results. How do we know? Show me or refer to specific results that support your interpretation.
Line 488: Once again, please refer to specific results/figures that support your interpretation.
Lines 518-521: This sentence perplexed me; your experimental “river” does not adjust its width or slope to maintain any form. Instead I think your experiment showed that plucking versus not plucking does not ultimately affect erosional efficiency, so I don’t know how that result can connect to rivers adjusting to account for plucking – your experiments seem to imply that real rivers shouldn’t need to account for plucking at all because plucking doesn’t change erosional efficiency. Am I misunderstanding something?

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ED: Reconsider after major revisions (23 Sep 2025) by Anastasia Piliouras

I have reviewed the revised manuscript alongside a second round of reviews from Al Neely (also reviewed the initial submission) and an anonymous reviewer #3. Based on these reviews and my own reading, it does not seem that the comments from the initial reviews were sufficiently addressed. Reviewer #3 also raised some useful points about the clarity of writing. I suggest that the authors revise their manuscript and resubmit it for additional consideration. In the revision, please do not consolidate the reviewer comments. Please address each individual comment separately so that we can more easily keep track of specific comments and responses.

Here I also provide a summary of the most important points that I think the authors need to address in a revision.

In revising your manuscript, please carefully consider the following:
1. Dr. Neely has asked for some important clarifications and information about the experimental setup and conditions. Please address these concerns and provide the requested information either in the main manuscript or the supplement, as possible.

2. All three reviewers (including the anonymous reviewer from the initial submission) have raised concerns about the applicability of these results to natural systems. I appreciate that the revised manuscript includes new subsections on application to natural systems and also other plucking studies, but those sections read more like a literature review than a discussion that integrates or synthesizes the new findings with the literature. Please follow the reviewer guidelines to revise these sections and consider how and if you can relate these findings to natural systems throughout the manuscript to convince the reader of the relevance.

3. Reviewer #3 has provided additional suggestions on how to streamline the manuscript to make it more concise and to better frame the story for the reader. I recommend following the suggestions for the broad restructuring (e.g., cutting some intro/background, revising what is included to make it more relevant) and ensuring each paragraph is readable on its own. However, I will leave it to the authors to determine whether individual phrases should be revised or cut for brevity, as I think this is a matter of personal writing style and is not up to the reviewer.

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AR by Marion Fournereau on behalf of the Authors (14 Nov 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (24 Nov 2025) by Anastasia Piliouras

RR by Alexander Neely (05 Dec 2025)

RR by Anonymous Referee #3 (22 Dec 2025)

Suggestions for revision or reasons for rejection

This version of the manuscript is much improved from the pervious version, although I still find the broad readability of the manuscript to be challenging. Many paragraphs now begin with a helpful topic sentence, but other sections (e.g. 4.2 and 4.3) are still challenging to parse as a more “casual” geomorphological reader (one who is not looking to conduct experiments or is keenly interested in the nuances of rock fracture). At present, the manuscript is a thorough and thoughtful consideration of the experimental design and results, but the Introduction and Discussion still fail to help draw in a broader audience for this work.
I understand it may be personal preference when crafting an Introduction, but one downside to having one big “Introduction” section rather than breaking out the knowledge gap and hypothesis tests from a “Background” section is that readers must work through quite a bit of background before getting to they “why” of this particular paper. I know in my previous review I highlighted that information in the introduction was often not relevant to the science question(s) being addressed in this work. I think this version has done a better job of presenting mostly relevant background info here, but I would still argue for a more focused statement of the knowledge gap and hypotheses within the first two paragraphs. At present the “why/how” of the paper is spread sporadically through the first 120 lines of the paper. The main knowledge gaps or “whys” of the paper are stated in lines 98-101, followed by a nice statement of “how.” I recommend letting those two sections shine earlier in the Introduction.
I also think the Discussion section would benefit from a synthesis figure, which might be a cartoon or annotated, selected experimental results to help walk the reader through the thoughtful discussion and textural synthesis in Section 4. (Table 1 does not accomplish this). It would be wonderful if the authors can tie any of the specific mechanisms to which they refer in the Discussion to field photos in this figure. Right now it is challenging to parse the results figures for any real-world application.
As a microcosm of this problem, the remarkable erosion for the 157° fracture dip sum experiment is now a little better explained in the text, but the text as is fails to explain why this outcome is significant beyond its quirkiness. Right now, (1) it is not immediately apparent what “sum of fracture dip” means when parsing the figures (here is where a cartoon or schematic would help), and (2) the authors do not connect this “optimal” fracture dip configuration in their experiment to any real-world scenario (are there fracture “sweet spots” in nature? What might those look like? Can field geomorphologists seek these configurations out?).
Again, I will suggest the authors consider some recent relevant experimental work when discussing dip angle: https://pubs.geoscienceworld.org/gsa/geology/article/53/9/780/659310/Dip-angle-controls-on-plucking-susceptibility-and

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ED: Reconsider after major revisions (08 Jan 2026) by Anastasia Piliouras

AR by Marion Fournereau on behalf of the Authors (04 Feb 2026) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (21 Feb 2026) by Anastasia Piliouras

I have read the most recent reviews, author responses, and manuscript revisions. I want to thank the authors and reviewers for their dedication to improving this manuscript. I find the latest version to be significantly improved over earlier iterations, and the authors have done a nice job addressing reviewer concerns. I think the addition of Figure 8 is especially helpful as a summary of your findings. I am recommending the manuscript for publication, but ask for the following technical corrections:

Retitle section 4.1 to "Benefits and limitations of the study design" or something similar, as the current subheading suggests this section is only about the material, while you actually discuss the experimental setup as well.

Remove the sentence you just added detailing experimental limitations in the abstract (L33-35 in tracked changes version). I understand this was recommended by a reviewer, but I do not think it is appropriate or needed here and it detracts from the importance of your experiments.

Remove "in our experiments" from the section 4.3 subheading, as this is not needed

Please give a close and thorough read to check for grammar throughout. There are many instances of incorrect grammar, some of which have been a source of confusion for reviewers. I am listing some examples from page 3 (line #s refer to tracked changes version), but please check throughout the entire manuscript.
L100: "Macroabrasion is a recent terminology" replace "terminology" with "term," as "terminology" is uncountable, or rephrase.
L116: "also defined as a similar two-step process" not "2 steps"
L119: remove comma after "discontinuities"
L126-127: I'm not entirely sure how to fix this one actually, depending on your intent, possibly "Intuition derived from field-based morphological constraints has been used to inform the nature and relative dominance of various processes." This sentence as written suggests that intuition informs the relative dominance, which I suspect is not correct. Perhaps just "Field-based morphological constraints have been used to inform..." Revise as appropriate.

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ED: Publish subject to technical corrections (26 Feb 2026) by Andreas Lang (Editor)

AR by Marion Fournereau on behalf of the Authors (05 Mar 2026) Author's response Manuscript

Journal article(s) based on this preprint

16 Mar 2026

New experiments to probe the role of fractures in bedrock on river erosion rate and processes

Marion Fournereau, Laure Guerit, Philippe Steer, Jean-Jacques Kermarrec, Paul Leroy, Christophe Lanos, Hélène Hivert, Claire Astrié, and Dimitri Lague

Earth Surf. Dynam., 14, 191–210, https://doi.org/10.5194/esurf-14-191-2026,https://doi.org/10.5194/esurf-14-191-2026, 2026

Short summary

Marion Fournereau, Laure Guerit, Philippe Steer, Jean-Jacques Kermarrec, Paul Leroy, Christophe Lanos, Hélène Hivert, Claire Astrié, and Dimitri Lague

Supplement

https://doi.org/10.5194/egusphere-2025-1541-supplement

Marion Fournereau, Laure Guerit, Philippe Steer, Jean-Jacques Kermarrec, Paul Leroy, Christophe Lanos, Hélène Hivert, Claire Astrié, and Dimitri Lague

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Apr 2025	68	15	2	85
May 2025	65	15	4	84
Jun 2025	45	12	3	60
Jul 2025	50	12	6	68
Aug 2025	81	10	3	94
Sep 2025	360	8	2	370
Oct 2025	19	5	1	25
Nov 2025	19	15	2	36
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Jan 2026	34	17	4	55
Feb 2026	28	13	2	43
Mar 2026	52	26	0	78

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Short summary

River bedrock erosion can occur by polishing and by the removal of entire blocks. We observe that when there is no to little fractures most erosion occurs by polishing whereas with more fractures, blocks can be removed at once leading to different patterns of erosion and riverbed morphology. Fractures affect barely mean erosion rate but change the location and occurrence of block removal. Our results highlight how river bedrock properties influence erosion processes and thus landscape evolution.


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