the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Standardized field methods for fracture-focused surface processes research
- 1Department of Geography & Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223, USA
- 2New Mexico Highlands University, Las Vegas, NM, USA
- 3Department of Geology, University of the South, Sewanee, TN 37383, USA
- 4Department of Geological and Environmental Sciences, Appalachian State University, Boone, NC, 28608, USA
- 5Department of Mechanical Engineering and Engineering Science, University of North Carolina at Charlotte, Charlotte, NC 28223, USA
- 6Department of Earth and Environmental Sciences, New Mexico Institute of Mining and Technology, Socorro, NM, 87801, USA
- 7Geological Survey of Israel, Jerusalem 9692100, Israel
- 1Department of Geography & Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223, USA
- 2New Mexico Highlands University, Las Vegas, NM, USA
- 3Department of Geology, University of the South, Sewanee, TN 37383, USA
- 4Department of Geological and Environmental Sciences, Appalachian State University, Boone, NC, 28608, USA
- 5Department of Mechanical Engineering and Engineering Science, University of North Carolina at Charlotte, Charlotte, NC 28223, USA
- 6Department of Earth and Environmental Sciences, New Mexico Institute of Mining and Technology, Socorro, NM, 87801, USA
- 7Geological Survey of Israel, Jerusalem 9692100, Israel
Abstract. Rock fracturing comprises a key component of a broad array of Earth surface processes due to its direct control on rock strength as well as rock porosity and permeability. However, to date, there has been no standardization for the quantification of rock fractures in surface processes research. In this work, we make the case for standardization within fracture-focused research and review prior work to identify various key datasets and methodologies. We then present a suite of standardized methods that we propose as ‘baseline’ for fracture-based research in surfaces processes studies. These methods have been shown in preexisting work from structural geology, fracture mechanics, and surface processes disciplines to comprise best practices for the characterization for cracks, clasts, and outcrops. These practical, accessible and detailed methods can readily be employed across all fracture-focused weathering and geomorphology applications. The wide adoption of a baseline of data, all collected using the same methods, will enable comparison and compilation of data among studies globally, and ultimately will lead to a better understanding of the links and feedbacks between rock fracture and landscape evolution.
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Martha Cary Eppes et al.
Status: open (until 04 Mar 2023)
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CC1: 'Comment on esurf-2022-61', Stephen Laubach, 12 Dec 2022
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A compilation and review of fracture analysis field methods for surface processes research ought to be a valuable contribution and within the scope of this journal.
I enjoyed this MS and I think it’s a valuable contribution.
The paper is well written and clearly illustrated.
There are several places in the text, noted below, where clarifications are needed. My comments are in the attached pdf
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AC2: 'Reply on CC1', Martha-Cary Eppes, 27 Jan 2023
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My co-authors and I have reviewed Dr. Laubach's thorough and helpful comments. We are very grateful for this input and look forward to implementing these changes in the manuscript.
The only suggestion of his for which we disagree (albeit not entirely) is the comment regarding the use of the terms 'crack' and 'fracture'. (His comment is copied below for ease of reading this reply).
Though it is suggested that such a distinction has been made in the literature, we can find no consistent use or definition, even in the Anders et al., 2014 paper suggested. In fact, in this paper - there is common interchange of the two terms:Â
"4.3. Microfractures and fault zones
Faults (shear cracks) are inherently macroscale features. Faults formed by the coalescence of Mode I microcracks (Scholz, 1968b, Lockner et al., 1991) and propagate via a cloud of microfractures formed in the stress concentration at the fault tip; when crack density reaches a critical value, this cloud of microfractures breaks the rock down into a cataclasite that allows shear displacement to occur (Cowie and Scholz, 1992)."The AGI Glossary of Geology also seems to interchange the terms, but simultaneously imply a difference: "fracture: (a) A general term for any surface within a material across which there is no cohesion, e.g. a crack. Fracture includes cracks, joints, and faults. (b) A crack in a rock where the movement of rock separated by the crack is normal to the surface." or "Â"crack [struc geol] A parting with crack-normal motion. Cf: joint [struc geol]. "ÂWe feel that to suggest that there is some size cut-off between when a crack becomes a fracture or vice-versa, or that by bringing a rock from the field to the lab could be interpreted as arbitrary and confusing. From a process standpoint, in the field of geomorphology, both small and large cracks/fractures contribute to the rock properties of interest, namely hydrology and strength.ÂÂAlso, to distinguish a 'crack' measured in the laboratory from a 'fracture' measured in the field, is to in some way discount the lab measurement as relevant to the field. I am sure that is not desirable by any of us.ÂWe acknowledge a clear distinction between microcrack/microfracture and crack/fracture being what is visible with the human eye. In this field methods paper, however, we explicitly ignore all microcracks/microfractures.ÂÂWe further acknowledge that despite there being no clear distinction in the literature, many geoscientists appear to have some distinction in their minds between the two terms fracture and crack.ÂÂWe further acknowledge that the word 'crack' has various perhaps negative connotations in popular culture.ÂÂThus, in order to be most clear and transparent our plan to address this comment is to 1) clearly define what we mean by the term 2) become consistent in our language in the manuscript, and 3) explicitly explain our decision making-process in the above why we have done so, laying out the argument above about no distinction really that we can find.ÂÂIt has sparked very interesting conversations with geomorphologists, rock physicists and structural geology colleagues!ÂÂMany thanks again, MCE and co-authorsÂComment on esurf-2022-61', from his attachment Stephen Laubach, 12 Dec 2022:Â
"On the use of ‘crack’ and ‘fracture’ interchangeably. Although this usage is widespread it has the potential to cause confusion, particularly where these may be language barriers. The text jumps back and from between ‘fracture’ and ‘crack’ and I found this distracting. In brittle structural geology a case has been made for restricting ‘crack’ to experimental and theoretical applications, and ‘fracture’ for features observed in the field. I believe this convention is stated in Anders et al. 2014, Microfractures: a review, J. Struct. Geol.) Maybe field-monitored examples you have described on fracture propagation in outcrops or clasts would fall into the category of ‘cracks’ by this convention. My advice is to make a distinction between these two terms along these lines and revise the MS accordingly. Even if the distinction has not been made in the past in this field, it would be useful to do so now "
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CC2: 'Reply on AC2 fracture versus crack', Stephen Laubach, 27 Jan 2023
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On the terminology or ‘fracture’ versus ‘crack’, I’m not sure that there really is any disagreement here. I do not think that such an arid topic as terminology is in any case worth disagreeing about. The distinction in Anders et al. was more a recognition that usage of these terms does vary within disciplines, and consequently different parts of Anders et al primarily use ‘fracture’ (for observational studies) or ‘crack’ (in theoretical or lab contexts). The crack usage cited above from Anders et al. is in the latter category (cites experimental studies). In writing Anders et al, we did try to consistently use the terms with those distinctions in mind. In making the original comment I did not mean to imply a size cut off, or say that only one term should be used, or to slight field observations (I’m primarily a field geologist). But the terminology in use to describe fractures can be confusing, and notwithstanding the frequently unhelpful definitions in the AGI glossary, it can aid comprehension to define terms and keep usage as consistent and simple as possible. Based on MCE and co-author’s comment, it seems we agree.
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CC2: 'Reply on AC2 fracture versus crack', Stephen Laubach, 27 Jan 2023
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AC2: 'Reply on CC1', Martha-Cary Eppes, 27 Jan 2023
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AC1: 'Comment on esurf-2022-61', Martha-Cary Eppes, 14 Dec 2022
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Dr. Laubach's detailed suggestions and comments are exactly what we were hoping to recieve in this public forum. Addressing these comments will strengthen the manuscript and its utility considerably.Â
Currently, however, a majority of us are at AGU, and/or have school aged children and family that require our undivided attention over the holidays.
We will provide a more detailed response to Dr. Laubach's suggestions - and any other comments received through the end of the year - starting no later than Jan 5, earlier if we are able. We thank you for your understanding and patience with this choice.Â
Eppes et al.,Â
Martha Cary Eppes et al.
Martha Cary Eppes et al.
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