Discrete Element Modelling of Pit Crater Formation on Mars
Round 1
Reviewer 1 Report
Dear Editor,
This is an excellently simple paper that presents numerical models of pit crater formation. I find no flaws in the scientific content or the presentation. I have made a few suggestions on the attached pdf that I think would improve the balance and clarity of the paper in places.
If you or the author require any clarification on my comments, please do not hesitate to contact me.
Kind regards,
Reviewer
Comments for author File: 
Comments.pdf
Author Response
I thank Reviewer 1 for his/her kind comments. I will document below the changes I have made in response to these comments. I will also document some more general changes I have made in the manuscript. I don't really use markup so I have highlighted all changes in red colour throughout.
Specific points: (in order)
ABSTRACT
I have used "surface expression" rather than map-view picture
Sentence line 19 moved
all struckthrough text removed
"scoop" removed throughout the manuscript
"in the limit" changed to In the extreme case
In general, Abstract also shortened and results discussed up-front.
INTRODUCTION
Long paragraph, spilt and also tightened.
Pit crater chains better explained
References added and also the few example of 3D data referred to
Little changes "surface expression" "an" rather than the etc all done
The scope of possible pit crater origins now expanded - also as a result of reviewer 2 comments.
Figure 1 - slopes added as suggested
METHODOLOGY
I have commented on the issue that the codes are "in-house" and not (yet) open-source and have been used in collaborations
MODEL PARAMETERS....
Void placement addressed - i.e. it is to avoid lateral boundary or wall effects
Regolith thickness of 100 m also addressed - it's a good minimum and later model shows no difference for a 1000 m thickness
Void widths and heights clarified
Density is a good compromise between fine soil and intact rock
Material parameters now linked to those perhaps regolith found on Mars
"Rates" - in frictional-cohesive materials this is not really an issue
Serial vs parallel etc better explained
Other experiments that were run are not available as supplementary material in this paper, partly due to their format.
Slope angles annotated
DISCUSSION AND CONCLUSIONS
As mentioned before "scoop" has been removed throughout
The Smart et al paper did not provide nearly enough information to make a comparison, no density, some parameters are micro etc etc
Reviewer 2 Report
Review of:
“Discrete Element Modelling of Pit Crater Formation on Mars”
by Stuart Hardy (Geosciences 2021).
General comments:
The purpose of the work is interesting and in my opinion this paper has to be introduced in the scientific community. The paper needs to improve the geological setting and contest related to the pit formation on Mars, and supported by more references. In my opinion it deserves to be published after minor revision.
Specific comments:
The abstract is too long; an abstract have to give a glimpe of the paper,informing the reader about the study,methodology and results,in summary. In my opinion it has to be rewritten. Too many part are the same that can be found in the introduction.
Pag. 1 line 10-13: Delete this part. It is written with the same words in the introduction below. Rewrite it shortly.
Pag 1 line 14-15: rewrite. The same of the comment above.
Pag.1 line 34-35: you have to give to the reader some results.
pag 1 line 43/44: this sentence can be used for “fresh”, from the erosional point of view, impact craters, because erosive processes can hide and/or remove both elevated rim and ejcta deposits in old impact craters. Thus, i suggest to explain that this is working for “young craters from the erosional point of view”and explain also that older craters, where erosion can hide rims and ejecta, show (anyway) a different morphology (see: Forsberg-Taylor et al. 2004 Journal of Geophysical Research 109, E05002 ; Watters et al., 2015 Journal of Geophysical Research Planets, 119, E004630).
Pag.2 line 54: here are describeb shortly only two hypotheses on the origin of the pits.
In my opinion you have to explain in detail also other possible origin of these pits, such as karstic and /or thermokarstic (for example), instead of writing “amongst other hypotheses”.
What are other possible origins? please explain to the readers and add references.
For example:
- collapse of sinkholes due to karstification processes in evaporite rocks that can develop expecially along fractures (line of weakness) like it happens on the Earth. The collapse can happen through dissolution due to water percolation if you have soluble rocks under the surface. It can be found in many evaporite deposits on Mars like in Sinus Meridiani, Valles Marineris ILDs, within craters in the equatorial area, etc. (see: Baioni & Tramontana 2015 Geomorphology, 245, 15-22; Baioni & Sgavetti 2013 Planetary and Space Science, 75, 173-181; Baioni & Tramontana 2016 Planetary and Space Science, 132, 57-65; ).
- collapse due to thermokarst processes related to sublimation and/or melt of ground ice, such as in Utopia Planitia (see Soare et al.2012 Planetary and Space Science 60, 131-139; Dundas et al., 2015 Icarus, 262, 154-169).
Pag.2 line 53-54: please add references. (I suggest; Borraccini et al., 2005 Journal Of Geophysical Research, Vol. 110, E06006; Sauro et al., 2020 Earth-Science Reviews 209, 103288; Cushing 2012 Journal of Cave and Karst Studies, Vol. 74,33-47).
Pag.2 line 84: please consider that it can also happen when the material is partially soluble (if we have evaporites) and the amount of material observed (maybe after a long period of erosion) that fill the pit is not related to the thickness or regolyth only.
pag.8 line 303-304: or the collapse material has been partially or totally eroded? Like it can happen if you have dissolution of evaporitic (i.e, soluble) material.
I attached the PDF file with my comments.
Comments for author File: Comments.pdf
Author Response
I thank Reviewer 2 for his/her kind comments. I will document below the changes I have made in response to these comments. I will also document some more general changes I have made in the manuscript. I don't really use markup so I have highlighted all changes in red colour throughout.
The abstract is too long; an abstract have to give a glimpe of the paper,informing the reader about the study,methodology and results,in summary. In my opinion it has to be rewritten. Too many part are the same that can be found in the introduction.
The abstract has been very much rewritten taking into account both Reviewer 2 and 1's suggestions.
Pag. 1 line 10-13: Delete this part. It is written with the same words in the introduction below. Rewrite it shortly.
Done.
Pag 1 line 14-15: rewrite. The same of the comment above.
Done.
Pag.1 line 34-35: you have to give to the reader some results.
The end of the abstract now contains the key results/conclusions of the study
pag 1 line 43/44: this sentence can be used for “fresh”, from the erosional point of view, impact craters, because erosive processes can hide and/or remove both elevated rim and ejcta deposits in old impact craters. Thus, i suggest to explain that this is working for “young craters from the erosional point of view”and explain also that older craters, where erosion can hide rims and ejecta, show (anyway) a different morphology (see: Forsberg-Taylor et al. 2004 Journal of Geophysical Research 109, E05002 ; Watters et al., 2015 Journal of Geophysical Research Planets, 119, E004630).
Done - clarified that the comparison is valid for fresh, young craters etc
Pag.2 line 54: here are describeb shortly only two hypotheses on the origin of the pits.
In my opinion you have to explain in detail also other possible origin of these pits, such as karstic and /or thermokarstic (for example), instead of writing “amongst other hypotheses”.
What are other possible origins? please explain to the readers and add references.
This part has been much expanded to include a spectrum of possible origins
For example:
collapse of sinkholes due to karstification processes in evaporite rocks that can develop expecially along fractures (line of weakness) like it happens on the Earth. The collapse can happen through dissolution due to water percolation if you have soluble rocks under the surface. It can be found in many evaporite deposits on Mars like in Sinus Meridiani, Valles Marineris ILDs, within craters in the equatorial area, etc. (see: Baioni & Tramontana 2015 Geomorphology, 245, 15-22; Baioni & Sgavetti 2013 Planetary and Space Science, 75, 173-181; Baioni & Tramontana 2016 Planetary and Space Science, 132, 57-65; ).
collapse due to thermokarst processes related to sublimation and/or melt of ground ice, such as in Utopia Planitia (see Soare et al.2012 Planetary and Space Science 60, 131-139; Dundas et al., 2015 Icarus, 262, 154-169).
Pag.2 line 53-54: please add references. (I suggest; Borraccini et al., 2005 Journal Of Geophysical Research, Vol. 110, E06006; Sauro et al., 2020 Earth-Science Reviews 209, 103288; Cushing 2012 Journal of Cave and Karst Studies, Vol. 74,33-47).
Pag.2 line 84: please consider that it can also happen when the material is partially soluble (if we have evaporites) and the amount of material observed (maybe after a long period of erosion) that fill the pit is not related to the thickness or regolyth only.
done.
pag.8 line 303-304: or the collapse material has been partially or totally eroded? Like it can happen if you have dissolution of evaporitic (i.e, soluble) material.
done
