Annual Coastal Boulder Mobility Detected in 2017–2021 Remote Sensing Imagery and Its Relation to Marine Storms (Gulf of Taranto, Mediterranean Sea)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is a revision of an earlier work focused on identifying and interpreting boulder displacements on the sea coast. With the objectives of this study and the main results clearly outlined, the paper reads better, and a reader is less likely to get lost among numerous boulders. I recommend the paper for publication, with the following comments/suggestions:

  1. Maybe, don’t personify the computer workstation? Examples of the latter: "...has been visually examined by a computer workstation (line 104)", "... geometrical features that can be determined by the computer workstation are the initial (xi) and final distances (xf) of the boulders from the coastline, and the related Transport Distance (TD). … the TD … was measured using the ruler tool." (line 141) I doubt that the computer workstation (rather than a human operating the workstation) was using the Google Earth ruler tool.   2. In the same excerpt: to be consistent with the rest of the article, (xi) and (xf) got to be the initial and final locations/positions, not the distances from the coastline.   3. Appendices usually provide very specific elaboration of methods employed, when including such elaborations in the main text would interrupt the logical flow of the article. However, Appendix A is a very generic talk about interpreting aerial imagery, with no specifics, such as how particular difficulties were overcome in this work, or any specific know-hows. I couldn’t understand from the paper or Appendix A to which degree the boulder detection was automated, rather than being the work of a human analyst (operating the computer workstation).  I’d suggest removing Appendix A.   4. Appendix E contains an interesting observation about very different effects of two storms with similar powers as measured by the Storm Power Index. Unfortunately, no insight on what might be the reason for that is offered. Then, the author lists Minimum Flow Velocities (V) required to set in motion the boulders (Table A12), but provides no info on how these velocities were computed, and why their values “appear consistent”. To be “consistent”, these velocities should be compared with the flow velocities of the respective storms, but I see no such comparison, nor any information on the actual flow velocities at all. I'd suggest removing this velocity stuff as speculative.   5. Typos. My notes from the first four pages, with the rest left to the author:  

return period have [been] calculated  (Line 67)

although also winds (line 80)

‘and the size described by’ (line 124) - should be either ‘[with] the size described by’ or ‘and the size [is] described by’

‘before being cover[ed] by lichen’ (line 165)

‘Surface karst forms, such as solution pans and pinnacles, has been used’ - have (plural) (line 166)

 

 

Comments on the Quality of English Language

Fluent English, but slightly negligent about gramma. Please proofread.

Author Response

Dear Reviewer,

thank you for time and effort to review the manuscript. The replies to your comments are below.

General comment) The paper is a revision of an earlier work focused on identifying and interpreting boulder displacements on the sea coast. With the objectives of this study and the main results clearly outlined, the paper reads better, and a reader is less likely to get lost among numerous boulders. I recommend the paper for publication, with the following comments/suggestions.

Reply: thank you again. I have considered all your comments/suggestions (see below).

Comment 1) Maybe, don’t personify the computer workstation? Examples of the latter: "...has been visually examined by a computer workstation (line 104)", "... geometrical features that can be determined by the computer workstation are the initial (xi) and final distances (xf) of the boulders from the coastline, and the related Transport Distance (TD). … the TD … was measured using the ruler tool." (line 141) I doubt that the computer workstation (rather than a human operating the workstation) was using the Google Earth ruler tool.

Reply: The sentences have been rephrased considering your comment.

Comment 2) In the same excerpt: to be consistent with the rest of the article, (xi) and (xf) got to be the initial and final locations/positions, not the distances from the coastline.

Reply: in this paper, (xi) and (xf) are defined as the initial and final distances from the coastline, respectively (see Tables A2, A4, A6, and A8). Each point is also identified by geographical coordinates (see Tables A3, A5, A7, and A9).

Comment 3) Appendices usually provide very specific elaboration of methods employed, when including such elaborations in the main text would interrupt the logical flow of the article. However, Appendix A is a very generic talk about interpreting aerial imagery, with no specifics, such as how particular difficulties were overcome in this work, or any specific know-hows. I couldn’t understand from the paper or Appendix A to which degree the boulder detection was automated, rather than being the work of a human analyst (operating the computer workstation). I’d suggest removing Appendix A.

Reply: Yes, you are right, Appendix A is a very generic talk about interpreting aerial imagery. As you suggested, I have removed it.

Comment 4) Appendix E contains an interesting observation about very different effects of two storms with similar powers as measured by the Storm Power Index. Unfortunately, no insight on what might be the reason for that is offered. Then, the author lists Minimum Flow Velocities (V) required to set in motion the boulders (Table A12), but provides no info on how these velocities were computed, and why their values “appear consistent”. To be “consistent”, these velocities should be compared with the flow velocities of the respective storms, but I see no such comparison, nor any information on the actual flow velocities at all. I'd suggest removing this velocity stuff as speculative.

Reply: Some insights into the reasons for the different effects of the two storms on the studied coast were discussed in Refs. [4] and [9]. Given your comment, references have been added in the text (see revised Appendix E, now Appendix D after removal of previous Appendix A). As mentioned in Section 4.2, the “next research target is to compute the wave characteristics approaching the nearshore… using the open-source SWAN (Simulating WAves Nearshore) code” (lines 491-493). We hope that through this planned study, this issue will be better understood. Regarding the minimum flow velocity computing, the equations of Refs. [1,71] have been used. This is explicit now (see emended caption of Table A12). Finally, the values reported in Table A12 are consistent (in terms of order of magnitude, as is now highlighted) with the ones of literature (line 875 of the final version).

Comment 5) Typos. My notes from the first four pages, with the rest left to the author:  

return period have [been] calculated (Line 67)

although also winds (line 80)

‘and the size described by’ (line 124) - should be either ‘[with] the size described by’ or ‘and the size [is] described by’

‘before being cover[ed] by lichen’ (line 165)

‘Surface karst forms, such as solution pans and pinnacles, has been used’ - have (plural) (line 166)

Reply: I have corrected the typos you reported and others I was able to find.

Comments on the Quality of English Language) Fluent English, but slightly negligent about gramma. Please proofread.

Reply: I have proofread to the best of my ability. I must sincerely thank you.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Author,

I’ve read your manuscript with great interest, attention, and pleasure. Too much is written in the geological and geomorphological literature about the movement of megaclasts by storms and tsunamis, but the factual evidence remains restricted. You provide an exciting example of megaclast displacement by severe storms, which stimulates thinking about the importance of this force on the geological scale. Moreover, you explain excellently how well-accessible and cheap instrument such as Google Earth engine can be employed in such studies. Well, the manuscript is informative and provides a really novel insight into the internationally-important scientific problem. It is based on a perfect project, the methodology and the outcomes of which are reported properly. The manuscript is written, organized, referenced, and illustrated optimally. Even the very critical examination of this work has permitted to find nothing to criticize. Nonetheless, some advice can help to make it a bit stronger (see below). Generally, this manuscript is well-suitable to “Geosciences”.

1)      Subsection 2.1: how boulders are detached from parent rocks there? By which force and how frequently?

2)      Line 123: why necessary cuboid? A boulder can be well-rounded!

3)      Line 462: were these waves tsunami?

4)      Section 4: how your really exciting findings are important to the understanding of the relative role of severe storms in megaclast displacement? How frequently do such storms happen? Would it be possible to compare the frequency of such storms to that of tsunamis?

5)      From the figures in the Appendix, I understand so that you have visited some displaced boulders. If so, have you recorded any physical destruction of these boulders together with displacement?

6)      Another question is whether the displacement of “your” bounders depended on their isolated or group position. Boulders occurring in groups may be more difficult to move because of their “cohesion”.

7)      Please, add a simple scale bar to all satellite images and photos available in your manuscript (both main text and appendix).

Generally, I like your work very much, and I wish you good luck with these studies!

Author Response

Dear Reviewer,

thank you for time and effort to review the manuscript. The replies to your comments are below.

General comment) I’ve read your manuscript with great interest, attention, and pleasure. Too much is written in the geological and geomorphological literature about the movement of megaclasts by storms and tsunamis, but the factual evidence remains restricted. You provide an exciting example of megaclast displacement by severe storms, which stimulates thinking about the importance of this force on the geological scale. Moreover, you explain excellently how well-accessible and cheap instrument such as Google Earth engine can be employed in such studies. Well, the manuscript is informative and provides a really novel insight into the internationally-important scientific problem. It is based on a perfect project, the methodology and the outcomes of which are reported properly. The manuscript is written, organized, referenced, and illustrated optimally. Even the very critical examination of this work has permitted to find nothing to criticize. Nonetheless, some advice can help to make it a bit stronger (see below). Generally, this manuscript is well-suitable to “Geosciences”.

Reply: thank you again for your appreciation.

Comment 1) Subsection 2.1: how boulders are detached from parent rocks there? By which force and how frequently?

Reply: As is reported in the text, the “coast is prone to boulder formation and displacement and, because of such characteristic, two selected sites … are periodically surveyed with direct observation since 2017” (lines 70-72). In Refs. [4,17] you can find some insights on your questions. There is still much research to be done.

Comment 2) Line 123: why necessary cuboid? A boulder can be well-rounded!

Reply: Yes, a boulder can be well-rounded. The pioneer hydrodynamics studies on boulder displacements regarded rectangular cuboid clasts (see e.g. [1,54,55,56,71]). This approach has been widely used in literature and is adequate also for our case study.

Comment 3) Line 462: were these waves tsunami?

Reply: These very small waves were induced by a western Mediterranean earthquake (for details see Ganas et al. 2020 (Ref. [59]).

Comment 4) Section 4: how your really exciting findings are important to the understanding of the relative role of severe storms in megaclast displacement? How frequently do such storms happen? Would it be possible to compare the frequency of such storms to that of tsunamis?

Reply: For an issue of this kind, it is necessary to have huge resources.

Comment 5) From the figures in the Appendix, I understand so that you have visited some displaced boulders. If so, have you recorded any physical destruction of these boulders together with displacement?

Reply: I have found one physical destruction. It is the one of the SUi boulder (see Figure A8). This clast fragmentation is documented in Ref. [20].

Comment 6) Another question is whether the displacement of “your” bounders depended on their isolated or group position. Boulders occurring in groups may be more difficult to move because of their “cohesion”.

Reply: Yes, you are right, this is another important issue to investigate. Considering the displacements of Table 3, some of them regarded boulder clusters. Unfortunately, I still don't have certain answers about your question. As a matter of fact, I reported two apparently contrasting examples (please, see the cases of PRi,j,k,l and PIa,b,c,d,e clusters, lines 336-339 and 389-394, respectively).

Comment 7) Please, add a simple scale bar to all satellite images and photos available in your manuscript (both main text and appendix).

Reply: Scale bars are at the bottom right of each GE image. In the photos taken on the coast, there is a 1 m-long tape measure for scale.

Author Response File: Author Response.docx