Upper Pleistocene and Holocene Storm Deposits Eroded from the Granodiorite Coast on Isla San Diego (Baja California Sur, Mexico)

Round 1

Reviewer 1 Report

Dear Editor, dear Authors,

In their manuscript “Late Pleistocene and Holocene Storm Deposits Eroded from Granodiorite Sea Cliffs on Isla San Diego (Baja California Sur, Mexico)” the authors investigated the wave height by Pleistocene and Holocene tropical cyclones needed to erode granodiorite boulders on the yet rarely studied Isla San Diego in the Baja California Sur (Mexico).

The manuscript presents a regional study that is based on the combination of a field campaign with numerical calculations and paleontological evidence to achieve the characterization of needed storm waves. Currently there is a lack of knowledge specifically for this island. From my perspective this study will be a good contribution to the regional literature.

However, the manuscript in its current state needs much improvement. Many parts are unclear, not straightforward and lack sometimes the correct terminology. Most importantly the discussion of the obtained results needs more attention by the authors and the nowhere leading comparisons (e.g., with boulders from Atlantic Europe) need to be cut or removed. Therefore, I would suggest major revisions at this point, by following the supplied comments and suggestions below and suggested changes in the .pdf document.

Comments:

General:

• Language: While the authors contributions state that the native speaking corresponding author has written the first draft of the manuscript, I would like to ask the authors to review the English once again. Especially for non-native speaking readers some sections may not be easy to understand as they appear to be written ‘flowery’ instead of straightforward to the point.

• Within the introduction the authors flip-flopped between rock types and the shape (coastal length) or size of the island. Please consider rearranging the introduction for more clarity.

• During field observations have there been any kind of imbrication or other typical features observed on storm boulder deposits been found? This has not been documented nor mentioned in the results section. Similar is the positioning of the corals and other fossils, are they attached to the boulders in the first place and transported with them or are they rather a hash layer of debris that is also transported. If the latter, are they also calculated by their density and size as they will likely be transported much further by the same waves. If the first are the corals for examples rotated from their living position and give thus an idea about the transportation mode of the boulders (e.g., rotation vs. creeping or saltation or similar).

• How do the authors determine that the boulders are of Pleistocene or Holocene age? Is this solely based on the paleontological evidence? And how do authors ensure that these are not secondary transported there, as the fossils are much smaller and lighter than the boulders, thus need less wave energy to be transported. There is not dating (luminescence or cosmogenic nuclides) in the manuscript.

• Are corals and other fossils (described in chapter 4.5) attached to the granodiorite boulder? Are they transported in living position or rotated? Have they been secondarily transported? They might be of Pleistocene age, but when were they transported/deposited?

• In chapter 4.6 the Holocene ridge offshore is described. Important here would be to know how deep the storm wave bases are in the Gulf of California? This is very relevant when focusing on the erosion of boulder that might be located under water, also for the generation of the offshore ridge. Is it affected by storm waves or is the ridge already below the storm wave base, thus unaffected?

• The discussion is in its current state the major issue with the manuscript. The results and findings by this study are not really discussed and crucial questions not answered. The entire discussion needs a thorough revision by the authors with a focus on the discussion of their results, observations, and findings. The next two comments will also deal with the discussion, especially with comparisons by the authors, which are either not fitting in the discussion or do not benefit any scientific purpose.

• The entire chapter 5.2 ‘Recent Hurricanes in the Region of Isla San Diego’ is currently placed in the discussion. However, nothing is discussing in this sub-chapter and the last sentence is rather a working hypothesis for this manuscript. Therefore, the author either need to add a discussion in context with their results, such as a link of specific boulder being transported by these events and if how far etc. Or, what is the better option, this chapter should be moved and being implemented into the introduction or the geographical setting.

• Chapter 5.4 makes not much sense. Why are the boulders compared to boulders in a different ocean and to boulder of different densities? The authors write themselves: “All these rock densities from island localities 441 in the North Atlantic Ocean surpass those for limestone, banded rhyolite, and andesite 442 found at localities in the Gulf of California.” So why would you compare them in the first place? As this sub-chapter give no scientific input nor a proper discussion of the results, I would suggest removing this chapter and to focus on the discussion of the obtained results from the Isla San Diego.

• Chapter 5.5 needs to be moved to most fittingly the geographic or methods chapter. Nothing is discussed here.

Specific comments:

Abstract

L6/7: I could not find this institute anywhere only a kayak rental shop. Is that correct?

L12: Please clarify this, a hurricane is a geographical name not a strength per se. Hurricanes or rather tropical storms can be classified in several sub-categories (mostly depending on their wind-speeds).

L28: See comment above regarding terminology.

L29: Is this sentence relevant for the science conducted? If not please delete.

Keywords

L32: Within the text authors shift between Upper and Late Pleistocene. (A) Is there a difference? (B) why not consistent with the title and always using Late Pleistocene?

L33: This is personal preference; it should be avoided to use keywords that are the same as in the title. Some journals even want this I am not sure about the guidelines of MDPI on this.

Introduction

L41: what is younger? Is there still active volcanic activity present based on the rifting? Please clarify

L41: As I suppose that the material in question is not actively flowing from a volcano anymore it should be rock here. Depending on their nature (flow) they might even be described as pyroclastic rocks

L50: The series of papers should be referenced here.

L53: Seriously? I doubt that. Isn't that the normal second step after measuring the dimensions to evaluate the boulder's density? From my personal experience (mostly with carbonate boulders) this is a standard to involve the rock density into any calculations, otherwise you just can't calculate the weight, nor the needed energy. It might be true for geomorphologists, but every scientist dealing with wave events (storms or tsunamis) is using this. Therefore, I would suggest altering this statement, or provide compelling references.

L64: Please explain how a reef could be inorganic? Yes, corals build up bodies of carbonates (inorganic), but reefs are always organic in nature.

L70: See comment above. Maybe write inorganic reef carbonates

L74: For clarity, this sentence should be separated in two sentences. The first part specifically about the Isla San Diego seems not in direct context to the second half - the comparison

L76: Well is this your hypothesis or that of Ruban (2019)? Why should your study on the quarternary Late Peistocene and Holocene boulders stimulate studies on Neogene deposits?  And what do you refer as the Neogene world? Do you mean the rocks of Neogene age? This make not much sense. A stronger sentence containing the authors hypothesi for the study on the Isla San Diego should be the final sentence of the introduction.

Geographical and Geological Setting

L85: to avoid repetition in the wording authors could either write: a) lasted for 9.5 million years or b) lasted until 3.5 million years BP

L87: I (not an American nor Mexican) would suggest to either cut this part completely, as is sounds just policial. Geologic structures do not care about human drawn borders on a map, nor how the same structure or fault in this case might be named. As far as I am aware the same fault zone continues into the Gulf of California. If not, please clarify this clearly here.

L97: I would suggest to move the 8m further up maybe connect the + with a line or so, otherwise where is very much going on in the lower tip of the island.

L101: Relevance? What is the connection to the science here? Please clarify or delete.

L105: This sentence is more or less methods, thus it should be moved there.

L112-120: The authors should consider to move this into the results under a chapter: Field observations or similar, as these are also results from your study there.

L114: see comments above regarind inorganic reef

Material and Methods

L127: The wording of this sentences sounds a bit off... How was the shorelines potential for storm deposits evaluated before field survey? Who is the "senior author"? The corresponding author? Please rephrase.

L143: What gulf sample? What is the location? The density of volcanics and intrusive rocks can drastically vary even within relatively proximity due to composition changes within a magma chamber, gas content, etc. etc. If this is from another site a reference would be useful.

L148: Granodiorite is not volcanic... it is crystalline or rather igneous, volcanic rocks are effusive rocks through an eruption of a volcano. Please correct.

L151: This reference (Pepe et al.) could be cut, as only the primary source is of importance

Equations (1) and (2): Please note somewhere which formula is from Nott and which from Nandasena. I believe the first is from Nott and the second from Nandasena, but this is not obvious without going into the primary literature

L153: In the density of seawater the salinity and temperature must be considered, as both factors might be very local and change the density.

Results

L182/ Fig. 3: In which direction is the diameter measures? The circle is not circular but oval.

L236/ Fig. 5: Is the 26.6 mm really mm or cm? In the graphs it says 16-30 cm. According to udden-wentwoth the boundary between coarse cobbles and fine boulder is at 256 mm or 25.6 cm. Please correct this.

L237/ Fig. 5: The correct terminology would be coarse cobbles and fine boulders. see for example Udden-Wentworth

L242/ Fig. 6: see comment above

L258: Shouldn't here the original reference by Nandasena et al. be cited, as it is their formula that was used for calculation. Pepe et al did only apply this formula. Please correct.

L263/ Table 1: Shouldn't here the original reference by Nandasena et al. be cited, as it is their formula that was used for calculation. Pepe et al did only apply this formula. Please correct.

L264: Here comes the information that would have been required in the methods section. Please provide it there.

L269: The equation is not from Pepe et al. it is from Nandasena et al.  -  Pepe et al. only applied the equation, but cited needs to be the primary literatur of the equation. Please correct this here!

L271: See comments above regarding this.

L340: See comments above regadring inorganic reefs.

Discussion

L369: See comments regarding this reference above.

L375/376: How can the authors assume the slope if the Isla San Diego based on field studies on other islands? This makes no sense. Was the slope inclination not measured? Maybe with SFM or GIS-based methods?

L378: See comments above regarding this reference.

L388-409: This entire sub-chapter is not discussion, this is introduction.  What is the connection to the discussion here?  This chapter should be moved and implemented in the introduction.

L415: These calculations only determine the minimum wave height for initial transport. However, how far have these boulders been transported? If the same boulder is transported only 10cm or 10 meters, there is a huge difference in needed wave energy. This should be clarified somewhere in the manuscript that the calculations only present a minimum wave height for what exact transport distance? And how do authors deal with the effect of multi-transport of boulders by several storms? As this manuscript considers storms from the Late Pleistocene until well today according to chapter 5.2, the effect of multiple storms must be considered (e.g., already 6 hurricanes within the last century)

L423: How is the effect of sea level variations since the Pleistocene considered in this statement?

L425: This is rather an outlook. And yes, this should be done to calculate the correct wave heights needed to transport a boulder a specific distance

L431-459: Chapter 5.4 makes not much sense. Why are the boulders compared to boulders in a different ocean and to boulder of different densities? The authors write themselves: “All these rock densities from island localities 441 in the North Atlantic Ocean surpass those for limestone, banded rhyolite, and andesite 442 found at localities in the Gulf of California.” So why would you compare them in the first place? As this sub-chapter give no scientific input nor a proper discussion of the results, I would suggest removing this chapter and to focus on the discussion of the obtained results from the Isla San Diego.

L436: See comments above regarding this reference.

L441: Ok, why are they then compared to these? Makes not much sense.

Conclusions

L471: What are super-storms? please clarify

L472: Late Pleistocene instead of Upper

L480: This was not discussed in the discussion, but should be!

Author Contributions

L495: Are MEJ and M.J. different authors? If not please standardize.

Appendix

All tables: Please correct reference Pepe et al. to the correct reference Nadasena et al.

Comments for author File: Comments.pdf

Author Response

We thank Reviewer #1 for his/her detailed response to our latest project on storm beds in Mexico’s Gulf of California.  The review includes 11 “general” observations in criticism of our work followed by 50 “specific comments” or queries keyed to lines in our original submission focused on Isla San Diego in the lower part of the expansive Gulf of California.  The greater part of changes now introduced are directed to those latter (line-specific) comments, which are most effectively dealt with by corrections or adjustments for better clarification inserted in the manuscript at key spots.  Among the general points raised by Reviewer #1, such as the need to discuss the presence or absence of clast imbrication (general comment 3), our team overlooked this point and we have taken steps to remedy the situation both in text and the introduction of a new diagram (now Figure 7 a, b, c).  The same applies to the general comment asking how we know the age of the storm deposit based on its fossil content (general comment 4), which is easy enough to do using established range zones for Pliocene and Pleistocene fossils in the gulf region.  Other criticisms are based on misunderstandings or flawed readings of the manuscript and/or field photos.  These are easily set right by the addition of clarifications to the text.  However, other observations are more opinionated in nature and we reserve the right to respectfully dismiss those criticisms.

Before responding to each of the “general” observations, the corresponding author (identified as second among the four authors) reacts to the first of the 50 specific comments at the top of that list. The first author is not affiliated with an academic organization or institute.  However, it is unfair to characterize her work address as merely a kayak rental shop. Yes, ecotourists do rent kayaks from her shop, but the shop’s proprietor is a highly respected naturalist who organizes kayak tours principally among the islands of the Loreto Bay National Marine Park and farther afield in the lower Gulf of California. She is not an employee the Mexican national park, but her role is roughly equivalent to the knowledgeable naturalists who accompany ecotourists visiting Ecuador’s Galapagos National Park.  Before organizing the present manuscript, the corresponding author sought the advice of the managing JMSE editor in its Beijing office and was given enthusiastic approval to proceed. As the instigating author, I wish to point out two things. First, I have previously published in academic circles with coauthors such as naturalists working in the Galapagos. This concept is not alien to me, especially when the individual so involved provided services that were essential to the project.  Secondly, during the past year limitations on fieldwork have been severely hampered by the covid-19 pandemic.  Based on first-person aerial surveillance, the corresponding author has long been aware of the suitability of a research project on Isla San Diego, but even under normal circumstances it is an out-of-the-way place hard to reach. From March 2000 to present, he has been in lockdown and forbidden to leave his home institution to engage in fieldwork or even to attend academic conferences of any kind. The first author was equipped with a highly detailed plan for completion of the project on site and she carried out that plan perfectly. For that reason, she (and by affiliation, her home address) are awarded first place in authorship.

General comment #1 (Request to edit the paper’s language): The text has been combed in an attempt to reduce the paper’s “flowery” tone, but the responsible author is a geologist and paleontologist with a long record of successful, peer-reviewed articles.  He does not come from the tradition in mathematics and engineering where terseness of expression is more common.  After more than 40 years of professional work, this writer is unlikely to alter his writing style. However, the first paper in this series on storm deposits in the Gulf of California published by the JMSE in 2018 has achieved 1364 abstract views and 1250 full-text reviews. The writer’s writing style appears not to have dissuaded prospective readers in the JMSE audience from accessing the paper.

General comment 2 (Request to address paragraph order in the paper’s introduction): In the reviewer’s opinion, the introduction’s structure “flip flops” between issues related to rock type and island size and/or coastal length of islands in the Gulf of California and other regions.  As it now stands, the paper’s introduction is a standard 3-paragraph entry to the problem organized in “hour-glass” fashion starting with an overview on the types (and coastal dominance) of different rocky shores in the Gulf of California and moving thereafter to a specific island with an under-represented lithology in the Gulf of California.  The third and final paragraph widens the paper’s scope to consider islands for comparison in the North Atlantic having rock types not represented in the Gulf of California. This is a valid approach, considering that two of the authors in the present paper are the organizers of a JMSE Special Issue that deals with variations in rock types on rocky shores subject to storms the world over. Minor adjustments are made to the language but the paragraph in the introduction remains unchanged.

General comment 3 (Request to document presence or absence of imbrication):  This is an especially well-founded criticism and the team has taken pains to re-evaluate the photographic evidence from Isla San Diego in search of clast imbrication.  See especially the addition of the new image for Figure7 and corresponding details provided in the text newly introduced in Section 4.5 specifically on the question of imbrication.  Our finding is that a limited amount of imbrication is visible mainly in the cross-section of the storm deposit as viewed from the tip of the island consistent with the island’s general axis. Less evidence of imbrication can be detected when looking at the cliff face perpendicular to the inferred arrival of storm impact against the island’s east-facing shore, but a reactivation surface is shown by an indentation in the cliff face (obscured by shadow).  Interpretation of the reactivation surface is added to the discussion section.

General comment 4 (Request for verification of Pleistocene or Holocene age for storm deposits): Ashore, the age of the conglomerated interpreted as a storm deposit is considered not only as Pleistocene but latest Pleistocene based on fossil content.  An older Pliocene age can be ruled out based on the known range zones of fossil corals in the Gulf of California and an older Pleistocene age is ruled out based on the relative elevation of the conglomeratic shore deposits on the island.  Older Pleistocene fossils are rarely found in associated with raised terraces in the Gulf of California.  These factors are newly taken into account in the revised and renumbered Section 4.6. The text clearly states that a Holocene age for the elongated “spit” and underwater ridge that extends from the tip of the island is unconsolidated (unlike the conglomerate in the island’s cliff face.  Moreover, the smallest clasts in this deposit are observed to move with waves, which suggests that the feature is subject to present-day modifications.

General comment 5 (Request for clarifications on the disposition of fossils included in the storm deposit):  Answers to questions regarding the fossils are already evident in the now renumbered Figure 8, where the representative fossils are illustrated.  In short, none of the fossils are attached to boulders, but seeing how the cobbles and boulders are cemented in place it is not possible for them to have been secondarily introduced at a later time.  Moreover, there is no possible source area for secondarily introduced fossils, as the nearest such place is located on the peninsular mainland some 11 nautical miles away.  Clarifications are added to the text.

General comment 6 (Request for additional dynamics related to the Holocene ridge): The extreme length of this feature and its composition closest to the island are important and clearly described in this section (now 4.7), but additional text is added to show that the proximal part of the ridge sits above storm wave base (also clear from the re-numbered Figure 9) although water depth at the distal end of the ridge is not known by us from direct measurement.  The height of storm waves during a hurricane that reached farther into the Gulf of California is based on direct observation as cited in one of our earlier papers, now added to the text.  We can state unequivocally that the proximal part of the ridge is subject to minor changes during storms, but the largest boulders are unlikely to shift except during the most intense storms.

General comments 7 & 8 (Request for reorganization of the discussion section): We have taken pains to separate presentation of raw data in our report from its interpretation in the Discussion section. This section is now expanded to consider the evidence for and against clast imbrication in the conglomerate with specific reference to the most common shape of granodiorite boulders in the deposit.  We continue to believe that the discussion section is the proper place to discuss Recent hurricane activity in the Gulf of California, because the strength of these storms is well known from the literature and has a direct bearing on how clasts may be entrained in the underwater Holocene ridge.  The comment that that observations are needed to” link specific boulders being transported by such events” and if so how far – are nonsensical because the granodiorite shores around Isla San Diego form plunging sea cliffs. The last part in the renumbered Section 5.4 refers to the potential usefulness of tagging boulders on the ridge to find out if they have shifted after the passage of a major storm.  In our opinion, this is one of the functions of a good discussion section to show what is known and not known and to suggest ways to add to a particular study in the future.

General comment 9 (Request to reconsider comparison with boulder deposits from islands in the North Atlantic Ocean):  In defense of retaining this section with some modification, it is worth to point out that the corresponding author and fourth author of the present paper organized a Special Session for the JMSE on Neogene storm deposits.  It is true that rock density is always considered in equations that purport to estimate wave heights related to storm surge against rocky shores.  We think it is not out of place to summarize the direct calculations we have made or are party to from localities in the North Atlantic, some of which entail highly unusual rock types.

General comment 10 (Request to move the note formerly in section 5.5 on the conservation status of Isla San Diego to the methods section): It is so done in the revision and we consider it important to state that we made no attempt to violate the rules regarding the protection of that island in the broader context of conservation regulations in place for all islands throughout the Gulf of California.

Line references: The 50 line references commented on by Reviewer #1 are too numerous to comment on individually.  Except for that specifically highlighted here, the requested modifications are made in the revised text (and so noted in font colored red).

From line 258 in the first draft of the paper, it is urged that we cite Nandasena et al. (2011) for the formula 2, I am embarrassed to admit that the incorrect equation 2 was provided in the paper’s earlier draft, in which the “u₂” (i.e. the minimum flow velocity to instigate boulder transoration) was unnecessarily given.  Both equations must be solved for Hs, which stands for the height of the storm wave at its breaking point.  I am sorry for the confusion, but all the characters in both equations are now correctly listed and Peppe et al. (2018) is correctly cited for his application of the modified equation to solve for wave height taking into consideration the issue of flow velocity raided by Nandasena et al. (2011).

We hope that Reviewer #1 will consider the preponderance of changes to the text (shown in font colored red) that agree with his/her recommendations.  We are grateful for these suggestions, which greatly improve the clarity of the paper.

Reviewer 2 Report

The Baja California Peninsula is known as one of the 'natural laboratories' to examine storm deposits and their palaeoenvironmental and palaeoecological peculiarities. The reviewed manuscript presents novel and internationally-important information about the Late Quaternary storms deposits of Isla San Diego. It is based on in-depth, field-based study and state-of-the-art modeling and interpretations. It is informative, well-written, and well-structured. The cited literature is fresh and enough. It is important that the new results are related to the outcomes of the previous research in Baja California. After several rounds of critical reading, I see nothing for serious improvements. Nonetheless, I feel necessary to specify a few minor points for small amendments.

• Isla Dan Diego or San Diego Island? Please, check how this is spelled in geographical dictionaries and think of whether Spanish word 'Isla' is ok in this case (is this a part of name or only geographical definition?).
• What is the age of granitoids?
• I'd prefer to see a simple stratigraphical scheme of the studied island where the new subdivisions (stages) of the Holocene are shown (see information at stratigraphy.org).
• Can you discuss how your results contribute to the knowledge of the origin and the general geological/geomorphological evolution of this small island?
• Subsection 5.5: do your results contribute to the higher heritage value of the island? I think so because so because storm deposits are local geoheritage.

Author Response

Thank you for taking the time to review our manuscript on storm beds from Isla San Diego in Mexico’s the Gulf of California.  We respond, here, to each of the five points you raise for small changes to our contribution.

The correct geographic name for our locality is in Spanish Isla San Diego. This name is now applied uniformly through the entire manuscript.  There may have been a typo in in the previous version of the paper.

The age of the granitoids has been determined radiometrically only in outcrops on the peninsuilar mainland and we now cite the relevant paper (see Section 2) by Gastil et al. (2014) giving an age for a Cretaceous origin between 97 and 90 million years ago.  No testing has been conducted on the comparable granitoids from gulf islands, and such testing would be beyond the scope of this paper.

At the urging of another reviewer, we added a new Figure 7 that shows a cross section through the southern tip of Isla San Diego with the Pleistocene conglomerate layers sitting on Cretaceous basement granodiorite.  The purpose was to show the minor level of clast imbrication, but we feel this figure serves as a very simple stratigraphic scheme.  The Holocene deposit does not occur on top of the Pleistocene but exists as beach and submarine bar appended to the tip of the island as shown in Figure 9.

Except for a previous report (in Spanish) by Lumbier (1919) giving only the rudimentary details of the islands size and general composition including the submarine Holocene ridge appended to the tip of the island, there is no other published report on the island’s geology and paleontology.  Ours is essentially the first to do so and this is clearly stated in the last paragraph of the introduction.

Finally, as for the previous subsection 5.5, it has been rephased and assigned to the conclusion of Section 2 (Geographical and Geological Setting) at the insistence of Reviewer #1.  It is there to emphasize that we have followed rules for access to the island.  It should be clear that our work does add materially to the value of local geoheritage, since it is the only detailed account of the island.

We hope that the changes made in response to your comments work to clear up any ambiguity and we thank you, again, for your help.  All changes to the manuscript are shown in red for ease of recognition.

Reviewer 3 Report

-Review of existing studies. You could add some more papers regarding movement of boulders such as following papers.
doi:10.1142/S0578563416400040
doi:10.1016/j.margeo.2010.10.005

-equation (2): "u" and "c" should be defined.
-More information should be added at each of six stations and sampled boulders and cobbles, such as elevations and distance from the shore.

It should be discussed how much the observed characteristics of boulders obtained in single field survey can represent the actual characteristics. Shouldn't it be affected by the recent events just before the survey? How much these characteristics can change depending on the recent events?

Author Response

Thank you for taking the time to review our manuscript on storm beds from Isla San Diego in Mexico’s the Gulf of California.  We respond, here, to each of the three points you raise for relatively small changes to our contribution.

First, the two papers that you recommended for inclusion in our report (Lorang, 2011 & Kennedy et al. 2016) have been added to the introduction.

Secondly, I am embarrassed to admit that the incorrect equation 2 was provided in the paper’s earlier draft, in which the “u” for which you requested the definition (i.e. the minimum flow elocity to instigate boulder transoration) was unnecessarily given.  Both equations must be solved for Hs, which stands for the height of the storm wave at its breaking point.  I am sorry for the confusion, but all the characters in both equations are full listed.

Thirdly, we have stated that the conglomerate deposit subaerially exposed on the island is cemented in place by a thin calcareous cement.  The 200 Pleistocene boulders measured for this study are consolidated and have not been shifted by post-Pleistocene storms.  On the other hand, the Holocene cobbles and boulders in the submarine ridge that extends outward from the south end of the island are unconsolidated and vulnerable to shifting my recent and future storm events.  We have added some lines to clarify that a co-ordinated program of tagging might be undertaken to see if future storms have such an impart -in both the submarine ridge and at the top of the subaerial deposit that in theory could be overtopped by a big storm wave.

     The zone where boulders were accessed for field measurements is well marked for Stations 1-3 in Figure 3. And otherwise described in the text for Stations 4-6.  Figure 3 shows a narrow gravel beach exposed at low tide in front of Stations 1-3. In the seaward direction, the foreshore drops off very rapidly.  The only possible source for the eroded boulders is the zone around the small sea caves.  As we newly argue in the revised text, we believe on the basis of clast imbrication (see new Figure 7 and related text) that sea level was higher in the late Pleistocene and that the crudely layered conglomerate is an over-wash deposit.  New sections to the text have been added to reinforce our interpretation that the now subaerial exposure is adequately dated to the late Pleistocene when global sea level was higher by 4-6 m than today.

We hope this answers your queries.  All changes to the manuscript are shown in red for ease of recognition.

Round 2

Reviewer 1 Report

Dear Editor, dear authors,

The authors substantially improved the manuscript and worked most suggestions in. From my perspective there are no more ‘boulders’ in the way for publication. Therefore, I suggest to accept the manuscript in its current state.

Best regards

Reviewer 3 Report

It was confirmed that authors appropriately revised the manuscript responding to the comments given in the first round review.