Tsunami Boulders on the Rocky Coasts of Ibiza and Formentera (Balearic Islands)

Round 1

Reviewer 1 Report

The paper is interesting and fits the journal scope. However, I have some suggestions listed below.

 

General comments:

- The abstract must be reformulated: please check the authors' guidelines.

- Although the introduction provides sufficient background and includes all relevant references it could be improved because the objectives of the study are not clearly defined.  

- The methods should be more developed. The authors indicate several equations but do not show them. Please provide the full set of equations used in the study. Moreover, the authors conducted a field survey; therefore the methods for the survey should be explained. The procedure for the dating of the boulders should be explained.

- The results and discussion could be merged into 1 single section.

- The link between the several methodologies is not clear: what tsunami source model can explain better the 2003 event? Do the hydrodynamic equations of boulder transport reproduced the boulders’ location observed during the field survey?

 

Specific comments:

L101: rearrange the text, figures, and tables to avoid gap pages;

L124: please explain in more detail why you focusing on the 2003 tsunami: was this the worst event ever recorded, or the authors choose it due to data, or any other reason. Moreover, it is not very common to a moderate earthquake (M 6.9) to generate a tsunami; please develop because the tsunami may have been generated with a combination of an earthquake+submarine landslide.

 

Figures 3 and 4: please verify copyright to publish figures from other authors.

Figure 3: it is not very clear: what do the green and gray rectangles mean? The font is too small; the authors may number each spot and include the information in a new table.

Figure 4: please explain in more detail the 3 fault mechanisms, or choose 1.

L144- L155: sources S-3, S-4, and s-6 are not described in detail or shown in Figure 4. Please reformulate the paragraph. Which source produces the best results for the 2003 event?

Figures 5 -11: field survey figures should be reformulated, the font size is too small;  the spot location of each photo is not very clear; please indicate in a more clear way where the selected boulders are located.

Author Response

Please see the attachment

 

Reviewer 2 Report

The manuscript reports the analysis of seven boulders located along the coasts of two Balearic Islands, Ibiza and Formentera. Based on their analysis of the morphology, position and orientation, the authors claim that such boulders have been deposited where they are as a consequence of the interaction with tsunamis waves impacting the coasts.

The work is interesting, unfortunately the authors tend to indulge in long descriptions of the results of in-situ observations, while in order to support the tsunamogenic origin of the boulder deposition they should provide a more clear description of the results of previous studies used in the paper (e.g. tsunami origin in the area), a sound presentation of the methodologies and models they have adopted, and a more detailed account of their modelling application and obtained results.

In particular, a simple frequency wave climate analysis is presented based on some available data. The type of data source should be specified. I assume the authors have used re-analysis data, which, as it is well known, tend to underpredict actual field measurements (see Mentaschi et al., 2015 CENG, among others). This should be mentioned. Moreover, results are presented in a very confusing manner. This should be improved.

The discussion on the possible source of tsunami and on tsunami wave height is again very confusing.  Explanation in terms of mechanism, location, magnitude, return period, etc., of the sources of tsunamis S-1, S-2, S-3, S4, S-5, S-6 is not given at all. The authors should provide the reader with the info needed, without forcing him/her to look for other source of information. Additionally, no details are given on the model used for the tsunami propagation. What does it mean wave elevation in Figure 4? Is that the tsunami wave height? Please clarify.

Concerning the adopted methodology, in Section 2 the authors should introduce and discuss in more details the hydrodynamic equation used to quarry or displace the boulders. The expression of the Transport Figure TF should be given, along with a description of all the parameters used to determine its value. Additionally, a clear discussion on the threshold value used for TF should be included. Finally, the authors state that they have analyzed more than 500 boulders, and that 106 of these had TF>1000. No results of such an analysis are presented in the manuscript. It would be nice to see some geo-statistics of such an analysis within the study area.

Description of the analyzed boulders is focused on their dominant direction compared to the dominant swell direction. The analysis discussed in the text is not always consistent with the analysis shown in the Figures. Moreover, the orientation of the boulders is not in itself a proof of tsunamogenic origin.

In Section 3.8 the application of the hydrodynamic model is presented. However, it is not clear how the authors define the region of “wave reach” (e.g. see lines 281-282).

 

It is suggested to add a metric reference in all the images referring to the in-situ survey. Image quality and readability of the Figures should be significantly improved.

English should be significantly improved.

Considering the above, this manuscript is not ready for publication yet, therefore, it suggests a major revision.

 

Specific comments

·         Section 1.2: it is not clear if the data used to describe the wave climate are physically measured or numerically modelled. By the way, since the analysis is limited only to wind wave characteristics it should not be called maritime climate.

·         Line 109: something is missing here. Please provide info on the peak period of the waves;

·         Lines 118-120: The sentence should be entirely re-written as it does not make sense as it is.

·         Figure 3: The quality of the image is quite poor and should be improved to guarantee readability

·         Line 137: The authors should summarize here the main mechanisms of tsunami generation suggested for the investigated area.

·         Line 155: “a process of refraction”. Should not be “a process of diffraction” in this case? Indeed, the presence of waves on the protected area is not due to the bathymetry, as refraction processes would, but it is due to later spreading of wave energy, i.e. to diffraction processes.

·         Figure 5: The info on the boulder orientation is missing.

·         Line 254: At what water depth the wave height of 9 m was measured?

·         Line 270: At what water depth the wave height of 8 m was measured?

·         Table 2: Since the methodology is not described, it is not clear what is the physical meaning of the results reported in the Table. Moreover, it is not clear what are the main physical assumptions which support such results.

·         Line 320: The figure 217 m does not appear in any place in the paper. It seems wrong. It should be 21.7 m perhaps.

·         Line 329: “overcome” should be “overtop”

·         Line 337: Reference to Fig. 2 should be eliminated.

 

 

Author Response

Please sea the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

General comments:

The authors have tried to answer most of my previous comments. In particular, I have appreciated the new Section 2, where a more detailed explanation of the model used in the analysis is presented, better supporting the obtained results. Several errors and biased analysis have been also removed.

However, as it stands now, the manuscript still needs several improvements as the reading does not flow as it should.

Presentation of the work done and of the results obtained should be better organized and made clearer. English should be carefully checked by an educated native-speaker or a professional translator. Structure of the phrases should be significantly modified.

 

Specific comments:

The Introduction should clearly state what are the advances proposed by the paper, compared to previous studies. Please indicate what was missing in existing literature and what is new in the present work. This is not clear at all. Section 2.1. This is an example of very confusing presentation of data and information For example, in Table 1, it is not clear to what wave conditions do refer the value of Hs and Tp? Mean wave climate? Please clarify. The authors use the 50-years return period as a reference for extreme storm events. However this is a return period relatively low. Particularly if compared with the return period of tsunami events. The authors should clarify why they have chosen such a low value. The caption of Figure 4 has not been modified to introduce the new figure on focal mechanisms. Presentation of Section 2 should be carefully revised, since there are many inconsistencies. For example at Line 222, the authors introduce only two of the model, whereas the model by Pignatelli (2009) is not even mentioned over the entire Section, although it is reported in Table 3. Symbols should be carefully checked throughout the paper. For example, capital A,B, and C are used at line 197 and lowercase a,b,c are used in Table 3. When presenting the models, the authors should indicate the value used for all the coefficients (drag, lift, friction, etc.) and how they have estimated them, including supporting references. In Section 3.8, Hs is the swell height or the storm wave height. The definition the authors provide does not make any sense to me. Check carefully references. For example, the title of reference [44] is not correct.

 

Minor comments (just some example of broken English):

Line 112: “wave parameters obtained from numerical modelling” Line 211: “based on bed thickness …” Line 403: “age” cannot be 1792 year. Rephrase.

Author Response

Please see the attachment