the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Mar 2024
Volcano Tsunamis and their effects on moored vessels safety: The 2022 Tonga event
Abstract. The violent explosion of the Hunga Tonga-Hunga Ha’apai volcano on January 15, 2022, was the origin of an atmospheric wave and a volcano-meteorological tsunami (VMT), both of which were recorded worldwide. The Tonga tsunami event caused resonance effects, leading to wave amplification in some far-field coastal areas like La Pampilla port in Callao, Peru, 10,000 km away from the volcano, where the rupture of the Vessel mooring lines occurred 15 hours after the eruption, resulting the spill of over 11,000 barrels of crude oil. This study aims to better understand the coastal effects of the Tonga tsunami, focusing on mooring loads in marine port environments. We examine how the VMT affected the safety of vessel moorings, hypothesising that atmosphere-induced acoustic ocean waves exerted hydrodynamic loading that endangered ships in port areas. A tsunami propagation obtained with a validated Boussinesq model at the local scale in Callao Bay provides the input to the mooring system model applied to a vessel with similar characteristics to the one docked at La Pampilla Port on the day of the Tonga event. This allows to study the effect of the VMT on overstressing and the potential mooring breakage. The results suggest that the Tonga tsunami event could be responsible for the movement and loss of positioning of the vessel. Furthermore, atmospheric waves significantly increased mooring stresses, particularly on the starboard quarter moorings. This event showed the need to prepare Tsunami Early Warning Systems and port authorities for detecting and managing VMTs induced by atmospheric acoustic waves. The work provides new insights into the far-field effects of the Tonga 2022 tsunami and discusses the lessons learned from such an uncommon event.
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RC1: 'Comment on egusphere-2024-663', Anonymous Referee #1, 11 Mar 2024
The manuscript under review is devoted to the important problem of the tsunami impact on ships in harbors. There are many descriptions of this tsunami type; in fact, the reviewer himself spoke with the masters of such ships, who said that the ship broke away from its anchors, became uncontrollable and rushed around the harbor like a chip. Meanwhile, typical calculations of tsunamis near the coast, even with an ultra-low spatial resolution of several meters, do not take into account the presence of ships in the harbor, which cannot be attributed to subgrid effects. This problem has not yet been considered in the literature at all. It is more common to look at tsunamis independently of various structures, and then calculate the impact of tsunami waves on objects, but even here there are not many papers on this item. The paper under review continues this topic.
In fact, the reviewed paper consists of two parts. The first calculates the characteristics of the tsunami caused by the volcanic eruption in the Tonga archipelago in January 2022. They have already been calculated repeatedly in a very large number of papers, some of which are cited here. It is said in the paper that large waves in the Peru region are caused mainly by atmospheric disturbances, thus, confirming other authors’ conclusions, including their own paper as well. Since the authors want to study a specific case of the moored vessel accident that occurred, the tsunami wave calculations done are necessary, so I have no remarks about this part of the work.
I just would like to note that the dominant period of 120 minutes obtained by the authors was also observed when the similar phenomenon, that took place in 1883 during the eruption of the Krakatau volcano, was being analyzed (Choi et al Simulation of the trans-oceanic tsunami propagation due to the 1883 Krakatau volcanic eruption. Natural Hazards and Earth System Sciences, 2003, vol. 3, 321 – 332; Pelinovsky et al. Analysis of tide-gauge records of the 1883 Krakatau tsunami. Tsunamis: case studies and recent developments, Advances in Natural and Technological Hazards Research, vol. 23, Springer, 2005, 57-77), so it would be worth mentioning in the paper.
The second part of the work is devoted to calculating the impact of tsunami waves on an moored vessel. The authors use the smallness of the ship length compared to the tsunami wavelength and write a system of ordinary differential equations for the forces and moments affecting the object. Unfortunately, I do not know the literature in this area of ship engineering and do not see any references in the reviewed paper to any textbook or guide to judge how popular exactly such equations are in engineering. But having looked at a number of references mentioned in the reviewed work, I see that this approach has already been used for tsunamis, in particular the 2011 Japanese tsunami. Therefore, I trust the results obtained. The authors confirm that the calculated stress exceeds the Minimum Breaking Load (Fig. 14), which may have been the cause of the accident.
I would like to point out minor inaccuracies in References (not completed data):
Ohgaki, K., Yoneyama, H., Suzuki, T., and IEEE: Evaluation on safety of moored ships and mooring systems for a tsunami attack, 2008
Tahar, A. and Kim, M. H.: Hull/mooring/riser coupled dynamic analysis and sensitivity study of a tanker based FPSO, https://doi.org/10.1016/j.apor.2003.02.001, 2004
In fact, I support publication of the paper under review in its present form with some minor changes.
Citation: https://doi.org/10.5194/egusphere-2024-663-RC1 -
AC1: 'Reply on RC1', Sergio Padilla Álvarez, 18 Mar 2024
Thank you very much for taking the time to review the document, they are very helpful in improving the content of the publication and we will include them as you suggest.
Best regards.
Citation: https://doi.org/10.5194/egusphere-2024-663-AC1
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AC1: 'Reply on RC1', Sergio Padilla Álvarez, 18 Mar 2024
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RC2: 'Comment on egusphere-2024-663', Anonymous Referee #2, 02 Apr 2024
General Comments:
The study by Padilla et al. on the effects of volcanic tsunamis on moored vessels investigates the rupture of the vessel mooring lines that occurred in Peru after the 2022 Tonga event. The authors present an analysis of sea level and barometric observations via wavelet analysis and spectral analysis at selected locations, numerical modeling of the atmospheric wave propagation and consequent sea-level oscillations, volcano-meteorological tsunami termed as such by the authors, via a Boussinesq model, and application of the computed tsunami current velocities and water elevations to their moored ship model, which is based on a set of ordinary differential equations from the analytical solution of that problem for the force and moment calculations. The study focuses on the oil-ship accident in Peru, addressing the problem of long wave impact on marine vessels, but due to atmospheric disturbances and provides insights on the potential stress increase on mooring lines.
The reviewer finds the study interesting and the problem worth exploring as the consequences of such events can be significant, although rare. At this point, the reviewer believes that the research objectives are reasonable, including the application of the analytical solution of the hydrodynamic loads on moored vessels to a real case. The attempt to reveal those methods to assess the impact on mooring lines via calculation of stress (and the potential increase), hence, addressing the potential threat of meteorologically generated sea level oscillations (in the tsunami frequency band) on the marine vessels is useful for future assessment of such events. Technically, I do not have many objections; the methodology followed for the tsunami calculations and impact assessment seems plausible. However, there is still room to improve the manuscript and how it is presented based on the specific comments below. Hence, the reviewer wants to see that the following comments are addressed in the manuscript before publication and thus encourages the authors to revise the manuscript.
Specific Comments:
- Abstract: Some of the sentences in the abstract are unclear, making it difficult to apprehend the overall study and major findings from the abstract. For example, the authors mention two vessels, one docked at La Pampilla Port on the day of the Tonga event and the other to which the mooring system model applied. They mention a ‘similarity’ between these two vessels, but the remark (here) that the authors would like to point out is not clear. On the other hand, one of the main findings given in the abstract is, “The results suggest that the Tonga tsunami event could be responsible for the movement and loss of positioning of the vessel.” One can already expect that considering the timing of the incident; so the authors should emphasize the results/outputs of the study supporting this statement. It is important to summarize those in the abstract. Another finding, “Furthermore, atmospheric waves significantly increased mooring stresses, particularly on the starboard quarter moorings.” should also be rewritten more precisely, including the answers to some questions like, is it any characteristics of atmospheric waves that increased the mooring stresses or is there any other mechanism serving to that increase? How much is that ‘significant’ increase and is it compared to which condition?
- Introduction:
- The author suggests somewhat linking paragraphs and sentences within the paragraphs for fluent reading.
- Figure 1: The reviewer highlights the need to help the reader: identification of oceanic and land features mentioned in the text; indicating the names of the important (surrounding) geographical objects on the map.
- Lines 56-58: This statement needs to be checked. The reviewer agrees that the VMT traveled at faster speeds, had a global reach, and somewhat affected the far-field coasts but did not cause noticeable damages or human fatalities since the observed amplitudes due to VMT were only in the order of 20-50 cm. Please clarify or support further with additional information and numbers (like the amplitudes or give specific examples/locations, etc.)
- Lines 69-70: It is not clear what the ‘previous ones’ here refer to. The authors can simply use ‘similarly’ to avoid confusion, if applicable. Furthermore, regarding the statement, ‘’This also applies to tsunamis induced by atmospheric disturbances, which, like the previous ones, have caused damage to ships, moored vessels, and small bays (Imamura et al., 2022; Thomson et al., 2009)’’, it would be useful to explain those incidents since they are directly related with the concept of the proposed study.
- Lines 74-75: The motions in the vessel’s horizontal plane are misnamed here. They should be sway, surge and yaw in the horizontal plane and heave, pitch and roll in the vertical plane!
- Figure 3: It would be helpful to the reader if the authors could show/write/name Callao Bay and La Pampilla Port on the map here and provide coordinates for La Pampilla Port, preferably in the figure caption.
- 2 Spectral Analysis: The reviewer strongly suggests explaining (in detail) the methodology that the authors applied in this analysis.
- 3 Tsunami Propagation Model:
- Lines 144-152: As the outputs of the study strongly depend on the results of tsunami propagation modeling, this part certainly needs to be improved. The methodology used for producing atmospheric input should be explicitly provided, as should the produced signal (preferably compared with barometric records).
- Lines 153-160: The reviewer would like to see the computational domains (their extents) employed in the study on a map, with corresponding resolutions in meters as well.
- 4. Stresses in moored ships model
- Figure 5: The reviewer suggests writing the equations in bigger font size and a darker color for visibility.
- As the tsunami current velocity is one of the inputs in the moored ships model as a time series, it is important to explain how it is handled in the vertical dimension and solved in the numerical model.
- Results:
- Lines 241-242: What is the rationale behind the selection of 310 m/s for the traveling speed of atmospheric waves, while the authors here give an estimation of 324 m/s? The reviewer also recommends a discussion of the significance of this speed selection as it is the primary factor for potential Proudman resonance effects.
- The reviewer thinks that the calibration/validation of the tsunami modeling results is significant, especially at the locations near the La Pampilla port, at LA and CL. Therefore, the discrepancies between the observed and simulated waveforms, especially time histories (which do not seem negligible as claimed) and their effects on the ship moored model need to be further discussed.
- Lines 328 – 330: The extracted time series from the hydrodynamic model (and inputted to the mooring system) should be provided.
- Line 329: The coordinates up to this point, including the maps, are given in decimal degrees, so they should be here with sufficient decimals (precision) considering the scale of the problem.
- Figure 12: A description of ‘cspd’ is needed in the caption.
- Lines 369-371: In my opinion, the sentence here should be modified because the reviewer understands the stress increase at specific mooring lines, and the authors intend to explain the potential reasons for this observation; however, if it is written like a direct conclusion rather than an observation and potential reasons, as is in the present form, then it is not clear how such conclusion is drawn and the analysis here seems not sufficient for this.
Original: The increase in stresses was due to the configuration of the mooring layout, tsunami wave direction, and hydrodynamic effects, which could cause the mooring line to break.
Alternative 1: The configuration of the mooring layout, tsunami wave direction, and hydrodynamic effects can be potential reasons for the increase in stresses, which could cause the mooring line to break. OR
Alternative 2: The increase in stresses was potentially due to the configuration of the mooring layout, tsunami wave direction, and hydrodynamic effects, which could cause the mooring line to break.
- Lines 373-375: “These results confirm that the atmospheric waves generated during the volcanic eruption have transmitted energy to the ocean, generating tsunami-like waves that have affected the far field.” Various studies of the Tonga event from different perspectives have already confirmed such a finding and have this conclusion. It is recommended to be more specific to the findings of this study here, maybe focusing on the impact of VMT on marine vessels or other comments are encouraged.
- The conclusion part could be stronger, highlighting the major findings in a more distinct manner and more discussions on the stress increase, and reasons for the amplification of amplitudes.. A thorough review and revision is recommended.
Minor Comments:
- There are some spelling and punctuation errors.
- The reviewer made several remarks in the annotated document.
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AC2: 'Reply on RC2', Sergio Padilla Álvarez, 02 Apr 2024
First thank you for taking the time to review the document. They are indeed very useful and accurate comments to improve the quality of the publication. As well as the revisions of the first referee, we will include them as you suggest.
We will now work on the corrected version of the document where your comments, suggestions and corrections will be included.
Best regards.
Citation: https://doi.org/10.5194/egusphere-2024-663-AC2
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